Z. Segal

A uniform temperature heat sink for cooling of electronic devices

Experimental investigation of a heat sink for cooling of electronic devices is performed. The objective is to keep the operating temperature at a relatively low level of about 323–333 K, using a dielectric liquid that boils at a lower temperature, while reducing the undesired temperature variation in the both streamwise and transverse directions. The experimental study is based on systematic measurements of temperature, flow and pressure, infrared radiometry and high-speed digital video imaging. The heat sink has parallel triangular microchannels with a base of 250 lm. Experiments on flow boiling of Vertrel XF in the microchannel heat sink are performed to study the effect of mass velocity and vapor quality on the heat transfer, as well as to compare the two-phase results to a heat sink cooled by single-phase water flow. 2002 Elsevier Science Ltd. All rights reserved.

Nonuniform temperature distribution in electronic devices cooled by flow in parallel microchannels

We fabricated a novel thermal microsystem (simulating a computer chip) consisting of a heater, microchannels, inlet and outlet plena and we studied the effect of the geometry on the flow and heat transfer. The vapor-water two-phase flow patterns were observed in the parallel microchannels through a microscope and high-speed video camera. It was observed that hydraulic instabilities occur. Existence of a periodic annular flow was also observed, which consists of a symmetrically distributed liquid ring surrounding the vapor core. Along the microchannel axis, the periodic dry zone appears and develops. The thermal visualization and temperature measurements of the heated device were carried out using infrared thermography. As long as the flow was single phase liquid, the forced convection heat transfer resulted in a moderate irregularity on the heated chip. These temperature differences do not cause damage to a real electronic device. The steady-state heat transfer for different types of microchannels has been studied also at the range of heat flux where phase change of the working fluid from liquid to vapor took place. Under conditions of flow boiling in microchannels, a significant enhancement of heat transfer was established. In the case of uniform heat flux the hydraulic instabilities lead to irregularity of temperature distribution on the heated chip. In the case of nonuniform heat flux the irregularity increased drastically.

Two-phase flow patterns in parallel micro-channels

Abstract Micro-channel heat sinks with two-phase flow can satisfy the increasing heat removal requirements of modern micro-electronic devices. Some of the important aspects associated with two-phase flows in micro-channels, is to study the bubble behavior and flow regimes in diabatic, parallel micro-channels. Most of the reports in the literature present data of only a single channel and mostly adiabatic. This does not account for flow mixing and hydrodynamic instability that occurs in parallel micro-channels, connected by common inlet and outlet collectors. In the present study, experiments were performed for air–water and steam–water flow in parallel triangular micro-channels. The experimental study is based on systematic measurements of temperature and flow pattern by infrared radiometry and high-speed digital video imaging. In air–water flow different flow patterns were observed simultaneously in the various micro-channels at a fixed values of water and gas flow rates. In steam–water flow, instability in uniformly heated micro-channels was observed. This work develops a practical modeling approach for two-phase micro-channel heat sinks and considers the discrepancy between flow patterns of air–water and steam–water flow in parallel micro-channels.

Convective boiling in parallel microchannels

Experiments were performed with clear water and with surfactant flowing in parallel triangular microchannels. The study is based on systematic measurements of temperature and flow pattern by infrared radiometry and high-speed digital video imaging. Different flow patterns were observed simultaneously in various microchannels at a fixed value of water or surfactant flow rates. Depending on flow and heat flux, pressure and temperature instabilities in the heated microchannels were studied. This work develops a practical modeling approach for two-phase microchannel heat sinks and also considers effect of surfactant on convective boiling in microchannels.

Convective Boiling in Parallel Micro-Channels

Experiments were performed with clear water and with surfactant flowing in parallel triangular micro-channels. The study is based on systematic measurements of temperature and flow pattern by infrared radiometry and high-speed digital video imaging. Different flow patterns were observed simultaneously in various micro-channels at a fixed value of water or surfactant flow rates. Depending on flow and heat flux, pressure and temperature instabilities in the heated micro-channels were studied. This work develops a practical modeling approach for two-phase micro-channel heat sinks and considers also effect of surfactant on convective boiling in micro-channels.© 2003 ASME

Investigation of Short Wings Roll-Stabilizers

The paper presents a detailed analysis of experimental data, concerning decay roll oscillations of ship models, and the determination of an effectiveness of Short Wings Roll-Stabilizers (SWIRS) as compared with bilge keels and active anti-rolling fins. The influence of end plates on the wing lift force, the SWIRS drag and the reduction of roll amplitudes owing to the increase of damping moments produced by roll-stabilizers are also considered.