Technical Tips about Heat Exchanger

For any heat-exchanger application, a user will benefit from the following suggestions:

• Consider heat exchangers early in system design.
• Avoid being excessively safe in specifying performance criteria.

 Asking for more temperature change, higher flow capability, and other just-in-case possibilities can easily double an exchanger’s size and cost. Consider the required effectiveness values; however remember that an exchanger’s size approaches infinity asymptotically as effectiveness approaches 1. So it takes considerably more heat-exchanger area to raise the effectiveness from 0.8 to 0.9 than it does to go from 0.7 to 0.8. High effectiveness—greater than 0.9—can be very costly.

Consider increasing pumping power rather than increasing an exchanger’s size. Higher velocity flow can produce or increase turbulence, which leads to an increased pressure drop and the need for more pumping power. Nevertheless, turbulence also increases the heat-transfer coefficient, in this manner decreasing the required heat-exchanger size. Accepting the increased pressure drop may be a more viable option than increasing size.

Remember that the main criterion is the product of the overall heat-transfer coefficient and the transfer area (U A)—not just the transfer area. For laminar-flow tubes, the total tube length, not the transfer area, is by and large the important factor; so 10 feet of 1/4-inch tubing works as well as 10 feet of 1-inch tubing.

Specify the smallest possible tubing for tube-type heat exchangers, since it gives the maximum thermal performance with the minimum volume. Nevertheless, be aware of the effects of fouling or particulates that may clog small tubes.

Seek turbulent flow to improve heat transfer, although that can be difficult with thick fluids and low flow rates.

Be conscious of fluid thermal conductivity when specifying the cooling or heating fluid. Perhaps amazingly, water frequently works the best

Match the inlet-port size to the piping sizes expected for the rest of the system.

Consider an exchanger’s lifetime and maintenance requirements.

Choose the type and thickness of material that will reduce failure caused by corrosion and erosion. Furthermore consider a system’s ease of mechanical or chemical cleaning in addition to filtration of the fluid streams.

Provide the heat-exchanger vendor with as much information on the total system as possible.

To maximize the performance of a heat exchanger means saving money, especially if the process is built for a long-term project. Here are some ways to improve the performance of a heat exchanger:

1. Heat transfer area

2. Fluid flow velocity
3. Temperature gradient