Integrated CFD and Experimental Analysis on Slinger Ring Condensate Discharge Mechanism for Energy-Efficient Window Air Conditioners

Abstract

As global demand for energy-efficient cooling technologies grows, optimizing window air conditioners (WACs) is crucial. This study integrates computational fluid dynamics (CFD) and experimental fluid dynamics (EFD) to analyze condensate transport induced by the slinger ring in a WAC system. To investigate condensate behavior, the WAC domain is divided into six regions based on the slinger ring’s rotational direction and impact. In the initial impact zone, large liquid structures adhere to the slinger ring before breaking into ligaments. In the upward transport region, condensate films rise along the wall due to centrifugal forces, forming short ligaments. In the rebound region, condensate impacts the top surface and transitions into droplets. In the accumulation zone, droplet coalescence occurs in a confined space, leading to localized mass buildup. In the dispersion region, condensate spreads widely due to increased rotational speed. In the splash zone, splashing and wave-like structures form near the reservoir surface. A newly identified mechanism of condensate mass discharge shows that mass ejection is concentrated in four key regions near the condenser coils. These findings offer insights into optimizing a slinger ring design for improved condensate dispersion. Future research should explore airflow variations and alternative slinger ring configurations to enhance WAC performance.

1. Introduction

The worldwide interest in energy-efficient air conditioning systems has led to extensive research on enhancing cooling performance while reducing power consumption. Among various air conditioning technologies, window air conditioners (WACs) remain widely used due to their cost-effectiveness and compact installation, making them an important target for efficiency improvements. To achieve higher cooling performance, manufacturers commonly integrate slinger rings into WAC systems. These rings, positioned around the condenser fan, utilize centrifugal forces to disperse condensate onto the condenser coils, thereby enhancing evaporative cooling and heat transfer efficiency.

The slinger effect, as described by Falkovich et al. [1], explains how condensate droplets sprayed by the slinger ring enhance evaporative cooling on the condenser surface. The process involves liquid breakup, droplet dispersion, and phase change, which leads to localized heat transfer enhancement through condensate film formation and subsequent evaporation. This mechanism aligns with experimental findings by Shen and Bansal [2], Bansal [3], Shen and Fricke [4], who demonstrated that dispersed condensate improves cooling efficiency by lowering the condenser surface temperature and increasing convective heat transfer.

Bansal [3] investigated condensate recirculation through a modified drainage system and found that incorporating a submerged sub-cooler and a slinger mechanism reduced WAC energy consumption by approximately 8%. Similarly, Shen and Bansal [2], Bansal [3], Shen and Fricke [4] conducted controlled psychometric chamber experiments to model the air-side heat transfer enhancement attributed to the slinger ring, estimating multipliers between 1.24 and 1.33. However, their approach relied on empirical correlations rather than a detailed mechanistic analysis of condensate transport, leading to discrepancies of up to 30% between modeled and experimental values.

To better understand the slinger ring’s contribution to cooling performance, researchers have explored the impact of condensate dispersion on forced convection and evaporative cooling efficiency. However, experimental studies alone cannot fully resolve the complex multi-phase interactions governing condensate transport, topology transformation, and mass discharge dynamics in WACs.

In addition to the slinger ring mechanism, several alternative strategies have been explored to enhance WAC efficiency. Researchers have investigated alternative refrigerants to replace conventional cooling fluids, with a focus on reducing environmental impact and improving thermodynamic efficiency (Shen and Bansal [2], Jung et al. [5], Uddin and Saha [6], Devotta et al. [7], Jabaraj et al. [8], Bolaji [9], Naphon [10], Hajidavalloo [11], Sawant et al. [12], Dhamneya et al. [13]). Other studies have examined heat pipes as a means of increasing heat exchange efficiency in compact air conditioning units (Naphon [10]), as well as evaporative cooling systems, which enhance latent heat removal from condenser coils (Hajidavalloo [11], Sawant et al. [12], Dhamneya et al. [13]). Additionally, electronically commutated motor (ECM) fans have been investigated for their ability to optimize airflow and reduce system-wide energy consumption (Bansal [3]). Afaynou et al. [14] and Chen et al. [15] studied the prospect of spray cooling in electronics and energy conversion industries to improve cooling efficiency in electronics and energy. While these alternative approaches have demonstrated potential for incremental improvements in WAC performance, they do not directly address the fundamental role of condensate transport in heat transfer enhancement, which remains a key area for optimization.

