4 The rear window of an automobile is defogged by attach- ing a thin, transparent, film-type heating element to its inner surface. By electrically heating this element, a uni- form heat flux may be established at the inner surface. (a) For 4-mm-thick window glass, determine the electrical power required per unit window area to maintain an inner surface temperature of 15°C when the interior air temperature and convection coefficient are T = 25°C and h₁ = 10 W/m². K, while the exterior (ambient) air temperature and convection coefficient are T 00,0 -10°C℃ and h = 65 W/m².K. = (b) In practice T, and h, vary according to weather conditions and car speed. For values of h, 2, 20, 65, and 100 W/m².K, determine and plot the electrical power requirement as a function of T for -30 ≤T≤ 0°C. From your results, what can you conclude about the need for heater operation at low values of h? How is this conclusion affected by the value of T? If h« V", where Vis the vehicle speed and n is a positive exponent, how does the vehicle speed affect the need for heater operation?
4 The rear window of an automobile is defogged by attach- ing a thin, transparent, film-type heating element to its inner surface. By electrically heating this element, a uni- form heat flux may be established at the inner surface. (a) For 4-mm-thick window glass, determine the electrical power required per unit window area to maintain an inner surface temperature of 15°C when the interior air temperature and convection coefficient are T = 25°C and h₁ = 10 W/m². K, while the exterior (ambient) air temperature and convection coefficient are T 00,0 -10°C℃ and h = 65 W/m².K. = (b) In practice T, and h, vary according to weather conditions and car speed. For values of h, 2, 20, 65, and 100 W/m².K, determine and plot the electrical power requirement as a function of T for -30 ≤T≤ 0°C. From your results, what can you conclude about the need for heater operation at low values of h? How is this conclusion affected by the value of T? If h« V", where Vis the vehicle speed and n is a positive exponent, how does the vehicle speed affect the need for heater operation?
Introduction to Chemical Engineering Thermodynamics
8th Edition
ISBN:9781259696527
Author:J.M. Smith Termodinamica en ingenieria quimica, Hendrick C Van Ness, Michael Abbott, Mark Swihart
Publisher:J.M. Smith Termodinamica en ingenieria quimica, Hendrick C Van Ness, Michael Abbott, Mark Swihart
Chapter1: Introduction
Section: Chapter Questions
Problem 1.1P
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Transcribed Image Text:4 The rear window of an automobile is defogged by attach-
ing a thin, transparent, film-type heating element to its
inner surface. By electrically heating this element, a uni-
form heat flux may be established at the inner surface.
(a) For 4-mm-thick window glass, determine the electrical
power required per unit window area to maintain an
inner surface temperature of 15°C when the interior air
temperature and convection coefficient are Tooi = 25°C
and h₁ = 10 W/m².K, while the exterior (ambient) air
temperature and convection coefficient are To
-10°C and h = 65 W/m².K.
=
00.00
(b) In practice T and h, vary according to weather
conditions and car speed. For values of h, = 2, 20,
65, and 100 W/m² K, determine and plot the
electrical power requirement as a function of To for
-30 ≤ T ≤ 0°C. From your results, what can you
conclude about the need for heater operation at low
values of h? How is this conclusion affected by the
value of T? If hx V", where V is the vehicle speed
and n is a positive exponent, how does the vehicle
speed affect the need for heater operation?
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