Consider an electrically heated brick house ( k = 0 .40 Btu/h .ft°F ) and whose walls are 9 ft high and 1 ft thick. Two of the walls of the house are 50 ft long and the others are 35 ft long. The house is maintained at 70°F at all times while the temperature of the outdoors varies. On a certain day, the temperature of the inner surface of the walls is measured to be at 55°F while the average temperature of the outer surface is observed to remain at 45°F during the day for 10 h and at 35°F at night for 14 h. Determine the amount of heat lost from the house that day. Also determine the cost of that heat loss to the homeowner for an electricity price of $0.09 kWh.
Consider an electrically heated brick house ( k = 0 .40 Btu/h .ft°F ) and whose walls are 9 ft high and 1 ft thick. Two of the walls of the house are 50 ft long and the others are 35 ft long. The house is maintained at 70°F at all times while the temperature of the outdoors varies. On a certain day, the temperature of the inner surface of the walls is measured to be at 55°F while the average temperature of the outer surface is observed to remain at 45°F during the day for 10 h and at 35°F at night for 14 h. Determine the amount of heat lost from the house that day. Also determine the cost of that heat loss to the homeowner for an electricity price of $0.09 kWh.
Solution Summary: The author calculates the amount of heat loss from the house on the day and also calculate the cost of that heat.
Consider an electrically heated brick house
(
k
=
0
.40 Btu/h
.ft°F
)
and whose walls are 9 ft high and 1 ft thick. Two of the walls of the house are 50 ft long and the others are 35 ft long. The house is maintained at 70°F at all times while the temperature of the outdoors varies. On a certain day, the temperature of the inner surface of the walls is measured to be at 55°F while the average temperature of the outer surface is observed to remain at 45°F during the day for 10 h and at 35°F at night for 14 h. Determine the amount of heat lost from the house that day. Also determine the cost of that heat loss to the homeowner for an electricity price of $0.09 kWh.
Consider a person standing in a room kept at 22°C at all times. Your house It has been observed that the inner surfaces of the walls, floor and ceiling are at an average temperature of 15°C. If this person's exposed surface area is 1.4 m2 and if the average external surface temperature is 30°C, this person and the surrounding surfaces Determine the radiation and heat transfer rate between One's emissivity, the Stefan-Boltzmann constant a=5,67x10 -8 W/m 2 K 4
1. A 1000-W iron is left on the iron board with its base exposed to the air at 20°C. The convection heat transfer coefficient between the base surface and the surrounding air is 35 W/m². °C. If the base has an emissivity of 0.6 and a surface area of 0.02 m², determine the temperature of the base of the iron.
2. The inner and outer surfaces of a 5-m x 6-m brick wall of thickness 30 cm and thermal conductivity 0.69 W/m °C are maintained at temperatures of 20°C and 5°C, respectively. Determine the rate of heat transfer through the wall, in W.
Ice water of 0°C is stored in a spherical container made of steel with an inner diameter of 3 m and a thickness of 1 cm. This container is located in a place where the external temperature is 25℃. The temperature of the entire container is assumed to be 0°C. If thermal resistance in the container is ignored, obtain (a) the heat transfer rate to ice water, and (b) the amount of ice that melts for 24 hours. The melting heat of ice at atmospheric pressure is 333.7 kJ/kg. The emissivity of the outer wall of the container is 0.75, and the convective thermoelectric transfer coefficient is 30 W/m2·K. The average temperature of the surrounding surface for radiation is 15℃.
***I would appreciate it if sir could write it in a way that I could read it well.**
Chapter 3 Solutions
Heat and Mass Transfer: Fundamentals and Applications
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