Abstract
This investigation was carried out to estimate the thermal properties, convective heat transfer coefficient, intraparticle heat conductivity and so on, in the heat transfer experiment of single kernel as the minimum unit of the packed bed.
The effect of moisture evaporation in the heat transfer experiment could be neglected because of adoption of dried material (5% w.b.), rough rice and barley.
The propriety of the method in the experiment and analysis was estimated in comparison between result of glass bead and the literature on glass bead. The results obtained from this study were summarized as follows:
1) The surface area of rough rice calculated from the equivalent diameter by Smiths' geometry index is 0.75 times as large as the mesured surface area (av=2636.1m2/m3). Therefore, the convective heat transfer coefficient of rough rice, hp, calculated from equivalent diameter, is overestimated about 35 percent.
2) The intraparticle heat conductivity was estimated from the sinking method of marcury tank.
rough rice: 0.267kcal/mhr°C, barley: 0.358kcal/mhr°C, glass bead: 0.547kcal/mhr°C
3) The convective heat transfer coefficient was obtained by measuring the center temperature of a particle.
rough rice: Nu=0.334 Re0.407 (60≤Re≤180)
barley: Nu=1.350 Re0.275 (20≤Re≤230)
glass bead: Nu=2+1.070Pr1/3 Re0.379 (60≤Re≤340)
4) The equation of the convective heat transfer coefficient, hp, was derived from the exact form equation with reference of the center temperature, which describes temperature distribution within a homogeneous particle. The Biot Number calculated from the value of hp, was larger than 0.1 over the experiment range (Va: 0.1-1.0m/s), and it was obious that intraparticle resistance of heat transfer shouldn't be neglected.
