A Brief Review of Heat Sink , Heat Pipe , and Vapor Chamber as a Key Function of Thermal Solution for Electronic Devices

DOI: http://dx.doi.org/10.24018/ejers.2020.5.11.1596 Vol 5 | Issue 11 | November 2020 1 Abstract — Electronics industry requires efficient design that can handle fast mathematical operations to compensate for the growing development and demand for processing power. These days, there are numerous equipment or parts inside machines called heating elements particularly with electrical or electronic devices and they should be cooled during the working process. However, with respect to their size, manufacturers are minifying day by day to satisfy requirements of users but the power should be maintained. Hence, elements withstand a high amount of heat and high heat flux (transition/mutability) is being generated during the working process. The main contribution of this study is to investigate thermal solutions using four cooling tools and to compare to each other and consider thermal design guidelines and factors as well. Furthermore, we review the appropriate thermal solutions for the produced heat from the electronic equipment and we present the effective and suitable tools which used to dissipate this heat. A heat sink, heat pipe, and vapor chamber are reviewed and compared depending on the previous studies that have implemented them.


I. INTRODUCTION
There is no doubt that the heat generated by the electronic devices reduces the efficiency of the devices and may lead to hurting of these devices. Therefore, the heat is a big problem and must be dissipated in proper ways that lead to improving the efficiencies of these devices.
Because of the progress or development of the electronic devices, the heat generated by the processors inside them is in increase. Consequently, we have to use the appropriate tools to dissipate the generated heat and match the rapid technological development of these devices.
Most of the previous studies investigated one of the cooling tools for electronic devices individually and deepened in the 1  description and carried out the mathematical and numerical analysis without addressing other cooling tools.
Based on that, the main contribution of this study is to review thermal solutions using, vapor chamber, heat sink and heat pipe and to compare to each other and consider thermal design guidelines and factors as well. Additionally, in this article, we will review the appropriate thermal solutions for the produced heat from the electronic equipment and will present the effective and suitable tools which used to dissipate the heat.

II. THERMAL MANAGEMENT SOLUTIONS
The obvious truth in the electronics industry is that the increase of the temperature generated by processors is inversely proportional to the age and efficiency of the electronic devices. Consequently, it is worth describing cooling tools that sustain cooling techniques that dissipate the associated heat which it represents the main idea of the thermal solution. For thermal management solutions to be more effective, we must deal with system hardware solutions, system software solutions, and optimal thermal design [13].

III. DESIGN GUIDELINES
Thermal design of the production of electronic devices is an important topic in research because thermal control solutions greatly affect the quality of the electronic product. Figure 1 shows the outline of the strategies for thermal design and its effect on electronic devices fabrication. In order to obtain a good thermal design solutions, all or most of the factors or effects which is found in Figure 1 must take into account.
Thermal design depends on understanding the concept of heat transfer and its branches such as conduction, convection and radiation.
In order to have a superb thermal design, we must proceed with the use of mathematics by analytical and numerical analyses, mathematical modeling, as well as verifying these methods by experiments.

IV. SAMPLES OF ELECTRONIC EQUIPMENT THERMAL SOLUTION
The samples, which are reviewed in this study, are mainly subjected to the same idea, but different in terms of performance and use and we try to compare between them depending on the previous studies that have implemented them. The samples are heat sinks, heat pipes, and the vapor chamber.

A. Heat Sinks
The heat sink works as a heat exchanger that is used to transfer the heat generated by the electronic devices to the surrounding medium. The heat sink is usually placed on the processor to cool it by dissipating the heat generated from the processor to the surrounding medium. In order, the heat sink can dissipate the largest amount of the heat, it is designed with parallel fins of aluminum or copper to increase the surface area that disperses heat quickly and efficiently. In the case, a fan is used with the heat sink to dissipate the heat very quickly from the surfaces of the fins, active cooling is called, while the use of this sink without a fan, passive cooling is called.
The desktop personal computer is one of the most common electronic devices that use a heat sink for cooling Central Processing Units (CPU). Fig. 2 shows the history of the development of the heat sink which is used to cool desktop PC with related to the thermal resistance (Rca). As it is known that the lower thermal resistance leads to increase the performance of the electronic devices. As shown in Fig. 1, the Type 1 of the heat sink has a high thermal resistance (Rca) reach to 0.5 ⁰C/W approximately which compared with Type 5 that consists from vapor chamber and heat pipe instead of heat sink which have high performance or lower thermal resistance which record 0.2 ⁰C/W or less.

