Question

A single thickness glass window on a house actually has layers of stagnant air on its two surfaces. If it did not, how much heat would flow out of a `80` `cmxx40` `cmxx3` `mm` window each hour on a day when outside temperature=`0^oC` and inside=`18^oC`?

Answer 1

`1728 kcal`

Explanation:

We know that heat flows from higher temperature to lower temperature. Heat can be transferred from one location to other by: one or more modes out of Conduction, Convection and Radiation.

In the given problem heat flows from hot face of the glass window pane to the cold its face. The heat flow is assumed exclusively by conduction mode. Now Quantity of Heat `Q` transferred by Conduction is given by

`Q=(KA(T_(Hot)-T_(Cold))t)/d`
Where, `K` is the thermal conductivity of the material,
`A` is area of cross section,
`T_(Hot)` is the higher temperature,
`T_(Cold)` is the cooler temperature,
`t` time for which heat transfer takes place,
`d` is the thickness of the material.
Thermal conductivity of Glass has not been given, it is assumed to be `0.0025(calcdot s^-1)//(cm^2 "^@C//cm)`

Inserting given values:
`Q=(0.0025xx(80xx40)(18-0)xx3600)/0.3`
`=(0.0025xx3200xx18xx3600)/0.3`
`=1728 kcal`