El presente proyecto de investigación realizado en la empresa Autoespar S.A. contiene un estudio de la infraestructura de servidores y servicio de TI que nos permite buscar la mejor opción tecnológica para el diseño un centro de datos virtual. Esta infraestructura estará acorde a los requerimientos y necesidades que la empresa demanda, con la finalidad de resolver los problemas más críticos, gestionar mejor los recursos, mejorar la disponibilidad de servicios y reducir el tiempo inactividad. El primer capítulo de este proyecto contiene la información de la empresa y la situación problemática que buscamos resolver. Asimismo, definiremos el objetivo principal y los objetivos específicos. El segundo capítulo, encontraremos el marco teórico consistente a nivel teórico y técnico que nos brindara el soporte a todos los puntos para este proyecto. El tercer capítulo nos muestra a detalle el análisis del problema identificado y definimos los requerimientos del proyecto acorde a los objetivos planteados. Finalmente se muestra el registro de interesados y EDT del proyecto. El cuarto capítulo nos muestra el diseño de la solución dividido en dos, el diseño lógico donde se ubicaran los cálculos requeridos para el diseño de la infraestructura virtual. Y el diseño físico, donde se brinda las especificaciones técnicas a considerar para la nueva infraestructura. Finalmente, el quinto capítulo, donde se detalla un plan de pruebas que nos permitirá validar el cumplimento de los objetivos específicos del proyecto a través de un laboratorio de pruebas que demuestra la factibilidad de este proyecto. / This research project carried out in the company Autoespar S.A. contains a study of the infrastructure of servers and IT services that allows us to find the best technological option for the design of a virtual data center. This infrastructure will be in accordance with the requirements and needs that the company demands, in order to solve the most critical problems, better manage resources, improve the availability of services and reduce downtime. The first chapter of this project contains the information of the company and the problematic situation that we seek to solve. Likewise, we will define the main objective and the specific objectives. The second chapter, we will find the consistent theoretical framework at a theoretical and technical level that will provide us with support at all points for this project. The third chapter shows us in detail the analysis of the identified problem and we define the requirements of the project according to the objectives set. Finally the registry of interested parties and WBS of the project is shown. The fourth chapter shows us the design of the solution divided into two, the logical design where the calculations required for the design of the virtual infrastructure are located. And the physical design, where the technical specifications to be considered for the new infrastructure are provided. Finally, the fifth chapter, where a test plan is detailed that will allow us to validate the fulfillment of the specific objectives of the project through a test laboratory that demonstrates the feasibility of this project. / Tesis

El presente trabajo de investigación propone una estrategia para proporcionar una infraestructura escalable en el tiempo y altamente disponible para todos los servicios de la organización. Para el diseño de esta infraestructura virtualizada se realizó un análisis profundo de la problemática actual y de sus necesidades como también de los requerimientos del cliente. En el desarrollo de la solución se tomará en cuenta las recomendaciones y buenas prácticas de los productos de cada fabricante, así como también el uso de la metodología VIM. Primero, expondremos información de la organización que se beneficiara del proyecto, luego se identificara la problemática actual y con los datos obtenidos definiremos los objetivos de estudio. Para finalizar, expondremos cual será la justificación del desarrollo del diseño. Segundo, se desarrollará el marco teórico que incluirá toda la información referente al desarrollo del proyecto y facilitará su comprensión. Tercero, en este capítulo se sustentará el análisis del problema identificado en el primer capítulo con datos reales, luego definiremos la identificación y justificación de los requerimientos del proyecto. Cuarto, se desarrollará las especificaciones técnicas del equipamiento tecnológico que se utilizará en el diseño, se incluirá los cálculos de la cantidad necesaria de los recursos de hardware de memoria RAM, almacenamiento y procesamiento. Quinto, se expondrá los resultados y validaciones que permitirán comprobar el cumplimiento de los objetivos de investigación en función a los indicadores del logro y sus métricas. / This research work proposes a strategy to provide a scalable infrastructure over time and highly available for all the organization's services. For the design of this virtualized infrastructure, a deep analysis of the current problem and its needs as well as the client's requirements was