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Evaporators play an important role in the pharmaceutical production process. With the implementation of the 13th Five-Year Plan and the deepening of the concept of environmental protection, evaporators, especially energy-saving and environment-friendly evaporators, will be very popular. The evaporator is an important equipment for pharmaceutical production, but the heat transfer function is indispensable for the evaporator. If the evaporator can not transfer heat, it means that a pile of scrap iron is worthless.
Taking a double-effect evaporator as an example, the author was informed that many factors affect the heat transfer of the double-effect evaporator during actual use. Here we will introduce in detail what factors will affect the transmission of the double-effect evaporator. heat.
In general, the evaporator is the main heat exchange device in the refrigeration unit. Like the condenser, the evaporator's heat transfer and heat exchange area, heat transfer temperature difference, and heat transfer coefficient are related. For the selected evaporator, the heat exchange area is certain, so in addition to properly increase the heat transfer temperature difference of the evaporator, it is mainly to increase the heat transfer coefficient of the evaporator. The increase of the heat transfer coefficient depends on the thermal physical properties of the hot and cold fluids, the flow conditions, the characteristics of the heat transfer surface, and the structural properties of the hair dryer. In the same way, analyzing these factors facilitates the adoption of appropriate measures in the design, installation, management, operation and maintenance of the evaporator to increase its heat transfer efficiency.
Next, the author will mainly analyze the factors affecting the boiling heat transfer coefficient of the refrigerant side. When the refrigerant liquid boils, a lot of air bubbles will be generated at the heat transfer surface first, the air bubbles will gradually become larger, and then they will break away from the wall surface, and then one by one air bubbles will continuously be generated at the wall surface. The more easily a wall is formed into a bubble, the more easily the bubble is separated from the wall, the more intense the boiling, and the greater the heat transfer coefficient.
It is reported that the factors affecting the boiling heat transfer coefficient mainly include the physical properties of the refrigerant liquid and the boiling temperature of the refrigerant. In addition, the boiling heat transfer coefficient of the refrigerant is also related to the configuration of the evaporator such as the diameter of the pipe, the length of the pipe, and the arrangement of the pipes; it is also related to the flow rate and direction of flow of the refrigerant and the presence or absence of lubricating oil in the refrigerant.
The main indicator for measuring the evaporator of an air-cooled chiller is the heat transfer coefficient and the heat transfer surface. In order to increase the efficiency of the evaporator, it should first increase its heat transfer coefficient. The key to improving the heat transfer coefficient is to improve the convection heat transfer between the refrigerant and the heat transfer tube wall.
Since the surface heat transfer coefficient of the refrigerant boiling is far greater than the heat transfer coefficient between the vapor and the pipe wall, the contact surface between the liquid and the pipe wall in the evaporator is large, and the steam generated when boiling is quickly discharged. When the heat transfer coefficient is constant, the size of the heat exchange surface determines the evaporation capacity of the evaporator. Increasing the number of heat transfer tubes and using ribbed tubes (finned tubes) can effectively increase the heat transfer surface, which is a common measure to increase evaporation capacity.
The evaporator has been widely used in the pharmaceutical production process. The author was informed that with the continuous advancement of technology, the evaporator technology has also been continuously improved. For example, the three-effect multi-stage evaporator R&D and production by Baokang Drying Machinery adopts the principle of tube-external heating. The material is heated for a short time, the evaporation speed is fast, and the concentration ratio is significant, which effectively maintains the original effect of the material. The energy-saving effect of this equipment is significant, saving about 70% of evaporation from a single-effect evaporator. The material is evaporated and concentrated in a closed system, and the environment is clean and comfortable; the unique defoaming device of the system equipment prevents the material from running.
In addition, the MVR evaporator is a new type of high-efficiency energy-saving evaporation device mainly used in the pharmaceutical industry. The device uses low-temperature and low-pressure steaming technologies and clean energy to generate steam for energy and separates water from the medium. It is currently internationally advanced. Evaporation technology is an alternative to conventional evaporators.
The pharmaceutical industry needs to evaporate a lot of water during the production process, which requires a lot of energy to heat the water to produce steam. Therefore, in the pharmaceutical field, evaporators are widely used. With the rapid development of the pharmaceutical industry and the expansion of market demand, evaporator manufacturers need to increase research and development efforts to overcome major problems and produce more scientific equipment to better meet market demand.
Heat transfer affects evaporator efficiency in the pharmaceutical industry
Evaporation is the heating of a solution containing a non-volatile solute to a boiling state where part of the solvent is vaporized and removed, thereby increasing the unit operation of the solute concentration in the solvent. In the pharmaceutical industry, evaporators are widely used. Evaporator is an important part of the four major refrigeration components. The low-temperature condensate “liquid†body passes through the evaporator and exchanges heat with the outside air. The “gas†heat absorption achieves the cooling effect.