Flow resistance deviation caused by material thickness deviation

Although the cause of the fin thickness deviation unit heat transfer area is not very different, but the influence of the flow resistance of the fluid is large, easy to cause the bias, thus affecting the performance of heat transfer. The following is to a set of data to illustrate: the same specifications (such as fin height, fin pitch, the same type) nominal thickness of 0 - 2 mm aluminum foil when the material thickness deviation of 0 - 03 mm (according to the requirements of GB/T 3880 - 1 - 2006), fin flow resistance is 19 63%; when the material thickness deviation of 0 - 015 mm (according to the requirements of HTA 2631 - 2008), fin flow resistance is 9 / 38%; when the material thickness deviation of 0 - 01 mm, fin flow resistance is 6 - 16%.

According to the first fin flow resistance deviation made, for multiple parallel heat exchanger equipment for large air, there exist a large deviation problem, which caused by the fluid flow is up to 9 - 4%, seriously affect the heat transfer performance. In order to ensure the performance of the heat exchanger, the design margin should not be less than 9. 4%. According to the third flow resistance deviation of the fin, the fluid flow caused by only 3%. The corresponding fin, consider the drift problem (the difference is 6 - 4%) required the design margin can be reduced to 3%. It can be seen that the thickness deviation of fin material should be strictly controlled when ordering and receiving materials.

                                           
        At the same time, as far as possible in the production management of fins, the same heat exchanger can be used in the same batch of material processing. Because the thickness tolerance of the same batch of materials is the same, the size tolerance of the fin is easy to reach, so as to reduce the tolerance of parts. If the same heat exchanger using different batches of material production fin, the size of the tolerance is different, resulting in each layer of the fin height is not the same, it is difficult to achieve the same fluid flow per layer. Therefore, in the production process should consider the effect of this factor on the efficiency of the heat exchanger, as far as possible the same heat exchanger using the same batch of materials processing, at least the same kind of fluid using the same batch of materials processing parts. The same fixed supply of materials, is one of the important measures to reduce the drift. Flow resistance deviation effect of fluid flow, supporting a number of heat exchangers used in parallel in large scale air separation equipment, will lead to serious bias, which not only make the heat exchanger overall resistance increased, but also seriously affect the heat transfer performance.