Experimental investigation and modeling of contact heat transfer

  • Experimentelle Untersuchung und Modellierung zur Kontaktwärmeübertragung

Ustinov, Victor Alexandrovic; Kneer, Reinhold (Thesis advisor); Mitrovic, Jovan (Thesis advisor)

Aachen (2018, 2020)
Dissertation / PhD Thesis

Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2018

Abstract

The subject of this thesis is an investigation and phenomena analysis of contact heat transfer between mechanically and thermally loaded components. Hence, experimental analysis of behavior of contact heat transfer over a wide range of influencing parameters and modeling of observed processes within the validation are investigated and developed in this thesis. This work consists of ten chapters dealing on research. The second chapter of this work provides a current state of the art of investigation of contact heat transfer of the last hundred years. It is reviewed from the methodology of estimation the thermal contact conductance - to numerical determination of contact heat transfer. Hence: steady-state, ultrasonic and non-invasive thermo-graphic technique are studied and their characteristics are compared. Theoretical models and methods of estimation contact heat transfer coefficients are also examined. It shown that previous models for estimating the contact heat transfer coefficients are based on experiments conducted commonly in vacuum conditions and valid only up to low contact pressures of about 10 MPa and are not applicable at high pressures nearing 250 MPa, which are relevant and important to the design of components in internal combustion engines. Furthermore, the term “Contact” stating in front of the heat transfer is also studied. In this matter, different methods and models for determination of contact area between bodies are reviewed. It is shown that any of these methods could not provide the value of the contact area in the applicable range of parameters. In summary, a new methodology to derive a contact heat transfer coefficient needed to be developed using a precise measuring technique for the range of contact pressures over 10 MPa also taking the exact value of contact area of analyzed bodies into account. Thus, in experiments, a force load machine to reconstruct the contact pressures in range from 1 to 250 MPa is used. For temperature field acquisition a high-speed infrared camera with an accuracy of 0,5 K is used. The surface characteristics are obtained using a stylus profile meter with the accuracy of 0,1 µm. The methodology of measurements and following data processing are given in the third chapter. Experiments were conducted for different material combinations with three different surface structures, while varying the contact pressures from 7 MPa to 230 MPa and the results of the experimental investigations are given in the forth chapter. Numerically, it was attempted to develop a new approach for the calculation of the contact heat transfer coefficient, based on results of experimental and numerical investigations, thermal and mechanical behaviors of materials under contact pressure, while taking into account the elastic and plastic deformations as a function of surface characteristics and the contact pressure. When selecting average surface roughness (Rz) as a characterizing parameter for surface structure, the results did not show a consistent trend. Thus, in this paper Rz was replaced by the real contact area between the two surfaces of interest. Hence, a similar approach based on fractal theory to the one used by researchers working on nucleate boiling [1, 2, 3, 4, 5] has been employed for the estimation of real contact area between two real solid bodies. Then, proposed method named Fk-model is reconstructed in a highly precise contact model and validated with the accurately performed experimental results. To simplify complicated evaluation of contact heat transfer coefficient, a simple engineering model is also developed. The engineering model proposed in this paper is based on a grade of surface finishing and known parameters of thermal and material characteristics. However, power-low and analytical models developed in cooperation during this project are also given and compared with the data obtained during this research. These results are reported in fifth chapter. Verification of proposed theoretical methods were experimentally validated with a new material and structure combinations, as well as with known literature data and the results are summarized in sixth chapter. In present work, attention on the phenomena of temperature oscillations during the loaded contact is found and accented. Phenomena analysis of the nature of these oscillations is studied according to stability and chaos theory. Hence, phase portraits of temperature and contact heat transfer oscillations for different pressures are presented and discussed. Possible mechanical influence of phenomena caused by test rig vibrations is also examined. According to performed analysis, recommendations to the further field of investigations are also given and can be found in seventh chapter. The knowledge on contact heat transfer phenomena acquired during this research are accumulated and formulated in chapter conclusions.

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