Moisture Transfer Coefficient Research Articles

How to design the drying of porous materials?

The convective drying of porous materials is studied at the pore scale using a two-component two-phase Lattice Boltzmann model. Capillary pumping from coarse to fine pores is found to enhance the drying in first drying period at high rate. A ‘toy’ model of four connected channels is developed to design the drying of porous materials. This approach has to be seen to supplement the continuum modelling of drying using known moisture transport properties and convective moisture transfer coefficient, allowing to better understand convective drying and design the pore structure to optimize the drying rate.

ბაზალტფიბრობეტონის ტენგამტარობის მახასათებლების დადგენა

Issues concerning cement-based composites basalt fiber concrete’s moisture conductivity are studied in the article. Composites moisture conductivity parameters (moisture diffusion, moisture transfer and relative moisture transfer coefficients) are identified by drying testing on specimens. Experiments are conducted by testing specimens of ( 0t 28 = day age) and containing moisture of ( W 4.5% 0 = according to mass) on drying. Specimens were dried up in the environment of 20% relative humidity. Drying process duration was (190 days) till the equilibrium moister content was met, when moisture transfer (drying) between environment and specimen stops, W 1% C = (according to mass). During drying process moisture loss in specimens were identified with periodic weighing. Cylindrical specimens (with isolated endings) were experiencing drying process from free lateral surfaces. Weight experiment data analyses determined curve of basal fiber concrete moister content changes in time. Parallel to tests cylinders moisture content change was calculated theoretically at any point in time for χ - coefficient’s different values. N number of theoretical curves is received. By comparing and analyzing experimental and theoretical data such a value of χ - coefficient is chosen that can ensure that theoretical curve can reflect experimental curve as much as possible. On the bases of a given data with corresponding formulas moisture conductivity characteristics of basalt fiber concrete: (moisture diffusion, moisture transfer and relative moisture transfer) values are determined.

Numerical modeling of laundry drying in a commercial laundry plant: Incorporating water potential as a driving force for heat and mass transfer

Increasing energy efficiency and reducing emissions in industrial processes through waste-heat recovery systems are vital. The energy-intensive nature of professional laundry care generates waste heat from machines such as washers, dryers, and boilers. We focused on a waste-heat recovery system tailored for this sector. An accurate drying model is essential for analyzing its energy-saving potential.This study presents a water-potential-based drying model using equilibrium thermodynamics. Two measurement experiments and numerical simulations were conducted to verify the accuracy of the proposed model, and the experimental results were incorporated into the simulations. The first experiment collected and determined laundry samples' basic information and hygrothermal properties, including the surface area, initial weight, and heat and moisture transfer coefficients. The second experiment attempted to determine each laundry item's equilibrium water content and capacity at various humidity levels. Through simulations, a comparison was made between the surface temperature and water content predictions of the existing and proposed models. Experimental results revealed that the laundry surface temperature remained constant during the constant-rate drying period. However, during the falling rate period, it was influenced by water content. The drying characteristics differ based on the material and quilting method. The proposed model improved the temperature and water content predictions by approximately 80.07% and 63.08%, respectively, compared with the existing model. This model can effectively assess laundry drying processes, including the latent heat flux assessment of the indoor environment.

Thin-Layer Drying of Burdock Root in a Convective Dryer: Drying Kinetics and Numerical Simulation

This work investigated the thin-layer drying kinetics of Vietnam burdock root in a convective dryer. The thin-layer drying models and mass transfer coefficient were determined by experiment and analysis approach. Furthermore, a numerical simulation was performed to describe the moisture distribution inside the material. The regression models and mathematical equations were determined by Statgraphics software and the EES software. The survey range in this work: 50-70oC air temperature, 1-2 m/s air velocity, 22 ± 5 mm slice diameter, and 5 ± 0.2 mm slice thickness. The results show that the Page model was the best model to describe the drying behavior of burdock root, with the correlation coefficient of R2 > 0.9992; the moisture diffusivity coefficient De = 3.4520 x 10-9-1.8516 x 10-8 m2/s; moisture transfer coefficient hm = 1.3256 x 10-7-7.8375 x 10-7 m/s. Furthermore, the simulation results visualize the moisture distribution inside the burdock root slice in the drying process.

