Performance Of Spiral Wound Heat Exchangers Research Articles

Numerical study on the effect of surface wettability on the falling film flow characteristics of the spiral wound tube heat exchanger

Falling film flow is critical in the shell-side heat transfer performance of spiral-wound heat exchangers, and the wettability of the tube surface has a significant effect on the falling film flow characteristics. Therefore, a three-dimensional numerical model with two rows of tubes was established to study the influence of surface wettability on the liquid film distribution outside the tubes of a spiral wound heat exchanger. The transient spreading characteristics of the liquid film under different wettabilities were studied, the thickness of the liquid film along the axial and circumferential directions of the tube surface was quantitatively measured, and the effects of the tube spacing and Reynolds number on the flow characteristics of the falling film were analyzed. The results indicate that for the upper half-tube, increasing the contact angle to a certain extent is beneficial for improving the uniform distribution of the liquid film, whereas for the lower half-tube, decreasing the contact angle can suppress the fluctuation of the liquid film. The influence of the contact angle on the axial spreading of the liquid film was greater than that in the circumferential direction. When the contact angle does not exceed 30°, increasing Re can improve the wetting ratio, otherwise, increasing Re number has a limited effect on improving the wetting ratio. A smaller tube spacing can increase the thickness of the liquid film outside the tube. When the tube spacing changed from 4 mm to 8 mm, the average liquid film thicknesses of the circular, elliptical and egg-shaped tube decreased by 4%, 30.7% and 59.6% respectively.

Experimental and numerical study on the falling film flow characteristics outside circular tube applied in floating liquefied natural gas (FLNG) under offshore conditions

Spiral wound heat exchanger (SWHE) relying on falling film evaporation and boiling is often used for FLNG. The performance of SWHE can be impacted strongly by the motion of the FLNG caused by the wave and typhoon. The falling film characteristics of SWHE outside circular tube are studied experimentally and numerically by a visualization experimental device based on the high-speed camera and a numerical model based on the dynamic grid. The results show that the wave crest of the liquid film moves to the titled side under offshore conditions. The evolution process of falling film flow pattern outside circular tube with the tilt angle of 9° can be divided into four stages: droplet formation and migration, liquid column formation and migration, liquid column coalescence, liquid sheet formation. A correlation permitting the prediction of the falling film flow pattern outside circular tube and the other one permitting the prediction of the average film thickness of circular tube are developed respectively based on the experimental and numerical data.

Numerical investigation on flow pattern transformation and heat transfer characteristics of two-phase flow boiling in the shell side of LNG spiral wound heat exchanger

The flow pattern transformation and heat transfer characteristics of refrigerant flow in the shell side of LNG spiral wound heat exchangers (SWHEs) have a significant influence on the performance of SWHEs. A numerical model was developed to predict the flow pattern and heat transfer characteristics of two-phase flow boiling in the shell side of SWHEs. In the model, a submodel for simulating flow pattern was developed by employing Volume of Fluid combined with a Continuous Surface Force (VOF-CSF model), and a submodel for the mass transfer rate was developed; the forces and the heat and mass transfer rates were introduced into the control equations as the source terms. The experimental validation of the model shows that, the deviation of heat transfer coefficient is within ±20%, and the predicted flow patterns are consistent with those observed ones. Based on the proposed model, the flow pattern maps were developed, and the flow pattern transformation principles and heat transfer characteristics in SWHE shell side under different conditions were analyzed. The maximum heat transfer coefficient for SWHE shell side is enhanced by 10.5% as the longitude tube pitch increases from 1 mm to 3 mm, and reduced by 8.9% as the tube diameter decreases from 12 mm to 8 mm.

