Moisture Evaporation Rate Research Articles

Numerical Study on the Variable-Temperature Drying and Rehydration of Shiitake

Variable-temperature convective drying (VTCD) is a promising technology for obtaining high-quality dried mushrooms, particularly when considering rehydration capacity. However, accurate numerical models for variable-temperature convective drying and rehydration of shiitake mushrooms are lacking. This study addresses this gap by employing a model with thermo–hydro and mechanical bidirectional coupling to investigate five dehydration characteristics (moisture ratio, drying rate, temperature, evaporation rate, and volume shrinkage ratio) and a drying load characteristic (enthalpy difference) during VTCD. Additionally, a mathematical model combining drying and rehydration is proposed to analyze the effect of VTCD processes on the rehydration performance of shiitake mushrooms. The results demonstrate that, compared to constant-temperature drying, VTCD-dried mushrooms exhibit moderate shrinkage rates and drying time (16.89 h), along with reduced temperature variation and evaporation rate gradient (Max. 1.50 mol/(m3·s)). VTCD also improves enthalpy stability, reducing the maximum drying load by 58.84% compared to 338.15 K constant-temperature drying. Furthermore, drying time at medium temperatures (318.15–328.15 K) greatly influences rehydration performance. This study quantitatively highlights the superiority of variable-temperature convective drying, offering valuable insights for optimizing the shiitake mushroom drying processes.

Field investigation of soil moisture profile in the seedbeds of clayey paddy fields composed of large clods (aggregates)

ABSTRACT Unstable germination and emergence of upland crops in clayey paddy fields is a pressing issue. As tillage leads to the formation of large clods measuring a few centimeters, the soil moisture content in the seedbed markedly decreases, potentially inhibiting germination of seeds. Although the effect of the clod size on the soil moisture profile was confirmed experimentally, the validity of this effect has not been tested in the field. In this study, we aimed to clarify the effect of clod size on the moisture profile and water balance in the seedbeds of clayey paddy field. We developed an apparatus for measuring soil moisture content in the soil layer with clods. This apparatus used a laser displacement sensor and large transparent plate horizontally fixed above the soil surface. Temporal changes in the soil moisture profile (0–10 cm depth) and evaporation rate of clayey paddy fields with different clod sizes were monitored during the sowing period of soybeans. We found that the larger the mean clod diameter (MCD), the greater the decrease in soil moisture content near the soil surface. In addition, soil moisture loss at the sowing depth (5 cm) was positively correlated with MCD. In terms of the water balance, the estimated upward water flux at a depth of 5 cm was less than 1 mm d−1 across all the plots and periods. By contrast, the estimated ratio of the apparent to molecular diffusion coefficient of water vapor in the dry soil layer of clayey paddy field with an MCD of 2.5 and 1.8 cm were 5.1 and 2.0, respectively. These results suggest that more significant soil moisture loss causing reduction of germination and emergence rate can occur in a clayey paddy field with large clods, likely owing to the increased enhancement of water vapor movement. To increase the germination and emergence rate, therefore, a numerical model that can evaluate the moisture profile of soil layer with clods should be developed and the sowing depth should be optimized based on the MCD.

Kinetic analysis and calculation correction methods for moisture evaporation rate in pine lignocellulosic biomass

This study investigates the kinetics of moisture evaporation in pine wood during the drying stage, focusing on analyzing thermogravimetric (TG) curves. The research is based on the kinetic rate model and TG curves obtained at various heating rates, specifically 5, 10, 15, and 20 K/min for the heat release rate, within a temperature range from room temperature to 473 K. Utilizing thermogravimetric experiments and the kinetic rate model, the apparent activation energy and pre-exponential factor are calculated. Further refinement of these calculations is achieved using the Nelder-Mead algorithm. The results show good agreement between the average values of the apparent activation energy (37.88 kJ/mol) and pre-exponential factor (4458.20 s−1) and experimental measurements in the initial and later drying stages, with discrepancies noted in the middle stage. Establishing a relationship between the correction coefficients of these parameters and the heating rate leads to a reduction in calculation errors. Notably, the pre-exponential factor is found to be influenced by heating rates, while the apparent activation energy remains relatively stable. Moreover, the errors are significantly reduced after correction, and the error curve of 10 K/min is the most significant. Overall, the proposed correction method holds promise for accurately calculating moisture evaporation rates in lignocellulosic biomass, offering valuable insights for biomass drying applications.

