Air Dehumidification Research Articles

Physical characteristics analysis and performance comparison of membranes for vacuum membrane dehumidifiers

The present study pertains to an experimental measurement investigation of membrane physical properties for vacuum membrane dehumidifiers. The membrane material used in an air dehumidification system is a key role for the dehumidification efficiency. To find the most suitable membrane for dehumidification, the membrane physical characteristics are examined by using three critical indexes of air permeance (AP) and water vapor permeance (WP), and selectivity (SE). Two categories of dehumidification membranes, i.e. composite and dense membranes, are applied in the vacuum membrane dehumidifier with a serpentine flow channel. Firstly, the vapor transfer rates of both composite and dense membranes are determined and the experimental data discloses that the composite membranes, such as Sulfone and Metal–organic framework (Mof) membranes, provide higher vapor transport ability, which is not suitable for the vacuum membrane-based dehumidifier. Then, the measurement of AP, WP, and SE is further performed for the dense membranes of Nafion. The result shows that the order of either AP or WP is N.211, N.212, N.115, and N.117, but the SE defined as WP/AP has a different tendency and the order is N.117, N.115, N.212, and N.211. Finally, the results of AP, WP, and SE in this dehumidifier are also compared with the previous experiment.

Energy performance analysis of a membrane dehumidification system

In warm and humid climates, a primary source of building energy consumption is dehumidification of conditioned air supplied to the building spaces. The system analyzed utilizes a selective membrane to remove water vapor from ambient air instead of a vapor compression cycle or a desiccant. This work analyzed a membrane dehumidification system with a focus on the system energy performance. A system performance goal was set by the project sponsor for an inlet air condition of 32.2 °C and 90% relative humidity, an outlet condition of 12.8 °C and 50% relative humidity and a total cooling load of 3.52 kW resulting in a target COP latent for the system of 3.34. Models of the basic system components were used to develop the system, analyze operating parameters and predict performance. The results indicate that the system requires two optimizations to meet the target performance: condenser pressure optimization and the use of multiple membrane segments operating at different pressures. Subsequently, a model was developed to analyze the performance of the final system configuration under a variety of operating conditions and yielded a maximum COP latent of 4.37 for membrane properties comparable to those of the earliest membrane module tested. This may be compared with a COP of about 3.5 for current refrigeration technology at these conditions. The best small membrane sample produced to date would increase the COP latent of the membrane system to well above 8, suggesting that the membrane system has high promise. Uncertainty analysis was also performed to assess the simulation results.

Study on the influencing factors of Heat and Humidity and Vocal Coupling Adsorption Characteristics of Runner

In order to realize the purpose of indoor air purification and dehumidification at the same time, the mathematical model of heat and humidity and VOC coupling adsorption was established. The coupled adsorption characteristics of heat and humidity and VOC and the influence law of each factor were simulated by using VB program. The results show that the higher the inlet humidity is, the better the water desorption is, but not the adsorption and desorption of toluene. And the higher the inlet temperature of the treated air is, the more unfavorable the adsorption and regeneration of moisture and VOC is. Different toluene concentration in the inlet of air affected mainly its own adsorption and desorption, but had little effect on the adsorption and desorption of water. The increase of humidity in the inlet of regenerated air is not conducive to the desorption of water, but can promote the adsorption and desorption of toluene. The increase of inlet temperature of regenerated air can promote the adsorption and desorption of water and VOC. The coupling of heat and moisture and VOC on the runner can be adsorbed and purified at the same time.

THEORETICAL ANALYSIS OF MEMBRANE AIR DEHUMIDIFICATION IN AIR CONDITIONING SYSTEMS

The paper presents a simulation of the process of removing moisture from the air in air conditioning systems using construction vapor-permeable membranes. The existing classical physical and mathematical models are considered and analyzed. Based on the analysis of classical models, a schematic and corresponding theoretical mathematical model of air dehumidification with a semipermeable building membrane with certain characteristics for possibilities of use in air conditioning systems is developed and presented. The data of calculations of moisture release from air for the developed model are given. As a result of analytical researches the correct data for possible use in air conditioning systems are received. Key words: air conditioning systems, air dehumidification, semipermeable membrane, permeability, membrane air dehumidification, convective flow, diffusion flow, moisture permeability.

