Investigating the In-Flow Characteristics of Multi-Operation Conditions of Cross-Flow Fan in Air Conditioning Systems

Abstract

Cross-flow fans are widely used in numerous applications such as low-pressure ventilation, household appliances, laser instruments, and air-conditioning equipment. Cross-flow fans have superior characteristics, including simple structure, small size, stable airflow, high dynamic pressure coefficient, and low noise. In the present study, numerical simulation and experimental research were carried out to study the unique secondary flow and eccentric vortex flow characteristics of the internal flow field in multi-operating conditions. To this end the vorticity and the circumferential pressure distribution in the air duct are obtained based on the performed experiments and the correlation between spectral characteristics of multiple operating conditions and the inflow state is established. The obtained results show that when the area of the airflow passage decreases while the area of the eccentric vortex area gradually increases, then the airflow of the cross-flow fan decreases, the outlet expands, and the flow pattern uniformity reduces. It was found that wakes form in the vicinity of the blade and the tail of the volute tongue, which generate pressure pulsation, and aerodynamic noise. The pressure distribution along the inner circumference shows that the total minimum pressure appears in the eccentric vortex near the volute tongue and the volute returns near the zone. Moreover, it was found that the total pressure near the eccentric vortex is significantly smaller than that of the main flow zone. As the flow rate decreases, the pressure pulsation amplitude of the eccentric vortex region significantly increases, while the static and total pressure pulsation amplitudes are gradually increased. Close to the eccentric vortex on the inner side of the blade in the volute tongue area, total pressure is low, total pressure on the outside of the blade is not affected, and pressure difference between the inner and outer sides is large. When the flow rate of the cross-flow fan is 0.4 Qd, there is no obvious peak at the harmonic frequency of the blade passage frequency. This shows that the aerodynamic noise is caused by the main unstable flow.

Comparative Evaluation of High-Speed Bearingless Cross-Flow Fan Designs for Lithography Excimer Lasers

“…From a fluid dynamic point of view, the CFF is characterised by its complex, nonaxisymmetric flow profile. It is defined by a double passage of air through the rotating blades and the formation of an eccentric vortex within the impeller [19][20][21][22][23][24]. In the literature, CFFs are referred to as "low-pressure fans" or "velocity generators", as they do not generate high static pressure [25].…”

Multi-Objective Optimization for the Radial Bending and Twisting Law of Axial Fan Blades

“…For this reason, a multi-objective evolutionary algorithm is required to return a set of promising solutions. This study uses the non dominated sorting genetic algorithms with elite strategy (NSGA-II) to solve the global optimization problem [29]. We take the blade parameters (β 0 , β 1 , θ 0 , θ 1 , A, B) of the fan as optimization variables and the fan performance parameters (ψ OPT , η OPT ) as the optimization objective.…”

Supercritical Operation of Bearingless Cross-Flow Fan

“…CFF rotors have a distinctive large length-to-diameter ratio and consist of several thin blades arranged in a circular manner to achieve the optimal fluid dynamic performance [7][8][9]. The long and thin blades result in a low mechanical bending stiffness.…”