Question

1.         Which thermodynamic parameter is being maximized when heat spontaneously flows from a hot region of a system to a cold one?

2.         Which thermodynamic parameter is being minimized when heat spontaneously flows from a hot region of a system to a cold region?

3.        Which thermodynamic parameter decreases during any spontaneous process?

Answer 1

1)

H eat engines are a compromise between the crisp ideals discussed in thermodynamic textbooks and the clanking, hissing realities of irreversible processes, This compromise produces wonderful machines, such as the automobile engine and the household refrigerator. In designing real devices, the goal is not to approach thermodynamic ideals by reducing irreversibilities but to balance cost, efficiency, size, power, reliability, simplicity, and other factors important to the needs of particular applications. Simplicity is the most striking feature of a natural engine, a reciprocating heat engine with no moving parts. As we will see, the basic operating cycle of the natural engine is so straightforward it can be applied to a wide variety of systems with working media that range from air to paramagnetic disks

Although the natural engine is new in concept, the underlying thermodynamic principles and processes are shared with conventional engines, such as the Stirling and Rankine engines. To set the stage for natural engines, we will first discuss a few conventional idealized thermodynamic cycles and the practical engines they suggest.

Conventional Heat Engines and Cycles In principle, any idealized thermodynamic heat engine cycle is functionally 2 reversible in the sense that it can be made to operate in either of two modes: prime mover or heat pump* (Fig. 1). In a prime mover, heat flows from high to low temperatures, and the engine converts a portion of that heat to work. In a heat pump, the flows of heat and work are reversed; that is, work done on the engine causes it to pump heat from low to high temperatures. Few practical engines are functionally reversible. The internal combustion engine is a prime mover only; the household refrigerator is a heat pump only: neither engine is ever operated in both modes

The most fundamental engine cycle operating between two temperatures is the functionally and thermodynamically reversible cycle propounded by Sadi Carnot in 1824. The cycle consists of alternating adiabatic and isothermal steps (Fig. 2). During an adiabatic step, no heat remains constant. Thus any flow of work causes a corresponding change in the temperature of the working medium. During an isothermal step, the temperature remains constant, and flows of entropy, work, and heat occur.

2)

n physics, thermodynamics (from the Greek ?????, therme, meaning " heat and ???????, dynamis, meaning " power") is thestudy of the transformation of energy into different forms and itsrelation to macroscopic variables such as temperature, pressure,and volume. Its underpinnings, based upon statistical predictionsof the collective motion of particles from their microscopicbehavior, is the field of statistical thermodynamics, a branch ofstatistical mechanics. Roughly, heat means "energy in transit"and dynamics relates to "movement"; thus, in essencethermodynamics studies the movement of energy and howenergy instills movement. Historically, thermodynamicsdeveloped out of need to increase the efficiency of early steam engines.

The starting point for most thermodynamic considerations are thelaws of thermodynamics, which postulate that energy can beexchanged between physical systems as heat or work. They alsopostulate the existence of a quantity named entropy, which canbe defined for any system. In thermodynamics, interactionsbetween large ensembles of objects are studied and categorized.Central to this are the concepts of system and surroundings. Asystem is composed of particles, whose average motions defineits properties, which in turn are related to one another throughequations of state. Properties can be combined to expressinternal energy and thermodynamic potentials, which are usefulfor determining conditions for equilibrium and spontaneous processes.

With these tools, thermodynamics describes how systemsrespond to changes in their surroundings. This can be applied to awide variety of topics in science and engineering, such asengines, phase transitions, chemical reactions, transport phenomena, and even black holes. The results ofthermodynamics are essential for other fields of physics and forchemistry, chemical engineering, aerospace engineering,mechanical engineering, cell biology, biomedical engineering,materials science, and economics to name a few.

3)

Thermodynamic parameters

Main article: Conjugate variables (thermodynamics)

The central concept of thermodynamics is that of energy, the ability to do work. As stipulated by the first law, the total energy of the system and its surroundings is conserved. It may be transferred into a body by heating, compression, or addition of matter, and extracted from a body either by cooling, expansion, or extraction of matter. For comparison, in mechanics, energy transfer results from a force which causes displacement, the product of the two being the amount of energy transferred. In a similar way, thermodynamic systems can be thought of as transferring energy as the result of a generalized force causing a generalized displacement, with the product of the two being the amount of energy transferred. These thermodynamic force-displacement pairs are known as conjugate variables. The most common conjugate thermodynamic variables are pressure-volume (mechanical parameters), temperature-entropy (thermal parameters), and chemical potential-particle number (material parameters).

Thermodynamic instruments

Main article: Thermodynamic instruments

There are two types of thermodynamic instruments, the meter and the reservoir. A thermodynamic meter is any device which measures any parameter of athermodynamic system. In some cases, the thermodynamic parameter is actually defined in terms of an idealized measuring instrument. For example, the zeroth law states that if two bodies are in thermal equilibrium with a third body, they are also in thermal equilibrium with each other. This principle, as noted by James Maxwell in 1872, asserts that it is possible to measure temperature. An idealized thermometer is a sample of an ideal gas at constant pressure. From the ideal gas law PV=nRT, the volume of such a sample can be used as an indicator of temperature; in this manner it defines temperature. Although pressure is defined mechanically, a pressure-measuring device, called a barometer may also be constructed from a sample of an ideal gas held at a constant temperature. Acalorimeter is a device which is used to measure and define the internal energy of a system.

