Wednesday, August 17, 2011
Tuesday, March 29, 2011
Tip #23 For Better Chemical Engineering: Laboratory fractionating columns
A laboratory fractionating column is a piece of glassware used to separate vaporized mixtures of liquid compounds with close volatilities. It can also be called a fractional column. Most commonly used is either a Vigreux column or a straight column packed with glass beads or metal pieces such as Raschig rings.
Image 1: Fractional distillation apparatus using a Liebig condenser
Fractionating columns help to separate the mixture by allowing the mixed vapors to cool, condense, and vaporize again in accordance with Raoult's law. With each condensation-vaporization cycle, the vapors are enriched in a certain component. A larger surface area allows more cycles, improving separation. This is the rationale for a Vigreux fractionating column or a packed fractionating column. Spinning band distillation achieves the same outcome by using a rotating band within the column to force the rising vapors and descending condensate into close contact, achieving equilibrium more quickly.
In a typical fractional distillation, a liquid mixture is heated in the distilling flask, and the resulting vapor rises up the fractionating column (see Image 1). The vapor condenses on glass spurs (known as trays or plates) inside the column, and returns to the distilling flask, refluxing the rising distillate vapor. The hottest tray is at the bottom of the column and the coolest tray is at the top. At steady-state conditions, the vapor and liquid on each tray reach a equilibrium. Only the most volatile of the vapors stays in gas form all the way to the top, where it may then proceed through a condenser, which cools the vapor until it condenses into a liquid distillate. The separation may be enhanced by the addition of more trays (to a practical limitation of heat, flow, etc.).
Image 1: Fractional distillation apparatus using a Liebig condenser
Fractionating columns help to separate the mixture by allowing the mixed vapors to cool, condense, and vaporize again in accordance with Raoult's law. With each condensation-vaporization cycle, the vapors are enriched in a certain component. A larger surface area allows more cycles, improving separation. This is the rationale for a Vigreux fractionating column or a packed fractionating column. Spinning band distillation achieves the same outcome by using a rotating band within the column to force the rising vapors and descending condensate into close contact, achieving equilibrium more quickly.
In a typical fractional distillation, a liquid mixture is heated in the distilling flask, and the resulting vapor rises up the fractionating column (see Image 1). The vapor condenses on glass spurs (known as trays or plates) inside the column, and returns to the distilling flask, refluxing the rising distillate vapor. The hottest tray is at the bottom of the column and the coolest tray is at the top. At steady-state conditions, the vapor and liquid on each tray reach a equilibrium. Only the most volatile of the vapors stays in gas form all the way to the top, where it may then proceed through a condenser, which cools the vapor until it condenses into a liquid distillate. The separation may be enhanced by the addition of more trays (to a practical limitation of heat, flow, etc.).
Friday, March 25, 2011
Tip #22 For Better Chemical Engineering: Six Sigma
Six Sigma is a business management strategy originally developed by Motorola, USA in 1986.[1][2] As of 2010[update], it is widely used in many sectors of industry, although its use is not without controversy.
Six Sigma seeks to improve the quality of process outputs by identifying and removing the causes of defects (errors) and minimizing variability in manufacturing and business processes.[3] It uses a set of quality management methods, including statistical methods, and creates a special infrastructure of people within the organization ("Black Belts", "Green Belts", etc.) who are experts in these methods.[3] Each Six Sigma project carried out within an organization follows a defined sequence of steps and has quantified financial targets (cost reduction or profit increase).[3]
The term Six Sigma originated from terminology associated with manufacturing, specifically terms associated with statistical modeling of manufacturing processes. The maturity of a manufacturing process can be described by a sigma rating indicating its yield, or the percentage of defect-free products it creates. A six sigma process is one in which 99.99966% of the products manufactured are statistically expected to be free of defects (3.4 defects per million). Motorola set a goal of "six sigma" for all of its manufacturing operations, and this goal became a byword for the management and engineering practices used to achieve it.
Six Sigma seeks to improve the quality of process outputs by identifying and removing the causes of defects (errors) and minimizing variability in manufacturing and business processes.[3] It uses a set of quality management methods, including statistical methods, and creates a special infrastructure of people within the organization ("Black Belts", "Green Belts", etc.) who are experts in these methods.[3] Each Six Sigma project carried out within an organization follows a defined sequence of steps and has quantified financial targets (cost reduction or profit increase).[3]
The term Six Sigma originated from terminology associated with manufacturing, specifically terms associated with statistical modeling of manufacturing processes. The maturity of a manufacturing process can be described by a sigma rating indicating its yield, or the percentage of defect-free products it creates. A six sigma process is one in which 99.99966% of the products manufactured are statistically expected to be free of defects (3.4 defects per million). Motorola set a goal of "six sigma" for all of its manufacturing operations, and this goal became a byword for the management and engineering practices used to achieve it.
Friday, March 18, 2011
Tip #21 For Better Chemical Engineering: Intro to PFRs
In a PFR, one or more fluid reagents are pumped through a pipe or tube. The chemical reaction proceeds as the reagents travel through the PFR. In this type of reactor, the changing reaction rate creates a gradient with respect to distance traversed; at the inlet to the PFR the rate is very high, but as the concentrations of the reagents decrease and the concentration of the product(s) increases the reaction rate slows. Some important aspects of the PFR:
* All calculations performed with PFRs assume no upstream or downstream mixing, as implied by the term "plug flow".
