Q3/ A 1.0-mm-diameter wire is maintained at a temperature of 400 C and exposed to a convection environment at 40 C with h-120 W/m2.C. Calculate the thermal conductivity that will just cause an insulation thickness of 0.2 mm to produce a "critical radius " How much of this insulation must be added to reduce the heat transfer by 75 percent from that which would be experienced by the bare wire?

Q3/ A 1.0-mm-diameter wire is maintained at a temperature of 400 C and exposed to a convection environment at 40 C with h-120 W/m2.C. Calculate the thermal conductivity that will just cause an insulation thickness of 0.2 mm to produce a "critical radius " How much of this insulation must be added to reduce the heat transfer by 75 percent from that which would be experienced by the bare wire?

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 2.59P

See similar textbooks

Similar questions

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
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.
1.10 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.
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.
One end of a 0.3-m-long steel rod is connected to a wall at 204C. The other end is connected to a wall that is maintained at 93C. Air is blown across the rod so that a heat transfer coefficient of 17W/m2 K is maintained over the entire surface. If the diameter of the rod is 5 cm and the temperature of the air is 38C, what is the net rate of heat loss to the air?
2. In determining the thermal conductivity of a plateflat insulator, the temperature was measured on both sides of the 25 mm thick plate and gave the results of 318.4 K and 303.2 K. FluxThe measured heat is 35.1 W.m-2. Illustrate the problem in a simple schematic/drawing, then calculate the thermal conductivity inbtu/h.ft.oF and in W/m.K! (0.033 ; 0.058) 3. A coil-shaped cooling pipe is made of SS-304 material. This pipe is 1 ft long, 0.4 inch outside diameter, and inch inside diameter. This coil cooling pipe is used to cool the water in the bath. The temperature of the inner coil pipe is 40oF while the outer coil in contact with water is 80oF. The thermal conductivity of SS-304 is a function of temperature where k(T) = 7.75 + (7.78 x 10-3).T where k is in Btu/h.ft.oF and T is in oF. Calculate the rate of heat dissipation in watts! (1287.7)
Q2- Water flows inside a steel pipe with an ID of 2.5 cm. The wall thickness is 2 mm, and the convection coefficient on the inside is 100 Wm? C. The convection coefficient on the outside is 10 W/n C. The pipe is covered with a layer of asbestos. 1-determine the thickness of the asbestos layer at the critical insulation radius of the pipe. 2-calculate the change percent of heat transfer with and without the insulation. 3-commet on your results,
A boiler furnace wall must have a heat loss no greater than 700 Btu/hr~ft2 and is madeof a material with a thermal conductivity of 0.60 Btu/hr~ft~F. The inner wall surfacetemperature is '2000°F, and the outer surface temperature is 800°F. What wall thick~ness is required?
Thermal Conductivity Problems: a. A wall is made of firebrick 6 inches thick and has a 50°C difference in temperature both sides. Calculate the heat transferred through the wall if the thermal conductivity of the brick is 0.65 BTU/hr-ft- oF. b. Compute the amount of heat flow per second through an iron plate 2 cm thick and the area of 5000 cm² if one face has a temperature of 150°C and the other face is 140°C? The thermal conductivity for iron is 80 W/m-K.
2. Calculate insulation thickness (minimum value) required for a pipe carrying steam at 180°C. The pipe size is 8" and the maximum allowable temperature of outer wall of insulation is 50 °C. Thermal conductivity of the insulation material for the temperature range of the pipe can be taken as 0.04 W/m K. The heat loss from steam per meter of pipe length has to be limited to 80 W/m. ANSWER: 102.5 mm
) A plane wall is having width ‘b’ mm and height 4 times of its width. The wall thickness is 120 mm. the thermal conductivity is 18 W/mK. The surface temperatures are at 700oC and 200o C The heat flow across the plane wall is 746 W Calculate the width, height and area of the wall?
Q/ Steam flowing through a long, thin-walled pipe maintains the pipe wall at a uniform temperature of 500 K. The pipe is covered with an insulation blanket comprised of two different materials, A and B. The interface between the two materials may be assumed to have an infinite contact resistance, and the entire outer surface is exposed to air for which Too = 300 K and h =25 W/m2, K. Calculate the total heat loss from the pipe and What are %3D the outer surface temperatures Ts,2(A) and Ts,2(B)? n- 50 mm 2- 100 mm T 2A) -k - 2 W/m-K T5, 218) -kg = 0.25 W/m-K T1- 500 K