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Summary: The evaporative cooling technique is an efficient approach for cooling application. This study aims to establish a performance evaluation method to advance the appropriate design for multistage indirect evaporative cooling systems. A mathematical formulation has been developed for the indirect evaporative cooler (IEC). After the validation, the mathematical model was used to analyze the evaluation criteria by considering the simultaneous influence of the cooling effectiveness, the pressure drop, and the cooling capacity of the multistage IEC operating in two modes. The Mode‐1 IEC is a conventional counterflow unit, while the Mode‐2 IEC employs a regenerative M‐cycle arrangement. The IECs are operated in a tandem arrangement. The multistage system is capable of improving the cooling performance and reducing the outlet air temperature. In addition, the multistage system displays a higher pressure drop resulting in a lager consumption of fan power. The analysis of performance evaluation criteria indicates that the appropriate maximum stage is suggested to be three‐stage and two‐stage for the Mode‐1 and the Mode‐2 IEC, respectively. [ABSTRACT FROM AUTHOR]

• A counter-flow hollow fiber membrane-based evaporative cooler is proposed. • A numerical model is established and validated by experimental data. • The regression models for performance prediction are derived by response surface methodology. • The desirability function is adopted to perform multi-objective optimization. • The accurate regression models can facilitate the regional applicability analysis. The proposed hollow fiber membrane-based evaporative cooler (HFMEC) is expected to be an alternative to the conventional direct evaporative cooler because of its advantages such as the isolation of air from liquid water and the large specific surface area. For the common counter-flow HFMEC with many influencing parameters, it is a bit laborious or even incompetent to rely on experiment or numerical simulation for the parametric study and optimization. Therefore, this study aims to develop accurate and rapid performance prediction models for the proposed HFMEC with the statistical method. An experimental test system for a counter-flow HFMEC was set up. 120 sets of simulations were carried out based on the experimentally validated numerical model and the response surface methodology. Five accurate and practical empirical equations were derived using simulated data: the considered eight input factors consisted of four operating parameters and four membrane module design parameters; the five output responses included the outlet air temperature, outlet air relative humidity, saturation effectiveness, cooling capacity per unit volume, and COP. These simplified equations were adopted to facilitate parameter sensitivity analysis and multi-objective optimization. A case study on the regional applicability of the counter-flow HFMEC demonstrated the ability of the derived equations to conveniently make performance predictions. The results indicated that the regression models could contribute to the rapid performance prediction of the counter-flow HFMEC, aiding in optimization and design. [ABSTRACT FROM AUTHOR]

The counter-flow hollow fiber membrane-based direct evaporative cooler (MDEC) was proposed as an energy-efficient and hygienic air cooling solution. The random sequential addition algorithm was used to simulate the randomness of fiber distribution within the MDEC in engineering practice. 3D numerical models were developed with a computational domain determined as a hexagonal prism containing multiple fibers. The experimentally validated model depicted the air state variation along the path under regular and random fiber distributions. The differences in wet-bulb effectiveness (ε wb) and coefficient of performance (COP) of MDEC with two configurations, regular and random fiber distributions, were compared for different packing fractions and air flow rates. Furthermore, dimensionless correlations for the shell-side friction factor (f), Nusselt number (Nu), and Sherwood number (Sh) were derived to generalize the results to other hollow fiber membrane modules employed in liquid/gas systems. The results showed that the channel flow effect and dead zone under the random configuration worsened the heat and moisture handling performance of MDEC. Compared with the regular configuration, both Nu and Sh were degraded by 11.6–55.6%, but f was desirably reduced by 28.8–49.8%. Balancing cooling capability and energy efficiency, a regular configuration with moderate packing fraction was more beneficial for engineering practice. • The counter-flow hollow fiber membrane module is proposed for evaporative cooling. • Random sequential addition algorithm is used to represent the randomness of fiber distribution. • 3D models with different fiber configurations and packing fractions are developed. • Regular fiber distribution with moderate packing fraction enables efficient cooling and energy saving. • Compared to regular distribution, shell-side Nu , Sh , and f are all reduced in random distribution. [ABSTRACT FROM AUTHOR]

