Views:1 Author:Site Editor Publish Time: 2020-04-21 Origin:Site
The heat transfer coefficient of a plate heat exchanger is an indicator of the level of certain heat transfer performance. For heat exchangers of different structures, the heat transfer coefficient is not the same during the same fluid treatment and temperature treatment process.
Represents water-to-water heat exchange equipment, using a plate heat exchanger with a heat transfer coefficient of about 3000 ~ 7000W / ㎡ * ℃. The tube heat exchanger is about 1000 ~ 2000. Here. It indicates that the plate type has higher heat transfer performance.
One heat, that is, the transient transmission during the solidification process is the first and most important, it is the driving force for the sustainable development of the solidification process.
The second migration refers to the existence of two interfaces when the metal is solidified, namely the solid-liquid interface and the metal-mold interface, and the two interfaces merge dynamically during the solidification process to cause dynamic migration, and the heat transfer phenomenon on the interface becomes extremely complicated .
The solidification process of the three-transfer metal is a three-dimensional heat transfer physical process that includes three transfers of momentum transfer, mass transfer and transfer transfer, and there are coupling, convection and radiant heat transfer in the transfer process. the way.
When the temperature difference between the fluid and the solid surface is 1K, the conversion of 1m * 1m wall area per second can be transferred. The size of h reflects the strength of convection heat transfer.
h is related to the factors that affect the heat transfer process, and can vary in a large range, so Newton's formula can only be selected as a definition of the heat transfer coefficient.
It does not find the internal relationship between the factors affecting convective heat transfer and h, nor does it bring any substantial simplification to the engineering calculation, but only transfers the complexity of the problem to the determination of the heat transfer coefficient.
Therefore, in engineering heat transfer calculations, the main task is to calculate h.
The heating surface is limited by the wall surface of the container, and the heat transfer coefficient is not high. In order to improve the heat transfer coefficient and make the liquid in the kettle heated evenly, a stirrer can be installed in the kettle.
When cooling water or no phase change heating agent is introduced into the jacket, spiral sections or other measures to increase turbulence can also be provided in the jacket to increase the reduced heat supply coefficient of the jacket to supplement heat transfer Insufficient surface, you can also install a coil inside the kettle, jacketed heat exchangers are widely used in the heating and cooling of the reaction process.
These two stages alternate. Usually two regenerators are used alternately, that is, when hot gas enters one device, cold gas enters the other device. It is often used as a regenerator in the metallurgical industry, such as a steel-making open hearth furnace.
It is also used in the chemical industry, such as air preheaters or combustion chambers in gas stoves, and regenerative cracking furnaces in artificial oil plants. Thermal heat exchangers are generally used in applications where the requirements for medium mixing are relatively low.