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.

An experiment to measure the thermal conductivity of food formulations was carried out by measuring the surface temperature of the food formulations which were formed into flat plates with a thickness of 10 mm. It is found that at steady-state conditions, there is a temperature difference of 40 ° C between the two surfaces, the heat transfer rate per unit area of 4700 W / m2 is measured near the center of the two surfaces. Calculate: the thermal conductivity of the product, = AnswerW / m ° C

An industrial cold room has four 200 mm thick walls made of concrete. The walls are insulated on the outside with a layer of foam 60 mm thick. Cladding with a thickness of 15 mm protects the foam on the outside from the elements. The composite wall surface temperatures are –3 °C on the inside and 18 °C on the outside of the room respectively. The thermal conductivities of concrete, foam and cladding are 0.75, 0.35 and 0.5 W/m K respectively. a) Assuming perfect thermal contact between the layers of the composite walls, draw the typical temperature distribution across the layers and determine the heat energy gained per hour through all 4 walls of the room with a total surface area of 20 m2 . What does this heat energy represent in terms of the refrigeration system of the cold room?

Steel pipe (outer diameter 100 mm) is covered with two layers of insulation. The inner layer, 40 mm thick, has a thermal conductivity of 0.07 W / (m K). The outer layer, 20 mm thick, has a thermal conductivity of 0.15 W / (m K). Pipes are used to deliver steam with a pressure of 700 kPa. The temperature on the outer insulation surface is 24 ° C. If the pipe is 10 m long, determine the following: (assuming that the conduction heat transfer resistance of the steel pipe and the vapor convection resistance are negligible). a. Heat loss per hour. = AnswerkJ / hour. b. Temperature between insulation layers. = Answer° C.