Yoram Kozak

• PhD
• Senior Lecturer at Tel Aviv University

The present study deals with close-contact melting of a vertical cylinder on a horizontal isothermal superhydrophobic surface with an array of circular posts. A new numerical model for this phenomenon is formulated under several simplifying assumptions. For the limiting case of perfect slip and thermal contact, based on the model assumptions, it is...

We numerically investigate the accuracy of the Particle Image Velocimetry (PIV) technique for the flow characterization in high-speed, compressible regimes, in particular in gas-phase detonations. We carry out synthetic PIV reconstruction of the flow field in a two-dimensional, planar detonation propagating under atmospheric conditions and modelled...

This work deals with a study of asymmetric melting in a vertical stainless steel pipe. The pipe is filled with a phase change material and heated asymmetrically by a resistive heater attached to a part of its circumference along its entire height. The pipe is exposed to natural or forced convection external conditions. The experimental results incl...

In this study, we numerically investigate the accuracy of the Particle Image Velocimetry (PIV) technique for the flow characterization in high-speed, compressible regimes, and in particular in gas-phase detonations. A two-dimensional, planar detonation at atmospheric conditions is modeled using a simplified single-step Arrhenius kinetics. The upstr...

Lagrangian particles can be used either to analyze different complex flows, as massless tracers, or to model multiphase flows, as particles with mass. As particles can have arbitrary positions within the computational domain, interpolation of different flow quantities from the Eulerian grid is essential. Low-order centered interpolation schemes gen...

The present study deals with a theoretical investigation of a close-contact melting (CCM) process involving a vertical cylinder on a horizontal isothermal surface, where the liquid phase is a non-Newtonian viscoplastic fluid that behaves according to the Bingham model. Accordingly, a new approach is formulated based on the thin layer approximation...

In this paper, we discuss a novel Lagrangian-particle tracking method for highly compressible turbulent reacting flows. Both time integration and interpolation schemes are developed with the goal of providing high solution accuracy in the presence of discontinuities in the flow field created by shock waves or flame fronts. It is demonstrated that s...

In a recent study of the dynamics of high-speed turbulent premixed methane-air and jet-fuel-air flames, we found that methane and heavy hydrocarbons exhibit opposite trends in terms of the turbulent burning velocity at low and high turbulent intensities. In particular, direct numerical simulations of statistically planar turbulent flames in a canon...

Highly compressible turbulent reacting flows involve complex phenomena, such as non-linear turbulence-chemistry interactions, and deflagration-to-detonation transition. Lagrangian-particle tracking can provide a powerful analysis framework of the flow complementary to Eulerian based formulation. Accurate advection of massless Lagrangian fluid parce...

The present study deals with development of a general model for close-contact melting (CCM), and its associated physical phenomena, namely, convection in the melt and solid bulk motion. An analysis of the literature reveals that although CCM is a well-known phenomenon, the existing numerical methods for solid-liquid phase change simulation, includi...

This paper presents a novel configuration suitable for latent-heat thermal energy storage systems based on the use of phase-change materials (PCMs). It is a double-pipe unit with a helical fin attached to the inner tube in which a heat-transfer fluid (HTF) flows. Experiments in the unit are performed both for regular conditions, when its shell is e...

It is well known that many materials do not solidify at their nominal phase-change temperature. Rather, nucleation occurs in them at a lower temperature. This phenomenon is usually termed “supercooling” or “subcooling” in the literature. Understanding, prediction and, if possible, prevention, or at least reduction, of supercooling are very importan...

The current research explores both experimentally and theoretically the thermal performance of transported insulated cold storage packages that can keep products at a low temperature. In order to sustain the product cold as long as possible, it is suggested to combine a conventional insulation with a phase-change material (PCM), thus taking advanta...

This research is an experimental investigation of a double-pipe heat storage unit. The inner pipe of the unit, through which a heat-transfer fluid (HTF) is supplied, is made of aluminum and has an outer helix-like fin. The annular space between the pipes is filled with a phase change material (PCM). Actually, this research presents a novel design o...

The present study deals with a new numerical approach for solid-liquid phase-change modeling. The new model is based on the enthalpy method and takes into account natural convection in the melt which can be coupled to the solid bulk sinking motion by the force balance on the solid bulk. A basic configuration is investigated, namely a two-dimensiona...

The present study deals with a latent heat thermal energy storage unit where an arbitrary number of phase-change materials (PCMs), arranged in a cascade, melt inside the tubes while a heat-transfer fluid flows across the tube bank. A mathematical model is solved numerically, and the effects of different parameters are explored, including the inlet...

The present study deals with melting in a horizontal double-pipe concentric storage unit with a longitudinally finned inner tube. This geometry, applicable for thermal energy storage, has been extensively studied in the past. However, close-contact melting (CCM), which may significantly increase the melting rate, has not been explored for this sort...

The present study deals with transient thermal management using phase change materials (PCMs). These materials can absorb large amounts of heat without significant rise of their temperature during the melting process. This effect is attractive for passive thermal management, particularly where the device is intended to operate in a periodic regime,...

In the present work, latent heat thermal storage devices that use an array of fins are studied experimentally and theoretically. The thermal storage charging/discharging process is driven by a hot/cold heat transfer fluid (HTF) flowing inside the tube from which heat is conducted to the fins that are in contact with the bulk of the PCM inside a cyl...

In the present study, the effects of close-contact melting (CCM) are studied for geometries suitable for latent heat thermal energy storage. Specifically, a vertical double pipe concentric storage unit with circumferentially finned inner tube is explored experimentally. It is demonstrated that CCM enhances significantly the heat transfer rate, shor...

The present work deals with a combined device in which the heat may be both absorbed by a phase-change material (PCM) and dissipated to the ambient air. Accordingly, the heat sink, made of aluminum 6061, has compartments where the PCM (eicosane C20H42) is stored and fins exposed to the air. The experiments are performed in both room- and elevated-t...

Phase-change materials (PCMs) can store large amounts of heat without significant change of their temperature during the phase-change process. This effect may be utilized in thermal energy storage, especially for solar-thermal power plants. In order to enhance the rate of heat transfer into PCMs, one of the most common methods is the use of fins wh...

The ability of phase-change materials (PCMs) to absorb large amounts of heat without significant rise of their temperature during the melting process may be utilized in thermal energy storage and passive thermal management. This paper deals with numerical modeling of a hybrid PCM-air heat sink, in which heat may be either absorbed by the PCM stored...

Phase-change materials (PCMs) can absorb large amounts of heat without significant rise of their temperature during the melting process. This effect is attractive for using in thermal energy storage and passive thermal management. One of the techniques enhance the rate of heat transfer into PCMs is by using fins made of a thermally high conductive...

Phase-change materials (PCMs) can absorb large amounts of heat without significant rise of their temperature during the melting process. This effect may be utilized in thermal energy storage and passive thermal management. In order to enhance the rate of heat transfer into PCMs, various techniques have been suggested, like fins, metal and graphite-...

The present study deals with the transient thermal management of electro-optical equipment using the phase-change materials (PCMs). These materials can absorb large amounts of heat without significant rise of their temperature during the melting process. This effect is attractive for using in the passive thermal management of portable electro-optic...