How do different media affect the pressure drop of the heat exchanger?

1. Fluid properties
Viscosity: When a liquid with high viscosity, such as heavy oil and polymer solution, flows in the tube, due to the large internal friction, the fluid forms a thicker boundary layer near the tube wall, resulting in increased flow resistance, which in turn causes a large pressure drop. For example, when dealing with liquids with high viscosity, the tube pressure drop can be appropriately relaxed to 100kPa.
Density: Fluids with high density have greater inertia. At the same flow rate, the flow resistance will also increase accordingly, resulting in increased pressure drop.
Thermal conductivity: A medium with high thermal conductivity has high heat transfer efficiency and can achieve better heat transfer effects at lower flow rates, thereby reducing pressure drop to a certain extent.
2. Flow rate
Flow rate: The greater the flow rate, the greater the kinetic energy of the fluid in the heat exchanger, and the more intense the collision and friction with the tube wall, resulting in an increase in pressure drop. Although increasing the flow rate can increase the heat transfer coefficient, it also increases the pressure drop. Therefore, a balance needs to be struck between the heat transfer effect and the pressure drop.
Flow velocity distribution: Uneven flow velocity distribution will lead to excessive local pressure drop, affecting the overall performance of the heat exchanger.
3. Flow mode
Laminar flow and turbulent flow: In the turbulent state, the mixing degree of the fluid is high, the heat transfer effect is good, but the pressure drop is also relatively large. In the laminar state, the fluid flows smoothly, the pressure drop is small, but the heat transfer effect is relatively poor.
Multi-pass flow: In a heat exchanger with multiple tube passes or multiple shell passes, the flow resistance is increased because the fluid needs to change the flow direction many times, resulting in an increase in pressure drop.
4. Heat exchanger structure
Tube pass and shell pass design: The structural design of the tube pass and shell pass has a direct impact on the pressure drop. For example, the arrangement of the tubes in the tube pass, the size of the tube diameter, the length of the tube, etc. will affect the flow resistance of the fluid. The baffle design in the shell pass will also affect the flow path and velocity of the fluid, and then affect the pressure drop.
Surface characteristics of heat exchange tubes: The roughness of the surface of the heat exchange tube will affect the flow resistance of the fluid. Too rough a surface will increase the friction resistance of the fluid, resulting in an increase in pressure drop.
5. Chemical properties of the medium
Corrosiveness: Corrosive media may cause corrosion to the tube wall and shell of the heat exchanger, resulting in thinning of the wall thickness, thereby affecting the pressure bearing capacity of the heat exchanger and indirectly affecting the pressure drop.
Deposition: Some media may deposit during the heat exchange process, forming a scale layer, increasing the flow resistance of the fluid, and causing an increase in pressure drop.
6. System configuration
Pipeline layout: The connection method between the heat exchanger and the external pipeline and the parameters such as pipeline length and diameter will also affect the pressure drop. Pipes that are too long, too thin, or have too many connections will increase the flow resistance of the fluid.
System pressure: The level of system operating pressure will also affect the pressure drop of the heat exchanger. In high-pressure systems, the flow resistance of the fluid is relatively small, but in low-pressure systems, the impact of pressure drop is more significant.
7. Operating conditions
Temperature: Changes in operating temperature will affect the viscosity and density of the fluid, and thus affect the pressure drop. Generally speaking, an increase in temperature will reduce the viscosity of the fluid, thereby reducing the pressure drop.
Pressure: Changes in operating pressure will also affect the pressure drop. Under high pressure conditions, the compressibility of the fluid decreases and the flow resistance is relatively stable, but under low pressure conditions, the change in pressure drop is more sensitive.
8. Precautions in practical applications
Reasonable selection of flow rate: When designing and operating shell and tube heat exchangers, the flow rate should be reasonably selected according to the properties of the medium and the heat exchange requirements to balance the heat transfer effect and pressure drop.
Regular maintenance: Regularly check and clean the heat exchanger to prevent scale accumulation and maintain the good operating condition of the heat exchanger.
Optimize system design: During the system design stage, the local resistance of the pipeline should be minimized, and the layout and connection method of the heat exchanger should be optimized to reduce the pressure drop.