How to improve the heat transfer efficiency of the heat exchanger?
How to improve the heat transfer efficiency of the heat exchanger in the application process? What are the factors that will affect the:
1 increase the logarithmic mean temperature difference
Heat exchanger flow regime, upstream downstream and mixed flow (both upstream and downstream). In the same condition, countercurrent logarithmic mean temperature difference maximum, minimum flow, mixed flow between the two asked. The method of improving the logarithmic mean temperature difference of the heat exchanger is as far as possible to use the mixed flow pattern of the counter current or near the counter current, to raise the temperature of the hot side fluid as far as possible, and to reduce the temperature of the cold side fluid.
2 determine the location of import and export
For the single plate heat exchanger flow arrangement, for convenient maintenance, the fluid inlet and outlet pipe should be arranged in the fixed end plate side heat exchanger. The medium temperature increases, the natural convection flow is stronger, the formation of the retention effect is more obvious, so the medium inlet and outlet position shall be hot fluid progress under the cold fluid inlet on the arrangement, in order to reduce the retention zone effect, improve the heat transfer efficiency.
3 improve heat transfer efficiency
Plate type heat exchanger 1.jpg plate heat exchanger is a heat exchanger, hot and cold fluid by changing the heat transfer plate, direct contact with the fluid and heat transfer plate, heat conduction and convection heat transfer. The key to improve the effect of the heat exchanger is to improve the heat transfer coefficient and logarithmic mean temperature difference.
4 improve the heat transfer coefficient at the same time, only improve the heat transfer coefficient of plate on both sides of the hot and cold, reducing the fouling layer resistance, selection of high thermal conductivity plate, plate thickness decreases, can effectively improve the heat transfer coefficient of heat exchanger.
A. enhances the surface heat transfer coefficient of the plate
Because the corrugated plate heat exchanger can make the fluid turbulence in small flow rate (Reynolds number 150), so it can obtain higher surface heat transfer coefficient, flow geometry surface heat transfer coefficient and plate corrugation and related media. The waveform of the board includes the shape, the shape, the sphere and so on. After years of research and experimentation, the corrugated cross section is triangular shaped (sine surface heat transfer coefficient, smaller pressure drop, the compression stress distribution is uniform, but the angle of difficult processing of the herringbone plate has higher surface heat transfer coefficient, and the greater the corrugated board, in the channel of medium flow rate is high, the surface the heat transfer coefficient is big.
B. to reduce the fouling layer thermal resistance
The key to reduce the fouling layer of the heat exchanger is to prevent scale formation. When the thickness of the plate is 1mm, the heat transfer coefficient is reduced by about 10%. Therefore, it is necessary to pay attention to monitor the water quality of the heat exchanger on both sides of the heat exchanger, prevent the board from scaling, and prevent the water debris attached to the plate. Some of the heating units to prevent theft of water and steel corrosion, add chemicals in the heating medium, so must pay attention to water and viscous agent causes debris contamination of plate heat exchanger. If there are sticky debris in the water, should be treated with special filter. When selecting the medicine, it is better to choose the non cohesive agent.
C. plate with high thermal conductivity
Plate material can choose austenitic stainless steel, titanium alloy, copper alloy, etc.. Thermal properties of stainless steel, thermal conductivity of about 14.4W/ (M? K), high strength, stamping performance is good, not easy to be oxidized, the price ratio of titanium alloy and copper alloy is low, most used in heating engineering, but its ability to resist chloride ion corrosion difference.
D. reduces plate thickness
The design thickness of the plate is not related to its corrosion resistance, which is related to the bearing capacity of the heat exchanger. Plate thickening, can improve the pressure of the heat exchanger. The herringbone plate combination, adjacent plates mutually inverted, corrugated contact with each other, forming a high density and uniform distribution of the fulcrum, the plate angle and edge seal alone L structure has been gradually improved, the heat exchanger has good bearing capacity. The maximum bearing capacity of domestic detachable heat exchanger has reached 2.5MPa. The thickness of the plate has great influence on the heat transfer coefficient, thickness of 0.1mm, the total heat transfer coefficient of symmetric plate type heat exchanger is increased by about 600W/ (M? K), non symmetrical about adding 500W/ (M? K). Under the premise of meeting the bearing capacity of the heat exchanger, the smaller plate thickness should be chosen as far as possible.