Paolo Di Marco

Effect of an Externally Applied Electric Field on Pool Film Boiling of FC-72

The paper reports the results obtained during an experimental study on film boiling on wires in the presence of an externally imposed electric field. The arrangement allowed achieving various combinations of pressure and subcooling independently of the environmental conditions. The test section was an electrically heated platinum wire with diameters of 0.1 and 0.2 mm. The working fluid was FC-72. The results showed that two different film boiling regimes, separated by an additional boiling transition, can exist in the presence of an electric field. The first regime, at low wire superheat, was strongly influenced by the electric field, showing a remarkable heat transfer enhancement with increasing voltage. The second regime, at higher superheat, was weakly dependent on the field strength and almost coincident with the zero field one. These results are analogous to the ones previously obtained using R113 as working fluid. The reasons for the occurrence of the transition were investigated. A simple model of the effect of the electric field on the interface behavior was developed, taking into account the variation of the thickness of the vapor layer with the increase of the heat flux, thus providing a possible explanation for the occurrence of the transition.

Nucleate pool boiling in the presence of an electric field: Effect of subcooling and heat-up rate

• The purpose of the paper is to experimentally assess the effect exerted by subcooling degree and heat-up rate (i.e., the rate of increase of thermal flux) on the phenomenon of nucleate boiling in the presence of an electric field. To this aim, an experimental facility was set up to investigate pool boiling on a heated platinum wire of 0.2-ram diameter. The working fluid was R-113 (C2C13F3). A cylindrical electric field (up to 21 MV/m at the heater surface) was imposed. The power was increased along a linear ramp, at a rate ranging from 2.5 mW/s to 6 W/s. Subcooling degrees up to 22 K (Ja = 0.146) were investigated. The results of zero-field measurements are in agreement with previous ones in the literature. The effect exerted by the electric field consists mainly of a strong increase in critical heat flux, whereas, for a given heat flux, the nucleate boiling performance can be either weakly degraded or slightly enhanced. The critical heat flux was found to remain nearly constant with increasing transient velocity up to a given heat-up rate and then to increase with it. The effect of subcooling on nucleate boiling is quite complex but, in any case, quite weak in the entire investigated range.

The Use of Electric Force as a Replacement of Buoyancy in Two-phase Flow

When an electrostatic field is applied to a medium, an electric force arises, originated by polarization and by the possible presence of free charge. If the medium is a two-phase fluid, this force drives the vapor (of lower dielectric permittivity) towards the zone of weaker electric field, giving the opportunity of separating phases and enhancing boiling heat transfer in microgravity conditions, where buoyancy is lacking. Electric force is also responsible for bubble deformation. In this paper, after a comprehensive description of electro-hydro-dynamics (EHD) mechanisms in a two-phase fluid, some relevant literature data about EHD-induced phase separation are reported, confirming the effectiveness of the technique. The electric force on a growing and rising bubble is then evaluated numerically in some simple cases, with a fem technique. Finally, original experiments on gas bubble detachment are analyzed in the attempt to enucleate the role of different mechanisms contributing to EHD enhancement. In particular, it is stressed that the role of electric forces in altering bubble shape and increasing bubble internal pressure seems to be the most significant in promoting bubble detachment.

The U-PHOS experience within the ESA student REXUS/BEXUS programme: A real space hands-on opportunity

U-PHOS (Upgraded PHP Only for Space) is a project developed by a team of students from the University of Pisa with the goal to analyze and characterize the behavior of a Pulsating Heat Pipe (PHP), one of the most attractive two phases passive systems for thermal management in space applications. The PHP consists of a sealed serpentine capillary tube filled with a working fluid. The heat is efficiently transported by means of the combined action of phase change and capillary forces, so no extra equipment is required. The project aims at investigating the thermal response of such a device under a milli-gravity condition, in order to assess its effectiveness in space conditions. U-PHOS is one of the selected experiment of the REXUS/BEXUS programme, which allows European university students to carry out scientific and technical experiments on research rockets and balloons, thanks to a bilateral agency agreement between the German Aerospace Centre (DLR) and the Swedish National Space Board (SNSB) in collaboration with ESA. 19 students from the University of Pisa, with different backgrounds, compose the U-PHOS team. Students had the chance to completely design, build and test the experiment, which will flight up to space in March 2017. This paper intends to describe the work done by the students, their organization and how this experience empowered their careers, from both an academic and professional point of view.

