A review of heat pipe application including new opportunities

This article introduces the paper 'A review of heat pipe application including new opportunities' published by 'Frontiers in Heat Pipes'.

1. Overview:

• Title: A REVIEW OF HEAT PIPE APPLICATION INCLUDING NEW OPPORTUNITIES
• Author: Masataka Mochizuki, Thang Nguyen, Koichi Mashiko, Yuji Saito, Tien Nguyen and Vijit Wuttijumnong
• Publication Year: March 2011
• Publishing Journal/Academic Society: Frontiers in Heat Pipes
• Keywords: cooling electronics, computer processor, global warming, data center, heat pipe, thermo-siphon, artificial permafrost storage

2. Abstracts or Introduction

This paper provides a detailed review of heat pipe applications, spanning from computer electronics to renewable energy systems. In the realm of computer electronics, the escalating performance and power consumption of computer processors have intensified heat dissipation challenges. Despite increased heat dissipation demands, the die size of processors has either reduced or remained constant due to advancements in nano-size circuit technology, leading to critically high heat flux. Heat flux, which was approximately 10-15 W/cm² in 2000, surged to over 100 W/cm² by 2010. This paper aims to offer insights into leveraging heat pipes to extend air cooling capabilities and optimize performance.

Addressing the global warming crisis, the paper emphasizes the role of heat pipes in minimizing carbon emissions. It explores applications such as collecting natural cold energy for data center and agricultural product cooling, cooling concentrated photovoltaic cells using Phase Change Material (PCM) and night sky radiation, preventing iceberg and glacier melting, solar heat collection for road snow melting, geothermal heat extraction using large-scale heat pipes, and employing ultra-large-scale heat pipes for earth temperature regulation.

3. Research Background:

Background of the Research Topic:

The escalating heat dissipation in modern processors, exceeding 100 W with heat fluxes surpassing 100 W/cm², renders passive cooling inadequate. While technologies like liquid cooling, thermoelectric cooling, and refrigeration offer solutions for high-performance computers, their adoption is limited by integration complexity, reliability concerns, manufacturing scalability, and higher costs. Air cooling remains the prevalent technology due to its maturity, operational simplicity, and cost-effectiveness. Effective cooling necessitates minimizing the temperature gradient between the heat source and radiating components, for which heat pipes and vapor chambers are recognized as optimal devices due to their minimal thermal resistance.

Status of Existing Research:

Data centers face significant operational costs due to electric power consumption, a substantial portion of which is attributed to cooling infrastructure. For every watt consumed by computing infrastructure, an additional one-third to one-half watt is required for cooling. This results in substantial expenses and environmental impact due to greenhouse gas emissions from non-renewable energy sources powering data centers. Prior research has explored energy conservation in data center cooling systems to mitigate electricity consumption and carbon emissions. Existing approaches include optimizing heat sink designs, enhancing fin efficiency, optimizing fan airflow, and integrating heat pipes or vapor chambers to improve heat spreading and transfer.

Necessity of the Research:

The paper highlights the necessity for innovative thermal management solutions to address the increasing heat dissipation demands in computer electronics and the growing concerns about energy consumption and environmental impact, particularly in data centers. It emphasizes the potential of heat pipe technology to enhance air cooling limits, reduce energy consumption, and minimize carbon emissions across various applications, necessitating a comprehensive review of its applications and opportunities.

4. Research Purpose and Research Questions:

Research Purpose:

The primary purpose of this paper is to provide a detailed review of heat pipe applications across diverse fields, from computer electronics to renewable energy, and to explore new opportunities for heat pipe technology to address contemporary challenges such as enhancing air cooling in high-performance electronics and mitigating global warming.

Key Research:

The key research areas explored in this paper include:

• Reviewing the evolution of heat pipe applications in computer electronics, focusing on extending air cooling capabilities.
• Investigating the application of heat pipes and vapor chambers in thermal management of computer processors and electronic devices.
• Analyzing the thermal performance and design considerations of heat pipe-based cooling solutions, including hybrid systems, remote heat exchangers, and vapor chambers.
• Exploring novel applications of heat pipes in renewable energy systems, such as cold energy storage for data centers, geothermal heat extraction, and cooling of concentrated photovoltaic cells.
• Examining the potential of ultra-large-scale heat pipes for global temperature regulation.

Research Hypotheses:

While the paper is a review and does not explicitly state research hypotheses in a traditional experimental sense, implicit hypotheses can be identified:

• Heat pipes and vapor chambers can significantly enhance air cooling capabilities for high-performance computer processors by improving heat spreading and transfer.
• Heat pipe-based cold energy storage systems can offer energy-efficient and cost-effective cooling solutions for data centers, reducing electricity consumption and carbon emissions compared to conventional chiller systems.
• Heat pipe technology can be effectively applied to various renewable energy applications to improve energy efficiency and sustainability.

