Desiccation Research Articles

Novel DABCO-Derived Ionic Liquids for Liquid Desiccant Air Conditioning

Novel DABCO-Derived Ionic Liquids for Liquid Desiccant Air Conditioning

Multi-hierarchical structured PTFE membrane for liquid desiccant dewatering via membrane distillation

Poly (tetrafluoroethylene) (PTFE) can be used for robust separation membranes owing to its exceptional chemical and thermal stabilities. Simultaneously achieving construction of hierarchical pore structures and re-entrant surface microstructures during the fabrication of PTFE membrane holds significant importance in addressing the issues of low flux and membrane wetting in membrane distillation (MD). Herein, we proposed a flexible method for manufacturing hierarchically structured PTFE membrane by combining electrospinning/spraying with sintering/welding. The present approach facilitated the controlled fabrication of a superhydrophobic PTFE membrane with slippery surface (exhibiting a water contact angle of 153.5°, and an ultralow sliding angle of 7.5°) without using fluoride-based solvents or external nanoparticles. Moreover, the anti-wetting mechanism and performance stability of the PTFE membranes in MD were thoroughly investigated. In liquid desiccant regeneration experiments, the 20 wt% LiCl solution was successfully concentrated to 28.64 wt%. Furthermore, the PTFE membrane demonstrated a stable flux (>30 kg m−2 h−1) and relatively low permeate conductivity (<15 μs cm−1) during treating simulated seawater for 30 h. The present work offers a new approach to fabricate multi-hierarchical structured superhydrophobic membranes for desalination and regeneration of liquid desiccants.

A Bubble Column Dehumidifier using Ionic Liquid Desiccant for Low-Humidity Industries: Insights into Transfer Processes Integrating Experiment and CFD Modelling

A Bubble Column Dehumidifier using Ionic Liquid Desiccant for Low-Humidity Industries: Insights into Transfer Processes Integrating Experiment and CFD Modelling

Temperature endurable face-sealing polyisobutylene film with contactable liquid desiccant for the encapsulation of OLEDs

We propose a face-sealed encapsulation solution with simple process and low cost. The polyisobutylene encapsulation patch mixed with calcium oxide particles is attached to the surface of the OLEDs that is exposed to the hygroscopic agent in a face-sealing manner. We find that this encapsulation scheme exhibited excellent waterproof performance. The encapsulated OLED has a long shelf lifetime in water under high temperature conditions, which is manifested in a long underwater shelf lifetime of T95 (luminance drops to 95 % of the initial luminance) of over 336 h at 60°C. We believe that this encapsulating technology can be applied to other organic optoelectronic devices, and the face-sealed encapsulating patch is flexible. This strategy can be extended to roll-to-roll processes to expand the application of flexible organic optoelectronic devices underwater.

Pilot study on liquid desiccant systems in greenhouse for water saving and climatecontrol

In regions with hot and arid climates, meeting the growing demands for irrigation and food production is crucial. Greenhouse farming offers a promising solution, significantly enhancing agricultural water efficiency by producing high-value crops with reduced freshwater consumption compared to traditional methods. However, the reliance on freshwater-dependent evaporative cooling systems in greenhouses poses a significant challenge, consuming up to 80 % of total freshwater usage. This challenge underscores the urgent need for innovative solutions to reduce freshwater use while maintaining optimal greenhouse conditions.This study proposes integrating a desiccant system with conventional evaporative cooling to improve humidity control and reduce freshwater consumption. This innovative approach enables greenhouse establishment in humid coastal areas previously deemed unsuitable, offering a sustainable alternative to traditional cooling methods. The proposed system includes liquid desiccant, desiccant pads, a chiller, and a fan, aiming to reduce or eliminate water use during nighttime cooling cycles. Additionally, the system has the potential to harvest water from ambient air, further reducing overall water consumption. Through this case study, we address the critical issue of freshwater overuse in greenhouse agriculture, presenting a solution that could revolutionize water management practices in arid and semi-arid regions.