Recent efforts have turned to computational fluid dynamics (CFD) simulations to further explore the slinger ring’s impact on WAC performance. Chang et al. [16] introduced computational simulations to evaluate the slinger ring’s effect on forced convection within WACs. Their study demonstrated that multi-phase flow induced by the slinger ring significantly enhances heat transfer performance compared to single-phase models. However, their analysis primarily focused on heat transfer enhancement and lacked a comprehensive investigation into condensate breakup, trajectory migration, and interactions with the condenser surface.

Despite the well-documented benefits of the slinger ring, no prior studies have numerically simulated or investigated the multi-phase fluid flow driven by the slinger ring to analyze condensate spraying mechanisms. The condensate behavior in these systems is highly complex, involving liquid breakup, surface adhesion, centrifugal forces, and air–liquid interactions. Understanding these phenomena is essential for optimizing slinger ring design and improving cooling efficiency.

Given these challenges, a combined approach integrating experimental fluid dynamics (EFD) and CFD is necessary to gain a comprehensive understanding of multi-phase condensate transport in WACs. CFD enables a detailed visualization and quantification of liquid breakup, droplet trajectory, and heat transfer interactions, while EFD provides experimental validation to ensure model accuracy and applicability. By integrating these approaches, this study aims to bridge critical knowledge gaps in slinger ring condensate transport mechanisms and contribute to the development of more energy-efficient WAC systems.

This study aims to conduct an integrated numerical and experimental analysis to investigate the topology transformation and transport of condensate induced by the slinger ring in a WAC system. To achieve this, the feasibility of CFD as a predictive tool for analyzing the multi-phase fluid flow in WACs is evaluated by validating numerical simulations against EFD results. The condensate topologies obtained from CFD simulations are compared with experimental observations to assess regional dependencies in liquid structure formation, ligament breakup, and droplet migration, providing insights into the mechanisms governing condensate transport. Additionally, the mass discharge of condensate near the condenser coils is analyzed to determine its correlation with slinger ring efficiency in dispersing condensate for optimal evaporative cooling. Finally, schematic maps are developed to illustrate condensate transport mechanisms, offering a framework for future slinger ring design optimization aimed at maximizing heat dissipation, reducing compressor workload, and improving the overall energy efficiency of WAC systems.

2. Computational and Experimental Methods

The current study emphasizes the examination of condensate distribution and topologies, which serve as key indicators of the slinger ring’s performance. Consequently, this study disregards the setup for heat transfer in WACs, thus excluding considerations of internal flow dynamics and variations in refrigerant properties within the coils. The CFD and EFD approaches employed in this study follow the methodologies outlined by Chang et al. [16]. Thus, a brief description of these methods is provided below.

2.1. Numerical Methods

The present study considers three-dimensional, unsteady, incompressible, turbulent multi-phase flow within a WAC featuring a slinger ring. This system is governed by the continuity and Reynolds-averaged Navier–Stokes equations in Cartesian tensor form:

$${\displaystyle \frac{\partial \rho }{\partial t}}+{\displaystyle \frac{\partial }{\partial t}}\left(\rho u_i\right)=0$$

(1)

$${\displaystyle \frac{\partial \rho }{\partial t}}\left(\rho u_i\right)+{\displaystyle \frac{\partial }{\partial x_j}}\left(\rho u_i{u}_j\right)=-{\displaystyle \frac{\partial p}{\partial x_i}}+{\displaystyle \frac{\partial }{\partial x_j}}\left[\mu \left({\displaystyle \frac{\partial u_i}{\partial x_j}}+{\displaystyle \frac{\partial u_j}{\partial x_i}}\right)\right]+{\displaystyle \frac{\partial }{\partial t}}\left(-\rho \overline{u_i^{\prime }{u}_j^{\prime }}\right)+F_i$$

(2)

In this formulation, t is time, $x_i$ represents the Cartesian coordinate, $u_i$ denotes the corresponding velocity components, p is the pressure, $\rho$ is the density, $\mu$ is the dynamic viscosity, and $F_i$ corresponds to external forces such as gravity. The $\kappa$-$\omega$ SST turbulence model is employed to close the Reynolds stress term $-\rho \overline{u_i^{\prime }{u}_j^{\prime }}$. The $\kappa$-$\omega$ SST turbulence model was selected due to its capability of resolving near-wall interactions while maintaining stability in free-stream regions. This model effectively captures multi-phase interactions and rotational flow characteristics, which are critical for replicating experimental observations.

