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[en] Highlights: • Field test was conducted on high-level cooling tower under crosswind conditions. • Inflow air uniformity coefficient decreases with the rising of crosswind velocity. • The uniformity coefficient decreases to 0.61 and 0.49 under θ1 = 5° and θ2 = 35°. • In 3.74 m/s, the ventilation rate reduces by 30.13% under 5° condition. • The ventilation performance is better under 5° condition. - Abstract: Field test was performed on the high level water collecting wet cooling towers (HWCTs) of a 1000 MW unit to investigate ventilation performance under crosswind conditions, the circumferential inflow air distribution rules and ventilation rate were analyzed in this paper. The test results manifest that crosswind destroys the uniformity of circumferential inflow air, increases the wind velocity in the windward side, and reduces wind velocity in the lateral and leeward side. Moreover, the uniformity coefficient of circumferential inflow air and ventilation rate continuously decrease with the increasing of crosswind velocity. In this study, θ represents the angle between cross walls and crosswind direction. When crosswind velocity reaches to 3.74 m/s, the uniformity coefficient decreases to 0.61 and 0.49 under θ1 = 5° and θ2 = 35°. Compared with 0.28 m/s condition, the ventilation rate reduces by 30.13% under θ1 = 5° and 34.36% under θ2 = 35°. Additionally, at the same crosswind velocity, the smaller the θ is, the better the ventilation performance becomes. Compared with θ2 = 35°, the uniformity of circumferential inlet air is better and the ventilation rate is larger than that under θ1 = 5° condition.
[en] This paper presents a GPC-PID control strategy for a cooling-coil unit in heating, ventilation and air conditioning systems. By analysis of the cooling towers and chillers, different models in the occupied period are considered in each operating condition. Because of the complication of components, well tuned PID controllers are unsatisfied, and the results are poor over a wide range of operation conditions. To solve this problem, a GPC-PID controller with hierarchical structure is proposed based on minimizing the generalized predictive control criterion to tune conventional PID controller parameters. Simulation and experiments show that the proposed controller is able to deal with a wide range of operating conditions and to achieve better performance than conventional methods
[en] An assessment of the effects of visible cooling tower plumes on the local environment can be a necessary part of any proposal for a new large industrial process. Predictions of the dispersion of plumes from cooling towers are based on methods developed for chimney emissions. However, the kinds of criteria used to judge the acceptability of cooling tower plumes are different from those used for stack plumes. The frequency of long elevated plumes and the frequency of ground fogging are the two main issues. It is shown that events associated with significant plumes visibility are dependent both on the operating characteristics of the tower and on the occurrence of certain meteorological conditions. The dependence on atmospheric conditions is shown to be fairly complex and simple performance criteria based on the exit conditions from the tower are not sufficient for assessments. (author)
[en] In this work, an experimental and a comparative study on terms of tower characteristics (KaV/L), water to air flow ratio (L/G) and efficiency for two film type packings are presented for a wide range of (L/G) ratio from 0.2 to 4. The packings used in this work are vertical corrugated packing (VCP) and horizontal corrugated packing (HCP). The obtained results showed that the performance of the cooling tower is affected by the type and arrangement of the packings. Also, the tower performance showed a decrease with an increase in the (L/G) ratio as is also observed in other types of cooling towers. The results showed the tower with vertical corrugated packing (VCP) has higher efficiency than the one with horizontal corrugated packing (HCP)
[en] A data-driven approach is utilized to model a chiller plant that has four chillers, four cooling towers, and two chilled water storage tanks. The chillers have varying energy efficiency. Since the chiller plant model derived from data-driven approach is nonlinear and non-convex, it is not practical to solve it by using the traditional gradient-based optimization algorithm. A two-level intelligent algorithm is developed to solve the model aiming at minimizing the total cost of the chilled water plant. The proposed algorithm can effectively search the optimum under the non-convex and nonlinear situation. A simulation case is conducted and the corresponding results are discussed. - Highlights: • Development of a data-driven based model of a complete chiller plant. • A two-level intelligent algorithm is proposed to optimize the chiller plant which is non-convex and nonlinear problem. • A simulation is conducted to verify the performance of the model and algorithm. • 14 percent of energy saving can be achieved with proposed method
[en] This paper presents a model-based optimization strategy for the condenser water loop of centralized heating, ventilation and air conditioning (HVAC) systems. Through analyzing each component characteristics and interactions within and between cooling towers and chillers, the optimization problem is formulated as that of minimizing the total operating cost of all energy consuming devices with mechanical limitations, component interactions, outdoor environment and indoor cooling load demands as constraints. A modified genetic algorithm for this particular problem is proposed to obtain the optimal set points of the process. Simulations and experimental results on a centralized HVAC pilot plant show that the operating cost of the condenser water loop can be substantially reduced compared with conventional operation strategies
