**1. Introduction**

Seminal advances in microelectronics technology have driven the Integrated Circuit Topographies (ICT) revolution over the last decades. Technologies of miniaturization, fabrication, and integrated circuit/system design are three vital parameters that have underpinned this revolution and allowed continuous and ongoing breakthroughs. However, the heat generated by electronic devices is always a fundamental problem that forced researchers to improve cooling systems to increase thermal efficiency. Since 85 °*c* is a critical temperature for electronic devices [1], exceed each 1 °*c* above critical temperature causes the reduction of 5% of devices life [2]. There are several methods to cool electronic devices as working fluid that are generally divided into (i) air cooling and (ii) liquid cooling. The efficiency of heat sinks increases due to the high thermal conductivity of liquids compared to air. Also, the increasing surface-to-volume ratio in heat sink leads to higher heat dissipation and extension of the electronic device's lifetime. Tuckerman and Pease [3] studied liquid cooling microchannel in single and multi-phase for the

first time. Several parameters have also been considered to improve microchannel heat sinks efficiency, such as changing the cross-sections, patterns, manifolds, and working fluids [4].

and soft lithography [9], laser cutting [10, 11], 3D printing [12, 13], microinjection molding [14] and glass etching for different applications like Point of Care (POC) and diagnosis [15, 16], microbiology [17, 18], drug delivery [19–21], oil and gas [22], micropump [23, 24], particle separation and enrichment [25–27], Organ on a chip

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

Microchannel and micro pin-fin are two types of heat sinks that are used in electronic cooling systems. The microchannel heat sink consists of extended parallel channels in different cross-sections (such as rectangular, hexagonal, triangular, etc.) that coolant flow passes from channels and absorbs heat from the chip. With advances in nano/micro-manufacturing techniques, another type of heat sink used in cooling circuits is a micro pin-fin heat sink. This heat sink type consists of pin-fin arrays in different shapes (like rectangular, hexagonal, elliptic, circular, etc.) and due to the high flow mixing rate, thermal performance increases compared to the

The thermal/hydraulic performance of the heat sink is affected by geometrical parameters (such as the shape of the cross-section, pattern, inlet/outlet arrangement) and flow parameters (such as working fluids and boiling flow) [35]. In this section, the effective parameters on the heat sink's thermal–hydraulic performance

Previous research indicates that changing pattern plays a fundamental role in enhancing the heat transfer rate [4]. The concept of periodic renewal of thermal boundary layers is a useful technique for enhancing heat transfer. Besides, secondary flows and fluid mixing are considered other factors for heat transfer enhance-

Furthermore, research has shown that increasing heat transfer will reduce the pressure drop penalty [2, 3, 36]. Therefore, setting a balance between the heat transfer enhancement and the pressure drop penalty is required for discovering the

Several works studied the impact of pattern designs on heat transfer including, periodic (wavy, zigzag, etc.) [38–42], serpentine [43, 44], pin-fin [45, 46], and oblique [47–50] and most efficient pattern designs are summarized in **Table 2**.

The impact of the microchannel heat sink's pattern on thermal performance was investigated numerically by Lin et al. [51]. They reported that due to dean vortices formation in the channel's cross-section, the fluid mixing enhanced, and the thermal boundary layers' thickness decreased. Therefore, wavy heat sinks had better thermal performance compared to conventional straight heat sink due to higher Nusselt number and lower thermal resistance. After Lin et al. [51], another research

microchannel shown in **Figure 1**. Results illustrated that with increasing the amplitude to wavelength ratio (relative waviness), the thermal performance increased

optimum pattern design. Some relations, such as efficiency index (ɳ) and Performance Evaluation Criteria (PEC), could help to identify these crucial

group, Sui et al. [38] investigated the effect of wave amplitudes in wavy

**3. Effective parameters on the efficiency of heat sinks**

[28–30], biosensor [31–34].

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

microchannel heat sink.

are presented.

*3.1.1 Patterns*

parameters [37].

**157**

**3.1 Geometrical parameters**

ment that can be formed in pattern design.

compared to the straight microchannel.

Some technical issues have been reported, like generating hotspots and pressure drop through the microchannel for different applications. For instance, Copeland et al. [5] illustrated the impact of pressure drop and temperature gradient on system functionality. Moreover, they reported high-pressure drops (2 bars) for reaching minimal thermal resistance due to the small size of channels. Although utilizing a pump could compensate, the generated pressure drop which is used in conventional applications, using these pumps on a micro-scale is almost impossible [6]. The thermal boundary layer in convectional channels is maintained in a fully-developed state; thus, the thermal resistance increases and caused non-uniform heat transfer performance, leading to an unreliable platform and system failure. A large number of researches have been carried out to address these limitations by changing geometrical parameters and fluid flow structures in a microchannel.

In the current study, all previously reported parameters relating to enhancing the heat sink efficiency are considered. The efficient parameters on the performance of micro heat sinks are divided into two main parts, i.e., (i) Geometrical and (ii) Flow parameters. Geometrical parameters include patterns, cross-sections, and manifolds of heat sinks that the prior studies in this area are sorted and are explained in detail, and a comprehensive table is presented for each section. Also, working fluids (nano-fluids, phase change materials (PCMs) slurries, and boiling flows) are investigated as subsections of flow parameters. Besides, almost all micro heat sink applications in real life are characterized and the most significant of them, such as PCs and laptops, PCRs, gaming consoles, and data servers, are explained in detail, and other applications are listed. Finally, the suggestions and future direction of heat sink research are presented.