The hollow fiber membrane-integrated evaporative cooler (MEC) is considered as a promising strategy for space air conditioning applications. For a counter-flow MEC, the appropriate fiber specification and flow configuration need to be identified to improve its comprehensive performance. A numerical model was developed to capture the coupled heat and mass transfer process, and its feasibility was verified by measured data. The influence of fiber specifications and flow configuration on its cooling, space-saving, energy and water conservation performance were investigated. The results revealed that a reasonable fiber specification required a packing fraction of about 0.1 and a length slightly longer than the air channel's entrance length, while the inner diameter and membrane thickness should be determined based on the priority index. The flow configuration of air flowing via shell-side and water going through tube-side was more suitable for counter-flow MEC, which was more energy efficient while maintaining cooling ability. In addition, the contribution of each component's resistance to the total heat and mass transfer resistance would fluctuate as the influencing factors changed. In general, the total heat transfer resistance was dominated by the air-side convective resistance, while the main contributor to the total mass transfer resistance was the membrane resistance. • The counter-flow hollow fiber membrane module is proposed for evaporative cooling. • A numerical model is developed and validated with experimental measurements. • The composition of the heat and mass transfer resistance is quantified. • Appropriate fiber specification and flow configuration are determined. [ABSTRACT FROM AUTHOR]

[Display omitted] • Vacuum-assisted hollow fiber membrane technology expands evaporative cooling applications. • A numerical model was developed and validated with experimental data. • Effects of operating parameters and membrane specifications on overall performance were studied. • Low shell-side pressure contributed to the improved performance, with COP up to 13.6. • The design insights of key parameters and future research directions were proposed. Conventional direct evaporative cooling systems suffer from persistent issues like air–water cross-contamination, mold growth, and scaling of paddings. Moreover, their widespread application in humid climates is hindered by ambient air conditions. This research presents a promising solution in the form of a vacuum-assisted hollow fiber membrane-based evaporative water cooler (VMEWC). It shifts from relying on air state to vacuum pressure for cold water production. A numerical model was established to reflect the coupled heat and mass transfer characteristics, employing Knudsen diffusion to describe water vapor migration within membrane pores. Experimental tests were performed on the constructed VMEWC system, revealing strong alignment between simulation and measured data, with a 2.2 % error in outlet water temperature predictions. Numerical studies explored the effects of six parameters (inlet water temperature, water velocity, shell-side pressure, fiber length, fiber inner diameter, and overall membrane structure parameter) on VMEWC's outlet water temperature (T w 2), cooling capacity per unit volume (Q v), and coefficient of performance (COP). The results emphasized that elevated inlet water temperature, reduced shell-side pressure, and a large overall membrane structure parameter effectively enhanced the overall performance of VMEWC. Under specific conditions, Q v and COP reached impressive values of 3753.1 kW/m3 and 13.6, respectively. This work provides a novel and practical perspective, offering references for advancing efficient and sustainable refrigeration technologies. [ABSTRACT FROM AUTHOR]

Evaporative cooling systems face limitations in producing cold water due to their dependence on ambient air conditions, air-water cross-contamination, and large equipment size. This study introduces a vacuum-assisted hollow fiber membrane integrated evaporative water cooler as a potential solution. To facilitate its deployment in applications such as building air conditioning and industrial processes, a robust design optimization framework was constructed. A numerical model was established and experimentally verified. Combining the response surface method, three regression models were derived for convenient performance prediction. The six input design parameters encompass operating conditions and membrane specifications. The three output performance metrics are outlet water temperature, coefficient of performance, and cooling capacity per unit volume. Multi-objective optimization using a genetic algorithm, under two inlet water temperature conditions, yielded well-balanced cooler designs with superior cooling performance, energy efficiency, and compactness. The regression models demonstrated high prediction accuracy, with R 2 surpassing 0.93. Compared to the original designs, the parameter combinations identified through the ideal point method realized over 40 % reduction in outlet water temperature, over 66 % increase in coefficient of performance, and over 138 % enlargement in cooling capacity per unit volume. Furthermore, validation of the obtained Pareto fronts confirmed the practical reliability of the design references. [Display omitted] [ABSTRACT FROM AUTHOR]