Dehumidification Process Research Articles

Performance analysis of coupling vapor compression cycle to freeze and humidification-dehumidification based high-performance desalination

Although freeze desalination has a lower latent heat of ice formation (334 kJ/kg), its energy performance is still insufficient because of energy loss associated with not using the waste heat of the active cooling system. To address this challenge, this research introduces an innovative hybrid desalination system that synergistically combines freeze, humidification-dehumidification (HDH), and vapor compression cycle (VCC) technologies. The novelty of our approach lies in simultaneously leveraging the VCC's cooling and thermal energy for freeze and dehumidification processes, respectively, which greatly increases the desalination energy performance over only achieving freeze desalination. A thermodynamic model is developed to analyze the proposed system, and a series of parametric analyses are carried out to determine the system configuration that obtains the highest performance. Ultimately, a higher ice recovery rate of 20 % offers the best total desalination performance of only 63 Wh/kg. Furthermore, the HDH desalination unit can make up the for loss of freeze desalination performance at higher feed seawater temperatures, ensuring robust performance even under high-temperature conditions.

Removal of moisture from air by cooling method

Moisture removal from air is a critical aspect of climate control in various industrial and residential applications. The cooling method, which relies on the condensation of water vapor by lowering air temperature below its dew point, is one of the most commonly used techniques for dehumidification. This study investigates the principles, effectiveness, and limitations of the cooling method in different environmental conditions. By examining the impact of factors such as ambient temperature, humidity levels, and cooling system design, this research aims to identify strategies for optimizing energy efficiency in dehumidification processes. Experimental results highlight the correlation between cooling temperature and condensation rates, emphasizing the need for advanced cooling technologies to reduce energy consumption. The findings contribute to the development of more sustainable and cost-effective dehumidification systems, offering valuable insights for enhancing HVAC performance and reducing environmental impact.

A multiphase flow model of water droplets dielectrophoretic-induced air dehumidification phenomena

Air humidity in indoor spaces plays a critical role in human comfort and health. Dehumidification systems are used for building humidity controls, but they can take significant energy consumption, especially in geographic locations with high outdoor humidity and warm climates. Consequently, there is a growing demand for innovative dehumidification processes that consume minimal energy. Dielectrophoretic air dehumidification represents one such promising approach. However, it has not garnered significant attention due to the absence of engineering models and simulation tools capable of evaluating its performance and limitations at large-scale airflows. A new numerical multiphase CFD model, which is also experimentally validated, is developed in a customized Reacting Foam solver based on OpenFOAM® version 9. The newly developed model seeks to decrease substantial energy consumption and lower costs by leveraging the dielectrophoretic phenomenon to regulate moisture levels in the air. The solver integrates a hybrid Eulerian-Lagrangian framework to track the droplet's trajectory and growth rate while solving the continuum equations for the moist air. An electrospray produces electrically charged droplets, which grow during their in-flight trajectories as water vapor condenses onto their surfaces. The role of electrostatic forces in promoting vapor condensation within a high-gradient electrical field is investigated, and the dielectrophoretic vapor nucleation process on charged water droplets is discussed. The CFD model was validated against results from the literature and from proof-of-concept experiments conducted by the authors, which showed a 2 % air dehumidification with a single electrospray and airflow rate of 5 cubic feet per minute. The simulation results indicated that augmenting the number of electrically charged spray droplets increased the dehumidification of the air to 25 %. The initial mean droplet diameter, the orientation of the injector and relative humidity significantly influence the assessment of dehumidification. Scaling up this approach to larger airflow volumes is identified as a potential future research direction.

Diagnostics and Multi-criteria Analysis of Methods for Drying Buildings After Flooding. Case Study

This article presents guidelines for moisture and mycological diagnosis procedures for buildings after flooding. This paper proposes a division of the diagnostic procedure according to the medium of action and collects and presents methods for drying building elements. 54 companies dealing with drying were analyzed. The task of dehumidification is to use various methods to reduce the moisture level of building partitions to the equilibrium moisture level. An analysis of dehumidification methods in terms of ease of application, duration of the dehumidification process and level of structural interference is presented. In Poland, there are no guidelines formulated in legal acts or instructions regarding the procedure for moisture diagnostics and nor drying. It was noted that in situ studies cannot always lead to determining the actual values of mass moisture and thus to creating a real model of partition drying.

