Numerical modeling of two-phase flashing propellant flow inside the twin-orifice system of pressurized metered dose inhalers

Pressurized metered-dose inhalers (pMDIs) are the most widely-prescribed inhaler devices for therapeutic aerosol delivery in the treatment of lung diseases. In spite of its undoubted therapeutic and commercial success, the propellant flow mechanics and aerosol formation by the pMDIs is poorly understood. The process involves a complex transient cavitating turbulent fluid that flashes into rapidly evaporating droplets, but details remain elusive, partly due to the difficulty of performing experiments at the small length scales and short time scales. The objective of the current work is the development of a numerical model to predict the internal flow conditions (pressure, temperature, velocity, void fraction, quality, etc.) and provide deeper insight into the atomization process and fluid mechanics involved in the twin-orifice of pMDIs. The main focus is propellant metastability, which has been identified by several past authors as a key element that is missing in accounts of pMDI performance. First the flashing propellant flow through single orifice systems (both long and short capillary tubes) was investigated using three different models : homogeneous equilibrium model (HEM), delayed equilibrium model (DEM) and improved delayed equilibrium model (IDEM). Both, the pure propellants and the propellant mixtures were used as working fluid. The numerical results were compared with the experimental data. For long capillary tubes the three models gave reasonable predictions, but the present results showed that DEM predicts the mass flow rate well for pure propellants and IDEM predicts the mass flow rate well for propellant mixtures. For short capillary tubes, the present results showed that DEM predicts the mass flow rate and pressure distribution along the short tube better compared to HEM and IDEM. The geometry of the twin-orifice system of a pMDI is complex and involves several singularities (sudden enlargements and sudden contractions). Various assumptions were made to evaluate their effect on the vaporisation process and to evaluate the flow variables after the shock at the exit of the spray orifice when the flow is choked. Also, three different propellant flow regimes were explored at the inlet of the valve orifice. A specific combination of assumptions, which offers good agreement with the experimental data was selected for further computations. Numerical investigations were carried out using delayed equilibrium model (DEM) with these new assumptions to validate the two-phase metastable flow through twin-orifice systems with continuous flows of various propellants studied previously by Fletcher (1975) and Clark (1991). A new correlation was developed for the coefficient in the relaxation equation. Along with this correlation a constant coefficient was used in the relaxation equation to model the metastability. Both the coefficients showed good agreement against the Fletcher's experimental data. The comparison with the Clark s experimental data showed that the new correlation coefficient predicted the mass flow rate well in compare to that of the constant coefficient, but over predicted the expansion chamber pressure. The DEM with both the coefficients for continuous discharge flows were applied to investigate the quasi-steady flashing flow inside the metered discharge flows at various time instants. The DEM results were compared with the Clark s metered discharge experimental data and the well established homogeneous equilibrium model (HEM). The comparison between the HEM and DEM with Clark s (1991) experimental data showed that the DEM predicted the mass flow well in compare to that of HEM. Moreover, both the models underpredicted the expansion chamber pressure and temperature. The findings of the present thesis have given a better understanding of the role played by the propellant metastability inside the twin-orifice system of pMDIs. Also, these have provided detailed knowledge of thermodynamic state, void fraction and critical velocity of the propellant at the spray orifice exit, which are essential step towards the development of improved atomisation models. Improved understanding of the fluid mechanics of pMDIs will contribute to the development of next-generation pMDI devices with higher treatment efficacy, capable of delivering a wider range of therapeutic agents including novel therapies based around

Numerical modeling of two-phase flashing propellant flow inside the twin-orifice system of pressurized metered dose inhalers

