A steam power plant receives heat from a furnace at a rate of 280 GJ/h. Heat losses to the surrounding air from the steam as it passes through the pipes and other components are estimated to be about 8 GJ/h. If the waste heat is transferred to the cooling water at a rate of 165 GJ/h, determine the thermal efficiency of this power plant.

When a man returns to his well-sealed house on a summer day, he finds that the house is at 35°C. He turns on the air conditioner, which cools the entire house to 20°C in 36 min. If the COP of the air-conditioning system is 2.8, determine the power drawn by the air conditioner. Assume the entire mass within the house is equivalent to 800 kg of air for which cy= 0.72 kJ/kg °C and cp = 1.0 kJ/kg-°C. 35°C 20°C W A/C The power drawn by the air conditioner is kW.

I am only interested in part 6-27(a). I see that Bartleby has answered this question before but I have a question regarding the yielding factor of safety. Why is the yielding factor of safety calculated as ( n=Sy/sigma_max), but not as ( n=Sy/Kf*sigma_max)? Since there is stress concentration factor.