Abstract:The lecture presents a survey of results found by the author and his team during recent years. An experimental technique for precise and systematic measurements of entire boiling curves under steady-state and transient conditions has been developed. Pool boiling experiments for well wettingfluids and fluids with a larger contact angle (FC-72, isopropanol, water) yield single and reproducible boiling curves if the system is clean. However, even minimal deposits on the surface change the heat transfer characteri… Show more
“…For the liquid phase, k = 2 as continuous phase and k = 1 for the dispersed or gas phase is considered. Next, ρ k and υ k represent density and velocity of corresponding phase k, and Γkl and M kl symbols denote the interfacial mass exchange and momentum exchange between two phases of k and l. Meanwhile, τ k and T k t are shear stress and Reynolds stress given as [21,22]:…”
The inner fluid flow within the micro-sac injector is investigated numerically via AVL-Fire CFD code particularly in a microscale dimension of nozzle hole is carried out in the present work. The structural parameters of the injector are left unchanged, while the physical properties of the fluid such as pressure gradient and fluid temperature are taken into account to survey their influence on vapor volume fraction evolution, vapor mass flow rate, cavitation inception, and discharge coefficient. The reliability of modeling results is confirmed by comparing obtained data with experimental one and numerical results of Payri et al. and a close match served as an indication for the accuracy of the methodology. The multiphase modality is activated for the two-fluid model application in the nozzle segment, while the interfacial source term accounts for the momentum exchange of phases in the cavitation drag model. According to results, increasing the fuel temperature is a factor for increasing turbulent kinetic energy; meanwhile, vapor volume fraction at different times shows a different trend. Concerning the discharge coefficient, it seems that increasing the fluid temperature reduces this parameter. In contrast, increasing the pressure gradient leads to a considerable increase in the discharge coefficient.
“…For the liquid phase, k = 2 as continuous phase and k = 1 for the dispersed or gas phase is considered. Next, ρ k and υ k represent density and velocity of corresponding phase k, and Γkl and M kl symbols denote the interfacial mass exchange and momentum exchange between two phases of k and l. Meanwhile, τ k and T k t are shear stress and Reynolds stress given as [21,22]:…”
The inner fluid flow within the micro-sac injector is investigated numerically via AVL-Fire CFD code particularly in a microscale dimension of nozzle hole is carried out in the present work. The structural parameters of the injector are left unchanged, while the physical properties of the fluid such as pressure gradient and fluid temperature are taken into account to survey their influence on vapor volume fraction evolution, vapor mass flow rate, cavitation inception, and discharge coefficient. The reliability of modeling results is confirmed by comparing obtained data with experimental one and numerical results of Payri et al. and a close match served as an indication for the accuracy of the methodology. The multiphase modality is activated for the two-fluid model application in the nozzle segment, while the interfacial source term accounts for the momentum exchange of phases in the cavitation drag model. According to results, increasing the fuel temperature is a factor for increasing turbulent kinetic energy; meanwhile, vapor volume fraction at different times shows a different trend. Concerning the discharge coefficient, it seems that increasing the fluid temperature reduces this parameter. In contrast, increasing the pressure gradient leads to a considerable increase in the discharge coefficient.
a b s t r a c tIn this article, we present the numerical simulations of a real cylinder head quench cooling process employing a newly developed boiling phase change model using the commercial CFD code AVL-FIRE v8.5. Separate computational domains constructed for the solid and liquid regions are numerically coupled at the interface of the solid-liquid boundaries using the AVL-Code-Coupling-Interface (ACCI) feature. The boiling phase change process triggered by the dipping hot metal and the ensuing two-phase flow is handled using an Eulerian two-fluid method. Multitude of flow features such as vapor pocket generation, bubble clustering and their disposition, are captured very effectively during the computation, in addition to the variation of the temperature pattern within the solid region. A comparison of the registered temperature readings at different monitoring locations with the numerical results generates an overall very good agreement and indicates the presence of intense non-uniformity in the temperature distribution within the solid. Overall, the predictive capability of the new boiling model is well demonstrated for real-time quenching applications.
“…A value of corresponds to the liquid phase and a value of to the void phase. This approach has been used similarly in other works, for example [9] , [10] , [11] as well as for the well-known experimental database by Garnier et al [12] . A moving average approach was used to calculate mean values for a given time interval containing a number of samples .…”
This data set contains local experimental data of heat flux, wall temperature and void data profiles for vertical subcooled flow boiling of refrigerant Novec 649 at a copper wall. This data article presents average boiling curves from single-phase convection to fully developed film boiling for six combinations of mass flux and subcooling. Void profiles are provided for void fraction, void detection frequency, void velocity and void ligament size for three characteristic states along each boiling curve. Thermocouples were used to measure heat flux and temperature. Optical single fiber and double fiber micro probes were used for obtaining void data profiles. A traversing mechanism was used to position the optical fiber micro probes relative to the heater surface.
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