Pressurized metered-dose inhalers (pMDIs) are the most widely-prescribed inhaler devices for therapeutic aerosol delivery in the treatment of lung diseases. In spite of its undoubted therapeutic and commercial success, the propellant flow mechanics and aerosol formation by the pMDIs is poorly understood. The process involves a complex transient cavitating turbulent fluid that flashes into rapidly evaporating droplets, but details remain elusive, partly due to the difficulty of performing experiments at the small length scales and short time scales. The objective of the current work is the development of a numerical model to predict the internal flow conditions (pressure, temperature, velocity, void fraction, quality, etc.) and provide deeper insight into the atomization process and fluid mechanics involved in the twin-orifice of pMDIs. The main focus is propellant metastability, which has been identified by several past authors as a key element that is missing in accounts of pMDI performance. First the flashing propellant flow through single orifice systems (both long and short capillary tubes) was investigated using three different models : homogeneous equilibrium model (HEM), delayed equilibrium model (DEM) and improved delayed equilibrium model (IDEM). Both, the pure propellants and the propellant mixtures were used as working fluid. The numerical results were compared with the experimental data. For long capillary tubes the three models gave reasonable predictions, but the present results showed that DEM predicts the mass flow rate well for pure propellants and IDEM predicts the mass flow rate well for propellant mixtures. For short capillary tubes, the present results showed that DEM predicts the mass flow rate and pressure distribution along the short tube better compared to HEM and IDEM. The geometry of the twin-orifice system of a pMDI is complex and involves several singularities (sudden enlargements and sudden contractions). Various assumptions were made to evaluate their effect on the vaporisation process and to evaluate the flow variables after the shock at the exit of the spray orifice when the flow is choked. Also, three different propellant flow regimes were explored at the inlet of the valve orifice. A specific combination of assumptions, which offers good agreement with the experimental data was selected for further computations. Numerical investigations were carried out using delayed equilibrium model (DEM) with these new assumptions to validate the two-phase metastable flow through twin-orifice systems with continuous flows of various propellants studied previously by Fletcher (1975) and Clark (1991). A new correlation was developed for the coefficient in the relaxation equation. Along with this correlation a constant coefficient was used in the relaxation equation to model the metastability. Both the coefficients showed good agreement against the Fletcher's experimental data. The comparison with the Clark s experimental data showed that the new correlation coefficient predicted the mass flow rate well in compare to that of the constant coefficient, but over predicted the expansion chamber pressure. The DEM with both the coefficients for continuous discharge flows were applied to investigate the quasi-steady flashing flow inside the metered discharge flows at various time instants. The DEM results were compared with the Clark s metered discharge experimental data and the well established homogeneous equilibrium model (HEM). The comparison between the HEM and DEM with Clark s (1991) experimental data showed that the DEM predicted the mass flow well in compare to that of HEM. Moreover, both the models underpredicted the expansion chamber pressure and temperature. The findings of the present thesis have given a better understanding of the role played by the propellant metastability inside the twin-orifice system of pMDIs. Also, these have provided detailed knowledge of thermodynamic state, void fraction and critical velocity of the propellant at the spray orifice exit, which are essential step towards the development of improved atomisation models. Improved understanding of the fluid mechanics of pMDIs will contribute to the development of next-generation pMDI devices with higher treatment efficacy, capable of delivering a wider range of therapeutic agents including novel therapies based around.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Sufism in Kashmir from the fourteenth to the sixteenth century

The histories of Medieval Kashmir, like those of many other parts of the subcontinent, mainly deal with courts and political developments. No attempt has yet been made to give a connected account of the religious developments and the ideological tensions in the Valley. The accounts of the introduction of Islam and Sufism into Kashmir are shrouded in myth and legend. Modern scholars, who deal primarily with political history of Kashmir, make occasional references to its saints, but their accounts are uncritical and generally based upon the later hagiological material. The present work seeks to unravel the tangled skein of legends concerning the Sufis of Kashmir and to present a connected study of the Sufi orders from the fourteenth to the sixteenth century. Both the Sufi orders introduced by the Iranian immigrants and the eclectic Rishi order which emerged locally have for the first time been examined and analysed in detail

Restaurant wastewater treatment technologies and potential of biofringe fibre

Restaurant industries are one of the pollution sources in the environment, due to the huge quantities of wastewater that was discharged into the public sewers and drains. However, the discharge of this untreated restaurant wastewater into the environment is considered one of the main issues. Nevertheless, other methods can be employed to safely discharge this contaminated wastewater into the environment

