Izboljšanje procesa vrenja z uporabo teksturiranih površin (BEST)

Načrtovanje naprav za učinkovito hlajenje visokozmogljivih sistemov je ključna naloga na različnih podočjih, kot so mikroelektronska vezja (Slika 1) in pogonski sistemi (tudi za vesoljske aplikacije). Učinkovitost hlajenja vpliva tudi na zanesljivost obratovanja in porabo energije naprav, ki jih uporabljamo v vsakdanjem življenju (npr. mobilni telefoni in različne vrste računalnikov). Čeprav se tehnologije hlajenja razvijajo že desetletja, je nadaljnja miniaturizacija mehanskih in elektronskih komponent še vedno povezana z pomanjkanjem učinkovitih metod odvajanja toplote, kar zavira tehnološki napredek.

Slika 1: Potopno hlajenje CPU-ja preko vrenja v dielektričnem fluidu.

Eden najučinkovitejših načinov prenosa toplote je mehurčkasto vrenje. Izboljšanje prenosa toplote pri vrenju lahko dosežemo z funkcionalizacijo površine preko določenih morfoloških značilnosti površine na mikro in nano nivoju, spremembo površinske kemije in modifikacijo omočljivosti površine. Navkljub več desetletjem raziskav na tem področju, temeljni mehanizmi izboljšanega prenosa toplote pri vrenju še niso popolnoma razjasnjeni. Poleg tega razvoj tehnologij za funkcionalizacijo površin temelji predvsem na metodologiji preizkšanja brez jasno postavljenih optimizacijskih pristopov kot posledica pomanjkanja zanesljivih fizikalnih ali kompleksnih empiričnih modelov za napoved njihove obratovalne zmogljivosti pri vrenju.

Glavna odprta vprašanja, identificirana na podlagi pregleda obstoječe literature, so (i) nedostopnost ustrezne, robustne in cenovno sprejemljive strategije funkcionalizacije površin, (ii) pomanjkanje eksperimentalnih pristopov za diagnostiko procesa vrenja pri zadostni časovni in krajevni ločljivosti in (iii) pomanjkanje zanesljivih modelov za napoved procesa vrenja, ki bi vključevali tudi mehanizme, ki se dogajajo na mikronski in submikronski velikostni skali. Ta odprta vprašanja projekt BEST naslavlja preko interdisciplinarnega pristopa izvajanja eksperimentov vrenja ob podpori naprednih diagnostičnih orodij, trenutno najboljših dostopnih tehnologij laserske funkcionalizacije površin in z vključevanjem obstoječih sinergijskih znanj dveh raziskovalnih skupin (ULFS in KU Leuven) z bogato zgodovino raziskav na področju dvofaznega prenosa toplote. Naše raziskave bodo omogočile izboljšanje trenutnega razumevanja prenosa toplote pri vrenju s poudarkom na dielektričnih fluidih, razvoj novih metod funkcionalizacije površin in razvoj robiustnih površin za izboljšanje prenosa toplote pri vrenju dielektrikov tako iz vidika koeficienta tolotne prestopnosti kot tudi kritične gostote toplotnega toka.

The design of efficient cooling-heating devices is a crucial task in several applications, such as microelectronics (Fig. 1) and aerospace engineering. The efficiency of these cooling-heating systems impacts our environment and the energy consumption of devices that we use in our daily life (e.g. mobile phones, tablets, computers). Although new cooling technologies have been developed for decades, the use of high-power-density devices today and future miniaturization of mechanical and electronic components is still coupled to a lack of efficient heat dissipation methods, leading to an enormous technological bottleneck.

Figure 1: CPU imersion cooling through nucleate boiling in dielectric fluid.

