Two water columns are at different temperatures, one being at 35°C and the other being at 18oC. The water columns are separated by a glass wall of area Im by 2m and a thickness of 0.005m. Calculate the amount of heat transfer. (Thermal Conductivity of glass is 1.6 W/mK) TABLE 13-13 Typical values of resistance for common building materials R for thickness shown, m K/W Building material R, m K/W Building board Kypoum, 9.5 mm particle board Building membrane 2 layers, 0.73 kg/m° felt 0.056 7.35 0.21 Glass single glazing, 3 mm double glazing. 6 mm air space triple glazing, 6 mm air space 0.16 0.32 047 Insulating material Blanket and batt mineral fiber from glass, approx. 90 mm approx. 150 mm approx. 230 mm approx. 275 mm glass fiber, organic bonded loose fill milled paper spray applied polyurethane foam 2.29 3.32 5.34 6.77 27.7 23 40 Roofing asphalt shingles buil-up, 10 mm 0.077 0.058 Masonry brick 1.15 concrete 0.6 Siding materials hardboard, 11 mm 0.12 0.10 plywood, 9.5 mm Aluminum or steel, over sheathing. bollow-backed insulating board backed, 9.5 mm insulating board backed, 9.5 mm, foil 0.11 0.32 0.52 Soils 0.44 Still air, 90 mm 0.4 Socie of esti Retii d Condienin

Two water columns are at different temperatures, one being at 35°C and the other being at 18oC. The water columns are separated by a glass wall of area Im by 2m and a thickness of 0.005m. Calculate the amount of heat transfer. (Thermal Conductivity of glass is 1.6 W/mK) TABLE 13-13 Typical values of resistance for common building materials R for thickness shown, m K/W Building material R, m K/W Building board Kypoum, 9.5 mm particle board Building membrane 2 layers, 0.73 kg/m° felt 0.056 7.35 0.21 Glass single glazing, 3 mm double glazing. 6 mm air space triple glazing, 6 mm air space 0.16 0.32 047 Insulating material Blanket and batt mineral fiber from glass, approx. 90 mm approx. 150 mm approx. 230 mm approx. 275 mm glass fiber, organic bonded loose fill milled paper spray applied polyurethane foam 2.29 3.32 5.34 6.77 27.7 23 40 Roofing asphalt shingles buil-up, 10 mm 0.077 0.058 Masonry brick 1.15 concrete 0.6 Siding materials hardboard, 11 mm 0.12 0.10 plywood, 9.5 mm Aluminum or steel, over sheathing. bollow-backed insulating board backed, 9.5 mm insulating board backed, 9.5 mm, foil 0.11 0.32 0.52 Soils 0.44 Still air, 90 mm 0.4 Socie of esti Retii d Condienin

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.

Chapter11: Heat Transfer By Radiation

Section: Chapter Questions

Problem 11.45P

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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
The heat transfer coefficient for a gas flowing over a thin float plate 3-m long and 0.3-m wide varies with distance from the leading edge according to hc(x)=10x1/4Wm2K If the plate temperature is 170C and the gas temperature is 30C, calculate (a) the average heat transfer coefficient, (b) the rate of heat transfer between the plate and the gas, and (c) the local heat flux 2 m from the leading edge. Problem 1.18
A 2.5-cm-OD, 2-cm-ID copper pipe carries liquid oxygen to the storage site of a space shuttle at -183Cand0.04m3/min. The ambient air is at 21C and has a dew point of 10C. How much insulation with a thermal conductivity of 0.02 W/m K is needed to prevent condensation on the exterior of the insulation if hc+h=17W/m2 K on the outside?
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.
3.10 A spherical shell satellite (3-m-OD, 1.25-cm-thick stainless steel walls) re-enters the atmosphere from outer space. If its original temperature is 38°C, the effective average temperature of the atmosphere is 1093°C, and the effective heat transfer coefficient is , estimate the temperature of the shell after reentry, assuming the time of reentry is 10 min and the interior of the shell is evacuated.
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
Question Consider heat loss through the two walls of a house on a winter night. The walls are identical, except that one of them has a tightly fit glass window. Through which wall will the house lose more heat? Explain.
A wall is constructed of two layers of 0.5-in-thick sheetrock (k = 0.10 Btu/h·ft·oF),which is a plasterboard made of two layers of heavy paper separated by a layer ofgypsum, placed 7 in apart. The space between the sheetrocks is filled with fibreglassinsulation (k = 0.020 Btu/h·ft·oF). Determine a) the thermal resistance of the wall, andb) its R-value of insulation in English units.
The emissivity of galvanized steel sheet, a common roofing material, is ε = 0.13 at temperatures around 300 K, while its absorptivity for solar irradiation is αS = 0.65. Would the neighborhood cat be comfortable walking on a roof constructed of the material on a day when GS = 750 W/m2, T∞ = 16°C, and h = 7 W/m2 · K? Assume the bottom surface of the steel is insulated.
A Thermopane window consists of two 3-mm-thick pane of glass separated by a stagnant air space of thickness 6 mm. The convection heat transfer coefficients for the inside and outside air are hi = 5 W/m2·K and ho = 50 W/m2·K, respectively. The inside and outside air temperatures are Ti = 25°C and To = 0°C, respectively. a) Determine the heat flux through the Thermopane window. b) Compare the above result to the same environment around a single-pane glass window of thickness L = 12 mm.
The author and his then 6-year-old son have conducted the following experiment to determine the thermal conductivity of a hot dog. They first boiled water in a large pan and measured the temperature of the boiling water to be 94°C, which is not surprising, since they live at an elevation of about 1650 m in Reno, Nevada. They then took a hot dog that is 12.5 cm long and 2.2 cm in diameter and inserted a thermocouple into the midpoint of the hot dog and another thermocouple just under the skin. They waited until both thermocouples read 20°C, which is the ambient temperature. They then dropped the hot dog into boiling water and observed the changes in both temperatures. Exactly 2 min after the hot dog was dropped into the boiling water, they recorded the center and the surface temperatures to be 59°C and 88°C, respectively. The density of the hot dog can be taken to be 980 kg/m3, which is slightly less than the density of water, since the hot dog was observed to be floating in water while…
Plot how hx (heat transfer coefficient) depends on the distance along a plate (x) and explain how this relationship .