Calculation Of Work And Heat In Ideal Processes Pdf

File Name: calculation of work and heat in ideal processes .zip
Size: 2813Kb
Published: 16.05.2021

Ideal Gas Processes

Figure 1. This boiling tea kettle represents energy in motion. The water in the kettle is turning to water vapor because heat is being transferred from the stove to the kettle. As the entire system gets hotter, work is done—from the evaporation of the water to the whistling of the kettle.

If we are interested in how heat transfer is converted into doing work, then the conservation of energy principle is important. The first law of thermodynamics applies the conservation of energy principle to systems where heat transfer and doing work are the methods of transferring energy into and out of the system.

The first law of thermodynamics states that the change in internal energy of a system equals the net heat transfer into the system minus the net work done by the system. Q is the net heat transferred into the system —that is, Q is the sum of all heat transfer into and out of the system.

W is the net work done by the system —that is, W is the sum of all work done on or by the system. We use the following sign conventions: if Q is positive, then there is a net heat transfer into the system; if W is positive, then there is net work done by the system.

So positive Q adds energy to the system and positive W takes energy from the system. Note also that if more heat transfer into the system occurs than work done, the difference is stored as internal energy.

Heat engines are a good example of this—heat transfer into them takes place so that they can do work. See Figure 2. Figure 2. The first law of thermodynamics is the conservation-of-energy principle stated for a system where heat and work are the methods of transferring energy for a system in thermal equilibrium. Q represents the net heat transfer—it is the sum of all heat transfers into and out of the system.

Q is positive for net heat transfer into the system. W is the total work done on and by the system. W is positive when more work is done by the system than on it. The first law of thermodynamics is actually the law of conservation of energy stated in a form most useful in thermodynamics.

The first law gives the relationship between heat transfer, work done, and the change in internal energy of a system. Heat transfer Q and doing work W are the two everyday means of bringing energy into or taking energy out of a system. The processes are quite different.

Heat transfer, a less organized process, is driven by temperature differences. Work, a quite organized process, involves a macroscopic force exerted through a distance. Nevertheless, heat and work can produce identical results. For example, both can cause a temperature increase.

Heat transfer into a system, such as when the Sun warms the air in a bicycle tire, can increase its temperature, and so can work done on the system, as when the bicyclist pumps air into the tire.

Once the temperature increase has occurred, it is impossible to tell whether it was caused by heat transfer or by doing work. This uncertainty is an important point. Heat transfer and work are both energy in transit—neither is stored as such in a system. However, both can change the internal energy U of a system. Internal energy is a form of energy completely different from either heat or work.

We can think about the internal energy of a system in two different but consistent ways. The first is the atomic and molecular view, which examines the system on the atomic and molecular scale. The internal energy U of a system is the sum of the kinetic and potential energies of its atoms and molecules.

Recall that kinetic plus potential energy is called mechanical energy. Thus internal energy is the sum of atomic and molecular mechanical energy. Because it is impossible to keep track of all individual atoms and molecules, we must deal with averages and distributions. A second way to view the internal energy of a system is in terms of its macroscopic characteristics, which are very similar to atomic and molecular average values. It has also been determined experimentally that the internal energy U of a system depends only on the state of the system and not how it reached that state.

More specifically, U is found to be a function of a few macroscopic quantities pressure, volume, and temperature, for example , independent of past history such as whether there has been heat transfer or work done. This independence means that if we know the state of a system, we can calculate changes in its internal energy U from a few macroscopic variables.

In thermodynamics, we often use the macroscopic picture when making calculations of how a system behaves, while the atomic and molecular picture gives underlying explanations in terms of averages and distributions. We shall see this again in later sections of this chapter. For example, in the topic of entropy, calculations will be made using the atomic and molecular view.

To get a better idea of how to think about the internal energy of a system, let us examine a system going from State 1 to State 2. The system has internal energy U 1 in State 1, and it has internal energy U 2 in State 2, no matter how it got to either state. By path, we mean the method of getting from the starting point to the ending point.

