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Doctoral Thesis
Author of thesis: Ing. Patrik Rapta, Ph.D.
Acad. year: 2026/2027
Supervisor: prof. Ing. Miroslav Jícha, CSc.
Reviewers: prof. Ing. Václav Dvořák, Ph.D., prof. Ing. Michal Masaryk, Ph.D.
The heat exchanged between the gas and the cylinder wall superheats the suction charge and lowers the volumetric efficiency of a reciprocating compressor. This heat transfer is routinely predicted by dimensionless correlations some of which are calibrated on internal combustion engines, which have not been tested directly against the instantaneous in-cylinder flux of a running compressor they are meant to reproduce. The instantaneous in-cylinder heat flux of a small air compressor was therefore measured directly over several pressure ratios, to identify the fluxes, to determine the heat transfer coefficients on selected surfaces, and to assess five published correlations. The surface temperature was recorded with flush-mounted coaxial thermocouples at the valve plate and at two liner positions. The heat flux was recovered through the semi-infinite-solid solution, and the gas temperature was reconstructed from the cylinder pressure with a self-consistent energy balance. The flux reaches tens of kilowatts per square metre and exceeds one hundred at the valve plate. It changes direction at least twice in each revolution and on average carries heat from the wall into the gas, superheating the charge by 35 to 85 K. The heat transfer coefficient is recovered reliably only as a two-term quantity with a magnitude and a phase, because the flux lags the gas-to-wall temperature difference. None of the five correlations reproduces the flux without refitting, and refitting reaches only a common residual floor set by the phase structure of the flux. The analysis also quantified the gas leakage and the suction-line acoustic resonance. The work is the first direct, crank-angle-resolved validation of in-cylinder heat-transfer correlations on a running compressor and shows that the quasi-static coefficient cannot represent the measured phase lag.
reciprocating compressor, in-cylinder heat transfer, semi-infinite solid, heat transfer correlations, phase lag
Date of defence
07.09.2026
Result of the defence
Defended (thesis was successfully defended)
Process of defence
Student prezentoval a obhájil výsledky získané při řešení disertační práce. Student zodpověděl uspokojivě položené dotazy. Komise konstatuje splnění cílů studia.
Language of thesis
Czech
Faculty
Fakulta strojního inženýrství
Department
Energy Institute
Study programme
Design and Process Engineering (D-KPI-P)
Composition of Committee
prof. Ing. Jiří Pospíšil, Ph.D. (předseda) doc. Ing. Jaroslav Katolický, Ph.D. (místopředseda) prof. Ing. Michal Masaryk, Ph.D. (člen) prof. Ing. Václav Dvořák, Ph.D. (člen) prof. Ing. Jan Jedelský, Ph.D. (člen) Ing. Ján Tuhovčák, Ph.D. (člen)
Supervisor’s reportprof. Ing. Miroslav Jícha, CSc.
Grade proposed by supervisor: A
Reviewer’s reportprof. Ing. Václav Dvořák, Ph.D.
Reviewer’s reportprof. Ing. Michal Masaryk, Ph.D.
Responsibility: Mgr. et Mgr. Hana Odstrčilová