Section 1 Introduction

## **Chapter 1**

## Introductory Chapter: Droplet Formation and Evolution

*Hongliang Luo*

## **1. Introduction**

Nowadays, decreasing carbon emissions becomes the global consensus. Therefore, in order to achieve carbon neutrality in the near future, many efforts should be done including energy transition, carbon capture, and carbon utilization. Among them, liquid-droplet flow can be applied in many industries, such as the internal combustion engine, colling machines, coating machines, hydraulic transmission equipment agricultural irrigation, and oil-gas transportation.

## **2. Liquid droplet formation**

Generally, nozzles or orifices are often applied to disperse the liquid into the air environment or another immiscible liquid. The discrete droplet is called the discrete phase, while the gas or other liquid is called the continuous phase. In addition, during the liquid-gas interaction, the liquid film may still break into small droplets. Therefore, in the industrial field, especially in the field of internal combustion engines, the discrete phase and continuous phase fluids move together, finally forming a common two-phase (gas-liquid) fluid. For example, the liquid fuel is firstly injected into the cylinder and atomized by the air movement. After fully mixed with air, fuel droplets are ignited and then explosively burned. The main mechanical behaviors of droplets are shown as follows:


## **3. Impingement and evaporation**

After droplet formation, it moves forward and may impact the solid wall or other phase, some behaviors then can be involved as shown in **Figure 1**.


**Figure 1.** *Droplet impacting behaviors.*

*Introductory Chapter: Droplet Formation and Evolution DOI: http://dx.doi.org/10.5772/intechopen.105390*

#### **Figure 2.**

*Behavior transition conditions.*

7. "Splash"—in which, following the collision of a droplet with a surface at very high impact energy, a crown is formed, jets develop on the periphery of the crown and the jets become unstable and break up into many fragments.

The existence of these impingement behaviors is governed by a number of parameters characterizing the impingement conditions. These include incident droplet velocity, size, temperature, incidence angle, fluid properties such as viscosity, surface tension, wall temperature, surface roughness, and if present wall film thickness and gas boundary layer characteristics in the near-wall region. Quantitative criteria for the behavior transitions from Bai and Gosman [1] and refined in the present work are presented in **Figure 2**.

All these droplet behavior including formation, evaporation, and evolution should be clarified to clearly understand the droplet dynamic. Especially for the current "carbon cycle" age, all the equipment should be re-design or developed with less CO2 emission to protect local environments. Among them, the droplets dynamic can be applied in many new technologies or even develop future renewable fuels.

## **Acknowledgements**

The author would like to acknowledge the National Natural Science Foundation of China [Grant 51909037] and the Foundation of State Key Laboratory of Engines [No. K2022-12].

## **Conflict of interest**

The authors declare no conflict of interest.

## **Author details**

Hongliang Luo1,2

1 Foshan University, Foshan, China

2 Hiroshima University, Higashi-Hiroshima, Japan

\*Address all correspondence to: luo@hiroshima-u.ac.jp

© 2022 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

*Introductory Chapter: Droplet Formation and Evolution DOI: http://dx.doi.org/10.5772/intechopen.105390*

## **References**

[1] Bai C, Gosman AD. Development of methodology for spray impingement simulation. Journal of Engines. 1995;**104**(3): 550-568

Section 2
