Wenke Zheng,Weihua Cai,Yiqiang Jiang,*

1 School of Architecture,Harbin Institute of Technology,Harbin 150090,China

2 Key Laboratory of Cold Region Urban and Rural Human Settlement Environment Science and Technology,Ministry of Industry and Information Technology,Harbin 150090,China

3 School of Energy Science and Engineering,Harbin Institute of Technology,Harbin 150001,China

4 School of Energy and Power Engineering,Northeast Electric Power University,Jilin 132012,China

Keywords:Spiral-wound heat exchanger Gas-liquid mixture Multiphase folw Distribution uniformity

ABSTRACT The non-uniformity of gas-liquid mixture is a critical issue which leads to the heat transfer deterioration of spiralwound heat exchangers(SWHEs).Two-phase mass flow rate and the content of gas are important parameters as well as structural parameters which have prominent influences on flow distribution uniformity of SWHE shell side.In order to investigate the influences of these parameters,an experimental test system was built using water and air as mediums and a novel distributor named“tubes distributor”was designed.The effects of mass flow rate and the content of gas on two-phase distribution performance were analyzed,where the mass flow rate ranged from 28.4 to 171.9 kg·h-1 and the content of gas changed from 0.2 to 0.8,respectively.The results showed that the mixture mass flow rate considerably influenced the liquid distribution than that of gas phase and the larger mass flow rate exhibited the better distribution uniformity of two-phase flow.It was also found that the tubes distributor had the better two-phase uniformity when the content of gas was around 0.4.Tube diameter played an important role in the distribution of gas phase and slit width was more significant for the uniformity of liquid phase.

1.Introduction

Spiral-wound heat exchangers(SWHEs)have been widely used in petrochemical enterprises,pharmaceutical industries,nuclear power stations and so on,mainly owing to their highly compact structure,high-pressure endurance and good thermal compensation[1-5].The fluid medium in the SWHE shell side is a downward flow which always suffers maldistribution leading to the deterioration of heat transfer performance[6].A uniform gas-liquid flow distribution is essential to maintain high heat transfer efficiency.Therefore,it is necessary to investigate the distribution characteristics of SWHE shell side to explore a uniform distributor for the gas-liquid flow.

Some scholars have investigated the flow maldistribution in singlephase heat exchangers including plate-fin heat exchangers(PFHEs)and SWHEs.Zhang et al.[7-9]and Jiao et al.[10,11]studied the singlephase flow maldistribution in the conventional header at the entrance of a heat exchanger and proposed a new kind of header with the second header.Wen and Li[12,13]also designed a novel header with punched baffle used in single-phase flow and compared the uniformity of the novel structure and the traditional one.Both new distribution structures had the better distribution performance.

Based on the research achievements of single-phase heat exchangers,many experts started to investigate the two-phase uniformity of gas-liquid mixture and found that two-phase non-uniformity was more complex than single-phase flow.Zou and Hrnjak[14,15]investigated the effect of mass flow rate on the two-phase distribution with R134a and PAG46 as mediums.The results showed that mass flow rate had important influence on flow uniformity and heat transfer capacity.Vist and Pettersen[16]experimentally studied the effects of the content of gas and heat load on two-phase distribution.It was found that the content of gas had larger effects on maldistribution than heat load.Osakabe et al.[17]built an experimental bench with water and air as mediums to test the impact of flow pattern.The results indicated that the smaller bubble was more beneficial to uniform distribution.

Some scholars also found that the parameters of distributor structure played a more important role in two-phase flow distribution than other parameters.In the study of Kim et al.[18],the triangular header had the best two-phase distribution performance than other headers.Tong et al.[19]carried out a quantitative systematic study on the influence of header structures on maldistribution and gave the better strategies including:(a)the enlargement of cross-sectional area of the distribution manifold,(b)the variation of cross-sectional areas of the outflow channels,(c)the linear tapering of cross-sectional area of the distribution manifold,and(d)the non-linear tapering of crosssectional area of the manifold by means of quarter-elliptical contouring of the manifold wall.On the other hand,Marchitto et al.[20-22]proposed a new kind of distribution structure named“fluted-type distributor”and measured its flow uniformity,after which the new structure achieved better distribution uniformity.

