1. It is commonly recommended that hot foods be cooled first to room temperature by simply waiting a while before they are put into the refrigerator to save energy. Despite this common sense recommendation, a person keeps cooking a large pan of stew twice a week and putting the pan into the refrigerator while it is still hot, thinking that the money saved is probably too little. The average mass of the pan and its contents is 5-kg. The average temperature of the kitchen is 20°C, and the average temperature of the food is 95°C when it is taken off the stove. The refrigerated space is maintained at 3°C, and the average specific heat of the food and the pan can be taken to be 3.9 kJ/kg-K. If the refrigerator has a coefficient of performance of 1.2 and the cost of electricity is Php 21.59 per kW-hr. Determine how much will be saved a year by waiting for the food to cool to room temperature before putting it into the refrigerator. Ans: Php 170.66 20°C Hoe food 95°C

Discuss the modes of heat transfer that determine the equilibrium temperature of the space shuttle Endeavour when it is in orbit. What happens when it reenters the earths atmosphere?

Q1. A 1200-Wiron is left on the ironing board with its base exposed to the air (Figure 1). About 90 percent of the heat generated in the iron is dissipated through its base whose surface area is 150 cm?, and the remaining 10 percent through other surfaces. Assuming the heat transfer from the surface to be uniform determine (a) the amount of heat the iron dissipates during a 1- hour period, in kWh and (b) the total cost of the electrical energy consumed during this 1-hour period. Take the unit cost of electricity to be $0.07/kWh. Iron 1200 W Figure 1

Mc Graw Hill It is commonly recommended that hot foods be cooled first to room temperature by simply waiting a while before they are put into the refrigerator to save energy. Despite this commonsense recommendation, a person keeps cooking a large pan of stew three times a week and putting the pan into the refrigerator while it is still hot, thinking that the money saved is probably too little. But he says he can be convinced if you can show that the money saved is significant. The average mass of the pan and its contents is 5 kg. The average temperature of the kitchen is 23°C, and the average temperature of the food is 95°C when it is taken off the stove. The refrigerated space is maintained at 3°C, and the average specific heat of the food and the pan can be taken to be 3.9 kJ/kg-°C. If the refrigerator has a coefficient of performance of 1.5 and the cost of electricity is $0.165/kWh, determine how much this person will save a year by waiting for the food to cool to room temperature…