Rotary and reciprocating compressors are both components of gas transfer systems. They both have the same purpose–to bring a gas into the system, inhale exhaust, then repeat the process. They both do this by changing the pressure at certain points in order to force gas in and exhaust out.
One key difference is that reciprocating compressors use pistons while rotary compressors do not. A reciprocating compressor has a piston move downwards, reducing pressure in its cylinder by creating a vacuum. This difference in pressure forces the cylinder door to open and bring gas in. When the cylinder goes back up, it increases pressure, thus forcing the gas back out. The up-and-down motion is called a reciprocating motion, hence the name.
Rotary compressors, on the other hand, use rollers. They sit slightly off-center in a shaft, with one side always touching the wall. As they move at high speeds, they accomplish the same goal as the reciprocating compressors–one part of the shaft is always at a different pressure than the other, so gas can come in at the low pressure point and exit at the high pressure point.
Advantages and Disadvantages
Reciprocating compressors are marginally more efficient than rotary compressors, generally being able to compress the same amount of gas with between 5 and 10 percent less energy input. However, since this difference is so marginal, most small-to-medium level users are best off using a rotary compressor. Reciprocating compressors are more expensive and require more maintenance, so it is often not worth the extra cost and headache for such a small difference in efficiency.
Large users, however, are generally best-served by reciprocating compressors. These are users for whom 5 percent represents a substantial figure, often substantial enough to justify the added expense.
Comparison Between Reciprocating and Rotary Compressors
Comparison between Reciprocating and Rotary Compressors can be done in aspects like pressure ratio, handled volume, speed of compressor, vibrational problem, size, air supply, purity of compressed air, compression efficiency, maintenance, mechanical efficiency, lubrication, initial cost, flexibility and suitability.
||Discharge Pressure of air is high. The pressure ratio per stage will be in the order of 4 to 7.
||Discharge pressure of air is low. The pressure ratio per stage will be in the order of 3 to 5.
||Quantity of air handled is low and is limited to 50m3/s.
||Large measure of air handled can be handled and it is about 500 m3/s.
||Speed of Compressor
||Low speed of compressor.
||High speed of compressor.
||Due to reciprocating section, greater vibrational problem, the parts of machine are poorly balanced.
||Rotary parts of machine, thus it has less vibrational problems. The machine parts are fairly balanced.
||Size of compressor
||Size of Compressor is bulky for given discharge volume.
||Compressor size is small for given discharge volume.
||Air supply is intermittent.
||Air supply is steady and continuous..
||Purity of compressed air
||Air delivered from the compressor is dirty, since it comes in contact with lubricating oil and cylinder surface.
||Air delivered from the compressor is clean and free from dirt.
||Higher with pressure ratio more than 2.
||Higher with compression ratio less than 2.
||Higher due to reciprocating engine.
||Lower due to less sliding parts..
||Lower due to several sliding parts..
||Higher due to less sliding parts.
||Complicated lubrication system.
||Simple lubrication system.
||Greater flexibility in capacity and pressure range.
||No flexibility in capacity and pressure range.
||For medium and high pressure ratio.
For low and medium gas volume.
|For low and medium pressures.
For large volumes.
The laws of thermodynamics dictate energy behavior, for example, how and why heat, which is a form of energy, transfers between different objects. The first law of thermodynamics is the law of conservation of energy and matter. In essence, energy can neither be created nor destroyed; it can however be transformed from one form to another. The second law states that isolated systems gravitate towards thermodynamic equilibrium, also known as a state of maximum entropy, or disorder; it also states that heat energy will flow from an area of low temperature to an area of high temperature. These laws are observed regularly every day.
Melting Ice Cube
Every day, ice needs to be maintained at a temperature below the freezing point of water to remain solid. On hot summer days, however, people often take out a tray of ice to cool beverages. In the process, they witness the first and second laws of thermodynamics. For example, someone might put an ice cube into a glass of warm lemonade and then forget to drink the beverage. An hour or two later, they will notice that the ice has melted but the temperature of the lemonade has cooled. This is because the total amount of heat in the system has remained the same, but has just gravitated towards equilibrium, where both the former ice cube (now water) and the lemonade are the same temperature. This is, of course, not a completely closed system. The lemonade will eventually become warm again, as heat from the environment is transferred to the glass and its contents.
Sweating in a Crowded Room
The human body obeys the laws of thermodynamics. Consider the experience of being in a small crowded room with lots of other people. In all likelihood, you’ll start to feel very warm and will start sweating. This is the process your body uses to cool itself off. Heat from your body is transferred to the sweat. As the sweat absorbs more and more heat, it evaporates from your body, becoming more disordered and transferring heat to the air, which heats up the air temperature of the room. Many sweating people in a crowded room, “closed system,” will quickly heat things up. This is both the first and second laws of thermodynamics in action: No heat is lost; it is merely transferred, and approaches equilibrium with maximum entropy.