carried out. In developing the solution, the recommendations and good practices of the products of each manufacturer will be taken into account, as well as the use of the VIM methodology. First, we will present information on the organization that will benefit from the project, then the current problem will be identified and with the data obtained we will define the study objectives. Finally, we will expose what will be the justification for the development of the design. Second, the theoretical framework will be developed that will include all the information regarding the development of the project and will facilitate its understanding. Third, this chapter will support the analysis of the problem identified in the first chapter with real data, then we will define the identification and justification of the project requirements. Fourth, the technical specifications of the technological equipment that will be used in the design will be developed, calculations of the necessary amount of RAM memory, storage and processing hardware resources will be included. Fifth, the results and validations will be exposed that will allow to verify the fulfillment of the research objectives based on the achievement indicators and their metrics. / Tesis

Molntjänster är ett snabbt växande område och utgör en viktig funktion i samhället och för verksamheter. Det som driver molntjänster är storskaliga datacenter som samlar tusentals servrar med infrastruktur. Dessa datacenter kräver en hög energianvändning för att drivas vilket utgör ett stort koldioxidutsläpp. Leverantörer upplever ökade krav i hållbarhetsfrågor och arbetar aktivt för att möta dessa krav. Verksamheter har därför en betydande roll i hur leverantörer arbetar med hållbarhet genom att ställa hållbarhetskrav. Det finns däremot utmaningar med att ställa hållbarhetskrav vilket är brist på kunskap, strategier och resurser.  Studien avser att identifiera de ekologiska hållbarhetsaspekter som verksamheter kan kravställa mot molntjänstleverantörer. Syftet med studien var att förmedla kunskap om vilka ekologiska hållbarhetsaspekter som kan appliceras i verksamheters kravspecifikation mot molntjänstleverantörer. Tidigare forskning beskriver hållbarhetsaspekter som molntjänstleverantörer kan applicera för att minska sitt koldioxidutsläpp. Dessa aspekter är: miljöcertifiering, nyckeltal, förnybar energi och energieffektiviserade strategier. Studien antog en kvalitativ forskningsansats. Datainsamlingen utfördes genom semistrukturerade intervjuer. Analysen utfördes med en tematisk analysmetod och det identifierades tre teman vilket är kunskapslucka, prioritering och resursbehov. Studien diskuterar dessa teman i relation till tidigare forskning kring hållbarhetsaspekterna och utmaningar.  Slutsatsen av studien är fem identifierade hållbarhetsaspekter som är: miljöcertifiering, nyckeltal, förnybar energi, geografisk plats och energieffektiviserade strategier. Dessa hållbarhetsaspekter kan verksamheter kravställa mot molntjänstleverantörer och kan reducera utmaningarna med att identifiera hållbarhetskrav. / Cloud services are a rapidly growing field and play a crucial role in society and businesses. What drives cloud services are large-scale data centers that house thousands of servers with infrastructure. These data centers require high energy consumption to operate, resulting in significant carbon emissions. Providers are facing increased demands for sustainability and actively working to meet these requirements. Businesses, therefore, have a significant role in influencing how providers approach sustainability by setting sustainability criteria. However, there are challenges in setting sustainability requirements due to a lack of knowledge, strategies, and resources. This study aims to identify the ecological sustainability aspects that businesses can demand from cloud service providers. The purpose of the study was to provide knowledge about the ecological sustainability aspects that can be included in businesses' specifications when selecting cloud service providers. Previous research describes sustainability aspects that cloud service providers can implement to reduce their carbon emissions. These aspects include environmental certification, key performance indicators, renewable energy, and energy-efficient strategies. The study adopted a qualitative research approach. Data collection was conducted through semi-structured interviews. The analysis was performed using thematic analysis, and three themes were identified: knowledge gap, prioritization, and resource requirements. The study discusses these themes in relation to previous research on sustainability aspects and challenges. The conclusion of the study highlights five identified sustainability aspects: environmental certification, key performance indicators, renewable energy, geographical location, and energy-efficient strategies. These sustainability aspects can be demanded by businesses from cloud service providers and can help address the challenges of identifying sustainability requirements.