* Reagents may be introduced into the PFR at locations in the reactor other than the inlet. In this way, a higher efficiency may be obtained, or the size and cost of the PFR may be reduced.
* A PFR typically has a higher efficiency than a CSTR of the same volume. That is, given the same space-time, a reaction will proceed to a higher percentage completion in a PFR than in a CSTR.
For most chemical reactions, it is impossible for the reaction to proceed to 100% completion. The rate of reaction decreases as the percent completion increases until the point where the system reaches dynamic equilibrium (no net reaction, or change in chemical species occurs). The equilibrium point for most systems is less than 100% complete. For this reason a separation process, such as distillation, often follows a chemical reactor in order to separate any remaining reagents or byproducts from the desired product. These reagents may sometimes be reused at the beginning of the process, such as in the Haber process.
Continuous oscillatory baffled reactor (COBR) is a tubular plug flow reactor. The mixing in COBR is achieved by the combination of fluid oscillation and orifice baffles, allowing plug flow to be achieved under laminar flow conditions with the net flow Reynolds number just about 100.
* All calculations performed with PFRs assume no upstream or downstream mixing, as implied by the term "plug flow".
* Reagents may be introduced into the PFR at locations in the reactor other than the inlet. In this way, a higher efficiency may be obtained, or the size and cost of the PFR may be reduced.
* A PFR typically has a higher efficiency than a CSTR of the same volume. That is, given the same space-time, a reaction will proceed to a higher percentage completion in a PFR than in a CSTR.
For most chemical reactions, it is impossible for the reaction to proceed to 100% completion. The rate of reaction decreases as the percent completion increases until the point where the system reaches dynamic equilibrium (no net reaction, or change in chemical species occurs). The equilibrium point for most systems is less than 100% complete. For this reason a separation process, such as distillation, often follows a chemical reactor in order to separate any remaining reagents or byproducts from the desired product. These reagents may sometimes be reused at the beginning of the process, such as in the Haber process.
Continuous oscillatory baffled reactor (COBR) is a tubular plug flow reactor. The mixing in COBR is achieved by the combination of fluid oscillation and orifice baffles, allowing plug flow to be achieved under laminar flow conditions with the net flow Reynolds number just about 100.
Thursday, March 17, 2011
Tip #20 For Better Chemical Engineering: Continuous Stirred-Tank Reactor
At steady-state, the flow rate in must equal the mass flow rate out, otherwise the tank will overflow or go empty (transient state). While the reactor is in a transient state the model equation must be derived from the differential mass and energy balances.In a CSTR, one or more fluid reagents are introduced into a tank reactor equipped with an impeller while the reactor effluent is removed. The impeller stirs the reagents to ensure proper mixing. Simply dividing the volume of the tank by the average volumetric flow ratethrough the tank gives the residence time, or the average amount of time a discrete quantity of reagent spends inside the tank. Usingchemical kinetics, the reaction's expected percent completion can be calculated. Some important aspects of the CSTR:
The reaction proceeds at the reaction rate associated with the final (output) concentration.
Often, it is economically beneficial to operate several CSTRs in series. This allows, for example, the first CSTR to operate at a higher reagent concentration and therefore a higher reaction rate. In these cases, the sizes of the reactors may be varied in order to minimize the total capital investment required to implement the process.
It can be seen that an infinite number of infinitely small CSTRs operating in series would be equivalent to a PFR.
The behavior of a CSTR is often approximated or modeled by that of a Continuous Ideally Stirred-Tank Reactor (CISTR). All calculations performed with CISTRs assume perfect mixing. If the residence time is 5-10 times the mixing time, this approximation is valid for engineering purposes. The CISTR model is often used to simplify engineering calculations and can be used to describe research reactors. In practice it can only be approached, in particular in industrial size reactors.
The reaction proceeds at the reaction rate associated with the final (output) concentration.
Often, it is economically beneficial to operate several CSTRs in series. This allows, for example, the first CSTR to operate at a higher reagent concentration and therefore a higher reaction rate. In these cases, the sizes of the reactors may be varied in order to minimize the total capital investment required to implement the process.
It can be seen that an infinite number of infinitely small CSTRs operating in series would be equivalent to a PFR.
The behavior of a CSTR is often approximated or modeled by that of a Continuous Ideally Stirred-Tank Reactor (CISTR). All calculations performed with CISTRs assume perfect mixing. If the residence time is 5-10 times the mixing time, this approximation is valid for engineering purposes. The CISTR model is often used to simplify engineering calculations and can be used to describe research reactors. In practice it can only be approached, in particular in industrial size reactors.
Wednesday, March 16, 2011
Tip #19 For Better Chemical Engineering: Chemical Reactors
In chemical engineering, chemical reactors are vessels designed to contain chemical reactions. The design of a chemical reactor deals with multiple aspects of chemical engineering. Chemical engineers design reactors to maximize net present value for the given reaction. Designers ensure that the reaction proceeds with the highest efficiency towards the desired output product, producing the highest yield of product while requiring the least amount of money to purchase and operate. Normal operating expenses include energy input, energy removal, raw material costs, labor, etc. Energy changes can come in the form of heating or cooling, pumping to increase pressure, frictional pressure loss (such as pressure drop across a 90o elbow or an orifice plate), agitation, etc.
Chemical reaction engineering is the branch of chemical engineering which deals with chemical reactors and their design, especially by application of chemical kinetics.