Integrated simulation method construction and process optimization for hot air drying of shiitake mushrooms

Currently, numerical simulations are conducted at the level of dryers without considering the actual moisture evaporation within agricultural materials. This departure from reality fails to meet the requirements of actual industrial production. To address this issue, this paper proposes a drying kinetic derivative model based on experiments conducted on shiitake mushrooms' drying kinetics. With the help of this model, we can determine the moisture evaporation rate under varying drying conditions. Based on the evaporation rate, a material-dryer integrated simulation method is developed to achieve coupling between the material and the dryer. Finally, the simulation method is used to investigate the non-uniform distribution of the moisture ratio of shiitake mushrooms in the dryer, optimize the inlet parameters of the dryer, and improve its internal structure. Through optimization, it was determined that the optimal angle for the baffle is 45° with a width of 65 mm, which can reduce the unevenness of moisture content by 25.84% and decrease the total drying time by 0.59 h. This research not only contributes to the thorough analysis of the distribution of various physical fields within the dryer, optimization of drying conditions, and structural parameters of the dryer but also offers valuable reference for studying and optimizing the drying industrial conditions of other materials. This research holds significant implications for the industrial advancement of the drying sector.

Can machine learning models predict soil moisture evaporation rates? An investigation via novel feature selection techniques and model comparisons

Can machine learning models predict soil moisture evaporation rates? An investigation via novel feature selection techniques and model comparisons

Effects of Process Conditions on Drying of Tomato Pomace in a Novel Daylight Simulated Photovoltaic-Assisted Drying System

The tomato pomace (TP), which is a by-product of the production of tomato paste, was dried in a novel custom-designed daylight simulated photovoltaic assisted dryer (DPVD). The different light applications (daylight, UV light, daylight + UV light, and without light), different air velocities (1.5 and 2 m/s), and different heating source modes (hot air and infrared) were applied to dry TP having a moisture content of 80.60 ± 0.73% to the moisture content of 7.66 ± 1.72%. The average water activity values of all dried samples were measured as 0.52 ± 0.08. Analysis was conducted to compare sun drying with the effects of process conditions on the quality (color properties, lycopene, β-carotene, and total mesophilic aerobic bacteria count) and performance (energy efficiency, exergy efficiency, specific moisture evaporation rate, and improvement potential) characteristics of TP. The effects of process conditions for each heating source mode were determined separately, and the improvement of the system performance for each mode was investigated. The effect of the process conditions on total aerobic mesophilic bacteria (TAMB) count was similar in general. In the infrared heating mode, the loss in lycopene and β-carotene contents was 59.55 ± 2.22 and 57.87 ± 2.51 minimum for 1.5 m/s air velocity without light application and for 2 m/s with ultraviolet + daylight application. In general, the performance of the system decreased in case of using ultraviolet light. The retention in the lycopene and β-carotene contents was higher in the infrared mode with light applications compared to hot air mode without light. The optimum drying conditions were air velocity of 2 m/s with “daylight” assistance in the hot air heating mode and with “ultraviolet + daylight” assistance in the infrared heating mode. All the energy and the daylight source used in drying applications were obtained from the sun, a renewable energy source, thanks to the photovoltaic panel and the solar tube units in the novel custom-designed drying system.

Analysis of drying characteristic, effective moisture diffusivity and energy, exergy and environment performance indicators during thin layer drying of tea in a convective-hot air dryer

