Liquid Carryover Research Articles

Liquid Piston Compression Heat Transfer Prediction via Thermal‐Resistance Network: Simulation, Experimental Validation, and Liquid Carryover Evaluation

Liquid piston compressors gain attention due to their potential for more efficient and isothermal compression compared to traditional solid piston compressors. Liquid piston compressors use a liquid column instead of a solid piston, allowing for innovative mechanisms to enhance heat transfer and achieve near‐isothermal compression. However, a validated analytical model for heat transfer in liquid piston compressors is still needed to understand the exhaust phase within a liquid piston. In this work, a thermal network model, able to predict the polytropic index to within 8% of the experimental results, is proposed. Moreover, thorough experimentation is conducted to measure the amount of liquid carried over to better understand the exhaust phase. In the results, it is revealed that the piston carries over 13–21 mL of liquid within the exhaust gas for 10–23 s of stroke. Notably, the difference in liquid carried over for the three‐stroke times is not statistically significant, indicating that the liquid carried over is a function of liquid piston design and not stroke time. Finally, most liquid piston applications consider only water; hence, for the first time, this research assesses the stability of a cycle using a nonflammable hydraulic fluid (Fuchs 46 M red) to enhance compressor longevity and material compatibility.

Liquid carry-over control using three-phase horizontal smart separators in Khor Mor gas-condensate processing plant

Liquid carry-over phenomenon, where liquid droplets escape with gas, is a prevalent operational challenge in gas–liquid separators. Liquid carry-over leads to foaming issue and performance reduction within separator downstream absorption processes. In order to ascertain whether liquid carry-over is inducing foaming within the gas sweetening process’s absorption tower at Iraq’s Khor Mor gas-condensate processing plant, this study initiated an evaluation of the liquid droplet size distribution in the gas product and gas/liquid separation efficiency of upstream Alpha, Bravo #1, Bravo #2, and Charlee separators that feed into the aforementioned tower by using the Horizontal Vessel and ProSeparator correlations in Aspen HYSYS v.11 software. The study revealed that Alpha and Bravo #2 experienced liquid carry-over issues. In response to these challenges, an innovative smart separator design, referred to as an adjustable separator, was proposed, employing the Arnold-Stewart semi-empirical procedure. This design allows for easy adjustment to accommodate changes in feed composition and operational conditions, mitigating the liquid carry-over problem. The smart design demonstrated a significant increase in gas/liquid separation efficiency for Alpha separator, improving by 31.11% under current conditions and 77.65% under future conditions. Similarly, under both current and future conditions, the smart design of Bravo #2 separator yielded an enhancement of 21.31% and 28.23%, respectively. These results suggest that the smart design can be considered an optimal solution for controlling liquid carry-over. This innovation not only maintains high gas/liquid separation efficiency but also prevents foaming, offering a robust solution for ensuring sustained operational performance and productivity in gas–liquid separation processes.

Enhancing control disorder and implementing V2X-Based suppression methods for electric vehicle CO2 thermal management systems

In recent years, the development of electric vehicles (EVs) thermal management systems has underscored the crucial role in ensuring driving safety and optimizing driving range has become increasingly prominent. However, the inherent dynamic complexity of EV operation coupled with automatic control systems, can sometimes lead to unstable behavior, resulting in performance degradation and safety risks for compressors and batteries. To effectively address this issue, an evaluation was conducted on the dynamic control characteristics of an EV thermal management system utilizing CO2 as the refrigerant in this study. Through mathematical modeling and experimental analysis, the erratic nature of the dynamic thermal process was first identified. The underlying reasons were elucidated, focusing on system control characteristics and intrinsic mechanisms. It was found that control disorder could induce abnormal actions in thermal management system components like compressors and expansion valve, leading to significant performance decline and issues such as liquid carryover in compressor suction. Furthermore, specific control disorder regions of CO2 heat pumps for EVs were delineated, providing a framework for assessing the likelihood of system control disorder. Notably, control disorder was more likely to occur under conditions of low indoor air flow rate, high ambient temperature, and low supply air temperature. Given the widespread nature of this issue and the lack of suitable solutions, two control disorder suppression schemes were developed using V2X technology and validated through simulation. Results showed that adoption of V2X communication technology prevented an average of 70.1 % COP degradation, ensuring stability and safety of compressors and batteries under various operating conditions. The research provides useful information for exploring the dynamic characteristics of CO2 thermal management systems, offering a novel approach to enhance the system stability and efficiency.