Boosting mold aerosol reduction and dehumidification performance in liquid desiccant systems using airborne ultrasound: An experimental study

Indoor mold exposure in hot-humid regions poses considerable risks to public health and food security. Ensuring safe, durable, and energy-efficient air disinfection is crucial for the air-conditioning field. While liquid desiccant air-conditioning (LDAC) systems eliminate condensation-related mold proliferation, their capability to combat airborne mold spores is limited due to the spores' robust resistance. This paper explores a novel airborne ultrasound-assisted liquid desiccant air-conditioning (US-LDAC) system. Experiments were conducted using culture-based methods to compare the system's disinfection capacities against Aspergillus niger spores, a desiccant-resistant species, under ventilation, liquid desiccation dehumidification, and airborne ultrasound-assisted liquid desiccant dehumidification modes. Moreover, the viability and morphological changes of mold spores exposed to airborne ultrasound, with and without liquid desiccants, were analyzed to verify the disinfection effectiveness and extrapolate the improving mechanisms. The results show that irradiating low-intensity airborne ultrasound (∼127 W, harmless mechanical waves) into the dehumidifier significantly increased the disinfection efficiency by 50 % and the dehumidification rate by over 90 % when airflow passed through the dehumidifier (∼0.4 s). The enhanced disinfection is attributed to ultrasonic cavitation, which facilitates the rupture of the desiccant-captured spores through microstreaming-induced shear forces. Notably, the improvements were more pronounced in humid air and with dilute desiccant solutions, suggesting that efficiency can be maintained with lowered desiccant concentrations. The US-LDAC system was particularly adept at removing mold aerosols (2.1–3.3 μm) which are easily inhaled. These findings propose a promising avenue for retrofitting existing LDAC systems to effectively reduce airborne molds and enhance dehumidification, thereby protecting indoor air quality.

A hybrid technology for enhancing VOC transfer in liquid desiccant dehumidifiers: Combining surfactant and internal cooling

Indoor air pollution control has increasingly focused on addressing the presence of volatile organic compounds (VOCs). In this regard, liquid dehumidification is a potential method for VOC removal. However, most of the recent studies focus on the utilization of conventional liquid desiccants and dehumidifiers without demonstrating their potential in VOC removal. To realize this potential and improve removal efficiency, a proper enhancement strategy is needed. In this paper, a hybrid technology named “surfactant + internal cooling” is proposed to enhance the VOC transfer mechanism. A theoretical model is proposed for predicting VOC transfer employing the hybrid technology presented in this study. The proposed technology is compared against other two conventional technologies in terms of removal performance, parameter distribution, and enhancement mechanism. Additionally, the impacts of some of the key parameters on the VOC removal characteristics when employing the hybrid technology are identified, and their respective distributions are characterized and investigated. The results showed that after the implementation of surfactant technology and internal cooling technology, the improvement rates compared to traditional adiabatic dehumidifiers are 22 % and 42 %, respectively. However, with the hybrid technology combining the surfactant and internal cooling, a maximum improvement rate of 63 % is reported. This enhancement can be attributed to the collaborative reduction of the Henry’s law constant by 62 % at the dual-scale level of micro-solution and macro-structure. Overall, it is demonstrated in this paper that the use of the hybrid technology can simultaneously improve the micro and macro driving forces driving the VOC transfer, enhancing the VOC removal performance. The findings of this study provide new insights to improve the performance of liquid desiccant dehumidifiers in VOC removal applications.

