1. Improve heat transfer efficiency
The plate heat exchanger is a wall to wall heat exchanger. The cold and hot fluids transfer heat through the plates of the heat exchanger. The fluid contacts the plates directly. The heat transfer modes are heat conduction and convection heat transfer. The key to improve the heat transfer efficiency of plate heat exchanger is to improve the heat transfer coefficient and logarithmic average temperature difference.
① In order to improve the heat transfer coefficient of heat exchanger, it is necessary to increase the surface heat transfer coefficient of both sides of the plate at the same time, reduce the thermal resistance of the dirt layer, select the plate with high thermal conductivity and reduce the thickness of the plate, so as to effectively improve the heat transfer coefficient of the heat exchanger.
a. Improving the surface heat transfer coefficient of plate
Because the ripple of plate heat exchanger can make the fluid produce turbulence at low velocity (Reynolds number - 150), it can obtain higher surface heat transfer coefficient. The surface heat transfer coefficient is related to the geometry structure of plate ripple and the flow state of medium. The wave shape of the plate includes herringbone, flat shape and spherical shape. After many years of research and experiment, it is found that the herringbone plate with triangular corrugated section (sinusoidal surface heat transfer coefficient is large, pressure drop is small, stress distribution is uniform under pressure, but processing is difficult?) herringbone plate has higher surface heat transfer coefficient, and the greater the angle of corrugated, the higher the medium flow velocity in the channel between plates, and the greater the surface heat transfer coefficient.
b. Reduce the thermal resistance of dirt layer
The key to reduce the thermal resistance of fouling layer in heat exchanger is to prevent the plate from scaling. The heat transfer coefficient decreases about 10% when the scale thickness is 1 mm. Therefore, it is necessary to monitor the water quality on both sides of the heat exchanger to prevent the plate from scaling and to prevent the debris from adhering to the plate. In order to prevent water stealing and steel corrosion, some heating units add chemicals to the heating medium. Therefore, attention must be paid to the contamination of heat exchanger plates by water quality and stickiness. If there is viscous debris in the water, it should be treated with a special filter. When choosing the medicament, it is better to choose the non viscous medicament.
c. Select the plate with high thermal conductivity
The plate material can be austenitic stainless steel, titanium alloy, copper alloy, etc. Stainless steel has good thermal conductivity, thermal conductivity of about 14.4 w / (m · K), high strength, good stamping performance, and is not easy to be oxidized. The price of stainless steel is lower than that of titanium alloy and copper alloy. It is widely used in heat supply engineering, but its resistance to chloride ion corrosion is poor.