|Wayan Nata Septiadi||1. Department of Mechanical Engineering, Udayana University, Kampus UNUD Bukit Jimbaran, Badung, Bali 80361, Indonesia 2. Heat Transfer Laboratory, Department of Mechanical Engineering, Udayana Unive|
|Komang Wahyu Tri Prasetia||Undergraduate Student of Mechanical Engineering Study Program, Udayana University, Kampus UNUD Bukit Jimbaran, Badung, Bali 80361, Indonesia|
|Made Ricki Murti||1. Department of Mechanical Engineering, Udayana University, Kampus UNUD Bukit Jimbaran, Badung, Bali 80361, Indonesia 2. Heat Transfer Laboratory, Department of Mechanical Engineering, Udayana Unive|
|I Gusti Ketut Sukadana||1. Department of Mechanical Engineering, Udayana University, Kampus UNUD Bukit Jimbaran, Badung, Bali 80361, Indonesia 2. Heat Transfer Laboratory, Department of Mechanical Engineering, Udayana Unive|
|Fazlur Rahman||Undergraduate Student of Mechanical Engineering Study Program, Udayana University, Kampus UNUD Bukit Jimbaran, Badung, Bali 80361, Indonesia|
|Gerardo Janitra Puriadi Putra||Undergraduate Student of Mechanical Engineering Study Program, Udayana University, Kampus UNUD Bukit Jimbaran, Badung, Bali 80361, Indonesia|
|Komang Manik Marianti|
Developments in recent electronics result in electronic components that produce heat, namely, Central Processing Units (CPUs). One solution to this problem is using a heat pipe. In this study, a cascade straight heat pipe (CSHP) is analyzed as a CPU cooling system with three effective lengths: 20 cm, 23 cm, and 26 cm. The first workload provided was Idle; the processor only ran the operating system without a software load, so that the processor utilization was only 1-10%. The second was full load, where the processor utilization was 95-100%. The CSHP-based CPU-cooling system with an effective length of 20 cm was able to reach processor temperatures of up to 43.32oC (idle) and 63.62oC (full load). For the effective length of 23 cm, processor temperatures of 46.99oC idle) and 64.81oC full load was attained. Lastly, while using the effective length of 26 cm, processor temperatures of 50.67oC idle and 65.21oC full load were reached. CPU cooling systems using CSHP are thermally resistant when in idle conditions; respectively, the temperatures for the effective lengths of 20 cm, 23 cm, and 26 cm are 0.168oC/W, 0.197oC/W, and 0.223oC/W. In contrast, for the same effective lengths, the thermal resistance at full load was 0.262oC/W, 0.236oC/W, and 0.224oC/W, respectively. Overall, the cascade heat pipe shows better cooling performance than a stock cooler.
Cascade heat pipe; Cooling system; Effective length; Thermal resistance
For several decades, the development of electronics, especially in terms of computers, has been experiencing very rapid progress (Septiadi et al., 2019). One such computer component that is progressing quite rapidly is the CPU (Brenner, 2007). The development of CPUs, i.e., smart technology with smaller, lighter dimensions with improved performance and efficiency, is advancing that stated by Cai et al., and Terrado et al., at research by Chen and Huang (2017). The development of smart technology has had an impact on certain computer components, producing heat flux and leading to overheating, which must be dissipated to ensure the performance and life of the computer system (Paiva and Mantelli, 2015).
In its development, various methods have been attempted to overcome the CPU cooling system problem. One of them involves the use of a heat pipe (Kusumah et al., 2019). A heat pipe is considered a very high-thermal conductance device (Reay et al., 2013) and is a type of high-efficiency passive heat-transfer technology. Heat pipes have a structure allowing high thermal conductivity and transfer while maintaining uniform temperatures between the evaporator and condenser (Jouhara et al., 2017). Research and development on heat pipe shapes have been conducted by several researchers; for example, loop heat pipes (Maydanik et al., 2018), U-shaped heat pipes (Kusuma et al., 2019), L-shaped heat pipes (Putra and Ariantara, 2017), flat heat pipes (Arya et al., 2018), oscillating heat pipes (Zhou et al., 2018), etc. The high heat dissipated from the condenser is proof that heat pipe technology has not reached its maximum potential (Putra et al., 2013).
Modification and enhancement of heat pipes have been performed in recent decades. Fins are some of the common things applied to heat pipes to enhance heat transfer by adding more surface area in the condenser (Ibrahim et al., 2018). According to Huang et al. (2019), fin surface area is affecting the capability of heat pipes to absorb heat; the temperature distribution is increasing as fin surface areas increase due to higher heat absorption. Normally, heat collected in the fin dissipates into the air via natural convection; consequently, the surrounding air temperature rises. This temperature rise can affect the thermal resistance between the fin and the air (Xie et al., 2020). In order to ensure the heat dissipation rate, an electric-powered fan is commonly used to improve the cooling performance by increasing airflow to the heatsink (Xiao et al., 2017). The deficiency of using a fan with a CSHP is that the heat from the CPU absorbed through the evaporator at level I is not released directly into the environment. The absorbed heat is then transferred to the heat pipe evaporator level II and finally discharged through the level II condenser, and theoretically, the temperature of the heat discharged will be smaller. Therefore, the use of electric-powered fans is no longer beneficial (Septiadi and Putra, 2014).
Modification on cascade heat pipe is conducted to enhance the thermal performance. An experiment with a loop heat pipe for high heat transfer capacity has been conducted by Maydanik et al. (2018). The result stated that after thermal tests, the loop heat pipe improves power and heat transfer-distance significantly without additional energy source (Maydanik et al., 2018). The effect of the heat pipe effective length also affects the velocity of the mass flow rate along the pipe, which also affects the final heat dissipation generated by the CPU (Muhammaddiyah et al., 2018; Winarta et al., 2019). Tan et al. (2005) conducted an analytical study of flat plate heat pipe effective length using a point source approach. They stated that heat source could affect heat pipe effective length through the formulation provided in the research. The heat pipe maximum capillary heat transport limit and heat pipe optimum heat source position can be determined through the effective heat transport length (Tan et al., 2005).
In order to improve the CSHP performance, an analysis of the CSHP effective length was conducted. This research aims to find the effective length of CSHP so it could handle the maximum heat produced by the CPU without fan assistance while still paying attention to space availability inside the case.
An experiment was conducted to analyze the effective length of cascade heat pipes as CPU cooling systems. This experiment was carried out to find the most effective cascade heat pipe length so that fan assistance for CPU cooling is not required.
The effective length ratio affects the rate of heat transfer in a CSHP as a CPU cooling system, where a smaller effective length variable has a higher heat transfer rate, and a higher effective length ratio has a lower heat transfer rate. This is due to the distance the fluid travels along with the length of the heat pipe. A cascade heat pipe’s effective length also influences the thermal resistance of the system. A shorter cascade heat pipe effective length results in higher thermal resistance and vice versa due to intense partial evaporation.
Cascade straight heat pipes show better cooling performance than stock coolers without fan assistance. Cascade straight heat pipes with 20-cm effective lengths have the best cooling performance among CSHPs. According to the results, CSHPs are applicable to replace conventional fan-assisted heat pipes as cooling devices for CPUs. Modification and improvement of CSHPs can vary the working fluid and heatsink design for better cooling performance.
Thanks go to the Ministry of Technology and Higher Education and the Udayana Institute for Research and Community Service for their financial support through the 2019 Penelitian Terapan Unggulan Perguruan Tinggi (PTUPT) scheme with contract number 492.29/UN14.4.A/LT/2019.
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