Добірка наукової літератури з теми "Thermosyphon mode"

During past two decades, at temperature 240-265°C, resource tests were carried out on 19 thermosyphons of full-scale sizes: 45х4 mm in diameter, 4.92 m in length. The thermosyphons were prepared with varying preliminary surface treatment methods, composition of the aqueous solution to be poured into the thermosyphons, location of titanium chips in the perforated capsules under the lid of the thermosyphons. With a period of 1 to 3 years, thermosyphons were removed from testing system for 30 hours to control the vacuum by thermal method that does not require depressurization. At the last control experiment, four thermosyphons are depressurized for the following purposes: to check the condition of their internal surface in different zones along the length; for the chemical analysis of the aqueous solution poured from them; to determine the structure and characteristics of the mechanical properties of the thermosyphon metal. The main aim of the tests is to justify maintaining the structure and mechanical properties of the metal for a long time, keeping a vacuum of 90-95% inside the thermosyphon, ensuring high heat transfer characteristics of the boiling operating mode of thermosyphons.

The dynamics of a closed thermosyphon are considered. Using an explicit construction, obtained through an inertial manifold, exact low-dimensional models are derived. The behavior of solutions is analyzed for different ranges of the relevant parameters, and the Lorenz model is obtained for a range of parameter values. Numerical experiments are performed for three- and five-mode models.

In the recent years, the interest towards the application of two-phase thermosyphons as an element of heat recovery systems has significantly increased. The application of thermosyphons is steadily gaining popularity in a wide range of industries and energy solutions. In the present study, a 2-D numerical modelling of a two-phase gas/liquid flow and the simultaneously ongoing processes of evaporation and condensation in a thermosyphon is presented. The technique volume of fluid was used for the modelling of the interaction between the liquid and gas phases. The operation of a finned tubes thermosyphon was studied at several typical operating modes. A parametric study over a non-ribbed and finned tubes thermosyphon was carried out. The commercial software ANSYS FLUENT 14.0 was used for the numerical analysis. It was proven that the numerical modelling procedure adequately recreates the ongoing flow, heat and mass transfer processes in the thermosyphon. The numerical result from the phase interaction in the thermosyphon was visualized. Otherwise, such visualization is difficult to achieve when only using empirical models or laboratory experiments. In conclusion, it is shown that numerical modelling is a useful tool for studying and better understanding of the phase changes and heat and mass transfer in a thermosyphon operation.

Thermal transfer behavior of small diameter thermosyphons with different fill ratio, the inner and outer temperature response at start-up, and the calculated vapor-liquid two-phase vertical flow regimes were studied. The thermosyphons were fabricated by different diameter glass tubes. The present study suggests that the best thermal conductive performance is obtained with 26% fill ratio. Inner and outer thermal behaviors were experimentally studied with innovative methods of attaching thermocouples on thermosyphon walls from both inside and outside. Experimental results indicated a very good temperature uniformity of thermosyphons. Furthermore, a 2D, planar CFD modeling using explicit Multi-Fluid VOF model in the Eulerian multiphase model was carried out to model the interaction/interface between gas and liquid as well as fluid flow movement inside the tube. Real-time vapor bubble generation, combination and vapor slug maps were derived from the simulation. A good agreement was observed between CFD acquired data and experimental observations. It is evidenced that CFD is a powerful tool to model and examine the complex flow and heat transfer in a thermosyphon.

