What Factors Affect the Heat Transfer Coefficient of a Plate Heat Exchanger?

Compared with many other types of heat exchangers, plate heat exchangers offer high heat transfer efficiency, easy cleaning, and simple maintenance. For these reasons, they are widely used in district heating systems, particularly in heating substations.

The heat transfer coefficient is one of the most important performance parameters when evaluating a plate heat exchanger. Many users and engineers want to know which factors affect the heat transfer coefficient and how the design can be optimized.

Ruipute provides the following analysis based on practical plate heat exchanger design and application experience.

1. The Importance of Pressure Drop Control

Pressure drop is a critical factor in the design and selection of a plate heat exchanger. It has a direct relationship with fluid velocity, heat transfer performance, equipment size, and pumping energy consumption.

Based on practical experience, in large-scale district heating projects, the pressure drop on the primary side is often controlled at approximately 100 kPa. This can provide a reasonable balance between heat transfer performance and equipment investment.

Under this condition, the required heat transfer area can meet the operating requirements while keeping the initial investment under control.

If the pressure drop is reduced to approximately 50 kPa, the system can still maintain good performance while potentially optimizing the overall investment. However, if the allowable pressure drop is reduced further to around 30 kPa, the required heat transfer area may increase by approximately 15%–20%.

A larger heat transfer area means higher initial equipment costs and potentially higher maintenance costs.

However, a low pressure drop can still be a reasonable choice for projects where the primary network has relatively low available pressure or where strict hydraulic requirements must be met.

Therefore, pressure drop should not simply be minimized. Instead, it should be optimized according to the actual operating conditions and the overall economics of the system.

2. The Influence of Operating Conditions

Operating parameters have a significant influence on the heat transfer coefficient of a plate heat exchanger.

The basic heat transfer relationship can be expressed as:

[Q = K \times A \times \Delta T_m]

Where:

• Q = Heat transfer capacity

• K = Overall heat transfer coefficient

• A = Heat transfer area

• ΔTm = Log Mean Temperature Difference (LMTD)

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The heat transfer coefficient is closely related to the actual operating conditions of the heat exchanger.

During the design and verification process, changes in operating parameters can directly affect the required heat transfer area. Important parameters include fluid flow rate, inlet and outlet temperatures, fluid properties, and allowable pressure drop.

For example, in many HVAC applications, the log mean temperature difference (LMTD) is relatively small. Therefore, a larger heat transfer area may be required to achieve the specified heat duty.

This is why accurate operating data are essential when selecting and sizing a plate heat exchanger.

3. Plate Corrugation Design

The corrugation pattern stamped onto the surface of a heat transfer plate plays an important role in determining the heat transfer coefficient and pressure drop.

The corrugations disturb the fluid flow inside the channels, promote turbulence, reduce the thickness of the thermal boundary layer, and consequently improve heat transfer.

Different manufacturers use different corrugation geometries and plate patterns to achieve different combinations of heat transfer performance and hydraulic resistance.

Herringbone Corrugation Angle

The herringbone angle is one of the important design parameters.

Generally, wider-angle herringbone patterns generate stronger flow resistance and turbulence, resulting in higher heat transfer performance. Narrower-angle patterns normally produce lower pressure drop but also provide relatively lower heat transfer enhancement.

Therefore:

• Wide-angle herringbone plates: Higher pressure drop and stronger heat transfer performance.

• Narrow-angle herringbone plates: Lower pressure drop and relatively lower heat transfer performance.

The appropriate corrugation pattern should be selected according to the required flow rate, heat duty, allowable pressure drop, and pumping capacity.

For applications where the flow rates on the two sides of the heat exchanger are significantly different, different plate patterns can also be combined in an appropriate proportion.

This approach allows engineers to balance the hydraulic and thermal performance of both circuits and achieve a more efficient overall design.

4. The Importance of Different Plate Designs

Plate heat exchangers need to operate under a wide variety of conditions and with different types of fluids. Therefore, a single plate pattern cannot provide the best performance for every application.

A diverse range of plate designs allows manufacturers to optimize heat transfer performance according to specific process requirements.

Different plate geometries can be developed for applications involving different:

• Flow rates

• Fluid properties

• Temperature differences

• Pressure drops

• Heat transfer requirements

• Fouling characteristics

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Ruipute has developed a variety of plate patterns optimized for different industrial processes and applications.

By selecting the appropriate plate geometry and channel configuration, the heat transfer coefficient can be optimized while maintaining an appropriate pressure drop.