Correlation Of Dimensionless Numbers Research Articles

Dissolution reaction kinetics and mass transfer during aqueous choline chloride pre-treatment of oak wood

Lignocellulosic biomass processing employing ionic liquids is of recent research interest for the biorefinery industry. The data on biomass dissolution kinetics in ionic liquids is important for designing scale-up pre-treatment reactor design. In this study, the reaction mechanism and kinetics of oak wood dissolution in aqueous choline chloride was investigated. In an extended effort, a correlation of dimensionless numbers was developed for the estimation the mass transfer coefficient. The analyses suggested that oak wood dissolution in choline chloride occurred in two stages. The diffusion of ionic liquid through the product layer was the dominating rate-controlling step in the first stage of dissolution followed by the surface chemical reaction in the second stage. The diffusivity of choline chloride into the oak wood matrix was ranging between 2.96E−14 and 2.84E−13 m2/s. The activation energy of the diffusion controlled stage and surface chemical reaction controlled stage was approximately 24.2 and 40.3 kJ mol−1, respectively. The proposed mathematical correlation for mass transfer coefficient fitted well with the experimental mass transfer coefficient values.

Active control of foams by physically based destruction mechanisms

AbstractFoams may be undesired in technical processes and need, thus, to be actively controlled. In food science engineering it is often not possible to apply chemical measures due to the required purity of the processed products. To overcome this challenge it is necessary to apply physically based foam destruction mechanisms. The present contribution deals with the prediction of foamability and the application of acoustical foam destruction from an experimental point of view. The results show that it is possible to classify the foamability of different fluids by a correlation of dimensionless numbers containing purely physico‐chemical properties (i.e. density, surface tension, viscosity). The foam stability is a consequence of the net balance of the foam generation and the foam decay. The respective time scales may be influenced by the process conditions, the fluid properties, and the selected physically based destruction mechanism. In the case of resonance excitation of foam bubbles by acoustic waves of defined frequencies selective foam destruction can be achieved. The bubbles in the foam start to oscillate and absorb energy depending on the bubble size, fluid properties, and ultrasound frequency. The resulting bubble breakdown leads to a shortening of the time scales of the foam decay.

Utilization of population balances in simulation of liquid-liquid systems in mixed tanks

A simulation model has been developed to model drop populations in a mixed tank. A multiblock mixed tank model has been used with the drop population balance equations developed in the literature. The drop breakage and coalescence functions used in the population balance model take into account the local turbulent energy dissipation values. The drop breakage and coalescence function parameters are fitted against drop size measurements from dense liquid-liquid dispersions, which were assumed fully turbulent. Since the local turbulence and flow values of a mixed tank are used in the present model, the fundamental breakage and coalescence phenomena can be taken into closer examination. Furthermore, the present model is capable of predicting inhomogeneities occurring in a mixed tank. It is also considered as an improved tool for process scale-up, compared to the simple vessel-averaged population balance approach, or use of correlations of dimensionless numbers only. The present model can use two sources of data for fitting parameters in the drop rate functions. One is the transient data of the measured drop size distribution as the impeller speed is changed. The other is the time-averaged data measured at different locations of the mixed tank. Different flow regions can be chosen from direct measurements or from the CFD simulations in a straightforward manner. CFD flow simulation results can be used when no experimentally obtained flow conditions are available. This is especially useful for nonstandard vessels, such as reactors containing cooling coils.

Determination of Fluid-particle Convective Heat Transfer Coefficient

Fluid-to-particle convective heat transfer coefficient (hfp) was determined by continuous particle center temperature measurements in a hold tube by a temperature sensor system using the transmitter particle technique. The fluid used was carboxy methyl cellulose (CMC) at concentrations of 0.5, 1.0, and 1.2% (w/w). The carrier fluid temperatures were 22.22, 65.56, 76.67, and 82.22 C. Temperature dependent viscosity parameters of CMC were determined and used in calculating hfp. Specific heat and thermal resistance of the sensor were experimentally determined and used in solving the energy balance equation to obtain hfp values. Values of hfp ranged from 108.08 to 195.83 W/m2 C. The results are expressed as a correlation of dimensionless numbers. The fluid viscosity significantly affected hfp at high temperatures. Decreasing fluid viscosity (by increasing fluid temperatures) increased hfp.

“Turbulent Flow in Alluvium”

SIR CLAUDE INGLIS, in. his letter published in Nature of October 19, p. 552, remarks that my formulae for alluvial flow are based on two fundamental relationships. It would be more correct to state that two independent fundamental equations are necessary to a complete solution, and that each of these equations consists of an empirical correlation of dimensionless numbers or 'arguments', derived from the essential variables. Dr. White has produced a partial solution, which effectively ignores the Reynolds number. The following solution appears to be complete.