The objective of this study is mainly to analyze the drying kinetic parameters, effective diffusivity, and thermodynamic performance indicators (energy, exergy, heat, and mass transfer coefficients) of tea under different drying conditions of different drying temperatures (DT) and thin layer thicknesses (TT). Experimental drying was conducted at drying temperatures of 70°C, 80°C, and 90°C with thin layer thicknesses of 10 mm, 15 mm, and 20 mm. The results show that a higher drying temperature and a lower thin layer thickness can increase evaporation moisture content and shorten drying time. By evaluating and comparing the fitting of five drying models adopted by the coefficient of determination (R2) and chi-square (χ2), it can be found that the logarithmic model is the best to describe drying behavior. The effective moisture diffusivity shows a positively correlated trend with the increase in DT and TT, with the value of activation energy ranging from 14.030 to 22.344 kJ mol−1 K−1. The specific moisture evaporation rate (SMER), energy efficiency, exergy efficiency, and sustainability index (SI) descend as the TT increases at all DT; the specific energy consumption (SEC) and improvement potential (IP) rate perform in an opposite manner, but the TT remains unchange. The conclusion drawn from the thermodynamic parameters is opposite to the aforementioned. As the TT increases, the heat and mass transfer coefficients show a significant decrease trend. In addition, the heat and mass transfer coefficients are given as functions of DT and TT, and further knowledge shows that the mass transfer coefficient is positively correlated with DT but the heat transfer coefficient is negatively correlated. In conclusion, this article provides new insights into the effects of drying characteristics, energy consumption characteristics and heat and mass transfer characteristics in the process of tea drying under different drying conditions, and provides certain theoretical reference bases for promoting the optimization of industrialized tea drying production machinery design and drying process optimization.

Composite hydrogels fabricated from konjac glucomannan and gellan gum: Rheological characterization and their potential application in sustainable agriculture

In this study, konjac glucomannan (KG) was incorporated in high acyl gellan (HAG) and low acyl gellan (LAG) hydrogels in different ratios. The addition of KG increased pseudoplasticity and thermal hysteresis values of the hydrogels. Improvement in elasticity and water holding capacity (WHC) was observed in KG-LAG hydrogels. The highest WHC (98.5 %) was observed for 1K1H (KG:HAG = 1:1) and 3K7L (KG:LAG = 3:7) hydrogels. The crystallinity of the composite hydrogels was lower than hydrogels prepared from individual biopolymers. The hydrogels exhibited a rough surface with minute pores in the cross-section, due to the aggregation of glucomannan on the gellan network in the composite hydrogels. While HAG and 1K1H hydrogels exhibited greater swelling at low pH (3.0), LAG and 3K7L exhibited greater swelling at high pH (11.0). At pH 7.0, the hydrogels exhibited swelling indices >300 %. Incorporation of 1K1H hydrogel at 10 % (w/w) in sandy loamy soil under semi-arid conditions increased the germination of fenugreek microgreens from 60 % to 80 % on the 15th day. Furthermore, the moisture evaporation rate of the soil reduced from 35 % to <15 %, positively impacting the physicochemical properties of the microgreens. The composite hydrogels were successful in achieving a controlled release of phosphate fertilizer.

Drying kinetics and mathematical modeling of seeds of two mango varieties at different temperatures and with different pretreatments

AbstractIncreasing global waste generation is not only a threat but also an opportunity to address energy insecurity and pollution using green valorization techniques. However, this requires pretreatment of waste and byproducts and optimization of drying to obtain high‐quality biofuels. Hence, this study aims to analyze the performance of currently used drying models, the influence of different drying temperatures, drying time, and seed pretreatment on the drying kinetics of two varieties of mango seed. Accordingly, whole seeds and crushed seeds were exposed to five drying temperatures (313–353 K) in a heating furnace. Weight loss was recorded systematically, converted into moisture ratio, and then fitted to four semitheoretical mathematical models, namely: (i) Lewis, (ii) Henderson and Pabis, (iii) Page, and (iv) Avhad and Marchetti models. The fitness of these models was compared using statistical parameters, such as R2, X2, root mean square error (RMSE), mean bias error (MBE), and mean absolute error (MAE). The results showed that seed pretreatment and increasing the drying temperature led to an increase in the rate of moisture evaporation and reduced the time required for drying. Among all models, the Avhad and Marchetti model provided higher R2 values of 0.9994 and 0.9991 for local and hybrid mango at 313 K, and 0.9977, and 0.9970 for local and hybrid crushed mango seeds at 353 K and 313 K, respectively; hence, it showed the best performance. The activation energy (Ea) showed a slight differences for both varieties of mango seed and among pretreatments in all mathematical models. The mean Ea values for local and hybrid mango seeds were 41.18 kJ mol−1 and 46.21 kJ mol−1, respectively. For whole and crushed local and hybrid mango varieties, the mean Ea values were 31.37 kJ mol−1, 40.80 kJ mol−1, 50.99 kJ mol−1, and 51.61 kJ mol−1. The likely reason for this variation might be differences in variety, chemical composition, growing conditions, and cellular structure of the seed varieties.

