Use finned tube condenser and evaporator, its fin spacing of how to choose
Life experience tells us: radiator area is larger, the higher surface temperature (that is, the bigger the temperature difference between surface temperature and air), the longer the heating time, the heat transfer, the greater the room more warm. This suggests that the convective heat transfer and heat transfer area is proportional to, and is directly proportional to the difference in temperature, and time is proportional to the. In order to compare the strength of the convective heat transfer under different conditions, we need to define a physical quantities, is called the "heat transfer coefficient. Heat transfer coefficient is refers to the unit area, the unit temperature difference (temperature difference between wall and fluid), convective heat per unit time. Its unit is J/(s. ㎡. ℃) or W/(㎡ ℃). The convective heat transfer coefficient is commonly used symbol h.
Example 3: steam generator, the tube is the boiling water, flue gas pipe outside, fin should add in the flue gas side. When, should be paid attention to in the design, should as far as possible on the side of the heat transfer coefficient of the tube, in order to add fin. (2) such as pipe on both sides of the heat transfer coefficient is very small, in order to strengthen heat transfer, should be in both at the same time adding fin, if there is difficulties, on the structure, both sides are without fin. In this case, if only on one side and fin, the increase of heat transfer is not have obvious effect. Case 1: the traditional tubular air preheater, air tube go, flue gas pipe outside. Because is gas for gas heat exchanger, on both sides of the heat transfer coefficient is very low, the tube and fin and difficult, have to light tube. Example 2: heat pipe air preheater, although is still a flue gas heating the air, but because of the flue gas and air are outside the pipe flow, so the flue gas side and air side can be conveniently used finned tube, the heat transfer is greatly increased. (3) if the tubes on either side of the heat transfer coefficient is large, it is not necessary to adopt finned tube. Case 1: water/water heat exchanger, heat cold water with hot water, on both sides of the heat transfer coefficient is high enough, there is no need to use the finned tube. But in order to further enhance the heat transfer, can use threaded pipe or corrugated pipe instead of light. Example 2: power plant, the condenser tube is water vapor condensation, the tube water. On both sides of the heat transfer coefficient is very high, in general, without using finned tube.
Because of the air side heat transfer "ability" far less than water side, limits the water side heat transfer "ability", makes the air side heat transfer process of the "bottleneck", limits the increase of heat transfer. In order to overcome the "bottleneck" of the air side effect, the surface mounted to the outside air side fin will be one of the most wise choice. After adding the fin, the air side heat transfer area of the great extension of the original, you fill the shortcoming of the air side heat transfer coefficient is low, make the heat transfer is greatly increased, the following the appended drawings. About add the effect of fin can also use this example to illustrate more image: in a border ports of entry and exit, assume that party a port has ten inspection, can release 5000 people per hour, while party b port only a wicket, and slowly, can release only 50 people per hour. So that party b side becomes the bottleneck of passenger clearance, makes the "ability" of party a can't play. In order to improve the clearance flow, the most effective way is in party b side open several test. And it is the same with the principle of the fin. In understanding the principle and function of finned tube, choose in what occasion finned tube, with the following principles: (1) the heat transfer coefficient on either side of the pipe if the difference is very big, it should be mounted in the side of the heat transfer coefficient small fin.
Finned Tube, also called fins pipe or Finned Tube, English name is "Fin Tube" or "Finned Tube", also sometimes called the "Extended Surface Tube", namely the Extended Surface Tube. As the name implies, finned tube is on the original surface of the pipe (whether outer surface or inner surface) treatment on a lot of fin, the original surface extension, and form a unique heat transfer element.