The interface between air and condensate is tracked using the Volume of Fluid (VOF) method, a widely used approach for interface capturing [17]. The VOF method ensures accurate interface tracking of condensate transport, capturing liquid breakup and droplet formation, which are validated against experimental observations. The VOF method assigns a volume fraction ($Q_h$) of the hth fluid to two immiscible fluids within a computational cell, ensuring that the total fraction in a cell sums to one $\left({\sum }_{h=1}^n{Q}_h=1\right)$. The fluid distribution is updated at each time step by solving the following transport equation:

$${\displaystyle \frac{\partial Q_h}{\partial t}}+u_i{\displaystyle \frac{\partial Q_h}{\partial x_i}}=0$$

(3)

A cell with $0<Q_{\delta }<1$ indicates the presence of a free surface.

The numerical computation employs a pressure–velocity coupling approach. For the overall solution procedure, the Semi-Implicit Method for Pressure-Linked Equations-Consistent (SIMPLEC) segregated algorithm was employed. For numerical discretization, diffusion terms were treated with a second-order central differencing approach, while convection terms utilized a second-order upwind method. To maintain accuracy, computations adhered to a convergence threshold of ${10}^{-6}$. The simulations were executed in STAR-CCM+, with further methodological specifics documented in its manuals.

This study focuses solely on the outdoor unit and external multi-phase flow to investigate the effect of the slinger ring on the condensate splash mechanism within the WAC, similar to Chang et al. [16]. The computational model and boundary conditions used in this study are shown in Figure 1, with the component specifications and specific boundary conditions provided in

Table 1. Component specifications of outdoor unit [16].

Components	Specifications
Condenser	369 mm (W) × 279.2 mm (H) × 19.77 mm (B)
Condenser fan	Diameter: 123 mm, Number of blades: 7
Slinger ring	Diameter: 133 mm, Depth: 10 mm
Motor	106.6 (D) × 200.0 mm (L)
Compressor	96.4 (D) × 88.2 mm (L)
Outdoor cover	239.33 mm (B) × 435.4 mm (W) × 281.2 mm (H), Number of holes: 83

and

Table 2. Initial and boundary condition for CFDs [16].

Boundaries	Conditions
Inlet	Pressure inlet (atmosphere)
Outlet	Outflow
Condensate supply	Mass flow rate (0.62 kg/h)
Wall	No-slip
Fan speed	1435 rpm
Initial filling height of condensate reservoir	9 mm

, respectively. The density (kg/${\mathrm{m}}^{\mathrm{3}}$) of the condensate and air are 997.56 and 1.18, respectively. The viscosity (Pa·s) of the condensate and air are 997.56 and 1.18, respectively. Consequently, the Reynolds number, calculated using the fan diameter as the characteristic length (Re = $\pi n{D}^2$⁄$\nu$), is $6.3\times {10}^5$.

The present study uses the same grid systems used in [16]. Thus, a brief description of grid systems is provided below. The present grid system is generated using the Cartesian cut-cell method. The front view and side view of the grid system is illustrated in Figure 2a,b. The sliding mesh technique is employed to simulate the rotational motion of the fan and slinger ring, partitioning the computational domain into stationary and moving regions. Figure 2c illustrates the fan, slinger ring, and their interface.

The rotating domain is defined by a smaller cylindrical region that encloses the fan and slinger ring. According to the grid dependence test by Chang et al. [16], a grid size of 11,600,000 cells is adopted to provide detailed flow field data for analyzing the characteristics of the splash phenomena.

2.2. Experimental Test Facility

Identical experimental facilities and operating conditions as [16] were employed. This study, however, conducts a significantly greater number of repeated experiments to meticulously capture the temporal and spatial variations in condensate topologies. This study aims to analyze condensate distribution and topology induced by the slinger ring, focusing solely on the outdoor unit while excluding condenser fins and coils.

Figure 3a presents photographs of the test model, where the slinger ring is mounted on the condenser fan and a reservoir collects the condensate. The experimental setup schematic is shown in Figure 3b. Component specifications and operating conditions match those in the CFD simulations, as detailed in Table 1 and Table 2.