Influence of main operating parameters on the incineration characteristics of municipal solid waste (MSW)

To study the influence of the main operating parameters on the incineration characteristics of municipal solid waste (MSW), a 375 t/d mechanical grate incinerator is selected as the research object, and the effects of primary air temperature, secondary air arrangement, and grate speed on the MSW incineration process are simulated, and experimental tests are carried out under different primary air temperature and grate speed conditions. The results show that the relative errors between the measured and simulated values of the incinerator outlet O2 content and the measurement point temperature are within ±5% for all test conditions. When the primary air temperature increases from 423 K to 503 K, the position where the MSW incineration ends moves 3.32 m towards the front of the grate, and the moisture evaporation and fixed carbon combustion rates also increase, but the maximum volatile release rate and the optimal incineration condition of the MSW occur at the primary air temperature of 483 K. The increase in grate speed delays the incineration process of MSW and decreases the moisture evaporation rate and fixed carbon combustion rate, but it worsens the incineration effect of MSW. When the grate speed increases from 6.94 m/h to 13.88 m/h, the MSW incineration process is delayed by 3.20 m, and the moisture evaporation and fixed carbon combustion rates decrease by 43 kg·m−2·h−1 and 9 kg·m−2·h−1, respectively. To achieve the optimal operating conditions, the secondary air volume ratio of the front and rear arches is 1.59:1, the secondary air direction of the front arch is 40° and 60°, and that of the rear arch is 0° for the primary air temperature of 463 K and 483 K, respectively. This study can provide useful insights for optimizing the design and operation of mechanical grate incinerators.

Early-age inhomogeneous deformation of 3D printed concrete: Characteristics and influences of superplasticizer and water-binder ratio

3D printed concrete (3DPC) commonly experiences significant shrinkage along the printing direction (x-direction) at the early-age for its high cementitious material content, low water-binder ratio and formwork-free manufacturing process. This shrinkage with gradient along the vertical direction (z-direction) can cause interlayer slippage and further deformation within each filament. To investigate these early-age deformations and their dependence on materials, digital image correlation (DIC) was used to monitor the inhomogeneous deformation of 3DPC at the age of 0.5–6.5 h. It was found x-direction inhomogeneous shrinkage pattern is correlated with early-age hydration process and elastic modulus. After conducting mechanic analysis, it was found that an individual filament could be treated as a Winkler foundation beam with frictional moment, which can provide a semi-quantitative explanation of the phenomenon that the bottom filament shows significant downward deflection, while other layers show minimal upward deflection or almost no deflection. Additionally, the influence of superplasticizer and water-binder ratio on early-age inhomogeneous deformation was monitored. There exists an optimal dosage range for superplasticizer that ensures both better printing quality and lower x-direction shrinkage, shrinkage gradient as well as bottom layer deflection. With the same printing quality, early-age shrinkage, shrinkage gradient and the bottom layer deflection were reduced by adopting higher water-binder ratio. The influence of materials on the moisture evaporation rate and early-age strength was also measured and correlated with early-age x-direction shrinkage, shrinkage gradient of 3DPC and the extent of early-age bottom layer deflection.

Effects of microplastic contamination on the hydraulic, water retention, and desiccation crack properties of a natural clay exposed to leachate

Microplastic (MP) can significantly affect soil behaviour and the ecosystem. This paper presents an experimental study to investigate the effects of MP contamination and leachate exposure on the desiccation cracks, hydraulic conductivity, and water retention properties of the natural black clay. The leachate was from a landfill in Australia. The black clay was incorporated with up to 2.0% MPs by weight (w/w) with diverse dimensions and mixed with water/leachate. The measured properties include saturated hydraulic conductivity (ksat), soil-water characteristic curves, moisture evaporation rates, and crack intensity factors. The results suggest that the inclusion of MPs significantly increases ksat, and this increase is more obvious for soils with larger dimensions and contents of MPs, e.g., ksat of the black clay with 2.0% of 500 μm MP increases significantly by 206% (p < 0.05). The black clay exposed to leachate exhibits a slight increase in ksat due to the low viscosity of leachate. The existence of MPs decreases the residual moisture contents and air-entry pressures, and so does the water retention capacity (v/v %) of the black clay. The exposure to leachate increases the air-entry pressures by 6.0%–15.8% of the clay. The evaporation rates increase with the dimensions and concentrations of MPs. The highest evaporation rate (0.96 g/h) can be observed in samples exposed to 2.0% 500 μm MP with water addition. For all samples, the crack intensity factors increase when MP content is between 0.2% and 1.0% and decreases slightly after that. After being exposed to leachate, the evaporation rates and crack intensity factors of the black clay are decreased by 2.4%–12.6% and 3.6%–13.7%, respectively.

