Cosimo Buffone

Experimental investigation of self-induced thermocapillary convection for an evaporating meniscus in capillary tubes using micro-particle image velocimetry

The present paper reports an experimental investigation of the self-induced liquid convection for an evaporating meniscus in small capillary tubes. The strong evaporative cooling at the triple contact line leads to a variation in temperature along the liquid–vapor interface, which generates a gradient of surface tension that in turn drives the observed convection. Ethanol and methanol in three tube sizes (600, 900, and 1630 μm) were investigated in this study. The flow pattern in the liquid phase has been characterized using a micro–particle image velocimetry (PIV) technique with a vector spatial resolution of 640 nm. Thermocapillary Marangoni convection is observed in horizontal diametrical sections of the horizontally oriented capillary tubes as two contrarotating vortices of similar strength, whereas in vertical diametrical sections a single clockwise vortex is mostly present. This distortion of the flow pattern could be attributed to gravity. The distortion and loss of symmetry in the vertical section...

Numerical investigation of the role of non‐uniform evaporation rate in initiating Marangoni convection in capillary tubes

A computational model is developed to describe convection in volatile liquids evaporating in capillary tubes. Experimental work has demonstrated the existence of such convective structures. The correlation between this convection and the phase change process has been experimentally established. Temperature distribution on the liquid‐vapour interface is considered in order to characterise the minimum of radial temperature gradient required to initiate and orientate Marangoni convection. Direct numerical simulation using finite volume approximation is used to investigate the heat and mass transfer in the liquid phase. The case of a capillary tube filled with a volatile liquid is investigated for various Marangoni numbers, to characterise heat and mass transfers under conditions close to realistic operating parameters. The simulation shows that a minimum irregularity in evaporative flux along the liquid‐vapour interface is necessary to trigger thermocapillary convection. The enhancement of heat and mass transfer by Marangoni convection is also investigated.

Standing wave in evaporating meniscus detected by infrared thermography

A standing wave has been detected in the evaporating meniscus formed on an organic liquid (acetone) inside a horizontally positioned capillary tube of 1 mm internal diameter. The standing wave is believed to originate from the interaction between surface tension and gravitational forces. We found that the standing wave ensues only at the upper part of the meniscus interface where gravity and surface tension act in the opposite direction. This experimental observation is similar to standing waves observed in floating zones in microgravity but different from travelling waves reported recently in volatile drops; in both cases the waves are produced by temperature differences along a liquid-vapour interface. By employing InfraRed thermography, we recorded the temperature distribution of the meniscus interface, and we found that the first characteristic frequency of the standing wave is around 0.3 Hz.

LIQUID METAL HEAT PIPES FOR COOLING ROCKET NOZZLE WALLS

In the present paper heat pipes are proposed as a very effective technology for difficult cooling problems, and especially where the flowrates of cryogenic liquid is insufficient, as in the case of future high specific impulse rocket engines. One extreme application of heat pipe technology (the Rubbia Engine with its 2000-3000 s impulse and its 8000-9000 K chamber temperature) has been chosen and the calculations performed indicate that heat pipe can effectively cool the throat region of one of the Engine modules.

Heat Pipe Performance Enhancement for Microelectronics Cooling

The heat dissipated by convection from the fins of the heat pipe condenser section is strongly limited by the thermal barrier of the oxide layer formed on their aluminum surface. A lot of work has been done to enhance the heat transfer coefficient of this heat pipe section by changing the fins roughness. The present experimental study demonstrates the enhancement in heat transfer coefficient by applying a more conductive coating on the condenser fins surface. A comparison between a conventional technique consisting of applying a rougher surface and this new technique is performed. Results clearly show the performance of the heat pipe exhibits a better enhancement in the case of a more conductive coating than a rougher one. The orientation of the heat pipe is also investigated to demonstrate the effect of gravity on the enhancement so observed. Hydrodynamics inside the heat pipe is considered to explain the findings.Copyright