Liquid Desiccant System Research Articles

Numerical Analysis of Optimising Liquid Desiccant Dehumidification for Sustainable Building Cooling: A Data-Driven Method Using Response Surface Methodology

Leveraging data-driven methods such as Response Surface Methodology (RSM) has considerable potential for sustainable building cooling via mitigating energy consumption and environmental impacts. This research focuses on using the RSM to improve liquid desiccant dehumidification for sustainable building cooling performance using a D-optimal design. Specifically, the research intends to investigate the actual influence of the inlet air conditions and desiccant concentration on the performance of liquid desiccant dehumidification systems, i.e., the moisture removal rates and dehumidifier efficiency. To systematically conduct this research, a set of experimental data gathered from the open literature is utilised. This includes a specific set of inlet parameters of air temperature (27–34.5 °C), ratio of air humidity (20.5–25 g/kg), and solution temperature (27.5–38.5 °C) as the independent variables. Also, the feedback variables include the moisture removal rates (MRR) and efficacy (ϵ). The associated results of the analysis of variation indicate that the ratio of air humidity has the greatest influence on the moisture removal rate. However, the solution temperature and the ratio of air humidity have the most influence on efficacy. In the event of response optimisation, the result at MRR and (ϵ) are 0.54 g/s and 0.50, respectively, with a minimum desirability of 0.992 and 1.

Characteristics of heat and mass transfer in moist air-ionic liquid desiccant bubbly systems: Parametric assessment of regeneration performance

Ionic liquids (ILs) have recently become an increasingly popular working medium for liquid-desiccant deep dehumidification as applied to low-humidity industries and, in particular, the use of IL desiccants in bubble columns regeneration has been proven to be an effective way to promote their deep dehumidification potential. The present work considers a moist air-IL desiccant bubbly deep dehumidification/regeneration system, focusing specifically on the heat and mass transfer characteristics of regeneration in bubble column. An experimental apparatus is constructed and used to explore the effects of key operating parameters (i.e., liquid height H, superficial velocity vs, solution temperature Ts) on regeneration performance. Furthermore, a semi-analytical model of bubbly regeneration heat and mass transfer is developed and used to perform parametric assessments. The results indicate that elevating the liquid height, as well as higher superficial velocities and solution temperatures all contribute to improved regeneration rates, each with distinct influencing mechanisms. A higher superficial velocity enhances the volumetric transfer coefficient through a combined effect (i.e., gas–liquid specific interfacial area, heat and mass transfer coefficients). The effect of the solution temperature on the volumetric transfer coefficient is mainly reflected in the heat and mass transfer coefficient as determined by the transfer potential difference, while the hydrodynamics play a relatively minor role in the system of interest. Bubbly regeneration differs from deep dehumidification in terms of the volumetric transfer and heat/mass transfer coefficients. Notably, the Lewis number of bubbly regeneration is generally between 0.6–1. In practical applications, it is necessary to consider the air-side pressure drop, droplet entrainment, and low-grade thermal energy utilization. Under recommended conditions (e.g., H = 0.3 m, vs = 3.0 cm/s, Ts = 60 °C), a regeneration rate of 49 g/h and moisture effectiveness of 79 % can be achieved. This study provides guidance for the design of moist air-IL desiccant bubbly deep dehumidification/regeneration systems.

Evaluation of bubble column dehumidifier using magnesium chloride desiccant

With growing emphasis on indoor air quality and energy conservation, the development of sustainable and efficient dehumidification systems has become increasingly crucial across various industries. Liquid desiccant dehumidification system (LDDS) offers a more efficient alternative to conventional methods by utilizing low-grade waste heat. Most direct-contact liquid dehumidification systems use expensive desiccants such as LiCl and LiBr. Our research focuses on exploring MgCl2, prevalent in saltwater bitterns, as a cheaper, less toxic alternative. The core principle of this system involves passing air through a column filled with the MgCl2 aqueous solution, leveraging the hygroscopic properties of MgCl2 to remove moisture from the air stream effectively. Various parameters such as hole size, air flow rate and desiccant concentration are investigated. We further developed a numerical model for the dehumidification process considering the rise time of the bubbles in the desiccant solution and mass transfer in the bubble. After dehumidification, the diluted desiccant solution can be revived using low-grade heat. Use of seawater bitterns, with major component as MgCl2, shows potential for building an environmentally friendly and cost-effective dehumidification system.

