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Keywords = subsonic steam jet

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Article
Entropy Assessment on Direct Contact Condensation of Subsonic Steam Jets in a Water Tank through Numerical Investigation
by Yu Ji, Hao-Chun Zhang, Jian-Fei Tong, Xu-Wei Wang, Han Wang and Yi-Ning Zhang
Entropy 2016, 18(1), 21; https://doi.org/10.3390/e18010021 - 7 Jan 2016
Cited by 18 | Viewed by 7196
Abstract
The present article analyzes the dissipation characteristics of the direct contact condensation (DCC) phenomenon that occurs when steam is injected into a water tank at a subsonic speed using a new modeling approach for the entropy generation over the calculation domain. The developed [...] Read more.
The present article analyzes the dissipation characteristics of the direct contact condensation (DCC) phenomenon that occurs when steam is injected into a water tank at a subsonic speed using a new modeling approach for the entropy generation over the calculation domain. The developed entropy assessment model is based on the local equilibrium hypothesis of non-equilibrium thermodynamics. The fluid flow and heat transfer processes are investigated numerically. To describe the condensation and evaporation process at the vapor-liquid interface, a phase change model originated from the kinetic theory of gas is implemented with the mixture model for multiphase flow in the computational fluid dynamics (CFD) code ANSYS-FLUENT. The CFD predictions agree well with the published works, which indicates the phase change model combined with the mixture model is a promising way to simulate the DCC phenomenon. In addition, three clear stages as initial stage, developing stage and oscillatory stage are discriminated from both the thermal-hydraulic results and the entropy generation information. During different stages, different proportion of the entropy generation rate owing to heat transfer, viscous direct dissipation, turbulent dissipation and inner phase change in total entropy generation rate is estimated, which is favorable to deeper understanding the irreversibility of DCC phenomenon, designing and optimizing the equipment involved in the process. Full article
(This article belongs to the Special Issue Exploring the Second Law of Thermodynamics)
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Full article ">Figure 1
<p>Schematic view of physical model used in the simulation of DCC process.</p> Full article ">Figure 2
<p>Molecular mechanisms of condensation and evaporation at vapor-liquid interface.</p> Full article ">Figure 3
<p>Transverse distribution for longitudinal velocity at selected locations (<span class="html-italic">z</span><sub>1</sub> = 265 mm, <span class="html-italic">z</span><sub>2</sub> = 280 mm) for different grid density (grid 1: black, 386,972 nodes; grid 2: red, 633,452 nodes; grid 3: blue, 914,597 nodes. <span class="html-italic">v</span><sub>max</sub> is the max velocity among the three grids).</p> Full article ">Figure 4
<p>Schematic view of simulation mesh of the hexahedral tank.</p> Full article ">Figure 5
<p>The comparisons of simulation steam shape and the experimental observations at different time; (<b>a</b>) <span class="html-italic">t</span> = 0.0 s; (<b>b</b>) <span class="html-italic">t</span> = 0.5 s.</p> Full article ">Figure 6
<p>The comparisons of the transverse temperature distribution at selected longitudinal locations between published data and present CFD predictions.</p> Full article ">Figure 7
<p>Velocity streamline in the <span class="html-italic">x</span> = 0 plane at different time. (<b>a</b>) <span class="html-italic">t</span> = 4 ms; (<b>b</b>) <span class="html-italic">t</span> = 8 ms; (<b>c</b>) <span class="html-italic">t</span> = 12 ms; (<b>d</b>) <span class="html-italic">t</span> = 16 ms; (<b>e</b>) <span class="html-italic">t</span> = 44 ms; (<b>f</b>) <span class="html-italic">t</span> = 120 ms.</p> Full article ">Figure 8
<p>Transverse profile of <span class="html-italic">V<sub>z</sub></span> for selected longitudinal position at different time; (<b>a</b>) <span class="html-italic">z</span> = 0.26 m; (<b>b</b>) <span class="html-italic">z</span> = 0.30 m.</p> Full article ">Figure 9
<p>Contours plot of temperature in the <span class="html-italic">x</span> = 0 plane at different times. (<b>a</b>) <span class="html-italic">t</span> = 4 ms; (<b>b</b>) <span class="html-italic">t</span> = 8 ms; (<b>c</b>) <span class="html-italic">t</span> = 12 ms; (<b>d</b>) <span class="html-italic">t</span> = 16 ms; (<b>e</b>) <span class="html-italic">t</span> = 44 ms; (<b>f</b>) <span class="html-italic">t</span> = 120 ms.</p> Full article ">Figure 9 Cont.
