Analysis of the boiling process of a solution of water and calcium carbonate on a thin metal foil

Mehurčkasto vrenje predstavlja najbolj učinkovit in tehnično obvladljiv mehanizem prenosa toplote. V sklopu naloge smo eksperimentalno ovrednotili proces vrenja ter zmesi kalcijevega karbonata in vode pri treh različnih gostotah toplotnega toka in treh različnih dolžinah trajanja procesa vrenja. Podatke, ki smo jih pridobili s spremljanjem temperaturnih polj z IR kamero, smo obdelali s programsko opremo Matlab. Pridobili smo ključne parametre vrenja, kot so gostota aktivnih nukleacijskih mest, čas rasti mehurčkov, frekvence nukleacij in velikosti odtisov mehurčkov. Vrenje v raztopini kalcijevega karbonata nam je privedlo do lokalno višjih koeficientov toplotne prestopnosti v fazi rasti mehurčkov. Prav tako je bilo ugotovljeno, da je v primeru zmesi kalcijevega karbonata lokalna gostota toplotnega toka v fazi rasti mehurčka izrazito nesimetrično razporejena okrog aktivnih nukleacijskih mest. Rezultati naših meritev so osnova za nadaljnjo študijo doprinosa različnih mehanizmov, ki nastopajo pri vrenju, na podlagi česar je možno v prihodnje tudi razvijati empirične ali mehanistične modele.Nucleate boiling is the most efficient and technically manageable heat transfer mechanism. In this thesis, we experimentally evaluated the boiling process of water and calcium carbonate/water mixture at three different heat fluxes and three different durations of experimental run. The data obtained by monitoring the temperature fields with a high-speed IR camera were processed with Matlab software. Key boiling parameters, such as density of active nucleation sites, bubble growth time, nucleation frequencies and bubble footprint diameters were obtained. Compared to pure water, boiling in calcium carbonate mixture provided higher local heat transfer coefficient during bubble growth phase. In addition to that, local heat fluxes shown significant asymmetric distribution around active nucleation sites during bubble growth. Results of our study can be used to further study contribution of different heat transfer mechanisms involved in nucleate boiling and also to develop empirical end mechanistic models