OCR Text |
Show that can yield accurate, rapid predictions. In the assessment of furnace performance, transient thermal behavior must be con-sidered[ l,2]. This is because the furnace system is constructed of high thermal capacity elements such as thermal insulating wall, the high temperature atmosphere, loads if the furnace is in operation and other equipment etc, thermal properties of each element causes time lags in heating time up to the intended temperature. It is thus important to confirm the thermal behavior of each element individually, desired to produce a furnace with high accuracy and high efficiency. In this study, to determine which factors predominant in producing the complicated heat transfer phenomena of industrial furnaces, the performance of typical two types of industrial furnaces in transient heating processes were investigated experimentally and with C F D. 2 Experimental apparatus and conditions 2.1 Experimental arrangement of directly gas-fired furnace The experimental arrangement of the directly gas-fired furnace used in this study is shown in figure 1. Figure 2 illustrates a cross-section of the thermal insulating wall. The thermal insulating wall is constructed from four layers of materials: carbon steel (S45C, thickness 1.5mm), rock-wool (125mm), ceramic wool felt (75mm), and stainless steel (SUS304, 1.5mm), from outside to inside of the furnace. O n the ceiling wall, the circulating fan driving motor and its bearings are mounted, and the fan-driving axle is installed through the ceiling wall (see figure 3). In the front wall, there is a door used for loading. Every gap between the door and surrounding walls is sealed with a heat-resistant material to prevent hot air leaks during furnace operation. A n exhaust pipe and a hot air inlet are located on both sidewalls. As illustrated in figure 1, exhaust pipes are located upper side and hot air inlets are located bottom side on both sidewalls. The exhaust pipes and hot air inlets on both sidewalls are arranged symmetrically about the fan-driving axle. O n the hot air inlet, a spacing pipe and a package burner are installed. The spacing pipe is used to obtain hot air inflow condition, so the pipe length is set at approximately the same length as the flame length formed after the burner to prevent formation of flame in the furnace. Inside of the furnace, a muffle, a circulating fan and a roller unit used for loading are installed. Figure 4 shows the experimental arrangement in the inner space. The muffle separates this inner space (its dimensions are 750 W x 550/3 x 1100//) into a working space (bOOW x 575 D x 600//) and a hot air channel. The ceiling plate of the muffle has a suction hole of diameter 180mm. The hot air in the working space is sucked out toward the ceiling wall through this hole by the circulating fan, and blown down between the muffle side plate and inner sidewall (hot air challel). Masses of the directly heating gas-fired furnace elements are tabulated in table 1. |