Numerical Simulation of Heat Exchangers

Advances in Numerical Heat Transfer Volume V

W. J. Minkowycz, E. M. Sparrow, J.P Abraham, J. M. Gorman, W. J. Minkowycz, E. M. Sparrow, J.P Abraham, J. M. Gorman

• Publisher: CRC Press
• Year: 2017
• ISBN:
  9781315355306
• Edition: 1
• Topic: Sciences physiques
• Subtopic: Thermodynamique

This book deals with certain aspects of material science, particularly with the release of thermal energy associated with bond breaking. It clearly establishes the connection between heat transfer rates and product quality. The editors then sharply draw the thermal distinctions between the various categories of welding processes, and demonstrate how these distinctions are translated into simulation model uniqueness. The book discusses the incorporation of radiative heat transfer processes into the simulation model.

1 Heat Exchangers and Their Fan/Blower Partners Modeled as a Single Interacting System by Numerical Simulation

E. M. Sparrow, J. M. Gorman, J. P. Abraham, and W. J. Minkowycz

CONTENTS

1.1 Introduction

1.2 Fan/Blower Fluid Flow Characteristics

1.3 Fan/Blower Curves and Application to Design

1.4 Fan with Rotating Blades: Array of Flat-Parallel Fins

1.4.1 Physical Situation

1.4.2 Governing Equations

1.4.3 Numerical Simulation Rotational Issues

1.4.4 Fan/Blower-Curve-Based Analysis

1.4.5 Heat Transfer Results and Discussion

1.4.6 Fluid Flow Results and Discussion

1.4.7 Retrospective View of the Flat-Fin Array Results

1.5 Fan with Rotating Blades: Application to a DNA Thermocycling Device

1.5.1 Physical Situation

1.5.2 Governing Equations

1.5.3 Heat Transfer Results and Discussion

1.5.4 Fluid Flow Results and Discussion

1.5.5 Retrospective View of the DNA Sampling Device Simulations

1.6 Fan with Rotating Blades: Pin-Fin Heat Sink

1.6.1 Physical Situation

1.6.2 Fan/Blower-Curve-Based Analysis

1.6.3 Heat Transfer Results and Discussion

1.6.4 Fluid Flow Results and Discussion

1.6.5 Retrospective View of the Pin-Fin Heat Sink Investigation

1.7 Fan with Rotating Blades: Air Blown into Pipe Inlet

1.7.1 Physical Situation and Solution Strategy

1.7.2 Heat Transfer Results and Discussion

1.7.3 Fluid Flow Results and Discussion

1.7.4 Retrospective View of the Investigation of Rotating Fan Flow Delivered to a Pipe Inlet

1.8 Concluding Remarks

References

ABSTRACT: Heat exchangers usually involve two or more fluids having different temperatures. The performance of heat exchangers depends critically on the nature of the participating fluid flows. Over the years of traditional heat exchanger design, the most accounted feature of the fluid flow has been its magnitude. This is because design procedures for heat exchangers have been closely connected to fan/blower/pump curves in which the magnitude of the delivered flow is linked to the pressure rise. However, those characteristic curves do not take into account swirl, eddies, backflow, cross-sectional nonuniformities, and unusually high turbulence, almost all of which are embedded in actual fluid flows delivered to heat exchangers. The focus of this chapter is to quantitatively demonstrate the necessity of taking into account all of the characteristic features of the fluid flow that is delivered to the heat exchanger. This is accomplished by treating the fan/blower/pump and the heat exchanger as a single interactive system. In such a treatment, it is mandatory that fan rotation is fully considered to ensure that all rotation-based flow characteristics are included. The composite system, consisting of the fluid mover and the heat exchanger, is solved by numerical simulation. The fluid flows produced by this approach are a more true representation of reality.

1.1 INTRODUCTION

The goal of this chapter is to present evidence of the importance of taking into account the realistic interactions between a fluid mover and the heat exchanger, which is the recipient of the fluid flow. The underlying motivation for this work is the development of a heat transfer design methodology that is more accurate and more realistic than what is the present norm. In particular, it will be shown that the design of a heat transfer device based solely on the magnitude specification of the delivered fluid flow is insufficient because other characteristics of the flow are neglected. Depending on the nature of the fluid mover, those characteristics may include swirl, eddies, backflow, cross-sectional nonuniformities, and unusually high turbulence. The result of neglecting these factors is a design that, if implemented, may be far less efficient than what was predicted.

The foregoing discussion suggests that an improved heat-exchanger design methodology should include the realities of the delivered fluid flow. To ensure that these realities are properly characterized, the actual flow delivered by the fluid mover must be determined. In that regard, it is tempting to use the fan/blower/pump curve provided by the manufacturer of the fluid mover. The flaw in doing so is that such curves are determined after all the complexities that are normally embedded in the fan/blower output have been eliminated (i.e., the actual flow has been sanitized). Therefore, the use of fan/blower/pump curves as input to a heat transfer analysis does not necessarily lead to a good design.

In this presentation, a new methodology for heat exchanger design will be set forth followed by a succession of specific problems to illustrate its use. Ample comparisons are included to provide an indication of the accuracy improvements that can be achieved by the use of this methodology. The need to treat heat exchangers and their fluid flow providers as a single system has received very little recognition in the published literature [1–3].

1.2 FAN/BLOWER FLUID FLOW CHARACTERISTICS

The two types of fans that generally are encountered in connection with heat exchangers are axial and centrifugal. These fans have characteristics that are specific unto themselves so that it is advantageous to treat them separately. For the applications that motivated the present chapter, thermal management of electric equipment, axial fans appear to be more useful. Consequently, the focus will be directed here toward axial fans and their applications. A typical likeness of an axial fan is shown in Figure 1.1. The fan consists of a square frame or housing, blades attached to a rotating hub, and supports for the hub and its attached moving components.

FIGURE 1.1 Photograph of a typical small axial fan.

The nature of the flow provided by a fan may depend on the nature of the resistance into which the discharge of the fan is blown. For illustrative purposes, the flow discharging from an axial fan into free air will be displayed by means of vector diagrams. The first pair of such diagrams is displayed on a longitudinal plane that includes the axis of the fan. In Figure 1.2a, the vectors have been normalized to have a common length. Such vectors give a picture of the directions of fluid flow. The vectors shown in Figure 1.2b have lengths that are directly proportional to the magnitude of th...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Table of Contents
• Preface
• Editors
• Contributors
• Chapter 1 Heat Exchangers and Their Fan/Blower Partners Modeled as a Single Interacting System by Numerical Simulation
• Chapter 2 On Computational Heat Transfer Procedures for Heat Exchangers in Single-Phase Flow Operation
• Chapter 3 Utilization of Numerical Methods and Experiments for the Design and Tests of Gasketed Plate Heat Exchangers
• Chapter 4 Numerical Methods for Micro Heat Exchangers
• Chapter 5 Review of Advances in Heat Pipe Analysis and Numerical Simulation
• Index