Question

Constants A picture window has dimensions of 1.40 m×2.50 m and is made of glass 5.80 mm thick. On a winter day, the outside temperature is -15.0 ?C , while the inside temperature is a comfortable 20.5 ?C . a)At what rate is heat being lost through the window by conduction? b)At what rate would heat be lost through the window if you covered it with a 0.750 mm-thick layer of paper (thermal conductivity 0.0500 W/m?K)?

Answer #1

**a)
we know, thermal conductivity og window glass, k_glass = 0.96 W/(m
k )**

**Rate of heat being lost, dQ/dt = k*A*dT/L**

**= 0.96*1.4*2.5*(20.5 - (-15))/(5.8*10^-3)**

**= 2.06*10^4 W
<<<<<<<<------------Answer**

**b)**

**when paper layer is used,**

**the heat flux through the glass must be equal to the
heat flux through the paper at steady state.**

**k_glass*(T_interior - T_interface)/t_glass =
k_paper*(T_interfcae - T_out)/t_paper**

**0.96*(20.5 - T)/0.0058 = 0.05*(T -
(-15))/0.00075**

**==> T = 10.3 degrees celsius**

**so, the rate of heat lost, dQ/dt = k_glass*A*(T_interior
- T_interfcae)/t_glass**

**= 0.96*(20.5 - 10.3)*1.4*2.5/(5.8*10^-3)**

**= 5.90*10^3 W
<<<<<<<<--------------------------Answer**

A picture window has dimensions of 1.40 m×2.50 m and is made of
glass 5.10 mm thick. On a winter day, the outside temperature is
-15.0 ∘C , while the inside temperature is a comfortable 21.0 ∘C
.
Part B
At what rate would heat be lost through the window if you
covered it with a 0.750 mm-thick layer of paper (thermal
conductivity 0.0500 W/m⋅K)?
**I'm getting 6713 W but it saying im wrong. Please help

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