Moisture Transfer Characteristics Research Articles

A Novel Numerical Model Considering Unsaturated Soil Properties and Computational Study on Heat and Moisture Transfer Characteristics of Helix Ground Heat Exchanger

Abstract A novel three-dimensional numerical simulation model for the helix ground heat exchanger was proposed in this paper, which takes into account unsaturated soil properties. This model is more suitable for real working conditions. To validate its accuracy, a miniature model heat transfer experimental platform was constructed. Additionally, the study conducted simulation research using three types of soil with significantly different thermal and moisture characteristics. Moreover, the comprehensive thermal conductivity and water diffusion coefficient of these three soil types were determined by relevant literature and experimental tests. The aim was to comprehensively explore the impact of different soil types on the heat and mass transfer of the helix ground heat exchanger. The results indicate that the numerical model developed in this paper accurately captures the heat and mass transfer characteristics of the helix ground heat exchanger to a certain extent. Increasing the comprehensive thermal conductivity and water diffusion coefficient of the soil can significantly enhance the heat exchange capacity of the exchanger. For instance, under sandy loam conditions, the heat exchange capacity is approximately 20.73% higher compared to clay loam conditions. The study also identifies two distinct areas around the helix ground heat exchanger: the severe change region and the soft change region. In the severe change region, there is a notable decrease in soil water content near the exchanger, which inevitably weakens the thermal conductivity of the soil. It is advised to minimize this effect through measures like active water spraying.

Moisture Transfer Characteristics and Microbiological Stability of Fermented Pre-gelatinized Plantain and Soybean Based Complementary Food Flours

The effect of gelatinization and fermentation on the moisture sorption characteristics and microbial stability of complementary foods from unripe plantain fruits and soybean seeds was evaluated. The plantain was heated to obtain 10%, 18%, 23%, 33%, 74% and 100% starch gelatinization. The samples were fermented, dried and ground to flour. Plantain and soybean flour were mixed by material balance to produce 16% protein complementary foods. Moisture sorption isotherms wereinvestigated at 10, 20, 30, and 40 ° C using the gravimetric method. The BET equation was fitted to the experimental sorption data, and the Clausius-Clapeyron equation was used to determine the isosteric heat of sorption. The microbial stability of the gruels was evaluated using the microbial challenge test with Staphylococcus aureus. With better results from fully gelatinized samples, gelatinization and fermentation reduced the hygroscopic properties of the dehydrated products, with the gelatinized fermented samples having the least equilibrium moisture contents, monolayer moisture values, surface area of sorbent, and net isosteric heats of sorption, an indication that these samples could be stored at temperatures as high as 40 ° C with extended shelf life. The microbiological stability of foods was enhanced by fermentation, since microbial growth was suppressed in fermented samples, offering perspectives for microbial stability of the products.

Numerical study on the heat and moisture transfer characteristics of FAM Z01 coated heat exchanger with different direction configuration of air flows

The internal cooling fluid is used to remove adsorption heat and improve dehumidification performance in desiccant coated heat exchangers (DCHEs), and its direction configuration not only has a significant impact on the heat and moisture transfer characteristics, but also sometimes determines the complexity of theoretical analysis. In this study, a simplified two-dimensional numerical model was developed to simulate the heat and moisture transfer within an air-cooling type FAM Z01 DCHE. The proposed model considers the local heat and moisture transfer mechanism and the effect of direction configuration of air flows. A parametric analysis is carried out for cross flow, counter current flow and cocurrent flow DCHEs. Results shows that the numerical model can receive a highly-reliable accuracy. The dehumidification performance indices of three DCHEs exhibit complex variation patterns under various parameters. The counter current flow DCHE demonstrates a better heat and moisture transfer performance compared to cross flow and cocurrent flow DCHEs. It can be found that the maximum relative deviation of dehumidification coefficient of performance DCOP between the cross flow DCHE and the other two DCHE is just 14.1%, indicating a feasible way for simplifying numerical modeling by transforming cross flow DCHE into counter current or cocurrent flow DCHE.

