Determination Of Rheological Parameters Research Articles

Refrigerant overheating in the compression circuit air heat pump

The authors considered the processes of phase transformation of the working fluid in the compression unit of the freon circuit in the section “thermal expansion valve (TEV) - evaporator - compressor”. By adjusting the expansion valve under the conditions of the bubble mode of boiling of the refrigerant, the evaporation process takes place, accompanied by the achievement of a certain excess of steam temperature. Determination of rheological parameters (droplet size, vapor viscosity, refrigerant droplet vaporization rate) is necessary so that when moving from the throttle valve (TEV) to the compressor inlet, they have time to go into the vapor phase or return to the mass of boiling liquid. The article presents the results of an analytical calculation of the parameters of the kinetics of evaporation of Freon droplets as they move in a steam flow. The results of such an analysis make it possible to formulate requirements for the optimal droplet size in the created vapor-liquid mixture in order to ensure their maximum evaporation and the required thermal efficiency of the AHP as a whole. The established patterns of evaporation of refrigerant droplets can be used to select the design and operation of the AHP.

Determination of rheological parameters of soft media strained with acceleration and Inertia

Determination of rheological parameters of soft media strained with acceleration and Inertia

Estabilidad física de bases emulsionadas e hidrosolubles con quitosana y acetato de quitosana

Context: Chitosan has received great attention because it is a functional, biodegradable, renewable and non-toxic biopolymer with multiple pharmaceutical applications, including stabilizing agent. Aims: To evaluate the physical stability of emulsified bases and hydrophilic gels containing chitosan or chitosan acetate as stabilizing agents. Methods: Stability of shelf-life formulations at room temperature and in refrigeration was evaluated over a period of 60 days and by thermal stress testing and centrifugal destabilization. The organoleptic characteristics, pH, conductivity and flow behavior were evaluated, the latter through the analysis of the rheograms, the determination of rheological parameters (consistency index, apparent viscosity, creep value and flow index), as well as their comparison statistics. The possible correlations between these parameters and the concentration of the biopolymers were also evaluated. Results: The bases elaborated with chitosan or its soluble derivative showed adequate physical stability during the study time. The effect of the storage temperature, as well as the type and concentration of the stabilizing agent used was evidenced. Emulsifier combinations provided less stability. A linear correlation between the rheological parameters and the biopolymer concentration was evidenced. Conclusions: Chitosan and chitosan acetate can be used as emulsifying agents in semi-solid and gelling bases in hydrophilic gels, due to the electrostatic stabilization and the viscosity they contribute to the system in relation to its concentration.

Determination of Rheological Parameters for Several Lubricants Applied in the High-Speed and High-Pressure Bearings

Traction coefficients of several domestic lubricants in various operating conditions were measured on a self-made test rig. The equations for calculating the average values of limiting shear stress and shear elastic modulus of the lubricants applied in the high-speed and high-pressure bearings were advanced. The example calculations for one lubricating oil and two lubricating grease were then made. The results show that the regression precisions of the equations above are satisfied. The equations also adapt to the other lubricants in the same operating conditions.

Estimation of rheological parameters using velocity measurements

In the present investigation, we develop a method for estimating rheological parameters of viscoelastic fluids using velocity measurement in a square straight channel. It is believed that a somewhat complicated patterns of secondary flows due to the non-zero second normal stress difference are more useful than the simple viscometric flows traditionally adopted in the determination of rheological parameters. The inverse problem of determining the rheological parameters from a set of velocity measurements is solved using a conjugate gradient method. When applied to a general constitutive equation encompassing the UCM model, the Oldroyd-B model and the PTT model, the present method is found to yield a reasonably accurate estimation of five rheological parameters simultaneously even with noisy velocity measurements.

Determination of rheological parameters of liquid crystals with zero anisotropy of diamagnetic susceptibility

A new method for determination of rheological parameters of liquid crystals with zero anisotropy of diamagnetic susceptibility is proposed, which is based on the measurement of the quadrupole splitting line of the NMR 2H spectrum. The method provides higher information content of the experiments, with the shear flow discarded from consideration, compared to that obtained by the classical Leslie-Ericksen theory. A comparison with the experiment is performed, the coefficients of anisotropic viscosity of lecithin/D2O/cyclohexane are determined, and a conclusion is drawn as concerns the domain shapes.

Determination of Rheological Parameters from Measurements on a Viscometer with Coaxial Cylinders – Choice of the Reference Radius

Knowledge about rheological behavior is necessary in engineering calculations for equipment used for processing concentrated suspensions and polymers. Power-law and Bingham models are often used for evaluating the experimental data. This paper proposes the reference radius to which experimental results obtained by measurements on a rotational viscometer with coaxial cylinders should be related.

Determination of Rheological Parameters from Measurements on a Viscometer with Coaxial Cylinders

The paper deals with measurements of non-Newtonian fluids on a viscometer with coaxial cylinders. The procedure for determining the rheological model parameters is recommended for power-law fluids and Bingham plastics.

Flow of Magnetorheological Fluids

For efficiently describing the flow of magnetorheological fluids (MRFs), a feasible model based on the Bingham equation is presented. It allows the determination of rheological parameters from parameters attained with a measuring equipment working in the flow mode. For flow velocities v<1cm/s the results agree with data given by the MRF-producer. For higher velocities v, so far not investigated, the results are plausible.

Comparison Between Models Used in the Determination of Rheological Parameters of Suspensions with a Helical Screw Impeller

In this paper, a comparison is made between two models used in the determination of rheological parameters of suspensions with a helical screw impeller. One of them is an improved numerical procedure described in a previous work. The second one (calibration methodology), valid for power law fluids, characterizes the rheological properties of suspensions by flow curves which present the dependence of the shear stress on shear rate. Tests of statistical significance do not allow us to distinguish between them. Since the mathematical complexity of the calibration methodology is lower than that of the improved numerical method, it is concluded that the former is preferred to the latter in the determination of rheological parameters of power law suspensions.