Desiccant Flow Rate Research Articles

Atmospheric water harvesting by osmotic distillation and direct contact membrane distillation using hydrophobic hollow fiber membranes

The use of a liquid desiccant air dehumidifier is an energy-efficient technology that can improve both indoor air temperature and humidity. However, the risk of concentrated liquid desiccant leakage into the air conditioning system during dehumidification can corrode the system, negatively impact indoor air quality, and potentially harm residents. To address this issue, this study investigates the effectiveness of osmotic distillation (OD) and direct contact membrane distillation (DCMD) for dehumidification and regeneration, respectively. The study analyzes the impact of inlet operating parameters, including liquid desiccant concentration, temperature, and flow rate, and air flow rate on the dehumidification performance and stability of the OD process. Calcium chloride was utilized as the liquid desiccant in this study. The results indicated that the dehumidification performance of the OD process improved with a higher desiccant concentration and lower desiccant temperature. However, the desiccant flow rate did not have a significant impact on dehumidification performance. Furthermore, the dehumidification performance decreased with a higher inlet air flow rate, but the moisture removal rate increased. The OD process demonstrated stable operation during the dehumidification process. DCMD was effective for desiccant regeneration, and no scaling occurred due to the deposition of calcium chloride crystals. However, the permeation flux of DCMD decreased as the feed concentration increased due to a decline in the feed vapour pressure and an increase in concentration polarization effect. In conclusion, the experimental results indicated that OD can effectively dehumidify humid air, while DCMD is a viable option for desiccant regeneration.

Investigating the impact of flow rate and moisture content for different concentration of liquid desiccant solution

The desiccant air conditioning system consists of two processes, namely cooling and dehumidification, in which the air temperature and humidity are controlled in order to provide comfortable thermal conditions. A typical system includes a dehumidifier, indirect evaporative cooler, and regenerator. The desiccant is selected depending on its ability to absorb water vapor present in the air. In this study, calcium chloride solution was used as a desiccant for the desiccant solution regeneration process, and a flat plate solar collector was employed. Different variables, such as the primary air flow rate, desiccant flow rate, and the concentration of the desiccant solution, were changed during the experiments. The impact of these variables on the performance parameters of the desiccant system such as moisture removal rate, moisture efficiency, enthalpy efficiency, sensible heat ratio, and the mass transfer coefficient was studied. The obtained results revealed that as the solution concentration and the flow rate of primary air increase, the moisture removal rate, sensible heat ratio, and mass transfer coefficient increase. A particular value of inlet primary air flow rate (0.18Kg/s), an increase in the inlet concentration of calcium chloride solution from 0.85 to 0.95 leads to a rise in moisture removal rate, sensible heat ratio, and mass transfer coefficient of (1.1 _1.65) g/s, (0.18-0.25), and (0.01075-0.0123) m/s respectively. While at a certain inlet concentration of a desiccant solution (0.95), increasing the inlet primary air flow rate from 0.1Kg/s to 0.18Kg/s leads to an increase in the moisture removal rate, sensible heat ratio, and mass transfer coefficient o (0.94-1.26) g/s, (0.24-0.26), and(0.0038 -0.011) m/s respectively.

Dehumidification performance improvement by using liquid desiccant blends – An experimental study

To minimize global warming and consumption of electricity, a desiccant-based air conditioning system has been proposed as a better alternative to control air humidity, compared to the conventional air conditioning system. In the present study, the performance of the hybrid desiccant was compared with the pure LiBr and KCOOH solution. Blends of LiBr and KCOOH at different weight ratios were used as desiccants. The performance of the system was compared based on its moisture removal rate and dehumidification effectiveness. The performance of the system increased with increasing desiccant flow rate, the concentration of the solute and the airflow rate. From the tested concentrations, the blend of 40% LiBr and 10% KCOOH concentration showed the highest MRR and dehumidification effectiveness among all blends of LiBr and KCOOH. From the study, it can be concluded that by using an optimized blend of LiBr and KCOOH as a desiccant in place of neat LiBr, the limitations of pure LiBr can be partly resolved without sacrificing much on the dehumidification performance.

Performance analysis of hybrid solid liquid desiccant material: Dehumidification and CO2 absorption

AbstractAs the population and living standard of human beings rises, energy requirement also increases rapidly. In developing country like India, a major part of energy requirement is fulfilled by thermal power‐based plants. It generates pollutant gases and water vapor responsible for global warming and other environmental problems. To overcome these problems in controlled area, a continuous experimental investigation has been performed based on the hybrid solid–liquid desiccant (HSLD) containing CaCl2 (0.33 M), lithium chloride (0.66 M), titanium dioxide (0.026 M), silicon dioxide (0.316 M), copper oxide (0.067 M) for dehumidification, and CO2 removal from the atmospheric air. In addition, CO2 removal capacity of HSLD has been performed from CO2 + air mixture containing variable CO2 to air as 0.33–5.46 (wt ratio). Present study suggest relative humidity of air is reduced from 75% to ~40% at 21.5°C. Outlet air contain 36.41, 72.83, 127.45, 200.27, 291.31, 418.76 ppm, 655.45, 1238.07, 2075.57 ppm CO2 for inlet condition of 0.33 (400.66), 0.51 (619.20), 0.75 (910.60), 0.97 (1165.56), 1.18 (1420.53), 1.44 (1730.13), 1.80 (2167.22), 2.70 (3241.72), 3.85 (4625.83) g CO2/g dry air (ppm) respectively desiccant flow rate of 6 L/min. Overall proposed HSLD could be effective for dehumidification and CO2 absorption.

Experimental Investigation of Thermal Performance Parameters of Drying Air Unit with a Different Flowrate of Liquid Desiccant Solution

Liquid desiccant air-conditioning systems remove directly the latent load from moist air and remove indirectly sensible load of this air by using an indirect evaporative cooling process. The liquid desiccant must subsequently be regeneration once again with a low-grade heat source like solar energy. In this study, calcium chloride solution was used as a desiccant. For the desiccant solution regeneration process, a flat plate solar collector was employed. Different variables, such as the primary airflow rate and desiccant flow rate, were changed during the experiments. The impact of these variables on the performance parameters of the desiccant systems such as moisture removal rate, moisture efficiency, enthalpy efficiency, sensible heat ratio, and the mass transfer coefficient was studied. The obtained results revealed that as the flow rate of primary air increases, the moisture removal rate, sensible heat ratio, and the mass transfer coefficient increase. For example, from 0.006 m/s to 0.0125m/s when the mass airflow rate increased from 0.1 kg/s to 0.18 kg/s.

Wickability-optimized textured liquid-desiccant air dehumidifiers for independent moisture management in energy-efficient buildings

Liquid-desiccant-based air conditioning systems are envisioned to enable independent humidity management, thereby improving the energy efficiency of future buildings. Existing liquid-desiccant-based air conditioning concepts, however, suffer from a poor liquid flow distribution deteriorating moisture removal rate. They are consequently flooded with the liquid-desiccant solution, which significantly degrades the energy efficiency of the dehumidification process. Here, the capillary forces and wickability effect of textured air dehumidifier surfaces are altered to minimize the liquid-desiccant flow rate of the fully wetted state, thereby transforming the physics of interfacial desiccant flow distribution. Consequently, the wickability-optimized air dehumidifier surface maximizes both moisture removal rate and dehumidification energy efficiency. It was interestingly found that the length scale of a textured air dehumidifier surface concept is optimized at an intermediate pattern density. Dry solid-air menisci appear at length scales exceeding the optimum pattern distance while the effective liquid–air interfacial area is reduced at smaller length scales, both of which degrade the moisture removal rate. At the optimum pattern density, the effective liquid–air interfacial area increases with the solution flow rate, thereby increasing the dehumidification rate. At a water vapor pressure potential of 3 kPa and a solution flow rate of 2.8 g/s, experimental results indicated a moisture removal rate of 0.16 g/m2-s for a textured surface concept with a capillary length scale of 3 mm, a 28% improvement compared with that of smooth-plate dehumidifier surfaces. A high moisture removal rate of the textured surface at a low desiccant flow rate led to a high thermal efficiency of 0.75 at a water vapor pressure potential of 5.6 kPa and a LiBr flow rate of 2.8 g/s. The insights gained from the present study accelerate the development of advanced textured surface concepts for next-generation liquid-desiccant-based air dehumidification systems offering independent humidity management for future energy-efficient buildings.

Regression Models for Performance Prediction of Internally-Cooled Liquid Desiccant Dehumidifiers

In this study, using response surface methodology and central composite design, regression models were developed relating 12 input factors to the supply air outlet humidity ratio and temperature of 4-fluid internally-cooled liquid desiccant dehumidifiers. The selected factors are supply air inlet temperature, supply air inlet humidity ratio, exhaust air inlet temperature, exhaust air inlet humidity ratio, liquid desiccant inlet temperature, liquid desiccant concentration, liquid desiccant flow rate, supply air mass flow rate, the ratio of exhaust to supply air mass flow rate, the thickness of the channel, the channel length, and the channel width of the dehumidifier. The designed experiments were performed using a numerical two-dimensional heat and mass transfer model of the liquid desiccant dehumidifier. The numerical model predicted the measured values of the supply air outlet humidity ratio within 6.7%. The regression model’s predictions of the supply air outlet humidity ratio matched the numerical model’s predictions and measured values within 4.5% and 7.9%, respectively. The results showed that the input factors with the most significant effect on the dehumidifying process in order of significance from high to low are as follows: supply air inlet humidity ratio, liquid desiccant concertation, length of channels, and width of channels. The developed regression models provide a straightforward means for performance prediction and optimization of internally-cooled liquid desiccant dehumidifiers.

Experimental Analysis and Parametric Study on the Dehumidification System Using Liquid Hybrid Desiccants-A Source of Sustainable Energy

The desiccant cooling mechanism is one of the alternate methods to control the air humidity compared to the conventional air conditioning system. An experimental investigation has been carried out in the current research using a hybrid desiccant in a liquid desiccant dehumidification system. Triethylene glycol (TEG) mixed with different proportions of magnesium chloride (MgCl2) has been used as the hybrid desiccants. The performance of the dehumidifier was measured using the parameter moisture removal rate and enthalpy effectiveness. The blends of TEG and MgCl2 gave a better moisture removal rate (MRR) as compared to 100% TEG. The MRR and moisture effectiveness increased with the increasing desiccant flow rate and air flow rate for all of the blend ratios. The blend with 25% MgCl2 and 75% TEG concentration had relatively high MRR and dehumidification effectiveness. The study reveals that if an optimized blend of TEG and MgCl2 is used as the desiccant instead of a neat TEG, it will overcome the high viscosity problems of TEG and become one of the promising candidates for sustainable energy sources.

Experimental Investigation of Solar based Liquid Desiccant Indirect Evaporative Cooling system

ABSTRACT Air conditioning by using vapor compression cycle is the most commonly used system although its operating energy cost is significantly high. Liquid desiccant dehumidifier with Indirect Evaporative Cooling (IEC) is another alternative suitable for hot and humid climatic conditions. The system works in two parts. In liquid desiccant dehumidifier section, moisture from humid air is removed and such air is passed through Indirect Evaporative Cooling system where air is cooled. An attempt was made to set up an experimental module with Scheffler solar concentrator to provide thermal energy for evaporation of liquid desiccant while a new type of polymer plate exchanger was used in evaporative cooling section instead of commonly used metal heat exchanger. The experimentation was carried using CaCl2 desiccant with varying flow rates between 2 and 4 l/min in dehumidifier section and reduction of relative humidity by 4 to 9% was achieved. As desiccant flow rate was increased, it resulted into higher carry over losses. Experimentally, it was found that for a flow rate of 3 l/min, the carry over losses are minimum. For this flow rate of desiccant, secondary-to-primary-air ratio of 0.8, water flow rate of 11 l/min, and air cooling by 4.7°C were achieved. Maximum wet bulb and dew point effectiveness were found to be 0.61 and 0.42, respectively, for secondary-to-primary-air ratio of 0.8. It could be concluded that a polymer plate heat exchanger-based system could be considered as efficient system than metal plate heat exchanger systems, because longer life, lighter weight, and low operating cost are the characteristics of polymers.

Water from Air: Desiccant System Design and Simulation

Air water generators that harvest water from air humidity have the potential to counter the ever-rising problem of drinking water scarcity. There are many different types of air water generation systems that work on various different principles. Desiccant based air water generation systems work on the principle of moisture absorption, consisting of a packed bed dehumidifier that absorbs the moisture from air. This reduces the energy requirement of the system. To discuss the efficiency of the system, it is crucial to understand the working of the packed bed column. In this paper, a mathematical model has been developed for a packed bed dehumidification system using aqueous CaCl2 as the liquid desiccant. This model has been developed using water saturation pressure and equilibrium relative humidity models. The packed bed model has been used to study the effect of various input parameters like air and desiccant flow rate, packing material, relative humidity and desiccant concentration, on the capacity of the desiccant to absorb water from air. The results so obtained can be used to predict the water that can be absorbed by the desiccant in the packed bed column for given inlet conditions.

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.

Experimental assessment of heat and mass transfer characteristics of solar-powered adiabatic liquid desiccant dehumidifier and regenerator

Abstract Coupled heat and mass transfer performance of an adiabatic solar-powered liquid desiccant dehumidification and regeneration scheme using lithium bromide(LiBr) solution has been conducted experimentally as well as numerically under subtropical climatic conditions. The application of a vacuum insulated photovoltaic and thermal module to provide desiccant regeneration heat as well as electrical power to drive the air fans and liquid pumps have been explored. A square channelled ceramic cordierite packing with a varying channel density of 20–80 m$^2$/m$^3$ has been used to establish the optimum direct air-LiBr contact ratio for maximum effectiveness. The aggregate crammed vertical dehumidifier and regenerator operational indices featured were effectiveness, moisture removal rate (MRR), heat and mass transfer constants and Lewis number. The influence of solar radiation, humidity and L/G ratios, air–desiccant flow rates and concentration on the indices have been scrutinized in details. A 3D predictive numerical thermal model based on falling liquid stream with constant thickness in counter-flow configuration has been developed and solved by a combination of separative appraisal and stepwise iterative technique. The heat and mass exchange coefficients significantly increased with the increase in Lewis number, air and desiccant flow rates for both the dehumidifier and regenerator vessels. The predicted results of heat and mass transfer coefficients, effectiveness and MRRs have been validated with experimental measurements within a general acceptable conformity of less than $\pm $10%.

Experimental Study of Dehumidification Process by CaCl2 Liquid Desiccant Containing CuO Nanoparticles

A conditioning dehumidifier system is a simple technology to improve air quality and also reduces air conditioning costs. This experimental study evaluated the performance of a liquid desiccant system by adding copper oxide nanoparticles (NPs). The effect of operating parameters, such as inlet air humidity ratio and desiccant flow rate on air dehumidification rate, was also investigated. The desiccant solution contained 48[Formula: see text]wt.% CaCl2 and 0.35[Formula: see text]vol.% of CuO NPs. Comparison of liquid desiccants demonstrated a mean difference of 4.5[Formula: see text]g/s[Formula: see text][Formula: see text][Formula: see text]m2 in the air dehumidification rate by solutions with and without CuO NPs.

Performance Comparison of Enthalpy Recovery Devices Using Liquid Desiccant and Desiccant Wheel

Abstract Heat recovery between outdoor air and indoor exhaust air is an effective approach for energy-saving in the air-conditioning system. Performances of enthalpy recovery devices using liquid desiccant (LD) and desiccant wheel (DW) are compared in the present study. Effects of key factors including desiccant flow rate, number of transfer units (NTUm), and air inlet parameters on recovery performance are analyzed. There exists the same ideal recovery efficiency with a given NTUm for these two kinds of devices. However, an optimal solution flow rate could be achieved for enthalpy recovery device using LD, while a higher rotation speed leads to a higher recovery efficiency for that using DW. Recovery efficiencies of the two devices increase with the increase in NTUm, while they have different ranges of NTUm. NTUm of the DW is usually superior to that of the LD, due to the material difference. Then, the optimum methods to improve recovery efficiency of the two devices are clarified, i.e., increasing NTUm for an enthalpy recovery device using LD and choosing a reasonable rotation speed for that using DW, respectively. The present research will be beneficial to cast light on the relation between enthalpy recovery devices using LD and DW.

Advancement on Mass Transfer Empirical Models of Electrodialysis Regeneration for the Liquid Desiccant

This manuscript aims to acquire current utilization coefficient and concentration increment models considering liquid desiccant flow rate for electrodialysis regeneration.

Experimental study on combined low temperature regeneration of liquid desiccant and evaporative cooling by ultrasonic atomization

Liquid desiccant cooling is a great alternative to vapour compression cooling for air-conditioning system in buildings with immense energy saving potential. After dehumidification of fresh air, the dehumidified water can be used further for evaporative cooling. However, the recovery of water from regenerator exhaust is a slow process and impractical to be utilised as feed water for evaporative cooling. To overcome this problem, low temperature regeneration of diluted desiccant solution with evaporative mist cooling can be achieved by ultrasonic technology. In this work, a novel regenerative evaporative cooler through the Maisotsenko Cycle (M-Cycle) integrated with an ultrasonic atomizer for liquid desiccant regeneration was fabricated. Moisture removal and effectiveness of the system were studied under various air and desiccant temperature, air and desiccant flow rate, humidity ratio and desiccant concentration. Low temperature (35–50 °C) regeneration of diluted desiccant was accomplished by 0.208–0.619 g s−1 of moisture removal rate. Room cooling supply air temperature below the wet-bulb temperature of intake air up to a minimum temperature of 19 °C was effortlessly achieved by evaporative cooling of atomized water mist from the regenerator.

Fluid to liquid membrane energy exchanger for simultaneous liquid desiccant regeneration and desalination applications–Theoretical and experimental analyses

In this paper, a thermal model developed for assessing the performance of the fluid to liquid membrane energy exchanger based liquid desiccant regenerator is presented. The model was validated with the experimental data and found accurate. Using the experimental inlet conditions reported in the literature for the structured packing chamber, the performance of the fluid to liquid membrane energy exchanger based liquid desiccant regenerator was theoretically predicted choosing water and air as working fluids and Lithium Chloride as a liquid desiccant. Further, studied the influence of inlet parameters such as working fluid and desiccant inlet temperature’s, hot liquid desiccant to cold working fluid ratio and desiccant concentration on vapour absorption rate. From this analysis, it is observed that membrane based liquid desiccant regenerator using water as a working fluid is best suitable for converting the weak desiccant into strong desiccant and for generating the pure water simultaneously (co-generation process). An experimental investigation was carried out for assessing the energy exchange process across the membrane based liquid desiccant regenerator using water as a working fluid. From the experimental analysis, it was found that desiccant temperature has a significant impact on the energy exchange process. The pressure drop across the membrane based liquid desiccant regenerator was also measured at different desiccant flow rates and concentration.

Parameter Optimization of Flat Plate Liquid Desiccant Dehumidification System using Taguchi Method

In this research paper, Taguchi method, an influential technique for the optimization of operational parameters, is used to analyse the dehumidification parameters for a flat plate liquid desiccant dehumidification system. An orthogonal array using analysis of variance (ANOVA) and signal to noise ratio (S/N) are applied to find the dehumidification parameters of a liquid desiccant dehumidification system (LDDS). Calcium chloride (CaCl2) is used as a liquid desiccant solution. In this study, desiccant flow rate, air velocity and desiccant solution concentration are kept as operating parameters to find out the optimal relative humidity for room comfort. Experimental findings have shown proficient agreement with this approach.

Study on desiccant solution control strategies for efficient liquid desiccant air conditioning system control performance

Frequent change in ambient conditions requires precise control of the desiccant solution operating parameters to suit the required conditioned space load. Either of the two control strategies shall be adopted for this, which are the dehumidifier solution inlet temperature (DSIT) control strategy and the dehumidifier solution inlet mass flow rate (DSIM) control strategy. This article aims to study the efficient control strategy selection approach for a specific air conditioning application since it leads to energy savings as well as thermal comfort. Initially, the optimum desiccant mass flow rate will be found for the liquid desiccant air conditioning system at peak ambient conditions. And the effect of the control strategies on system performance has been analytically investigated at different ambient conditions. A significant reduction in the solution heat addition rate has been observed with both control strategies with the addition of an air-solution heat exchanger. It has also been seen that the required chiller load is nearly same with both control strategies but a little drop (3%–14.5% variation) was observed with the DSIT strategy at low ambient conditions. However, a considerable drop in solution pumping power due to the significant reduction in solution mass flow rate and its pressure drop with the DSIM strategy suggests that it is an energy-efficient control strategy.

Energy, entransy and exergy analyses of a liquid desiccant regenerator

In the present study, the energy exchange between the liquid desiccant and the ambient air, entransy dissipation during coupled heat and mass transfer processes and exergy destruction with respect to the reference state for the liquid desiccant regenerator are analyzed. Expressions for energy, exergy and entransy (EEE) of the regenerator are derived and also quantified along the height of the liquid desiccant regenerator. By varying the operating parameters such as desiccant temperature and concentration, air temperature and humidity ratio and air and desiccant flow rates, the performance of the regenerator is investigated in terms of entransy, exergy and desorption efficiencies. From the EEE analyses, it is observed that by increasing the desiccant temperature from 60.3 °C to 65.2 °C and decreasing the air humidity ratio from 18.7 gwv/kgda to 14.3 gwv/kgda simultaneously, the overall energy exchange, exergy destruction and entransy dissipation are increased by 26%, 37% and 39%, respectively. Further, the entropy generation along the tower height is also investigated and observed that for a given set of operating conditions, with increase in distance along the tower height, the entropy generation increases by 96% and decreases by 35% for the air side and the solution side, respectively.