Answer:
Thermal efficiency(ηth) = 1 - (TH/Tc), where TH is temperature of hot reservoir and Tc is temperature of cold reservoir.
ηth = 1 - (300/Tc)
We can assume a value for TH to be 400°C
Then,
ηth = 1 - (300/400) = 1 - 0.75 = 0.25
Explanation:
Thermal efficiency, ηth, of an heat engine is define as the ratio of the work it does, W, to the heat input at the high temperature, QH.
The thermal efficiency is expressed mathematically as:
ηth= QH/W
OR
Thermal efficiency(ηth) = 1 - (TH/Tc).
In other words, the fraction of heat that is converted to work is the thermal efficiency. That is, the measure of performance of engines that uses heat energy in their operation. It has no dimension.
Examples of such engines are:
Steam turbine;
Any internal combustion engine;
A refrigerator.
In operation of a refrigeration or heat pumps, thermal efficiency indicates the extent to which the energy added by work is converted to net heat output. Since it is dimensionless number, we must always express W, QH, and QC in the same units
