A flat-plate collector gets incident of solar radiation at a rate of 260 Btu/h-ft' and has the collector properties as shown. If the collector has an average temperature of 120°F and ambient air temperature is 67°F, determine the ratio (%) of efficiency difference between the single glazing collector and the double glazing collector to the efficiency of the single glazing collector. Typical flat-plate solar collector properties U, W/m2C U, Btu/h-t2F Ta No gazing Single glazing Double glazing 0.90 0.85 0.80 2.8 0.5 1.7 0.3 90 00 221

The front window of an automobile has a thickness of 4 mm and is defrosted by the passage of a stream of hot air through the inner surface. The thermal conductivity of glass is around 0.78 W/(m oC). Assume the ambient air temperature is -10°C and the external convection coefficient is 65W/(m2 K). If the hot air blowing to defog the glass internally is at 40 ºC and the internal convection coefficient corresponds to 30 W/(m2 K), the internal surface temperatures will be _____________. However, if the car accelerates and maintains high speed, the external convection coefficient should _____________  [increase or decrease?] and if the condition is maintained long enough the temperature of the inner surface of the glass should _____________  [increase or decrease?].

If you have a room (10*7*3.5m) and you have 2 solar windows (the dimension of the window (2.5*2m)) located in the largest wall and the solar gain of them 1.5 kW/day and you have a door (1.6*2.5 m) in the northern wall and the temperature inside = 21°c and the average temperature outside = 10°C and the natural air change = 0.9 time /hour/day and the characteristics of materials are shown in the table below Elements U value Window 1.4 W/m.K Door 2.5 W/m.K South and North wall 0.5 W/m .K East and west wall 0.65 W/m .K Roof 0.45 W/m.K Floor 0.7 W/m .K If you know that you have 6 fixture lighting units of 50 W and the efficiency of them 70% and their runtime is 10 hours /day and there are 3 persons one of them is cooking and the two other are sleeping and they are present 4 hours/day and if you have the following appliance Appliance Running time Rotisserie 0.2 hour Large refrigerator 5 hours Blender 0.2 hour From your heat balance result decide if we will need a cooling or a heating system…

1) Draw the thermal resistance network representing heat transfer through the shell. 2) Determine the heat rate transfer under steady state conditions (W) 3) Determine the emissive power being emitted from the outside of the cylindrical tank (W). You can ignore emission from the top and bottom surfaces.