Growth of Two-Phase Bubble-Drop in a Three-Phase Direct-Contact Heat Transfer System: Experimental Study

Abstract

Optimizing the continuous phase hydrostatic pressure and the temperature differential between working phases is essential in designing direct contact heat exchangers. This study presents an experimental investigation into the influences of the continuous phase active height, corresponding to hydrostatic pressure, and the temperature differential between the working liquids on the evaporation dynamics of a single volatile drop in an immiscible fluid. The experiments were carried out within a Perspex rectangular column with 100 × 100 × 600 mm dimensions. N-pentane (C₅H₁₂) at its saturation temperature was utilized as the dispersed phase, while the continuous phase comprised warm water at three distinct temperatures, resulting in three distinct Jacobian numbers (Ja = 18, 30, and 45). Three active water heights (300, 400, and 500 mm) were investigated to assess the impact of hydrostatic pressure on droplet evaporation. A high-speed camera was employed to capture the droplet's evaporation along the continuous phase's active height, and the images were analyzed using FASTCAM (PFV-4) and AutoCAD (3D) software. The key parameters measured included droplet volume (or diameter), open angle (β), vaporization ratio (x), and the total time required for complete droplet evaporation. The experimental findings indicate that the droplet's diameter, open-angle (β), and vaporization ratio (x) increased over time and were notably influenced by the continuous phase hydrostatic pressure. Additionally, the growth rate of the two-phase drop-bubble accelerated, and the total time for complete evaporation decreased as the active height of the continuous phase was reduced. An empirical correlation for the two-phase drop-bubble size $\left(D/D_o\right)$ in terms of Ja, H, H_o, and $\tau$ was developed and compared successfully with the experimental data with a maximum error of about $\mp 13\%.$