A common annoyance in cars in winter months is the formation of fog on the glass surfaces that blocks the view. A practical way of solving this problem is to blow hot air or to attach electric resistance heaters to the inner surfaces. Consider the rear window of a car that consists of a 0.4-cm-thick glass (k = 0.84 W/mK and α = 0.39 × 10-6 m²/s). Strip heater wires of negligible thickness are attached to the inner surface of the glass, 4 cm apart. Each wire generates heat at a rate of 25 W/m length. Initially the entire car, including its windows, is at the outdoor temperature of To = 3°C. The heat transfer coefficients at the inner and outer surfaces of the glass can be taken to be hi = 6 and ho = 20 W/m² K, respectively. Using the explicit finite difference method with a mesh size of Ax = 0.2 cm along the thickness and Ay = 1 cm in the direction normal to the heater wires, determine the temperature distribution throughout the glass 15 min after the strip heaters are turned on. Also, determine the temperature distribution when steady conditions are reached (5th Ed, prob. 5.116). - Thermal symmetry line Inner Outer surface surface Glass Heater 25 W/m -0.2 cm 1 cm -Thermal symmetry line

Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)
8th Edition
ISBN:9781305387102
Author:Kreith, Frank; Manglik, Raj M.
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Chapter1: Basic Modes Of Heat Transfer
Section: Chapter Questions
Problem 1.48P: A horizontal, 3-mm-thick flat-copper plate, 1-m long and 0.5-m wide, is exposed in air at 27C to...
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A common annoyance in cars in winter months is the formation of fog on the
glass surfaces that blocks the view. A practical way of solving this problem
is to blow hot air or to attach electric resistance heaters to the inner
surfaces. Consider the rear window of a car that consists of a 0.4-cm-thick
glass (k = 0.84 W/mK and α = 0.39 × 10-6 m²/s). Strip heater wires of
negligible thickness are attached to the inner surface of the glass, 4 cm
apart. Each wire generates heat at a rate of 25 W/m length. Initially the
entire car, including its windows, is at the outdoor temperature of To =
3°C. The heat transfer coefficients at the inner and outer surfaces of the
glass can be taken to be hi = 6 and ho = 20 W/m² K, respectively. Using the
explicit finite difference method with a mesh size of Ax = 0.2 cm along the
thickness and Ay = 1 cm in the direction normal to the heater wires,
determine the temperature distribution throughout the glass 15 min after the
strip heaters are turned on. Also, determine the temperature distribution
when steady conditions are reached (5th Ed, prob. 5.116).
-
Transcribed Image Text:A common annoyance in cars in winter months is the formation of fog on the glass surfaces that blocks the view. A practical way of solving this problem is to blow hot air or to attach electric resistance heaters to the inner surfaces. Consider the rear window of a car that consists of a 0.4-cm-thick glass (k = 0.84 W/mK and α = 0.39 × 10-6 m²/s). Strip heater wires of negligible thickness are attached to the inner surface of the glass, 4 cm apart. Each wire generates heat at a rate of 25 W/m length. Initially the entire car, including its windows, is at the outdoor temperature of To = 3°C. The heat transfer coefficients at the inner and outer surfaces of the glass can be taken to be hi = 6 and ho = 20 W/m² K, respectively. Using the explicit finite difference method with a mesh size of Ax = 0.2 cm along the thickness and Ay = 1 cm in the direction normal to the heater wires, determine the temperature distribution throughout the glass 15 min after the strip heaters are turned on. Also, determine the temperature distribution when steady conditions are reached (5th Ed, prob. 5.116). -
Thermal
symmetry line
Inner
Outer
surface
surface
Glass
Heater
25 W/m
-0.2 cm
1 cm
-Thermal
symmetry line
Transcribed Image Text:Thermal symmetry line Inner Outer surface surface Glass Heater 25 W/m -0.2 cm 1 cm -Thermal symmetry line
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