Although some modified structures had been proposed to improve the two-phase maldistribution,the gas-liquid mixture uniformity of one inlet port structure like single-phase heat exchangers did not satisfy the requirement of heat transfer improvement of heat exchangers.Then some experts put forward another distribution structure which separated the two-phase mixture firstly and distributed gas phase and liquid phase respectively before mixing.Based on the investigations of Saad et al.[23-25],Yuan et al.[26,27]and Zheng et al.[28-30],this new distribution structure had the better two-phase distribution uniformity than the structure with single inlet.

However,most investigations are about the distribution performance of PFHEs.So far,little has been done on the flow distribution performance of SWHEs.Many studies related to SWHEs focused on the heat transfer coefficients in the shell side[31-38]and tube side[39-52]of SWHEs,among the least of available literatures on twophase flow distribution in SWHEs.However,a recent attempt as presented through Wang et al.[6]is recommended.Therefore,the lack of researches on two-phase distribution constitutes the main barrier to the application of SWHEs and a fact that calls for more deep investigations on the same,probably leading to more new resolute ideas.

In line with the above,in order to supplement the insufficiency of distribution investigation in SWHEs and lay the foundation for the application of SWHEs,this paper intends to study the two-phase flow distribution performance in the shell side of SWHEs.A novel two-phase distributor suitable for SWHEs was designed as the test section and its distribution performance was studied.An experimental bench was built with water and air as working fluids.The effects of mass flow rates,the content of gas and the structural parameters on the gas-liquid distribution characteristics were analyzed.

2.Experimental

2.1.Experimental system

An experimental apparatus was built for the study of distributor distribution characteristics.The system consists of two supply lines of gas and liquid that merge into the pipeline(as shown in Fig.1)in which gas and liquid are air and water,respectively.The main devices include:a liquid tank(W-01),a liquid pump(P-01),a gas compressor(AC-01),a gas storage(GT-01),a test section(T-01),a mixer(M-01),eight three-way reversing valves(V-01-08),eight gas-liquid separators(S-01-08),eight collecting containers(GB-01-08)and some pipes.

The gas generated by the compressor(AC-01)flows through the gas storage(GT-01)and mixer(M-01)with liquid from the liquid pump in the mixer.The gas-liquid mixture flows into the test section(T-01)and then is divided.The two-phase mixture flows out of the test section through eight branches and passes eight three-way reversing valves(V-01 to V-8)located behind the test section.When the experiment starts the three-way reversing valves(V-01 to V-8)open to the liquid tank and the two-phase mixture flows into the liquid tank in which liquid takes part in the next cycle and gas is released to the atmosphere.When the distribution performance of the test section is begun to measure the three-way reversing valves(V-01 to V-08)open to the gas-liquid separators(S-01-08).The gas-liquid mixture enters into the separators and is separated there.Gas flows out of the separators and is measured by the metal float flow meters before releasing to the atmosphere.Liquid flows out of the separators and enters into the collecting containers(GB-01-08).The three-way reversing valves(V-01 to V-08)open to the liquid tank after the measuring time is over.Then the average mass flow rate of liquid and gas in the measuring time is used to evaluate the distribution performance of test section.

2.2.Test section

Fig.1.Schematic diagram of the experimental system.P-01:liquid pump,T-01:test section,GB-01-GB-08:8 barrels,S-01-08:8 liquid-gas separators,W-01:liquid tank,AC-01:gas compressor,GT-01:gas storage tank,V-01-08:8 three-way reversing valves,M-01:mixer,W:liquid pipe,A:gas pipe,WA:gas liquid mixing pipe.