The experiment aims to visually track condensate dispersion induced by the slinger ring, providing insights into its distribution near the condenser coils. A high-speed camera (240 fps, 2532 × 1170 resolution) captures the condensate’s topology changes and splashing behavior.

The second experiment quantifies condensate distribution in each tube to analyze its dispersion on the inner surface near the condenser coils. This measurement serves as a key metric for evaluating the slinger ring’s effectiveness, as the amount of condensate sprayed or adhered to the inner walls and coils directly indicates its efficiency. These experiments help establish the distribution of condensate on planes adjacent to the condenser coils. The regions where condensate mass discharge is most prominent are identified by measuring the mass of condensate on the surface adjacent to the condenser coils. The measurement setup consists of tubes connected to the wall near the condenser coils, where condensate sprayed by the slinger ring is collected. For this purpose, 13 tubes are arranged in rows and 20 tubes in columns. Figure 3c provides a photographic view of the measurement devices equipped with tubes used to capture condensate mass discharge, following the same setup as described by Chang et al. [16].

2.3. Validation

For quantitative comparison, the total condensate mass discharge ($M_T$) is analyzed as it moves through the designated measurement section adjacent to the condenser. $M_T$ serves as a potential barometer to the heat transfer effectiveness of the slinger ring, as noted by Chang et al. [16]. The present study adopts the same methodology of Chang et al. [16] to evaluate the total condensate mass discharged due to the slinger ring. $M_T$ is determined by summing the condensate quantities across all tubes. Subsequently, $M_T$ values are normalized by dividing them by the maximum $M_T$ observed during the longest time periods. The mass discharge ratio ($M_{T,R}$) is determined by normalizing $M_T$ with its maximum value. The normalized time is set relative to the final time of each study.

Figure 4 shows the time histories of $M_{T,R}$ for the present study and Chang et al. [16]’s EFD and CFD. The present CFD and EFD results reveal about the same temporal variation of $M_{T,R}$ with Chang et al. [16]’s EFD and CFD. Namely, during the initial and the steady states, the temporal evolutions of $M_{T,R}$ consist of a fast and linear increase, respectively.

3. Results and Discussion

3.1. Transformation and Migration of the Condensate

To assess the effectiveness of the numerical approach in capturing multi-phase flow behavior in a window air conditioner, a comparative evaluation was conducted using CFD and EFD results. CFD-derived condensate structures were analyzed alongside experimental findings to validate regional transport characteristics.

Figure 5 presents a side-by-side comparison of the WAC domain, illustrating how condensate transitions and disperses within the reservoir under the influence of the slinger ring. The analysis highlights distinct flow behaviors across multiple regions, emphasizing the impact of rotational forces on condensate dynamics. Both the EFD and CFD results demonstrate a regional dependence in the transportation and transformation of the condensate. Thus, in order to analyze in detail the regional dependence of the transformation of the condensate by the slinger ring and enable a detailed comparison of the condensate topologies between EFD and CFD, the entire area is divided into six local regions, as indicated in Figure 4. Accurately resolving regional condensate topology variations is essential for understanding localized transport mechanisms that influence mass discharge efficiency and overall condensate dispersion. Each region exhibits distinct topology transformations, from film stretching and ligament formation to droplet detachment, which directly impact system cooling performance. These regions are divided based on the rotational direction of the slinger ring and its initial impact position on the condensate in the reservoir. Thus, first, the left corner region is denoted as R1.

3.1.1. Region 1

Within region R1, the EFD observed the formation of liquid films and ligaments in R1 during the initial phase, as shown in Figure 6a, where surface tension and viscous forces predominantly influence the development of these structures. These observations are consistent with those reported by Shao et al. [18], who noted that surface tension and viscous forces help maintain the integrity of liquid films and sheets, preventing their deformation and breakup.

The current CFD shows the formation of large liquid structures resulting from the impact of the slinger ring on the condensate in the reservoir, as depicted in Figure 6b. These large liquid structures adhere to the surface of the slinger ring near its lowest position, where it contacts the free surface, leading to the formation of a liquid film, also shown in Figure 6b. This liquid structure in CFD closely resembles that observed in EFD in Figure 6a. The extensive liquid sheet propagates toward the left side of the shroud, suggesting that the condensate propelled by the slinger ring collides with the shroud wall. As the separated liquid sheet disintegrates into ligaments, both EFD and CFD results consistently capture the formation of liquid films and ligaments, which define the condensate topologies in the early stage.

