Refrigerated and heated water baths are designed for controlling temperature. They are used for warming or cooling liquid samples to sustain or impede reactions. In addition to heating and cooling samples, some varieties are available with built-in shakers to agitate samples. Proper water bath design includes a number of physical and mechanical features, and the electronic temperature controls. Conventional water bath designs use separate heating and cooling devices immersed in the bath liquid, although other systemic styles are available. To maintain an even temperature, the bath fluid must be stirred vigorously. However this must be accomplished without the formation of air bubbles or vortices in the fluid, which could interrupt the temperature transmission, or negatively impact the samples. The temperature control system, including the temperature sensor or thermistor, must be responsive enough to maintain uniform temperatures for long periods.
The choice of fluid to be used within water baths depends on a number of factors. The most important factors to consider include the recommendations of the bath manufacturer, whether the bath is designed for a specific fluid or group of fluids, the sensor being used to measure fluid temperature and its reliability, and the temperature range over which it will be tested. Oil and water are the most commonly used fluids in baths and circulators. However, a variety of high-dielectric fluids are available for temperatures below 32ºF and above 212ºF, where the use of water would not be feasible. The fluid should have the right viscosity for the operating temperature range to permit proper stirring action.
It is important to match the fluid to the operating temperature range of the water baths in use. A high-temperature fluid in a cold bath would result in an excessively viscous fluid, which could negatively impact the ability of the stirring mechanism to maintain an even temperature distribution, or worse damage to the stirring mechanism. Conversely, using a fluid at a temperature above its flash point is hazardous.
When operating heated water baths, there are a number of safety issues to keep in mind. Heated baths are inherently dangerous as they are often used in conjunction with flammable liquids, or liquids that are at extremely elevated temperatures. Water baths should always be used on top of durable surfaces that are stable and will not collapse. They should also be kept away from other flammable materials as their radiant heat could cause combustion. Finally, they should be allowed to cool completely before being moved.