Operational characteristics and controlling strategies of a novel dual-return-air dehumidification evaporative cooling system (DDEC)

Dehumidification evaporative cooling (DEC) systems exhibit superior environmental adaptability compared to conventional evaporative cooling systems. However, the dehumidification process in DEC is coupled with its cooling process, presenting challenges in adapting to varying environmental conditions. To address this issue, this study proposes a novel dual-return-air dehumidification evaporative cooling system (DDEC) that utilizes two return airflows to control both dehumidification and cooling efficiency. A thermodynamic model based on COMSOL LiveLink with MATLAB for the DDEC has been established and validated, enabling an analysis of the impact of operational parameters on its performance and the identification of key parameters. The results show that there are an optimum inlet flow rate (1100 m3/h) and a third flow rate control factor (0.2) that maximize the coefficient of performance (COP), giving the maximum COP of 0.87 and 0.35 respectively. Moreover, the first and second air flow rate control factors only have a significant influence on the supply air humidity of the DDEC. A higher regenerative temperature can reduce both the temperature and humidity ratio of the supply air but tends to decrease COP. Finally, a single-directional controlling strategy is proposed and analyzed for the DDEC application in different environments.

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.

Performance analysis and multi-objective optimization of a novel solid oxide fuel cell-based poly-generation and condensation dehumidification system

The application of energy supply systems based on fuel cells contributes to meeting the requirement of sustainable development, and developing high-efficiency, low-pollution, and multifunction poly-generation systems coupled with fuel cells is increasingly attractive. This study proposes a novel combined cooling, heating, power poly-generation and dehumidification system including a solid oxide fuel cell, a gas turbine, a double effect absorption refrigerator, a condensation dehumidification unit, an organic Rankine cycle, and a heat exchanger. Thermodynamic, economic, and environmental analysis models of the entire system are developed to evaluate system comprehensive performance. The effects of system parameters such as the inlet temperature of fuel cell, steam to carbon ratio, air flow rate, and high temperature generator temperature on system performance are analyzed. The analysis findings reveal that the proposed system can provide power, cooling, and heating of 551.904 kW, 20.307 kW, and 193.009 kW, and the dehumidification capacity per unit is 14.516 g/kg when 1.238 kg/s of humid air is treated. The system exergy efficiency is found to be 70.534 %, and the system cost rate is 15.578 $/h with carbon dioxide emission being 0.301 kg/kWh at the design condition. Two groups of multi-objective optimizations of the whole system are further conducted to acquire the optimal system performance and working conditions. The optimization results demonstrate that the optimal exergy efficiency of 72.912 % appears at point C1 in the first group of optimization with the lowest carbon dioxide emission being 0.293 kg/kWh, and the optimal qualities of humid air are found to be 1.606 kg/s at C2 and D2 in the second group of optimization. After optimization, the system carbon dioxide emission is decreased by 0.008 kg/kWh, the exergy efficiency is increased by 2.378 %, and the quality of humid air in dehumidification process is developed by 0.368 kg/s. In summary, the proposed poly-generation and dehumidification system can meet multifunction energy demands and achieve good performance, and the research work could also provide theoretical basis for developing evaluation and optimization technologies of fuel cell-based poly-generation systems.

Energy saving of vacuum-based membrane dehumidification with indirect evaporative cooling in a low sensible-heat-ratio building

In hot and humid climates, dehumidification generally consumes more energy than cooling, and conventional mechanical vapor compression system is not efficient for dehumidification. Vacuum-based membrane dehumidification system have been developed as a more environmentally friendly alternative for dehumidification due to non-refrigerant system and isothermal dehumidification process. In this study, a novel hybrid air conditioning system that combines vacuum-based membrane dehumidification with an indirect evaporative cooler for pre-cooling is proposed to achieve efficient air conditioning in building with low sensible heat ratio. The energy performance of the proposed system is investigated by detailed thermodynamic simulations and compared with conventional variable air volume (VAV) system and indirect evaporative pre-coolers combined VAV system. The simulation results show that when the average sensible heat ratio of the space is 0.73 and the COP of the vacuum-based membrane dehumidifier is 1.0, the proposed system can reduce energy consumption by 16.1 % compared to conventional VAV system and by 6.4 % compared to indirect evaporative pre-cooler combined VAV system during the cooling season. The energy performance of the proposed system is significantly affected by the sensible heat ratio of the building and the energy efficiency of the vacuum-based membrane dehumidifier. When the COP of the vacuum-based membrane dehumidifier reaches 2.0, the proposed system can achieve an energy savings of 48.2 % compared to conventional VAV system.

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.

Performance Evaluation of a Solar Humidification – Dehumidification Desalination Unit

This paper is to investigate the use of solarenergy in desalination by humidification and dehumid-ification process (HD). Here, a proposal for the desalinationunit has been come out with cylindrical shape containing the evaporator in the middle and surrounded by the condenser.The hot feed water coming from the solar thermal system issprayed at the top of the evaporator where the air flowsfrom the bottom. In the evaporator the air is humidified until it gets out saturated, then introduced to the condenser,where it is dehumidified to obtain the fresh water andcirculated back to the evaporator. Practically there aremany parameters influence on the performance of thisdesalination unit, which are environmental, design and operational. In the current study these parameters are takenin consideration to formulate mathematical models whichgovern the performance of the main components of this unit,which are the evaporator, the condenser and the solarthermal system. The deduced mathematical models have been interpreted in many programs in visual basic languageas a computer software. This software contains many pageswhich help in introducing and analyzing the most influentialparameters. In this case many operational parameters havebeen studied such as feed water temperature, mass flow rate and salinity, in addition to cooling water mass flow rate andinlet temperature, as well as quantity of solar irradiancewith others. At these inputs many outputs have beenobtained which are related to the performance of thedesalination unit such as fresh water productivity, energy consumption, humidifier volume, recovery ratio and gainoutput ratio.

