Critical heat flux in a closed two-phase thermosyphon

A closed two-phase thermosyphon experimental setup with the possibility of recording the coolant and its vapors temperatures was developed. We proved the use of the V. M. Borishansky and S. S. Kutateladze correlations for the determination of the critical heat flux in closed two-phase thermosyphons with the ratio of their internal diameter to the length of the heat supply zone in the range of 1 / 2 внут и d L < < .


Introduction
It is known [1] that the heat exchange rate in a closed two-phase thermosyphon (CTPT) depends on the heat flux q. Under conditions of attaining critical values of q and higher than q cr , the heat exchange rate decreases. The minimum thermosyphon filling ratio depends on the critical heat flux (CHF), geometric dimensions (internal diameter, evaporator length) and coolant thermal properties [2].
The aim of this work is to determine the critical heat flux in closed two-phase thermosyphons with the ratio of their internal diameter to the length of the heat supply zone in the range of 1 / 2 внут и d L < < .

Results
The scheme of the experimental setup simulating the work of the CTPT is in Fig. 1. . The operating principle of the setup ( Fig. 1) is given in detail in [19].
It is known [20] that the boiling process in a thermosyphon differs from the boiling process in a large volume. When It was found that the divergence between the values of the critical heat flux obtained on the basis of: 1) the theoretical contributions of the occurrence of a "flooding" [10] regime in the thermosyphon is 92%; 2) S. S. Kutateladze hydrodynamic theory of the heat transfer crisis during boiling is 27%.
The results of the critical heat flux calculation for the experimental setup developed are shown in Table 1 [7]; Z. Nejat [8] 1013.0 R. K. Sakhuja [9]; G. B. Wallis [10] 1390.3 O. L. Pushkina, Yu. L. Sorokin [11] 12605.7 C. L. Tien, K. S. Chung [12] 5403.4 S.S. Kutateladze hydrodynamic theory of the heat transfer crisis during boiling H. Imura, K. Sasaguchi, H. Kozai, S. Numata [2] 1345.2 Y. Haramura; Y. Katto [3] 1105.3 J. H. Lenhard; V. K. Dhir [4] 1263.8 V. M. Borishanskiy [5] 1207.8 E. E. Kazakova [6] 1016.8 S.S. Kutateladze [13] 1355.8 B. P. Avksentyuk; S. S. Kutateladze [14] 1186.3 N. Zuber [15] 1157.1 W. M. Rohsenow, P. Grifts [16] 1356.3 I. Mudawar, A. H. Howard, C. O. Gersey [17] 1279.5 C. K.Guan, J. F. Klausner, R. Mei [18] 990.6 The average value of the critical heat flux obtained from thirteen correlations with the exception of the dependencies O. L. Pushkina, Yu. L. Sorokin [11] and C. L. Tien, K. S. Chung [12], for the closed two-phase thermosyphon experimental setup is Kutateladze [14] does not exceed 3%. The minimum error (less than 1%) was obtained in the calculation using the formula of V. M. Borishanskiy [5]. It should be noted that this is the only correlation from the formulas presented which takes into account the liquid viscosity influence on the critical heat flux. It is possible to determine CHF based on the theoretical contributions of the occurrence of a "flooding" regime in a thermosyphon by using correlations based on the Wallis numbers [7][8][9][10] (the dependences are based on the balance of inertial and hydrostatic forces). Correlations based on Kutateladze numbers [11][12] (based on the balance of dynamic forces, surface tension and gravity forces) can not be used for the experimental setup developed. Large deviation of O. L. Pushkina, Yu. L. Sorokin [11] and C. L. Tien, K. S. Chung [12] dependencies, most likely, was due to the fact that in the formulas derivation it was assumed that there was no influence of any vertical channel geometric characteristic on the CHF. Adequate values of critical heat fluxes (950-1400 kW/m 2 ) at atmospheric pressure, according to the dependencies can be obtained for longer thermosyphons

Conclusion
It is established that in order to calculate the critical heat flux in closed two-phase thermosyphons with the ratio of their internal diameter to the length of the heat supply zone in the range of 1 / 2 This work was carried out at the Kutateladze Institute of Thermophysics SB RAS and financially supported by the Russian Science Foundation (project number 15-19-10025).