In this paper, an experimental investigation of a Iaminar wall jet in the presence of a heated wall with stationary particles on its surface, is reported. The wall jet was submitted to external acoustic vibrations amp...In this paper, an experimental investigation of a Iaminar wall jet in the presence of a heated wall with stationary particles on its surface, is reported. The wall jet was submitted to external acoustic vibrations amplifying the coherent structures appearing in the laminar region. A wind tunnel was used at very low Reynolds number. Mean velocity and turbulence intensity were measured by a constant temperature anemometer. Measurements were taken in the transition and turbulent regions. Embedded particles were outside the viscous sublayer and it was observed that their presence modifies significantly the flow characteristics in particular the boundary layer is thickened. This study can bring a better understanding of the structure of a flow when it is heated and forced on a rough wall.展开更多
Numerical studies under supercritical pressure are carried out to study the heat transfer characteristics in a single-root coolant channel of the active regenerative cooling system of the scramjet engine, using actual...Numerical studies under supercritical pressure are carried out to study the heat transfer characteristics in a single-root coolant channel of the active regenerative cooling system of the scramjet engine, using actual physical properties of pentane. The relationships between wall temperature and inlet temperature, mass flow rate, wall heat flux, inlet pressure, as well as center stream temperature are obtained. The results suggest that the heat transfer deterioration occurs when the fuel temperature approaches the pseudo-critical temperature, and the wall temperature increases rapidly and heat transfer coefficient decreases sharply. The decrease of wall heat flux, as well as the increase of mass flow rate and inlet pressure makes the starting point of the heat transfer deterioration and the peak point of the wall temperature move backward. The wall temperature increment induced by heat transfer deterioration decreases, which could reduce the severity of the heat transfer deterioration. The relational expression of the heat transfer deterioration critical heat flux derives from the relationship of the mass flow rate and the inlet pressure.展开更多
To reach the target of smaller pressure drop and better heat transfer performance, packed beds with small tube-to-particle diameter ratio(D/dp<10) have now been considered in many areas. Fluid-to-wall heat transfer...To reach the target of smaller pressure drop and better heat transfer performance, packed beds with small tube-to-particle diameter ratio(D/dp<10) have now been considered in many areas. Fluid-to-wall heat transfer coefficient is an important factor determining the performance of this type of beds. In this work, local fluid-to-wall heat transfer characteristic in packed beds was studied by Computational Fluid Dynamics(CFD) at different Reynolds number for D/dp=1.5, 3.0 and 5.6. The results show that the fluid-to-wall heat transfer coefficient is oscillating along the bed with small tube-to-particle diameter ratio. Moreover, this phenomenon was explained by field synergy principle in detail. Two arrangement structures of particles in packed beds were recommended based on the synergy characteristic between flow and temperature fields. This study provides a new local understanding of fluid-to-wall heat transfer in packed beds with small tube-to-particle diameter ratio.展开更多
文摘In this paper, an experimental investigation of a Iaminar wall jet in the presence of a heated wall with stationary particles on its surface, is reported. The wall jet was submitted to external acoustic vibrations amplifying the coherent structures appearing in the laminar region. A wind tunnel was used at very low Reynolds number. Mean velocity and turbulence intensity were measured by a constant temperature anemometer. Measurements were taken in the transition and turbulent regions. Embedded particles were outside the viscous sublayer and it was observed that their presence modifies significantly the flow characteristics in particular the boundary layer is thickened. This study can bring a better understanding of the structure of a flow when it is heated and forced on a rough wall.
基金the funding supports from National Natural Science Foundation of China (Grant No.51076035 and No.11079017), HIT.NSRIF.2008. 24
文摘Numerical studies under supercritical pressure are carried out to study the heat transfer characteristics in a single-root coolant channel of the active regenerative cooling system of the scramjet engine, using actual physical properties of pentane. The relationships between wall temperature and inlet temperature, mass flow rate, wall heat flux, inlet pressure, as well as center stream temperature are obtained. The results suggest that the heat transfer deterioration occurs when the fuel temperature approaches the pseudo-critical temperature, and the wall temperature increases rapidly and heat transfer coefficient decreases sharply. The decrease of wall heat flux, as well as the increase of mass flow rate and inlet pressure makes the starting point of the heat transfer deterioration and the peak point of the wall temperature move backward. The wall temperature increment induced by heat transfer deterioration decreases, which could reduce the severity of the heat transfer deterioration. The relational expression of the heat transfer deterioration critical heat flux derives from the relationship of the mass flow rate and the inlet pressure.
基金supported by the National Natural Science Foundation of China(5127618151476173)the National Basic Research Program of China(2011CB 710705)
文摘To reach the target of smaller pressure drop and better heat transfer performance, packed beds with small tube-to-particle diameter ratio(D/dp<10) have now been considered in many areas. Fluid-to-wall heat transfer coefficient is an important factor determining the performance of this type of beds. In this work, local fluid-to-wall heat transfer characteristic in packed beds was studied by Computational Fluid Dynamics(CFD) at different Reynolds number for D/dp=1.5, 3.0 and 5.6. The results show that the fluid-to-wall heat transfer coefficient is oscillating along the bed with small tube-to-particle diameter ratio. Moreover, this phenomenon was explained by field synergy principle in detail. Two arrangement structures of particles in packed beds were recommended based on the synergy characteristic between flow and temperature fields. This study provides a new local understanding of fluid-to-wall heat transfer in packed beds with small tube-to-particle diameter ratio.
