https://orcid.org/0000-0003-1997-7295
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ABSTRACT
Okra (Abelmoschus esculentus L.), like most fruits and vegetables, deteriorates quickly after harvesting due to its high moisture content and respiration rate. To preserve it and mitigate the post-harvest losses, a developed evacuated tube solar dryer (ETSD) with heat pipes was used to dry fresh okra. Thermal profiling of the ETSD was carried out to investigate the range of temperature gain inside the drying chamber. The effect of different blanching temperatures, viz. 70, 80, and 90°C, on drying characteristics and physical properties like color, water activity, and rehydration kinetics of okra were investigated. The energy efficiency of the collector ranged from 13.21% to 42.67%. Similarly, the convective mass transfer coefficient was calculated and ranged from 3.41 × 10−07 to 8.57 × 10−07 m/s. The okra blanched at 80°C, showing maximum greenness retention and lower water activity. The rehydration ratio was 6.05, 7.19, 7.73, and 7.41 for control, and okra blanched at 70, 80, and 90°C. The rehydration kinetics were analyzed using four distinct models: Peleg, Weibull, exponential, and first order. The Weibull model demonstrated the most accurate fit to the data. It is suggested that okra blanched at 80°C and dried under ETSD gives better retention of color and a higher mass transfer and rehydration rate.
GRAPHICAL ABSTRACT
Nomenclature
| BI | = | Browning Index |
| ETSC | = | Evacuated tube solar collector |
| ETSD | = | Evacuated tube solar dryer |
| EU | = | Energy utilization (kJ/s) |
| EUR | = | Energy utilization ratio |
| HP | = | Heat pipe |
| MR | = | Moisture ratio |
| RMSE | = | Root means square error |
| = | Volumetric flow rate of the drying air (m3/s) | |
| = | Energy efficiency (%) | |
| = | Hue angle | |
| = | Heat energy inflow (J/s) | |
| = | Drying air temperature (°C) | |
| = | Rate of mechanical work output (J/s) | |
| X | = | Characteristics: thickness of sample (m) |
| = | Dry air density (kg/m3) | |
| Cpa | = | Specific heat of air (J/kg °C) |
| ha∞ | = | Ambient air enthalpy (J/kg) |
| hi | = | Air enthalpy at the dryer inlet (J/kg) |
| hsat | = | Enthalpy of the saturated vapor (J/kg) |
| Ig | = | Solar intensity (W/m2) |
| W | = | Humidity ratio of air (kgH2O/kgDA) |
| h | = | Hour |
| ho | = | Air enthalpy at the dryer outlet (J/kg) |
| = | Mass flow rate of air (kg/s) | |
| = | Drying rate (g/g.dm-h) | |
| Wt | = | Instantaneous weight at time t |
| Me | = | Equilibrium moisture content of the sample (db) |
| Wi | = | Initial weight of samples |
| Dem | = | Effective moisture diffusivity (m2/s) |
| = | Moisture content of the okra at time t | |
| Mi | = | Initial moisture content (%) |
| Δt | = | Time interval (h) |
| R2 | = | Coefficient of determination |
| Ac | = | Collector area (m2) |
| Tdo | = | Dryer outlet temperature |
| v | = | Air velocity (m/s) |
| vi | = | Air velocities at dryer inlet (m/s) |
| vo | = | Air velocities at dryer outlet (m/s) |
| = | Temperature at Collector outlet (°C) | |
| = | Temperature at collector inlet (°C) | |
| Ta | = | Ambient air temperature (°C) |
| Rha | = | Ambient relative humidity (%) |
| χ2 | = | Chi-square |
Acknowledgements
The authors are thankful to National Institute of Food Technology Entrepreneurship and Management, Kundli, Haryana, India for providing the necessary support and infrastructure to conduct this study. This manuscript is submitted under NIFTEM publication reference number NIFTEM-P-2024-003.
Disclosure statement
No potential conflict of interest was reported by the author(s).
Data availability statement
The data used and/or analyzed during the present work are available on reasonable request.
Additional information
Notes on contributors
Dhiraj Kumar Yadav
Dhiraj Kumar Yadav received his Bachelor of Technology (Agricultural Engineering) from CSAUAT, Kanpur, in 2018. He received his Master of Technology in Process and Food Engineering from G.B. Pant University of Agriculture and Technology, Pantnagar, in 2020. Presently, he is pursuing Ph.D. in Food Engineering from the National Institute of Food Technology Entrepreneurship and Management, Kundli, Haryana, India. He has published several research articles in peer reviewed (Scopus, Web of Science) journals. His areas of interest are solar thermal technologies, food processing through novel techniques, solar drying, modeling, and food product development.
Vinkel Kumar Arora
Vinkel Kumar Arora is an Associate Professor in Department of Food Engineering at the National Institute of Food Technology Entrepreneurship and Management, Kundli, Haryana, India. He holds Ph.D. and M.Tech in Mechanical Engineering with a specialization in CAD/CAM and modeling. He has more than fourteen years of teaching, and research experience, with focus on noval solar drying technologies and 3D printing of foods. He has published more than 50 papers in international Journals and authored 1 Book. His areas of interest included 3D printing of foods, solar thermal technologies, and IoT-based technologies in food processing.