Q3 A Wire 12 mm in diameter is to be insulated to maximize its current carrying capacity. For certain reasons the outside diameter of insulation should be 36 mm, the heat transfer coefficient for the outer surface to be 12 w/m'C. what is the percentage would the insulation increase the energy carrying capacity of the wire Q4) A circumferential copper fins (1.5 cm long and 3mm thick) of rectangular profile are mounted on a 2.5 m tube having a diameter of 3 cm. The fins are exposed to convection environment at 22°C, with heat transfer coefficient 58 W/m?.°C. Determine the increase in heat transfer from the tube as a result of adding fins if the number of fins are 250. Thermal conductivity 386 W/m.°C , T°= 100 °C -1-

Q3 A Wire 12 mm in diameter is to be insulated to maximize its current carrying capacity. For certain reasons the outside diameter of insulation should be 36 mm, the heat transfer coefficient for the outer surface to be 12 w/m'C. what is the percentage would the insulation increase the energy carrying capacity of the wire Q4) A circumferential copper fins (1.5 cm long and 3mm thick) of rectangular profile are mounted on a 2.5 m tube having a diameter of 3 cm. The fins are exposed to convection environment at 22°C, with heat transfer coefficient 58 W/m?.°C. Determine the increase in heat transfer from the tube as a result of adding fins if the number of fins are 250. Thermal conductivity 386 W/m.°C , T°= 100 °C -1-

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 2.1DP

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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
1.3 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.
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.
An electric wire having a diameter of 1.5 mm and covered with a plastic insulation (thickness = 2.5 mm) is exposed to air at 300 K and ho=20 W/m2.K. The insulation has a thermal conductivity (k) of 0.4 W/m.K. Assuming the wire surface temperature is constant at 400 K and is not affected by the covering a)Calculate the value of the critical radius. b)Calculate the heat loss per meter of wire length with no insulation. c)Calculate the heat loss per meter of wire length with insulation.
An electric wire having a diameter of 1.5 mm and covered with a plastic insulation (thickness = 2.5 mm) is exposed to air at 300 K and ho = 20 W/m2.K. The insulation has a thermal conductivity (k) of 0.4 W/m.K.Assuming the wire surface temperature is constant at 400 K and is not affected by the coveringa) Calculate the value of the critical radius.b) Calculate the heat loss per meter of wire length with no insulation.c) Calculate the heat loss per meter of wire length with insulation. p.s Could you write the solution clearly? It is hard to understand when written in text. A paper photo with solution would be better. Thanks in advance
For your company you need to mass produce 20-cmx10-cm heat sinks to dissipate heat quickly from an equipment. After considering several other parameters, you have short-listed two possible designs: A. 72 straight pin fins made of an alloy (thermal conductivity 240 W/m-°C) that costs $9,000 per m³. Each pin is 4 cm long and 1-cm diameter. E.=3'18; $204 B. 64 straight rectangular fins made of another alloy (thermal conductivity 180 W/m.°C) that costs $12,000 per m³. Each pin is 4 cm long and has 2-cmx1-cm cross-section. Eo =7:94%$ 6·14 The convection coefficient of the operating condition is approximated as 15 W/m2.°c. Consider that the manufacturing cost is same for both designs but the material cost differs. Calculate and compare the cost and performance (in terms of heat transfer gains by the heat sinks) of the two heat sinks so that a decision can be made to select a design.
The diagram below shows a composite wall 1 m deep. The first layer of thickness LA is made of special refractory material (kA=0.50 W/m.K). The second layer, 0.30 m thick, consists of insulating material A (kB=0.1 W/m.K) and insulating material B (kC = 0.35 W/m.K). The temperature on the inner face of A (Tsup) is equal to 900°C and the ambient temperature (Tamb) is equal to 25°C. The heat transfer coefficient h is equal to 10 W/m2.K. The rate of heat through the oven wall is constant and equal to 2500 W. Determine the thickness of the layer LA that forms wall A. What is the correct option? Present the calculation. a. 1,02 m b. 56 cm c. 27 cm d. 70 cm e. 12 cm
The diagram below shows a composite wall 1 m deep. The first layer of thickness LA is made of special refractory material (kA=0.50 W/m.K). The second layer, 0.30 m thick, consists of insulating material A (kB=0.1 W/m.K) and insulating material B (kC = 0.35 W/m.K). The temperature on the inner face of A (Tsup) is equal to 900°C and the ambient temperature (Tamb) is equal to 25°C. The heat transfer coefficient h is equal to 10 W/m².K. The rate of heat through the oven wall is constant and equal to 2500 W. Determine the thickness of the layer LA that forms wall A
nt Select D 0 261.40 ( 142. СС 60 Home Insert Space 300c° Insert Draw View Exercise 5 the bobul 3-75 Consider a 5-m-high 8-m-long, and 0.22-m-thick wall whose representative cross section is as given in the figure. The thermal conductivities of various materials used, in W/m-K, are k, = kp = 2, kg = 8, ke=20, kp = 15, and kg = 35. The left and right surfaces of the wall are maintained at uniform temperatures of 300°C and 100°C, respectively. Assuming heat transfer through the wall to be one-dimensional, determine (a) the rate of heat transfer through the wall; (b) the temperature at the point where the sections B, D, and E meet; and (c) the temperature drop across the section F. Disregard any contact resistances at the interfaces. RA p Re RB RC Ro RE ******** ве R=RA + ROBC+R DE + Rr ****** 300°C Ri 1000 1 сгу اللينفب اللوطن يمني نفتي المتريال 5 cm | +100 cm оста 6 cm Pencil + 100°C 0.12 M 10 C
Find the minimum amount of diameter for the insulation of a cylindrical electrical cable? Radius of the cable is 3 mm, length is 2 m, thermal conductivity is 20 W/(m^2*K) and convective coefficient is 5 WI(m*K) 12 mm 4 mm not sufficient information 3 mm 8 mm
one piece DU - Moodle English (en) - ESLIon -t yet swered The temperature distribution through a furnace wall consisting of firebrick and high-temperature block insulation and steel plate is measured as shown in the figure below. The thermal conductivity of fire brick is 1.13 W/(m. K). Find the heat loss per unit area of the furnace wall. rked out of 2 3 4 5 Flag question 760°C 758°C Block insulation 727°C | Outside air Hot gasef 68.42°C 26.5°C 68.5°C 6.35cm 12.7cm 0.635cm Select one: O a. 5.50 W/m2 O b. 550 W/m? O c. 55.0 W/m2 O d. 40 W/m2 Fire bri ck Steel casting
Q2: 0.2 m diameter, 4 mm thick, k-120 W/m.ºC disc is welded to 10 cm diameter hot bar at 120 °C (heater). The system is exposed to air at 20 °C, heat transfer coefficient is 12 W/m².°C. Calculate the rate of heat transfer through the disc.