Experimental and numerical study of zonal heat and moisture migration inside artificial ice rinks

Ice rinks feature typical non-uniform indoor environment with evident vertical and horizontal parameter differences. A validated CFD model established based on the on-site measurement is utilized to investigate the indoor environment along with the zonal heat and moisture transfer characteristics in a recreational ice rink. It is demonstrated that there are both cooling and heating demands inside the ice hall due to different control standards for various functional regions. Zonal mixing induces a large amount of additional load with 53.5% of the heat brought by the dehumidifiers eventually flowing into the ice sheet and carried away by the refrigeration system. The ice sheet cooperates with the dehumidifiers to dislodge the indoor moisture gain. The importance of proper design of ventilation systems and adequate physical separation is emphasized. Zonal migration coefficients are proposed, and the variation range influenced by different factors are investigated. The migration coefficients between the near-ice zone and the occupied ice field are around 4 W/(m2·K) and 5 g/(s·m2), and those between the occupied and unoccupied ice field are around 14 W/(m2·K) and 18 g/(s·m2). The findings provide a simplified calculation method for regional heat and moisture flow, and are beneficial for the optimization of system design and energy conservation in ice rinks.

Moisture Transfer Characteristics in Silicone Oil–Silicone Rubber Insulation System Considering Swelling Effect

Moisture Transfer Characteristics in Silicone Oil–Silicone Rubber Insulation System Considering Swelling Effect

Numerical simulation of heat and moisture transfer in protective clothing under high pressure steam exposure: Effect of fabric properties and steam conditions

Steam disasters often exist during applied thermal engineering. Steam protective clothing plays a crucial role in safeguarding workers in various industries such as navy, petrochemicals, and others, by protecting them from steam hazards and ensuring their health and safety. This study aims to develop a numerical model that accurately simulates the heat and moisture transfer characteristics of thermal protective fabrics when exposed to steam. Subsequently, the integration of skin bio-heat transfer and burn integral models with the steam heat transfer model was performed to provide predictions of skin burns. In addition, the heat transfer mechanism of steam through fabrics to skin and the factors affecting the steam protection of fabrics were also analyzed by parametric studies. The accuracy of model simulation was verified by steam exposure tests with difference of second and third degree burn time less than 0.4s. The findings demonstrated the significant influence of moisture transfer and basic fabric properties on the steam protective performance. Among them, fabric thickness, specific heat and initial moisture content of fabrics have obvious influence. The influence of fabric's moisture regain is slightly smaller, and the impact of thermal conductivity is the least. The steam temperature also shows great effect, but the velocity of steam flow has little effect. This work provides theoretical guidance for the research and development of high performance protective materials and clothing from steam hazards. It is helpful for the virtual design and performance evaluation of steam protective clothing.

The Numerical Study on Indoor Heat and Moisture Transfer Characteristics of an Ancient Palace Building in Beijing

The heritage of ancient buildings is an important part of the world’s history and culture, which has extremely rich historical–cultural value and artistic research value. Beijing has a large number of ancient palace buildings, and because of the age of their construction, many of them have problems with varying degrees of peeling and molding on the inner surfaces of the envelope. To solve the problems of damp interiors of palace buildings, a mathematical model of indoor heat and moisture transfer was established based on an ancient wooden palace building in Beijing. The model was validated by fitting the measured and simulated data. And the effects of outdoor relative humidity, soil moisture, wall moisture, and other factors on indoor heat and moisture transfer of ancient buildings were simulated and analyzed via the control variables method. The results showed that the measured and simulated data are within the error range, which verifies the accuracy of the model. And the simulation of indoor humidity matched the measured humidity. Thus, the simulation results were consistent with the actual situation. The variable trend of the relative humidity of the indoor environment with the outdoor humidity is inconsistent from plane to plane, i.e., it increases or remains constant with the increase in the outdoor humidity. Indoor ambient relative humidity increased with increasing wall moisture. And the indoor average temperature is 24.5 °C, and indoor relative humidity ranged between 87.4% and 92.4%. Soil moisture and wall moisture were the main factors affecting indoor relative humidity.

