(Thermal Conductivity Question) Need Help

In summary, the first question involves finding the heat lost in a glass window with given dimensions and thermal conductivity. The second question asks for the temperature of the outside surface of the same window when used in a room with specified temperatures and heat transfer coefficients. Both questions can be solved using the formula dQ/dt = kA(delta T)/x, where dQ/dt is the heat flow, k is the thermal conductivity, A is the area, delta T is the difference in temperatures, and x is the thickness of the glass.
  • #1
MoZeS
1
0

Homework Statement



1) The inner and outer surfaces of a glass window of area 2.5 m2 are at 22 ºC and 0 ºC respectively. What is the heat lost in 1 second if the glass is 5mm thick and has a thermal conductivity of 1.1 Wm^-1K^-1 ?

2) The same sheet of glass as described in the [above Question] is used as a window in a room at 23 ºC when the general outside temperature is -14 ºC. If the inner and outer heat transfer coefficients are both 17.0 Wm^-2K^-1, what is the temperature of the outside surface of the glass?

Can Anyone help me solve these two questions, Please? (with the formula used)

:)
 
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  • #2
Hi MoZeS, welcome to PF.

You have given the thermal conductivity and note that there is a unit: W/(m K)
So what does the thermal conductivity express?
 
  • #3
dQ/dt=kA(d theta/dx)
given,A=2.5m^2, x=5mm, k=1.1 Wm^-1K^-1
dQ/dt=kA(final temp-initial temp.)/x
=(1.1)(2.5)(22)/(5x10^-3)
=1.21x10^4W
Q=1.21x10^4J since, Q/t=1.21x10^4W
Q=1.21x10^4W/1s
therefore W/s = J
part 2, try on ur own ...
is same formulae...
dQ/dt=1.21x10^4W
so, subst. in the equation and find the final temp.
 
  • #4
Welcome to PF lyming.
Please note that we don't give out complete solutions here at PF. Moreover, I don't really see what formula you are using (what is theta?) and how you are getting Q from dQ/dt. Also, there must be some mathematical errors, because I happen to know that W = J / s while you write W/s = J.

Finally, I think no looked up formula is needed at all and one can infer the answer by simply looking at the units of the given conductivity.
 
  • #5
I see this one's been dead a while, but if someone want to help me out here...
I get the first part, but I'm struggling on the second one.
Do I still need to use the 1 second? And how to do I change the heat flow to temperature? Or is there a delta Temp used to solve this part?
 

FAQ: (Thermal Conductivity Question) Need Help

What is thermal conductivity?

Thermal conductivity is the property that describes how well a material can transfer heat. It is measured in units of watts per meter per Kelvin (W/mK).

How is thermal conductivity measured?

Thermal conductivity is typically measured using a device called a thermal conductivity meter. This device uses a heat source and sensors to measure the rate at which heat is transferred through a material.

What factors affect thermal conductivity?

The main factors that affect thermal conductivity are the type of material, its density, and its temperature. Materials with high density and low thermal resistance tend to have higher thermal conductivity.

Why is thermal conductivity important?

Thermal conductivity is important in many fields of science and engineering, as it affects the efficiency of heat transfer and can impact the performance of materials and devices. It is also crucial in understanding the behavior of materials under different temperature conditions.

How can I improve thermal conductivity?

There are several ways to improve thermal conductivity, such as using materials with high thermal conductivity, increasing the density of the material, or using thermal conductive coatings. In some cases, the shape and design of the material can also affect its thermal conductivity.

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