Heat and Mass Transfer in Beds of Particles Undergoing Sublimation Dehydration

1973 ◽  
Vol 95 (4) ◽  
pp. 516-520 ◽  
Author(s):  
L. L. Hardin ◽  
D. F. Dyer
Keyword(s):  
Theoretical Work ◽  
Test Case ◽  
Drying Time ◽  
Number Of Layers ◽  
Bed Thickness ◽  
Drying Rates ◽  
Size Of Particles ◽  
Particle Bed ◽  
Particle Beds ◽  
Sublimation Dehydration

A theoretical analysis as well as an experimental study of sublimation freeze-drying is reported. The theoretical and experimental results compare within 10 percent for a test case. In addition, the theoretical work confirms that drying rates increase linearly with bed thickness for particle bed drying, as reported in earlier experiments. Drying times for a slab and particle beds with the same mass and dryer surface area are compared. It is shown that the drying time for the particle bed can be reduced by more than a factor of two compared to the equivalent slab. It is also shown that the optimum way to increase the drying rate of particle beds is to increase the number of layers rather than the size of particles.

scholarly journals Convective Drying of Sewage Sludge Layer in Through-flow

2020 ◽  
Vol 66 (9) ◽  
pp. 481-493
Author(s):  
Andraž Lipolt ◽  
Brane Širok ◽  
Marko Hočevar ◽  
Lovrenc Novak
Keyword(s):  
Sewage Sludge ◽  
Drag Force ◽  
Layer Structure ◽  
Measured Data ◽  
Matter Content ◽  
Convective Drying ◽  
Coefficient Of Determination ◽  
Dry Matter Content ◽  
Drying Time ◽  
Drying Rates

Drying of the sewage sludge layer was investigated in a convective laboratory dryer at air temperatures of 65 °C and 80 °C and air speeds of 0.53 m/s and 0.83 m/s. The sludge layer was formed by loading cylindrical extrudates on a grate of 0.5 m × 0.5 m size. The drying air was directed through the layer, as typically encountered in industrial belt dryers. Under such setup, the sludge layer structure and porosity significantly affect the air flow conditions and thus the drying rates. Shrinkage and cracking of the material during drying caused changes in the layer’s porous structure, that affected the pressure drop and the drag force due to passing of air through the layer. The decreasing of drag force over time was modeled by a simple function that showed excellent agreement to the selected measured data. The sludge layer drying kinetics was determined by fitting the measured data to the most common drying models. Two models, the modified Nadhari and the Wang Singh model, were determined as most suitable for modeling of drying curves. The total drying time per kilogram of sludge was modeled as a function of drying air temperature, drying air velocity and initial sludge dry matter content. The coefficient of determination (R2) of the model is 0.944. Total drying times between 43 minutes per kilogram and 76 minutes per kilogram of sludge were obtained for the investigated range of drying air conditions.

scholarly journals Effect of pre treatment methods on fruits drying of grapes under warm air condition

2018 ◽  
Vol 33 (01) ◽  
Author(s):  
Priti Jain ◽  
S. P. Shrivastava ◽  
Sheela Pandey
Keyword(s):  
Olive Oil ◽  
Soy Lecithin ◽  
Drying Time ◽  
Treatment Methods ◽  
Pre Treatment ◽  
Drying Rates

In the present study, grapes pretreated with different concentrations of potassium carbonates plus olive oil and soy lecithin with different dipping times. A dryer was built to perform the experiment under controlled condition of drying air at temperature 50°C and velocity 1.0 m/s. Grapes dipped into 1percentage olive oil plus 6percentage K2CO3 emulsion, at 50°C for 2 min. prior to drying showed shorter drying times and comparatively good quality raisin, whereas grapes dipped into 1.5percentage soy lecithin, at same conditions resulted in a total drying time slightly higher than the most effective pre treatment. The drying rates of grapes were modeled by the page equations. Grapes that are naturally dried usually darken in colour, whereas dipped grapes stay yellow-green.