Computational modeling of spatial variation in moisture content and temperature distribution in corn at different superheated steam temperatures

The Superheated steam has been shown to be more effective than hot air for drying corn. Modeling studies have been carried out in fluidized bed dryers to determine the moisture and heat transfer characteristics of corn, but there are no modeling studies for a single corn kernel. Knowledge of heat and mass transfer characteristics in a single kernel would produce a better understanding of steam characteristics needed for specific drying rates. The study sought to determine the influence of steam temperature and velocity on the drying rate of a corn kernel. It used computational fluid dynamics (CFD) to model the transfer of heat and moisture between the corn kernel and superheated steam. The simulation used cone geometry to represent the corn kernel. The kernel had characteristic dimensions and 20% initial moisture content. The condition of the steam, which was typical of that found in industry, had temperatures of 120–200°C and velocities of 0.5–1.5 m/s. There was a decrease in the duration of the initial condensation phase as the temperature of superheated steam increased from 120°C to 200°C. The highest steam temperature and velocity resulted in the shortest duration for steam condensation. Contrary to what has been reported, there was no moisture loss from the corn kernel when exposed to superheated steam at 120°C, which may be due to how heat was retained in the drying chamber. Thus, the processes of tapping steam and retaining heat are important elements in the operation of industrial steam driers.

Study on heat and moisture transfer characteristics of HPCMs

Phase change materials (PCMs) could be used in envelopes to moderate indoor temperature while hygroscopic materials could be used in envelopes to moderate indoor humidity. However, it remains unsolved whether these two materials are mixed to generate a better effect than single materials. Therefore, a transient model for coupled heat and moisture transfer through hygroscopic PCMs (HPCMs) was presented. The numerical cases of periodic boundary conditions and realistic weather conditions were conducted to investigate the heat and moisture transfer characteristics of three gypsum-based HPCMs containing different mass ratios of microencapsulated PCMs. Quantitative analyses were conducted to capture the effects of hygrothermal properties on heat and moisture transfer characteristics of HPCMs. The numerical results show that the mixing of PCMs and hygroscopic materials could generate a better temperature-humidity controlling effect than pure hygroscopic material, and the condensation risks inside the envelopes could also be reduced. Both the studied cases indicate that the HPCMs could be applied in building envelopes to passively moderate the indoor temperature and humidity simultaneously, reducing the building energy consumption and condensation risks inside the envelopes. The effects of hygroscopic and moisture transfer properties on temperature-control performance of HPCMs are relatively small, while the thermal properties play an important role in the improvement of temperature-humidity controlling performance of HPCMs with the increase of PCM concentration.

A Darcy-Law Based Model for Heat and Moisture Transfer in a Hill Cave

A hill can be regarded as an environmental carrier of heat. Water, rocks and the internal moisture naturally present in such environment constitute a natural heat accumulator. In the present study, the heat and moisture transfer characteristics in a representative hill cave have been simulated via a method relying on the Darcy’s law. The simulations have been conducted for both steady and unsteady conditions to discern the influence of permeability and geometric parameters on the thermal and moisture transfer processes. The reliability of the simulation has been verified through comparison of the numerical results with the annual observation data. As revealed by the numerical findings, the internal temperature of the hill accumulator is proportional to the permeability, outside surface temperature, overground height, underground constant temperature layer depth, and underground temperature of the hill, and it is inversely proportional to the horizontal size of the hill. Moreover, in the considered case, the order of magnitude of the permeability of the hill is contained in the range 10⁻¹⁵–10⁻¹³, and displays a certain sensitivity to the rainwater seepage.