There are a couple main basic vessel types:
- A tank
- A pipe or tubular reactor
Both types can be used as continuous reactors or batch reactors. Most commonly, reactors are run at steady-state, but can also be operated in a transient state. When a reactor is first brought back into operation (after maintenance or inoperation) it would be considered to be in a transient state, where key process variables change with time. Both types of reactors may also accommodate one or more solids (reagents, catalyst, or inert materials), but the reagents and products are typically liquids and gases.
There are three main basic models used to estimate the most important process variables of different chemical reactors:
- batch reactor model (batch),
- continuous stirred-tank reactor model (CSTR), and
- plug flow reactor model (PFR).
Furthermore, catalytic reactors require separate treatment, whether they are batch, CST, or PF reactors, as the many assumptions of the simpler models are not valid.
Key process variables include
- Residence time (τ, lower case Greek tau)
- Volume (V)
- Temperature (T)
- Pressure (P)
- Concentrations of chemical species (C1, C2, C3, ... Cn)
- Heat transfer coefficients (h, U)
A chemical reactor, typically tubular reactor, could be a packed bed. The packing inside the bed may have catalyst to catalyze the chemical reaction. A chemical reactor may also be a fluidized bed; see Fluidized bed reactor.
Chemical reactions occurring in a reactor may be exothermic, meaning giving off heat, or endothermic, meaning absorbing heat. A chemical reactor vessel may have a cooling or heating jacket or cooling or heating coils (tubes) wrapped around the outside of its vessel wall to cool down or heat up the contents.
Via {link}
Friday, February 25, 2011
Tip #19 For Better Chemical Engineering: Overview
It would take too long to list all the products that are impacted by chemical engineers, but knowing what industries employ them may help you comprehend the scope of their work. Chemical engineers work in manufacturing, pharmaceuticals, healthcare, design and construction, pulp and paper, petrochemicals, food processing, specialty chemicals, polymers, biotechnology, and environmental health and safety industries, among others. Within these industries, chemical engineers rely on their knowledge of mathematics and science, particularly chemistry, to overcome technical problems safely and economically. And, of course, they draw upon and apply their engineering knowledge to solve any technical challenges they encounter.
Don't make the mistake of thinking that chemical engineers only make things, though. Their expertise is also applied in the area of law, education, publishing, finance, and medicine, as well as many other fields that require technical training.
Specifically, chemical engineers apply the principles of chemistry to solve problems involving the production or use of chemicals and other products. They design equipment and processes for large-scale chemical manufacturing, plan and test methods of manufacturing products and treating byproducts, and supervise production.
Chemical engineers also work in a variety of manufacturing industries other than chemical manufacturing, such as those producing energy, electronics, food, clothing, and paper. In addition, they work in healthcare, biotechnology, and business services. Chemical engineers apply principles of physics, mathematics, and mechanical and electrical engineering, as well as chemistry. Some may specialize in a particular chemical process, such as oxidation or polymerization. Others specialize in a particular field, such as nanomaterials, or in the development of specific products. They must be aware of all aspects of chemical manufacturing and how the manufacturing process affects the environment and the safety of workers and consumers.
Chemical engineers face many of the same challenges that other professionals face, and they meet these challenges by applying their technical knowledge, communication and teamwork skills, the most up-to-date practices available, and hard work. Benefits include financial reward, recognition within industry and society, and the gratification that comes from working with the processes of nature to meet the needs of society.
Source: http://www.careercornerstone.org/chemeng/chemeng.htm
Don't make the mistake of thinking that chemical engineers only make things, though. Their expertise is also applied in the area of law, education, publishing, finance, and medicine, as well as many other fields that require technical training.
Specifically, chemical engineers apply the principles of chemistry to solve problems involving the production or use of chemicals and other products. They design equipment and processes for large-scale chemical manufacturing, plan and test methods of manufacturing products and treating byproducts, and supervise production.
Chemical engineers also work in a variety of manufacturing industries other than chemical manufacturing, such as those producing energy, electronics, food, clothing, and paper. In addition, they work in healthcare, biotechnology, and business services. Chemical engineers apply principles of physics, mathematics, and mechanical and electrical engineering, as well as chemistry. Some may specialize in a particular chemical process, such as oxidation or polymerization. Others specialize in a particular field, such as nanomaterials, or in the development of specific products. They must be aware of all aspects of chemical manufacturing and how the manufacturing process affects the environment and the safety of workers and consumers.
Chemical engineers face many of the same challenges that other professionals face, and they meet these challenges by applying their technical knowledge, communication and teamwork skills, the most up-to-date practices available, and hard work. Benefits include financial reward, recognition within industry and society, and the gratification that comes from working with the processes of nature to meet the needs of society.
Source: http://www.careercornerstone.org/chemeng/chemeng.htm
Thursday, February 24, 2011
Tip #18 For Better Chemical Engineering: Career Guidance
Pre-University students should take as many math and science courses as possible, both during school and as part of after-school programs. Students aged 5-9 should do additional math, puzzles, and building or design projects. Students aged 9-12 should take extra math, and if inspired, explore pre-algebra and geometry. Students aged 12-18 might consider taking advanced algebra, chemistry, calculus, geometry, trigonometry, physics, building, design, and engineering concept courses.
There are also several lessons and activities, and projects and competitions that can help provide students with an interest in engineering first hand exposure to electrical engineering principals. Students who implement these activities and participate in projects or competitions have a better understanding of engineering and its impact on society. They'll be better able to determine if engineering is the career path for them by sharing their interest with other students, and experiencing hands-on applications of engineering. Summer programs and internships are another great way for students at the pre-university level to explore engineering.