Synthesis, functionalization and coordination chemistry of dibenzotetraaza[14]annulenes

This comprehensive review summarizes recent advances in the synthesis and coordination chemistry of dibenzotetraaza[14]annulenes (DBTAAs) reported between 2010 and 2021. Owing to the smaller N4 donor cavity compared to that of the porphyrin core, it is not surprising that DBTAA offers versatile and unique coordination modes towards metal ions. The structural modification of the DBTAA core allows for the fine-tuning of their spectroscopic properties. DBTAA and derivatives have been utilized across a wide range of research disciplines such as in electronic devices and biological assays. The feasible preparation of ligands and their metal complexes suggests DBTAAs as potential alternatives to porphyrins

Synthesis and crystallographic characterisation of pyridyl- and indoleninyl-substituted pyrimido[1,2-b]indazoles

Pyridyl- and indoleninyl-substituted pyrimido[1,2-b]indazole were synthesised in good to high yields from the condensation reaction of 1,3-dialdehydes with 3-aminoindazoles. The structural features of the compounds were determined by NMR (1H, 13C and 19F), FT-IR and HR-MS. The spectroscopic assignments were confirmed by X-ray crystallography for two derivatives, i.e., 9-Bromo-3-(pyridin-4-yl)pyrimido[1,2-b]indazole (1b) and 10-Methoxy-3-(pyridin-4-yl)pyrimido[1,2-b]indazole (1c), which further provides support for significant delocalisation of π-electron density over the entire fused ring system. The molecular packing was assessed by conventional methods together with Hirshfeld surface analyses. In 1b, the molecular packing features pyrimidyl-N–H···N(pyrimidyl), π(pyrazolyl)···π(pyrimidyl) and Br···N interactions within a two-dimensional array. In 1c, pyrimidyl-C–H···N(pyrazolyl) and pyridyl-C–H···O(methoxy) interactions feature within a three-dimensional architecture

Strengthening user authentication for better protection of mobile application systems

For most of us now, life is incomplete if living without mobile phones. This is because mobile phones are like a necessity to many people nowadays. Statistics have shown that more than seven billion people in the world are having these devices in 2015. This also means 97% of the human world populations are actually mobile phone users. Besides, more than 50% of the mobile phone users are using smarts phones which are capable of downloading a lot of mobile application systems (apps). It is estimated that more than 200 million apps are being downloaded in 2007 and this number is believed to be growing. Unfortunately, many of these apps involve the transfer of important and confidential personal data or business information. How to ensure this sensitive information is well protected from being stolen or misused by unauthorized parties? One of the ways to secure this communication is to properly control the access to the system by strengthening the user authentication. Thus, this paper focuses on one the techniques to enhance the protections of mobile apps to prevent intrusions by unpermitted users. The enhancement is focusing on improving the multi-factor elements and the text ciphering technique of the user authentication. In this study, random number and time are added in the existing text-based multifactor user authentication. Besides, encryption and hash are used as the text ciphering technique to improve the protection. To measure how secure the proposed enhancement is, an independent testing body has been appointed to perform Vulnerability Test and Functionality Test to the apps. If all these tests are passed, it can be said that the proposed enhancement is strong enough to protect the apps from being intruded. Based on the test results provided by the testing body, CyberSecurity Malaysia, the apps has passed all the Vulnerability Test and Functionality Test. This shows that the control of the access to these apps are strong and able to prevent from being accessed by unpermitted users. This also means the proposed enhancement is able to give better protections to ensure the mobile apps can't be easily broken into by unauthorized mobile phone users

Indoleninyl-substituted pyrimido[1,2-b]indazoles via a facile condensation reaction

A new series of pyrimido[1,2-b]indazoles bearing indolenine moieties was synthesized through a simple condensation reaction with up to 94% yield. The present method features the versatile formation of a pyrimidine ring with a broad range of substrates, great functional group compatibility and facile synthetic operation. The work offers opportunities in drug development as well as in materials scienc