Energ. Estimated Electricity Consumption of Global Data Centres 2020-2030 [Online]. Some practical design variations of pulsating heat pipes (adapted from [3]). 95 (may), 297303. (2020).

There may exist an optional adiabatic zone in between. Investigation on thermal Design of a Rack with the Pulsating Heat Pipe for Cooling CPUs. Produced by Electronic Cooling. With the heat source located on the back, leftward side of the reservoir, the liquid ammonia turns to vapor. In an actual working PHP, there exists a temperature gradient between the evaporator and the condenser section. A similar phenomenon will be observed if the system is quasi-statically cooled to a new equilibrium condition A and B (exaggerated representation for clarity) [6]. oscillating hanwen Appl. From the above research and analysis, we can see that the working fluid in the alternating cross-section or gradual cross-section channel will add an additional cyclic power due to the non-uniform structure on the basis of the original cyclic driving force, which increases the internal pressure disturbance and effectively drives the directional flow of the internal working fluid. This all but eliminates the possibility of damage caused by freezing. Exp. Int. No.2, Heding Rd., Zhongli Dist. On the contrary, Groll and Khandekar (2003) pointed out that a working fluid with a larger surface tension increases the friction force of the liquid plug movement, thereby increasing the flow pressure drop. In practice, these devices are extremely nuanced.

Experimental Investigations of Heat Transfer Mechanisms of a Pulsating Heat Pipe. Its operation depends on the ability of the working fluid to achieve high enough vapor pressure when heated to push the liquid condensate back to the evaporator section of the device. CCA Heat Sinks Embedded with Oscillating Heat Pipes article featured in Electronics Cooling, Air Force, small business develop technologies that help electronics stay cool article featured in Air Force SBIR STTR Advantage. Since their invention in the early nineties, they have so far found market niches in electronics equipment cooling. 1) The material is easy to obtain, the structure is simple and compact, the shape can be changed according to the application scenario, and the manufacturing cost is low (Kim and Kim, 2018). Therefore, it is considered that a smaller surface tension is better. Masanet, E., Shehabi, A., Lei, N., Smith, S., and Koomey, J. (2017). Groll, M., and Khandekar, S. (2003). However, these subjects are beyond the scope of this article. 28 (11-12), 13121317. 166, 114734. doi:10.1016/j.applthermaleng.2019.114734.

114, 12241239. The lower heat transfer coefficient of steam causes the heat transfer efficiency to drop, and the tube wall temperature rises sharply, reaching the heat transfer limit (i.e., the state of dry-out). Appl. Exp. Different forms of pulsating heat pipes: (A) Closed-loop PHP; (B) closed-loop PHP with a check valve; (C) open-loop PHP. From the above analysis, we know that there are many factors affecting the thermal and hydraulic performance of PHPs, which are intricate. Two-phase passive devices are proven present day solutions. A comprehensive theory of operation and a reliable database or tools for the design of PHPs according to a given microelectronics-cooling requirement still remain unrealized [5]. Int. The reason for the diametrically opposite conclusions is related to the experimental settings of each scholar. (2003a) found in the visualization experiment that the flow patterns of the working fluid in the tube changes mainly as follows: bubbly flow, plug flow, jet flow, semi-annular flow (the evaporation section is mainly annular flow, and the condensation section is mainly plug flow). The indicators to measure the operating performance of the PHP usually include the temperature of evaporator, the temperature variation amplitude and frequency, and the thermal resistance. (2001) was used to simulate the vapor slugs and liquid plugs behavior in 2-turns closed-loop and open-loop PHPs. 51776195). Tseng et al. doi:10.1007/s12206-014-0751-9. The established mathematical and physical models have made many assumptions and simplifications, so that the calculated results are quite different from the actual results. Tubes are usually charged with either water or ethanol to between 30-80% of their volume and evacuated. However, according to the authors knowledge, there are few research reports on the application of PHPs in data center thermal management so far. Nucleation and denucleation are the two modes that enable PHPs to start. (2018). Typically, rotating heat pipes are used to remove heat generated in motors and other rotating machinery such as RF rotary joints used in telecommunications.

