臺灣博碩士論文加值系統

In the present study, a numerical method was developed to investigate the heat transfer performance of a spiral heat exchanger. In the spiral heat exchanger, two long metal strips are wound concentrically to create hot-flow channel and cold-flow channel. The flow of the two fluids through a spiral heat exchanger was considered counter-current, the hot-flow circulates counter-clockwise and the cold-flow circulates clockwise. The upper surface, lower surface and outer-most side of the spiral heat exchanger were assumed to be insulated. A heat transfer effectiveness and an exergy recovery effectiveness were defined and evaluated based on the calculated non-dimensional temperatures of the two counter-flow fluids in the heat exchanger. At small NTU value, the heat transfer effectiveness value initially increases with the NTU value; while at higher NTU values, after reaching the maximum heat transfer effectiveness, the heat transfer effectiveness value starts to slightly decrease. For a set of Nt and NTU values, the heat transfer effectiveness reaches a minimum value at C*=1.0. As the C* approaches zero or infinity, the heat transfer effectiveness would approach the maximum. Conversely, for a set of NTU, Nt, inlet temperature of hot flow and cold flow, and overall pressure drop factor values, as the C* approaches zero or infinity, the exergy recovery effectiveness of the spiral heat exchanger is at the minimum. The exergy recovery effectiveness reaches a maximum as the C* value nears 1.0. The result also shows that, at small values of Nt (Nt < 40), the heat transfer effectiveness value and the exergy recovery effectiveness value slightly increase with the Nt value; while these two values remain almost the same when the number of turns is larger than 40 turns.

Acknowledgement i
Abstract ii
Table of contents iii
List of Tables and Figures v
Nomenclature vii
Chapter 1 Introduction 1
1.1 Preface 1
1.2 Spiral heat exchanger and main applications 2
1.3 Survey of literature 4
1.4 Objective of the Thesis 12
Chapter 2 Energy Equations for a Spiral Heat Exchanger 13
2.1 Length of a Curve in Polar Coordinates 13
2.2 Length of Archimedes’ spiral in polar Coordinates 14
2.3 Geometry of a spiral heat exchanger 17
2.4 Mathematical modeling 20
2.4.1 Energy balance for hot flow 20
2.4.2 Energy balance for cold flow 22
2.4.3 Dimensionless energy equations 24
2.5 Heat transfer effectiveness of heat exchanger 28
Chapter 3 Numerical Analysis 30
3.1 The case for hot-flow capacity rate less than cold flow capacity rate 30
3.1.1 Finite-difference equations for the hot flow 30
3.1.2 Finite-difference equations for the cold flow 31
3.2 The case for hot-flow capacity rate lager than cold flow capacity rate 33
3.2.1 Finite-difference equations for the hot flow 33
3.2.2 Finite-difference equations for the cold flow 35
3.3 Computer simulation program 36
3.4 Error Analysis of numerical scheme 37
3.4.1 Equation for checking the accuracy of numerical scheme 37
3.4.2 Error analysis of numerical scheme 38
3.5 Results of heat transfer analysis 39
Chapter 4 Exergy Analysis 45
4.1 General form of exergy change rate in a flow 45
4.1.1 Concept of exergy analysis 45
4.1.2 Exergy change rate for ideal gas flow 46
4.1.3 Exergy change rate for incompressible flow 47
4.1.4 General form of exergy change rate in a flow 48
4.2 Exergy analysis for the spiral heat exchanger 49
4.3 Exergy recovery effectiveness 50
4.4 Dimensionless exergy recovery effectiveness equations 56
4.4 Results of exergy analysis and discussion 57
Chapter 5 Conclusions 61
References 63

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