Design and investigation of a pulsating heat pipe for electronic cooling

Abstract

The purpose of this study is to design and investigate a pulsating heat pipe device (PHP). A PHP is a two-phase flow heat transfer device which can handle high heat fluxes with passive internal flow. It is made of a continuous loop serpentine, partially filled with a working fluid that can cool systems, such as electronic devices. It differs from a conventional heat pipe device in design and operation, potentially bringing some advantages when compared to the latter. Firstly, no wick structure is required to assist the condensed working fluid to flow to the evaporator, making it cheap to construct and flexible to integrate into different applications. Secondly, more working fluid is used in a PHP, potentially enhancing heat transfer in it.

The performance of a PHP can be measured by the thermal resistance, which is defined as the average temperature difference between the evaporation and condensation, divided by the supplied power to the device. The lower the thermal resistance, the more efficient the heat transfer in the PHP is. Despite the great efforts that many experimental and numerical works have put into fully understanding PHPs behaviour, since it was patented in the 90s, a lot remains unknown. This is mainly because of the chaotic two-phase, nonlinear internal flow of the device.

In this thesis, after the initial stage of designing and manufacturing a glass PHP, investigating how different parameters affect the thermal resistance was conducted. This included testing the PHP performance while varying different filling ratios for different working fluids (isopropanol and distilled water), different inclination angles of the device, in addition to different supplied power levels to the PHP. Results, validated by previous similar conducted studies showed that the optimal filling ratio for the designed PHP ranged between 40%-70% for both tested fluids. With increased power supplies, the thermal resistance of the device decreased. When comparing the performance of both working fluids, isopropanol seemed to perform better in all working conditions compared to distilled water. As for the inclination, a PHP in vertical position (assisted by gravity), had a more stable pulsating motion. While when in horizontal position, the device failed to operate in a fully pulsating mode, making the designed demonstrator gravity dependent.

Popular Abstract

With the ever-increasing demand for connectivity and the rapid development of technology and electronic manufacturing, products are constantly becoming more compact and increased cooling demands are placed on electronic devices. You might wonder, how can these devices operate efficiently, for long hours, and not get overheated?

This is mainly because electronic devices usually have an internal cooling device, that works to prevent overheating when operating. This is vital since the increase in temperature leads to deteriorating the performance of these products noticeably. There are several types of cooling devices used for electronics, some of the most common ones are heat pipes. Various types of heat pipes exist, and what is known as conventional heat pipes are often integrated into applications for cooling purposes. However, with the increasing cooling demands of the industry, sometimes, conventional heat pipes exhibit limits. For this purpose, pulsating heat pipes (PHPs), seem to be an optimal solution. They are called pulsating heat pipes because when they operate, an internal fluid, which is filled in the heat pipe before operation, moves in a pulsating motion . For a PHP to function, heat needs to be supplied to it and the pipe must be designed in a specific way. It can bring several advantages when compared to other methods used for cooling because the geometry is very simple, as it`s only made of several tubes, additionally, no external device is needed to assist the operation of the pipe. Generally, pulsating heat pipes have very small tube sizes, as this is required for them to function properly, making it also easier to integrate into compact electronics, with production costs that can be reduced.

Pulsating heat pipes are not commercially available yet and a lot is not known about how these pipes function. This thesis aimed to design and build a demonstrator pulsating heat pipe, in addition to test how it performed when varying certain parameters, to better understand the device operation. Finally, the demonstrator was built in glass, this made it possible to capture some images of the fluid and see how it moves inside, which could help improve understanding on the topic.

Pulsating heat pipes are promising cooling devices, which could potentially solve some limits that the industry is facing . However, a lot has to be understood about these devices before being able to have them commercially available, making them an intriguing topic for further research.

• author: Hammad, Sulafa
• supervisor: Lei Wang; Mikael Johansson
• organization: Department of Energy Sciences
• course: MVKM05 20231
• year: 2023
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: Pulsating heat pipes (PHP), Electronic cooling, two phase flow heat transfer
• publication/series: Publication
• report number: LUTMDN/TMHP-23/5531-SE
• ISSN: 0282-1990
• language: English
• id: 9133930
• date added to LUP: 2023-08-14 15:54:40
• date last changed: 2023-08-14 15:54:40