Numerical analysis on heat and mass transfer of the planar membrane dehumidifier

The ambient air with the excessive moisture needs to be dehumidified for a comfortable environment using air conditioning. The planar membrane-based dehumidifier (PMD) is a potential technology to remove moisture in humid air. The performance of PMDs with different operating conditions is evaluated via numerical simulations with focuses on influences of the flow channel geometry, i.e. aspect ratio (AR) of width over height, on the dehumidification performance firstly. The result discloses channels with AR = 2 have the best coefficient of performance (COP). Thus, three-dimensional dehumidifiers are simulated to further understand the physical mechanism of air dehumidification. Finally, an in-depth parametric analysis is carried out with emphasis on the influence of governing parameters on PMD performances, such as dehumidification rate (DR), dew point approach temperature (DPAT), pressure drop (ΔP), and COP. The results show that enhancing mass flow rates leads to an ascending tendency of DR, DPAT, and ΔP, but a descending tendency of COP. Increasing the inlet temperature of dry side results in the reduction of both DR and DPAT, but the increase in ΔP, resulting in the deterioration of the COP. Additionally, the counterflow PMD always has better dehumidification performance than parallel one for various governing parameters.

Performance Investigation of a Hollow Fiber Membrane-Based Desiccant Liquid Air Dehumidification System

The membrane-based desiccant liquid air dehumidification system is a promising technology for efficient humidity control in buildings. The use of a membrane module allows, among other things, for a compact design with a relatively large heat and mass transfer area and eliminates carryover of solution droplets. In this paper, a cross-flow, hollow-fiber membrane module was proposed for air dehumidification and regeneration of lithium chloride. A two-dimensional heat and mass transfer model for cross-flow in a membrane module used for air dehumidification and liquid desiccant regeneration was developed. The effectiveness, moisture removal rate and moisture removal rate were studied numerically and validated against experimental results. Based on the numerical simulations, the most favorable ranges of operating conditions were determined. It was found that the operating conditions significantly impact the dehumidification performance. The proposed dehumidifier maintains its performance in a wide range of inlet air humidity ratios. For dehumidification, the recommended temperature of the incoming solution was in the range of 14–18 °C, while for regeneration the solution range was 40–50 °C. The packing fraction was suggested in the range of 0.30–0.40. These results can help design membrane-based liquid dehumidification systems.

Modelling and simulation of water vapor adsorption in silica gel bidisperse beds

Desiccant cooling systems are widely recognized as an alternative technology to vapor compression cooling. Desiccant systems are attractive for air conditioning applications due to the possible use of low-grade heat and green refrigerants in their operation. In such systems, air dehumidification is achieved using bed compacted with desiccant materials such as silica gel, activated alumina, and zeolite. Desiccant systems, on the other hand, present a low coefficient of performance due to the poor heat and mass transfer in the adsorbent bed. A way to enhance the heat and mass transfer in desiccant systems can be accomplished by optimizing the adsorbent packing in the bed. This paper presents a numerical investigation of the dynamics of water vapor adsorption in silica gel bidisperse bed. The adsorbent bed is compacted with particles of two different sizes to reduce the voids between the adsorbent particles and hence increase the amount of desiccant and the adsorbed water mass in the bed. The effect of bidisperse packing in the air dehumidification capacity and adsorbed water mass is studied. The influence of the pressure drop applied on the adsorbent column and the inlet air conditions in the dehumidification process is also investigated. The numerical results showed that bidisperse packing increases the dehumidification capacity (improvement of 22.9%) and the amount of water adsorbed (improvement of 25%) in the bed compared to the case where monodisperse packing is applied to the system, contributing to the improvement in the performance of desiccant beds in air conditioning applications.

