Observation and analysis of the detachment frequency of coalesced bubbles in pool boiling liquid nitrogen

The detachment frequency of coalesced bubbles is one of the important parameters in the boiling heat transfer model at high heat flux. Although some researches on detachment frequency of coalesced bubbles have been done for common liquids, the work on cryogenic liquids is relatively insufficient. A visual experimental apparatus was built for observing the boiling in liquid nitrogen. The growth process of coalesced bubbles was recorded by a high-speed camera, emphasizing on the detachment frequency of coalesced bubbles from the circular, horizontal heating surfaces. The effects of the heating surface material, the surface diameter and the heat flux on the detachment frequency were analyzed. The available empirical correlations from common liquids are compared with our experimental data to check their applicability in liquid nitrogen, where the detachment frequency is 13.47 s−1.

► A visual experimental system is built for observing the boiling in liquid nitrogen.
► Growth process of the coalesced bubbles is recorded by a high-speed camera.
► The detachment frequency is measured for various heating surface and heat flux.
► The measured detachment frequency of coalesced bubbles is 13.47 s−1.
► Applicability of the correlations for common liquids in liquid nitrogen is checked.