Three electric resistance heaters of length L = 250 mm and diameter D = 25 mm are submerged in a 10-gal tank of water, which is initially at 295 K. The water may be assumed to have a density and specific heat of p = 990 kg/m³ and c = 4180 J/kg K. (a) If the heaters are activated, each dissipating 91 500 W, estimate the time required to bring the water to a temperature of 335 K. = (b) If the natural convection coefficient is given by an expression of the form h = 370 (T, - T)¹/³, where T, and T are temperatures of the heater surface and water, respectively, what is the temperature of each heater shortly after activation and just before deactivation? Units of h and (T, - T) are W/m² · K and K, respectively. (c) If the heaters are inadvertently activated when the tank is empty, the natural convection coefficient associated with heat transfer to the ambient air at T = 300 K may be approximated as h = 0.70 (T. -T.)¹/3. If the temperature of the tank walls is also 300 K and the emissivity of the heater surface is & = 0.85, what is the surface temperature of each heater under steady-state conditions?

Three electric resistance heaters of length L = 250 mm and diameter D = 25 mm are submerged in a 10-gal tank of water, which is initially at 295 K. The water may be assumed to have a density and specific heat of p = 990 kg/m³ and c = 4180 J/kg K. (a) If the heaters are activated, each dissipating 91 500 W, estimate the time required to bring the water to a temperature of 335 K. = (b) If the natural convection coefficient is given by an expression of the form h = 370 (T, - T)¹/³, where T, and T are temperatures of the heater surface and water, respectively, what is the temperature of each heater shortly after activation and just before deactivation? Units of h and (T, - T) are W/m² · K and K, respectively. (c) If the heaters are inadvertently activated when the tank is empty, the natural convection coefficient associated with heat transfer to the ambient air at T = 300 K may be approximated as h = 0.70 (T. -T.)¹/3. If the temperature of the tank walls is also 300 K and the emissivity of the heater surface is & = 0.85, what is the surface temperature of each heater under steady-state conditions?

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.

Chapter2: Steady Heat Conduction

Section: Chapter Questions

Problem 2.24P

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