1. Heat Loss Through a Wall

2. Through which of the following will there be the most heat transfer via conduction? a) solid iron b) wood c) liquid water d) vacuum

3. Through which of the following will there be the most heat transfer via radiation? a) solid iron b) wood c) liquid water d) vacuum

4. Through which of the following will there be the most heat transfer via convection? a) solid iron b) wood c) liquid water d) vacuum

5. Today’s PAL a)Consider a house window with a size of 1 meter by 1.5 meters and 0.75 cm thick. Inside the house it is 20 C and outside it is 10 C. Compare the heat loss through the window by both conduction and radiation. Which is greater? (Use k glass =1.1W/(mK) a)Imagine you replace the window with a double-pane window composed of two 0.25 cm thick windows with 0.25 cm of vacuum in between. Which is greater now?

6. Today’s PAL a)Conduction: dQ/dt=kADt/L = (1.1W/mK)(1.5m 2 )(10K)/(.00 75m)= 220 W Radiation: dQ/dt = sA(T 4 - T env 4 ) = (5.67X10- 8Wm2/K 4 )(1.5m 2 )(293K 4 - 283K 4 ) = 81W Conduction is larger a)There will be NO conduction thru vacuum, but it does not change the radiation. Radiation is larger now