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Abstract

The potential applications of loop heat pipes (LHPs) are the nuclear power space systems, fuel cell thermal management systems, waste heat recovery systems, medium temperature electronic systems, medium temperature military systems, among others. Such applications usually operate in temperature ranges between 500–700 K, hence it is necessary to develop an LHP system that will meet this requirement. Such a thermal management device require to meet various technical problems and challenges currently existing in the development of LHP working in medium temperatures, including: (1) selection of appropriate working fluid; (2) selection of appropriate LHP construction material; (3) construction of suitable test rig capable of testing at elevated temperatures; (4) development of new testing methods. Currently, there are no proven working fluids that can be used in LHPs in medium temperature ranges. Water can be applicable only at temperatures up to 570 K. Caesium can be applicable at temperatures above 670 K. Organic fluids usually tend to generate non-condensable gasses and/or decompose at elevated temperatures and their viscosity dramatically increases. For halides, most of them are very reactive or toxic and their full property data are not available or the majority of the physical properties are predicted, also live tests and their environmental impact data are not adequate. As for casing/LHP construction material, there are no full chemical compatibility tables with most of the medium temperature working fluids and the reactivity of fluids significantly limits the potential materials. Also, testing such an LHP is an endeavour as the reactivity of medium temperature fluids and the use of obscure metals create new challenges. Altogether creates multiple challenges in the development, testing, handling and operating of LHP in the medium temperature range.
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Bibliography

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[2] Zhang Y. (Ed.): Heat Pipes: Design, Applications and Technology. Nova, 2018.
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[11] Blauciak K., Szymanski P., Mikielewicz D.: The influence of loop heat pipe evaporator porous structure parameters and charge on its effectiveness for ethanol and water as working fluids. Materials 14(2021), 7029.
[12] Nikitkin M.N., Bienert W.B., Goncharov K.A.: Non condensable gases and loop heat pipe operation. SAE Tech. Pap. 981584. In: Proc. 28th Int. Conf. on Environmental Systems, 1998.
[13] Wrenn K.R., Wolf D., Kroliczek E.J.: Effect of non-condensible gas and evaporator mass on loop heat pipe performance. SAE Tech. Pap. 2000-01-2409. In: Proc. 30th Int. Conf. on Environmental Systems, 603–614, 2000.
[14] Ishikawa H., Ogushi T., Nomura T., Noda H., Kawasaki H., Yabe T.: Heat transfer characteristics of a reservoir embedded loop heat pipe (2nd report, influence of noncondensable gas on heat transfer characteristics). Heat Transf. Asian Res. 36(2007), 8, 459–473.
[15] Singh R., Akbarzadeh A., Mochizuki M.: Operational characteristics of the miniature loop heat pipe with non-condensable gases. Int. J. Heat Mass Tran. 53(2010), 17–18, 3471–3482.
[16] He J., Lin G., Bai L., Miao J., Zhang H.: Effect of non-condensable gas on the operation of a loop heat pipe. Int. J. Heat Mass Tran. 70(2014), 449–462.
[17] Prado-Montes P.: Development of an elevated temperature loop heat pipe for space applications and investigation of non-condensable gas impact on its performance. PhD thesis, Polytechnic University of Madrid, Madrid 2014.
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[19] Mishkinis D., Prado P., Sanz R., Radkov A., Torres A., Tjiptajardja T.: Loop heat pipe working fluids for intermediate temperature range: from –40°C to +125°C. In: Proc. 1st. Int. Conf. on Heat Pipes for Space Applications, Moscow, Sept. 2009.
[20] Mikielewicz D, Błauciak K.: Investigation of the influence of capilary effect on operation of the loop heat pipe. Arch. Thermodyn. 35(2014), 3, 59–80.
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Authors and Affiliations

Paweł Szymański
1
Dariusz Mikielewicz
1

  1. Gdansk University of Technology, Faculty of Mechanical Engineering and Ship Technology, Narutowicza 11/12,80-233 Gdansk, Poland
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Abstract

Article presents the results of the effect of humidity on early shrinkage of normal concrete with variable W/C ratio. As known for a long time, shrinkage is dependent of many factors. One of them is the W/C ratio and the quantity of water which is located in the concrete mix. In article there were discussed changes taking place in the concrete mix, the methods of research and the partial results obtained by the authors of the paper. Shrinkage is a phenomenon well known and studied by various research centers. The total amount of shrinkage may depend on various factors such as humidity, temperature, composition of the concrete mix, the W/C ratio, the size of the item. The study was conducted to determine the amount of shrinkage in its early stages. It is very important for concrete floors contractors, precast manufacturers to start at the right time finishing work and prevent the formation of shrinkage cracks.

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Authors and Affiliations

Józef Jasiczak
Paweł Szymański
Piotr Nowotarski

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