# Experimental Study of a Novel Prototype of Dual-Cycle Two-Phase Cooling System for a Data Cabinet
## 2 Description of the Dual-Cycle Two-Phase Cooling System
As the outdoor temperature rises, the FC alone becomes insufficient to meet the heat dissipation needs, prompting the chiller unit to supplement the cooling capacity, thereby shifting the system into hybrid cooling mode. If the outdoor temperature continues to increase beyond a certain threshold, the FC is bypassed using a three-way valve, directing the two-phase working fluid directly into the PHE. At this stage, the entire cooling capacity is supplied by the chiller unit, marking the transition to full chiller cooling mode. Both the PCTCS and PBTCS are outfitted with FCs of uniform specifications, each possessing a heat transfer area of approximately 45 m\({}^{2}\). The condenser fans of the FC are adjustable through a frequency converter, with a maximum output of 250 W. An exhaustive account of the equipment and instrumentation is presented in Table 2. For precise measurement of the system's operational pressure, several pressure sensors have been strategically placed. Specific parameters and locations of these sensors are depicted in Figure 1 and elaborated upon in Table 3. For a refrigerant in a two-phase state, the \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameter** & **Regular Cold Plate** & **Microchannel Cold Plate** \\ \hline W\({}_{\text{c}}\) (mm) & 1 & 0.1 \\ W\({}_{\text{f}}\) (mm) & 1 & 0.1 \\ H\({}_{\text{c}}\) (mm) & 2 & 3 \\ H\({}_{\text{b}}\) (mm) & 2 & 2 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Cold plate internal dimensions. Figure 3: Internal structure of the server and cold plate evaporator: (a) server internal structure; (b) internal structure of cold plate evaporator. corresponding saturation temperature can be determined from its pressure. Taking the external loop reservoir of the PCTCS in the table as an example, the pressure is denoted as p\({}_{203}\), and the temperature calculated from this pressure is represented as T\({}_{203}\). This temperature represents the lowest temperature point in the entire refrigerant loop. Symbol P\({}_{101}\) is the inlet pressure of the liquid phase manifold. Because the measurement point is the liquid phase, the actual refrigerant temperature cannot be obtained by pressure conversion. The numbering convention is as follows: 1 xx represents the measurement points in the internal cooling loop for chip cooling; 2 xx represents the measurement points in the external cooling loop for chip cooling; and 3 xx represents the measurement points in the backplane cooling loop. Given the energy-saving potential of the DTCS, it is imperative to establish an energy-saving evaluation model. The cooling system has no water loss, so its water usage effectiveness (WUE) is zero; power usage effectiveness (PUE) is an index used to evaluate the energy efficiency of a data center and is the ratio of the total energy consumption of a data center to the energy consumption of IT devices. The total energy consumption profile of data centers predominantly comprises the following three components: IT equipment power, cooling system, and losses in supply and distribution [37; 38]. Other aspects like lighting and fire control system power consumption are comparatively minor and can be considered negligible. The coefficient of performance (COP) of each cooling system is calculated by dividing the cooling capacity by the power. \[\text{PUE = }\frac{P_{DC}}{P_{\text{IT}}}\ =\ \text{pPUE}+\frac{P_{other}}{P_{ \text{IT}}}, \tag{1}\]