The paper presents the performance evaluation of a modified indirect solar dual collector dryer (MIS2CD) integrated with a thermal storage system for drying myrobalan slices. The design of the solar ...collector and solar collector with thermal storage was to supply uninterrupted thermal energy to the drying chamber during sunny and sunset hours. To evaluate the dryer performances, one lot (20 kg) of myrobalan was dried in the MIS2CD, and as a result, the thermal efficiency and energy supply period of MIS2CD increased by 12 ± 02% and 41 ± 1.2%, respectively. Drying characteristics of myrobalan slices in MIS2CD, TD, and OSD were studied and compared. A two-term exponential model best explains the drying kinetics of myrobalan slices dried in MIS2CD. The dried sample in MIS2CD results in lesser ΔE* values than TD and OSD methods. The highest exergy efficiency of 78.2% and lower exergy losses were recorded. The energy payback period of the MIS2CD was evaluated as 1.42 years. The CO
2
emitted and CO
2
reduced reduction are calculated for drying myrobalan in MIS2CD for a lifetime (20 years) of 67.85 kg and 20.65 tons, respectively. The capital cost of the solar dryer design was estimated depending on the economic considerations of the state. The drying hours were increased in MIS2CD against OSD by 59% on the annual sunny days (210 days). The sample drying period MSD and TD to reach the final moisture level of 7% was 9 h and 5 h, respectively. The total economic benefit is 22,622 INR (annually), and the 2.08 benefit–cost ratio for myrobalan dried in MIS2CD compared to TD. The MIS2CD’s payback period is nearly 2.18 years, much less than the dryer’s lifetime.
Graphical Abstract
The drying and denaturation characteristics of native, iron-depleted (apo-), and iron-saturated (holo-)lactoferrin (LF) were studied in convective air-drying (CD) process using single droplet drying. ...The extent of loss of LF due to denaturation and changes in the secondary structures during CD and isothermal water heating (IHT) were measured. The holo-LF was found to be most stable among these three forms both at 70 and 95°C. The apo-LF was the least stable compared to other two. The secondary structural features of LF were altered to significantly higher extent when subjected to IHT than to CD both at 70 and 95°C. Holo-LF should be preferred when producing LF powder through a convective drying process.
Advances in the study of the rate processes in spray drying have helped improve product quality. Single droplet drying (SDD) is an established method for monitoring the drying kinetics and ...morphological changes of an isolated droplet under a controlled drying environment, mimicking the droplet convective drying process in spray drying. To enhance particle quality requires understanding of both the particle formation process and knowledge of how different particle properties are affected by the drying conditions used. The latest development in the SDD technique enables evaluation of these aspects by incorporating a dissolution test in the drying experiment. The experiment is realized by attaching a solvent droplet to a dried/semi-dried single particle in situ and then video-recording the resultant morphological changes. Some of the particle (e.g., crystallinity) properties obtained under different drying conditions can be modelled using the measured droplet drying kinetics. This paper reviews the applications of SDD experiments in measuring the drying kinetics and monitoring the droplet morphological changes during drying. Some examples of extending the glass filament SDD technique to examine particle functionalities are discussed. SDD experiments are shown to be a powerful tool for particle engineering due to its ability to study both the external convective transport process of a single droplet and to understand the different particle functionalities of the resultant single dried particle.
Electrohydrodynamic (EHD) is a promising process for reducing the energy consumption of convective drying processes. In this study, a combined convective-EHD drying system was designed, constructed, ...and examined as an economical drying system for drying mushroom slices. The effects of two levels of velocities (0.4 and 2.2 m/s) and four levels of voltages (0, 20, 25, and 30 kV) on drying kinetics, drying rate, final moisture content, and specific energy consumption of EHD system (SECEHD), convective system (SECtunnel), and combined convective-EHD system (SECtotal) were studied. The results confirmed that by applying electric field at 0.4 m/s air velocity, the enhancement in the drying rate increased with the applied voltage. The combination of 30 kV voltage with the air velocity of 0.4 m/s could significantly increase the drying rate and simultaneously reduce the specific energy consumption of the combined convective-EHD system. However, a cross-flow with the high velocity of 2.2 m/s diminished corona wind effect. Results showed that increasing velocity alongside decreasing voltage reduced the SECEHD, but SECtunnel and SECtotal declined as velocity diminished. In fact, 30kV-0.4 m/s treatment resulted in statistically similar averaged drying rate and final moisture content to 0kV-2.2 m/s, 20kV-2.2 m/s, 25kV-2.2 m/s, and 30kV-2.2 m/s treatments, but it represented considerably less SECtotal value in comparison to them. As such, the appropriate combination of electric field intensity with air velocity such as 30kV-0.4 m/s treatment is a promising solution for reducing the substantial energy consumption of industries using convective drying technique.
•Kinetics and energy consumption of a convective-Electrohydrodynamic drying system were studied.•Decreasing voltage and increasing velocity decreased the specific energy consumption of Electrohydrodynamic system.•Decreasing velocity decreased the specific energy consumption of tunnel and combined systems.•30kV-0.4 m/s treatment led to similar averaged drying rate and moisture content to 2.2 m/s treatments.•30kV-0.4 m/s treatment showed considerably less specific energy consumption than 2.2 m/s treatments.
In this study, the effects of convective (60, 70, 80 and 90°C), microwave (120 and 350 W) and freeze-drying methods on the drying kinetics, color, total phenolic (TP) content and antioxidant capacity ...of pineapples were examined. The statistic tests proved that the Midilli et al., Two Term, Wang and Singh and Page models were superior to the other models and yielded the closest predictions to the experimental values. The lowest change in the color parameter (∆E) value (4.83) was obtained by freeze-drying the pineapples. The dried samples demonstrated a decrease in the TP content compared to the fresh samples and a decrease in the antioxidant capacity. The best antioxidant capacity and TP content values were obtained via freeze drying and microwave drying at 350 W, respectively. According to the results obtained from this study, convective, freeze drying and microwave methods are suitable for drying pineapple.
This study investigated the influence of different drying air temperatures (40, 50, 60 and 70 °C) on moisture removal ratio and drying rate of pre-cooked and uncooked palmyra (Borassus aethiopum) ...seed-sprout fleshy scale (SFS) slices and quality of the resultant flours. Through drying kinetic analysis, it was found that the drying process of pre-cooked and uncooked palmyra SFS slices took place in the falling rate period and the drying time decreased with increasing air temperature in all samples. The colour parameters (L*, a* and b*) were affected by the drying air temperature and treatment type (pre-cooked and uncooked), with significantly higher ΔE values in uncooked samples compared to the pre-cooked samples. Drying of uncooked SFS slices maintains relatively high total antioxidant activity and low content of vitamin C compared to the pre-cooked samples. Beta-carotene, total phenol and total flavonoid contents however showed no specific trend in pre-cooked and uncooked SFS samples. Generally, pre-cooking palmyra SFS before drying significantly (P ˂ 0.05) improved their water absorption capacity, swelling index and swelling capacity while decreasing bulk density. However, treatment type and drying air temperature was observed to greatly (P ˂ 0.05) influenced all pasting properties without any observable trend. Based on the results, the quality of palmyra SFS flour showed opposite behaviours, thus indicating a compromise decision on processing conditions involved to meet the quality properties of interest.
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•Pre-cooked and uncooked palmyra seed-sprout fleshy scale (SFS) were dried at 40–70 °C.•Drying rate of pre-cooked and uncooked palmyra SFS took place in the falling rate period.•Colour values of both pre-cooked and uncooked palmyra SFS were affected during drying process.•Uncooked palmyra SFS retained higher antioxidant activity and lower vitamin C compared to pre-cooked samples.•Pre-cooking of palmyra SFS before drying improved WAC, SI and SC while decreasing bulk density.
This study focuses on the drying kinetics of cob and light-earth layers comprising a hybrid walling system. Volumetric water content sensors are immersed and placed at different positions on the ...walls of a building to measure the drying kinetics. In addition, an experimental analysis of the effect of temperature, relative humidity (RH), and wind velocity variations on thermal conductivity in a climatic chamber under winter and summer conditions was conducted. The analysis of samples in laboratory aims to investigate the hygrothermal properties of cob and light-earth materials, and their dependency on the aforementioned parameters. The in situ drying kinetics of both materials involves water content reduction and stabilization; however, in the laboratory, although the water content of materials decreases, the drying is incomplete. Which may be due to the limited wind speed. The hydrothermal properties show that open porosity affects water vapor permeability and modifies the RH of cob and light-earth. At 23 °C, when the relative humidity (RH) range was 10–30%, the absorbed water vapor of cob and light earth was 0–2%. However, when the RH is 40–90%, the absorbed water vapor of light earth (2–9%) exceeds that of cob (0.5–2%). Moreover, the response to relative humidity (RH) with regard to the mixing law of components and samples differs. The resistance factor to water vapor diffusion values for cob and light-earth are 12.9 and 8.2, respectively. In this study, the thermal conductivity measurements under summer and winter conditions provide the relationship between the thermal conductivity, density, and water content of cob and light-earth materials.
•In situ and laboratory drying kinetics of cob and light-earth materials are analyzed.•Climatic chamber results exhibit good correlation with in situ observations.•Sorption and desorption mixing laws are explored.•Impact of porosity on hygroscopic behavior is significant.
Kiln drying of rubberwood lumbers is a complex transport phenomenon for realistic modeling and simulation. To decouple this complexity, researchers usually divide their research into two parts. The ...first one is single-lumber drying kinetics to describe how wood lumber responds to its surface conditions. Then they combine this drying kinetics with a lumped transport model or dispersion model or computational fluid dynamics. The mathematical models are then solved numerically to predict the industrial kiln drying behaviors. This work focuses on the drying kinetics of stacked rubberwood lumbers using hot air at different air velocity (0.5, 1.5, 2.5, 3.5, 4.0 m/s), relative humidity (6–67% relative humidity (RH)) and temperature (60–100 °C). The drying kinetics followed the conventional drying theory. However, the two drying periods, namely constant and falling rate (CRP and FRP), were not distinct. As the air velocity increased, the transition from CRP to FRP is faster. The middle of the transition period (at critical moisture content, CMC) moves closer to the fiber saturation point (FSP). The overall mass transfer coefficients in the falling rate period for stacked rubberwood drying were lower than those predicted by the Ananias correlation. Hence, a modified formula was proposed, representing the overall moisture transfer coefficients as a function of air velocity, temperature, relative humidity, and lumbers thickness for the range of variables under investigation satisfactorily. In general, the drying rate and the overall moisture transfer coefficient increased with increasing air velocity, drying temperature, and decreasing RH. Relative humidity directly affects the driving force of moisture transfer rate because higher RH is associated with higher equilibrium moisture content. A lumped parameter model for kiln drying was also developed. After being integrated with the estimated mass transfer coefficient, the model can predict the moisture profiles in lab-scale kiln drying satisfactory, although the model needs more validation data. These kinetic parameters and correlation for stacked rubberwood drying can be used in more complex models and process optimization in future research.
Mechanical Engineering; Thermodynamics; kiln drying, drying kinetics, energy cost saving, mass transfer coefficient, rubber wood lumbers.
► Temperature effects on droplet shrinkage of 50wt.% skim milk during drying. ► Shrinkage behaviour of high solids content deviated from ideal shrinkage kinetics. ► Rapid shell formation maintained ...spherical shape and hindered solute diffusion. ► Effects of solids content on particle formation were discussed. ► A general correlation of shrinkage kinetics at 10–50wt.% solids range was reported.
Industrial spray drying of milk powder production utilises high solids feed at around 50wt.% or higher; however there are only a few fundamental studies investigating the droplet drying behaviour. The present work studied the shrinkage behaviour of 50wt.% skim milk droplet during drying. Temperature effects on both shrinkage kinetics and total diameter reduction were found to be different from low solids milk drying. A high drying temperature at 110°C led to negligible droplet shrinkage at X range between 1 and 0.3kg/kg. An increase in temperature resulted in larger particles after drying. The high initial solids could sustain the droplet shape and hinder solute diffusion; as such droplet shrinkage behaviour deviates from the description of ideal shrinkage kinetics. A general correlation of shrinkage coefficient b was established for skim milk with initial solids content of 10–50wt.%, useful for estimating droplet shrinkage kinetics within this range.
Freeze-drying is a gentle drying technique to dry high value products, such as pharmaceuticals, without impacting the quality of the product. However, this method is very time and cost intensive. It ...is known that larger pores reduce the duration of primary drying due to facilitated mass transport. However, next to the pore size, other structural parameters exist whose influence on drying kinetics is still unknown. Therefore, the aim of this article is to investigate the influence of the microstructure (pore size, shape and orientation) on local primary drying kinetics. In the study, freeze-drying experiments on maltodextrin and sucrose solutions (c1 = 0.05 and c2 = 0.15 w/w) were carried out in a lyomicroscope. Two-dimensional images were recorded during the whole drying process and in the dry state and analyzed on the movement of the sublimation front, pore size, orientation and shape. Different microstructures were created by using different freezing parameters, namely two different cooling rates and solid concentrations. It could be shown that for pores with a high aspect ratio, the pore orientation was more important for the drying kinetics than the pore size, while for pores with a lower aspect ratio the pore size was the decisive parameter.
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