For many scientists and technologists including students, rigorous engineering principles are harder to grass due to the generally higher mathematics required. Here it is demonstrated that it is feasible to generate a ‘complex’ mathematical engineering model through largely descriptive expressions (i.e. by talking), gradually leading the students to make progress. Putting the known parameters (talked about it one by one intuitively) gradually into groups of formulas with little fear and see where one may get to end up with a final model. As an example, freeze-drying of a porous solid matrix has been ‘talked about’, ‘muscling’ all those concerned into good enough mathematical result(s) that correlates well the moisture loss over time which is often the prime objective in freeze-drying modeling. It is shown to be possible to find more examples in future that can be ‘talked through’ for easier understanding by the students.

Freeze-drying is widely used to preserve heat-sensitive products, but conventional static processes suffer from long drying times and limited heat transfer. Dynamic freeze-drying, which involves mixing of frozen material during sublimation, can enhance heat and mass transfer efficiency. In this study, milk powders obtained by spray drying (commercial sample), static freeze-drying, and dynamic freeze-drying were compared. Dynamic drying was carried out in an oscillating drum system using frozen beads of 1 mm and 5 mm diameter. The powders were characterized in terms of flowability, moisture content, water activity, specific surface area, microstructure and thermal properties. Results showed that dynamic freeze-dried powders exhibited superior flowability (lowest Carr Index), stable moisture content over 70 days of storage, and specific surface areas approximately ten times higher than those of static freeze-dried or spray-dried powders. SEM analysis confirmed a fine and homogeneous porous microstructure in dynamically dried samples. The glass transition temperatures were also markedly higher and DVS analysis revealed no recrystallization up to 90% RH for 5 mm beads, demonstrating exceptional stability of the amorphous phase. The freezing process is the critical point for most of the differences found between static and dynamic freeze-drying. These findings demonstrate that dynamic freeze-drying can produce free-flowing, stable, and structurally enhanced milk powders, representing a promising alternative to conventional drying methods.

During microwave vacuum drying (MVD) of Macrobrachium rosenbergii meat, quality degradation and flavor loss becomes more pronounced in the later stage of drying, highlighting the necessity of developing MVD-based combination technique. Herein, a combined drying strategy was employed with MVD as the first-stage of drying, followed by hot air drying (HAD), heat pump drying (HPD), and vacuum freeze drying (VFD), respectively. Effects of moisture transition point (50%, 40%, and 30%, wet basis) on the drying kinetics, physicochemical properties, microstructure, and volatile flavor compounds were systematically analyzed, and overall quality was evaluated using comprehensive scoring and hierarchical cluster analysis. The results indicated that the MVD-VFD combination at a 30% moisture transition point (30-VFD) achieved the best overall performance, characterized by minimal lipid oxidation (0.41 mg MDA·kg−1), moderate hardness (186.28 N), the highest porosity (9.63%), and superior water-holding capacity. Scanning electron microscopy revealed a uniform porous structure, while flavor analysis demonstrated a well-balanced aroma profile, resulting in the highest comprehensive quality score. In contrast, MVD-HAD led to darker color, higher hardness, greater energy consumption, and increased protein oxidation, whereas MVD-HPD required longer drying times and produced denser structures with limited rehydration capacity. Overall, the MVD-VFD strategy, particularly at a 30% moisture transition point, provides an effective approach for producing high-quality dried M. rosenbergii meat with improved energy efficiency, highlighting its strong potential for industrial application in aquatic product drying.

Drying of sulfur-bearing minerals using the conventional kiln dryers poses potential risks such as release of carbon emissions, toxic gases and loss of volatile substances due to sulfide phase transition. This has driven interest in alternative drying methods that enable selective moisture removal and precise temperature control. This study evaluates the effectiveness of microwave heating for drying sulfur-bearing minerals through experiments and numerical modeling. Material properties, including thermal conductivity, heat capacity, initial moisture content, bulk porosity, density and tangent loss, were thoroughly examined. A sequential finite element model of electromagnetic heating, incorporating moisture-dependent material properties, was developed and its results were compared against the experimental measurements. Results show that at an input microwave energy as low as 25 kW.hr/t, the moisture extraction can be at a rate of 0.05 grams per kW.hr/t. This increases progressively with input energy, reaching values of approximately 0.25 grams per kW.hr/t at input microwave energies larger than 100 kW.hr/t. Complete drying was attained at a microwave energy dosage of 202.49 kW.hr/t, yielding drying efficiency of 72.05%. The findings suggest that for materials with an initial moisture content of 20%, microwave heating maintained the volume temperature below the safety maximum value of 110 °C.

This study investigated segmented drying strategies for Gastrodia elata (RGE), combining microwave hot-air rolling-bed drying (MHRD) with hot-air drying (HD). Four transition points (60%, 45%, 30%, and 15% moisture content) were applied to examine their effects on drying performance, moisture migration, rehydration, and bioactive retention. The segmented approach significantly altered drying kinetics and water state dynamics. Under the drying conditions of microwave power density 0.8 W/g and hot-air velocity 2.5 m/s, the mid-to-late transition points, particularly at 15%, produced dried products with enhanced color (L*=51.98), rehydration ratio (4.84), and microstructure. Chemical profiling confirmed its high contents of phenolic (3.03 g GAE/kg), gastrodin (4.422 g/kg), and p-hydroxybenzyl alcohol (1.413 g/kg). An LSTM model was developed to predict moisture content and moisture ratio. The model achieved high predictive accuracy (R2 > 0.99). This work provides insight into how MHRD-HD influences the dried RGE, offering a practical framework for intelligent drying through AI-assisted moisture prediction.

Drying efficiency, temperature uniformity, and dried product quality are three crucial indicators for evaluating the performance of a drying process. To enhance these aspects and minimize the loss of samples, a pilot-scale radio frequency (RF) system, operating at 27.12 MHz and 6 kW and combined with hot air, was employed to dry cauliflower with both uniform density (where the cauliflower had the same density) and combined densities (where the cauliflower had different densities in different zones) in a rectangular container. During the hot air-assisted RF drying process, the temperatures of the cauliflower with both uniform and combined densities initially increased, subsequently decreased, and then increased again. Due to the higher electrical intensity at the corners and edges of the container, the highest temperatures were observed there, while the center exhibited the lowest temperatures. In contrast, the moisture content of the samples displayed an opposite pattern. After the drying process, samples with a combined density exhibited better heating uniformity than those with a uniform density, as indicated by the lower heating uniformity index. As the total drying times of the samples with uniform and combined densities were 285 min and 240 min, respectively, the samples with the combined density exhibited higher drying efficiency. The drying process of the samples was described by the logarithmic model. After the drying process, the dried samples with a combined density showed lower total color difference (ΔE) and lower vitamin C loss rates than those with a uniform density (p < 0.05). The results of this research offer valuable insights into the drying samples with high moisture content during RF drying technology.

Drying is a critical stage in tobacco shred processing. The study focuses on the design of a rotary drum drying system with four independent temperature control zones in order to solve the problems of traditional rotary drum dryers: coarse temperature control, excessive energy consumption, and inconsistent product quality. By establishing a segmented dynamic temperature control strategy, precise adaptation to the multi-stage characteristics of the drying process was achieved. Taking tobacco shred drying as the research object, an orthogonal experimental approach was employed to systematically analyze the effects of seven factors—such as drum zonal wall temperature and hot air parameters—on the drying performance. The findings indicate that convective heat transfer from hot air is the dominant drying mechanism, with a-contribution rate exceeding 80%. Heat conduction from the drum wall shows notable spatial heterogeneity. The wall temperatures in Zones 2 and Zone 3 account for 6.59% and 4.88% of the influence on moisture content variation, respectively, which are substantially higher than that of Zone 4 (0.45%). By increasing the wall temperatures of the middle and front zones (Zones 2 and Zones 3) to 115–130 °C and applying low-temperature control (95–105 °C) to the tail zone (Zone 4), drying efficiency can be improved; and the risk of over-drying at the tail end is reduced, thus achieving both energy optimization and quality assurance. These findings provide new perspectives for improving drying equipment to enhance energy utilization and achieve precise control of the final moisture content.