https://orcid.org/0000-0001-9311-9462
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ABSTRACT
Dried foods are higher in nutrients than their fresh counterparts. Numerical modeling, such as computational fluid dynamics (CFD), can be used to simulate the drying process and its method, thereby the effort to fine-tune the physical experimentation can be minimized considerably. In the present study, a CFD simulation model is developed based on the experimental investigation of the drying of Amaranth leaves in the CFD optimized drying chamber of a heat pump dryer (HPD). The distribution of the fluid domain and the influence of various circumstances on heat and mass transfer are investigated. In order to solve the mass transfer equation, an external model is developed in “C” language for the source term of moisture generation in the moisture transport equation and energy equation. This external model is then linked to the model using a user defined function (UDF) in the FLUENT CFD software. The calculated and measured drying temperature and moisture fraction are presented as a function of drying time. The obtained transient simulation results of the drying process are validated with the experimental results. The results of the CFD simulation are in accordance with the experimental results as per the physics of the problem. The maximum deviation between the experimental and CFD moisture-time plot is observed to be less than 8%. The difference between CFD and experimental results is attributed to temperature assumption, heat losses, and air leakage in the drying chamber. The new CFD methodology established in this study can be utilized as a generic procedure for evaluating the effectiveness of a HPD for drying various types of leaves.
Nomenclatures
| T | = | Temperature of drying air, [°C] |
| v | = | Velocity of drying air, [m/s] |
| Kl | = | Thermal conductivity of leaf, [W/(m.K)] |
| Ka | = | Thermal conductivity of air, [W/(m.K)] |
| Dwl | = | Diffusivity of water in leaf, [m2/s] |
| Dwa | = | Diffusivity of water in air, [m2/s] |
| ρ | = | Density, [kg/m3] |
| k | = | Turbulent kinetic energy, [m2/s2] |
| ε | = | Turbulent dissipation rate, [m2/s3] |
| µ | = | Dynamic viscosity, [kg/(m-s)] |
| µt | = | Turbulent viscosity, [kg/(m-s)] |
| ν | = | Kinematic viscosity, [m2/s] |
| ϕ | = | General quantity transported by the airflow |
| Sk | = | Source term in transport equation for turbulent kinetic energy, [W/m3] |
| Sε | = | Source term in transport equation for dissipation rate, [kg/sm3] |
Acknowledgements
Easwari Engineering College and Anna University in Chennai provided the essential infrastructure for the experimental studies, and the authors would like to express their gratitude to them.
Disclosure statement
No potential conflict of interest was reported by the authors.
Additional information
Notes on contributors
Ayyasamy Krishnamoorthy Babu
Dr. Ayyasamy Krishnamoorthy Babu is currently an Associate professor of Mechanical Engineering at the SRM Easwari Engineering College, Tamilnadu, Chennai. A.K. Babu received his B.E. degree in Mechanical Engineering from University of Madras in 1994, and his Ph.D in Mechanical Engineering from Anna University in 2020. He has published a considerable number of refereed technical papers. His current research interests include energy conservation and drying of leafy vegetables.
Govindaraj Kumaresan
Dr. Govindaraj Kumaresan received his B.E. in Mechanical Engineering from Alagappa Chettiar College of Engineering and Technology, Karaikudi in 1997 and a Ph.D. in Solar thermal system from Anna University in 2010. He is currently an Associate Professor in the Institute for Energy Studies, Department of Mechanical Engineering, Anna University, Chennai, India. His research interests include solar and drying control systems, renewable energy, and computational fluid dynamics. He has several publications in international journals and conference proceedings.
Vincent Antony Aroul Raj
Dr. Vincent Antony Aroul Raj is a Professor in the Department of Mechanical Engineering, SRM Easwari Engineering College, Chennai, India. He has over 20 years of research and teaching experience. Dr.V. Antony Aroul Raj obtained his B.E. degree in Mechanical Engineering from Pondicherry Engineering College (1993) and a Ph.D. in Energy Engineering from Anna University, Chennai, India (2011). He has to his credit, more than 15 research publications in international journals with high impact factors and in various conferences, both in India and abroad.
Sharmila Babu Vishal Surya
Sharmila Babu Vishal Surya graduated with a Bachelor of Engineering in Mechanical Engineering in 2023 from the SRM Institute of Science and Technology in Kattankulathur, India. He has published quite a few technical papers in journals and conferences. The drying of food items and computational fluid dynamics are two of his current research interests.