J. The efficient use of energy is the core issue of data centers, and the only way to achieve a low-carbon, environmentally friendly and sustainable society. The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. Where, the chaotic behavior characteristics of PHPs, the coupling effect of fluid mechanics and thermodynamic characteristics, and the mechanism of heat and mass transfer between vapor slugs and liquid plugs need to be further studied. In order to make the vapor slug penetrates the liquid plug, the total force acting on the liquid plug will be overcome by the momentum generated by the slugs, namely: Where 0r02vu2rdr is the momentum generated by the expansion of the bubble, (p2p1)r02 is the pressure difference between the two ends of the liquid plug,2r0(cosrcosa) is the resistance caused by the hysteresis of the contact angle, and 2r0(0L1wdx) refers to the frictional shear force received by the liquid plug movement. 23 (16), 20212033. It consists of a porous structure with a planar evaporating end and five condensation ends, and is 98mm 60mm 52mm in size. Summary of the total thermal resistance of PHP cooler from different researches. 20 (2), 150154. The experimental study conducted by Yang et al. This aspect requires further investigation [10].So, the performance not only depends on a large number of parameters described above, but also on the flow pattern. (2012) designed and manufactured two kinds of flat plate PHPs with the structure of double-sided rectangular and triangular channel. TV Temperature of the spherical bubble (C), rglobe Radius of the spherical bubble (m), Pv Internal pressure of the spherical bubble (Pa), RContact Thermal resistance between the heat source and the evaporator (C/W), RPHP Thermal resistance of the PHP (C/W), RCond Heat conduction resistance of the tube wall material (C/W), RAir Heat dissipation resistance of the air side (C/W), THeatsource Average temperature of the heat source (C), Te Average temperature of the evaporator (C), Tc Average temperature of the condenser (C), u Velocity of liquid plug pulsation (m/s), M Number of liquid plugs in each parallel pipe, Keywords: data centers, pulsating heat pipe, heat dissipation, energy saving, review, Citation: Li C and Li J (2021) Passive Cooling Solutions for High Power Server CPUs with Pulsating Heat Pipe Technology: Review. Also, a wick can reduce the possibility of structural damage when using water as working fluid because less water is needed. Schematic diagram of a CPU cooler based on PHP (Shang et al., 2021). Where Tn and TV are the temperature of the small bubble at the cavity and the spherical bubble respectively, hlv is the latent heat of vaporization, is the surface tension coefficient of vapor-liquid interface, Pv is the internal pressure of the spherical bubble, rn and rglobe are the radius of the small bubble at the cavity and the spherical bubble respectively. THeatsource, Te,TcandTair respectively represent the temperature of the heat source, the average temperature of the evaporator, the average temperature of the condenser and the ambient temperature, and Q is the total heat transfer. Heat Transfer Performance of Flexible Oscillating Heat Pipes for Electric/hybrid-Electric Vehicle Battery thermal Management. Burban, G., Ayel, V., Alexandre, A., Lagonotte, P., Bertin, Y., and Romestant, C. (2013). Generally speaking, when the PHP is in the vertical state (that is, the evaporation section is located below the condensation section), gravity will help the condensed liquid return to the evaporation section, and the thermal performance of the PHP is the best (Chien K. et al., 2012; Paudel and Michna, 2014). Heat Mass Transfer 85, 2328. Through the use of transparent quartz glass tubes with high-speed cameras, electrical capacitance tomography, neutron imaging, infrared imaging technology and other experimental visualization methods, domestic and foreign scholars have done a lot of researches on the influence of geometric parameters (Wang J. et al., 2015; He et al., 2020; Xie et al., 2020), physical parameters (Wang et al., 2019; Wang et al., 2020; Zhou et al., 2021) and operating parameters (Jian et al., 2012; Ahmad and Jung, 2020; Xie et al., 2020) of PHPs on its performance, and it is summarized as follows: The appropriate choice of pipe diameter is directly related to whether PHPs can run smoothly. 5) The combined effect of forced convection formed by oscillating motion and phase change heat transfer makes the heat transfer efficiency as high as 90%, while the heat transfer efficiency of traditional heat pipes are 6070% (Zhang and Faghri, 2008; Leu and Wu, 2017). High Temp 48 (4), 565571. To understand the heat transfer mechanism of PHPs, further experimental analysis, numerical simulation and theoretical research are needed to be conducted.

MAR.. doi:10.1016/j.ijheatmasstransfer.2018.11.002, Xie, F., Li, X., Qian, P., Huang, Z., and Liu, M. (2020). Eng. Eng. Experimental studies have shown that (Shafii et al., 2001; Vassilev et al., 2007), when the filling rate is 0.20.8, a series of liquid plugs and vapor slugs in the PHP can be formed to ensure normal pulsating operation. The hot end overheating leads to secondary heat dissipation difficulties, the cold end undercooling leads to CPU chip surface condensation affects its performance and life, and the manufacturing cost is too high, which also restricts the large-scale application of thermoelectric refrigeration technology. The calculation equation of thermal resistance can be obtained from Eq. In other words, the condenser must be above the evaporator. Handbook: Mechanical Engineers. Instead, loop heat pipes use a refrigerant like ammonia where high pressure can be achieved at electronics operating temperatures.

Heat Transfer 21 (2), 405409. Jectc 03 (1), 2734. (2011). Since PHPs are usually made of copper, aluminum or silicon, Table 1 summarizes the types of working fluids that are compatible with copper/aluminum/Si PHPs between 0 and 100C. On the other hand, under certain operating conditions, flow pattern transition to annular flow may occur. (2018) proposed a three-dimensional structure PHP module suitable for high heat flux chips. Therm. Their complex operational behavior, which is not yet fully understood, has raised an ever growing academic interest. doi:10.1115/1.1409266, Shang, F., Yang, Q., Fan, S., Liu, C., and Liu, J. Sci. At present, the efficient and green cooling scheme is one of the key researches and development points to ensure the stable and safe operation of power electronic devices and achieve energy saving and consumption reduction. Most studies have shown (Tong et al., 2001; Khandekar et al., 2003a; Groll and Khandekar, 2003) that the closed-loop PHPs can form a cycle, where the thermal performance is better than that of the open-loop. Aprianingsih, N., Winarta, A., Ariantara, B., Putra, N., Kusrini, E., Juwono, F. H., et al. doi:10.1016/j.applthermaleng.2018.02.045, Qu, J., Wu, H., and Cheng, P. (2012). Data centers are becoming more powerful and more integrated with the continuous development of smart cities, which brings us more technological convenience, but also generates a large amount of waste heat. Experimental Investigation of a Pulsating Heat Pipe for Hybrid Vehicle Applications. A loop heat pipe is similar to a loop thermosyphon but can operate against gravity with the evaporator above the condenser. Typical pressure-enthalpy diagram.In this way a sustained non-equilibrium state exists between the driving thermal potentials and the natural causality, which tries to equalize the pressure in the system. (2017) studied the effect of hydrogenated MWNTs nanoparticles and pure water on the thermal performance of PHPs. Thermal Analysis and Entropy Generation of Pulsating Heat Pipes Using Nanofluids. Therm. The results show that heat transfer accounts for more than 90% of the total heat transfer. The thermal performance of PHPs will indeed be improved to a certain extent, but it also increases manufacturing and maintenance costs accordingly.



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