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고분자 전해질 연료전지 스택 제작 및 시스템 최적화
No full textThe polymer electrolyte membrane fuel cell (PEMFC) is a promising energy conversion tech-nology for future sustainable development. The PEMFC has many advantages such as high power density, low operating temperatures, low emissions, silent operation, and fast start-up and shut-down. Furthermore, it has infinite possibilities for use in a wide and variety of applications from small scale mobile devices and robots to large scale cars and power plants. Many research groups in the world have been investigating about PEMFCs, but they have mainly focused on the single cell level or material properties. PEMFC Stack or system level studies are very important topics for fuel cell applications, because the performance of single cells and the performance of stacks are totally different. The stack consists of single cells but it is not as simple as stacking of single cells. In this study, to make a more effective stack, I tried to analyze the thermal distribution of the bi-polar plate of the stack in terms of three designs: (1) 100cm2 rectangular bi-polar plate, (2) 200cm2 square cell bi-polar plate, and (3) 200cm2 alternative square design bi-polar plate. I also employed four methods: (1) 100cm2 rectangular bi-polar plate without cooling, (2) 100cm2 rectan-gular bi-polar plate with water cooling, (3) 200cm2 square cell bi-polar plate with air cooling, and (4) 200cm2 alternative square design bi-polar plate with air cooling using COMSOL simulations. To optimize clamping pressure at the stack assembly, stack clamping pressure conditions were: (1) single cell 5000N axial load, (2) single cell 50 in lb bolt torque, (3) single cell 90 in lb bolt torque, (4) 16 cell stack 5000N axial load, and (5) 16 cell stack 90 in lb bolt torque. These pressure conditions have been analyzed by solid-works simulation and experimental load tests with pres-sure sensitive films. Furthermore, to find optimal stack operating conditions, I evaluated stack per-formance depends on gas and stack temperature: 40, 50, 60, and 70℃, relative humidity: dry, 60,80, and 100%, and pressure conditions: 0psi, 10psi, 20psi, and 30psi. In thermal distribution analysis, 100cm2 rectangular bi-polar plate with water cooling and 200cm2 alternative square design bi-polar plate with air cooling show well distributed simulation result. The temperature differences of two design are around 2℃ in the simulation. The clamping pressure simulation and experiments are present pressure distributions in every layer in the stack. The big-gest pressure was applied at end plate and gasket, bipolar plate, MEA, GDL in this order. The op-timal conditions of this stack from experiments are operation at 10psi pressure, 60% relative hu-midity of react gases, and 70℃ stack temperature. ⓒ 2013 DGIST1.Introduction 1
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1.1 Understanding PEMFC Stacks 2
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1.2 Motivation and Objectives 5
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1.2.1 Motivation for research 5
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1.2.2 Objectives 6
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1.3 Studies of PEMFC Stacks 6
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1.3.1 Thermal Management 7
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1.3.2 Clamping Pressure 11
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1.3.3 Parametric Studies of PEMFC Stacks 17
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2. Experiments 23
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2.1 Thermal Distribution Management 23
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2.1.1 Secondary Current Distribution 26
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2.1.2 Transport of Concentrated Species 28
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2.1.3 Free and Porous Media Flow 29
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2.1.4 Heat Transfer 31
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2.2 Clamping Pressure Optimization 32
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2.2.1 Computer Simulation 32
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2.2.2 Experimental Load Testing 34
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2.3 Fuel Cell Evaluation System 37
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2.3.1 Overview of the Fuel Cell Evaluation System 37
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2.3.2 The External Dew Point Humidifier 39
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2.3.3 Stack Preparation and Assembly 41
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2.3.4 Experiment Apparatus 50
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3. Results and Discussion 54
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3.1 Thermal Distribution Management Simulation Result 54
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3.1.1 100 cm2 Cell without CoolingCase 1 54
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3.1.2 100 cm2 Cell with Water CoolingCase 1 57
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3.1.3 200 cm2 Square Cell with Air CoolingCase 2 61
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3.1.4 200 cm2 Alternative Square Cell with Air CoolingCase 3 64
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3.2 Clamping Pressure Result 68
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3.2.1 Single Cell with 5000 Newton Axial Load 68
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3.2.2 Single Cell with 50 Inch Pounds Torque 69
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3.2.3 Single Cell with 90 Inch Pounds Torque 71
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3.2.4 Fuel Cell Stack, 16 Cells, 5000 Newton, all layers 73
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3.2.5 Fuel Cell Stack, 16 Cells, 90 Inch Pounds per Bolt, all layers 78
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3.2.6 Experimental Load Testing 84
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3.3 Operating Conditions of PEMFC Stacks 88
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3.3.1 Initial Tests 90
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3.3.2 Back Pressure Optimization. 92
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3.3.3 Relative Humidity Optimization 98
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3.3.4 Stack Operating Temperature Optimization 100
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4. Summary and Conclusion 106
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References 110
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Appendix A 119
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요약문 126고분자 전해질 연료전지는 미래의 지속 가능한 발전을 위해서 각광 받고 있는 에너지 변환 기술이다. 고분자 전해질 연료전지는 높은 파워 밀도, 낮은 동작 온도, 적은 방출 물질, 조용한 동작 소음, 빠른 시작과 정지 등의 많은 장점을 가지고 있다. 게다가, 작은 범위의 휴대용 장비와 로봇으로부터 자동차나 발전소 같은 큰 범위의 넓고 다양한 응용분야에 무한한 가능성을 가지고 있다. 전 세계의 많은 연구그룹들이 고분자 전해질 연료전지에 대해 연구되어 왔으나, 그들 대부분은 하나의 셀 단위나 물질 특성에 관련된 연구가 많았다. 고분자 전해질 연료전지 스택이나 시스템 단위의 연구는 하나의 셀의 성능과 셀을 여러 개 결합한 스택의 성능이 완전하게 다르기 때문에 연료전지의 응용 관점에서 매우 중요한 주제이다.
이 연구에서는 좀 더 효율적으로 스택을 만들기 위해서 세가지 디자인의((1) 100cm2의 직사각형 분리판, (2) 200cm2 정사각형 분리판, (3) 200cm2 다른 형태의 정사각형 분리판) 분리판 온도 분포에 대해 해석하였다. 그리고 분리판 온도 분포를 해석하는 데는 네 가지의 방법((1) 냉각 없는 100cm2 직사각형 분리판, (2) 물 냉각을 사용한 100cm2 직사각형 분리판, (3) 공기 냉각을 이용한 200cm2 정사각형 분리판, (4) 공기 냉각을 이용한 200cm2 다른 형태의 정사각형 분리판)을 컴솔을 사용하여 분석하였다. 스택의 쪼임 압력을 최적화 하기 위해서는 다섯 가지((1) 단위 셀에 5000N 힘, (2) 단위 셀에 50 인치 파운드의 토크, (3) 단위 셀에 90 인치 파운드의 토크, (4) 16 셀 스택에 5000N의 힘, (5) 16 셀 스택에 90인치 파운드의 토크)의 쪼임 압력 조건을 사용하였다. 이 압력 조건들은 솔리드 워크 시뮬레이션과 압력 필름을 이용한 실제 로드 테스트를 통해서 해석하였다. 그리고 스택의 적정 동작 조건을 찾기 위해서 스택의 성능을 가스와 스택의 온도(40, 50, 60, 70 ℃), 상대 습도(dry, 60, 80, 100℃), 압력(0, 10, 20, 30 psi) 조건에서 실험하였다.
온도 분포 해석 결과, 물 냉각을 사용한 100cm2 직사각형 분리판과 공기 냉각을 이용한 200cm2 다른 형태의 정사각형 분리판에서 온도가 가장 골고루 분포되는 전사모사 결과를 보여주었다. 두 디자인에서의 온도차는 2℃에 불과 하였다. 쪼임 압력 전사모사와 실험 결과로 스택의 각 층에 얼마의 압력이 가해지는지 자세히 알 수 있었다. 가장 큰 압력이 전달 되는 부분은 막음판이었으며, 가스킷, 분리판, 막 전극 접합체, 가스 확산층 순으로 압력이 전달 되었다. 스택의 동작에 가장 적합한 최적 조건은 10psi 의 압력에서 60%의 상대습도를 가진 수소와 산소가 공급되며 70℃의 스택 온도를 가지는 경우이다. ⓒ 2013 DGISTMasterdCollectio
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