B. Heat Pipe
A high effective thermal conductivity is the core advantage of the heat pipe. The heat pipe consists of three main parts: 1) the evaporator which its task is the heat absorbing from the processor; 2) the adiabatic part, the temperature in this part is constant without change; 3) the condenser which expels the heat.
The internal components of the heat pipe are made up of the wall which is made usually from copper, the part that touches the inner wall is a wick, and the third component is the working fluid which is mostly distilled water.
As shown in Fig. 3, the operation principle of the heat pipe: the heat is absorbed by the evaporator leads to evaporate the working fluid, which is transferred to the condenser, where the fluid condenses and then returns to the evaporator again, due to the effect of the pressure drop between evaporator and condenser.
There are many types of the heat pipes such as cylindrical heat pipe, flat heat pipe, micro-heat pipe, and oscillating heat pipe. Fig. 3. Cylindrical heat pipe structure [15].
Although this type of heat pipe is widely used and developed, it still has some weaknesses. In order to enhance this system, a complicated structure (wick) is in need to take the working fluid back to the heating area. However, its performance may decrease because of the blending between condensed working fluid and evaporating vapor. Nevertheless, it is difficult to manufacture a fine product with this design .

C. Vapor Chamber
The vapor chamber has the same operating principle as the heat pipe. The heat pipe is a round pipe while the vapor chamber is a flat shape [14]. The comparison between the structure of the heat pipe and the vapor chamber is shown clearly in Fig. 4. The vapor chamber performance is better than the heat pipe because the vapor chamber is flat in shape, which causes the uniform heat distribution on the large surface that leads to dissipate heat more. In addition, the vapor chamber easier to connect to the processor because it is flat and also can add extra surfaces on it such as fins to dissipate heat the heat faster [14]. Fig. 4. Comparison between the structure of the heat pipe and the vapor chamber [15], [16]. Fig. 5 shows the heat sink with heat pipes for desktop computer cooling. It is noted that the increase in the number of the heat pipes in the heat sink leads to decrease the thermal resistance which increased efficiency that is due to the heat pipe has a very high thermal conductivity as compared to the copper rod. This type is used to cool the CPU of the desktop computer because of it has a large size and cannot be used in Laptops. Fig. 5. Heat sink with heat pipes for desktop computer cooling [6], [8]. Fig. 6 shows the model that combines of three tools: the heat pipe, the heat sink, and the fan. The evaporator part of the heat pipe connects with the CPU and absorbs heat from the processor then transfers the heat to the edge of the electronic device and the heat sink is mounted on the end of the heat pipe (condenser part of the heat pipe) which the heat sink transfers heat from the heat pipe to the surrounding area outside the electronic device and fan is used to accelerate heat dissipation. This type is used for cooling the laptops as it also remote heat exchanger is called. Fig. 6. Heat sink with fan and heat pipe for laptops cooling [6], [17]. Table 1 shows a comparison between the vapor chamber, the heat sink, the heat pipe, and the heat sink with the heat pipe in terms of thermal resistance, cost, and efficiency.

V. COMPARISON BETWEEN THE COOLING TOOLS OF ELECTRONIC DEVICES
It is clear from Table 1 that the heat pipe and vapor chamber are highly efficient but they have a relatively high cost and this does not reduce the importance of the heat sink because it can be used extensively in desktop computers cooling and electronic devices of large size and it has low cost and easy to manufacture and installation and to be more efficient and reduce the thermal resistance it is combined with heat pipe.

VI. CONCLUSION
A brief review of the appropriate thermal solutions for the produced heat from the electronic equipment and the effective and suitable tools which used to dissipate this heat are presented. Vapor chamber, heat sink and heat pipe are reviewed and compared between them depending on the previous studies that have implemented them. It has been shown from this quick review that the thermal solutions for the electronic devices are very important and must take into account many factors in the thermal design must be paid attention to the rapid development of electronic devices. The heat pipe and the vapor chamber proved to be more performance than the heat sink.
It is recommended to study thermal solution using the piezo fan in a detailed and precise manner, which is important in the development of technology.
The biggest challenge is how we can benefit from the dissipated heat from electronic devices to convert it into clean energy such as an electrical energy, which will use to charge these devices.