MODELING OF MASS TRANSFER PARAMETERS DURING DEEP-FAT FRYING OF FRIED MELON CAKE (ROBO)

In this investigation, the mechanism of mass (moisture and fat) transfer during deep-fat frying of robo (fried melon cake) was carried out. The plots of dimensionless concentration ratios against time were used to determine moisture transfer parameters including moisture diffusivity, moisture transfer coefficient, moisture transfer Fourier number, moisture transfer Biot number and activation energy and fat transfer kinetic parameters such rate constants and activation energy at different frying temperatures of 140, 155 and 170 0C. All moisture parameters increased linearly with frying oil temperatures except moisture transfer Biot number which deceased linearly with increase in temperature with correlation coefficient (R2) ≥ 0.99. There was also positive linear relationship between fat transfer rate constant and frying temperatures (R2 ≥ 0.99). An Arrhenius type of relationship was found between temperature and the effective moisture diffusivity and fat transfer rate constant (R2≥0.99) with activation energies values calculated as 25.66 and 42.18 kJ/mol, respectively. Both moisture loss and fat desorption after initial adsorption of 60 seconds were adequately modeled by the first-order kinetics adopted with high correlation coefficient (R2) value and were time and temperature dependent as revealed by Arrhenius analysis performed on the experimental data.

Experimental Determination of Transport Parameters of Dragon Fruit Slices by Infrared Drying

Infrared drying is an advanced drying method that preserves the nutritional value of the dried object. Currently, dragon fruit drying on a static tray by hot air circulation reveals disadvantages of long drying time and ununiform moisture distribution. In this study, Vietnam red dragon fruit was dehumidified in a vertical cylindrical infrared dryer. The drying mode includes radiation intensity in the range of 4 to 6 kW/m2 and air velocity in the range of 1 to 3 m/s to investigate moisture transfer parameters and vitamin content in dragon fruit. The drying time was fixed at 10 hours to evaluate the final moisture content and vitamin contents. Henderson and Pabis drying model was adopted with the coefficient of determination greater than 0.98. Results show that the moisture diffusivity in the infrared drying was achieved in the range of 2.3e-9 to 3.9e-9 m2/s. Moisture transfer coefficient of the dragon fruit varied in the range of 4e-5 to 1.2e-4 m/s. The Biot number in the drying by an infrared lamp ranged from 40 to 80. Vitamin C in dried dragon fruit has a high content of up to 13.5 mg/100 g. The current dragon fruit drying by infrared lamp reveals negligible surface resistance to mass transfer. The infrared drying of dragon fruit is a feasible alternative to preservation. Also, seeking of an optimal tray rotation speed may be further improvement of the drying rate.

Moisture Transport Coefficients Determination on a Model Pharmaceutical Tablet

In this work, a novel methodology to determine moisture transport coefficients for MMC PH101 tablets is presented. Absolute permeability, moisture diffusion, moisture transfer, and water vapor permeability coefficients were estimated on compressed powder tablets produced with different compression pressures (20 MPa to 200 MPa with an interval of 20 MPa). The ASTM D6539 standard test was used to measure the absolute permeability. The moisture transfer coefficient was determined from measured absolute permeability. The moisture diffusion coefficient was obtained with the tablet average pore radius, which was determined with the water droplet penetration method. Descriptive and phenomenological models derived from the measurements were confronted with existing and adopted models, and a good agreement was found. The obtained models are of the function of the microstructural properties of the tablet (average pore radius and average porosity). The tablet average porosity was found to be the principal parameter that governs the behavior of the moisture transport coefficients. The findings of this study might be applicable to obtain a series of input parameters for modelling software, such as COMSOL Multiphysics®, to infer delamination, sticking, and failure propensity from the effect of moisture.