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.

Exploring the potential of graphene oxide membranes for vapor permeation

This review explores the applicability of graphene oxide (GO) membranes in vapor permeation, emphasizing their unique properties and promising capabilities. In the context of eco-friendly separation processes, such as pervaporation (PV) and vapor permeation (VP), GO membranes can selectively permeate water vapor to separate vapor mixtures. Their distinct structure, featuring slip flow and precise water molecule alignment in angstrom-scale interlayer spaces, facilitates fast water transport. This review proposes the selective adsorption–pore flow–evaporation model as a plausible mechanism for vapor permeation through GO membranes. Despite extensive research on GO membranes for PV in separating mixtures, their application in VP remains underexplored. Nevertheless, their selectivity for water vapor and effectiveness in gas dehumidification processes emphasize their applicability for chemical dehydration (purification). Future research in this field can advance membrane technologies, offering more sustainable and efficient separation processes across various industries for purifying and recycling chemicals and separating azeotropic mixtures.

Multi-objective optimization of solar-driven hollow fiber membrane dehumidification system based on MOPSO

The solar-driven hollow fiber membrane dehumidification (SHFMD) system is a renewable, energy-saving, and highly effective dehumidification system. It provides an effective solution to the problem of air-entrained liquid droplets during the traditional solution dehumidification process. The system's mathematical model was established and the reliability of the mathematical model was verified by experimental data. To enhance the comprehensive performance of the system, the multi-objective particle swarm optimization (MOPSO) algorithm is used in this paper to optimize the multi-objective parameters of the system. The objective function is the total exergy destruction of the system and the dehumidification capacity of the system. The optimization variables are cold water temperature, cold water flow rate, solution flow rate, air flow rate, and hot water flow rate. The optimization is performed using the multi-objective particle swarm optimization (MOPSO) algorithm to obtain the Pareto front, and the points of the Pareto front are normalized. Finally, the optimal trade-off point of the Pareto frontier is obtained. Each operating parameter of the optimal point of the Pareto front is also analyzed. The results show that the air flow rate and cold water flow rate have the most influence on the conflict between the total exergy destruction of the system and the dehumidification capacity of the system.

Design and development of water purifier using humidification and dehumidification process by using renewable energy

Design and development of water purifier using humidification and dehumidification process by using renewable energy

Experimental study on a compact solar driven two-stage humidification-dehumidification desalination system with shared dehumidifier

The low-cost and low-grade solar driven humidification-dehumidification desalination is considered a promising process for small and medium capacity freshwater production. Nevertheless, the enhancement of the unit volume water production rate is hindered by the disparity in mass transfer coefficient and the incongruity between heat and mass flow rate in the humidification and dehumidification process. This paper proposes a compact solar driven two-stage humidification-dehumidification desalination system with shared dehumidifier. It contains two humidifiers and a dehumidifier, wherein the dehumidifier is stacked between the vertically placed humidifiers. The circulating air is humidified by hot seawater in the top and bottom humidifiers respectively, and then goes to the middle dehumidifier to condense via a freshwater absorption process. Its design scheme and operating principle are introduced and a mathematical model describing its internal energy and mass flow process is established. An experimental setup with compound parabolic concentrator areas of 6 m2 is developed, and a sequence of experiments is carried out. The results indicate that its freshwater productivity can reach 29.6 kg/h with a gained output ratio of 0.84 when the feed seawater temperature is 80 ℃. Due to its compact structure, the freshwater production per volume unit per day reaches up to 224.1 kg/(day⋅m3). This work may promote the development of solar humidification and dehumidification systems towards low cost and high efficiency.