When the time period is close to the steady state, the EFD observations reveal the formation of droplets resulting from the breakup of ligaments, as shown in Figure 6c. It can be inferred that the increased shear forces contribute to the transition of liquid topology from ligaments to droplets. Previous studies [18,19,20,21,22], which explored the transition of liquid structures into droplets, similarly reported that ligament dynamics lead to droplet formation. The present CFD results also clearly depict droplets forming in this region of R1, supporting the EFD findings, as shown in Figure 6d. Thus, the current CFD effectively reconstructs the evolution of the condensate topology in R1.

3.1.2. Region 2

The region of R2 is located above R1 and spans the narrow gap between the slinger ring surface and the shroud wall on the left side. During the initial period, the EFD observed the presence of a liquid film and small ligaments in R2, as shown in Figure 7a. As the flow becomes increasingly unstable and develops strong shear forces, these liquid film structures break down into smaller ligament formations. The CFD results reveal that the condensate film on the left wall is pushed upward, as depicted in Figure 7b. The rotation of the slinger ring generates centrifugal forces that act on the fluid, compressing and pushing the liquid film upward along the shroud wall. This leads to the formation of shorter ligaments from the liquid film. This change in condensate topology occurs earlier in the diverging shape, which facilitates the diffusion and spread of the condensate, as shown in Figure 7b.

At the statistically steady state, the slinger ring predominantly sprays droplets in the R2 region. These droplets impinge on the shroud wall, where they partially cohere and form a liquid film. The behavior of the sprayed droplets and their cohesion on the shroud wall in R2 is almost identically captured by both the EFD and CFD results, as shown in Figure 7c and Figure 7d, respectively. Consequently, the numerical simulation of the condensate topology changes, as well as the region-dependent onset of condensate structure deformation, is in strong agreement with the findings from the EFD.

3.1.3. Region 3

The region of R3 encompasses the upper left quadrant. During the initial period, the EFD observes that the liquid film and cohered condensate from R2 continue to move upward along the wall, as shown in Figure 8a. Some of this condensate reaches the upper left corner, turns right, and eventually falls freely from the left top wall. The transformation and migration of the condensate in R3, driven by the slinger ring, are well represented by the CFD, closely matching the experimental results, as shown in Figure 8b. Specifically, the CFD simulates the impingement of condensate with ligament structures on the top wall and captures the free fall of rebounding droplets, as observed in Figure 8b.

In the steady state, the experimental results show the formation of a thick liquid film on the top wall due to the cohesion of droplets sprayed by the slinger ring, as depicted in Figure 8c. Similarly, the CFD results reveal droplets in this region, replacing the ligaments observed during the initial period, as shown in Figure 8d. Additionally, the CFD shows the appearance of films on the left side wall, aligning well with the experimental observations. However, the formation of the liquid film on the top wall is less distinct in the CFD, likely due to early dissipation caused by numerical factors related to the interface capturing method. Furthermore, the CFD illustrates that droplets, upon impacting the left top corner and top wall regions, rebound from the surface and disperse.

3.1.4. Region 4

In R4, located near the uppermost position of the slinger ring close to the top wall, contraction and diffusion patterns form along the fan’s clockwise rotation. It appears that a significant amount of condensate has already detached from the slinger ring before reaching this region. As a result, there is insufficient condensate to form large liquid structures such as sheets or films on the slinger ring. In this region, the condensate is primarily sprayed as droplets from the slinger ring onto the top wall, where they cohere and accumulate in the narrow gap due to contraction. These accumulated condensates move toward the right side along the slinger ring’s rotational direction, driven by the centrifugal force of the slinger ring and the diffuser effect acting on the fluid. The cohered condensate on the right side of the top wall breaks into ligaments, which eventually form droplets that fall freely.

Both the EFD and CFD results exhibit nearly identical patterns in the transformation and transport of the condensate in R4, as shown in Figure 9a and Figure 9b, respectively. The long liquid film on the top wall, along with the ligaments extending downward from the end of the liquid film, is accurately simulated by the present CFD.

