Liquid Flow Distribution Research Articles

Thermal performance analysis of supporting column ultra-thin vapor chamber with graded microgroove

To analyze the thermal behavior of a graded microgroove ultra-thin vapor chamber with supporting column, a three-dimensional steady-state numerical model coupled with graded capillary force network, which involves hydraulic and heat transfer on hydraulic and heat transfer performance on ultra-thin vapor chamber with different supporting column sizes. This model considers the influence of supporting column with varying diameters and intervals on liquid flow and temperature distribution, as well as the effects of a graded capillary force network on heat transfer limit of ultra-thin vapor chamber. The numerical results show that the additional heat transfer provided by the central support column causes an outward shift in the saturation temperature of vapor, creating a new liquid reflux path at the condensation surface. The accuracy of the model is verified by the preparation of ultra-thin vapor chamber with a graded microgroove a graded microgroove. Compared with the experimental results on conventional microgrooves, graded microgrooves can improve the heat transfer limit by 29.3%. According to the theoretical analysis model, the graded capillary force network can effectively resist incremental increases in vapor pressure drop, enhancing the efficiency of gas–liquid circulation of ultra-thin vapor chamber.

Thermal performance of a two-pass microchannel evaporator

Microchannel evaporator is one of the key components in many thermal systems such as heat exchanger of HAVC and refrigeration system. The evaporation heat transfer performance of microchannel evaporator, which usually has many flow paths, is highly affected by the distribution of liquid flow that will seriously deteriorate the flow boiling performance due to the lack of liquid supply, local dryout, etc. In this study, a novel two-pass microchannel evaporator (L × W × H = 103 × 64 × 20 mm) is designed and fabricated. The width, height and length of each individual channel are 0.6, 1 and 65 mm, respectively. To significantly improve liquid redistribution after the first-pass, evenly distributed spacers with different diameter holes were placed in the connecting flow path. Additionally, the channel number ratio between the first and second pass plays an important role. Therefore, three different channel ratios of 1:1, 1:2, and 3:5 were selected in this study. The heat transfer and flow characteristics of the two-pass microchannel evaporator using working fluid HFE-7100 were experimentally studied for flow rate varying from 30 ml/min to 110 ml/min. The inlet subcooling keeps about 30 K. Also, visualization studies were conducted for the explanations. The experimental results indicate that the thermal performance is superior in microchannel evaporator with channel ratio of 1:2. By considering Reynolds number of each channel in the first pass, microchannel evaporator with channel ratio of 1:1 outperforms other two evaporators. Furthermore, the wall temperature uniformity of this evaporator is better than others. The achieved heat flux of 20 W/cm2 is much higher than the reported studies. The overall two-phase HTC of this microchannel evaporator is about 4.5 kW/m2K.

Theoretical Study of Liquid Flow and Temperature Distribution in OF-Cooled Power Transformers

The objective of the paper is to analyse the effects of various geometrical and operating parameters on the liquid flow distribution in OF-cooled power transformers. Our investigation includes two cases: one with a simplified winding geometry and another that closely resembles the actual winding geometry. The analyses were carried out using computational fluid dynamics (CFD) and custom, internally developed thermo-hydraulic models. Our findings confirm that buoyancy forces rather than the pump drive the liquid flow within the windings of an OF-cooled power transformer. The results also show that the liquid flow distribution, which is influenced by the winding geometrical properties and liquid properties, has a significant impact on the hot-spot temperatures of the windings. The comparison between the results of the CFD simulations and the results of the simple model demonstrates a high level of agreement in calculating both the mass flow rates and temperatures.