Why is this independence important? This path independence means that internal energy U is easier to consider than either heat transfer or work done. Figure 3. Two different processes produce the same change in a system. If the system starts out in the same state in a and b , it will end up in the same final state in either case—its final state is related to internal energy, not how that energy was acquired.

In part 1, we must first find the net heat transfer and net work done from the given information. In part b , the net heat transfer and work done are given, so the equation can be used directly. The net heat transfer is the heat transfer into the system minus the heat transfer out of the system, or. We can also find the change in internal energy for each of the two steps. First, consider No matter whether you look at the overall process or break it into steps, the change in internal energy is the same.

The system ends up in the same state in both parts. Human metabolism is the conversion of food into heat transfer, work, and stored fat. Metabolism is an interesting example of the first law of thermodynamics in action.

We now take another look at these topics via the first law of thermodynamics. Considering the body as the system of interest, we can use the first law to examine heat transfer, doing work, and internal energy in activities ranging from sleep to heavy exercise.

What are some of the major characteristics of heat transfer, doing work, and energy in the body? For one, body temperature is normally kept constant by heat transfer to the surroundings. This means Q is negative. Another fact is that the body usually does work on the outside world. This means W is positive. Now consider the effects of eating. Eating increases the internal energy of the body by adding chemical potential energy this is an unromantic view of a good steak.

The body metabolizes all the food we consume. Basically, metabolism is an oxidation process in which the chemical potential energy of food is released. This implies that food input is in the form of work. Food energy is reported in a special unit, known as the Calorie.

This energy is measured by burning food in a calorimeter, which is how the units are determined. In chemistry and biochemistry, one calorie spelled with a lowercase c is defined as the energy or heat transfer required to raise the temperature of one gram of pure water by one degree Celsius. Nutritionists and weight-watchers tend to use the dietary calorie, which is frequently called a Calorie spelled with a capital C.

One food Calorie is the energy needed to raise the temperature of one kilogram of water by one degree Celsius. This means that one dietary Calorie is equal to one kilocalorie for the chemist, and one must be careful to avoid confusion between the two. Again, consider the internal energy the body has lost. There are three places this internal energy can go—to heat transfer, to doing work, and to stored fat a tiny fraction also goes to cell repair and growth. Heat transfer and doing work take internal energy out of the body, and food puts it back.

If you eat just the right amount of food, then your average internal energy remains constant. The reverse is true if you eat too little. This process is how dieting produces weight loss. Life is not always this simple, as any dieter knows. The body stores fat or metabolizes it only if energy intake changes for a period of several days. Once you have been on a major diet, the next one is less successful because your body alters the way it responds to low energy intake.

Your basal metabolic rate BMR is the rate at which food is converted into heat transfer and work done while the body is at complete rest. The body adjusts its basal metabolic rate to partially compensate for over-eating or under-eating.

The body will decrease the metabolic rate rather than eliminate its own fat to replace lost food intake. You will chill more easily and feel less energetic as a result of the lower metabolic rate, and you will not lose weight as fast as before. Exercise helps to lose weight, because it produces both heat transfer from your body and work, and raises your metabolic rate even when you are at rest.

Weight loss is also aided by the quite low efficiency of the body in converting internal energy to work, so that the loss of internal energy resulting from doing work is much greater than the work done. It should be noted, however, that living systems are not in thermalequilibrium. The body provides us with an excellent indication that many thermodynamic processes are irreversible.

Isothermal process

Figure 1. This boiling tea kettle represents energy in motion. The water in the kettle is turning to water vapor because heat is being transferred from the stove to the kettle. As the entire system gets hotter, work is done—from the evaporation of the water to the whistling of the kettle. If we are interested in how heat transfer is converted into doing work, then the conservation of energy principle is important. The first law of thermodynamics applies the conservation of energy principle to systems where heat transfer and doing work are the methods of transferring energy into and out of the system.

