1. The wall of a refrigerated van is made of steel sheet, glass wool and plywood....
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1. The wall of a refrigerated van is made of steel sheet, glass wool and plywood. The outer surface is made up of Ls = 5mm steel sheet (Ks=25 W/mK) and the inner surface is made up of Lp=15mm plywood (Kp=0.05 W/mK). Glass wool (LG=25mm, KG=0.01 W/mK) is placed between the inner and outer surface. The temperature of the cold environment inside the van is Ti=-20C, while the outside surface is exposed to To=-30C. The average values of convective heat transfer coefficients at the inner and outer surfaces of the wall are 12 W/mK and 20 W/mK respectively. The surface area of the wall is 0.85m. Determine (a) The individual components of the thermal resistance to heat flow (b) The rate of heat flow through the wall. (c) The temperatures at (i) the outer surface of the wall, (ii) the interface between steel sheet and glass wool, (ii) the interface between glass wool and plywood, and (iv) the inner surface of the wall (40 Points) Ta Steel sheet Glass wool Plywood kp kG ks T Fluid film at the outer surface Fluid film at the inner surface 2. A 1.5m long electrical resistance wire with diameter 4mm has a measured voltage drop of 25V for a current flow of 40A. The thermal conductivity of the wire material is 24 W/(m.K). Determine (a) the rate of generation of thermal energy per unit volume within the wire (b) the maximum temperature in the wire if the surface temperature is kept at 600K. (30 Points) 3. A 2m high and 1m wide plate with thickness 0.3m has one of its sides maintained at 450K while the other is maintained at 350K. The thermal conductivity of the plate can be assumed to vary linearly in that temperature range as K(T) = K(1+ T) where Ko= 18W/mK and = 8.7X104 K-. Assuming 1-dimensional heat transfer and no edge effect, determine the rate of heat conduction through the plate. (30 points) 1. The wall of a refrigerated van is made of steel sheet, glass wool and plywood. The outer surface is made up of Ls = 5mm steel sheet (Ks=25 W/mK) and the inner surface is made up of Lp=15mm plywood (Kp=0.05 W/mK). Glass wool (LG=25mm, KG=0.01 W/mK) is placed between the inner and outer surface. The temperature of the cold environment inside the van is Ti=-20C, while the outside surface is exposed to To=-30C. The average values of convective heat transfer coefficients at the inner and outer surfaces of the wall are 12 W/mK and 20 W/mK respectively. The surface area of the wall is 0.85m. Determine (a) The individual components of the thermal resistance to heat flow (b) The rate of heat flow through the wall. (c) The temperatures at (i) the outer surface of the wall, (ii) the interface between steel sheet and glass wool, (ii) the interface between glass wool and plywood, and (iv) the inner surface of the wall (40 Points) Ta Steel sheet Glass wool Plywood kp kG ks T Fluid film at the outer surface Fluid film at the inner surface 2. A 1.5m long electrical resistance wire with diameter 4mm has a measured voltage drop of 25V for a current flow of 40A. The thermal conductivity of the wire material is 24 W/(m.K). Determine (a) the rate of generation of thermal energy per unit volume within the wire (b) the maximum temperature in the wire if the surface temperature is kept at 600K. (30 Points) 3. A 2m high and 1m wide plate with thickness 0.3m has one of its sides maintained at 450K while the other is maintained at 350K. The thermal conductivity of the plate can be assumed to vary linearly in that temperature range as K(T) = K(1+ T) where Ko= 18W/mK and = 8.7X104 K-. Assuming 1-dimensional heat transfer and no edge effect, determine the rate of heat conduction through the plate. (30 points)
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Related Book For
Fundamentals of Thermal-Fluid Sciences
ISBN: 978-0078027680
5th edition
Authors: Yunus A. Cengel, Robert H. Turner, John M. Cimbala
Posted Date:
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