There are also several lessons and activities, and projects and competitions that can help provide students with an interest in engineering first hand exposure to electrical engineering principals. Students who implement these activities and participate in projects or competitions have a better understanding of engineering and its impact on society. They'll be better able to determine if engineering is the career path for them by sharing their interest with other students, and experiencing hands-on applications of engineering. Summer programs and internships are another great way for students at the pre-university level to explore engineering.
Tip #17 For Better Chemical Engineering: Be Curious
Lastly I am going to say be curious. Be curious about problems, be curious about solutions, and be curious about all those tools (equations, connectors, and machine tools) that will help you find solutions to problems. If you let your mind just sit waiting for a solution to easily manifest itself, it won’t. You have to be curious and be active about wanting to become a better engineer.
I plan on posting a lot of the things I have learned during my first few years as an engineer within this blog category. I am trying to remain open to new solutions everyday and not believe that what I learned in college will get me through tomorrow. I hope to learn ten times the amount about processes that are out there within the next year and another 10 times that the next. Only then will I begin to easily see creative solutions to some of those most difficult problems.
Other Interesting Articles and Categories:
Become Good at Everything - A How-to
Starting a Business
Setting Intermediate Goals
Source: http://www.erikvossman.com/
Wednesday, February 23, 2011
Tip #16 For Better Chemical Engineering: Know your tools
If you want to sit around and do equations all day then go to a big name school that’s completely hands-off. If you want to learn how to engineer things and design great things then don’t say no when someone says you want to get some Machine Shop time. Those really greasy rough looking guys/gals that spend all day turning cranks and programming CNC machines (CNC stands for computer numerically controlled) could probably design circles around some of the A+ engineers that have come out of top schools like Michigan. If you know a person who works as a machinist, pick his or her brain and try to get them to show you around a mill or a lathe for a bit. It will be the most informative Saturday afternoon you could have.
Don’t be afraid of the tools that are out there. Even if you don’t pick on up know what they are, how they work, and how best to design for them. When I first arrived at Tissue Genesis, Inc I was told to redesign a plastic molded piece that used a heat staker and a sonic welder. I had no idea what these machines were let alone how to design for them. Then I began calling companies, asking for design tips, sheets that showed design tips, googling everything I could, and basically asking as many questions as possible. In the end I was able to redesign the piece (actually 10 down to 7 main pieces) sonic weld 2 pieces onto a larger one and save $15 a disposable in the heat staking procedure. That was all from just asking a lot of questions and learning about all the tools that are out there.
Some great catalogs to get you started are:
McMaster Carr
MSC Industrial Tools
Tip #15 For Better Chemical Engineering: Taking things apart
A big thing I learned in my last year of undergrad and I continue to notice on the job is that people who take things apart are able to find more solutions. This stems from knowing what’s out there. If you take say a typical desktop computer apart you know that there are a lot of circuit boards, come wiring harnesses, and a fan. That would be one way to look at it. But if you begin to look at each board you see what type of surface mount resistors were used, what processor was used, are there gold leads? Then you look at the wiring harness; what type of connectors were used and why do you think they were used, is the wire stranded or single, can the connectors withstand humidity? Then you look at the fan; where is it placed, why is it in that location, how much power does it consume? Then you begin to look at the whole computer tower and how the parts fit together; why is a board where it is, what about the wiring routes, what looks like it needs the fan the most, will the computer stop running if you place the fan in a different location?
Once you begin to look at the interconnections of each of the pieces you begin to realize why the engineers responsible for it used it. Then, and this can make you some money, you may see a solution to a problem that the current design causes. If you take enough things apart or read enough about how things are made you will have more solutions to the problems you face as an engineer. Good things to take apart are, radios, printers, clocks, TVs, engines, phones, keyboards, computers, speakers, toasters, phones, drills, air tools, and anything else that interests you.
WARNING: Some of the above mentioned items can shock the crap out of you and cause some wicked damage, please be careful and don’t take it apart without consulting someone who knows about it or a super online resource.
Super Online Resources:
HowStuffWorks.com
About.com
Bill Nye the Science Guy
Wikipedia.org
Source: http://www.erikvossman.com/
Tuesday, February 22, 2011
Tip #14 For Better Chemical Engineering: Online Resources
A few of the online resources that are key for any Chemical Engineer:
www.lib.berkeley.edu/CHEM/
http://www.mcmaster.com/
Keep these around at all times and use them as much as possible to solve any problem!
Tip #13 For Better Chemical Engineering: Problem Solving
First off you should want to solve problems. If you don’t like to solve problems you are going to most likely be miserable as an engineer. If you are in classes right now you are probably wondering, as I did, why the heck your professors are making you do problem sets that take 10-15 hours to complete, and make you search several sources (textbooks, computer programs, online resources, even scientific papers) to complete one single problem. Well the answer to this is one they never told me during my years at Michigan, or at least not loud enough it would wake me up.
You do all that problem solving and looking up to train your mind to look at problems from all angles. Of course you’re never going to be asked to solve a mass transfer problem without referencing a formula, but if you know that the formula is there, you can begin to see the problem from that angle before you even know the answer. Think of all those problems you are doing as a way to increase your mental toolbox. Every ME problem you do, or CHE problem allows you another look at a very similar problem. You’ve also more than likely said, “All these problems are the same” in some sort of frustration. When you’re on the job you may only have access to 50% of the tools needed. If you didn’t do problems to prepare yourself you wouldn’t be able to tell your boss, he who signs you paychecks and OKs bonuses, “here’s the answer, if we just go at it from this obscure angle it’s simple.”
