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BACKGROUND: Combined infrared (CIR) and convective drying is a promising technology in dehydrating heat‐sensitive foods, such as fruits and vegetables. This novel thermal drying method, which involves the application of infrared energy and hot air during a drying process, can drastically enhance energy efficiency and improve overall product quality at the end of the process. Understanding the dynamics of what goes on inside the product during drying is important for further development, optimization, and upscaling of the drying method. In this study, a multiphase porous media model considering liquid water, gases, and solid matrix was developed for the CIR and hot‐air drying (HAD) of sweet potato slices in order to capture the relevant physics and obtain an in‐depth insight on the drying process. The model was simulated using Matlab with user‐friendly graphical user interface for easy coupling and faster computational time. RESULTS: The gas pressure for CIR‐HAD was higher centrally and decreased gradually towards the surface of the product. This implies that drying force is stronger at the product core than at the product surface. A phase change from liquid water to vapour occurs almost immediately after the start of the drying process for CIR‐HAD. The evaporation rate, as expected, was observed to increase with increased drying time. Evaporation during CIR‐HAD increased with increasing distance from the centreline of the sample surface. The simulation results of water and vapour flux revealed that moisture transport around the surfaces and sides of the sample is as a result of capillary diffusion, binary diffusion, and gas pressure in both the vertical and horizontal directions. The nonuniform dominant infrared heating caused the heterogeneous distribution of product temperature. These results suggest that CIR‐HAD of food occurs in a non‐uniform manner with high vapour and water concentration gradient between the product core and the surface. CONCLUSIONS: This study provides in‐depth insight into the physics and phase changes of food during CIR‐HAD. The multiphase model has the advantage that phase change and impact of CIR‐HAD operating parameters can be swiftly quantified. Such a modelling approach is thereby significant for further development and process optimization of CIR‐HAD towards industrial upscaling. © 2020 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Abstract: BACKGROUND: Drying is a method used to preserve agricultural crops. During the drying of products with high moisture content, structural changes in shape, volume, area, density and porosity occur. These changes could affect the final quality of dried product and also the effective design of drying equipment. Therefore, this study investigated a novel approach in monitoring and predicting the shrinkage of sweet potato during drying. Drying experiments were conducted at temperatures of 50–70 °C and samples thicknesses of 2–6 mm. The volume and surface area obtained from camera vision, and the perimeter and illuminated area from backscattered optical images were analysed and used to evaluate the shrinkage of sweet potato during drying. RESULTS: The relationship between dimensionless moisture content and shrinkage of sweet potato in terms of volume, surface area, perimeter and illuminated area was found to be linearly correlated. The results also demonstrated that the shrinkage of sweet potato based on computer vision and backscattered optical parameters is affected by the product thickness, drying temperature and drying time. A multilayer perceptron (MLP) artificial neural network with input layer containing three cells, two hidden layers (18 neurons), and five cells for output layer, was used to develop a model that can monitor, control and predict the shrinkage parameters and moisture content of sweet potato slices under different drying conditions. The developed ANN model satisfactorily predicted the shrinkage and dimensionless moisture content of sweet potato with correlation coefficient greater than 0.95. CONCLUSION: Combined computer vision, laser light backscattering imaging and artificial neural network can be used as a non‐destructive, rapid and easily adaptable technique for in‐line monitoring, predicting and controlling the shrinkage and moisture changes of food and agricultural crops during drying. © 2017 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

A wheat harvest system simulation Model (WHSSM) was developed and used to investigate the economics of using aerated storage to minimise the impact of weather damage during wheat harvesting. The economic returns from grain production with and without aerated storage were examined using 15 years (1991–2005) of weather data for Goondiwindi, Queensland, Australia. The effect of different drier capacities was investigated. For continuous flow driers and batch driers, the optimum harvest moisture contents in the given farm setup were 14 and 13%, respectively. No positive effects from using aerated storage were achieved if growers use either high or medium capacity driers. Aeration cooling was however useful in supporting low-capacity drier with inadequate drying capacity or batch driers when the grain is harvested at high moisture contents. The results of this study highlight the importance of optimising the integration between agricultural machinery used, crop performance and perceived weather risk. [Copyright &y& Elsevier]

This paper presents an economic model for analyzing the cost behavior of dehumidifier timber drying process. Various costs, including those of air drying, are identified and quantified. Reasonable assumptions are made to simplify the calculation process. For species of both softwoods and hardwoods, the optimum air drying strategies are investigated based on two scenarios of existing commercial dehumidifier dryers and well-run high performance dehumidifier dryers. This paper finds that when the timber maximum air drying degrade rate is less than 5%, air drying adds significant value to the operation of dehumidifier dryers. This benefit accelerates with the extent of air drying. With the use of high performance dehumidifier dryers, the importance of air drying tends to decrease. The cost of air drying is very sensitive to both the assumed interest rate and timber maximum air drying degrade rate. [ABSTRACT FROM AUTHOR]

• A novel hybrid system based on a concentrating CPC solar collector was proposed for drying purposes. • The drying time can be reduced as 83 min using hybrid operation. • The maximum value of vitamin C obtained after the drying procedure was recorded as 375.941 mg/100 g. • The daily average solar fraction can vary from near 30 to 100% depending on the operation mode. In this study, a hybrid drying system incorporating a compound parabolic concentrator (CPC) solar collector and an electric auxiliary heater was developed to make advances in sustainable tomato drying. The proposed dryer was designed to operate in a combined mode with solar energy as the prime source of energy, and the auxiliary unit was only used in the cases with the absence of solar radiation or limitation in generated solar power. Experimental tests were carried out to investigate the drying performance at different levels of sample thickness, airflow rate, and drying temperature. Using image processing and high-performance liquid chromatography (HPLC) techniques, the quality of the dried products was also evaluated in terms of the changes in color, shrinkage, and vitamin C content. Results indicated that the average drying time was about 231 min, while the shortest time was obtained as 83 min, suggesting an improved performance compared to similar works. It was found that drying temperature is the key factor influencing the rate of color changes, and shrinkage is only affected by the thickness of tomato slices. The experimental data further showed that the destruction of vitamin C was mostly influenced by the drying air temperature and sample thickness. The maximum energy and exergy efficiencies of the solar collector were determined as 25 and 6% at the maximum and minimum airflow rates, respectively. [ABSTRACT FROM AUTHOR]

Intermittent infrared and convective drying (IIRCD) is a novel drying method that can enhance energy efficiency and quality of dried product. The mechanism of drying using this method is not yet fully understood. Mathematical models that describe the drying process of IIRCD for agricultural crops do not exist. In this study, a physics based mathematical model was developed to understand the mechanism of drying sweet potato using IIRCD. The model was based on shrinkage dependent diffusivity and evaporation phenomenon. COMSOL Multiphysics finite element software was employed for the model simulation. The simulation results of moisture and temperature distribution were validated by experimental drying data. The results fitted closely with experimental data. Drying of sweet potato using IIRCD was found to be more efficient in terms of final product quality compared to convective hot-air drying method. © 2018 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved. [ABSTRACT FROM AUTHOR]

Abstract This study examined the performance of different combined infrared (IR) and hot-air drying (HAD) strategies for sweet potato. Experiments were conducted for simultaneous infrared and hot-air drying, two-stage sequential hot-air and infrared drying, two-stage sequential infrared and hot-air drying, and intermittent infrared and hot-air drying in a laboratory scale combined infrared and hot-air dryer. The drying air temperature varied between 50 and 70 °C, the infrared intensity was 1100 W/m2, the air-velocity was 1.5 m/s, and the pulse ratio (PR) ranged from 1 to 3. Results indicated that the drying rate, drying time, effective moisture diffusivity, shrinkage, specific energy consumption (SEC), colour attributes and phytochemical compounds of sweet potato were affected by the different drying combination strategies. The drying kinetics, product shrinkage, and sample temperature were also influenced by drying time and air temperature. The two-term exponential model adequately explained the drying behaviour of sweet potato for all the different combination strategies. The intermittent IR and HAD combination strategy proved to be the most suitable based on the combined effect of total drying time (113–120 min), SEC (27.67–41.44 kWh/kg), total colour change (17.15–26.48) and bioactive compounds. Highlights • Performance of different combined infrared (IR) and hot-air drying (HAD) strategies for sweet potato was studied. • Drying kinetics, shrinkage, specific energy consumption and colour attributes were affected by the combination strategy. • Drying air temperature and time significantly affected the efficacy of the different IR and HAD strategies. • Drying using intermittent IR and HAD was found to be the most suitable strategy for sweet potato. [ABSTRACT FROM AUTHOR]

This study seeks to investigate the potential of using combined computer vision (CV) and laser-induced backscattering imaging (LLBI) in monitoring the quality attributes of sweet potato during drying. CV and backscattered images of 4 mm thickness sweet potato slices were captured after every one-hour of drying, at drying temperatures of 50–70 °C. Reference quality properties, such as moisture content, L∗, a∗ and b∗ colour coordinates were measured hourly under the same drying conditions. Principal component analysis (PCA) and partial least square regression (PLS) were applied to the extracted combined CV (based on RGB) and backscattering imaging parameters to analyse the quality changes of sweet potato during drying. The results showed that there was significant effect of drying temperature and time on combined CV and backscattering imaging parameters. The combined optical method showed good correlation with moisture content and colour properties i.e L∗ and a∗ of sweet potato with R 2  > 0.7. Specifically, the redness (a∗) gave the highest coefficient of determination (R 2 ) of 0.80, while the moisture ratio (MR) showed the lowest root mean square error of validation (RMSEV) with the value of 0.18. Thus, this study has shown that combined CV and backscattering imaging parameters can serve as a non-destructive tool for detecting the changes in quality parameters of sweet potato during drying. [ABSTRACT FROM AUTHOR]

Fruits and vegetables are very perishable commodities that have enormous industrial and commercial importance. To preserve its quality attributes, increase shelf life, and reduce transport weight, fruit and vegetable can be processed by drying. Over the years, conventional drying techniques have been widely applied, both industrially and commercially for the processing and preservation of fruits and vegetables. However, most of the conventional techniques are time and energy consuming, and affect important quality attributes of final products. Recently, there has been increased interest in the use of non-thermal drying methods in combination with other conventional drying techniques for preserving fruits and vegetables. These methods have been reported to enhance the quality attributes of dried products, reduce drying time and energy demand, and increase the overall drying efficiency. In this regard, the development of a cost effective non-thermal hybrid drying systems, such as combined ultrasound (US) and hot-air drying, ultraviolet (UV) and hot-air drying, and pulse electric field (PEF) and hot-air drying have recently been researched on. These drying techniques have become potential substitute for conventional industrial and commercial dryers, owing to their advantage of producing quality dried fruit and vegetable products, with reduced drying time and energy consumption. This study therefore attempts to highlight recent developments of the commonly used non-thermal combined convective hot-air drying (CHAD) techniques for fruits and vegetables, with emphasis on drying time, drying rate, quality attributes of products, and modelling approach. This study further highlights the primary constraints for industrial application of this technology as the inadequate medium of transmission for power ultrasound, cost of design and installation, and the limited study on (UV) and PEF assisted CHAD. The necessity for conducting more detailed studies on non-thermal assisted convective hot-air drying of fruits and vegetables was emphasized. [ABSTRACT FROM AUTHOR]