heat pipes measuring heat transfer

[will123123]

Can anyone advise on a suitable experimental method for measuring the heat transfer of a particular heat pipe at different temperatures.
The best I can come up with at the moment is to locate heaters at one end, having the other end in a liquid reservoir and insulate the whole system. Then monitor the heat transfer by the temperature increase of the reservoir at the cool end.
I appreciate the manufacturer of the heat pipe can give me some data,but unfortunately I would like the information for a range of temperatures at both the hot and cool ends.

 

[MintJulep]

The problem with your method is that the temperatures will not be constant.

You need to have a system where you can control the temperatures of both ends.

If all else is well insulated then the power input to the hot end that is necessary to maintain a constant temperature will be equal to the heat transfer to the cold end.

 

[IRstuff]

Seems like it would be easier to use a solid thermal conductor, rather than water. Insulate, hold the exposed ends at fixed temperatures, and measure the interface temperature. Assuming you know the thermal conductivity of the solid conductor, you can determine the heat flow, and therefore determine the apparent thermal conductivity of the heatpipe.

TTFN
faq731-376

 

[Compositepro]

There is also the variable of heat transfer coefficient for getting heat in and out of the pipe.

You could just plot the temperatures of the (stirred) hot and cold tanks with time after you have shut-off the heating or cooling source. The rate of change of temperature (the slope of the curve)times the heat capacity of the tank is the heat flux. You can subtract-out the insulation heat losses by doing a run without the heat pipe installed.

 

[jharris3]

Look up - Modeling, Designing, Fabricating, and Testing of Channel Panel Flat Plate Heat Pipes

http://digitalcommons.usu.edu/etd/21/

Its a master's thesis that, aside from its own information, has some very good heat pipe references where various ways of conducting experiments was performed.

As for your problem, I have some questions.

Have you used any equations to predict the various operating limits? (ie sonic, entrainment, viscous, boiling, capillary)

Have you asked the manufacturer first? They sometimes have extensive performance information available in a format that is what you really need?

Do you need temperature ranges for the evaporator (heated end) or do you need power input/heat flux?

Are you considering whether or not the pipe works with or against gravity?

How big is the pipe? Is there enough room around it to have all the aparatus?

How much money do you want to spend? An accurate and credible setup would require some sophisticated control as MintJulep suggests. (and do you still think you will have more & better information than the manufacturer? They have to guarantee this stuff. If the liturature isn't on their website they can often provide the information in short order.)

MintJulep & IRstuff have some good suggestions. Compositepro's suggestion will work if you want to include the startup and shutdown response of the pipe.

Enjoy! you are going to have fun with this!

 

[will123123]

Thank you for the replies - in answer to some of the questions.

I agree with MintJulep that ideally controlling heat input and cooling is the best way to characterise the heat pipes. However, we are more of a design company with only limited testing facilities and with limited budget. I am hoping to get at least comparative data of heat transfer between different temperature conditions.

The manufacturer has good data for heat transfer, for vertical and horizontal positions, but only for single evaporator and condenser conditions. You would like to get some data for a range of temperatures.

The particular pipe I am working with at the moment is 30mm by 300mm by 2.5mm.

The idea proposed by compositepro is something that we can carry out and sound as if it would work quite well

 

[jharris3]

Ok,

Insulate between your chosen evaporator and condensor sections very well so that you eliminate the adiabatic section as part of the condenser.
Then set up your condenser section with a block of aluminum or copper that you can clamp down well. This will keep the contact resistence between your pipe and cooler low which turns out to affect overall performance quite a bit.
Make up some kind of "hopper" - a slide out of some small angle or something or maybe even some modified kitchen items - and at this point you can use ice blocks or crushed ice in the hopper to feed your cooler from the top.

From there I think you get the idea and can work out something for the bottom - the goal is to keep the ice in firm contact with the cooling blocks at all times. The temperature should stay within a good statistical distance from 0C. Blocks give you something firm to push against.

Another idea is to use one of those portable refrigerator/coolers that have a peltier plate. Then you might be able to control the temperature if you work up some electronics too.

Set your evaporator to specific power densities so that you can understand what your Overall Heat Transfer Coefficient is more easily (everything will already be in square meters)

Change the size of your condenser to find out different ways you can use the pipe at each power density.

This should be a cheap way to get what you want with a little more precision.