Average Effective Diffusivity Research Articles

Performance enhancement of indirect solar dryer with offset strip fins: Experimental investigation and comparative analysis

In the present study, two indirect type solar dryers were designed, fabricated and experimentally investigated, one is equipped with a conventional flat plate collector, and the other is integrated with offset strip fins (OSF). The objective is to study the effect of OSF on the performance of the dryer. A series of experimental tests were conducted at the applied research unit in the semi-arid region of Ghardaia using locally available materials. The first test was starting the solar dryers with an empty chamber and the second with filled product. The peak and average temperature difference at the outlet of the collector were 11.3 and 8 °C respectively, in favor of OSF absorber. The courgette was dried to 0.69 (kg water/kg dry basis) from an initial moisture content of 26.24 (kg water/kg dry basis) in 20 h 18 min and 35 h 45 min in the solar dryer with OSF and without, respectively. The results show a high drying rate using the dryer with OSF compared the dryer with conventional collector. Also, Midilli-Kucuk model provided the best agreements between experimental and predicted moisture ratios. Average effective moisture diffusivity of 1.798x10−09 and 1.179x10−09 m2/s for the dryer with OSF and without, respectively. A 33 % increase in economic efficiency in favor the OSF dryer with 0.95 years payback period. Also, a reduced amount of GHGs makes the dryers environmental friendly.

Performance evaluation of innovative sensible energy storage material integration as an obstacle in solar collectors for drying applications

This research paper presents an innovative approach to enhance the performance of solar collectors in drying processes by integrating a sensible energy storage material within the airflow passage as an obstacle. The study involves a real-time comparative analysis of different collector configurations, under identical meteorological conditions, including flat collector, finned collector and rock integrated collector. The experimental results demonstrate that at high flow rate the collector equipped with fins achieves higher outlet temperatures, with a maximum of 59.8 °C, compared to 58.2 °C for the collector without fins. Additionally, for low and intermediate flow rates, the collector utilizing rocks as the energy storage material exhibits a maximum outlet temperature of 70.2 °C, while the collector with fins reaches 76.8 °C. Notably, the collector with rocks demonstrates a temperature gain of 13.6 °C during the night period. The drying efficiency of both solar dryers is evaluated, and they achieve a final moisture content of 6 % from an initial moisture content of 88 % (kg water/kg wet basis) in 1452 and 1722 min in solar dryer with fins and rocks, respectively. The drying rate is observed to be higher in the solar dryer with fins compared to the one with rocks. Midilli-Kucuk model provided the best agreements between experimental and predicted moisture ratios. Furthermore, the average effective moisture diffusivity is found to be higher in the solar dryer with fins (6.39485E-10 m2/s) compared to the one with rocks (1.33512E-10 m2/s).

Study On Activation Energy, Moisture Diffusivity Effectiveness and Mathematical Modelling of Thin Layer Drying Kinetics of Red Pepper (Capsicum Annum L.)

The thin-layer drying behavior of red pepper sample was examined using seven mathematical models that were found in the literature. According to the R2, RMSE, and v2 values with respect to the experimental and predicted moisture ratios the models were contrasted. The drying process happened throughout the period of falling rates. The findings demonstrated that the most acceptable model is the Midilli model for describing the drying behavior of thin layer pepper samples. The effective moisture diffusivity and moisture content were shown to be correlated by a third order polynomial relationship. As the moisture content of the pepper samples decreased the moisture diffusivity effectiveness increased, with an energy activation of 40.54 KJ/mol, the average effective diffusivity over the temperature range investigated was between 4.7 x 10-9 to 13.3 x 10-9 m2/sec.

Non-thermal ultrasonic contact drying of pea protein isolate suspensions: Effects on physicochemical and functional properties

Pea protein isolate (PPI) is a popular plant-based ingredient, typically produced through alkaline-isoelectric precipitation and thermal drying. However, high temperatures and long drying times encountered in thermal drying can denature PPI and cause loss of functionality. This study investigated the use of an innovative ultrasonic dryer (US-D) at 30 °C for drying PPI suspensions, compared to conventional hot air drying (HA-D) at 60 °C. US-D led to an increase in the drying rate and correspondingly reduced the drying time by 55 %, when compared to HA-D. The average effective moisture diffusivity in the US-D process was 325 % higher than that in the HA-D process. The resulting PPI exhibited higher solubility, emulsification, and foaming properties than HA-D PPI, with a unique surface morphology and higher surface area. This study demonstrated that drying with acoustic energy is a promising approach for producing dried plant protein ingredients with improved functional properties, reduced processing time, and increased production efficiency.

