1. The thermal conductivity of a sheet of rigid, extruded insulation is reported to be k=0.029 W/m.K. The measured temperature difference across a 20 mm thick sheet of the material is T1- T2=10 °C. (a) What is the heat flux through a 2mx2m sheet of the insulation? (b) What is the rate of heat transfer through the sheet of insulation? 2. The heat flux that is applied to the left face of a plane wall is q"=20 W/m². The wall is of thickness L = 10 mm and of thermal conductivity k=12 W/m.K. If the surface temperatures of the wall are measured to be 50 °C on the left side and 30 °C on the right side, do steady-state conditions exist? 3. 3. A square isothermal chip is of width w = 5 mm on a side and is mounted in a substrate such that its side and back surfaces are well insulated; the front surface is exposed to the flow of a coolant at T∞ = 15 °C. From reliability considerations, the chip temperature must not exceed T=85 °C Coolant To, h 007 W Chip If the coolant is air and the corresponding convection coefficient is h=200W/m²-K, what is the maximum allowable chip power? If the coolant is a dielectric liquid for which h=3000 W/m2-K, what is the maximum allowable power?

1. The thermal conductivity of a sheet of rigid, extruded insulation is reported to be k=0.029 W/m.K. The measured temperature difference across a 20 mm thick sheet of the material is T1- T2=10 °C. (a) What is the heat flux through a 2mx2m sheet of the insulation? (b) What is the rate of heat transfer through the sheet of insulation? 2. The heat flux that is applied to the left face of a plane wall is q"=20 W/m². The wall is of thickness L = 10 mm and of thermal conductivity k=12 W/m.K. If the surface temperatures of the wall are measured to be 50 °C on the left side and 30 °C on the right side, do steady-state conditions exist? 3. 3. A square isothermal chip is of width w = 5 mm on a side and is mounted in a substrate such that its side and back surfaces are well insulated; the front surface is exposed to the flow of a coolant at T∞ = 15 °C. From reliability considerations, the chip temperature must not exceed T=85 °C Coolant To, h 007 W Chip If the coolant is air and the corresponding convection coefficient is h=200W/m²-K, what is the maximum allowable chip power? If the coolant is a dielectric liquid for which h=3000 W/m2-K, what is the maximum allowable power?

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.

Chapter1: Basic Modes Of Heat Transfer

Section: Chapter Questions

Problem 1.20P: A high-speed computer is located in a temperature-controlled room at 26C. When the machine is...

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1.2 The weight of the insulation in a spacecraft may be more important than the space required. Show analytically that the lightest insulation for a plane wall with a specified thermal resistance is the insulation that has the smallest product of density times thermal conductivity.
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.
Using Table 1.4 as a guide, prepare a similar table showing the orders of magnitude of the thermal resistances of a unit area for convection between a surface and various fluids.
1.4 To measure thermal conductivity, two similar 1-cm-thick specimens are placed in the apparatus shown in the accompanying sketch. Electric current is supplied to the guard heater, and a wattmeter shows that the power dissipation is 10 W. Thermocouples attached to the warmer and to the cooler surfaces show temperatures of 322 and 300 K, respectively. Calculate the thermal conductivity of the material at the mean temperature in W/m K. Problem 1.4
As a designer working for a major electric appliance manufacturer, you are required to estimate the amount of fiberglass insulation packing (k = 0.035 W/m K) that is needed for a kitchen oven shown in the figure below. The fiberglass layer is to be sandwiched between a 2-mm-thick aluminum cladding plate on the outside and a 5-mm-thick stainless steel plate on the inside that forms the core of the oven. The insulation thickness is such that the outside cladding temperature does not exceed 40C when the temperature at the inside surface of the oven is 300C. Also, the air temperature in the kitchen varies from 15Cto33C, and the average heat transfer coefficient between the outer surface of the oven and air is estimated to be 12.0W/m2K. Determine the thickness of the fiberglass insulation that is required for these conditions. What would be the outer surface temperature when the inside surface of the oven is at 475C?
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.
Wearing layers of clothing in cold weather is often recommended because dead-air spaces between the layers keep the body warm. The explanation for this is that the heat loss from the body is less. Compare the rate of heat loss for a single 2-cm-thick layer of wool [k=0.04W/(mK)] with three 0.67-cm layers separated by 1.5 mm air gaps. The thermal conductivity of air is 0.024 W(mK).
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.
1.1 On a cold winter day, the outer surface of a 0.2-m-thick concrete wall of a warehouse is exposed to temperature of –5°C, while the inner surface is kept at 20°C. The thermal conductivity of the concrete is 1.2 W/m K. Determine the heat loss through the wall, which is 10-m long and 3-m high. Problem 1.1
Please answer question3 please show me step by step.
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The thermal conductivity of a sheet of rigid, extruded insulation is reported to be k = 0.029 W/m-K. The measured temperature difference across a 25-mm-thick sheet of the material is T| – T2 = 10°C. (a) What is the heat flux through a 3 m x 3 m sheet of the insulation, in W/m?? (b) What is the rate of heat transfer through the sheet of insulation, in W? (c) What is the thermal resistance of the sheet due to conduction, in K/W? Part A What is the heat flux through a 3 m x 3 m sheet of the insulation, in W/m2? i W/m?