Developing an efficient regime for the thermal stabilization of polyacrylonitrile roving in a “Vulon” furnace

Abstract

A mathematical model is constructed to describe conjugate radiative-convective heat transfer in the working space of a "Vulon" furnace, which is designed for the thermal stabilization of raw materials used in the production of carbon fibers. A program was written in the language C++ to realize the model in the environment Builder 6.0. The program was used to study the thermal performance of the furnace, and temperature regimes were devised to allow problem-free thermal stabilization of polyacrylonitride rovings. It is shown that the stabilization operation can be automated by controlling the power supplied to electric heaters installed in the channels of the furnace.The Scientific Research Institute of Graphite has developed a technology and a furnace -the "Vulon" furnacefor the thermal stabilization of polyacrylonitride (PAN) roving. The technology and the furnace are based on the principle of staged heating. A schematic diagram of the Vulon furnace is shown in Fig. 1. The working space of the furnace consists of a system of superimposed horizontal channels serially connected to one another in the direction of motion of the roving. Electric heaters are secured to the roof and floor of each channel. The roving is drawn through the channels' center and is heated inside each channel by the electric heaters and hot air that is preheated to 160°C in a recuperator before entering the furnace. If necessary, the air can be additionally heated to 230°C in a calorifier and then be heated by the electric heaters in the furnace's channels.To study the thermal performance of the Vulon furnace and develop an efficient regime for the thermal stabilization of PAN roving, we constructed a mathematical model of heat transfer in the channels of the furnace and created a program to realize the model on a computer.The mathematical model is based on the following physical model of the stabilization operation and the furnace. Each furnace channel is represented as a parallelepiped whose length is 10 times greater than its width and height. The fiber rovings that are undergoing heating move along the axis of the channel and divide it into a top part and a bottom part. The rovings collectively form a continuous flat sheet whose thickness is equal to the thickness of the roving and whose width is equal to the maximum width of the group of rovings. The maximum width of the group is determined with allowance for the gaps between the rovings. Electric heaters are installed on the roof and floor of each channel, forming individual sections. As a first approximation, we assume that the heaters in each section of each channel form a continuous flat surface. Voltage is supplied separately to each section. The roving being processed is drawn through the channel at speeds ranging from 20 to 100 m/h. The air in the channels moves at speeds no greater than 5 m/sec.The following assumptions were used in constructing the mathematical model:-no allowance is made for the heat lost through the lateral surfaces of the channels; -the top and bottom surfac...