Taking a Bath
Consider a situation where a person takes a very long bath. Immediately during and after filling up the bathtub, the water is very hot — as high as 120 degrees Fahrenheit. The person will then turn off the water and submerge his body into it. Initially, the water feels comfortably warm, because the water’s temperature is higher than the person’s body temperature. After some time, however, some heat from the water will have transferred to the individual, and the two temperatures will meet. After a bit more time has passed, because this is not a closed system, the bath water will cool as heat is lost to the atmosphere. The person will cool as well, but not as much, since his internal homeostatic mechanisms help keep his temperature adequately elevated.
Flipping a Light Switch
We rely on electricity to turn on our lights. Electricity is a form of energy; it is, however, a secondary source. A primary source of energy must be converted into electricity before we can flip on the lights. For example, water energy can be harnessed by building a dam to hold back the water of a large lake. If we slowly release water through a small opening in the dam, we can use the driving pressure of the water to turn a turbine. The work of the turbine can be used to generate electricity with the help of a generator. The electricity is sent to our homes via power lines. The electricity was not created out of nothing; it is the result of transforming water energy from the lake into another energy form.
Basic terms for Mechanical Engineering
List of basic terms for Mechanical Engineering
1. Torque or Turning Force
7. Specific Weight
8. Specific Volume
9. Specific Gravity
10. Specific Heat
13. Discharge of Fluid
14. Bernoulli’s Equation
15. Device for Fluid
16. Mach Number
17. Hydraulic Machine
18. Draft Tube
19. Thermodynamics Laws
- zeroth law
- First law
- second law
21. calorific value of fuel
22. Boiler/Steam Generator
24. Air Preheater
25. Boiler Draught
32. Rating of fuel-
33. Stoichiometric Mixture/ Stoichiometric Ratio
34. Heat Transfer
35. Thermal Conductivity
36. Heat Exchanger
38. 1 tonne Refrigeration
41. Gear Train
42. Gyroscopic Couple
43. Heat Treatment
45. Non-ferrous metal
52. Nuclear Fission
53. Nuclear Fussion
55. Machine Tool
56. Cutting Tool
Torque or Turning Force:
It is the total amount of force which is required to create acceleration on moving substance.
Two forces those acts on equally,parallely & oppositely on two separate points of same material.
It is the amount of moving effect which is gained for action of turning force.
It is the force that can prevent equal & opposite force. That means, it is the preventing force. If one force acts on outside of a material, then a reactive force automatically acts to protest that force. The amount of reactive force per unit area is called stress. e.g. Tensile Stress, Compressive Stress, Thermal Stress.
If a force acts on a substance, then in that case if the substance would deform. Then the amount of deformation per unit length of that substance is called strain.
It is one type of device which is being distorted under certain amount of load & also can also go to its original face after the removal of that load.
- To store energy.
- To absorb energy.
- To control motion of two elements.
Load per unit deflection. The amount of load required to resist the deflection.
Weight per unit volume of the fluid.
Volume per unit mass of the fluid.
It is the ratio of specific weight of required substance to specific weight of pure water at 4 degree centigrade temperature.
The amount of heat required to increase 1 unit temperature of 1 unit mass.
The amount of resistance of one layer of fluid over other layer of fluid.
It is the ratio of dynamic viscosity to density.
When a body is immersed in a liquid, it is lifted up by a force equal to weight of liquid displaced by the body. The tendency of liquid to lift up an immersed body is buoyancy. The upward thrust of liquid to lift up the body is called buoyancy force.
P/γ +V²/2g +Z = Constant
Where, P = pressure,V = velocity,Z = Datumn Head
Devices for fluid:
It measures discharge of fluid.
It measures discharge of fluid.
It measures discharge of fluid.
Pitot tube :
It measures velocity of fluid.
It is the ratio of the velocity of fluid to the velocity of sound.
M=1 —————– Sonic flow
M> (1-6) ———– Super-Sonic flow
M>6 —————- Hyper-Sonic flow
Fluid discharge/Fluid flow:
Quantity of fluid flowing per second.
(through a section of pipe/ through a section of channel)
where, V= velocity of fluid,A= cross-sectional area of pipe/channel
Note: 1m³ = 1000 L1 cusec = 1 ft³/sec1 ft = 0.3048 m
It attaches with reaction turbine . Its function is to reduce energy loss from reaction turbine & it also reduce pressure at outlet which is must blow the atmospheric pressure.
If two body are in thermal equilibrium with a third body then these two body are also in thermal equilibrium with each other.
First Law of Thermodynamics:
In a closed system, work deliver to the surrounding is directly proportonal to the heat taken from the surrounding.And also, In a closed system, work done on a system is directly proportonal to the heat deliver to the surrounding.
Second Law of Thermodynamics:
It is impossible to make a system or an engine which can change 100 percent input energy to 100 percent output.
It is a thermodynamic property.
ds = dq/T
where, ds = change of entropy, dq = change of heat, T = Temperature.
