A heat exchanger is a system used to transfer heat between two or more fluids. Heat exchangers are used in both cooling and heating processes.The fluids may be separated by a solid wall to prevent mixing or they may be in direct contact. They are widely used in space heating, refrigeration, air conditioning, power stations, chemical plants, petrochemical plants, petroleum refineries, natural-gas processing, and sewage treatment. The classic example of a heat exchanger is found in an internal combustion engine in which a circulating fluid known as engine coolant flows through radiator coils and air flows past the coils, which cools the coolant and heats the incoming air. Another example is the heat sink, which is a passive heat exchanger that transfers the heat generated by an electronic or a mechanical device to a fluid medium, often air or a liquid coolant.
Types Of Heat Exchanger
There are many different types of heat exchanger available, the three main types that Thermex supplies are;
Shell and Tube; Shell and Tube Heat Exchangers consist of a large number of small tubes which are located within a cylindrical shell. The tubes are positioned into the cylinder using a tube bundle or “tube stack” which can either have fixed tube plates (permanently fixed to the body) or, in the case of Thermex Heat Exchangers a floating tube stack which allows the tube bundle to expand and contract with varying heat conditions as well as allowing the tube bundle to be easily removed for servicing and maintenance.
Plate Type; Plate Heat Exchangers operate in very much the same way as a shell and tube heat exchanger, using a series of stacked plates rather than tubes. Plate heat exchangers are usually brazed or gasketed depending on the application and fluids being used. Their compact stainless steel construction makes them an ideal choice for use with refrigerants or in food and beverage processing.
Air Cooled; Air Cooled Heat Exchangers are commonly used in vehicles or other mobile applications where no permanent cool water source is available. Thermex designs and supplies combination cooling packs (or combi-coolers) which combine an engine jacket water cooler, oil cooler and charge air cooler into a single unit reducing space requirements and improving efficiency. Cool air is provided either by a fan or by air flow caused by the movement of the vehicle.
How is a Heat Exchanger designed?
To be able to select a heat exchanger, we need to know;
- Primary circuit fluid type, temperature and flow rate (usually the hot fluid)
- What you want to take out of the primary circuit (Heat dissipation or a target outlet temperature)
- Secondary circuit fluid type, temperature and flow rate (usually the coolant)
The fields above are only the basics. When putting an enquiry together you should also make Thermex aware of any pressure loss limitations and any other special requirements.
Please click here to download the Thermex data sheet template which highlights the required fields for heat exchanger selection. The data sheet should also be saved and sent to us if you require a quotation for a heat exchanger.
How to make a heat exchanger more efficient.
Heat exchanger efficiency can be defined in many ways, in terms of thermal performance there are several key factors to consider;
Temperature differential – As discussed in point 3 (temperature cross-over) the difference between the hot fluid and coolant is very important when designing a heat exchanger. The coolant always needs to be at a lower temperature than the hot fluid. Lower coolant temperatures will take more heat out of the hot fluid than warmer coolant temperatures. If you had a glass of drinking water at room temperature for example, it is much more effective to cool it down using ice rather than just cool water, the same principle applies to heat exchangers.
Flow rate – Another important factor is the flows of the fluids in both the primary and the secondary side of the heat exchanger. A greater flow rate will increase the capability of the exchanger to transfer the heat, but a greater flow rate also means greater mass, which can make it more difficult for the energy to be removed as well as increasing velocity and pressure loss.