462698 Drying of Almonds: Single Particle
Drying is important in many food processing applications, and particularly so in the dry fruits industry. We have experimentally as well as computationally investigated drying of almonds. Drying of almonds exhibit many characteristic key features: non-spherical shape, swelling/ shrinkage as a function of moisture content, uneven drying because of peculiar shape and proximity of other almonds and so on. Mettler Toledo Halogen Moisture Analyzer unit was used to quantify drying kinetics of a single almond particle. In this widely used equipment, internal flow patterns and therefore heat and mass transfer depend on natural circulation.
In this work, we have used detailed three dimensional computational fluid dynamics (CFD) model to simulate flow, heat and mass transfer in Mettler Toledo unit while drying of almond particles. Systematic experiments with a single re-wetted almond were conducted in Mettler Toledo Moisture Analyzer Excellence Plus HX204 unit at three set temperatures of 55, 65 and 75 oC. Acquired transient moisture data was used to estimate key parameters of interest (drying kinetics and effective diffusivity).
A comprehensive CFD model was developed and used to simulate natural convection within the moisture analyzer. Radiation heat transfer was modelled using the discrete ordinate mode (ANSYS Inc). The computational model was validated by comparing simulated and measured temperature near almond nut. The temperature near almond surface was found to be lower (by about 5 C) than the temperature set point of the moisture analyzer. Actual measured temperature near the almond surface was used while obtaining drying kinetics. Simulated flow results were used to estimate local heat transfer coefficients for almond surfaces. Based on estimated effective diffusivity and analogy between thermal and concentration boundary layers, distribution of mass transfer coefficient around almond surface was estimated. The results provide quantitative information about non-uniform heat and mass transfer and therefore non-uniform drying of a single almond particle.
The presented approach, models and results will be useful for enhancing utility of the results obtained with moisture analyzer units and improve ability to extend the results obtained with such units to industrial systems. The results and models presented here will also provide useful basis for further work on multiple almond particles and on tray dryers.
Authors would like to Thank CSIR for funding this research via its Indus MAGIC (CSC123) project.
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