5. . . ) In a manufacturing process, a long, coated plastic rod (p = 2200 kg/m³, c = 800 J/kg K, k =20 W/m K) of diameter D = 20 mm is initially at a uniform tempera- ture of 25°C and is suddenly exposed to a cross flow of air at T.. 350°C and V = 50 m/s. = (a) How long will it take for the surface of the rod to reach 175°C, the temperature above which the special coating will cure? h Additional hint: Bi = Lc. The k characteristic Lc is defined as V / As, or the ratio between Volume and Surface area. For cylinder, V = 1 D² * Length As = 4 πD * Length.

A glass window of width W = 1 m and height H = 2 m is 5 mm thick and has a thermal conductivity of k 1.4 W/m K. If the inner and outer surface temperatures of the glass are 15°C and -20°C, respectively, on a cold winter day, what is the rate of heat loss through the glass? To reduce heat loss through windows, it is cus- tomary to use a double pane construction in which adjoining panes are separated by an air space. If the spacing is 10 mm and the glass surfaces in contact with the air have temperatures of 10°C and -15°C, what is the rate of heat loss from a 1 m x 2 m window? The thermal conductivity of air is k, = 0.024 W/m.K.

Air at 25 ° C blows over the hot steel plate whose surface temperature is maintained at 200 ° C. The plates have dimensions of 50 cm x 50 cm and a thickness of 2.5 cm. The convection heat transfer coefficient on the upper surface is 25 W / (m² ° C). The thermal conductivity of steel is 45 W / (m ° C). Calculate the hourly heat loss from the plate surface. a. heat loss per hour = AnswerkJ. b. If the reverse side surface temperature is maintained, specify hourly heat loss = AnswerkJ.

Q3) A fused-quartz sphere has a thermal diffusivity of 9.5 x 107 m²/s, a diameter of 2.5 cm, and a thermal conductivity of 1.52 W/m. °C. The sphere is initially at a uniform temperature of 25 °C and is suddenly subjected to a convection environment at 250 °C. The convection heat-transfer coefficient is 110 W/m². °C. Calculate the temperatures at the center and at a radius of 5 mm after a time of 8 min.