A refined dynamic liquid dehumidification model for the packed dehumidifier considering time-varying thermal mass of the desiccant

Liquid desiccant dehumidification technology is a promising, energy-efficient dehumidification approach. It can flexibly adapt to variations in renewable energy supply and users' demands, making it an inherently dynamic process. However, optimizing this process from a dynamic perspective is often neglected. This is mainly due to the challenges in establishing a dynamic dehumidification model, where the desiccant's thermal mass and heat and mass transfer coefficients should be time-dependent. In this paper, a refined dynamic dehumidification framework using the finite difference method is developed, where governing equations for the mass and species conservations are rebuilt taking the thermal mass and desiccant concentration as time-dependent variables. Auxiliary equations determining evolutions of the desiccant's thermal mass and heat and mass transfer coefficients are derived based on the continuity equation and analogy method, respectively. Subsequently, the experiments are carried out and serve as a benchmark to check the simulations. It suggests the simulated results using the refined model align well with the experimental data and demonstrate around 50 % better predictive accuracy compared to the existing method, indicating the feasibility of the refined model. The refined model also contributes to rapid adaptation of the dehumidification process to meet specific needs. In a specific case, this could result in energy savings of 60 % for the regeneration of the desiccant solution. This study provides a reference for quantifying evolutions of the liquid desiccant's thermal mass based on an understanding of the physical process. It lays a solid foundation for modeling the dynamic dehumidification process at the design stage and assists in operating an energy-saving dehumidification system.

Developing an integrated simulator and optimizer model for liquid desiccant dehumidification system “LDDSim”

This study introduces “Liquid Desiccant Dehumidification Simulator” (LDDSim), a novel software tool aimed at simplifying the construction of adiabatic liquid desiccant systems, with a particular focus on innovative series two-stage regenerator configurations. LDDSim enables parametric studies and optimizations, enhancing system design and selection. Moreover, LDDSim facilitates thorough system analyses through informative graphical outputs and employs multi-objective optimization tools to boost efficiency. This paper outlines the software’s main inputs, outputs, subroutines, inference engine, and complexity analysis and verification using a real case study utilizing multiple-effect regeneration (MER). Results highlight the advantages of employing a series two-stage regenerator, such as lower power consumption and more flexibility in space compared to single-stage setups. Furthermore, system optimization efforts led to a significant reduction in power consumption while maximizing dehumidifier efficiency and moisture removal rate, yielding promising results with a 36.2 % decrease in power consumption, alongside a dehumidifier efficiency of 94.02 % and a moisture removal rate of 9.84 g/s. LDDSim is a valuable tool for engineers and researchers in liquid desiccant dehumidification systems for design, simulation and optimization.

A Review of the Thermophysical Properties and Recent Development Trends on Liquid Desiccants for HVAC Applications

A Review of the Thermophysical Properties and Recent Development Trends on Liquid Desiccants for HVAC Applications

Experimental investigation and performance analysis of a spray-type ionic liquid desiccant dehumidifier

Ionic liquid desiccants (ILDs) have vapor pressures similar to lithium chloride and no corrosion and crystallization problems, so they are considered a promising alternative to halide salt desiccant solutions. However, the cost of ILDs is more expensive than conventional halide salts, which limits their practical application. Thus, this study developed a spray-type dehumidifier using an ionic liquid desiccant to increase dehumidification performance and reduce the required amount of ILDs. The presented dehumidifier was tested at various operating conditions. Also, a theoretical model was established to analyze heat and mass transfer coefficients of the dehumidifier. Results indicate that the increase in the flow rate ratio of solution to air benefits absorption performance, and the mass flux of solution is suggested to exceed 170 mL s−1 to avoid the occurrence of air bypass. Moreover, compared with the packed bed type, the spray type can reduce the required solution flow rate by 35 % and save power consumption by 19 % under the same moisture removal rates. The dehumidification effectiveness of the presented dehumidifier was up to 0.64 and comparable to the conventional packed bed dehumidifier using lithium chloride solutions.

