System Identification of Conveyor Belt Microwave Drying Process of Polymer Foams Using Electrical Capacitance Tomography.

Marzieh Hosseini,Marko Vauhkonen,Guido Link,Mahdi Aliyari Shoorehdeli,Anna Kaasinen,Timo Lähivaara

doi:10.3390/s21217170

Abstract

The microwave drying process has a wide application in industry, including drying polymer foams after the impregnation process for sealings in the construction industry. The objective of the drying process is to reach a certain moisture in the foam by adjusting the power levels of the microwave sources. A moisture controller can be designed to achieve this goal; however, a process model is required to design model-based controllers. Since complex physics governs the microwave drying process, system identification tools are employed in this paper to exploit the process input and output information and find a simplified yet accurate model of the process. The moisture content of the foam that is the process output is measured using a designed electrical capacitance tomography (ECT) sensor. The ECT sensor estimates the 2D permittivity distribution of moving foams, which correlates with the foam moisture. Experiments are conducted to collect the ECT measurements while giving different inputs to the microwave sources. A state-space model is estimated using one of the collected datasets and is validated using the other datasets. The comparison between the model response and the actual measurements shows that the model is accurate enough to design a controller for the microwave drying process.

Highlights

The microwave drying process is a promising technology for drying dielectric materials because of volumetric and selective heating, resulting in fast water evaporation [1,2].Considerable energy and time efficiency are important features of this technology and are acquired by applying a high-power microwave (MW) to materials with high moisture content [3,4].One of the main objectives of the microwave drying process is to reach a desired moisture content in the drying material after the process [3,5]
An electrical capacitance tomography (ECT) sensor was installed at the exit of a microwave oven to construction industry
An ECT sensor was installed at the exit of a microwave oven to estimate the polymer foam permittivity, which correlates with the foam moisture

Summary

Introduction

The microwave drying process is a promising technology for drying dielectric materials because of volumetric and selective heating, resulting in fast water evaporation [1,2].Considerable energy and time efficiency are important features of this technology and are acquired by applying a high-power microwave (MW) to materials with high moisture content [3,4].One of the main objectives of the microwave drying process is to reach a desired moisture content in the drying material after the process [3,5]. The microwave drying process is a promising technology for drying dielectric materials because of volumetric and selective heating, resulting in fast water evaporation [1,2]. Considerable energy and time efficiency are important features of this technology and are acquired by applying a high-power microwave (MW) to materials with high moisture content [3,4]. The physics behind the microwave drying process is very complex as the equations governing the process depend on both time and position [6]. These types of systems are called distributed parameter systems (DPS), and they are typically modeled with partial differential equations (PDEs). Two coupled PDEs are required to model the heat and moisture transfer in the microwave drying process, making the modeling more challenging

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