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Projects / Programmes source: ARIS

Investigation of turbulent heat transfer in an annulus through advanced experimental and computational methods

Research activity

Code Science Field Subfield
2.03.00  Engineering sciences and technologies  Energy engineering   

Code Science Field
T200  Technological sciences  Thermal engineering, applied thermodynamics 

Code Science Field
2.03  Engineering and Technology  Mechanical engineering 
Keywords
trubulent heat transfer, experiments, computational fluid dynamics simulations
Evaluation (rules)
source: COBISS
Researchers (7)
no. Code Name and surname Research area Role Period No. of publicationsNo. of publications
1.  16435  PhD Boštjan Končar  Energy engineering  Researcher  2018 - 2021  367 
2.  23297  PhD Marko Matkovič  Energy engineering  Researcher  2018 - 2021  151 
3.  34279  PhD Blaž Mikuž  Energy engineering  Researcher  2020 - 2021  151 
4.  35548  PhD Jure Oder  Energy engineering  Researcher  2018 - 2021  58 
5.  35549  PhD Matej Tekavčič  Process engineering  Researcher  2018 - 2021  93 
6.  12057  PhD Iztok Tiselj  Energy engineering  Head  2018 - 2021  467 
7.  50515  Boštjan Zajec  Energy engineering  Junior researcher  2018 - 2021  41 
Organisations (1)
no. Code Research organisation City Registration number No. of publicationsNo. of publications
1.  0106  Jožef Stefan Institute  Ljubljana  5051606000  90,600 
Abstract
Annular geometry considered in this proposal, can represents an approximation of the pipe or channel geometry. When difference of outer and inner diameters is small, the annulus becomes similar to the channel geometry of two flat parallel plates. Annulus with outer diameter much larger than the inner diameter is a useful approximation of heated cylinder (or pipe) cooled with fluid flow on the outer side. Such geometry is frequently found in nuclear reactors and in many heat exchangers. Annular geometry will be studied within the proposed project that has two goals:    1) New test section will be developed on the existing experimental loop for measurements of conjugate heat transfer. The most promising concept is based on a heated inner annulus wall and transparent outer wall. Conjugate heat transfer in the force convection regime will be analysed on the inner wall with various nonintrusive measuring techniques such as IR thermography, Particle Image Velocimetry and possibly Phase Shift Interferometry.  2) Second objective of the proposed research are direct numerical simulations of conjugate turbulent heat transfer in the geometry of our experimental device. DNS is known as the most accurate approach for description of turbulent flows; it is very accurate but feasible only at Reynolds numbers up to around 10000, which might be too low for our experiment. Simulations at an order of magnitude higher Reynolds number will be performed with LES (Large Eddy Simulations) method. We will validate existing LES models with the measurements and DNS results and we will upgrade LES sub-grid models for temperature field equations in conjugate heat transfer simulations.    To the best of our knowledge, the results of the proposed research will describe penetration of the turbulent temperature fluctuations into the solid walls on the geometry of the annulus with unmatched experimental and computational accuracy in today's literature. There are very accurate experimental databases available for certain geometries, but have not been analysed with simulations of similar accuracy. On the other side, there are several computational databases, which were not verified with the experiments. Our research should bridge this gap between the experiments and simulations in the field of turbulent conjugate heat transfer.
Significance for science
Measured temperatures, velocities and their fluctuations will represent an immensely valuable database for fundamental heat transfer studies. The same is true for the DNS/LES databases that will be created. Such databases will benefit the whole heat transfer community. All databases will be in the open domain. They will be of particular importance for the nuclear engineering, where the annular geometry prevails. Measurements and simulations of conjugate heat transfer in the same annular geometry of our experimental device will be the first results of that kind and will bridge the gap between the experiments and simulations in the field of turbulent conjugate heat transfer. Validation of the LES models, required grid density in the fluid and in the solid domain will also represent an original and valuable result. A major contribution is expected if we manage to develop LES model that will allow accurate simulations of conjugate heat transfer and predictions of the temperature fluctuations inside the solid domain. Development and improvement of the sub-grid models for the conjugate heat transfer LES will be a very important and original result of our project. Possible new research area that may emerge from our proposed research will be an opportunity to develop conjugate heat transfer models for industrial CFD codes, which are based on RANS (Reynolds Averaged Navier-Stokes) models of turbulence. Another research direction based on our results is improved accuracy of thermal fatigue predictions, which would improve reliability and safety of the processing systems exposed to temperature fluctuations.
Significance for the country
Electricity production, nuclear Industry, nuclear safety Despite the growing share of wind and solar electricity in the past two decades, nuclear power still represents the second largest (after the hydro) low-carbon source of electricity on the planet. Moreover, comparison of the combined growth rate of the wind and sun electricity in the past two decades and the growth of the nuclear energy in the seventies of the previous century, which took place on the planet with considerably smaller global economy and population, shows that the growth rate of wind and solar is actually slower (Cao et. al, 2016). Last few years of the German "Energiewende" demonstrate that it will be very difficult to decarbonize our electricity systems without the contribution from the nuclear. These developments justifiy investments in nuclear engineering R&D. Accurate prediction of heat transfer characteristics is crucial for efficient operation of all heat engines including the nuclear power plants. The study of temperature fluctuations at the contact of the liquid and the wall in this project proposal could significantly improve the accuracy of the thermal fatigue assessments. This topic is of particular importance for the Nuclear Power Plant Krško and for other power plants in Europe and in the World, which put large efforts into the ageing management of their components and strive towards safe life extension and the consequential economic benefits. Moreover, this type of knowledge would be extremely valuable also for many other fields of process industry. For example; the heat-storage tanks of the solar thermal power plants are exposed to large temperature variations. Although these plants are not economically competitive today, the new knowledge in the proposed project could help to design and extend the lifetime of these installations. Research infrastructure of the JSI The project will represent a strong motivation and a push to upgrade the computer clusters of the JSI-Reactor computing centre or upgrade of the computers in the central JSI computing center, which is trying to consolidate and to centralize the rather dispersed computing resources of the JSI research departments. The project will be also a strong push for the thermal hydraulic laboratory of the JSI Reactor Engineering Division. Nuclear expertise for decision making Indirect consequence of the proposed project will result in new knowledge relevant to maintain the status of the JSI as an official Technical Support Organization that delivers technical and scientific services to Slovenian nuclear safety administration. Thus, maintaining the nuclear expertise means a direct support for the Slovenian government to make independent national assessments, to support the planning, operation and decommissioning of the nuclear facilities, and to ensure a scientific and technical backup for the authorities.
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