Dehumidification Performance Research Articles

Thermal-hydraulic performance investigation of an aluminium plate heat exchanger and a 3D-printed polymer plate heat exchanger

• A novel polymer plate heat exchanger is fabricated using a 3D-printing method. • Domestic scale polymer and aluminium heat exchangers fabricated and tested. • Both heat exchangers display very similar dry surface performance. • Polymer heat exchanger demonstrates good dehumidification performance. • Dehumidification capacity is 25% less in polymer heat exchanger compared to metal. Polymer heat exchangers have gained interest due to their favourable qualities over metal heat exchangers, including being lightweight, low cost, and having reduced fouling and corrosion. In this work, two identical prototype, counter-flow, air-to-air, plate heat exchangers were fabricated, one from aluminium and the other from thermoplastic using a fused filament fabrication 3D printer. The results have shown that under dry operating conditions, typical of certain domestic appliances, both heat exchangers demonstrate similar thermal characteristics where the thermal effectiveness is greater than or equal to 0.50. Under wet conditions, the aluminium heat exchanger out performs the polymer heat exchanger, and this effect increases with an increasing temperature difference between the heat exchanger’s hot-side inlet and cold-side inlet. In terms of both thermal and dehumidification capacity, the aluminium heat exchanger can outperform the polymer heat exchanger by as much as 22% and 38%, respectively. Despite the lower performance of the polymer heat exchanger, the absolute capacity and dehumidification rate are still reasonable and show promise for the use of polymer heat exchangers as a good alternative to metal heat exchangers in heat recovery applications in domestic appliances, for example, in clothes dryers or dehumidifiers, where operation takes place under both dry and wet operating conditions.

A flat-plate spiral-channeled membrane heat exchanger for methane dehumidification: Comparison of kraft paper and thin-film composite membrane

Membrane heat exchangers were used for moisture and heat recovery from a hot and humid natural gas stream in indirect contact with an air stream. A plate membrane module with spiral channels on each side was designed to configure gas and air streams in co-current and counter-current flow. Two types of membranes, a commercial kraft paper, and a laboratory-made thin-film composite membrane, were used as the module core. The thermal efficiency and the water recovery from the humid gas were calculated and compared under different operating conditions. At a unit flow ratio of air/gas, the greatest effectiveness was achieved at a methane flow of 100 cm3/min, but water recovery increased at higher gas flows. For the counterflow configuration, an air/methane flow ratio of 2 was sufficient to achieve the highest total effectiveness and water recovery; however, larger air/gas ratios were beneficial to improve heat and moisture transfer for the co-current configuration. The highest water recovery by the kraft paper and composite membrane was achieved (approximately 15 mgH2O/cm2.h) for the input gas with the highest humidity. The dehumidification performance of kraft paper as a porous and hydrophilic membrane was slightly better than that of the composite membrane containing a dense hydrophilic polymer thin film in most cases. A relatively low heat transfer coefficient was found for the module, which was increased by using higher gas flow rates at higher humidity conditions.

Assessment of process parameters in a dehumidification process using biomass-based wood shaving as a packing material

In the current study, the performance of the counterflow dehumidification test rig using wood shaving packing has been analysed. Wood shaving packing with the density 500 kg/m3 was used along with the CaCl2 desiccant with varying concentration. Mass flow rate of air was varied and the dehumidification performance parameters like moisture removal rate, dehumidification efficiency, coefficient of performance, change in relative humidity, change in the pressure and mass transfer coefficient were evaluated. Output parameters were compared with the commercially available cellulose packing with the wettability of 632 m2/m3. Results showed that, even though the performance of wood shaving packing is slightly less than the Celdek packing, performance of wood shaving is promising at 40% desiccant solution concentration. Maximum relative humidity difference, coefficient of performance and dehumidification efficiency obtained with wood shaving pad material were found to be 19%, 1.88 and 69.5%, respectively.

Study on heat transfer and dehumidification performance of desiccant coated microchannel heat exchanger

The desiccant coated heat exchanger is capable of dealing with sensible load and latent load of hot and humid air. The heat and moisture transfer coefficients of the desiccant coated microchannel heat exchanger (DMHE) are derived theoretically and increase with the airflow velocity in the heat exchanger. The microchannel structure optimization is implemented. It is found that the smaller the fin pitch and flat tube pitch are, the greater the heat and moisture transfer coefficients are. The thicker the desiccant coating, the larger the moisture transfer coefficient, the smaller the heat transfer coefficient. The experimental results show that the dehumidification capacity and the thermal performance coefficient of DMHE are 1.59 kgh−1 and 2.09 respectively with the regeneration hot water at 60 °C. The Taguchi method is employed to evaluate the influence of cooling water temperature, airflow velocity, and water flow rate on the dehumidification performance of DMHE. The airflow velocity is the main factor affecting the dehumidification capacity, where lower cooling water temperatures and faster the airflow velocity increases the dehumidification performance.

Experimental study on a cross-flow energy recovered indirect evaporative cooling (ERIEC)-assisted liquid desiccant dehumidifier (LDD) with improved spraying nozzle and surface wetness

The film wetted area is a significant factor affecting the heat and mass transfer of liquid desiccant. In this article, a mathematical model with wetness coefficient of cross-flow energy recovered indirect evaporative cooling (ERIEC)-assisted liquid desiccant dehumidifier (LDD) based on a finite-element method was developed to predict the effect of wetness coefficient on the plate heat exchanger (PHE) effectiveness and dehumidification efficiency, taking into account the thermal resistance and incomplete wetting of liquid film. In addition, an experimental system of a cross-flow ERIEC-assisted LDD was established to validate the model; the validation of the model demonstrated good agreement with the experimental data to within 10%. With this model, increasing the wetness coefficient from 0.1 to 1, the PHE effectiveness gradually increased from 3.7% to 39.1% and the dehumidification efficiency increased gradually from 3.5% to 35.2%. This meant that the nonwetting or partial wetting of liquid film hindered the dehumidification performance. Therefore, a novel TiO2 super-hydrophilic coating was applied to raise the wetness coefficient and improve the dehumidification performance. Within the experimental range, spraying a super-hydrophilic coating (1% nanosized TiO2 solution) in the primary channel of the dehumidifier could increase the PHE effectiveness and dehumidification efficiency by 2.5–5% and 5–30%, respectively.

Influence of Surface Modification on the Transient Dehumidification Performance of Fin-and-tube Heat Exchanger

In this study, surface modifications subject to hydrophilic and hydrophobic conditions are made for copper fin-and-tube heat exchanger to examine the dehumidification performance. Polydimethylsiloxane was used to coat on the surface of heat exchangers to increase the hydrophobicity with a contact angle of 105° while the uncoated copper surface is 76°. The effects of fin spacing and relative humidity on the transient dehumidifying performance are examined in details. The experimental results indicate that surface modification imposes negligible influence on the heat transfer performance. Hydrophobic surface promotes dropwise condensation and may form water bridging which may impede the droplets from falling, thereby showing some 3.4 times higher pressure drop than the hydrophilic one. Upon condensation on the hydrophilic surface, the size of the droplets plays pivotal influence on the transient pressure drop of the heat exchangers. The flow visualization indicates that liquid films prevails on the fin surfaces due to high surface wettability. However, the behavior of transient pressure drop depends on the relative humidity (RH) considerably. For RH = 50%, the required time to reach steady state is much longer than that of RH = 80%. Interestingly, an overshoot of pressure drop vs. time before reaching the steady state is clearly seen for RH = 65%. This phenomenon is associated with the dynamic condensate removal from the fin surface. The droplet distribution density is comparatively uniform at a low frontal velocity (i.e. 0.5 m s−1). Upon raising frontal velocity, the droplet distribution density becomes less uniform with fewer droplets adhering on the fin surfaces. Hence, the wet and dry pressure drop ratio exhibits a decreasing trend at a higher frontal velocity.

Preparation and Application of UiO-66 in Desiccant-Coated Heat Exchanger-Based Desiccant Cooling Systems

Dehumidification performance of a high-efficient compact desiccant cooling component named desiccant-coated heat exchanger (DCHE) highly depends on coated desiccant materials. Currently, mesoporous...

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.

Size effects of carboxylated magnetite nanoparticles on the membrane dehumidification performance

This study aims to understand the effects of different nanoparticle sizes on the dehumidification performance of thin-film nanocomposite membranes (TFN). Carboxylated magnetite (C-Fe3O4) nanoparticles of different sizes (5–30 nm) were embedded in a polyamide layer (PA) over the polysulfone (PSf) substrate. The structural and morphological characteristics of the nanoparticles and coated membranes were explored using various analytical techniques such as FT-IR, SEM, DLS, the zeta-potential, EDS, AFM, and the water contact angle. Mixed-gas permeation tests showed that there were performance peak points at specific nanoparticle concentrations. These performance peaks shifted toward a high concentration of nanoparticles with a decrease in the magnetite size. The M5(0.3) membrane with 0.3 w/w% of 5 nm magnetite particles showed the highest water vapor permeance of 1886 GPU and the highest water vapor/nitrogen gas selectivity of 688 at 30 °C and 70% relative humidity (RH). These results are in good agreement with data pertaining to the hydrophilicity of the TFN membrane. The amounts of C-Fe3O4 nanoparticles deposited on the surfaces of the M5(0.3), M15(0.3) and M25(0.3) membranes were found to be 6.95, 6.27 and 5.44 µg/cm2, respectively. The impact of the pressure, RH% and temperature on the water vapor permeation were also studied and discussed.

Quantitative evaluation of carbon materials for humidity buffering in a novel dehumidification shutter system powered by solar energy

Recently, solid dehumidification systems have been widely used in various industries and are effective in buffering the humidity in the environment. The dehumidification materials and structure of the system have a significant influence on the over system performance. This study aims to quantitatively evaluate dehumidification materials produced from activated carbon fibre cloth (ACFC) and coconut-shell activated carbon (CAC) for suitability in a dehumidification shutter system. First, the physical and chemical properties of ACFC and CAC were characterised via N2 adsorption–desorption isotherms, thermogravimetric analysis, and Fourier transform infrared spectroscopy. Second, the adsorption of water vapour was experimentally investigated, including adsorption kinetics, adsorption isotherms, and thermodynamics, and fitted by various models. The results show that the specific surface areas of ACFC and CAC were 1425 m2/g and 986 m2/g, respectively, while the total pore volume were 0.748 cm3/g and 0.554 cm3/g, respectively. At a relative humidity of 98% and an adsorption temperature of 298 K, the maximum water vapour adsorption capacities of ACFC and CAC were 395.6 mg/g and 277.6 mg/g, respectively. More importantly, ACFC retained a high adsorption capacity after five adsorption/regeneration cycles, indicating that it is an effective and renewable adsorbent for dehumidification. Third, a novel dehumidification shutter system was designed and constructed. The dehumidification performance and thermal comfort indices of the system were then analysed. In conclusion, the dehumidification shutter system fabricated using ACFC is a feasible and effective way to buffer the indoor humidity when solar energy is chosen as the renewable regeneration heat source.

Investigation of dehumidification performance and flow characteristics of wavy vacuum membrane-based dehumidification modules

This work investigates the dehumidification performance of vacuum membrane-based dehumidification with difference wavy membranes. Firstly, this paper constructs four different models of wavy membrane support layers, and proposes their explicit functions. In addition, the accuracy of different turbulence models under wavy boundary condition are compared. Using the verified turbulence model, this paper studies the dehumidification performance of four wavy membrane-based dehumidification modules. Finally, according to the details of flow field, the mechanism behind these dehumidification phenomena are discussed. Results indicate that low-Reynolds number k–ε turbulence model has a higher accuracy than other models in wavy boundary. Wavy membrane does not always increase the dehumidification efficiency, even if it can always increase dehumidification area. When waviness is in the range of 0∼0.06, the dehumidification effect of four wavy membranes are weaker than that of flat membrane, and the flow resistance of four wavy membranes are higher than that of flat membrane. Vertical velocity induced by wavy membrane is the key factor to enhancing dehumidification performance, and a steeper wavy membrane shape at the tail of backflow is beneficial to dehumidification. This work demonstrates the basic dehumidification mechanism of wavy membrane and can provide suggestions for diversified development of vacuum membrane-based dehumidification module.

Experimental Study on the Regeneration Process of the Dehumidification System of Lithium Bromide Solution Based on Computer

Dehumidification is a common problem in production and life. solution dehumidification method is to use salt solution with strong hygroscopicity as dehumidifier, the salt solution is in direct communicate with the treated air because of the pressure variance between the water vapor force on the side of the salt solution and the water vapor force of the treated air, the moisture is driven to transfer between the air and the hygroscopic solution, thus the change of air humidity is realized. In short, the high concentration of lithium bromide and other aqueous solutions absorb the water vapor in the atmosphere by the force difference between the water vapor and the treated air, thus completing the dehumidification process of the air. After the solution absorbs water in the air, it needs to be concentrated and regenerated to restore moisture absorption capacity. Many scholars at home and abroad have studied the solution dehumidification system. Florida Solar Energy Center Swami proposed a system for regeneration of solutions using roofs as solar absorbing surfaces in 1998. Nelson dehumidification performance of Li Cl solution as dehumidifier was studied. Due to the fact that the surface vapor pressure, specific heat capacity, corrosion and other physical and chemical properties of lithium bromide are better than those of lithium chloride and calcium chloride under the same PH and equal concentration, I have studied the regeneration process of dehumidification system of lithium bromide solution based on computer.

Research on falling film dehumidification performance of microencapsulated phase change materials slurry

In the process of liquid desiccant dehumidification, the temperature-rise of the desiccant solution caused by moisture absorption will seriously affect the dehumidification capacity and performance. It is expected that the temperature rise of solution can be restrained by adding microencapsulated phase change materials (MicroPCMs) into the liquid desiccant solution. In this paper, based on computational fluid dynamics (CFD) method, two-dimensional models of flat plate and corrugated plate falling film dehumidification of the microencapsulated phase change material slurry (MPCMS) were developed and validated. The dynamic boundary method was used to determine the interfacial mass transfer coefficient. The influences of several factors on the dehumidification performance, including the concentration of MicroPCMs, the inlet temperature of the MPCMS and the falling film plate configuration, were investigated. The results show that, adding MicroPCMs into the liquid desiccant solution is beneficial to the dehumidification performance improvement. The inlet temperature of MPCMS is a very critical variable. When the inlet temperature of the slurry is in the phase transformation temperature range of MicroPCMs, with the adding of the microcapsule, the temperature rise in dehumidification process can be restrained, and the moisture removal performance can be improved significantly. When the MPCMS inlet temperature is at the phase transformation onset point, and the concentration of MicroPCMs is 5%, the water condensation rate is 14.2% higher than that of the base solution. Moreover, it’s not that the more microcapsules added, the larger mass transfer coefficient is. There is an optimum concentration of MicroPCMs to achieve the maximum interfacial mass transfer coefficient. The corrugated plate configuration is more conducive to the dehumidification enhancement by the MPCMS.

Mass transfer enhancement of falling film liquid desiccant dehumidification by micro-baffle plates

Mass transfer enhancement of falling film liquid desiccant dehumidifier (LDD) is of significance for efficiency improvement of liquid desiccant air-conditioning (LDAC). This study investigated liquid film patterns and dehumidification processes of falling film LDD for smooth and baffle plates. Five baffle plates with different baffle height and spacing were adopted in the study. The CFD simulation with VOF model was adopted for the moist air and liquid desiccant two-phase flow. Moreover, the heat and mass transfer model based on the penetration theory was developed by UDF program to predict the dehumidification process. After numerical validation with previously experimental measurement, the liquid film patterns, water vapor concentration fields, outlet water vapor mass fraction, gas-liquid flow fields and liquid film waves were obtained and analyzed. The results showed that the moisture removal enhancement ratio reaches 7.3%, 18.3%, 25.1%, 19.4% or 16.8% for the baffle plate A, B, C, D or E respectively, compared with the smooth plate case. Therefore, the dehumidification performance of the LDD can be significantly improved by the baffle plate. The liquid film waves, the flow eddies and high-value TKE distribution near the gas-liquid interface induced by the baffle plates are the main mechanisms to enhance the dehumidification performance of the falling film LDD. Moreover, the above enhancement mechanisms will be more significant for higher baffle height and smaller baffle spacing under the present conditions. The simulation results may be useful for the dehumidification performance enhancement in the realistic falling film LDD applications.

Development of structurally modified OER catalysts with enhanced performance and longevity for PEM-based electrolytic air dehumidification

PEM-based electrolytic air dehumidification is innovative in dehumidification that requires high precision and small space due to its high efficiency, compactness, and cleanness. However, the system dehumidification performance and durability are limited by using commercial Anatase-IrO2 catalysts. In this study, two types of structurally modified OER catalyst materials, ATO-IrO2 and ND-MnO2-IrO2, are developed to improve the performance of the system. System experiments showed that, compared to the commercial catalysts, the use of ATO-IrO2 and ND-MnO2-IrO2 as the anode catalyst can improve the dehumidification performance by 45% and 20%, respectively. Furthermore, in 50-h accelerated aging tests, the attenuation rates of the ATO-IrO2 and ND-MnO2-IrO2 systems are 3% and 8% respectively, which are far lower than the 35% attenuation of commercial catalyst. The results indicate that, as catalysts with a classic core-shell structure, ATO-IrO2 and ND-MnO2-IrO2 still have a significant impact on improving the performance of the electrolytic dehumidification systems.

Front-end Solar Temperature And Humidity Control System

Solid dehumidification is one of the important components of the dehumidification air-conditioning system. As an important method of solid dehumidification, the dehumidification performance and regeneration performance of fixed-bed dehumidification have an important impact on the operation and energy saving of the dehumidification air-conditioning system. In view of the high air temperature and high humidity in South China, our design organically combines dehumidification fixed beds, semiconductor refrigeration devices, foam ceramic insulation panels and double-glazed windows. We have designed a photovoltaic-driven modular solar temperature regulating and dehumidifying purification wall suitable for building dehumidification. The dehumidification window can use daytime solar radiation to regenerate the dehumidification fixed bed after absorbing moisture, reducing the energy consumption of regeneration. At the same time, the design can also use semiconductor refrigeration devices to adjust the temperature and humidity of the window inlet air to improve the window's dehumidification and regeneration performance. We tested and studied the dehumidification and regeneration performance of the device under different working conditions through experimental tests, which provided a basis for the engineering application and theoretical analysis of the device.

Dehumidification performance of liquid desiccant system with aqueous-CaCl2 solution in a humid climatic condition

The liquid desiccant solution can able to dehumidify the air by absorbing the water vapour content present in the air. The current work aims to test the dehumidification performance of liquid desiccant system with aqueous CaCl2 and ABS (Acrylonitrile butadiene styrene) packing in a humid climatic condition of India i.e., Kozhikode. The experimental setup is made with packed type dehumidifier. The dehumidification performance such as specific moisture removal, moisture removal rate and dehumidification effectiveness are studied with the effect of variation of solution flow rate, air flow rate, outdoor humidity ratio and solution temperature. The increase in solution flow rate and outdoor humidity ratio positively affect the dehumidification performance whereas the increase in solution temperature negatively affects the dehumidification performance. The increase in air flow rate increases the moisture removal rate but decreases the specific moisture removal and the effectiveness. The dehumidification performance shows a promising results, particularly performs better in higher outdoor humidity conditions. The dehumidification performance can be further improved by adding the cooling system.

Effect of changes in the regeneration temperature and the regeneration airflow velocity on the system performance of the solid desiccant air conditioning

This paper presents the effect of changes in operating parameters on the solid desiccant air conditioning system performance. It has consisted of the regeneration temperature and the regeneration airflow velocity parameters. These parameters were examined in two operation modes, the former ranging from 2 m/s–0.83 m/s at constant regeneration temperature, and the latter ranging from 75°C–46.4°C at constant regeneration airflow velocity. The results indicate a smaller decline in dehumidification performance for the constant regeneration temperature operating mode than the constant airflow velocity operating mode. On the contrary, the system performance and the recovery energy ratio at the latter operating mode gives a higher value than the former operating mode. These results suggest that when the dehumidification performance becomes the main function in the system, the regeneration airflow velocity should not be too low to avoid a significant reduction in system performance.

Computational analysis of spray type counter flow liquid desiccant dehumidifier

The liquid desiccant air conditioning system (LDAC) is considered as the substitute for the conventional air conditioning system mainly because of its energy-saving characteristics. The dehumidifier is one of the most important components in LDAC, therefore, it is chosen as the system for analysis. A 3D computational model of the spray type dehumidifier with counter flow configuration was created and analysed its mass transfer characteristics for two different cases. 2D CFD models studied by various researchers failed to elaborate on the actual flow process. In order to fill this gap 3D model was created and the analysis was conducted to investigate the influence of flow rate of air and desiccant on the mass transfer performance of the dehumidifier. Air and desiccant flow rate have direct influence on the mass transfer performance of the dehumidifier. In this study, the dehumidification performance is evaluated through the simulation by increasing the desiccant flow rate and simultaneously reducing the airflow rate and the results are observed. ANSYS-FLUENT® software is used for the current analysis. The increase in desiccant flow rate and decrease in air flow rate tends to improve the change in humidity ratio (specific moisture removal) from 4.2 to 6.3 g/kg of dry air. The temperature variation of solution keeps increasing as the moisture transfer increases. The rise in temperature of the solution is higher than the air during moisture transfer due to exothermic process. Similarly the equilibrium humidity ratio of solution increased due to moisture absorption during dehumidification, which indicates the decrease in solution concentration during dehumidification. The heating of solution and air during dehumidification will affect the moisture transfer rate, which can be avoided by adding a cooling unit to the liquid desiccant system.

Research on performance of mine dehumidification and cooling system based on heat pump

A heat pump-based mine solution dehumidification and cooling system is used in deep mines, which can not only reduce the temperature and humidity of the working face, but also recycle the low-grade heat energy and improve the utilization rate of energy.Under the condition of long distance air supply, within the range of 10m from the heading face, the equivalent temperature of the air can fall to 24.7 °C, the cooling range is 5.6 °C, and the relative humidity decreases by 23.79%. Compared with the original cooling system, the COP value of the system can reach 3.43 under the same working conditions, 19% higher than the original cooling equipment.