A Modeling Study for Moisture Diffusivities and Moisture Transfer Coefficients in Drying of “<i>Violet de Galmi</i>” Onion Drying

In the present work, the mass transfer characteristics, namely moisture diffusivity and moisture transfer coefficient of “Violet de Galmi” variety of onions were evaluated using the analytical model. Onions were dried in a single layer at different temperatures (40℃, 50℃, 60℃, and 70℃) and for a relative humidity of drying air of 20%. The results showed a reasonably good agreement between the values predicted by the correlation and the experimental observations. This model computed the Biot number, effective moisture diffusivity, and mass transfer coefficient. Effective diffusion coefficient values are obtained between 0.2578 × 10-9 m2·s-1 and 0.5460 × 10-9 m2·s-1. Mass transfer coefficients of “Violet de Galmi” onion drying vary between 3.37 × 10-7 m·s-1 and 13.38 × 10-7 m·s-1. Numbers of mass transfer Biot are found between 0.9797 and 2.9397. The activation energy Ea is 31.73 kJ·mol-1.

Effect of climatic conditions on the performance of a multistage dynamic dehumidifier test rig

Due to climatic change, there is a rise in air conditioning demand. Conventional air conditioning unit has drawbacks like environmental pollution and excessive energy consumption. Packed type liquid desiccant dehumidification system is environmentally friendly and energy-saving compared to the conventional vapor compression cycle. A multistage dehumidifier test rig has been fabricated with Calcium Chloride as the desiccant in the present work. Celdek packing soaked in the desiccant solution reciprocates with varying linear velocity and interacts with the air. Experiments are conducted by varying air velocities, camshaft speed, inlet relative humidity and inlet dry bulb temperature. Performance parameters such as moisture transfer coefficient, coefficient of performance, moisture removal rate and dehumidification efficiency are determined. Four pad unit gave better dehumidification over three and two pads. The system gave maximum COP, moisture removal rate and dehumidification efficiency equal to 2.17, 4.87 g/s and 73.54%, respectively. With the increase in the inlet RH and DBT there is a rise in the coefficient of performance, moisture removal rate and dehumidification efficiency. Air entering the room is found to be of good quality with no carryover of the desiccant.

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.

A Review of Models for Estimation of Moisture Evaporation Rate from Clothes Inside a Clothes Dryer

Heat pump tumble dryers, air-vented dryers and condenser dryers are widely used as clothes dryers. Clothes dryers use hot air to absorb moisture from textiles to get them dry after a wash by passing drying air through the drum. To simulate the drying process of clothes in the drum and to obtain the moisture evaporation rate, it is necessary to use an accurate model to predict the moisture transfer coefficient from the textile to the air in the drum as well as the mass transfer area between the drying air and the textile. In this study, a comprehensive review of the literature on the prediction of the moisture evaporation rate inside the drum of a clothes dryers was conducted. It was found that researchers generally used constant values, fitting models, dimensionless correlations, and Chilton–Colburn analogy to predict the area–mass transfer coefficient. Moreover, few researchers used the effectiveness model for the prediction of moisture evaporation rate. The comprehensive review of the literature showed that all of the previous models for prediction of the moisture evaporation rate have some limitations in terms of generality or accuracy. Therefore, the development of a new accurate model for prediction of the moisture evaporation rate inside the drum of clothes dryers is crucial.

Effect of air velocity, temperature, and relative humidity on drying kinetics of rubberwood

