The 5-mm-thick bottom of a 200-mm-diameter panmay be made from aluminum
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Fundamentals of Heat and Mass Transfer
- 3-18E Consider an electrically heated brick house (k = 0.40 Btu/h ft-°F) whose walls are 9 ft high and 1 ft thick. Two of the walls of the house are 50 ft long and the others are 35 ft long. The house is maintained at 70°F at all times while the temperature of the outdoors varies. On a certain day, the temperature of the inner surface of the walls is measured to be at 55°F while the average temperature of the outer surface is observed to remain at 45°F during the day for 10 h and at 35°F at night for 14 h. Determine the amount of heat lost from the house that day. Also determine the cost of that heat loss to the homeowner for an electricity price of $0.09/kWh. FIGURE P3-18E 9 ft TiD=70°F 50 ft 35 ftarrow_forwardA crucible of molten metal at 1800°C is placed on the foundry floor. The foundry man covers it with a metal sheet to reduce heat loss to the room. If the transfer factor, F, between the melt and the sheet is 0.4, and that between the top of the sheet and the room is 0.8, how much will the heat loss to the room be reduced by the sheet if the transfer factor between the uncovered melt and the room had been 0.8?arrow_forwardThe 5-mm-thick bottom of a 200-mm-diameter pan may be made from aluminum (k = 240 W/m.K) or copper (k = 390 W/m-K). When used to boil water, the surface of the bottom exposed to the water is nominally at 110°C and heat is transferred from the stove to the pan at a rate of 1200 W. What is the temperature of the surface in contact with the stove for each of the two materials? Aluminum: T = i °℃ Copper: T = °℃ iarrow_forward
- 6. A cylindrical electric heater of outside diameter D = 2.5 cm and length L= 2 m is immersed horizontally into a pool of mercury at 100°C. If the surface of the heater is maintained at an average temperature of 300°C, calculate the rate of heat transfer to the mercury.arrow_forwardWhat is the total required heating energy in raising the temperature of a given amount of water when the energy supplied is 1000 kwh with heat losses of 25%?arrow_forwardRoom 4 mx 6 mx6m Fan FIGURE P1-31 A student living in a 4-m × 6-m X 6-m dormitory room turns his 150-W fan on before she leaves her room on a summer day hoping that the room will be cooler when she comes back in the evening. Assuming all the doors and win- dows are tightly closed and disregarding any heat transfer through the walls and the windows, determine the temperature in the room when she comes back 10 hours later. Use specific heat values at room temperature and assume the room to be at 100 kPa and 15°C in the morning when she leaves.arrow_forward
- Q2 A 2 kW resistance heater wire with thermal conductivity of k = 20 W/m °C, a diameter of D = 5 mm, and a length of L= 0.7 m is used to boil water. If the outer surface temperature of the resistance wire is Ts= 110°C, determine the temperature at the center of the wire. Q3: Consider a 20-cm-thick large concrete plane wall (k = 0.77 W/m °C) subjected to convection on both sides with T1 = 27°C and h₁ = 5 W/m² °C on the inside, and T2 = 8°C and h₂ = 12 W/m² °C on the outside. Assuming constant thermal conductivity with no heat generation and negligible radiation, (a) express the differential equations and the boundary conditions for steady one-dimensional heat conduction through the wall, (b) obtain a relation for the variation of temperature in the wall by solving the differential equation, and (c) evaluate the temperatures at the inner and outer surfaces of the wall. Ans: (a) Ans: 121.4 °C dT (L) -k dx -=h₂ [T(L)-T₂] (b) T(x) = 20-45.44x Q4: A double pane window consists of 3 mm thick…arrow_forward3500J / s of energy is transferred from a heat source to the surface of the part. The heated region is circular and the heat density decreases as the radius increases. Find out whether the heat density is sufficient to melt the metal since 70% of the heat is concentrated in a circle with a diameter of 3.75 mm.arrow_forward105°C, determine the temperature of the outer surface of the bottom of the pan. 19. The inner and outer glasses of a 2-m x 2-m double pane window are at 18°C and 6°C, respectively. If the 1-cm space between the two glasses is filled with still air, determine the rate of heat transfer through the window, in kW.arrow_forward
- A hole is drilled on a soft steel. The power consumed by the drill is 0.25 kW. Since this driling process takes 3 minutes, determine the amount of heat (kJ) released during the process.arrow_forwardWrite your answer in 4 decimal places. DO NOT round off intermediate values. Use T(K) = T(°C) + 273. A 1-m-inner diameter liquid oxygen storage tank at a hospital keeps the liquid oxygen at 90 K. This tank consists of a 0.5-cm-thick aluminum (k = 170 W/m· K) shell whose exterior is covered with a 10-cm thick layer of insulation (k = 0.02 W/m K). The insulation is exposed to the ambient air at 20 °C and the heat transfer coefficient on the exterior side of the insulation is 5 W/m2. K. The temperature of the exterior surface of the insulation is °Carrow_forwardThe temperature of 1.9 kg of water is 100.0°C, but the water is not boiling, because the external pressure acting on the water surface is 3.0 x 105 Pa. Using the vapor pressure curve for water given in the figure, determine the amount of heat that must be added to the water to bring it to the point where it just begins to boil. Pressure, Pa 4 x 105 3 x 105 2x 105 1.01 105 0.53 105 bat 0 50 0 50 83 100 Temperature, C 100 °C 150 1.01 105 Pa 83 C 0.53 × 105 Pa Storage settingsarrow_forward
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