Hydrofluorocarbons R134a, R1234yf and R404a were used as working fluids. The velocity and temperature profiles were solved with a FORTRAN code. The thermo-physical properties calculation was based on a Van der Waals equation of state. The governing equations of partial differential equations were solved numerically using the finite difference method. The laminar natural convection in supercritical fluid along vertical flat plate with uniform heat flux was simulated in the present work. The proposed procedure provides a good balance between accuracy and simplicity for design purposes. Although the van der Waals model shows larger deviations from the reference (NIST-based) values, the simple correction procedure proposed dramatically improves its predictions near the critical point. This was expected since it was originally designed to describe hydrocarbons behavior. The Peng-Robinson EoS provided results that demonstrated significant improvement from the van der Waals EoS when compared to NIST-based values. The graphical comparison consisted of thermal expansivity versus temperature plots at various reduced pressures (0.8, 0.9, 1.0, 1.1, and 1.2). This comparison was done for carbon dioxide and four n-alkanes (C 1 through C 4 ). Since no direct experimental data for expansivities were found, calculated expansivities were compared to values computed from PVT data extracted from the NIST database. Values at near-critical and supercritical conditions were calculated. A previously developed model based on the van der Waals EoS was enhanced by proposing a correction procedure. As to the improved natural convection heat transfer correlation, the average error between the simulation results and the calculated values is approximately 8%, which can better describe the natural convection heat transfer of cryogenic supercritical helium in the spherical enclosure.Ī model for thermal expansivity (β) of gases at high pressure was developed based on the Peng-Robinson equation of state (EoS). The results show that the increase of the inflation pressure in the cavity is helpful to enhance the natural convection heat transfer of the cryogenic supercritical helium, and the temperature distribution in the cavity tends to be more uniform when the inflation pressure in the cavity increases. Finally, an improved natural convection heat transfer correlation modified by introducing the density ratio is obtained. At the same time, the relationship between the Rayleigh number and Nusselt number is studied in detail. Then, the effects of inflation pressure and heating power on the flow and heat transfer characteristics are simulated. Firstly, a three-dimensional numerical model is established and verified with experimental data. This work mainly focuses on the natural convection of cryogenic supercritical helium in a spherical enclosure. Research tasks discussed in this dissertation are expected to enable the design of numerous applications that require high power density, spanning from particle accelerators over X-ray radiography and radiotherapy to electrical power systems.Īs an ideal pressurized gas, helium, especially supercritical helium, has been widely used in the pressurization system of various launch vehicles and spacecraft. It also gives a quantitative evaluation of the critical anomaly of electric discharge in supercritical fluids. The method provides a new way to understand electrical breakdown characteristics of supercritical fluids by analyzing the mean free path of electrons and the cluster size. A theoretical method that combines the electron kinetics theory and the unique property of supercritical fluids at nanometer scale, also considers the mean free path of electrons, is developed. Investigations on dielectric properties of promising candidate supercritical fluids and mixtures, such as trifluoroiodomethane (CF3I), oxygen (O2), and perfluorinated nitriles, are conducted theoretically and experimentally. ![]() The breakdown characteristics of pure supercritical fluids and their mixtures are investigated and demonstrated experimentally in uniform electrostatic field. Substances to investigate their dielectric properties. The electron kinetic process and Boltzmann analyses are conducted on different Of dielectric properties of supercritical fluids and their mixtures, especially near the critical ![]() The objective of the proposed research is to further the fundamental understanding
0 Comments
Leave a Reply. |
Details
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |