In order that the plate heat exchanger can better exert the heat exchange effect, it needs to be determined comprehensively according to factors such as equipment type, area used, and occasions when selecting the type. When selecting the plate heat exchanger, you can also choose according to the following principles when purchasing.
1. Determination of the flow: When the flow of fluid on both sides is approximately the same, it should be arranged as equal as possible; when the flow of fluid on both sides is greatly different, the side with the smaller flow should be arranged according to multiple processes or using unequal cross-section channels. Plate heat exchanger.
2. Selection of single plate area of plate heat exchanger: If the single plate area is too small, the number of plates is large, the floor area is large, and the resistance drop is reduced. On the contrary, if the single plate area is too large, the number of plates is small and the area is small. The resistance drop is small, but it is difficult to ensure a proper flow rate between the plates.
3. Selection of flow velocity between plates: The flow velocity of fluid between plates affects heat transfer performance and pressure drop. High flow rate, high heat transfer coefficient and increased resistance drop; otherwise, the opposite is true. Generally, the flow velocity between the plates is 0.2-0.8m / s, and the plate heat exchanger should try to make the speed between the two fluid plates consistent. When the flow velocity is less than 0.2m / s, the fluid cannot reach the flow state, and a large dead zone will be formed; if the flow velocity is too high, the resistance drop will increase sharply, and the flow velocity between the gas plates is generally not greater than 10m / s.
4. Selection of flow direction: During single-phase heat exchange, the countercurrent has a large average temperature difference. Generally, the fluid should be arranged as countercurrent in the design of the plate heat exchanger. When the fluid on both sides is an equal flow, it is countercurrent; when the fluid of the liquid nitriding furnace on both sides is an unequal flow, the cocurrent and countercurrent occur alternately, and the average temperature difference is smaller than that of the pure countercurrent.
In addition, the requirements must be met when selecting: reasonably realizing the prescribed process conditions; the structure is safe and reliable; easy to manufacture, install, operate and maintain;
Working principle of plate heat exchanger:
A plate heat exchanger is a heat exchanger made of thin metal plates pressed into heat exchange plates with a certain corrugated shape, then stacked and fastened with plywood and bolts. Thin rectangular channels are formed between the various plates, and heat is exchanged through half of the plates. The working fluid flows through the narrow and tortuous channels formed between the two plates. The hot and cold fluids pass through the flow channel in turn, and an interlayer plate in the middle separates the fluid, and heat is exchanged through this plate.
Plate heat exchanger structure:
The plate heat exchanger is mainly composed of a frame and a plate. Sheets made of various materials are pressed with various forms of abrasive tools into corrugations of different shapes, and corner holes are opened in the four corners of the sheet for the flow channel of the medium. The periphery of the plate and the corner holes are sealed with rubber gaskets. The frame is composed of a fixed pressure plate, a movable pressure plate, upper and lower guide rods, clamping bolts and the like. The plate heat exchanger is formed by stacking the plates in the middle of a fixed compression plate and a movable compression plate, and then clamping them with clamping bolts. In the design and selection of plate heat exchangers, there are generally certain requirements on pressure drop, so it should be checked. If the check pressure drop is higher than the allowable pressure drop, the design selection calculation needs to be performed again until the process requirements are met.