A wall of a house, shown in the figure, consists of the items in the accompanying table. If the inside and outside room temperature are 35"C and 15"C, with anexposed area of 150 m2. The total R-factor, Heat transfer through the wall and total thermal resistance in the sequence is given by optionNoItemsThermal resistance(R') (C/W)0.5Outside film resistanceFace brick11.82.72.Cement mortar2.5Cinder blockAir space6.1.5Gypsum boardInside film resistance0.9170.71. 2. 3.4.5. 6. 7.laall lista. 7837 m2-CW, 9.1540 Watt, 91.9 oCW Ob. 5645 m2-C/W, 14145 Watt. 158 oC/W Oc 6528 m2-C/W, 0.5487 Watt 194 oC/W Od. 1590 m2-CAW, 1.8867 Watt 106 oC/Wاحل اختداریا345

The inside room temperature is Ti=35 °C. The outside air temperature is To=15 °C

A wall of a house, shown in the figure, consists of the items in the accompanying table. If the inside and outside room temperature are 35"C and 15°C, with an exposed area of 150 m2. The total R-factor, Heat transfer through the wall and total thermal resistance in the sequence is given by option Thermal resistance (R') ("C/W) 0.5 No Items Outside film resistance 2. Face brick 1.8 2.7 2.5 3. Cement mortar Cinder block 4. Air space Gypsum board Inside film resistance 1.5 0.9 5. 6. 0.7 i. 2. 3. 4. 5. 6. 7.

A wall of a house, shown in the figure, consists of the items in the accompanying table. If the inside and outside room temperature are 35"C and 15°C, with an exposed area of 150 m2. The total R-factor, Heat transfer through the wall and total thermal resistance in the sequence is given by option Thermal resistance (R') ("C/W) 0.5 No Items Outside film resistance 2. Face brick 1.8 2.7 2.5 3. Cement mortar Cinder block 4. Air space Gypsum board Inside film resistance 1.5 0.9 5. 6. 0.7 i. 2. 3. 4. 5. 6. 7.

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.

Chapter8: Natural Convection

Section: Chapter Questions

Problem 8.39P

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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.
2.51 Determine by means of a flux plot the temperatures and heat flow per unit depth in the ribbed insulation shown in the accompanying sketch.
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.)
Repeat Problem 1.35 but assume that instead of surface temperatures, the given temperatures are those of the air on the left and right sides of the wall and that the convection heat transfer coefficients on the left and right surfaces are 6 and 10W/m2K, respectively.
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.
2.15 Suppose that a pipe carrying a hot fluid with an external temperature of and outer radius is to be insulated with an insulation material of thermal conductivity k and outer radius . Show that if the convection heat transfer coefficient on the outside of the insulation is and the environmental temperature is , the addition of insulation actually increases the rate of heat loss if , and the maximum heat loss occurs when . This radius, is often called the critical radius.
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A hot-water pipe (k = 0.75 W/m K) for house heating in winter season, made of 3/4-inch schedule 40 pipe (OD = 25.5 mm; thickness = 2.0 mm) contains water at 60 C. The convective heat transfer coefficient inside and outside the pipe are 950 W/m^2 K and 20 W/m^2 K, respectively. Insulation is added such that air around the pipe is at 20 C. The thermal conductivity of the insulation is 0.2 W/m K. Determine the heat loss per meter of pipe length from the pipe with insulation of 25 mm thick in W.
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