Creating an efficient cooling system

[jvlim]

Hi. I have a closed container about 1.1L in volume and within this chamber is a continuous heat source. I am trying to regulate the container temperature without purging out or fanning the air contained inside the chamber out. I want the air within the chamber to circulate and I thought of creating a cooling system. I need help, I used copper coil 3/16 (size) about 5 feet long spiraled on top of this container (about 2 in high) and the 2 ends are connected to a pump continuously circulating water. I have reached a temperature about 45 degrees within the chamber and I can't seem to cool down the temperature inside the chamber. I need help in designing an efficient cooling system that can reduce the temperature inside to 30 degrees Celsius. Thanks

 

[voko]

What is the power of the internal heat source?

Secondly, your description of the cooling system suggests to me that the water circulates in a closed loop - how is it then cooled? Or is it taken from a bigger reservoir and dumped somewhere?

 

[jvlim]

Thanks for the response...The heat source is actually a sensor, which has a heater in it, it draws 150 mA from my 5V supply and a heating resistance which amounts to 33 ohms, so the power generated per sensors would be about 750 mW, I have 12 of them so the total amount of power is 9Watts. I am trying to a simple heat exchanger using the copper coil to absorb the heat and eventually to the water flowing through it, by absorbing the heat I was hoping to cool down the temperature inside the chamber...Thanks

 

[jvlim]

Sorry I forgot to mention that I have 2 (5V) voltage regulator inside the container converting a 9V DC input to 5V, generating 2[(9v-5v)*1A)] = 8W. So the total power dissipation inside the chamber is 8W + 9W = 17W

 

[voko]

Still not clear: is the water circuit open or closed? Put otherwise, is it fresh water entering the circuit, or is it recirculated?

 

[jvlim]

I used a water that is recirculating (recycled). The pump pushes the water from the container to the copper tubing then back to the its container. Its a loop, the pump gets the water from the container and the end of the copper tube goes back to the cntainer...Thanks

 

[Nugatory]

I used a water that is recirculating (recycled). The pump pushes the water from the container to the copper tubing then back to the its container. Its a loop, the pump gets the water from the container and the end of the copper tube goes back to the cntainer...Thanks

In that case, all you've done is construct an elaborate water heater. You're going to have to cool the water somehow, perhaps with something similar to an automobile radiator.

 

[voko]

Have you measured the temperature of the water tank when the temperature of the box stabilizes at 45 degrees? I suspect that with this setup you shifted the problem of cooling your box to the problem of cooling your water tank (unless the water tank is HUGE). How big is the tank, anyway? Are there any sort of cooling aids to the tank?

 

[jvlim]

I can't quite understand and no I haven't measured yet the temperature of the container when the temperature in the box stabilized at 45 deg C. The container is quite small its just 800 ml. How do you think I could remedy this? Thanks

 

[jvlim]

In that case, all you've done is construct an elaborate water heater. You're going to have to cool the water somehow, perhaps with something similar to an automobile radiator.

I tried adding Ice cubes in the water container but it also did not work, the chamber temperature did not decrease...Am I doing it right? Thanks

 

[voko]

I suggest you measure the temperature of the water when the temp. of the box stabilizes before we go further.

As I see it now, you may have two problems.

1. Poor thermal contact or otherwise deficient heat transfer from the box to the water.

2. Insufficient cooling of circulating water.

 

[jvlim]

Ok...thnx...I'll go back to this in a while. I would just want to ask. If I use a PC radiator (the one used in PC cooling) will this be a better solution. Thanks

 

[voko]

PC radiators are designed to be able to dump a lot more heat than your setup generates, so one should be able to do the job in principle, ON THE CONDITION that it must be thermally well coupled to the box. You may have seen that when they need to cool CPUs and GPUs, they essentially glue the chip to a radiator (or heat exchanger) with thermally conductive paste; that is an example of good thermal coupling.

 

[jvlim]

Ok thanks...

 

[CWatters]

Consider the heat path from source to room air. It sounds like it goes...

Sensors etc
Air gap
Walls of container
Cooling pipe
Cooling water
Heat radiator?
Room air

In which case the problem might be the air in the box. It might help to mount the heat sources on the inside walls of the box or stir the air in the box using a small fan.

 

[WhatIsGravity]

It sounds like your water cooling coil is outside the volume you want to regulate the temperature of? If so, it's probably not going to do much for cooling the inside temperature, especially with the (relatively) small watts of heat transfer you're talking about. What kind of thermal stability do you need?

Just a suggestion, but if you're project is rich, I'd suggest Peltier coolers and heat pipes, and if not, perhaps a tub of ice water?

 

[enorbet]

It sounds like your water cooling coil is outside the volume you want to regulate the temperature of? If so, it's probably not going to do much for cooling the inside temperature, especially with the (relatively) small watts of heat transfer you're talking about.

Agreed. Depending on the thermal characteristics of the materials from which the box is made, this is likely to be a weak link in the exchange process. It might warrant building the box quite literally from finned heat sinks for a cheap solution increasing the surface area of transfer.

Just a suggestion, but if you're project is rich, I'd suggest Peltier coolers and heat pipes, and if not, perhaps a tub of ice water?

I am very curious about your experience with Peltiers. In my experience Peltiers always have been something like Stirling Engines - look cool (pun kinda intended) on paper but in actual use, complicate every issue they deal with and perform poorly.

 

[WhatIsGravity]

My only real experience with Peltier coolers is that they can result in negative efficiencies. About 20% efficient across a few mm of heat transfer... it's hard to dump that much heat.

 

[AlephZero]

You said you want the inside temperature to be below 30C. What is the outside temperature? The smaller the temperature difference, the harder it will be to get rid of the heat without a something that acts as a refrigerator, i.e. some part of the cooling system is below room temperature.

Computer components will usualy work fine at temperatures up to at least 45C. The 20C difference between 45C and a room temperature of say 25C is four times bigger than the 5C difference between 30C and 25C, so the same cooling system would get rid of at least four times as much heat.