CONSTRUCTAL DESIGN AND OPTIMISATION OF SINGLE AND STACKED MICROCHANNEL HEAT SINKS

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MOTIVATION

Constructal design, which is the use of constructal law for better engineering design, is the greatest motivation for this work [18, 19, 30, 31]. It involves the generation of configurations taking into consideration the global objectives and global constraints. With the use of constructal law in the design and geometric optimisation of microelectronic structures, a configuration is not assumed but allowed freedom to morph until optimum dimensions are obtained.

AIM OF THE RESEARCH

The aim of the current research is to carry out numerical investigations on conjugate heat transfer in different types of micro heat sinks based on constructal theory and design. Also, a new heat sink will be modelled to improve the thermal performance of existing micro heat sinks. The geometric optimisation of the heat sinks will be achieved by using a computational fluid dynamics code, which has a goal-driven optimisation algorithm. The design parameters chosen become design variables and a search for the optimal geometry based on these design variables and the objective function will be carried out using the optimisation algorithm of the computational fluid dynamics software.

OBJECTIVES OF THE RESEARCH

The objectives of the study are as follows:  to geometrically optimise the micro heat sinks (single and stacked microchannels) in such a way that the global thermal conductance is maximised or peak temperature of the solid substrate being cooled is minimised for fixed and varied axial lengths;  to geometrically optimise a new design of micro heat sink, which combines microchannels and micro pin fins for fixed and varied axial lengths and compare the thermal performance of this new design with the conventional microchannel heat sinks;  to investigate the performance of different micro heat sinks based on the temperature non-uniformity of the solid substrate that is cooled and propose a best choice of micro heat sink based on both maximum thermal conductance and temperature non-uniformity.

SCOPE OF THE STUDY

In this thesis, the constructal design approach is employed to efficiently optimise the geometries of different micro heat sinks with forced convective heat transfer and steady, laminar and incompressible fluid flow using CFD and numerical optimisation. The micro heat sinks considered are the single, two- and three-layered microchannels, the combination of the single microchannel and three different shapes of micro pin fins, and the combination of the two-layered microchannel and the circular-shaped micro pin fins. A fixed total volume of these heat sinks is investigated for fixed and varying axial lengths.

TABLE OF CONTENTS :

ABSTRACT
DEDICATION
ACKNOWLEDGEMENTS
LIST OF FIGURES
LIST OF TABLES
NOMENCLATURE
PUBLICATIONS IN JOURNALS, BOOKS AND CONFERENCE PROCEEDINGS
CHAPTER 1: INTRODUCTION
- 1.1. BACKGROUND
- 1.2. MOTIVATION
- 1.3. AIM OF THE RESEARCH
- 1.4. OBJECTIVES OF THE RESEARCH
- 1.5. SCOPE OF THE STUDY
- 1.6. RESEARCH METHODOLOGY
- 1.7. MATERIAL SELECTION
- 1.8. ORGANISATION OF THE THESIS
CHAPTER 2: LITERATURE REVIEW
- 2.1. INTRODUCTION
- 2.2. SINGLE MICROCHANNEL HEAT SINKS
- 2.3. STACKED MICROCHANNEL HEAT SINKS
- 2.4. MICRO PIN-FIN HEAT SINKS
- 2.5. CONSTRUCTAL DESIGN AND HEAT SINKS
- 2.6. RESPONSE SURFACE OPTIMISATION AND HEAT SINKS
- 2.7. CONCLUSION
CHAPTER 3: NUMERICAL MODELLING AND OPTIMISATION
- 3.1. INTRODUCTION
- 3.2. NUMERICAL MODELLING PROCEDURE
- 3.3. GEOMETRY AND GRID GENERATION
- 3.4. CONSERVATION OF MASS
- 3.5. CONSERVATION OF MOMENTUM
- 3.6. CONSERVATION OF ENERGY
- 3.7. BOUNDARY CONDITIONS
- 3.8. NUMERICAL SOLUTION PROCEDURE
- 3.9. NUMERICAL OPTIMISATION
  - 3.9.1. Response surface methodology and computer experiments
- 3.10. CONCLUSION
CHAPTER 4: CONSTRUCTAL DESIGN AND OPTIMISATION OF SINGLE AND STACKED MICROCHANNEL HEAT SINKS
- 4.1. INTRODUCTION
- 4.2. SINGLE MICROCHANNEL HEAT SINK
  - 4.2.1. Physical model
  - 4.2.2. Case Study 1: Optimisation results for fixed axial length and
  - uniform surface heat flux
  - 4.2.3. Case Study 2: Optimisation results for varying axial length and
  - uniform surface heat flux
  - 4.2.4. Case Study 3: Optimisation results for varying axial length and uniform heat load
- 4.3. STACKED MICROCHANNEL HEAT SINKS
  - 4.3.1. Brief introduction
  - 4.3.2. Physical model
  - 4.3.3. Case Study 1: Comparison between the results of single and multi- layered microchannels with fixed axial length and uniform heat flux
- 4.3.4. Case Study 2: Comparison between the thermal performances of single and two-layered microchannel with varying axial length, fixed pressure drop and uniform heat load
- 4.3.5. Effect of increasing heat load on the thermal performance of single and two-layered microchannels with varying axial length
- 4.4. CONCLUSION
CHAPTER 5: COMBINED MICROCHANNEL AND MICRO PIN-FIN HEAT SINK
- 5.1. INTRODUCTION
- 5.2. COMBINED SINGLE MICROCHANNEL AND MICRO PIN FINS
- 5.2.1. Physical model and design variables
- 5.2.2. Case Study 1: Optimisation results for fixed axial length and uniform heat flux
- 5.2.3. Case Study 2: Optimisation results for reduced axial length and uniform surface heat flux
- 5.2.4. Case Study 3: Optimisation results for varying axial length and constant heat load

CHAPTER 6: TEMPERATURE NON-UNIFORMITY ON THE HEATED BASE OF A SOLID SUBSTRATE
- 6.1. INTRODUCTION
- 6.2. TEMPERATURE VARIATION ALONG AXIAL LENGTH OF HEATED BASE
  - 6.2.1. Effect of single microchannel cooling on temperature variation
  - 6.2.2. Effect of combined single microchannel and circular-shaped pin-fin cooling on temperature variation
  - 6.2.3. Effect of two-layered microchannel cooling with parallel-flow configuration on temperature variation of the solid substrate cooled by the different heat sinks
- 6.3. CONCLUSION
CHAPTER 7: CONCLUSIONS AND RECOMMENDATIONS
- 7.1. INTRODUCTION
- 7.2. CONCLUSIONS
- 7.3. RECOMMENDATIONS
- REFERENCES