Heat Transfer from stainless steel tank of waters
Heat Transfer from stainless steel tank of waters
(OP)
I am using Liquid Cooled Variable Frequency Drives and am wondering if it would be possible to cool the drives sufficiently using a large stainless steel tank full of water and then a pump to cycle water through the VFDs. The ambient temperature will be a constant 30C. I am not really familiar with this type of application, being a power electronics guy, and am wondering what formulas I need to consider in sizing the tank for heat transfer to the ambient air.





RE: Heat Transfer from stainless steel tank of waters
Heat has to get out of the tank faster than your drives put heat into the tank. If not the water in the tank gets hotter and hotter.
If your drives are off for a long time each day then maybe the water will be cool by morning. Or maybe not.
And by the way, lots of nasty things like Legionella like to live in big tanks of warm water.
All in all, you'll be much better off with a properly sized water-to-air heat exchanger or cooling tower.
RE: Heat Transfer from stainless steel tank of waters
We would determine the size of the tank based on how large it needs to be to reject 36,230 Btu/hr.
The environment we are working in is an underground mine where water to air heat exchangers seem to not stand up to the dust.
I am wondering if this might be a simpler solution.ie, a big tank recirculating water as opposed to a fluid cooler.
RE: Heat Transfer from stainless steel tank of waters
What is the the warmest inlet water that the drives will be happy with?
Heat loss calculator here
http://www
RE: Heat Transfer from stainless steel tank of waters
losses = 7.9kw
flow rate = minimum= 20L/60s, maximum 40L/60s
nominal flow rate = 25L/60s
pressure drop across drive = 1.96bar @ 40L/60s, 0.43bar @ 20L/min
ambient temperature 30C
how big would the tank need to be, assuming it was constructed of stainless steel, and filled with water, in order to never allow the rejected heat by the drives to raise the temperature of the tank above 40C.
RE: Heat Transfer from stainless steel tank of waters
RE: Heat Transfer from stainless steel tank of waters
how long will they be off, allowing the water to cool down again ?
RE: Heat Transfer from stainless steel tank of waters
The drives will be run continuously for 6 hours, and then given 2 hour breaks.
RE: Heat Transfer from stainless steel tank of waters
If the water in the tank is at 40C you'll get about 6 watts per square foot of tank surface.
7900 W/6W/ft^2 = 1316 square feet of tank surface needed.
For a cube that's almost 15 feet each edge.
Probably bigger than you want?
RE: Heat Transfer from stainless steel tank of waters
RE: Heat Transfer from stainless steel tank of waters
but how long would it take for the water to heat up to 40deg ?
Assume 10' cube of water, 5 faces radiating, 1 VFD ...
After 1hr you've spat out 8 kW.hrs, this'll increase the water temperature, so now the water can radiate heat to the outside (30deg air).
In the second hour the energy input to the water is (8-radiation heat calc'd above) kW.hrs ...
Assumes a recirculation fan inside the water, to distribute the heat.
hours 7 and 8 of the cycle radiate heat only, dropping the temp of the water. back to 30deg ??
RE: Heat Transfer from stainless steel tank of waters
I didn't count pumping heat, so make it 7 just to be safe.
I'm thinking this is a non-starter. But hey, it's your hole in the ground.
RE: Heat Transfer from stainless steel tank of waters
RE: Heat Transfer from stainless steel tank of waters
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RE: Heat Transfer from stainless steel tank of waters
RE: Heat Transfer from stainless steel tank of waters
However, tank size is a bit misleading, since the critical component is the heat transfer coefficient, which is proportional to the air cooling efficiency divided by the area. We've used liquid to air heat exchangers that dump 500W on a 5ºC delta at 1 gpm liquid flow and 90 CFM air flow in about 1/2 cubic ft volume. Assuming 10kW load, then you'd need something like 2000 CFM fresh air flow. In a mine, that's probably a nontrivial task.
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RE: Heat Transfer from stainless steel tank of waters
Would a geothermal cooling design be an option? (Of course that all depends on mine depth)
RE: Heat Transfer from stainless steel tank of waters
In undeground coal mines MSHA(Mine Sasfety and Health Act) requires minimum of 3,000cfm airflow sweepinig the mine face in front of the miner to deal with methane evolving and respirable dust. So maybe the wind chill is available?
RE: Heat Transfer from stainless steel tank of waters
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RE: Heat Transfer from stainless steel tank of waters
This is also a good candidate for running a thermal FEA/CFD analysis to optimize your design and reduce the total flow of coolant, etc to reach your target temperature.
James Spisich
Design Engineer, CSWP
RE: Heat Transfer from stainless steel tank of waters
Or, similar to James' suggestion, make a cooling circuit with a pump and above ground heat exchanger.
RE: Heat Transfer from stainless steel tank of waters
Ted