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.

Comparative analysis of radiant air-conditioning systems combined with two different types of solar-powered dehumidification methods

Abstract This paper proposes a solar liquid desiccant radiation air-conditioning system(SLDRS) and a solar desiccant wheel radiant air-conditioning system(SDWRS) that combine with a phase change energy storage radiation terminal, solar energy, and heat pump system. The models of the two systems are simulated with the transient system tool (TRNSYS) to compare the refrigeration and dehumidification effects and energy saving of the two systems. The results show that the total refrigeration capacity of the SLDRS is reduced by 20.45% compared with the solar desiccant wheel radiation air-conditioning system, the monthly average dehumidification capacity is increased by 37.09%, and the total energy consumption is reduced by 712.9 KW·h. It is evident that the cooling and dehumidifying effect and energy efficiency of the SLDRS are superior to those of the SDWRS.

Design of ionic liquids as a desiccant for the liquid desiccant type air conditioning system

Abstract Recently, liquid desiccant air conditioners (LDACs) have gained rapidly growing interest as an important candidate for an energy-efficient air conditioner. By enabling moisture absorption from the air, ionic liquids (ILs) can serve as a novel desiccant source for LDACs. For insights into the design and optimization of ILs to this end, we herein present a survey of studies on dehumidification and other relevant properties of ILs and offer some molecular perspective on their feasibility as a desiccant.

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.

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.

Review on dehumidification technology in low and extremely low humidity industrial environments

Many industrial environments have low-humidity requirements. However, most research focuses on dehumidification systems in civil buildings, while research on industrial low humidity environments is extremely limited. This paper aims to summarize the research of dehumidification systems in low-humidity industrial environments, and provide some suggestions for the selection and improvement of dehumidification systems. Firstly, the environmental control requirements of industrial plants are reviewed and categorized into low humidity and extremely low humidity based on a relative humidity of 45 %. Then, the performance and applicability of condensation dehumidification systems, desiccant wheel (rotary dehumidifier) dehumidification systems and liquid desiccant dehumidification systems in typical industrial environments are summarized. Several preliminary system selection and configuration methods are presented. It is shown that the traditional condensation system is only suitable for low humidity plants. The desiccant wheel-based system is more capable of deep dehumidification, with a humidity ratio of less than 4 g/kg of supply air, while the liquid desiccant-based system can achieve high air volume operation of 10000 m3/h. Furthermore, their ranking under different scenarios is still outstanding issues. Evaluation indicators that weigh factors such as initial investment, operating costs, and control effectiveness need to be urgently proposed. Long term on-site testing is strongly recommended.

Effect of Air Parameters on LiCl-H2O Film Flow Behavior in Liquid Desiccant Systems

The wettability and stability of a solution’s film on the filler surface are the key factors determining heat and mass transfer efficiency in liquid desiccant air conditioning systems. Therefore, this study investigates the effects of different air parameters on the flow behavior of a lithium chloride solution’s film. The effects of air velocity, air flow pattern, and pressure on the wettability and critical amount of spray are discussed. The results show that the main mechanism by which the air velocity affects the wettability is that the shear stress generated by the direction of the air velocity disperses the direction of the surface tension and weakens its effect on the liquid film distribution. In addition, in the counter flow pattern, the air flow blocks the liquid film from spreading longitudinally and destroys the stability of the liquid film at the liquid outlet, which increases the critical amount of spray. The pressure distribution is similar under different operating pressures when the flow is stable; thus, pressure has little effect on wettability. The simulation results under 8 atm are compared with the experimental results. It is found that the sudden increase in the amount of moisture removal when the amount of spray changes from 0.05 to 0.1 m3/(m·h) in the experiment is caused by the change in the liquid film flow state. In addition, the results show that within the range of air flow parameters for the liquid desiccant air conditioning system, air flow shear force is not the main factor affecting the stability of the solution’s film, and there is no secondary breakage of the solution’s film during the falling-film flow process.

