## 1 Introduction
The results show that the spatial distribution of small drops was improved for larger contact angles, and thus the thermal performance was improved. Improved and more comprehensive modeling of full DWC for a vertical smooth surface was introduced by [PERSON] et al. [20]. In the analysis, the model considers sensible heat transfer through both drops and bare surfaces. The coexistence of DWC and FWC areas on the condensing surface is an alternate method of achieving surface renewal. This can be achieved by inserting hydrophilic regions between hydrophobic regions. Surface renewal within the DWC region is caused by drops reaching the maximum size and then sweeping the area under, as well as drops merging into the neighboring hydrophilic regions. As a result, regions of less thermal resistance occur more regularly and enhance overall thermal performance. [PERSON] et al. [21] have established an analysis for a dropwise-filmwise hybrid system by integrating DWC and FWC models. With the DWC width limiting the maximum radius, the influence of the maximum radius in the DWC region and film thickness in the FWC region have been studied. Another model for dropwise-filmwise condensation of steam on a vertical plate was proposed by [PERSON] and [PERSON] [22]. The model is based on a modification of [PERSON]'s drop size distribution for large drops. Results show that two optimum heat fluxes exist when the drop maximum radius to DWC region width ratio is less than and equal to unity. [PERSON] et al. [23] developed a mathematical model of drop size distribution to analyze drops during DWC. The model combined a power law growth model, an exponentially decaying population model, and a Gaussian probability model for growth variation to characterize different behaviors of DWC with different surface characteristics. Anotherpaper used a CFD commercial package to simulate the condensation heat transfer and droplet behavior and analyze the effect of surface wettability and rotational speed for the inner surface of a dryer paddle [24]. The study used the two-phase volume of the fluid model to show the interface between the phases. The results showed that decreasing the contact angle prompted an increase in heat transfer coefficient because the filmwise condensation turned into dropwise condensation. Alongside the modeling approach, many experimental works have been performed to evaluate thermal performance and sustain DWC heat transfer. One experimental work was conducted by [PERSON] and [PERSON] for vertical copper and mild steel plates near atmospheric pressure [25]. [PERSON] [26] used a micropillar within a hydrophilic condensing surface technique that helped in achieving sustainable DWC. The technique comprises having small spacing between pillars, meaning nucleation and the departure of drops from the top of pillars are achievable. [PERSON] et al. [27] visually investigated the effect of the condensation process on the wettability interval using grooved surfaces. A comparison of the condensate dynamic behavior on a plain hydrophobic surface, a plain hydrophilic surface, a hydrophobic grooved surface, and a hydrophilic surface was conducted. An enhancement of the humid air condensation heat transfer performance was achieved by assessing the wettability interval using a grooved surface. Experimental work on dropwise-filmwise condensation has also been investigated. Enhancement of filmwise condensation was achieved experimentally by distributing horizontally oriented dropwise condensation surfaces [28]. Results show that optimum width exists on two arrangements for coexisting condensation. Another experimental work for dropwise-filmwise on a vertical plate was conducted with and without the presence of non-condensable gases [29]. They concluded that the coexistence of both condensation modes shows better thermal performance only when non-condensable gases are present. The incorporation of hydrophobic and less hydrophobic vertical stripes on tube surfaces was experimentally investigated by [PERSON] et al.