Monday, February 21, 2011
Tip #12 For Better Chemical Engineering: Early Start
Becoming a good chemical engineer isn’t something that will happen straight out of college (takes a lot of bumps to make it work!), some may say you are born with the skills; that may be partly true, but I believe you need to acquire the thought process that engineers have through years of experience. You can speed up the process if you know what to look for and how to handle problem situations.
I have always liked math growing up and once I got to college figured I should go into some sciences. Plus reading wasn’t a big priority for me yet. Engineering seemed like a good fit because it seemed like the most rewarding. Becoming an engineer offers you the opportunity to learn the skills needed to be the designer of things, get patents, get your name written into history books, literally. There are many disciplines to choose from such as mechanical, chemical, electrical, civil, etc. I chose Chemical Engineering because of its being the oldest and most demanded general engineering.
That’s neither here nor there though. You came here most likely to learn HOW TO BECOME A GOOD ENGINEER, MAYBE EVEN GREAT. Well, I won’t give you any sure fire way but I will give it all away!
Saturday, February 13, 2010
Tip #11 For Better Chemical Engineering: The Design Process
I will be doing a few posts on the the design process of a chemical engineer. This post will be a quick over view of the design process and I will go into more detail with the subsequent posts.
The five steps used for solving design problems are:
1. Define the problem
2. Gather pertinent information
3. Generate multiple solutions
4. Analyze and select a solution
5. Test and implement the solution
2. Gather pertinent information
3. Generate multiple solutions
4. Analyze and select a solution
5. Test and implement the solution
The first step in the design process is the problem definition. This definition usually contains a listing of the product or customer requirements and specially information about product functions and features among other things. In the next step, relevant information for the design of the product and its functional specifications is obtained. A survey regarding the availability of similar products in the market should be performed at this stage. Once the details of the design are clearly identified, the design team with inputs from test, manufacturing, and marketing teams generates multiple alternatives to achieve the goals and the requirements of the design. Considering cost, safety, and other criteria for selection, the more promising alternatives are selected for further analysis. Detail design and analysis step enables a complete study of the solutions and result in identification of the final design that best fits the product requirements. Following this step, a prototype of the design is constructed and functional tests are performed to verify and possibly modify the design. When solving a design problem, you may find at any point in the process that you need to go back to a previous step. The solution you chose may prove unworkable for any number of reasons and may require redefining the problem, collecting more information, or generating different solutions.
These posts intends to clarify some of the details involved in implementing the design process. Therefore a description of the details involved in each step of the design process is listed below. Although the descriptions of the activities within each step may give the impression that the steps are sequential and independent from each other, the iterative nature of the application of the process should be kept in mind throughout these posts.
Friday, January 29, 2010
Tip #10 For Better Chemical Engineering: Pumps
Pumps play a very important roll in any engineer and especially for chemical engineers. Knowing how to operate and maintain a pump as well as read a pump curve play a key roll in running a plant or any process. There are 2 main types of pumps centrifugal (Kinetic), and positive displacement pump.
There are two main categories of pumps - kinetic and positive displacement. Almost all pumps fall into one of these two categories. The main difference between kinetic and positive displacement pumps lies in the method of fluid transfer. A kinetic pump imparts velocity energy to the fluid, which is converted to pressure energy upon exiting the pump casing. A positive displacement pump moves a fixed volume of fluid within the pump casing by applying a force to moveable boundaries containing the fluid volume.
Kinetic pumps can be further divided into two categories of pumps – centrifugal and special effect. Special effect pumps include jet pumps, reversible centrifugal, gas lift, electromagnetic and hydraulic ram. Special effect pumps are not commonly used relative to centrifugal pumps, so they will not be covered in this course.
Positive displacement pumps are also divided into two major pump categories – reciprocating and rotary. Reciprocating pumps transfer a volume of fluid by a crankshaft, eccentric cam or an alternating fluid pressure acting on a piston, plunger or a diaphragm in a reciprocating motion. Rotary pumps operate by transferring a volume of fluid in cavities located between rotating and stationary components inside the pump casing. The relative features of reciprocating and rotary pumps, as well as centrifugal pumps, will be covered in this course.
Capacity
The wide variety of centrifugal pumps manufactured offer a relatively large range of available capacities. Radial-flow and mixed flow pumps are used for low to medium capacity applications. For high capacity applications, axial-flow pumps are capable of delivering flow rates in excess of 100,000 gpm. Centrifugal pumps are not stable at low flow rates, although there are special low-flow centrifugal pumps available that can deliver flow rates less than 10 gpm. However, for extreme low-flow applications ( Reciprocating and rotary pumps are capable of capacities ranging from low to medium, with flow rates peaking at 10,000+ gpm. In theory, reciprocating pumps can be manufactured to deliver more capacity, but they become prohibitively large and expensive at high flow rates. Both reciprocating and rotary pumps are capable of delivering product at extremely low flow rates (fractions of a gpm), making them particularly suitable for many chemical injection applications.
