Estimation And Error Analysis Of Convective Mass Transfer Coefficient Of Sludge In Hot Air Drying

Evaluating Hot air drying Convective mass transfer coefficient accurately plays an important role in creating new Heat and mass transfer machines and optimizing equipment. Because the moisture content of the surface of the material is difficult to be determined, the estimation of the convective mass transfer coefficient of the hot air drying method is focused on the average dry base moisture content by dry method of the material. When the thickness of the material is larger, the average dry base moisture content and the surface partial dry base moisture content difference is bigger, so the error of estimation of the hot air drying convective mass transfer coefficient is bigger, and it cannot be popularized in the mechanical design and optimization. Be aimed at the defects of traditional calculation method, this paper with the Griddle Cake sludge as the object of study were hot air convection drying test, estimation of hot air drying the convective mass transfer coefficient and the error was analyzed.First, to different drying conditions, sample thickness 5mm, lOmm and 15mm, drying temperature of 40℃、50℃ and 60℃, the air velocity 1.1m/s,3.1m/s and 5.1m/s on the Griddle Cake sludge drying test, analysis and comparison of the test dry basis moisture content and fitting of dry basis moisture content, observation drying rate estimated by the method of definition and the derivation of the fitted drying curve. The results show that the moisture content of the test dry base is in good agreement with the fit of the dry base moisture content, and the fitting dry base moisture content can be used to estimate the convective mass transfer coefficient of hot air drying. The drying rate of drying curve fitting derivative is instantaneous; the drying rate is estimated by the method of definitions within a certain time period.Next, evaluated the hot air drying Convective mass transfer coefficient of Griddle Cake sludge by the method of inverse evaluation and direct calculation method. The second Fick diffusion law is calculated by inverse evaluation, comparing the Hot air drying results of Griddle Cake sludge with computational simulation results, and determing the Dry basis moisture content of located Griddle Cake sludge’s surface. Hot air drying convective mass transfer coefficient is calculated under the circumstances of different drying temperatures, air velocities and sample thicknesses by the method of mean theory. The direct calculation method is different, and the dry basis moisture content of located Griddle Cake sludge’s surface is replaced by experimental mean dry basis moisture content. The results show that the hot air drying convective mass transfer coefficient is correct and range from 5.5×10-6m/s to 2.9×10-5m/s by the method of inverse evaluation. The one is smaller evaluated by direct evaluation method, ranging from 6.9×10-8m/s to 4×10-7m/s. Hot air drying Convective mass transfer coefficient is not influenced by the air velocity, drying temperature and sample thickness. Error is an alternative to Griddle Cake sludge surface local dry basis moisture content of fitting average dry basis moisture content is too large, resulting in the direct calculation of the denominator of the formula is too large, so hot air drying the convective mass transfer coefficient is too small. The external drying conditions can’t influence the drying velocities then influence the Convective mass transfer coefficient.