One of the most effective ways to remove heat from a surface is through boiling. The enhancement of heat removal can be obtained by functionalizing the surface through tailoring the roughness, chemical properties, wettability, and creating particular geometrical micro- and nano-features like fins, channels, or cavities. Even though extensive literature exists on this topic, the fundamental mechanisms of heat transfer enhancement are not yet fully understood. Furthermore, the development of surface strategies for boiling enhancement mostly follows the time-consuming trial-and-error approach, because a physical or semi-empirical model for predicting boiling heat transfer coefficient on functionalized surfaces is simply non-existent.

The major knowledge gaps (KGs) identified in literature are (KG1) the unavailability of an appropriate, robust and cost-effective surface functionalization strategy for boiling enhancement, (KG2) the lack of high-resolution measurement diagnostic tools to evaluate boiling performance (KG3) the absence of reliable boiling models including micro-scale phenomena. To solve the knowledge gaps, we propose to conduct trans-disciplinary experimental research activities with a team of Ph.D. students and postdoctoral researchers who will create new synergies by sharing skills, knowledge, and insights. Our research will allow improved physical modelling and will shed light upon the flexibility of our novel surface modification methods to create appropriate surface features for stable and enhanced boiling performance for most commonly used dielectric fluids in boiling heat transfer.

Na podlagi pregleda obstoječe literature in identificiranih odprtih vprašanj smo znotraj našega projekta identificirali tri glavne cilje:

(O1) Razvoj lokalno funkcionalnizoiranih površin za potrebe izvajanja eksperimentov s poudarkom na (i) preučevanju dinamike posameznega mehurčka in (ii) doseganju jasno definirane gostote aktivnih nukeacijskih mest in natančno definirano porazdelitvijo teh mest.

Trenutno stanje realizacije O1: 70%

(O2) Omogočiti eksperimetalni vpogled v lokalne in globalne mehanizme prenosa toplote, ki nastopajo pri pri vrenju dielektričnih fluidov na funkcionaliziranih površinah.

Trenutno stanje realizacije O1: 65%

(O3) Razvoj modelov za napovedovanje zmogljivosti površin pri vrenju in optimizacijo površin za doseganje kritične gostote toplotnega toka od trenutnega stanja (tj. več sto kW/m2) do vrednosti preko 1 MW/m2.

Trenutno stanje realizacije O1: 40%

Za učinkovito doseganje ciljev je načrt realizacije projekta razdeljen na tri delovne sklope (WP1-WP3) z jasno definiranimi nalogami.Opredeljeni vodja vsakega sklopa spremlja napredek in realizacijo nalog, vodi izmenjavo informacij med delovnimi sklopi in poroča vodji projekta ter organizira aktivnosti za diseminacijo projektnih rezultatov.

Based on the existing literature and the identified knowledge gaps, three main objectives are identified within our project:

(O1) Our first objective is to create features (cavities, grooves, holes) locally on specific regions of the boiling surface in order to (i) allow investigation of single bubble dynamics and (ii) achieve surfaces with pre-defined nucleation site density and nucleation site distribution.

Current realisation status of O1: 70%

(O2) Our second objective is to provide an insight about local and global mechanisms governing the boiling performance of dielectric fluids on functionalized surfaces.

Current realisation status of O1: 65%

(O3) Finally, our third objective is to develop predictive heat transfer models and optimize the surface features to enhance heat transfer performance of dielectric fluids beyond the current design capabilities (i.e. several hundreds of kW/m²) and go above the 1 MW/m² limit.

Current realisation status of O1: 40%

To reach the project objectives, the project realisation plan is distributed along three operational work packages (WP1-WP3) with several task. Each work package has its leader, who closely monitors the progress, data exchange between WPs and reports to the project leader as well organises the data dissemination.

[1] ZUPANČIČ, Matevž, FONTANAROSA, Donato, MOŽE, Matic, BUCCI, Mattia, VODOPIVEC, Matevž, NAGARAJAN, Balasubramanian, VETRANO, Maria Rosaria, CASTAGNE, Sylvie, GOLOBIČ, Iztok. Enhanced nucleate boiling of Novec 649 on thin metal foils via laser-induced periodic surface structures. Applied thermal engineering. [Print ed.]. Jan. 2024, vol. 236, pt. d, str. 1-13, ilustr. ISSN 1359-4311. [COBISS.SI-ID 170665731].

