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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. 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.

Magistrsko delo obsega zasnovo in analizo osnovnih gradnikov magnetokalorične hladilne naprave: aktivnega magnetokaloričnega regeneratorja in izvora magnetnega polja. V ta namen je bil zasnovan in numerično analiziran aktivni magnetokalorični regenerator, rezultati analize pa so služili kot podlaga za zasnovo strukture elektromagneta. Z numerično simulacijo smo analizirali delovanje elektromagneta in s tem povezane elektromagnetne izgube. Rezultati kažejo, da so glavne izgube posledica uporovnega segrevanja navitja. Te posledično vplivajo na hladilno moč aktivnega magnetokaloričnega regeneratorja. Delo na podlagi večparametrične analize podaja smernice za izbiro najoptimalnejše strukture elektromagneta in aktivnega magnetokaloričnega regeneratorja. Smernice bodo služile za implementacijo rezultatov v realni napravi. This thesis presents the design and analysis of the two main parts of the magnetocaloric refrigeration device: an active magnetocaloric regenerator and a magnetic field source, respectively. For the purpose of the analysis the active magnetocaloric regenerator was designed and numerically evaluated. The results were later used as the basis for design of the magnet assembly. Numerical simulation was performed in order to analyse the performance of the electromagnet and related electromagnetic losses. Results reveal that the main loss occurs due to the resistance heating of the coils. These losses affect the cooling power of the active magnetocaloric regenerator. The results of the multi-parametric analysis provide important guidelines for the selection of the optimal structure of the electromagnet and the active magnetocaloric regenerator. These will serve for implementation of the results in the real prototype device.