Hydraulic resistance, experimental results

A considerable amount of work has been published on optimizing the experimental conditions for minimum analysis time under various constraints [52]. One complication arises from the definition of reduced mobile-phase velocity. The actual mobile-phase velocity depends largely on the molecular-diffusion coefficient of the analyte. Thus, very small particles can be used for the analysis of high molecular mass compounds, which have low values. The actual flow rate required will remain compatible with pressure constraints despite the resulting high pneumatic or hydraulic resistance. Detailed results obviously depend greatly on the mode of chromatography used. 

AHSTRACT Modelling and computing of thermal biomass treatment processes involving thick layers requires that the gas permeability and hydraulic resistance of such layers be known. The paper presents the results of experimental research into the hydraulic resistance of the thick layer comprised of two biomass varieties sunflower husks and sawdust. The research was conducted within the range of Re alteration from 5-70, and layer porosity change 0.2-0.7,... 

The results of experimental research into husks and sawdust hydraulic resistance as related to air velocih and layer density are prcscnicd in Figure 2 and Figure 3-... 

An effect not considered in the above models is the added resistance, caused by fouling, to solute back-diffusion from the boundary layer. Fouling thus increases concentration polarization effects and raises the osmotic pressure of the feed adjacent to the membrane surface, so reducing the driving force for permeation. This factor was explored experimentally by Sheppard and Thomas (31) by covering reverse osmosis membranes with uniform, permeable plastic films. These authors also developed a predictive model to correlate their results. Carter et al. (32) have studied the concentration polarization caused by the build-up of rust fouling layers on reverse osmosis membranes but assumed (and confirmed by experiment) that the rust layer had negligible hydraulic resistance. 

Garstecki et al. conducted careful experiments [13] in which they varied (i) the geometry of the device, (ii) the rates of flow of the two fluids, (iii) the viscosity of the continuous fluid and (iv) the value of the interfacial tension. These experimental results verified that at low values of the Capillary number - which are t5 ical to those t5 ical for flows in microsystems -indeed the mechanism of break-up is similar to that observed in the flow-focusing system. Namely, as the tip of the dispersed phase enters the main channel, and fills its cross-section, the hydraulic resistance to flow in the thin films between the interface and the walls of the obstructed microchannel creates an additional pressure drop along the growing droplet. This pressure drop has a primary influence on the d5mamics of break-up namely, once the main channel is obstructed by the growing droplet, the upstream interface of... 

The experimental results are presented graphically dependencies of hydraulic resistance of regime-the design parameters. Figs. 4 and 5. 

The influence of freezing water in capillary pores is a very complex phenomenon and various processes accompany simple hydraulic pressure of ice on hardened cement paste, but the model proposed by Powers was universally accepted as explaining the destructive influence on concrete elements with acceptable agreement with experimental results. That model is considered as a basis for standardized requirements for the design of structures. Furthermore, there is strong experimental evidence that the distribution of the voids is a key factor governing the frost resistance of concrete. This statement is supported by experience and investigations in several countries where the temperature in winter falls below zero. An example of such... 

Results of an experimental research of a hydraulic resistance of a rotor depending on the angular speed of twirl are presented in Figure 3.6. By drawing full lines, experimental values of a hydraulic resistance of a twirled vortex generator, and dotted, which is computed by formula (3.9)... 

As a result of processing, the experimental data received by authors in bench and industrial conditions, for calculation of hydraulic resistance of a deduster with vortex generator type TB VC, the equation is offered. 

PEM resistance in operational PEFC as a function of the fuel cell current density, comparing experimental data (dots) and calculated results from a performance model based on the hydraulic permeation model for various applied gas pressure differences between anode and cathode compartments. (Reprinted from S. Renganathan et al. Journal of Power Sources 160 (2006) 386-397. Copyright 2006, with permission from Elsevier.)... 

Reynolds numbers are of value in the various fields because lesis of models are directly comparable to full-scale results of geometrically similar shapes if the Reynolds ratio for the model equals that of the actual or full-scale project. This has its practical applications in the field of hydrodynamics, in the study of water resistance of hulls or floats, and in the study of water velocities, levee problems, etc., of large rivers. It is used also to establish the best proportions of hydraulic turbines through the use of models. Much of the science of aeronautics rests upon experimental data obtained in wind tunnels. Dangerous inaccuracies might exist in drawing conclusions for actual construction from model tests, unless either the model were, tested at a Reynolds number equal to that of the completed project, or due corrections and allowances were made for the Reynolds number. See also Heat Transfer. 

Fig. 10 Membrane resistance in H2/O2 fuel cell as a function of proton current density. Experimental data, normalized to the resistance 9ts of the saturated membrane at various temperatures have been extracted from Ref. 94. They are compared to the values calculated in the hydraulic permeation model (main figure) and to the results of the diffusion model, taken from Ref. 7 (inset).

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