Preface

Heat transfer, its mechanism, augmentation, and applications are an aid to various aspects of engineering design. With energy saving and environmental protection high on the scientific community's agenda, the augmentation and application of heat transfer are highly significant. *Heat Transfer - Fundamentals, Enhancement and Applications* is a contribution to these endeavors.

This book has four sections: "Fundamentals of Heat Transfer and Mechanism", "Different Forms of Heat Transfer and Applications in Various Aspects", "Heat Transfer Enhancement and Techniques", and "Fouling and Its Mitigation in Heat Exchangers".

Boiling and condensation heat transfer are manyfold higher than convective heat transfer. Chapter 1, "Boiling and Condensation", provides a brief overview of these two heat transfer phenomena. A detailed explanation is given of different classifications of boiling, including pool, flow, subcooled and saturated boiling, and different boiling regimes (natural convection boiling, nucleate boiling, transition boiling, film boiling). Types of condensation (drop and film-wise), their heat transfer aspects and applications are also presented. The chapter also includes information about advanced heat transfer enhancement techniques available for boiling and condensation.

Energy conversion is a very contemporary concern. Thermal radiation is converted into heat in many activities: drying agricultural products, space heating, desiccant regeneration, timber seasoning and natural ventilation. Indigenous materials can be used for solar air heating. Solar thermal air heaters have low performance because the convection heat transfer coefficient of the air is low, and the heat loss to the environment is considerable. Chapter 2, "Heat Transfer in Double-Pass Solar Air Heater: Mathematical Models and Solution Strategy", presents two mathematical models of convection and radiant heat transfer in double-pass solar air heaters, which are commonly used because they produce higher air temperature than that of a single pass heater. In this case, the average temperature model was solved by dealing with a system of linear algebraic equations and the other model was derived as ordinary differential equations and solved by numerical integration.

Chapter 3, "Transfer of Heat through a Thin Liquid Film", discusses heat transfer in thin liquid film past a stretching surface in the presence of Joule heating, radiation, viscous dissipation, and magnetic effect. The nonlinear coupled partial differential equations were reduced to nonlinear ordinary differential equations, which were then solved using the shooting method. The effects of Prandtl and Eckert numbers over the temperature distribution were incorporated. Increasing unsteadiness parameter values on the thermal conductivity of the fluid are reported.

Chapter 4, "Heat and Mass Transfer of a Decoupling Cooling System: A Desiccant-Coated Heat Exchanger and a Dew-Point Evaporative Cooler", investigates a de-coupling cooling technology where latent cooling load and sensible cooling load were handled separately by a desiccant-coated heat exchanger-based dehumidifier and a dew-point evaporative cooler. The undesired moisture in the outdoor air was discarded through adsorption and the dehumidified air was then cooled by the dew-point evaporative cooler to the desired temperature. Performance was investigated numerically by analyzing the heat and mass transfer.

Chapter 5, "Dropwise Condensation and Heat Transfer", discusses the fundamentals of condensation, heat transfer and relevant equations for dropwise condensation. Dropwise condensation is much more effective than film-wise condensation because water droplets formed on the nucleation sites accumulate, enhancing heat transfer as they detach from the surface. As the contact angle of the water droplet increases, the heat flow resistance between the substrate and the vapor decreases, and the heat transfer coefficient and the condensation rate both increase. Augmentation in boiling heat transfer was performed by modifying the texture of the bare surface using the thermo-solution immersion method.

Forced cooling in a very large-scale integrated circuit became a turning point to reconsider how to improve the capacity to cool down highly energy-consuming devices and systems. Researchers have sought to enhance equipment performance in heat and mass transfer engineering, and these techniques are discussed in Chapter 6, "Boiling Heat Transfer on the Micro-Textured Interfaces". Micro-/nano-textured aluminum and copper devices can enhance the boiling heat transfer process to the subcooled water. Forced water cooling over a surface with convex micro-textures was achieved by varying the Reynolds number, and the resulting heat transfer characteristics were investigated. The newly constructed boiling curve on the micro-textured interfaces is also presented here.

The use of multiple laser tracks leads to nonuniform hardness in the surface of components. In Chapter 7, "Multi-Track Overlapping by Laser-Treated and Its Effects on the Microstructural Behavior of Al-Fe Alloy Assessed by FEM", a numerical simulation was applied, using the finite element method, optimized through the multigrid technique, to study the influence of multi-track overlapping on the microstructure processed by laser surface remelting. The experimental and numerical simulation results of the multi-track overlapping were validated.

Chapter 8, "A Review on Condensation Process of Refrigerants in Horizontal Microfin Tubes: A Typical Example", explores the application of micro fins in refrigeration systems. Proper refrigerant with good thermodynamic properties helps optimize the equipment. Micro fin tubes can be used to improve heat transfer performance while reducing the size, weight, and amount of refrigerant in the system and maintaining a suitable environment.

Thermal management of modern electronic equipment is discussed in Chapter 9, "Internal and External Influences on Hydro-Thermal Behavior of Micro-channel Flow". Heat generation has become a recurring problem in high-powered electronic systems, energy storage batteries, fuel cells, etc. Operation of these electronic devices at higher temperatures reduces their performance, lifespan and reliability. Microchannel flow is one of the effective solutions for many thermal engineering problems.

Global energy production and consumption levels from fossil fuels (coal, oil, and natural gas) are unsustainable, with energy consumption expected to increase threefold in the next 30 years. Fossil-fueled power plants convert heat into mechanical energy and then to electrical energy using a heat exchanger. Researchers are investigating various ways of saving energy by increasing the heat transfer coefficient, and hence the performance, of a heat exchanger with smaller dimensions. Chapter 10, "The Combined Method to Improve Heat Transfer Coefficient on Heat Exchanger", focuses on the enhancement of thermal properties of the cooling fluids by introducing nanofluids to enhance the overall performance of the heat exchanger. The combination of nanofluids and ultrasonic vibrations was found to improve overall heat transfer performance in heat exchangers.

Chapter 11, "Enhancing Surface Heat Transfer Characteristics Using Laser Texturing", reports the use of a pulsed laser system to manufacture parallel streamwise riblets on the plates of a heat exchanger. The alteration of surface morphology for enhancement of heat transfer or drag reduction on a surface has been the subject of research for some time. Although skin drag reduction positively lowers energy consumption and enhances heat transfer, there has been little notable research in this area. Surface roughness is thought to keep heat transfer efficiency high in two flow regimes, laminar and turbulent.

Heat exchangers are used extensively in everyday life. The outlet temperature on the secondary side of the heat exchanger can be controlled by the flow on the primary side under given inlet temperature conditions on the primary and secondary sides, using an electronic controller. Chapter 12, "Digital Twin of Heat Exchanger", has investigated alternative models in the trade-off between the accuracy of the calculation and speed.

Fouling material deposits on the heat exchanger surface are usually gradually solidified by the action of heat, and since they have lower thermal conductivity than the substrate, heat exchanger performance is gradually reduced, eventually causing it to be shut down for maintenance. Chapters 13 and 14, "Fouling and Mechanism", and "Fouling in Industrial Heat Exchangers: Formation, Detection and Mitigation", discuss fouling, its formation mechanisms and mitigation approaches. Design concepts, and the operation, cleaning, and maintenance of heat exchangers in industrial practices are also covered.

Although this work was an addition to my routine academic workload, it was thoroughly enjoyable. I would like to thank my students for their patience in receiving delayed support from me. Lastly, I would like to thank my wife, Nilufa Parveen, and son, Kazi Mehrab Newaz, for their sacrifices in our daily life for the duration of this work.

> **Salim Newaz Kazi** Faculty of Engineering, Department of Mechanical Engineering, University of Malaya, Kuala Lumpur, Malaysia

Section 1

Fundamentals of Heat

Transfer and Mechanism

**1**

Section 1
