1. Consider a flat plate solar collector placed horizontally on the flat roof of a house. The collector is 5 ft wide Ty50°F sky and 15 ft long, and the average temperature of the Solar collector 70°F exposed surface of the collector is 100'F. The emissivity of the exposed surface of the collector is 0.9. Determine the rate of heat loss from the collector by convection and radiation during a calm day when the ambient air temperature is 70°F and the effective sky temperature for radiation exchange is 50°F. Take the convection heat transfer coefficient on the exposed surface to be 2.5 Btu/h ft2. F

A horizontal, 3-mm-thick flat-copper plate, 1-m long and 0.5-m wide, is exposed in air at 27C to radiation from the sun. If the total rate of solar radiation absorbed is 300 W and the combined radiation and convection heat transfer coefficients on the upper and lower surfaces are 20 and 15W/m2K, respectively, determine the equilibrium temperature of the plate.

Consider a hot automotive engine, which can be approximated as a 0.5-m-high, 0.40-m-wide, and 0.8-m-long rectangular block. The bottom surface of the block is at a temperature of 100°C and has an emissivity of 0.95. The ambient air is at 20°C, and the road surface is at 25°C. Determine the rate of heat transfer from the bottom surface of the engine block by convection and radiation as the car travels at a velocity of 80 km/h. Assume the flow to be turbulent over the entire surface because of the constant agitation of the engine block.

Consider a 1.2-m-high and 2-m-wide glass windowwith a thickness of 6 mm, thermal conductivity k = 0.78W/m·K, and emissivity « = 0.9. The room and the wallsthat face the window are maintained at 25°C, and the averagetemperature of the inner surface of the window is measuredto be 5°C. If the temperature of the outdoors is 25°C,determine (a) the convection heat transfer coefficient on theinner surface of the window, (b) the rate of total heat transferthrough the window, and (c) the combined natural convectionand radiation heat transfer coefficient on the outer surface ofthe window. Is it reasonable to neglect the thermal resistanceof the glass in this case?

Q6: A large vertical plate 6.1 m high and 1.22 m wide is maintained at s constant temperature of 57:C and exposed to atmospheric air at 4-C. Caleulate the heat lost by the plate. Answers: Q

An automotive engine can be approximated asa 0.4-m-high, 0.60-m-wide, and 0.7-m-long rectangularblock. The bottom surface of the block is at a temperatureof 75°C and has an emissivity of 0.92. The ambient airis at 5°C, and the road surface is at 10°C. Determine therate of heat transfer from the bottom surface of the engineblock by convection and radiation as the car travels at avelocity of 60 km/h. Assume the flow to be turbulent over theentire surface because of the constant agitation of the engineblock. How will the heat transfer be affected when a 2-mmthickgunk (k = 3 W/m?K) has formed at the bottom surface asa result of the dirt and oil collected at that surface over time?Assume the metal temperature under the gunk still to be 75°C.

The Biot number during a heat transfer process between a sphere and its surroundings is determined to be 0.02. Would you use lumped system analysis or the transient temperature charts when determining the midpoint temperature of the sphere? Why?

In a new residential project, you strongly believethat double-paned windows are ‘better’ than singlepaned windows. Compare the rate of heat loss betweensingle and double-paned windows (1.5 m x 1 m) if thethickness of each pane is (th = 0.4 cm) and (k = 0.9W/m.K). The indoor and outdoor temperatures are 18°C and 2 °C, respectively. Thickness of the air gapbetween the double-paned windows is (th = 1 cm), and(k = 0.022 W/m.K). Image credit: Windowwhirl

Define the cooling of a boiled egg by forced and natural convection.

A 10-m-long section of a 6-cm-diameter horizontal hot-water pipe passes through a large room whose temperature is 27°C. If the temperature and the emissivity of the outer surface of the pipe are 73°C and 0.8, respectively, determine the rate of heat loss from the pipe by (a) natural convection and (b) radiation.