Numerical study of Two-Phase flow behavior during dryout in a Two-Phase closed thermosyphon under thermal boundary conditions

This paper presents a two-dimensional axisymmetric two-phase closed thermosyphon (TPCT) model filled with R-134a refrigerant using the Volume of Fluid (VOF) method, Lee model, and Continuum Surface Force (CSF) method within Computational Fluid Dynamics (CFD) and simulates the flow characteristics inside the TPCT during the occurrence of dry out. Specifically, it discusses the two-phase flow in the condensation and evaporation sections when dry out occurs. The results indicate that the condensation section exhibits varying forms of vapor–liquid interface waves at different times. Phenomena such as liquid carryover and entrainment become increasingly prominent over time, contributing significantly to refrigerant blockages and dryout in the evaporation section. The mechanism behind dryout in the evaporation section is revealed to be the result of the initially continuous falling film being disrupted by fluctuations in the liquid–vapor interface, leading to the premature drying of thin liquid films in the troughs of these waves.

Mitigating Liquid Carry-Over and Foaming in a Gas Processing Plant through the Installation of Vertical Scrubbers

Mitigating Liquid Carry-Over and Foaming in a Gas Processing Plant through the Installation of Vertical Scrubbers

APPLICATION OF TWISTER SUPERSONIC GAS-LIQUID SEPARATOR FOR IMPROVED NATURAL GAS RECOVERY IN A PROCESS STREAM

Natural gas is one of the most precious natural resources that generates foreign earnings for its host nation. Energy is the building block of modern society and natural gas is one of the cleanest primary energy sources. The production and subsequent recovery of natural gas is a challenging aspect of the entire natural gas value chain. One of the problems associated with natural gas utilization is the extraction and conditioning of the gas, as most of the fractions are extracted with certain percentages of water and other contaminants. To solve the problem of liquid carryover and gas entrainment in gas processing and recover an excellent volume of gas, several types of gas separators have been developed. This case study aims to solve the problem of gas wastage and recurrent plant downtime. Notore Chemical Industries is our focus as one of the largest natural gas consumers, situated in Rivers State Nigeria. The company has several plant downtimes due to the inefficiency of the conventional separator. The inefficiency of the installed knock-out drum separator in dispersing the condensate from the feed supplied by Nigerian Gas Company (NGC) and delivering the required dry gas to the plant battery limit has been one of the leading causes of the plant recording downtime. This work presents a reliable separation process using the Twister supersonic gas separator to recover a high percentage of dry natural gas (Methane). Feed gas data was collected from the plant after several visits and a computer-based simulation was conducted. From the simulation using the Aspen Hysys package, it was seen that the Twister supersonic gas separator is more efficient than the knockout drum separator. Less methane and less condensate were produced using the knockout drum separator at 0.699% and 0.092% respectively while the Twister supersonic gas separator produced methane and condensate at 95.15% and less condensate at 0.0047% respectively.

Selecting Optimum Dimensions for a Three-Phase Horizontal Smart Separator for Khor Mor Gas-Condensate Processing Plant

The Khor Mor gas-condensate processing plant in Iraq is currently facing operational challenges due to foaming issues in the sweetening tower caused by high-soluble hydrocarbon liquids entering the tower. The root cause of the problem could be liquid carry-over as the separation vessels within the plant fail to remove liquid droplets from the gas phase. This study employs Aspen HYSYS v.11 software to investigate the performance of the industrial three-phase horizontal separator, Bravo #2, located upstream of the Khor Mor sweetening tower, under both current and future operational conditions. The simulation results, regarding the size distribution of liquid droplets in the gas product and the efficiency gas/liquid separation, reveal that the separator falls short of eliminating all liquid droplets of specified sizes from the gas phase to meet efficiency requirements, weather with or without a mist extractor. Consequently, an analysis of various structural parameters of the vessel is undertaken to determine their impact on the carried-over liquid mass flow rate and the vessel’s gas/liquid efficiency. The findings recommend a new design concept termed the "smart separator" for Bravo #2, applicable to both current and anticipated operational scenarios. The smart separator demonstrates a remarkable enhancement in gas/liquid separation efficiency, showcasing improvements of 21.31% and 24.02% under existing and future operating conditions, respectively. This innovative design proves effective in controlling liquid carry-over and maintaining high-efficiency levels, even as vessel inlet flow rates increase over time, thus preventing foaming phenomena in downstream processes caused carried-over liquids.

Investigation on the formation mechanism and flow characteristics of liquid carry-over in gas–liquid cyclone separator

The liquid carry-over (LCO) phenomenon brings about the performance deterioration of gas–liquid cyclone separator and an increase in pressure drop. However, the formation mechanism of the LCO and its manifestation in the separator cylinder and the overflow pipe have not been fully understood. This work investigated the flow process of the LCO by visual observation and quantitative measurement of the overflow liquid flow rate and liquid holdup. The transient gas–liquid flow feature in the overflow pipe and spatiotemporal relationship between the separator inlet and outlet were characterized by time-frequency analysis and wavelet coherence of liquid holdup, respectively. The results showed that the size of air core determines two kinds of sources of the LCO, including the surrounding liquid direct entry into the overflow pipe and the film short-circuit flow beneath the top wall of the separator. When the air core can continuously wrap up the overflow inlet, the film short-circuit flow became the primary source of the LCO, which was embodied in the significant reduction of the overflow liquid flow rate. Three flow patterns, namely, slug flow, churn flow, and annular flow, were classified in the overflow pipe. The inlet intermittent flow of the separator led to the distribution of churn flow expanding toward higher gas velocity, which was interpreted by flow pattern transition theory. The time-averaged overflow liquid holdup was well predicted by drift-flux model. The results are beneficial to the proposal of inhibition methods of the LCO and structure design of the separator.

Dynamic risk analysis of evolving scenarios in oil and gas separator

Risk assessment models in the oil and gas (O&G) industry has begun to transform from time-static models like fault tree, event tree or bowtie to dynamic risk assessment (DRA) models, as the latter is able to better capture the real-time-dependent risk behavior of safety barriers. Currently, most existing works on DRA in O&G industry mainly rely on event-driven data, such as failures or accident data from similar systems for risk updating. These data can be collected only when accidents or near-misses have occurred, which limits the prediction capability of the DRA model. To address this drawback, a DRA model is developed in this paper that uses condition-monitoring data for risk updating. A significant advantage of using condition-monitoring data is that the risk can be updated before accidents or failures occur, giving the operation team more time to take preventive actions.The developed approach comprises of an offline and an online phase. In the offline phase, a conventional risk assessment is performed based on fault tree models to calculate the risks at the beginning of the operation. Through the offline analysis, we can also identify the most critical safety barriers by examining their contribution to the risk indexes. Critical safety barriers are selected for condition-monitoring. In the online phase, the condition-monitoring data are used to update the reliability of the safety barriers in real-time based on a sequential Markov Chain Monte Carlo (MCMC) algorithm using a Bayesian framework. The updated reliabilities of the safety barriers are, then, used in the offline risk assessment model for a DRA.The developed approach is applied for a DRA of liquid carryover from an oil and gas separator to downstream equipment, using real-time data from the separator's safety barriers. The results show that the developed method provides a more accurate representation of the system's performance, enabling early detection of potential failures and reducing uncertainty in risk estimates. The proposed DRA model demonstrated its effectiveness in predicting failures of safety barriers in real-time, giving operational teams ample opportunity to take corrective action. This leads to improved decision-making in the O&G industry, enabling timely response to changes in risk levels. The use of condition-monitoring data enhances the accuracy of risk estimations, representing a crucial advance in DRA applications in the O&G sector.

Effect of Temperature, Pressure, and Type of Gas Injected on the Formation and Decay of Mineral Oil-Based Foams.

In three-phase gravity separators used in gas and oil production, foaming can occur by either depressurization or injection of gas in the equipment. This formed foam can be harmful, causing various problems such as liquid carry-over, gas carry-under, decreased capacity, and difficulty in level measurement. The mechanism of foam formation by gas injection in separators motivated the present study. Thus, this work proposes the analysis of the influence of certain physical-chemical parameters such as temperature (20-40 °C), pressure (1-10 bar), and types of gases (nitrogen and methane) on the formation of the column and stability of the foam formed, in ISO14 mineral oil + sodium laureth sulfate + water, through gas injection in separator conditions. To carry out this analysis, an experimental apparatus was designed and assembled consisting of a transparent foam formation cell of 0.5 m height and 5 cm internal diameter. Parameters such as foamability, foaminess, and the collapse curve were also evaluated to characterize the foam formed. In addition, simplified models of foam formation and decay by gas injection were proposed based on models already available in the literature, which were validated with the experimentally obtained results. The experimental results showed good agreement when compared to the literature, referring to the behavior of temperature (higher temperature, lower stability), pressure (higher pressure, higher stability), and type of injected gas (dependency on solubility). In addition, maximum errors of 26% (in height) and 11% (decay phase) were obtained for the formation and decay models, respectively.

Investigation of the Effect of Side Arm Orientation of the T-Junction on Gas–Liquid Stratified Flow

T-junctions are important structures used in a number of industries to separate gas and liquid. This work studied the effect of the orientation of the side arm on the separation efficiency using a computational fluid dynamics (CFD) approach, and a new mechanical model is developed based on force analysis to predict the liquid carryout threshold. Laboratory experiments from published works are used to verify the CFD simulation and the new model. In this work, the angle of the side arm to the horizontal plane, α, and the angle of the side arm to the main arm’s axial direction, β, are investigated. The results show that with increasing β, the liquid carryover threshold increases accordingly, demonstrating that the liquid can be more easily carried to the side arm, while the liquid-carrying performance in the side arm is not sensitive to the inclination angle, β. Hence, in the new model, the inclination angle of is ignored. Experimental data are collected to validate the new model. The results show that this model can accurately predict the liquid carryover threshold, and the relative error is 4.16%.

Hollow fiber membrane integrated water cooler: A novel liquid cooling solution

To address the issues of water–air cross-contamination, liquid droplet carryover, and high maintenance costs of traditional water-mediated evaporative cooling systems, the hollow fiber membrane integrated water cooler (MWC) is proposed as a novel liquid cooling solution. The MWC incorporates hydrophobic porous membranes that enable water vapor migration while avoiding direct contact between liquid water and air. In addition, the MWC offers advantages over conventional evaporative cooling paddings in terms of high specific surface area, corrosion resistance, and anti-scaling. To evaluate the cooling performance of a countercurrent MWC, an experimental bench was built to test its outlet water temperature under various operating conditions. The developed numerical model was verified with the measured data. Then, the influence of nine critical parameters, including operating conditions and membrane module specifications, on the outlet water temperature and cooling efficiency of the countercurrent MWC was numerically investigated. The results show that evaporative heat dissipation contributes to more than 80% of the total heat exchange in MWC. Cold and dry ambient air, high inlet water temperature, low water velocity, and high air/water ratio contribute to superior cooling capability. Moreover, the cooling performance of MWC improves with increasing fiber length, inner diameter, packing fraction, and decreasing membrane thickness. In addition, the MWC offers a cooling capacity per unit volume of up to 1094.72 kW/m3, an order of magnitude greater than conventional wet cooling towers. Overall, this work presents theoretical guidelines for optimizing the operating conditions and configuration of countercurrent MWCs.

