A silicon wafer with thickness of 925 µm is being heated with a uniform heat flux at the lower surface. The silicon wafer has a thermal conductivity that varies with temperature and can be expressed as k(T) = (a + bT + cT2) W/m·K, where a = 450, b = -1.29, and c = 0.00111. To avoid warping, the temperature difference across the wafer thickness cannot exceed 2°C. If the upper surface of the silicon wafer

A silicon wafer with thickness of 925 µm is being heated with a uniform heat flux at the lower surface. The silicon wafer has a thermal conductivity that varies with temperature and can be expressed as k(T) = (a + bT + cT2) W/m·K, where a = 450, b = -1.29, and c = 0.00111. To avoid warping, the temperature difference across the wafer thickness cannot exceed 2°C. If the upper surface of the silicon wafer

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.

Chapter7: Forced Convection Inside Tubes And Ducts

Section: Chapter Questions

Problem 7.17P: Determine the rate of heat transfer per meter length to a light oil flowing through a 2.5-cm-ID,...

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Determine the rate of heat transfer per meter length to a light oil flowing through a 2.5-cm-ID, 60-cm-long copper tube at a velocity of 0.03 m/s. The oil enters the tube at 16C, and the tube is heated by steam condensing on its outer surface at atmospheric pressure with a heat transfer coefficient of 11.3 kW/m K. The properties of the oil at various temperatures are listed in the following table: Temperature, T(C) 15 30 40 65 100 (kg/m3) 912 912 896 880 864 c(kJ/kgK) 1.80 1.84 1.925 2.0 2.135 k(W/mK) 0.133 0.133 0.131 0.129 0.128 (kg/ms) 0.089 0.0414 0.023 0.00786 0.0033 Pr 1204 573 338 122 55
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.
In a multilayered rectangular 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 for the third layer it is 0.1 ° C/W. The overall temperature gradient in the multilayered wall from one side to another is 70° C. a. Determine the heat flux through the wall. b. If the thermal resistance of the second layer is doubled to 0.4° C/W, what will be its influence in % on the heat flux, assuming the temperature gradient remains the same?
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 0.3 ° 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 50 ° C. a. Determine the heat flux through the walls. = Answer watts / m2. b. If the thermal resistance of the second layer is changed to 0.1 ° C / W, what is the effect in% on heat flux, assuming the temperature gradient remains the same? = AnswerAnswer %.
On a multi-layered rectangular 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 50 ° C. a. Determine the heat flux through the walls. = Answer watts / m2. b. If the thermal resistance of the second layer is changed to 0.3 ° C / W, what is the effect in% on heat flux, assuming the temperature gradient remains the same? = AnswerAnswer %.
The wall of a refrigerator is made of fiberglass insulation (k = 0.035 W/mK) glued between two 1 mm thick layers of metal plate (k = 15.1 W/mK). The refrigerated space is kept at 2°C, and the average heat transfer coefficients on the inner and outer wall surfaces are 4 W/m²K and 9 W/m²K, respectively. The average temperature in the kitchen is 24°C. It is observed that condensation occurs on the external surface of the refrigerator when the temperature of the external surface drops to 20°C. Determine the minimum thickness of fiberglass insulation that should be used on the wall to prevent condensation on the outside surface.
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%.
The cylinders that come out of the heat treatment furnace are cooled in a stagnant air environment in a horizontal position. The cylinders have a diameter of 100 mm and a length of 0.1 m. The temperature of the cylinders is 440 ° C and the ambient temperature is 20 ° C. Calculate the heat transfer from 10 cylinders to the environment. a) 3125 W b) 2350 W C) 1848 W d) 1354 W e) 2750 W
The wall of a refrigerator is constructed of fiberglass insulation (k = 0.035 W/m⋅K) sandwiched between two layers of 1-mm-thick sheet metal (k = 15.1 W/m⋅K). The refrigerated space is maintained at 2 °C, and the average heat transfer coefficients at the inner and outer surfaces of the wall are 4 W/m2⋅K and 9 W/m2⋅K, respectively. The kitchen temperature averages 24 °C. It is observed that condensation occurs on the outer surfaces of the refrigerator when the temperature of the outer surface drops to 20 °C. Determine the minimum thickness (in mm) of fiberglass insulation that needs to be used in the wall in order to avoid condensation on the outer surfaces.
The case-to-ambient thermal resistance of a power transistor that has a maximum power rating of 15 W is given to be 25°C/W. If the case temperature of the transistor is not to exceed 80°C, mark the power at which this transistor can be operated safely in an environment at 40°C.. a)Between 1.0 to 1.5 W b)Between 1.5 to 2.0 W c)Between 2.0 to 2.5 W
A 2-m x 1.8-m section of wall of an industrial furnace burning natural gas is not insulated, and the temperature at the outer surface of this section is measured to be 80°C. The temperature of the furnace room is 30°C, and the combined convection and radiation heat transfer coefficient at the surface of the outer furnace is 10 W/m² • °C. It is proposed to insulate this section of the furnace wall with expanded perlite insulation (k = 0.052 W/m • °C) in order to reduce the heat loss by 90%. Assuming the outer surface temperature of the metal section still remains at about 80°C, determine the thickness of the insulation that needs to be used. ANSWER:_______cm
Steam at 235°C is flowing inside a steel pipe (k = 61 W/m ∙ °C) whose inner and outer diameters are 10 cm and 12 cm, respectively, in an environment at 20°C. The heat transfer coefficients inside and outside the pipe are 105 W/m2 ∙ °C and 14 W/m2 ∙ °C, respectively. Determine (a) the thickness of the insulation (k = 0.038 W/m ∙ °C) needed to reduce the heat loss by 95 percent and (b) the thickness of the insulation needed to reduce the exposed surface temperature of insulated pipe to 40°C for safety reasons.