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Introduction to Heat Transfer
- A cooling system is to be designed for a food storage warehouse for keeping perishable foods cool prior to transportation to grocery stores. The warehouse has an effective surface area of 1860 m2 exposed to an ambient air temperature of 32C. The warehouse wall insulation (k=0.17W/(mK)) is 7.5 cm thick. Determine the rate at which heat must be removed (W) from the warehouse to maintain the food at 4C.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_forward1.60 Two electric resistance heaters with a 20 cm length and a 2 cm diameter are inserted into a well-insulated 40-L tank of water that is initially at 300 K. If each heater dissipates 500 W, what is the time required for bringing the water temperature in the tank to 340 K? State your assumption for your analysis.arrow_forward
- 1.19 A cryogenic fluid is stored in a 0.3-m-diameter spherical container is still air. If the convection heat transfer coefficient between the outer surface of the container and the air is 6.8 , the temperature of the air is 27°C, and the temperature of the surface of the sphere is –183°C, determine the rate of heat transfer by convection.arrow_forwardAn electrical transmission line of 1.2-cm diameter carries a current of 200 amps and has a resistance of 310-4 ohm per meter of length. If the air around this line is at v, determine the surface temperature on a windy day, assuming a wind blows across the line at 33 km/h.arrow_forwardConsider a 2-m-high electric hot-water heater thathas a diameter of 40 cm and maintains the hot water at 55°C.The tank is located in a small room whose average temperatureis 27°C, and the heat transfer coefficients on the innerand outer surfaces of the heater are 50 and 12 W/m2·K,respectively. The tank is placed in another 46-cm-diametersheet metal tank of negligible thickness, and the spacebetween the two tanks is filled with foam insulation (k =0.03 W/m·K). The thermal resistances of the water tank andthe outer thin sheet metal shell are very small and can be neglected. The price of electricity is $0.08/kWh, and the home owner pays $280 a year for water heating. Determine the fraction of the hot-water energy cost of this household that is due to the heat loss from the tank. Hot-water tank insulation kits consisting of 3-cm-thick fiberglass insulation (k = 0.035 W/m·K) large enough to wrap the entire tank are available in the market for about $30. If such an insulation is installed on…arrow_forward
- An average man has abody surface area of 1.8m2 and a skin temperature of 33degrees celcius .The convection heat transfer coefficient for a clothed person walking in still air is expressed as {h,8.6V^0.53}FOR 0.5<v<2m/s,where V is the walking velocityin m/s.Assuming the average surface temperature of the clothed person to be 30degrees celcius, determine the rate of heat loss from an average man walking in still air at 10degrees celcius by convectionat a walking velocity of (a)0.5m/s (b)1.0m/s (c)1.5m/s (d)2.0m/sarrow_forwardA Gasoline engine operating on an air standard condition has a clearance volume of 15cm^3 and a displacement volume of 100cm^3. Determine the theoretical thermal efficiency of the engine.arrow_forwardWhy does heat transfer increase initially with radius of insulation and then decrease beyond critical radius? Explain in details.arrow_forward
- / Hot square plate (1 m ×1 m) is to be cooled by attaching aluminum circular pin fins (D=0.25 cm, L= 3 cm) distributed with distance 0.6 cm as illustrated in Figs.(1-a) & (1-b). If the fin base temperature is 100°C, cooling air temperature is 30°C and h= 35 W/m. °C. Determine the total rate of heat transfer from the finned plate and the effectiveness of the fins? Assume k= 237 W/m.°C and nr=tanh mL/ mL.arrow_forwardConsider two identical people each generating 60W of metabolic heat steadily while doing sedentary work anddissipating it by convection and perspiration. The first personis wearing clothes made of 1-mm-thick leather (k =0.159 W/m·K) that covers half of the body while the secondone is wearing clothes made of 1-mm-thick synthetic fabric(k = 0.13 W/m·K) that covers the body completely. Theambient air is at 30°C, the heat transfer coefficient at theouter surface is 15 W/m2·K, and the inner surface temperatureof the clothes can be taken to be 32°C. Treating the bodyof each person as a 25-cm-diameter, 1.7-m-long cylinder,determine the fractions of heat lost from each person by perspiration.arrow_forwardA cartridge electrical heater is shaped as a cylinder of length L = 300 mm and outer diameter D = 30 mm. Under normal operating conditions, the heater dissipates 2 kW while submerged in a water flow that is at 20°C and provides a convection heat transfer coefficient of h = 5000 W/m2 · K. Neglecting heat transfer from the ends of the heater, determine its surface temperature Ts and the thermal resistance due to convection. If the water flow is inadvertently terminated while the heater continues to operate, the heater surface is exposed to air that is also at 20°C but for which h = 50 W/m2 · K. What are the corresponding thermal resistance due to convection and surface temperature? What are the consequences of such an event?arrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning