*3.2.1.2 Phase change material (PCM)*

Advanced liquid coolants such as PCM are reported as effective substitutions for conventional coolants to enhance the heat transfer rate of microchannel heat sinks [91]. Furthermore, using phase change material (PCM) improves the coolants' thermophysical properties using the latent heat of melting.

PCM slurries are created by adding micro/nano encapsulated PCM particles to the base fluid (water, ethylene glycol, and paraffin). The PCM reveals a higher heat transfer rate when the PCM particles undergo a phase change transition [92–95]. One of the disadvantages of using nanofluids and PCM slurries is the higher viscosity than the base fluid, which imposes high pumping power on the system. Therefore, establishing a balance between heat transfer enhancement and pressure drop penalty is essential to distinguish the optimum advanced coolant [89]. Some of the significant nanofluids and PCM slurries used as working fluids are listed in **Table 5**.


#### **Table 5.**

*Different types of working fluids used in previous investigations.*

In order to reach the optimal flow distribution, maldistribution should be reduced along the microchannel. In most cases, Rectangular header shapes with vertical configurations cause low MLD compared to horizontal ones, and I-type has a symmetrical flow distribution that attracts most of the researchers for different

**type**

V/V/V & V/V/V

H/H/H & V/V/V

B: front

**Outlet type**

V/V/V & V/V/V

H/H/H & V/V/V

A: Side & B: front

V V N.A. N.A.

hierarchical manifold V V N.A. N.A.

U/Z-type H/H H/H Z-type U-type

**Max MLD Min MLD**

Tri. & Z-type Rec. & I-type

Rec. in high flow rate & Trp./Tri. in low flow rate

Rec. in low flow rate & Trp./Tri. In high flow rate

A B

Flow parameter is another crucial parameter in the heat sinks thermal performance and according to the latest research, flow parameters can be classified into

The right selection of coolant fluid is a critical factor in removing the generated heat and according to literature, the air-cooling systems have received more attention in the past. However, with advances in electronic technology and the miniaturization of devices, conventional (air) cooling systems cannot remove more than 100 W/cm<sup>2</sup> generated heat by electronic devices. Therefore, liquid cooling such as water due to high specific heat capacity, high thermal conductivity, and more availability is considered more than ever [85]. Nowadays, with advances in nanotechnology, researchers classified working fluids into two categories, (1) nanofluids and (2) phase change material (PCM) slurries. They reported that improved thermophysical properties and higher thermal conductivity could be the advantages

Since fluids conductivity plays a vital role in the heat transfer from a solid surface to a fluid domain, conventional heat transfer coolant such as water, ethylene glycol, and paraffin have low thermal properties compared to metals and even

two categories: (1) working fluids and (2) Boiling flow.

**Author Parameters Inlet**

*Advances in Microfluidics and Nanofluids*

shape

Tri./Trp./Rec. header shape & C/I/Z-type

Rec./Trp./Tri. header

location of the inlet and outlet

*Review literature about manifolds influence on flow distribution.*

Type of entrance flow A: Side &

Junye Wang and Hualin Wang [81]

Guodong Xia et al.

C.Anbumeenakshi et al. [76]

Chun-Kai Liu et al.

Wang Yabo et al.

[77]

[82]

[83]

[84]

**Table 4.**

Kevin P. Drummond et al.

applications.

**3.2 Flow parameters**

*3.2.1 Working fluids*

of these liquid coolants [86].

*3.2.1.1 Nanofluids*

**164**

### *3.2.2 Boiling flow*

From the cooling performance perspective, two-phase flow boiling in microchannel heat sinks is more efficient than its single-phase equivalent. A temperature lower than the critical temperature and the coolant's boiling points provide sufficient factors for increasing heat transfer rate. Due to the nature of boiling and turbulent flow in the microchannel, while requiring a low rate of coolant flow and maintaining the wall temperatures relatively uniform, the boiling heat transfer coefficient is much higher than conventional systems [107]. The main problems in this type of system are higher pressure drop and instability of the system. Due to the biphasic flow inside the channels and the creation of larger bubbles, the higher pressure drop in the system may occur because of the channels' poor design.

**4.1 Computers and laptops**

*DOI: http://dx.doi.org/10.5772/intechopen.96467*

cooling companies.

**4.2 Gaming consoles**

**Figure 6.**

**167**

High-performance computing is the ability to process data and perform complex calculations at high speeds. One of the most common questions any manufacturer receives from customers is, "Why does my laptop or computer generate so much heat?" Heat is a normal byproduct of computer operation; for instance, a highperformance computer generates considerable heat than a lower performance computer. So, if the computer cannot disburse its heat, it may overheat, and device life will reduce. Therefore, this is a significant challenge for the manufacturer to solve. A heat sink is a thermally conductive device placed over a CPU or GPU to absorb some generated heat. Faster and multi-core processors require more high-efficiency heat sinks to keep their temperatures within acceptable levels. Nowadays, some

*Effective Parameters on Increasing Efficiency of Microscale Heat Sinks and Application…*

Asus [110], Alphacool [111], CoolIT Systems [112], Cool Innovations Inc. [113], Xtreme Performance Gear (XPG) [114], Coolermaster [115], Antec [116], Swiftech [117] and Thermaltake [118] are popular companies that work in cooling field. According to their operating principles, all companies used water as a cooling fluid. **Figure 6** shows some of the micro pin-fin/channel heat sinks manufactured by

As shown in **Figure 6a–c**, some companies use a straight pattern microchannel, and others use a pin-fin pattern (presented in **Figure 6d** and **e**). Although complex patterns increase the heat transfer rate, they cause a significant pressure drop. Some companies use different patterns without considering the pressure drop penalty,

According to Section 3.1.3, fluid and temperature MLD are decreased by using Itype flow arrangements and vertical inlet/outlet type. It concludes that the vertical inlet/outlet and I-type arrangements are implemented in commercialized products. Some of the heat sinks are made by several manufacturers and use vertical inlet/ outlet type. Asus ROG GX700 is the first liquid-cooled gaming laptop in the world and the liquid coolant is circulated around the heat-generating components like GPU by pumps. The coolant then heads back to the cooling module, where two heat

Many consoles were designed with cooling fans in the past, but due to advances in thermal engineering, novel consoles are designed with liquid cooling fins and heat sinks to keep the internal components safe from high generated heat.

PlayStation 5 (PS5) is the new video game console developed by Sony [119] Interactive Entertainment that utilized a heat sink with a hard copper plate with

companies professionally work in cooling system designing fields.

such as a micro pin-fin pattern to enhance heat sink performance.

sinks (radiators) help dissipate heat, that is shown in **Figure 7a**.

*(a) Alphacool, (b) Swiftech, (c) Thermaltake, (d) and (e) cool innovations Inc.*

Numerous studies have been conducted to explore the convection heat transfer characteristics of two-phase flow boiling in micro pin-fin/channel heat sinks in recent years. Wei Wan et al. [108] experimentally examined the effect of crosssection shape on flow boiling characteristics of micro pin-fin heat sinks. Four types of staggered micro pin-fins with different cross-section shapes, i.e., square, circular, diamond, and streamline, were tested in this study. Results showed that the square shape presents the higher boiling heat transfer, followed by circular and streamlined ones. The diamond micro pin-fins presented the smallest pressure drop, while their main problem is instability at moderate to high heat fluxes. The streamline micro pin-fins presented the largest two-phase pressure drop. Besides, the square and circular micro pin-fins showed their superiority in reducing two-phase flow instabilities. Matthew Law and Poh-Seng Lee [49] conducted an experimental study of flow boiling heat transfer and pressure characteristics in straight-finned and oblique-finned microchannels. They reported that the oblique-finned microchannels' thermal performance is higher than straight-finned ones due to the increase in the density of bubbles generated in the convective boiling regime. The high pressure-drop in oblique-finned microchannels causes a sudden change in the flow orientation, where the fluid is being forced to flow through secondary channels. The pressure drop fluctuations in the oblique-finned pattern are much lower compared to the straight-finned; consequently, the pressure instabilities in the oblique-finned microchannels are relatively smaller than the straight-finned microchannels.
