How can you choose the best heat exchanger for your needs?

1 Type of heat exchanger

There are many types of heat exchangers, each with its own advantages and disadvantages. Some of the most common types are shell-and-tube, plate, spiral, and air-cooled heat exchangers. Shell-and-tube heat exchangers consist of a series of tubes inside a shell, where one fluid flows through the tubes and another fluid flows over them. Plate heat exchangers have a stack of thin metal plates with corrugated surfaces, where the fluids flow in alternate channels between the plates. Spiral heat exchangers have two metal strips wound around a central core, forming spiral channels for the fluids. Air-cooled heat exchangers have finned tubes or coils that are exposed to ambient air, which acts as the cooling medium. The type of heat exchanger you choose depends on factors such as the pressure, temperature, and corrosiveness of the fluids, the required heat transfer area and efficiency, the available space and maintenance access, and the initial and operating costs.

2 Size of heat exchanger

The size of a heat exchanger is determined by the heat transfer area, which is the surface area available for heat exchange between the fluids. The heat transfer area depends on the heat duty, which is the amount of heat that needs to be transferred between the fluids, and the overall heat transfer coefficient, which is a measure of how well the heat exchanger transfers heat. The overall heat transfer coefficient depends on the thermal conductivity, thickness, and fouling resistance of the materials, as well as the convection coefficients and temperature differences of the fluids. To calculate the size of a heat exchanger, you need to use an appropriate heat transfer equation, such as the log mean temperature difference (LMTD) method or the effectiveness-number of transfer units (NTU) method. The size of a heat exchanger affects its performance, cost, and space requirements.

3 Design of heat exchanger

The design of a heat exchanger refers to the configuration and arrangement of its components, such as the tubes, plates, fins, baffles, and shells. The design of a heat exchanger affects its heat transfer rate, pressure drop, fouling tendency, and reliability. Some of the design parameters that you need to consider are the number, shape, and layout of the tubes or plates, the type and spacing of the fins, the angle and pitch of the baffles, and the diameter and length of the shell. The design of a heat exchanger should be optimized to achieve the desired performance and efficiency, while minimizing the cost and maintenance.

4 Performance of heat exchanger

The performance of a heat exchanger is evaluated by its effectiveness, which is the ratio of the actual heat transfer to the maximum possible heat transfer, and its pressure drop, which is the difference in pressure between the inlet and outlet of the heat exchanger. The effectiveness and pressure drop of a heat exchanger depend on the type, size, and design of the heat exchanger, as well as the properties, flow rates, and temperatures of the fluids. The performance of a heat exchanger should be tested and verified using experimental or numerical methods, such as the Wilson plot or the computational fluid dynamics (CFD) simulation. The performance of a heat exchanger should be monitored and controlled to ensure its optimal operation and safety.

5 Properties of fluids

The properties of the fluids that flow through a heat exchanger are important factors that influence the selection of a heat exchanger. Some of the properties that you need to know are the specific heat, density, viscosity, thermal conductivity, and heat capacity of the fluids, as well as their phase, state, and composition. The properties of the fluids affect the heat transfer rate, pressure drop, and fouling potential of the heat exchanger. The properties of the fluids also determine the compatibility and suitability of the materials and components of the heat exchanger. The properties of the fluids should be measured and verified using accurate and reliable methods, such as the calorimetry or the thermocouple.

6 Flow rates and temperatures of fluids

The flow rates and temperatures of the fluids that enter and exit a heat exchanger are essential parameters that define the heat transfer process and the thermal performance of the heat exchanger. The flow rates and temperatures of the fluids depend on the heat duty, the heat source and sink, and the system design and operation. The flow rates and temperatures of the fluids affect the heat transfer coefficient, the temperature difference, and the effectiveness of the heat exchanger. The flow rates and temperatures of the fluids also influence the thermal stress, fatigue, and expansion of the heat exchanger. The flow rates and temperatures of the fluids should be controlled and regulated using appropriate valves, pumps, and sensors.

7 Here’s what else to consider

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