PREFACE: DROPS, BUBBLES, AND THIN FILMS, SPECIAL ISSUE HONORING PROFESSOR OLEG KABOV

On January 10th, 2016, Professor Oleg Kabov, a world renowne d expert in the field of interfacial heat and mass transfer and the founding Editor-in-Chief of the journal Interfacial Phenomena and Heat Transfer (IPHT), celebrated his 60th birthday. To mark the occasion, several of his colle agues conceived the idea of a special issue to celebrate his achievements and to provide an overview of some recent de velopments in the research areas pioneered and/or enhanced by Professor Kabov. We review his contributions to these areas here while also providing some biographical information. Oleg Kabov graduated from Tomsk Polytechnic Institute (now National Tomsk Polytechnic Research University) in 1978, and in the same year he moved to Novosibirsk to join th e laboratory of Professor S.S. Kutateladze at the Institute of Thermophysics. For many decades, this institu te has been one of the leading heat and mass transfer research centers in the world, in part due to the pioneering c o tributions of Kutateladze and his collaborators toward the understanding of physical mechanisms of boiling and con densation. Other important research areas developed at the Institute of Thermophysics include studies of waves o n liquid films, vortex flows, heat and mass transfer in disperse systems, phase transformation at cryogenic tempe ratur s, detonation, rarified gas dynamics, and synthesis of advanced materials. Professor Kabov defended his PhD the sis at the Institute of Thermophysics in 1987 under the direction of Professor I.I. Gogonin by working on proble ms of film condensation on arrays of finned tubes. The photograph in Fig. 1 (left) goes back to the early days at the K utateladze laboratory. The colleagues at the Institute of Thermophysics quickly recognized Oleg’s scientific potent ial. In 1987, at the age of just 31, he became the head of a new laboratory for heat transfer enhancement, see Fig. 1 (ri ght). Professor Vladimir E. Nakoryakov, an outstanding scientist who was the Director of the Institute of Thermophy sics between 1986 and 1997, proposed and strongly supported the establishment of this laboratory. In search of novel research directions for his laboratory, P rofessor Kabov turned his attention to studies of gravitydriven liquid films flowing over heated surfaces. This work re sulted in a remarkable discovery (Kabov, 1998). While

Chapter 27 – Electric Forces

The enhancement of heat and mass transfer using a static electric field is an interesting process for industrial applications due to its low energy consumption and potentially high level of evaporation rate enhancement. However, to date, this phenomenon is still not understood in the context of the evaporation of sessile drops. This chapter encompasses the existing literature about the effect of an electrical field established by two plate electrodes on sessile drops. First, the investigations about the influence of the electric field on the contact angle and the drop shape are discussed. Next, the studies about the enhancement of evaporation under an electrical field are summarized. Finally, we conclude with a discussion of possible future investigations.

Selected papers presented at the ECI 8th international conference on boiling and condensation heat transfer

SUJOY KUMAR SAHA,1 PAOLO DI MARCO,2 JACOPO BUONGIORNO,3 and JOHN W. ROSE4 1Mechanical Engineering at Bengal Engineering and Science University Shibpur, West Bengal, India 2School of Engineering, University of Pisa, Pisa, Italy 3Department of Nuclear Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA 4School of Engineering and Materials Science, Queen Mary, University of London, London, United Kingdom

Influence of Force Fields and Flow Patterns on Boiling Heat Transfer Performance

Recent experimentation of boiling in different environments, namely in reduced or enhanced gravity and/or in the presence of electric fields, have shed new light on the comprehension of boiling phenomena and have focused the objectives of future investigation. The recent results achieved by the author and other research groups around the world are reported and discussed in the paper. After a short introduction on some fundamental phenomena and their dependence on force fields, pool and flow boiling are dealt with. In particular, it is stressed that due to increased coalescence peculiar flow regimes take place in reduced gravity, influencing the heat transfer performance. The application of an electric field may, in some instances, delay or avoid these regime transitions. In boiling at high flowrate, the phenomena are dominated by inertia and thus gravity-independent; however the threshold at which this occurs has still to be determined.Copyright