Bulent Kozanoglu

Drying of Pepper Seed Particles in a Superheated Steam Fluidized Bed Operating at Reduced Pressure

A series of drying experiments was performed in a reduced-pressure superheated steam fluidized bed, employing pepper seed particles and some novel data were obtained. Experiments were carried out using different chamber pressures (40–67 kPa), temperatures (90–122°C), steam velocities (2.35–4.10 m/s), and mass flow rates (0.0049–0.0134 kg/s). In the majority of the experiments, the moisture gain observed in some other studies in the warm-up period of the process was prevented through some supplementary heat provided to the column. The drying rate was found to be increasing by operating temperature; however, it was not affected much by the superficial gas velocity and the operating pressure. Nevertheless, the reduced pressure operation increases the degree of superheating that appears as the most important parameter of the process. The experimental results showed that the equilibrium moisture content decreases by the increasing degree of superheating. On the other hand, the critical moisture content assumes higher values for the greater degrees of superheating. It was concluded that a relatively lower temperature process can be achieved through a reduced-pressure superheated steam fluidized bed.

Hydrodynamics of large particle fluidization in reduced pressure operations: an experimental study

Abstract Experiments were carried out to study effect of vacuum conditions over hydrodynamics of fluidization in large particle beds. Fluidization is one of the most attractive industrial processes due to its very high rates of heat and mass transfer provided by a good contact between particles and fluid. A series of experiments was carried out to analyze the hydrodynamics of a vacuum fluidized bed. A fluidization column, made of glass, with an i.d. of 100 mm was employed and the vacuum conditions were established through a vacuum pump. The tests were run with 10 different types of large particles (2250–7730 μm) under various temperatures and vacuum pressures. Experimental results show that the minimum fluidization velocity increases, decreasing the operation pressure. This tendency fully confirms the results obtained by Llop et al. [Chem. Eng. Sci. 51 (1996) 5149] under vacuum conditions. Using the experimental results two equations, one for sharp particles the other one for round particles, were developed to predict the minimum fluidization velocity and the results were compared with the other equations proposed in the technical literature. On the other hand, the experimentally obtained values of bed voidage under minimum fluidization conditions were found to be insensitive to operation pressure as also observed by Chitester et al. [Chem. Eng. Sci. 39 (1984) 253].

Drying Kinetics of Paddy in a Reduced Pressure Superheated Steam Fluidized Bed

Drying kinetics of paddy are experimentally studied in a superheated steam fluidized bed operating at reduced pressure. During the experiments, different operating pressures (40–67 kPa), operating temperatures (98–118°C), superficial steam velocities (2.9–4.0 m/s), and mass flow rates (0.0061–0.0103 kg/s) were employed. The condensation problem, typically observed in the initial part of the process, was eliminated in the majority of the experiments through some additional heat supplied into the column by electrical resistances. The experiments demonstrated that drying rates increase by increasing operating temperature. Nevertheless, the operating pressure and the superficial steam velocity showed only limited influences over the process. The degree of superheating was identified as the principal parameter controlling the phenomenon. It was also observed that higher degrees of superheating generate lower equilibrium moisture contents and a superheating steam fluidized bed operating at reduced pressure can achieve drying processes at relatively lower temperatures.

Influence of Particle Size on Vacuum–Fluidized Bed Drying

The effect of particle size on the vacuum–fluidized bed drying process was experimentally studied using pepper seed particles with two distinct diameters. In the constant drying rate period, the small particles demonstrated stronger drying rates resulting from higher mass transfer coefficient values and larger contact area for per unit particle humidity. The experimental results also showed that the falling drying rate period was controlled in the beginning by the particle diameter and later by the effective porosity of the particle. Consequently, in the beginning of the falling drying rate period the small particles presented higher drying rates, whereas toward the end of the period, the large particles, with higher effective porosity, produced stronger drying rates than the small ones. The effects of the vacuum pressure and the superficial gas velocity throughout the process were only observed in the constant drying rate period, whereas the higher operating temperatures enriched the drying rates in both periods.

Convective heat transfer around vertical jet fires: An experimental study

The convection heat transfer phenomenon in vertical jet fires was experimentally analyzed. In these experiments, turbulent propane flames were generated in subsonic as well as sonic regimes. The experimental data demonstrated that the rate of convection heat transfer increases by increasing the length of the flame. Assuming the solid flame model, the convection heat transfer coefficient was calculated. Two equations in terms of adimensional numbers were developed. It was found out that the Nusselt number attains greater values for higher values of the Rayleigh and Reynolds numbers. On the other hand, the Froude number was analyzed only for the subsonic flames where the Nusselt number grows by this number and the diameter of the orifice.

Hydrodynamics of Reduced Pressure Fluidization Employing Particles with Variable Density

A series of experiments was carried out to study the hydrodynamics of a fluidized bed operating at reduced pressure and employing particles with variable moisture content; that is, of variable density. In these experiments, four different types of particles were used and fluidization characteristics very similar to the ones encountered in atmospheric pressure operations were observed. A novel method to measure the minimum fluidization velocity of particles with varying density was proposed. The experimental results demonstrated that the minimum fluidization velocity increased with decreased operating pressure, increased operating temperature, and increased particle moisture content. However, the bed voidage under minimum fluidization conditions showed very little sensitivity to variations in operating pressure. Two equations were developed to predict the minimum fluidization velocity and the results were compared with the experimental data as well as with the predictions of equations available in the tech...

Drying Characteristics of Coriander Seed Particles in a Reduced Pressure Superheated Steam Fluidized Bed

Drying characteristics of coriander seed particles were experimentally analyzed in a reduced pressure superheated steam fluidized bed. The typical moisture gain, reported in some other studies during the warm-up period of the process, was reduced in most of the cases by supplying additional heat into the column. The experimental results demonstrated that the drying rate increases and the equilibrium moisture content decreases by increasing the operating temperature. However, variation of the operating pressure (40–67 kPa) and the superficial steam velocity (2.3–4.0 m/s) did not present significant effects on the moisture contents. The degree of superheating was found to be the most important parameter for the process. The experiments also showed that the equilibrium moisture content decreases upon increasing the degree of superheating. Finally, employing a reduced pressure superheated steam fluidized bed appears as an option to carry out drying processes at relatively lower temperatures.