Experimental Study of the Behavior of Phase Change Materials during Interrupted Phase Change Processes

This research article explores the behavior of a phase change material (PCM) when it undergoes interrupted melting and freezing, through experimental investigations using a heat flow meter apparatus. A fatty acid-based organic PCM, encapsulated within polyethylene and thin aluminum foil layers, was experimentally tested in this study. Experiments were designed to represent multiple interrupted phase change scenarios that could occur within PCMs applied in buildings. The experimental results were analyzed and compared with previously reported assumptions in numerical models dealing with PCM hysteresis and interrupted phase change processes. These comparisons indicated that the assumptions used in the different numerical models considered can capture the interrupted phase change phenomena with varying degrees of accuracy. The findings also highlighted the need for additional experimental research on different phase change processes that can occur in building applications of PCMs.

Experimental setup for studying two-phase flows in micro-and minichannels at ultra-high heat fluxes: methodology and first experimental results

The study of phase-change phenomena under high and ultra-high heat fluxes is urgent because of fast development of electronics and microelectronics. We have developed a test section with power of 3.5 kW with a heater of 1x1 cm2 and adjustable geometry of the channel for achieving ultra-high heat fluxes in flow boiling and shear-driven liquid film experiments. The methodology of calculating heat losses in the test section is proposed and verified by flow boiling experiment versus another well studied test section. Observed trend of decrease of relative heat losses with increase in the heat flux makes it possible to assume that the heat flux as high as 2.5 kW/cm2 can be reached by this test section.

Experimental and numerical evaluation of thermodynamic effect on NACA0015 hydrofoil cavitation in hot water

In this study, the cavitation in hot water, which implies tight interaction of thermodynamic effect, phase change phenomena, and flow behavior, was studied by a combination of experiment and numerical simulation. The experiment in water up to 90°C was performed in the high temperature and high-pressure water tunnel with NACA0015 as a cavitator. The temperature inside the cavity was measured using the high-accuracy thermistor probe. According to the result, the temperature depression in the cavity was increased proportionally with the increase of freestream temperature. The inverse thermodynamic effect was observed with the increase of cavity length when temperature increased. The maximum temperature depression of about 0.41°C was measured in the water at around 90°C. The temperature drop was reasonably captured in simulation by coupling our simplified thermodynamic model with our cavitation model and governing equations. The tendency of temperature depression in the cavity agreed well with experimental data under different flow conditions.

Kinetic Simulations of Compressible Non-Ideal Fluids: From Supercritical Flows to Phase-Change and Exotic Behavior

We investigate a kinetic model for compressible non-ideal fluids. The model imposes the local thermodynamic pressure through a rescaling of the particle’s velocities, which accounts for both long- and short-range effects and hence full thermodynamic consistency. The model is fully Galilean invariant and treats mass, momentum, and energy as local conservation laws. The analysis and derivation of the hydrodynamic limit is followed by the assessment of accuracy and robustness through benchmark simulations ranging from the Joule–Thompson effect to a phase-change and high-speed flows. In particular, we show the direct simulation of the inversion line of a van der Waals gas followed by simulations of phase-change such as the one-dimensional evaporation of a saturated liquid, nucleate, and film boiling and eventually, we investigate the stability of a perturbed strong shock front in two different fluid mediums. In all of the cases, we find excellent agreement with the corresponding theoretical analysis and experimental correlations. We show that our model can operate in the entire phase diagram, including super- as well as sub-critical regimes and inherently captures phase-change phenomena.

Coupled in-nozzle flow and spray simulation of Engine Combustion Network Spray-G injector

A coupled Eulerian-Lagrangian approach was employed to Engine Combustion Network (ECN) Spray-G simulations. The Eulerian in-nozzle flow simulation was conducted with a small plenum attached to the nozzles, and the results were fed to the Lagrangian spray simulation. For Eulerian simulation, the homogeneous relaxation model (HRM) coupled with the volume of fluid (VOF) method was used. HRM proved to be good at predicting the phase change phenomena due to vaporization mechanisms, that is, both cavitation and flash boiling. As a one-way coupling, quantities such as rate of injection (ROI), mass injected through each hole, discharge coefficient, spray plume angle and half cone angle predicted from the Eulerian simulations were used as the initial and boundary conditions for the subsequent Lagrangian spray simulations using the blob injection model. Non-flashing (Spray-G1) and flashing (Spray-G2) spray was simulated, and the results were validated quantitatively against the published data in terms of the liquid and vapor penetration lengths, and good agreements were obtained. Furthermore, the simulation predicted the liquid and gas axial velocity and sauter mean diameter for Spray-G1 condition in agreement with the droplet size and particle image velocimetry (PIV) measurements from literature.

The Multi-Phase Flow Test Facility “EMMA” to Investigate Local Heat Transfer Coefficients and Liquid Water Films at Wet Steam Conditions

Conventional power plants are obliged to compensate for the fluctuations in power generation, due to the rising amount of renewable energies, to ensure grid stability. Consequently, steam turbines are more frequently facing load variation and startup/shut-down cycles leading to an increase of thermal stress induced by phase change phenomena. The review of existing test facilities providing measurement data of heat transfer coefficients influenced by multiphase phenomena, such as surface wettability and dry-out, revealed the necessity for a new measurement application. This paper presents the design of the Experimental Multi-phase Measurement Application “EMMA” to generate the required conditions in combination with an academic turbine housing geometry. The performed investigations are focused on the local distribution of heat transfer coefficients (HTC) and the surface wettability affected by phase change phenomena. Two main film formation mechanisms can be observed, depending on the thermal gradient between the fluid and the wall. These are a) saturated/superheated steam in contact with a sub-cooled wall leading to film-wise/drop-wise condensation and b) primary condensed wet steam droplets depositing on a superheated wall, leading to evaporation. Both, the liquid film and the local heat transfer are measured simultaneously. An overview of applicable thickness measurement methods for transparent liquid films is given and the applied optical measurement system is further described. Moreover the HTC measurement methods are presented considering the occurring case of phase change.