Drying of Almonds I: Single Particle

Abstract

Drying is an essential unit operation required in food processing industries, particularly in the dry fruits industry. Drying of almonds exhibit many characteristic features such as non-spherical shape, swelling/ shrinkage as a function of moisture content, uneven drying because of their peculiar shape and proximity to other almond kernels and so on. In this study, we have investigated the drying of almonds through experiments and computational modeling. In this regard, Mettler Toledo Halogen moisture analyzer unit was used to conduct experiments for a single almond kernel. In this widely used equipment, internal air flow patterns and therefore heat and mass transfer depend on natural circulation of air. A detailed three dimensional computational fluid dynamics (CFD) model was used to simulate the air flow pattern, heat and mass transfer in the drying unit. Carefully designed experiments with a single almond kernel were carried out at different temperatures to estimate key parameters of interest (drying kinetics and effective diffusivity). The CFD model was also used to quantify non-uniform heat and mass transfer and therefore non-uniform drying of a single almond kernel. The presented approach, models and results might be useful to improve the performance of drying units in industrial systems.The results and models presented here will also provide a basis for further work on multiple almond kernels and on tray dryer unit.

CFD modelling of almond drying in a tray dryer

“…It is therefore essential to develop fully coupled model equations for flow, temperature, moisture variation and solids temperature representing processes occurring in a tray dryer which need to be solved simultaneously. Based on our earlier work for single and multiple particles (Chilka and Ranade [9,10] ), it showed that temperature equilibrium within the almond particle was achieved quickly. The Biot number for heat transfer and mass transfer for almonds is 0.17 and 2.1, respectively.…”

“…Based on the single particle work, the effective diffusivity of an almond kernel was estimated, as reported by Chilka and Ranade . As for tray drying, there could be a temperature variation in the unit, hence diffusivity needs to be estimated at respective air temperatures.…”

“…As for tray drying, there could be a temperature variation in the unit, hence diffusivity needs to be estimated at respective air temperatures. The Arrhenius equation was used for this purpose (Equation ) and the corresponding parameters were used from the earlier work on a single particle by Chilka and Ranade …”

Drying of Almonds II: Multiple Particles

“…Detailed CFD models were developed to simulate flow and heat transfer within the unit and across all the particles. Influence of neighboring almond particles on heat and mass transfer coefficients was quantified by comparing the results with the single particle results from earlier work [3] . This presented experimental data, approach and models will be useful to understand the drying kinetics of almonds in different drying units.…”

“…Earlier work was carried out for drying of a single almond kernel [3] to identify suitable drying kinetics model for almonds, estimation of heat transfer coefficient, mass transfer coefficient and effective diffusivity. The moisture variation for single almond during the drying process was predicted using simulations which matched quite well with experimental measurements.…”