Influence of mechanical vibration on nucleate boiling heat transfer at different pressures

The paper presents results of experimental study on the influence of mechanical vibration on heat transfer and evaporation dynamics in nucleation boiling of saturated water (for the pressure interval 10 – 101.3 kPa). Relevance of the study is due to a demand in increasing the heat transfer efficiency for power installations and heat-processing systems operating at low pressures under conditions of external mechanical impact. Regardless numerous publications on boiling under atmospheric pressure, the influence of vibrations at low pressures remains scarcely investigated. This study demonstrated that the applied vibrations result in the earlier start of boiling, lower overheating for the heated surface and a higher heat flux at a fixed overheating. The most explicit phenomenon is observed at low pressures. For the case of atmospheric pressure, this vibration influence declines and observed mainly for the initial nucleation boiling. Analysis of video materials shows that the vibration impact results in a reduction of bubble diameter at departure, separation frequency and an increase in the nucleation site density, especially at low pressures. Experimental results confirm that mechanical vibrations are an efficient tool for boiling process control and can be used in designing and optimization of heat engineering systems operating within in a wide pressure range.