Pressure
Centrifugal pumps and rotary pumps are best suited for low to medium pressure applications. Reciprocating pumps are usually specified for high pressure service, with capabilities exceeding 100,000 psi. Multi-stage centrifugal pumps can deliver at pressures of 6,000+ psi and may be the most economical choice at this pressure in high capacity applications. But, in most applications exceeding 1,000 psig, reciprocating pumps are more suitable, particularly in low to medium capacity service. Both reciprocating and rotary pumps will continually increase pressure when pumping against a closed discharge to the extent allowed by the driver’s horsepower. This can result in overpressure of the pump or piping components, so it is necessary to install a relief valve on the discharge of the pump capable of discharging the full capacity of the pump. A centrifugal pump’s pressure rise is limited to the shut-off pressure on the pump curve, which is always less than the design pressure of the pump (and the piping system if properly designed). A relief valve is only needed if no other measures are provided to detect low flow conditions and shut down the pump to prevent damage. The relief valve need only be sized to pass the minimum flow rate required to maintain stable flow and prevent excessive temperature rise.
Smooth or Pulsating Flow
Centrifugal pumps and most rotary pumps provide smooth, non-pulsating flow, while reciprocating pumps produce a pulsating flow. A pulsating flow may require special design considerations in the piping system. If the pump is not located near the suction source, then acceleration head can contribute to low NPSHA problems, which may require the installation of a suction stabilizer. A pulsation dampener may need to be installed in the discharge piping to reduce pressure surges resulting from the pulsating flow.
Variable or Constant Flow
Centrifugal pumps operate on a variable-flow, variable-head curve. As the discharge pressure decreases, the pump delivers a higher flow rate. At any given speed, reciprocating and rotary pumps operate at a constant flow rate regardless of the discharge pressure. There are specific applications that require either constant flow or variable flow. Metering pumps rely on a constant flow at varying pressures, which makes reciprocating pumps and rotary pumps suitable for this application. Piston pumps used for metering will often use an adjustable stroke length to allow the operator to vary the flow rate to meet the system requirements. Centrifugal pumps are favored where process conditions often require varying flow rates. For example, a level control valve must throttle the flow rate from a vessel to maintain a constant level in the vessel. A centrifugal pump is well suited to handle this process condition, whereas a positive displacement pump would either require a continuous recycle to suction or a variable speed driver to accommodate the variable flow.
Self-priming
Reciprocating and rotary pumps are self-priming. This is an important consideration where a prime cannot be maintained on the pump. Centrifugal pumps are not inherently self-priming, although some manufacturers do specially design self-priming units. External priming sources, such as an eductor or vacuum pump can also be employed.
Costs and Space Considerations
In an overlap region where the conditions are suitable to use a centrifugal, reciprocating or a rotary pump, the following rules generally apply: The reciprocating pump will generally have higher initial capital costs and will require more space relative to the centrifugal pump or the rotary pump. The reciprocating pump will generally have higher maintenance costs relative to the centrifugal pump or the rotary pump. The centrifugal pump will generally have higher annual power consumption costs relative to the reciprocating pump or the rotary pump because of lower efficiencies. Of course, there are many exceptions. These are just general guidelines. A pump that is selected for an application outside of its optimum operating parameters will almost certainly not follow these rules. For example, a rotary pump operating in a high pressure, abrasive-slurry service would probably have higher maintenance costs than a properly selected reciprocating pump. The close running clearances (particularly for high pressure service) required in the rotary pump would likely result in premature wear and frequent maintenance.
Fluid Handling
Centrifugal pumps are suitable for transferring a variety of fluids ranging from clean, clear non-abrasive fluids to abrasive-slurries. However, a centrifugal pump is not the best choice for pumping highly viscous fluids due to dramatic drops in efficiency at high viscosities. Centrifugal pumps are not normally specified for viscosities higher than about 4,000 SSU. Centrifugal pumps are also not well suited to pumping entrained air. Most centrifugal pumps can handle up to about 2% entrained gas and specially-designed pumps can handle up to about 10%.
Reciprocating pumps are well suited for transferring clear, non-abrasive fluids, as well as abrasive slurries. In fact, the relatively low velocities of moving parts within a reciprocating pump make it particularly resistant to erosion in abrasive-slurry applications, provided that the pump is properly designed for the service. Reciprocating pumps maintain high efficiencies when pumping highly viscous fluids and can easily handle 50% and higher volumes of entrained gas.
Rotary pumps can also handle high viscosity fluids and high volumes of entrained gas. In fact, many rotary pumps operate at their best efficiency at higher viscosities. However, rotary pumps are not well suited for pumping corrosive fluids or fluids with abrasive solids because of close clearances between rotating and static pump components.
Summary
The comparisons between different pump categories presented in this course are general. The information is intended to familiarize the student with some of the basic differences between centrifugal, reciprocating and rotary pumps. However, there are many different subcategories of pumps within these broad categories and there are many regions of overlap where multiple types of pumps in the same category and even in different categories would be suitable. Since every pump application is unique, each of the factors that influence the pump selection must be considered in detail.
14 Engineering Challenges The World Must Face
Engineers from around the world will hold discussions at The University of Texas at El Paso to address critical problems affecting the planet.
The National Academy of Engineering has called engineers to action by identifying the 14 “Grand Challenges” that need to be solved in order to improve quality of life and health, create a sustainable future and increase renewable energy.
UTEP will host “Building Partnerships and Pathways to Address Engineering Grand Challenges Conference” Feb. 8-10 at Union Building East, third floor, Tomás Rivera Conference Center. More than 80 research and government institutions from the United States, Europe, Latin America and Canada will participate.
