There are various factors influencing the heat transfer efficiency of plate heat exchangers and tube heat exchangers. The following is an introduction to these factors for each type:
Plate Heat Exchanger
1.Plate Structure and Material
- Plate Shape:
The specially designed corrugated plates can increase fluid disturbance and promote the formation of turbulence, thus enhancing the heat transfer effect. For example, chevron – shaped corrugated plates, with their corrugation angles, heights, and spacings, can affect the flow path and velocity distribution of the fluid. Appropriate parameters can effectively improve the heat transfer efficiency.
- Plate Material:
Different materials have different thermal conductivity coefficients, which affect the speed of heat transfer. For instance, stainless – steel plates have a moderate thermal conductivity coefficient and good corrosion resistance; titanium plates have a slightly lower thermal conductivity coefficient than stainless – steel, but they have strong corrosion resistance and are suitable for special media. Materials with high thermal conductivity can transfer heat more efficiently.
2.Fluid Flow Velocity:
Increasing the flow velocity of the fluid between the plates can reduce the thickness of the boundary layer, enhance convective heat transfer, and improve the heat transfer efficiency. However, if the flow velocity is too high, it will increase the flow resistance, resulting in higher energy consumption and may also cause vibration, affecting the stability of the equipment. It is necessary to find a balance between the flow velocity and the resistance to take both the heat transfer efficiency and the operating cost into account.
3.Fluid Physical Properties:
Physical property parameters of the fluid, such as specific heat capacity, thermal conductivity, and viscosity, affect the heat transfer efficiency. A fluid with a large specific heat capacity can carry more heat per unit mass for a temperature change; high thermal conductivity is conducive to heat transfer; and a fluid with low viscosity has good fluidity and is likely to form turbulence. For example, water has relatively high specific heat capacity and thermal conductivity, making it a good heat – exchange medium.
4.Plate Fouling:
During operation, dirt will form on the surface of the plates, such as scale, rust, and microbial deposits. This increases the thermal resistance, hinders heat transfer, and reduces the heat transfer efficiency. Regular cleaning and maintenance to keep the plates clean can reduce the fouling thermal resistance and maintain high – efficiency heat transfer.
5.Sealing Performance:
If the plate heat exchanger is not well – sealed, it will cause leakage between the two heat – exchange fluids, reducing the effective heat – transfer area and affecting the heat transfer efficiency. Ensuring the good performance of the sealing gaskets and the quality of installation to prevent leakage is crucial for maintaining the heat transfer efficiency.
Tube Heat Exchanger
1.Tube Diameter and Length
- Tube Diameter:
A smaller tube diameter can make the fluid flow at a higher velocity inside the tube, enhancing the degree of turbulence and increasing the heat – transfer coefficient. However, if the tube diameter is too small, it will increase the flow resistance and the risk of blockage. During the design, the tube diameter needs to be determined by comprehensively considering the fluid properties, flow rate, and allowable pressure loss.
- Tube Length:
Increasing the tube length can extend the heat – exchange time of the fluid and increase the heat transfer amount. However, an overly long tube length will increase the flow resistance and the equipment footprint and manufacturing cost. In practical applications, the impact of the tube length on the heat transfer efficiency and other factors needs to be weighed.
2.Tube Bundle Arrangement:
Common arrangements of the tube bundle include equilateral triangle, square, and rotated square. The equilateral – triangle arrangement can cause large disturbances to the fluid outside the tubes, resulting in a high heat – transfer coefficient, but it is more difficult to clean the outside of the tubes; the square arrangement is convenient for cleaning and has a low flow resistance, but the heat – transfer coefficient is relatively low. The rotated – square arrangement is in – between. Selecting the appropriate arrangement according to the fluid properties and operating requirements affects the heat transfer efficiency.
3.Shell – Side Baffles:
Installing baffles on the shell – side can guide the fluid to scour the tube bundle vertically, increasing the fluid velocity and disturbance, and improving the heat – transfer coefficient on the shell – side. The spacing and form of the baffles will affect the fluid flow state and heat – transfer effect. An appropriate baffle spacing can not only enhance heat transfer but also control the flow resistance within a reasonable range.
4.Flow State of Fluid in Tubes:
When the fluid in the tubes is in a turbulent state, the heat transfer efficiency is higher than that in a laminar state. By increasing the flow velocity, changing the tube diameter, or adding internal inserts in the tube, the fluid can be changed from a laminar state to a turbulent state or the degree of turbulence can be increased, enhancing the heat – transfer effect.
5.Tube Wall Fouling:
Similar to the plate heat exchanger, dirt will accumulate on the tube wall during operation, increasing the thermal resistance and reducing the heat transfer efficiency. Regular cleaning to prevent fouling is very important for maintaining the efficient operation of the tube heat exchanger. The difference is that cleaning the tube heat exchanger is relatively more complex, and an appropriate cleaning method needs to be selected according to the specific structure and dirt type.