5- A wall is constructed of a section of stainless steel (k=16 W/m. C; 4.0 mm thick) with identical layersof plastic on both sides of the steel. The overall heat-transfer coefficient, (considering convection on bothsides of the plastic), is 120 W/m2. C. If the overall temperature difference across the arrangement is60°C, calculate the temperature difference across the stainless steel. Take A-1m2. Answ(18-C)

Given data as per question For stainless steel k=1.6 W/m°C, thickness=4 mm=4×10-3 m Overall heat…

Answered: 5- A wall is constructed of a section…

5- A wall is constructed of a section of stainless steel (k of plastic on both sides of the steel. The overall heat-tran sides of the plastic), is 120 W/m2. C. If the overall te

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.

Chapter3: Transient Heat Conduction

Section: Chapter Questions

Problem 3.16P: 3.16 A large, 2.54-cm.-thick copper plate is placed between two air streams. The heat transfer...

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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.
2.30 An electrical heater capable of generating 10,000 W is to be designed. The heating element is to be a stainless steel wire having an electrical resistivity of ohm-centimeter. The operating temperature of the stainless steel is to be no more than 1260°C. The heat transfer coefficient at the outer surface is expected to be no less than in a medium whose maximum temperature is 93°C. A transformer capable of delivering current at 9 and 12 V is available. Determine a suitable size for the wire, the current required, and discuss what effect a reduction in the heat transfer coefficient would have. (Hint: Demonstrate first that the temperature drop between the center and the surface of the wire is independent of the wire diameter, and determine its value.)
A high-speed computer is located in a temperature-controlled room at 26C. When the machine is operating, its internal heat generation rate is estimated to be 800 W. The external surface temperature of the computer is to be maintained below 85C. The heat transfer coefficient for the surface of the computer is estimated to be 10W/m2K. What surface area would be necessary to assure safe operation of this machine? Comment on ways to reduce this area.
1.37 Mild steel nails were driven through a solid wood wall consisting of two layers, each 2.5-cm thick, for reinforcement. If the total cross-sectional area of the nails is 0.5% of the wall area, determine the unit thermal conductance of the composite wall and the percent of the total heat flow that passes through the nails when the temperature difference across the wall is 25°C. Neglect contact resistance between the wood layers.
3.17 A 1.4-kg aluminum household iron has a 500-W heating element. The surface area is . The ambient temperature is 21°C, and the surface heat transfer coefficient is . How long after the iron is plugged in does its temperature reach 104°C?
An electronic device that internally generates 600 mW of heat has a maximum permissible operating temperature of 70C. It is to be cooled in 25C air by attaching aluminum fins with a total surface area of 12cm2. The convection heat transfer coefficient between the fins and the air is 20W/m2K. Estimate the operating temperature when the fins are attached in such a way that (a) there is a contact resistance of approximately 50 K/W between the surface of the device and the fin array and (b) there is no contact resistance (in this case, the construction of the device is more expensive). Comment on the design options.
3.16 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.
One side of a copper (401 W/m-oC) block 5 cm thick is maintained at 175 oC, the other side is covered with fiberglass (k = 0.026 W/m-0C) 2.5 cm thick. The outside of the block is maintained at 38 oC, and the total heat flow is 44 kW. Find the overall heat transfer coefficient. (four decimal places for final answer)
A 1-in Sch 40 stainless steel pipe with a thermal conductivity of 45 W/m-K can move 1,000 kg of saturated steam per hour at 150 °C. Refractory material 0.25 inches thick with a thermal conductivity of 0.025 W/m-K insulates the pipe. At a temperature of 25 °C, the pipe is exposed to the outside air. There is a 1135 W/m2 internal heat transfer coefficient.40 W/m2-K is the outside heat transfer coefficient, whereas -K. Suppose that only the radial direction is involved in steady-state heat transfer and that radiation effects are negligible. ✓ Determine how much heat is being lost through these pipes to the environment.a. 399.1 W/mb. 1525.0 W/mc. 618.4 W/md. 1128.7 W/me. none of the above √ How about the insulated pipe's surface temperature?a. 118.5 °Cb. None of the abovec. 101.5 °Cd. 216.3 °Ce. 292.2 °C
The outer facing of a room is constructed from 25 cm thick brick, 2.5 cm of mortar, 10 cm of limestone (k = 0.186 W/m-K) and 1.2 cm of plaster (k = 0.096 W/m-K). Thermal conductivities of mortar and brick are both 0.52 W/m-K. Assume that the heat transfer coefficients on the inside (plaster side) and the outside (brick side) surfaces of the wall to be 6 and 12 W/sq. m, respectively. Calculate the rate of heat transfer per 10 sq. m of the wall surface from the room at 18 C to the outside air at 36 C.
5- A spherical tank with internal diameter of 2 m made of 2.0-cm-thick stainless steel (k=15 W/m.K) is used for storing a fluid at a temperature of 1 ºC. The tank is covered with a 4-cm-thick layer of an insulation (k=0.25 W/m.K). The surrounding air is at 15ºC. The inside and outside heat transfer coefficients are 35 and 10W/m2.K, respectively. Required: Draw the thermal resistance network (thermal circuit) and label the associated resistance and determine the following:a) The individual thermal resistance associated with the thermal circuit.b) The total thermal resistance valuec) The rate of heat transferd) The temperature difference across the tank shell and the insulation layer.
A single-cylinder air-cooled lawn mower engine operates under steady conditions. The cylinder temperature cannot exceed 300 ⁰C. To cool the engine, annular fins are placed around the cylinder. The fins are 0.3 cm thick and are 2 cm long from base to tip. The fins are made of cast iron (k = 52 W/mK). The outside diameter of the engine cylinder at the base of the fin is 0.3 m. Assume that the engine operates in 30 ⁰C air and that the heat transfer coefficient on the sides and tip of the fin is 12 Wm^-2K^-1. Determine the number of fins needed to cool a 3 kW engine to the given temperature if the engine has an efficiency of 30 % and 50 % of the total heat given off by the engine actually is dissipated through the fins ?