Experimental investigation of a mixed desiccant solution of potassium formate and ionic liquid

Liquid desiccant technology is a promising energy-efficient alternative to conventional temperature and humidity control systems. In the quest to identify the optimal fluid for liquid desiccant systems, alternative desiccant solutions have been explored in terms of their feasibility and compatibility in dehumidification systems. This study proposes and characterises a new type of less expensive mixture of potassium formate (HCO2K) and 1-ethyl-3-methylimidazolium acetate ([EMIM][OAc]). This novel desiccant solution was investigated in terms of corrosiveness to metals, moisture absorption and desorption ability, cost-effectiveness compared to conventional desiccant solutions. The corrosiveness of desiccant solutions to copper-nickel, copper and steel was tested at room temperature and at 60 °C. Experiments were conducted in a climatic chamber with temperatures of 25–31 °C and relative humidities of 80–90% for the absorption process and temperatures of 50–70 °C and relative humidities of 20–30% for the desorption process to assess the moisture absorption and desorption capacities and mass fraction variations of the desiccant solutions. The mixed desiccant of HCO2K/[EMIM][OAc] in the ratio 60/10% wt. showed a moisture absorption capacity of 0.146 gH2O/gsol (compared to 0.18 gH2O/gsol for aqueous lithium chloride at 33.3% wt.) for a temperature and relative humidity of the climatic chamber of 25 °C and 90%, respectively. Its low corrosiveness, good moisture absorption and desorption capacity and higher cost-effectiveness make it a promising alternative to conventional desiccants, such as aqueous solutions of lithium chloride.

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.

Optimizing the amount of solution in packed liquid desiccant systems for sustained dehumidification

Liquid desiccant dehumidification technology, driven by renewable energy, presents an energy-efficient solution to dehumidification. However, a large solution amount is always configured to extend the dehumidification process and address the unavailability of renewable energy. This is due to a lack of design guidance regarding the optimal desiccant solution amount. This study aims to address this gap by offering guidelines, with a particular focus on the dehumidification duration. Initially, a benchmark for the solution amount is defined for convenient quantification in further study. Then, a theoretical analysis of the dehumidification degradation process is conducted. Results reveal that dehumidification duration is primarily constrained by the temperature rise of the desiccant solution, rather than the solution amount. Consequently, a natural cooling unit, instead of mechanical cooling, is introduced to remove the temperature rise. Following this guideline, multiplying the benchmark for the solution amount can significantly extend the dehumidification duration from minutes to hours, while increasing it by tens of times can extend further to days. Furthermore, the solution amount can be reduced by over 90 % with the design guideline compared to the traditional method. This study paves a way to significantly reduce the solution amount and relevant costs for liquid desiccant dehumidification systems.

A data-driven model for a liquid desiccant regenerator equipped with an evacuated tube solar collector: Random forest regression, support vector regression and artificial neural network

The application of a solar-assisted liquid desiccant air-conditioning system equipped with evacuated tubes, focusing on the assessment and comparison of various artificial intelligence (AI) models is investigated. Specifically, Support Vector Regression (SVR), Multi-Layer Perceptron Artificial Neural Network (MLP-ANN), and Random Forest Regression (RFR) models are assessed for predicting key performance indicators: mass removal rate, efficiency, and effectiveness. Additionally, different optimizers within the Artificial Neural Network (ANN) framework—such as Adam, Stochastic Gradient Descent (SGD), and RMSprop—are systematically examined and tuned. The study encompasses the selection of the most suitable AI model for each target variable, considering parameters such as ambient temperature, solar radiation, timestamp, airflow rate, and initial solution concentration as influential factors in the modeling process. It is found that the best predictor model for effectiveness is SVR with RBF kernel. For MRR and efficiency, it is MLP-ANN with respectively AdamW and NAdam optimizers. The disparity of prediction of the MRR, efficiency and effectiveness target are respectively 0.72%, 1.07% and 0.5%, on average, indicating a precise prediction. Furthermore, including timestamps as model inputs significantly boosts accuracy, an aspect often neglected in prior research, leading to a noticeable minimum 5% rise in the R2 score.