[2] MOŽE, Matic, ZUPANČIČ, Matevž, SEDMAK, Ivan, FERJANČIČ, Klemen, GJERKEŠ, Henrik, GOLOBIČ, Iztok. Revisiting the corresponding-states-based correlation for pool boiling critical heat flux. Energies. May 2022, vol. 15, iss. 10, str. 1-19, ilustr. ISSN 1996-1073. [COBISS.SI-ID 107631363]

[3] BREGAR, Tadej, VODOPIVEC, Matevž, PEČNIK, Tim, ZUPANČIČ, Matevž, GOLOBIČ, Iztok. Pool-boiling performance on thin metal foils with graphene-oxide-nanoflake deposit. Nanomaterials. [Online ed.]. Aug. 2022, vol. 12, iss. 16, str. 1-17, ilustr. ISSN 2079-4991. [COBISS.SI-ID 118246915]

[4] MOŽE, Matic, ZUPANČIČ, Matevž, STEINBÜCHER, Miha, GOLOBIČ, Iztok, GJERKEŠ, Henrik. Nanosecond laser-textured copper surfaces hydrophobized with self-assembled monolayers for enhanced pool boiling heat transfer. Nanomaterials. [Online ed.]. Oct. 2022, vol. 12, iss. 22, str. 1-20, ilustr. ISSN 2079-4991. [COBISS.SI-ID 129879555]

[5] HADŽIĆ, Armin, MOŽE, Matic, ARHAR, Klara, ZUPANČIČ, Matevž, GOLOBIČ, Iztok. Effect of nanoparticle size and concentration on pool boiling heat transfer with TiO[sub]2 nanofluids on laser-textured copper surfaces. Nanomaterials. [Online ed.]. 2022, vol. 12, iss. 15, str. 1-22, ilustr. ISSN 2079-4991. [COBISS.SI-ID 117262083]

[6] MOŽE, Matic, HADŽIĆ, Armin, ZUPANČIČ, Matevž, GOLOBIČ, Iztok. Boiling heat transfer enhancement on titanium through nucleation-promoting morphology and tailored wettability. International journal of heat and mass transfer. [Print ed.]. Oct. 2022, vol. 195, str. 1-17, ilustr. ISSN 0017-9310. [COBISS.SI-ID 112393987]

[7] HADŽIĆ, Armin, MOŽE, Matic, ZUPANČIČ, Matevž, GOLOBIČ, Iztok. Superbiphilic laser-microengineered surfaces with a self-assembled monolayer coating for exceptional boiling performance. Advanced functional materials. [Online ed.]. Mar. 2024, vol. 34, iss. 10, [article no.] 2310662, str. 1-14, ilustr. ISSN 1616-3028. [COBISS.SI-ID 173601027]

[8] BERCE, Jure, HADŽIĆ, Armin, MOŽE, Matic, ARHAR, Klara, GJERKEŠ, Henrik, ZUPANČIČ, Matevž, GOLOBIČ, Iztok. Effect of surface wettability on nanoparticle deposition during pool boiling on laser-textured copper surfaces. Nanomaterials. [Online ed.]. Feb. 2024, vol. 14, iss. 3, [article no.] 311, str. 1-17, ilustr. ISSN 2079-4991. [COBISS.SI-ID 184768771]

[9] BERCE, Jure, ARHAR, Klara, HADŽIĆ, Armin, ZUPANČIČ, Matevž, MOŽE, Matic, GOLOBIČ, Iztok. Boiling-induced surface aging and crystallization fouling of functionalized smooth and laser-textured copper interfaces. Applied thermal engineering. [Print ed.]. Apr. 2024, vol. 242, [article no.] 122540, str. 1-17, ilustr. ISSN 1359-4311. [COBISS.SI-ID 182964995]