oscillating heat pipes

FIGURE 9. 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. Int. Khandekar S., Schneider, M., and Groll, M., Mathematical Modeling of Pulsating Heat Pipes: State of the Art and Future Challenges, 5th ASME/ISHMT Joint International Heat and Mass Transfer Conference, ISBN 0-07-047443-5, Kolkata, India, 2002, pp. Also, a wick can reduce the possibility of structural damage when using water as working fluid because less water is needed.

The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. Wickless (L) and Partial Wick (R) Thermosyphons. In this case, the liquid and vapor phases inside the device must exist in equilibrium at the saturated pressure corresponding to the fixed isothermal temperature. For more information on these devices, please check out our Thermosyphon Technology Overview article. Understanding Operational Regimes of Closed Loop Pulsating Heat Pipes: an Experimental Study. Compared with pure water, the performance of PHPs was improved in a lower concentration of hydrogenated MWNTs nanofluid.

Start-up, Heat Transfer and Flow Characteristics of Silicon-Based Micro Pulsating Heat Pipes. doi:10.1016/j.applthermaleng.2017.05.191, Kim, J., and Kim, S. J. The evaporation of the thin liquid film makes the effect of latent heat particularly important. The smaller the value, the smaller the power consumption and the higher the energy utilization rate. Eng. The temperature curve of the evaporating section of PHPs changes from rising to a sudden decrease, and then to a continuous oscillation state, marking the successful startup of PHPs (Hu and Li, 2011). Thermal LIVE 2022 is a two-day, free online learning and networking event for electronics and mechanical engineers to learn about the latest topics in thermal management.

TABLE 1. Heat Mass Transfer 89 (oct), 176185. Int. Nucleation and denucleation are the two modes that enable PHPs to start. The power consumption of the data center is mainly composed of communication and network equipment, power supply and distribution systems, lighting systems and auxiliary equipment, as well as heat dissipation and cooling systems (Capozzoli and Primiceri, 2015). The results show that the surfactant solution is favorable to the operation of PHPs at the concentration of 10ppm under all experimental input heat loads.

In practice, these devices are extremely nuanced. The factors affecting the heat transfer limit include the working fluid types, filling rate, flow rate, pressure, cross-sectional area, inclination angle, liquid film thickness, and wall temperature.

When the air flow rate is 1.24m3/min and the heating power is 300W, the thermal resistance is about 0.16K/W, with efficient heat dissipation capacity.

Pulsating Heat Pipes: Progress and Prospects, in Energy and the Environment - Proceedings of the International Conference on Energy and the Environment. Review of the Development of Pulsating Heat Pipe for Heat Dissipation.

When vapor turns to liquid condensate, the centrifugal force generated by the rotating pipe pushes the liquid back to the evaporator end.

Summary of heat dissipation of high-power chips based on PHPs. Therm. Many research literatures only consider the impact of a single variable on a single performance, and the value is discrete, but in actual operation, the performance of PHPs is coupled with each other, and the influencing factors are also mutually coupled and continuous, various parameters need to be optimized to improve its heat transfer performance. oscillating heat pipe Amsterdam, Netherlands: Applied Thermal Engineering. 31 (2), 622638. (2017) studied the effect of hydrogenated MWNTs nanoparticles and pure water on the thermal performance of PHPs.

28 (11-12), 13121317. 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). Schematic diagram of a CPU cooler based on PHP (Shang et al., 2021). (2020). 135, 19.

However, different scholars have reached conflicting conclusions regarding the main forms of heat transfer under different experimental or simulated conditions.

doi:10.1016/j.applthermaleng.2015.08.106, Wang, J., Xie, J., and Liu, X. Loop thermosyphons do not necessarily need a wick at the evaporator.

Jung, C., and Kim, S. J. Further heating expands the vapor slugs, pushing the slugs of water toward the condenser, much in the same way a coffee percolator works.

These include: Constant conductance heat pipes (standard or CCHP) and vapor chambers are by far the most prevalent type of heat pipe used for cooling electronics. The thermal performance data is also included. Experimental Studies of Surface Modified Oscillating Heat Pipes. Start-up, Heat Transfer and Flow Characteristics of Silicon-Based Micro Pulsating Heat Pipes. Development and Investigation of Compact Cooler Using a Pulsating Heat Pipe. ohp oscillating schematic Eng. pipe heat pulsating 707-719, 2003. 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.