In adiabatic process, entropy can not change. Actually,lacking or mal-adroitness of tranfering energy of a system is entropy.
Calorific Value of fuel:
It us the total amount of heat obtained from burning 1 kg solid or liquid fuel.
It is a clossed vessel which is made of steel. Its function is to transfer heat to water to generate steam.
It is a part of boiler. Its function is to heat feed water which is supplied to boiler.
It is a part of boiler. Its function is to increase temperature of steam into boiler.
It is a part of boiler. Its funtion is to preheats the air to be supplied to furnace and it recover heat from exhaust gas.
It is an important term for boiler. It is the difference of pressure above and below the fire grate. This pressure difference have to maintain very carefully inside the boiler. It actually maintains the rate of steam generation. This depends on rate of fuel burning. Inside the boiler rate of fuel burning is maintained with rate of entry fresh air. If proper amount of fresh air never entered into the boiler, then proper amount of fuel inside the boiler never be burnt. So, proper fresh air enters into the boiler only by maintaining boiler draught.
Nozzle is a duct of varying cros-sectional area. Actually, it is a passage of varying cross-sectional area. It converts steam’s heat energy into mechanical energy. It is one type of pipe or tube that carrying liquid or gas.
It is the process of removing burnt gas from combustion chamber of engine cylinder.
Actually, power output of engine depends on what amount of air enter into the engine through intake manifold. Amount of entry air if increased, then must be engine speed will increased. Amount of air will be increased by increasing inlet air density. The process of increasing inlet air density is supercharging. The device which is used for supercharging is called supercharger. Supercharger is driven by a belt from engine crankshaft. It is installed in intake system.
Turbocharging is similar to the supercharging. But in that case turbocharger is installed in exhaust system whereas supercharger is installed in intake system. Turbocharger is driven by force of exhaust gas. Generally, turbocharger is used for 2-stroke engine by utilizing exhaust energy of the engine, it recovers energy otherwise which would go waste.
Its function id to regulate mean speed of engine when there are variation in the load. If load incrases on the engine, then engine’s speed must decrease. In that case supply of working fluid have to increase. In the otherway, if load decrease on the engine, then engine’ speed must increase. In that case supply of working fluid have to decrease.Governor automatcally, controls the supply of working fluid to the engine with varying load condition.
It is the one of the main parts of the I.C. engine. Its main function id to store energy in the time of working stroke or expansion stroke. And, it releasesenergy to the crankshaft in the time of suction stroke, compression stroke & exhaust stroke. Because, engine has only one power producing stroke.
Rating of fuel:
Octane number. Octane number indicates ability of fuel to resist knock.
Cetane Number. Cetane number indicates ability of ignition of diesel fuel. That means, how much fast ignites diesel fuel.
It is the chemically correct air-fuel ratio by volume. By which theoretically sufficient oxygen will be gotten to burn all combustible elements in fuel completely.
It is a science which deals with energy transfer between material bodies as a result of temperature difference.There are three way to heat transfer such as-ConductionConvectionRadiation
It is the quantity of heat flows between two parts of solid material by conduction. In this case following consideration will be important fact-
- Time—— 1 sec
- Area of that solid material——– 1 m²
- Thickness of that solid material—— 1m
- Temperature difference between two parts of that material—— 1k
It is one type of device which can transfer heat from one fluid to another fluid. Example- Radiator, inter-cooler, preheater, condenser, boiler etc.
It is the process of removing heat from a substance. Actually, extraction of heat from a body whose temperature is already below the temperature of its surroundings.
1 tonne of refrigeration:
It is amount of refrigeration effect or cooling effect which is produced by uniform melting of 1 tonne ice in 24 hours from or at 0 degree centigrade or freezing 1 tonne water in 24 hours from or at 0 degree centigrade.
It is the addition of moisture to the air without change dry bulb temperatur.
It is the removal of moisture from the air without change dry bulb temperature.
Meshing of two or more gear. It can transmit power from one shaft to another shaft.
Operation involving heating and cooling of a metal in solid state for obtaining desirable condition without being changed chemical composition.Its object-increase hardness of metal.increase quality of metal ( heat, corrosion,wear resistance quality )improve machinability.
1. Cast Iron – (2-6.67)%C, Si, Mn, P, S
2. Steel – (0-2)%C
3. Wrought Iron – 99.5% Fe
1. Brass – (Cu+Zn)
2. Bronze –
(Sn+Cu) —— Tin Bronze
(Si+Cu) ——- Silicon Bronze
(Al+Cu) ——- Aluminium Bronze
It is the difference between basic dimension of mating parts. That means, minimum clearance between mating parts that can be allowed.
It is the difference between upper limit of dimension. It is also the permissible variation above and below the basic size. That means maximum permissible variation in dimensions.
It is the difference in size between mating parts. That means, in that case the outside dimension of the shaft is less than internal dimension of the hole.
It is the ability to resist deformation.