Дисертація на здобуття наукового ступеня кандидата технічних наук за спеціальністю 05.14.06 «Технічна теплофізика та промислова теплоенергетика». – Національний технічний університет України «Київський політехнічний інститут імені Ігоря Сікорського», Міністерство освіти і науки України, Київ, 2018. Робота присвячена підвищенню енергетичної ефективності та спрощенню інтеграції сонячних систем на основі комбінованих сонячних колекторів у фасади і дахи будівель за рахунок використання як елемента теплопоглинальної поверхні алюмінієвих канавчатих теплових труб. Встановлено, що на ефективність роботи комбінованого сонячного колектора з алюмінієвими канавчатими тепловими трубами у режимі термосифона істотно впливають теплотехнічні характеристики теплових труб, які своєю чергою залежать від таких параметрів: діаметр парового простору, теплофізичні властивості робочої рідини, довжини зон нагріву і конденсації, а також загальна довжина алюмінієвих канавчатих теплових труб. Підвищення теплопередавальної здатності алюмінієвих канавчатих теплових труб можна досягти завдяки забезпеченню подачі гарантованої кількості теплоносія в зону нагріву та вибору оптимальних конструктивних параметрів теплових труб при відповідних режимах роботи. Аналіз розрахунків та експериментальних даних показав, що комбінований сонячний колектор з алюмінієвими канавчатими тепловими трубами дає змогу підвищити ефективність отримання електричної енергії до 18 % за рахунок охолодження фотоелектричних перетворювачів, при цьому максимальна електрична потужність комбінованого сонячного колектора становила 135 Вт/м2. Крім електроенергії, одночасно можна отримати до 457 Вт тепла з 1 м2 теплопоглинальної поверхні за температури вихідного теплоносія 25 ºС і густини сонячного потоку 900 Вт/м2. На основі теоретичного аналізу виявлено найбільш оптимальні режими експлуатації комбінованого сонячного колектора – режим функціонування за значень 30–50 ºС температурного перепаду між теплопоглинальною поверхнею та навколишнім середовищем. Нова конструкція комбінованого сонячного колектора має більш ефективну роботу порівняно з роздільними тепловими сонячними колекторами та фотоелектричними батареями за низьких температур на теплопоглинальній поверхні (нижче 50 ºС) і зазвичай за більш високих значень сонячного потоку (більше 600 Вт/м2).
Thesis for the Candidate degree in Technical Science on the specialty 05.14.06 «Technical thermophysics and industrial thermal power engineering». – National Technical University of Ukraine "Igor Sikorsky Kyiv Polytechnic Institute", Ministry of Education and Science of Ukraine, Kyiv, 2018. The work is devoted to increasing energy efficiency and simplification of integration of solar systems on the basis of the photovoltaic thermal (PV/T) collector in the facades and roofs of buildings due to use as an element of the absorbing surface of aluminum grooved heat pipes (AGHP). It is established that the efficiency of the operation of the PV/T collector with AGHP in the thermosyphon mode is significantly influenced by the thermal characteristics of the HP, which in turn depends on the following parameters: the diameter of the steam space, the thermophysical properties of the working fluid, the lengths of the heating and condensation zones, and the total length of the AGHP. Increasing the thermal conductivity of AGHP can be achieved by providing a guaranteed amount of coolant to the heating zone and selecting the optimal design parameters of the HP at the appropriate operating modes. A new approach to the implementation of PVT collectors on the basis of AGHPs is proposed. In this case, AGHPs perform a complex role – at the same time it is a highly efficient thermal conductor and a system of cooling solar cells. The design of an aluminum heat pipe with a grooved capillary structure for PVT collectors has been developed. An n-pentane is chosen as the optimum coolant for a two-phase system. The developed samples of heat pipes can provide the operation of the PVT collector in the thermal mode from 0 oC to 120 oC. In this case, the temperature range of its operation is from −40 °C to +230 °C. The analysis of calculations and experimental data showed that the PV/T collector with AGHP allows to increase the efficiency of obtaining electric energy up to 18 % due to the cooling of the PV, while the maximum electric power PV/T collector was 135 W/m2. In addition to electricity, simultaneously, it is possible to get up to 457 W of heat from 1 m2 of heat-absorbing surface, at a temperature of the output coolant 25 oС and a density of solar flux of 900 W/m2. On the basis of theoretical analysis, the most optimal modes of operation of the PV/T collector were identified – the most optimal one is the mode of PV/T collector functioning at values of 30–50 oC of the temperature difference between the absorbent surface and the environment. The new PV/T collector design has a more efficient performance compared to separate thermal solar collectors and photoelectric batteries at low temperatures on an absorbent surface (below 50 oC), and usually at higher solar flux values (over 600 W/m2). The first developed programs and methods of research of PVT collectors in artificial and natural light developed an engineering methodology for calculating the thermal characteristics of PVT collector with AGHPs during their operation in a thermosyphon mode. The recommendations for the production of PVT collectors and their use in solar power systems are given. The results of the work in the future can be used at the enterprises of LLC «Effectprof» (Kyiv), PC Sumy SPO M.V. Frunze (Sumy), PE Scientific-Implementation Firm "Thermal Technologies" (Kiev), which are engaged in the development, manufacture and implementation of heat-exchange equipment and energy-efficient systems. For further implementation, it is necessary to carry out works on designing and manufacturing an industrial design of PVT collector or facade PVT collector and to conduct tests in the field.
