[Plate Heat Exchanger]Working Principle of Plate Heat Exchanger Selection of Plate Heat Exchanger
Classification of Plate Heat Exchanger
Under normal circumstances, we mainly distinguish plate heat exchangers according to the structure, that is, according to the shape, which can be divided into four categories: ① Removable plate heat exchangers (also called plate heat exchangers with sealing gaskets) Heater)
②Welded plate heat exchanger
③Spiral plate heat exchanger
④Plate coil heat exchanger (also called honeycomb heat exchanger) device).
Among them, welded plate heat exchangers are further divided into: semi-welded plate heat exchangers, fully welded plate heat exchangers, plate and shell heat exchangers, and brazed plate heat exchangers.
The commonly used classifications are as follows:
1. According to the heat exchange area in the unit space, the plate heat exchanger belongs to the compact heat exchanger, which is mainly related to the Compared with the shell and tube heat exchanger, the traditional shell and tube heat exchanger occupies a larger area.
2. According to the process use, there are different names: plate heater, plate cooler, plate condenser, plate preheater;
3. According to the process combination, It is divided into single-pass plate heat exchanger and multi-pass plate heat exchanger;
4. According to the flow direction of the two media, it is divided into co-current (parallel flow) plate heat exchanger and counter-flow plate heat exchanger , cross-flow (cross-flow) plate heat exchanger, the latter two are used more;
5. According to the size of the gap of the flow channel, it is divided into conventional gap plate heat exchanger and wide gap plate heat exchanger ;
6. According to the corrugation, the plate heat exchanger has a more detailed distinction, which will not be repeated, please refer to: plate heat exchanger plate corrugated form.
7. According to whether it is a complete set of products, it can be divided into stand-alone plate heat exchangers and plate heat exchanger units.
The working principle of the plate heat exchanger
1. The structure principle of the plate heat exchanger
The detachable plate heat exchanger is a It is formed by a number of punched corrugated sheets at certain intervals, sealed around by gaskets, and overlapped with a frame and a compression screw. The four corner holes of the plates and gaskets form the distribution pipe and the collecting pipe of the fluid. Reasonably separate the hot and cold fluids so that they flow in the flow channels on both sides of each plate, and conduct heat exchange through the plates.
2. The working principle of the plate heat exchanger
The plate heat exchanger is a heat exchange plate with a certain corrugated shape pressed from a thin metal plate, and then stacked, using a plywood. , A heat exchanger made of bolts. Thin rectangular channels are formed between the various plates, and heat is exchanged through the half plates. The working fluid flows through the narrow and tortuous channel formed between the two plates. The hot and cold fluids pass through the flow channel in turn, and there is an interlayer plate in the middle to separate the fluids, and heat exchange is carried out through this plate. The structure and heat exchange principle of the plate heat exchanger determine that it has the characteristics of compact structure, small footprint, high heat transfer efficiency, large operation flexibility, wide application range, small heat loss, and convenient installation and cleaning.
The role of plate heat exchangers
I. Civil
1: Central heating
Plate type Due to its compact structure, easy operation and maintenance, and high heat transfer efficiency, heat exchangers have become the preferred heat exchange products for heat exchange stations in urban central heating projects, suitable for water-water heat exchange systems, steam-water heat exchange systems and domestic hot water supply system, which play an important role in rationally distributing heat energy and improving the level of thermal management.
2: Air conditioning system
Plate heat exchangers are widely used in the heat exchange of chilled water in air conditioning systems, and plate heat exchangers are installed between the cooling tower and the condenser near the condenser The chiller can act as a condenser to prevent corrosion or blockage of the equipment, and can save the running time of the chiller during transitional seasons.
3: Pressure blocker for high-rise buildings
In high-rise buildings, HVAC systems that use water, ethylene glycol, etc. as heat exchange media often have extremely high static Pressure, using the plate heat exchanger as the pressure blocker, can decompose the higher static pressure into several parts of smaller pressure, thereby reducing the system’s pressure requirements for pumps, valves, cold and hot water units and other equipment, saving equipment investment and operating costs.
4: Ice storage system
The ice storage system using plate heat exchangers plays a role in regulating peak-shaving and valley-filling of the power grid. That is, the chiller is used for cooling at night, and the ice is stored in the ice storage tank to meet the cooling demand for the next day and reduce the peak load of the air conditioner, thereby effectively saving energy and operating costs.
2. Industry
Plate heat exchangers have been widely used in metallurgy, mining, petroleum, chemical industry, electric power, medicine, food, chemical fiber, papermaking, light textile, shipbuilding, heating It can be used for heating, cooling, evaporation, condensation, sterilization, waste heat recovery and other situations.
Selection of plate heat exchanger
1. Plate type selection
The plate type or corrugated type should be based on the heat exchange occasion actual needs. In the case of large flow and small allowable pressure drop, the plate type with low resistance should be selected, otherwise, the plate type with large resistance should be selected. Depending on the fluid pressure and temperature, determine whether to choose a detachable type or a brazed type. When determining the plate type, it is not appropriate to choose a plate with a small veneer area, so as to avoid too many plates, a small flow rate between the plates, and a low heat transfer coefficient. This problem should be paid more attention to for larger heat exchangers.