Kinetic model describing self-limiting CO2 diffusion in supported amine adsorbents

A reaction–diffusion shrinking core model describing the decay in diffusivity of supported amine sorbents upon CO2 sorption under both simulated direct air capture and point source capture conditions is described. The decay in CO2 diffusivity is associated with crosslinking in the aminopolymer samples and general pore blockage in the amino-silane derived samples, which occurs as CO2 is adsorbed. The model is used to extract four kinetic parameters that govern the CO2 uptake kinetics and working capacity: an apparent reaction rate constant, an initial effective diffusivity, and two dimensionless decay parameters. Ideally, an initially reaction limited system would allow for direct determination of the intrinsic reaction rate constant; however, sorption experiments suggest mass transfer resistances related to gas mixing, external boundary layers and intraparticle diffusion are present. Reaction rate constants are determined and agree well with theoretical values predicted with the Eyring equation parameterized using density functional theory energies from literature sources. The kinetic performance is expressed as the average effective diffusivity as a function of average conversion, which can be correlated to the dispersion of sorption sites on the support and the morphology of the active sorbent phase. Four supports are impregnated or grafted with amines, SBA-15, single-walled zeolite nanotubes (ZNT), Syloid SiO2, and γ-Al2O3. Due to its pore structure, γ-Al2O3 supported amines can be modeled at the μm scale or at the nm scale, where the shell balance is on the μm-sized macroporous particle aggregate or on the nm-sized amine film on the surface of the Al2O3 nanoparticles, which comprise the spherical particle aggregates. Faster diffusion rates are maintained under 400 ppm rather than 10% CO2 due to a slower reaction rate giving a slower decay in diffusivity. This work provides a first principles kinetic analysis of CO2 sorption where previous models are semi-empirical and use arbitrary kinetic parameters.

Performance assessment of passive indirect solar dryer comparing without and with heat storage unit by investigating the drying kinetics of carrot

The present study examined the drying kinetics of carrots and the effectiveness of passive indirect solar dryer without (setup-I) and with (setup-II) thermal energy storage (TES). A module containing paraffin wax as a TES unit was incorporated after the test was completed in setup-I to create setup-II. The sample slices were dried in setup-I and setup-II at a drying rate of 0.5 and 0.59 kg/h, respectively. In setup-I, the sample dried from 9.13 to 0.478 dry basis (db) in 16 h, whereas, setup-II took 15 h. The thermal efficiency of the solar heater and actual heat supply for the same were 56.84 & 60.79% and 705.64 & 730.45 W, respectively. Similarly, the average heat and mass transfer coefficients (h and hm) were 6.32 & 7.08 W/m2 K and 0.0055 & 0.0062 m/s, and average effective diffusivity (De) for the same setups were 6.7 × 10−9 and 7.24 × 10−9 m2/s, respectively. Furthermore, the specific energy consumption and specific moisture extraction rate for the same were 3.5 & 0.28 kWh/kg and 0.29 & 3.62 kg/kWh, respectively. Setups I and II had an average drying efficiency of 7.5 and 10.25%, respectively. The activation energy was evaluated for both setups. The De, h and hm were correlated with moisture content for both setups. In addition to helping the drying process to be completed in a day, setup-II performed better in all the evaluated parameters than setup-I. To ensure the reliability of the results, an experimental uncertainty analysis was conducted.