Kiln drying of rubberwood lumbers is a complex transport phenomenon for realistic modeling and simulation. To decouple this complexity, researchers usually divide their research into two parts. The first one is single-lumber drying kinetics to describe how wood lumber responds to its surface conditions. Then they combine this drying kinetics with a lumped transport model or dispersion model or computational fluid dynamics. The mathematical models are then solved numerically to predict the industrial kiln drying behaviors. This work focuses on the drying kinetics of stacked rubberwood lumbers using hot air at different air velocity (0.5, 1.5, 2.5, 3.5, 4.0 m/s), relative humidity (6–67% relative humidity (RH)) and temperature (60–100 °C). The drying kinetics followed the conventional drying theory. However, the two drying periods, namely constant and falling rate (CRP and FRP), were not distinct. As the air velocity increased, the transition from CRP to FRP is faster. The middle of the transition period (at critical moisture content, CMC) moves closer to the fiber saturation point (FSP). The overall mass transfer coefficients in the falling rate period for stacked rubberwood drying were lower than those predicted by the Ananias correlation. Hence, a modified formula was proposed, representing the overall moisture transfer coefficients as a function of air velocity, temperature, relative humidity, and lumbers thickness for the range of variables under investigation satisfactorily. In general, the drying rate and the overall moisture transfer coefficient increased with increasing air velocity, drying temperature, and decreasing RH. Relative humidity directly affects the driving force of moisture transfer rate because higher RH is associated with higher equilibrium moisture content. A lumped parameter model for kiln drying was also developed. After being integrated with the estimated mass transfer coefficient, the model can predict the moisture profiles in lab-scale kiln drying satisfactory, although the model needs more validation data. These kinetic parameters and correlation for stacked rubberwood drying can be used in more complex models and process optimization in future research.

Experimental analysis of a new generation of membrane liquid desiccant air-conditioning (LDAC) system with free convection of desiccant for energy economic management

Abstract A new generation of membrane liquid desiccant air-conditioning (LDAC) system with free convection of desiccant is investigated experimentally. The free convection LDAC systems have benefits over conventional air conditioning (AC) systems with the added advantage of system operation with no circulating pump. The prototype system made up of mainly two externally cooled hollow fiber membrane (HFM) liquid-to-air energy exchangers worked as dehumidifiers and regenerators. The performance of the system studied under the standard summer air conditions, and a thorough study was done to reveal its behavior as an AC system in different airflow rates. The coefficient of performance (COP) of the system is 0.85 at the base condition, and the sensible heat factor (SHF) of the dehumidifier ranged between 0.24 and 0.4 for different operating conditions. The heat and moisture removal rate and sensible heat factor increased while the electrical and thermal coefficients of performance (ECOP and TCOP) decreased by the airflow rate increase. While the value of TCOP is approximately the same for all operating conditions, the ECOP is very sensitive to airflow rate, and its value reduced by 82% as the value of airflow rate tripled. It is inferred that unlike the forced energy transfer loops, it is mainly the solution side transfer coefficients that determine the system performance, and between the heat and moisture transfer coefficients, the latter is more effective on system performance.

DEVELOPMENT EXPERIENCE AND WAYS OF IMPROVEMENT OF IRRIGATION MANAGEMENT SYSTEMS

The paper provides an overview of models and software used in decision support systems in irrigation. The models of biomass accumulation or evapotranspiration are the base of decision support systems in irrigation. The overview of the most famous systems is given, as well as an innovative irrigation control system "Irrigation online" is presented. 
 The objective of the work is to share the experience of development and implementation of irrigation management systems and outline the ways of their improvement.
 The "Irrigation online" system consists of hardware and software components. The part of the system's hardware is located in the field consisting of iMetos or Davis weather stations, as well as of own-developed equipment. The software part, intended for storing, processing and providing recommendations, is hosted and run on a server. It sends the recommendations about start watering and necessary irrigation rates to a user’s computer or mobile device.
 The system is based on modelling of moisture transfer, automated measurements of soil moisture and meteorological indicators in the field and weather data from automated forecast web-sites. Water retention curve of soil and the dependence of the moisture transfer coefficient on the head, which are the input parameters of the model, are given for every layer according to the van Genuchten-Mualem Model.
 The application of the system took place in 2019 in SE EF“Askaniiske” Kherson region and LLC “APC “Mais” in Cherkasy region. The system "Irrigation Online" provided the recommendations on watering winter rape, wheat, corn, soybeans, alfalfa and potatoes. 
 The system provided the recommendations on watering winter rape, wheat, corn, soybeans, alfalfa and potatoes. It was specified that the use of the system "Irrigation Online" enables to schedule irrigation regimes, the implementation of which requires watering with less (by 15-25%) in comparison with the current irrigation rates, due to which more favourable conditions for the maximum realization of crop varieties and hybrids potential are created. It is accompanied by enhancing the environmental safety of irrigation as a result of minimization of irrigation water losses for infiltration.
 Irrigation control system "Irrigation Online" uses a range of soil moisture suction pressure rather than a soil moisture range as an optimum moisture supply range for plants. For setting up irrigation terms and rates, the value of suction pressure, which corresponds to the part of water field capacity when it is determined by water retention curve of soil, is taken. The pre-irrigation threshold of suction pressure is the value, which at non-irrigation for some short period will not cause water stress for plants 
 Monitoring of meteorological parameters and soil moisture level in the "Irrigation Online" system allows daily adjusting irrigation terms and rates for next 5 day period and significantly improves the accuracy of their forecasting.