Experimental investigation and correlation development for liquid carryover during reflood

A correlation is developed for the liquid carryover fraction during both constant and oscillatory reflood with application to nuclear power accidents. The correlation, semi-empirical in nature, is based on extensive experiments in a 7 × 7 rod bundle array at the Nuclear Regulatory Commission/Pennsylvania State University Rod Bundle Heat Transfer (NRC/PSU RBHT) facility. Liquid carryover and entrainment can significantly impact quench behavior and maximum cladding temperatures during a postulated accident; therefore, accurate predictions of these phenomena are critical. The parameters associated with the stability at the liquid–vapor interface, and hence the liquid entrainment and subsequent carryover are established. These parameters provide the basic form of the correlation with experimental data from the NRC/PSU RBHT facility to determine the model coefficients. Using a weighted least-squares method that minimizes the error between modeled and experimental carryover fraction, we implemented a genetic algorithm to identify the parameters of this correlation. The proposed model is compared with experimental data and predictions from the NRC’s TRACE code and lies within 20% error margin.

Numerical investigation and prediction of phase separation in diverging T-junction

Purpose In plethora of petroleum, chemical and heat transfer applications, T-junction is often used to partially separate gas from other fluids, to reduce work burden on other separating equipment. The abundance of liquid carryovers from the T-junction side arm is the cause of production downtime in terms of frequent tripping of downstream equipment train. Literature review revealed that regular and reduced T-junctions either have high peak liquid carryovers (PLCs) or the liquid appears early in the side arm [liquid carryover threshold (LCT)]. The purpose of this study is to harvest the useful features of regular and reduced T-junction and analyze diverging T-junction having upstream and downstream pipes. Design/methodology/approach Volume of fluid as a multiphase model, available in ANSYS Fluent, was used to simulate air–water slug flow in five diverging T-junctions for eight distinct velocity ratios. PLCs and LCT were chosen as key performance indices. Findings The results indicated that T (0.5–1) and (0.8–1) performed better as low liquid carryovers and high LCT were achieved having separation efficiencies of 96% and 94.5%, respectively. These two diverging T-junctions had significantly lower PLCs and high LCT when compared to other three T-junctions. Results showed that the sudden reduction in the side arm diameter results in high liquid carryovers and lower LCT. Low water and air superficial velocities tend to have low PLC and high LCT. Research limitations/implications This study involved working fluids air and water but applies to other types of fluids as well. Practical implications The novel T-junction design introduced in this study has significantly higher LCT and lower PLC. This is an indication of higher phase separation performance as compared to other types of T-junctions. Because of lower liquid take-offs, there will be less frequent downstream equipment tripping resulting in lower maintenance costs. Empirical correlations presented in this study can predict fraction of gas and liquid in the side arm without having to repeat the experiment. Social implications Maintenance costs and production downtime can be significantly reduced with the implication of diverging T-junction design. Originality/value The presented study revealed that the diameter ratio has a significant impact on PLC and LCT. It can be concluded that novel T-junction designs, T2 and T3, achieved high phase separation; therefore, it is favorable to use in the industry. Furthermore, a few limitations in terms of diameter ratio are also discussed in detail.

The impact of water, BTEX compounds and ethylene glycol on the performance of perfluoro(butenyl vinyl ether) based membranes for CO2 capture from natural gas

Glassy perfluoropolymers offer a remarkable resistance towards many species that can alter the separation performance of conventional polymeric membranes. In this study, the performance of Cytop® and CyclAFlor™ random copolymers of perfluoro(butenyl vinyl ether) (PBVE) and perfluoro(2,2-dimethyl-1,3-dioxole) (PDD) are studied for the first time for carbon dioxide capture in the presence of impurities that are common in raw natural gas. Water vapor sorption isotherms were S-shaped for both polymers, indicating the formation of water clusters. The water permeability decreased with vapor activity in both perfluoropolymers as the formation of these clusters decreased water diffusivity. The presence of the water clusters, however, had no impact on the performance of Cytop® and poly(50%PBVE-co-50%PDD) for CO2/CH4 separation. Typical concave sorption isotherms were obtained for toluene and xylene in poly(50%PBVE-co-50%PDD), while convex isotherms were observed in Cytop®. It was speculated that this change in isotherm shape may have been due to the small number of larger free volume elements within Cytop®, as observed in x-ray diffraction analysis. Neither toluene nor xylene had a significant impact on CO2 and CH4 permeabilities in Cytop®, while a gradual decrease in both permeabilities was noted for poly(50%PBVE-co-50%PDD) as the vapor activity increased, due to either competitive sorption or pore blocking. Finally, liquid glycol carryover caused no change on the performance of Cytop® membranes, while a slight drop in the CO2/CH4 separation factor for poly(50%PBVE-co-50%PDD) was observed.

