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Cause Analysis of Heat Exchanger Data of Cooler

Number of visits: Date:2014-10-30 16:06

  In recent years, by the impact of foreign products and technology tend to increase with the amount of wind, many products have reached the level of foreign popular, high up to 236m3 / h. Foreign individual up to 29Om3 / h. Of course, the increase in air flow to a certain extent, so that the heat transfer coefficient of the chiller has been greatly improved, but should also take into account the increase in air volume will inevitably increase power consumption and reduce its economy. Especially in the use of low-temperature cold storage, the fan heat basically by the air volume of the cubic rise, it will greatly increase the cooling load: (5) and the relationship between the finned tube material from theory to practice illustrate the choice of different materials on the wing The same area, structure, air volume conditions, the aluminum tube, aluminum sets of chillers than the steel pipe, air conditioning, air conditioning, cooling fan, Steel jacket cooling fan unit cooling area of ​​its heat load is about 18-40%: We have two of the same area, the structure of the air flow of aluminum tubes, aluminum and steel, steel chillers in the test bench for testing, its The result is that the heat transfer coefficient of the former is about 20 to 35% higher than that of the latter, but this advantage decreases as the evaporation temperature decreases and the surface frost thickens. Of course, different manufacturers of products or differences。

  And the fin tube arrangement and structure of the relationship between the well-known, cross-row than the row flow resistance but heat exchange strong. So in order to pursue efficient heat exchange, in the chiller without exception, have adopted a fork row way. According to the current prevalence of air volume are allocated with a larger situation, the air side are higher in the Reynolds number Re under the conditions of flow, heat transfer. At this point the air side of the coefficient of heat dissipation in the direction of the depth of the coil change, due to large initial disturbance cloud, stable rows will gradually increase, it is possible from the second row since the gradual stabilization, after several rows of coils produced The perturbation effect has been a secondary factor. If the reduction in the number of rows along the air flow direction; reduce the cross-section of the tube spacing; reduce the distance will increase the air side of the heat coefficient increases, and thus the finned coil heat transfer coefficient can be increased。

  In order to adapt the chillers to use under the frosting condition, if the variable-slice structure is adopted, the heat transfer efficiency can be maintained under the frosting condition and the defrosting cycle can be prolonged. We in the low-temperature test room through the actual test results, the use of variable-chip structure and the conventional structure of the chill-chip compared to the chill found that in the non-frost conditions, the use of variable chip structure of the cooling fan does not account for heat transfer coefficient However, in the frost condition, especially when the surface of the windward fin has been thicker frost layer, the evaporation temperature is lower, the actual measured heat transfer coefficient than the dry conditions decreased by about 32%, In addition, the same structure of the chiller, the use of the same air volume, different wind pressure of the fan, almost similar in the frost and the cooling fan is the same, The evaporator temperature conditions, the use of higher air pressure fan of the cooler, can maintain a relatively high heat transfer coefficient values; some designers, in order to destroy the fin surface thermal boundary layer and the fin surface made into wrinkles, , Slits and other shapes, that this can reduce the thermal resistance and enhance heat transfer. In fact, the use of the chiller in the frost condition is harmful and useless. In the design, manufacture, try to reduce the contact thermal resistance (such as the use of finned coil overall galvanized; to enhance the expansion tube technology; increase the root of the fin and tube surface contact surface, etc.); handle short wind problems; Heat pipe and other new technologies, can be different degrees of heat transfer performance。

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