Question

In: Mechanical Engineering

Q5. State whether the following are true or false with brief justifications: (i) The maximum thermal...

Q5. State whether the following are true or false with brief justifications:

(i) The maximum thermal efficiency for any power cycle operating between two thermal reservoirs at temperatures T1 and T2 (T1 > T2) is 1- T2/T1.
(ii) Transferring heat from a cold object to a hot object is forbidden according to the Clausius statement of the second law.

(iii) A cycle that does not violate the Kelvin-Planck statement cannot violate the Clausius statement of the second law.
(iv) For a reversible power cycle, if we hold the temperature of the cold reservoir (TC) constant, we can increase the thermal efficiency ? to any value smaller than 1 (100%) by varying TH.

(v) A system interacting with air at different heights in the atmosphere is interacting with only one thermal reservoir, i.e., the atmosphere.

Expert Solution

(i) The maximum thermal efficiency for any power cycle operating between two thermal reservoirs at temperatures T1 and T2 (T1 > T2) is 1- T2/T1.

yes...

Carnot's theorem states:

All heat engines between two heat reservoirs are less efficient than a Carnot heat engine operating between the same reservoirs.
Every Carnot heat engine between a pair of heat reservoirs is equally efficient, regardless of the working substance employed or the operation details

(ii) Transferring heat from a cold object to a hot object is forbidden according to the Clausius statement of the second law.......yes

The second law of thermodynamics states that the total entropy of an isolated system can never decrease over time. The total entropy can remain constant in ideal cases where the system is in a steady state (equilibrium), or is undergoing a reversible process.

Heat cannot spontaneously flow from cold regions to hot regions without external work being performed on the system, which is evident from ordinary experience of refrigeration, for example. In a refrigerator, heat flows from cold to hot, but only when forced by an external agent, the refrigeration system.

(iii) A cycle that does not violate the Kelvin-Planck statement cannot violate the Clausius statement of the second law.....yes

without external work heat cannot pass from colder to hotter temprature ..so as plank statement that there is no heat cycle which can operate at 100%.

(iv) For a reversible power cycle, if we hold the temperature of the cold reservoir (TC) constant, we can increase the thermal efficiency ? to any value smaller than 1 (100%) by varying TH.

yes...efficiency =1- TC/TH

we can increse TH to increase efficiency to lower than 1.

(v) A system interacting with air at different heights in the atmosphere is interacting with only one thermal reservoir, i.e., the atmosphere.

yes

samet mamat answered 2 years ago

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