This paper presents the results of the
flow boiling patterns of FC-72 in a microtube. The internal diameter of the tube is 0.48聽mm, with a heated length of 73聽mm. The mass flux varies from 50 to 3000聽kg/m
2聽s. The聽microtube is made of Pyrex in order to obtain the visualisation of the
flow pattern along the heated聽channel. Different types of
flow pattern have been observed: bubbly
flow, deformed bubbly
flow, bubbly/slug
flow, slug
flow, slug/annular
flow, and annular
flow. The
flow pattern
map is compared with those obtained for larger tubes (2.0, 4.0, and 6.0聽mm). Flow patterns in the microtube present less chaotic behaviour and regular vapour-liquid interfaces. Besides, as the tube diameter decreases, the intermittent
flow regime shifts from the saturated boiling region towards the subcooled boiling region.
The experiments show the presence of flow instabilities in a large portion of the tests at low mass flux聽and low subcooling. Flow patterns in presence of flow instabilities are mainly characterized by bubbly/slug flow and slug/annular flow.
The experimental results of flow pattern are compared with the flow pattern maps of .