Abstract:
Nucleate boiling is an extremely efficient heat transfer mechanism capable of providing low temperature difference between the surface and the fluid. It is utilized both in everyday life and in engineering in applications ranging from cooling of electronic components and nuclear fuel rods to thermal management of equipment in spaceflight. Due to persistent technological advances, device miniaturization and increasing safety requirements, the need for efficient heat removal from critical components is also on the rise, which is in turn increasing the number of basic and applied research projects dealing with efficient heat transfer with the support of not only heat exchanger and electronic component manufacturers, but also leading institutions in space technology including ESA, NASA and CMSA.
The prevailing boiling heat transfer enhancement method is surface modification. The eHEATs project aims to study boiling performance enhancement by developing state-of-the-art functionalized surfaces using direct laser texturing. This method allows modification of surface properties on the macro-, micro- and nanoscale (hierarchical structures) and affects the surface chemistry, which is fundamental for the development of surfaces with suitable topography and wettability for enhanced heat transfer using various fluids. Due to the distinctly interdisciplinary nature of the project, outstanding researchers from the fields of mechanical engineering, physics, laser technology and material science will be involved in the research.
The interaction of three phases and an abundance of influencing parameters makes nucleate boiling a deeply complex dynamic phenomenon, the research of which requires an experimental approach. Boiling performance evaluation within the eHEATs project will be carried out using high-speed IR thermography to capture the unsteady temperature fields and high-speed video recordings to visualize the bubble dynamics. The data will be processed using custom algorithms to obtain key information about the boiling process. The development of enhanced boiling surfaces will at first be based on theoretical nucleation criteria and capillary wicking models. Following experimental testing, the surfaces will be optimized using a recently developed statistical percolative model based on evaluating interactions of randomly or discreetly distributed active nucleation sites. The purpose of the optimization will be increasing the nucleation frequency, achieving uniform active nucleation site distribution, and preventing horizontal bubble coalescence and local hotspots on the boiling surface, all of which will help surpass the performance of the current generation of structured boiling surfaces.
Flexibility of the laser texturing method allows the creation of thin metallic layers, which the eHEATs project will use to develop hybrid surfaces by combining laser texturing and nanoscale coatings to study enhanced heat transfer in microgravity. Topography and surface chemistry analyses will be used to systematically study the aging of surfaces due to exposure to boiling, which is a key factor in further development and implementation in real systems. Such research is unprecedented, making the results unique and groundbreaking on a global scale.
The eHEATs project will not only provide better understanding of the mechanisms behind enhanced boiling heat transfer but will also establish a new field of developing environment-friendly and fast methods for surface functionalization. The content of the project is directly related to successfully completed and ongoing projects, the leaders of which are a part of the eHEATs team: ARRS L2-7172; ARRS J2-1741; ARRS BI-US/15-16-066; ESA 4200020289. By strengthening the cooperation with major foreign research agencies (ESA, CMSA and Massachusetts Institute of Technology - MIT), the eHEATs project will importantly contribute to developing the next generation technology in the field of enhanced heat transfer.
The phases of the project and their realization:
In order to achieve set objectives, the activities of this project are organized into 5 Work Packages. These include project management (WP1), R&D activities (WP2-WP4), and dissemination and exploitation of project results (WP5).
T1.1 Progress and cost reporting (M1-M36)
Ongoing activities in accordance with Slovenian law and ARRS rules.
T1.2 Monitoring, control and quality management (M1-M36)
Ongoing activities in order to (i) ensure the timely accomplishment of WP goals and results, (ii) brief participants on progress of the project and possible issues, which require decisions regarding risk management and mitigation, and (iii) the exchange of key results, especially between the WPs with one-way or two-way interconnections.
T2.1 Preliminary development and production of functionalized surfaces (M1-M9)
This task is sucesfully finished and includes development of laser texturing method, oxidation of copper, hydrothermal oxidation of titanium and CVD hydrophobization. Results regarding hydrothermal oxidation are in the submission process.
T2.2 Development of functionalized surfaces on thin metal layers (M6-M16)
This task is still ongoing and continues the activites from T2.1 with adiitional development of nanoscale surface structures with drop-casting of nanoparticles.
