8.) A supply of 50 kg of chicken at 6 C contained in a box is to be frozen to -18 C in a freezer (Figure). Determine the amount of heat that needs to be removed. The container box is 1.5 kg, and the specific heat of the box material is 1.4 kJ/kg • K. m=50kg h=247 kJ/kg Chicken m= 50 kg T=6°C T=-18°C freezing =-2.8°C C3=3.32 kJ/kg.K Ch=1.77 kJ/kg.K Container =1.5 kg Cbox=1.4 kJ/kg.K

8.) A supply of 50 kg of chicken at 6 C contained in a box is to be frozen to -18 C in a freezer (Figure). Determine the amount of heat that needs to be removed. The container box is 1.5 kg, and the specific heat of the box material is 1.4 kJ/kg • K. m=50kg h=247 kJ/kg Chicken m= 50 kg T=6°C T=-18°C freezing =-2.8°C C3=3.32 kJ/kg.K Ch=1.77 kJ/kg.K Container =1.5 kg Cbox=1.4 kJ/kg.K

Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)

8th Edition

ISBN:9781305387102

Author:Kreith, Frank; Manglik, Raj M.

Publisher:Kreith, Frank; Manglik, Raj M.

Chapter2: Steady Heat Conduction

Section: Chapter Questions

Problem 2.1P: A plane wall, 7.5 cm thick, generates heat internally at the rate of 105 W/m3. One side of the wall...

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A plane wall, 7.5 cm thick, generates heat internally at the rate of 105 W/m3. One side of the wall is insulated, and the other side is exposed to an environment at 90C. The convection heat transfer coefficient between the wall and the environment is 500 W/m2 K. If the thermal conductivity of the wall is 12 W/m K, calculate the maximum temperature in the wall.
2.30 An electrical heater capable of generating 10,000 W is to be designed. The heating element is to be a stainless steel wire having an electrical resistivity of ohm-centimeter. The operating temperature of the stainless steel is to be no more than 1260°C. The heat transfer coefficient at the outer surface is expected to be no less than in a medium whose maximum temperature is 93°C. A transformer capable of delivering current at 9 and 12 V is available. Determine a suitable size for the wire, the current required, and discuss what effect a reduction in the heat transfer coefficient would have. (Hint: Demonstrate first that the temperature drop between the center and the surface of the wire is independent of the wire diameter, and determine its value.)
The tip of a soldering iron consists of a 0.6-cm- diameter copper rod, 7.6 cm long. If the tip must be 204C, what are the required minimum temperature of the base and the heat flow, in watts, into the base? Assume that h=22.7W/m2KandTair=21C.
54. As shown in the figure, to dissipate heat from an electrical appliance, thin plates of metal with a thermal conductivity of 10 Btu/h·ft·F are used. Find the number of the plates to dissipate 10.55 W at steady state operation. Data: Tbase = 85 F, Tf = 65 F, h = 1 Btu/h·ft2·F, L = 10 in, b = 1 in, δ = 0.03 in. [Ans.: 15].
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An electric windshield defroster is used to remove 0.25-in of ice from a windshield. The properties of the ice are Tsat = 328F, uif = hif = 144 Btu/lbm, and v = 0.01602 ft3/lbm. Determine the electrical energy required per square foot of windshield surface area to melt this ice and remove it as liquid water at 328F. What is the minimum temperature at which the defroster may be operated? Assume that no heat is transferred from the defroster or ice to the surroundings.
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