It is the property to resist fracture.
When a material is subjected to repeated stress below yield point stress, such type of failure is fatigue failure.
It is a nuclear reaction by which one big nucleous divided into two or more nucleous.
It is also a nuclear reaction by which one big nucleus will produced by adding two small nucleus.
It is the process of joining two similar or dissimilar metal by fusion.
Arc Welding –
* need D.C current
* produced (6000-7000) Degree Centegrade Temperature
Gas Welding –
* Oxy – acetylene flame join metals
* Oxygen & acetylene gas works
* produced 3200 Degree Centegrade Temperature
It is the power driven tool. It cut & form all kinds of metal parts.
Example – 1. Lathe 2. Drill Press 3. Shaper 4. Planer 5. Grinding 6. Miling 7. Broaching 8. Boring
Tool Materials for Cutting Tool:
1. High Carbon Steel
2. High Speed Steel (W+Cr+V)
3. Carbide (W Carbide+Ti Carbide+Co Carbide)
It is the method of dividing periphery of job into equal number of division. Actually, it is the process of dividing circular or other shape of workpiece into equal space, division or angle.
It is one type of device which hold & locate workpiece and also guide & control cutting tool. It uses in drilling, reaming and tapping.
It is one type of device which hold and locate workpiece. It uses in miling, grinding, planning & turning.
Introduction to Robotics
Robotics is a relatively young field of modern technology that crosses traditional engineering boundaries. Understanding the complexity of robots and their applications requires knowledge of electrical engineering, mechanical engineering, systems and industrial engineering, computer science, economics, and mathematics. New disciplines of engineering, such as manufacturing engineering, applications engineering, and knowledge engineering have emerged to deal with the complexity of the field of robotics and factory automation.
The term robot was first introduced into our vocabulary by the Czech playwright Karel Capek in his 1920 play Rossum’s Universal Robots, the word robota being the Czech word for work. Since then the term has been applied to a great variety of mechanical devices, such as teleoperators, underwater vehicles, autonomous land rovers, etc. Virtually anything that operates with some degree of autonomy, usually under computer control, has at some point been called a robot. In this text the term robot will mean a computer controlled industrial manipulator of the type shown in Figure 1.1.
This type of robot is essentially a mechanical arm operating under computer control. Such devices, though far from the robots of science fiction, are nevertheless extremely complex electro-mechanical systems whose analytical description requires advanced methods, presenting many challenging and interesting research problems.
An official definition of such a robot comes from the Robot Institute of America (RIA): A robot is a reprogrammable multifunctional manipulator designed to move material, parts, tools, or specialized devices through variable programmed motions for the performance of a variety of tasks.
The key element in the above definition is the reprogrammability of robots. It is the computer brain that gives the robot its utility and adaptability. The so-called robotics revolution is, in fact, part of the larger computer revolution.
Even this restricted version of a robot has several features that make it attractive in an industrial environment. Among the advantages often cited in favor of the introduction of robots are decreased labor costs, increased precision and productivity, increased flexibility compared with specialized machines, and more humane working conditions as dull, repetitive, or hazardous jobs are performed by robots.
The robot, as we have defined it, was born out of the marriage of two earlier technologies: teleoperators and numerically controlled milling machines. Teleoperators, or master-slave devices, were developed during the second world war to handle radioactive materials. Computer numerical control (CNC) was developed because of the high precision required in the machining of certain items, such as components of high performance aircraft. The first robots essentially combined the mechanical linkages of the teleoperator with the autonomy and programmability of CNC machines.
The first successful applications of robot manipulators generally involved some sort of material transfer, such as injection molding or stamping, where the robot merely attends a press to unload and either transfer or stack the finished parts. These first robots could be programmed to execute a sequence of movements, such as moving to a location A, closing a gripper, moving to a location B, etc., but had no external sensor capability. More complex applications, such as welding, grinding, deburring, and assembly require not only more complex motion but also some form of external sensing such as vision, tactile, or force-sensing, due to the increased interaction of the robot with its environment.
It should be pointed out that the important applications of robots are by no means limited to those industrial jobs where the robot is directly replacing a human worker. There are many other applications of robotics in areas where the use of humans is impractical or undesirable. Among these are undersea and planetary exploration, satellite retrieval and repair, the defusing of explosive devices, and work in radioactive environments. Finally, prostheses, such as artificial limbs, are themselves robotic devices requiring methods of analysis and design similar to those of industrial manipulators.
Classification of Robotic Manipulators
Robot manipulators can be classified by several criteria, such as their power source, or way in which the joints are actuated, their geometry, or kinematic structure, their intended application area, or their method of control. Such classification is useful primarily in order to determine which robot is right for a given task. For example, a hydraulic robot would not be suitable for food handling or clean room applications. We explain this in more detail below.