Novel connectivity tensor for a systematic assessment of topology and anisotropy of real membranes and microporous structures

In this work, an original and complete systematic topological assessment of anisotropy, connectivity and tortuosity of real 3D porous structures is presented. Several novelties are introduced here, like: the definition of the Average Effective Diffusivity Tensor (AEDT), allowing us to assess the desired topological parameters, the novel concept of connectivity tensor based on the inverse of the (diagonal) tortuosity tensor, the development of a new procedure of digital reconstruction of real 3D structures for CFD purpose, and a novel methodology for the connectivity tensor calculation, which avoids time-dependent diffusivities. After a detailed explanation of methodology and related validation using well-known 3D structures, we analyse two different real digitally-reconstructed 3D structures: LTL zeolite and clinoptilolite. As key-result, the internal voids distribution is characterised in terms of several existing and new topological parameters, all obtained from the mathematical properties of tortuosity and connectivity tensors. Among them, particular useful are the here-defined directionality factors, which indicate the preferential diffusional paths. The proposed approach is relatively easy and can be effectively applied not only to characterise existing materials, but also to design novel ones (in form of catalysts, selective membranes and/or adsorbents) with desired and predictable topological and mass transport properties.

Solar drying of peppermint leave: Thermal characteristics, drying kinetics, and quality assessment

In the present study, thermal performance of greenhouse solar dryer (GHSD) was analyzed at full load of peppermint leaves for dehydration. The experiments were conducted in both GHSD and sun drying processes to compare drying characteristics, thermal properties, and quality assessment of peppermint leaves. The maximum drying cabin temperature attained during the experimentation was 58.3 °C at solar radiation 864W/m2. Initial moisture content of peppermint leaves 81.25% reduced to 11.22% and 22% within 10 h in GHSD and sun drying, respectively. Drying rate was obtained as 0.65 kg water/kg solid.hr and 0.61 kg water/kg solid.hr for GHSD and sun drying process at the end of the experiment. Verma et al. model accurately defined the drying characteristics of peppermint leaves in GHSD and sun drying. Average effective moisture diffusivity (Deff), mass transfer coefficient (hm) and heat transfer coefficient (h) of peppermint leaves were increased by 12.76%, 17.71%, and 64.23%, correspondingly in GHSD compared to sun drying. Activation energy (Ea) of peppermint leaves was computed as 32.25 kJ/mol in GHSD, while in sun drying method, it was 59.68 kJ/mol. Water activity (Aw) peppermint leaves were 0.850, 0.705, 0.385 and 0.850, 0.765, 0.520 at 8, 14, 19 h in GHSD and sun drying.

Moisture Diffusion in Passion Fruit Seeds under Infrared Drying

In order to contribute for a better understanding of the moisture diffusion in infrared (IR) drying of residual seeds from passion fruit processing, the effective moisture diffusivity (Deff) in the particles was determined from experimental drying kinetics using two different approaches, in which it is considered either as a constant parameter during the process or as dependent on moisture ratio (XR). Experiments were conducted with the seeds arranged in a single layer and exposed to three IR source temperature levels (50, 65 and 80°C). The IR source was set at a distance of 15 cm from the samples. The average effective moisture diffusivity was in the range from 2.76 x 10-11 to 11.03 x 10-11 m2 s-1. The activation energy for IR drying was 53.3 kJ/mol. Results of Deff as a function of XR, obtained using the slope method, indicated that at higher IR source temperatures the vapor diffusion is the main mechanism of moisture transport, while at lowest drying temperature, the process is controlled by both liquid and vapor diffusion.

DRYING KINETICS AND QUALITY EVALUATION OF THAI RICE NOODLES USING FAR-INFRARED RADIATION

This study investigates the drying characteristics and quality (color, texture, water activity, rehydration ratio, and microstructure via scanning electron microscopy) of dried Thai rice noodles using far-infrared radiation. Infrared (IR) radiation to dry rice noodles increases porosity. It will assist retain the shape of the Thai rice noodle and reduce the browning reaction when restored by soaking in hot water. The experiments were conducted with infrared power of 200, 400, and 600 W; air velocity of 1.0 m/s; and distance between the sample and radiator of 200 mm. Then, the drying kinetics of Thai rice noodles dried by far-infrared radiation were investigated. The results showed that the drying of Thai rice noodles with far-infrared occurred when the drying rate decreased. The drying rate was 1.07×10−2–4.92×10–2 gwater/gdry mass·min, and the drying time was 60–270 min. The higher the infrared power, the faster the drying rate and the shorter the drying time. The experimental data were fitted to various thin-layer drying models. The Midilli–Kucuk model was the best model to obtain the highest R2 value, the lowest root mean square error, and c2 values. The average effective moisture diffusivity (Deff)avg increased with increasing infrared power. Quality results, such as color tone, water activity, hardness, and rehydration ratio, were compared with commercially available dried products. Infrared drying was found to improve the quality of the dried noodles.

