ejercicios transferencia, Apuntes de Estudios Espaciales

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2-70 In a food processing facility, a spherical container of inner radius r, = 40 cm, outer radius r, = 41 cm, and thermal conductivity k = 1.5 W/m - *C is used to store hot water and to keep it at 100*C at all times. To accomplish this, the outer sur- face of the container is wrapped with a 500-W electric strip heater and then insulated. The temperature of the inner surface of the container is observed to be nearly 100*C at all times. As- suming 10 percent of the heat generated in the heater is lost through the insulation, (a) express the differential equation and the boundary conditions for steady one-dimensional heat con- duction through the container, (£) obtain a relation for the vari- ation of temperature in the container material by solving the differential equation, and (c) evaluate the outer surface tem- perature of the container. Also determine how much water at 100%C this tank can supply steadily if the cold water enters at 20%. Insulation Spherical container FIGURE P2-70