Power Source. Typically, robots are either electrically, hydraulically, or pneumatically powered. Hydraulic actuators are unrivaled in their speed of response and torque producing capability. Therefore, hydraulic robots are used primarily for lifting heavy loads. The drawbacks of hydraulic robots are that they tend to leak hydraulic fluid, require much more peripheral equipment (such as pumps, which require more maintenance), and they are noisy. Robots driven by DC- or AC-servo motors are increasingly popular since they are cheaper, cleaner and quieter. Pneumatic robots are inexpensive and simple but cannot be controlled precisely. As a result, pneumatic robots are limited in their range of applications and popularity.
Application Area. Robots are often classified by application into assembly and non-assembly robots. Assembly robots tend to be small, electrically driven and either revolute or SCARA (described below) in design. The main non-assembly application areas to date have been in welding, spray painting, material handling, and machine loading and unloading.
Method of Control. Robots are classified by control method into servo and non-servo robots. The earliest robots were non-servo robots. These robots are essentially open-loop devices whose movement is limited to predetermined mechanical stops, and they are useful primarily for materials transfer. In fact, according to the definition given previously, fixed stop robots hardly qualify as robots. Servo robots use closed-loop computer control to determine their motion and are thus capable of being truly multifunctional, reprogrammable devices.
Servo controlled robots are further classified according to the method that the controller uses to guide the end-effector. The simplest type of robot in this class is the point-to-point robot. A point-to-point robot can be taught a discrete set of points but there is no control on the path of the end-effector in between taught points. Such robots are usually taught a series of points with a teach pendant. The points are then stored and played back. Point-to-point robots are severely limited in their range of applications. In continuous path robots, on the other hand, the entire path of the end-effector can be controlled. For example, the robot end-effector can be taught to follow a straight line between two points or even to follow a contour such as a welding seam. In addition, the velocity and/or acceleration of the end-effector can often be controlled. These are the most advanced robots and require the most sophisticated computer controllers and software development.
Geometry. Most industrial manipulators at the present time have six or fewer degrees-of-freedom. These manipulators are usually classified kinematically on the basis of the first three joints of the arm, with the wrist being described separately. The majority of these manipulators fall into one of five geometric types: articulated (RRR), spherical (RRP), SCARA (RRP), cylindrical (RPP), or Cartesian (PPP).
Each of these five manipulator arms are serial link robots. A sixth distinct class of manipulators consists of the so-called parallel robot. In a parallel manipulator the links are arranged in a closed rather than open kinematic chain.
A robot manipulator should be viewed as more than just a series of mechanical linkages. The mechanical arm is just one component in an overall Robotic System, illustrated in Figure 1.3, which consists of the arm, external power source, end-of-arm tooling, external and internal sensors, computer interface, and control computer.
Even the programmed software should be considered as an integral part of the overall system, since the manner in which the robot is programmed and controlled can have a major impact on its performance and subsequent range of applications.
Accuracy and Repeatability
The accuracy of a manipulator is a measure of how close the manipulator can come to a given point within its workspace. Repeatability is a measure of how close a manipulator can return to a previously taught point. The primary method of sensing positioning errors in most cases is with position encoders located at the joints, either on the shaft of the motor that actuates the joint or on the joint itself. There is typically no direct measurement of the end-effector position and orientation. One must rely on the assumed geometry of the manipulator and its rigidity to infer (i.e., to calculate) the end-effector position from the measured joint positions. Accuracy is affected therefore by computational errors, machining accuracy in the construction of the manipulator, flexibility effects such as the bending of the links under gravitational and other loads, ear backlash, and a host of other static and dynamic effects. It is primarily for this reason that robots are designed with extremely high rigidity. Without high rigidity, accuracy can only be improved by some sort of direct sensing of the end-effector position, such as with vision.
Once a point is taught to the manipulator, however, say with a teach pendant, the above effects are taken into account and the proper encoder values necessary to return to the given point are stored by the controlling computer. Repeatability therefore is affected primarily by the controller resolution. Controller resolution means the smallest increment of motion that the controller can sense. The resolution is computed as the total distance traveled by the tip divided by 2n, where n is the number of bits of encoder accuracy. In this context, linear axes, that is, prismatic joints, typically have higher resolution than revolute joints, since the straight-line distance traversed by the tip of a linear axis between two points is less than the corresponding arc length traced by the tip of a rotational link.
In addition, rotational axes usually result in a large amount of kinematic and dynamic coupling among the links with a resultant accumulation of errors and a more difficult control problem. One may wonder then what the advantages of revolute joints are in manipulator design.
The answer lies primarily in the increased dexterity and compactness of revolute joint designs. For example, Figure 1.4 shows that for the same range of motion, a rotational link can be made much smaller than a link with linear motion. Thus, manipulators made from revolute joints occupy a smaller working volume than manipulators with linear axes. This increases the ability of the manipulator to work in the same space with other robots, machines, and people. At the same time revolute joint manipulators are better able to maneuver around obstacles and have a wider range of possible applications.