A thermodynamic reservoir is a system which is so large that it does not appreciably alter its state parameters when brought into contact with the test system. It is used to impose a particular value of a state parameter upon the system. For example, a pressure reservoir is a system at a particular pressure, which imposes that pressure upon any test system that it is mechanically connected to. The earth's atmosphere is often used as a pressure reservoir.

It is important that these two types of instruments are distinct. A meter does not perform its task accurately if it behaves like a reservoir of the state variable it is trying to measure. If, for example, a thermometer, were to act as a temperature reservoir it would alter the temperature of the system being measured, and the reading would be incorrect. Ideal meters have no effect on the state variables of the system they are measuring.

it can be defined as the study of systems involving heat and work.

Thermodynamic states

Main article: Thermodynamic state

When a system is at equilibrium under a given set of conditions, it is said to be in a definite state. The state of the system can be described by a number ofintensive variables and extensive variables. The properties of the system can be described by an equation of state which specifies the relationship between these variables. State may be thought of as the instantaneous quantitative description of a system with a set number of variables held constant

Thermodynamic processes

Main article: Thermodynamic processes

A thermodynamic process may be defined as the energetic evolution of a thermodynamic system proceeding from an initial state to a final state. Typically, each thermodynamic process is distinguished from other processes, in energetic character, according to what parameters, as temperature, pressure, or volume, etc., are held fixed. Furthermore, it is useful to group these processes into pairs, in which each variable held constant is one member of a conjugate pair. The seven most common thermodynamic processes are shown below:

1. An isobaric process occurs at constant pressure.
2. An isochoric process, or isometric/isovolumetric process, occurs at constant volume.
3. An isothermal process occurs at a constant temperature.
4. An adiabatic process occurs without loss or gain of heat.
5. An isentropic process (reversible adiabatic process) occurs at a constant entropy.
6. An isenthalpic process occurs at a constant enthalpy.
7. A steady state process occurs without a change in the internal energy of a system.

Main article: Thermodynamic instruments

There are two types of thermodynamic instruments, the meter and the reservoir. A thermodynamic meter is any device which measures any parameter of athermodynamic system. In some cases, the thermodynamic parameter is actually defined in terms of an idealized measuring instrument. For example, the zeroth law states that if two bodies are in thermal equilibrium with a third body, they are also in thermal equilibrium with each other. This principle, as noted by James Maxwell in 1872, asserts that it is possible to measure temperature. An idealized thermometer is a sample of an ideal gas at constant pressure. From the ideal gas law PV=nRT, the volume of such a sample can be used as an indicator of temperature; in this manner it defines temperature. Although pressure is defined mechanically, a pressure-measuring device, called a barometer may also be constructed from a sample of an ideal gas held at a constant temperature. Acalorimeter is a device which is used to measure and define the internal energy of a system.

A thermodynamic reservoir is a system which is so large that it does not appreciably alter its state parameters when brought into contact with the test system. It is used to impose a particular value of a state parameter upon the system. For example, a pressure reservoir is a system at a particular pressure, which imposes that pressure upon any test system that it is mechanically connected to. The earth's atmosphere is often used as a pressure reservoir.

It is important that these two types of instruments are distinct. A meter does not perform its task accurately if it behaves like a reservoir of the state variable it is trying to measure. If, for example, a thermometer, were to act as a temperature reservoir it would alter the temperature of the system being measured, and the reading would be incorrect. Ideal meters have no effect on the state variables of the system they are measuring.

it can be defined as the study of systems involving heat and work.

Thermodynamic states

Main article: Thermodynamic state

When a system is at equilibrium under a given set of conditions, it is said to be in a definite state. The state of the system can be described by a number ofintensive variables and extensive variables. The properties of the system can be described by an equation of state which specifies the relationship between these variables. State may be thought of as the instantaneous quantitative description of a system with a set number of variables held constant

Thermodynamic processes

Main article: Thermodynamic processes

A thermodynamic process may be defined as the energetic evolution of a thermodynamic system proceeding from an initial state to a final state. Typically, each thermodynamic process is distinguished from other processes, in energetic character, according to what parameters, as temperature, pressure, or volume, etc., are held fixed. Furthermore, it is useful to group these processes into pairs, in which each variable held constant is one member of a conjugate pair. The seven most common thermodynamic processes are shown below:

1. An isobaric process occurs at constant pressure.
2. An isochoric process, or isometric/isovolumetric process, occurs at constant volume.
3. An isothermal process occurs at a constant temperature.
4. An adiabatic process occurs without loss or gain of heat.
5. An isentropic process (reversible adiabatic process) occurs at a constant entropy.
6. An isenthalpic process occurs at a constant enthalpy.
7. A steady state process occurs without a change in the internal energy of a system.