*3.1.3 Manifolds*

Designing the manifolds is another primary geometrical parameter that researchers focus on to achieve a high-performance heat sink. Studying manifolds can be classified into three categories, including (a) location of inlet and outlet, (b) fluid inlet and outlet configuration (horizontal or vertical), and (c) header shape types. Some differences between experimental and theoretical results have been reported due to the maldistribution (MLD) in microchannel's branches and forming non-uniform temperature distribution in the edges of multiple microchannels. On the other hand, no difference was observed in single microchannels' results [72–75]. So, it can be concluded that an essential goal of studying manifolds is to achieve uniform flow and temperature distribution and remove hot spots for obtaining optimal performance.

Anbumeenakshi and Thansekhar [76] experimentally examined the effect of header shapes and inlet configurations in flow MLD in a rectangular microchannel heat sink (**Figure 5**). Results illustrated that trapezoidal and triangular types showed better flow uniformity at low flow rates. Also, the rectangular header improved flow MLD at high flow rates.

Xia et al. [77] analyzed the effects of three inlet and outlet flow arrangements (I, C, and Z-type), as well as header shapes (triangular, trapezoidal, and rectangular). The results illustrate that the I-type arrangement generated a uniform flow distribution compared to other configurations. Similarly, the rectangular header shape produced better flow uniformity than other headers. Critical parameters for flow distribution in the manifold are summarized in **Table 4**.

Note. H: Horizontal, V: Vertical, Min: Minimum, Max: Maximum, Rec: Rectangular, Trp: Trapezoidal, Tri: Triangular, MLD: Maldistribution, and N.A: Not Applicable/Not Available.

#### **Figure 5.**

*Different header shape and inlet configurations. (a) Trapezoidal-inline. (b) Rectangular-inline. (c) Triangular-inline. (d) Trapezoidal-vertical. (e) Rectangular-vertical. (f) Triangular-vertical [76].*


According to results, a microchannel with a rectangular cross-section presented maximum performance compared to other microchannel cross-sections. The shape with no sharp corners obtains higher performance in micro pin-fins. It is hard to conclude precisely the best cross-section because the applied conditions play a

significant role in micro pin-fin/channels heat sink performance.

*Flow streamline of (a) square, (b) circular, and (c) triangular micro pin-fin [67].*

**Size of a heat sink**

L = 20 mm

L = 12 mm

Microchannel N.A. q″ = 1000

L = 35 mm

L = 16 mm

W = 12.5 mm L = 25 mm

L = 125 mm

L = 12.7 mm

L = 10.3 mm

L = 30.4 mm

Micro pin-fin N.A. Heat

Micro pin-fin W = 52.80 mm

Micro pin-fin W = 10 mm

**Heat flux/ Power input**

<sup>q</sup>″ = 35 <sup>105</sup> (W/m2 )

> <sup>q</sup>″ = 500 (kW/m<sup>2</sup> )

> (kW/m<sup>2</sup> )

Heat power = 300 W

<sup>q</sup>″ = 32 <sup>104</sup> (W/m2 )

> <sup>q</sup>″ = 37.2 (kW/m2)

Heat power = 273 W

> <sup>q</sup>″ = 144 (W/cm<sup>2</sup> )

power = 300 W

<sup>q</sup>″ = 10, 50 and 100 (W/cm<sup>2</sup> )

**Type of shapes**

Rectangular, Circular, Trapezoidal

Hexagonal, Circular, Rhombus

> Trapezoidal, Triangular, Rectangular

Rectangular

Triangular

Hexagonal fin Plate fin

Square, Circular, Hexagonal

Oblique fin

Rhombus, Hydrofoil, Sine

cylindrical perforated fins

elliptical pin fin with different aspect ratio

N.A. Square, Circular,

**sink**

Yanjun Zhang et al. [68] Microchannel W = 2 mm

A.A. Alfaryjat et al. [64] Microchannel W = 22 mm

Gongnan Xie et al. [70] Microchannel W = 35 mm

Mushtaq Ismael Hasan [53] Micro pin-fin W = 6 mm

Yong Jiun Lee et al. [49] Microchannel W = 12.7 mm

Dawei Yang et al. [56] Micro pin-fin W = 10.3 mm

*Note. L: Length, W: Width, and N.A: Not Applicable/Not Available.*

*Summary of some studies in a different type of cross-sections.*

Plate pin-fin

S. Subramanian et al. [45] Micro pin-fin

**Author Type of heat**

*Advances in Microfluidics and Nanofluids*

Hamdi E. Ahmed and Mirghani I. Ahmed [69]

Tehmina Ambreen and Man-Hoe Kim [65]

Fatima Zohra Bakhti and Mohamed Si-Ameur [57]

Kewalramaniet al. [71]

Gagan V.

**Table 3.**

**162**

**Figure 4.**


metal oxides [87]. The use of nanoparticles is an effective method for modifying the heat transfer properties of fluids. Masuda et al. [88] were the first to study changes in the thermal conductivity and dynamic viscosity of base liquids with the addi-

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

The nanofluid and PCM's thermodynamical properties are defined based on the

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'

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

**fluid)**

water

Mingoo Choi and Keumnam Cho [99] Water 5% Paraffin slurry as PCM Bahram Rajabifar [86] DI water n-Octadecane as PCM and

Lisi Jia et al. [101] Water TiO2 as the nanoparticles

water

Hamideh Sardarabadi et al. [104] Water Multi-walled carbon nanotubes O. Pourmehran et al. [95] Water *Cu*O as the nanoparticles Arash Karimipour et al. [105] Water *Al*2*O*3 and *AgO* as the

Min Li [103] Paraffin Nano-graphite

Vivek Kumar and Jahar Sarkar [106] Water *Al*2*O*3–MWCNT

**Phase two (particles)**

ZnO as the nanoparticles

Alumina as nano particles

*Al*2*O*3 as the nanoparticles

*Al*2*O*3 as the nanoparticles

Water RT82 as a PCM and

TiO2 and

nanoparticles

nanoparticles, nanotubes, and various distributed sizes were developed to investi-

Due to nanotechnology nanofluids advancement, different types of

gate the stability and of nanofluidic during the cooling process [90].

thermophysical properties using the latent heat of melting.

**Author Phase one (base**

K.S. Suganthi et al. [96] Ethylene glycol and

Thaklaew Yiamsawas et al. [102] Ethylene glycol and

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

Jasim M. Mahdi and Emmanuel C. Nsoforet

Zhou. Nianyong et al. [97] Water — A.M. Bayomy et al. [98] Water —

tional fine metallic and non-metallic oxide particles.

base fluid (i.e., DI water) [89].

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

*3.2.1.2 Phase change material (PCM)*

**Table 5**.

[100]

**Table 5.**

**165**

### **Table 4.**

*Review literature about manifolds influence on flow distribution.*

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 applications.
