A 5-cm-thick beef steak is being frozen in a -30°C room. The product has 73% moisture content, density of 970 kg/m³, and thermal conductivity (frozen) of 1.1 W/(m K). Estimate the freezing time using Plank's equation. The product has an initial freezing temperature of – 1.75°C, and the movement of air in the freezing room provides a convective heat-transfer coefficient of 5 W/(m² K).

Plate glass 5 mm thick at 200°C is to be cooled from both sides using air at 40°C. If surface cracks are to be avoided, determine the maximum value of convective heat transfer coefficient. Material properties are density = 2500 kg/m3, specific heat 670 J/kgK. Thermal conductivity 0.744 W/mk. Also determine the time required in this to cool the plate to 80°C.

A 10 cm-thick beef steak is being frozen in a -40°C room. The product has 73% moisture content, density of 970 kg/m³, and thermal conductivity (frozen) of 1.1 W/(m K). Estimate the freezing time using Plank’s equation. The product has an initial freezing temperature of  -1.75°C, and the movement of air in the freezing room provides a convective heat-transfer coefficient of 10 W/(m² K). a. tf =... h

A 300 mm thick wall (k= 1.5 W/mK, p = 2600 kg/m³, cp = 1000 J/kg⚫K) has a uniform original temperature of 900 °C. At the time t = 0, its both surfaces are suddenly exposed to air (T∞ = 25 °C, h = 30 W/m²K). (a) Calculate the Biot number of the wall. Does it have a uniform temperature? (b) After 3 hours, what is the temperature at the middle plane (@x = 0)? Symme try ½ L= 300 mm h = 30 W/m² K wall T∞ = 25°C h = 30 W/m² K To=25°C 9. Ah (T-To G=ept Hot air x p = 2600 kg/m³ k=1.5 W/m K 900c Hot air Tr= 96w arrume te Now.