(2004) shows a practical industrial product based on pulsating heat pipe applied to heat dissipation of high heat flux computer CPU. However, according to the authors knowledge, there are few research reports on the application of PHPs in data center thermal management so far. Effects of Superhydrophobic and Superhydrophilic Surfaces on Heat Transfer and Oscillating Motion of an Oscillating Heat Pipe. The temperature uniformity of the PHP-based CPU cooler becomes better as the cooling wind speed increases. In contrast to a conventional heat pipe, there is no additional capillary structure inside the tube. 26 (1), 7381. Transfer 53 (11), 112.

Since there are no any moving parts, no additional energy is needed, which will make the PUE value infinitely close to 1, achieving extremely high energy efficiency. oscillating pipe heat

Although PHP has been studied for several decades, it is mostly about the basic research on the factors affecting its startup performance and heat transfer performance, and has few practical applications in commercial cooling systems.

Therm.

At this time, the working fluid will move at a very high speed at the moment of startup, and the plug flow will quickly transform into the annular/semi-annular flow with latent heat and high heat transfer coefficient, making the temperature of the evaporator show a downward trend.

For a data center with a small space and high heat flux density, the heat flux density can generally reach 60100W/cm2, and even reach 200W/cm2 in special cases (Ebrahimi et al., 2014). doi:10.1016/j.ijheatmasstransfer.2013.01.059, Shafii, M. B., Faghri, A., and Zhang, Y. Cramming More Components onto Integrated Circuits. As a result, many customers build the OHP technology inside their existing structures to create multi-functional ones that provide both thermal and mechanical protection. doi:10.1016/j.rser.2015.12.350, Hao, T., Ma, X., Lan, Z., Li, N., Zhao, Y., and Ma, H. (2014b). (2008) showed that the 2mm closed-loop PHP has the best thermal performance when the inclination angle is 90, but the thermal performance will no longer be related to the inclination angle when the pipe diameter is reduced to 1mm.

As shown in Figure 3, heating at the evaporator continuously tries to push point A upwards on the liquid saturation line of the pressure-enthalpy diagram. 54, 8592.

Green Grid Metrics: Describing Data Center Power Efficiency.

As shown in Figure 2, a liquid plug and two vapor slugs were taken as the research objects. Oscillating heat pipes (OHPs) use pressure-driven, two-phase fluid flow to rapidly transfer heat between heat sources and heat sinks. (2019) detected the fluid-solid interface temperature by an infrared camera, and heat flux density as well as the flow pattern changes at the corresponding temperature were observed.

doi:10.1016/j.applthermaleng.2017.01.097, Qu, J., Wang, C., Li, X., and Wang, H. (2018). The conclusion shows that when the cooling wind speed is 0.3m/s, the startup time is the shortest, the startup temperature is the lowest (only 34.0C), and the startup performance reaches the best state. Amsterdam, Netherlands: Powder Technology. oscillating 856-862. At present, PHPs can be roughly divided into two types: closed-loop and open-loop according to the structural design. Heat Transfer 123 (6), 11591172. heat oscillating pipe doi:10.1016/j.egypro.2015.12.168, Chao, D., Li, J., and Lu, Q. Thermal LIVE 2022 is a two-day, free online learning and networking event for electronics and mechanical engineers to learn about the latest topics in thermal management. In general, the working fluid needs to meet the following conditions: 1) Appropriate phase change latent heat.

The established mathematical and physical models have made many assumptions and simplifications, so that the calculated results are quite different from the actual results. doi:10.1016/j.ijheatmasstransfer.2014.12.010, Xiahou, G., Zhang, J., Ma, R., and Liu, Y. Aprianingsih, N., Winarta, A., Ariantara, B., Putra, N., Kusrini, E., Juwono, F. H., et al. (2021).

doi:10.1016/j.applthermaleng.2016.03.163, Wang, J., Ma, H., and Zhu, Q.

