Choosing a PolyScience ProductHow to find the right product from our broad range of liquid temperature control solutions.
PolyScience produces a broad range of liquid temperature control equipment. In most cases, our products are not designed for a specific application but rather are engineered to provide stable heating or cooling over common operating temperature ranges. If your application requires maintaining a temperature near or below ambient temperature, then a refrigerated product such as a Recirculating Chiller or Circulating Bath is appropriate. The choice will depend on several factors. The following guidelines will help you determine the type of product, and model, best suited to your application:
- Fluid operating temperature range and set-point
- Cooling capacity (heat removal if set-point is near/below ambient)
- Ambient temperature (affects cooling capacity)
- Temperature stability (we offer choices from ±0.005°C to ±0.1°C)
- External application (open or closed-loop determines pump type)
- Reservoir size (if a bath is required)
- Pump pressure and/or flow rate (if pumping to an external application)
- External probe/programmability
Because air-cooled, refrigerated products rely on ambient air to remove heat from the refrigeration system, the ambient air temperature will affect a unit's cooling capacity. As a general practice when selecting a refrigerated product, decrease the product's cooling capacity rating 1.3% for every 1° that the ambient air temperature exceeds 20°C. For example, if the ambient temperature where the Circulator or Chiller is located is 22°C, then the cooling capacity of the product will be reduced by 2.6%. At set-points near ambient, heating products that lack refrigeration will have difficulty maintaining temperature and stability.
A typical Circulating Bath uses the ambient air to remove heat from the refrigeration system which, in turn, removes heat from the process fluid.
A typical air-cooled Chiller uses the ambient air to remove heat from the refrigeration system which, in turn, removes heat from the process fluid.
Selecting a Circulating BathHow to select the best Circulating Bath for your application.
The best PolyScience Circulating Bath for your application will depend on a number of factors. Here are some guidelines to help with your selection.
1. Working Temperature and Stability – You will need a Refrigerated/Heated Circulator if your working temperature will ever be near or below ambient. Applications that require maximum temperatures above 160°C or ±0.01°C temperature stability require Circulators with Performance or Advanced Series Temperature Controllers.
2. Cooling/Heating Demand – A Circulator with a small reservoir is generally suitable if you require external circulation only and the heating/cooling demand is moderate. If the external heating/cooling demand is high or you will be putting samples in the internal reservoir, a Circulator with a larger reservoir will be required.
3. External Circulation – All PolyScience Temperature Controllers can be used for close-loop external circulation. If open-loop external circulation is required, or if your application requires a flow rate above 3 gpm (11 l/min), a Circulator with a Performance or Advanced Series Controller is required.
Circulating Bath Heating and Cooling Performance
Selecting a ChillerHow to select and size the proper Chiller.
Chillers provide heat removal for a wide variety of processes and equipment. When properly sized and selected, a chiller increases production speed and accuracy, protects valuable process equipment, and reduces water consumption and related costs. If it is undersized, the chiller will not cool properly; if it is oversized, it will be inefficient due to excessive cycling. In addition to having an adequate cooling capacity, the chiller must deliver the cooling fluid at the proper pressure and flow rate.
Here are the four basic factors that affect chiller sizing and selection:
Desired coolant temperature – This is the coolant temperature at the inlet of your process or equipment. It is important to measure the temperature at this point to allow for coolant heating as it travels from the chiller to the process. The longer the distance to be covered, the higher the potential heat gain. This heat gain can be minimized by insulating the cooling line and positioning the chiller as close as practical to the equipment or process being cooled.
Heat load – This is the amount of heat that needs to be removed. It is usually expressed in BTUs/hour or watts. The heat load value is often provided by the equipment manufacturer. If not, it can be calculated using the following formula:
Heat load = Flow rate x Fluid density x Fluid specific heat x Constant x ΔT°
Coolant flow and pressure – These parameters are normally provided by the equipment manufacturer and are a function of the surface area and the heat transfer characteristics of the process/material being cooled. It is crucial that your chiller deliver coolant at the proper flow rate and pressure. If the flow rate or pressure is too high, the equipment being cooled may be damaged; if it is too low, the heat removal will be inadequate. PolyScience can help you specify the type and size of coolant pump most suitable for your needs.
Condenser heat dissipation – The final factor influencing chiller/heat exchanger selection is how the heat removed will be dissipated. Chillers with air-cooled condensers exhaust heat into the surrounding air and require only power and ventilation for operation. Chillers with water-cooled condensers transfer heat to the facility's cooling water supply.
Naturally, there are other factors – such as heating capability, external temperature tracking, deionized water capability, etc. – that affect how a chiller is ultimately configured. PolyScience will take all of these into consideration when helping you select the best chiller for your particular application. Here is a summary of the information you'll need to know to ensure that the chiller you select is the best one for your application:
- Desired coolant temperature at the inlet to your equipment or process
- Anticipated heat load, as calculated or specified by the equipment manufacturer
- Cooling fluid flow rate and pressure requirements
- Maximum room (ambient) temperature where the chiller will be located
- Internal heat dissipation, space, and portability needs
- Special requirements, such as remote temperature tracking or piping for deionized water
It is generally recommended that 20% to 50% be added to the calculated heat load to provide a safety factor if the chiller will be operated at ambient temperatures above 20°C (68°F), at high altitude, or if the heat output of the device is variable. This will also provide a margin of safety for future cooling needs. That said, resist the temptation to build more of a safety margin into your chiller than is necessary; an oversized chiller will not cool your equipment any more effectively, but will cost more to purchase and operate.
Suggested Chiller Fluid
The most common and acceptable coolant is a mixture of 50% distilled water and 50% glycol (polycool EG-25). This combination will provide the best results for set-point temperatures between -25°C and +80°C (-13°F and +176°F). Although ethylene glycol is not required for set-point temperatures above freezing (0°F/+32°F), it is highly recommended as glycol helps lubricate pump seals and fluid temperatures inside the chiller may be below freezing.
Cooling capacity curves are representative of the model shown and may vary depending on pump type, heat load, and ambient conditions.
Selecting a Chiller PumpImportant considerations when choosing a pump for your Chiller
Considerations For Pump Selection
Turbine Pumps – Provide moderate flow and moderate pressures (20-90 psi, 1.4-6.9 bar.) which makes them well suited to applications that require higher pressure or experience a higher system pressure drop, such as long tubing runs or pumping vertically. A robust design makes turbine pumps very reliable and forgiving to impurities in the fluid stream. Bronze turbine pumps are standard; stainless steel pumps are available.
Positive Displacement Pumps – Have performance characteristics similar to turbine pumps and are suitable for high viscosity fluids, or pumping higher or further from the cooling product and the application. They produce moderate flow at high pressure; up to 100 psi (6.9 bar). Brass positive displacement pumps are standard; stainless steel positive displacement pumps are available.
Centrifugal Pumps (Magnetic Drive) – Offer higher relative flow rates at lower pressures and are suitable for applications that are in close proximity to the chiller or require lower pressure, such as glass condensers. Centrifugal pumps are very quiet and require little maintenance, but they are more sensitive to pressure drops. Chillers with this pump option that are attached to a device with a solenoid valve coolant shut-off require the external bypass accessory.
Product Selection GuidesQuickly compare the key performance specifications of products within various categories.