7-3-16[BKO]Ex: 7-3A 4-cylinder SI engine with a cylinder displacement of 0.5 L and a clearance volume of 62.5 mL is running at 3000 rpm. At the beginning of the compression process, air is at 100 kPa and 20oC. The maximum temperature during the cycle is 1800 K. Employing the cold-air standard Otto cycle, determine (a) the power developed (Wnet) by the engine, (b) the thermal efficiency (th), and (c) the MEP. (d)What-if Scenario:What would the thermal efficiency be if the maximum temperature were raised to 2200 K? (e) What would the thermal efficiency be if the ideal gas model were used?Answers:(a) 30.6 kW, (b) 58.5%, (c) 613 kPa, (d) 58.5%, (e) 53.55%

7-4-16[BKS]Ex: 7-5An air standard Diesel cycle has a compression ratio of 18. The heat transferred to the working fluid per cycle is 2000 kJ/kg. At the beginning of the compression process, pressure is at 100 kPa and temperature is at 25oC. Employing the perfect gas (PG) model for the working fluid, determine (a) the pressure (p) at each point in the cycle, (b) the cut-off ratio, (c) the thermal efficiency (th), (d) the net work per unit mass (wnet), and (e) the MEP. (f)What-if Scenario:What would the thermal efficiency be if the heat transfer were 1500 kJ/kg?Answers:(a) 5729 kPa, 487.8 kPa, (b) 3.1, (c) 58.6%, (d) 1171.5 kJ/kg, (e) 1450 kPa, (f) 60.7%

7-5-21[BKA]Ex: 7-6The Diesel cycle described in Example Ex: 7-5 is modified into a Dual cycle by breaking the heat addition process into two equal halves so that 1000 kJ/kg of heat is added at constant volume followed by 1000 kJ/kg of heat addition at constant pressure. Determine (a) the temperature (T) at each point in the cycle, (b) the thermal efficiency (th), (c) the net work per unit mass (wnet), and (d) the MEP. (e)What-if Scenario:What would the thermal efficiency be if 75% of the total heat transfer took place at constant volume?Answers:(a) T2 = 947 K, T3 = 2340 K, T4 = 3335 K, T5 = 1209 K, (b) 67.3%, (c) 1346 kJ/kg, (d) 1667 kPa, (e)68.3%

7-5-22[BKH]Ex: 7-7An ideal Stirling cycle running on a closed system has air at 100 kPa, 300 K at the beginning of the isothermal compression process. Heat supplied from a source of 1700 K is 800 kJ/kg. Determine (a) the efficiency (th), (b) the net work output per kg of air (wnet). Assume variable specific heats. (c)What-if Scenario:What would the efficiency be if the argon were the working fluid?Answers:(a) 82.3%, (b) 658.8 kJ/kg, (c) 82.3%10-1-37[BKW]Ex: 10-1An ideal vapor-compression refrigeration cycle uses R-12 as the working fluid with a mass flow rate of 0.1 kg/s. The temperature of the atmosphere, the warm region where heat rejection from the condenser takes place, is 25oC and that of the refrigerated space is -10oC. If a temperature difference of 5oC is maintained between the refrigerant and the surroundings in the evaporator and condenser, determine (a) the cooling power in tons, (b) the net power input, and (c) the COP. (d)What-if Scenario:What would the answers be if the R-12 were replaced with more environmentally friendly R-134a?Answers:(a) 3.3 tons, (b) 2.48 kW, (c) 4.7, (d) 4.19 tons, 3.2 kW, 4.610-1-39[BPO]Ex: 10-3A refrigerator with a cooling capacity of 5 ton uses ammonia as the refrigerant. The condenser and evaporator maintain a pressure of 1500 kPa and 200 kPa respectively. The compressor has an isentropic efficiency of 80%. If the vapor leaving the evaporator is superheated by 5oC and the liquid leaving the condenser is supercooled by by 5oC, determine (a) the compressor power, (b) the mass flow rate of ammonia, and (c) the COP. (d)What-if Scenario:What would the COP be if the vapor ere superheated 10oC above the saturation temperature at the evaporator exit?Answers:(a) 6.26 kW, (b) 0.016 kg/s, (c) 2.81, (d) 2.7810-1-40[BPS]Ex: 10-5A two-stage cascade refrigeration plant uses R-22 as the working fluid in both the stages. The lower cycle operates between the pressure limits of 120 kPa and 380 kPa and the topping cycle has a condenser pressure of 1200 kPa. The heat exchanger that couples the two cycles requires a minimum temperature difference of 5oC between the heating and the heated streams. If the mass flow rate in the lower cycle is 0.08 kg/s, determine (a) the mass flow rate in the upper cycle, (b) the cooling capacity, and (c) the COP. (d)What-if Scenario:What would the COP be if a single cycle operated between 1200 kPa and 120 kPa?Answers:(a) 0.11 kg/s, (b) 4.53 tons, (c) 2.7, (d) 2.58

10-1-41[BPA]Ex: 10-6A two-stage compression refrigeration plant uses R-22 as the working fluid and operates between the pressure limits of 120 kPa and 1200 kPa with the intermediate pressure being 380 kPa. Assuming the cycle operates ideally, determine (a) the fraction of refrigerant that flows through the evaporator, and (b) the COP. (c)What-if Scenario:How would the COP vary if the intermediate pressure is varied from one extreme, 120 kPa, to another, 1200 kPa?Answers:(a) 0.78, (b) 2.96, (c) 2.58-increase-decrease-2.5

10-2-19[BPH]Ex: 10-7An ideal gas refrigeration based on the reverse Brayton cycle is used to maintain a cold region at 10oC while rejecting heat to a warm region at 40oC. The minimum temperature difference between the working fluid, which is air, and the cold or warm region is 5oC. Air enters the compressor, which has a compression ratio of 3, at 101 kPa with a volumetric flow rate of 100 m3/min. Using the perfect gas model, determine (a) the cooling capacity in ton, (b) the net power input, and (c) the COP. (d)What-if Scenario:What would the COP be if the ideal gas model were used?Answers:(a) 27.5 ton, (b) 35.8 kW, (c) 2.71, (d) 2.72