Nanofluid in Heat Exchangers for Mechanical Systems

Numerical Simulation

Zhixiong Li, Ahmad Shafee, Iskander Tlili, M. Jafaryar

• Publisher: Elsevier
• Year: 2020
• ISBN:
  9780128219249
• Topic: Technology & Engineering
• Subtopic: Materials Science
• Index: Technology & Engineering

Nanofluid in Heat Exchanges for Mechanical Systems: Numerical Simulation shows how the finite volume method is used to simulate various applications of heat exchanges. Heat transfer enhancement methods are introduced in detail, along with a hydrothermal analysis and second law approaches for heat exchanges. The melting process in heat exchanges is also covered, as is the influence of variable magnetic fields on the performance of heat exchange. This is an important reference source for materials scientists and mechanical engineers who are looking to understand the main ways that nanofluid flow is simulated and applied in industry.

• Provides detailed coverage of major models used in nanofluid analysis, including the finite volume method, governing equations for turbulent flow, and equations of nanofluid in presence of variable magnetic field
• Offers detailed coverage of swirling flow devices and melting processes
• Assesses which models should be applied in which situations

Chapter 1

Fundamentals of heat exchangers

Abstract

Economic reasons (material and energy saving) leads to make efforts for making more efficient heat exchange. The heat transfer enhancement techniques are widely used in many applications in the heating process to make possible reduction in weight and size or enhance the performance of heat exchangers. These techniques are classified as active and passive techniques. The active technique required external power, while the passive technique does not need any external power. The passive techniques are valuable compared with the active techniques because the swirl inserts manufacturing process is simple and can be easily employed in an existing heat exchanger. Insertion of swirl flow devices enhances the convective heat transfer by making swirl into the bulk flow and disrupting the boundary layer at the tube surface due to repeated changes in the surface geometry. An effort has been made in this chapter to carry out an extensive literature review of various turbulators (coiled tubes, extended surfaces (fin, louvered strip, winglet), rough surfaces (corrugated tube, rib) and swirl flow devices such as twisted tape, conical ring, snail entry turbulator, vortex rings, coiled wire) for enhancing heat transfer in heat exchangers. It can be concluded that wire coil gives better overall performance if the pressure drop penalty is considered. The use of coiled square wire turbulators leads to a considerable increase in heat transfer and friction loss over those of a smooth wall tube.

Keywords

Friction factor; Heat exchanger; Heat transfer performance; Nusselt number; Passive heat transfer; Swirl flow devices; Turbulators

1.1. Introduction

1.1.1. Importance of heat exchangers

Heat exchangers have different applications ranging from conversion, recovery of thermal energy in different industrial, domestic, and commercial uses. Some public examples include cooling in thermal processing of chemical, condensation in power, agricultural products, pharmaceutical, steam generation, sensible heating, cogeneration plants, waste heat recovery, and fluid heating in manufacturing. Enhancement in heat exchanger's performance can make more economical design of heat exchanger which can aid to make energy, material, and cost savings related to a heat exchange process.

The importance of increasing the thermal performance of heat exchangers has caused development and use of many techniques termed as heat transfer enhancement. These methods augment convective heat transfer by reducing the thermal resistance in a heat exchanger. Utilization of augmentation techniques leads to increase in heat transfer coefficient but at the cost of increase in pressure drop. To reach high heat transfer rate while taking care of the augment pumping power, various techniques have been presented in recent decade. Recently, swirl flow devices have widely been used for increasing the convective heat transfer in various industries. This application is because of their low cost and easy setting up. The main aim of this chapter is to introduce the different ways to improve heat transfer performance. An extensive literature review of various turbulators (coiled tubes, extended surfaces (fin, louvered strip, winglet), rough surfaces (corrugated tube, rib), and swirl flow devices such as twisted tape, conical ring, snail entry turbulator, vortex rings, coiled wire) has been carried out.

1.1.2. Important definitions

In this part, a few significant terms usually used in heat transfer enhancement work are introduced. Thermal performance factor is commonly used to estimate the performance of different inserts such as wire coil, twisted tape, etc. It is a function of the heat transfer coefficient and the friction factor. The thermal performance factor of an insert device is good if this device can reach significant increase of heat...