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week_14 - Week 14— Problems 14—1 a What is the...

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Unformatted text preview: Week 14— Problems 14—1. a) What is the difference between a reversible thermodynamic process and an ' irreversible thermodynamic process? b) A gas is expanded by a factor of 3 in (i) a reversible isotherm and (ii) an irreversible isotherm. Draw these processes on a P— V diagram. 14-2. Show that (i) two ischores, (ii) two isobars, (iii) two isotherms and (iv) two adiabatics can never intersect. \. 14—3. Given that in an adiabatic process is an ideal gas is described by the equation PV” = Const. 7 = fl , CV Show that an equivalent way of writing this equation is TV "I = Const. 14-4. Why is it necessary to introduce entropy? 14-5. Draw the Carnot Cycle on a P-V Diagram and show that if TH, Tc are the temperatures of the hot and cold reservoirs respectively and DQH, DQC the heats picked up and rej ected then D9” "+ DQC TH Tc =0 14-6. In a Carnot Cycle the temperature of the hot reservoir is 100°C. What must be the temperature of the cold reservoir if we desire an efficiency of 0.4? 14-7. A heat pump is essentially a device which takes heat from a cold reservoir and rejects it into a hot reservoir. Its coefficient of performance is QH TH . . COP = —— = v ,where W = (Q — Q ) IS the energy input. If a heat QH “ QC TH — T C H C pump is used in your house when the temperature outside is 0°C and inside is 25°C and the input is l M. What is the COP and how much energy per cycle is delivered. ...
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