Question

in the compression stroke of the gas engine the work done on the gas by the piston is 70 kj/kg and the heat rejected to the cooling water is 42 kj /kg calculate the change os specific internel energy stating whether it is gain or loss

Answer 1

Answer on Question #71025, Physics / Molecular Physics | Thermodynamics

In the compression stroke of the gas engine the work done on the gas by the piston is $70\mathrm{kJ/kg}$ and the heat rejected to the cooling water is $42\mathrm{kJ/kg}$ calculate the change of specific internal energy stating whether it is gain or loss.

Solution:

Heat given to the cooling water

$$Q = -42\ \mathrm{kJ/kg}$$

Work input

$$W = -70\ \mathrm{kJ/kg}$$

Using the formula,

$$Q = (U_2 - U_1) + W$$ $$-42 = (U_2 - U_1) - 70$$

So, the change of specific internal energy

$$\Delta U = -42 + 70 = 28\ \mathrm{kJ/kg}$$

Hence gain in internal energy $= 28\ \mathrm{kJ/kg}$

Answer. $28\ \mathrm{kJ/kg}$ (gain).

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