Drying Kinetics of Wheat (Triticum aestivum L., cv. ‘Pionier’) during Thin-Layer Drying at Low Temperatures

Abstract

The management of moisture is one of the main challenges in anticipating and averting food decay and food losses during postharvest processing and storage. Hence, it is imperative to reduce the moisture of freshly harvested products to safe-storage limits in order to inhibit the occurrence of diverse biochemical, microbiological and other moisture-related deteriorative reactions which can contribute to quality degradation. A viable alternative to conventional hot-air drying is the application of low temperatures for drying, which has scarcely been investigated. In this regard, experimental-based modeling is a requisite to gain insights into drying processes. Thus, this study focused on investigating the drying kinetics of wheat (Triticum aestivum L.) cv. ‘Pionier’ under a coherent set of drying air temperatures (T = 10–50 °C), relative humidity (RH = 20–60%), and airflow velocity (v = 0.15–1.00 ms−1). A robust and automated measurement system using a high precision balance was utilized as a basis for the real-time and continuous acquisition of drying data. The analysis of the experimental results facilitated the establishment of generalized drying model for low temperatures able to describe at a high accuracy the behavior of moisture ratio X* (R2 = 0.997, RMSE = 1.285 × 10−2, MAPE = 6.5%). An analytical model for predicting the effective diffusion coefficients D (R2 = 0.988, RMSE = 4.239 × 10−2, MAPE = 7.7%) was also developed. In conclusion, the anticipated drying model has demonstrated the capability of modeling the drying behavior of wheat at low temperatures with a high temporal resolution and should be employed in the design, analysis and modeling of cooling, aeration and low-temperature drying processes of wheat bulks.

Numerical Study of Low-Temperature Ventilation Drying in a Wheat Grain Silo Considering Non-Uniform Porosity Distribution

“…A modified dual-parameter thin-layer drying model was used in this paper to study the drying behaviors inside the wheat pile during mechanical ventilation. The modified dual-parameter model can be expressed as follows [18]:…”

“…where t is the time, and its unit is minutes; k and n are the empirical coefficients of the grain drying model, respectively, which can be expressed as k = 2.8 × 10 −3 × e 0.059T × r −0.139 × v 0.025 and n = 0.784, respectively; We is the equilibrium moisture for the dry basis grain; W is the dry basis moisture of the grain at time t; r is the relative humidity of dry air; r ≤ 0.99, v is the dry air velocity; and T is the temperature of the dry air. The semi-empirical equation of equilibrium moisture is as follows [18]:…”

“…where C 1 , C 2 , and C 3 are the empirical coefficients of the model, with values of 0.129, −6.460 × 10 −4 , and 2.944 [18], respectively.…”

“…A tetrahedral mesh partitioning scheme was adopted after optimizing the geometric model of the silo. The total grid number was 680,000, and the transient calculation time step (i.e., time interval) was set as 6 s. −6.460 × 10 , and 2.944 [18], respectively.…”

“…Considering the influence of non-uniform porosity in the simulation of the lowtemperature drying of a wheat grain pile is not enough for prediction accuracy, and the selection of the drying model is more important. However, the heat and moisture transfer inside the grain pile during the drying process is complex [18]. For this reason, many drying models have been used to study the drying process for wheat grain piles [19].…”