Characteristics of plate heat exchanger

Characteristics of plate heat exchanger

The removable plate heat exchanger with working pressure up to 8Mpa is sealed by backing plate. The sealing perimeter is long, and the support condition of the two seals of the corner hole is poor. The gasket cannot get enough pressing force, so the maximum working pressure is only 2.5MPa. Brazed and all welded plate heat exchangers have changed the sealing form of detachable plate heat exchanger, and plate shell heat exchanger has changed the inlet (outlet) form of two kinds of fluids, which has increased the working pressure of plate heat exchanger. At present, the working pressure of brazed and all welded plate heat exchanger is up to 3.5 ~ 4MPa, and that of shell and plate heat exchanger is up to 8Mpa. In the detachable heat exchanger, the corrugated tubular channel is formed by reinforcing the conventional corrugated plates, which can not only enhance the heat transfer, but also increase the pressure bearing capacity of the plate heat exchanger.

1. High heat transfer coefficient plate heat exchanger has high heat transfer coefficient, which is about 3-5 times of that of shell and tube heat exchanger. The main reason is that when the fluid flows in the shell side of shell and tube heat exchanger, there are bypass between baffles, baffles, heat exchange tubes, tube bundles and shells. The fluid passing these bypass does not fully participate in heat exchange. However, there is no bypass in the plate heat exchanger, and the ripple of the plate can make the fluid produce turbulence at a small flow rate, and the turbulence effect is obvious (when the Reynolds number is about 150, it is turbulence), so the higher heat transfer coefficient can be obtained.

2. Two kinds of fluids in the large plate heat exchanger with logarithmic average temperature difference can realize pure countercurrent, generally in the downstream or countercurrent mode. But in shell and tube heat exchanger, two kinds of fluid flow in shell side and tube side respectively. In general, it is the flow mode of cross flow. The logarithmic mean temperature difference is reduced. The plate heat exchanger can achieve temperature crossing, and the temperature difference at the end can reach 1 ℃; the shell and tube heat exchanger can not achieve temperature crossing (that is, the outlet temperature at the secondary side cannot be higher than the outlet temperature at the primary side), and the temperature difference at the end can only reach 5 ℃.

3. NTU large NTU indicates the heat transfer capacity of the heat exchanger relative to the heat capacity flow of the fluid. For example, for the determined heat transfer coefficient K and heat capacity GCP, the size of NTU means the size of heat exchanger, that is, the size of heat transfer area. NTU of shell and tube heat exchanger is about 0.2 ~ 0.3 (average 0.25). NTU of (BRS) plate heat exchanger is about 1.0 ~ 3.0 (average 2.0). For example, NTU = (14-9) / 1.5 = 3.33 when primary water is 14-9 ℃, secondary water is 13-7 ℃, primary water flow is 60m3 / h, and secondary water flow is 50m3 / h for heat exchange. If symmetrical (BRS) plate heat exchanger is used, 3.33 / 2.0 = 1.66 ≈ 2 flow, a = 95m2; if shell and tube heat exchanger is used, 3.33 / 0.25 = 13.32 ≈ 14 flow, a = 320m2.

IV. with strong temperature and pressure resistance, the design working pressure can reach 8Mpa, and the design working temperature can reach 1000 ℃.

V. the area of large-scale single board is up to 18m2, and the area of single board is up to 10000m2. Vi. the area of miniaturized single board is smaller than A4.

VII. Small floor area. From the third analysis, because of the large NTU of plate heat exchanger, the size of the required heat exchanger is also small when the heat exchange is the same. In addition, the structure of the plate heat exchanger is compact, and the heat exchange area per unit volume is 2-5 times of that of the shell and tube heat exchanger, and there is no need for the shell and tube heat exchanger to reserve a maintenance site to draw out the tube bundle, so the floor area of the plate heat exchanger is 1 / 5-1 / 10 of that of the shell and tube heat exchanger.

VIII. The plate thickness of the light weight plate heat exchanger is only 0.6-0.8mm, and the heat transfer tube thickness of the shell and tube heat exchanger is 2.0-2.5mm; the shell of the shell and tube heat exchanger is much heavier than the frame of the shell and tube heat exchanger; therefore, when the heat exchange is the same, the heat exchange area required by the plate heat exchanger is smaller than that of the shell and tube heat exchanger, and its weight is about 1 / 5 of that of the shell and tube heat exchanger.

IX. the removable plate heat exchanger with working pressure up to 8Mpa is sealed by backing plate, with long sealing perimeter and poor support at two seals of angle hole, so the gasket can not get enough pressing force, so the maximum working pressure is only 2.5MPa. Brazed and all welded plate heat exchangers have changed the sealing form of detachable plate heat exchanger, and plate shell heat exchanger has changed the inlet (outlet) form of two kinds of fluids, which has increased the working pressure of plate heat exchanger. At present, the working pressure of brazed and all welded plate heat exchanger is up to 3.5 ~ 4MPa, and that of shell and plate heat exchanger is up to 8Mpa. In the detachable heat exchanger, the corrugated tubular channel is formed by reinforcing the conventional corrugated plates, which can not only enhance the heat transfer, but also increase the pressure bearing capacity of the plate heat exchanger.

X. if more than two kinds of medium heat exchange are needed, the plate heat exchanger can be equipped with intermediate baffles. Shell and tube heat exchanger can not realize the heat exchange of various media.