Color changes and drying kinetics modeling of basil seed mucilage during infrared drying process

The physicochemical properties and color of dried seed mucilage (gums) depend on the condition and method of drying. So, in this study, the effects of infrared (IR) dryer system parameters such as IR power (150, 250, and 375 W), distance of mucilage from lamp surface (4, 8, and 12 cm), mucilage thickness (0.5, 1.0, and 1.5 cm) on drying kinetics and color indexes (L*a*b*) of basil seed mucilage (BSM) were examined in an IR dryer system. IR drying kinetic of BSM was modeled using mathematical approach. Thus, experimental moisture ratio data were fitted to 8 various empirical models. It was found that Page model has the best fit to show the kinetic behavior and acceptably described the IR drying behavior of BSM with the highest correlation coefficient values and the lowest standard error values. The average effective moisture diffusivity (Deff) increased from 1.69 × 10−9 to 9.21 × 10−9 m2/s with increasing lamp power from 150 W to 375 W, while it was decreased from 7.93 × 10−9 to 2.65 × 10−9 m2/s and 7.81 × 10−9 to 1.82 × 10−9 m2/s with increasing the distance of mucilage from 4 to 12 cm and the reduction of mucilage thickness from 1.5 to 0.5 cm, respectively. The increasing in IR radiation power has a positive influence on the lightness (increasing L* index) of dried BSM and it reduced color changes index (ΔE) from 13.04 to 11.51. The results showed that IR drying method has great industrial potential in saving processing time as well as energy with better maintenance of color and quality of dried BSM.

INFRARED DRYING KINETICS OF COATED PEACH SLICES WITH BASIL SEED AND XANTHAN GUMS

The objective of the current work was aimed to estimate the influence of novel edible coatings based on basil seed and xanthan gums, and infrared (IR) radiation power on the drying efficiency of coated peach slices were investigated in an IR dryer system. Moisture ratio data of IR drying of peach slices were fitted to 7 various empirical thin-layer equations. It was found that Page model has the best fit to show the kinetic behavior and acceptably described the IR drying behavior of coated peach slices with the lowest mean square error (MSE), root mean square error (RMSE), mean absolute error (MAE), and standard error (SE) values and the highest correlation coefficient (r) value. The values of MSE, RMSE, and MAE for all experiments were in the ranges of 0.00017-0.00047, 0.013-0.022, and 0.011-0.018, respectively. The average drying time of uncoated peach slices, coated by xanthan gum and coated by basil seed gum were 52.78, 60.00, and 76.22 min, respectively. The average effective moisture diffusivity (Deff) of uncoated and coated peach slices with basil seed and xanthan gums increased from 2.18×10-9 m2/s to 4.56×10-9 m2/s with increasing IR lamp power from 150 W to 375 W.

Effect of contacting pattern and various surfactants on phenol extraction efficiency using emulsion liquid membrane

Abstract Emulsions prepared using different surfactants, including Span-80, BKC and CTAB, are studied for their stability and phenol remsoval efficiency. The effect of contacting pattern on ELM extraction efficiency is compared in Beaker – Stirrer apparatus and Bubble Flow Recirculation column. The emulsion prepared using Span-80 is relatively more stable than emulsions prepared using other surfactants. The emulsion stability during the extraction process is relatively higher in the Bubble Flow Recirculation column (15 min) than in the Beaker – Stirrer apparatus (10 min). At optimized conditions, the phenol removal efficiency of the emulsion prepared using Span-80 in Beaker – Stirrer apparatus is 96% and in Bubble Flow Recirculation column is 78%. Kinetic studies reveal that the extraction follows zeroth-order kinetics with an average phenol effective diffusivity of 0.0004 s at an initial phenol concentration ranging from 100–500 PPM.

Influence of Infrared Drying on Drying Kinetics of Apple Slices Coated with Basil Seed and Xanthan Gums

ABSTRACT Edible coatings can guarantee the quality of agricultural products, and performance as a low oxygen barrier, carbon dioxide, and water vapor, allowing reducing water loss or controlling water adsorption. The objective of the current work was aimed to evaluate the effects of novel edible coatings based on basil seed and xanthan gums, and infrared (IR) drying efficiency of coated apple slices. Seven empirical thin-layer models were fitted to the moisture ratio data. It was found that Page model had the best fit to show the kinetic behavior and acceptably described the IR drying behavior of coated apple slices with the lowest mean square error (MSE), root mean square error (RMSE), mean absolute error (MAE), and standard error (SE) values and the highest correlation coefficient (r) value. The values of MSE, RMSE and MAE for all experiments were in the ranges of 0.00014–0.00058, 0.012–0.024 and 0.009–0.021, respectively. The average drying time of uncoated apple slices, coated by xanthan gum and coated by basil seed gum were 48.00, 60.22, and 84.78 min, respectively. The average effective moisture diffusivity (Deff) of uncoated and coated apple slices with basil seed and xanthan gums increased from 1.70 × 10−9 m2/s to 4.45 × 10−9 m2/s with increasing IR lamp power from 150 W to 375 W.

Drying kinetics of tomato (Solanum lycopersicum) and Brinjal (Solanum melongena) using an indirect type solar dryer and performance parameters of dryer

Tomato (Solanum lycopersicum) and brinjal (Solanum melongena) are food products that are frequently wasted in Indian markets as their shelf lives are only a few days. An indirect type solar dryer (ITSD) has been developed. It’s performance and drying kinetics of brinjal and tomato slices have been analyzed. The moisture content of tomato decreased from 15.667 to 0.803 kg/kg of dry basis (db) and that of brinjal reduced from 10.111 to 0.498 kg/kg of db. The drying curve was fitted with the different models of existing studies. The average effective moisture diffusivity is estimated and it is 3.60 × 10−9 and 4.00× 10−9 m2/s for tomato and brinjal, respectively. Mass transfer coefficient was in the range of 0.82 × 10−4 to 2.85 × 10−3 m/s for tomato and 1.11 × 10−4 to 3.32 × 10−3 m/s for brinjal. The heat transfer coefficient was in the range of 0.089 to 2.888 W/m2 K and 0.1066 to 3.3564 W/m2 K for tomato and brinjal, respectively. The activation energy for tomato and brinjal was 21.19 and 19.46 kJ/mol, respectively. The average thermal efficiency of the collector and dryer was 59.05% and 31.4% during tomato drying and 58.42% and 25.16% for brinjal drying, respectively.

Evaluation of effective diffusivity correlations for soybeans in thin layer drying

Soybean is one of the main crops in the world and drying plays an important role in maintaining the quality of the grains. The present study aimed to evaluate different existing models regarding the ability to predict the effective diffusivity of soybeans, an important parameter in studies of the operation. The slope method was used to determine the effective diffusivity, starting from the second Fick's Law, with negligible shrinkage and external mass transfer resistance. The parameter was analyzed as being dependent on both temperature and moisture content. The correlation proposed by Dotto et al. (2018) was the one with the lowest average error (0.048%) for the consideration of an average effective diffusivity. In order to consider a punctual effective diffusivity, modifications were made to the Dotto model, providing a maximum error of 2.6%.

Raman and photoacoustic spectroscopies of SnO2 thin films deposited by spin coating technique

SnO2 thin films were grown on glass substrate using a spin-coating technique. The films grown in different layers and subjected to pressure-assisted heat treatment (PAHT) were characterized by Raman spectroscopy and Photoacoustic measurements. Raman spectroscopy showed the SnO2 presence in the grown thin film and in the substrate. In addition, PAHT can change the adsorbed oxygen and the oxygen vacancies in the film. These changes strongly influence the band gap energy of samples, which were investigated by photoacoustic spectroscopy and showed a blueshift in samples after PATH treatment. A depth profile analyze with excitation on the substrate indicated a slow attenuation of the photoacoustic signal relative to tin dioxide up to 120 μm, which represents SnO2 presence up to 40 μm deep in the glass substrate. The average effective thermal diffusivity, determined by two-beam phase-lag photoacoustic method was α=(0.017 ± 0.001) cm2/s, according the literature for pure tin dioxide.

Development of indirect type solar dryer and experiments for estimation of drying parameters of apple and watermelon

In the present paper, an indirect type solar dryer (ITSD) has been developed for apple and watermelon drying. The performance of ITSD and drying kinetics of watermelon and apple slices have been analyzed. From the experimental analysis, diffusion coefficient, surface transfer coefficients and activation energy of apple and watermelon were estimated. Experimental outcomes showed that the temperature inside the drying cabinet varied with time because of frequent variation in solar intensity. The average thermal efficiency of the collector and dryer was 54.5% and 25.39% during apple drying and 56.3% and 28.76% for watermelon drying, respectively. Moisture content of apple decreased from 6.16 to 0.799 kg/kg of dry basis (db) and that of watermelon reduced from 10.76 to 0.496 kg/kg of db. Drying curve was fitted with different models of existing studies. Average effective moisture diffusivity was estimated and it was 4.28 × 10−9 m2/s and 4.01 × 10−9 m2/s for apple and watermelon, respectively. Mass transfer coefficient is found to be in the range 1.584 × 10−4 to 3.158 × 10−3 m/s for apple and 5.17 × 10−4 to 4.98 × 10−3 m/s for watermelon. Heat transfer coefficient was in the range of 0.16 to 3.19 W/m2 K and 0.52 to 5.04 W/m2 K for apple and watermelon, respectively. Activation energy for apple and watermelon is 17.34 and 18.71 kJ/mol, respectively.

Effective moisture diffusivity and drying simulation of walnuts under hot air

This study was conducted to determine the effective moisture diffusivity of walnuts for the understanding of drying mechanism and improved drying simulation. The drying characteristics of walnut shell and kernel were investigated during the single layer drying of in-shell walnuts at 43, 55, 65 and 75 °C with hot air. The values of average effective moisture diffusivity for walnut shell and kernel ranged from 1.51 × 10−9 to 9.28 × 10−9 m2/s and 1.13 × 10−9 to 2.85 × 10−9 m2/s, respectively. The 3rd order polynomial-exponential relationship well correlated the effective moisture diffusivity with sample moisture content (MC) and temperature (Radj2 > 0.983). A mathematical model with changing moisture diffusivity and heterogeneous components was developed. It simulated the in-shell walnut drying characteristics using finite element approach with good accuracy (Radj2 > 0.985). The outcomes provide important information for the understanding of moisture transfer mechanisms and have practical value for the optimization of operating conditions in the walnut drying industry.

Osmotic Dehydration of Cassava Cubes: Kinetic Analysis and Optimization

The present work had the objective of studying the osmotic dehydration process of cassava cubes (ManihotesculentaCrantz.) in ternary solutions containing water, sucrose, and sodium chloride. The osmotic dehydration process was studied by using a 24 factorial planning with central points at different conditions of temperature (19-63°C), solute concentration (23-67% w/w), operating time (70-190 min.) and NaCl concentration (0-20% w/w). The process optimization was verified through the performance ratio of minimum solids gain, in conjunction with the maximum moisture loss and reduction of water activity of the material. From the analysis, the optimum condition for osmotic dehydration of cassava cubes was temperature52°C, concentration of the osmotic solution 56%solute,10% NaCl concentration,160 minutes of immersion time and 180 rpm . The study of osmotic dehydration kinetics in the optimized condition showed that the moisture loss reached equilibrium in 180 minutes and the solids gain in 30 minutes. The model of Azuara and contributors was fitted to experimental data of moisture lost and total solids gain, in the optimal condition and good agreement were obtained. From this comparison, the average effective diffusivity coefficients of moisture (1.99x10-8m2/s) and total solids (2.77x10-8m2/s) were estimated.