An ideal heat engine is an imaginary engine in which energy extracted as heat from the high-temperature reservoir is converted completely to work. But according to the Kelvin-Planck statement , such an engine would violate the second law of thermodynamics, because there must be losses in the conversion process. The net heat added to the system must be higher than the net work done by the system. For a refrigeration or heat pumps, thermal efficiency indicates the extent to which the energy added by work is converted to net heat output. Since energy is conserved according to the first law of thermodynamics and energy cannot be be converted to work completely, the heat input, Q H , must equal the work done, W, plus the heat that must be dissipated as waste heat Q C into the environment. Therefore we can rewrite the formula for thermal efficiency as:. To give the efficiency as a percent, we multiply the previous formula by


path and point functions, thermodynamic process, cycle, heat, work etc. (Sections equations (Section ). 4. Introduce and the process. Sign convention for work and heat transfer: Most thermodynamics books consider the work Another version of this law is that “the entropy of perfect crystals is zero at absolute.


Plate Heat Exchanger Working Principle

Plate Heat Exchangers were first produced in the s and have since been widely used in a great number of sectors. A plate exchanger consists of a series of parallel plates that are placed one above the other so as to allow the formation of a series of channels for fluids to flow between them. Inlet and outlet holes at the corners of the plates allow hot and cold fluids through alternating channels in the exchanger so that a plate is always in contact on one side with the hot fluid and the other with the cold. The size of a plate can range from a few square centimeters mm x mm side up to 2 or 3 square meters mm x mm side.

Thermal Efficiency

Isochoric process

In this section we will talk about the relationship between ideal gases in relations to thermodynamics. We will see how by using thermodynamics we will get a better understanding of ideal gases. In the realm of Chemistry we often see many relations between the former and its relations to Physics. By utilizing both Chemistry and Physics we can get a better understanding for the both mentioned.

An isochoric process , also called a constant-volume process , an isovolumetric process , or an isometric process , is a thermodynamic process during which the volume of the closed system undergoing such a process remains constant. An isochoric process is exemplified by the heating or the cooling of the contents of a sealed, inelastic container: The thermodynamic process is the addition or removal of heat; the isolation of the contents of the container establishes the closed system; and the inability of the container to deform imposes the constant-volume condition. The isochoric process here should be a quasi-static process.


Combining this result with the ideal gas equation of state. T2. T1. = way of including the temperature effects on specific heat for ideal gases during Steady State, Steady Flow in a Flow Channel of Arbitrary Cross-section with Work and Heat.


1st Law of Thermodynamics

TLV Euro Engineering has revealed five steps that industrial businesses can take to improve their steam plant efficiency. In many industries, steam plants now provide a crucial energy source, delivering reliable high-quality steam for the production process. However, rising gas prices and a need to reduce CO2 emissions has led to an increasing focus on the efficiency of steam plants. While there are many ways to improve efficiency they often involve considerable investment e.

The garage door is metal with no insulation. Browse photos and search by condition, price, and more. Ship to your home or buy online and pickup in-store.

This typically occurs when a system is in contact with an outside thermal reservoir , and the change in the system will occur slowly enough to allow the system to continue to adjust to the temperature of the reservoir through heat exchange see quasi-equilibrium. Simply, we can say that in isothermal process. Isothermal processes can occur in any kind of system that has some means of regulating the temperature, including highly structured machines , and even living cells. Some parts of the cycles of some heat engines are carried out isothermally for example, in the Carnot cycle.

3 Response
  1. Amitee S.

    are related by an equation of state. For an c) Is the heat less than, greater than or equal to the work? For an ideal gas, we can represent these processes.

  2. Karen M.

    The ideal gas law is the equation of state of a hypothetical ideal gas in which there is no molecule to molecule interaction.

  3. Elita M.

    To understand and perform any sort of thermodynamic calculation, we must first understand the fundamental laws and concepts of thermodynamics.

Leave a Reply