Wrists and End-Effectors
The joints in the kinematic chain between the arm and end effector are referred to as the wrist. The wrist joints are nearly always all revolute. It is increasingly common to design manipulators with spherical wrists, by which we mean wrists whose three joint axes intersect at a common point. The spherical wrist is represented symbolically in Figure 1.5.
The spherical wrist greatly simplifies the kinematic analysis, effectively allowing one to decouple the positioning and orientation of the end effector. Typically, therefore, the manipulator will possess three degrees-of-freedom for position, which are produced by three or more joints in the arm. The number of degrees-of-freedom for orientation will then depend on the degrees-of-freedom of the wrist. It is common to find wrists having one, two, or three degrees-of-freedom depending of the application. For example, the SCARA robot shown in Figure 1.14 has four degrees-of-freedom: three for the arm, and one for the wrist, which has only a rotation about the final z-axis.
It has been said that a robot is only as good as its hand or end-effector. The arm and wrist assemblies of a robot are used primarily for positioning the end-effector and any tool it may carry. It is the end-effector or tool that actually performs the work. The simplest type of end-effectors are grippers, which usually are capable of only two actions, opening and closing. While this is adequate for materials transfer, some parts handling, or gripping simple tools, it is not adequate for other tasks such as welding, assembly, grinding, etc. A great deal of research is therefore devoted to the design of special purpose end-effectors as well as to tools that can be rapidly changed as the task dictates. There is also much research on the development of anthropomorphic hands. Such hands have been developed both for prosthetic use and for use in manufacturing.
The usual need to look up values from various tables and charts makes the conventional hand calculation
quite laborious, time consuming and prone to errors and inaccuracies because of the tendency to simplify
truncate or interpolate tabulated values. Listed below are the suggested applications and methodology of
two computer programs Elite CHVAC and TRACE 700 that may be used in the cooling and heating load
CHVAC is a commercial Heating, Ventilation and Air Conditioning software platform developed by Elite
Software. This computer program calculates the maximum heating and cooling loads in commercial and
Listed below are capabilities of CHVAC:
- Calculates peak heating and cooling loads
- Calculates both heating & cooling airflow CFM requirements
- Calculates run out and main trunk duct sizes
- Automates compliance with ASHRAE Standard 62
- Provides overall building envelope report
- Spreadsheet file compatibility
- Performs complete psychrometric analysis
- Prints bar graphs and exploded pie charts
- Exterior shading handles overhangs, fins, & glass tilt
- Uses exact ASHRAE CLTD procedures
- Built-in design weather data for hundreds of cities
- Analyzes up to 12 months per calculation
- Calculates 24 hours per design day
- Allows unlimited number of zones per project
- Zones may be grouped under 100 air handlers
- Zones may be optionally grouped under VAV boxes
- Allows 12 walls, 12 windows, and 5 roofs per zone
- Allows simultaneous infiltration and ventilation
- Allows different summer and winter air rates
- Allows varying indoor conditions within a project
- Allows 6 master roof types,8 master wall types, 8 master partition types, and 20 master glass types
- Allows glass to be tilted from 0 to 180 degrees
- Allows for roof and wall color effects
- Provision for both VAV and constant volume systems
- Proper handling of return air plenum loads
- Accounts for people diversity in total building load
- Computes supply fan horsepower and heat gains
- Accounts for both draw-thru and blow-thru fans
- Calculates reheat requirements if necessary
- Computes supply and return duct gains and losses
- Allows direct specification of supply CFM quantities
- Allows specification of minimum supply air quantities
- Allows heating only, cooling only, or both
- Excess supply air can be handled as reheat, reserve capacity, or by adjusting the leaving coil conditions
- Leaving coil conditions can be specified with a desired dry bulb temperature or a relative humidity
- Calculates chilled and hot water coil flow rates
- Allows for pretreated outside air
- Allows heating and cooling safety factors
- Lighting & equipment watts along with no. of people can be entered directly or on a per square foot basis
CHVAC performs calculations using the CLTD/CLF procedures described in the ASHRAE Handbook of Fundamentals. The programs use exact CLTD and MSHGF table values where possible, otherwise direct
calculations are made. This calculation technique allows the programs to calculate for any building
orientation and still produce output results that can be easily verified by hand.
CHVAC is a true Windows program that uses all the latest data entry techniques such as toolbars, hyper linked help, and form tabs. All input data is checked at the time of entry so that no improper data can be entered. Five types of data are requested: general project data, outdoor design data, building material data, air handler data, and specific zone data. The general project data includes the project and client name, designer, building opening and closing hours, internal operating load schedules, and any desired safety factors. The outdoor design data includes the summer and winter outdoor design conditions (automatically looked up for you if a city reference is given) and the desired ventilation and infiltration rates. The building material data includes the definition of master building material types for roofs, walls, partitions, glass sections, and exterior shading. A user defined material library is available for saving the data on common material types. The air handler data includes the fan and terminal type, the desired heating and cooling supply air temperatures and data for duct heat gains and losses. The zone data includes the zone name, floor length and width, number of people, equipment watts, lighting watts, external shading data, and specific roof, wall, partition, floor, and glass data.
