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I have a tank of oil which I plan to heat 24/7 with constant 15 kW. I want to dissipate this energy using water as a coolant. I have the outside unit of an out of order split type air conditioner that could be used as a radiator to heat the environment.

Can I dissipate this much energy on such a radiator?

How should I exchange heat between the oil and the water? I thought of a heat exchanger used in floor heating. I saw some rated 70 kW and above. But I can't imagine how it works seeing it's small size.

The tank is about (1*1*1) m, filled with oil. I would use only as much oil as needed to immerse the electronics I want to keep cool at <50 °C. The energy to be dissipated is constant 15 kW. The A/C radiator with a fan is installed ~5 m above ground, the tank being on the ground. I want cooling to work also in the hottest summer, topping at about 40 °C on the hottest days of July. The system must be closed, because I don't have infinite amount of water.

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    $\begingroup$ I schematic drawing would help here. Also, with no idea of the sizes of things you're working with, we have no real way to help you with your problem. $\endgroup$
    – grfrazee
    Commented Mar 9, 2016 at 15:12
  • $\begingroup$ A power rating is next to useless. What we need to know is how much heat (energy) is in the oil, and how fast you want to get rid of it. One of the simplest things to do is to lower a coil of copper tubing into the oil and run cold water through it. Does the cooling system need to be closed, or could you just run the hot water into a drain somewhere? $\endgroup$
    – Dave Tweed
    Commented Mar 9, 2016 at 15:49
  • $\begingroup$ Is there any reason you can't circulate the oil and cool that with a radiator ? $\endgroup$
    – Chris Johns
    Commented Mar 9, 2016 at 19:48
  • $\begingroup$ It is expensive, so I try to use as little as possible. $\endgroup$
    – Nandor
    Commented Mar 9, 2016 at 19:53
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    $\begingroup$ This question is really confusing. Where is the 15 kW of heat coming from? Why are you heating the oil if you want to use it to keep something cool? Are you trying to use the oil to cool 15 kW of equipment and now you're wondering how to get the heat out of the oil? How does the "out of order air conditioner" figure into this? Why do you want to use water as a second transfer medium if the ultimate goal is to put the heat into the air? What is so special about the oil that you have a cubic meter of it, but only want to use "as much oil as needed"? $\endgroup$
    – Dave Tweed
    Commented Mar 10, 2016 at 2:48

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The problem with using oil to cool the plant and the cooling the oil with a heat exchanger is that you are introducing a bottleneck into your system in that you are relying on convection to transfer heat from the hot surface to the heat exchanger through the oil.

Apart from anything else this greatly complicates the analysis and control of the problem. A big risk is that the average temperature of the oil could be within acceptable limits but you start to vapourise it at the hot surface which drastically drops the heat transfer rate and is difficult to detect or do anything about.

In this sort of context cost effectiveness can be as much about a simple and conservative solution which can be made to work with a fairly modest design input and this approach often ends up cheaper in the end than something which takes a lot of development and modelling to get working effectively.

Using forced convection by circulating the oil itself greatly simplifies the problem and gives you a lot more direct control over the rate of heat transfer simply by increasing the flow rate.

As you already have a cubic foot of oil in the tank the extra you would need to fill piping and a radiator is not huge, bearing in mind also that water used for cooling usually requires additives to prevent corrosion etc which in themselves may not be cheap.

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