The microlayer at the bottom of the bubble in nucleate boiling plays an important role in heat transfer. In this paper, the characteristics of microlayer under high heat flux are studied by laser interferometry. The thickness of the microlayer, the temperature distribution of the microlayer at the bottom of the bubble, the micro-contact angle, and the heat flux of the microlayer were studied. The results show that the uneven temperature distribution at the bottom of the bubble causes the deformation of the microlayer. The increase of evaporative heat flux of early stage the microlayer results in the bending of the thickness distribution of the microlayer.

This study was devoted to the theory of microlayer evaporation and bubble dynamics. In subcooled flowing boiling, a theoretical study of the mechanism of heat and mass transfer in vapor bubbles during boiling heat transfer has been carried out. The forces on mononuclear boiling bubbles during subcooled flow boiling are analyzed. In addition, the effect of microlayer evaporation was considered, and microlayer evaporation force has been introduced. Evaporation of the microlayers as between the bottom of a bubble and the heated wall, evaporation of the layer of superheated liquid around the bubble, the condensation of the vapors at the top of a bubble are taken into account on the basis of the bubble dynamics. The prediction models for bubble forces, departure and lift-off diameters were improved. The influence of force on the bubble under the same working conditions was also investigated. Compared with previous experimental results, it was found that the improved model could forecast the diameters of the bubble departure and bubble lift-off well.

Based on the dynamic microlayer and macrolayer evaporation models, the mechanisms of single bubble micro and macrolayer evaporation were studied. The nucleate boiling heat transfer and the dynamic characteristics of a single bubble in micro and macrolayers are closely related to the wall temperature. The present work investigates the effects of time and distance on the formation of micro and macrolayer during the growth of a single bubble on a heated horizontal wall. A new complex microlayer and macrolayer model is established. The initial microlayer thickness, dry spot radius, and macrolayer thickness are calculated. The model is compared with experimental data on the evaporation of water and ethanol in the presence of nucleating bubbles. It is found that the previous experimental data are within the range of ±25% of the proposed model, and the predicted data of the model are in good agreement with the experimental data.

It is well established that the microlayer beneath the bubble plays a pivotal effect in the heat trans-fer in nucleation boiling. However, experimental studies of microlayers in small channel flow boiling are scarce due to measurement difficulty. In this study, laser interferometry and high-speed camera tech-niques were used simultaneously to investigate the microlayer dynamic characteristics beneath boiling bubbles in a small channel. It is found that the microlayer's interference fringe is still not a complete "Newtonian ring" in small horizontal channels. The downstream of the bubble, the microlayer still shows a "wedge" structure, and the initial microlayer thickness distribution is similar to that of the pool boiling. The microlayer is not entirely evaporated, and the rewetting phenomenon occurs simultaneously with the evaporation of the microlayer. The newly dry spot area and the rewetting area show the characteristics of first increasing to a maximum and then decreasing. (c) 2022 Elsevier Ltd. All rights reserved.

Based on dynamic microlayer evaporation model. Heat transfer mechanism of nuclear boiling and microlayer thickness under single bubble on heated surface. It has a lot to do with the temperature of the wall. Therefore, this paper studies the mechanism of bubble microlayer and makes comparative analysis with its experiments. It is helpful to master nuclear boiling heat transfer more comprehensively. In the study of individual bubble microlayer thickness. The effects of time and radius on wall temperature are considered in this paper. The theoretical formula of initial thickness of microlayer is deduced. The theoretical formula is compared with the experimental data of microlayer evaporation under the nucleation bubble. It was found that the experimental data fell within ±25% of the formula range. It is consistent with the previous experimental research.

The microlayer present at the bottom of the bubble plays a very important role in heat transfer during nucleation boiling. In this paper, the dynamic characteristics of microlayer at the bottom of boiling bubble in a small channel were studied by laser interferometry method and high speed camera, and the results were compared with pool boiling experiments. The results show that the bubbles have an obvious tendency to slip in the flow boiling. The microlayer interference fringe is deformed and no longer a complete Newtonian ring. By analyzing the thickness distribution of microlayer in different directions in flow boiling and the change of micro-contact angle in the flow direction, it was found that the micro-contact angle in the flow direction became larger with the growth of bubbles.