Moisture Content Change of Korean Red Pine Logs During Air Drying: II. Prediction of Moisture Content Change of Korean Red Pine Logs under Different Air Drying Conditions

Air drying was carried out on 15 Korean red pine logs to provide a prediction model of the moisture content (MC) change in the wood during drying. The final MC was 17.4% after 880 days since the beginning of air drying in the summer for 6 Korean red pine logs with 68.7% initial MC. The final MC was 16.0% after 760 days since the beginning of air drying in the winter for 9 Korean red pine logs with 35.8% initial MC. A regression model with R-squared of 0.925 was obtained as a result of multiple regression analyses with initial MC, top diameter, temperature, relative humidity, and wind speed as independent variable and and MC change during air drying as dependent variable. The initial MC and top diameter, which is the characteristic of Korean red pine, have greater effect on the MC decrease during air drying compared to meteorological factors such as the temperature, relative humidity, and wind speed. Two-dimensional mass transfer analysis was performed to predict the MC distribution of Korean red pine logs during air drying. Two prediction models with different air drying days and different meteorological factors for the determination of the diffusion coefficient and surface emission coefficient were presented. The error between the different two methods ranged from 0.1 to 0.8% and the difference from the measured value ranged from 2.2 to 3.6%. By measuring the internal MC during air drying of Korean pine logs with various initial MC and diameter, and calculating the moisture transfer coefficient in wood for each meteorological condition, the error of the prediction model can be reduced.

Experimental and numerical investigation of transport phenomena and kinetics for convective shrimp drying

In this study, an experimental apparatus was used to produce dried shrimp. From experiments with various air velocities and temperatures, the drying constant, moisture transfer coefficient and moisture diffusivity were obtained by using a Bi-Di correlation. An equation for determining the drying constant was established to determine the drying parameters for different drying conditions. To obtain the targeted moisture, i.e., a moisture content of 0.25 (dry basis, d.b.), drying with the highest temperature and air velocity (60 °C, 2 m/s) took 3.6 h, while the lowest temperature and air velocity (50 °C, 1 m/s) required up to 5.8 h. The transport parameters were then used to simulate the temperature and moisture content distribution inside the shrimp using ANSYS software for a certain drying condition. The results showed that the shrimp temperature increased rapidly, reaching the dry air temperature after approximately 15 min. The moisture content in the tail was markedly lower than that at the centre, which is the thickest part of the shrimp. The data from this study can be used to optimize the energy consumption in shrimp convective drying technologies.

Prediction of moisture transfer parameters for convective drying of shrimp at different pretreatments

Abstract By the analytical model proposed by Dincer and Dost, the mass transfer parameters (moisture transfer coefficient and moisture diffusivity) of shrimp samples were determined. Three sets of drying experiments were performed with three samples of shrimp: without boiling (WB), boiled in salt solution (SB) and boiled in salt solution and subjected to liquid smoking process (SBS). The experiments were performed under controlled conditions of drying air at temperature of 60°C and velocity of 1.5 m/s. Experimental dimensionless moisture content data were used to calculate the drying coefficients and lag factors, which were then incorporated into the analytical model for slab and cylinder shapes. The results showed an adequate fit between the experimental data and the values predicted from the correlation. The boiling is the most recommended pretreatment, because provided a shorter drying time, with high values of moisture transfer coefficient and moisture diffusivity.