<p dir="ltr">Ensuring a high quality of experience for Internet applications is challenging owing to the significant variability (e.g., of traffic patterns) inherent to both cloud data-center networks and wide area networks. This thesis focuses on optimizing application performance by both conducting measurements to characterize traffic variability, and designing applications that can perform well in the face of variability. On the data center side, a key aspect that impacts performance is traffic burstiness at fine granular time scales. Yet, little is know about traffic burstiness and how it impacts application loss. On the wide area side, we focus on video applications as a major traffic driver. While optimizing traditional videos traffic remains a challenge, new forms of video such as 360◦ introduce additional challenges such as respon- siveness in addition to the bandwidth uncertainty challenge. In this thesis, we make three contributions.</p><p dir="ltr"><b>First</b>, for data center networks, we present Millisampler, a lightweight network traffic char- acterization tool for continual monitoring which operates at fine configurable time scales, and deployed across all servers in a large real-world data center networks. Millisampler takes a host-centric perspective to characterize traffic across all servers within a data center rack at the same time. Next, we present data-center-scale joint analysis of burstiness, contention, and loss. Our results show (i) bursts are likely to encounter contention; (ii) contention varies significantly over short timescales; and (iii) higher contention need not lead to more loss, and the interplay with workload and burst properties matters.</p><p dir="ltr"><b>Second</b>, we consider challenges with traditional video in wide area networks. We take a step towards understanding the interplay between Content-Delivery-Networks (CDNs), and video performance through end-to-end measurements. Our results show that (i) video traffic in a session can be sourced from multiple CDN layers, and (ii) throughput can vary signifi- cantly based on the traffic source. Next we evaluate the potential benefits of exposing CDN information to the client Adaptive-Bit-Rate (ABR) algorithm. Emulation experiments show the approach has the potential to reduce prediction inaccuracies, and enhance video quality of experience (QoE).</p><p dir="ltr"><b>Third</b>, for 360◦ videos, we argue for a new streaming model which is explicitly designed for continuous, rather than stalling, playback to preserve interactivity. Next, we propose Dragonfly, a new 360° system that leverages the additional degrees of freedom provided by this design point. Dragonfly proactively skips tiles (i.e., spatial segment of the video) using a model that defines an overall utility function that captures factors relevant to user experience. We conduct a user study which shows that majority of interactivity feedback indicating Dragonfly being highly reactive, while the majority of state-of-the-art’s feedback indicates the systems are slow to react. Further, extensive emulations show Dragonfly improves the image quality significantly without stalling playback.</p>

Recent years have witnessed a surge in demand for infrastructure and services to cover high demands on processing big chunks of data and applications resulting in a mega Cloud Datacenter. A datacenter is of high complexity with increasing difficulties to identify, allocate efficiently and fast an appropriate host for the requested virtual machine (VM). Establishing a good awareness of all datacenter’s resources enables the allocation “placement” policies to make the best decision in reducing the time that is needed to allocate and create the VM(s) at the appropriate host(s). However, current algorithms and policies of placement “allocation” do not focus efficiently on awareness of the resources of the datacenter, and moreover, they are based on conventional static techniques. Which are adversely impacting on the allocation progress of the policies. This thesis proposes a new Agent-based allocation/placement policy that employs some of the Multi-Agent system features to get a good awareness of Cloud Datacenter resources and also provide an efficient allocation decision for the requested VMs. Specifically, (a) The Multi-Agent concept is used as a part of the placement policy (b) A Contract Net Protocol is devised to establish good awareness and (c) A verification process is developed to fully dimensional VM specifications during allocation. These new results show a reduction in response time of VM allocation and the usage improvement of occupied resources. The proposed Agent-based policy was implemented using the CloudSim toolkit and consequently was compared, based on a series of typical numerical experiments, with the toolkit’s default policy. The comparative study was carried out in terms of the time duration of VM allocation and other aspects such as the number of available VM types and the amount of occupied resources. Moreover, a two-stage comparative study was introduced through this thesis. Firstly, the proposed policy is compared with four state of the art algorithms, namely the Random algorithm and three one-dimensional Bin-Packing algorithms. Secondly, the three Bin-Packing algorithms were enhanced to have a two-dimensional verification structure and were compared against the proposed new algorithm of the Agent-based policy. Following a rigorous comparative study, it was shown that, through the typical numerical experiments of all stages, the proposed new Agent-based policy had superior performance in terms of the allocation times. Finally, avenues arising from this thesis are included. / Al al-Bayt University in Jordan.

