Pressure Drop And Heat Transfer Enhancement In Wire Mesh Screen

ABSTRACT

In this paper, the insertion effect of a woven wire mesh to cross flow heat exchanger will be studied under steady state laminar flow conditions. 3-D numerical model was developed for the bare heat exchanger and the other wire mesh modules. The mesh wire diameter is 2.5 mm, porosity of 0.75, permeability of 10-10 and layer-to-layer spacings of (3,5,10,15,20 and 25 mm).Air flows with velocity range up to 3.5 cm/s through rectangular duct of 50 cm X 25 cm with inlet temperature of 25oC before it is heated with corrugated water tube (19 mm in diameter) with hot water inlet velocity of 1 m/s and temperature of 50 oC. The thermal and hydraulic performance were evaluated. Results showed that an enhancement in overall heat transfer coefficient was achieved of 250 % for the 3 mm spaced module while the air pressure drop increases significantly.

TABLE OF CONTENTS

Cover page

Title page

Approval page

Dedication

Acknowledgement

Abstract

CHAPTER ONE

INTRODUCTION

1.1      Background of the study

• Problem statement
• Aim and objective of the study
• Scope of the study
• Applications of heat transfer enhancement
• Definitions of Terms

CHAPTER TWO

LITERATURE REVIEW

• Review of the study
• Review of heat transfer enhancement techniques
• Review of related studies

CHAPTER THREE

NUMERICAL METHOD

• Physical model
• Governing equations
• Solution method
• Boundary Conditions
• Mesh dependence test

CHAPTER FOUR

4.1      Results and Discussion

CHAPTER FIVE

• Conclusion and Recommendation

References

CHAPTER ONE

1.0                                               INTRODUCTION

1.1                                 BACKGROUND OF THE STUDY

Heat exchangers are extensively used in several industry equipment’s such as thermal power plants, chemical processing plants, air conditioning, equipment etc. The mechanisms of enhancing heat transfer are classified as active or passive methods and there are several studies have reported that the use of porous media for enhancement heat transfer yields higher heat transfer performance than the other techniques. Porous media with high thermal conductivity have emerged as an effective method of heat transfer enhancement due their large surface area to volume ratio and intense mixing of the flow. Examples of industrial application involving porous media are chemical catalytic reactors, petroleum reservoirs, and geothermal energy thermal storage. By using the porous media as transport medium, fluid mixing and the heat exchange area between the solid matrix and fluid phase will be increase and leads to significant enhancement in heat transfer.

Energy problems crowd into the headlines at ever more frequent intervals and become more difficult to solve. The use and cost of energy affects each of us every day of our lives. Therefore, energy consumption must be rationalized with the global increase in energy demand. Many industrial and domestic applications involve heat exchangers, which if its performance enhanced, can provide savings in both energy utilization and cost. The performance enhancement could be achieved either by active ways or passive ways. One of the most used passive techniques in engineering applications is fins. (Wang, Dong, Cao, Peng, & Jiang, 2020) conducted an experimental study to evaluate hydrothermal performance of a harmonica tube with and without mini-fins. Different configurations for the harmonica tube with smooth channels and channels with mini-fin. The results showed that the transition from the laminar to turbulent flow regimes shifts to a smaller Reynolds number due to the presence of the mini-fins as compared to the smooth channels. (Dogan & Sivrioglu, 2012) performed an experimental and numerical investigation on the effects of clearance gap on mixed convection heat transfer from array of fins in a horizontal channel. The fluid velocity entering the horizontal channel was varied between (0.02 up to 0.023 m/s) which makes the flow in the laminar regime. The results show that the heat transfer rate increases with the decrease in the clearance gap. (Kewalramani et al., 2019) performed an experimental and numerical study to evaluate the hydraulic and thermal performance of elliptical pin fin micro heat sink applied with constant heat flux from the bottom. The fluid flow and heat transfer for micro elliptical shaped pin fin heat sink is studied numerically and experimentally in this study. Results showed that the hydraulic and thermal performance of micro pin fin heat sinks is dependent on the porosity and aspect ratio of the micro pin fin. (El Maakoul et al., 2017) numerically investigated the thermohydraulic performance of air to water double pipe heat exchanger with helical fins. Results showed that for the same tube length, helical fins have about 3%–24% heat transfer surface area higher than longitudinal fins. Both arrangements of heat exchangers the same weight. For the same mass flow rate ,tube length and pumping power the heat transfer rate with helical fins is higher than that with longitudinal fins. (Huisseune et al., 2010) conducted an experimental study to evaluate the thermohydraulic performance a single row heat exchanger with helical fins tubes. The heat transfer rate and flow friction factor correlations are determined. The transversal pipe pitch was parametrically varied. The heat transfer rate correlation can predict 95% of the data within mean deviation of 4.49%. (Dong et al., 2010) carried out an experimental and numerical study to evaluate the thermohydraulic performance of wavy fin and flat tube heat exchangers. The study showed three numerical simulations and experimental investigation of air flow and heat transfer characteristics over the wavy fin heat exchanger. The experimental results show that, For the range of Re of air (from1000 to 5500), the standard k-ε mode (SST) is more suitable to simulate the air flow and heat transfer of wavy fin. On the other side the porous media inserts such that metal foams, wire mesh screens and lattice frame materials are promising candidates that could achieve enhancement higher than fins. Various experimental and numerical studies are performed to evaluate the thermal behavior of metal foam heat exchangers. (Mahajan, 2001) conducted an experimental study upon high porosity metal foams. The study presents the analytical correlations and experimental data for the effective thermal conductivity of such porous media. The study also presents results on “pool” boiling of Fluor inert fluids in such foams. (Angirasa, 2002) conducted an experimental study to investigate forced convection heat transfer with two aluminum metallic fibrous materials having different porosities of 0.93 & 0.97. The study tested the effectiveness of metal foams heat exchangers. Results show that the tested patterns with the lower porosity have lower thermal resistance and higher heat transfer rates. (Lu et al., 2006) performed an analytical study to evaluate both thermal and hydraulic performance of high porosity open-cell metal-foam filled heat exchangers. The enhancement in the thermal performance is 40 times higher than the smooth pipes but the pressure drop will be also higher. (Mancin et al., 2012) studied, through experimentation, the thermo-hydraulic performance of five different copper foam samples with different pore densities of (5,10,20 and 40 PPI), and different porosities varying between 0.905 and 0.934. Results showed that Cu-5-6.7 sample appears to have the best performance on the other hand. The results of the experiment show that the Cu-10-9.5 copper foam sample can be considered a suitable and viable solution for the design of innovative thermal management solutions for electronic cooling applications. (Kamath et al., 2013) showed through experiment the effect of thermal conductivity on heat transfer and pressure drop in a vertical channel embedded with aluminum and copper foams of high porosity. Copper foams of porosity of 0.87 and aluminum foams of porosity 0.95 gave the same heat transfer performance for the same velocity range and heat flux condition. (Hwang et al., 2002) conducted an experimental study to measure convective heat transfer and friction factor for flow across aluminum foams for air flow through rectangular channel. Results show that both the friction factor and the volumetric heat transfer coefficient increase with decreasing the foam porosity at a fixed Reynolds number. In addition, the aluminum foam of (ε =0.8) has the best thermal performance under the same pumping power constraint among the three aluminum foams investigated. (Fugmann et al., 2015) conducted both numerical and experimental study to evaluate the thermohydraulic performance of woven wire gas-To-liquid heat exchanger An enhancement in the convective heat transfer coefficient was achieved with using woven wire mesh. Correlations for predicting the friction factor and Nusselt number were derived using measurement data. (Dyga & Płaczek, 2010) showed by experimentation, the hydrothermal performance of heat exchangers with wire mesh packing. Results showed that differences between heat fluxes (in an empty and packed channel) compensates for the higher demand for energy to pump the gas through wire mesh packing. In the circumstances of this research the enhancement from using wire mesh packing up to 40%.

1.2                                   PROBLEM STATEMENT

Conventional resources of energy are depleting at an alarming rate, which makes future sustainable growth of energy extremely complicated. As a result, significant importance has been placed on the development of various augmented heat transfer surfaces and devices. The study of improved heat transfer performance is referred to as heat transfer enrichment, augmentation or intensification. In general, this means an increase in heat transfer coefficient. Energy and materials-saving considerations, as well as financial incentives, have led to efforts to produce more capable heat exchange devices. General thermal-hydraulic goals are to decrease the size of a heat exchanger needed for a specified heat duty, to advance the capacity of an existing heat exchanger, to reduce the approach temperature difference for the process streams, or to reduce the pumping power.

1.3                     AIM AND OBJECTIVES OF THE STUDY

The main aim of this work is to study the pressure drop and heat transfer enhancement in wire mesh screen

The objectives of the study are:

1. To study the effect of wire mesh insert on heat transfer and pressure drop in double pipe heat exchanger
2. To numerically investigate the heat transfer and pressure drop of cross-flow woven wire mesh heat exchanger.

• To determine the pressure drop and heat transfer in heat exchanger

1.4                                    SCOPE OF THE STUDY

The scope of the study covers an experiment which involves the insertion effect of a woven wire mesh to cross flow heat exchanger will be studied under steady state laminar flow conditions. 3-D numerical model was developed for the bare heat exchanger and the other wire mesh modules. The mesh wire diameter is 2.5 mm, porosity of 0.75, permeability of 10-10 and layer-to-layer spacings of (3,5,10,15,20 and 25 mm). Air flows with velocity range up to 3.5 cm/s through rectangular duct of 50 cm X 25 cm with inlet temperature of 25^oC before it is heated with corrugated water tube (19 mm in diameter) with hot water inlet velocity of 1 m/s and temperature of 50^oC. The thermal and hydraulic performance were evaluated.

1.5       APPLICATIONS OF HEAT TRANSFER ENHANCEMENT

All the industries in the world are under financial pressure to increase the energy efficiency of their processing plants to compete in today’s global market. Hence, these industries must spend in inventive thermal technologies that would considerably reduce unit energy utilization in order to reduce overall cost. Important applications of heat transfer enhancement are listed below:

1. Automotive Industries
2. Heating, Ventilating, Refrigeration and air conditioning

• Process Industries

1. Power sector
2. Industrial Heat Recovery

1.6                                   DEFINITION OF TERMS

WIRE MESH SCREEN: is a woven metal fabric having either square or rectangular “working openings” between wires — produced on large weaving machines called looms. “Working openings” are the clear spaces or distances between wires in both directions of the woven wire fabric. Usually openings 1/4 inch and over are referred to as space cloth. Wire mesh with openings less than 1/4 inch are referred to by its mesh count.

HEAT TRANSFER ENHANCEMENT: is the process of increasing the effectiveness of heat exchangers. This can be achieved when the heat transfer power of a given device is increased or when the pressure losses generated by the device are reduced.

PRESSURE DROP: is the difference in total pressure between two points of a fluid carrying network. A pressure drop occurs when frictional forces, caused by the resistance to flow, act on a fluid as it flows through the tube.