Use of open-circuit water for cooling of laboratory equipment (e.g., Liebig condensers) is depreciated, and will ultimately be prohibited at USC. The once-through flow of water from faucet to sink is unsustainable, a waste of a natural resource, and was/is the source of several serious floods (extending over multiple rooms and more than one floor) because water tubes had detached from condensers when water pressures had risen dramatically.
There are several alternatives to the open-circuit water for cooling purposes:
- A chiller unit can be employed, but is an expensive option, and really only needed if below-room-temperature cooling is required for an extended time period.
- Air-cooling; for example, air-cooled condensers such as the Heidolph™ Findenser™ can be used for refluxing and distillation. These work particularly well inside a fume hood due to the continuous draft. However, they are somewhat costly.
- Closed-circuit water cooling is easily improvised using an aquarium pump and bucket of water. This method has been successfully applied within certain USC Chemistry labs for over 15 years for all their refluxing and distillation needs, including reactions run under reflux for 24 hours or longer. NOTE: If water does leak, the biggest possible spill is one bucketful of water, which is unlikely to cause major damage or expense. See information below for setting up this cost-effective option.
Improvising a Closed-Circuit Cooling System
Below is a list of items needed:
- Medium-size Plastic Bucket
- Submersible Pump
- Use a low-power pump to reduce temperature rise on long operation and to ensure water pressure is minimal, reducing probability of leakage or tubes becoming detached.
- Recommend pump model Little Giant™ Model 1, Cat. #501003 (see the manufacturer’s web page). This has proven effective over more than 15 years use at USC for this purpose. The pump is widely available from pump vendors (e.g., this vendor web page).
- Power outlet fitted with a GFCI (Ground Fault Current Interrupter, also known as a residual current device). GFCIs protect against hazardous electrical shock in the event electrical insulation to water is compromised – visit the OSHA web page for more information on GFCIs.
- Some outlets have a GFCI built-in; look for the “test” and “reset” buttons.
- Alternatively, a portable GFCI can be plugged into a regular outlet.
- Flexible tubing; un-reinforced PVC is suitable (e.g., Tygon™)
- Suitable fitting to connect tubing to pump. The Little Giant™ Model 1 pump has a male ¼” NPT threaded outlet. Thus, a ¼” female NPT hose barb will be required; easily available from lab suppliers, general industrial vendors, or hardware stores.
- Apparatus to be cooled, e.g., Liebig condenser
- Hose Clamps. Given the minimal pressure and low flooding potential, hose clamps are optional if the tubing is a sufficiently tight push-fit on the condenser. However, a stainless steel hose clamp is recommended on the pump hose barb, as the tubing will be permanently attached at that point.
Set up the system as follows:
- Use a GFCI-protected electrical supply; see “Items Needed.”
- The submersible pump should ALWAYS be immersed in water before being switched on. Running a submersible pump for a short time dry will not cause any problems; however, if left running out of water the pump will eventually overheat and be permanently damaged (or even become a fire hazard).
- The water inlet should be at the lowest point on the condenser. This is because the water flow will reliably force bubbles downward. If water flow enters at the top of the condenser, this opens the possibility of the condenser becoming partly filled with air after a few hours.
- The bucket may be placed in any convenient position, and need not be directly adjacent to the system being cooled if this is impractical. However, if the bucket is more than about six feet lower than the condenser, the water flow may not begin spontaneously (due to the limited maximum head of small pumps). If the bucket is positioned too low, the flow can be started by briefly raising the bucket and will continue when the bucket is lowered again; however, in this condition the system may develop an air lock and eventually stop flowing.
- The higher the water level in the bucket, the larger the area for heat loss to the surroundings.
- If refluxing for an extended time (hours), the water will become warm (though not hot). Unless the solvent has an exceptionally low boiling point (e.g., diethyl ether, pentane), this has no adverse effects. If a very low boiling solvent must be refluxed for hours, the temperature rise can be minimized by:
- Positioning the bucket inside a fume hood
- Using a high water level in the bucket (to maximize the area for heat loss)
- Moderating the power input into the heating mantle (which will not change the temperature inside the flask, provided the solvent is still boiling)
- Using ice-slush as the initial bucket fill
- Adding ice periodically, if needed
- If run for an extended time, particularly if in a fume hood draft, check the water level at least daily and top up as needed
- Deionized water is not essential, but is recommended if an adequate supply is available as it cuts down on limescale over time.
