EVALUATION OF THERMAL PERFORMANCE IMPROVEMENTS IN 1.5U SERVER OVER 1U SERVER USING CFD 

Electronics cooling has become a significant concern for the electronics industry, government organizations, businesses, and universities due to the rise of high data processing and storage capacity demands caused by the internet of things (IoT) and telecommunications. The complexity and cost of thermal management for electronic devices have increased as a result. This project focuses on the thermal management of servers, which continue to improve in performance, primarily due to advancements in their processors. However, adopting the new generation of processors causes miniaturization of components, leading to increased heat flux manifolds. Since each component has an upper-temperature limit, heat must be dissipated to the ambient to keep the server components within their working limit and prevent failure. In practice, consumers still prefer air-cooled servers due to their simplicity, low capital and maintenance costs, as opposed to liquid-cooled servers that have issues with leaks, complex setups, and high costs.

The study is conducted on a 1U traditional air-cooled server. The form factor of 1 rack unit or unit (1U) is the smallest rack available to fit in the standard rack unit. The thickness of 1U is equivalent to 1.75 inches or 44.45mm. This 1U study is further validated against the physical results provided by the Dell R&D Team. To improve thermal performance, a new form factor 1.5U server is created, in which different fans, a new baffle design, and a heat sink with the same dimensions but with an increased fin height are analyzed.

Thermal analysis is conducted to determine the maximum operating temperature of the motherboard, central processing units (CPUs), dual in-line memory modules (DIMMs), and hard disk drives (HDDs). The airflow pattern is also studied to identify low-velocity regions in different zones and optimize the design to improve cooling performance. The results show that the total airflow through the 1U server with eight very high-performance (VHP) fans is 112.6 CFM, where the flow through the PSU is fixed at 14 CFM each. The case temperature of CPU-1 and CPU-2 is operating at 86.5°C and 86.9°C, respectively, which is above the maximum allowed case temperature limit of 84°C. The DIMMs DRAMs operate at 57.8°C, below the temperature limit of 85°C. The mean air inlet temperature of downstream components such as PCIe cards, OCP cards, BOSS, and PSUs is close to the specified temperature range of 55°C. The power consumed by the fan is 191.49W, calculated using the fifth-order polynomial correlation function.

A thermal analysis of the new form factor 1.5U server is also performed by installing new fans, creating new baffle designs to divert airflow, and increasing the fin height. The results show that the total airflow through the 1.5U server with six very high-performance (VHP) fans is 158.2 CFM, where the flow through the PSU is fixed at 14 CFM each. The case temperature of CPU-1 and CPU-2 is operating at 80.2°C and 81.2°C, respectively, which is under the maximum allowed case temperature limit of 84°C. The DIMMs DRAMs operate at 54.9°C, below the temperature limit of 85°C. The mean air inlet temperature of downstream components such as PCIe cards, OCP cards, BOSS, and PSUs is operating within the specified temperature range of 55°C. The power consumed by the fan is 299.23W, calculated using the fourth-order polynomial correlation function.

The new form factor 1.5U server demonstrates a significant thermal improvement compared to the traditional 1U server. The total airflow through the server is increased by 41.05%, which is an important factor in thermal cooling. The case temperature of CPU-1 and CPU-2 is reduced by 7.28% and 6.56%, respectively, and the DIMMs DRAM temperature is reduced by 5.02%. Even when the fans of the 1.5U server are running at 80% PWM, the server still performs its functional task under the specified temperature limit. Compared to a 1U server operating at 100% PWM, the 1.5U server operating at 80% PWM shows a relative thermal performance improvement and reduces fan power consumption by 20.16%. Additionally, the case temperature of CPU-1 and CPU-2 is reduced by 4.51% and 3.57%, respectively, making the new form factor server more energy-efficient than the 1U server.

The new generation DIMMs and processors that generate more heat dissipation are also simulated, and it is observed that the CPU-1 and CPU-2 are operating at a case temperature of 84.9°C and 85.9°C, respectively, which is above the temperature limit. However, when compared with the 1U server, the 1.5U server outperforms it with a thermal improvement of 1.84% and 1.15%, respectively. The baffles design and heat sink can be easily improved to bring these temperatures under the limit and work on air-cooled servers in the next generation.