Диссертация на соискание ученой степени кандидата технических наук по специальности 05.14.06 «Техническая теплофизика и промышленная теплоэнергетика». – Национальный технический университет Украины «Киевский политехнический институт имени Игоря Сикорского», Министерство образования и науки Украины, Киев, 2018. Работа посвящена повышению энергетической эффективности и упрощению интеграции солнечных систем на основе комбинированных солнечных коллекторов в фасады и крыши зданий за счет использования в качестве элемента теплопоглощающей поверхности алюминиевых канавчатых тепловых труб. Установлено, что на эффективность работы комбинированного солнечного коллектора с алюминиевыми канавчатыми тепловыми трубами в режиме термосифона существенно влияют теплотехнические характеристики тепловых труб, в свою очередь зависят от следующих параметров: диаметр парового пространства, теплофизические свойства рабочей жидкости, длины зон нагрева и конденсации, а также общая длина алюминиевых канавчатых тепловых труб. Повышение теплопередающих способности алюминиевых канавчатых тепловых труб можно достичь благодаря обеспечению подачи гарантированного количества теплоносителя в зону нагрева и выбора оптимальных конструктивных параметров тепловых труб при соответствующих режимах работы. Анализ расчетов и экспериментальных данных показал, что комбинированный солнечный коллектор с алюминиевыми канавчатыми тепловыми трубами позволяет повысить эффективность получения электрической энергии до 18% за счет охлаждения фотоэлектрических преобразователей, при этом максимальная электрическая мощность комбинированного солнечного коллектора составляла 135 Вт/м2. Кроме электроэнергии, одновременно можно получить до 457 Вт тепла с 1 м2 теплопоглощающей поверхности при температуре исходного теплоносителя 25 °С и плотности солнечного потока 900 Вт/м2. На основе теоретического анализа выявлены наиболее оптимальные режимы эксплуатации комбинированного солнечного коллектора – режим функционирования при значениях 30–50 °С температурного перепада между теплопоглощающей поверхностью и окружающей средой. Новая конструкция комбинированного солнечного коллектора имеет более эффективную работу по сравнению с раздельными тепловыми солнечными коллекторами и фотоэлектрическими батареями при низких температурах на теплопоглощающей поверхности (ниже 50 °С) и обычно при более высоких значениях солнечного потока (более 600 Вт/м2).