Application of biomass-based wood shaving packing in a liquid desiccant dehumidification system – a source of sustainable energy

ABSTRACT The present work focuses on the construction of a counter flow dehumidification test rig where calcium chloride liquid is used as the desiccant and is made to spray on the novel organic packing made of wood shaving with different densities and porosities. The mass flow rate of the air is varied and the performance parameters such as moisture removal rate (MRR), dehumidification effectiveness, coefficient of performance (COP), sensible heat factor (SHR) and mass transfer coefficient have been investigated. Results demonstrated an increase in the relative humidity, mass transfer coefficient and drop in the COP, MRR and dehumidification efficiency with the increase in the flow airflow rate. On increasing the CaCl2 concentration, dehumidification performance parameters such as MRR, COP and mass transfer coefficient are found to be increased. Out of the three different densities tested, 500 kg/m3 shows best performance with MRR, ΔRH and dehumidification effectiveness being 9.7%, 18.7% and 4.9% lower than the Celdek pad when measured at 5 m/s of air velocity for 30% desiccant concentration. Optimisation of the input parameters has been done and the results revealed that air velocity should be maintained within the range of 4–5 m/s to minimise energy consumption and optimum performance.

Heat and mass transfer characteristics of vertical falling film cylindrical plastic surfaces under partial wetting conditions for liquid desiccant regeneration

The regenerator plays a dominant role in the overall energy-economic performance of liquid desiccant systems. Nevertheless, very few studies have been reported on falling film liquid desiccant regenerators. Most of the previous studies targeted experimental/numerical modelling needs of regeneration process under design conditions. In the current research workexperimental investigation of regeneration process is carried out to study the coupled heat and mass transfer process for adiabatic regeneration of LiCl liquid desiccant over outer surface of vertical Plain and Modified polypropylene cylindrical surfaces under design (complete wetting) and part load (partial wetting) operating conditions. Modified cylindrical surfaces are developed to compensate the poor wetting of the plastic surfaces. New generalised one-dimensional numerical philosophy is proposed to accommodate the need of part load operating conditions by inclusion of actual wetting of the working surface as well as convective heat transfer happening from dry patches of solid surface to the flowing air. The heat and mass transfer coefficients are determined by solving the governing coupled heat and mass balance non-linear differential equation using the numerical finite difference method. It is found that the Modified surface offered an average improvement of 35.8% in the mass transfer coefficient under partial wetting conditions. New Sh and Nu number correlations are proposed by incorporating heat and mass transfer driving potentials and new parameter wetting factor. The developed correlations predicted the change in humidity and temperature across the regenerator with an average error of 6.2% and 7.5%, whereas from the existing two correlations found in the literature, the first one predicted the same experimental observations with an average error of 54.6% and 36.2%, while second one predicted with an average error of 77.3% and 22.0%, respectively. The results highlighted that the assumption of complete wetting of working surface under part load operating conditions leads to significant error in prediction of air outlet conditions. The proposed correlations will be helpful for numerical modelling and simulation of falling film regenerators under wide range of liquid loading conditions.

Dynamic simulation of a novel liquid desiccant air-conditioning system for greenhouse cooling and water recovery

