Concept explainers
Consider a large
Both sides of the plate are exposed to an environment at
Explain where in the plate the highest and the lowest temperatures will occur, and determine their values.
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Heat and Mass Transfer: Fundamentals and Applications
- Heat is transferred at a rate of 0.1 kW through glass wool insulation (density=100kg/m3) with a 5-cm thickness and 2-m2 area. If the hot surface is at 70C, determine the temperature of the cooler surface.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_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
- 1.19 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_forwardA 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_forwardTo warm up some milk in a thin-walled glass cylindrical container whose diameter is 6 cm. The height of the milk in the glass is 7 cm. The milk container is placed into a large pan filled with hot water at 60°C. The milk is stirred constantly, so that its temperature is uniform at all times. If the heat transfer coefficient between the water and the glass is 120 W/m2.°C, determine how long it will take for the milk to warm up from 3°C to 38°C. Take the properties of the milk to be the same as those of water. Can the milk in this case be treated as a lumped system? Use the lumped system analysis to solve the problem. The properties of water and milk at 20°C are, k = 0.607 W/m.°C,p=998 kg/m', and C, = 4.182 kJ/kg.°C. Answer: 5.8 min. ملاحظه: تكون هنا قيمة (0.1 < Bi( ويفترض لايطبق التحليل الكتلي , ولكن استخدم نفس التحليل والمعادلات في المحاضرة وكذلك في المثال لان الحليب يخلط باستمرار ولذلك تكون درجة حرارته منتظمه و متغيره مع الزمن لانه يكتسب حراره من الماء ويسخن وترتفع درجة حرارته مع…arrow_forward
- The rate of heat flow through a hallow sphere of inner radius 0.25 m and outer radius 0.35m, whose thermal conductivity is 5 W/mK, maintained at temperatures of 400°C and 300°C respectively equal toarrow_forwardIt is measured that a 2-m2 wall has a heat transfer rate of 7200 W. If the thickness of the wall is 0.02-m and the temperature difference on either side of the wall is 60ºC, determine the thermal conductivity in W/m K.arrow_forward3- Stainless steel ball bearings have a diameter of 1.2 cm are to be quenched in water. The balls leave the oven at a uniform temperature of 900°C and are exposed to air at 30°C for a while before they are dropped into the water. If the temperature of the balls is not to fall below 850°C prior to quenching and the heat transfer coefficient in the air is 125 W/m² - °C, determine how long they can stand in the air before being dropped into the water. Given: Stainless steel [ k= 15.1 W/m.°C, p= 8085 kg/m3, and Cp= 0.480 kJ/kg.°C. and a=3.95 × 106 m³/s]arrow_forward
- A long 20 cm diameter shaft made of stainless steel 304 comes out of an oven at a uniform temperature of 600°C. The shaft is then allowed to cool slowly in an environment at 200°C with an average heat transfer coefficient of h = 80 W/m².K. Determine [a] the temperature at the center of the shaft and [b] the temperature of the outer surface of the shaft 45 minutes after the start of the cooling Given: Find: Schematic: Assume: Property Data: k= 14.9 W/m°C p= 7900 kg/m³ Cp = 477 J/kg:K a= 3.95 x 10-6 m²/sarrow_forwardConsider a solid sphere of radius r=50 cm. The heat is generated steadily inside the sphere at a rate of (15000) W/m³. The conductivity of the sphere is 10 W/m.K. Surface of the sphere is cooled by cooling water whose temperature and convection heat transfer coefficient are 10°C and 125 W/m².K. Determine the temperatures at the center and surface of the sphere. Find the total heat transfer rate from surface of the sphere.arrow_forwardCalculate the heat transfer in kj per hour through a solid brick wall 9 cm, 3 m high and 219 mm thick, when the outer surface is at 5C and the inner surface 17C, the coefficient of thermal conductivity of the brick is 0.6 W/m-K.arrow_forward
- Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning