Energy Saving Techniques for Phase Change Memory (PCM)

In recent years, the energy consumption of computing systems has increased and a large fraction of this energy is consumed in main memory. Towards this, researchers have proposed use of non-volatile memory, such as phase change memory (PCM), which has low read latency and power; and nearly zero leakage power. However, the write latency and power of PCM are very high and this, along with limited write endurance of PCM present significant challenges in enabling wide-spread adoption of PCM. To address this, several architecture-level techniques have been proposed. In this report, we review several techniques to manage power consumption of PCM. We also classify these techniques based on their characteristics to provide insights into them. The aim of this work is encourage researchers to propose even better techniques for improving energy efficiency of PCM based main memory.Comment: Survey, phase change RAM (PCRAM

Exploiting Inter- and Intra-Memory Asymmetries for Data Mapping in Hybrid Tiered-Memories

Modern computing systems are embracing hybrid memory comprising of DRAM and non-volatile memory (NVM) to combine the best properties of both memory technologies, achieving low latency, high reliability, and high density. A prominent characteristic of DRAM-NVM hybrid memory is that it has NVM access latency much higher than DRAM access latency. We call this inter-memory asymmetry. We observe that parasitic components on a long bitline are a major source of high latency in both DRAM and NVM, and a significant factor contributing to high-voltage operations in NVM, which impact their reliability. We propose an architectural change, where each long bitline in DRAM and NVM is split into two segments by an isolation transistor. One segment can be accessed with lower latency and operating voltage than the other. By introducing tiers, we enable non-uniform accesses within each memory type (which we call intra-memory asymmetry), leading to performance and reliability trade-offs in DRAM-NVM hybrid memory. We extend existing NVM-DRAM OS in three ways. First, we exploit both inter- and intra-memory asymmetries to allocate and migrate memory pages between the tiers in DRAM and NVM. Second, we improve the OS's page allocation decisions by predicting the access intensity of a newly-referenced memory page in a program and placing it to a matching tier during its initial allocation. This minimizes page migrations during program execution, lowering the performance overhead. Third, we propose a solution to migrate pages between the tiers of the same memory without transferring data over the memory channel, minimizing channel occupancy and improving performance. Our overall approach, which we call MNEME, to enable and exploit asymmetries in DRAM-NVM hybrid tiered memory improves both performance and reliability for both single-core and multi-programmed workloads.Comment: 15 pages, 29 figures, accepted at ACM SIGPLAN International Symposium on Memory Managemen

열전 에너지 하베스팅 응용 가능한 형상 유지 상전이 복합재료

학위논문 (박사)-- 서울대학교 대학원 : 공과대학 재료공학부, 2019. 2. 윤재륜.Energy storage plays a considerable part in absorbing heat energy for thermoelectric energy conversion. Thermal energy storage (TES), one of the most popular systems for recycling energy, generally employs a phase change material (PCM) as a working material due to its high latent heat, appropriate phase transition temperature range, and high thermal stability. The latent heat thermal eneergy storage (LHTES) is a good example of PCMs applications and the energy storage density can be improved by combing these PCMs with thermoelectric devices. The PCMs can absorb or release a great deal of thermal energy isothermally during the heating and cooling process. However, have a leakage problem during the melting and cooling process, the field applications are restricted. To manufacture the form stable PCMs, some supporting materials are required to improve the dimensional stability of PCMs. Utilizing 3D porous materials as a supporting material has been reported and comparing with conventional supporting materials, the 3D porous materials have larger pore volume than other materials to be filled up by the pure PCMs. Therefore, graphene aerogel has been investigated as a supporting material to prevent the leakage of PCMs due to its large surface area and complicated internal structure. As for thermoelectric effect, the Seebeck effect induces electrons to move from hot side to cold side of the energy harvesting device and form stable PCMs are placed on the side of PN cells to achieve the thermoelectric energy harvesting during melting and coolng process. Chapter I provides an descriptions of phase change materials (PCMs) and organic PCMs which has been widely utilized in the energy storage. The goal of work and the advanced portion of this study is generally employed. The two different PCMs are placed on the sides of PN cells and the theory of this combination is fully mentioned. The Seebeck effect is utilized for the thermoelectric energy harvesting and the functions of PCMs are discussed sufficiently. The multiple energy harvesting, arriving phase transitions concept, and the optimum couple of PCMs are introduced and the novelty of each part is examined in this chapter. In addition, the modified supporting material is a new method to improve the energy storage and subsequently contribute to the thermoelectric energy harvesting. The goal of this work related to the supporting materials are briefly described. Chapter II introduces the form stable phase change materials (PCMs) by using microencapsulation method which can exhibit a smart response to the heating and cooling steps. The encapsulated form stable PCM composites sustain their intrinsic solid state upon melting process. The pure PCM inside the microcapsule started to solid-liquid phase transition upon heating and recovered from liquid to the solid state after removing the heat source. Therefore, the form stable PCM microcapsules lead to the volume expansion and shrinkage on the melting and crystallization process. The volume change of PCM composites gave rise to the degree of filler arrangement which sufficiently increased the electrical conductivity. The graphene and carbon nanotube (CNT) powders are generally utilized as excellent fillers for obtaining the electrical conductivity under the temperature variation. The temperature is initially increased from 25 °C to final 90 °C and decreased to the room temperature after removing the heat source. After that, the electrical conductivity of both graphene and CNT showed large magnitude modification and further demonstrated the volume expansion of PCM microcapsules are effectively changed the internal electrical resistivity under the phase transition process. Chapter III demonstrates the single PN cell energy harvesting system with two different PCMs and measure the induced current under heating and cooling process. The current is generated due to the temperature difference between the two sides of PN cell and maintained when the hot side temperature is higher than that of cold side. Based on the result of single PN cell energy harvesting system, two different PCMs are selected for the energy harvesting based on the Seebeck effect. Normally, the PN junction is blocking the current movement on the reverse bias which results in the electric energy that is measured merely when the temperature of the hot side is higher than that of cold side. The energy barrier is existed and hard to detect the induced current when the temperature of the cold side exceeds that of the hot side of PN cell semiconductors. Thus, the additional energy harvesting system needs to be introduced and the multiple energy harvesting system is mentioned effectively. The harvested current is obtained two times as the change of temperature on the PCMs. After achieving the multiple energy harvesting based on reversed temperature difference, it needs to increase rate of arriving phase transition field on both melting and cooling process. To address this problem, the supporting material is modified by increasing the filler weight fraction and form stable PCMs consist multiple energy harvesting system exhibits the expected result upon phase transitions. The conductive filler can perform as a thermal carrier and the harvesting system is carried out sufficiently. The optimum component of two PCMs are proved by utilizing different filler embedded PCMs. The multiple current is obtained and the optimum energy harvesting system could exhibit the largest peak area for thermoelectric energy conversions. To predict the temperature difference between the two PCMs, the numerical analysis is calculated during the heating and cooling cycles, and the Seebeck effect is demonstrated by employing a finite element method (FEM). The numerical calculation showed the energy harvesting system is controllable in a systematic manner and useful for practical applications. In Chapter IV, the modified supporting material is applied to manufacture the form stable phase change material (PCM) and the one section is infiltrated some of PDMS to emerge a flexible properties. Due to the combination of the skeleton under the aerogel structure, the modified PDMS/aerogel can prevent the shrinkage under the infiltrating process and filled up more working material into the pore space. The fabricated PCMs with PDMS shows larger temperature gradients and current peaks upon melting and cooling process. The energy harvesting system is able to store and release more thermal energy by utilizing modified PCMs and increase the thermoelectric energy conversion efficiencies. Furthermore, the other section for increasing the harvesting efficiency is modified the supporting material by chemical cross-linking method. To solve the shrinkage problem more effectively, the supporting material is dealt with the cross-linker and enhanced its mechanical properties to sustain the initial structure. The cross-linked supporting material could infiltrate more pure PCMs than that of raw materials and mechanically stable to prevent the disruption under the melting process. The stable form stable PCMs are certainly placed on the multiple PN cells to construct a new energy harvesting system and observe a harvested current during the phase transition process. As a result, the system is produced more electrical current under the solar simulator and hold a thermal stable properties during melting and cooling cycles. In Chapter V, the pyroelectric effect by combining with the PCM composites is a new approach for thermoelectric energy harvesting. The pyroelectric film is more and more attracted because of simple control, and electrical polarization. In this field, pyroelectric electrodes enable convert thermal to electrical energy conversion as occurring the pyroelectric effect. Unlike the PN junction modules that depend on the temperature difference, pyroelectric energy harvesters demand continuous temperature variations induced by the heat source in order to generate the electrical current. In this work, the phase change materials (PCMs) act as a thermal energy absorber and reservoir to generate the induced voltage upon heating and cooling. The glass transmission including pyroelectric device demonstrates a new thermal energy applications and further indicates the optimum pyroelectric system under the phase transition process. In Chapter VI, the conclusion of this doctoral dissertation is described. The goal of this work is presented under a combination of previous Chapter II and Chapter IV. The single PN cell based energy harvesting system, multiple energy harvesting system, arriving phase transition applications, and the optimum component PCMs are generally proved and the final results are also mentioned in order to suggest the practical applications. In addition, the restiction of these PN cell energy harvesting system is described and the upcoming research about the thermoelectric energy conversion is developed in this chapter.상변이 물질은 상이 바뀜에 따라서 많은 에너지를 흡수하거나 방출하는 성질을 가지고 있고 저장된 열에너지를 우리는 잠열이라고 부른다. 잠열에너지 그리고 상변이 과정인 온도변화가 거의 없는 이 구간을 이용하여 많은 연구가 진행되고 있다. 우리는 상변이 물질이 저장하고 방출하는 에너지를 반도체 열전소자랑 같이 결부 시켜 열량을 흡수하거나 방출하는 과정에서 나타나는 에너지 하베스팅 연구를 진행하고자 하였고 거기에 따른 에너지 하베스팅 효율도 같이 탐구하고 결과를 나타냈다. 제 1장에서는 상변이 물질에 대한 구체적인 서술을 진행하였고 상변이 물질 종류 및 가장 많이 사용하는 유기폴리머 상변이 물질에 대한 기능을 설명 하였고 상변이 물질이 상이 변하는 기본 원리 그리고 상변이 물질의 잠재적인 사용범위에 대한 서술을 하였고 마이크로 갭슐 구조에 대한 형상유지 그리고 상변이에 대한 전기전도도 변화를 보여주었고 반도체 열전소자의 원리 그리고 제백효과에 대한 간략한 서술도 진행 하였다. 또한 상변이 물질과 반도체 열전소자의 사용원인 응용역할에 대한 내용도 서술하였고 파이로 효과 그리고 파이로 전극을 이용한 에너지 하베스팅에 관한 간략한 설명을 진행 하였고 본 연구의 중요성 창의성에 대해서도 언급하였다. 제 2 장에서는 마이크로 캡슐 구조로 형상 유지 가능한 상변이 물질을 제조 하였고 캡슐 구조인 상변이 물질은 상전이 과정에서 볼륨 팽창을 발생 시킨다. 그래핀 그리고 카본 나노튜브가 들어간 상변이 복합재료는 온도변화에 대한 볼륨 팽창 그리고 볼륨 팽창에 대한 전기저항의 변화를 감지 하였고 상전이 과정에서 볼륨 변화가 많고 따라서 전기전도도의 변화도 상전이 변화에 비례한다는 것도 증명하였다. 제 3장에서는 두가지 다른 상변이 물질을 사용한 에너지 하베스팅 연구에 대한 서술을 순서적으로 설명하였고 먼저 진행하게 된 반도체 열전소자가 하나만 들어있고 높은 온도구간대에서 상변이가 발생하는 상변이 물질과 낮은 온도 구간대에서 상변이가 발생하는 상변이 물질을 베이스로 온도차에 의한 에너지 하베스팅 결과를 설명 하였고 두번째 내용인 두 상변이 물질 온도가 서로 역전되는 현상을 주름 잡고 반도체 소자 두개를 사용하고 상변이 물질 위치를 서로 바뀌게 디자인 함과 동시에 온도차이가 역전되여도 여전히 에너지 하베스팅이 진행되는 것을 알 수 있다. 열전도도를 증가시켜 상변이 과정으로 빨리 진행됨과 동시에 에너지 하베스팅도 빨리 진행되는 연구를 진행함과 동시에 필러 농도가 증가됨에 따라서 에너지 하베스팅 효과도 변화가 발생하는 것을 확인 하게 되였다. 나중에는 여러 필러 농도가 다른 상변이 물질을 에너지 하베스팅에 결부 시겼고 결과 가장 적절한 두 조합을 얻는데 성공 하였다. 제 4장에서는 기존 연구에 따른 적절한 두 조합을 베이스로 에너지 효율 관련 연구를 진행 하였고 결과 에너지 효율은 저장된 토탈 에너지 즉 함침된 상변이 물질 질량이 많을수록 저장하거나 방출하는 에너지가 더 많고 따라서 전기에너지로 전환되는 양도 많아짐을 알 수 있다. 함침된 상변이 물질 양을 증가시키는 것을 연구 목적으로 먼저 에어로겔이 상변이 물질을 함침하는 과정에서 모세관 힘에 의한 구조변화가 발생되고 볼륨 축소가 발생함으로서 함침되는 상변이 물질의 양도 어느 정도 손실을 보게 되는 것을 알 수 있다. 에어로겔이 볼륨 축소가 되는 것을 막기 위하여 일단은 PDMS를 에어로겔 내부에 균일하게 분산시키고 따라서 분산된 PDMS가 에어로겔 축에 접착 됨으로서 외부의 힘에 의한 탄성을 가지게 되고 따라서 볼륨을 유지시키게 된다. 함침된 상변이 물질 양도 증가되고 따라서 에너지 하베스팅 되는 효율도 증가 되는 것이다. 또한 에어로겔 기계적 물성을 어느 정도 증가시켜 더 안정적인 에어로겔 구조를 만들었고 함침된 상변이 물질 양도 또한 어느 정도 증가된다. 이는 전기에너지로 전환되는 효율을 증가 시키고 함침된 상변이 물질이 녹는 점보다 더 높은 온도환경에서도 더 안정적인 구조를 가질 수 도 있다. 제 5장에서는 파이로 효과에 대한 간략한 서술과 상변이 물질을 파이로 전극에 대한 응용 원리 그리고 파이로 에너지 하베스팅에 대한 설명을 진행 하였다. 서로 다른 상변이 물질을 사용한 파이로 시스템은 성공적으로 전기에너지를 하베스팅 하였고 외부조건이 다름에 따라서도 안정적인 파이로 효과를 유도하였다. 또한 태양빛의 투명한 유리에 대한 투과를 초점으로 투명한 파이로 전극 시스템을 구축 하였고 상변이 물질을 태양에너지를 흡수하고 외부에너지가 없는 상황에서는 저장된 잠열에너지를 방출하는 스마트한 파이로 에너지 효과를 관찰 하였다. 상변이 물질의 파이로 전극에 대한 응용은 새로운 잠재적인 사용가치를 언급할 수 있었고 더 간단하고 컨트롤이 스마트 한 시스템을 구축할 수 있음을 말해주고 있다. 제 6장에서는 본 논문의 결론을 서술하였고 연구 결과 그리고 연구 목적 및 선행연구와는 어떤 차이점이 있는지를 설명 하였다. 또한 이런 연구를 진행함에 있어서 존재하는 문제점과 앞으로 더 연구를 진행해야 될 방향 그리고 극복해야 할 이론 베이스도 서술 하였고 연구를 통한 실제응용 전망에 대해서도 간략한 서술을 진행 하였다.Abstract i List of Figures ix List of Tables xix Chapter I. Introduction 1 1.1. What is phase change material? 1 1.2. Research background 6 1.2.1. Form stable phase change materials 6 1.2.2. Microencapsulated phase change materials 8 1.2.3. Phase change materials for energy harvesting 10 1.2.4. Modified phase change materials for energy harvesting 12 1.2.5. Phase change materials for pyroelectric energy harvesting 16 1.3. Objective of present work 17 Chapter II. Microencapsulated phase change materials 20 2.1. Overview 20 2.2. Review of PCM microcapsules 21 2.2.1. Introduction 21 2.2.2. Theoretical background of microencapsulation 21 2.2.3. Microencapsulation for PCMs 22 2.2.4. Conclusions 22 2.3. Graphene powders/PCM for microcapsules 23 2.3.1. Introduction 23 2.3.2. Preparation of graphene powders 24 2.3.3. Preparation of PCM encapsulated composite 25 2.3.4. Numerical simulation 25 2.3.5. Results and discussion 29 2.3.6. Conclusions 42 2.4. Carbon nanotubes/PCM for microcapsules 43 2.4.1. Introduction 43 2.4.2. Preparation of PCM encapsulated composite 44 2.4.3. Numerical analysis 44 2.4.4. Results and discussion 47 2.4.5. Conclusions 57 2.5. Summary 58 Chapter III. PCMs for energy harvesting 59 3.1. Overview 59 3.2. Review of PCMs 61 3.2.1. Introduction 61 3.2.2. Theoretical background 63 3.2.3. Combination of PCMs 65 3.2.4. Conclusions 66 3.3. Single PN cell for thermoelectric energy harvesting 67 3.3.1. Introduction 67 3.3.2. Energy harvesting system 69 3.3.3. Numerical analysis 71 3.3.4. Preparation of PCM composites 73 3.3.5. Results and discussion 75 3.3.6. Conclusions 92 3.4. Multiple PN cells for thermoelectric energy harvesting system 93 3.4.1. Introduction 93 3.4.2. Energy harvesting system 95 3.4.3. Numerical analysis 101 3.4.4. Preparation of PCM composites 102 3.4.5. Results and discussion 103 3.4.6. Conclusions 117 3.5. GNP fillers affecting the rate of phase transitions 118 3.5.1. Introduction 118 3.5.2. Energy harvesting system 120 3.5.3. Numerical analysis 122 3.5.4. Preparation of PCM composites 124 3.5.5. Results and discussion 126 3.5.6. Conclusions 152 3.6. Optimization of PCM composites with GNP ratios 153 3.6.1. Introduction 153 3.6.2. Energy harvesting system 155 3.6.3. Numerical analysis 157 3.6.4. Preparation of PCM composites 158 3.6.5. Results and discussion 162 3.6.6. Conclusions 179 3.7. Summary 180 Chapter IV. Modified PCMs for energy harvesting 181 4.1. Overview 181 4.2. Review of modified PCMs 183 4.2.1. Introduction 183 4.2.2. Theoretical background 184 4.2.3. Combination of PCMs 185 4.2.4. Conclusions 186 4.3. PDMS modified PCMs for energy harvesting 187 4.3.1. Introduction 187 4.3.2. Preparation of energy harvesting system 189 4.3.3. Numerical analysis 191 4.3.4. Preparation of PDMS embedded PCM composites 192 4.3.5. Results and discussion 193 4.3.6. Conclusions 212 4.4. Cross-linked aerogel/PCMs for energy harvesting 213 4.4.1. Introduction 213 4.4.2. PCM composites for energy harvesting system 215 4.4.3. Numerical analysis 218 4.4.4. Preparation of modified PCM composites 220 4.4.5. Results and discussion 222 4.4.6. Conclusions 246 4.5. Summary 247 Chapter V. PCMs for pyroelectric energy harvesting 248 5.1. Overview 248 5.2. Review of PCMs 249 5.2.1. Introduction 250 5.2.2. Theoretical background 251 5.2.3. Pyroelectric effect by combination of PCMs 251 5.2.4. Conclusions 252 5.3. Multiple PCM composites for pyroelectric applications 253 5.3.1. Introduction 253 5.3.2. Design of PCM based pyroelectric generator 254 5.3.3. Numerical analysis 256 5.3.4. Results and discussion 257 5.3.5. Conclusions 268 5.4. Glass transmission of light source for pyroelectric applications 269 5.4.1. Introduction 269 5.4.2. Design of pyroelectric power generator 270 5.4.3. Numerical analysis 272 5.4.4. Results and discussion 273 5.4.5. Conclusions 278 5.5. Summary 279 Chapter VI. Concluding Remarks 280 Bibliography 283 Korean Abstract 308Docto

Optimal behavior of responsive residential demand considering hybrid phase change materials

Due to communication and technology developments, residential consumers are enabled to participate in Demand Response Programs (DRPs), control their consumption and decrease their cost by using Household Energy Management (HEM) systems. On the other hand, capability of energy storage systems to improve the energy efficiency causes that employing Phase Change Materials (PCM) as thermal storage systems to be widely addressed in the building applications. In this paper, an operational model of HEM system considering the incorporation of more than one type of PCM in plastering mortars (hybrid PCM) is proposed not only to minimize the customerâ s cost in different DRPs but also to guaranty the habitantsâ  satisfaction. Moreover, the proposed model ensures the technical and economic limits of batteries and electrical appliances. Different case studies indicate that implementation of hybrid PCM in the buildings can meaningfully affect the operational pattern of HEM systems in different DRPs. The results reveal that the customerâ s electricity cost can be reduced up to 48% by utilizing the proposed model.The work of M. Shafie-khah and J.P.S. Catalão was supported by FEDER funds through COMPETE and by Portuguese funds through FCT, under FCOMP-01-0124-FEDER-020282 (Ref. PTDC/EEA-EEL/118519/2010) and UID/CEC/50021/2013, and also by the EU 7th Framework Programme FP7/2007-2013 under Grant agreement No. 309048 (project SiNGULAR)

Phase change material in automated window shades

The purpose of this report is to detail the development process for a phase change material window shading system, which stores solar thermal energy and later releases it indoors to provide nighttime space heating. To do this, wax-filled louvers with thermally absorptive front faces were developed and outfitted with a control system, which utilized historical weather data to orient the louvers to specific solar azimuthal angles, thus maximizing the thermal absorption. The system was tested against other common window treatments in a pair of thermally comparable testing structures, and was found to provide energy savings as high as 50%

Thermal analysis of lithium ion battery-equipped smartphone explosions

Thermal management of mobile electronics has been carried out because performance of the application processor has increased and power dissipation in miniaturized devices is proportional to its functionalities. There have been various studies on thermal analyses related to mobile electronics with the objectives of improving analysis methodologies and cooling strategies to guarantee device safety. Despite these efforts, failure to control thermal energy, especially in smartphones, has resulted in explosions, because thermal behaviors in the device under various operating conditions have not been sufficiently conducted. Therefore, several scenarios that caused the failure in thermal management of smartphone was analyzed to provide improved insight into thermal design deducing the parameters, that affect the thermal management of device. Overcurrent in battery due to malfunction of battery management system or immoderate addition of functionalities to the application processor are considered as reliable causes leading to the recent thermal runaways and explosions. From the analyses, it was also confirmed that the heat generation of the battery, which have not been considered importantly in previous literature, has significant effect on thermal management, and heat spreading could be suppressed according to arrangement of AP and battery. The heat pipe, which is utilized as a cooling device in mobile electronics, was also included in the thermal analyses. Although the heat pipes have been expected to improve the thermal management in mobile electronics, it showed limited heat transfer capacity due to its operating conditions and miniaturization. The demonstrated results of our analysis warn against vulnerabilities of smartphones in terms of safety in design

Investigating thermal performance of PCM plates for free cooling applications in South Africa

Abstract: Free cooling involves using a thermal energy storage medium such as a phase change material (PCM) in order to store the ambient “cold” during the night when ambient air temperatures are lower compared to the indoor building temperatures and release this stored “cold” by using a heat transfer fluid (i.e. air) into the building during the day when higher ambient temperatures are experienced especially during the summer months. This paper assesses the free cooling potential in South Africa by using a set of Rubitherm RT25HC PCM plates. The performance of these PCM plates is assessed by benchmarking the ambient air cooled by the PCM plates during the day against the defined thermal comfort temperatures requirements. The influence of varying the air flow rate on the availability of thermal comfort temperatures at the PCM rig outlet is also studied. The results clearly show the potential of using PCM’s as a means of cooling higher ambient air temperature which is experienced in hot summer months to within thermal comfort temperatures for human occupancy in a building