3.1.5. Region 5

The region on the right side, designated as R5, is characterized by a relatively wide space between the slinger ring surface and the right wall of the shroud, as shown in Figure 10. During the initial period, when the fan’s rotational speed is low, gravity predominates over the forces acting on the condensate sprayed by the slinger ring. As a result, the transport range of the condensate is limited to the area near the slinger ring. In this phase, the condensate attached to the slinger ring falls almost freely, moving downward in a vertical direction.

As the rotational speed of the condenser fan increases, the intensifying inertial and centrifugal forces cause the liquid film to separate earlier from the slinger ring surface, forming ligaments. These separated condensates, propelled by the slinger ring, disperse over a wider radial and circumferential range. As a result, the sprayed condensates cover a broader area in R5. Both the EFD and CFD results show nearly identical patterns of ligament and droplet formation from the slinger ring spray, as illustrated in Figure 10a and Figure 10b, respectively.

As the flow becomes more unstable, the liquid structures break down into smaller droplets that travel farther. These droplets eventually reach the region near the right top corner, creating small spots on the shroud surface, as shown in Figure 10. The slinger ring predominantly sprays droplets toward the right side wall, where they adhere upon impact. The adhered droplets coalesce, forming wide and uniformly distributed film structures along the right side wall. Both the EFD and CFD results confirm this behavior, showing nearly identical patterns, as seen in Figure 10a and Figure 10b, respectively.

3.1.6. Region 6

In R6, which covers the right-side bottom region, the initial impact of the slinger ring on the condensate in the reservoir creates a breaking wave-like topology, with droplets observed near the gap between the slinger ring surface and the free surface, as shown in Figure 11a and Figure 11b for the EFD and CFD, respectively. Additionally, the ripple effect on the free surface caused by the slinger ring’s impact is observed in both the EFD and CFD results. As the flow develops, the slinger ring sprays condensate as droplets from its surface flow into the bottom reservoir, as depicted in Figure 11b. This transformation of the condensate by the slinger ring in R6 aligns with the experimental findings. The sprayed droplets impact the free surface, causing splashing in the reservoir. Some droplets also reach the shroud wall, where they eventually cohere and form a liquid film.

The transition from liquid films to ligaments and droplets plays a key role in condensate dispersion, affecting its redistribution, mass discharge efficiency, and system-wide evaporative cooling potential. While liquid films provide continuous surface coverage, their transformation into ligaments and droplets increases the available surface area for evaporation but reduces direct condenser wetting. This transition enhances transport efficiency by facilitating uniform condensate distribution and reducing localized accumulation.

3.2. Condensate Mass Discharge

Figure 12 illustrates the distributions of the mass discharge rate ($M_R$) in the plane near the condenser coils during steady-state operation, showing linearly increasing temporal behavior for both EFD and CFD. The condensate mass discharge crossing this plane occurs mainly in four regions: the left lower side area, left top area, right lower side area, and right bottom area, as depicted in Figure 12a for the EFD results. The occurrence of these regions is associated with the rotational direction of the slinger ring. Consequently, the condensate mass discharge areas are largely confined to these four regions on the plane near the condenser coils within the present experimental timeframe. The current numerical simulation produces a very similar distribution of $M_R$ in the plane near the condenser coils during steady state, closely matching the EFD findings, as shown in Figure 12b.

3.3. Mechanism of the Mass Discharge

As discussed above, the condensate undergoes a topology transformation from liquid films and sheets to ligaments, eventually forming droplets due to the action of the slinger ring. This makes the slinger system a prominent example of the mechanical spray group [23]. Typically, devices in this group use various impacts and disturbances to generate sprays. In this case, the primary mechanisms of condensate deformation are the impacts and blowups caused by the slinger ring, which facilitate the polydispersity of the droplets.

To clearly illustrate the changes in condensate topology caused by the slinger ring, a schematic map of the condensate topology is presented in Figure 13. This map corresponds to the observed condensate topologies in the six local regions, as detailed in Figure 5, Figure 6, Figure 7, Figure 8, Figure 9 and Figure 10, for an integrated study of the EFD and CFD results. Additionally, the mechanisms governing the transportation of condensate for mass discharge are identified in Figure 14, which relate to the distribution of condensate mass discharge near the condenser coils, as shown in Figure 12.