An ejector based Transcritical Regenerative Series Two-Stage Organic Rankine Cycle for dual/multi-source heat recovery applications

The Transcritical Regenerative Series Two-stage Organic Rankine Cycle (TR-STORC) was shown to deliver improved performance than Series Two-stage ORC (STORC) and single-stage ORC for dual-source heat recovery applications. However, TR-STORC utilizes partial evaporation for regeneration which requires precise control of two-phase flows. In real-time operations involving dual/multiple heat sources, this is difficult to achieve due to fluctuating heat inputs, leading to liquid carryover and subsequent corrosion of turbine blades. This study explores a novel Transcritical Ejector Regenerative STORC (TER-STORC), which replaces the need for two phase flows with a avapor-vapor regeneration via an ejector operating entirely with fully evaporated vapor (FE mode). Partial evaporation (PE) mode of TER-STORC requiring two-phase flows is also analyzed for comparison. Results indicate that the FE mode of TER-STORC can achieve performance comparable to PE mode and TR-STORC. FE mode of ejector operation is less sensitive to variations in ejector pressure drop than PE mode while delivering 0.2–4% lower power outputs with lower heat exchanger requirements than TR-STORC by up to 18%.At the engine design point, only a 2% drop in power output is seen for FE mode compared to TR-STORC. TER-STORC presents a robust system with reduced complexity for multisource heat recovery.

Global Sensitivity Analysis and Bayesian Calibration on a Series of Reflood Experiments with Varying Boundary Conditions

Best estimate plus uncertainty for the safety assessment of nuclear power plant transient requires, among others, estimating the probability density function (PDF) of physical model parameters in thermal-hydraulic system codes. In that context, Bayesian calibration based on experimental data from separate-effect test facilities are increasingly popular to inform the PDF of a single thermal-hydraulic phenomenon. These calibrations are, however, time intensive, especially when considering multiple time-dependent outputs. Calibrating on many tests with different boundary conditions and potentially different phenomena to derive PDFs applicable to complex transients appears intractable, even using hierarchical modeling. In this paper, we start investigating this problem by considering a set of Flooding Experiments with Blocked Arrays reflood tests with different boundary conditions. We use TRACE v5.0p3 to model time- and space-dependent temperature profiles, pressure drops, and liquid carry-over. Global sensitivity analysis helps screen out noninfluential parameters and gain a detailed understanding of the modeled physics of reflood. The analysis shows that, for all tests, the outputs were sensitive to a similar set of influential model parameters. In turn, Bayesian calibration yields similar posterior PDFs for the influential parameters, and forward propagation of these posterior PDFs yields similar confidence intervals. As such, the information of the investigated tests can well be represented by a unique posterior PDF. Such simplifications, although not general, are welcome to help manage the intensive calibration effort necessary for dealing with complex thermal-hydraulic transients encountered in nuclear power plants.

