I need complete solutions and 4 decimal places in all solutions. 6.) The wall of a refrigerator isconstructed of fiberglass insulation (k= 0.035 W/m-°C) sandwichedbetween two layers of 1-mm-thick sheet metal (k = 15.1 W/m--°C). Therefrigerated space is maintained at 3°C, and the average heat transfercoefficients at the inner and outer surfaces of the wall are 4 W/m2-°C and9 W/m2-°C, respectively. The kitchen temperature averages 25°C. It is%3Dobserved that condensation occurs on the outer surfaces of therefrigerator when the temperature of the outer surface drops to 20°C.Determine the minimum thickness of fiberglass insulation that needs to beused in the wall in order to avoid condensation on the outer surfaces.

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The wall of a refrigerator is nstructed of fiberglass insulation (k= 0.035 W/m-°C) sandwiched ween two layers of 1-mm-thick sheet metal (k = 15.1 W/m--°C). The igerated space is maintained at 3°C, and the average heat transfer efficients at the inner and outer surfaces of the wall are 4 W/m²-ºC and /m²-°C, respectively. The kitchen temperature averages 25°C. It is

The wall of a refrigerator is nstructed of fiberglass insulation (k= 0.035 W/m-°C) sandwiched ween two layers of 1-mm-thick sheet metal (k = 15.1 W/m--°C). The igerated space is maintained at 3°C, and the average heat transfer efficients at the inner and outer surfaces of the wall are 4 W/m²-ºC and /m²-°C, respectively. The kitchen temperature averages 25°C. It 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.

Chapter3: Transient Heat Conduction

Section: Chapter Questions

Problem 3.10P: 3.10 A spherical shell satellite (3-m-OD, 1.25-cm-thick stainless steel walls) re-enters the...

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2.9 In a large chemical factory, hot gases at 2273 K are cooled by a liquid at 373 K with gas-side and liquid-side convection heat transfer coefficients of 50 and , respectively. The wall that separates the gas and liquid streams is composed of a 2-cm thick oxide layer on the gas side and a 4-cm thick slab of stainless steel on the liquid side. There is a contact resistance between the oxide layer and the steel of . Determine the rate of heat loss from hot gases through the composite wall to the liquid.
An electronic device that internally generates 600 mW of heat has a maximum permissible operating temperature of 70C. It is to be cooled in 25C air by attaching aluminum fins with a total surface area of 12cm2. The convection heat transfer coefficient between the fins and the air is 20W/m2K. Estimate the operating temperature when the fins are attached in such a way that (a) there is a contact resistance of approximately 50 K/W between the surface of the device and the fin array and (b) there is no contact resistance (in this case, the construction of the device is more expensive). Comment on the design options.
2.38 The addition of aluminum fins has been suggested to increase the rate of heat dissipation from one side of an electronic device 1 m wide and 1 m tall. The fins are to be rectangular in cross section, 2.5 cm long and 0.25 cm thick, as shown in the figure. There are to be 100 fins per meter. The convection heat transfer coefficient, both for the wall and the fins, is estimated to be K. With this information determine the percent increase in the rate of heat transfer of the finned wall compared to the bare wall.
1.10 A heat flux meter at the outer (cold) wall of a concrete building indicates that the heat loss through a wall of 10-cm thickness is . If a thermocouple at the inner surface of the wall indicates a temperature of 22°C while another at the outer surface shows 6°C, calculate the thermal conductivity of the concrete and compare your result with the value in Appendix 2, Table 11.
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.
The interior wall of a large, commercial walk-in type meat freezer is covered under normal operating conditions with a 2-cm thick layer of ice. One day, a power outage cuts electricity to the refrigeration system of the freezer. Estimate the time required to melt this layer of ice if it has a mass density of 700kg/m3 and a latent heat of fusion of 334 kJ/kg. Consider the air temperature inside the freezer to be 20C with a heat transfer coefficient of 2W/m2K for convection from the freezer surface to air, and clearly state the assumptions made in your calculations.
3.10 A spherical shell satellite (3-m-OD, 1.25-cm-thick stainless steel walls) re-enters the atmosphere from outer space. If its original temperature is 38°C, the effective average temperature of the atmosphere is 1093°C, and the effective heat transfer coefficient is , estimate the temperature of the shell after reentry, assuming the time of reentry is 10 min and the interior of the shell is evacuated.
3.17 A 1.4-kg aluminum household iron has a 500-W heating element. The surface area is . The ambient temperature is 21°C, and the surface heat transfer coefficient is . How long after the iron is plugged in does its temperature reach 104°C?
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.
Q1) The wall of a drying oven is constructed by sandwiching an insulation material of thermal conductivity k=0.05 W/m K between thin metal sheets in which heat is generated uniformly at a rate of 2x10 W/m. The oven air is at T,-300°C, and the corresponding convection coefficient is h-30 overall coefficient for convection and radiation from the outer surface is ho=10W/m2K. Express the mathematical formulation of temperature (T f(x)) during steady operation. W/m? K. The air is To= 25°C, room at and the T. Oven air Room air Tooj h Toop ho 1t tt
(1) The temperature of inner surface of insulation wall is t,=100°C, while the outer surface releases the heat by convection to surroundings air with temperature of -20°C. The thickness of the insulating layer is 5 cm and its thermal conductivity of 0,05 W/(m-K). What is the value of heat transfer coefficient on the outside this wall if its surface temperature t, is of 0°C.
Consider a pipe with inner diameter of 0.5 m, wall thickness of 8 mm and thermal conductivity of 60 W/m-K. The pipe is used for transporting nanocoolant at an average temperature of 70 °C and submerged in cool water at temperature of 5 °C. The average convection heat transfer coefficient on the inner and outer of the pipe surfaces are estimated to be 250 W/m²-K and 150 W/m²-K, respectively. a) Derive the temperature distribution equation for the pipe wall. b) Evaluate the inner surface temperature of the pipe. c) Derive the mathematical expression for the rate of heat loss from the nanocoolant in the pipe. d) Evaluate the heat flux through the outer surface of the pipe.