2. Selection of flow and flow channels
Flow refers to a group of parallel flow channels in the same flow direction of a medium in a plate heat exchanger, while flow channels refer to a plate heat exchanger. Inside, a medium flow channel composed of two adjacent plates. In general, several flow channels are connected in parallel or in series to form different combinations of cold and hot medium channels.
The process combination should be calculated according to heat transfer and fluid resistance, and determined under the condition that the process conditions are met. Try to make the convective heat transfer coefficients in the cold and hot water flow channels equal or close to obtain the best heat transfer effect. Because the heat transfer coefficient obtains a larger value when the convective heat transfer coefficients on both sides of the heat transfer surface are equal or close. Although the flow velocity between the plates of the plate heat exchanger varies, the average flow velocity is still used for the calculation of heat exchange and fluid resistance. Since the “U”-shaped single-flow nozzles are all fixed on the pressing plate, it is easy to disassemble and assemble.
3. Pressure drop check
In the design and selection of plate heat exchangers, there are generally certain requirements for pressure drop, so it should be checked. If the check pressure drop exceeds the allowable pressure drop, it is necessary to re-calculate the design and selection until the process requirements are met.
4. Calculation method
The calculation of heat transfer coefficient and pressure drop is obtained from the performance curve of each manufacturer’s product. Performance curves (criterion correlations) are generally derived from product performance testing. For the plate type that lacks performance test, the reference dimension method can also be used to obtain the criterion correlation formula of the plate type according to the characteristic geometric dimensions of the plate type. Some general software in the world use this method.
5. Selection software
Regarding the selection software of plate heat exchangers, generally each manufacturer has its own selection software according to its own plate type. The commonly used software in the world are HTRI, HTFS and so on. The general calculation software is rarely published. Some domestic websites, such as the heat exchange support website, provide online calculation software for plate heat exchangers for reference.
Application range of plate heat exchangers
1. Solar energy utilization
Participate in the heat transfer medium glycol in solar collector panels Wait for the antifreeze heat exchange process to achieve the purpose of utilizing solar energy.
2. Chemical industry
Manufacture of titanium oxide, alcohol fermentation, ammonia synthesis, resin synthesis, rubber manufacturing, cooling phosphoric acid, cooling formalin, alkali carbon industry, electrolytic alkali production.
3. Iron and steel industry
Cooling quenching oil, cooling electroplating liquid, cooling reducer lubricating oil, cooling rolling mill, wire drawing machine coolant.
4. Metallurgical industry
Heating and cooling of aluminate mother liquor, cooling of sodium aluminate, cooling of lubricating oil of aluminum smelting mill.
5. Machinery manufacturing industry
Cooling of various quenching fluids, cooling of presses, lubricating oil for industrial mother machines, and heating of engine oil.
6. Food industry
Salt, dairy, soy sauce, vinegar sterilization and cooling, animal and vegetable oil heating and cooling, beer, wort heating and cooling in beer production, sugar production , Gelatin concentration, sterilization, cooling, manufacture of sodium glutamate.
7. Textile industry
Heat recovery of various waste liquids, cooling of boiling phosphating fibers, cooling of viscose liquid, cooling of acetic acid and acetic anhydride, cooling of aqueous alkali solutions, Heating and cooling of filaments.
8. Paper industry
Cooling black water, heating and cooling of bleaching salt and lye, heat recovery of cellophane waste liquid, heating and cooking acid, cooling sodium hydroxide aqueous solution, Recovery of waste liquid from bleached paper, condensation of exhaust gas, and preheating of concentrated pulp-like waste liquid.
9. Central heating
District heating with waste heat from thermal power plants, heating domestic water, and boiler district heating.
10. Oil industry
Heating and cooling synthetic detergent, heating whale oil, cooling vegetable oil, cooling sodium hydroxide, cooling glycerin, emulsified oil.
11. Electric power industry
Cooling of generator shaft pump, cooling of transformer oil.
12. Ships
Diesel engines, central coolers, jacket water coolers, piston coolers, lubricating oil coolers, preheaters, seawater desalination systems (including multi-stage and Single-stage).
13. Seawater aquaculture and seedling raising
The matching boiler to warm the seawater for seedlings has saved the use of coal, thereby saving energy and environmental protection and improving efficiency.
14. Others
Medicine, petroleum, ceramics, glass, cement, geothermal utilization, etc.
BR series products, the whole machine is equipped with two kinds of ordinary structure (used in less frequent dismantling and washing conditions) and suspended structure (used in more frequent dismantling and washing conditions).
The ordinary structure is composed of the main parts such as herringbone corrugated plate, gasket, pressing plate, upper and lower positioning bolts, and pressing bolts.
The suspended structure is composed of the main parts such as herringbone corrugated sheet, gasket, fixed pressing plate, middle plate, movable pressing plate, bracket, upper and lower positioning beams, and pressing bolts.
The plate heat exchanger has the advantages of high heat transfer coefficient, low pressure drop, compact structure, light weight, small footprint, convenient area and process combination, strong part versatility, wide choice of materials, and easy scale It has been widely used in food, machinery, metallurgy, petrochemical and shipbuilding and other fields, and has become the leading heat exchange equipment in urban central heating projects. In order to ensure the normal operation of the plate heat exchanger and prolong the service life of key components (such as plates and rubber pads), it is particularly important to understand the failure of the plate heat exchanger and its causes and treatment methods.
