A dormitory at a large university, built 50 years ago, has exterior walls constructed of
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Fundamentals of Heat and Mass Transfer
- A dormitory at a large university, built 50 years ago, has exterior walls constructed of Ls = 25-mm-thick sheathing with a thermal conductivity of ks = 0.1 W/m-K. To reduce heat losses in the winter, the university decides to encapsulate the entire dormitory by applying an L; = 25-mm-thick layer of extruded insulation characterized by k; = 0.029 W/m-K to the exterior of the original sheathing. The extruded insulation is, in turn, covered with an Lg = 5-mm-thick architectural glass with kg the heat flux through the original and retrofitted walls when the interior and exterior air temperatures are Ti = 22°C and T.o -2.5°C, respectively. The inner and outer convection heat transfer coefficients are h; = 5W/m2-K and ho = 1.4 W/m-K. Determine 25 W/m2-K, respectively. The heat flux through the original walls is i W/m?. The heat flux through the retrofitted walls is i W/m?.arrow_forwardConsider a composite wall of overall height H = 30 mm and thickness L = 40 mm. Section A hasthickness LA = 15 mm and thermal conductivity of 3 W/(m·K). Sections B and C each have heightHB = 15 mm and thickness LB = 25 mm. The thermal conductivity is 1 W/(m·K) in section B and 2W/(m·K) in section C. The temperatures of the left and right faces of the composite wall are T1 =60°C and T2 = 30°C, respectively. The top and bottom of the wall are insulated. A) Draw a thermal circuit based on heat flux for the composite wall shown above.Assume that the temperature is uniform “vertically” in material A. Indicate thetemperatures, thermal resistances, and heat flux in the circuit diagram. Show theequations for the thermal resistances in the circuits. Do NOT need to perform anycalculations in this part.B. Draw a thermal circuit based on heat flux for the composite wall shown above.Assume that the temperature is NOT uniform “vertically” in material A and heat onlyflows along horizontal direction.…arrow_forwardA thick-walled tube of stainless steel with thermal conductivity k = 19 W/m°C has inner diameter of 10 em and outer diameter of 30 em is covered with 5 cm layer of asbestos insulation with thermal conductivity k = 0.2 W/m°C. If the inside of the pipe and outside of insulator temperature is maintained at 600°C and 106 °C respectively. Determine the heat loss per meter length of pipe and the tube-insulation interface temperature.arrow_forward
- Consider two concentric spheres of radii R1 and R2 (R1<R2). The inner sphere has a temperature of T1=20°C and the outer sphere has a temperature of T2=100°C. The material between the two spheres has a thermal conductivity of k=0.5 W/(m⋅K). Calculate the heat flow from the outer sphere to the inner sphere. Determine the equation of the thermal Ohm's law for this system.arrow_forwardQUESTION 2 The wall of a refrigerated truck consists of 1.5mm sheet steel outer surface, 10mm plywood at the inner surface and 20mm of glass wool in between. The inside temperature is -15°C and outside temperature is 240C. Take the thermal conductivities of the materials as follows: - 0,052W/mK = 23,2W/mK k for glass-wool = 0,14W/mK k for plywood k for steel %3D %3D %3D Calculate: 2.1. the rate of heat flow per unit area; 2.2. the interface temperature. If the glass-wool is replaced by a 5mm cork board with a thermal conductivity of 0.043W/mK; 2.3. What percentage change in heat flow is obtained? 2.4. What must be the thickness of the cork board be, to achieve the same heat flow as in (2.1.).arrow_forwardX Your answer is incorrect. A dormitory at a large university, built 50 years ago, has exterior walls constructed of L, = 25-mm-thick sheathing with a thermal conductivity of k, = 0.1 W/m-K. To reduce heat losses in the winter, the university decides to encapsulate the entire dormitory by applying an L; = 25-mm-thick layer of extruded insulation characterized by k; = 0.029 W/m-K to the exterior of the original sheathing. The extruded insulation is, in turn, covered with an Lg = 5-mm-thick architectural glass with kg = 1.4 W/m-K. Determine the heat flux through the original and retrofitted walls when the interior and exterior air temperatures are T = 22°C and To = O°C, respectively. The inner and outer convection heat transfer coefficients are h; = 5 W/m?-Kand h, 00, 25 W/m2-K, respectively. The heat flux through the original walls is 1.46 W/m?. The heat flux through the retrofitted walls is 0.92 W/m?.arrow_forward
- Steel pipe (outer diameter 100 mm) is covered with two layers of insulation. The inner layer, 40 mm thick, has a thermal conductivity of 0.07 W / (m K). The outer layer, 20 mm thick, has a thermal conductivity of 0.15 W / (m K). Pipes are used to deliver steam with a pressure of 600 kPa. The temperature on the outer insulation surface is 24 ° C. If the pipe is 8 m long, determine the following: (assuming that the conduction heat transfer resistance of the steel pipe and the vapor convection resistance are negligible). a. Heat loss per hour. = kJ / hour. b. Temperature between insulation layers. = ° Carrow_forwardThe inner diameter of a pipe made of %1 C steel used in the drying machine of a textile factory is D1 = 160 mm and the thread diameter is D₂= 170 mm. The pipe is insulated with 25 mm thick glass wool. The heat transfer coefficient between the air and the pipe surface at 90 °C temperature inside the pipe is 80 W/m²K. The temperature of the ambient air outside the insulation is 20 °C and the air comes perpendicular to the cat wool surface at a speed of 10 m/s. Find the total heat transfer coefficient according to the inside diameter of the pipe. Calculate the heat transfer per unit length of pipe per unit time ?arrow_forwardA steel pipe (outside diameter 100 mm) is covered with two layers of insulation. The inside layer, 40 mm thick, has a thermal conductivity of 0.07 W/(m K). The outside layer, 20 mm thick, has a thermal conductivity of 0.15 W/(m K). The pipe is used to convey steam at a pressure of 600 kPa. The outside temperature of insulation is 24°C. If the pipe is 10 m long, determine the following, assuming the resistance to conductive heat transfer in steel pipe and convective resistance on the steam side are negligible: a. The heat loss per hour. b. The interface temperature of insulation.arrow_forward
- A thick-walled tube of stainless steel with thermal conductivity k = 19 W/m°C has inner diameter of 10 em and outer diameter of 30 cm is covered with 5 cm layer of asbestos insulation with thermal conductivity k = 0.2 W/m°C. If the inside of the pipe and outside of insulator temperature is maintained at 600°C and 100°C respectively. Determine the heat loss per meter length of pipe and the tube-insulation interface temperature.arrow_forward2. A refrigerated cold room wall has a thickness of 100mm and a thermal conductivity 0.14 W/m-K. The room wall has a 60mm thick internal lining of cork having a thermal conductivity of 0.05 W/m.K. The thermal conductance between the exposed faces and the respective atmosphere is 12 W/m²-K. If the room is maintained at 0°C and the external atmospheric temperature is 20°C, Calculate the heat loss rate through 1m² of the wall.arrow_forwardSteel pipe (outer diameter 100 mm) is covered with two layers of insulation. The inner layer, 40 mm thick, has a thermal conductivity of 0.07 W / (m K). The outer layer, 20 mm thick, has a thermal conductivity of 0.15 W / (m K). Pipes are used to deliver steam with a pressure of 800 kPa. The temperature on the outer insulation surface is 24 ° C. If the pipe is 10 m long, determine the following: (assuming that the conduction heat transfer resistance of the steel pipe and the vapor convection resistance are negligible). a. Heat loss per hour. = AnswerkJ / hr. b. Temperature between insulation layers. = Answer ° C.arrow_forward
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