Liquid desiccant-based deep dehumidifier working with a novel ionic liquid: Prediction model and performance comparison

Deep dehumidification system with energy conservation and stable operation is expected to be used in industrial occasions with low-humidity environment. Compared with solid desiccant dehumidification, liquid desiccant-based dehumidification is a promising alternative because of its advantages of continuous operation and low regeneration temperature. However, corrosion and crystallization problems exist with liquid desiccant-based deep dehumidifier (LDDD) using salt solutions. In this work, LDDD using a novel ionic liquid (IL) was introduced, and the heat and moisture transfer model was established based on the finite difference method. Meanwhile, the moisture transfer characteristics were numerically simulated under different operating parameters (i.e., inlet humidity ratio wa,in, air velocity va, solution mass concentration X, solution temperature ts and solution volume flow Vs). Besides, the significance of various factors and their interactions were analyzed based on response surface methodology. The numerical model is validated against the experiment of the LDDD test bench with a relative deviation of 3%-8%. Numerical results show that the LDDD using IL can achieve deep air dehumidification, and outlet humidity ratio of less than 4 g/kgda is possible. In particular, the order of significance for influencing factors of outlet humidity ratio is: wa,in > X > ts > va > Vs. Moreover, it is found that dehumidification rate of 60% LiBr solution (saturated state) is less than that of 90% IL. This study establishes a prediction model of moisture transfer between IL and air under the coupling of multiple physical fields, and provides guidance for the application of LDDD using ILs.

Moisture Transfer Characteristics and Kinetics Determination for Insulated Paperboard in Hot-Pressing Process

The transport characteristics and kinetics of moisture in hot-pressing are crucial to controlling the insulated paperboard drying process. The effects of operating temperature (110, 120, and 130 °C) on moisture transfer characteristics of an insulated paperboard were investigated. The results showed that the hot-pressing process consists of four successive stages, i.e., the warm-up stage, the boiling-point temperature stabilization stage, the temperature slowly rising stage, and the constant temperature stage. It was observed that a higher temperature mainly affected the medium and later stages of the hot-pressing process. When the operating temperature increased from 110 to 130 °C, the maximum value of the drying rate increased by 16.04%, and the drying time decreased by 62.50% consequently. Furthermore, a new mathematical model used to describe the moisture transfer kinetics for the insulated paperboard hot-pressing was developed in this paper. The results from the proposed new model were evaluated with another eight commonly used models. It showed better predictions and satisfactorily described the moisture transfer kinetics of the insulated paperboard compared with other models under the investigated hot-pressing conditions. The values of R2, χ2, and root mean square error (RMSE) of the new model varied from 0.99961 to 0.99999, 0.00001 to 0.00005, and 0.00120 to 0.00599, respectively.

Study on the heat and moisture transfer characteristics of aerogel-enhanced foam concrete precast wall panels and the influence of building energy consumption

The novel building materials continue to emerge, but there is not enough research on their performance. To explore the hygrothermal characteristics of the aerogel-enhanced foam precast concrete wall panels, a mathematical model was established and verified by experiments. The heat and moisture transfer performance parameters were tested by experiments, and the functional relations of related parameters have been fitted. Two typical cities in China, Shanghai in hot summer and cold winter area (HSCW) and Beijing in cold area (CA) were taken as examples. The hygrothermal characteristics of wall panels were numerically calculated for 5 years. The results show that the internal temperature and humidity of the wall panels in the two regions showed irregular periodic changes. The heating and cooling loads of the wall panel were calculated by the coupled heat and moisture transfer model and heat transfer model, respectively. Under the conditions of considering the eastward solar radiation and ignoring the radiation, the comparison of the results of the same model shows that the cooling load deviation in Shanghai is more than 55%, while the deviation in Beijing is as high as 62.4%. While the maximum deviation of the heating load between the two areas is only about 9.5%. Secondly, the results of the two models under the same working conditions are compared, and the maximum deviation of the cooling load in the two areas is only 11.2%. The maximum heating load deviation is only 4.1%, and the minimum is 1.34%. In addition, the impact of solar radiation on the cooling load in two climate zones far exceeds the heating load, and it has a greater impact on Shanghai.

An exploration on the performance of using phase change humidity control material wallboards in office buildings

In this study, a composite double-layer wallboard with shape-stabilized phase change humidity control materials (PCHCM) has been proposed for building usage. This novel PCHCM can absorb/release both heat and moisture to moderate indoor hygrothermal environment. Based on a numerical analysis in an office building in Wuhan (30.52°N, 114.32°E), China, the effects of PCHCM on both building energy consumption and indoor hygrothermal environment has been investigated. Firstly, a simulation model has been developed for the building integrated with PCHCM wallboards in EnergyPlus, combining both heat and moisture transfer finite solution algorithms. After a validation of the model, both heat and moisture transfer characteristics of the proposed composite wallboards were simulated, and its effects on indoor temperature, humidity and building energy consumption were analyzed. The simulation results showed that this novel PCHCM wallboard can effectively improve indoor hygrothermal environment, with reduced energy consumption by about 8.3% in summer and 24.9% in winter, comparing to the actually used materials in the case study building.

Characteristics of Moisture Transfer and Surface Crack Development of a Single Lignite Particle Driven by Humidity Difference.

The research on moisture transfer characteristics and surface crack development of a single lignite particle (SLP) driven by humidity difference is helpful to achieve a better understanding of the fragmentation characteristics of lignite during the moisture transfer process. This is of great significance to the safe operation of a drying system. The characteristics of moisture transfer within SLP driven by humidity difference were studied in different stages. Six drying equations commonly used in the literature were selected to describe the moisture transfer behavior. The apparent diffusion coefficient (Deff) of moisture in each stage was calculated to compare the driving forces of moisture transfer in different stages. The surface crack rate (CR) was used to quantitatively analyze the fragmentation characteristics of SLP caused by moisture transfer. The results showed that the moisture transfer process of SLP driven by humidity difference can be divided into three stages, and stage I is the main moisture removal stage. The larger the particle size, the longer the stage I, while less moisture is removed in this stage. A logarithmic drying equation best simulates the moisture transfer process of SLP. The larger the particle size, the larger the Deff value in each stage. The driving force of moisture transfer in stage I is the largest, which is the opposite of a thermal drying process. CR for SLP has experienced a rapid increase – stable at the highest value – rapid decrease – stable during the moisture transfer process driven by the humidity difference.

APPLICABILITY OF VECTOR AUTOREGRESSIVE MODEL TO ESTIMATION OF INTERNAL MOISTURE CONDITION OF CONCRETE EXPOSED TO ORDINARY NATURAL ENVIRONMENT

To investigate the applicability of VAR-X model to estimating moisture condition of concrete exposed to ordinary natural environment, concrete internal humidity data reported previously were analyzed with weather data from Japan Meteorological Agency. The first 90 days were used for parameter estimation and the second 60 days were used to validate the model and predicted values. The results are summarized below. (1) Within the scope of this study, VAR-X model was applicable to the humidity data in the non-rainfall environment. VAR-X model was also able to predict the internal humidity for 60 days based on the estimated parameters and weather data (temperature and humidity), and the RMSE ranged from 0.87 to 2.04%. (2) It was judged that the VAR-X model was not appropriate to be applied to the humidity data of rainfall environment. The main reason for this is that the impact of rainfall was underestimated by assuming constant coefficients in the model. (3) The mechanisms of humidity fluctuation in concrete are discussed, which include the absorption and release of water and the temperature dependence of concrete water content. Based on the mechanism, difference between rainfall and non-rainfall environment was pointed out and the conditions under which the VAR-X model can be applied are discussed. (4) Methods of utilization and improvement of VAR-X model were discussed for cases where the moisture transfer characteristics of concrete changed and where the data increased or decreased in high humidity region. The advantages of time series analysis, including VAR-X model, were also pointed out in comparison with conventional physical models. VAR-X model can predict humidity fluctuations in concrete using weather data when certain conditions are met. In the future study, the model will be modified and its application to the durability evaluation of various materials will be investigated.