Experimental and numerical simulation study on the offshore adaptability of spiral wound heat exchanger in LNG-FPSO DMR natural gas liquefaction process

For studying the performance of spiral wound heat exchangers (SWHEs) applied in the LNG-FPSO (LNG Floating Production Storage and Offloading unit) dual mixed refrigerant (DMR) liquefaction process, an experimental device and a numerical simulation model of DMR liquefaction process are established. Based on the experimental results and the REFPROP software, the effects of sloshing on the performance of SWHE are selected as the disturbances to test the responses of the DMR liquefaction process. The results show that the sloshing-induced reduction of SWHE heat transfer performance is within 50% for all sloshing cases. The decrease of specific power consumption of DMR liquefaction process is within 13%, when the SWHE is under sloshing angles from 3° to 9° and sloshing periods from 6 s to 30 s.

Effect of flow configuration on the performance of spiral-wound heat exchanger

The effects of flow configuration on the heat transfer performance of a spiral wound heat exchanger were experimentally investigated. The spiral-wound heat exchanger was made from stainless steel tubes of 6 mm outside diameter and consisted of 4 helical coils centrally connected in series, with a longitudinal and transverse pitch of 12 mm. Three air flow configurations were tested, namely axial, radial, and mixed axial-radial flows. The overall heat transfer coefficient was determined from the experimental data and the shell-side convection heat transfer coefficient was calculated from the tube-side convection heat transfer coefficient and the total thermal resistance. The measurements were conducted for tube-side Reynolds number in the range of 9000–10,000 (for water flow inside the tubes) and shell-side Reynolds number in the range of 500–6000 (for air flow outside the tubes based on maximum velocity). The results showed that the mixed axial-radial flow configuration has the highest heat transfer coefficient and pressure drop followed by the axial and radial flow configurations. Correlations of Nusselt number, Colburn-j factor, and friction factor were developed for the different flow configurations and a comparison with the Nusselt number correlations for heat transfer over bank of tubes was presented. The correlations are in good agreement with experimental data and has correlation coefficient in the range of 78–98%.

Effects of spacing bars on the performance of spiral-wound heat exchanger and the fitting of empirical correlations

The effects of different arrangement styles of spacing bars on flow and heat transfer performance of spiral wound heat exchanger were numerically studied. The results show that, when the spacing bar are arranged in staggered style, the fluids in the low-velocity regions would flow into high-velocity regions because of the viscous force and the region near the spacing bar are easier to form eddies which enhance the interactions of the fluid in adjacent tube layer. The local details of temperature and flow field suggest that the staggered arrangement could strengthen both disturbance of the velocity field and heat transfer in the shell side. To evaluate the performance of the different arrangements of spacing bar, the TEFs (thermal performance factors) are calculated and the values indicate that the staggered arrangement of spacing bar has positive impact on the performance of SWHEs. However, the quantity of spacing bar has no significant influence on flow and heat transfer performance. The correlations of Nu number and friction factor f are fitted. The Nu number and friction obtained from correlations are in good agreement with numerical simulation data, the average errors of Nusselt number and friction factor are 4.66% and 7.49%, respectively.

A mathematical model of floating LNG spiral-wound heat exchangers under rolling conditions

To develop a simulation tool for the design of spiral-wound heat exchangers (SWHEs) for floating LNG, a mathematical model of floating LNG SWHEs under rolling conditions is proposed in this paper. In the mathematical model, the mass flow rate distribution at arbitrary tilt angles is obtained by computing three-dimensional mass transfer among adjacent control volumes to distinguish the gas and liquid rich regions, and then the heat transfer models for gas and liquid rich regions are respectively developed, capable of reflecting the influence of tilt on the performance of SWHEs. An overall alternative iterative algorithm is developed to solve the equations of the presented model. The validation shows that the mean deviation of the predicted and tested mass flow rate distribution and heat exchange capacity are within 16.3% and 3.2%, respectively. The impact of rolling amplitude on the heat transfer performance based on the proposed model is analyzed, and the results indicate that the heat exchange capacity decreases with the increase of the rolling amplitude, and the decrease is from 2.2% to 6.7% under the rolling amplitude from 3° to 15°, when the mass flow rate of shell-side inlet is well distributed.