Chapter 8, Problem 8.43CU

SHOW COMPLETE AND LEGIBLE SOLUTION. FAST ANSWERS WILL BE GIVEN UPVOTE. ANSWER B ONLY.

Answer true (T) or false (F) as appropriate1. Entropy is a measure of irreversibilities in processes.2. The entropy of the universe must always decrease.3. The thermal efficiency of a Carnot engine is the maximum possible.4. The gas turbine operates on the Rankine cycle.5. The steam turbine operates on the Brayton cycle.

Which of the following descriptions about entropy is/are TRUE? I. It is positive for an isolated system. II. It is zero for a reversible process. III. It is negative for an irreversible process. A. I and II only B. All I, II and III C. II and III only D. I and III only

True Or False

5. (Calculation questions, A cycle 1-2-3-4-1 is proposed, in which 1-2 is a reversible adiabatic process, 2-3 is a reversible constant temperature endothermic process, 3-4 is a reversible adiabatic process, 4-1 is an irreversible adiabatic process, and 1, 2, 3 and 4 are three equilibrium points respectively. Can this cycle be realized and why?

An open feedwater heater is a direct-contact heat exchanger used in vapor power plants. Shown in the figure below are operating data for an open heater with H,0 as the working fluid operating at steady state. Ignoring stray heat transfer from the outside of the heat exchanger to its surroundings and kinetic and potential energy effects, determine the rate of entropy production, in kW/K. (Hint: Use the first law to find the mass flow rates) Also determine state point 1 and 2 on a T-s diagram, then mix them and show the outcome is 3. Show 3 on the T-s diagram. P2 = 3 bar x2 = 0.92 (2) P3 = 3 bar saturated liquid m3 = 80 kg/s P1 = 3 bar T1 = 36°C Open Feedwater (3) Heater

Consider an ideal vapor compression system using R-134a. Its condensing pressure is 185 psia (sat. temp. 120 F) and evaporating pressure is 33 psia (sat. temp. 20 F). Using the attached P-h state diagram, answer the questions below. (You may want to have a ruler to help read the chart.) a) Show the ideal cycle. Label the states (1,2,3,4). b) Calculate the COP for this ideal cycle. c) Determine the refrigerating effect per refrigerant circulated [Btu/lbm], d) For ATsc = 10 F of subcooling, how much does it change the refrigeration effect [% change]. e) Determine the COP for part d. f) Determine the increase in COP for ATsh = 1 F of superheat. To answer this question, compare the cycle in part e that has 0 F superheat with a cycle that has 20 F of superheat and calculate 4COP/ATsh- %3D

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11. An ideal gas undergoes the following three step internally reversible cycle: step 1: Isothermal expansion at T1 from pressure Pi to aP1; step 2: Adiabatic expansion to pressure bP1; step 3: A linear process on T-s plot. Sketch the cycle on T-s plot. Show that T temperature in state 3, i.e., T3 is given by n T y-1, b .In 2. Find the magnitude and a direction of heat transfer for each step. Express the cyclic efficiency in terms of a, b and y.