|Wayan Nata Septiadi||1. Department of Mechanical Engineering, Faculty of Engineering, Udayana University, Jalan Raya Kampus Unud, Jimbaran, Badung, Bali 80361, Indonesia 2. Heat Transfer Laboratory, Department of Mechani|
|I Gusti Agung Ayu Desy Wulandari||Department of Mechanical Engineering, Faculty of Engineering, Udayana University, Jalan Raya Kampus Unud, Jimbaran, Badung, Bali 80361, Indonesia|
|Made Ricki Murti||1. Department of Mechanical Engineering, Faculty of Engineering, Udayana University, Jalan Raya Kampus Unud, Jimbaran, Badung, Bali 80361, Indonesia 2. Heat Transfer Laboratory, Department of Mechani|
|Wayan Ainun Wildan Ula||Department of Mechanical Engineering, Faculty of Engineering, Udayana University, Jalan Raya Kampus Unud, Jimbaran, Badung, Bali 80361, Indonesia|
|I Kadek Odik Widiantara||Department of Mechanical Engineering, Faculty of Engineering, Udayana University, Jalan Raya Kampus Unud, Jimbaran, Badung, Bali 80361, Indonesia|
|I Wayan Gede Widyantara|
Computer Central Processing Unit (CPU) technology is being developed rapidly for better work performance together with smaller size. This technology development produces significant heat flux increase on the processor. In this paper, a cascade straight heat pipe (CSHP) is created for a better CPU cooling system which is a fully passive system using nanofluids and hybrid nanofluid as the working fluid. Heat loads were given to the CSHP at 10 watts, 20 watts, 30 watts, and 40 watts, respectively. Based on the experiment’s result, the CSHP with Al2O3-TiO2-water working fluid showed the best performance, decreasing 41.872% of the simulator plate temperature at maximum load while also having the highest condenser output temperature. The CSHP with Al2O3-water working fluid decreased 35.243% of the simulator plate temperature. The CSHP with water working fluid decreased only 28.648% of the simulator plate temperature and had the lowest condenser output temperature. The CSHP with Al2O3-TiO2-water showed the lowest thermal resistance and the highest coefficient of heat transfer.
Heat pipe; Heat transfer; Nanofluid
The progress of technological developments for the last few decades can be seen in several fields (electronics, power generation, etc.) (Ranga Babu et al., 2017). Smart technologies have rapidly developed, applying scientific knowledge for practical purposes with an evolutionary process, especially in computer hardware technology, as a solution to facilitate and improve the performance of human work (Brenner, 2007).
Central Processing Units (CPUs), the core of a computerized system, are experiencing rapid technology development (Paiva & Mantelli, 2015). The development of CPU technology leads to smart technology with the dimension decrease and has higher performance (Chen & Huang, 2017). However, this makes the CPU heat flux increase significantly (Elnaggar et al., 2011). The need for a high-performance cooling system with small dimensions without any additional power needs is a major issue faced by the computer industry (Elnaggar et al., 2011; Liu et al., 2015). Many solutions have been created to overcome CPU heat flux management problems, as in the conventional way by the application of forced convection heat transfer (Elnaggar et al., 2011). However, the conventional method is less efficient in removing heat, especially on smaller sized devices, because it requires higher power to support the fan performance.
Heat pipe is a heat transfer technology that uses a pipe (commonly made of copper, aluminum, etc.) containing liquid as a heat conductor from the end of the evaporator to the other end of the cooling section (heat removed) (Gupta et al., 2018). The heat pipe’s inner wall is filled with capillary axis (wick) as transferring media to return the condensate. Condensate moves by the principle of capillarity (Putra & Septiadi, 2014). Various types of heat pipe have been investigated, such as Heat Pipe Heat Exchanger (HPHE) and Oscillating Heat Pipe (Muhammaddiyah et al., 2018; Winarta et al., 2019).
Research on using heat pipes as processor cooling systems began in 2003 to 2014 (Kim et al., 2003) with a study of Pentium IV CPU PC cooling system performance using aluminum heat sink with fan assistance has disadvantages (shapes, noise generated from the fan causing noise and ineffective heat transfer), so that heat pipe as cooling system which is smaller than heatsink does not need to use a fan for a support.
Cascade heat pipe (CHP) is a heat pipe design that has multilevel construction, combining two heat pipes into one system (Putra et al., 2015). The oscillating heat pipe (OHP) is an up-and-coming passive thermal transfer device that transports heat through the thermally excited oscillating motions of a working fluid.
Limited energy and material resources as well as undesirable man-made climate change make science seek for new and innovative strategies to save, transfer, and store heat energy (Buschmann, 2013). In recent years, conventional heat transfer fluids have been replaced by more advanced fluids for better heat transfer (Madhesh & Kalaiselvam, 2014). Various studies of heat pipe application as a cooling system have been conducted using nanofluid as a working fluid, including one by Putra et al. (2014).
A study investigated the synthesis of ZnO nanoparticle-based thermal fluids as the working medium for a conventional heat pipe with screen-mesh wick. The experiments were performed to measure the and heat pipe thermal resistances. The results showed distribution of temperature and thermal resistance to decrease as the concentration and the crystallite size of the nanoparticle increased (Saleh et al., 2013).
Putra et al. conducted a study employing a collar application as a wick on an LHP using nanofluid as the working fluid. With the collar wick, the temperature differences in the heat absorber with condenser sections were less than in the one that used the sintered copper powder wick. Working fluids of nanofluids resulted in lower temperature differences than using water-based working fluid; i.e., the thermal resistance of the LHP was lowered by using the collar wick and nanofluids (Putra et al., 2014).
Ahlatli et al. (2016) conducted an experimental study of the thermal performance of carbon nanotube nanofluids in solar microchannel collectors. They investigated the effects of pumping power, heat transfer, and pressure drop on the heat and flow characteristics of nanofluid. The results showed that as the weight of nanofluids increased, the measured heat transfer, pump power, and pressure drop increased.
Septiadi et al. (2018) conducted a study synthesizing two nanoparticles to create hybrid nanofluids. The study determined how nanoparticle composition affects the thermal conductivity value with the lowest agglomeration value. This research was conducted by dispersing Al2O3-TiO2 nanoparticles in water.
The cascade straight heat pipe or CSHP-based CPU cooling system with the best cooling performance in this study was the system using Al2O3-TiO2-water working fluid, which reduced 41.872% of the simulator plate temperature and had the lowest condenser output temperature. The second-best performance was in the use of Al2O3-water working fluid, which decreased 35.243% of the simulator plate temperature, while the poorest cooling system was in the use of water, which decreased 28.648% of the simulator plate temperature. The lowest thermal resistance given by CSHP at each heat loading was in the use of Al2O3-TiO2-water working fluid, and the coefficient of heat transfer given by Al2O3-TiO2-water use was the highest. These findings show that Al2O3-TiO2-water hybrid nanofluid working fluid gives the best cooling performance of the CSHP for CPU cooling system.
The authors gratefully acknowledge the Ministry of Technology and Higher Education and the Udayana Institute for Research and Community Service for financial support through the 2019 Higher Education Primary Research Grant (PTUPT) scheme with Contract Number 492.29/UN14.4.A/LT/2019.
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