Optimization Of The Heat Transfer Temperature Difference Field Of Multi-stream Plate-fin Heat Exchanger

Plate-fin heat exchanger(PFHE), as one of the high performance compact heat exchanger, is widely used in petrochemical, gas separation and gas liquefaction industry. Compared with the two-stream heat exchanger, multi-stream heat exchanger is much more complex due to the various fluids, complicated structure and heat transfer process. The mutual influence and the commutative coordination between velocity field and temperature-difference field of each channel with other numerous factors make it difficult to analysis performance and optimization in multi-stream plate-fin heat exchanger.With the research object of the multi-stream process in the plate-fin heat exchanger of natural gas liquefaction process based on mixed refrigerant in the paper, fully synergistic and separate heat exchange models were defined. Using Aspen plus simulation to compare the heat transfer graph of two processes, the results showed that separate heat exchange can not meet the heat transfer process requirements.Exergy analysis for fully synergistic and separate heat transfer process was discussed, results showed that exergy loss of separate heat transfer is more than ten times to the fully synergistic heat transfer. Furthermore, exergy efficiency of fully synergistic heat transfer up to 92.82%, but the exergy efficiency of several different heat flow ratio in separate heat transfer is about 45% which indicated that fully synergistic heat transfer can reduce the heat loss and enhance the exergy efficiency in the multi-stream heat transfer process.To study the impact of the passage arrangement on the plate-fin heat exchanger performance, software Aspen Muse was used to compare several different zigzag diagram of different passage arrangement in multi-stream heat exchange. The zigzag diagram supplied the assessment of passage arrangement.In the simulation process, Aspen Muse existed some limitations so that the multi-stream plate-fin heat exchanger model was established. The model called the Aspen Plus mixed refrigerants physical properties database to calculate the properties and used VBA programming. The calculation of the boiling heat transfer coefficient was done using Chen formula, the calculation of the condensation heat transfer coefficient was done using Shah formula.On the basis of simulation program this paper established, the multi-stream process in the plate-fin heat exchanger of natural gas liquefaction process based on mixed refrigerant was calculated. To compare and analyze the impact of adjacent cold streams’ synergy on the whole heat transfer process, the heat transfer resistance between adjacent cold streams was changed to calculate. On the analysis of temperature-difference field, it is found that if there is no synergy between the adjacent cold streams, heat transfer process will not work, the better synergy between the adjacent cold streams, the heat of multi-stream heat exchange process is much more. The results showed that the synergy between the cold streams has great effect on the whole multi-stream heat exchange process. Therefore, in multi-stream plate-fin heat exchanger design, the correlation calculations of synergy heat transfer between the adjacent cold streams should be considered.