A view on the performance comparison between adiabatic and internally-cooled dehumidification processes using liquid desiccant

Humidity control is emphasized in various fields. However, the effectiveness comparison between adiabatic dehumidifier (AD) and internally-cooled dehumidifier (ICD) was only conducted in limited cases, without comprehensive understanding of different cooling mediums and working conditions. In this study, the component effectiveness of these two dehumidifiers is parametrically compared. When chilled water serves as cooling medium, AD has sensible effectiveness of 0.65 and latent effectiveness of 0.84 under baseline case, while those of ICD are 0.52 and 0.85 respectively. AD performs better under higher sensible loads, and ICD is more capable of dealing with more moisture transfer. Low water temperature, low air-desiccant ratio and adequately low water-desiccant ratio also highlight the superiority of AD. When secondary air serves as cooling medium, AD always has higher effectiveness than ICD in the studied range, and the superiority is more significant at lower temperature and humidity of secondary air. Sensible effectiveness of 0.44 and latent effectiveness of 0.78 for AD are obtained under baseline case, while those of ICD are 0.07 and 0.74 respectively. ICD has better adaptivity than AD at a circumstance with great variation of operation parameters. The results contribute to enlightening insights for further design of moisture capture components.

A hybrid solar-driven membrane distillation-assisted liquid desiccant air conditioning system: Mathematical modeling and feasibility analysis

Membrane distillation (MD) is a promising method for liquid desiccant (LD) regeneration as it can mitigate LD carryover and produce freshwater as a by-product. Previous research on MD regeneration was mainly focused on performance evaluation and optimization of the regenerator itself. This paper proposed a hybrid solar-driven direct contact MD (DCMD) regeneration-assisted liquid desiccant air conditioning (LDAC) system for air dehumidification, cooling, and freshwater production. A mathematical model for the DCMD regenerator was first developed by considering both temperature and concentration polarizations. This model was validated against the experimental data in terms of the outlet channel temperature and LD solution concentration in the feed tank with relative deviations of ± 9.8 % and ± 0.5 %, respectively. The DCMD model was further integrated into an LDAC system with a batch-wise operation. To investigate the technical feasibility of the proposed system, a one-week simulation was conducted in a residential house during summer in a tropical climate area of Australia. The results showed that the latent heat load was effectively removed from the process air and the regenerated liquid desiccant solution can meet the dehumidification requirement with a concentration over 30.0 wt%. The dehumidification rate and regeneration rate were at 0.49–1.25 kg/h and 0.95–4.25 kg/h, respectively. Solar energy contributed to 52 %-78 % of the total system thermal energy consumption. Furthermore, this system can produce 11.0–12.8 kg of water daily.

A review of internal cooling strategies in liquid desiccant dehumidification and cooling systems

Air conditioning systems have become an integral part of society, and their utilization is increasing day by day. Most air conditioning systems use the vapor compression refrigeration (VCR) principle, which is a 190-year-old technology and has undergone significant changes to improve its performance and efficiency. However, the major drawback of VCR is its high energy consumption and use of highly polluting refrigerants. In this 21st century, energy conservation and environmental protection are the need of the hour. To mitigate the challenges, the search for alternative cooling systems that are eco-friendly and have less energy consumption is gaining wide attention. Liquid desiccant systems are gaining popularity due to less energy consumption and being eco-friendly. Therefore, this study attempts to review the recent developments in liquid desiccant technology by focusing on internal cooling strategies. As the internal cooling improves the overall performance of the liquid desiccant by controlling the liquid temperatures. Therefore, this review highlights the various methods, configurations and mathematical simulations in internal cooling, which are less explored in the available literature.