T2.3 Optimization of functionalized surfaces (M10-M24)
This task is still ongoing. Currently, the most has been done on optimisation of laser texturing method and development of heat flux partitioning algorithm used to optimize the distribution of active nucleation sites. Results have been published in journal Applied Thermal Engineering.
T2.4 Surface development scale-up (M25-M30)
Activities not started yet.
T3.1 Boiling experiments using pure fluids (M6-M20)
This task is still ongoing. Most of the resutls were currently achieved with pure water and dielectric fluid Novec 649 (alternative to more expensive FC-72).
T3.2 Boiling experiments using mixtures (M8-M20)
This task is still ongoing. Most of the resutls were currently achieved with self-rewetting mixture of water and n-butanol (published in two scientific papers) and water-glycerin mixture. Results of water-glycerin are in the paper submission process.
T3.3 Boiling in microgravity conditions (M13-M28)
Algorythms to decect bubble shape and process transient temperautre fields, that are under development in the course of this project, were alreaddy partially implemented into the RUBI experimental data (boiling in microgravity project with ESA and other scientific groups, which are experts in two-phase heat transfer). Preliminary results were accepted for publication in journal Applied Thermal Engineering. Due to the limitations caused by the pandemic, the future microgravity activities are uncertain. There is a possibility that new developed functionalized surfaces will not be tested in microgravity conditions before the end of this project.
T3.4 Evaluation of boiling performance of optimized functionalized surfaces (M21-M34)
Activities not started yet.
T4.1 Development of an experimental setup for long-term boiling tests (M10-M14)
Long-term boiling setup is under development. We suceeded to complete one working setup and first results are already availible for post-processing. We aim to develop another three setups that will allow us to run 4 experiments in parallel. Due to delayed deliveries (consequence of pandemic), this task is also delayed for a few months.
T4.2 Analysis of untreated and functionalized advanced surfaces (M10-M18)
We sucesfully analysed untreated and functionalized surfaces via SEM imaging, contact angle measurement and roughness parameters. Additional XPS analysis will be performed prior to starting long-term boiling tests, when all four boiling setups will be completed (from task T4.1).
T4.3 Long-term boiling tests (M15-M34)
This task is ongoing. First results of long term boiling experiments are under evaluation. We aim to publish one scientific paper from the obtained results in 2022. In addition, one student will complete its Master Thesis within this project task.
T4.4 Analysis of untreated and functionalized advanced surfaces after boiling (M28-M36)
Activities not started yet.
T5.1 Presentation of the project results to the general public (M3-M36)
Currently published results to the general public:
1. BUCCI, Mattia, PRIBOŠEK, Jaka, GOLOBIČ, Iztok, ZUPANČIČ, Matevž. Can the transport of intensity equation be used to perform non-intrusive temperature measurements in liquids?. V: GOLOBIČ, Iztok (ur.). Akademija strojništva 2021 : inženirstvo - s povezovanjem do trajnostnih rešitev, Ljubljana, 28. oktober 2021 : [10. mednarodna konferenca]. Ljubljana: Zveza strojnih inženirjev Slovenije - ZSIS, 2021. Letn. 10, št. 3/6, str. 62-63, ilustr. Svet strojništva, letn. 10, št. 3/6. ISSN 1855-6493. https://www.zveza-zsis.si/content/svet_strojnistva/svet_strojnistva_okt21.pdf. [COBISS.SI-ID 83968771]
