What is the solution for this question 5.49 A long cylinder of 30-mm diameter, initially at a uni-form temperature of 1000 K, is suddenly quenched in alarge, constant-temperature oil bath at 350 K. The cyl-inder properties are k = 1.7 W/m · K, c = 1600 J/kg · K,and p = 400 kg/m', while the convection coefficient is50 W/m? · K.(a) Calculate the time required for the surface of thecylinder to reach 500 K.(b) Compute and plot the surface temperature historyfor 0 5.39 Consider an acrylic sheet of thickness L = 5 mm thatis used to coat a hot, isothermal metal substrate at T,:300°C. The properties of the acrylic are p= 1990 kg/m',c = 1470 J/kg •K, and k = 0.21 W/m · K. Neglecting thethermal contact resistance between the acrylic and themetal substrate, determine how long it will take forthe insulated back side of the acrylic to reach its soft-ening temperature, Tsoft = 90°C. The initial acrylic tem-perature is T; = 20°C.%3D352 / 1046

5.39 Consider an acrylic sheet of thickness L = 5 mm that is used to coat a hot, isothermal metal substrate at T, = 300°C. The properties of the acrylic are p= 1990 kg/m², c = 1470 J/kg · K, and k = 0.21 W/m • K. Neglecting the thermal contact resistance between the acrylic and the metal substrate, determine how long it will take for the insulated back side of the acrylic to reach its soft- ening temperature, Tyoft = 90°C. The initial acrylic tem- perature is T; = 20°C. %3D 352/ 1046

5.39 Consider an acrylic sheet of thickness L = 5 mm that is used to coat a hot, isothermal metal substrate at T, = 300°C. The properties of the acrylic are p= 1990 kg/m², c = 1470 J/kg · K, and k = 0.21 W/m • K. Neglecting the thermal contact resistance between the acrylic and the metal substrate, determine how long it will take for the insulated back side of the acrylic to reach its soft- ening temperature, Tyoft = 90°C. The initial acrylic tem- perature is T; = 20°C. %3D 352/ 1046

Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)

8th Edition

ISBN:9781305387102

Author:Kreith, Frank; Manglik, Raj M.

Publisher:Kreith, Frank; Manglik, Raj M.

Chapter2: Steady Heat Conduction

Section: Chapter Questions

Problem 2.30P: 2.30 An electrical heater capable of generating 10,000 W is to be designed. The heating element is...

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Two inches of urethane foam will reduce heat loss close to 1000% when applied to a 2-inch diameter uninsulated steel pipe. Assume the pipe wall thickness is 0.25-inches, the pipe interior convective heat loss (hi) is 500 BTU/hr-ft2-oF, and the pipe outside convective heat loss ho 20 BTU/hr-ft2-oF, k steel is 25 BTU/hr-ft-oF, and k insulaton is 0.023 BTU/hr-ft-oF. (hint - calculate heat loss with and without insulation.
(a) The temperature at the surface of the heating rod, T1. (b) If the salt solution temperature is 300 degree Celcius, what is the value of convection heat transfer coefficient, h of the salt solution ? (c) If the heating rod is not covered by metallic cylinder and corresponds to the result of part (a) and (b), how much the rate of energy transfer to the salt solution ? (d) Compare and discuss the difference of heat transfer with and without the matallic cylinder.
Solve for this : An engine cover is made from 1 cm thick stainless steel plate (k = 14 W/m K). Air on the inside of the engine cover is heated to 340°C with a heat transfer coefficient of 7 W/m2K. Outside of the engine coverthe ambient air has a temperature of 70°C. If oil was spilled on the outside of the engine cover (ambient side), it could ignite if the surface temperature were to exceed 200°C. In this configuration, would spilled oil ignite? Use calculations to justify your answer. If a 4 mm thermal coating (k = 1.1 W/m K) was applied tothe outside of the engine, what would the outside temperature of the engine cover be reduced to?
A 6-in. polished copper sphere is heated electrically to maintain a surfacetemperature of 280 °F. If the sphere is suspended in a large room where theair and the wall temperatures 80 °F, how much heat, in BTU/hr, must besupplied to the sphere?
A metal composite wall consists of two outer metal skins (k = 100 W/m.k) 2 mm thick which sandwich an insulating composite (k = 15 W/m.k). If the composite material is 96 mm thick, and the temperature difference across the outer metal skins is 75 degree celsius, state the heat flux q to the nearest kW.
(a) If the insulation is 27.5 mm thick and its inner and outer surfaces are maintained at Ts,1=800 K and Ts,2=490 K, respectively, what is the rate of heat loss per unit length (q′) of the pipe, in W/m?(b) Determine the rate of heat loss per unit length (q′), in W/m, and outer surface temperature Ts,2, in K, for the steam pipe with the inner surface temperature fixed at Ts,1=800 K, inner radius r1=0.06 m, and outer radius r2= 0.18 m. The outer surface is exposed to an airflow (∞T∞=25°C) that maintains a convection coefficient of h=25 W/m2·K and to large surroundings for which Tsur= T∞=25°C. The surface emissivity of calcium silicate is approximately 0.8.
1.63 Liquid oxygen (LOX) for the space shuttle is stored at 90 K prior to launch in a spherical container 4 m in diameter. To reduce the loss of oxygen, the sphere is insulated with superinsulation developed at the U.S. National Institute of Standards and Technology's Cryogenic Division; the superinsulation has an effective thermal conductivity of 0.00012 W/m K. If the outside temperature is on the average and the LOX has a heat of vaporization of 213 J/g, calculate the thickness of insulation required to keep the LOX evaporation rate below 200 g/h.
1.3 A furnace wall is to be constructed of brick having standard dimensions of Two kinds of material are available. One has a maximum usable temperature of 1040°C and a thermal conductivity of 1.7 W/(m K), and the other has a maximum temperature limit of 870°C and a thermal conductivity of 0.85 W/(m K). The bricks have the same cost and are laid in any manner, but we wish to design the most economical wall for a furnace with a temperature of 1040°C on the hot side and 200°C on the cold side. If the maximum amount of heat transfer permissible is 950 , determine the most economical arrangement using the available bricks.
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2.2 A small dam, which is idealized by a large slab 1.2 m thick, is to be completely poured in a short Period of time. The hydration of the concrete results in the equivalent of a distributed source of constant strength of 100 W/m3. If both dam surfaces are at 16°C, determine the maximum temperature to which the concrete will be subjected, assuming steady-state conditions. The thermal conductivity of the wet concrete can be taken as 0.84 W/m K.
A small sphere (emissivity = 0.745, radius = r1) is located at the center of a spherical asbestos shell (thickness = 1.72 cm, outer radius = r2; thermal conductivity of asbestos is 0.090 J/(s m Co)). The thickness of the shell is small compared to the inner and outer radii of the shell. The temperature of the small sphere is 727 °C, while the temperature of the inner surface of the shell is 406 °C, both temperatures remaining constant. Assuming that r2/r1 = 6.54 and ignoring any air inside the shell, find the temperature in degrees Celsius of the outer surface of the shell.
8.9 One end of a 9-in long × 7-in diameter copper bar is heated to 59.4°F, the far end of the bar is held at 23°C. If the sides of the bar are covered with thermal insulation, what is the rate of heat transfer? 8.11 When the far end of the copper bar in Prob. 8.9 has a 30-ft2 cooling fin attached to the end of the bar and is cooled by air convection, the temperature of the fin rises to t °F. If the temperature of the air is 23°F and the coefficient of heat transfer of the surface is 0.22 BTU/h, what is the value of t?