Development of an empirical correlation to predict the effectiveness of heat and mass transfer from textiles in a rotating drum

The clothes dryer is one of the most energy-consuming household appliances. Modeling the rotating drum within clothes dryers presents significant challenges due to the concurrent heat and mass transfer between the air and textiles, exacerbated by the random motion of textiles within the drum. To address the intricacies of drum modeling, many researchers have traditionally assumed a constant value for the area-mass transfer coefficient, neglecting its dependence on operational parameters. This study proposes a novel dimensionless correlation for predicting the moisture evaporation rate, based on the concept of heat and mass transfer effectiveness. To develop the correlation, we conducted an extensive series of 36 experiments, taking into account various factors such as textile type, textile size, textile mass, drum size, rotational speed of the drum, air temperature, relative humidity, airflow rate, and moisture content. The new correlation with previous ones were compared using ten sets of independent experimental data. The average absolute deviation of the present correlation was found to be 11.63 %, while Gluesenkamp et al.'s correlation exhibited a deviation of 5970.8 %, and Novak et al.'s correlation showed a deviation of 62.90 %. Newly proposed correlation demonstrates superior agreement with the independent data sets when compared to other empirical correlations.

Assessment of Growth, Yield, and Nutrient Uptake of Mediterranean Tomato Landraces in Response to Salinity Stress.

Salinity is a major stress factor that compromises vegetable production in semi-arid climates such as the Mediterranean. The accumulation of salts in the soil can be attributed to limited water availability, which can be exacerbated by changes in rainfall patterns and rising temperatures. These factors can alter soil moisture levels and evaporation rates, ultimately leading to an increase in soil salinity, and, concomitantly, the extent to which crop yield is affected by salinity stress is considered cultivar-dependent. In contrast to tomato hybrids, tomato landraces often exhibit greater genetic diversity and resilience to environmental stresses, constituting valuable resources for breeding programs seeking to introduce new tolerance mechanisms. Therefore, in the present study, we investigated the effects of mild salinity stress on the growth, yield, and nutritional status of sixteen Mediterranean tomato landraces of all size types that had been pre-selected as salinity tolerant in previous screening trials. The experiment was carried out in the greenhouse facilities of the Laboratory of Vegetable Production at the Agricultural University of Athens. To induce salinity stress, plants were grown hydroponically and irrigated with a nutrient solution containing NaCl at a concentration that could maintain the NaCl level in the root zone at 30 mM, while the non-salt-treated plants were irrigated with a nutrient solution containing 0.5 mM NaCl. Various plant growth parameters, including dry matter content and fruit yield (measured by the number and weight of fruits per plant), were evaluated to assess the impact of salinity stress. In addition, the nutritional status of the plants was assessed by determining the concentrations of macro- and micronutrients in the leaves, roots, and fruit of the plants. The key results of this study reveal that cherry-type tomato landraces exhibit the highest tolerance to salinity stress, as the landraces 'Cherry-INRAE (1)', 'Cherry-INRAE (3)', and 'Cherry-INRAE (4)' did not experience a decrease in yield when exposed to salinity stress. However, larger landraces such as 'de Ramellet' also exhibit mechanisms conferring tolerance to salinity, as their yield was not compromised by the stress applied. The identified tolerant and resistant varieties could potentially be used in breeding programs to develop new varieties and hybrids that are better adapted to salinity-affected environments. The identification and utilization of tomato varieties that are adapted to salinity stress is an important strategy for promoting agriculture sustainability, particularly in semi-arid regions where salinity stress is a major challenge.