[en] Highlights: • The cooling performance of a NDDCT under crosswind condition was investigated. • The resistance of radiators was simulated using a viscous force based equation. • A gentle breeze or stronger wind may influence the cooling performance of a NDDCT. • Vortices and circumferential non-uniformity are the main degrading factors. • An enclosure approach to cooling efficiency enhancement is found to be effective. - Abstract: Cooling performance of a natural draft dry cooling tower degrades in presence of crosswind. Upon an in service natural draft dry cooling tower of a 660 MW unit in China, a computational fluid dynamics approach with validation is adopted to investigate the cooling performance at various wind speeds. The first order viscous force based resistance mechanism is used in simulating the air flow resistance for the radiators. Numerical results confirm previous findings that the cooling performance of the natural draft dry cooling tower degrades with the increment of wind velocity when wind velocity is higher than 4 m/s, but the performance reduction is relatively less. The circumferential non-uniform ventilation and the vortices inside the tower contribute the most to the degrading of the cooling performance when crosswind is present. To enhance the overall cooling performance, an enclosure with an opening at the windward side is proposed to increase the pressure level outside the side and back radiators. Numerical results show that such an enclosure could enhance the cooling performance at all investigated wind speeds, with 36% increase of the ventilation rate and about 7 °C decrement of the cycling water temperature at 20 m/s.
[en] Cooling towers are one of the biggest heat and mass transfer devices that are in widespread use. In this paper, we use a detailed model of counter flow wet cooling towers in investigating the performance characteristics. The validity of the model is checked by experimental data reported in the literature. The thermal performance of the cooling towers is clearly explained in terms of varying air and water temperatures, as well as the driving potential for convection and evaporation heat transfer, along the height of the tower. The relative contribution of each mode of heat transfer rate to the total heat transfer rate in the cooling tower is established. It is demonstrated with an example problem that the predominant mode of heat transfer is evaporation. For example, evaporation contributes about 62.5% of the total rate of heat transfer at the bottom of the tower and almost 90% at the top of the tower. The variation of air and water temperatures along the height of the tower (process line) is explained on psychometric charts
[en] Highlights: • Self-adaptive Jaya algorithm is proposed for optimal design of thermal devices. • Optimization of heat pipe, cooling tower, heat sink and thermo-acoustic prime mover is presented. • Results of the proposed algorithm are better than the other optimization techniques. • The proposed algorithm may be conveniently used for the optimization of other devices. - Abstract: The present study explores the use of an improved Jaya algorithm called self-adaptive Jaya algorithm for optimal design of selected thermal devices viz; heat pipe, cooling tower, honeycomb heat sink and thermo-acoustic prime mover. Four different optimization case studies of the selected thermal devices are presented. The researchers had attempted the same design problems in the past using niched pareto genetic algorithm (NPGA), response surface method (RSM), leap-frog optimization program with constraints (LFOPC) algorithm, teaching-learning based optimization (TLBO) algorithm, grenade explosion method (GEM) and multi-objective genetic algorithm (MOGA). The results achieved by using self-adaptive Jaya algorithm are compared with those achieved by using the NPGA, RSM, LFOPC, TLBO, GEM and MOGA algorithms. The self-adaptive Jaya algorithm is proved superior as compared to the other optimization methods in terms of the results, computational effort and function evalutions.
[en] A thermodynamic analysis of the counter flow wet cooling tower (CWCT) is performed in this paper. Both energy and exergy formulations are developed and validated for the system. Four types of exergy transfer processes occurring inside the CWCT are investigated schematically. A parametric study is conducted under various operating conditions in order to investigate the effects of thermal efficiency and water-to-air ratio on the exergy performance of the CWCT. Unlike past studies, the transiting exergy contained in the inlet and outlet water is not considered. It is found that the exergy efficiency is always less than 25%. The exergy parameters including evaporation water loss, exergy efficiency, exergy input, internal and external exergy losses are very sensitive to the thermal efficiency when it is very close to 1.0 at lower water-to-air ratios. - Research highlights: → We model counter flow wet cooling towers and make a detailed exergy analysis. → Four types of exergy transfer processes are investigated schematically. → Only a small part of exergy input, less than 25%, is effectively utilized.