2. MOŽE, Matic, HADŽIĆ, Armin, ZUPANČIČ, Matevž, GOLOBIČ, Iztok. Comparison of pool boiling performance of hydrophilic and superhydrophobic nanostructured titanium surfaces. V: GOLOBIČ, Iztok (ur.), CIMERMAN, Franc (ur.), ZUPANČIČ, Matevž (ur.). Engineering - a world of new opportunities : proceedings of the 9th AMES International Conference, Ljubljana, Slovenia, December 15th, 2020 = Inženirstvo - svet novih priložnosti : zbornik 9. Mednarodne konference strojnih inženirjev Slovenije, Ljubljana, 15. december 2020. 1st ed. Ljubljana: Association of Mechanical Engineers of Slovenia - AMES: = Zveza strojnih inženirjev Slovenije - ZSIS, 2021. Str. 84-85, ilustr. Svet strojništva, letn. 9, št. P1. ISBN 978-961-95250-0-5. ISSN 1855-6493. https://www.zveza-zsis.si/wp-content/uploads/2021/01/e-Zbornik-AS2020.pdf. [COBISS.SI-ID 50411267]
3. ZUPANČIČ, Matevž, GREGORČIČ, Peter, GOLOBIČ, Iztok. Pool boiling performance of laser-textured surfaces with timedependent wettability. V: COELHO, Pedro J. (ur.). EUROTHERM 2021 : 8th European Thermal Sciences Conference, 20-22 September 2021, virtual : proceedings. [S. l.]: IOP publishing, 2021. Str. 1-4, ilustr. Journal of physics. Conference series (Online), vol. 2116. ISSN 1742-6596. https://iopscience.iop.org/article/10.1088/1742-6596/2116/1/012004, DOI: 10.1088/1742-6596/2116/1/012004. [COBISS.SI-ID 89534979]
T5.2 Presentation of the project results to the scientific community (M6-M36)
Currently published results to the scientific comunity:
1. ZUPANČIČ, Matevž, GREGORČIČ, Peter, BUCCI, Mattia, WANG, Chi, AGUIAR, Gustavo Matana, BUCCI, Matteo. The wall heat flux partitioning during the pool boiling of water on thin metallic foils. Applied thermal engineering. [Print ed.]. Jan. 2022, vol. 200, str. 1-16, ilustr. ISSN 1359-4311. https://www.sciencedirect.com/science/article/pii/S1359431121010644?via%3Dihub, DOI: 10.1016/j.applthermaleng.2021.117638. [COBISS.SI-ID 80131843]
2. ZUPANČIČ, Matevž, ZAKŠEK, Peter, GOLOBIČ, Iztok. Experimental investigation of single-bubble growth during the saturated pool boiling of water and self-rewetting aqueous n-butanol mixtures. Case studies in thermal engineering. 2021, vol. 28, str. 1-21, ilustr. ISSN 2214-157X. https://www.sciencedirect.com/science/article/pii/S2214157X21006766, DOI: 10.1016/j.csite.2021.101513. [COBISS.SI-ID 79463683]
3. TAKEYAMA, Mao, ZUPANČIČ, Matevž, KUNUGI, Tomoaki. Influence of hydrodynamic interactions among multiple bubbles on convective heat transfer in nucleate boiling. Experimental thermal and fluid science. [Print ed.]. 1 Oct. 2021, vol. 128, str. 1-11, ilustr. ISSN 0894-1777. https://www.sciencedirect.com/science/article/pii/S0894177721000984?via%3Dihub#!, DOI: 10.1016/j.expthermflusci.2021.110449. [COBISS.SI-ID 66639875]
4. MOŽE, Matic, VAJC, Viktor, ZUPANČIČ, Matevž, GOLOBIČ, Iztok. Hydrophilic and hydrophobic nanostructured copper surfaces for efficient pool boiling heat transfer with water, water/butanol mixtures and Novec 649. Nanomaterials. [Online ed.]. 26 Nov. 2021, vol. 11, iss. 12, str. 1-26, ilustr. ISSN 2079-4991. https://www.mdpi.com/2079-4991/11/12/3216, DOI: 10.3390/nano11123216. [COBISS.SI-ID 87305987]
5. MOŽE, Matic, VAJC, Viktor, ZUPANČIČ, Matevž, ŠULC, Radek, GOLOBIČ, Iztok. Pool boiling performance of water and self-rewetting fluids on hybrid functionalized aluminum surfaces. Processes. [Online ed.]. Jun. 2021, vol. 9, no. 6, str. 1-27, ilustr. ISSN 2227-9717. https://www.mdpi.com/2227-9717/9/6/1058, DOI: 10.3390/pr9061058. [COBISS.SI-ID 67560707]
6. BERCE, Jure, ZUPANČIČ, Matevž, MOŽE, Matic, GOLOBIČ, Iztok. A review of crystallization fouling in heat exchangers. Processes. [Online ed.]. Aug. 2021, vol. 9, iss. 8, str. 1-24, ilustr. ISSN 2227-9717. https://www.mdpi.com/2227-9717/9/8/1356, DOI: 10.3390/pr9081356. [COBISS.SI-ID 72562947]
T5.3 Presentation of the project results to industrial partners (M30-M36)
Activities not started yet.