Discharge Zone 1 in Figure 14 primarily corresponds to R1, with its upper boundary overlapping R2, as shown in Figure 12. In this discharge zone, the initial period is dominated by liquid films, sheets, and ligaments, driven by surface tension and viscous forces. At steady state, the behavior is defined by sprayed droplets impinging on the shroud surface due to centrifugal and inertial forces, as depicted in Figure 13. These droplets are splashed and rebounded, contributing to the mass discharge across the plane near the condenser coils, as outlined in Figure 14. In the upper region of Zone 1, corresponding to R2, the condensate mass discharge mechanism is primarily driven by droplet rebound and coalescence, as shown in Figure 14. This region is characterized by a narrow gap between the slinger ring surface and the left side wall, where the cohered condensate accumulates and spreads over time, eventually contributing to mass discharge into the tubes.

Discharge Zone 2 corresponds to R3, near the left top corner, as shown in Figure 13 and Figure 14. The condensate detached from the slinger ring is primarily sprayed as droplets, which then break up into smaller droplets. These smaller droplets adhere to the top corner wall, forming a liquid film that gradually spreads, as depicted in Figure 14. Some droplets rebound from the left top wall, contributing to the mass discharge in this region.

Discharge Zone 3 is located near the right side wall below the top wall, as shown in Figure 14, corresponding to R5, where the condensate topologies consist of droplets and films, as depicted in Figure 13. The slinger ring sprays droplets toward the right side wall, where the droplets adhere after breaking up. Additionally, droplets falling from the cohered condensate on the top wall in R4 are also sprayed toward the right wall by the slinger ring. Over time, the adhered droplets coalesce and accumulate. Notably, the right side wall of the shroud is inclined outward, creating a narrow space near the wall. The accumulated condensate spreads outward in this narrow space, which becomes the primary mechanism for mass discharge in Zone 3, as shown in Figure 14.

Zone 4 of the condensate mass discharge is located in the right bottom region near the free surface of the reservoir, as shown in Figure 12, corresponding to R6 in the topology map in Figure 14. Freely falling and sprayed droplets splash onto the free surface of the reservoir. The splashed condensate then enters the tubes, which serves as the primary mechanism for mass discharge, as depicted in Figure 14. The slinger ring’s impact on the free surface causes the reservoir to overflow, forming a breaking wave in the left bottom corner, as observed earlier in Figure 13, further contributing to the mass discharge. Additionally, cohered condensate films run down the shroud wall due to gravity, accumulating in the left bottom corner. The accumulated condensate in this corner also causes overflowing of the reservoir, contributing to the mass discharge.

In the splash and ejection zones, ligaments are stretched and broken into smaller droplets due to aerodynamic and centrifugal forces, which facilitate more uniform condensate distribution and enhance mass discharge efficiency. Increased condenser wetting due to enhanced condensate dispersion plays a significant role in improving evaporative cooling efficiency. A more uniform distribution of condensate over the condenser surface reduces localized dry spots, enhances latent heat absorption, and lowers the condenser temperature. This ultimately improves system efficiency by reducing the workload on the compressor and decreasing overall power consumption. The distribution of condensate plays a crucial role in improving evaporative cooling efficiency. The slinger ring enhances condensate dispersion across the condenser surface, increasing wetting and facilitating a phase change. This leads to improved heat dissipation, reducing localized hot spots and lowering the overall condenser temperature. As a result, refrigerant cycle losses are minimized, reducing the compressor workload and enhancing system efficiency while lowering power consumption.

The influence of airflow variation on condensate dispersion and evaporative cooling efficiency was observed in both CFD and EFD results. Higher airflow velocities enhanced ligament breakup and droplet dispersion, while lower airflow rates allowed for longer residence time and more sustained evaporation. However, excessive airflow speeds risked premature droplet detachment from the condenser surface, reducing cooling effectiveness. The strong agreement between CFD and EFD results is attributed to the careful selection of turbulence modeling, realistic boundary conditions, and high-resolution grid implementation. The numerical simulations effectively capture mass discharge patterns and condensate behavior, validating the accuracy of the CFD approach.