The three-day conference will focus on finding innovative solutions to challenges that face our society.
The 14 “Grand Challenges” include:
Providing access to clean water
Preventing nuclear terror
Engineering better medicines
Advancing health informatics – Developing better health information systems to improve medical visits, counter pandemics and biological or chemical attacks.
Making solar energy economical
Developing carbon sequestration methods -- capturing and storing excess carbon dioxide to prevent global warming
Securing cyberspace
Reverse-engineering the brain – engineers are trying to create computers capable of emulating human intelligence.
Managing the nitrogen cycle – Engineers can help restore balance to the nitrogen cycle with better fertilization technologies and by capturing and recycling waste. Controlling the impact of agriculture on the global cycle of nitrogen is a growing challenge for sustainable development.
Providing energy from fusion – Fusion is the energy source for the sun. Human-engineered fusion has been demonstrated on a small scale. The challenge is to scale up the process to commercial proportions, in an efficient, economical, and environmentally benign way.
Restoring and improving urban infrastructure
Engineering the tools of scientific discovery
Enhancing virtual reality -- Virtual reality is an illusory environment, engineered to give users the impression of being somewhere they are not. It can be used for training, treatment, and communication.
Advancing personalized learning -- Instruction can be individualized based on learning styles, speeds, and interests to make learning more reliable.
The mission of the conference is to enhance student interest in engineering and science, and emphasize the critical role engineers play in solving issues impacting our planet.
The event is open to the public. To register, log on to engineering.utep.edu/grandchallenges Free registration ends Jan. 31. Registration will reopen on site Feb. 8 at a cost of $125 per person.
Keynote speakers will include:
- Victor Mendez, administrator of the Federal Highway Administration. A graduate of UTEP, Mendez received a Bachelor of Science degree in civil engineering in 1980. He earned a Master of Business Administration degree from Arizona State University. He previously served as Director of the Arizona Department of Transportation.
- Ray Orbach, director of the Energy Institute at The University of Texas at Austin. Orbach received his Bachelor of Science degree in physics from the California Institute of Technology in 1956. He received his Ph.D. in physics from the University of California, Berkeley. He was previously the U.S. Department of Energy's first undersecretary for science.
- Semahat S. Demir, director of the Biomedical Engineering Program at the National Science Foundation. Demir has led, developed and/or participated in 15 NSF and interagency funding programs. She is a fellow of the American Institute of Medical and Biomedical Engineers (AIMBE) and has received 55 professional awards and honors.
Researchers from different disciplines, industries and institutions of higher education will engage in discussions, share best practices for successfully establishing partnerships and identify what is needed to overcome obstacles to creating alliances among universities, industries and national laboratories.
“With a tremendous effort by the members of the organizing committee, we have been able to attract some of the brightest minds in the world in the areas of energy, urban infrastructure and biomedical technology to UTEP for this conference” said Richard Schoephoerster, dean for the College of Engineering.
The goal is to identify opportunities for synergetic research and strategic partnerships among research universities, Minority Serving Institutions (MSIs) and industry; to identify the actions needed to create a culture of collaboration that facilitates the formation of research partnerships; and to showcase the capabilities of faculty from MSIs.
“The recommendations coming as a result of the discussions over the three-day event will set the stage for research and development into these pressing societal needs, and UTEP will be positioned as a major participant in those efforts,” Schoephoerster said.
“This is entirely in line with our effort to become a Tier One research institution, and with our efforts to create opportunities for our students to contribute to a diverse engineering workforce,” he added.
The event is sponsored by the National Science Foundation with additional support from industry sponsors Freeport-McMoRan Copper & Gold, Lockheed Martin, Shell and Boeing.
Source: The University of Texas at El Paso
http://engineering.nitews.com/110e2
The National Academy of Engineering has called engineers to action by identifying the 14 “Grand Challenges” that need to be solved in order to improve quality of life and health, create a sustainable future and increase renewable energy.
UTEP will host “Building Partnerships and Pathways to Address Engineering Grand Challenges Conference” Feb. 8-10 at Union Building East, third floor, Tomás Rivera Conference Center. More than 80 research and government institutions from the United States, Europe, Latin America and Canada will participate.
The three-day conference will focus on finding innovative solutions to challenges that face our society.
The 14 “Grand Challenges” include:
Providing access to clean water
Preventing nuclear terror
Engineering better medicines
Advancing health informatics – Developing better health information systems to improve medical visits, counter pandemics and biological or chemical attacks.
Making solar energy economical
Developing carbon sequestration methods -- capturing and storing excess carbon dioxide to prevent global warming
Securing cyberspace
Reverse-engineering the brain – engineers are trying to create computers capable of emulating human intelligence.
Managing the nitrogen cycle – Engineers can help restore balance to the nitrogen cycle with better fertilization technologies and by capturing and recycling waste. Controlling the impact of agriculture on the global cycle of nitrogen is a growing challenge for sustainable development.
Providing energy from fusion – Fusion is the energy source for the sun. Human-engineered fusion has been demonstrated on a small scale. The challenge is to scale up the process to commercial proportions, in an efficient, economical, and environmentally benign way.
Restoring and improving urban infrastructure
Engineering the tools of scientific discovery
Enhancing virtual reality -- Virtual reality is an illusory environment, engineered to give users the impression of being somewhere they are not. It can be used for training, treatment, and communication.