Prediction of chloride ingress into blended cement concrete: Evaluation of a combined short-term laboratory-numerical procedure

Chloride-induced corrosion is commonly recognized to be a major cause of deterioration of coastal reinforced concrete structures (CRCS). Therefore, prediction of chloride penetration into concrete is a major concern in durability based design of CRCS. In this study, moisture transfer coefficient (MTC) and chloride diffusion coefficient (CDC) of some concrete specimens were determined by short-term laboratory tests and these parameters are used to numerically predict the chloride profile of the specimens subjected to long-term field tidal exposure. Thus, two series of concrete specimens with a constant water to cementitious materials ratio (w/cm) of 0.40 and different replacement levels of silica fume (SF) and natural zeolite (NZ) were prepared. The first group of the samples was exposed to the tidal condition of natural marine environment of the Qeshm Island, located in the south of Iran, for 50 months after curing in laboratory, while the second group of the samples was prepared for short-term laboratory tests to determine the MTC and CDC. Moreover, a finite element based convection–diffusion model was developed to predict the chloride penetration in the long-term field exposed specimens using short-term laboratory-determined MTC and CDC. The long-term field test results confirmed the feasibility of the proposed combined short-term laboratory-numerical procedure. In addition, the results showed that the chloride concentration decreased in the diffusion zone and increased in the convection zone with increase of SF replacement level of up to 10%. The similar trend was also observed for NZ mixtures with replacement level of up to 20%.

Synthesis and characteristics of composite phase change humidity control materials

A new kind of phase change humidity control material (PCHCM) was prepared by using PCM microcapsules and different hygroscopic porous materials. The PCHCM composite can regulate the indoor hygrothermal environment by absorbing or releasing both heat and moisture. The PCM microcapsules were synthesized with methyl triethoxysilane by the sol–gel method. The vesuvianite, sepiolite and zeolite were used as hygroscopic materials. The scanning electron microscopy (SEM) was used to measure the morphology profiles of the microcapsules and PCHCM. The differential scanning calorimetry (DSC) and the thermal gravimetric analysis (TGA) were used to determine the thermal properties and thermal stability. Both the moisture transfer coefficient and moisture buffer value (MBV) of different PCHCMs were measured by the improved cup method. The DSC results showed that the SiO2 shell can reduce the super-cooling degree of PCM. The super-cooling degrees of microcapsules and PCHCM are lower than that of the pure PCM. The onset temperature of thermal degradation of the microcapsules and PCHCMs is higher than that of pure PCM. Both the moisture transfer coefficient and MBV of PCHCMs are higher than that of the pure hygroscopic materials. The results indicated the PCHCMs have better thermal properties and moisture buffer ability.

Experimental Investigation on Moisture Transfer of Carbon Nanotube Membranes

With the development of society and economy, the contradiction between the increasing demand of indoor air quality and the energy saving policy of building becomes more and more obvious. Therefore, it is very important to introduce efficient energy recovery device in the fresh air system. In recent years, more and more attention has been paid to the membrane based heat exchanger due to its unique advantages. The mass transfer properties of the membrane will directly affect the heat recovery efficiency. Much research has shown that carbon nanotube (CNT) exhibits strong mass transfer capacity in many different fields. Therefore, we apply CNT-based membrane in heat exchanger for energy saving in building. In this paper, a test rig is built to investigate the mass transfer properties of the CNT-based membrane. The research contents are as follows:(1)The moisture transfer characteristics of CNT composite membranes, commercial heat exchanger membranes, commercial CNT membranes are compared;(2)The effect of inlet humidity on the moisture transfer characteristics of CNT membrane is investigated;(3)The effect of the air flow rate on the moisture transfer characteristics is investigated. Results show that the moisture transfer performance of CNT composite membranes is better than that of commercial heat exchanger membranes; The moisture transfer coefficient of CNT does not change significantly with the change of the inlet humidity and the average mass transfer coefficient of CNT is 17×10-3 m/s; The moisture transfer coefficient of the CNT increases with the increase of the air flow rate from 9.7×10-3 m/s to 14.6×10-3 m/s.