The CHVAC program provides eleven types of reports,which can be selectively previewed onscreen or printed as desired. CHVAC supports all printers that work with Windows and numerous full color reports are available.The reports are: General Project Data, Air Handler Input Data, Zone Input Data, Detailed Project Zone Loads, Air System Zone Summary, Total Building, Air System, and Zone Load Profiles, Air System Total Load Summary, Air System Psychrometric Analysis, Overall Building Envelope Report, Pie Charts, Bar Graphs, and the Total Building Load Summary. Air system summary data can be exported to your favorite spreadsheet.
TRACE ® 700
The TRACE Load ® 700 program is a commercial Heating, Ventilation and Air Conditioning software platform developed by Trane’s CDS Group.
The Load phase of the program computes the peak sensible and latent zone loads, as well as the block sensible and latent loads for the building. In addition, the hourly sensible and latent loads, including weather-dependent loads, are calculated for each zone, based on the weather library. The building heating/cooling load calculations, used in the load phase of the program for annual energy consumption analysis, are of sufficient detail to permit the evaluation of the effect of building data such as orientation, size, shape and mass, heat transfer characteristics of air and moisture, as well as hourly climatic data. The Design phase of the TRACE program calculates the design supply air temperatures, heating and cooling capacities, and supply air quantities given the peak load files generated by the Load phase. For applications where the building design parameters are known, you can override the calculation of these values using optional entries to the System phase. This gives you the ability to simulate existing buildings
with installed equipment that may not be sized according to the loads calculated in the program’s Load Phase.
Beyond this, the calculations used to simulate the operation of the building and its service systems through a full-year operating period, are of sufficient detail to permit the evaluation of the effect of system design, climatic factors, operational characteristics and mechanical equipment operating characteristics on annual energy usage. Manufacturers’ data is used in the program for the simulation of all systems and equipment. The calculation procedures used in TRACE are based upon 8,760 hours of operation of the building and its service system. These procedures use techniques recommended in the appropriate ASHRAE publications or produce results that are consistent with such recommended techniques. The following are the program features:
Project Navigator View
- Organizes entries by task to lead you through the modeling process
- Displays the status of each modeling step
- Accommodates up to 4 alternatives per project
Project Tree View
- Organizes all rooms, systems, and plants in a hierarchical list
- Displays all information about a system, zone, or room on 1 screen
- Supports cut, copy, and paste to save entry time
- Displays cooling set point for every room in the project on 1 screen
- Makes it easy to check and edit your work
Task-oriented display guides you through the modeling process as follows:
Select weather information
- Provides both design and typical weather data by location
- Choose from 400 climate locations
- Import standard weather files for a full-year (8760) analysis
- Describe the construction, airflows, thermostat settings, heat sources, and schedules by room
Create airside systems
- Choose from more than 30 methods of air distribution
- Add energy recovery, economizers, and dedicated ventilation/makeup air
Assign rooms to systems
- Create thermal zones and assign them to systems
- Determine airflows, coil loads, and fan sizes for each airside system
If the only requirement is to calculate the cooling and/or heating loads and the project does not require energy analysis and economic evaluation, it is recommended that the Program Load ® 700 be utilized instead of Full TRACE 700.The only difference is that Trace Load ® 700 users only have access to the Load Design section (from Project Information to Assign Rooms to Systems). Full TRACE 700 users will have full access to the Load, Energy and Economic sections.
The advantage of using only Trace Load ® 700 is that all the added features and capabilities (applicable to load design) in full TRACE 700 program are also available to the Trace Load ® 700 users. Also, same file extensions and libraries will enable users of both programs to transfer archived files back and forth without any additional steps needed.
Finite Element Analysis FEA Terms and Definitions (A to Z) Part-5
(A to Z) of Finite Element Analysis
TEMPERATURE CONTOUR PLOTS
A plot showing contour lines connecting points of equal temperature.
TETRAHEDRON TETRAHEDRAL ELEMENT
A three dimensional four sided solid element with triangular faces.
The material property defining the thermal inertia of a material. It relates the rate of change of temperature with time to heat flux.
The material property relating temperature gradient to heat flux.
The equivalent loads on a structure arising from thermal strains. These in turn arise from a temperature change.
The components of strain arising from a change in temperature.
THERMAL STRESS ANALYSIS
The computation of stresses and displacements due to change in temperature.
THIN SHELL ELEMENT THICK SHELL ELEMENT
In a shell element the geometry is very much thinner in one direction than the other two. It can then be assumed stresses can only vary linearly at most in the thickness direction. If the through thickness shear strains can be taken as zero then a thin shell model is formed. This uses the Kirchoff shell theory If the transverse shear strains are not ignored then a thick shell model is formed. This uses the Mindlin shell theory. For the finite element method the thick shell theory generates the most reliable form of shell elements. There are two forms of such elements, the Mindlin shell and the Semi -Loof shell.
