Image-based Measuring Method For Particle Mixing And Heat Transfer Process In A Pan Coater

Pan coater is important process equipment widely used in pharmaceut ical industries for water-so luble and organic film coat ing o f candy, tablets and pills. The main factors affect ing the coating qualit y is the mixing process and heat transfer process of part icles. However, these two processes are strongly coupled wit h each other, leading to difficult ies in the design and operat ion opt imizat ion of pan coater. Up to now, many efforts have been devoted to theoret ical studies of the part icle mixing dynamics and thermal dynamics. However, due to the lack of appropriate measurement methods, the experimental research on the interplay o f part icle mixing and heat transfer process is relat ively rare, and is most ly limited to the measurement of a single process with invasive measuring techniq1 ues such as thermocouples, which is unable to acquire the actual process informat ion in the coater and the measured data is thus limited in the usage for verificat ion o f theoret ical models. Therefore, it is urgent to develop a non-invasive measuring method to obtain more accurate process informat ion fo r the particle mixing and heat transfer in the pan coater.In the framework of a research pro ject funded by Ministry o f Education of China, a non-invasive technique is proposed in this paper for BY600 coater based on opt ical imaging for the measurement of both mixing and heat transfer process. Wit h the proposed technique, the mixing t ime and heat transfer t ime is measured and compared to each other for different operat ing condit ions, which is o f theoretical importance and engineering interests. The main work accomplished in this paper includes:(1) An opt ical-infrared image acquisit io n system is designed using a RGB camera and an infrared camera(IR camera), which is able to simultaneously take videos o f mixing process and heat transfer process. Based on the user so ftware of the IR camera, a VC++ program is developed to for the acquisit io n and analysis o f the temperatures on pixel level.(2) Measuring methods are proposed for the measurement o f particle mixing process and heat transfer process based on opt ical image and infrared image, respectively. Wit h the optical images, the t ime evo lut ion of the feature variables o f part icle mixing process(contact s) is calculated; with infrared images, the temperature variance o f the interest area is introduced and measured to characterize the heat transfer process. Experiment s show that the contact s profile and the temperature variance pro file can describe well the dynamic change o f the mixing process and the heat transfer process with time.(3) Under the experiment condit io n, the contact s pro file(for the mixing process) and the temperature variance pro file(for the heat transfer process) are found to sett le down after a short period o f t ime, similar to the step response of a first-order system. Based on least-square regressio n, quant itat ive formula is given in the paper for the calculat ion of the mixing t ime and heat transfer t ime.(4) Based on the proposed measuring procedures, eight series of experiments are conducted under different rotat ion speeds and init ial temperatures to measure and co mpare the pro files o f the mixing processes and the heat transfer process. The mixing t ime and heat transfer t ime are also co mpared. For this, a dimensionless variable is introduced to normalize the profiles since the two processes are physically different. Co mparison shows that: under the experimental condit io ns, the mixing time and the heat transfer t ime decreases wit h increasing rotat ional speed; when the init ial temperature is increased, the mixing t ime keep s constant while the heat transfer process needs longer time to reach steady state, which is consistent with theoret ical results reported in literature. This indirect ly proves the effect iveness o f the image-based measurement method proposed in the paper.