Numerical investigation of surface evaporation and thermocapillarity effects on natural convection within a contained fluid in cryogenic tank

Abstract

Quantification of liquefied gas surface evaporation in partially filled cryogenic tank is important in both design process and operations control later. This paper focuses on effects of external heat leaks on the surface evaporation and the natural convection of a liquefied gas contained in cryogenic cylindrical tank with consideration of thermocapillarity. The evaporation mass flow rate is assumed negligible; however, the absorbed heat during the process is considered and defined according the Hashemi-Wesson model. The physical problem was formulated in dimensionless form, and then solved numerically using finite volume procedure. The external heat leaks and the surface evaporation heat flux were quantified by means of Nusselt number. Several simulations have been conducted based on the Rayleigh number (10+4 ≤ Ra ≤ 10+5), Marangoni number (0 ≤ Ma ≤ 2000) and the cavity aspect ratio (0.5 ≤ AR ≤ 2). Results showed that as Ra increases, the heat transfer rate from wall to fluid increases as well as the evaporation rate. Large value of Ma can reduce the surface evaporation heat flux up to 5% due to thermocapillary flow. High filling level reduces surface evaporation up to 42% for AR = 0.5, whereas low filling level promotes it to 46% for AR = 1.5, with respect to AR = 1. Free surface and side wall Nusselt numbers are strongly dependent on Ra, Ma and AR, and both have been correlated in simple formulas within engineering tolerance ±5%.