These existing researches indicated that the distributors with separate gas and liquid distribution have the better two-phase distribution performance than the typical manifold with single inlet.Based on these investigations,a new kind of distributor named“tubes distributor”was designed for SWHEs as shown in Fig.2.This structure has the better distribution characteristic than the manifold with two-phase mixture distribution because it separates and distributes gas and liquid flows respectively.The advantage of the tubes distributor is that the interaction between gas and liquid is weakened,making it more easy to distribute gas or liquid alone.It is comprised of a center barrel,an upper baffle,a lower baffle and many tubes with slits.This distributor is located above the tube bundle in SWHEs and gas-liquid mixture flows through the distributor from top to bottom.The two-phase mixture flows into the center barrel and separates in the center baffle due to the influence of gravity and inertia.After flowing into the space between the center barrel and SWHE shell side,gas flows through the upper baffle,tubes and lower baffle before entering the heat transfer area in SWHE shell side.Liquid accumulates to a certain height and flows from the center barrel to SWHE shell side in the liquid space between the upper baffle and lower baffle.Liquid enters the tubes from the slits and mixes with gas.Then gas-liquid mixture flows into the heat transfer area under the distributor.

The structure of tubes distributor is complex and the flow mechanism is complicated.When studying the distribution performance,it is necessary to simplify the distributor structure to fit in the experiment and measurement requirements.The physical model and three dimensions of the test section are shown in Fig.3.It is one over sixteen of the whole tubes distributor which is made of organic glass and stainless steel.There are eight tubes with two symmetric slits in the test section.Tube 1 is near the center barrel and tube 8 is around the shell side.This test section takes the radical distribution of tubes distributor into account and neglects the circular distribution because tubes distributor disposes of central symmetry structure.The two-phase mixture flows into the test section from the inlet and is separated at the center baffle by inertia and gravity.Liquid flows into the liquid space and enters into the tubes from slits.Gas enters the gas space and flows pass the tubes with liquid.

Fig.3.Physical model of test section.

3.Data Reduction

3.1.Evaluating index

The flow ratio is adopted as one of the distribution evaluation indices[16,20-22].The flow ratios of gas flow rate,liquid flow rate,and mixture flow rate are defined as Eq.(1):

where N is the overall number of tube pairs;k denotes the k-phase(g,l,and m represent the gas,liquid,and mixture phases,respectively),and j refers to the tube pair under consideration.When the flow ratio is near one,the distribution performance is good.

To evaluate the distribution performance under different conditions,another evaluation indicator has been used,which is named as‘standard deviation’[20-22].The expression is shown as Eqs.(2)and(3):

where STDkis a synthetic index of maldistribution.If the distribution characteristics of a distributor are good,STDkis small and close to zero.

3.2.Uncertainty analysis

The evaluation index of the distribution test is based on flow rates of gas and liquid,so the uncertainty comes from the data acquisition system,through which flow rates of gas and liquid are recorded.The gas mass flow rates were recorded through the usage of gas flow meters and the liquid mass flow rates were calculated by liquid weight in containers,where the operating time was recorded by a chronograph.In order to calculate the system's uncertainty,the method proposed by Schultz and Cole[53]has been utilized:

where Uviand URare the error of each parameter and the total error,respectively.The maximum absolute uncertainty is found to be less than 6%.The accuracy of the measurements is shown in Table 1.

4.Results and Discussion

4.1.Influence of mass flow rate to the two-phase distribution performance

The mass flow rate plays an important role in the flow distribution characteristics within heat exchangers.This section investigates the influence of two-phase mass flow rate on flow uniformity within the test section.During experiments,the inlet mass flow rates changed from28.4 kg·h-1to 171.9 kg·h-1while the content of gas was fixed at about 0.3.The values of flow ratios of eight tubes and STDkwere derived from the performed flow rate variation.Table 2 lists the relevant parameters.