This study integrates CFD and EFD to provide a comprehensive analysis of condensate transport induced by the slinger ring. While CFD enables detailed visualization of condensate dynamics, EFD serves as an essential validation tool. CFD captures fine-scale condensate breakup, ligament formation, and droplet dispersion, whereas EFD accounts for real-world surface adhesion effects and environmental variability. Minor discrepancies between the two methods were observed, particularly in regions where surface tension and turbulence-induced interactions influenced condensate behavior. These findings highlight the complementary nature of CFD and EFD in studying multi-phase fluid transport in WACs.

4. Conclusions

This study conducted a comprehensive experimental and numerical investigation into the topology transformation and transport mechanisms of condensate induced by the slinger ring in a window air conditioner (WAC). By analyzing six distinct regions within the system, key condensate transport characteristics and underlying physical mechanisms were identified, providing insights into how the slinger ring influences condensate motion.

The results revealed that regional condensate behavior can be classified into six zones, each exhibiting unique flow characteristics. In the initial impact region, large liquid structures adhered to the slinger ring before breaking into ligaments, while in the upward transport region, condensate films were pushed upward along the wall due to centrifugal forces, forming short ligaments. In the rebound region, condensate impacted the top surface and transitioned into droplets, whereas in the accumulation zone, droplet coalescence in a confined space led to localized mass buildup. The dispersion region was characterized by widespread condensate spread due to increased rotational speed, and in the splash zone, splashing and wave-like structures were observed near the reservoir surface.

Furthermore, the mass discharge mechanism was mapped across four key regions near the condenser coils, revealing that droplet impact, coalescence, and ligament breakup played crucial roles in determining condensate distribution. The analysis demonstrated that CFD simulations accurately captured the condensate topology transformations observed in experiments, with a high level of agreement between numerical and experimental results. Additionally, mass discharge analysis confirmed that CFD and EFD results aligned well, with the highest condensate ejection occurring in four dominant discharge regions. To further illustrate the complex transport dynamics, schematic maps and a mechanistic framework were developed, providing a comprehensive visualization of the processes governing condensate transport and discharge. These findings highlight the importance of understanding condensate behavior for optimizing slinger ring design, which directly contributes to enhancing evaporative cooling and improving the energy efficiency of WAC systems.

This study highlights the importance of capturing regional variations in condensate topology to optimize slinger ring performance. A key factor in condensate transport is the transition from liquid films to droplets, which affects both the condensate transport and the condensate dispersion. This transition can be controlled through the use of an optimized slinger ring, enhancing overall system performance. Optimizing the slinger ring improves condensate dispersion, ensuring uniform condenser coil wetting and minimizing localized dry spots, thereby optimizing heat transfer efficiency. Optimizing condensate dispersion improves evaporative cooling efficiency, reduces compressor workload, minimizes refrigerant cycle losses, stabilizes system performance, and lowers power consumption. Additionally, regional variations in condensate behavior highlight the need for precise modeling and validation. While this study provides fundamental insights into condensate transport mechanisms, further research is needed to fully capture the thermal effects and system-wide performance implications.

Future studies should further investigate the advantages of the slinger ring over conventional condensate management methods under varying environmental conditions. Accurately predicting droplet breakup, ligament formation, and condensate dispersion requires advanced multi-phase modeling techniques. Additionally, integrating heat transfer analysis is necessary to fully assess the impact of condensate wetting on cooling performance. The sensitivity of slinger ring performance to geometric and operating variations highlights the need for extensive parametric studies, which require significant computational resources. Future research should focus on refining CFD models for improved accuracy, incorporating detailed thermal interactions, and validating numerical results against a broader range of experimental conditions. Moreover, research on optimizing slinger ring configurations based on different airflow and humidity conditions would further enhance its applicability in real-world WAC systems.

CFD modeling must incorporate airflow tuning strategies to optimize performance under different environmental conditions. Predictive CFD analysis enables virtual prototyping, reducing the need for extensive testing. Challenges in CFD simulations include accurately modeling droplet breakup, ligament formation, and heat transfer interactions. Refining these models and validating them with experimental data will improve predictive accuracy. Exploring alternative designs, such as modified blade geometries, hydrophobic coatings, and adaptive speed control, could further enhance condensate dispersion. AI-driven adaptive cooling technologies will play a crucial role in future WAC advancements, dynamically optimizing system performance based on environmental conditions. These innovations will contribute to more efficient and climate-resilient air conditioning systems. By expanding on this research, the efficiency of WAC systems can be further improved, ultimately contributing to the development of next-generation energy-efficient air conditioning technologies.