We present dynamic, hour-by-hour modelling of a multi-stage nanofiltration regeneration system for liquid desiccant air-conditioning (NF-LDAC) of horticultural greenhouses in 17 locations covering four climate types. Four technologies are compared: fan ventilation, evaporative cooling (EvapC), conventional air-conditioning (AC), and NF-LDAC. The comparison is based on acceptable conditions for cultivation and coefficient of performance (COP). On average, fan ventilation and EvapC achieve acceptable conditions for 2 months per year, compared to 5.4 and 10.5 months for AC and NF-LDAC respectively. The highest COP value of 7.6 for NF-LDAC is reached at Colombo (Sri Lanka), followed by 5.3 at Mecca (Saudi Arabia). The permeate of the multi-stage regenerator can be recycled for irrigation, providing water savings. The highest water saving of 63% is at Mecca. These results are inferior but more realistic than those from an earlier idealised and steady-state model, which predicted a COP of 12.4 and water savings of 100% at Mecca. Nevertheless, in hot desert climates, NF-LDAC maintains acceptable conditions for year-round cultivation and saves water that is scarce in such climates. Future advances in nanofiltration membrane fabrication could increase the COP of NF-LDAC to 12.1 at Colombo and 7.4 at Mecca.

Solar driven liquid desiccant dehumidification system: Measurements and annual system simulations

Liquid desiccant air conditioning (LDAC) systems are used for dehumidification of air to low dew point temperatures. In the presented study a TRNSYS model of a LDAC unit is developed and validated with laboratory measurements. This model is coupled with a solar thermal system that provides heating water for the regeneration process. With this model dynamic annual system simulations can be carried out to simulate the dehumidification of a building. The solar fraction is evaluated for various infiltration rates of the building and solar collector areas with an internally cooled as well as an adiabatic absorption process.The simulation results reveal that high solar fractions of 70% to 81% can be achieved when dimensioning the solar thermal system to cover the regeneration heat demand on a good summer day. This is due to the good correlation of solar irradiance and dehumidification load. Without internal cooling of the absorption process (adiabatic conditions), the solar fraction is reduced by about 10percent points for the same size and operating conditions.

The impact of wettability on the performance of a two row wavy fin and tube liquid desiccant system for dehumidification and regeneration

This study investigates the challenge of enhancing wettability in falling film type dehumidifiers/regenerators, a crucial factor in optimizing the performance of building air conditioning systems. The emergence of Severe Acute Respiratory Syndrome (SARS) has underscored the need for improved indoor air quality (IAQ) and energy efficiency. This research specifically addresses the suboptimal wettability issue in fin and tube liquid desiccant systems, which is essential for efficient dehumidification and regeneration processes. The experimental setup employed a cross-flow configuration within the heat exchanger elements, where the flow of ionic liquid intersected with horizontal airflow through cooling and heating coils. By systematically adjusting the wettability on the heat exchanger surfaces, the study examined its impact on relative humidity and dry bulb temperature at the system's inlet and outlet. The results indicate that the wetting fraction on fin and tube surfaces significantly influences the delta humidity ratio of air. In the dehumidification phase, for instance, the delta air humidity ratios varied between 9.4 and 9.7 g/kg with corresponding wetting ratio values ranging from 0.47 to 0.5. Similarly, during regeneration, delta air humidity ratios fluctuated from 9.08 g/kg to 9.6 g/kg, with wetting fractions between 0.47 and 0.5. In conclusion, this study offers in-depth insights into the impact of wettability on the efficiency of fin and tube liquid desiccant systems. These findings have implications for enhancing IAQ and energy efficiency in building air conditioning, particularly in tropical regions like Indonesia.

A Study on the Regeneration Performance Characteristics of an Internally Heated Regenerator in a Liquid Desiccant System

This paper presents a study of the regeneration performance characteristics of an internally heated regenerator applicable to a liquid desiccant system. The internally heated regenerator used in this study was designed and manufactured to provide good regeneration performance. An experimental setup was established to test the regeneration performance. LiCl aqueous solution was used as working fluid. Variables to evaluate regeneration performance characteristics of the internally heated regenerator were dry bulb temperature, relative humidity and velocity of regeneration air, mass flow rate, temperature and concentration of the LiCl aqueous solution. The experimental conditions were chosen by using a 1/2 fractional factorial DOE. Regeneration rate and regeneration effectiveness were taken as results. From the results, solution concentration and regeneration air relative humidity have strong effects on the regeneration rate. The regeneration effectiveness was affected mostly by regeneration air velocity and LiCl aqueous solution temperature.