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?

Elements Of Electromagnetics

7th Edition

ISBN:9780190698614

Author:Sadiku, Matthew N. O.

Publisher:Sadiku, Matthew N. O.

ChapterMA: Math Assessment

Section: Chapter Questions

Problem 1.1MA

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1.51 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)¹³, 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
To = 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
0.85, what is the surface temperature of each
heater under steady-state conditions?
is &
=

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