Heat pumps, thermodynamic laws

Applying the first and second laws of thermodynamics of the open system to each of the four processes of the basic vapor heat pump yields ... 

Kinetically one can compare the rubber elastic extension to the compression of a gas, as illustrated in Fig. 5.167. The thermodynamic equations reveal that reversible rabber contraction can just as well drive a heat pump as reversible gas expansion. Raising temperature, increases the pressure of a gas, analogously it takes a greater force to keep a rabber band extended at higher temperature. The two equations for this fact are known as the ideal gas law p = PoTV(/(ToV) with PoV/r = R, the gas... 

Scenario I In this scenario, space heating is compensated by heat pump and thermal energy of fuel cell. Almost all thermal energy is consumed as shown in the Table VI.7. Usable energy efficiencies are 74.39 % for I. law and 52.2 % for II. law. Surplus electrical energy efficiencies from case-5 to case-8 are 48.62 %, 66.44 %, 60.48 % and 53 %, respectively (Table VI.7). Maximum used energy efficiencies are at case-5 where minimum unused electrical energy and values are 55.35 % for I. law and 29.99 % for n. law of thermodynamics (Table VI.8). 

At first sight it might appear that the second law of thermodynamics is violated for reverse diffusion to occur. This is not so. One process may depart from equilibrium in such a sense as to consume entropy provided it is coupled to another process that produces entropy even faster. This is, of course, the basic principle of any pump, whether it moves water uphill or moves heat towards a higher temperature region. For the second law requirement <7 > 0 to hold it is allowable for to be less than zero, corresponding to reverse diffusion for 1, provided <72 and 0-3, due to species 2 and 3 diffusion, be such that the overall entropy production rate is positive (a + 0-2 + <73 > 0). 

The gas used for heat transfer had to be circulated through the reactor core channels, the heat exchangers and the connecting pipework. It was essential for the power needed to pump the gas round the system (the blowing power) to be only a small fraction of the heat power released in the pile. The laws of thermodynamics dictated that only about 25% of the pile heat could be turned into electrical energy. If the blowing power were 10% of the heat power, it would be 40% of the electrical power and hence the net electrical power output would be greatly reduced. 

Another rule of tlie second law of thermodynamics is as follows heat cannot flow from one body to another body at a higher temperature without other changes being involved. The transfer of heat from a cooler body to a warmer one can take place only because of work A done under the action of external forces on the working body. The thermodynamic cycle initiated in the reverse direction is used in refrigerators and thermal pumps. 

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