Consider Problem 4.5 for the case where the plate is of square cross section,
(a)Derive an expression for the shape factor,
(b)Derive an expression for the shape factor,
(c)Evaluate the shape factors that can be used to determine the maximum and average temperatures along
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Fundamentals of Heat and Mass Transfer
- The Diamond Ring Solution. The processing chip on the computer that controls the navigation equipment on your spacecraft is overheating. Unless you fix the problem, the chip will be damaged and the navigation system will shut down. You open the panel and find that the small copper disk that was supposed to bridge the gap between the smooth top of the chip and the cooling plate is missing, leaving a 2.2 mm gap between them. In this configuration, the heat cannot escape the chip at the required rate. You notice by the thin smudge of thermal grease (a highly thermally conductive material used to promote good thermal contact between surfaces) that the missing copper disk was 2.2 mm thick and had a diameter of 1.3 cm. You know that the chip is designed to run below 75 °C, and the copper cooling plate is held at a constant 5.0 °C. (a) What was the rate of heat flow from the chip to the copper plate when the original copper disk was in place and the chip was at its maximum operating…arrow_forwardMetal spheres, 10 mm in diameter, are to be annealed by heating them to 827°C then allowing them to cool slowly in air at 27°C to the point where they are in thermal equilibrium with the air. 2000 balls are annealed in one hour’s time. What is the total rate of their heat transfer if they are made of steel, lead, or copper? a.Sketch the problem. b.Draw lines identifying the control volume, or control mass. c.Identify the states with numbers, letters, or descriptions such as “in” and “out”. d.Write down the knowns and unknowns. e.Identify what is being asked for. f.State all assumptions.arrow_forward3.8 Determine (i) the pressure drop, and (ii) the convective heat transfer coefficient from hot air ( Tin = 500 K, Pin = 101.3 kPa, m sphere = 3.8 cm, o = 0.45, T init = 300 K, c sphere = 0.8 kJ/kgK, k sphere = 1.05 W/mK). = 3.5 kg/s) to a cold-packed bed of spheres (L vessel = 6.0 m, D vessel = 1.50 m, D Answer. (a) Ap = 9.46 kPa ; (b) h = 115arrow_forward
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- 5.10 A flaked cereal is of thickness 2L = 1.2 mm. The density, specific heat, and thermal conductivity of the flake are p = 700 kg/m³, cp = 2400 J/kg K, and k = 0.34 W/mK, respectively. The product is to be baked by increasing its temperature from T₁ = 20°C to T, = 220°C in a convec- tion oven, through which the product is carried on a con- veyor. If the oven is L₁ = 3 m long and the convection heat transfer coefficient at the product surface and oven air temperature are h = 55 W/m² K and T. = 300°C, respectively, determine the required conveyor velocity, V. An engineer suggests that if the flake thickness is reduced to 2L = 1.0 mm the conveyor velocity can be increased, resulting in higher productivity. Determine the required conveyor velocity for the thinner flake. 2L = 1.2 mm Conveyor belt Cereal product V L₂ Oven h = 55 W/m².K T_= 300°Carrow_forwardConsider the tea kettle in Example 2.10. Suppose that the kettle holds 1 kg of water (about 1 liter) and that the flame impinges on 0.02 m? of the bottom. (a) Find out how fast the water temperature is increasing when it reaches its boiling point, and calculate the temperature of the bottom of the kettle immediately below the water if the gases from the flame are at 500°C when they touch the bottom of the kettle. Assume that the heat capacitance of the aluminum kettle is negligible. (b) There is an old parlor trick in which one puts a paper cup of water over an open flame and boils the water without burning the paper (see Experiment 2.1). Explain this using an electrical analogy. [(a): dT[dt = 0.36°C/s.]arrow_forwardA cold storage room has a wall consists of an inside finish of 0.60 in cement plaster(k = 0.67), two layers of corkboard each 2.5 in thick (k = 0.03) and an outside layer of building tile. The value of U for the entire wall is 0.058, the internal air filmcoefficient is 1.65, the inner temperature is 23°F and the outside temperature is85°F. Calculate the heat flow through the unit wall area, Btu/hr.ft2A. 1.47 B. 2.47 C. 3.47 D. 4.47arrow_forward
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