Low-temperature Drying Research Articles

Understanding the low-temperature drying process of sludge with machine learning in a sewage-source heat pump drying system.

Heat pump drying technology based on sewage heat source is an eco-friendly sludge drying method. It can effectively reduce the pollution of natural water bodies by waste heat while reducing energy consumption. However, the drying characteristics of sludge in this case remain unclear. Here, we proposed and constructed a novel sewage-source heat pump sludge low-temperature drying system, and combine sludge drying theory with machine learning algorithms to model and analyze the drying process. The results revealed that the performance of the machine learning models was significantly better than that of the existing numerical simulation models. After Bayesian optimization, the XGBoost model showed superior prediction effect. In addition, the interpretable analysis of the model indicated that in the constant rate stage, the drying rate is mainly influenced by external air parameters, with temperature being the most critical factor. When temperature exceeds 50°C, the effect of relative humidity becomes significant. During the falling rate stage, the dominant factors begin to gradually shift from external air parameters to internal characteristics within the sludge itself, with dry basis moisture content becoming the new key factor. When air velocity exceeds 1.5m/s, the response of drying rate to air velocity is significantly influenced by changes in dry basis moisture content. The results of this study indicated that it is feasible to use machine learning models for predicting and explaining the low-temperature drying process of sludge. This provides valuable insights for the application of machine learning models in the development and management of drying strategies.

Effect of Drying Temperature on Sensory Quality, Flavor Components, and Bioactivity of Lichuan Black Tea Processed by Echa No. 10.

Lichuan black tea (LBT) is a well-known congou black tea in China, but there is relatively little research on its processing technology. Echa No. 10 is the main tea tree variety for producing LBT. This study investigated the sensory quality, flavor components, and bioactivity of Echa No. 10 Lichuan black tea (LBT) at different drying temperatures (70, 80, 90, 100, 110, 120, and 130 °C). During 80-120 °C, increasing the drying temperature enabled a higher sweet aroma concentration and enhanced the sweetness in the taste, in contrast to reducing the floral, fruity, and sweet aromas, and increasing the bitterness and astringency, at >120 °C. Additionally, with an increasing drying temperature, the contents of tea polyphenols and total catechins significantly decreased, with the theaflavins decreasing first and then increasing, and the alcohols, aldehydes, esters, and hydrocarbons increasing first and then decreasing. Meanwhile, compounds (including linalool, (Z)-linalool oxide (furanoid), (E)-linalool oxide (furanoid), cis-β-Ocimene, and methyl salicylate) contribute more to the floral and fruity aromas at <110 °C. Furthermore, low-temperature drying favors the antioxidant and inhibitory effects of the α-amylase, α-glucosidase, and glucose absorption activity. Both the tea quality and bioactivity results revealed 80-110 °C as the optimal drying temperature range for LBT.

Optimization of lyophilization cycle for the formulation and stability assessment of Doxycycline Hyclate

Background and Aim:Doxycycline hyclate, prone to instability in solution, is unsuitable for liquid dosage forms. Lyophilization, a low-temperature drying process, addresses this limitation by converting the drug into a stable solid. This study aimed to optimize the lyophilization cycle for doxycycline hyclate, enhancing its stability, handling, and transport in injectable form Methods: Pre-formulation studies included solubility analysis, pH determination, water content measurement, FTIR, DSC, photostability, and compatibility studies. Twelve lyophilization cycles were designed, optimizing four formulations by varying temperature, pressure, and cycle duration. Formulations were assessed for cake appearance, solution clarity, pH, reconstitution time, and assay. The optimized formulation underwent additional evaluations for diluent and filter compatibility, in vitro antibacterial activity (disk diffusion), and stability under accelerated and photostabilityconditions.Results:Formulation F3 from Trial 3 exhibited superior performance, with a uniform, smooth cake appearance, clear reconstitution, stable pH, rapid reconstitution time, low water content (0.98%), and minimal organic impurities. Diluent and filter compatibility tests revealed no adverse interactions. The formulation remained stable under light and accelerated conditions, showing dose-dependent antibacterial activity comparable to the innovator’s product.Conclusion:The optimized lyophilization cycle significantly enhanced doxycycline hyclate's stability, handling, and transport. The injectable formulation demonstrated excellent stability, reliable antibacterial activity, and clinical suitability, offering a safer, more convenient alternative to liquid formulations.

