Design, development and numerical characterization of indirect domestic hybrid solar dryer

Abstract

A novel design of domestic hybrid solar dryer system has been proposed and analysed with Computational Fluid Dynamics (CFD) using Ansys Fluent 19.2 software under unload condition. Further, Experiments under unload and load con ditions were performed at Delhi Technological University (DTU), Delhi in the month of November 2021. From unload experimentation, thermal performance pa rameters namely thermal efficiency, HUF (heat utilisation factor) and COP (coeffi cient of performance) of solar collector in indirect type domestic hybrid solar dryer were evaluated. The maximum values of thermal efficiency, HUF, and COP were noted as 59%, 0.68, and 0.32 at 13:00 hours. The theoretical results were in fair agreement with experimental results as evaluated using linear regression analysis. Moreover, ITDHSD (indirect type domestic hybrid solar dryer) was found superior to other developed solar dryers in terms of maximum collector thermal efficiency. From experiments under load condition, various parameters such as thermal performance, exergy and drying kinetics of tomato slices were analysed. Moisture in tomato slices was dried from 95% to 9% (wet basis) in 10 hours of solar drying in ITDHSD during the winter season. Drying curve obtained was fitted with differ ent existing empirical models and Prakash and Kumar model was found suitable for tomato drying in ITDHSD. Overall drying efficiency of the system was estimated as 41.05%. Furthermore, exergy efficiency values varied from 32.86% to 58.26% with variable mass flow rate. Overall exergy efficiency was 46% during tomato drying experimentation. Various exergy sustainability indicators have been esti mated in this research work and the primary aim was to observe improvement po tential in the system. Improvement potential, waste exergy ratio and sustainability index of the ITDHSD system were estimated in the range of 0.006966 - 0.065984, 0.41 - 0.67, and 1.55 - 2.39, respectively. Furthermore, environmental, economical, and quality parameters for drying tomato flakes were evaluated for ITDHSD system. Embodied energy during dryer fabrication was estimated as 1434.176 kWh. Energy payback time, total CO2 miti gation, and earned carbon credit for tomato drying in dryer were projected as 4.21 years, 12.28 Tonnes, and $364. Initial capital cost for drying system fabrication was xxiv $245. The drying system can pay back all initial costs in 6 months of operation as estimated for tomato flakes drying. Moreover, quality of dried tomato flakes in dryer and open sun drying was estimated and compared. Indirect type domestic hy brid solar dryer provided better quality dried tomato flakes than open sun drying method as estimated from sensory analysis, rehydration ratio, shrinkage and hard ness test. Moreover, a unique sinusoidal corrugated solar collector was also designed and proposed to improve performance of ITDHSD system. The design was created using Ansys Spaceclaim 2022 version R2 software and further simulated using An sys Fluent 2022 version R2 software. Mass flow rate for the dryer system was op timised and inlet velocity of 0.6 m/s (0.0221 kg/sec) was found appropriate for crop drying. While performing simulation input parameters such as ambient air temper ature, solar insolation etc. for the winter season were used for the analysis. It was observed that collector will provide better results and average drying temperature of 324 K - 332 K was noted when solar insolation was varied in a range of 500 W/m2 to 1000 W/m2 . ITDHSD system embedded with sinusoidal corrugated ther mal collector can provide better drying and wide variety of crops can be dried in the developed dryer. Indirect type domestic hybrid solar dryer (ITDHSD) had potential to pro vide an economical, efficient, and environmentally friendly alternative to traditional drying methods. The results demonstrate that the ITDHSD system can help to re duce energy consumption, greenhouse gas emissions, and improve the quality of dried products, making it an attractive option for domestic users as well as small scale agricultural producers. The findings of this study can provide useful insights for designing and implementing sustainable and cost-effective drying systems for other food products.