Study of gas-liquid two-phase flow redistribution characteristics in the rod bundle channel using wire-mesh sensor

In subchannel analysis, the gas and liquid flow distribution phenomenon plays an important role in understanding rod bundle channels’ two-phase turbulent mixing mechanism. This paper obtained gas-liquid flow distribution data inside a vertical coupled subchannel rod bundle channel by utilizing a double-set wire-mesh sensor (WMS). To achieve evolutions of two-phase flow distributions, one subchannel was injected with gas and water called the donor channel, and the other injected with water is called the receptor channel. Four axial locations (Z/Dh = 28.95, 57.90, 86.86, and 115.81) were measured for each flow condition to obtain the evolution of the flow distribution. 36 flow conditions were acquired with 〈jg〉 from 0.073 to 1.02 m·s−1 and 〈jl〉 from 0.93 to 1.86 m·s−1 at Z/Dh = 115.81, including bubbly, cap-bubbly, and slug flow. The gas flow distributions were obtained by the cross-correlation calculation of the phase distribution data measured by a double-set WMS. The gas-phase flow rate relative errors acquired by WMS and rotameters are within ± 10%. To obtain the liquid flow distribution, the inter-subchannel equal-slip ratio assumption was introduced, which is according to the truth that two-phase flow characteristics between the adjacent subchannel are similar for most cases in this study. Further, obtained two-phase flow distribution data were verified and evaluated by Han et al.’s drift-flux model, and the relative errors for most cases are less than ± 20%. Results show that, under bubbly flow, the two-phase flow redistribution is weak. 90% of the gas was restricted in the donor channel, and the liquid flow was approximately distributed in both channels. With the increment of void fraction, two-phase flow redistributions are more severe. The liquid-phase recirculation flow was found in the receptor channel, under cap-bubbly and slug flow, which results in a higher gas-liquid flow in the donor channel than in the receptor channel. The rules of two-phase flow distributions indicate that the liquid-phase flow redistribution is more moderate than the gas phase. The drastic change in the gas-phase flow redistribution starts with the cap-bubbly flow. In addition, the current two-phase flow data indicates that the two-phase flow redistribution between the donor and the receptor channels does not follow the equal-volume principle postulated in the existing two-phase turbulent mixing model. Furthermore, current data also imply the relationship between void and mass flux distribution is not linear as assumed in the existing two-phase turbulent mixing model.

Simulation of the liquid flow distribution in laboratory-scale additively manufactured structured packings

This article introduces a technique to simulate the liquid flow inside different additively manufactured structured packings with enclosing column wall on laboratory scale using the software OpenFOAM. The physical problem is handled by means of a periodic setup and makes use of common numerical discretization techniques of the software. The periodic setup reduces the required computational resources while permitting simulations of the liquid distribution in a large part of the column even for complex packing structures. A novel post-processing tool is used for a systematic evaluation of the liquid distribution. When optimizing packing structures, these computational fluid dynamics simulations eliminate the necessity to manufacture every developed geometry. As a proof of concept, this work simulates the liquid flow inside two additively manufactured packing structures. The results are validated with experimental data and show, that an improved liquid distribution can be obtained inside laboratory-scale packing structures.

Non-uniform liquid flow distribution in an alkaline water electrolyzer with concave-convex bipolar plate (CCBP): A numerical study

Non-uniform liquid flow distribution in an alkaline water electrolyzer with concave-convex bipolar plate (CCBP): A numerical study

Design of nozzle diverter channel system based on uniform distribution performance

Aiming at the nozzle-diverted channel system, two diverted channels with different configurations were designed and optimized, and the liquid flow characteristics in the diverted channel were studied. A finite element simulation model was established to analyze the influence of different diverted channel systems on the uniform distribution performance of the liquid, and the two diverted channels were tested for the uniform distribution of liquid flow. The results show that the diverting effect of the two kinds of diverting disk channels is relatively uniform. However, the distribution performance of the four-bifurcated diverting disk channel is better than that of the double-bifurcated diverting disk channel. The pressure loss is relatively less; the energy consumption is less, so the four-bifurcated diverting disk channel system is selected as the optimal design. The experimental results are consistent with the simulation results.

