magistrsko delo
Uroš Jeke (Author), Matjaž Hriberšek (Mentor), Matej Zadravec (Co-mentor)

Abstract

Vlažen zrak je zmes, ki obdaja večino tehniških naprav in sistemov. Največja količina vlage, ki jo pri konstantnem tlaku in določeni temperaturi sprejme prostornina zraka, se imenuje točka rosišča. Če je količina vlage višja, kot jo lahko sprejme, pride do pojava kondenzacije. Nasproten pojav je uparjanje. Kondenzacija na stenah trdnih površin velikokrat ovira normalno delovanje v tehničnih napravah in je nezaželena. V programskih paketih, ki jih uporabljamo za raziskovalno delo, posebnih uporabniških modelov za upoštevanje gibanja vlažnega zraka ter kondenzacije in uparjanja na trdnih površinah ni na voljo. V nalogi je predstavljen splošen matematično-fizikalni model za implementacijo v obstoječe programske komplete za računalniško dinamiko tekočin. Model smo uporabili v programskem paketu za računalniško dinamiko tekočin Ansys CFX. Simulacije računalniške dinamike tekočin (RDT) smo izvedli za tok vlažnega zraka v 3D pravokotnem kanalu. Zrak teče nad vodno površino, pri čemer prihaja do uparjanja vode. Uparjanje ohlaja vodno površino, dokler se ne vzpostavi ravnotežje med prevodom toplote iz zraka in latentne toplote, ki se porabi za uparjanje. Spremljali smo kombiniran prenos toplote in snovi, ki sta potekala v različnih smereh. Ugotovili smo, da je vpliv naravne konvekcije pri vrednosti Reynoldsovega števila 844 v primerjavi s konvektivnim tokom zanemarljiv. Z brezdimenzijsko kriterialno analizo Sherwoodovega in Nusseltovega števila smo potrdili analogijo med prenosom toplote in snovi. Na medfazni meji vode in zraka lahko predpišemo kot robni pogoj enostransko difuzijo snovi. Vpliv enostranske difuzije vode v tok zraka je zanemarljiv. Toplotna in koncentracijska mejna plast sta si zelo podobni. Koncentracijska mejna plast je malo krajša. V dolžini obravnavanega kanala se nista povsem razvili. Izdelan model je prvi korak h končnemu modelu kondenzacije in uparjanja v programskem paketu Ansys CFX.

Keywords

računalniška dinamika tekočin;kondenzacija;uparjanje;prenos snovi;prenos toplote;naravna konvekcija;mešana konvekcija;Nusseltovo število;Sherwoodovo število;Stefanov tok;

Data

Language: Slovenian
Year of publishing:
Source: Maribor
Typology: 2.09 - Master's Thesis
Organization: UM FS - Faculty of Mechanical Engineering
Publisher: [U. Jeke]
UDC: 536.423.4(043.3)
COBISS: 16451862 Link will open in a new window
Views: 2778
Downloads: 428
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Other data

Secondary language: English
Secondary title: CFD modeling of condensation and evaporation of moisture on solid surfaces
Secondary abstract: Humid air is a mixture present in all kind of technical devices and systems. The dew point is the temperature at a constant pressure at which water vapour from the humid air condensates into liquid water. The reversed phenomenon is called evaporation. Condensation on solid surfaces is a frequent problem for the normal operation of technical devices. Computer programmes for Computational fluid dynamics, which are used for researching the transport phenomena, do not contain special user models for moving moist air, condensation and evaporation on solid surfaces. The general mathematical and physical model for implementation in existing CFD software packages is introduced. The model was used in Ansys CFX. Simulations were performed for humid air flowing in a 3D rectangular duct. Moist air flows over the water surface and the water evaporates. Evaporation cools down the water surface until the heat transfer from the air equals the latent heat of the evaporation. We observed the combined heat and mass transfer in opposite directions. We conclude that the effect of the natural convection in comparison with the convective flow at Reynolds number 844 can be neglected. We confirmed the heat and mass transfer analogy with the dimensionless criteria analysis of the Sherwood and Nusselt numbers. On the phase layer between the liquid water and air we presume one-side diffusion boundary condition. The effect of water diffusion is found to be negligible. The concentration and the heat boundary layers are very similar, but the former is slightly shorter. Along the studied rectangular duct they did not fully develop. This model is the first step to a complete model of condensation and evaporation in Ansys CFX software for Computational Fluid Dynamics.
Secondary keywords: computational fluid dynamics;condensation;evaporation;mass transfer;heat transfer;natural convection;mixed convection;Nusselt number;Sherwood number;Stefan's current;
URN: URN:SI:UM:
Type (COBISS): Master's thesis/paper
Thesis comment: Univ. v Mariboru, Fak. za strojništvo
Pages: XII, 58 f.
Keywords (UDC): mathematics;natural sciences;naravoslovne vede;matematika;physics;fizika;heat;thermodynamics;statistical physics;termodinamika;toplota;statistična fizika;effect of heat input and temperature on volume and structure of bodies;
ID: 995354