Table 1 Test range and accuracy of instruments

Table 2 The experimental data of different mass flow rates

Fig.4 shows the gas and liquid flow ratios of 8 tubes for different mass flow rates.It can be seen that the gas flow rate of each tube is different from each other as well as the liquid flow rate,so it proves that the distributor has a certain degree of flow non-uniformity.Fig.4(a)presents the gas flow ratio m*gof each tube.It can be clearly seen that the values of m*gincrease from tube 1 all along to tube 8 when the mixture mass flow rates equal to 28.4 kg·h-1and 76.1 kg·h-1,which in turn indicates that the gas mass flow rate increases from tubes near the center barrel to the tubes around the shell side.The main reason is that the gas phase flows from the center barrel to the shell side which makes the gas space near the shell have the larger gas static pressure,and then the tubes near the shell side have the larger gas flow rate.When the mixture mass flow rate ranges from 123.6 kg·h-1to 171.9 kg·h-1,although the gas flow rates of tubes 5-8 are larger than those of tubes 1-3 which still means that the tubes near the center barrel has less gas flow rate than that in tubes around the shell,tubes 4,5 and 6 have the largest gas flow rate among all tubes.It is clear that the tubes in the center of the test section have larger gas flow rate than other tubes.This is because that the increase of mass flow rate changes the pressure distribution in the gas space to make the part above tubes 4,5 and 6 have the larger static pressure.It is also noticed that different mass flow rates alter the gas distribution in each tube,and have the significant influence on the gas distribution tendency.One reason is the static pressure variation in the gas space,the other reason is that the increase of liquid flow rate elevates the liquid level height,therefore,as more liquid enters into the tubes from slits,the resistance from liquid phase to gas phase increases.Consequently,the gas distribution changes accordingly.

Fig.4(b)shows the liquid flow ratios m*lin each tube.It can be seen that the largest value of m*lis 1.44 while the least is 0.53 under the mass flow rate of 28.4 kg·h-1.When the mixture flow rate is 76.1 kg·h-1,m*lis in the range of 0.79-1.24.Moreover,m*lranges from 0.85 to 1.16 and 0.88 to 1.17 for 123.6 kg·h-1and 171.9 kg·h-1,respectively.It indicates that with the increase of mass flow rate,the value of liquid flow ratio gradually gets closer to one,which makes an undisputable truth that the liquid distribution gets better as the mixture mass flow rate increases.This is because the improvement of liquid flow rate makes the liquid level height rise and more liquid flow into the tubes,and thus the local resistance of the slits to liquid varies.At the same time,the augmentation of gas flow rate leads to the increase of flow resistance from gas phase to liquid phase.For the above reasons,the liquid distribution performance improves.It is also pertinent to note that tube 5 always has the least liquid flow ratio among all tubes at each mixture mass flow rate.This is mainly because the slit width of tube 5 is less than that of others to pass less liquid.It indicates that the structural design and manufacturing processes of different test rig components may also,in a way or another,restrict their flow distribution characteristics.

Fig.4.Effect of mixture mass flow rates on m*g(a)and m*l(b).

STDkis a composite indicator which can evaluate the distribution characteristics more clearly than flow ratio.Fig.5 depicts STDkat different mass flow rates.The values of STDldecrease by 55.7%-62.3%based on 28.4 kg·h-1with the increasing mixture mass flow rate.This means the liquid uniformity improves when the mixture mass flow rate increases.The main reason is that the elevation of mass flow rate boosts the liquid height to make liquid static pressure larger and weaken the influence of local resistance at slit width.It can be also noticed that the variation of STDlvalues at the range of 28.1-76.1 kg·h-1is quicker than the case of 76.1-171.9 kg·h-1flow range.In other words,it states that under low mixture mass flow conditions,a slight increase of the same mixture mass flow rate can result in a much quicker liquid distribution uniformity improvement.The values of STDgfirstly increase at flows ranging from 28.4 kg·h-1to 76.1 kg·h-1,and then slightly decrease under the flow range of 76.1-171.9 kg·h-1.The variation of the STDgis from 22.8%to-39.3%based on that of 28.4 kg·h-1.This phenomenon illustrates that the gas flow uniformity firstly gets worse and then improves with the enlargement of mixture mass flow rates.However,the two-phase uniformity rises by 48.75%-64.17%on the basis of STDmat 28.4 kg·h-1.Then,it can be concluded that the two-phase distribution performance is better when the mixture mass flow rate is larger than 76.1 kg·h-1.The two-phase flow uniformity is more similar to the liquid phase because the content of gas is small.