Effects of different drying methods on content of main chemical compounds in Callicarpae Nudiflorae Folium

This study aims to identify the main chemical compounds, investigate the effects of different drying methods on the quality, and determine the appropriate drying method of Callicarpae Nudiflorae Folium. UPLC-UV-Q-TOF-MS was employed to characterize and identify 35 main compounds, including phenylethanoid glycosides, flavonoids, and iridoids in Callicarpae Nudiflorae Folium. A method for the simultaneous determination of 8 compounds with strong UV absorption and high content was established to evaluate the quality of Callicarpae Nudiflorae Folium dried by different methods. UPLC-UV-Q-TOF-MS combined with principal component analysis(PCA) was employed to compare the Callicarpae Nudiflorae Folium samples treated by microwave drying at different power(119, 231, and 385 W), drying in the shade, sun drying, and oven drying at different temperatures(50, 60, 70, 80, 90, and 100 ℃). The total content of decaffeoyl acteoside, picroside Ⅲ, galuteolin, forsythin B, acteoside, isoacteoside, 6-hydroxyluteolin-7-glucoside, and caffeic acid in Callicarpae Nudiflorae Folium, as well as the content of most compounds, decreased with the rise in drying temperature and with the decrease in microwave power. Considering the content of compounds, low carbon, and energy saving, microwave drying at 231 W, low-temperature drying, or natural drying is recommended for the production of Callicarpae Nudiflorae Folium. This study provides a scientific basis for the selection of drying methods for Callicarpae Nudiflorae Folium at the place of origin and for the improvement of quality standards.

Effect of different drying temperature settings on the color characteristics of Tencha

Color is critical factor in the commercialization of Matcha. In this study, sensory evaluation, color difference analysis, as well as targeted and non-targeted analyses were employed to investigate the impact of different drying temperature settings on the color characteristics of Tencha. The findings revealed that compared to a single drying temperature setting, a two-stage or multi-stage drying process more effectively preserved the color quality of Tencha. Specifically, a setting involving an initial period of high-temperature drying followed by low-temperature drying (samples T_6, T_7, T_10, and T_13) resulted in superior tea color quality, characterized by higher chlorophyll content and lower levels of lutein and β-carotene. Chemometric analysis identified chlorophylls and their derivatives (chlorophyll a/b, pheophytin a/b, pyropheophytin a/b) as the key factors influencing Tencha's color. These results can provide valuable insights for optimizing tea processing methods to enhance quality.

Low-Temperature Rapid Drying of Viscous Sludge Via Non-Phase Change Based on Particle High-Speed Self-Rotation and Medium Dispersion in Cyclone

Drying operations are of grave importance to realize the reduction and utilization of sewage sludge resources, but the conventional thermal evaporation drying (TED) technology faces challenges due to the need for a large amount of thermal energy to conquer the phase-change latent heat of moisture. Herein, we report a non-phase change technology based on particle high-speed self-rotation in a cyclone for fast, low-temperature drying of viscous sludge with high moisture contents. Dispersed phase medium (DPM) is introduced into the cyclone self-rotation drying (CSRD) reactor to enhance the dispersion of the viscous sludge. The effects of carrier gas temperature, feeding rate, size, and proportion of DPM particles in the drying process are systematically examined. Under optimal operating conditions, the weighted content of moisture in the viscous sludge could be reduced from 80% to 15.01% in less than 5 s, achieving a high drying efficiency of 95.79%. Theoretical calculations also reveal that 89.26% of the moisture is removed through a phase change pathway, contributing to a 522-fold increase in the drying rate of CSRD compared to TED technology. This investigation presents a sustainable effective approach for high moisture viscous sludge treatment with low energy consumption and carbon emissions.