Solar Assisted Dehydrator for Decentralized Controlled and Homogeneous Multi-Product Drying

2020 ◽  
Vol 143 (1) ◽  
Author(s):  
Waseem Amjad ◽  
Muhammad Waseem ◽  
Anjum Munir ◽  
Abdul Ghafoor ◽  
Furqan Asghar ◽  
...  
Keyword(s):  
Three Dimensional ◽  
Air Distribution ◽  
Drying Time ◽  
Specific Product ◽  
Heating Source ◽  
Batch Type ◽  
Evacuated Tube Collector ◽  
Drying Rates ◽  
Evacuated Tube ◽  
Drying Chamber

Abstract Batch type food dryers are common for drying agricultural produce due to simple in design, but they are prone to nonuniform drying and significant heat cost exclusively if they fall in the medium to large size range. The current study illustrates a solar hybrid food dryer using a gas burner and solar collector (evacuated tube collector, ETC) as heating source along with an inline perforation inside the drying chamber to obtain spatial drying homogeneity. Air distribution was assessed through three-dimensional simulation using computational fluid dynamics (CFD) analysis. Performance trials were conducted under three heating options (ETC, gas, and dual) using green chilies at 60 °C. Throughout drying chamber, under all heating modes, the average difference in drying rates ranged from 0.61 to 1.30 kg water/kg dry matter, demonstrating homogeneous drying. Simulated and experimental results of air distribution were found to be in agreement with each other. Using three options for thermal heating (ETC, gas, and dual) and an overall 58% efficiency for evacuated tube collector, the specific energy for moisture evaporation was found to be 4.5–5.7 MJ/kg and specific product energy 19.2–24.9 MJ/kg. In case of dual heating option, the energy supplied by solar and gas sources for a 20 hours period was 50.64% (160.22 MJ) and 49.35% (156.13 MJ), respectively. Compared with dual heating option, energy cost can be reduced by 68% if only solar energy is used as a heating option but with a protracted drying time.

WEATHER EFFECTS ON HAY DRYING RATES

1974 ◽  
Vol 54 (3) ◽  
pp. 479-484 ◽  
Author(s):  
H. N. HAYHOE ◽  
L. P. JACKSON
Keyword(s):  
Moisture Content ◽  
Dry Matter ◽  
Weather Data ◽  
Potential Evaporation ◽  
High Quality ◽  
Drying Time ◽  
Weather Effects ◽  
Maximum Production ◽  
Drying Rates

Observations taken at Nappan, N.S. of drying rates of field-cured hay and the corresponding weather data are reported. Three consecutive good days were chosen as the standard for good hay drying weather. Based on 30 yr of weather records, the highest probability (36%) of having this good weather at Nappan occurs in the first 2 wk of July. Maximum production of digestible dry matter in hay occurs about mid-June. Rapid storage of high quality forage is desirable. To facilitate harvest, early cuttings of forage should be taken as ensilage. An equation is developed which relates the observed moisture content in the field to the accumulation of potential evaporation from the time of cutting. The effect of precipitation on drying time is considered. An index based on potential evaporation and precipitation is proposed as a measure of the suitability of weather data for predicting field drying rates. A good drying day is defined in terms of this index and used in the estimation of the probability of sequences of good drying days from 30 yr of weather data from Nappan, N.S.

Influence of Drying Conditions and Mathematical Models on the Thin-Layer Drying of Mushrooms

2014 ◽  
Author(s):  
A. Stegou-Sagia ◽  
D. V. Fragkou
Keyword(s):  
Mass Transfer ◽  
Thin Layer ◽  
Mathematical Models ◽  
Drying Methods ◽  
Suitable Model ◽  
Drying Time ◽  
Thin Layer Drying ◽  
Drying Behavior ◽  
Drying Models ◽  
Drying Rates

In the present research, experimental data from several studies about drying behavior of mushrooms have been selected and used to compare different drying methods and different mathematical thin layer drying models to simulate mushroom drying rates. The white button (Agaricus Bisporus), the oyster (Pleurotus Ostreatus) and the milky mushroom slices have been considered for drying in different dryers such as hot air cabinet dryer and fluidized bed dryer with different slice thicknesses, drying air temperatures (45 °C to 90 °C) and drying air velocities (0.2 m/s to 5 m/s). The entire drying process has taken place in the falling rate period, assuming that internal mass transfer occurred by diffusion in mushroom slices. The study shows that the drying air temperature and the drying air velocity have an effect on the moisture removal from mushrooms and also on the drying time. Mathematical models have been proved to be useful for design and analysis of heat and mass transfer during drying processes. All the drying models considered in this study could adequately represent the thin layer drying behavior of mushrooms. Furthermore, as it is obvious, any type of mushrooms has its own most suitable model.

scholarly journals Drying rates of Rubi grapes submitted to chemical pretreatments for raisin production

2006 ◽  
Vol 41 (3) ◽  
pp. 503-509 ◽  
Author(s):  
Vânia Regina Nicoletti Telis ◽  
Vânia Araújo Lourençon ◽  
Ana Lúcia Gabas ◽  
Javier Telis-Romero
Keyword(s):  
Olive Oil ◽  
Soybean Lecithin ◽  
Aqueous Suspension ◽  
Convective Drying ◽  
Factorial Designs ◽  
Soy Lecithin ◽  
Drying Time ◽  
Drying Rates ◽  
Chemical Pretreatments ◽  
Drying Curves

The objective of this work was to determine the most appropriated chemical treatment to be used to dry grapes cv. Rubi for raisin production. Drying curves for convective drying with air at 50ºC, in a tray drier, were obtained for grapes submitted to chemical pretreatments with different concentrations of potassium carbonate and olive oil, and different dipping times, according to factorial designs. Convective drying curves were also obtained for grapes pretreated in aqueous suspensions of soybean lecithin, at varied lecithin concentrations and dipping times. Page model was adjusted to the experimental drying curves, and the calculated drying times showed that the best pretreatment consisted in dipping grapes for 2 minutes in a 5% olive oil and 6% K2CO3 emulsion, at 50ºC, which resulted in a drying time close to that of the pretreatment with 2.5% of olive oil, but with a lower consumption of this substance. In addition, the immersion of grapes in an aqueous suspension of 2% soy lecithin, at 50ºC, for 5 minutes, resulted in a total drying time slightly higher than the most effective pretreatment.

Through air drying assisted by infrared radiation: the influence of radiator power on drying rates and temperature

2018 ◽  
Vol 33 (4) ◽  
pp. 581-591
Author(s):  
Aron Tysén ◽  
Hannes Vomhoff ◽  
Lars Nilsson
Keyword(s):  
Infrared Radiation ◽  
Power Level ◽  
Infrared Camera ◽  
Drying Time ◽  
Air Drying ◽  
Hot Air ◽  
Ir Heating ◽  
Chemical Pulps ◽  
Drying Rates ◽  
Positive Effect

Abstract The use of infrared radiation for heating the web in the through air drying process was investigated in lab scale. The hypothesis was that infrared radiation should be a more efficient method to transfer drying energy to the wet web compared to hot air, but that a certain air flow is still required as a transport medium for the evaporated water. A trial program comprising handsheets made of two types of bleached chemical pulps, five grammages (15, 22, 30 and 60 g/m²), and dried with five radiator power levels was performed on a lab scale through air drying equipment. Drying times of the samples were determined from temperature data recorded with an infrared camera. The use of infrared radiation shortened drying times, especially for low grammage samples. The shortening of the drying time ranged between 10 and 45 %. The most substantial shortenings were obtained for the lowest grammages and the highest radiator power level. However, the increase of power did not linearly shorten drying time. After an initial shortening at the lowest power level, the positive effect of the IR heating decreased as the power was further increased.

Process optimization of paddy drying in cross-flow aerated drying cum storage bin

2020 ◽  
Vol 44 (03) ◽  
pp. 7-15
Author(s):  
Sruthi N. U. ◽  
U. C. Lohani ◽  
N. C. Shahi ◽  
J. P. Pandey
Keyword(s):  
Air Temperature ◽  
Specific Energy Consumption ◽  
Cross Flow ◽  
Moisture Diffusivity ◽  
Airflow Rate ◽  
Experimental Conditions ◽  
Heating Chamber ◽  
Drying Time ◽  
Drying Rates ◽  
Drying Conditions

A cross-flow aerated drying cum storage bin was developed and the drying conditions for paddy was optimised. The drying cum storage bin consisted of a cylindrical outer drum with two inner basins having perorated walls made of galvanised iron to hold paddy, and a central perforated vertical duct. A blower (1.5 kW) connected at the base supplies air to the heating chamber (with 1 kW heater coil) and moves vertically through the central duct. The hot air passes horizontally through the grain bulk taking the moisture and moves towards the perforated walls of the bin and exit through the space between the drum and the basins. Drying experiments were conducted with bed thickness of 15 cm to study the drying characteristics of paddy and evaluate the performance of the dryer. Paddy was dried from 18 to 12% (wb) moisture content with the independent parameters selected being drying air temperature (35, 40 and 45 °C) and airflow rate (15, 21 and 27 m3 /h). The drying time varied 1.5 to 4.75 hours over the entire experimental conditions. The analysis of drying rates for both top and bottom bins showed minimum variation indicating uniform drying throughout the depth of the bin. The estimated optimum conditions of drying were 45°C temperature and 27 m3 /h airflow rate. The predicted values of responses at optimised conditions were 1.51 hours of drying time, 6.05x10-7 m2 /s of effective moisture diffusivity, 0.078 W/m2 K of heat transfer coefficient, and 8.23x105 kJ/kg of specific energy consumption. Further, exergy analysis indicated that exergy loss increased with increase in drying air temperature and airflow rate.

scholarly journals Potential of Pulsed Electric Fields for the preparation of Spanish dry-cured sausages

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Leire Astráin-Redín ◽  
Javier Raso ◽  
Guillermo Cebrián ◽  
Ignacio Álvarez
Keyword(s):  
Electric Fields ◽  
Meat Products ◽  
Pulsed Electric Fields ◽  
Water Transfer ◽  
Curing Process ◽  
Drying Process ◽  
Drying Time ◽  
Pilot Plant Scale ◽  
Drying Rates ◽  
Meat Samples

Abstract The aim of this investigation was to lay the groundwork of the potential application of Pulsed Electric Fields (PEF) technology for accelerating the drying process of meat and meat products, and specifically in this work of Spanish dry-cured sausages “longaniza”. PEF treatments were applied to pork loin samples, and the influence of different PEF parameters on the process were evaluated. An optimal PEF treatment of 1 kV/cm, 200 μs of pulse width and 28 kJ/kg was determined as the most suitable to electroporate meat cells and to improve water transfer by achieving a water content reduction of 60.4% in treated-meat samples dried at 4 °C. The influence of PEF on meat drying rate was also studied on minced pork and the results showed that with a particle size of 4.0 mm higher drying rates were achieved. To validate the results, Spanish cured sausages were prepared from treated and untreated minced pork and stuffed into gauzes and natural pork casings at pilot plant scale. After the curing process, the application of PEF to sausages stuffed into gauze reduced the drying time from 17 to 9–10 days, a reduction of 41–47%, confirming the effects described at lab scale and the potential of PEF for accelerating the sausage-drying process.

Comparison of Drying Rates of Ground Western Red Cedar with Hemlock, Birch, Aspen, and Spruce/Pine/Douglas Fir

2020 ◽  
Vol 36 (2) ◽  
pp. 159-165 ◽  
Author(s):  
Hamid Rezaei ◽  
Jim Lim ◽  
Shahab Sokhansanj
Keyword(s):  
British Columbia ◽  
Wood Species ◽  
Smoke Point ◽  
Douglas Fir ◽  
Drying Rate ◽  
Small Particles ◽  
Drying Time ◽  
Red Cedar ◽  
Western Red Cedar ◽  
Drying Rates

HighlightsWRC and SPF generate the largest fraction of small particles (<0.5 mm) during grinding.WRC is slightly low in total sugars, high in lignin content (should make durable pellets), and high in extractives.Aspen followed by WRC has the highest drying rate and the shortest drying time amongst all samples.Smoke point is similar for all wood species and is ~180°C.Abstract.Western red cedar () and yellow cedar () are among the most valuable tree species in British Columbia. These species make up about 20% of the coastal timber volumes and mostly are used as lumber for construction applications where resistance against decay is important. The use of red cedar for pellet production has been uncertain because it appears cedar has a tendency to cause fires in rotary drum dryers when compared to other wood species like pine and Douglas Fir. The scientific reasons for the reported fire incident are not known. The goal of the current study is to investigate the drying rates and the range of combustion temperature for western red cedar and five other wood species that either are used or have potential to be used for palletization purposes in British Columbia. Red cedar and Spruce/Pine/Fir (SPF) generate the largest fraction of small particles (<0.5 mm) during grinding. Almost 93% of cedar particles are less than 1 mm. Cedar has a high carbon content and low oxygen content that causes cedar has higher calorific value than other species. During a drying process, aspen following by cedar has the highest drying rate and the shortest drying time amongst all samples. The smoke point is similar for all wood species and is ~180°C. So, in the case of high temperature drying (beyond the smoke point) of mixed feedstocks with similar size, red cedar dries faster and starts smoking at dryer output. Keywords: Chemical composition, Drying rate, Physical characterization, Smoke point, Western red cedar.

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