4.2.Influence of the content of gas of the two-phase distribution performance

The existing research describes the content of gas as one very important parameter for the two-phase distribution performance which is defined as Eq.(5).This section focuses on the effect of the content of gas on flow distribution characteristics of tubes distributor.The arrangement of the content of gas varies from 0.21 to 0.8 with the mixture mass flow rate at 100 kg·h-1.Table 3 lists the relevant parameters.

Fig.5.Effect of mixture mass flow rates on STDk.

The effects of the content of gas on two-phase distribution are shown in Fig.6.From Fig.6(a),it can be seen that gas has the similar distribution tendency at different contents of gas which means that the tubes near the shell side have the larger gas flow rate.However,the range of m*gat the content of gas of 0.405 is 0.82-1.09 which is less than that of other contents of gas,which means that the test section has the better gas flow uniformity at the content of gas of 0.405.It can be also seen that when the content of gas is fixed at 0.595 and 0.799,tubes 5 and 6 have the larger m*gvalues than that at the content of gas of 0.21 and 0.405.The reason is that the gas distribution performance is affected by static pressure in gas space and the flow resistance from liquid phase in tubes.When the content of gas enhances,gas mass flow rate increases which makes the static pressure in gas space enlarge to a certain extent.Liquid level height lowers and results in the reduction of flow resistance from liquid phase to gas phase.Therefore,gas distribution tendency carries out the variation.

Fig.6(b)presents the liquid flow ratios at different contents of gas.The range of m*lis 0.83 to 1.2,0.85 to 1.18,0.8 to 1.23 and 0.78 to 1.27 when the content of gas is 0.21,0.405,0.595 and 0.799,respectively.Tube 5 always has the least liquid mass flow rate because of the large liquid flow resistance coming from the manufacturing process of the test section.When the content of gas is at 0.21 and 0.405,tube 7 has the larger liquid flow rate than tube 6.When the content of gas is fixed at 0.595 and 0.799,the situation is opposite.This is because the local resistance in the lower part of tube 7 is larger than that in the upper part.When the elevation of the content of gas makes the liquid level height reduce,the liquid mass flow rate lowers accordingly.It can be also noticed that the liquid mass flow rates at content of gas of 0.595 and 0.799 have larger fluctuation than other contents of gas,and this is because the larger gas flow rate makes the gas phase intubes entrain liquid droplets more easily.When liquid level height is lower,liquid is more easily affected by the gas turbulence.In addition,the average liquid mass flow rate of each tube is little.Therefore,the variation of liquid mass flow rate results in large fluctuation of m*l.

Table 3 The experimental data of different contents of gas

Fig.6.Effect of different contents of gas on m*g(a)and m*l(b).

Fig.7 displays STDkat different contents of gas.The value of STDmis 0.132,0.099,0.138 and 0.19;STDlis 0.128,0.121,0.144 and 0.198;STDgis 0.16,0.094,0.158 and 0.214 when the content of gas is 0.21,0.405,0.595 and 0.799,respectively.It can be noticed that the STDkbecomes worse after better,where the best uniformity is approximately located at the content of gas value of 0.405.The values of STDlrange from-8.91% to 54.68% and the values of STDgrange from-41.25% to 33.75%.What results in the tendency is that the increase of the content of gas produces more gas and larger gas velocity.The increasing gas velocity leads to the larger flow resistance and better two-phase flow uniformity.Nevertheless,the increase of the content of gas causes the lower liquid level height to make the flow resistance decrease.The total flow resistance increases first and then decreases to make the two-phase flow uniformity become worse after better,where the largest flow resistance is approximately located at the content of gas value of 0.4.It is also observed that STDlis larger than STDgfor the content of gas of 0.405,which is the other way around for the content of gas of 0.21,0.59 and 0.799.This indicates that non-uniformity of liquid is severer than that of gas at the content of gas of 0.405.Based on STDmat the content of gas of 0.21,the uniformity of the mixture increases by 30.9%-51.1%.It can be deduced that when the range of the content of gas is around at 0.4,the better two-phase distribution is realized.