<p>Rising interest in high-performance servers in data centers to support the increasing demands for cloud-computing and storage have challenged thermal management systems. To prevent these increased power density servers from overheating due to the high heat fluxes dissipated, new cooling methods have continued to be investigated in recent years. One such solution is pumped two-phase cooling which shows promise over traditional air cooling due to the reduced power consumption it requires to operate, while also being able to dissipate large amounts of heat from the small components in servers.</p> <p>    </p> <p>Although pumped two-phase systems as a cooling strategy have existed for multiple decades, sub-optimal component design have hindered the potential efficiencies achievable. This is especially prevalent in the condenser where, in order to meet required metrics, these heat exchangers are commonly oversized due to maldistribution at low vapor qualities and a lack of understanding about the condensation behavior within certain geometries.</p> <p><br></p> <p>Through the work presented in this thesis, the capabilities of an air-cooled microchannel condenser model are explored for future use in optimization studies for data center applications. To perform this research, an investigation into the boundary conditions of these systems and common condenser modeling strategies were carried out. Using this knowledge, a flexible discretized condenser model was developed to capture the behavior of pumped two-phase cooling in data centers under a wide range of operating conditions. In conjunction, an experimental test setup was sized, designed, and constructed to provide validation for the model. Then, using the model, some initial parametric studies were conducted to identify the sensitivity effects of various parameters on overall condenser performance. In this initial study, some favored boundary conditions and geometries were found that both minimize refrigerant pressure drops and maximize heat transfer. For an air-cooled condenser operating with R1234ze(E), these include: refrigerant entering the condenser around 40% quality, operating at moderate refrigerant mass fluxes through the channels (130 - 460 kg/m^2-s), and designing microchannel condenser tubes with many tightly packed square ports. Continued investigation into the contributing parameters of weight in the future using the tools developed in this thesis will lead to further optimized condenser designs and operating conditions.</p>

No description available.

This work proposes a new approach to fast detection of abnormal behaviour of cooling, IT, and power distribution systems in micro data centers based on machine learning techniques. Conventional protection of micro data centers focuses on monitoring individual parameters such as temperature at different locations and when these parameters reach certain high values, then an alarm will be triggered. This research employs machine learning techniques to extract normal and abnormal behaviour of the cooling and IT systems. Developed data acquisition system together with unsupervised learning methods quickly learns the physical dynamics of normal operation and can detect deviations from such behaviours. This provides an efficient way for not only producing health index for the micro data center, but also a rich label logging system that will be used for the supervised learning methods. The effectiveness of the proposed detection technique is evaluated on an micro data center placed at Computing Infrastructure Research Center (CIRC) in McMaster Innovation Park (MIP), McMaster University. / Thesis / Master of Science (MSc)

Given the coinciding growth-trend in the production of consumer electronics and generation of data, the increase in server halls and data centers, as a means for hosting storage capacity for the generated data, has been prominent over the last decades. The establishment of data centers in already existing infrastructure can entail major changes in terms of energy system design. The activity of data processing and storage is power intensive and as the centers demonstrate substantial heat generation, one of the most important fractions of the energy use comes from the need to provide cooling. The study is a techno-economic analysis purposed for determining the feasibility of different cooling systems for a data center in Sweden. The investigated building currently hosts an industrial printing press hall in which paper printing has been conducted for the several decades. This press hall is subject to a refurbishment process to eventually be converted into a data center. In order to achieve the objectives, a data center building model is developed, designated for the estimation of the internal heat generation and demand for cooling. The design and energy requirements of a number of cooling solutions are then investigated and evaluated using a number of performance metrics: Power Usage Effectiveness (PUE), Capital Expenditure (CapEx), Operational Expenditure (OpEx) and Life Cycle Cost (LCC). More specifically the systems incorporate technologies for utilizing air-based free cooling, ground-source free cooling through borehole ground source heat