Effect of inclination on flow and thermal characteristics of air-water two-phase flow: an experimental investigation

Abstract

An experimental analysis towards establishing the effect of inclination on flow and thermal characteristics of air-water two-phase flow is presented. The experimental setup consists of a mixing section, a visualization section, a test section and an outlet section. The test section consists of two sets of pressure transducers, heater element and RTD sensors for surface temperature and inlet and outlet bulk fluid temperature measurements. The test setup can be inclined maximum up to 30º of inclination. Various flow patterns like stratified, slug, plug, wavy, annular and other mixed type are observed and captured at 0º, 2º, 5º and 7º for the range of the liquid (Re SL) and gas (Re SG) superficial Reynolds numbers of 500-10000 and 500-30000 respectively. Flow regime map is established based on this flow visualization. For inclined configuration the stratified regime is observed to be replaced by slug and slug/wavy type of flow regime and the transition between slug-plug and slug-slug/wavy takes place at higher Reynolds numbers. Surface and bulk fluid temperatures are recorded for constant wall heat flux condition, by varying the superficial Reynolds numbers of gas and liquid phases to establish the local and average two-phase heat transfer coefficient. It is observed that Re SL has a pronounced effect on heat transfer coefficient in comparison to Re SG. With the change in inclination this effect becomes more evident. A heat transfer correlation is deduced from the present experimental observation which includes the basic parameters like Reynolds number and Prandtl number, pressure drop and inclination effect.

Effect of inclination on heat transfer coefficient during flow boiling in a mini-channel

“…The studies of Ghajar and Kim [2], Ghajar and Tang [3] but also the one from Vaze and Banerjee [4] were performed with air-water flows in horizontal and upward flows with inclination angles of 2°, 5°…”

“…The digital level may also be expressed by considering the black body temperature Tbb given by the infrared camera, corresponding to a case where there is no reflexion of the ITO coating: = ( ) 4 (4) The equalisation of equations (3 and (4 enables the following expression of the outer wall temperature:…”