Chapter 5, Problem 5.4P

Which of the following about entropy is FALSE? A When energy leaves a hot reservoir as heat, the entropy of the reservoir decreases. B The entropy of an ideal gas increases when expands isothermally. C) The flow of energy as heat from a cold source to a hot sink is considered to be spontaneous. D The increase in entropy is expressed in terms of its heat capacity when a substance is heated. A process can already be considered as totally reversible if A Both external and internal irreversibilities are absent. B) There is no external irreversibility. © If the process can be reversed by any possible means. D There is no internal irreversibility.

_______________ is a form of energy. It is transferred from one body (at a higher temperature) to the other body at a lower temperature.

1. In a turbine, steam enters with an enthalpy of 1275 Btu/lbm and leaves with an enthalpy of 1115 Btu/lbm. The transferred heat is 13 Btu/lbm. Find the turbine work in hp where the steam flow rate is 5 lbm/sec? 2. During a steady flow process, the pressure of the working substance drops from 200 to 20 psig, the speed increases from 100 to 800 fps, The internal energy of the open system increases by 15 Btu/lbm, and the specific volume increases from 1 to 10 ft3/lb. The heat lost of the open system is equivalent to 1 kW. Determine the work in hp for a mass flow rate of 12 lbm per min.

don't copy ,explain.

The working gas of a thermodynamic cycle is air. The gas originally starts at 100kPa, 1m³ and 27°C First, the pressure of the gas is doubled keeping the volume fixed. Second, the volume of the gas is doubled at constant pressure. Third, the gas undergoes an adiabatic expansion. Fourth, the gas undergoes an isothermal contraction back to its original state a) Make a table of the pressure, volume, and temperature at the start of each process. b) Make a table of the change in internal energy, heat flow, work done, change in enthalpy and change in entropy during each leg of the cycle. ● ● c) Draw P-v and T-s diagrams, indicating P, V & T at the start of each process & AU, Q, W, AH & AS for each leg. d) Calculate the thermal efficiency of the cycle.

During a steady flow process, the pressure of the working substance drops from 180 psia to 30 psia, the speed increases from 210 fps to 1050 fps, the internal energy of the open system decreases 30 Btu/lb, ad the specific volume increases from 2 to 10ft^3/lb.Heat loss is 20 Btu/lb. Determine the horsepower for 12 lb/min mass flow. Ans. 66hp

The first step of a thermodynamic cycle is an isobaric process with increasing volume. The second is an isochoric process, with decreasing pressure. The last step may be either an isothermal or adiabatic process, ending at the starting point of the isobaric process. Sketch a graph of these two possibilities, and comment on which will have greater net work per cycle.

How do free energy machines work?

1. A gas undergoes isobaric process with a constant pressure of 2000 Pa. If the heat of 800 J is added to the process, the volume expands from 0.120 m to 0.200 m. What is the change in its internal energy? 2. An engine absorbs 500 J of heat and reject 100 J of heat to cold reservoir in each cycle. What is its efficiency? 3. From Question 2, how much work does the engine do in three cycles? 4. A refrigerator has a coefficient of performance of 2.0. In each cycle it absorbs 3.4x10 J of heat from the cold reservoir. During each cycle, how much heat is released to the high-temperature reservoir? 5. During running, you lost 4.0x10 J of heat, and your internal energy also decreased by 1.6x10* J. How much work did you do in the match?