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Uporaba toplotnih stikal in toplotnih diod v sistemu s cikličnim spreminjanjem temperature
ID Klinar, Katja (Author), ID Kitanovski, Andrej (Mentor) More about this mentor... This link opens in a new window, ID Arkar, Ciril (Co-mentor)

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Abstract
Doktorsko delo obravnava prenos toplote pri magnetnem hlajenju z uporabo trdninskih toplotnih diod in tekočinskih toplotnih stikal. V prvem sklopu smo razvili 1D numerični model magnetokalorične naprave z vgrajenima dvema toplotnima diodama. Osredotočili smo se na lastnosti materialov, primernih za toplotne diode ter na toplotno rektifikacijo v tranzientnem režimu delovanja. Rektifikacijski koeficient smo določali tudi z uporabo nevronskih mrež. V drugem sklopu smo razvili 1D numerični model za simulacije statičnih toplotnih stikal. Z občutljivostno analizo smo določili najvplivnejše parametre, nadgraditev modela z genetskim algoritmom pa je omogočila optimizacijo dimenzij toplotnega stikala in magnetokaloričnega materiala glede na največjo temperaturno razliko med izvorom in ponorom toplote. Delovanje dveh konceptov toplotnih stikal smo analizirali eksperimentalno s principom elektroomočenja in ferohidrodinamike. Delovanje slednjega smo testirali tudi v magnetokalorični hladilni napravi. Rezultati numeričnih analiz potrjujejo sposobnost delovanja magnetokaloričnih naprav s toplotnimi stikali oz. toplotnimi diodami pri višjih delovnih frekvencah od trenutno uporabljenih aktivnih magnetnih regeneratorjev, česar pa v okviru dela tega nismo mogli eksperimentalno potrditi. Na področju toplotnih diod zaradi omejenega stanja tehnike in razpoložljivosti ustreznih materialov, pri toplotnih stikalih pa zaradi manjšega preklopnega razmerja ter daljšega odzivnega časa od pričakovanega. Kljub temu pa smernice hitrega razvoja mikrotehnologije, obdelave materialov in izdelave novih materialov kažejo na možnost eksperimentalne potrditve koncepta v prihodnjih letih.

Language:Slovenian
Keywords:toplotna stikala, toplotne diode, prenos toplote, upravljanje s toploto, magnetokaloričen
Work type:Doctoral dissertation
Typology:2.08 - Doctoral Dissertation
Organization:FS - Faculty of Mechanical Engineering
Place of publishing:Ljubljana
Publisher:[K. Klinar]
Year:2022
Number of pages:XXXII, 195 str.
PID:20.500.12556/RUL-141996 This link opens in a new window
UDC:536.24:66.045:621.57(043.3)
COBISS.SI-ID:130116355 This link opens in a new window
Publication date in RUL:14.10.2022
Views:449
Downloads:104
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Secondary language

Language:English
Title:The application of thermal switches and thermal diodes in a system with cyclical temperature change
Abstract:
This doctoral thesis deals with the heat transfer in magnetic cooling using solid-state thermal diodes and fluidic thermal switches. In the first part we developed a 1D numerical model of a magnetocaloric device with two built-in thermal diodes. We focused on the properties of the materials suitable for thermal diodes and thermal rectification in a transient operating regime. The rectification ratio was also determined using neural networks. In the second part, we developed a 1D numerical model for the simulations of static thermal switches. We determined the most influential parameters with a sensitivity analysis, and the upgrade of the model with a genetic algorithm allowed the optimization of the dimensions of the thermal switch and the magnetocaloric material according to the maximum temperature span established between the heat source and the heat sink. The operation of two concepts of thermal switches was analysed experimentally: one was based on electrowetting and the other on ferrohydrodynamics. The operation of the latter was also tested in a magnetocaloric refrigeration device. The results of the numerical analyses confirmed that magnetocaloric devices with thermal switches or thermal diodes can operate at higher frequencies than the currently used active magnetic regenerators, but we were not able to confirm this experimentally within the scope of this work. The reason for this in the case of thermal diodes is the limited state of the art and the unavailability of suitable materials, and in the case of thermal switches, the switching ratio was smaller and the response time longer than expected. Nevertheless, the guidelines for the rapid development of micro-technology, new material processing and machining, indicate the possibility of an experimental confirmation of the concept in the coming years.

Keywords:thermal switches, thermal diodes, heat transfer, thermal management, magnetocaloric

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