Experimental and numerical analysis of the internal flow of a rotary atomizer

Using high-speed imaging technique and the volume of fluid (VOF) method, an experimental and numerical analysis of the flow behavior inside a rotary atomizer was conducted. To scrutinize the effect of gravity on the internal flow of the nozzle, the experiments and CFD simulations were carried out at horizontal (without gravity effect) and vertical (with gravity effect) configurations. The mass flow rate exiting the nozzle orifices was measured; the flow behavior inside the nozzle orifices was investigated; the thickness of the rivulet and film inside the nozzle orifices was compared to existing analytic models. It was found that gravity had a significant impact on the flow distribution inside the nozzle cavity. The liquid flow distribution exiting the nozzle orifices was not uniform in the vertical configuration (due to gravity). Four wave patterns were identified on the surface of the nozzle disk: smooth film, concentric wave, spiral wave, and arc-shaped wave.

Experimental and numerical study on the performance of a new dual-inlet gas–liquid cylindrical cyclone (GLCC) based on flow pattern conditioning

Gas-Liquid Cylindrical Cyclone (GLCC) is a compact and efficient separation device used in oil and gas separation field. A new dual-inlet GLCC which can change the flow area ratio was designed and examined. The liquid separation efficiencies under five flow area ratios were experimentally measured. The liquid film velocity distribution was measured by MATLAB PIVlab. The finite volume method (FVM) was used to discretize the control equations. The liquid film thickness, gas–liquid flow distribution ratio and liquid flow streamline were obtained. The simulated liquid film velocities were seen to be consistent with experimental observations. Experimental and simulation results showed that by changing the flow area ratio of the upper and lower inlet pipes, the flow distribution in the upper and lower inlet pipes changed, liquid entering the upper GLCC cylinder reduced, the liquid film tangential velocity near the lower inlet increased and the change of liquid film axial velocity tended to be stable. The new type of GLCC expanded the safe operational separation envelop (envelop of the no LCO).

Liquid flow distribution in trickle bed reactors containing trilobed extrusions packed using different techniques

The performance of the Trickle Bed Reactor (TBR) critically depends on the gas-liquid flow distribution in the reactor, which in turn depends on the catalyst shape, size, and structure. Extensive research has been carried out with spherical particles (catalyst),whereas industrially more complex-shaped particles (Cylindrical, Trilobe, and Quadrilobe) are used. Little work has been reported for the liquid distribution in packed beds employing these shapes.In this work, the liquid distribution was investigated in a cylindrical column of internal diameter 100 mm, containing particles of diameter 1.3 mm trilobed extrusions and length 1.8–8.8 mm. The influence of different loading methods - Central single source, solid cone, and hollow cone, gas and liquid flow rates, variation along the height of the column were studied. Air-water system was used. Pressure drop was measured with the help of a manometer and Maldistribution index (Mf) was calculated based on the variation of quantity of water collected at column outlet.It was observed that the Mf decreased with the increase in both the gas and liquid flow rate which was due to better spreading of the fluids with the increasing gas and liquid flow rate. The decrease in the Mf with the increasing gas and liquid flow rate indicates better distribution as reported in the literature 0 (best distribution) and 1 (worst distribution). Further, it was also noted that the pressure drop increased with the increasing gas and liquid flow rate. The hollow cone packing method shows the better distribution confirmed from the bulk voidage, Mf profiles, pressure drop variation, and flow profiles. A correlation has been proposed for the two-phase pressure drop for three packing methods.

Numerical study of two-phase flow in multi-channels plate heat exchanger

Plate heat exchangers (PHEs) have been acquired a considerable attention and have been popularly used for both single-phase and two-phase flows in the air-conditioning systems. During the study of the flow distribution of the PHEs, the two-phase flow distribution is analysed experimentally. However, since the observation of the internal flow field of the PHE is very difficult, Computational Fluid Dynamics (CFD) can be used to better predict the fluids flow field inside the plate heat exchanger. In this study, ANSYS FLUENT is used to model the flow field composed of the K050 chevron PHE to observe the two-phase flow and uneven flow distribution. Moreover, the effect of the distributor on the gas-liquid distribution in the multi-channels flow field is also evaluated. The major effort of this paper is to investigate the effect of the two-phase flow distribution in multi-channels PHE with and without an inflow distributor. For the multi-channels PHE without distributor, the simulation results show that the flow must operate at high Reynolds numbers to obtain better enhancement in the flow distribution. If the PHE operates under Reynolds number less than 1500, the vapor-liquid distribution is non-uniform. Furthermore, it is observed that when the inflow distributor is added, the two-phase flow distribution of the vapor phase improves significantly. However, the flow distribution of the liquid phase is better under low Reynolds numbers condition. In addition, it has been shown that as Reynolds number increases, the liquid flow distribution is not affected by the inflow distributor.

