How do I find the right fluid cooler?

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You didn't mention your location, but I'll assume U.S. Your process is being cooled by this Dowtherm A, correct? It's a shame to throw this much heat away at this high temperature instead of putting it to good use. But, if you just want to cool it, I think an air-cooled heat exchanger would be best.

Here's a couple of references (usual disclaimers, you can Google air-cooled heat exchanger):

Hudson Products is an established company. Their site has some good info.

Thermal Transfer Systems

Make sure material of construction and the physical design is compatible with Dowtherm A (Dow should be good reference) at this temperature. This would probably need to be installed outdoors. Control can be a challenge. Some options are variable speed or pitch fan, louvers, fluid bypassing, or a combination of these. You aldo have to consider the prevention of over-cooling on cold days - from the information you gave, there seems to be a case for the return oil to already be at 300 degrees where no heat needs to be removed. On a cool day, natural draft can remove a lot of heat even with the fan off so shutters may be required.

If you aren't comfortable with this, I'd recommend hiring someone more qualified to design your system.

Thank you bigg, Yes it is in the US, it is a outside installation,this is what I have been looking for as we cannot use a heat exchanger, My system is not being cooled by dowtherm , but does have optimum operation at 250 to 300 degrees, I have researched the dowtherm and it properties, I have figured in the system to account for temp changes, just having a tough time finding components to operate at the higher temps to controll this application, We are filtering and removing moisture from the dowtherm. We Know our systems work, but we also know these temps at their max are a bit higher than we are used to. I figured if we could cool it to our specs and have a cooling system that is variable and controllable through our electronics we could achieve our goal. Thank you again

If your goal is to clean/filter the fluid and return it to the system, I would suggest using a regenerative heat exchanger and a smaller non-regenerative (something like what bigg already gave). This would prevent wasting all of the heat.

Based on a napkin calc (and if my numbers are way off, then feel free to correct), but based on simply rejecting all the heat to atm and assuming that the big process (whatever it is) has to add that heat back and your system runs 24/7, it will have an operational cost of roughly $70k/yr in reheating the fluid. Even if you were to overcome the temperature problems, spending that kind of money to filter a fluid seems like a HUGE waste. If the above is correct, then I can't see this being seen as a successful project unless you drop that cost.

(assumptions of 275 gph, average specific heat of 0.5 BTU/lbm-F, density of 55 lbm/cf, temperature change of 200F, and $0.10/KW-hr to reheat)

Why does the fluid exceed the desired temperature range?

Maybe the heating process needs a better control arrangement, then you do not need to bother with a heat exchanger?

What about simply passing your fluid through radiators with temperature controlled fans blowing across them - simple, and you have a large temp differential to ambient.

Admittedly the radiators would have to be rather special to cope with 650 degrees F, but doable.

Apologies to all Americans, I, like most Brits think in ºC these days. Your biggest problem is the large variation in input temperature. Even with VSDs I doubt that there is a standard air cooled unit on the market that can cope efficiently with a Δt varying between 0 and 150ºC. The turn down ratios are not that high on standard units. I would suggest two coolers what can be run in series to cope when the Δt is high. Either unit could be bypassed when the Δt is low to balance the duty, and this also provides a reduced capacity backup when one unit is down for servicing. Specifying a larger special unit to cope with your parameters will cost nearly as much as two smaller standard units and will cost more in electricity to run, have a shorter servicing interval, and use more costly spares, all without the backup feature.

Good idea - Or simply install an over sized fluid cooler (rather than the expense and additional piping costs for two in series) with a receiver and additional passes in a single fluid cooler and a "head Master" or temperature controlled bypass valve that would allow the "received" fluid to then pass through the additional circuits in the cooler to accomplish the proper TD's for the equipment.

Caught the post late last night and was too tired to respond then.

Chatioc's response is your best value (matched with Bigg's). I suggest a plate and frame style HX unit- several good manufacturers out there- that will give you a 2F approach so your air-cooled unit will only have to throw away (or add) less than 1% of the energy.

Those pressures are well within their capacity.

If you do not need to heat the DowthermA but are using it as a "direct" cooling medium, you can still use the P&F units with water to make steam (or- better yet, High Temp Hot Water) that you might need somewhere else in your processes.

Good luck.

The problem with water cooled HX at the proposed temperatures is scale formation. To avoid sccale requires very careful control of the water quality and chemistry.

The simple solution is air cooled. Unless you have an intermittent user for the waste heat near this operation.

ditto your comment on scale formation. I've seen exactly that when cooling hot oil with cooling water. Even if your water outlet temp is below 100 degF or so, there will be hot spots where scale will form. Unless you're using boiler quality water.