tailieunhanh - Evaporation Condensation and Heat transfer Part 4

Tham khảo tài liệu 'evaporation condensation and heat transfer part 4', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 110 Evaporation Condensation and Heat Transfer With increasing this parameter the deviation is observed for all lengths of the heaters used in this work Pav lenko et al. 2006 . Thus there is an area wheresurface drying is determined not by the hydrodynamic crisis. The basic idea of the hydrodynamic model is the fact that under the pre-crisis conditions the liquid-gas interface becomes unstable and the flow separates. The bulk of the liquid is separated from heating surface by generated vapor and a crisis is reached when for remaining on the heating surface microlayer holds the heat balance the total evaporation . Such model describes well the experimental data at low values of estimated parameters We1 high velocities of liquids . At higher values of We 1 experimental data have the value which is 2 or more times lower than that predicted by the model formula Mudawar et al. 1987 which obviously can not be used for the description of CHF in these ranges of determining parameter. The authors of Pavlenko et al. 2006 proposed the hypothesis about new types of dry out crisis whose nature is caused by the loss of thermal stability of dry spots in the lower part of the flow and associated upstream propagation of critical temperature disturbance. It is reasonable to verify this experimental hypothesis by direct numerical simulation. The intensity of heat transfer is described by the curves shown in Fig. 13a and 13b which use the experimental data Pavlenko et al. 2006 Grigorév et al. 1977 forthick-wall heater made of duralumin and the thin wall constantan heater. Fig. 13. a Curve of heat transfer in film nitrogen flow on a bounded heat-transfer surface from duralumin 1 experimental data Matse kh Pavlenko 2005 for the heater of length 64 mm Rqn 285 2 interpolation curve with the use of the data Matsekh Pavlenko 2005 3 data of Grigorév et al. 1977 . b mdel curves of heat transfer under film flow of liquid nitrogen on a constantan foil Re in 690 1 three-zone model at 1 2 .