In the compression stroke of an IC engine the heat rejected to the cooling water is 65 kJ/kg and the work input is 108 kJ/kg. The change in specific internal energy of the working fluid would be:

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BHEL Engineer Trainee Mechanical 24 Aug 2023 Official Paper
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  1. Gain in internal energy of 173 kJ/kg.
  2. Loss in internal energy of 43 kJ/kg.
  3. Gain in internal energy of 43 kJ/kg.
  4. Loss in internal energy of 173 kJ/kg.

Answer (Detailed Solution Below)

Option 3 : Gain in internal energy of 43 kJ/kg.
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Detailed Solution

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Concept:

The first law of thermodynamics states that the change in internal energy of a system is given by:

\( Δ U = Q - W \)

Where:

  • ΔU = Change in internal energy (kJ/kg)
  • Q = Heat added to the system (kJ/kg)
  • W = Work done by the system (kJ/kg)

Given:

Heat rejected to cooling water, Q = -65 kJ/kg

Work input, W = 108 kJ/kg

Calculation:

Applying the first law of thermodynamics:

\( Δ U = Q - W \)

\( Δ U = (-65) + (108) \)

\( Δ U = 43\) kJ/Kg

Since Δ U is positive, it indicates a gain in internal energy.

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