Fig.7.Effect of the content of gas on STDk.

4.3.Influence of the structural parameters of the two-phase distribution performance

Structural design parameters are very important for the two-phase distribution performance.The tube diameter and slit width are main design parameters for the tubes distributor.In this section,the effects of the tube diameter and slit width on two-phase flow uniformity are analyzed.The mass flow rate of two-phase flow is about 100 kg·h-1and the content of gas is about 0.3.

4.3.1.The influence of tube diameter

Fig.8 displays the gas and liquid flow ratios under different tube diameters.From Fig.8(a),it can be seen that the gas distribution performance has the similar tendency to each other at different tube diameters.It is found that the tubes near the shell side have the larger gas mass flow rate than that near the center barrel.The range of m*gis 0.81 to 1.16,0.72 to 1.18 and 0.74 to 1.26 when the tube diameter is 5 mm,10 mm and 15 mm,respectively.It can be concluded that the large tube diameter was harmful for the gas flow uniformity because of the augmented range of m*gwith the increasing tube diameter.Larger tube diameter makes the gas flow area in tubes increase,and then the gas velocity in tubes decreases which lowers the flow resistance from liquid and structure to gas.As a result,the gas distribution performance becomes worse.The liquid flow ratios at different tube diameters are shown in Fig.8(b).It can be seen that the least liquid mass flow rates are recorded at diameters of 5,10,and 15 mm for tubes 6,5,and 1,respectively.It is clear that although the liquid mass flow rates of tubes near the shell side are larger than those in the neighborhood of the center barrel,the machining process still has the important effect on the liquid distribution.The range of m*lis 0.86 to 1.22,0.82 to 1.24 and 0.75 to 1.29 when the tube diameter is 5,10 and 15 mm,respectively.It can be found that the increase of tube diameter makes the liquid uniformity deteriorate.The increase of gas non-uniformity affects the liquid distribution performance,consequently,the uniformity of liquid changes worse with the increasing tube diameter.

Fig.9 presents STDkof different tube diameters.The value of STDmis 0.122,0.13 and 0.168;STDlis 0.127,0.137 and 0.169;STDgis 0.093,0.119 and 0.156 when the tube diameter is 5,10 and 15 mm,respectively.It is clearly seen that the gas distribution performance becomes worse with the increase of tube diameter.The gas phase nonuniformity rises by 28%to 67.7%as tube diameter varies from 5 mm to 10 mm and 15 mm.The larger tube diameter leads to the little local resistance which makes the space near the shell side have the larger static pressure.This results in the larger mass flow rate in the tubes near the shell side.In comparison with gas phase,liquid phase and two-phase mixture receive less influence of the change of tube diameter because the liquid distribution is restricted by the slit width.The liquid distribution uniformity decreases by 7.87%to 33.1%on the basis of tube diameter at 5 mm,in the meanwhile,the uniformity of two-phase mixture decreases by 6.55%to 37.7%.

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Fig.8.Effect of tube diameter on m*g(a)and m*l(b).

Fig.9.Effect of tube diameter on STDk.