Wickability-optimized textured liquid-desiccant air dehumidifiers for independent moisture management in energy-efficient buildings

Liquid-desiccant-based air conditioning systems are envisioned to enable independent humidity management, thereby improving the energy efficiency of future buildings. Existing liquid-desiccant-based air conditioning concepts, however, suffer from a poor liquid flow distribution deteriorating moisture removal rate. They are consequently flooded with the liquid-desiccant solution, which significantly degrades the energy efficiency of the dehumidification process. Here, the capillary forces and wickability effect of textured air dehumidifier surfaces are altered to minimize the liquid-desiccant flow rate of the fully wetted state, thereby transforming the physics of interfacial desiccant flow distribution. Consequently, the wickability-optimized air dehumidifier surface maximizes both moisture removal rate and dehumidification energy efficiency. It was interestingly found that the length scale of a textured air dehumidifier surface concept is optimized at an intermediate pattern density. Dry solid-air menisci appear at length scales exceeding the optimum pattern distance while the effective liquid–air interfacial area is reduced at smaller length scales, both of which degrade the moisture removal rate. At the optimum pattern density, the effective liquid–air interfacial area increases with the solution flow rate, thereby increasing the dehumidification rate. At a water vapor pressure potential of 3 kPa and a solution flow rate of 2.8 g/s, experimental results indicated a moisture removal rate of 0.16 g/m2-s for a textured surface concept with a capillary length scale of 3 mm, a 28% improvement compared with that of smooth-plate dehumidifier surfaces. A high moisture removal rate of the textured surface at a low desiccant flow rate led to a high thermal efficiency of 0.75 at a water vapor pressure potential of 5.6 kPa and a LiBr flow rate of 2.8 g/s. The insights gained from the present study accelerate the development of advanced textured surface concepts for next-generation liquid-desiccant-based air dehumidification systems offering independent humidity management for future energy-efficient buildings.

Modelling of 3D liquid dispersion in a rotating packed bed using an Eulerian porous medium approach

Liquid dispersion is very important for the modelling of liquid flow in a rotating packed bed (RPB) when an Eulerian porous medium approach is employed. For investigating the effect of the liquid dispersion in a practical RPB, a 3D Eulerian porous medium model has been established coupled with the appropriate interfacial, drag and dispersion forces formulations. The sensitivity of the parameters employed in these formulations has been thoroughly analyzed. New forms of the porous resistance model and the effective interfacial area correlation have been developed for the non-uniform two-phase flows. The simulation results show that the effect of the capillary pressure and mechanical dispersion forces on the liquid flow distribution and holdup in the RPB is clear and important. In addition, the effects of the dispersion force on the liquid holdup under different design and operational parameters have been thoroughly analyzed and it is found that the effect of the dispersion forces on the liquid holdup is almost the same for different nozzle widths and the porosities of the packing investigated. The investigation demonstrates that utilizing the Eulerian method can substantially reduce the simulation time and efforts when compared to the pore resolved method, such as the Volume of Fluid method without loss in accuracy. This provides a feasible approach to simulate RPBs in full 3D and for RPB technology scaling up and optimizations.

