Chapter 1, Problem 1.61P

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

Air must be compressed in a well-insulated piston cylinder from a volume of 6.4 litres to a volume of 1 litres. If the air is initially at 398 K, what is the minimum work per unit mass of air required to carry out this compression? Give your answer in k) to the nearest whole number. For air: Co = 1.005 kj/kg K and cy= 0.718 kj/kg K.

In adiabatic process, the system has Q=max. value O W=0 O Q=0 O U-0 O * A vertical piston-cylinder device contains water and is being heated on top of a range. During the process, 65 Btu of heat is transferred to the water, and heat losses from the side walls amount to 8 Btu. The piston rises as a result of evaporation, and 5 Btu of work is done by the vapor. Determine the change in the energy of the water .for this process 61 Btu O 52 Btu 55 Btu 60 Btu * hp compressor in a facility that operates at full load-75 for 2500 h a year is powered by an electric motor that has an efficiency of 93 percent. If the unit cost of electricity is $0.11/kWh, the annual electricity cost of this :compressor is 16,540 $ 19,180 $ O 5,380 $ O 14,300 $ O barometric pressure or 1 atmospheric 1 pressure is equal to 1.019 kgf/cm2 1 kgf/cm2 0.9 kgf/cm2 0 kgf/cm2 O