Plank's equation is being used to estimate the convective heat transfer coefficient in a food being frozen in an air blast freezer. It took a product 20 min to freeze in the freezer. The product is in the shape of an infinite cylinder with a diameter of 2 cm. The properties of the product are as follows: Thermal conductivity of frozen material = 1.8 W/(m K), density = 890 kg/m3, and latent heat of fusion = 260 kJ/kg, initial freezing point = -1.9 °C. The initial temperature of the product is 25 °C and the air temperature is -35 °C.
A plate containing 500 g of cooked string beans is being reheated in a microwave oven operating at 2.45 GHz. The beans have a specific heat capacity of 3560 J/(kg K), a density of 900 kg/m3, a dielectric constant of 70 and a loss tangent of 0.286. If the temperature of the beans rises 30 °C after 40 seconds of heating in a microwave oven, determine the effective electric field strength within the oven.
Two different products are being tempered in a microwave oven at the same time. Product 1 has the following properties: mass = 2 kg, density = 950 kg/m3, dielectric loss factor = 30, specific heat capacity = 3980 J/(kg K). Product 2 has the following properties: mass = 4 kg, density = 900 kg/m3, dielectric loss factor = 20, specific heat capacity = 3550 J/(kg K).
If Product 1 increases in temperature by 18 °C after 65 seconds of irradiation, what is the
power output of the oven? Assume all energy output from the oven is absorbed by the food.
Moist air flowing at 2 kg/s and a dry bulb temperature of 43 °C and a wet bulb temperature of 22 °C mixes with another stream of moist air at 25 °C and relative humidity of 40%. What must the flow rate of the second gas be if the mixture is to have a relative humidity of 30%?
Problem 9.8 in Singh and Heldman
Moist air at 35 °C and 55% relative humidity is heated using a common furnace to 70 °C. From the psychrometric chart, determine how much heat is added per m3 initial moist air and what the final dew-point temperature is.