On the heat transfer mechanism in three phase fluidized beds

Heat‐transfer coefficient in viscous liquid–solid circulating fluidized beds

“…It has been generally observed and understood that the radial temperature profile in the region adjacent to the heater surface is much steeper than that in the bed proper in the conventional liquid–solid fluidized beds (Chiu and Ziegler,1983; Kang and Kim,1988; Kang et al,1991). In the riser of the liquid–solid circulating fluidized bed, a similar trend of temperature profile in the radial direction can also be found (Figure 2).…”

“…In the riser of the liquid–solid circulating fluidized bed, a similar trend of temperature profile in the radial direction can also be found (Figure 2). From the radial temperature profile, it is apparently recognized that two resistances are connected in series for the transportation of heat from the heater surface to the bed proper, as in the case of conventional liquid–solid fluidized beds (Kang and Kim,1988; Kang et al,1991; Kim and Kang,1997; Muroyama et al,1986). Based on this two resistances–in–series model, the overall heat transfer resistance can be expressed as where h , h h , and h b are the overall heat‐transfer coefficient, heat‐transfer coefficient in the region adjacent to the heater surface and that in the bed proper, respectively.…”

“…Based on this two resistances–in–series model, the overall heat transfer resistance can be expressed as where h , h h , and h b are the overall heat‐transfer coefficient, heat‐transfer coefficient in the region adjacent to the heater surface and that in the bed proper, respectively. The value of h h can be obtained from the heat balance around the heater surface (Kang and Kim,1988; Kang et al,1991), by means of the following equation where T h and T δ are the temperatures of the heater surface and region around it, respectively. The value of T δ has been determined by extrapolating the radial temperature profile to the heater surface by means of the finite‐difference method (Kang et al,1991; Muroyama et al,1986; Patel and Simpson,1977) because the region adjacent to the heater surface is essentially a very thin liquid film around the heater (Chiu and Zieagler,1983; Wasmund and Smith,1967).…”

“…The heat transfer coefficient was calculated as where Q is the heat flux from the heater surface to the riser; A is the effective surface area of the heater; and T h and T m are the temperature of the heater surface and the mean temperature of the riser, respectively. The heat flux was obtained from the DC power supplier and the temperature difference between the immersed heater and the riser was determined by (Chiu and Ziegler,1983; Kang et al,1988,1991) …”

Solid-liquid circulating fluidized bed: a way forward

“…Shin et al (2005) have investigated the effect of particle size and viscosity on HTC in the riser column of SLCFB. The heat transfer resistance between the immersed heater and the bed has been estimated based on the two resistances in series model as in the case of conventional SLFB (Muroyama et al 1986, Kang and Kim 1988, Kang et al 1991, Kim and Kang 1997. It was also reported that HTC increases with an increase in particle size due to the fact that the larger particles can have a larger inertial force to move and generate the turbulence in the viscous liquid medium.…”