A drying oven consists of a long semicircular duct of diameter D=1 m. Materials to be dried cover the base of the oven while the wall is maintained at 1200 K. Length of the oven (into paper direction) is 1 m. Water coated material is maintained at 325 K. Assume both the wall and the material to be blackbodies. (1) What is heat transfer rate? (2) Given at temperature 325 K, water needs heat 2.378 × 106 J/kg in order to be dried (from liquid water to steam). How much water can be dried per second based on the heat transfer rate from (1)? T₁ = 1200 K T₂ = 325 K — D = 1 m D= m→

Question No.13: a) What is a gray body? Derive the expression for radiation heat exchange between two gray surfaces connected by single refractory surface. b) A 60mm thick plate with a circular hole of 30mm diameter along the thickness is maintained at uniform temperature of 277°C. Find the loss of energy to the surroundings at 20°C, assuming that the two ends of the hole to be as parallel discs and the metallic surfaces and surroundings have black body characteristics.

A thin, disk-shaped silicon wafer of diameter D=20 cm on a production line must be maintained at a temperature of 100 deg C. The wafer loses heat to the room by convection and radiation from its upper surface, while heat is supplied at a constant flux from below. The surrounding air is at 20 deg C, while all surrounding surfaces (which can be treated as blackbodies) can be approximated to be isothermal at a temperature of 15 deg C. The wafer-to-air heat transfer coefficient is 30 W/m2-K and the emissivity of the wafer’s surface (which can be approximated to be gray) is 0.85. How much heat (in W) must be supplied to the wafer?

A furnace is of cylindrical shape with a diameter of 1.2 m and a length of 1.2 m as shown in Figure 3. The top surface has an emissivity of 0.70 and is maintained at 500 K. The bottom surface has an emissivity of 0.50 and is maintained at 650 K. The side surface has an emissivity of 0.40. Heat is supplied from the base surface at a net rate of 1400 W. Estimate the temperature of the side surface and the net rates of heat transfer between the top and the bottom surfaces, and between the bottom and side surfaces.

A proposed method for generating electricity from solar irradiation is to concentrate the irradiation into a cavity that is placed within a large container of a salt with a high melting temperature. If all heat losses are neglected, part of the solar irradiation entering the cavity is used to melt the salt while the remainder is used to power a Rankine cycle. (The salt is melted during the day and is resolidified at night in order to generate electricity around the clock.) 9R = Est-3.45 MW i Salt Tsalt = 1000°C Mirror MW qR Consider conditions for which the solar power entering the cavity is asol = 7.10 MW and the time rate of change of energy stored in the salt is Est = 3.45 MW. For a cavity opening of diameter D, = 1 m, determine the rate of heat transfer to the Rankine cycle, qr, in MW. The temperature of the salt is maintained at its melting point, Tsalt = Tm= 1000°C. Neglect heat loss by convection and irradiation from the surroundings. Sun Heliostats

A manufacturing facility located at 32° N latitude has a glazing area of 60 m² facing west that consists of double pane windows made of clear glass (SHGC = 0.766). To reduce the solar heat gain in summer, a reflective film that will reduce the SHGC to 0.35 is considered. The cooling season consists of June, July, August, and September, and the heating season, October through April. The average daily solar heat fluxes incident on the west side at this latitude are 2.35, 3.03, 3.62, 4.00, 4.20, 4.24, 4.16, 3.93, 3.48, 2.94, 2.33, and 2.07 kWh/day · m² for January through December, respectively. Also, the unit costs of electricity and natural gas are $0.09/kWh and $0.45/therm., respectively. If the coefficient of performance of the cooling system is 3.2 and the efficiency of the furnace is 0.90, determine the net annual cost savings due to installing reflective coating on the windows. Also, determine the simple payback period if the installation cost of reflective film is $20/m². Answers:…