9-86 Flat-plate solar collectors are often tilted up toward the sun in order to intercept a greater amount of direct solar radiation. The tilt angle from the horizontal also affects the rate of heat loss from the collector. Consider a 1.5-m-high and 3-m-wide solar collector that is tilted at an angle 0 from the horizontal. The back side of the absorber is heavily insulated. The absorber plate and the glass cover, which are spaced 2.5 cm from each other, are maintained at tempera- tures of 80°C and 40°C, respectively. Determine the rate of heat loss from the absorber plate by natural convection for 0 = 0°, 30°, and 90°.

9-86 Flat-plate solar collectors are often tilted up toward the sun in order to intercept a greater amount of direct solar radiation. The tilt angle from the horizontal also affects the rate of heat loss from the collector. Consider a 1.5-m-high and 3-m-wide solar collector that is tilted at an angle 0 from the horizontal. The back side of the absorber is heavily insulated. The absorber plate and the glass cover, which are spaced 2.5 cm from each other, are maintained at tempera- tures of 80°C and 40°C, respectively. Determine the rate of heat loss from the absorber plate by natural convection for 0 = 0°, 30°, and 90°.

Elements Of Electromagnetics

7th Edition

ISBN:9780190698614

Author:Sadiku, Matthew N. O.

Publisher:Sadiku, Matthew N. O.

ChapterMA: Math Assessment

Section: Chapter Questions

Problem 1.1MA

See similar textbooks

Similar questions

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.
Consider two concentric horizontal cylinders of diameters 55 cm and 65 cm, and length 125 cm. The surfaces of the inner and outer cylinders are maintained at 54C and 106C,respectively. If the annular cavity is filled with (a) water and (b) Air. With natural transport between rollersfind the speed of heat transfer.
Four power transistors, each dissipating 12 W, are mounted on a thin vertical aluminum plate 22 cm * 22 cm in size. The heat generated by the transistors is to be dissipated by both surfaces of the plate to the surrounding air at 25°C, which is blown over the plate by a fan. The entire plate can be assumed to be nearly isothermal, and the exposed surface area of the transistor can be taken to be equal to its base area. If the average convection heat transfer coefficient is 25 W/m2·K, determine the temperature of the aluminum plate. Disregard any radiation effects.
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.
Define Nusselt number and discuss when is heat transfer through a fluid conductionand when is it convection? For what case is the rate of heat transfer higher?
When is the heat transfer through a fluid conduction and when is it convection? For which case is the rate of heat transfer higher? How does the convection heat transfer differ from the thermal conductivity of the fluid?
Solar radiation is incident on the glass cover of asolar collector at a rate of 700 W/m2. The glass transmits88 percent of the incident radiation and has an emissivityof 0.90. The entire hot water needs of a family in summercan be met by two collectors 1.2 m high and 1 m wide. Thetwo collectors are attached to each other on one side so thatthey appear like a single collector 1.2 m * 2 m in size. Thetemperature of the glass cover is measured to be 35°C on aday when the surrounding air temperature is 25°C and thewind is blowing at 30 km/h. The effective sky temperaturefor radiation exchange between the glass cover and the opensky is 240°C. Water enters the tubes attached to the absorberplate at a rate of 1 kg/min. Assuming the back surface of theabsorber plate to be heavily insulated and the only heat lossto occur through the glass cover, determine (a) the total rateof heat loss from the collector, (b) the collector efficiency,which is the ratio of the amount of heat transferred to…
Why is this equation fundamental in the analysis of heat transfer? Why is this a big deal for engineers?
The boiling temperature of nitrogen at atmosphericpressure at sea level (1 atm) is -196°C. Therefore, nitrogenis commonly used in low-temperature scientific studies sincethe temperature of liquid nitrogen in a tank open to the atmosphereremains constant at -196°C until the liquid nitrogen inthe tank is depleted. Any heat transfer to the tank results inthe evaporation of some liquid nitrogen, which has a heatof vaporization of 198 kJ/kg and a density of 810 kg/m3 at1 atm.Consider a 4-m-diameter spherical tank initially filledwith liquid nitrogen at 1 atm and -196°C. The tank isexposed to 20°C ambient air with a heat transfer coefficientof 25 W/m2·K. The temperature of the thin-shelled sphericaltank is observed to be almost the same as the temperatureof the nitrogen inside. Disregarding any radiation heatexchange, determine the rate of evaporation of the liquidnitrogen in the tank as a result of the heat transfer from theambient air.
An average man has abody surface area of 1.8m2 and a skin temperature of 33degrees celcius .The convection heat transfer coefficient for a clothed person walking in still air is expressed as {h,8.6V^0.53}FOR 0.5<v<2m/s,where V is the walking velocityin m/s.Assuming the average surface temperature of the clothed person to be 30degrees celcius, determine the rate of heat loss from an average man walking in still air at 10degrees celcius by convectionat a walking velocity of (a)0.5m/s (b)1.0m/s (c)1.5m/s (d)2.0m/s
A 3 m internal diameter spherical tank made of 1 cm thick stainless steel (k =15 W/mK) is used to store water at 4℃, as shown in Figure 2.2. Inner surfaceof the tank is 4℃, while the outer surface of the tank is painted with blackcolour paints with emissivity, ? = 0.88 measured at temperature 5℃. It islocated outdoor at 40℃ and is subjected to wind at 25 km/h. Determine the total heat transfer rate to the ice water.
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?