In recent years, the steel-truss natural draft dry cooling technique has received attention owing to its advantages in better aseismic capability, shorter construction period, and preferable recycling. For cooling towers generating the draft force of air flow, its configuration may impact the thermal and flow performance of the steel-truss natural draft dry cooling system. With regard to the issue, this work explored the thermal and flow characteristics for the steel-truss natural draft dry cooling systems with four typical engineering tower configurations. By numerical simulation, the pressure, flow, and temperature contours were analyzed, then air mass flow rates and heat rejections were calculated and compared for the local air-cooled sectors and overall steel-truss natural draft dry cooling systems with those four tower configurations. The results present that tower 2 with the conical/cylindrical configuration had slightly lower heat rejection compared with tower 1 with the traditional hyperbolic configuration. Tower 3 with the hyperbolic/cylindrical configuration showed better thermo-flow performances than tower 1 at high crosswinds, while tower 4 with the completely cylindrical configuration appeared to have much reduced cooling capability under various crosswind conditions, along with strongly deteriorated thermal and flow behaviors. As for engineering application of the steel-truss natural draft dry cooling system, the traditional hyperbolic tower configuration is recommended for local regions with gentle wind, while for those areas with gale wind yearly, the hyperbolic/cylindrical integrated cooling tower is preferred.

Limestone-gypsum wet flue gas desulfurization (WFGD) often produces a certain amount of wastewater with complex water quality and heavy metal pollution which should be treated properly before release. Spaying the desulfurization wastewater into flue duct and using exhausted flue gas heat for evaporation is a promising and economical technology for achieving zero wastewater discharge in thermal power plant. To enable a more in-depth understanding on evaporation of FGD wastewater spray, a visual wind tunnel test rig based on the atomized droplet laser measuring system was built to reveal the impact factors on droplet thermal-fluid behavior. The dominant impact factors such as compressed air pressure and flow rate in air-blast spray nozzle, hot air temperature and velocity in the evaporation tunnel were analyzed to discuss the droplet size distribution and evaporation performance through alternating operate condition. A discrete mathematical model that combines both Eulerian and Lagrangian framework was established to validate the experiment result. It is concluded that introducing high pressure compressed air into the nozzle can contribute to the dispersion of droplets and enhance the evaporation rate. Proper flow rate in spray nozzle is required to avoid incomplete droplets evaporation. Air temperature and velocity in the evaporation tunnel apply positive impact on droplet size distribution and evaporation performance. Numerical simulation results of both dominant factors impact on evaporation behavior and total evaporation rate showed consistency with the experimental outcome.

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This paper presents a numerical study that aims at investigating the effects of different parameters on the dynamic performance of single and multi-layer encapsulated phase material (PCM) thermocline tanks. A transient, one-dimensional, two-phase, concentric-dispersion model is formulated to evaluate such performance. Encapsulated paraffin waxes having different melting-points are used as PCMs, with water as heat transfer fluid. Comprehensive comparisons between single-PCM and multiple-PCMs systems are numerically analyzed first. Second, the effects of the PCM volume fraction (VF) and the inverse Stefan number have been discussed. The results show that among the various cases the single-PCM70 system has the highest performance in terms of charging and discharging efficiency, followed by a multiple-PCMs system with average performance. Compared with the PCM40 case, the PCM70 case has a 29% increase in the output energy from the system. The VF of PCMs influences the system output, both in terms of energy storage and release, the heat storage period and the total energy stored increased by 4.5%, when the VF of the PCM70 increases from 33.33% to 50%, respectively. Furthermore, it increases the system’s overall efficiency and total utilization ratio by 13.7% and 25%, respectively, when compared to the arrangement in which the PCM40 occupies 50% of the total bed height. The effect of the inverse Stefan number has a significant impact on the system’s utilization ratio. Compared with all other 3-PCM systems, the scenario with the lowest inverse Stefan number in the middle PCM has the highest charging and discharging efficiencies of 83.9% and 80.8%, respectively. The findings may be beneficial for the design and optimization of packed-bed tanks.