Les systèmes électriques occupent de nos jours une place de plus en plus importante dans le domaine du transport aérien, ferroviaire et automobile. Ce progrès s'est accompagné de la miniaturisation des systèmes(convertisseurs) qui nécessitent un refroidissement très performant. Alors que les systèmes de refroidissement traditionnels atteignent leurs limites, une des solutions consiste à utiliser des boucles fluides diphasiques reposant sur le changement de phase liquide-vapeur du fluide de travail, en particulier les boucles diphasiques gravitaires. L'objectif de cette thèse est double: proposer un modèle détaillé de la boucle ainsi qu'un modèle réduit capable de calculer les variables en tout point de la boucle et en tout instant mais beaucoup moins gourmand en temps de calcul. Concernant tout d'abord le modèle détaillé, les équations de l'écoulement monodimensionnel et compressible du fluide à l'état monophasique et diphasique en régime transitoire sont résolues par la méthode d 'Euler explicite et par la méthode des volumes finis. Le mélange liquide-vapeur se comporte comme un mélange homogène, en équilibre mécanique et thermique. Les lois de fermeture du modèle sont déduites des lois d'état du type "Stiffened Gas". En ce qui concerne le modèle réduit, une extension de la méthode d'identification modale est proposée. La structure du modèle réduit est tout d'abord déterminée en effectuant la projection de Galerkine des équations de conservation continues. Ensuite les paramètres dumodèle réduit sont identifiés par la résolution d'un problème d'optimisation. Le modèle réduit ainsi construit est alors validé sur plusieurs cas présentant des dynamiques différentes
Today, electrical systems are becoming increasingly important in the air, rail and automotive sectors.The immediate consequence of this progress is the miniaturization of systems (converters) requiring very important cooling means. Whereas conventional cooling solutions are reaching their limit, an alternative one can be sought in two-phase loops based on the liquid-vapor phase change of a working fluid, in particular two-phase loop thermosyphon. The objective of this thesis is twofold : to propose a detailed model of a two phase loop thermosyphon as well as a reduced model able to calculate the variables at any location of the loop at any time with a much smaller computing time. First, the equation of the transient one-dimensional compressible one-phase and two-phase fluid flow is solved using the explicit Euler method of order 1 and the finite volume method. The liquid-vapor mixture is modeled as a homogeneous mixture at mechanical and thermal equilibrium. The closure laws of the model are deduced from the "Stiffened Gas" state laws. For the reduced model, an extension of the modal identification method is proposed. The structure of the reduced model is first determined carrying out the Galerkin projection of the continuous conservation equations.Then the parameters of the model are identified by the resolution of an optimization problem. The reduced model thus constructed is then validated on several cases with different dynamics

Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2011.
ENGLISH ABSTRACT: The feasibility of a closed loop thermosyphon for the Reactor Cavity Cooling System of the Pebble Bed Modular Reactor has been the subject of many research projects. Difficulties identified by previous studies include the hypothetical inaccuracies of heat transfer coefficient correlations available in literature. The aim of the research presented here is to develop inside-pipe heat transfer correlations that are specific to the current design of the RCCS. In order to achieve this, a literature review is performed which identifies reactors which employ closed loop thermosyphons and natural circulation. The literature review also explains the general one-dimensional two-fluid conservation equations that form the basis for numerical modelling of natural circulation loops. The literature review lastly discusses available heat transfer coefficient correlations with the aim of identifying over which ranges and under which circumstances these correlations are considered accurate. The review includes correlations commonly used in natural circulation modelling in the nuclear industry in aims of identifying correlations applicable to the modelling of the proposed RCCS. One of the objectives of this project is to design and build a one-third-height-scale model of the RCCS. Shortcomings of previous experimental models were assessed and, as far as possible, compensated for in the design of the model. Copper piping is used, eliminating material and surface property uncertainties. Several sight glasses are incorporated in the model, allowing for the visual identification of two-phase flow regimes. An orifice plate is used allowing for bidirectional flow measurement. The orifice plate, thermocouples and pipe-in-pipe heat exchangers are calibrated in-situ to minimize experimental error and aid repeatability. Twelve experiments are performed with data logging occurring every ten seconds. The results presented here are limited to selected single and two-phase flow operating mode results. Error analyses and repeatability of experimental measurements for single and two-phase operating modes as well as cooling water mass flow rates are performed, to show repeatability of experimental results. These results are used to mathematically determine the experimental inside-pipe heat transfer coefficients for both the evaporator and condenser sections. Trends in the heat transfer coefficient profiles are identified and the general behaviour of the profiles is thoroughly explained. The RCCS is modelled as a one-dimensional system. Correlations for the friction factor, heat transfer coefficient, void fraction and two-phase frictional multiplier are identified. The theoretical heat transfer coefficients are calculated using the mathematical model and correlations identified in the literature review. Fluid parameters are evaluated using experimentally determined temperatures and mass flow rates. The resulting heat transfer coefficient profiles are compared to experimentally determined profiles, to confirm the hypothesis that existing correlations do not accurately predict the inside-pipe heat transfer coefficients. The experimentally determined coefficients are correlated to 99% confidence intervals. These generated correlations, along with identified and established twophase heat transfer coefficient correlations, are used in a mathematical model to generate theoretical coefficient profiles. These are compared to the experimentally determined coefficients to show prediction accuracy.
