a) An infinite composite slab is made up of glass wool insulation packed in the space...

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a) An infinite composite slab is made up of glass wool insulation packed in the space between two thin metal sheets (0.5 mm thick). The metal sheets are 2 cm apart. The outer faces of the metal sheets are in contact with the hot air at 700 °C on one side and room temperature air at 30 °C on the other, and the values of the convective heat transfer coefficients on the hot and cold faces are 15 and 10 W/m²K respectively. Calculate the steady state rate at which heat flows per unit area through the slab, if the thermal conductivity of the glass wool insulation varies with temperature in the following manner: K=0.035(1+0.007T) W/mK Where 'T' is the temperature in °C. State the assumptions made. b) Mercury vapour is condensed on the shell side of a shell and tube heat exchanger by means of cooling water passing through the tubes. The heat transfer coefficients on the condensing vapour side and on the water side are 15,000 and 2000 W/m²K and the tubes, which are made of stainless steek (k = 9 W/mK), have a 2 cm ID and are 2mm thick. Calculat the overall heat transfer coefficient for the heat exchanger. c) A steel tube (k = 43.26 W/mK) of 5.08 cm 1.D. and 7.62 O.D. is covered with a 2.54 cm layer of asbestos insulation (k 0.208 W/mK). The inside surface of the tube receives heat by convection from a hot gas at a temperature of T-316 °C with a heat transfer coefficient h = 284 W/m³K, while the outer surface of the insulation is exposed to the ambient air at Tb= 38 °C with a heat transfer coefficient of hb = 17 W/m²K. Estimate (i) the loss to ambient air for 3 m length of the tube (ii) the temperature drops across the tube material and insulation layer. a) An infinite composite slab is made up of glass wool insulation packed in the space between two thin metal sheets (0.5 mm thick). The metal sheets are 2 cm apart. The outer faces of the metal sheets are in contact with the hot air at 700 °C on one side and room temperature air at 30 °C on the other, and the values of the convective heat transfer coefficients on the hot and cold faces are 15 and 10 W/m²K respectively. Calculate the steady state rate at which heat flows per unit area through the slab, if the thermal conductivity of the glass wool insulation varies with temperature in the following manner: K=0.035(1+0.007T) W/mK Where 'T' is the temperature in °C. State the assumptions made. b) Mercury vapour is condensed on the shell side of a shell and tube heat exchanger by means of cooling water passing through the tubes. The heat transfer coefficients on the condensing vapour side and on the water side are 15,000 and 2000 W/m²K and the tubes, which are made of stainless steek (k = 9 W/mK), have a 2 cm ID and are 2mm thick. Calculat the overall heat transfer coefficient for the heat exchanger. c) A steel tube (k = 43.26 W/mK) of 5.08 cm 1.D. and 7.62 O.D. is covered with a 2.54 cm layer of asbestos insulation (k 0.208 W/mK). The inside surface of the tube receives heat by convection from a hot gas at a temperature of T-316 °C with a heat transfer coefficient h = 284 W/m³K, while the outer surface of the insulation is exposed to the ambient air at Tb= 38 °C with a heat transfer coefficient of hb = 17 W/m²K. Estimate (i) the loss to ambient air for 3 m length of the tube (ii) the temperature drops across the tube material and insulation layer.