Study On Passage Arrangement And Distribution Of Multi-stream Heat Exchanger In BOG Re-liquefied System

Multi-stream heat exchanger is the key equipment in BOG re-liquefied system of smallLNG carrier, which is a tube and shell heat exchanger. There is not sophisticated theories andmethods about passage arrangement and distribution in tube-side yet. In view of this, thispaper provides reference for the design of multi-stream heat exchanger by study the impact ofpassage arrangement and distribution in tube-side for the heat transfer performance ofmulti-stream heat exchanger and the stress distribution of tube sheet. In this paper, the mainworks and research result are follows:(1) A three-dimension finite element model of multi-stream heat exchanger is establishedby FLUENT software. And then select standard k-ε turbulence model in the software.Multi-stream heat exchanger with six different tube-side passage arrangement is numericalsimulated. The simulation results show that the mode of tube-side passage arrangement willnot impact the heat transfer performance of multi-stream heat exchanger while the tube-sidepassage distribution proportion is constant. Multi-stream heat exchanger with seven differenttube-side passage distribution proportion is numerical simulated. Analyzing the heat transfercharacteristic and found the optimal tube-side passage distribution proportion of multi-streamheat exchanger exist. Then choosing different material as the refrigerant in pre-cooling stageof BOG re-liquefied system，to study the optimal tube-side passage distribution proportionwhen the refrigerant in pre-cooling stage is different. Choosing different flow ratio of thetube-side fluid，to simulate the optimal tube-side passage distribution proportion when theflow ratio of the tube-side fluid is different. The conclusion is meaningful for improving theheat transfer performance of multi-stream heat exchanger and reducing the overall powerconsumption of the BOG re-liquefied system.(2) A three-dimension finite element model of tube sheet in multi-stream heat exchangeris established by ANSYS software. Multi-stream heat exchanger with six different tube-sidepassage arrangement is numerical simulated. On basis of this model the temperature field andthe stress field under different tube-side passage arrangement is analyzed. First of all, temperature distribution of tube sheet under six passage arrangement is analyzed, and foundthe maximum temperature decrease with the increase of the number of the tube-side passageand the temperature distribution of tube sheet tend to be more uniform. Then, stress of tubesheet under three conditions are analyzed, and found the maximum stress of tube sheetdecrease with the increase of the number of tube-side passages, but the rate of descentdecrease with the increase of the number of passages. The conclusion is meaningful forreducing the thermal stress of tube sheet in multi-stream heat exchanger and ensuring the safeoperation of BOG re-liquefied system.