Engineering biomimetic cellulose fabric for sustainably and durably cooling human body

It is essential and challenging to develop sustainable and durable passive radiative cooling materials for long-term effectively maintaining human thermal comfort when undergoing intensified global warming in our low-carbon society. Herein, inspired by the distinct structure-property relationship of fruits-branches in fruiter, this work designs an approach of fibrillation of cellulosic fibers (branches of fruiter) followed by in-situ synthesis of SiO2 nanoparticles (fruits of fruiter) easily to prepare sustainable, robust, customizable, and scalable cooling cellulose fabric. Such coupling strategy of cellulosic-fiber fibrillation and SiO2 in-situ growth strongly roughens cellulose fabric, more specifically, sufficient micro- and nano-sized cellulose fibrils and SiO2 particles, which enables our cooling cellulose fabric to effectively reflect solar light with 97% reflectance (0.4–1.0 µm) and emit mid-infrared light with 0.97 emissivity (8–13 µm). As a result, the developed cooing cellulose fabric spontaneously cools the human body with a temperature drop of 7.4 °C in high-temperature summer. It should be noted that the developed strategy realizes extraordinary adhesion performance between nanosized SiO2 and fibrillated cellulosic fibers, endowing cooling cellulose fabric with durable yet effective cooling distinction despite enduring 100-time mechanical washing and 100-day exposure to air, as well as high strength (∼48 MPa), desirable moisture evaporation rate and breathability. The present work demonstrates a promising strategy how durability, functionality, and customizability can be integrated in future material design.

Creation of a methodology for determining the intensity of moisture evaporation within vacuum drying of fruits

The study objects were the Republic of Kazakhstan selection apple sorts: “Baiterek”, “Sarkyt” and “Saya”, also pear sorts: “Syilyk”, “Zhazdyk” and “Nagima”. Study of the process of moisture evaporation within vacuum drying of the fruits has essential value in the nutritional value saving. Basically, the product evaporative capacity is characterized by the evaporation resistance coefficient ‒ µ. Also during moisture removal, thermodynamic state of moisture changes that is described by water activity indicator ‒ aw. Experimental determination of these parameters allows for the analyzing moisture evaporation during vacuum drying process. Studies have established the following evaporation resistance coefficients: µ=2.03±0.07 for apple sorts and µ=2.3±0.05 for pear sorts. Either water activity decreases from 1.0 to 0.62±0.01 for apple sorts and from 1.0 to 0.65±0.04 for pear sorts. Two drying periods are discovered. The first drying period: 5.45–6.10 h for apple sorts; and 6.12–6.25 h. for pear sorts. The second drying period duration: 4.15–3.50 h for apple sorts; and 4.35–4.48 h for pear sorts. The critical humidity value: 27.1±2.1 % for apple sorts; and 30.1±2.5 % for pear sorts. Comparative analysis of calculated and experimental data shows maximum deviations 22.5 % for apple sorts and 23 % for pear sorts. The proposed equation for the calculating a moisture evaporation rate, considering the product properties and the hygroscopic parameters of air, can be used in practice to study the moisture evaporation dynamics from the product surface. The study results allow for the selecting an optimal mode for vacuum drying of apples and pears sorts in order to safe nutritional value and to produce biologically active additives for the food industry

Combined Heat and Mass Transfer Associated with Kinetics Models for Analyzing Convective Stepwise Drying of Carrot Cubes.

Stepwise drying is an effective technique that promotes energy saving without additional capital cost. The stepwise drying mode was investigated for energy consumption and dried product qualities using a coupled heat and mass transfer model associated with kinetics equations of volume shrinkage and degradation of β-carotene in carrot cubes. Simulations were performed using a finite element method with extension of a chemical species transport. Validation experiments were carried out under constant drying modes at 60 °C, 70 °C and 80 °C using a lab-scale convective hot air dryer. The verified models were subsequently employed to investigate the effects of two step-up drying modes (60 to 70 °C and 60 to -80 °C). The optimal drying condition was determined using the synthetic evaluation index (SI) with criteria of high specific moisture evaporation rate (SMER), low shrinkage ratio and β-carotene degradation. Simulated results showed comparable agreement with experimental data of moisture content, shrinkage ratio and β-carotene ratio. Step-up drying of 60 to 70 °C gave the highest SMER of 0.50 × 10-3 kg of water evaporated per kWh, while the operation at constant temperature of 80 °C gave the lowest value of 0.19 × 10-3 kg of water evaporated per kWh. Model-predicted results showed less shrinkage of carrot cubes, but higher degradation of β-carotene under step-up drying compared to single-stage drying under temperature of 60 °C. Based on the highest SI value (0.36), carrot cubes were optimally dried under step-up mode of 60 to 70 °C.