exchangers (GHEs), mechanical cooling through compressor-driven machines as well as District Cooling (DC). The results of the study show that free cooling is a viable solution for covering the vast majority of the yearly cooling requirements, during sufficiently low outdoor temperatures. Free cooling, provided through borehole GHE’s, is feasible as a partial solution from a technical point of view, to provide cooling capacity during warmer periods. However, it can not alone act to provide a major part of the relatively high and constant cooling capacity requirements throughout the year. All of the investigated scenarios display a similar energy performance in terms of total PUE, at values well below the national average of 1.37. It is also seen, that the scenario that displays the lowest LCC includes a combination of free cooling and compressor-driven cooling. This holds for the studied sensitivity cases. It is found that a combined system incorporating borehole GHE’s and compressor cooling machines perform the best in terms of a low PUE. However, the relative difference in energy performance turns out to be lesser than the relative difference in LCC, when substituting the borehole GHE’s for additional cooling machine capacity. / I takt med digitaliseringen och en ökad global användningen- och produktionen av hemelektronik, vilket föranlett en ökad generering av data, har antalet datahallar blivit allt fler de senaste decennierna. Datahallens syfte är att hantera och bereda lagringskapacitet för den data som genereras vilket involverar en rad energikrävande processer. Upprättandet av datahallar i redan befintlig infrastruktur kan medföra förändringar när det kommer till utformningen av byggnadens energisystem. Att bedriva datalagring och informationsbehandling kräver påtagliga mängder elektricitet vilket medför stor intern värmealstring och därtill behov av aktiv kylning.  Denna studie, som valt att benämnas som en tekno-ekonomisk fallstudie, undersöker lämpligheten i implementeringen av olika kylsystem för ett byggnadskomplex i Stockholm. I byggnadens lokaler återfinns idag en industrihall där det sedan flera decennier bedrivits tryckeriverksamhet. Industrihallen är föremål för en konverteringsprocess för att på sikt bli en datahall. Studien är centrerad kring denna konverteringsprocess. För att utvärdera kylbehoven för den framtida datahallen har en modell utvecklats som uppskattar interna värmelaster samt reglerar inomhusklimatet efter rådande krav på inomhuskomfort. Därefter studeras utformning och energibehov för flera olika typer av kylsystemlösningar där en utvärdering av dessa system görs utifrån indikatorerna Power Usage Effectiveness (PUE), Capital Expenditure (CapEx),Operational Expenditure (OpEx) and Life Cycle Cost (LCC). Mer konkret undersöks kombinerade kylsystem som utnyttjar luftburen frikyla, geotermisk frikyla via bergvärmeväxlare (GHEs), mekanisk kyla via kompressordriven kylmaskin samt regional fjärrkyla. Resultaten från studien visar att frikyla från kylmedelskylare är en lämplig lösning för att täcka majoriteten av datahallens kylbehov över ett år, med undantag för årets varmare perioder. Geotermisk frikyla via borrhål är möjlig som partiell lösning ur ett tekniskt perspektiv, men kan inte enskild leverera en majoritet av effekt- eller energibehovet av kyla. Resultatet visar också att alla undersökta scenarier uppvisar en liknande energiprestanda i termer av total PUE, med värden som underskrider det nationella genomsnittet 1,37. Lägst LCC påvisades för ett system som kombinerar luftburen frikyla via kylmedleskylare och mekanisk kyla via kompressordrivna kylmaskiner. Denna låga LCC är signifikant vilket påvisas i utförd känslighetsanalys. Slutligen konstateras att ett system innefattande luftburen och geotermisk frikyla i kombination med kompressordrivna kylmaskiner resulterar i lägst PUE bland de undersökta scenarierna. Den relativa skillnaden i energiprestanda visar sig vara mindre än den relativa skillnaden i LCC, när geotermisk frikyla ersätts med ytterligare kapacitet från kylmaskiner.

[pt] Diante dos constantes avanços da tecnologia os dispositivos eletrônicos vêm passando por um processo de miniaturização, ao mesmo tempo em que sustentam um aumento de potência. Essa tendência se mostra um desafio para seu gerenciamento térmico, uma vez que os sistemas de resfriamento típicos para eletrônicos utilizam ar como fluido de trabalho, e o seu baixo coeficiente de transferência de calor limita sua capacidade de atender às necessidades térmicas da indústria atual. Nesse sentido, o resfriamento bifásico tem sido considerado uma solução promissora para fornecer resfriamento adequado para dispositivos eletrônicos. Circuitos de termossifão bifásico combinam a tecnologia de resfriamento bifásico com sua inerente natureza passiva, já que o sistema não requer uma bomba para fornecer circulação para seu fluido de trabalho, graças às forças da gravidade e de empuxo. Um dissipador de calor de microcanais, localizado bem em cima do dispositivo eletrônico, dissipa o calor gerado. Isto o torna uma solução de baixo custo e energia. Além disso, ter um circuito de termossifão operando com um refrigerante de baixo GWP, como o R-1234yf, resulta em baixo