The structures forcing function and the consequent response is defined in terms of time histories. The Fourier transform of the time domain gives the corresponding quantity in the frequency domain.
TRACE OF THE MATRIX
The sum of the leading diagonal terms of the matrix.
A systematic method for generating element shape functions for irregular node distributions on an element.
Solution techniques that transform coordinate and force systems to generate a simpler form of solution. The eigenvectors can be used to transform coupled dynamic equations to a series of single degree of freedom equations.
A forcing function that varies for a short period of time and then settles to a constant value.
The component of the system response that does not repeat itself regularly with time.
Special elements that have sides with different numbers of nodes. They are used to couple elements with different orders of interpolation, typically a transition element with two nodes on one edge and three on another is used to couple a 4 -node quad to an 8 -node quad.
TRANSIENT HEAT TRANSFER
Heat transfer problems in which temperature distribution varies as a function of time.
Two dimensional or surface elements that have three edges.
A one dimensional line element defined by two nodes resisting only axial loads.
The failure stress (or equivalent stress) for the material.
UNDAMPED NATURAL FREQUENCY
The square root of the ratio of the stiffness to the mass (the square root of the eigenvalue). It is the frequency at which an undamped system vibrates naturally. A system with n degrees of freedom has n natural frequencies.
UNDER DAMPED SYSTEM
A system which has an equation of motion where the damping is less than critical. It has an oscillatory impulse response.
A diagonal matrix with unit values down the diagonal.
UPDATED LAGRANGIAN TOTAL LAGRANGIAN
The updated Lagrangian coordinate system is one where the stress directions are referred to the last known equilibrium state. The total Lagrangian coordinate system is one where the stress directions are referred to the initial geometry.
UPWINDING IN FLUIDS
A special form of weighting function used in viscous flow problems (solution to the NavierStokes equations) used in the weighted residual method to bias the results in the direction of the flow.
VARIABLE BANDWIDTH (SKYLINE)
A sparse matrix where the bandwidth is not constant. Some times called a skyline matrix.
The first time derivative of the displacement.
VIRTUAL CRACK EXTENSION CRACK PROPAGATION
A technique for calculating the energy that would be released if a crack increased in size. This gives the energy release rate which can be compared to the critical energy release (a material property) to decide if a crack will propagate.
An arbitrary imaginary change of the system configuration consistent with its constraints.
VIRTUAL WORK VIRTUAL DISPLACEMENTS VIRTUAL FORCES
Techniques for using work arguments to establish equilibrium equations from compatibility equations (virtual displacements) and to establish compatibility equations from equilibrium (virtual forces).
The damping is viscous when the damping force is proportional to the velocity.
VISCOUS DAMPING MATRIX
The matrix relating a set of velocities to their corresponding velocities
VOLUME DISTORTION VOLUMETRIC DISTORTION
The distortion measured by the determinant of the Jacobian matrix, det j.
VON MISES STRESS
An “averaged” stress value calculated by adding the squares of the 3 component stresses (X, Y and Z directions) and taking the square root of their sums. This value allows for a quick method to locate probable problem areas with one plot.
VON MISES EQUIVALENT STRESS TRESCA EQUIVALENT STRESS
Equivalent stress measures to represent the maximum shear stress in a material. These are used to characterize flow failures (e.g. plasticity and creep). From test results the VonMises form seems more accurate but the Tresca form is easier to handle.
The dynamic calculation involving the prediction of the history of stress and pressure waves in solids and fluids.
The wavefront of a symmetric matrix is the maximum number of active nodes at any time during a frontal solution process. It is a measure of the time required to factorise the equations in a frontal solution. It is minimized be element renumbering.
A technique for transforming a set of partial differential equations to a set of simultaneous equations so that the solution to the simultaneous equations satisfy the partial differential equations in a mean sense. The form used in the finite element method is the Galerkin process. This leads to identical equations to those from virtual work arguments.
The stability of rotating systems where centrifugal and Coriolis are also present.
White noise has a constant spectral density for all frequencies.
WILSON THETA METHOD
An implicit solution method for integrating second order equations of motion. It can be made unconditionally stable.
Within a digital computer a number is only held to a finite number of significant figures. A 32bit (single precision) word has about 7 significant figures. A 64bit (double precision) word has about 13 significant figures. All finite element calculations should be conducted in double precision.
The material property relating a uniaxial stress to the corresponding strain.
ZERO ENERGY MODES ZERO STIFFNESS MODES
Non-zero patterns of displacements that have no energy associated with them. No forces are required to generate such modes, Rigid body motions are zero energy modes. Buckling modes at their buckling loads are zero energy modes. If the elements are not fully integrated they will have zero energy displacement modes. If a structure has one or more zero energy modes then the matrix is singular.