How to improve the heat transfer efficiency of heat exchanger units?

The working principle of a heat exchanger: The fluid medium flows through the corrugated gaps within the heat exchanger at a very low flow rate, creating turbulent flow, thereby achieving a relatively high heat transfer coefficient. We can conclude that heat transfer efficiency is closely related to the shape and structure of the corrugated plates within the heat exchanger and the flow state of the fluid. What specific methods can be used to improve the heat transfer efficiency of a heat exchanger?

The plate is the heat transfer core of the plate heat exchanger. Its thermal conductivity and flow channel design directly determine the basic heat transfer capacity and must be optimized from the source first.

1.Choose materials with high thermal conductivity as plates

We can choose 304 stainless steel, 316L stainless steel, copper alloy and titanium alloy as plates. Stainless steel has good thermal conductivity and a relatively reasonable price. It has high strength, good stamping performance, and is not easily oxidized in harsh environments.

2.Matching efficient plate corrugated structure

The corrugation design of the plate determines the flow channel shape and directly affects the intensity of fluid disturbance (the stronger the disturbance, the thinner the boundary layer and the higher the convective heat transfer coefficient). The corrugation type should be selected according to the fluid viscosity and heat transfer requirements:

3.Reasonable design of plate quantity and flow channel combination

The number of plates determines the total heat transfer area (A), and the flow channel combination (single-pass/multi-pass) affects the fluid flow rate. It is necessary to accurately match it according to the "heat transfer load":Calculation of the number of plates: According to the formula Q=K×A×ΔTₘ (Q is the heat exchange load, ΔTₘ is the logarithmic mean temperature difference), after determining the K value and ΔTₘ, reversely calculate the required minimum heat transfer area. Then, based on the effective area of ​​a single plate (e.g., the commonly used plate area is 0.1-0.5㎡), calculate the number of plates. It is recommended to reserve a 10%-15% margin to cope with short-term load fluctuations.

Flow channel combination optimization: Increase or decrease the number of flow paths to increase the flow velocity to the turbulent range (Re > 300 is recommended in the plate flow path). If the flow velocity is too low (for example, Re = 150 in a single flow path, laminar flow), change to a "two-flow path" (the fluid flows back and forth in the plate, doubling the path and flow velocity, and increasing Re to 300, thus entering turbulent flow).

4.Reduce the thickness of the plates in the heat exchanger unit

Thermal conductivity is greatly affected by the thickness of the plate itself. Research experiments have shown that in a symmetrical plate heat exchanger, every 0.1mm reduction in plate thickness can increase the overall heat transfer system by 600W, while in an asymmetrical device, it can increase by 500W. Therefore, under the premise of meeting the mechanical performance requirements of the heat exchanger, the thinner the plate thickness is designed, the greater the thermal conductivity.

5.Shape of the corrugated section

Although the stress distribution during compression is relatively uniform when the corrugated cross-section is triangular, the heat transfer coefficient of the herringbone plate, which is relatively difficult to process, is higher. In addition, the larger the angle of the corrugated design, the higher the flow velocity of the medium in the flow channel between the plate branches, so the heat transfer coefficient will be greater.

6.Clean the scale on the plate in time

When the scale on the plate is greater than 1mm, the overall heat transfer efficiency of the equipment will be reduced by 10%. Therefore, filtering equipment should be added at the inlet and the heat exchanger should be cleaned regularly. Only in this way can the thickness of the scale on the plate be reduced and the heat exchange efficiency be stabilized at a relatively level state.