4.3.2.The influence of slit width

Fig.10 shows the values of m*at different slit widths.From Fig.10(a),it indicates that the distributor has the similar gas distribution tendency which is that the tubes near the shell side have the larger gas mass flow rate.The range of m*gis 0.72 to 1.18,0.76 to 1.2 and 0.73 to 1.27 when the slit width is 0.5 mm,1 mm and 1.5 mm,respectively.It can be obtained that when the slit width is 1.5 mm,the test section gets the worst gas uniformity under the experimental conditions.The main reason is that the increasing slit width lowers the liquid level height which reduces the flow resistance from liquid phase to gas phase.This leads to more uneven gas distribution.Fig.10(b)plots m*lof every tube under different slit widths.It depicts that the trend of liquid distribution is more clear when the slit widths are 1 mm and 1.5 mm,and the tubes near the shell side have more liquid flow rate than other tubes.The range of m*gis 0.82 to 1.24,0.81 to 1.27 and 0.76 to 1.35 when the slit width is 0.5 mm,1 mm and 1.5 mm,respectively.It can be concluded that the test section gets worse liquid distribution performance when the slit width is large.The reason is that the larger slit width leads to the decrease of effect of machine accuracy on local resistance which gives rise to the less local resistance for liquid flow.In the meantime,the influence of gas flow on liquid uniformity is boosted obviously.Both effects deteriorate the liquid uniformity.

Fig.10.Effect of slit width on m*g(a)and m*l(b).

Fig.11.Effect of slit width on STDk.

The values of STDkof different slit widths are shown in Fig.11.The value of STDmis 0.13,0.156 and 0.20;STDlis 0.137,0.162 and 0.214;STDgis 0.119,0.123 and 0.153 when the slit widths are 0.5,1 and 1.5 mm,respectively.The uniformity of gas phase deteriorates from 3% to 28.6% on the basis of slit width at 0.5 mm.Compared with gas phase,the uniformity of liquid phase exacerbates by 18.2%to 56.2%and the uniformity of two-phase mixture decreases by 20%to 53.8%.Obviously,this illustrates that the little slit width is helpful for the twophase uniformity because the gas phase,liquid phase and two-phase mixture have the bad flow distribution performance when slit width is large.In addition,it can be found that the variation of slit width has greater influence on liquid phase and two-phase mixture uniformity than gas phase.

5.Conclusions

This study proposed a new distributor named“tubes distributor”for gas-liquid mixture distribution in the SWHE shell side.An experimental bench was built to test the distribution characteristics of the new distributor.And the influences of mixture mass flow rate,the content of gas and the structural parameters on the two-phase distribution were studied experimentally.The following conclusions are drawn.

(1)The tubes near the shell side of the tubes distributor have the larger gas flow rate than those near the center barrel.The local resistance caused by processing and manufacturing accuracy lead to a certain degree of non-uniformity for the tubes distributor.

(2)Mixture mass flow rate has more significant effects on the distribution characteristic of liquid phase than that of gas phase.Within the increasing mass flow rates,the liquid flow distribution uniformity improves by 55.7%-62.3%.In the meanwhile,the gas distribution performance gets worse and then becomes better afterwards by-22.8%-39.3%.The mass flow rate for the better two-phase distribution uniformity is larger than 76.1 kg·h-1.

(3)The two-phase distribution characteristics are better after it is worse with the increase of the content of gas.The liquid flow uniformity changes from-8.91%to 54.68%when gas distribution performance ranges from-41.25%to 33.75%.For the tubes distributor,the content of gas around at 0.4 is beneficial for twophase flow distribution in the shell side of SWHEs.

(4)Tube diameter and slit width have remarkable influence on gasphase uniformity.With the increase of tube diameter,the twophase uniformity becomes worse by 26%-67.7% for gas phase and 7.87%-33.1% for liquid phase.With the increasing slit width,gas and liquid flow uniformity decreases by 3%-28.6%and 18.2%-56.2%,respectively.

This investigation focused on the gas-liquid distribution performance of tubes distributor in the SWHE shell side.However,due to the restriction of experimental conditions,the influences of structural parameters including slit height,liquid space height,and shell diameter,on two-phase flow uniformity has not been analyzed.In addition to this,the experimental mediums are air and water for gas phase and liquid phase respectively which have discrepancy with the practical working mediums.This also restricts the application of tubes distributor in the field of chemical industry.Therefore,more work should be done for the development of tubes distributor in SWHEs.In the future,the effects of more structural parameters on the gas-liquid flow uniformity will be investigated numerically using practical working mediums and results are validated by experimental data.