Research On Hot-air Drying Characteristics And Heat And Mass Transfer Model Of Carnation

The carnation (Dianthus Caryophyllus), which contains various essential microelements of human body such as potassium (K), calcium (Ca), sodium (Na), ferrum (Fe), magnesium (Mg), manganese (Mn), copper (Cu), zinc (Zn) etc., could enhance blood circulation and metabolism. For woman the carnation shows higher value, it regulates endocrine systems and beautifying which could slow down the ageing process. However, there is little published work concerning the drying characteristics of carnation. Therefore, the aim of this study was to investigate the drying characteristics as well as heat and mass transfer model of carnation during convection drying, which is expected to be used for the industrialization of carnation.1) The temperature, air velocity and loading weight were taken as the factors of single-factor test to study the drying characteristics of carnation. The appropriate factors and levels were temperature60℃to80℃, air velocity1.0m/s to4.0m/s and loading weight2kg/m2to8kg/m2. The analysis results showed that the influence of all the three factors on the drying characteristics of carnation were evidenced, with higher drying temperatures and air velocity as well as less loading weight corresponding to faster drying processes.2) The temperature and air velocity were taken as the factors of comprehensive test to study the thin-layer drying characteristics of carnation. Three different diffusion models, namely the monomial proliferation, the exponential and Page model, were fitted to the experimental data. The results showed that the Page model (Mr=e-ktn) is the best mathematical model for describing drying processes, in which k=exp(0.0857+0.003v-9.829), n=-0.001T+0.030v+1.184.The checking results using the Page model were in good agreement with the determined results, which suggested that this mathematical model could be applied to demonstrate the process of hot-air thin layer drying for carnation.3) The temperature, air velocity and loading quantity were taken as the factors of quadratic regression orthogonal test follow the indexes of average drying rate and unit dehydrate energy consumption. The results showed that the temperature in proportion to the average drying rate but in inverse proportion to the unit energy consumption, the air velocity in proportion to average drying rate and unit energy consumption, the loading quantity in inverse proportion to the average drying rate and unit energy consumption.4) The greater the average drying rate and the lower the unit dehydrate energy consumption was, the better the drying technology was. The regression equations of the two indexes were established. The optimal technological condition for drying carnation using MATLAB programming was80℃of temperature,4.0m/s of air velocity and6.2kg/m2of loading weight.5) Based on the irreversible thermodynamics, the heat and mass transfer model that only contain the moisture content and temperature gradients was obtained by calculate the entropy of the system as well as derivations. The equations were discretized using the inner node method of control volume in cartesian coordinate system and the values of temperature and humidity were obtained through the ADI and TDMA method.These conclusions are obtained as follows:(1) The Page model that demonstrates the process of thin layer drying for carnation accurately could be used to calculate the moisture content in this process, which is essential for the designing of equipment for carnation drying and guiding the practical production.(2) Based on the orthogonal regression test, the merit function of technological process for carnation drying was established. The optimal technological condition is obtained, in which the drying time and energy consumption could be reduced by increased the temperature, air velocity and load quantity appropriately.(3) The variations of temperature and moisture content in the process of thin layer drying for carnation could be calculated by solved the system of heat and mass transfer equations, which would provide references for the drying technology of sheet materials to a certain extent.