Natural convective flow field and cooling capability in compact electronic equipment have been investigated. Temperature and velocity measurements were carried out using a channel model of electronic equipment. The channel model having a vertical duct with rectangular section was used as experimental model. The channel model has two copper walls simulating the printed circuit boards and two transparent acrylic walls simulating the case walls. The clearance between the copper walls and the wall surface heating conditions were taken as parameters of channel model. The clearance between the copper walls was varied from 5mm to 15 mm. The experiments were conducted at three different thermal conditions: symmetric heating, asymmetric heating and one-sided heating. Velocity profiles of natural cooling flow in the channel were quantitatively measured using a particle image velocimetry (PIV). From the results, it is clarified that the changes in the velocity profiles strongly depend on the thermal conditions.
This paper describes a transient cooling technology using a Phase Change Materials (PCMs) for electronic equipment. We designed an electronic module including some paraffin waxes as the PCM and measured the transient temperature rise values. We used two different paraffin waxes having different melting point. It was shown that the transient temperature rise was decreased by the thermal absorption effect due to the latent heat of the PCM. And it was also confirmed that the proposed thermal network method could be used for analysis of electronic modules with phase change process.
Experiments on flow pattern, heat transfer and pressure drop of flow boiling of pure CO2 and CO2-oil mixtures in horizontal smooth and micro-fin tubes have been carried out. The smooth tube is a stainless steel tube with an inner diameter of 3.76 mm. The micro-fin tube is a copper tube with a mean inner diameter of 3.75 mm. Experiments were carried out at mass velocities from 100 to 500 kg⁄(m2·s), saturation temperature of 10 °C, and the circulation ratio of lubricating oil (PAG) is from 0 to 1.0 mass%. Flow pattern observations mainly showed the slug and wavy flow for the smooth tube, but the annular flow for the micro-fin tube. As compared with flow patterns in case of pure CO2, an increase in frequency of slug occurrence in slug flow region, and a decrease in liquid amount at the top of the tube in annular flow region were observed in case of CO2-oil mixtures. For pure CO2, the flow boiling heat transfer was dominated by nucleate boiling at low vapor quality region, and the heat transfer coefficients for the micro-fin tube were higher than those of the smooth tube. For CO2-oil mixtures, the flow boiling heat transfer was dominated by convective evaporation especially at high vapor quality region. In addition, the heat transfer coefficient decreased remarkably when the oil circulation ratio was larger than 0.1 mass%. For pressure drop characteristics, in case of pure CO2, the homogeneous model agreed with the experimental results within ± 30 % for the smooth tube. The pressure drops of the micro-fin tube were 0˜70 % higher than those predicted with the homogeneous model. Furthermore, the pressure drops increased at the high oil circulation ratio and high vapor quality conditions. The increases in the pressure drops were considered due to the increase in the thickness of the oil film and the decrease in the effective flow cross-sectional area.
Influence of the Rayleigh-Taylor instability on heat and mass transfer in chemically reacting flow for the reciprocal resolvable solvents has been studied using Hele-Shaw cell. In order to investigate how the Rayleigh-Taylor instability affects on the propagation of the reaction front, ethanol was added into the solvent. Measurements at the reaction front demonstrated that the predominant method of mass transfer changes from the diffusion to the convection depending on the mass fraction of ethanol. When the Atwood number, At, is greater than 0, mass transfer is controlled by the natural convection. In such case, the mass flow rate increases due to the increment of the contact area between protons (H+) and hydroxide ions (OH-). In such case, the temperature in the cell becomes higher than that for At < 0. Furthermore, mass transfer has been investigated with changing the type of acid aqueous solution. As hydrochloric acid (HCl) dissolves fully in the aqueous solution, enough amount of H+ is present to react with OH-. On the other hands, since the dissolution rate from acetic acid (CH3COOH) to proton is very slow, few protons exist in the aqueous solution. As the result, the propagation of the reaction front in CH3COOH-sodium hydroxide (NaOH) system was slower than that in HCl-NaOH system.