7-3-16 [BKO] Ex: 7-3 A 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 (W net) by the engine, (b) the thermal efficiency (ηth), 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% 5 kJ/kg. At the beginning of the compression process. (d) 1171. (f) 60.1.7416 [B KS ] Ex: 75 An air is 1500 standard Diesel cycle has a compression ratio of 18.8 kPa.6%. determine (a) the pressure (p) at each point in the cycle. pressure is at 100 kPa and temperature is at 25oC. The heat transferred to the working fluid per cycle 2000 kJ/kg. (e) 1450 kPa. and (e) the MEP. (c) 58. (b) 3. Employing the perfect gas (PG) model for the working fluid. (d) the net work per unit mass (wnet). (b) the cut-off ratio.7% . (c) the thermal efficiency (ηth). (f) What-if Scenario: What would the thermal efficiency be if the heat transfer were kJ/kg? Answers: (a) 5729 kPa. 487. T3 = 2340 K.7-521 [BKA ] Ex: 76 The 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.3%. T4 = 3335 K. (d) 1667 kPa. and (d) the MEP. (c) 1346 kJ/kg.3% . (b) 67. (c) the net work per unit mass (wnet). (b) the thermal efficiency (ηth). T5 = K. (e) What-if Scenario: What would the thermal efficiency be if 75% of the total heat transfer took place at constant volume? 1209 Answers: (a) T2 = 947 K. (e)68. Determine (a) the temperature (T) at each point in the cycle. Heat supplied from a source of 1700 K is 800 kJ/kg. (c) What-if Scenario: What would the efficiency be if the argon were the working fluid? Answers: (a) 82.8 kJ/kg. (b) 658. (c) 82. Determine (a) the efficiency (ηth). Assume variable specific heats.3% . 300 K at the beginning of the isothermal compression process.7-5ideal 22 [BKH] Ex: 7-7 An Stirling cycle running on a closed system has air at 100 kPa.3%. (b) the net work output per kg of air (wnet). 10-1- 37 [BKW] Ex: 10-1 An ideal vaporcompression refrigeration cycle uses R-12 as the working fluid with a mass flow rate of 0.2 kW.3 tons. (b) the net power input. (d) What-if Scenario: What would the answers be if the R-12 were replaced with more environmentally friendly R-134a? Answers: (a) 3. 4. is 25oC and that of the refrigerated space is -10oC.7.19 tons. (d) 4.48 kW. and (c) the COP. The temperature of the atmosphere. (b) 2. (c) 4. If a temperature difference of 5oC is maintained between the refrigerant and the surroundings in the evaporator and condenser.1 kg/s. determine (a) the cooling power in tons. the warm region where heat rejection from the condenser takes place.6 . 3. and (c) the COP. If the vapor leaving the evaporator is superheated by 5oC and the liquid leaving the condenser is supercooled by by 5oC.10-1-39 [BPO] Ex: 10-3 A refrigerator with a cooling capacity of 5 ton uses ammonia as the refrigerant. determine (a) the compressor power. The condenser and evaporator maintain a pressure of 1500 kPa and 200 kPa respectively. The compressor has an isentropic efficiency of 80%. (d) What-if Scenario: What would the COP be if the vapor ere superheated 10oC above the saturation temperature at the evaporator exit? . (b) the mass flow rate of ammonia. (b) 0.016 kg/s.81. (d) 2.78 10-1-40 [BPS] Ex: 10-5 A two-stage cascade refrigeration plant uses R-22 as the working fluid in both the stages.26 kW. (c) 2. 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.Answers: (a) 6. . determine (a) the mass flow rate in the upper cycle.7. (b) 4. (b) the cooling capacity.11 kg/s. (c) 2. If the mass flow rate in the lower cycle is 0.53 tons. (d) 2. (d) What-if Scenario: What would the COP be if a single cycle operated between 1200 kPa and 120 kPa? Answers: (a) 0.58 .08 kg/s.The heat exchanger that couples the two cycles requires a minimum temperature difference of 5oC between the heating and the heated streams. and (c) the COP. to another.58-increase-decrease-2. Assuming the cycle operates ideally. 1200 kPa? Answers: (a) 0. and (b) the COP. (b) 2.10-1-41 [BPA] Ex: 10-6 A 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. 120 kPa.78. (c) What-if Scenario: How would the COP vary if the intermediate pressure is varied from one extreme. (c) 2. determine (a) the fraction of refrigerant that flows through the evaporator.96.5 . 10-2-19 [BPH] Ex: 10-7 An 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. which is air. The minimum temperature difference between the working fluid. and the cold or warm region is 5oC. which has a compression ratio of . Air enters the compressor. (b) 35. (c) 2. Using the perfect gas model. (d) 2. (d) What-if Scenario: What would the COP be if the ideal gas model were used? Answers: (a) 27.5 ton. determine (a) the cooling capacity in ton. and (c) the COP.8 kW.71. at 101 kPa with a volumetric flow rate of 100 m3/min. (b) the net power input.72 .3.