) The wall of a refrigerator is constructed of fiberglass insulation (k =0.035 W/m °C)sandwiched between two layers of 1-mm-thick sheet metal (k =15.1 W/m °C). The refrigerated space ismaintained at 3°C, and the average heat transfer coefficients at the inner and outer surfaces of the wall are4 W/m2 °C and 9 W/m2 °C, respectively. The kitchen temperature averages 25°C. It is observed that2.condensation occurs on the outer surfaces of the refrigerator when the temperature of the outer surfacedrops to 20°C.(a). Sketch the thermal circuit(b) Determine the minimum thickness of fiberglass insulation that needs to be used in the wall in order toavoid condensation on the outer surfaces.

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Answered: ) The wall of a refrigerator is…

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.

Chapter6: Forced Convection Over Exterior Surfaces

Section: Chapter Questions

Problem 6.36P

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3.16 A large, 2.54-cm.-thick copper plate is placed between two air streams. The heat transfer coefficient on one side is and on the other side is . If the temperature of both streams is suddenly changed from 38°C to 93°C, determine how long it takes for the copper plate to reach a temperature of 82°C.
1.1 On a cold winter day, the outer surface of a 0.2-m-thick concrete wall of a warehouse is exposed to temperature of –5°C, while the inner surface is kept at 20°C. The thermal conductivity of the concrete is 1.2 W/m K. Determine the heat loss through the wall, which is 10-m long and 3-m high. Problem 1.1
Heat is transferred at a rate of 0.1 kW through glass wool insulation (density=100kg/m3) with a 5-cm thickness and 2-m2 area. If the hot surface is at 70C, determine the temperature of the cooler surface.
A cooling system is to be designed for a food storage warehouse for keeping perishable foods cool prior to transportation to grocery stores. The warehouse has an effective surface area of 1860 m2 exposed to an ambient air temperature of 32C. The warehouse wall insulation (k=0.17W/(mK)) is 7.5 cm thick. Determine the rate at which heat must be removed (W) from the warehouse to maintain the food at 4C.
Estimate the rate of heat loss per unit length from a 5-cm ID, 6-cm OD steel pipe covered with high-temperature insulation having a thermal conductivity of 0.11 W/(m K) and a thickness of 1.2 cm. Steam flows in the pipe. It has a quality of 99% and is at 150C. The unit thermal resistance at the inner wall is 0.0026(m2K)/W the heat transfer coefficient at the outer surface is 17W/(m2K) and the ambient temperature is 16C.
A domestic refrigerator with inner dimensions of 0.7 m by 0.7 m at the base and height 1 m was designed to maintain a set temperature of 6 ˚C. The bodies consist of two 10-mm-thick layers of Aluminium (k = 225 W/mK) separated by a 30 mm polyurethane insulation (k=0.028 W/mK). If the average convection heat transfer coefficient at the inner and outer surfaces are 11.6 W/m2K and 14.5 W/m2K respectively, calculate: the outer surface temperature of the Aluminum in 0C to 2 decimal places
A cast iron pipe is used to transfer steam with an inlet temperature of 350 C. Inner radius of the pipe is 5 cm. The thickness of the pipe (k=20 W/(mK)) is 0.5 cm and there is an insulation (k=0.07 W/mK) over the pipe with a thickness of 4 cm. Environmental temperature is -5 C. Determine the steady heat loss from the pipe if the steam convection coefficient is 70 W/(m^2K) and environment convection coefficient is 20 W/(m^2K)? Is insulation thickness enough? a)167 W, yes b)187 W, yes c)147 W, yes d)120 W, no e)none
A hot surface at 100°C is to be cooled by attaching 3-cm-long, 0.25-cm-diameter aluminum pin fins (k = 237 W/m·K) to it, with a center-to-center distance of 0.6 cm. The temperature of the surrounding medium is 30°C, and the heat transfer coefficient on the surfaces is 35 W/m2 ·K. Determine the rate of heat transfer from the surface for a 1-m x 1-m section of the plate. Also determine the overall effectiveness of the fins.
On a multi-layered square wall, the thermal resistance of the first layer is 0.005 ° C / W, the resistance of the second layer is 0.2 ° C / W, and the third layer is 0.1 ° C / W. The overall temperature gradient in the wall is multilayered from one side. to the other side is 70 ° C. a. Determine the heat flux through the walls. = Answerwatts / m2. b. If the thermal resistance of the second layer is changed to 0.4 ° C / W, what is the effect in% on heat flux, assuming the temperature gradient remains the same? = AnswerAnswer%.
A plane wall surface at 200°C is to be cooled with aluminum pin fins of parabolic profile with blunt tips. Each fin has a length of 25 mm and a base diameter of 4 mm. The fins are exposed to an ambient air condition of 25°C and the heat transfer coefficient is 45 W/m2·K. If the thermal conductivity of the fins is 230 W/m·K, determine the heat transfer rate from a single fin and the increase in the rate of heat transfer per square meter surface area as a result of attaching fins. Assume there are 100 fins per square meter surface area.
Convective heat transfer coefficient is 15 W/(m*K), surface area of the fin is 2 m^2, the temperature at the base is 70 C and the ambient temperature is 20 C. Determine the fin efficiency if the actual heat transfer rate from the fin is 500 W? not sufficient information 66 % none of the given 15 % 33 %
A 10-m long pipe carrying brine at – 8°C passes through a room at 30°C. The outside diameter of the pipe is 15 cm and the convection coefficient has a value of 18 W/m2 ·K. In order to reduce the heat gain, molded insulations of 2.5 cm, 4 cm, 6 cm and 8 cm thicknesses with conductivities of 0.06 W/m-K, 0.05 W/m-K and 0.03 W/m-K, respectively, were installed to the pipe. Determine the heat loss on the pipe.

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