   Chapter 11, Problem 48P

Chapter
Section
Textbook Problem

A thermopane window consists of two glass panes, each 0.50 cm thick, with a 1.0-cm-thick sealed layer of air in between. (a) If the inside surface temperature is 23°C and the outside surface temperature is 0.0°C, determine the rate of energy transfer through 1.0 m2 of the window. (b) Compare your answer to (a) with the rate of energy transfer through 1.0 m2 of a single 1.0-cm-thick pane of glass. Disregard surface air layers.

(a)

To determine
The rate of energy transfer through the window.

Explanation

Given info: Thickness of the glass plane is 0.50 cm thick, 1.0 cm thick sealed layer of air in between, area of the window through which the energy gets transferred is 1.0m2 , Inside temperature is 23°C and outside temperature is 0.0°C .

Air trapped between two glass panes of the thermo pane. The thickness and the thermal conductivity of the glass pane and air differ.

Formula to calculate R factor for glass pane is,

Rpane=2(Lpanekpane)

• Rpane is the R factor for pane,
• Lpane is the thickness of the glass pane,
• kpane is the thermal conductivity of the glass pane,

2 indicates glass pane on either side of the trapped air.

Formula to calculate R factor for air is,

Rair=(Lairkair)

• Rair is the R factor for air,
• Lair is the thickness of the trapped air,
• kair is the thermal conductivity of the trapped air,

The R factor for the thermo pane is,

R=2(Lpanekpane)+(Lairkair)                       (I)

Formula to determine the rate of energy transferred through 1.0m2 of the window is,

P=A(ΔT)R                                       (II)

• P is the rate of energy transfer,
• A is the area through which is energy transferred,
• ΔT is the difference in temperature,

Use equation (I) to rewrite equation (II)

(b)

To determine
The comparison of the rate of energy transfer through double walled thermo pane and single thick pane of glass.

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