If you’re in a pinch and don't have use of a recirculating chiller, it is possible to jury-rig one using a bucket of ice water and a pump. The cooling capacity you can achieve with such a setup would essentially depend on the size of the bucket and the amount of ice used.
Of course, there are pros and cons to using this method, which we’ll explore in this post. Aside from that, we’ll look at the types of common water pumps that might be suitable for such a setup.
Pros of a Jury-Rigged Chiller
The major benefit of using this method is that you don’t have to purchase a chiller, making it a far less expensive option.
It also enables you to reach lower temperatures than with a chiller when using water as the coolant liquid. Using water in a chiller, you generally shouldn’t set the temperature lower than 10°C, in order to prevent icing inside the reservoir. On the other hand, ice water can approach 0°C, giving you more flexibility.
Cons of a Jury-Rigged Chiller
One of the major cons of this method is that it’s very impractical to have to keep bags of ice at hand as they take up valuable freezer space. If you're buying bags of ice on a regular basis, it could become expensive quickly, making this a less viable long-term solution. You could make the ice yourself, but this would add another level of impracticality. Ice machines which can produce ice quickly and in large quantities, are often as expensive or more expensive than a chiller, so producing ice en masse isn’t an economical alternative.
Another drawback is that you can’t achieve very low temperatures (below 0°C). Most chillers have the option to use a coolant other than water and temperature settings down to -15°C, and some can operate at far lower temperatures. Although, it’s worth noting that you shouldn’t set the temperature of your chiller too low as its cooling capacity will decrease at lower temperatures.
A concern when using a jury-rigged chiller is the risk of losing your cooling capacity if you underestimate how much ice you need. If that happens, you would likely end up flooding your vacuum pump with condensation, as you will no longer be condensing the vapors in the chiller, and the vapors will instead condense in the vacuum pump once exposed to atmospheric pressure.
While a flooded vacuum pump is sometimes recoverable, it could be a very expensive mistake. What’s more, the loss of cooling capacity will happen without warning, as opposed to when using a chiller which would set off an alarm if it goes over-temperature.
Types of Pumps You Might Consider
If you do decide to go with this method, you’re going to need a pump with a high enough flow rate for your application. Flow rates for our chillers vary and can be lower than 1 gallon per minute (gpm) and up to 8 gpm. Larger rotary evaporation systems require higher flow rates.
Common types of inexpensive water pumps can give you similar pumping speeds. For example, this VicTsing submersible pump, intended for use with aquariums or fountains, can give you a rate of 1.3 gpm and costs under $10. Other similar pumps will give you higher flow rates; the Hydor Koralia Nano Aquarium Circulation Pump comes in three models with rates ranging from (4 gpm - 9.4 gpm).
You can even find a relatively inexpensive pond pump with rates over 90 gpm, but this would be far too high for a rotovap application.
Another option is a pool pump such as the Hayward CPVC Vertical Immersible Seal-Less Pump with a rate of 10 gpm, although this is many times the price of an aquarium pump.
Aside from the flow rate, you need to take into account the pump pressure. Too high of a pressure puts stress on the glass condenser coil, and can increase the risk that it shatters. Pump pressures should definitely be no higher than 100 psi, but pressures far lower (10 - 20 psi) are preferable in most circumstances.
There are certainly options available when it comes to setting up a jury-rigged chiller, and it could save you a lot of money. However, it’s an impractical long-term solution and won’t be suitable for applications in which you need to chill your coolant below 0°C.