# Experimental Study of a Novel Prototype of Dual-Cycle Two-Phase Cooling System for a Data Cabinet
## 3 Results and Discussion  
### Chip Temperature Distribution and Heat Transfer Temperature Difference  
Figure 4 illustrates the temperature performance of server chips at different locations under varying, set control temperatures. During the testing, all servers were maintained at full-load operation. The cooling system ensured the stable operation of all servers, with no significant correlation between chip temperature and the server's position height. Specifically, when the temperature of the reservoir T\({}_{203}\) was set at 48 \({}^{\circ}\)C, the chip temperature remained stable at approximately 76 \({}^{\circ}\)C, with temperature fluctuations within all servers controlled within 2 \({}^{\circ}\)C. Additionally, for the two CPU chips within the same server, despite temperature differences, there was no consistent pattern of the first or second chip exhibiting persistently higher temperatures, demonstrating good temperature uniformity. Unlike water-cooled systems that absorb chip heat through sensible heat, two-phase cooling systems absorb heat primarily through a phase change process, during which the temperature remains constant. Simultaneously, it can be observed that as the temperature of the reservoir T\({}_{203}\) increases, the chip temperature also gradually rises, but the increase in chip temperature is less than the increase in the set control temperature. The temperature of the external loop reservoir T\({}_{203}\) is maintained at a set point by adjusting the speed of the variable frequency fans. Figure 5 illustrates the T-Q diagrams of the cooling system at reservoir temperatures of 28 \({}^{\circ}\)C and 48 \({}^{\circ}\)C. In this system, the heat transfer temperature difference is primarily divided into the following three parts: the temperature difference between the chip and the cold plate \(\Delta\)T\({}_{1}\), the heat loss within the cooling system (i.e., fluid heat loss) \(\Delta\)T\({}_{2}\), and the heat loss between the outdoor condenser and the outdoor environment \(\Delta\)T\({}_{3}\). \begin{table}
\begin{tabular}{c c c} \hline \hline
**Name** & **Parameter** & **Microchannel Cold Plate** \\ \hline Temperature & T & 0.14 \({}^{\circ}\)C \\ Differential pressure & \(\Delta\)p & 0.3\% \\ Mass flow rate & \(\dot{m}\) & 0.104 kg/s \\ Cooling capacity & Q & 4.36\% \\ Coefficient of performance & COP & 7.12\% \\ Partial power usage effectiveness & pPUE & 0.26\% \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Uncertainties of parameters in the experimental tests. From the figure, it can be clearly observed that the temperature difference between the CPU core temperature T\({}_{\text{CPU}}\) and the evaporation temperature T\({}_{102}\), is relatively large. This temperature difference encompasses multiple heat transfer processes, including the conductive temperature difference from the chip core to the package shell, the heat transfer temperature difference of the thermal interface material, and the heat exchange temperature difference of the cold plate. By comparing Figure 5b,c, it is found that the \(\Delta\)T\({}_{1}\) of the microchannel cold plate is reduced by 3.6 \({}^{\circ}\)C compared to a regular cold plate, indicating that optimizing the cold plate structure can effectively reduce this part of the heat transfer temperature difference. It is worth noting that when the reservoir temperature T\({}_{203}\) is increased from 28 \({}^{\circ}\)C to 48 \({}^{\circ}\)C, the heat transfer temperature difference \(\Delta  
pressure leads to a corresponding decrease in saturation temperature, and this pressure change is more sensitive to low-pressure working fluids. At the same time, it was found that when the reservoir temperature T\({}_{203}\) is increased to 48 \({}^{\circ}\)C, the heat transfer loss of the cooling system fluid \(\Delta\)T\({}_{2}\) is significantly reduced, indicating that increasing the saturation temperature helps to reduce the temperature loss caused by two-phase flow resistance.