5. Research Methodology

Research Design:

This paper employs a review-based research design, synthesizing existing literature, experimental data, and conceptual designs related to heat pipe applications. It systematically examines the evolution, principles, and performance characteristics of heat pipes in various thermal management contexts.

Data Collection Method:

The paper primarily relies on data and findings reported in previously published research, experimental studies, and technical literature. It includes analysis of thermal performance data, design specifications, and conceptual schematics of heat pipe-based cooling solutions. Figures and data presented are directly referenced from existing research and experimental work.

Analysis Method:

The analysis method is qualitative and descriptive, involving a detailed examination and synthesis of information gathered from the reviewed literature. The paper analyzes the thermal principles of heat pipes and vapor chambers, evaluates their performance in different applications, and discusses design considerations and optimization strategies. Comparative analysis is used to assess the advantages of heat pipe solutions against conventional cooling technologies.

Research Subjects and Scope:

The research scope encompasses a broad range of heat pipe applications, including:

• Computer Electronics Cooling: Focusing on desktop, notebook, and server processors, and graphic processing units (GPUs).
• Renewable Energy Systems: Covering cold energy storage for data centers and agricultural products, geothermal heat extraction, solar energy applications (CPV cooling, road snow melting), and potential applications for global temperature regulation.
• Heat Pipe Technology: Including various types of heat pipes (grooved, sintered, composite wick), vapor chambers, thermosiphons, and micro-channel heat pipes.

6. Main Research Results:

Key Research Results:

• Heat Pipe Application in Computer Electronics: Heat pipes and vapor chambers are established as effective thermal solutions for computer electronics, enabling air cooling to meet increasing heat dissipation demands. Design evolutions, including hybrid systems, remote heat exchangers, and vapor chambers, have pushed the limits of air cooling.
• Thermal Resistance Analysis: The paper details the thermal resistance network in CPU cooling and demonstrates how heat pipes and vapor chambers reduce thermal resistance, particularly spreading resistance. Figures 3 and 11 illustrate the trend of thermal resistance reduction with advanced heat pipe cooling solutions.
• Notebook and Desktop Cooling Examples: Hybrid heat pipe systems, remote heat exchangers, and vapor chambers are presented as effective solutions for notebook thermal management. Desktop cooling solutions have evolved from normal extrusion heat sinks to vapor chamber-based designs to enhance performance (Figures 5, 6, 9, 10, 11, 12).
• Graphic Processor Cooling: Advanced three-dimensional thermal management devices using vapor chambers and heat pipes are shown to provide superior cooling for high-performance GPUs (Figures 13, 14).
• Piezo Fan Integration: Piezo fans are explored as a low-power, low-noise air cooling alternative, demonstrating comparable performance to traditional fans with advantages in acoustics and cost (Figures 15, 16, 17, 18, 19).
• Future Technologies: Micro-channel vapor chambers (MVC-IHS) and removal of integrated heat spreaders (IHS) are proposed as future directions to improve heat spreading and reduce thermal resistance in processor cooling (Figures 20, 21, 22, 23).
• Renewable Energy Applications:
  • Cold Energy Storage: Heat pipe-based cold storage systems for data centers are presented as energy-efficient alternatives to chiller systems, leveraging natural cold energy during winter (Figures 28, 29, 30, 31, 32, 33).
  • Geothermal Heat Extraction: Large-scale loop heat pipes are proposed for efficient geothermal heat extraction, with experimental results demonstrating significant heat extraction rates (Figures 45, 46).
  • CPV Cooling: Heat pipes and phase change materials (PCMs) are explored for cooling concentrated photovoltaic (CPV) cells, utilizing thermosiphons and night sky radiation for efficient thermal management (Figures 42, 43, 44).
  • Ultra-Large-Scale Heat Pipes: Conceptual designs for ultra-large-scale heat pipes for global temperature regulation are introduced, though acknowledged as highly conceptual (Figures 48, 49, 50).

Analysis of presented data:

• Figure 3: Demonstrates the relationship between thermal resistances (Rja, Rjc, Rca) and heat dissipation, showing the increasing significance of Rca as power increases and the need for efficient cooling solutions.
• Figure 4: Compares the cooling capability of air cooling versus liquid cooling, highlighting the superior heat transfer capacity of liquid cooling.
• Figure 14: Shows the thermal performance of vapor chamber and heat pipe solutions for cooling high-performance GPUs, indicating improved thermal resistance with increased airflow.
• Figure 17: Compares the thermal performance of piezo fans, axial fans, and blowers, showing piezo fans' comparable performance with lower noise and power consumption.
• Figure 21: Illustrates the thermal spreading resistance comparison between solid Cu-IHS and MVC-IHS, showing the advantage of MVC-IHS in reducing spreading resistance, especially for larger IHS sizes.
• Figure 24: Presents heat pipe performance comparison with different working fluids, showing improved heat transfer with 1-Butanol 1wt% compared to water.
• Figure 26: Shows vapor chamber performance improvement with design optimizations, achieving higher heat transfer capacity.
• Figure 38: Displays experimental results of ice formation in a heat pipe cold storage system, validating the concept.
• Figure 46: Presents test results for geothermal heat extraction using a large-scale heat pipe, demonstrating significant heat extraction capability.

Figure Name List:

• Fig. 1 Types of heat pipes
• Fig. 2 Heat pipe application
• Fig. 3 Thermal resistances
• Fig. 4 Thermal performance comparison between air cooling and liquid cooling
• Fig. 5 Hybrid cooling system
• Fig. 6 Remote heat exchanger
• Fig. 7 Examples of various remote heat exchangers designs
• Fig. 8 Examples of various shapes and sizes of vapor chamber
• Fig. 9 Vapor chamber solution
• Fig. 10 Trend of thermal solution in laptop
• Fig. 11 Summary of thermal design trend for cooling desktop PCs
• Fig. 12 Examples of heat pipe heat sink thermal designs for cooling desktop PCs
• Fig. 13 Vapor chamber and heat pipe thermal solution for cooling high performance graphic processors
• Fig. 14 Thermal performance of vapour chamber and heat pipe thermal solution for cooling high performance graphic processors
• Fig. 15 Basic principle of piezo fan
• Fig. 16 Thermal solution consist of heat pipes with spreader plate and piezo fan
• Fig. 17 Thermal performance comparison between piezo fan, axial fan and air blower
• Fig. 18 Raked piezo fan
• Fig. 19 Thermal performance of raked piezo fan
• Fig. 20 Micro-channel vapor chamber
• Fig. 21 Thermal spreading resistance comparison between Cu-IHS and MVC-IHS
• Fig. 22 Skive micro-fin structure
• Fig. 23 Thermal solution without IHS
• Fig. 24 Heat pipe performance comparison of different fluids
• Fig. 25 Vapor chamber improvement ideas
• Fig. 26 Vapor chamber performance improvement
• Fig. 27 Schematic micro-channel two-phase pump loop
• Fig. 28 Power consumption in data centers
• Fig. 29 Typical example of current thermal management system in data centers
• Fig. 30 Concept of cold energy storage for cooling data centers
• Fig. 31 Thermosiphon diode characteristics
• Fig. 32 Ice storage system to support data center failure time
• Fig. 33 Structure comparison between current system (top) and the proposed ice storage system (bottom)
• Fig. 34 Precooler for chiller inlet water
• Fig. 35 Hourly temperature and wind speed for Poughkeepsie, New York, USA, 2008
• Fig. 36 Pre cooler design for 8800 kW data center
• Fig. 37 Pre cooler design for 8800 kW data center
• Fig. 38 Experimental test results of ice formation
• Fig. 39 Concept of ice removal on the surface of the evaporator
• Fig. 40 Permafrost storage system
• Fig. 41 Freezing index
• Fig. 42 CPV Cooling by thermosiphons with fin heat exchangers
• Fig. 43 CPV cooling by use of PCM and night-time sky radiation
• Fig. 44 Sky temperature vs ambient temperature
• Fig. 45 Large scale heat pipe for geothermal extraction heat
• Fig. 46 Test results for geothermal heat extraction by a large-scale heat pipe (diameter 150 mm and 150 m long)
• Fig. 47 Example of energy consumption in Japan
• Fig. 48 Concept of ultra-large scale heat pipe for cooling the earth
• Fig. 49 Design of ultra-large scale heat pipe for cooling the earth
• Fig. 50 Space elevator by NASA

7. Conclusion:

Summary of Key Findings:

This review paper underscores the versatility and effectiveness of heat pipe technology in thermal management across diverse applications. In computer electronics, heat pipes and vapor chambers are crucial for meeting the cooling demands of high-performance processors, extending the limits of air cooling. Novel applications in renewable energy, such as cold energy storage for data centers, geothermal heat extraction, and CPV cooling, demonstrate the potential of heat pipes to contribute to energy efficiency and sustainability. The paper also explores conceptual applications like ultra-large-scale heat pipes for global temperature regulation, highlighting the broad scope of heat pipe technology.

Academic Significance of the Study:

This review provides a comprehensive overview of heat pipe technology, consolidating research and applications across different domains. It contributes to the academic field by:

• Systematically categorizing and summarizing the evolution and advancements in heat pipe applications.
• Providing a detailed analysis of thermal performance and design considerations for heat pipe-based cooling solutions.
• Identifying and exploring novel and emerging applications of heat pipes in renewable energy and environmental sustainability.
• Offering a valuable resource for researchers and engineers in thermal management, computer electronics, and renewable energy fields.

