1. Choose the right answer The isentropic work of a turbine is a) Less than the
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Question
1. Choose the right answer The isentropic work of a turbine is a) Less than the actual work b) Greater than the actual work c) Equal to the actual work 2. Choose the wrong statement below (a) The thermal efficiency of all reversible heat engines is 100%. (b) For all reversible processes, the second-law efficiency is 100%. (c) The thermal efficiency of a heat engine cannot be greater than its second-a efficiency (d) The second-law efficiency of a process is 100% if no entropy is generated during that process. 3. Which of the following statements is eorrect? In a compression process a) The pressure will increase while the temperature remains constant b) The temperature will increase while'tlie pressure remains constant c) Both pressure and temperature will increase 4. Choose the right answer The heat added to diesel cycle occurs at a) Constant volume b) Constant pressure c) Constant volume and constat pressure. 5. Choose the right answer Exergy destruction is a result of a) Heat transfer b) Work production c) Process irreversibilities d) None of theseExplanation / Answer
1. (b) The isentropic work of turbine is always GREATER than the actual work because in isentropic work we consider the process to be reversible and adiabatic so there would be no entropy generation but in actual process there are irreversibilities associated with turbine which in turn causes entropy generation and decrase the actual work.
2. (a) The thermal efficiency of reversible heat engine is NOT 100%.certainlt its efficiency is maximum and equal to carnot efficiency but ir can never be 100% as it will violate the kelvin planks statement in case of 100% efficiency.
3. (c) In compression process both temparature and pressure will rise because as we know that temperature is a measure of internal energy of molecules of a substance.so when we compress the pressure exerted by molecules against each other will increase the internal energy of molecules which increases the temperature of the whole substance.
4. (b) Heat added to diesel engine at constant pressure because diesel take long time to burn and the progressive burn will increase the pressure but the expansion of the cylinder will decrease the pressure so the pressure remains constant.
5. (c) Exergy destruction is a result of process irreversibilities because in irreversibile process entropy would be generated which will destroy the exergy or available energy of the system.
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