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The concrete slab of a basement is 11 in long. 8 in wide,and 0.20 m thick. During the winter, temperatures arenominally 17°C and 10°C at the top and bottom surfaces, respectively. If the concrete has a thermal conductivityof
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Fundamentals of Heat and Mass Transfer
- 2.2 A small dam, which is idealized by a large slab 1.2 m thick, is to be completely poured in a short Period of time. The hydration of the concrete results in the equivalent of a distributed source of constant strength of 100 W/m3. If both dam surfaces are at 16°C, determine the maximum temperature to which the concrete will be subjected, assuming steady-state conditions. The thermal conductivity of the wet concrete can be taken as 0.84 W/m K.arrow_forward1.37 Mild steel nails were driven through a solid wood wall consisting of two layers, each 2.5-cm thick, for reinforcement. If the total cross-sectional area of the nails is 0.5% of the wall area, determine the unit thermal conductance of the composite wall and the percent of the total heat flow that passes through the nails when the temperature difference across the wall is 25°C. Neglect contact resistance between the wood layers.arrow_forward2.38 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.arrow_forward
- 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.arrow_forward2.55 A long, 1-cm-diameter electric copper cable is embedded in the center of a 25-cm-square concrete block. If the outside temperature of the concrete is 25oC and the rate of electrical energy dissipation in the cable is 150 W per meter length, determine temperatures at the outer surface and at the center of the cable.arrow_forward3.16 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_forward
- The concrete slab of a basement is 11 m long, 8 m wide, and 0.5 m thick. During the winter, temperatures are nominally 17°C and 10°C at the top and bottom surfaces, respectively. If the concrete has a thermal conductivity of 1.4 W/m-K, what is the rate of heat loss through the slab, in W? If the basement is heated by a gas furnace operating at an efficiency of 7, = 0.90 and natural gas is priced at = $0.02/MJ, what is the daily cost of the heat loss, in dollars per day? W q = Ca = i $/darrow_forwarda flat wall is covered with a layer of insulation 1.0 in. thick whose thermal conductivity is 0.8 Btu/hr-ft- F. the temperature of the wall on the inside of the insulation is 600F. the wall loses heat to the environment by convection on the surface of the insulation. the average value of the convection heat transfer coefficient on the inslation surface is 950 Btu/hr-ft^2-F. compute the bulk temperature of the environment if the outer surface of the insulation does not exceed 105 F.arrow_forwardA 5cm copper plate has a thermal conductivity of 395??−?is used as a heat sink for a semiconductor. A 1mm layer of thermal paste lies in between the two and it has a thermal conductivity of 10??−?. Solve for the heat transferred at a 5cmx5cm area if the semiconductor is 80C, while the copper plate has a temperature of 30C since it is exposed to ambient air temperature.arrow_forward
- 5. A pipe with an outside diameter of 2.5 inches is insulated with 2 inches layer of asbestos (k = 0.396 Btu- in/hr-ft²-°F), followed by a layer of cork 1.5 inches thick (k = 0.30 Btu-in/hr-ft²-°F). If the temperature at the inner surface of the pipe is 290°F and at the outer surface of the cork is 90°F, calculate the heat loss per 100 ft of insulated pipe. (Btu/hr)arrow_forwardA plane wall 7.5 cm thick(k=21W/mK) generates heat internally at the rate of 0.35 MW/m³. One side of the wall is insulated , and the other side is exposed to a environment at 93 °C, h=570W/m°K. i-Calculate the maximum temperature in the wall. ii-What is the temperature value at the half length of the wall.arrow_forwardQUESTION 3: Warm air is blown over the inner surface of the windshield of an automobile to defrost ice accumulated on the outer surface. The windshield has a thickness of 5 mm and thermal conductivity of 1.4 W/m-K. The outside ambient temperature is -10°C and the convection heat transfer coefficient is 200 W/m²-K, while the ambient temperature inside the automobile is 25°C. Determine the value of the convection heat transfer coefficient for the warm air blowing over the inner surface of the windshield necessary to cause the accumulated ice to begin melting.arrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning