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.

Computational modeling is an efficient and effective tool for modeling of drying process for food products. Developing validated computational models for drying processes is essential to build energy efficient drying units, producing uniform quality of dried products. This work presents drying behavior of almonds with a specific focus on understanding interaction among multiple almonds. Eight (2x2x2) particles, and twenty-seven (3x3x3) particles arranged in the shape of a cuboid were used to conduct drying experiments in a Mettler Toledeo Moisture Analyzer unit. Experiments were conducted to measure the moisture loss data with respect to drying time using Almond kernels. Experimental data was used to understanding drying kinetics as well as variation in moisture content with respect to their positions in a cuboid. Computational fluid dynamics (CFD) based simulations were carried out for the flow, heat transfer and drying of particles in the unit. Actual geometry of individual particles were considered in simulations, to predict the variation in velocity, heat and mass transfer coefficients for all the particles. Simulations predicted moisture loss data that matches well with the experimentally measured values. Average moisture for each layer was also compared for various intermediate drying times. Simulation results captured the overall drying process for multiple particles system adequately.The results are compared with the results obtained with drying of a single almond. The approach, models and presented results will be useful for designing large scale drying units for almonds.

Drying is important in many food processing applications, and particularly so in the dry fruits industry. This work is focused on developing computational models for simulating the drying of almonds in a tray dryer. It is important to quantitatively understand heat and mass transfer within and around a single almond particle as well as the particle‐particle interactions and their implications for dryer design. In this work, we have developed a systematic CFD modelling framework for modelling almond drying in a tray dryer. A single tray filled with almonds (∼2 kg) were dried at three set temperatures viz., 55, 65, and 75 °C. Air relative humidity at the inlet and outlet locations, and the weight of almonds were measured during drying for each experiment. An additional set of experiments were conducted in which almonds were filled only in the half section of the tray, keeping the other half empty. The same amount of almonds were used, to have multiple layers of almonds in the tray, and the set temperature for the experiment was 75 °C. Flow, heat, and mass transfer in the tray dryer were simulated using commercial CFD software Ansys Fluent. The validated computational model was used to simulate various cases including larger and more trays. The developed approach and models will be useful to select the appropriate dryer configuration and optimize its design. The developed models will also be useful to identify suitable operation conditions for the drying of almonds as well as other food products.