Browsing by Subject "heat transfer fluid"
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Item High Flash-point Fluid Flow System Aerosol Flammability Study and Combustion Mechanism Analysis(2013-12-02) Huang, Szu-YingThe existence of flammable aerosols creates fire and explosion hazards in the process industry. Due to the operation condition of high pressure circumstances, heat transfer fluids tend to form aerosols when accidental leaking occurs on pipelines or storage vessels. An aerosol system is a complicated reactive system; there are neither systematic flammability data similar to the case with pure gases, nor clearly described ignition-to-combustion process of a droplet-air mixture system. The flammable regions of three main, widely-used commercial heat transfer fluids: Paratherm NF (P-NF); Dowtherm-600 (D-600); and Plate Heat Exchange Fluid (PHE), were analyzed by electro-spray generation with laser diffraction particle analysis method. The aerosol ignition behavior depends on the droplet size and concentration of the aerosol. From the adjustment of differently applied electro-spray voltages (7-10 kV) and various liquid feeding rates, a flammable condition distribution was obtained by comparison of droplet size and concentration. All of the fundamental study results are to be applied to practical cases with fire hazards analysis, pressurized liquid handling, and mitigation system design once there is a better understanding of aerosols formed by high-flash point materials. On the other hand, the process of combustion from initial stage to global flame formation was simulated with COMSOL-multi-physics in terms of heat transfer, droplet evaporation, and fluid dynamics of liquid-air interaction. The local temperature change through time, as an indicator of luminous flame appearance, was analyzed to describe the flame development and ignition delay time of aerosols. We have conducted a series of simulation regarding physical formula in description of this combustion process, and will conclude with how temperature distribution influenced the appearance of luminous flames, which was the symbol of successful ignition of aerosol. The mitigation implementing timing and location can be characterized with further understanding of this combustion process. The potential application of the ignition delay will be beneficial to the mitigation timing and detector sensor setting of facilities to prevent aerosol cloud fires. Finally, the scientific method of aerosol flammability study was discussed for its potential impacts on experimental results. A modeling point of view was introduced, with the analysis of electric field application on fuel droplets, and the related fundamental study of the ignition phenomenon on aerosol system. Existing charges from electrospray is beneficial for the monodispersity and control of aerosols for fundamental study. However, the additional charges accumulated on the droplet surfaces are likely to have impacts on flammability due to the excess energy they applied to the aerosols system and droplet-droplet distraction or turbulences. This is a re-visit of aerosol flammability study method, with a conclusion that charges did have positive impact on droplets? ignition concentration range with a balancing effect on turbulence increase to reduce the ignition chance.Item Measurement and prediction of aerosol formation for thesafe utilization of industrial fuids(Texas A&M University, 2004-09-30) Krishna, KiranMist or aerosol explosions present a serious hazard to process industries. Heat transfer fluids are widely used in the chemical process industry, are flammable above their flash points, and can cause aerosol explosions. Though the possibility of aerosol explosions has been widely documented, knowledge about their explosive potential is limited. Studying the formation of such aerosols by emulating leaks in process equipment will help define a source term for aerosol dispersions and aid in characterizing their explosion hazards. Analysis of the problem of aerosol explosions reveals three major steps: source term calculations, dispersion modeling, and explosion analysis. The explosion analysis, consisting of ignition and combustion, is largely affected by the droplet size distribution of the dispersed aerosol. The droplet size distribution of the dispersed aerosol is a function of the droplet size distribution of the aerosol formed from the leak. Existing methods of dealing with the problem of aerosol explosions are limited to enhancing the dispersion to prevent flammable concentrations and use of explosion suppression mechanisms. Insufficient data and theory on the flammability limits of aerosols renders such method speculative at best. Preventing the formation of aerosol upon leaking will provide an inherently safer solution to the problem. The research involves the non-intrusive measurement of heat transfer fluid aerosol sprays using a Malvern Diffraction Particle Analyzer. The aerosol is generated by plain orifice atomization to simulate the formation and dispersion of heat transfer fluid aerosols through leaks in process equipment. Predictive correlations relating aerosol droplet sizes to bulk liquid pressures, temperatures, thermal and fluid properties, leak sizes, and ambient conditions are presented. These correlations will be used to predict the conditions under which leaks will result in the formation of aerosols and will ultimately help in estimating the explosion hazards of heat transfer fluid aerosols. Heat transfer fluid selection can be based on liquids that are less likely to form aerosols. Design criteria also can incorporate the data to arrive at operating conditions that are less likely to produce aerosols. The goal is to provide information that will reduce the hazards of aerosol explosions thereby improving safety in process industries.Item Thermal Performance of a Novel Heat Transfer Fluid Containing Multiwalled Carbon Nanotubes and Microencapsulated Phase Change Materials(2011-08-08) Tumuluri, KalpanaThe present research work aims to develop a new heat transfer fluid by combining multiwalled carbon nanotubes (MWCNT) and microencapsulated phase change materials (MPCMs). Stable nanofluids have been prepared using different sizes of multiwalled carbon nanotubes and their properties like thermal conductivity and viscosity have been measured. Microencapsulated phase change material slurries containing microcapsules of octadecane have been purchased from Thies Technology Inc. Tests have been conducted to determine the durability and viscosity of the MPCM slurries. Heat transfer experiments have been conducted to determine the heat transfer coefficients and pressure drop of the MWCNT nanofluids and MPCM slurries under turbulent flow and constant heat flux conditions. The MPCM slurry and the MWCNT nanofluid have been combined to form a new heat transfer fluid. Heat transfer tests have been conducted to determine the heat transfer coefficient and the pressure drop of the new fluid under turbulent flow and constant heat flux conditions. The potential use of this fluid in convective heat transfer applications has also been discussed. The heat transfer results of the MPCM slurry containing octadecane microcapsules was in good agreement with the published literature. The thermal conductivity enhancement obtained for MWCNTs with diameter (60-100 nm) and length (0.5-40?m) was 8.11%. The maximum percentage enhancement (compared to water) obtained in the heat transfer coefficient of the MWCNT nanofluid was in the range of 20-25%. The blend of MPCMs and MWCNTs was highly viscous and displayed a shear thinning behavior. Due to its high viscosity, the flow became laminar and the heat transfer performance was lowered. It was interesting to observe that the value of the maximum local heat transfer coefficient achieved in the case of the blend (laminar flow), was comparable to that obtained in the case of the MPCM slurry (turbulent flow). The pressure drop of the blend was lower than that of the MWCNT nanofluid.