Ql: Find the following:A) The heat transfer per unit area through the composite wall in Figure below.Assume one-dimensional heat flowB) The temperature at the point where the sections B, D and C meetKA = 100 W/m.°CKg= 20 W/m. °CA = 0.1 m?Kc = 40W/m.°CKp = 65 W/m.°CT= 370°CT= 66°CH F 75 cm →fa5.0 cm-|2.5 cm Q2: A 2.5 -mm-diameter electrical wire is insulated by a 2-mm-thick rubberizedsheath (* = 0.11 W/m K), and the wire/sheath interface. The convection heattransfer coefficient of the outer surface of the sheath is 10 W/m² K, and thetemperature of the ambient air is 20 C. If the temperature of the insulation may notexceed 50 C, what is the maximum allowable electrical power that may bedissipated per unit length of the conductor? What is the critical radius of theinsulation?

As given above that T1=370°C and T2=66°C , AC=0.1 m2 ;LA= 2.5 cm, LB=LD=7.5 cm , LC=5 cm ; So the…

Q1: Find the following: A) The heat transfer per unit area through the composite wall in Figure below Assume one-dimensional heat flow B) The temperature at the point where the sections B, D and C meet KA = 100 W/m.°C Kg = 20 W/m. °c A = 0.1 m² Kc = 40 W/m.C ° Kp = 65 W/m.C T= 370°C T= 66°C 25 cm - E 7.5 cm →-5.0 cm»|

Q1: Find the following: A) The heat transfer per unit area through the composite wall in Figure below Assume one-dimensional heat flow B) The temperature at the point where the sections B, D and C meet KA = 100 W/m.°C Kg = 20 W/m. °c A = 0.1 m² Kc = 40 W/m.C ° Kp = 65 W/m.C T= 370°C T= 66°C 25 cm - E 7.5 cm →-5.0 cm»|

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 2.21P

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Similar questions

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.
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.
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?
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.
Show that the rate of heat conduction per unit length through a long, hollow cylinder of inner radius ri and outer radius ro, made of a material whose thermal conductivity varies linearly with temperature, is given by qkL=TiTo(rori)/kmA where Ti = temperature at the inner surface To = temperature at the outer surface A=2(rori)/ln(ro/ri)km=ko[1+k(Ti+To)/2]L=lenthofcyclinder
A plane wall, 7.5 cm thick, generates heat internally at the rate of 105 W/m3. One side of the wall is insulated, and the other side is exposed to an environment at 90C. The convection heat transfer coefficient between the wall and the environment is 500 W/m2 K. If the thermal conductivity of the wall is 12 W/m K, calculate the maximum temperature in the wall.
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.)
2.38 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.
Example 2: Double-pane window, each window have: Height = 0.8 m Width 1.5 m Thickness = 4 mm k (glass) = 0.78 W/m.K separation between two glasses (air) = 10 mm k (air) = 0.026 W/m.K Temperature of inner surface = 20°C Temperature of outer surface = -10°C Convection heat transfer coefficient on the inner surface h1= 10 W/m2·°C Convection heat transfer coefficient on the outer surface h2= 40 W/m2·°C Determine the heat transfer through the window?
Example 1: Single-pane window, the window have: Height = 0.8 m Width 1.5 m Thickness = 4 mm k (glass) = 0.78 W/m.K Temperature of air at inner surface = 20°C Temperature of air at outer surface = -10°C Convection heat transfer coefficient on the inner surface h1= 10 W/m2·°C Convection heat transfer coefficient on the outer surface h2= 40 W/m2·°C Determine the heat transfer through the window?
10 cm thick and 1 m wide long when a steel plate is at temperature Ti = 240 ° C, T0 = 40 ° C It is immersed in the hot oil bath. With sheet Heat transfer coefficient between oil h = 600 W / m2K and p = 7833 kg / m3 for steel , cp = 465 J / kgK, k = 43 W / mK, α = 1.2x10-5 m2 / s. a)How much the core temperature of the steel plate after time becomes 100 ° C ? b)What is the temperature inside 3 cm from the surface of the steel plate? c)Within this period, per unit length plate what will be the amount of heat that passes?