Canadian Journal of Chemical Engineering
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The residence time distribution (RTD) of the liquid phase in air‐water flow through helical coils has been studied. Upward and downward cocurrent flows have been investigated in three coils with curvature ratios ranging from 11 to 60.7. The ranges of the Reynolds numbers for the gas and the liquid varied from 1500 to 3000 and 620 to 3200, respectively. A model has been proposed that describes the liquid phase RTD as combination of two different residence time distributions applicable for turbulent and laminar liquid flows.
Experimental investigations have been carried out to evaluate the two‐phase pressure drop and the holdup for gas‐Newtonian liquid flow through helical coils. 24 helical coils and three different liquids were used for the experiments. Empirical correlations have been developed to predict the two‐phase friction factor and the liquid holdup as functions of various physical and dynamic variables of the system. Statistical analysis of the correlations suggests that they are of acceptable accuracy.
Experimental results on flow pattern, hold–up and pressure drop are presented for cocurrent upward and downward air water flow in helical coils. A tube of 0.01 m internal diameter was used and the ratio of coil to tube diameter was varied from 11 to 156.5. Water flow rate was varied from 4.9 × 10‐6 m3/s to 92 × 10‐6 m3/s while the range of gas flow rate covered was 83 × 10‐6 m3/s to 610 × 10‐6 m3/s.
A new mechanistic approach is proposed to correlate pressure drop data in coils. The proposed model retains the identity of each phase and separately accounts for the effects of curvature and tube inclination resulting from the torsion of the tube. This makes it possible to use a single model to predict pressure drop for both upward and downward two–phase flow in coiled tubes. Required correlations for hold–up, interfacial friction factor and friction factors for individual phases are provided.
The augmentation in heat transfer can be achieved by improving either transport phenomena with geometry perturbation or thermal conductivity of the fluid itself. In the present study, the simultaneous effects of both the geometry and improved thermal conductivity have been tried on heat transfer enhancement by using two different nanofluids (Al2O3‐water and TiO2‐water). An innovative three‐dimensional device called a coiled flow inverter (CFI) is proposed for the process intensification. The CFI is made up of helical coiled tube, which is bent periodically to 90 ° at equidistant length. In addition to a CFI, the performance characteristics of helical coil and straight tube have been investigated. The Reynolds numbers are in the range of 25–4000, while the nanoparticle volume fraction varied from 0.25–4 %. It was noted that the heat transfer in a CFI improved considerably as compared to helical coil and straight tube of same dimension. The Nusselt number in helical coil augments by 2.5 times to that of straight tube. In the CFI, the Nusselt number further enhanced by 23–35 % as compared to helical coil, with 0–4 % increase in the nanoparticle volume fractions. The new correlations are developed to predict the Nusselt number and friction factor for the flow of nanofluids in the CFI. The number of merit in the CFI to that of straight tube are 1.6–1.8 times, with 0–4 % nanoparticle volume fractions. The present study may motivate the design and development of novel compact heat exchangers as well as a new‐generation microfluidic device.
In coiled tubes of non‐circular cross‐section the orientation of the cross‐sectional plane with respect to the direction of the centrifugal force has a significant effect on residence time distribution (RTD) which has been recognized for the first time. This aspect has been experimentally investigated in helically coiled tubes of square cross‐section, under the conditions of negligible and significant molecular diffusion.
It has been known for some time that many continuous chemical reactors give the greatest conversion when axial dispersion is minimized, i.e., when plug flow occurs. This paper considers the problem of attaining plug flow in continuous flow systems. The geometrical configuration of a tube wound into a helix is suggested us a convenient and efficient means of producing secondary currents which promote plug flow. On the basis of tracer distribution tests and pressure drop data it is conclusively shown that helical coils are far superior to straight tubes or packed beds in minimizing axial dispersion and approaching plug flow.
This paper reviews recent results obtained in our laboratory and elsewhere which show the importance of particle size distribution (PSD) in fluidized beds. Fines content in itself, often used as a descriptor, is not a sufficient parameter to characterize the PSD effect. Broadening the PSD affects gas flow through the dense phase, produces smaller bubbles, leads to more particles in the dilute phase and causes earlier transition to the turbulent hydrodynamic regime of fluidization. Chemical conversion is therefore enhanced by broadening the PSD, and the enhancement increases when the bed operates in the turbulent regime.
For processes described by linear transfer functions with additive disturbances, the best possible control in the mean square sense is realized when a minimum variance controller is implemented. It is shown that an estimate of the best possible control can be obtained by fitting a univariate time series to process data collected under routine control. No ‘identifiabüity’ constraints need be imposed. The use of this technique is demonstrated with pilot plant and production data.
Methane (CH4) reforming was carried out in an internal combustion engine (an “engine reformer”). We successfully produced syngas from the partial oxidation of natural gas in the cylinder of a diesel engine that was reconfigured to perform spark ignition. Performing the reaction in an engine cylinder allows some of the exothermicity to be captured as useful work. Intake conditions of 110 kPa and up to 480 °C allowed low cycle‐to‐cycle variability (
This work reports the synthesis of particles based on poly(3‐hydroxybutirate‐co‐3‐hydroxyvalerate) (PHBV) polymer that were impregnated with progesterone. The PHBV particles were obtained by supercritical CO2 (scCO2) anti‐solvent expansion (SAS). scCO2 was also used at a high pressure (25 MPa) and moderate temperature (323 K) for the impregnation of progesterone into the PHBV particles at different impregnation times. In vitro release tests showed that the half‐time of progesterone release in a hydro‐alcoholic medium, for the samples produced with impregnation times of 2–32 h, was 3–5 h, with the higher release times generally related to smaller impregnation times.
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