An Exploration on the Performance of Using Phase Change Humidity Control Material Wallboards in Office Buildings

In this study, a composite double-layer wallboard with shape-stabilized phase change humidity control materials (PCHCM) has been proposed for building usage. This novel PCHCM can absorb/release both heat and moisture to moderate indoor hygrothermal environment. Based on a numerical analysis in an office building in Wuhan (30.52°N, 114.32°E), China, the effects of PCHCM on both building energy consumption and indoor hygrothermal environment has been investigated. Firstly, a simulation model has been developed for the building integrated with PCHCM wallboards in EnergyPlus, combining both heat and moisture transfer finite solution algorithms. After a validation of the model, both heat and moisture transfer characteristics of the proposed composite wallboards were simulated, and its effects on indoor temperature, humidity and building energy consumption were analyzed. The simulation results showed that this novel PCHCM wallboard can effectively improve indoor hygrothermal environment, with reduced energy consumption by about 8.3% in summer and 24.9% in winter, comparing to the actually used materials in the case study building.

Study of Humidity on Moisture Transfer Characteristics in Iron Ore Sintering

The cold permeability of a sinter bed is a complex function of the granules’ effective mean diameter and bed moisture. The binding force provided by moisture before fusion commences crucial in determining the strength of a sinter. However, excess moisture is detrimental to the propagation of the heat front, because it reduces the bed’s permeability. The source of moisture can be either the inherent moisture in the bed or from the incoming gases due to suction in the bottom of the bed. An unsteady-state mathematical model was developed in the current study to describe the moisture transport phenomena during the iron ore sintering. The model was then validated using experimental data from laboratory sintering pot tests. Using the help of the model, the effect of humidity on the moisture characteristics was then investigated. The temperature profiles revealed that the change in the solid temperatures was less than 5% with increasing humid conditions.

Moisture Sorption Characteristics as Influenced by Application of Hurdles in Dambu-nama Production

Moisture transfer characteristics of dambu-nama (DN) as influenced by addition of citric acid, salt and sugar as hurdles were investigated. Four products comprising DN with 0.1% citric acid + 2% salt and 2% sugar (DNC0.1); DN+ 0.2% citric + 2% salt + 2% sugar (DNC0.2); DN + 0.3% citric acid +2% salt + 2% sugar (DNC0.3) and a control DN without citric acid , salt or sugar (DNC0) were produced and subjected to moisture sorption studies at different temperatures (30, 40, 50 and 60oC) and relative humidities of(10-96%). Incorporation of the hurdles into dambu-nama resulted in increase in monolayer moisture contents, surface areas, net isoteric heats and entropy of sorption. The isotherms obtained were best described by the Henderson model followed by the GAB and Oswin models. The hurdles also resulted to a J-shaped isotherm instead of the sigmoidal isotherm shape.

Heat and mass transfer in refrigerated container used for tomatoes' transportation—Numerical and laboratory investigation

AbstractTo preserve vegetables fresh during long‐distance transportation, it is essential to study the heat and mass transfer characteristics inside refrigerated containers with vegetables for preventing vegetables from spoiling and withered. Based on a mechanical refrigerated container filled up with tomatoes, a 3‐D turbulence numerical model considering the heat and mass transfer characteristics of tomatoes was built in this paper. Then the dynamic temperature field, humidity field and water dissipation inside the container were calculated by the new built model for three different stacking methods. In addition, the numerical model was verified through laboratory investigation. The results indicate that in the steady state, the temperature field in the tomato storage area is higher and more layered than the surrounding environment area. The relative humidity in the container falls sharply in the initial period and then gradually increases and stabilizes in the end. When the container's loading rate is constant, compared with dense stacking method, the stacking method with 100 mm interval has a better effect for refrigerated transport. The temperature in the tomato storage area is lower, the relative humidity is higher, and the water dissipation of the tomatoes is less than the dense stacking method.Practical ApplicationsA 3‐D turbulence numerical model considering the heat and mass transfer characteristics of tomatoes was built to investigate the heat and mass transfer characteristics inside refrigerated containers. The difference between the numerical results calculated with the new built model and the experimental results do not exceed 2%, which is less than the 5% error limit in engineering, indicating that the numerical model established in this paper can effectively reflect the heat and moisture transfer characteristics inside mechanical refrigerated container filled with tomatoes. It can provide theoretical guidance for the optimized design of cargo stacking method in refrigerated containers. What's more, the 3‐D turbulence numerical model has important guiding significance for the study of the temperature and humidity distribution inside mechanical refrigerated container, which can guide the optimal design of the container.