View Full Version : Heat Transfer Exam Question
alexdouglas1969
24-03-2007, 03:22 PM
Exam question:
Heat transfer takes place whenever there is a:
a Pressure difference
b Temperature difference
c Specific heat difference
d Latent heat difference
Any thoughts on this question would be very welcome, thanks.
Thanks
:)
Brian_UK
24-03-2007, 07:25 PM
The answer has to be 'B' surely.
It doesn't matter what the type of heat is it's the fact that there is a difference that makes the transfer occur.
alexdouglas1969
24-03-2007, 11:13 PM
Well our tutor would agree with you but thinking of the psychrometric chart - I would say 'C' is more correct - after all, temperature is not heat...
Anyone else got an opinion?
Brian_UK
24-03-2007, 11:18 PM
OK, I'll pose this question...
How do you quantify the difference between two items of different latent heat?
(Latent Heat is defined as the heat (http://www.taftan.com/thermodynamics/HEAT.HTM) which flows to or from a material without a change to temperature. The heat will only change the structure or phase of the material. e.g. melting or boiling of pure materials)
(The amount of heat transferred delta Q is proportional to the temperature difference delta T between the objects and the heat capacity c of the object.)
The answer is "B" as you need a Delta T for either specific heat or latent heat to be absorbed or given up.
So I agree with Brian on this one, without this principle which is the second Law of Thermodynamics we all would be out of a job.
Ian
alexdouglas1969
25-03-2007, 02:21 PM
Have given this some more thought now - obviously not C as specific heat is amount of energy per unit mass to raise by one degree (or temperature unit) so C just does not make sense - I agree B is correct. Thanks for the help, I was stuck on the definition of temperature - for example the same level of heat can be given by different temperature scales, therefore a difference in temperature does not necessarily cause flow of energy... what a muddle... thanks... !!!11
frank
25-03-2007, 04:46 PM
The temperature scale (Fahrenheit, Celcius, Rankine, Kelvin) is a MEASURE of temperature (heat energy) from a base point, whereas Specific heat or Latent heat are a measure of heat carrying capacity.
Pressure has nothing to do with temperature in this instance.
Frank
specific heat is a measure of heat carrying capacity whereas latent heat is the amount of heat required to change phase so not really heat carrying potential, or am I being a tad pedantic.
Ian
frank
26-03-2007, 09:11 PM
Hi Ian
Nit Picking, hmm, maybe. Seems we've covered it now though :D
You know what I was trying to say ;)
SURESH YADAV
13-12-2008, 11:51 AM
Heat tranfer depends only where, there is difference in temprature.......
There is no transfer if there is no temperature difference.
The answer is B.
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