<p>Contours plot of temperature in the <span class="html-italic">x</span> = 0 plane at different times. (<b>a</b>) <span class="html-italic">t</span> = 4 ms; (<b>b</b>) <span class="html-italic">t</span> = 8 ms; (<b>c</b>) <span class="html-italic">t</span> = 12 ms; (<b>d</b>) <span class="html-italic">t</span> = 16 ms; (<b>e</b>) <span class="html-italic">t</span> = 44 ms; (<b>f</b>) <span class="html-italic">t</span> = 120 ms.</p> Full article ">Figure 10
<p>Transverse profile of temperature for selected longitudinal position at different time; (<b>a</b>) <span class="html-italic">z</span> = 0.26 m; (<b>b</b>) <span class="html-italic">z</span> = 0.30 m.</p> Full article ">Figure 11
<p>Contours plot of vapor void fraction in the <span class="html-italic">x</span> = 0 plane at different time. (<b>a</b>) <span class="html-italic">t</span> = 4 ms; (<b>b</b>) <span class="html-italic">t</span> = 8 ms; (<b>c</b>) <span class="html-italic">t</span> = 12 ms; (<b>d</b>) <span class="html-italic">t</span> = 16 ms; (<b>e</b>) <span class="html-italic">t</span> = 44 ms; (<b>f</b>) <span class="html-italic">t</span> = 120 ms.</p> Full article ">Figure 11 Cont.
<p>Contours plot of vapor void fraction in the <span class="html-italic">x</span> = 0 plane at different time. (<b>a</b>) <span class="html-italic">t</span> = 4 ms; (<b>b</b>) <span class="html-italic">t</span> = 8 ms; (<b>c</b>) <span class="html-italic">t</span> = 12 ms; (<b>d</b>) <span class="html-italic">t</span> = 16 ms; (<b>e</b>) <span class="html-italic">t</span> = 44 ms; (<b>f</b>) <span class="html-italic">t</span> = 120 ms.</p> Full article ">Figure 12
<p>Instantaneous condensation rate in the <span class="html-italic">x</span> = 0 plane at different time. (<b>a</b>) <span class="html-italic">t</span> = 4 ms; (<b>b</b>) <span class="html-italic">t</span> = 8 ms; (<b>c</b>) <span class="html-italic">t</span> = 12 ms; (<b>d</b>) <span class="html-italic">t</span> = 16 ms; (<b>e</b>) <span class="html-italic">t</span> = 44 ms; (<b>f</b>) <span class="html-italic">t</span> = 120 ms.</p> Full article ">Figure 12 Cont.
<p>Instantaneous condensation rate in the <span class="html-italic">x</span> = 0 plane at different time. (<b>a</b>) <span class="html-italic">t</span> = 4 ms; (<b>b</b>) <span class="html-italic">t</span> = 8 ms; (<b>c</b>) <span class="html-italic">t</span> = 12 ms; (<b>d</b>) <span class="html-italic">t</span> = 16 ms; (<b>e</b>) <span class="html-italic">t</span> = 44 ms; (<b>f</b>) <span class="html-italic">t</span> = 120 ms.</p> Full article ">Figure 13
<p>Total EGR per unit volume in the <span class="html-italic">x</span> = 0 plane at different time. (<b>a</b>) <span class="html-italic">t</span> = 4 ms; (<b>b</b>) <span class="html-italic">t</span> = 8 ms; (<b>c</b>) <span class="html-italic">t</span> = 12 ms; (<b>d</b>) <span class="html-italic">t</span> = 16 ms; (<b>e</b>) <span class="html-italic">t</span> = 44 ms; (<b>f</b>) <span class="html-italic">t</span> = 120 ms.</p> Full article ">Figure 14
<p>The variation of contributions of four kinds of irreversibility to total entropy generation with time.</p> Full article ">
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