## 1 Introduction  
The vapor phase is generally converted into the liquid phase during condensation. The condensate accumulates on the heat transfer surface and the liquid film becomes thicker and thicker, leading to the increasing of thermal resistance and flow resistance. [PERSON] et al. [1] proposed the concept of \"liquid-separation condensation\" to enhance the condenser performance. The configuration of a liquid-separation condenser (LSC) is shown in Figure 1a. The condensate can be promptly removed by the vapor-liquid separator in the headers. To deal with the alleviated mass flow rate due to the liquid drainage, the flow area should be shrunk accordingly to keep the pace of variations in mass flux. In this way, the thickness of the liquid film is largely reduced and the vapor quality is significantly improved, which finally enhances the heat transfer coefficient (HTC), as shown in Figure 1b. Researchers have verified the superiorities of LSC. [PERSON] [3] theoretically found that HTC of LSC can be 34.6% higher and the pressure drop can be 74.4% lower than the conventional condenser. [PERSON] et al. [4] experimentally confirmed that when the mass flux is higher than 590 km/(m\({}^{2}\)-s), LSC has a higher heat transfer coefficient and 30.5-52.6% lower pressure drop, simultaneously. They further pinpointed that LSC has superior comprehensive performance in terms of penalty factor and minimum entropy generation number [5]. [PERSON] et al. [6] discovered that the condenser inserted with a T-junction unit can improve the heat transfer capacity by approximately 5.1%. At the level of the thermal systems, LSC also exhibits its advances in air conditioning systems, heat pump, and organic Rankinecycle (ORC). [PERSON] et al. [7] found that the Energy Efficiency Ratio (EER) at cooling mode and Coefficient of Performance (COP) at heating mode in an air conditioning with LSC are 9.8% and 7.3% higher than these in baseline system, respectively. They further pointed out that using LSC can reduce avoidable exergy destruction of the compressor by 45.5% [8]. [PERSON] et al. [6] found that the refrigeration system with LSC results in a higher COP by 6.6% compared to a conventional condenser. [PERSON] et al. [9] revealed that the heat pump with LSC has a higher COP and lower power consumption. [PERSON] et al. [10] concluded that the ORC with LSC achieves a 21.43% lower average electricity production cost than conventional ORC. In short, liquid-separation condensation is a promising technology that enables the improvement of both the condenser performance and thermal system efficiency. As one of the essential parameters, the vapor quality (\(x\)) largely determines HTC during condensation. The higher the vapor quality is, the higher the HTC becomes. In principle, for a superior HTC in LSC, it is preferable to have a high vapor quality that is close to one after the vapor-liquid separation. Therefore, the performance of the liquid-separation unit that dominates the redistributions of vapor quality and mass flow rate is vital to LSC. More attention should be paid to the liquid-separation unit. Up to now, only two kinds, namely the T-junction header and the orifice-baffle header, are extensively employed in LSC. LSC with a T-junction header is based on the differential inertia force of the liquid and vapor. It was proposed by [PERSON] et al. [11]. [PERSON] et al. carried out a comprehensive study on this T-junction header, including a visualization experiment [12], theoretical model [13] and the CFD model [14]. They found that the liquid drainage ratio (\(F_{\text{L}}\)) can be 100% at low inlet mass flux, and it reduces with the increasing of the inlet mass flux or inlet quality. However, in the T-junction header, the liquid and vapor can only be separated one, which limited the improvement of HTC in LSC. Alternatively, the vapor-liquid separation in the orifice-baffle header is on the basis of gravitation force.