Numerical analysis of the hybrid rocket motor with axial injection based on oxidizer flow distribution

This paper studies the effects of liquid oxidizer flow distribution on combustion characteristics and performance of hybrid rocket motor with axial injection through numerical simulations of two-phase flow. Axial injection is widely used in hybrid rocket motor, however, the regression of burning surface may change combustion efficiency of the motor at different moments. Consequently, it is necessary for hybrid rocket motor to design injector patterns that could increase the average combustion efficiency in the whole operating process. The orifice injector plate is divided into three areas, which are recorded as zone I, zone II and zone III, respectively. Oxidizer flow distribution is achieved through changing the diameter of injector holes in various zones, and three-dimensional steady numerical simulations of two-phase flow of hybrid rocket motor with axial injector patterns at different moments are conducted. The motor adopts 98% hydrogen peroxide and hydroxyl-terminated polybutadiene as the propellants. Numerical analysis reveals that oxidizer flow distribution mainly influences the flow field structure in the pre-combustion chamber and front part of fuel grain port. Increasing oxidizer mass flow rate in zone III is beneficial for the chamber head thermal environment. Relative position in the radial direction of fuel grain inner surface and oxidizer distributed in the injector plate affects fuel regression rates, and the influence mainly exists in the front part of solid fuel grain. When the oxidizer mass flow rate in zone I is equal, the average fuel regression rate rises with the increase of oxidizer flow rate in zone II at initial moment, and decreases as the oxidizer in zone II increases at middle moment. The average combustion efficiency increases with the increase of oxidizer mass flow rate in zone II when the oxidizer in zone I remains unchanged. Both the average combustion efficiency and the chamber head thermal protection need to be considered in the design of axial injector patterns. Research results of this paper provide an important reference for the design of high performance injector patterns of hybrid rocket motor.

CFD simulation of flow distribution in the randomly packed bed Dixon ring

ABSTRACT The maldistribution in randomly packed beds with a high diameter ratio is a result of wall-flow formation and channeling. In this study, the thin randomly packed bed (dp/D = 1/8) filled with Dixon ring is simulated with a porous media model. The motivation of our study is to understand the effect of surface tension and liquid inlet velocity on the height of the wall-flow formation. Furthermore, the flow structure in this packed bed was described by numerical simulation. The results show that increasing the liquid inlet velocity and surface tension causes a faster distribution of liquid flow that led to faster formation of wall flow. Increasing the surface tension from 0.05 to 0.07 N/m causes the lower wall-flow formation from 0.19 m to 0.15 m in liquid velocity of 0.015 m/s and 0.09 to 0.06 in liquid velocity of 0.08 m/s. According to the findings, the 30% increasing the surface tension (from 0.07 N/m to 0.085 N/m) led to 30% decreases in height of wall-flow formation in the case of lower liquid velocity (0.015 m/s) and 50% decreases in the height of wall-flow formation in case of higher liquid velocity (0.08 m/s).

Computational fluid dynamics simulation of multi‐phase flow characteristics in an industrial‐scale randomly packed tower

AbstractA three‐dimensional (3‐D) two‐phase Eulerian–Eulerian‐based computational fluid dynamics (CFD) simulation method coupled with a porous media model was developed in this study to simulate the air–water two‐phase flow in an industrial‐scale randomly packed air cooling tower (RPACT). The authors discussed the effects of gas kinetic energy factor, liquid load, packing materials, and packed bed height on the hydrodynamic performances of the gas–liquid counter‐current flow in the proposed RPACT. The simulation results show that the pressure drop increases with the gas or liquid load increases. Liquid load influences the pressure drop, liquid holdup, and wall film flow rate sensitively. A smaller liquid load, a middle range of gas kinetic energy factor, a relatively greater porous resistance coefficient of packing material, and a higher packed bed height can achieve a more uniform liquid flow distribution in an RPACT. The optimum operating conditions for the present RPACT are determined as gas kinetic energy factor is from 1.76 to 2.11 [(m/s) (kg/m3)0.5], liquid load is in the range of 32.40–67.73 m3/h, and the plastic Cascade ring (filled in the second packing layer) with a height of 10 m. The presented CFD models are useful for engineers to design and optimize the structure and operation conditions of industrial‐scale RPACTs.

