A hollow spherical steel has an inner diameter of 30cm and outer diameter of 37cm. It is covered with insulation of 5cm thick. The inner surface of the steel is kept at a constant temperal of 100°C and outside insulation is 30°C. The thermal conductivity of the material is 0.65 W/m-k. By what percentage will the rate of loss be decreased if the thickness of the insulation is increased by 4cm? O a. 16.65% O b. 83.35% O c. 79.57% O d. 20.43% Qe None
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- 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.A hollow spherical steel has an inner diameter of 30cm and outer diameter of 37cm. It is covered with insulation of 5cm thick. The inner surface of the steel is kept at a constant temperature of 100°C and outside insulation is 30°C. The thermal conductivity of the material is 0.65 W/m-k. By what percentage will the rate of loss be decreased if the thickness of the insulation is increased by 4cm? O a. 16.65% O b. 83.35% O c. 79.57% O d. 20.43% O e. None
- A rectangular wall of length "L" m and height "H" m is made from a thick bricklayer. The rectangular wall has a surface area as 11 m2 & Thermal conductivity as 0.53 W/mK. The wall is subjected to heat transfer due to the outside temperature 43 °C and inside temperature 24 °C. If the energy loss is 11219 kJ in 484 minutes. (HINT: 1 minute = 60 %3D seconds) Determine the following -- i) Heat transfer rate, ii) Thickness of the wall.A steam pipe (inner diameter = 150 mm and outer diameter = 160 mm) havingthermal conductivity 58 W/m. °C is covered with two layers of insulation, ofthickness 30 mm and 50 mm respectively and thermal conductivities 0.18 W/m. °Cand 0.09 W/m .°C respectively. The temperature of the inner surface of steam pipeis 320°C and that of the outer surface of the insulation layers is 40°C.Determine the quantity of heat lost per meter length of steam pipe and layercontact temperature,It is designed in such a way that the internal temperature of a commercial heat treatment furnace can reach up to 165 oC. All surfaces of the furnace consist of firebrick (10 cm), insulation material and sheet metal (3mm) from the inside out. Given that the outdoor temperature is 22 oC, the outer sheet will be allowed to go up to 35 oC, which is a temperature that will not disturb in contact with hands. In this case, determine the insulation material thickness to be used. The thermal conductivity coefficient of the insulation material is insulation 0.066 W / m oC, 60 W / m oC for sheet metal and 115 W / m oC for firebrick. Indoor heat transfer coefficient will be accepted as 25 W / m2 oC and 12 W / m2 oC for outdoor environment.
- A cold storage room has a walls constructed of 0.102-m corkboard contained between double wooden walls each 0.0127 m thick. What is the rate of heat loss if wall surface temperature is - 12.2 o C inside and 21.1 o C outside? Also what is the temperature at the interface between the outer wall and the corkboard? Values of kwood = 0.1073 W/mo C and kcorkboard = 0.0415 W/mo CConsider an apartment in a tower block as a cube of side L = 7.26 m. Since this apartment is designed to be rented by a student, it has no windows. The floor and ceiling are perfectly insulated, but the wall is made of concrete of thickness d = 19.1 cm. The thermal conductivity of the concrete is k = 0.567 Wm¬'K-1. Part 1) The outside temperature is stable at Tout = 35.6°C. What is the heat load (rate of heat transfer) on the air conditioner if the occupant wants to keep the inside temperature stable at Tn = 20.3°C? P = kW Part 2) A layer of insulation of thickness dins = 30.7 mm and thermal conductivity kins = 0.0105 Wm¬1K-l is added to the walls. What is the heat load now? P = kW Part 3) The occupant complains that the apartment is dank and dark, so the landlord is forced to install windows and a door. These are constructed, but then drafts from the gaps around the windows and doors allow the air in the apartment to change every 2 hours. How much additional heat load does changing…What is the critical radius of insulation for a sphere equal to? k = thermal conductivity in W/m-K h = heat transfer coefficient in W/m?K (a) 2kh (c) k/h (b) 2k/h (d) V2kh
- Its thickness is 1.18 m, its thermal conductivity is 2.75 W/m.°C and its surface area is 15m2Consider a wide plane wall. Inside of the base plateThere is a uniform heat flux produced on its surface with the help of the resistance wire inside.590 W/m2 on the left surface of the wall at x=0net heat fluxand the temperature on this surface was measured as 590 °C. On the wallassuming that there is no heat generation and that the thermal conductivity is constant;a) The differential equation for continuous one-dimensional heat conduction in the wall, andSet the boundary conditions.b) Solve the differential equation to obtain a relation for the temperature change at the wall.c) Calculate the heat loss rate from the wall.yo lo:ll O %AV L. مرتضی نشط الآن Q5: The piston cylinder device (radius=10 cm) contains a liquid with a pressure 100 kpa and temperature of 20 ° C and has a liquid convection heat coefficient =93 WmK. Connect its fixed side to a cubic piece of aluminum (side length 15 cm) with a thermal conductivity coefficient of aluminum = 239 W mK. At the bottom of the aluminum piece there is a heat source with a temperature of 150 ° C, noting that the heat source is located in a vacuum chamber. Radiation thermal resistance = 3.17 K/W. Calculate the change in piston height during I sec. if you know that there is no change in the internal energy of the piston cylinder device. Note IK Watt 1KJ/s : AaTwo rods ( fins) having same dimensions , one made of brass ( k = 85 Wm K) and the other of copper ( k = 375 W/m K ) , having one of their ends inserted into a furnace . At a section 10.5 cm a way from the furnace , the temperature of brass rod 120oC . Find the distance at which the same temperature would be reached in the copper rod ? both ends are exposed to the same environment .