Experimental Study on the Resistance and Splash Performances of Water Collecting Devices for Mechanical Draft Cooling Towers

In recent years,water collecting systems,with the associated advantages of energy saving and noise reduction,have become the foundation for the development of a scheme to optimize the structure of cooling towers.To explore the feasibility of this approach for mechanical draft cooling towers,a small-scale experimental device has been built to study the resistance and splash performances of three U-type water collecting devices(WCDs)for different water flow rates and wind speeds.The experimental results show that within the considered ranges of wind speed and water flow rate,the pressure drop of the different WCDs can vary significantly.The resistance and local splash performances can also be remarkably different.Some recommendations about the most suitable system are provided.Moreover,a regression analysis of the experimental data is conducted,and the resulting fitting formulas for resistance and splash performance of WCD are reported.

Fragment spatial distribution of prismatic casing under internal explosive loading

Non-cylindrical casings filled with explosives have undergone rapid development in warhead design and explosion control.The fragment spatial distribution of prismatic casings is more complex than that of traditional cylindrical casings.In this study,numerical and experimental investigations into the fragment spatial distribution of a prismatic casing were conducted.A new numerical method,which adds the Lagrangian marker points to the Eulerian grid,was proposed to track the multi-material interfaces and material dynamic fractures.Physical quantity mappings between the Lagrangian marker points and Eulerian grid were achieved by their topological relationship.Thereafter,the fragment spatial distributions of the prismatic casing with different fragment sizes,fragment shapes,and casing geometries were obtained using the numerical method.Moreover,fragment spatial distribution experiments were conducted on the prismatic casing with different fragment sizes and shapes,and the experimental data were compared with the numerical results.The effects of the fragment and casing geometry on the fragment spatial distributions were determined by analyzing the numerical results and experimental data.Finally,a formula including the casing geometry parameters was fitted to predict the fragment spatial distribution of the prismatic casing under internal explosive loading.

Simulation Study on Flow and Heat Transfer of Cross-Arrangement Tube Bundle

The air precooler of SABRE engine(Synergetic Air-Breathing Rocket Engine)is a tube bundle type of heat exchanger consisting of thousands of small tubes.The cold helium gas flows in the small tube bundle,and the high-speed hot air circulates outside the tubes and exchanges heat with the helium in the tubes.In this study,the cross-arrangement tube bundle consisting of small tubes with outer diameter of 1mm was taken as the research object.The system simulation calculation and data sorting were carried out.It is found that the empirical correlation of the conventional tube bundle is no longer applicable to the small tube and the reasons for inapplicability are explained by analysis of flow field.In addition,the results show that the average heat transfer coefficient of cross small/micro tube bundle isn’t affected by heat flux,but increases with the increase of Reynolds number,increases with the increase of transverse spacing,and decreases with the increase of longitudinal spacing.The flow resistance coefficient isn’t affected by heat flux and longitudinal spacing,but decreases with the increase of Reynolds number,and decreases with the increase of transverse spacing.

Influences of nozzle parameters and low-pressure on jet breakup and droplet characteristics

Experiments were carried out to investigate the influences of nozzle geometric parameters and injection pressure on jet breakup characteristics using a high-speed photography(HSP)technique.The flow rates and spraying ranges of sprinkler with different nozzles were measured.In this research,HSP technique was also used to photograph the drops emitted by sprinkler with different nozzles at different pressures,photographs were taken at different horizontal distances from the sprinkler and the equivalent circle diameter was used to represent the particle sizes.Based on HSP technology,the effects of flow velocity and nozzle geometric parameters on jet breakup length were studied,and the droplet diameters with different nozzle types were obtained.The result showed that for the sprinkler with different nozzles,the breakup length decreased with the increases of pressures.At the nearby(3-9 m)region and distant(12-18 m)region of sprinkler,the droplet diameters of sprinkler with type B nozzle were the largest,which meant the sprinkler with type B nozzle was the optimal choice by synthesizing the droplet diameter distribution.The fitting relationship of jet breakup length with Reynolds number and Weber number(Re and We),and the regression equation of the end droplet diameters were deduced with errors of less than 5%and 4%respectively.

Bearing capacity and failure behavior of disconnectable coupling joint with double row wedges(DCJD)used in the prestressed internal bracing

A disconnectable coupling joint with double row wedges(DCJD)is a crucial component of the prestressed internal bracing in subway foundation pits.However,only a few studies have been conducted on the bearing capacity of the joints;moreover,the yield load and compression stiffness of DCJDs are typically determined from experience.The aim of this study was to quantitatively determine the bearing capacity and propose accurate formulas for calculating the yield load and compression stiffness of DCJDs.Hence,a DCJD was selected from a foundation pit in Beijing,China,and loading experiments were conducted under axial force.Load–displacement and load–strain curves were obtained,and the failure modes of the joint were analyzed.The experimental results were verified through several finite element models.Subsequently,parametric analyses were performed to investigate the effects of the dimensions of the key position on the DCJD’s bearing capacities.Moreover,regression analysis was used to obtain the formulae for estimating the initial compression stiffness and yield load of the DCJD.Finally,the fitting formulae results were compared with the numerical and experimental results.The comparisons showed that the fitting formulae were highly accurate in estimating the bearing capacity of the DCJD.