Heat flow topology-driven thermo-mass decoupling strategy: Cross-scale regularization modeling and optimization analysis

The liquid desiccant dehumidification (LDD) is both eco-friendly and highly effective in humidity control, widely investigated across diverse angles. This study expands the application of the newly devised heat current method to examine the liquid desiccant dehumidification process. It introduces a new regularized temperature, which includes using a heat flow topology driven thermo-mass decoupling strategy, and constructing the heat current model by defining both the thermal resistance and moisture resistance. It significantly extends the application of the heat current method, clarifying the thermo-mass coupling energy transfer mechanism. The findings indicate that key factors influencing system performance indicators include total thermal conductivity (αA), solution mass flow rate (ms), air-solution mass flow rate ratio (RA/S,D), and heat source temperature (tH). Furthermore, under the influence of distinct thermal conductivities, the optimal output values for performance indicators, including moisture removal rate, exergy efficiency and entransy efficiency, are determined as 8.4 g/s, 71.2%, and 12.3%, respectively. The results of synergistic influence analysis reveal that, for the performance indicator entransy efficiency, msand RA/S,D display a significant degree of synergistic influence, resulting in a strong positive effect and benefiting 68.53% of the total area. Multi-objective optimization indicates a trade-off relationship among the system performance evaluation indicators moisture removal rate, exergy efficiency and entransy efficiency, with optimal solution values of 3.25 g/s, 65.92%, and 12.01%, respectively.

Investigation of purge angle on the air inhomogeneity reduction and energy efficiency improvement of the desiccant wheel dehumidification system

ABSTRACT The rotary desiccant wheel dehumidification system has been extensively applied to achieve deep dehumidification in the modern environment with low humidity ratio. The effect of mixing destruction caused by the temperature and humidity inhomogeneity on the thermodynamic performance of the desiccant wheel deep dehumidification (DWDD) system has not been thoroughly illustrated. This research aims to reduce the mixing destruction and improve the overall energy efficiency of the DWDD system. Numerical analyses were carried out to investigate the mixing destruction characteristics of the deep dehumidification process. The results revealed that the mixing exergy destruction gradually becomes a prominent factor as regeneration temperature and humidity ratio increase under deep dehumidification, and there is a significant temperature and humidity ratio gradient in the transition angles from the regeneration side to the process side. The purge angle is regulated to reduce the average temperature and humidity ratio on the process side and lower the air inhomogeneity. The exergy efficiency of the desiccant wheel can be improved from 44.8% to 73.9% at the regeneration humidity ratio of 20 g/kg under the effective purge angle of 30°, indicating a considerable enhancement of exergy efficiency under the effective purge angle at a high regeneration humidity ratio.

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.

Variation and correlation between water retention capacity and gas permeability of compacted loess overburden during wetting-drying cycles

Landfill gases can have numerous detrimental effects on the global climate and urban ecological environment. The protective efficacy of the final cover layer against landfill gases, following exposure to periodic natural meteorological changes during long-term service, remains unclear. This study conducted centrifuge tests and gas permeability tests on compacted loess. The experiments examined the impact and relationship of wetting-drying cycles and dry density on the soil water characteristic curve (SWCC) and gas permeability of compacted loess. Research findings reveal that during the dehumidification process of compacted loess, the gas permeability increases non-linearly, varying the gas permeability of soil with different densities to different extents under wetting-drying cycles. Two models were introduced to describe the impact of wetting-drying cycles on gas permeability of loess with various dry densities, where fitting parameters increased with the number of wetting-drying cycles. Sensitivity analysis of the parameters in the Parker-Van Genuchten-Mualem (P-VG-M) model suggests that parameter γ′s accuracy should be ensured in practical applications. Finally, from a microstructural perspective, wetting-drying cycles cause dispersed clay and other binding materials coalesce to fill minuscule pores, leading to an increase in the effective pores responsible for the gas permeability of the soil. These research results offer valuable guidance for designing water retention and gas permeability in compacted loess cover layers under wetting-drying cycles.

Performance analysis of heat pump polygeneration system

A heat pump polygeneration system is a promising technology to meet daily needs such as drinking water, power, space cooling or heating, and hot water generation. This work is focused on integrating the solar heat pump and two-stage humidification–de-humidification with a minimum space requirement. In this integrated cycle, the desired outputs i.e. condenser heat and evaporator heat are used for maximizing hot water and desalinated water production with minimal thermal pollution. For warm or hot air generation, an air reheater device is used after the heat pump. By using the switching operation, the air reheater is used accordingly as per climatic conditions. So in this integrated cycle, a coconut coir-packed humidifier is used for the humidification process, and a water-cooled heat exchanger and heat pump evaporator are used for the dehumidification process to meet the desired outputs from the system. The MATLAB simulation tool is used to simulate the thermodynamic model of the integrated cycle, and it is focused on studying the effect of mass flow rate, atmospheric temperature, relative humidity, evaporator temperature, and hot/cold water temperature, on outputs, as well as the energy conversion factor of the plant and cycle. At 25°C ambient air temperature, the energy conversion factor of the plant and cycle are 0.866 and 2.2, respectively. Similarly, at 75% humid air and 35°C surrounding air temperature, the gained output ratio and coefficient of performance are 4.03 and 1.964, respectively. And also, the plant and cycle energy conversion factors are 0.903 and 2.4.