Air Feed Flow Rate Research Articles

Model-Based Sensitivity Analysis and Experimental Investigation of Perlite Grain Expansion in a Vertical Electrical Furnace

The new vertical electrical furnace which has been designed and operated at NTUA successfully produces expanded perlite of superior quality, unleashing its potential for high-performance thermal and acoustic insulation applications in the manufacturing and construction industries. A detailed sensitivity analysis has been performed on the basis of our dynamic model for perlite grain expansion, in order to quantitatively understand and systematically evaluate the effect and relative importance of feed quality and operating conditions on macroscopic (grain velocity and temperature evolution) and microscopic (steam bubble pressure, grain size) perlite particle state variables. Experimental campaign observations illustrate furnace efficiency and are in acceptable agreement with the model. Perlite feed quality (origin, chemical composition, effective water content, initial particle size distribution) is critical for adequate expansion and must be determined in advance of high-temperature processing. Process operating conditions (air feed flow rate and temperature, heating chamber wall temperature) are instrumental toward adequate expansion of a given perlite feed. Ambient air injection accomplishes sufficient expansion of the finer raw perlite fractions only, while preheated air injection achieves coarse fraction expansion but induces a risk of grain overheating and disintegration. Process efficiency increases dramatically when the furnace wall temperature is maintained within the 1100–1200 °C range.

Oxygen Permeation through U-Shaped K2NiF4-Type Oxide Hollow-Fiber Membranes

The first oxygen permeation data for a dense hollow-fiber membrane based on a K2NiF4-type oxide are reported. The U-shaped (Pr0.9La0.1)2(Ni0.74Cu0.21Ga0.05)O4+δ (PLNCG) hollow-fiber membranes were prepared by a phase-inversion spinning process. The dependences of the oxygen permeation on the feed air flow rate, sweep helium flow rate, oxygen partial pressure on the shell side, and operating temperature were experimentally investigated. The effects of the bulk diffusion and the surface exchange on the oxygen permeation flux through the U-shaped PLNCG hollow-fiber membranes are also discussed. During around 320 h of operation, a steady oxygen permeation flux of 1.0 mL/(min·cm2) was obtained at 975 °C under conditions of an air feed flow rate of 180 mL/min and a helium sweep flow rate of 55 mL/min. XRD and SEM analyses of the spent hollow-fiber membrane showed the good stability of the U-shaped PLNCG hollow-fiber membranes.

Study on air-bubbling strengthened membrane distillation process

In this work, a novel air-bubbling vacuum membrane distillation (AVMD) process was constructed on the basis of traditional vacuum membrane distillation (VMD) process. Compressed air was pressed into the lumen side of the hollow fiber membranes together with the hot feed solution just at the inlet of membrane module. So gas/liquid two-phase flow was formed in membrane lumen. Hydrophobic polyvinylidene fluoride (PVDF) hollow fiber microporous membranes were employed in this work. The effects of operating conditions, such as the feed air flow rate, the feed temperature and concentration on the performance of AVMD process were studied. The surface morphology of the PVDF membranes used in the VMD and AVMD process was characterized by scanning electronic micrograph (SEM). The results showed that the permeate flux increased as the air flow rate and/or feed temperature enhanced. The permeate flux of VMD process was 22 kg/m2h when tested at 75°C with a feed flow rate of 120 l/h and a vacuum pressure of 0.085 MPa. While, the flux of AVMD process reach 40 kg/m2h with the aid of a gas flow rate of 60 l/h. The flux of the two processes both declined gradually as the feed concentration increased from 3.5 g/l to 300 g/l, but that of AVMD was much slower. The conductivity of the product water was kept lower than 3 &mgr;S/cm. SEM paragraphs showed that there’s much more salt deposition on the surface of the membrane used in VMD process than that used in AVMD process.

ANALOGY BETWEEN HEAT AND MASS TRANSFER IN THREE SPOUTED BED ZONES DURING THE DRYING OF LIQUID MATERIALS

ABSTRACT This work, presents an experimental study of simultaneous heat and mass transfer in spouted bed zones during the drying of liquid materials. Distilled water was used as the liquid material and glass beads as inert material. The effect of the inlet gas temperature (100 to 140 °C), the feed air flow rate relative to air flow at minimum spouting (1.1 to 1.3), and liquid feed flow rate to the bed were investigated. The similarity between heat and mass transfer was analyzed using the Lewis and Chitton-Colburn analogies. Results showed that the ratio between the heat and mass transfer Chilton-Colbum factors lay between 1,31 and 1.74.