Numerical investigation into the inclination effect on conjugate pool boiling and the condensation of steam in a passive heat removal system

Abstract

In this study, the effect of the tube inclination angle on simultaneous condensation inside and pool boiling outside a smooth tube is investigated numerically. Such conjugate phase-change phenomena happen in many heat exchangers, particularly in passive heat removal systems. The simulated domain is a pool filled with water liquid at atmospheric pressure, with a submerged tube with inner and outer diameters of 19 mm and 25 mm respectively. The fluid inside the tube is considered to be the steam at the saturation temperature of 250 °C, which is a very common operating condition in many heat removal systems. The flow field is considered to be turbulent, unsteady and three dimensional. The effect of conduction through the tube thickness is also taken into account. The Eulerian-Eulerian multiphase flow approach is utilized to express the governing equation of the problem. ANSYS FLUENT 17.1 is also used to solve the governing equations. The effects of various parameters, such as tube orientation, steam mass flux and inlet steam quality on the condensation and pool boiling heat transfer coefficients, are investigated. The results show good agreement with the available experimental data. The condensation heat transfer coefficient is found to increase with an increase in the inlet steam quality and steam mass flow rate. The results of the effect of inclination on the heat transfer coefficient are also compatible with the previous experimental works. Moreover, the results show that there is a partial maximum point for the total heat transfer coefficient at an inclination angle between θ = -60° and θ = -30°.

Numerical simulation of pool boiling on smooth, vertically aligned tandem tubes

“…Where δt denotes the time scale set to 0.05 [27][28]. The correlation of Ranz and Marshall [46] is used for computing the Nul at the interface as:…”

“…In contrast to well-established, longstanding experimental studies, the numerical simulation of pool boiling on heated surfaces is still in development [18]. [28] concluded that there will be a region between 30° to 60° for the inclination angle. In the experimental work of Kang [16], which is selected as the base database for the present work the optimum inclination angle was found to be 30°.…”

“…Choosing a flux partitioning method over an interface tracking method for the present work can be justified as the use of interface tracking methods for boiling simulations is limited to the study of bubble formation and departure from a single or limited number of bubble nucleation sites and it cannot be extended to real applications due to its exorbitant computational costs for tracking bubble evolution from numerous sites on heated surfaces [28][29][30][31]. In contrast, if a flux partitioning method is adjusted properly, it will produce reliable prediction of boiling heat transfer coefficient without any need for the highly accurate tracking of vapour-liquid interfaces.…”

“…Eq. 14).We use the well-known realisable k-ε method to model liquid-and gas-phase turbulence as its suitable performance for the simulation of the pool boiling has been approved previously approved[27][28]. The mathematical formulation for the method k-ε is presented by[35,36]:  k k k k k k k k k k k k k k k k k int T T k k…”

Experimental study of subcooled flow boiling heat transfer on micro-pin-finned surfaces in short-term microgravity

“…Phase change heat transfer with high heat flux, small heat dissipation area, and low working temperature, is a very efficient method compared with the single-phase heat transfer. Until now, many experimental studies on passive technologies, such as mixture fluid [1], nanofluids [2][3][4][5], surface modification [6,7], and simulation work [8] in relation to passive technologies have been performed to enhance pool boiling heat transfer. Meanwhile, pool boiling in different gravity conditions has been investigated in the last decade by numerous researchers [9][10][11][12][13][14][15], and there are many review papers regarding pool boiling in microgravity [16][17][18][19][20].…”