Culinary properties, nutritional quality, and in vitro starch digestibility of innovative gluten-free and climate smart cowpea-based pasta

This study investigates the processability, culinary and rheological properties, biochemical composition and in-vitro starch digestibility of new gluten-free pasta formulated with whole cowpea flour alone or combined with teff and/or amaranth leaf flour(s). These pasta are compared with three wheat-based pasta with fiber content increasing from 4% to 16% g/100g, 16% g/100g being the average fiber content of cowpea-based pasta. The pasta were processed using low temperature extrusion and drying. The antioxidant properties of amaranth leaf flour facilitated extrusion by limiting excessive aggregation of the dough during hydration/mixing that is attributed to lipoxygenase activity of cowpea flour. The optimal cooking time and cooking losses of cowpea-based pasta were similar to wheat-based pasta with comparable fiber content, highlighting fiber as a key factor influencing culinary properties. Adding teff to cowpea-based pasta reduced cooking losses and firmness. Although some micronutrients were lost during pasta processing and cooking, the consumption of a cooked portion of 100 g of dry cowpea-based pasta still covered FAO nutritional recommendations for protein, fiber, iron, zinc, and vitamin B9 targeting adult women. Adding amaranth leaves helped meet recommended beta-carotene levels. The in vitro slowly digestible starch content of cowpea-based pasta is similar to or higher than that of wheat-based pasta.

Performance analysis of heat pump drying system combined with rotor dehumidification for low temperature drying of mango slices

In order to solve the problems of low drying efficiency and poor drying quality existing in the current closed heat pump drying system (CHPD), a closed carbon dioxide heat pump drying system (CHPRD) with the function of combining rotor dehumidification was designed. This study investigates the drying kinetics and quality characteristics of CHPRD in low-temperature drying processes using mango as the drying material through experimental studies and theoretical analysis. The experimental results showed that the drying rate of CHPRD increased by 29% and 17.8%, the moisture removal rate per unit energy (SMER) by 14.2% and 12.5%, and the coefficient of performance (COP) by 17.3% and 12.0%, respectively, compared with that of CHPD in the low-temperature drying process with loading amounts of 400 and 450 g, respectively. In terms of drying quality, the rehydration factor (Rf ) of CHPRD-dried mango slices increased by 6.0% and 5.0%, the ascorbic acid content increased by 15.0% and 14.4%, and the color difference (ΔE) was lower by 11.0% and 5.6%, respectively. These improvements indicate that CHPRD provides better drying kinetics and higher quality of dried material. Based on the experimental data, simulation fitting was conducted, revealing that the two-term model is the best mathematical model to simulate the drying characteristics of CHPRD for mango.

A Review on Sludge Drying after High Pressure Filter Pressing

Sludge drying is a key step in municipal sludge treatment. After mechanical dewatering, the water content of sludge is usually between 50% and 70%, which needs further drying. The main drying technologies include thermal drying, solar drying, ultrasonic drying and microwave drying, among which thermal drying technology is the most mature. Research shows that low-temperature drying technology has obvious advantages in reducing the release of harmful substances, energy consumption and cost. In terms of technology application, domestic sludge drying process is mainly divided into direct drying and indirect drying. Direct drying directly evaporates water through high-temperature gas, while indirect drying makes use of heat conduction effect to contact with high-temperature media. At present, indirect drying technology is mainly used in China, such as paddle type, disc type and thin layer drying. In particular, the low-temperature heat pump drying technology excels in terms of safety, footprint and energy consumption, with its ability to operate at lower temperatures, reduce the release of hazardous gases, and achieve environmental and economic benefits in a closed-cycle mode. This technology is suitable for small and medium-sized wastewater treatment plants and shows clear advantages in cases of budgetary constraints.

Enhancing Stability of n-Type Doped Organic Semiconductors through Low Boiling Point Solvent-Assisted Room Temperature Drying.

The development of n-type organic semiconductors (OSCs) has been lagged behind that of p-type OSCs, mainly due to the limited availability of the electron deficient π-conjugated backbones and facile electron trapping by ambient oxidants. Improving the performance of n-type OSCs through n-doping is essential for realizing p-n junction diodes and complementary circuits. Conventional vacuum deposition doping is costly and time-consuming, while solution doping risks thermal damage through necessary annealing. Therefore, the development of a simpler, more affordable n-doping method is crucial. In this study, we have developed a solution-processed n-doping method using an organic cationic dye in a low boiling point solvent that can be dried at room temperature in 1 h, which eliminates the need for annealing. The effects of different organic cationic dyes and reducing agents on the n-type OSC were evaluated. After n-doping, electron mobility and photoresponsivity in the sample increased by 5.5 and 20 times, respectively, compared to undoped samples. Furthermore, there was no significant degradation in the electron mobility of the n-doped samples under ambient conditions after 15 days. Studying n-doping with various organic cationic dyes in different OSC materials, embracing further research into their applications and mechanisms, would advance the field of organic electronics.

Inhibition of bleaching of stored red hot pepper through appropriate postharvest technologies and practices

The colour qualities of hot red pepper are the major issue in pepper value chain. Due to poorly coordinated scientific evidence, information on the factors causing colour loss and the inhibition mechanism is not well known. Therefore, this review paper aimed to summarize the inhibition mechanism of stored red hot pepper bleaching through appropriate postharvest technologies and practices. The information in this paper was gathered from a variety of sources, including journal articles, books, book chapters, workshop proceedings, FAO reports, and AOAC official methods of analysis. According to these studies, carotenoids, surface colour, and extractable colour (ASTA value) are the primary colourants that define hot red pepper. The findings demonstrate that low-temperature drying methods, such as open sun drying, are best for preserving the red hot pepper powder’s colour quality, while higher temperatures cause the colour to darken. Blanching, the use of desiccants (CaCl2), and chemical dipping are pretreatments that preserve the best colour quality by hastening the drying time. Similarly, storage of red hot pepper powder at lower temperatures (5oC) resulted in less colour degradation. In other words, materials used for packaging that have a high barrier to light, moisture, and air, such as laminated aluminium, amber or black polyethylene, and high-density polyethylene, maintained a higher level of colour quality. Through their influence on drying and processing times, breeding technologies, varieties, and maturity level also impact colour quality. In conclusion, the colour quality of red hot pepper is highly influenced by environmental, biological, and processing methods. It is, therefore, critical to use appropriate drying and pretreatment techniques, storage time, well-managed storage temperature, appropriate processing methods and packing materials, and improved agronomic practices for the sustainable management of colour fading and adulteration that can occur throughout the value chain.

Performance Optimization and Numerical Simulation Study of Sludge Low-Temperature Drying System

Performance Optimization and Numerical Simulation Study of Sludge Low-Temperature Drying System

Drying characteristics of sewage sludge pre-conditioned by CaO and sawdust under low-temperature drying conditions

ABSTRACT Heat pump drying is a low-carbon method of sludge drying. The operating temperature of a heat pump is generally not more than 70℃. To improve the drying efficiency of heat pump dryers, the effects of air parameters and additives on sludge drying characteristics at low temperatures were studied. The sludge drying experiments were conducted at an air temperature 50-70℃ and an air velocity of 0.5-1.7 m/s. The experimental results showed that the increase of air temperature, velocity and the addition ratio of additives can accelerate the sludge drying process. The average and maximum drying rates of sludge pre-conditioned by CaO and sawdust increased by 14.23% and 25.71%, respectively, compared with those of pure sludge. The two-way analysis of variance (ANOVA) revealed that the influence of air temperature on the sludge drying was higher than that of air velocity. Five reference models were fitted by the drying experiment data. The Page model has the highest R2, so it is the most suitable model to predict the drying time of sludge at low temperatures.

Efficacy of mosquito repellent finishes on polyester fabrics using four essential oils against the vector of the West Nile virus, Culex pipiens (Diptera: Culicidae)

One of the most common ways to prevent mosquito bites is to use treated textiles, which can be used to repel mosquitoes in the form of nets, clothing, uniforms, and other items. Four eco-friendly essential oils: lemongrass (Cymbopogon citratus), eucalyptus (Eucalyptus camaldulensis), clove (Dianthus caryophyllus), and marjoram (Origanum vulgare), were evaluated and used to finish polyester fabrics (PE) to give them a pleasant odor and antibacterial properties, as well as mosquito repellent as medical textiles. A low-temperature drying process and thermal stabilization technique were used to bond the polyester to the fragrance-containing compounds. The effect of essential oil finishes on polyester textile properties has been studied using various techniques such as mechanical measurements, contact angle, ultraviolet tests, infrared spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscopy, GC-MS analysis, etc. Scanning electron microscopy showed the physical adsorption of oil on PE surfaces and the penetration of oil droplets between PE fibers. The ability of polyester textiles treated with essential oils of lemongrass, eucalyptus, clove, and marjoram to kill Staphylococcus aureus, Escherichia coli, Candida albicans, and Aspergillus niger was also tested. Polyester fabrics treated with clove showed the strongest antibacterial effect, surpassing that of eucalyptus oil. 12 essential oils were screened to determine their superiority in repelling mosquitoes at a concentration of 1% through the CDC bottle and WHO cone tests. Cymbopogon citratus (LT50 = 60.03 min) oil was the most effective against Cx. pipiens, followed by Eucalyptus camaldulensis (LT50 = 61.65 min) and Dianthus caryophyllus (LT50 = 64.73 min) with CDC tests. It was found that finishing PE with clove and eucalyptus oils provided 76 and 68% protection from Culex pipiens mosquitoes, even after 6 cycles of washing. This approach is innovative because it meets the goal of having antibacterial, mosquito-repellent, and pleasant-smelling fabrics as requirements for economically viable medical textiles. There is an urgent need to engineer textiles, with or without insecticides, to effectively repel mosquitoes. Our data showed the efficiency of polyester fabric treated with clove and eucalyptus oils in repelling mosquitoes after 6 washings.

Fuel Wood Pellets Produced from Sawdust of Scots Pine Mature and Juvenile Wood: Self-Heating and Off-Gassing Tests at Industrial Scale

This study investigated self-heating and off-gassing of Scots pine (Pinus sylvestris) wood pellets made from sawdust generated from separated mature and juvenile wood. The pellets were produced at an industrial scale and stored in large piles of about 7.2 tonnes. The production process involved drying the sawdust using three different methods and to varying moisture contents. The results indicated significant influences of both raw material type (F(6) = 61.97, p < 0.05) and drying method (F(2) = 65.38, p < 0.05) on the self-heating of the pellets. The results from the multiple regression analysis further showed that both the raw material type and pellet moisture content significantly influenced the temperature increase, with strong correlations observed for pellets produced using low-temperature drying (F(3, 14) = 83.52, multiple R2 = 0.95, p < 0.05), and medium temperature drying (F(3, 13) = 62.05, multiple R2 = 0.93, p < 0.05). The pellets produced from fresh mature wood sawdust were found to be more prone to self-heating and off-gassing while steam drying the sawdust at high temperature and pressure led to a significant reduction in heat and gas generation across all materials. The heightened self-heating and off-gassing in mature wood pellet can be attributed to a higher proportion of sapwood in the raw material. The probable explanations to the observed differences are in line with biological mechanisms for self-heating and off-gassing, as well as the chemical oxidation of fatty and resin acids.

Association between low-temperature drying and ozonation processes to control pests and preserve maize quality

Association between low-temperature drying and ozonation processes to control pests and preserve maize quality

Effect of Phenolic Resin Coating Thickness on Mechanical Properties and Corrosion Resistance of Metal Materials

In the realm of petrochemical and other industries, metal materials face threats such as impact and high-temperature electrochemical corrosion. Consequently, there has been significant attention towards organic coatings that effectively attenuate impact forces while simultaneously providing a barrier against corrosive agents. The thermosetting phenolic resin 2130, known for the facile curing process, exceptional thermal stability, water resistance, corrosion resistance, and superior mechanical properties post-curing, finds extensive applications in the field of coatings. To address the challenge of depositing a complete and uniform resin coating on complex workpieces, coatings with varying thicknesses on the surface of 304 stainless steel were deposited via rotary evaporation combined with long-term low-temperature drying. The relationship between coating thickness and mechanical properties, as well as corrosion resistance, was investigated and analyzed through a comprehensive approach involving mechanical testing, electrochemical analysis, and long-term service weight loss assessment. The results demonstrated that the coatings deposited on the metal surface exhibited excellent integrity and compactness. Moreover, an increase in coating thickness led to a significant reduction in material corrosion rate. The coatings exhibited excellent substrate adhesion and flexibility, thereby providing effective protection against impact on the metal substrate. The relationship between the thickness of the coating and the surface roughness was evident, while the flexibility of the coating first increased and then decreased with the increase of coating thickness. When the coating thickness was 7 μm, the maximum surface roughness of the coating measured 0.44 μm. Under these conditions, the impact toughness of the coating reached the peak, exhibiting a ductile fracture mode and showcasing superior comprehensive mechanical properties. The findings of this study will offer theoretical support for the investigation and formulation of resin coatings in subsequent industrial production.

Spectral analysis of various types of wood as the basis of low-temperature drying technology in vacuum conditions

The research was carried out at the expense of the grant of the Russian Science Foundation No. 23-76-01090, https://rscf.ru/project/23-76-01090 /. The characteristics of various types of wood (oak, aspen, pine) were obtained in the laboratory on the basis of the South Ural State Agrarian University using the infrared Fourier spectrometer FSM 2201. For these rocks, the wavelengths at which the maximum absorption of radiation occurs are determined, which is consistent with the operating modes of the film electric heater. The obtained result will become the basis for further research aimed at developing and creating a prototype of an infrared vacuum drying plant and an automatic control system for regulating and investigating the process in a discharged environment.

Comparative experiment on the use of a film electric heater for drying wood in vacuum conditions

The research was carried out at the expense of the grant of the Russian Science Foundation No. 23-76-01090, https://rscf.ru/project/23-76-01090/. The article outlines the need for woodworking enterprises to re-equip existing ones and create new technologies for deep processing. The trends of the Russian market dictate the conditions for choosing primarily domestic equipment, in this regard, the development of innovative, energy-saving, environmentally friendly wood processing technologies is relevant. Drying plants with the use of film electric heaters in vacuum conditions are a promising area of research. The proposed development will reduce the carbon footprint, with the output of high-quality lumber and reduced energy costs. The materials present the results of an experiment on the use of a film electric heater for drying wood in vacuum conditions in comparison with the traditional technology of its application. As a result, drying in vacuum conditions allowed to reduce the process by 35%, electric energy costs by 25%. The obtained result indicates the feasibility of further research in the field of low-temperature drying in vacuum conditions.

Application of Aronia Melanocarpa Fruit Powder Obtained by an Innovative Low-Temperature Drying Method for Facial Care Masks

Application of Aronia Melanocarpa Fruit Powder Obtained by an Innovative Low-Temperature Drying Method for Facial Care Masks