Numerical and experimental study on the falling film flow characteristics with the effect of co-current gas flow in hydrogen liquefaction process

Liquid hydrogen storage and transportation is an effective method for large-scale transportation and utilization of hydrogen energy. Revealing the flow mechanism of cryogenic working fluid is the key to optimize heat exchanger structure and hydrogen liquefaction process(LH2). The methods of cryogenic visualization experiment, theoretical analysis and numerical simulation are conducted to study the falling film flow characteristics with the effect of co-current gas flow in LH2spiral wound heat exchanger.The results show that the flow rate of mixed refrigerant has a great influence on liquid film spreading process, falling film flow pattern and heat transfer performance. The liquid film of LH2mixed refrigerant with column flow pattern can not uniformly and completely cover the tube wall surface. As liquid flow rate increases, the falling film flow pattern evolves into sheet-column flow and sheet flow, and liquid film completely covers the surface of tube wall. With the increase of shear effect of gas-phase mixed refrigerant in the same direction, the liquid film gradually becomes unstable, and the flow pattern eventually evolves into a mist flow.

Research on the falling film flow and heat transfer characteristics of FLNG spiral wound heat exchanger under sea conditions

As the key equipment of floating liquefied natural gas(FLNG)process,the performance of spiral wound heat exchanger(SWHE)influences operation costs and reliability of the whole system.The sea conditions destroy the falling film flow state of the refrigeration and then affect the heat transfer performance of FLNG SWHE.In order to design and optimize the SWHE,a cryogenic experimental device of FLNG process and a numerical model of falling film flow have been constructed to study the effects of sea conditions on the falling film flow and heat transfer characteristics of SWHE.The cryogenic experimental results show that the pitching conditions have larger effects on the heat transfer performance than yawing.Under the pitching angle of 7°,the natural gas temperature and gaseous refrigerant temperature increase by 3.22°C and 7.42°C,respectively.The flow rates of refrigerant and feed natural gas have a great impact on the heat transfer performance of SWHE under pitching and compound sloshing conditions.When the tilt angle increases to 9°,the tube structure with outer diameter D=8 mm and pipe spacing S=4 mm is recommended to reduce the drying area of the pipe wall surface.

Numerical Study of Heat Transfer Characteristic for Subcooled Falling Film outside the Shaped Tubes under Rolling Motion

The heat transfer performance of spiral wound heat exchanger used in the floating liquefied natural gas(FLNG)may be significantly affected by the sloshing conditions.In this paper,a three-dimensional numerical model combined with the dynamic mesh technology is conducted to study subcooled falling film heat transfer under static and sloshing conditions.The three-dimensional velocity distribution of the liquid film on the shell side is observed.The effects of cross-section shape of heat exchange tubes,Reynolds numbers and sloshing parameters on heat transfer characteristics are analyzed.The results indicate that the heat transfer performance of the egg-shaped tube is superior to that of the elliptical and circular tube under both static and sloshing conditions due to significant heat transfer improvement in the lower half of the tube.The heat transfer coefficients of three different kinds of tubes decrease under sloshing conditions.When the rolling amplitude is 6°,the average heat transfer coefficients of the circular tube,elliptical tube and egg-shaped tube are reduced by 2.1%,3.7%and 4.9%respectively.Under the current sloshing parameters,increasing the rolling amplitude,the heat transfer coefficients of three different tubes are slightly increased,while the sloshing period has little effect on heat transfer.The egg-shaped tube and elliptical tube are greatly affected by sloshing motion at the low Reynolds number,while the effect is relatively small at the high Reynolds number.