First, the principle of heat exchanger
The relative flow of fluids in the heat exchanger generally have two kinds of downstream and countercurrent. Downstream, the temperature difference between the two fluids at the entrance to the largest, and along the surface of the heat transfer gradually decreases to the exit of the temperature difference is the minimum. Countercurrent, along the heat transfer surface of the two fluid temperature difference is more evenly distributed. In the cold, hot fluid import and export temperature under certain conditions, when the two fluids are no phase change, to countercurrent average temperature difference between the largest downstream minimum.
In the completion of the same heat transfer conditions, the use of countercurrent can make the average temperature difference increases, the heat transfer area of the heat exchanger is reduced; if the heat transfer area is unchanged, the use of countercurrent can make the heating or cooling fluid consumption is reduced. The former can save equipment costs, the latter can save operating costs, so in the design or production use should try to use countercurrent heat transfer.
When the cold, hot fluid two or one of the phase change (boiling or condensation), due to the phase change only released or absorbed latent heat of vaporization, the temperature of the fluid itself does not change, so the fluid import and export temperatures are equal, and then the temperature difference between the two fluids on the choice of the direction of flow of the fluid has nothing to do. In addition to the downstream and countercurrent of the two flow direction, there are wrong flow and folding and other flow direction.
In the heat transfer process, reduce the thermal resistance in the wall heat exchanger to improve the heat transfer coefficient is an important issue. Thermal resistance mainly comes from the wall between the two sides of the viscous in the heat transfer surface of the fluid layer (called the boundary layer), and heat exchanger use in the wall on both sides of the formation of the dirt layer, the thermal resistance of the metal wall is relatively small.
Increase the fluid flow rate and perturbation, can thin the boundary layer, reduce the thermal resistance to improve the heat-giving coefficient. But increase the fluid flow rate will make the energy consumption increase, so the design should be in the reduction of thermal resistance and reduce energy consumption to make reasonable coordination between. In order to reduce the thermal resistance of the dirt, you can try to delay the formation of dirt, and regularly clean the heat transfer surface.
General heat exchanger are made of metal materials, including carbon steel and low alloy steel are mostly used in the manufacture of medium- and low-pressure heat exchangers; stainless steel in addition to different corrosion-resistant conditions, austenitic stainless steel can also be used as a high and low temperature materials; copper, aluminum and its alloys are mostly used in the manufacture of low-temperature heat exchangers; nickel alloys are used in high-temperature conditions; non-metallic materials in addition to the production of gaskets parts, some of which have been Began to use for the production of non-metallic materials corrosion-resistant heat exchanger, such as graphite heat exchanger, fluorine plastic heat exchanger and glass heat exchanger.
Second, the plate heat exchanger selection calculation
The above introduces the principle of heat exchanger and plate heat exchanger selection calculation. I hope the above information can help you. More please stay tuned.