Investigation of a Wheel Liquid Desiccant Cooling System Performance via ANSYS CFX

A liquid desiccant cooling system is an alternative air-conditioning system with significant energy-saving potential. This system is commonly used in the industrial sector, such as in dehumidifiers. The key component of the liquid desiccant cooling system is its dehumidification performance. Therefore, a study on a liquid desiccant dehumidifier has been conducted to predict its performance using computational fluid dynamics analysis. In these simulations, the effects of the temperature of the liquid desiccant and the velocity of air flow on the absorption process between the liquid desiccant and air were studied. The same applies to the velocity profile, which helps determine the airflow pattern within the dehumidifier. The model was constructed using ANSYS FLUENT and Autodesk Inventor. The model is the rotary desiccant wheel dehumidifier which was used to dehumidified the air.. ANSYS CFX was used for simulating the velocity profile to achieve the airflow pattern in the dehumidifier. The volume of fluid was selected as the multiphase method for the second simulation process. The temperature and mass fraction of water were monitored within the air during the counterflow simulation between the liquid desiccant and the air. The liquid desiccant chosen for this study was LiCl. The simulations were conducted at specific air velocities, and the behavior within the dehumidifier was observed. The analysis results revealed that the air entering the rotary desiccant wheel dehumidifier experienced a drop in velocity after passing through the desiccant wheel in the middle. Additionally, turbulence occurred after the air passed through the wheel and the dehumidifier’s wall. Based on these findings, the design of an optimal dehumidifier and the selection of an appropriate air velocity for cooling can be carried out.

Feasibility Analysis of Indirect Evaporative Cooling System Assisted by Liquid Desiccant for Data Centers in Hot-Humid Regions

The rapid development of data centers (DCs) has led to a marked increase in energy consumption in recent years, which poses a direct challenge to global efforts aimed at reducing carbon emissions. In regions with hot and humid climates, the energy demand is largely driven by air conditioning systems necessarily to maintain appropriate operational temperatures. This study proposes a novel multi-stage indirect evaporative cooling (IEC) system, incorporating a liquid desiccant in the primary air channel to address the cooling demands of such DCs. Our approach involves a two-stage process where the first stage uses a liquid desiccant-based IEC (LD-IEC) for air dehumidification and the second stage utilizes the treated air from the first stage as the secondary air to enhance the cooling effect. A simulation model of the proposed system is established with validation, and the performance of the multi-stage system was also discussed based on different operation modes. Furthermore, a case study was conducted to investigate the feasibility of using this system in the DC under a typical hot and humid zone. The findings reveal that the first-stage LD-IEC is capable of diminishing the wet-bulb temperature of the ambient air. Furthermore, the case study demonstrates that the proposed system can greatly improve the temperature drop by 72.7% compared to the single IEC, which noticeably reduces the operation time of energy-intensive supplementary cooling equipment from 5092 h to 31 h given the supply air temperature threshold of 25 °C. In summary, the proposed system could substantially decrease reliance on traditional cooling systems, which demonstrates a promising avenue to fully use this passive cooling technology for cooling DCs.

Performance enhancement analysis of a liquid desiccant dehumidifier with internal cooling for indoor benzene removal

Indoor volatile organic compounds (VOCs) pollution is becoming increasingly serious, posing a huge threat to human health. The removal of VOCs has always been a challenge in air purification processes. In this regard, conventional VOC removal methods are often not ideal. Liquid desiccant (LD) dehumidification is a new removal method proposed recently and becoming increasingly used in many applications. Previous studies dealing with LD mainly focused on adiabatic dehumidifiers, but the results are not very promising. The main reason for this is the significant temperature rise of the LD solution, which seriously affects the mass transfer of the VOC. To enhance mass transfer performance, it is important to suppress temperature rise. In this study, internal cooling (IC) technology is introduced to enhance benzene mass transfer. A mathematical model is established for modeling and assessing the mass transfer process. The benzene transfer characteristics are studied and compared, considering dehumidifiers with and without IC. The effects of the cooling water, air, LD solution, and transfer parameters on the benzene mass transfer performance are evaluated and identified. Additionally, the distribution differences of the key parameters along the dehumidifier are revealed. The results indicated that benzene transfer performance can be significantly enhanced by adopting IC, with a performance improvement of 28.42%. This improvement is attributed to the decrease in the LD solution temperature caused by IC and the corresponding Henry’s constant. The cooling water parameters, airflow rate, LD solution status, and NTUbenzene are the key factors affecting the removal performance. Overall, employing IC can effectively improve the transfer driving force for benzene, resulting in better benzene transfer performance. This study demonstrates the feasibility and promising potential of using IC technology to enhance benzene transfer in LD dehumidifiers.

