Impact of triple contact lines and interface instabilities on heat-transfer in a vertical grooved plate falling film evaporator at subatmospheric pressure

Falling film evaporators are preferred to flooded evaporators in thermal units using water as a refrigerant, as they offer higher heat and mass transfer performance at operating pressures significantly lower than atmospheric pressure (⁓ 10 mbar). In order to further enhance heat and mass transfer in falling-film evaporator, an experimental and numerical study of thermal performances obtained on a grooved plate-type heat exchanger using distilled water as working fluid was carried out at absolute pressure ranging from 13 mbar to 23 mbar, logarithmic mean temperature difference ranging from 1 to 14 K and Reynolds numbers from 80 to 460 (conditions representatives to conditions obtained in thermal systems using water as refrigerant).The impact of the triple contact line evaporation and the development of interface instabilities on obtained thermal performances are discussed based on experimental data and data obtained from three different simple models based on steady state thermal energy balance. It is shown that heat transfer to triple lines plays a major role in the performance of grooved plate evaporators, accounting for 40 to 50% of transfers for a Reynolds number included between 100 and 400. The intensification factor due the development of waves could reach 10% at Re = 500. Models allow to predict the performances with a relative difference with experimental data standing at 8% for Re around 388. • Experimental data are obtained on a vertical grooved plate falling film evaporator. • Experiments were conducted at absolute pressure ranging from 13 to 23 mbar. • Time-evolution of film thickness is measured at different positions in the grooves. • Intensification factor due to film thickness reduction is estimated. • Impact of triple lines on heat transfer characterized for different interface geometries.