Experimental analysis of hybrid dryer combined with spiral solar air heater and auxiliary heating system: Energy, exergy and economic analysis

The simultaneous energy and food resources management can be a challenging problem for researchers working in this field. Solar dryers are equipment that can employ solar energy in order to dry degradable food for long-term storage. However, these systems should also utilize an auxiliary energy source because of non-availability of continuous access to the solar radiation. In this paper, a cabin solar dryer equipped with a heating element as an auxiliary heat source has been used to dry four types of products. The tested products consist of apple, kiwi, banana slices, as well as quince julienne strips. The experiments were performed in four days during autumn, when the solar energy had a low level intensity and the heating element was employed for aiding the energy supply. Temperature and humidity have been measured using temperature and humidity sensors mounted at the inlet and outlet of the collector and dryer cabin. Then the thermal efficiency of the collector and the cabin is investigated via the energy and exergy analysis, and the thermal performance of the system is analyzed. Lastly, an economic analysis is presented to calculate the production cost of per kilogram of products. The results show that thermal efficiency, drying process exergy, produced exergy and specific moisture evaporation rate (SMER) of julienne strips of quince are higher than those of other products. Although banana slices have better conditions in terms of these parameters among the sliced products. Due to the results, it was found that the quince julienne strips have the highest cost about 1.137 $/kg and the lowest drying rate about 0.188 kg/h. On the contrary, the minimum cost belongs to the apple slices about 0.478 $/kg and the maximum drying rate about 0.3224 kg/h.

Evaluation of the Drying Characteristics of Coffee Grounds with Electric and Gas Combustion Heat Sources

The water content of the coffee grounds discharged from coffee beverage production facilities and coffee stores is about 75 wt.%. When the coffee grounds is used as solid energy source, drying technology is important because the high water content of the coffee grounds causes lower heating values reduction and combustion deterioration. In particular, it is necessary to maintain a constant water content of the dried coffee grounds with low energy consumption. In this study, two types of coffee ground batch dryer were tested: an electric heating and a gas burning system. After coffee grounds were injected into each dryer, vapor evaporation, drying rate, specific moisture evaporation rate, and drying efficiency were measured. The drying systems applied the moisture intensity (pulse, P) sensor and an automatic control program to maintain the moisture content of the dried coffee grounds. The drying performance and efficiency of the electric heating dryer were 21% and 33% higher than the gas burning dryer, respectively. The water content of dried coffee grounds is about 2.1 wt.%, and the ash content is 1.5 wt.%. The lower calorific value of dried coffee grounds is 5,710 kcal/kg, satisfying Bio-SRF (solid refuse fuel, Korea) quality standard. Therefore, when the dried coffee grounds is used as a solid energy source, it is advantageous to reduce the amount of greenhouse gas and save fossil fuels compared to the case of landfilling the dried coffee grounds.

The evolution of early-age cracking of cement paste cured in low air pressure environment

In recent years, infrastructure constructions have rapidly developed in plateau areas. The research on the surface cracks of cement-based materials in low air pressure environment in plateau areas is critical in improving the long-term durability of concrete structures as well as the harmony between the building and environment. In this work, the evolution of early-age cracking in cement pastes cured in low air pressure environment was examined by drying measurement, thermogravimetric analysis (TG), nitrogen adsorption-desorption, and micromorphology. The cumulative moisture loss and evaporation rate, total crack area, degree of hydration, and microstructure analyses were evaluated to analyze the evolution mechanism of early-age cracking. The results indicate that the development of early-age cracking on cement paste surfaces is related to air pressure. The moisture evaporation of cement paste accelerates in low air pressure environment, making early-age cracking and pores more noticeably exposed to the cement paste surface. Further, the cement hydration decreases and the volume of micropores and mesopores of cement paste increases in low air pressure environment, forming a loose and porous microstructure and increasing the risk of early-age cracking on the cement paste surface.