Numerical Investigation of Influence of Extent and Position of a Bypass on the Performance of a Single Unit Liquid Desiccant Based Evaporative Cooler

Air-conditioning of buildings is more energy-consuming with widely used vapour compression refrigeration systems in hot and humid areas. Alternatively, evaporative cooling does not show much effect in sultry regions because of increased humidity despite the minimum energy consumption. Indirect evaporative cooling is a promising alternative to direct evaporative cooling systems, but it suffers from low cooling effectiveness and is unsuitable for highly humid regions. Considering the above facts an alternative liquid desiccant-assisted modified M-cycle cooling system is proposed and examined numerically in the present work. The proposed cooling and dehumidification system is a simple unit incorporating chemical dehumidification and regenerative evaporative cooling in a single unit. A simultaneous heat and mass transfer model is developed for the numerical analysis. The numerical code is written in MATLAB and is validated with results available in the literature. Further, numerical analysis was carried out for the effect of various parameters on the performance of the proposed cooling system. The study shows an improvement of 19.2% in dew point effectiveness by incorporating an intermediate opening in the plate separating the product air and working air channels.

Interfacial structure and transport properties of concentrated lithium chloride solutions under an electrostatic field

Efficient moisture exchange between liquid desiccants and air is essential for optimizing dehumidification and air-conditioning systems, with the interfacial layer playing a critical role. This work investigates the influence of electrostatic fields (E-fields) on the structural and transport properties of the liquid-vapor interface between aqueous lithium chloride solutions and air at a microscopic scale using molecular dynamics (MD) simulations. Our research reveals that negative normal E-fields deplete ions within the interfacial layer, weakening their interactions with water molecules. Conversely, positive normal E-fields enrich surface ions, attracting a higher concentration of water molecules to the interface. The E-field enhances interactions between water molecules, increasing hydrogen bonds (H-bonds) at the interface. This weakens cohesion between water molecules and the liquid phase, ultimately reducing surface tension and the associated interfacial free energy barrier, facilitating the departure of water molecules from the liquid phase. Negative normal E-fields demonstrate greater advantages due to their pronounced alteration of the interface structure and the polarization of water molecules.

Theoretical Study on Falling Film Fin-Tube Dehumidifier Integrated With an Evaporative Cooler

Abstract The current work presents the theoretical analysis of a falling film fin-tube dehumidifier integrated with an evaporative cooler using CaCl2 as a liquid desiccant. In a fin-tube dehumidifier, the fins are provided outside the tubes to sustain the solution temperature during dehumidification. The evaporative cooler is compiled with a dehumidifier to provide cool air over the fins for maintaining the solution and air temperature. The theoretical model examines the heat and mass transfer between the air and the solution, which are moving in a counterflow direction inside the tubes. The study first presents the validation of the theoretical model with the experimental findings. The maximum disparity between theoretical and experimental results for moisture reduction with solution volume flowrate is found to be ±6.2%, whereas it is discovered to be ±13.8% for moisture reduction with airflow rate. The paper then discusses the air and solution parameters variation along the tube height and the impact of air and solution inlet parameters on system performance. The findings indicate that the variation in outlet air humidity ratio with tube height from 0 to 1 m is observed highest, 0.0264 kg/kg d. a. to 0.0233 kg/kg d. a., for a solution volume flowrate of 12.5 LPM and an airflow rate of 0.05 kg/s. The maximum variation in moisture effectiveness with tube height is observed from 0.0045 to 0.292 at 5 LPM solution volume flowrate and 0.05 kg/s airflow rate.