Heat exchanger design

A heat exchanger is a device in which heat transfer occurs between inlet and outlet medium. Medium are separated by plates or walls of pipes (depending on the type of heat exchanger). Medium flow can be:

  • Direct flow – medium move in one direction;
  • Counter flow – medium move towards each other;
  • Cross flow – medium move perpendicular, crosswise.

How does heat exchanger work?

The working principle of heat exchanger is based on the transfer of heat from one medium to another through the separating wall. For example, in a high-temperature recuperator for metallurgical furnaces, the incoming air is heated by the exhaust gases, and enters the furnace already hot, which increases the performance of the furnace and increases the quality of metal products. Cold flows enter the heat exchanger; heat up from the plates, which receive heat from the outgoing flows. The efficiency and parameters of the heat exchanger depend on the area of the heat transfer surface.

The technical characteristics of heat exchangers depend on the temperature of the inlet and outlet medium, the density and flow rate, as well as a number of other conditions. An important factor is the heat exchanger type and material for medium separators (heat exchange surfaces). If the plates material is a metal with a high heat transfer capacity (for example, aluminum), the heat exchanger power increases, and the weight decreases.

Flow rates can be adjusted with optional equipment. To increase the temperature of the primary medium, the rate of incoming flow can be reduced, including by force using special devices. For the same performance of various heat exchangers, a different volume is required.

In shell-and-tube units, the fluid is heated when it passes through tubes that are washed by another fluid. With increase in the heat transfer surface (number of pipes) while maintaining the dimensions of the apparatus, there is a decrease in volume for the heating fluid, which can lead to a loss in performance. To increase power, it is necessary to increase the dimensions of the shell.

The plate heat exchanger design provides an improved performance without changing the external dimensions of the device. Solution is to add more plates, as a result, the number of channels increases and the cross-section is reduced, the flow rate decreases and power increases. If the intake air volume is insufficient, the flow rate can be increased and regulated by additional devices.