Predicting pMDI formulation thermophysical properties using activity coefficient models

The Kigali amendment to Montreal protocol sets the timetable for phasing out of pMDI propellants HFA134a and HFA227ea, creating a requirement for green propellants to take their place. To assist this transition, accurate prediction of thermophysical properties that control aerosol generation of new formulations is crucial. A relevant challenge is how to predict property data such as saturated vapour pressure, surface tension and viscosity of propellant/excipient/drug mixtures using the smallest possible programme of physical testing. It is proposed to use a thermodynamic framework based on activity coefficients to model intermolecular forces between constituents, which are known to control multi-component thermophysical property behaviour. It is proposed to use the UNIFAC method, which is based on detailed physical understanding of molecular functional groups and their interactions, with the ability to capture azeotropic behaviour. Surface tension, viscosity and vapour pressure measurements of mixtures of HFA134a with ethanol at 20°C have been studied to validate the technique. Utilizing UNIFAC parameter fitting to the experimental dataset with non-linear least-squares optimization, a root mean square deviation (RMSD) of 7% in predicted surface tension, 6% in predicted viscosity and 2% in predicted vapour pressure was obtained. Previously unavailable UNIFAC interaction parameters for HFA-alcohol mixtures were created. The capability is highly versatile, accepting various thermophysical property data and giving good agreement with measured values for existing formulation mixtures. The framework can be readily applied to mixtures of green propellants such as HFA152a to extend experimental data when available and support insights into thermophysical properties and aerosol generation

Theoretical validation of test results for the pressure drop values of circular pins with maximum length to diameter ratio of 3.0 using existing equations and test data for heat exchanger application

Paper presented at the 8th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Mauritius, 11-13 July, 2011.Pins are a very common type of extended surface used in the field of heat transfer; their main use being in the electronics field. In this report, the use of pins as an extended surface is considered for a Heat Exchanger application in the aerospace field. The Heat Exchanger uses forced convective heat transfer mechanism for the dissipation of heat and the implicated fluid is air. For this application the pin layout and design is completely unique in that the pin’s maximum length to diameter ratio is 3.0 and the layout of the pins produces an X T value of 7, which has not been explored in any previous work. The Length: Diameter ratio of these new pins is very small when compared to the Length: Diameter ratios of tubes currently used in heat exchangers to enhance heat transfer. Moreover, the distance between the pins in this arrangement is much greater than those for the tubes. Testing has been performed on this pin design and the theoretical validation of those test results is one of the main aspects discussed in this report. Due to the innovative nature of the pin designs, there is insufficient existing test data or established equations that can be used. Assumptions are made in order to be able to apply the current equations for pressure drop calculations with valid justifications. The theoretical results for the total pressure drop show an average deviation of 6% from the test results for mass flow rates between 0.14 kg/s and 0.36 kg/s. The maximum pressure drop was found to be caused by the pins and it was in the range of 89%-91%of the total. In this article, the limitations of existing equations are discussed and the gap in the theoretical knowledge regarding novel pin designs is highlighted.mp201

An untroduction to computational fluid dynamics the finite volume method/ Versteeg

x, 257 hal. : ill. tab. : 26 cm

An Introduction to Computational Fluid Dynamics

If your new or interested in the field of CFD this book with introduction to cfd by john d anderson should be in your personal library

Microstructural analysis of non-woven fabrics using scanning electron microscopy and image processing. Part 2:Application to hydroentangled fabrics

The image analysis techniques developed in Part 1 to study microstructural changes in nonwoven fabrics are applied to measure the bre orientation distribution and bre length distribution of hydroentangled fabrics. The results are supported by strength and modulus measurements using samples from the same fabrics. It is shown that the techniques developed can successfully be used to assess the degree of entanglement of hydroentangled fabrics regardless of their thickness

The effect of nozzle geometry on the flow characteristics of small water jets

A wide variety of processes make use of plain orifice nozzles. Fuel injectors for internal combustion engines incorporate these nozzles to generate finely atomized sprays. Processes such as jet cutting, jet cleaning, and hydroentanglement, on the other hand, use similar nozzles, but require coherent jets. The spray or jet characteristics depend on the stability of the flow emerging from the orifice. This problem has been extensively researched for nozzles with diameters above 300 μm. Much less is known about the characteristics of jets produced by nozzles with smaller diameters, where viscous effects and small geometric variations due to manufacturing tolerances are likely to play an increasing role. Results are presented of a wide-ranging investigation of geometry effects on the flow parameters and jet characteristics of nozzles with diameters between 120 and 170 μm. Nozzles with circular cross-section and conical, cone-capillary and capillary axial designs were investigated. For conical and conecapillary nozzles, the effect of cone angle and effects due to interactions between adjacent nozzles in the multi-hole cone-capillary nozzles were studied. For capillary nozzles, the effects of diameter variations and inlet edge roundness for capillary nozzles were considered. Furthermore, the effect of varying the aspect ratio (ratio of major and minor axes) of elliptical nozzles was studied. Flowrate and jet impact force measurements were carried out to determine the discharge coefficient Cd, velocity coefficient Cv, and contraction coefficient Cc of the nozzles for supply pressures between 3 and 12 MPa. Visualizations of the jet flow were carried out in the vicinity of the nozzle exit in order to identify near-nozzle flow regimes and to study jet coherence. The relationship between nozzle geometry, discharge characteristics, and jet coherence is examined

3D simulation of flow In a right angled channel junction with a pit

by Abhishek K. Pandey and Pranab K. Mohapatr