Разработка и исследование осушителя и подогревателя воздуха на базе элементов Пельтье

A functional flow diagram of an energy-saving dehumidifier and an air heater based on Peltier elements has been developed. A method for calculating the heat-power and design parameters of a thermoelectric assembly is presented. Physical modeling of the process of dehumidification and heating of air in a thermoelectric installation has been carried out. The results of tests of a working model of the thermoelectric dehumidifier and air heater are presented. Rational operating modes of the installation have been substantiated, and its energy efficiency in the heat pump mode has been shown.

Determination of Dehumidification Capacity of Water Wall with Controlled Water Temperature: Experimental Verification under Laboratory Conditions

Water elements with flowing water on the surface are common in buildings as a form of indoor decoration, and they are most often perceived as passive humidifiers. However, by controlling water temperature, they can be also used for air dehumidification. The dehumidification capacity of indoor water elements was investigated experimentally under laboratory conditions. For the experimental verification of dehumidification capacity, a water wall prototype with an effective area of falling water film of 1 m2 and a measuring system were designed and developed. A total of 15 measurements were carried out with air temperatures ranging from 22.1 °C to 32.5 °C and relative humidity from 58.9% to 85.6%. The observed dehumidification capacity varied in the range of 21.99–315.36 g/h for the tested measurements. The results show that the condensation rate is a dynamic process, and the dehumidification capacity of a water wall strongly depends on indoor air parameters (air humidity and temperature). To determine the dehumidification capacity of a water wall for any boundary conditions, the equations were determined based on measured data, and two methods were used: the linear dependence between humidity ratio and condensation rate, and nonlinear surface fitting based on the dependence between the condensation rate, air temperature, and relative humidity.

Next generation air conditioner for sustainable cooling solutions

Generally in summer, air conditioning systems are essential for improving the human comfort and productivity. The mechanical vapor compression system (VCS) is probably the most used system. However, the refrigerant used in VCS is harmful to the environment and the initial cost is high. So, the aim of this study is to introduce a sustainable, energy-efficient and climate-friendly air conditioning system in which there is no refrigerant. The proposed system is the integration of two modules i.e., Direct evaporative cooling (DEC) module and vacuum-assisted isothermal membrane-based air dehumidification (VIMAD) module, where the DEC module will cool and humidify the entering air stream and then this cool and humidified air will enter into the VIMAD module and the air will get dehumidified. Finally, the output will be cool and dehumidified air at the exit of the system. In this paper, the proposed system is explained. Moreover, the basic principle of the DEC, the background of DEC and the basic principle of the VIMAD system, background on the types of membrane materials that can be used in VIMAD are explained. Also, the effects of various parameters on the performance of the DEC and VIMAD are presented.

Effects of ambient air dehumidification, air temperature, and drying duration on rough rice quality and pasting properties using fluidized bed and fixed bed dryers

AbstractBackground and objectivesHigh humidity ambient air is a common phenomenon in the United States ​Mid‐​South region, resulting in a delay in the drying process to avoid rewetting rough rice. Ambient air dehumidification could have the potential to overcome this challenge and result in a continuous drying process. Therefore, the present study explored the effects of ambient air dehumidification, air temperature, and drying duration on rough rice quality and pasting properties in a fluidized bed and fixed bed drying systems.FindingsA fluidized bed and a fixed bed drying systems were used to study the effects of dehumidification settings (with and without), air temperature (40°C, 45°C, and 50°C), and drying duration (30 min, 45 min, and 60 min) on rice quality and pasting properties in triplicates. Silica gel was used as a desiccant for ambient air dehumidification. The results showed that the range of moisture removal to be 4.5 to 7.1 (%, dry basis) for 1 hr in a fluidized bed rice drying. The maximum water absorbed by air achieved 0.382 and 0.434 kg for fluidized bed and fixed bed dryers, respectively, after 60 min of drying, at 50°C, and with air dehumidification. The peak viscosity of rough rice was lower for all fluidized bed experiments (2,712.8 cP) than the fixed bed drying experiments (2,815.8 cP).ConclusionsThe results showed that head rice yield and rice whiteness did not reduce in fluidized bed drying significantly than the fixed bed drying. Head rice yield was negatively correlated with rice whiteness. Ambient air dehumidification improved moisture removal from rough rice and can be employed during humid conditions. Pasting properties also supported the notion of attaining good quality rice dried in a fluidized bed system compared with a fixed bed drying system. Head rice yield was positively correlated with the peak and trough viscosities signifying the increase in milling yield with the rice water‐absorbing capacity and resistance to cooking textural breakdown.Significance and noveltyThe study proved that utilizing dehumidified air in a fluidized bed drying system could dehydrate rough rice without reducing quality. The system successfully utilized silica gel to dehumidify ambient air, allowing continuous ambient air in‐bin on‐farm drying of rough rice.