Practical Implications:

The practical implications of this study are significant for various industries:

• Computer Electronics Industry: Provides guidance for designing and implementing efficient heat pipe-based cooling solutions for high-performance processors, enabling continued performance scaling while managing thermal challenges.
• Data Center Industry: Offers insights into energy-efficient cold energy storage systems using heat pipes, reducing operational costs and environmental impact.
• Renewable Energy Sector: Demonstrates the potential of heat pipes in enhancing the efficiency and viability of renewable energy technologies such as geothermal and solar power.
• Environmental Engineering: Explores innovative concepts for leveraging heat pipes to address global challenges like climate change and energy sustainability.

Limitations of the Study and Areas for Future Research:

As a review paper, this study is limited by the scope and availability of existing research. Specific experimental details and in-depth quantitative analyses are dependent on the cited sources. Areas for future research include:

• Further experimental investigation and optimization of micro-channel vapor chambers (MVC-IHS) and no-IHS cooling solutions for processor thermal management.
• Detailed feasibility studies and performance evaluations of heat pipe-based cold energy storage systems in diverse climates and data center configurations.
• Continued development and testing of large-scale and ultra-large-scale heat pipe systems for geothermal energy extraction and conceptual applications like global temperature regulation.
• Exploration of new working fluids and wick structures to enhance heat pipe performance, particularly for high heat flux and renewable energy applications.
• Further research into piezo fan technology and its integration with heat pipe cooling solutions for low-power and low-noise applications.

8. References:

• Brill, K.G., 2010 Heat Density Trends in Data Processing, Computer Systems, and Telecommunications Equipment: Perspectives, Implications, and the Current Reality in Many Data Centers, The Uptime Institute, 2005.
• Mashiko, K., Mochizuki, M., Watanabe, Y., Kanai, Y., Eguchi, K., and Shiraishi, M., Proc. of the Fourth Int'l. Heat Pipe Symp., University of Tsukuba, May 16-18, 1994, Japan.
• Mochizuki, M., Nguyen, T., Agata, H., and Kiyooka, F., “Advanced Thermal Solution Using Vapor chamber Technology For Cooling High Performance Desktop CPU In Notebook Computer", The 1st International Symposium on Micro & Nano Technology, 4-7 March 2004, Honolulu, Haiwai, USA.
• Mochizuki, M., Nguyen, Thang., Saito, Y., Wuttijumnong, V., Wu, X., Nguyen Tien, "Revolution in Fan Heat Sink Cooling Technology to Extend and Maximize Air Cooling for High Performance Processor in Laptop/Desktop/Server Application”, ASME Summer Heat Transfer Conference & InterPACK '05, July 17-22, 2005, San Francisco, USA.
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• Nguyen, T., Mochizuki, M., Mashiko, K., and Saito, Y., "Advanced Heat Sink Combined With Heat Pipe For Cooling PC", Proc. of the 4th JSME-KSME Thermal Engineering Conference, October 1-6, 2000, Kobe, Japan.
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• Saito, Y., Mochizuki, M., Hasegawa, M., Suzuki, T., Amano, K., and Tomojiri, S., Proc. of the Fourth Int'l. Heat Pipe Symp., University of Tsukuba, May 16-18, 1994, Japan.
• Sauciuc, I., Moon, S., Chiu, C., Chrysler, G., Lee, S., Paydar, R., Walker, M., Luke, M., Mochizuki, M., Nguyen, T., and Takenaka, E., "Key Thermal Challenges for Low Form Factor Thermal Solution", Semitherm 2005, March 2005, Dallas, USA.
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• Schmidt, R., Iyengar, M., Steffes, J., and Lund, V., "Co-generation, grid independent power and cooling for a data center," Proc. of ASME 2009 InterPACK Conf., IPACK 2009, July 19-23, 2009, San Francisco, CA, USA.
• Singh, R., Akbarzadeh, A., Mochizuki, M., Nguyen, T., and Wuttijumnong, V., "Experimental Investigation of the Miniature Loop Heat Pipe with Flat Evaporator", ASME Summer Heat Transfer Conference & InterPACK '05, July 17-22, 2005, San Francisco, USA.

9. Copyright:

• This material is "Masataka Mochizuki, Thang Nguyen, Koichi Mashiko, Yuji Saito, Tien Nguyen and Vijit Wuttijumnong"'s paper: Based on "A REVIEW OF HEAT PIPE APPLICATION INCLUDING NEW OPPORTUNITIES".
• Paper Source: https://www.researchgate.net/publication/273362114

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