Advancing personalized learning -- Instruction can be individualized based on learning styles, speeds, and interests to make learning more reliable.
The mission of the conference is to enhance student interest in engineering and science, and emphasize the critical role engineers play in solving issues impacting our planet.
The event is open to the public. To register, log on to engineering.utep.edu/grandchallenges Free registration ends Jan. 31. Registration will reopen on site Feb. 8 at a cost of $125 per person.
Keynote speakers will include:
- Victor Mendez, administrator of the Federal Highway Administration. A graduate of UTEP, Mendez received a Bachelor of Science degree in civil engineering in 1980. He earned a Master of Business Administration degree from Arizona State University. He previously served as Director of the Arizona Department of Transportation.
- Ray Orbach, director of the Energy Institute at The University of Texas at Austin. Orbach received his Bachelor of Science degree in physics from the California Institute of Technology in 1956. He received his Ph.D. in physics from the University of California, Berkeley. He was previously the U.S. Department of Energy's first undersecretary for science.
- Semahat S. Demir, director of the Biomedical Engineering Program at the National Science Foundation. Demir has led, developed and/or participated in 15 NSF and interagency funding programs. She is a fellow of the American Institute of Medical and Biomedical Engineers (AIMBE) and has received 55 professional awards and honors.
Researchers from different disciplines, industries and institutions of higher education will engage in discussions, share best practices for successfully establishing partnerships and identify what is needed to overcome obstacles to creating alliances among universities, industries and national laboratories.
“With a tremendous effort by the members of the organizing committee, we have been able to attract some of the brightest minds in the world in the areas of energy, urban infrastructure and biomedical technology to UTEP for this conference” said Richard Schoephoerster, dean for the College of Engineering.
The goal is to identify opportunities for synergetic research and strategic partnerships among research universities, Minority Serving Institutions (MSIs) and industry; to identify the actions needed to create a culture of collaboration that facilitates the formation of research partnerships; and to showcase the capabilities of faculty from MSIs.
“The recommendations coming as a result of the discussions over the three-day event will set the stage for research and development into these pressing societal needs, and UTEP will be positioned as a major participant in those efforts,” Schoephoerster said.
“This is entirely in line with our effort to become a Tier One research institution, and with our efforts to create opportunities for our students to contribute to a diverse engineering workforce,” he added.
The event is sponsored by the National Science Foundation with additional support from industry sponsors Freeport-McMoRan Copper & Gold, Lockheed Martin, Shell and Boeing.
Source: The University of Texas at El Paso
http://engineering.nitews.com/110e2
Wednesday, January 27, 2010
Tip #9 Of Better Chemical Engineering: Calculation
I must say in my short time of being an engineer is that you need to be able to do quick calculations. And, by that I mean quick multiplications and back of the envelope calculations. These calculations will help show that you are smart and quick and can come to a conclusion quickly. Also you will always be able to back up any solutions you come to on the job with a quick calculation or some sort of similar derivation. Also being able to calculation rough derivations to prove you understand what is going on and what needs to be done to fix it. That is all. Know your calculations!
Sunday, January 24, 2010
Tip #8: Stay Current
Another problem I have noticed with many engineers is that they do not stay current. Here are a few quick easy ways to stay current:
-Read Scientific Journals
-Reread old material from school
-Buy at least one handbook for what you are doing (e.g. Albright's Chemical Engineering Handbook)
-Keep update on what is going on in the world (e.g. Digg's science section)
-Take online courses or go back to school
-Read free online courses (MIT's website)
There are many more ways to stay current and as I come across them I will spread the word!
-Read Scientific Journals
-Reread old material from school
-Buy at least one handbook for what you are doing (e.g. Albright's Chemical Engineering Handbook)
-Keep update on what is going on in the world (e.g. Digg's science section)
-Take online courses or go back to school
-Read free online courses (MIT's website)
There are many more ways to stay current and as I come across them I will spread the word!
Thursday, January 21, 2010
Tip #7: Find The Job
Here is a quick run over on how I found my job:
-Craigslist: This is the best resource to get your resume out to multiple areas. All craigslist requires is one resume that can be across multiple cities. There are also so many different companies now using Craigslist to reach a potential worker. Responding to these ads had the highest reply rate for me. I believe this is because it takes a more personal approach to reply to Craigslist ads. Make sure to always respond to the information in the ad in your initial email.
-Indeed: www.indeed.com is the singles greatest search engine and resource for finding a job. Indeed will constantly search all of the other job sites and email you updates how ever frequently you want. I used this site to constantly keep update on new job postings.
When replying to a job post:
-Make sure to tailor your resume to the job listing.
-Make the initial email short and to the point. Make sure to respond to the job list.
-Do not use a generic response or email.
-Craigslist: This is the best resource to get your resume out to multiple areas. All craigslist requires is one resume that can be across multiple cities. There are also so many different companies now using Craigslist to reach a potential worker. Responding to these ads had the highest reply rate for me. I believe this is because it takes a more personal approach to reply to Craigslist ads. Make sure to always respond to the information in the ad in your initial email.
-Indeed: www.indeed.com is the singles greatest search engine and resource for finding a job. Indeed will constantly search all of the other job sites and email you updates how ever frequently you want. I used this site to constantly keep update on new job postings.
When replying to a job post:
-Make sure to tailor your resume to the job listing.
-Make the initial email short and to the point. Make sure to respond to the job list.
-Do not use a generic response or email.
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