impacto para o meio ambiente, uma vez que é um refrigerante ecologicamente correto e o sistema tem baixo ou nenhum consumo de energia. Este trabalho fornece um modelo numérico detalhado para a simulação de um circuito de termossifão bifásico, operando em condições de regime permanente. O circuito compreende um evaporador (chip e dissipador de calor de micro-aletas), um riser, um condensador refrigerado a água de tubo duplo e um downcomer. Equações fundamentais e constitutivas foram estabelecidas para cada componente. Um método numérico de diferenças finitas, 1-D para o escoamento do fluido por todos os componentes do sistema, e 2-D para a condução de calor no chip e evaporador foi empregado. O modelo foi validado com dados experimentais para o refrigerante R134a, mostrando uma discrepância em relação ao fluxo de massa em torno de 6 por cento, para quando o sistema operava sob regime dominado pela gravidade. A pressão de entrada do evaporador prevista apresentou um erro relativo máximo de 4,8 por cento quando comparada aos resultados experimentais. Além disso, a maior discrepância da temperatura do chip foi inferior a 1 grau C. Simulações foram realizadas para apresentar uma comparação de desempenho entre o R134a e seu substituto ecologicamente correto, R1234yf. Os resultados mostraram que quando o sistema operava com R134a, ele trabalhava com uma pressão de entrada no evaporador mais alta, assim como, com um fluxo de massa mais alto. Por causa disso, o R134a foi capaz de manter a temperatura do chip mais baixa do que o R1234yf. No entanto, essa diferença na temperatura do chip foi levemente inferior a 1 grau C, mostrando o R1234yf como comparável em desempenho ao R134a. Além disso, o fator de segurança da operação do sistema foi avaliado para ambos os refrigerantes, e para um fluxo de calor máximo do chip de 33,1 W/cm2, R1234yf mostrou um fator de segurança acima de 3. Isso significa que o circuito de termossifão pode operar com segurança abaixo do ponto crítico de fluxo de calor. Dada a investigação sobre a comparação de desempenho dos refrigerantes R134a e R1234yf, os resultados apontaram o R1234yf como um excelente substituto ecologicamente correto para o R134a, para operação em um circuito de termossifão bifásico. / [en] Given the constant advances in technology, electronic devices have been going through a process of miniaturization while sustaining an increase in power. This trend proves to be a challenge for thermal management since commonly electronic cooling systems are air-based, so that the low heat transfer coefficient of air limits its capacity to keep up with the thermal needs of today s industry. In this respect, two-phase cooling has been regarded as a promising solution to provide adequate cooling for electronic devices. Two-phase thermosyphon loops combine the technology of two-phase cooling with its inherent passive nature, as the system does not require a pump to provide circulation for its working fluid, thanks to gravity and buoyancy forces. A micro-channel heat sink located right on top of the electronic device dissipates the heat generated. This makes for an energy and cost-efficient solution. Moreover, having a thermosyphon loop operating with a low GWP refrigerant such as R-1234yf results in low impact for the environment since it is an environmentally friendly refrigerant, and the system has low to none energy consumption. This work provides a detailed numerical model for the simulation of a two-phase thermosyphon loop operating under steady-state conditions. The loop comprises an evaporator (chip and micro-fin heat sink), a riser, a tube-in-tube water-cooled condenser and a downcomer. Fundamental and constitutive equations were established for each component. A finite-difference method, 1-D for the flow throughout the thermoysphon s components and 2-D for the heat conduction in the evaporator and chip, was employed. The model was validated against experimental data for refrigerant R134a, showing a mass flux discrepancy of around 6 percent for when the system operated under gravity dominant regime. The predicted evaporator inlet pressure showed a maximum relative error of 4.8 percent when compared to the experimental results. Also, the chip temperature s largest discrepancy was lower than 1 C degree. Simulations were performed to present a performance comparison between R134a and its environmentally friendly substitute, R1234yf. Results showed that when the system operated with R134a, it yielded a higher evaporator inlet pressure as well as a higher mass flux. Because of that, R134a was able to keep the chip temperature lower than R1234yf. Yet, that difference in chip temperature was slightly lower than 1 C degree, showing R1234yf as comparable in performance to R134a. In addition, the safety factor of the system s operation was evaluated for both refrigerants, and for a maximum chip heat flux of 33.1 W/cm2, R1234yf showed a safety factor above 3. This means the thermosyphon loop can operate safely under the critical heat flux. Given the investigation on the performance comparison of refrigerants R134a and R1234yf, results pointed to R1234yf being a great environmentally friendly substitute for R134a for the two-phase thermosyphon loop.