The heat and mass transfer analogy factor, Nu/Sh for two-dimensional and three-dimensional boundary layers.

摘要

The similarity of the heat and mass transfer equations indicate they will have similar solutions, in particular if the Prandtl number is equal to the Schmidt number. This is called the heat and mass transfer analogy. Generally, the Prandtl number may be different from the Schmidt number. Therefore, conversion of mass transfer results into heat transfer results requires a conversion factor. It is called the analogy factor.; The analogy factor is required to convert mass transfer measurements to heat transfer results. Mass transfer experiments are relatively simple and inexpensive compared to heat transfer experiments. They are free from conduction and radiation errors. They do, however, require the analogy factor to convert mass transfer coefficients into heat transfer coefficients.; The best way to determine the analogy factor is to conduct heat transfer and mass transfer experiments with equivalent experimental and geometric conditions. For the present heat transfer experiments, a thermal boundary layer measurement technique is selected with constant wall temperature boundary condition, and for the mass transfer experiment, the naphthalene sublimation technique is selected with constant wall concentration boundary condition.; Many studies have been conducted with a constant wall heat flux condition due to its simplicity in experiments. However, it is not an equivalent condition for the constant wall concentration boundary condition in the mass transfer experiment. The constant wall temperature boundary condition in the heat transfer experiment is equivalent to the constant wall concentration boundary condition in the mass transfer experiment. Therefore, constant wall temperature boundary condition is enforced for the heat transfer experiment in the present research.; The heat transfer coefficient and the mass transfer coefficient are measured in a turbine cascade under similar flow conditions. The analogy factor in both two and three dimensional flows is evaluated and confirmed on the pressure and suction sides of a blade, and on the endwall, both with and without fillets. It shows good agreement with the theoretical values which were already published. With the proven analogy factors, mass transfer coefficients can be converted into heat transfer coefficients with confidence.; In addition to the heat and mass transfer analogy, mass transfer measurements have been conducted with the fillets with turbine blade leading edge. So far many efforts to increase power output from the turbines have been made. A leading edge fillet was presented with reduced aerodynamic loss. However, the effect of the fillet hasn't been investigated enough to check heat transfer characteristics. The comparison between the plain blade and the blade with the fillet confirms the thermal characteristics of the fillet with turbine blade leading edge.; With the fillets and low turbulence intensity, the passage vortex is delayed, but gain its strength as much as without the fillet. On the pressure side, higher mass transfer region is observed. With the fillets and high turbulence intensity, the passage vortex is not observed on the endwall as with the plain blade and high turbulence intensity. Higher mass transfer region is clearly observed on the pressure from the end of fillet to the middle of the blade.