|
|
Role of thermal near field in cryogenic Rayleigh-Bénard convection
Věžník, Tomáš ; Schmoranzer,, David (referee) ; Urban, Pavel (advisor)
This bachelor thesis is focused on the eect of the thermal near feld (NF) radiation on (i) the onset of Rayleigh-Bénard convection (RBC) and (ii) the thermal inuence on the temperature sensors used in RBC studies. In the frst part, the theoretic base for both studied areas, RBC and NF, is presented. Further, the ways of fnding the onset of RBC, the temperature profles, the basic equations for heat transfer in far feld and near feld and the description of the apparatus used for the measurements of radiative heat transfer are given too. In the practical part, the process of measurement is presented and the model that we obtained for describing the dependence of the coefcient of radiative heat transfer between two Cu surfaces is demonstrated. Afterwards, the data are used to analyse the eect of NF on the onset of convection, and to calculate the inuence on the temperature profle measurements with cryogenic temperature sensors and, at last, the comparison of total heat transferred over the experimental cell with NF heat transfer over the thermal boundary layers arising in RBC is done. A goal of this thesis was to fnd out whether the eect of NF can explain the contradictory results of determining the onset of convection in cryogenic RBC (expressed by critical Rac) based on the measurements of the heat transfer in RBC and of the eectivity of heat transfer at high values of Ra numbers in cryogenic experiments. The current evaluations clearly demonstrate that the eect of NF on studied phenomena is by several orders of magnitude smaller than other relevant eects and can thus justly be neglected.
|
|
| |
|
| |
|
|
Role of thermal near field in cryogenic Rayleigh-Bénard convection
Věžník, Tomáš ; Schmoranzer,, David (referee) ; Urban, Pavel (advisor)
This bachelor thesis is focused on the eect of the thermal near feld (NF) radiation on (i) the onset of Rayleigh-Bénard convection (RBC) and (ii) the thermal inuence on the temperature sensors used in RBC studies. In the frst part, the theoretic base for both studied areas, RBC and NF, is presented. Further, the ways of fnding the onset of RBC, the temperature profles, the basic equations for heat transfer in far feld and near feld and the description of the apparatus used for the measurements of radiative heat transfer are given too. In the practical part, the process of measurement is presented and the model that we obtained for describing the dependence of the coefcient of radiative heat transfer between two Cu surfaces is demonstrated. Afterwards, the data are used to analyse the eect of NF on the onset of convection, and to calculate the inuence on the temperature profle measurements with cryogenic temperature sensors and, at last, the comparison of total heat transferred over the experimental cell with NF heat transfer over the thermal boundary layers arising in RBC is done. A goal of this thesis was to fnd out whether the eect of NF can explain the contradictory results of determining the onset of convection in cryogenic RBC (expressed by critical Rac) based on the measurements of the heat transfer in RBC and of the eectivity of heat transfer at high values of Ra numbers in cryogenic experiments. The current evaluations clearly demonstrate that the eect of NF on studied phenomena is by several orders of magnitude smaller than other relevant eects and can thus justly be neglected.
|
guest ::
