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A new building to be located in a cold climate is beingdesigned with a basement that has an
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Introduction to Heat Transfer
- 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.arrow_forwardHeat 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.arrow_forwardIn 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?arrow_forward
- The walls of the refrigerated storage room are 10 m long and 3 m high and constructed with 90 mm concrete blocks (k = 0.935 W / [m ° C]) and 8 cm fiber insulation board (k = 0.048 W). / [m ° C]). The cold room temperature is -10 ° C and the convective heat transfer coefficient is 40 W / (m² K); the outside air temperature is 30 ° C with the outer wall surface convection heat transfer coefficient of 10 W / (m² K). Calculate the overall heat transfer coefficient. Overall heat transfer coefficient = Answer W / (m² K).arrow_forwardThe sum of the resistances for the outside wall of a house is 8.0 K-m2/W. For a temperature difference of 25°C across the wall and a total surface area of 150 m2, determine the heat flow through the wall.arrow_forwardThe 4-mm-thick rear window of an automobile is defogged by passing warm air over its inner surface. Warm air temperature is at T,1 = 40C and corresponding convection coefficient is h1 =30 W/(m2·K). Outer ambient temperature T,2 = 5C and corresponding convection coefficient is h2 = 70 W/(m2·K). The size of the window is 0.5 m (height) 1.5 m (width). A. Draw two thermal circuits (one based on heat rate and one based on heat flux) considering the convection occurring over inner and outer surfaces and the conduction through the window. Show the equations for the thermal resistances in the circuits.B. Determine the total thermal resistance based on heat flux in m2K/W andoverall heat transfer coefficient U in W/m2K. Find the thermal conductivity of glass (sodalime at 300K)C. Determine the inner and outer temperatures of the glass (that are Ts,1 and Ts,2 shown above).arrow_forward
- Steam at 200ºC flows in a cast iron pipe (k = 80 W/m⋅ºC) whose inner and outer diameters are D1 = 0.20 m and D2 = 0.22 m, respectively. The pipe is covered with 2-cm-thick glass wool insulation (k = 0.05 W/m⋅ºC). The heat transfer coefficient at the inner surface is 75 W/m2⋅ºC. If the temperature at the interface of the iron pipe and the insulation is 194ºC, the temperature at the outer surface of the insulation isarrow_forwardA 100-liter water tank is heated from a 2-kW electrical source. The water is heated up from 20∘C and reached into a terminal temperature of 70∘C. How much is the thermal resistance of the tank? (specific heat of water Cp=4.2kJ/kg)arrow_forwardA 12-m-long and 5-m-high wall is constructed of two layers of 1-cm-thick sheetrock (k = 0.17 W/m·K) spaced 16 cm by wood studs (k = 0.11 W/m·K) whose cross section is 16 cm * 5 cm. The studs are placed vertically 60 cm apart, and the space between them is filled with fiberglass insulation (k = 0.034 W/m·K). The house is maintained at 20°C and the ambient temperature outside is 29°C. Taking the heat transfer coefficients at the inner and outer surfaces of the house to be 8.3 and 34 W/m2·K, respectively, determine (a) the thermal resistance of the wall considering a representative section of it and (b) the rate of heat transfer through the wall.arrow_forward
- The interior of a refrigerator has inside dimensions 60 cm x 45 cm base area and 120 cm high. The composite wall is made of 3 mm mild steel sheets (k=40.278 W/m-oC) with 6 cm of glass wool (k=0.052 W/m-oC) insulation sandwiched between them. The average values of convective heat transfer coefficients at the interior and exterior wall are 11.33 W/m2-oC and 14.53 W/m^2-oC, respectively. (a) Draw and label the schematic layout and the equivalent thermal circuit, (b) Calculate the individual resistance of this composite wall and the resistances at the surfaces. (c) For the air temperature inside the refrigerator at 6.5 oC and outside of 25 oC, determine the rate at which heat must be removed from the refrigerator.arrow_forwardThe temperature at the inner and outer surfaces of a boiler wall made of 25 mm thick steel and covered with an insulating material of10 mm thickness are 300 C and 50C respectively. If the thermal conductivities of steel and insulating material are 58W/mC and 0.116W/mC respectively, determine the total resistance through the boiler wall. (Note area of sample boiler wall is 8 m2)arrow_forwardHot oil flows at a temperature of 165 oC through a steel pipe with an outer diameter of 38.0mm and a wall thickness of 3.0mm. Since the heat conduction coefficient of the pipe material is 40W / m oC, the inner and outer surface heat transfer coefficients of the pipe are 4000 and 15W / m2 oC, respectively, and the outdoor temperature is 22 oC a) The insulation material on the pipe is removed, that is, when the bare pipe is a total of 50 (m) Find the total heat flux from the long pipe to the outside. b) If the pipe surface is covered with an insulation material with a thickness of 5 cm and a heat transfer coefficient of 0.065W / moC, how many% decrease in heat loss?arrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning