Dehumidification Effectiveness Research Articles

Design, worst case study, and sensitivity analysis of a net-zero energy building for sustainable urban development

This paper presents a trigeneration facility based on a biogas driven gas turbine cycle for electricity production and an air to water heat pump for simultaneous extraction of cooling and potable water, and evaluates its robustness and effectiveness under different climatic conditions and variable demands. The air to water heat pump, which consists of an inside evaporator fan, expansion device, condenser, evaporator, and a compressor, is installed for supplying the cooling load of a hospital building in summer. In the refrigeration cycle, R134a absorbs heat from the inside warm air for space cooling and releases it to the saline water for driving a desalination process. Maximum values of cooling and electrical demands of a standard hospital building, where is located in south of Iran, over the hottest day of 2018 are considered for the worst case implementation. Engineering equation solver and general algebraic mathematical modeling system are employed to develop the non-linear optimization strategy, find the best operating point of the air to water heat pump based trigeneration plant, and minimize its energy cost under the greatest load level. Moreover, the sensitivity of the gained output ratio of desalination cycle to the relative humidity of the air entering and leaving the humidifier, the dehumidifier and humidifier effectiveness, and the top and bottom temperatures are comprehensively analyzed. The relative humidity of air entering the humidifier and the larger dehumidifier effectiveness have the significant effects on increasing the gained output ratio of the desalination cycle. Due to intense solar irradiation in summer, the seawater temperature naturally increases, which results in larger gained output ratio and higher mass flow rate of pure water.

Experimental evaluation of desiccant dehumidification and air-conditioning system for energy-efficient storage of dried fruits

The ideal storage zones of dried fruits in comparison with dried foods and feeds are established on the psychrometric chart. The study investigates the combined effect of the desiccant dehumidification and Maisotsenko-Cycle evaporative cooling for the dried fruits storage. Two configurations of desiccant air-conditioning systems (S-I and S-II) are proposed, and their performance is evaluated under the ambient conditions of Fukuoka, Japan. It is established on the basis of parametric and thermodynamic analysis of both the system configurations (S-I and S-II) that S-II could yield better system performance. The psychrometric evaluation of S-II revealed that it can provide the optimal conditions for the storage of dried fruits at low regeneration temperature. However, modification in the proposed system configuration (S-II) is suggested for the storage of dried foods and feeds.Practical application: Conventional dehumidification and air-conditioning options are either expensive or inefficient for dried fruit storage buildings. The study provides a way forward of using thermally driven desiccant systems which are energy-efficient and environment-friendly. Worldwide, the building industries are actively involved in the development of such systems but their application for dried fruit storage buildings are not explored in detail. Therefore, the study provides thermodynamic details of dried fruits storage in relation with experimental evaluation of desiccant and evaporative cooling systems. Provision of such systems to the storage buildings will provide distinct control of humidity and temperature for optimal storage.

Regeneration energy analysis and optimization in desiccant wheels using purge mechanism

As the desiccant wheel has been commonly used for dehumidification in drying process and cooling systems, purge mechanism has been commercially applied to reduce the energy consumption and improve its performance. Accordingly, a general optimization study would be essential to maximize this mechanism's advantages for desiccant wheels in various dimensions and design parameters. This study aims to use a non-dimensional model to propose best purging configurations for various desiccant wheel designs. This model applies non-dimensional conservation equations and finite volume as the solving method to simulate the dehumidification effect of rotatory desiccant wheels with the purging capability. Based on non-dimensional parameters, two optimization schemes have been designated to find effective and optimum purge angles. Effective purge angle corresponds to the purge set up which minimizes the humidity ratio of process outlet. The optimum purge angle makes the desiccant wheel have maximum coefficient of performance (COPDW). The optimum and effective purge angles for different dimensionless dehumidification angles, rotational speeds, numbers of transfer units (NTU) and regeneration temperatures are determined. In addition, the regeneration energy reduction made by purging mechanism has been evaluated. It is found that the energy consumption in the regeneration section reduced by applying the purge mechanism. Increasing regeneration temperature and NTU leads to higher energy saving. Besides, the optimum purge angle is observed to be higher than the effective one in all configurations.

A mathematical model to predict the performance of desiccant coated evaporators and condensers

Desiccant coated heat exchangers (DCHEs), utilizing an inner cooling source to remove sorption heat, are promising alternatives for evaporators and condensers (DCEs/DCCs) in vapor compression (VC) heat pumps. A mathematical model is necessary to facilitate the design, analysis and performance prediction of the component and the relevant systems. In this study, a three-dimensional model of DCEs/DCCs is proposed, accounting for the two-phase phenomena, the periodical switchover, the solid-side resistance, the fluid transport in multiple directions and the coupled heat and mass transfer. Study reveals that, high latent load (inlet humidity) reduces the sensible heat handling capacity of the DCEs, while the dehumidification capacity is almost independent of its sensible heat load. DCEs possess a satisfying effect of dehumidification above the dew point, thus it is unnecessary to employ low evaporation temperature. Meanwhile, the adsorption-desorption temperature difference of 30 °C seems to be the optimal value for the commonly adopted evaporation temperatures (10 °C-20 °C). For a specific coating thickness, there is a critical switchover period where the best performance of dehumidification is obtained. Switchover period shorter than the critical time should be avoided, and elongating the switchover cycle helps balance the ability of the system to handle the sensible and latent heat loads at the same time.

Energetic, entropic and economic analysis of an open-air, open-water humidification dehumidification desalination system with a packing bed dehumidifier

In the present paper, an open-air, open-water configuration is introduced into the humidification dehumidification desalination system, to recover the industrial waste heat. Thermodynamic performance, from the energetic and entropic standpoints, and the relevant economic performance of the desalination system are acquired. The theoretical analysis shows that top water production, gained-output-ratio and specific energy consumption reach 96.45 kg h−1, 1.70 and 0.38 kWh kg−1, respectively, while the lowest investment and cost of water production arrive at 848.86$ and 8.04 × 10−3$ kg−1. It is concluded that the thermodynamic performance and cost of water production for the desalination system will benefit, once the humidification and dehumidification effectiveness rise, while the bottom investment is found at a lower humidification effectiveness. Furthermore, the performance comparison between the newly proposed and previous solar and heat pump powered desalination systems confirms the economic advantages.

Transient performance of coupled heat and mass transfer in cross-flow hollow fiber membrane module for air dehumidification

Membrane-based liquid desiccant dehumidification has great advantages over traditional method, particularly in avoiding liquid droplets moving into the process air. This paper proposes a simple model to predict the transient performance of the hollow fiber membrane-based dehumidification module. To simplify the fiber-to-fiber influence, the modeled membrane module is assumed to be a parallel-plates heat mass exchanger. The model has been calibrated and validated with a transient experiment reasonably well. Impacts of various parameters on the transient performance were studied by using the proposed model. The results show that the variation of air temperature is more significant than air humidity. The absorption heat of water vapor is the main resistance of heat and mass transfer. It initially restricts the growth of the cooling effectiveness, and then limits the driving potential for moisture transfer. Therefore, it brings the dehumidification effectiveness down. It is found that reducing the heat capacity rate ratio can reduce the equilibrium time, and increase the cooling and dehumidification effectiveness. The high packing density increases the dehumidification effectiveness with a negligible effect of somewhat drop in cooling effectiveness. By contrast, the geometry of the fiber packing arrangement has little influence on dynamic performance of the module formed by numerous fibers. The membrane module can fit the change of weather conditions by varying solution temperature on the inlet of the dehumidifier with the help of this dynamic model. The cooling and dehumidification effectiveness also increase to improve heat and mass transfer performance of the dehumidifier under the adjustment.

Dehumidification Performance of LiCl in Falling Film Type Liquid Desiccant Dehumidifier

In the present study, CFD analysis of falling film type liquid desiccant dehumidifier is carried out to predict its performance In these simulations it is studied how the flow pattern of liquid desiccant effects the interaction between the moist air and the liquid desiccant.Two dimensional model was simulated by using the software ANSYS (FLUENT). The volume of fluid (VOF) was selected as the multiphase method for the simulation process. The water vapor/humidity content in the air is given by using species transport model and the variation of amount of water hold by the air is simulated. The liquid desiccant considered for study is LiCl with 30% concentration and the mass fraction of water vapor used in air is varied from 0.01 to 0.02. The properties of LiCl at 30% concentration were calculated and inlet parameters of air and desiccant are fed to the software as input. The model was subjected to different inlet mass fractions and determined the dehumidification effectiveness.

Design and optimization of novel dehumidification strategies based on modified nucleation model in three-dimensional cascade

To decrease the wetness loss and increase the efficiency in nuclear plant steam turbine, several novel dehumidification strategies are presented in this paper and the dehumidification effect is tested. The modified nucleation model is built firstly, and the accuracy of the modified nucleation model combined with several droplet growth models is investigated and discussed. Secondly, the non-equilibrium condensation (NQC) characteristics in Dykas cascade are studied, the relationship among the parameters is obtained. Secondly, five novel dehumidification strategies are presented, and the dehumidification effect is evaluated. With the passage layer increasing, the ability of the wetness loss reduction is gradually enhanced. When the passage layer increases to 5, the wetness loss is reduced to 1.15 kJ/kg, but which is at the cost of reducing the blade strength. And the LNB_LNE_LWC is the best choice by balancing the dehumidification effect and the blade strength, succeeding in reducing the wetness loss to 1.42 kJ/kg. At last, the NQC characteristics in three-dimensional cascade are investigated numerically, the structure dehumidification effect with different passage layers is evaluated in detail. The results in this paper can give a scientific basis and reference for the design and optimization of the dehumidification strategy in nuclear plant steam turbine.

Thermodynamic investigation and optimization of a heat pump coupled open-air, open-water humidification dehumidification desalination system with a direct contact dehumidifier

This paper focuses on a novel heat pump powered desalination system, in which the heat pump is coupled into the humidification dehumidification desalination subsystem with open-air, open-water configurations. Based on the conservation equations in accordance with the flow streams within the system, thermodynamic investigations, at the energetic and entropic viewpoints, are conducted. Thereinto, parametric analysis of the HPPDS is first achieved to assess the influence extents from the critical conditions, and then the thermodynamic optimization based on the algorithm of particle swarm optimization is also completed. The research results indicate the best system performance reaches 89.27 kgh−1 for the water production and 4.17 for the gained-output-ratio. The performance of the heat pump powered desalination system is very sensitive to the alternation of the prescribed parameters, except the dehumidification effectiveness. Finally, the maximum water production and gained-output-ratio can be optimized to 150.75 kgh−1 and 8.12, respectively, and a fully coupled heat pump powered desalination system is acquired without an auxiliary heater. With respect to the economic performance, the cost of the fresh water is gained as 0.016$L−1 at the optimized conditions.

Numerical investigation of novel dehumidification strategies in nuclear plant steam turbine based on the modified nucleation model

To decrease the wetness loss and increase the safety in nuclear plant steam turbine, several novel dehumidification strategies are presented in this paper and the dehumidification effect is tested by employing the modified model. The modified nucleation model is built firstly, and the accuracy of the modified nucleation model combined with several droplet growth models is investigated and discussed, the results show that the modified nucleation model combined with the Young's droplet growth model (ϕ=0.75,α=9) shows a satisfactory ability to describe the non-equilibrium condensation process. Secondly, the non-equilibrium condensation characteristic is studied in Dykas cascade, the relationship among the parameters is obtained, four phases and five feature nodes of the non-equilibrium condensation process are revealed, which provides a basis for the dehumidification strategy study. Thirdly, five novel dehumidification strategies are presented, and the dehumidification effect is evaluated. The results show that the passage adopted in the LWE (Location of the wetness emerging) has the best dehumidification effect, which lays the foundation for the dehumidification study in nuclear plant steam turbine three-dimensional cascade. Fourthly, the non-equilibrium condensation characteristic is studied numerically in nuclear plant steam turbine, with the span increasing, the LMF (Liquid mass fraction) gradually reduces. At last, the dehumidification strategies with different passage layers are investigated and whose effect are analyzed and discussed. With the passage number increasing, the LMF decreases quickly, and the location of the LMF forming moves backward gradually. Besides, when the passage layer increases to 8, the dehumidification effect almost keeps constant, and the wetness loss is reduced from 3.01 kJ/kg to 2.51 kJ/kg, the dehumidification effect is remarkable. The results in this paper can give a scientific basis and reference for the nuclear plant steam turbine design and dehumidification strategy optimization.

Drying in a desiccant wheel dehumidification system-assisted hot air dryer: desiccant wheel effectiveness and carrot drying

A desiccant wheel dehumidification system was used in this study to reduce humidity of the air supplied to a hot air dryer. Desiccant wheel effectiveness was determined based on the ideal adiabatic dehumidification process. Best results of adiabatic dehumidification effectiveness and adiabatic enthalpy effectiveness in the range of 0.89 to 0.99 were achieved. Specific adsorption of silica gel in the desiccant wheel was rotational speed dependent. The desiccant wheel system could reduce the relative humidity from 70 to 44%. Drying of cylindrical carrot in the desiccant wheel dehumidification system-assisted hot air dryer was also conducted in this study. The drying temperatures were varied from 80 to 120˚C. The desiccant material regeneration process reused exhaust drying air for heat exchanging with the regenerating air, higher drying temperature caused higher moisture evaporated from the desiccant material. Comparing between dehumidified hot air drying and conventional hot air drying, greater drying rates of dehumidified hot air drying were achieved at the drying temperatures of 100 and 120˚C.

Performance analysis and design implementation of a novel polymer hollow fiber liquid desiccant dehumidifier with aqueous potassium formate

A novel cross-flow liquid desiccant polymer hollow fiber dehumidifier (PHFD) is investigated numerically in this paper. The main objective of this research is to simulate, and validate the numerical model for future design implementations. The experimentally verified simulation data will be used to develop a set of design and implementation tables and charts as the guidance for selecting the number of fibres and the solution-to-air mass flow ratio of the PHDF under given conditions. A numerical model is developed to simulate the performance of the proposed innovative dehumidifier. This model is validated against three sets of data, i.e. the experimental obtained testing results, analytical correlations and the modelling results from the literature. The influence of various operating conditions such as inlet air properties (i.e. velocity, relative humidity) and inlet solution properties (i.e. temperature, concentration, mass flow rate) on the dehumidification sensible, latent, and total effectiveness, moisture removal rate are numerically analyzed. Dimensionless parameters including the number of heat transfer unit (NTU) and the number of mass transfer unit (NTUm), the solution to air mass flow rate ratio (m*), and the air to solution specific humidity ratio (ωr∗) have been used to evaluate the system performance. The results show that the increase in NTU and NTUm lead to a substantial change in dehumidification effectiveness. When the NTU increases from 0.47 to 7, the sensible effectiveness rises from 0.35 to 0.95. Increasing ωr∗ is another good option for increasing the amount of the absorbed moisture without influencing the latent effectiveness. For an increase of ωr∗ from 1.4 to 2.2, the air inlet and outlet specific humidity difference varies in the range of 0.008 kg/kg and 0.018 kg/kg.

Experimental study of a membrane-based liquid desiccant dehumidifier based on internal air temperature variation

A membrane-based liquid desiccant dehumidifier with the separated air stream and liquid desiccant channels has the ability to solve its working fluid carryover problem in the traditional direct contact system. The sensible, latent, total effectiveness and air moisture removal rate are adopted for the dehumidifier performance evaluation in this paper, and the dehumidifier main operating parameters are investigated experimentally to identify their influences and internal air temperature variations, including inlet air relative humidity (RH), inlet solution concentration and temperature, heat capacity rate ratio (Cr*) and number of heat transfer units (NTU). It is found that both the inlet air RH and solution temperature have the negative influences on the dehumidifier effectiveness, while the desiccant solution concentration has little positive influence; the air moisture removal rate rises sharply with the inlet air RH and solution concentration. The highest sensible, latent and total effectiveness achieved in this study are 0.823, 0.802 and 0.810 respectively when both Cr* and NTU are equal to 12. However the operating condition with NTU = 8 and Cr* = 6 is recommended with the corresponding sensible, latent and total effectiveness of 0.758, 0.71 and 0.728 respectively.

Numerical investigations and performance comparisons of a novel cross-flow hollow fiber integrated liquid desiccant dehumidification system

The heat and mass transfer process of a novel cross-flow hollow fiber integrated liquid desiccant dehumidification system is analyzed numerically. Compared with other porous media or packing towers in dehumidification applications, hollow fibre membranes have significant advantages including low weight, corrosion resistance and no liquid droplet carryover. A novel air-KCOOH cross-flow dehumidification system was designed and manufactured, with 5500 hollow fibres formed into a circular module. The variations of the dehumidification effectiveness and moisture removal rates were studied numerically and validated against experimental results under the incoming air mass flow rates of 0.08–0.26 kg/s and relative humidity from 55% to 75%. The dehumidification performance comparisons for the proposed system using CaCl2, LiCl and KCOOH as the desiccants have been conducted. The results demonstrated that under the same m*(ratio between solution mass flow rate to the air mass flow rate), the proposed system using 62% KCOOH could achieve approximately the same latent effectiveness compared with 40% CaCl2 and 32% LiCl, with at least 3.1% sensible effectiveness improvement. Therefore, it could be concluded that the proposed system using KCOOH as desiccant could be more applicable for dehumidification purpose compared with other systems using conventional liquid desiccants.

A proposed hyper-gravity liquid desiccant dehumidification system and experimental verification

Liquid desiccant air conditioning systems have received more attention in recent years for their lower energy consumption. A novel hyper-gravity liquid desiccant dehumidification system was proposed in this paper. Rotating packed bed (RPB) uses a rotating part to create an artificial centrifugal force which is stronger than gravity, thus owning the advantages for gas-liquid heat and mass transfer process intensification. This work considered the feasibility of applying a countercurrent-flow RPB for air dehumidification. An experimental apparatus is established to verify the proposed liquid desiccant dehumidification system. More than 145 reliable experimental data have been collected. The effects of the rotating speed of RPB and inlet parameters of air and desiccant solution are investigated. The results show that both dehumidification effectiveness and moisture removal rate can be improved significantly by increasing the rotating speed of the RPB, solution flow rate and solution inlet concentration. Dehumidification effectiveness can reach 0.621 at the rotating speed of 1500 r/min. Compared with conventional dehumidifiers the desiccant solution consumption of RPB dehumidifier is less under the same dehumidification effectiveness. Besides, the effects of the rotating speed, air flow rate and solution flow rate on the pressure drop of the RPB dehumidifier are presented.

Multilayered artificial neural network for performance prediction of an adiabatic solar liquid desiccant dehumidifier

Abstract In this study, a multi-layered artificial neural network (ANN) algorithm was developed and trained to predict the performance of a solar powered liquid desiccant air conditioning (LDAC) system particularly the adiabatic packed tower dehumidifier using Lithium Bromide (LiBr) desiccant. A reinforced technique of supervised learning based on error correction principle rule coupled with perceptron convergence theorem was applied to create the algorithm. The parameters such as temperature, flow rates and humidity ratio of both air and desiccant fluid were fed as inputs to the ANN algorithm and their respective outputs used to determine dehumidifier effectiveness and moisture removal rate (MRR). The ANN model when subjected to validity tests using vapour pressure of LiBr desiccant solution at specific random temperatures and concentrations, gave astounding outcomes with precise estimation to R2 values of 0.9999 for all desiccant concentration levels. Due to the variation in solar radiation, the MRR and effectiveness fluctuated with the change in desiccant and air temperatures, giving maximum differences of 0.2 g/s and 1.8% respectively between the predicted and measured values depicting a perfect match. With respect to humidity ratio, MRR was accurately predicted by ANN algorithm with maximum difference of 3.4969% while the mean variation was −0.5957%. With respect to air temperature, the dehumidifier effectiveness was perfectly predicted by the ANN algorithm to an average accuracy of 0.53% and extreme positive deviation of 4.14%. The MRR was replicated to a mean variation of 0.013% and highest point difference of 0.08%. In all the above cases, the mean and maximum differences between the ANN model and experimental values were far below the allowable limit of ± 5%, hence the algorithm was deemed to be successful and could find use in air conditioning scenarios. The ANN algorithm’s capability and flexibility test of processing unforeseen inputs was accurate with negligible deviations and prospects of predicting the desiccant’s vapour pressure, dehumidifier effectiveness and MRR within all ranges of temperature and concentration which then eliminates the need for use of charts.

Comparison of two hygroscopic materials for a solar-assisted desiccant-based air handling unit

Solar-driven air-conditioning systems are an interesting solution to reduce greenhouse gas emissions as they are essentially powered with a renewable energy source. Among the solar heating and cooling systems, desiccant-based air handling units (AHUs) are a very promising alternative as they require low temperature thermal energy for operation in cooling mode. In this paper the experimental plant of University of Sannio (Benevento, Southern Italy), consisting of an AHU with a desiccant wheel using as hygroscopic material silica gel is coupled with solar thermal collectors. This AHU has been also simulated with a different material for the desiccant wheel, the MIL101@GO-6 (MILGO). It is a composite material, consisting of graphite oxide dispersed in the MIL101 metal organic framework network structure, that shows a better dehumidification effectiveness. The energy and environmental performance of a desiccant-based solar heating and cooling system with this new material have been evaluated with respect to the conventional AHU based on cooling dehumidification. Yearly based dynamic simulations of the plant serving a university classroom located in Benevento have been performed. Furthermore, a comparison with the air-conditioning system equipped the currently adopted material (silica gel) has been carried out too. The optimal plant configuration varying collector type (flat plate and evacuated tube), tilt angle and surface has been found.

Experimental Analysis of Solar Assisted Liquid Desiccant Cooling System

Dehumidifier is that the most vital unit in liquid drier air conditioning system, this paper experimental analysis of solar assisted liquid desiccant cooling system (SALDCS) by Li Cl-H2O as a desiccant. A capable solar energy and cooling technique is through the employment of a liquid drying agent system, wherever humidness is absorbed directly from the method air by direct contact with the drying agent, the desiccant is then regenerated by solar hot water or air. The solar assisted desiccant dehumidifier system is operated variable operating conditions, air flow rate (0.05 to 0.11 kg/sec), desiccant concentration (30% to 40%) and desiccant temperature (maximum 40oC). Effectiveness of dehumidifier verified by experimentally, it results effectiveness decreased by the air flow rate & desiccant temperature, increased by desiccant concentration, the same process done with inter cooler (Indirect evaporative cooler) better dry-air cooling rate observed.

Experimental analysis of dehumidification performance of counter and cross-flow liquid desiccant dehumidifiers

In a liquid desiccant dehumidifier, the air-to-solution flow direction plays an important role in the dehumidification performance and the physical size of the dehumidifier tower. In this research, the dehumidification performance of counter-flow and cross-flow liquid desiccant dehumidifiers were compared via a series of experiments carried out in the environmental test chamber. To predict the dehumidification performance of both flow type dehumidifiers in various operating conditions, empirical models returning the dehumidification effectiveness and the enthalpy effectiveness, which were adopted as performance indices, were also derived based on the experimental data. From the sensitivity analysis conducted by using the proposed empirical correlations, it was observed that when the inlet air humidity ratio increased from 10.1 g/kg to 22.7 g/kg, the dehumidification effectiveness and enthalpy effectiveness of the counter-flow liquid desiccant dehumidifier increased from 51.2% to 82.4% and 40.2% to 72.5%, respectively. Meanwhile, both effectiveness values of the cross-flow dehumidifier increased from 62.3% to 63.4% and 46.3% to 55.0%, respectively. Likewise, when inlet solution temperature varied from 15.2 to 31.1 °C, the dehumidification effectiveness and enthalpy effectiveness of the counter-flow type dehumidifier decreased from 71.7 to 45.4% and 64.4 to 47.3%, respectively, while those of a cross-flow type dehumidifier decreased from 65.3 to 54.8% and 55.8 to 45.2%. Consequently, one may conclude that the cross-flow liquid desiccant dehumidifier would provide relatively stable dehumidification performance regardless of the changes in operating parameter, but the cross-flow dehumidifier may have limited dehumidification performance, especially at the lower desiccant solution temperature and in highly humid process air conditions.

Numerical simulation and analysis of the vertical and double pipe soil - air heat exchanger

A quasi-3-D soil-air heat and mass transfer model was established to simulate the process of heat and moisture exchange in the vertical and double soil-air heat exchanger. At the same time, the heat and moisture exchange were considered in the model, and the air-flow parameter equation and heat transfer control equation were combined. The MATLAB was used for the calculation procedure, and the model was solved using an iterative method. The average relative error of the numerical calculation was less than 2%. Moreover, the heat exchanger performance influence factors were validated. The simulation results showed that: with the lengthening of the heat exchanger, the smaller the air-flow, the shorter the running time, the air temperature and moisture content at the outlet of the heat exchanger were lower, the cooling and dehumidification effect were more obvious. However, the magnitude of change gradually decreased, and finally stabilized.