MAXIMISE PRODUCTION VIA DCS LEVEL CONTROL SCHEME

In PETRONAS LNG Complex, the Acid Gas Removal Unit (AGRU) stability is crucial to ensure maximisation of LNG production. Foaming in Absorber Column, C-91101 is a commonly encountered problem in MLNG TIGA LNG Trains. Severe foaming incident results in liquid carry-over to the downstream unit and cause total LNG Train trip as per safeguarding. As a countermeasure, a new control scheme residing at the DCS level was specially designed and commissioned in both Train 7 & 8. This is an integrated initiative between Advanced Process Control (APC), Technologist, and Operation team to support production maximisation and sustenance. Operated with 100% uptime, this control scheme ensures standardized action to be taken and provides overall dynamic stability at AGRU, allowing for production maximisation without jeopardizing the absorber column’s tray integrity. This initiative leads to LNG Big Cargo Equivalent (BCE) loss reduction from 0.9 BCE (2015) to an average of 0.09 BCE (2016 – 2019), which is equivalent to a 90% improvement.
 Keywords: Advanced Process Control (APC), DCS, DCS Level Control Scheme, Foaming, Liquefied Natural Gas (LNG)

Effect of sodium hydroxide solution concentration on liquid entrainment in a steam boiler

Liquid entrainment or carryover is a phenomenon that liquid droplets are carried out from a boiler or steam drum during steam generation. The droplets may convey some dissolved solids and cause damage to steam equipment such as scaling deposits in valves and steam piping and erosion of turbine blades. The appearance of dissolved solids in boiler water mainly comes from the internal water treatment process by dosing some chemical substances into the boiler in order to prevent corrosion and scale formation. Trisodium phosphate (Na3PO4) is one of chemical substances commonly added during boiler operation to control the pH of boiler water. However, it can cause the occurrence of sodium hydroxide (NaOH) solution which results in the increase of total dissolved solid (TDS) concentration in boiler water. Therefore, this study is aimed to develop a test section in order to investigate the parameters affected by liquid entrainment in the boiler. The experiment is performed in ambient conditions under an air-water system. Three variable factors are taken into consideration, including the concentration of NaOH solution, the height of the water level in the test tank, and the gas superficial velocity which represents the flow velocity of steam during steam generation. The results show that the increase of the gas superficial velocity and the water level height in the tank resulted in the enhancement of the entrainment rate. The increase of the water level height played an important role on the liquid entrainment. The increase of NaOH concentration directly impacted the existing film bubbles and the longer stability of foam bubbles at the water surface which resulted in a higher entrainment rate. Therefore, TDS control was one of the most important factors which could be incorporated with the appropriate height of the water level and the consistency rate of steam generation in order to minimize the liquid entrainment.

Numerical study on the moisture transfer characteristics of membrane-based liquid desiccant dehumidifiers: Resistance distribution and concentration polarization

Membrane-based liquid desiccant dehumidifiers have received increasing attentions due to their main advantage of preventing liquid carryover in air handling process, but the low dehumidification efficiency limits their further applications. The underlying mechanism of their moisture transfer deterioration is not entirely clear yet, and further efforts are needed to effectively identify and reduce the mass transfer resistances in the dehumidification process. In this work, considering impressionable transmembrane permeation flux, the resistance distribution of moisture transfer in the quasi-counter flow flat-plate membrane-based liquid desiccant dehumidifier is studied by a three-dimensional conjugate heat and mass transfer model. The velocity, temperature and concentration fields in dehumidifying process are analyzed in baseline condition, especially on the membrane surfaces. Analogy to a thermal circuit, the normalized moisture transfer resistances through gaseous, solid and liquid phases are defined to describe their relative importance. Causes of these normalized resistances in variable conditions are analyzed in terms of concentration polarization and boundary layer theory. Furthermore, the resistance variation is compared with the latent effectiveness, to reveal their inherent relation. The results suggest that moisture transfer resistances are mostly originated from the membrane and air side, and thus dehumidifying enhancement is more likely to emerge from the air-side concentration polarization alleviation in synergy with the appropriate improvement of membrane porosity. Among all operating parameters, the air inlet temperature and solution flow rate have relatively limited effect on the total resistance, while increasing solution concentration, followed by decreasing solution temperature, can significantly reduce the moisture transfer resistances at a nondecreasing latent effectiveness. In addition, the latent effectiveness shows a similar variation tendency to that of the air-side moisture transfer resistance, but it cannot reflect the total resistance variation. These results can help researchers and designers make decisions on where and how to improve the performance of membrane-based liquid desiccant dehumidifiers.