Abstract
The ventilation resistance of air flow through rice grain layers is one of the key parameters affecting drying uniformity as well as the energy consumption of the drying process. In order to reveal the variation of characteristics of the ventilation resistance with paddy grain moisture content, the air velocity and the bed layer depth are needed. A second order model was fitted to pressure drop using the response surface methodology and the results are compared with those of the Ergun model. The results showed that the pressure drop increases with the increase of paddy grain moisture content, air velocity and the bed layer depth, and the interactions between the air velocity and the bed layer depth have the most significant influence on the pressure drop. Moreover, a second-order polynomial pressure drop model based on RSM was established and compared with the Ergun model. The results showed that the pressure drop model established by RSM is similar to that of the Ergun model.
Highlights
The pressure drop of the grain bed layer is the key parameter for designing and optimizing the structure of the drying chamber, and it is one of the most important references for selecting the power of a fan [1,2]
A high-pressure drop may make it difficult for the air to flow through the bed layer and further lead to the increase of non-uniformity of the drying process, while a low-pressure drop may lead to wasting the power of the fan [3]
The results showed that the resistance of airflow increases with the increase of air velocity and bed layer depth, while resistance increases with the decrease of moisture content
Summary
The pressure drop of the grain bed layer is the key parameter for designing and optimizing the structure of the drying chamber, and it is one of the most important references for selecting the power of a fan [1,2]. Zhang et al [10] investigated the pressure drop of the air (with velocity ranges of 0.1 to 0.6 m/s) flow through the bed layer with depth ranges of 100 to 1000 mm, and found that the simulation accuracy of the pressure drop using Ergun model is reliable only when the air velocity is under 0.2 m/s It can be summarized from the above analyses that the flow resistance of the grain bed layer are mainly determined by the traditional models and the characteristics of the air flow resistance are investigated by using single factor test. An experiment followed by Box–Behnken Design was conducted to investigate the influences of the independent variable including paddy grain moisture content (Mc), air velocity (vair ), and paddy layer depth (L) on the pressure drop (∆p). The influences of the single factor as well as the interactions between any two independent variables on ∆p were investigated and a ternary quadratic model for ∆p was established and compared with the traditional Ergun model
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