Distribution of liquid flow in a pore network during evaporation

The variation of the distribution of the liquid flow in porous media during evaporation is still a puzzle. We resolve it with the pore network modeling approach. The distribution of the evaporation-induced liquid flow in a pore network composed of about 2.5 million pores is determined. The probability density function of the magnitude of the normalized liquid flow rate is obtained. For the low normalized liquid flow rate, the probability density function is power-lawlike. The power-law exponent depends on both the liquid saturation and the location of the moving meniscus in the main liquid cluster. The evaporation-induced liquid flow in the pores in the pore network can be correlated. Whether the liquid flow distributions in various zones in the pore network are similar or not relies significantly on the location of the moving meniscus in the main liquid cluster. The functions depicting the relation between the power-law exponent and the local liquid saturation for the zones adjacent to and away from the open side of the pore network are different. These findings from the pore scale studies provide insights into developing the accurate continuum model for evaporation in porous media.

CFD study of oscillatory motion effect on liquid flow distribution into structured packed divided wall column

Packed distillation columns are key equipment in natural gas pre-treatment process within LNG production process train operated at offshore. In this work, the impact of offshore operating conditions and that of divided wall column shape were explored via developing transient three-dimensional CFD model for a divided wall distillation column filled with structured packing. Inter-phase drag force, porous resistance force, mass transfer, and liquid dispersion were incorporated into volume averaged equations to map the distortion in liquid distribution in response to column oscillatory motion. The results show that introducing a dividing-wall into distillation column affects fluids partition and distribution. Column motions induce complex fluid flows in radial direction that result in oscillatory patterns around the steady-state solution of vertical column. Furthermore, liquid distributions in a divided wall column under influence of column motion differ with respect to column system positions throughout rotational axes, mass transfer also fluctuates according to column oscillations. A position with a dividing wall making an angle of 45˚ with rotational axis gives a scenario in which rolling motion resembles to pitching motion. The thereof position leads to moderate liquid maldistribution in comparison to liquid maldistribution from scenario with dividing wall parallel to rotational axis.

Computational analysis of gas–liquid flow in an idealised CANDU reactor header under conditions that are relevant to small-break loss-of-coolant and loss-of-flow accidents

Extensive numerical simulations of isothermal air/water flow in an idealised model of the header/feeder system of a CANDU nuclear reactor were performed under conditions that are relevant to postulated loss-of-flow accidents (LOFA) and small-break loss-of-coolant accidents (SBLOCA). Following our recent work, in which the present CFD methodology was validated against in–house experimental results, we used the volume of fluid method to solve the system of multi-phase flow governing equations and the detached eddy simulation model to close this system in turbulent flow. We computed the steady-state liquid flow distribution to the different feeders for different combinations of inlet water and air mass flow rates and different mass extraction rates, namely, values of the ratio of the leak liquid mass flow rate and the inlet liquid mass flow rate, and found that, in general, this distribution tends to become more uniform as the inlet flow rate of either the liquid or the gas increases. A “free surface” separating air above from an air–water mixture below was observed in many cases, generally moving downward with decreasing inlet flow rates and increasing mass extraction ratio. The liquid distribution to non-leaking feeders was not affected significantly by a change in the location of the leak. Time histories of flow properties following a step change in boundary conditions showed that the change of flow rate through each feeder can be represented by a first-order model with a time constant of roughly 1 s. As part of the validation of the present CFD analysis, the computed local pressure loss coefficient for a leaking feeder was found to be in excellent agreement with previously published experimental results. The static pressure loss across the header, estimated from available semi-empirical two-phase flows models was, in most cases, found to be within 10% of the CFD solution.

Advanced flow profiler for two-phase flow imaging on distillation trays

A profound knowledge of the two-phase cross-flow on large-scale distillation trays is pivotal to their efficient design and operation. For such trays, a novel flow profiler comprising of multiple dual-tip probes for simultaneous local conductivity measurements is proposed in this work. The profiler is applied for a DN800 air/water column simulator equipped with sieve trays. 3D distribution of liquid holdup and tracer-based liquid flow in the two-phase dispersion are assessed in high resolution. Non-uniform holdup is found along the dispersion height. Contrarily, the liquid flow is largely uniform and symmetric with respect to the tray centerline. Prior to measurements, the profiler design, electronic scheme, measurement principle and data processing schemes are described.