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Title:Toplotne lastnosti fluidov pri visokih tlakih
Authors:Zajc, Gašper (Author)
Knez, Željko (Mentor) More about this mentor... New window
Škerget, Mojca (Co-mentor)
Goričanec, Darko (Co-mentor)
Files:.pdf MAG_Zajc_Gasper_2017.pdf (3,62 MB)
MD5: 4C5178E16A90D0E459BBB845A5CFF86F
 
Language:Slovenian
Work type:Master's thesis/paper (mb22)
Typology:2.09 - Master's Thesis
Organization:FKKT - Faculty of Chemistry and Chemical Engineering
Abstract:Namen magistrske naloge je bil preučevanje in ovrednotenje toplotnih lastnosti alternativnih nosilcev toplotne energije pri visokih tlakih, kjer smo se podrobneje posvetili ogljikovemu dioksidu in etanu ter njuni azeotropni mešanici. Ti fluidi lahko predstavljajo okolju prijaznejšo alternativo kakor trenutno najbolj razširjeni fluorirani ogljikovodiki. V magistrskem delu smo poleg eksperimentalnega dela v laboratoriju izvajali še razne simulacije v računalniškem programu Aspen Plus V8.8. V eksperimentalnem delu smo postavili delujoč kontinuirni dvocevni toplotni prenosnik, kjer smo merili koeficiente toplotne prestopnosti CO2, etana in njune azeotropne zmesi v odvisnosti od tlaka (od 5 MPa do 30 MPa), temperature (od 20 °C do 65 °C) in pretoka vode (pri 1 L/min in 2 L/min), ki je predstavljala hladen tok v našem protitočnem prenosniku. V drugem delu smo teoretično simulirali obratovanje subkritičnih toplotnih črpalk s CO2 in azeotropno zmesjo CO2 – etan. Opravili smo tudi simulacijo, kjer smo iskali optimalno sestavo azeotropne zmesi, ki bi dajala najvišje izkoristke procesa. Idejna zasnova teh simulacij je nastala zaradi različnih pogojev vrelišča azeotropnih zmesi v razmerju s čistimi snovmi, kar bi lahko potencialno znižalo obratovalne stroške toplotnih črpalk. Glavne ugotovitve so bile: Vsi merjeni visokotlačni fluidi so kazali maksimume toplotne prestopnosti tik nad kritičnimi pogoji. Ti vrhovi so se nato z višanjem tlaka nižali in premikali proti vedno višjim temperaturam. Tvorba teh vrhov je bila posledica specifične toplote fluida, ki je kazala enaka odstopanja nad kritično točko. Ugotovili smo tudi, da azeotropne zmesi tvorijo koeficiente toplotnih prestopnosti med obema komponentama, ki jo sestavljata. Simulativni rezultati analiz obratovanja toplotnih črpalk so kazali potencialne izboljšave izkoristkov procesa z vpeljavo azeotropne zmesi, vendar samo v določenih primerih. Na podlagi znižanja temperature vrelišča azeotropa CO2 – etan smo lahko obratovanje procesa izboljšali na kondenzatorju, vendar smo ga zaradi tega istočasno poslabšali na uparjalniku.
Keywords:CO2, etan, azeotrop, toplotni prenosnik, toplotna črpalka, superkritični fluid
Year of publishing:2017
Publisher:[G. Zajc]
Source:Maribor
UDC:54.139:621.577(043.2)
COBISS_ID:21028630 New window
NUK URN:URN:SI:UM:DK:GZWUHYTM
Views:657
Downloads:98
Metadata:XML RDF-CHPDL DC-XML DC-RDF
Categories:KTFMB - FKKT
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Licences

License:CC BY-NC-ND 4.0, Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International
Link:http://creativecommons.org/licenses/by-nc-nd/4.0/
Description:The most restrictive Creative Commons license. This only allows people to download and share the work for no commercial gain and for no other purposes.
Licensing start date:14.09.2017

Secondary language

Language:English
Title:Heat properties of fluids at high pressures
Abstract:The aim of this Master thesis was to study and evaluate the heat properties of alternative heat energy carriers at high pressures, where we mainly focused on carbon dioxide, ethane, and their azeotropic mixture. These fluids could represent an environmentally friendlier alternative to the most commonly used fluorinated hydrocarbons. In this work, besides the experimental part which was done in a laboratory, we also performed various simulations in a computer program called Aspen Plus V8.8. In the experimental part we constructed a working continuous double pipe heat exchanger where we measured the total heat transfer coefficients of CO2, ethane, and their azeotropic blend at various pressures (from 5 MPa to 30 MPa), temperatures (from 20 °C to 65 °C) and water flows (at 1 L/min and 2 L/min). Water represented the cold stream in our counter-current exchanger. In the second part, we theoretically simulated the operating parameters of subcritical heat pumps with CO2 and the azeotropic blend CO2 – ethane. We also performed simulations to determine the optimal composition of the azeotropic mixture, which would give the highest process efficiency. The conceptual design of these simulations was derived from the different boiling properties of azeotropic mixtures compared to pure substances, which could potentially decrease the operational cost of heat pumps. The main findings were: All measured high-pressure fluids displayed a maximum in heat transfer slightly above their critical conditions. These peaks would then decrease with increasing pressures and move to increasingly higher temperatures. The formation of these peaks was due to the specific heat of the fluid, which showed a similar deviation above the critical point. We were also able to determine that the heat transfer coefficients of the azeotropic blend form between the values of both pure substances that compose it. The analysis of the simulative results of heat pump performance shows that the introduction of an azeotropic blend could potentially increase the efficiency of the process, but only in some specific cases. Because of the drop in boiling temperature of the azeotrope CO2 – ethane, we could improve the performance of the condensator, but we therefore simultaneously decreased the performance of the evaporator.
Keywords:CO2, ethane, azeotrope, heat exchanger, heat pump, supercritical fluid


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