Performance Characteristics of Two-Phase Refrigerant Cooling for Batteries in Electric Vehicles under Fast Charging Conditions
- 주제(키워드) Battery thermal management , Refrigerant cooling , Electric vehicle
- 발행기관 고려대학교 대학원
- 지도교수 김용찬
- 발행년도 2020
- 학위수여년월 2020. 8
- 학위구분 박사
- 학과 대학원 기계공학과
- 세부전공 열및유체공학전공
- 원문페이지 146 p
- UCI I804:11009-000000231865
- DOI 10.23186/korea.000000231865.11009.0001170
- 본문언어 영어
- 제출원본 000046045921
초록/요약
Recently, lithium-ion batteries (LIBs), which have higher energy densities and power performances, have been recommended as the most suitable energy storage for electric vehicles (EVs). However, the performance characteristics of the lithium-ion batteries are strongly influenced by the temperature range. Therefore, an efficient battery thermal management system (BTMS) is essential for LIBs with high cooling performance and long lifetime. The conventional BTMSs, which have been applied in EVs such as air cooling and liquid cooling, are limited to maintaining the battery within the proper temperature range during fast charging under harsh environmental conditions. Moreover, as the power level of the battery continues to increase, the cooling capacity of BTMS should be enhanced. The objective of this study is to investigate the performance improvement of a novel two-phase refrigerant cooling over a conventional liquid cooling for batteries of EVs. The two-phase refrigerant cooling system is configured by simply expanding the refrigerant unit used in the existing air conditioning (AC) system. The two-phase refrigerant with high heat transfer coefficient flows directly into the refrigerant cooling module without the secondary heat transfer by battery chiller to mitigate system complexity and improve cooling performance. Based on full-scale experiments under fast charging conditions, the thermal performance of the two-phase refrigerant cooling is compared with that of the conventional liquid cooling with the same outer size. According to vapor quality and superheat of refrigerant, the maximum temperature and temperature distribution on the battery cells and cooling channels are measured and compared with those of the liquid cooling. Especially, the effect of two-phase flow instability on EVs is investigated by measuring the pressure drop oscillation in the refrigerant cooling module. The heat transfer coefficients between the two-phase refrigerant and liquid coolant are calculated under the various charging rates and working fluid conditions. Furthermore, the variations in the battery capacity and internal resistance of battery cells during battery aging are estimated to investigate the effects of the cell temperature profile on the battery lifespan. The two-phase refrigerant cooling satisfies the maximum cell temperature limit of 45 °C even under harsh environmental conditions. During battery aging, the two-phase refrigerant cooling provides 16.1% higher battery capacity and 15.0% lower internal resistance compared with the liquid cooling under harsh environmental conditions. Overall, the two-phase refrigerant cooling is regarded as a preferred alternative to the conventional liquid cooling owing to its reliable performance even with a simple and lightweight structure.
more목차
Chapter 1. Introduction 1
1.1 Background 1
1.2 Literature review 8
1.2.1 Battery thermal management systems in EVs 8
1.2.2 Two-phase refrigerant cooling 13
1.2.3 Applied to commercialized EVs 16
1.3 Objective and outline of this study 22
Chapter 2. Experimental setup and data reduction 24
2.1 Battery pack with the two-phase refrigerant cooling system 24
2.2 Comparison of liquid cooling and refrigerant cooling modules 28
2.3 Experimental setup 31
2.4 Test condition 38
2.5 Data reduction 43
Chapter 3. Battery test apparatus 46
3.1 Introduction 46
3.2 Validity of battery test apparatus 48
3.2.1 Configuration of actual cell module 48
3.2.2 Configuration of the battery test apparatus 53
3.2.3 Validity of battery test apparatus 57
3.3 Summary 62
Chapter 4. Thermal characteristics of two-phase refrigerant 63
4.1 Introduction 63
4.2 Results and discussion 64
4.2.1 Effect of the minichannel configurations 64
4.2.2 Effect of the refrigerant vapor quality 67
4.2.3 Effect of the refrigerant pressure 75
4.2.4 Characteristics of pressure drop oscillation 79
4.3 Summary 83
Chapter 5. Performance comparison of the two-phase refrigerant cooling with liquid cooling 84
5.1 Introduction 84
5.2 Results and discussion 86
5.2.1 Temperature distribution on battery cells 86
5.2.2 Validity of cooling performance under transient condition 90
5.2.3 Comparison of heat transfer coefficients 94
5.2.4 Capacity fade and internal resistance during battery aging 97
5.3 Summary 105
Chapter 6. Concluding Remarks 106
6.1 Conclusions 106
6.2 Future works 108
References 109
Appendix A. Uncertainty analysis 119
Appendix B. Parallel flow type refrigerant cooling module 122
Appendix C. Economic analysis 124
