Temperature distribution in beech wood during vacuum drying

Temperature distribution in beech wood during vacuum drying. The temperature distribution and changes in humidity in beech wood in the form of friezes during drying in a vacuum were analysed. The intensity of the occurring phenomena of desorption and the volumetric flow of moisture through the anatomical structures of the wood, depending on the absolute pressure and the temperature of the process, was determined. It was found that the fastest temperature increase took place in the subsurface layers directly adjacent to the heating plates. The introduction of conditioning between the drying phases made it possible to even out the humidity and temperature distribution in the entire element. On the basis of the analysis of changes taking place between the volumes of the three components of wood, it was found that the volume of moisture in the form of vapor removed in the initial phase of drying is over 20 times greater than the volume of voids in wood structures, and in the following phases it decreases to 0.27. The average volume of vapour removed from 1 m3 of wood at the temperature of 55℃ is 13.9 m3/h, decreasing in the following phases to 9.1 m3/h at the drying temperature of 60℃ and then 3.1 m3/h at the temperature of 65℃. The drying rates for these phases reach the value of 0.15%/h, 0.17%/h and 0.075%/h, respectively. Direct measurements of wood moisture, made during the experimental course of the drying process at an absolute pressure of 150 hPa, follow the equivalent moisture, determined on the basis of the Hailwood-Horrobin model, taking into account the appropriate calculation factors.

The influence of continuous and periodic microwave drying on rosemary: drying and temperature kinetics

Continuous microwave is a heavily studied drying method known for its effectiveness and efficiency, however, it leads to overheating in most cases. The primary objective of the present research is conducting and evaluating a comparative study of continuous and periodic microwave drying on rosemary for various power levels (6, 9 and 12 W/g) and different pulse ratios to overcome the overheating challenge. The evaluation and assessment were based on drying and temperature kinetics. Drying kinetic study revealed that periodic and continuous microwave drying at 12 W/g had the least drying duration of 12.5 and 11 mins, respectively. Likewise, both processes had the highest drying rates of 0.364 and 0.461 kg H2O/ kg dry basis min. The temperature kinetic study showed that the periodic microwave drying (71.4°C) resulted in a lower maximum sample temperature than continuous microwave drying (79.2°C). The periodic microwave drying with higher pulse ratios had a more even heating throughout the drying process than lower pulse ratios. Thereby, periodic microwave drying at 12 W/g and the highest pulse ratio was deemed to be the most suitable drying process for rosemary. The four thin layer models, namely Page, Modified Page, Midilli & Kucuk and Modified Midilli & others, were the most suitable to describe the drying kinetics of rosemary.

Study of secondary heat sources over India during southwest monsoon 2002

The southwest monsoon of 2002 has three unusual features viz., (i) delay in advance over westernmost parts of India by one month, (ii) absence of depressions/storms over Bay of Bengal and Arabian Sea and (iii) -51% departure of all India rainfall in July. These features of intra-seasonal variability have been studied in this paper. Apparent heat source (Q1) and apparent moisture sink (Q2) over Indian region have been estimated using daily NCEP-reanalysis data, for June - September 2002 to study the intra-seasonal variations of the secondary heat sources in relation to observed intra-seasonal variations of circulation and rainfall over India.The intensities of vertically integrated heat source < Q1 > and moisture sink < Q2 > are found to coincide with the excess rainfall zone over India in June 2002, whereas the intensities of < Q1 > and < Q2 > over central parts of the country in July 2002 are not comparable. This indicates absence of convective rainfall and increased sensible heating over India in July. The x-t diagram of heating and drying rates at 500 hPa along 22.5° N shows large positive heating and drying rates of the order of 16° C per day over the western trough region around 26 June. Following this event, low positive or negative values are observed over central India in July.The y-t diagram of vertical velocity at 500 hPa shows strong subsidence near the foot hills of Himalayas during the season. This has affected the formation of depressions or storms over Bay of Bengal and Arabian Sea. Adiabatic and diabatic heating as well as drying in the troposphere has led to the break-like situation over India in July 2002 and weaker monsoon circulation during August and September. The analysis has brought out the impact of northern hemispheric mid-latitude circulation on intra-seasonal variability of southwest monsoon 2002 more clearly.

Drying of porous materials at pore scale using lattice Boltzmann and pore network models

Drying at macroscale shows a first drying period with constant drying rate followed by second drying period showing a receding moisture front, phenomena that can be tailored upon need. In order to study the drying of materials, we present a new hybrid computational method, where the dynamics of the liquid-vapor interfaces is modelled by lattice Boltzmann modelling (LBM) in the two-phase pores, while the single-phase flow in the pores filled solely by vapor or liquid is solved by pore network model (PNM). This hybrid method is validated by comparison with reference full LBM simulations. The hybrid method combines the advantages of both methods, i.e., accuracy and computational efficiency. LBM and the hybrid LBM-PNM method are used to study the drying of porous media at pore scale. We analyse two different pore structures and consider how capillary pumping effect can maximize the drying rate. Finally, we indicate how optimized drying rates are relevant when designing facade or pavement solutions that can mitigate higher surface temperatures in urban environments by evaporative cooling.

Potential of microwave drying technology for increase drying rate and physical quality of kaffir lime (Citrus hystrix DC) leaves

The effects of microwave power on microwave drying rates and the physical quality of kaffir lime leaves were studied. Three power levels were used in this study, high (723 watts), medium (537 watts), and low (420 watts). The moisture content, drying rate, color (L, a, b), and organoleptic parameters of each power level will be compared with the oven drying method (60°C). The result shows that the final moisture content of the high, medium, and low power of microwave drying are 6.06, 4.26%, and 6.16%db respectively, which is lower than oven drying, 16.62%db. Besides, the drying rate of microwave drying is 26.39-48.71%db/minute, higher than oven drying 0.32%db/minute. Dried kaffir lime leaves with medium level power (537 watt) has the lowest color difference (ΔE = 1.0 ± 0.29) compared to fresh leaves. While, the color and aromatic preference test dried kaffir lime leaves by microwave drying was preferable than oven drying.

Development a Solar Dryer for low income group Farmers for sub cooled region

Solar dryer is a device that use solar energy to dry substances, especially food and agriculture product. Drying is one of the indispensable techniques for large-scale food preservation. There are already various types of solar dryer available but need a better performing solar dryer which can perform better in low sunshine hours and also in off sunshine hours. In present work combination of trapezoidal and tunnel type structured solar dryer developed for experimental trials. It showed better efficiency and effectiveness in compared to the existing solar dryers with respect to previous design available so far. After the experiments, it is found that maximum temperature rise was recorded 76°C however ambient temperature was 24 °C. At same time % reduction in weight was highly appreciable after three to four hour drying. Results of drying rates up to 50% after three hour drying. So present solar dryer is economical and potential solution to preserve the vegetables and crops to improve income of formers.

Design and evaluation of a refractance window lab-scale dryer

Purpose Refractance window drying (RWD) has been identified as the method that can give high-quality products at a relatively low production cost. However, knowledge about its use and adoption remains lacking both in academic curricula and industry in the developing world. Design/methodology/approach A lab-scale batch RWD of a closed-loop control system was designed, fabricated and evaluated for drying rates, evaporation rate, the energy of evaporation, energy efficiency and throughput. Testing was done using mango and tomato pulps. Findings Drying rates at 95°C of 1.32 gg−1min−1 and 0.854 gg−1min−1 at 2 and 3 mm, respectively, for tomato, 0.6 gg−1min−1 and 0.33 gg−1min−1 at 2 and 3 mm for mango pulp were obtained. The dryer had an evaporation rate of 4.63 × 10–4 kg/s and 4.25 × 10–4 kg/s, the energy of evaporation of 1.05 kW and 0.96 kW and thermal energy efficiency of 25.64% and 21.73% while drying tomato and mango pulps, respectively. Dryer throughput of 0.6 kg/h of dried mango Pulp and 0.47 kg/h of dried tomato pulp was obtained. Originality/value The designed RWD can be adequately used in laboratory experiments on different products to produce powders. This will enable the transfer of knowledge about RWD technology in developing countries.

Modelling the kinetics of microwave drying of shallot (Allium cepa) slices

Convective drying is typically used to dry shallot (Allium cepa) commercially. However, a long drying time with a relatively low efficiency has led to the pursuit of new and improved drying methods. Microwave drying was chosen to be used due to its numerous advantages such as improved drying time, high drying efficiency and better product quality. In this research, three microwave power (180 W, 300 W, 450 W) and convective drying at 100°C were used. Results showed that drying kinetics (moisture content and drying rates) decreased the fastest at higher microwave power and the slowest using convective drying. In order to determine the best model to describe the thin-layer drying kinetics, four semi-empirical models were used namely Newton, Page, Logarithmic and Two-term models. Page model was found to be the best in describing the thin-layer microwave drying kinetics. Effective diffusivity values increased with higher microwave power and were found to be in the range of 6.62 × 10−6 m2/s to 3.69 × 10−5 m2/s with convective drying being the lowest (6.62 × 10−6 m2/s) and 450W being the highest (3.69 × 10−5 m2/s). Microwave drying is therefore able to improve drying kinetics compared to convective drying.

Optimizing Spray-Dried Porous Particles for High Dose Delivery with a Portable Dry Powder Inhaler

This manuscript critically reviews the design and delivery of spray-dried particles for the achievement of high total lung doses (TLD) with a portable dry powder inhaler. We introduce a new metric termed the product density, which is simply the TLD of a drug divided by the volume of the receptacle it is contained within. The product density is given by the product of three terms: the packing density (the mass of powder divided by the volume of the receptacle), the drug loading (the mass of drug divided by the mass of powder), and the aerosol performance (the TLD divided by the mass of drug). This manuscript discusses strategies for maximizing each of these terms. Spray drying at low drying rates with small amounts of a shell-forming excipient (low Peclet number) leads to the formation of higher density particles with high packing densities. This enables ultrahigh TLD (>100 mg of drug) to be achieved from a single receptacle. The emptying of powder from capsules is directly proportional to the mass of powder in the receptacle, requiring an inhaled volume of about 1 L for fill masses between 40 and 50 mg and up to 3.2 L for a fill mass of 150 mg.

Use of diffusive and empirical models to predict drying rate of acerola seeds (Malpighia sp.)

The thin layer drying process of acerola seeds was analyzed using a flat plate geometry diffusion model, Page's model, and a two-part model proposed based on the diffusion equation. These models were fitted to experimental drying kinetics data of acerola seeds for an air flow speed of 1.5 m/s, at temperatures of 40, 50, 60 and 70°C, using non-linear regression by Levenberg-Marquardt method. The diffusion model was used to determine the diffusion coefficients and activation energy. The predicted and experimental results were compared using the determination coefficient (R2) and mean square error (MSE) of the estimates as criteria. The results showed that the diffusion model is not suitable for predicting the drying rate of acerola seeds, while Page’s equation and the two-part proposed model can be safely used to predict the drying rates.