A chiller is an important part of many rotovap setups as it’s responsible for cooling the coolant that flows through the condenser. It’s possible to avoid purchasing a chiller, for example by using a dry ice condenser or juryrigging your own chiller, but in most cases, a suitable chiller will be needed.
When shopping for an appropriate chiller for your setup, the most important factors to consider are:
- Minimum temperature and cooling capacity
- Pump pressure
- Pump flow rate
In this post, we explain these factors in detail to help you find the right chiller for the job.
1. Minimum Temperature and Cooling Capacity
The minimum temperature that your chiller can maintain needs to be at or below the temperature at which you need to maintain your coolant for condensation to occur at an optimal rate. That temperature is determined by the boiling point of your solvent. The “rule of 20” is a good guide when deciding what temperature to set your chiller at. That is, your chiller should be able to provide a coolant stream that is at least 20°C below the boiling point of your solvent.
You may be tempted to set the temperature far below that to increase the speed of condensation. However, this can be counterproductive as cooling capacity decreases at lower temperatures. For example, a chiller with a cooling capacity of 500 W at 20°C will have a lower cooling capacity at 10°C.
When shopping for a chiller, a good rule of thumb is to check the heating capacity of your rotovap’s heating bath; if your chiller can’t match it in terms of cooling capacity at your desired setpoint temperature, it’s not going to be able to keep up. When looking at manufacturer specifications, you’ll often find multiple cooling capacities listed for a range of temperatures.
Manufacturer specifications for IKA’s R2 Basic chiller.
Setting your temperature too low could result in a cooling capacity that’s below the heating capacity of the bath. If your chiller is underpowered at its set temperature, your coolant won’t reach the desired temperature, and there will not be enough heat transfer to condense the evaporated solvent coming from the evaporating flask.
Instead, the vapor will flow into the vacuum pump, increasing wear and tear on the pump’s components and shortening its lifespan. It may even flood the pump, causing irreparable damage. Plus, if you have an over-temperature alarm on your chiller, setting too low a temperature may cause the alarm to sound and the chiller to shut off completely.
2. Pump Pressure
Another important factor to consider is the maximum pressure of your chiller pump. When subjected to too high a pressure, often in the range of 10–15 psi, the risk of the condenser breaking is increased.
Some manufacturers list maximum pressure in their specifications, but most don’t. As a very general guide, most centrifugal pumps have a maximum pressure of 10 psi making them suitable to use with regular glassware. On the other hand, positive displacement and turbine pumps, tend to have higher output pressures so using them may increase the risk of your glassware breaking.
The pump in the Ai C15 Compact Recirculating Chiller has a maximum pressure of 2.9 psi.
3. Pump Flow Rate
The flow rate of your chiller pump has an impact on the residence time of the coolant in the condenser. The lower the flow rate, the longer the coolant stays in the condenser warming up. As it warms, heat transfer from the evaporated solvent to the coolant is less efficient. In this case, there’s an increased risk that not all of your solvent vapor will be recondensed.
This isn’t a common issue as most chillers have ample flow rate relative to their cooling power, but it’s something to be aware of.
The pump flow rate of the H50-500 Water Chiller is 3.5 L/min.
