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CPOTE2020 logo
6th International Conference on
Contemporary Problems of Thermal Engineering
Online | 21-24 September 2020

Abstract CPOTE2020-1062-A

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Flow boiling in minigaps and minichannel multiports - visualizational studies

Michał KLUGMANN, Gdańsk University of Technology, Poland
Paweł DĄBROWSKI, Gdansk University of Technology, Poland
Dariusz MIKIELEWICZ, Gdańsk University of Technology, Poland

The topic of boiling heat transfer in miniscale geometries focuses the ever increased interest of researchers in recent years. However, most of the works are related to mini- and microchannels and much less to minigaps. Meanwhile, the minigaps allow for more comprehensive experimental studies, i.e. flow visualizations due to flat, two-dimensional configuration of flow. The results of experimental investigations of a model plate heat exchanger, composed of a single plate with a heat exchange surface of 0.1 m x 0.2 m, made of brass are presented. The working fluid is pure ethanol. Between the plate and the cover of the exchanger, a 0.5 mm and 1.0 mm thick minigaps are arranged. Minigap 0.5 mm has been compared with an equivalent minichannel structure (a set of 50 parallel minichannels) with an equal cross-sectional area (rectangular 1 mm x 1 mm). The section cover was transparent in order to make simultaneous registration of flow structures along with the measurements. The heat is supplied using a water circuit, where the temperature and flow of the water can be regulated in the constant temperature water tank. The flow configuration of the exchanger is countercurrent, with the vertical flow of ethanol from the bottom to top. The inlet and outlet manifolds are arranged as trapezoidal (Z-type design). Authors have analysed the efficiency of heat transport and pressure drop depending on the system operation parameters. Attention was paid to the issue of even distribution of the working medium (flow maldistribution). The visualizations have been thoroughly analysed in order to better understanding of the process. The main advantages of the presented work are: a) direct comparison of minigap and minichannel structures while standardizing all other parameters, b) simultaneous visualization made with the use of fast shutter speed camera for better understanding of the process.

Keywords: Minigap, Flow structures, Minichannel, Flow visualization, Flow boiling
Acknowledgment: The work presented in this paper was funded from the National Science Centre Poland research project No. UMO-2015/19/D/ST8/03201 in the years 2016–2019 and from the National Science Centre, Poland research project No. 2017/27/N/ST8/02785 in the years 2018-2020.