3. A power cycle operates between hot and cold reservoirs at 500 K and 310 K respectively. At steady state the power output developed is: 0.1 MW. What is the minimum rate of energy rejection by heat transfer to the cold reservoir, in MW

0.163 MW

Explanation:

To get the minimum rate of energy rehection by heat transfer to cold reservoir, it implies that the power cycle operates in reversible cycle. The efficiency of reversible cycle whose value will be same as efficiency of power cycle will be given by

Efficiency of reversible cycle

n = (Th-Tc) / Th where T represent temperature, n efficiency, subscripts h and c hot and cold respectively

Substituting 500 and 310 for hot and cold temperatures respectively then efficiency

n = (500-310) / 500=0.38

Efficiency of power cycle, n = Power output/Qh

Qh = 0.1/0.38 = 0.263

Net power output, W = Qh - Qc

Qc=Qh-W = 0.263-0.1=0.163 MW