Exergy analysis on optimal desiccant solution flow rate in heat exchanger for air dehumidification using liquid desiccant

The heat exchanger for air dehumidification using liquid desiccant is mainly composed of an air-solution heat exchanger (dehumidifier) and a solution-refrigerant heat exchanger, wherein there are three liquids, i.e., air, desiccant solution, and refrigerant. The same air dehumidification process can be achieved by different solution flow rates ( m s ). Limited studies have revealed which solution flow rate is optimal ( m s,opt ) for minimizing the exergy input of the heat exchanger ( Ex cooler ). Thus, the analytical solution for the effectiveness of the entire heat exchanger ( ε ) is theoretically deduced in this study, by the virtue of which, the m s,opt can be determined by solving ∂ ε / ∂ m s = 0. Results reveal that ε can be improved from 0.50 to 0.56 and Ex cooler can be saved by 17.9% in the given case, when the flow rate ratio of solution to air increases from 0.7 to the optimal value 1.5. Moreover, the air-solution-refrigerant flow rate matching plays an important role in the heat exchanger effectiveness . As a media fluid between the variable-temperature fluid (air) and the constant-temperature fluid (refrigerant), there is no solution flow rate to make the air-solution flow rate matching and solution-refrigerant flow rate matching simultaneously achieved. A compromised m s,opt should be pursued to balance the air-solution mismatching and the solution-refrigerant mismatching. It is anticipated that the findings of this research can be used for achieving an efficient air dehumidification process in the heat exchanger using liquid desiccant.

Parametric study on pressure-based packed bed adsorption system for air dehumidification

Compressed air free from traces of water vapour is vital in many applications in an industrial sector. This study focuses on parametric optimization of a pressure-based packed bed adsorption system for air dehumidification through the Taguchi method and Genetic Algorithm. The effect of operational parameters, namely absolute feed air pressure, feed air linear velocity, and purge air flow rate percent on adsorption uptake rate of molecular sieve 13X-water pair, are studied based on L25 orthogonal array. From the analysis of variance, it has been found that absolute feed air pressure and purge air flow rate percent were the parameters making significant improvement in the adsorption uptake rate. A correlation representing the process was developed using regression analysis. The optimum adsorption conditions were obtained through the Taguchi method and genetic algorithm and verified through the confirmation experiments. This system can be recommended for the industrial and domestic applications that require product air with the dew point temperature below 0°C.

Energy and Exergy Analysis of an Absorption and Mechanical System for a Dehumidification Unit in a Gelatin Factory

In this paper, an energy and exergy analysis is applied to the air dehumidification unit of a liquid desiccant system in an industrial gelatin conveyor dryer. The working fluid is a binary solution of lithium chloride (LiCl) in water. Dry air is used in order to decrease the amount of liquid in the gelatin. Therefore, the environmental air must have its absolute humidity reduced from about 12 g/kg to the project target, which is 5 g/kg. The process is a cycle using an absorption desiccant unit (LiCl in water), where the weak solution absorbs water vapor from the air. In the regenerator, condensation of the solution (desorption) from the moist air occurs. As a result, the steam consumption of the desorber and electrical power used for the vapor compression chiller (with ammonia, NH, as working fluid) are the primary sources of cost for the factory. To improve the plant’s energy and exergy behaviors, the process is evaluated using a mathematical model of the system processes. In addition, we evaluate the substitution of the vapor compression chiller by an absorption unit (lithium bromide (LiBr) in water). The performance indicators of the compression vapor systems showed the best results. Even when using the condenser’s energy to pre-heat the solution, the installed system proved to be more effective.

Air dehumidification using various TEG based nano solvents in hollow fiber membrane contactors

In this study, tri-ethylene glycol (TEG) based nanofluids of carbon nanotubes (CNT), silica (SiO2) and aluminum oxide (Al2O3) in different weight percents of 0.01 and 0.05 wt% were employed to improve the properties of TEG for water vapor absorption in a hollow fiber membrane contactor (HFMC). To do so, the impact of various operational parameters including nanofluid type, nanoparticles (NPs) concentration, liquid and gas flow rate on water vapor separation were elucidated. According to obtained results, CNT nanofluid was more capable on water vapor absorption toward SiO2 and Al2O3, so that the injection of CNT nanofluid led to water vapor absorption enhancement up to 10.8 % as compared to TEG solution alone. The results also indicated that the gas flow rate has an inverse relationship with the amount of water vapor absorption efficiency, whereas increasing the liquid flow rate has no tangible effect on absorption efficiency, which is because of the very high solubility of water vapor in TEG. Ultimately, dynamic light scattering (DLS) analysis was carried out to evaluate the stability of nanofluids and size distribution of nanostructures in the base fluid.

Optimization of parameters for air dehumidification systems including multilayer fixed-bed binder-free desiccant dehumidifier

In air dehumidification systems, the optimization of operating conditions is as important as the improvement of the dehumidifier itself under varying loads. Therefore, a comprehensive parameter analysis and optimization study of a novel air dehumidification system, which consists of a multilayer fixed-bed binder-free desiccant dehumidifier and a water cooling and heating device, is proposed herein. First, a mathematical model to predict the transient heat and mass transfer in the air dehumidification system is established and validated by comparing with the experimental results. Second, the cyclic performance of the system is analyzed and the influences of each parameter, including operating, structural, and adsorption and transport parameters, are analyzed. Third, the optimization of operating parameters is conducted based on the combination of a backpropagation (BP) neural network and genetic algorithms (GAs). The operating parameters are optimized by maximizing the energy efficiency and dehumidification performance and a trade-off relation is identified between them. For three typical load conditions, it is successfully demonstrated that the optimum energy efficiency and dehumidification performance can be determined from the Pareto front obtained by an elitist non-dominated sorting GA (NSGA Ⅱ) within the requirement specifications and the optimum operating parameters can also be determined by the combination of a BP neural network and a NSGA Ⅱ.

Microstructure silica leached by NaOH from semi-burned rice husk ash for moisture adsorbent

Purpose: This work aims to study the water vapor adsorption property of fine silica particles from semi-burned rice husk ash. The semi-burned rice husk ash is selected as the raw material since it contains high silica and is easily found as a by-product of pottery furnace combustion. Design/methodology/approach: The silica adsorbent from semi-burned rice husk ash was prepared through a sol-gel method using various NaOH concentrations. In doing so, the different pH precipitation was also observed. Here, the fine silica powder was obtained by pulverizing dry sol-gel. The product characterizations were conducted based on water adsorption capacity at different air relative humidity. Findings: The results show no significant effects of different treatments in the extraction and gelation process. The fine silica particles exhibit large porous surfaces with agglomerated nano-sized particles that formed pores. This porous structure is related to the distributions of pore size of each sample, which mostly obey the mesoporous characteristics. From sorption isotherm, weak adsorbent-adsorbate bonding was observed and demonstrated multilayer adsorption of mesoporous materials. Research limitations/implications: The study of water adsorption was carried out at room temperature, which can change at any time, even though has no significant effect on the humidity. However, it is needed to study the adsorption in an incubated area to receive a constant temperature. Practical implications: The products namely silica prepared from semi-burned rice husk ash show a high moisture uptake, especially at a high relative humidity region. This property can be comparable with the other silica preparation methods. So, this product can be a highly potential adsorbent for air or gas dehumidification systems. Originality/value: The silica-based semi-burned rice husk ash as a water adsorbent is more sustainable than commercial silica. This is a positive contribution to find a potentially develop water vapor adsorbent with good adsorption capacity. Besides, the synthesis process is a simple and low-cost process.

Air dehumidification with advance adsorptive materials for food drying: A critical assessment for future prospective

In food processing, drying is an important unit operation for preserving the product quality by moisture content reduction. However, some drying processes suffer from technical and economical drawbacks mainly related to low process efficiency, high energy cost, and product quality degradation. Drying food products using dehumidified air at low temperature is one of the smart options to solve the abovementioned problems. This review presents some challenges and opportunities for dehumidifying air to enhance the driving force for drying. The potential of some solid materials, namely zeolite, silica-based materials, activated carbons (ACs), and other biomass-based materials, as moisture adsorbents for air dehumidification in food drying applications is also discussed. This paper also comprehensively reviews the recent perspectives and emerging technologies in the development of efficient adsorbent materials for air dehumidification, moisture adsorption–desorption characteristics, and its potential for food drying application. Moreover, some crucial parameters for advancing the research and development of adsorptive dehumidification systems are criticized in this review paper.

Heat and mass transfer modeling of an energy efficient Hybrid Membrane-Based Air Conditioning System for humid climates

In this work, a mathematical model was made for a Hybrid Membrane-Based Air Conditioning System to evaluate the performance of the proposed system. The hybrid system consisted of a cross-flow membrane air dehumidifier unit and a membrane contactor unit as humidifier. The model was further validated using simulation and experimental data from the literature. The effects of the parameters such as dehumidifier stage cut, pressure ratio and humidifier geometry were studied. Then, the performance of the system was evaluated in terms of sensible, latent and total cooling capacity and latent heat ratio. The hybrid system produced fresh air with minimum temperature of 13.5 °C and humidity ratio below 12 g/kg providing a thermal comfort condition for human activities. Also, the results showed that the maximum total cooling capacity was 3.3 kW when the dehumidifier pressure ratio was 20, and LHR of the hybrid system was in the range 0.35–0.63. The results also showed that the membrane air-conditioner had a low energy consumption, saving energy up to 66% in comparison to the conventional air-conditioners. The proposed membrane air-conditioner is capable to operate in a wide range of humidity in the Persian Gulf region, while maintaining the thermal comfort conditions.

Desiccant solutions, membrane technologies, and regeneration techniques in liquid desiccant air conditioning system

Liquid desiccant air dehumidification has gained substantial attention recently due to its attractive energy-saving capability, high moisture retention, and low regeneration temperature. However, there are still unresolved limitations in liquid desiccant air conditioning systems (LDACs). Among on-going studies are the search for greener desiccant solvents, high-performance membrane, and regeneration techniques hybridization. This review discusses up-to-date development of the performance influential components of LDACs, such as desiccant properties, regeneration techniques, membranes, energy sources, and hybrid system configurations. The corrosive nature of conventional halide salt solutions, non-biodegradability and high viscosity property of most ionic liquids necessitate the search for alternative solvents in LDACs. Deep eutectic solvents (DES) properties, such as non-corrosive, hygroscopic, biodegradable, and low viscosity idealize promising alternative desiccant solutions. Therefore, DES may be usefully explored and further investigated in LDACs to establish the degree of their capacities in replacing conventional desiccants. Non-thermal regeneration techniques and nanoparticle enhanced membranes were also found to improve the overall energy performance of the LDAC system. Non-thermal regeneration techniques can operate below 40°C and reduce energy utilization between 10% and 50% in indoor space cooling. The coefficient of performance (COP) of this regeneration category is capable of being as high as 6, which is an indication of its promising energy-saving propensity. Highlights Review on liquid desiccant materials and the potential of deep eutectic solvents as bio-desiccants for air dehumidification. Nanoparticles enhanced ion exchange membrane tendency to eliminate membrane fouling and improve regeneration performance. Non-thermal liquid desiccant regeneration techniques eliminate re-cooling energies requirement in LDACs.