START UP MECHANISM OF PULSATING HEAT PIPE, in Proceedings of the national Conference on Thermal Fluid Science and Tribo Application TFSTA2016). In addition, Chi (1976) synthesized the physical parameters of working fluid and found a index that can be used to evaluate its poor performance, that is, Figure of Merit (FOM), which can be calculated by Eq. 20 (2), 150154. Advances and Unsolved Issues in Pulsating Heat Pipes.

However, according to the theoretical analysis of Ma et al. Rotating Heat Pipe.

J. Evaporation of an Isolated Liquid Plug Moving inside a Capillary Tube. Manage. Heat Mass Transfer 107 (apr), 204212. Appl. Figure of Merit for PHP working fluids. Estimated Electricity Consumption of Global Data Centres 2020-2030 [Online].

9:755019. doi: 10.3389/fenrg.2021.755019.

9.

(2008) found that the average temperature difference and thermal resistance are significantly reduced when the working fluid is Ag/H2O nanofluid.

Int. The result is that the thermal solution now has a higher thermal resistance (less condenser area) so the evaporator stays warmer than it would if a standard heat pipe heat sink had been used.

21, 2001, pp. 17, 1992, pp. 126, 10631068. oscillating pipe nanofluids pipes The data center market is getting bigger and bigger, and with huge energy consumption. Azar, K., The History of Power Dissipation, ElectronicsCooling, Vol.6, No.1, January 2000. 95 (may), 297303. The smaller pipe diameter results in smaller liquid plugs amplitude, higher frequency, greater heat transfer per unit area, and higher thermal conductivity. (2018). 3) Since the working fluids pulsate in the same direction, the two-phase flow does not interfere with each other. Figure 9 depicts that the heat source temperature of the aluminum finned radiator is higher than the limited temperature of CPU (70C), reaching 81.6C when the input power is 80W. While the heat source temperature value of the vertical radiator is 64.3C, and the temperature distribution is more uniform, showing excellent heat dissipation performance. (2015) designed the evaporation section to 5cm and the condensing section to 8cm.

A Novel Thermal Module with 3-D Configuration Pulsating Heat Pipe for High-Flux Applications. Eng. Analysis of Heat Transfer in Unlooped and Looped Pulsating Heat Pipes.

The results demonstrate that most of the heat transfer (95%) is in the form of sensible heat rather than latent heat of vaporization, and the latter is mainly the cause of the oscillating flow. As a general rule, thermosyphons are simply wickless heat pipes although they sometimes include a grooved wick that helps increase the surface area of the internal wall and allow liquid condensate to more easily return to the evaporator. In theory, its a remarkably simple execution. Eng. 1845-1862. Rahman, M. L., Afrose, T., Tahmina, H. K., Rinky, R. P., and Ali, M. (2015). Summary of the total thermal resistance of PHP cooler from different researches.

Thermo-hydrodynamics of Closed Loop Pulsating Heat Pipe: an Experimental Study.

doi:10.1016/j.expthermflusci.2014.02.007.

Rahman et al. It also allows optimization of the fluid charge, effectively reducing the required liquid. Kim and Kim (2018) concluded that the greater the ratio of the evaporation section to the condensation section of the single-turn PHP, the shorter the startup process. Eng. The operating mechanism in the PHPs is relatively complicated, and the degree of understanding of it is still insufficient. Therm. Its structure consists of three parts along the axial direction, including evaporator, adiabatic zone and condenser. Experimental Study on a Three-Dimensional Pulsating Heat Pipe with Tandem Tapered Nozzles. Investigation of the Evacuation Pressure on the Performance of Pulsating Heat Pipe. Int. The heat pipe(s) and associated condenser (fin stack) must be designed to handle power and ambient temperature at the highest specification rating. The heat transfer and hydraulic performance of PHPs are affected by various factors. Physically this means that, during the flow of a partially wetting fluid (e equilibrium contact angle), the evaporation occurring at the thin-film region can be continuously replenished by the drainage of thin-film, due to the flow itself. Sponsored byMaster Bond (2017), as shown in Figures 4A,B. Fluid Sci.

The total power per server can reach 300800W, and the power of a single rack can reach 2030KW. Energ. Jo et al. However, when ambient temperature decreases and/or when the heat source is not at full duty cycle, the NCG expands to fill an increasing portion of the heat pipe vapor space.

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oscillating heat pipes