Experimental investigation of transition process from nucleate boiling to microbubble emission boiling under transient heating modes

Abstract

This study investigated the transition from nucleate boiling to microbubble emission boiling (MEB) on a small heating surface under transient heating modes. During the short unstable boiling process after critical heat flux with a rapid increase in wall temperature, capillary waves were observed over the vapor film at subcooling of 30–40 K. The visualization results in this process demonstrated that the partial collapse of vapor film induced strong jet toward the heating surface and therefore avoided complete dryout thereon. This mechanism certainly plays an important role in the transition to stable MEB. Further comparison between the wall temperature and boiling states indicates that the wall temperature at onset point of stable MEB is determined by the predominance of MEB mode over film boiling in the transition process. Effects of liquid subcooling and surface oxidation on the transition process were also investigated at the same time.

Spatial–temporal thermal‐fluid behaviors of microbubble emission boiling (MEB)

“…One can distinguish the growths of the bubbles much smaller than the heated surface. In the S‐MEB as shown in the rows (2) and (4), the vapor bubbles almost cover the heated surface, and exhibit violent oscillations by the growths and condensations as depicted by previous researches 8,9,18 . Such behaviors of the vapor bubbles were described as “some bubbles crash shrinking rapidly toward their center, and others collapse after being contracted in their middle” and “violent spouting of minute bubbles from the surface.” 17 The behaviors are almost identical despite the difference of Δ T sub .…”

“…It has been indicated that stable MEB is realized under relatively high degree of subcooling Δ T sub ≔ T sat − T ∞ , where T sat is the saturation temperature under the pressure concerned, and T ∞ is the ambient temperature of the bulk. Effect of Δ T sub on the heat transfer characteristics were examined intensively 5‐9 . Not only the effect of the temperature of the bulk liquid, but also the characteristics of the heated surfaces and the geometries has been discussed; such as their wettability 10,11 and shape and/or size (on squared surface 10 ; in micro/mini channels 12,13 ; on wires 12,14 ).…”

“…Kumagai et al 17 described the vapor bubble behaviors in the S‐MEBs and the C‐MEB. The correlation between boiling noises and vapor bubble behaviors in the MEB under various degree of subcooling were investigated by Tang et al 18 Variation of spatial behaviors of the vapor bubbles over the heated surface were indicated as a function of intensity of the MEB 9 …”

A study on transition process to MEB by limiting boiling space

“…This temperature range is lower than the temperature where vapor explosion occurs, which is not the temperature of spontaneous nucleation; thus, non-steady heat conduction due to direct contact supports heat transfer. Figure 10 presents the surface temperature at CHF and onset of MEB as a function of subcooling, similar to Tang et al (2019b). In this study, both CHF and MEB onset data points in an open space at a subcooling of 40 K in Fig.…”

Thermodynamic Performance Study on the Novel Efficient Flow Pattern Global Construction Evaporator

“…Shafaee et al [10] studied the heat transfer characteristics of corrugated tubes with R-600a at a high evaporating temperature (331 K); they found that the heat transfer coefficient at quality of 0.7 is 1.6 times that at a quality of 0.6, but the heat transfer coefficient at quality of 0.6 is only 1.2 times that at quality of 0.1. Tang et al [11] experimentally investigated nuclear boiling heat transfer characteristics in novel inter-micro-finned tube with water;…”