板翅式换热器物流分配特性及换热的研究/Fluid Flow Distribution and Heat Transfer
Plate-fin heat exchanger (PFHE) plays an important role in aerospace, chemical engineering and HVAC, because of its high heat transfer efficiency and compactness. As the result of all sorts of problem in design, manufacture, assembly, installation and operation of heat exchangers, the fluid flow maldistribution happens in PFHE, which leads to the performance deterioration of the heat exchanger. How to improve the fluid flow distribution so as to enhance the efficiency of heat exchanger attracts the attention of a lot of researchers.
The influences of the conventional distributor and header configurations used in industry at present on the fluid flow distribution in PFHE were numerically investigated for the first time. The numerical results showed that the fluid flow maldistribution is very serious in the heat exchanger. On the basis of the analysis of the fluid flow maldistribution, some improved header and distributor configurations were computed. The computational results indicated that the improved header and distributor configurations can effectively improve the performance of fluid flow distribution in the heat exchanger. It was also found that nonuniform inlet velocity, inlet angle and punched ratio are the main factors affecting the distribution performance of distributor.
The available experimental system only used to study liquid flow distribution has been expanded to investigate gas flow distribution, two-phase flow distribution and heat exchange. For the experimental study, an intellective data acquisition system with high precision has been developed based on the computer. It can accurately measure the parameters of the pressure, flow rate and temperature in the experimental system. The heat exchangers were simulated according to the configuration of PFHE used wildly in the industry for the experimental research.
The experimental study of the influence of different inlet configurations on the gas fluid flow maldistribution in PFHE has been completed. It is found that very serious is the fluid flow maldistribution caused by the header and distributor, which are used widely at present in the air separation plant. The influence of the fluid Reynolds number on the fluid flow maldistribution in PFHE is very heavy. The correlations of the flow nonuniformity parameter and the fluid Reynolds number under the different inlet configurations have been obtained
The header configuration with perforated plate was brought forward. The experimental investigations of the influence of the orifice diameter, the distribution of orifice, the perforated plate length and the dimension of header on the fluid flow maldistribution in PFHE have been performed. The experimental results showed that the header configuration with perforated plate greatly improves the fluid flow distribution in PFHE and the ratio of the maximum flow velocity to the minimum flow velocity of the heat exchanger drops from 3~4 to 1.1~1.2. The header configuration with the staggered arrangement perforated plate brings about the best improvement.
The two-phase fluid flow distribution in PFHE was experimentally studied. The experimental results indicated that the two-phase fluid flow maldistribution among the passages of PFHE is more obvious than the single-phase flow. Inlet flow rate and dryness are the main factors affecting the two-phase fluid flow distribution in PFHE. The liquid phase nonuniformity is more serious than that of the gas phase and the flow nonuniformity in the lateral direction is more serious than that in the gross flow direction.
On the basis of the study of fluid flow maldistribution in PFHE, the influence of fluid flow maldistribution on the performance of heat exchangers was studied experimentally. It is shown that the fluid flow maldistribution leads to a great loss of the heat exchanger effectiveness. The correlation of the flow nonuniformity parameter and the heat exchanger effectiveness loss has been obtained by the experimental study.
The numerical results are compared with the experimental results. They are basically consistent which indicates that the mathematical model and the calculating method are reliable. The method and conclusions of this paper are of great significance on the optimum design of PFHE.