AFRIKAANSE OPSOMMING: Die haalbaarheid van ‘n natuurlike sirkulasie geslote lus vir die Reaktor Holte Verkoeling Stelsel (RHVS) van die Korrelbed Modulêre Kern-Reaktor (KMKR) is die onderwerp van talle navorsings projekte. Probleme geïdentifiseer in vorige studies sluit in die hipotetiese onakkuraatheid van hitte-oordrag koëffisiënt korrelasies beskikbaar in literatuur. Die doel van die navorsing aangebied is om binne-pyp hitte-oordrag koëffisiënt korrelasies te ontwikkel spesifiek vir die huidige ontwerp van die RHVS. Ten einde dit te bereik, word ‘n literatuurstudie uitgevoer wat kern-reaktors identifiseer wat gebruik maak van natuurlike sirkulasie lusse. Die literatuurstudie verduidelik ook die algemene een-dimensionele twee-vloeistof behoud vergelykings wat die basis vorm vir numeriese modellering van natuurlike sirkulasie lusse. Die literatuurstudie bespreek laastens beskikbare hitte-oordrag koëffisiënt korrelasies met die doel om te identifiseer vir welke massavloei tempo waardes en onder watter omstandighede hierdie korrelasies as korrek beskou is. Die ontleding sluit korrelasies in wat algemeen gebruik word in die modellering van natuurlike sirkulasie in die kern industrie met die hoop om korrelasies vir gebruik in die modellering van die voorgestelde RHVS te identifiseer. Een van die doelwitte van die projek is om ‘n een-derde-hoogte-skaal model van die RHVS te ontwerp en te bou. Tekortkominge van vorige eksperimentele modelle is geidentifiseer en, so ver as moonlik, voor vergoed in die ontwerp van die model. Koper pype word gebruik wat die onsekerhede van materiaal en opperkvlak eindomme voorkom. Verkseie deursigtige polikarbonaat segmente is ingesluit wat visuele identifikasie van twee-fase vloei regimes toelaat. ‘n Opening plaat word gebruik om voorwaartse en terugwaartse vloeimeting toe te laat. Die opening plaat, termokoppels en hitte uitruilers is gekalibreer in plek om eksperimentele foute te verminder en om herhaalbaarheid te verseker. Twaalf eksperimente word uitgevoer en data word elke tien sekondes aangeteken. Die resultate wat hier aangebied word, is beperk tot geselekteerde enkel- en tweefase vloei meganismes van werking. Fout ontleding en herhaalbaarheid van eksperimentele metings, om die herhaalbaarheid van eksperimentele resultate te toon. Hierdie is gebruik om wiskundig te bepaal wat die eksperimentele binne-pyp hitte-oordrag koëffisiënte is vir beide die verdamper en kondenseerder afdelings. Tendense in die hitte-oordrag koëffisiënt profiele word geïdentifiseer en die algemene gedrag van die profiles is deeglik verduidelik. Die RHVS is gemodelleer as 'n een-dimensionele stelsel. Korrelasies vir die wrywing faktor, hitte-oordrag koëffisiënte, leegte-breuk en twee-fase wrywings vermenigvuldiger word geïdentifiseer. Die teoretiese hitte-oordrag koëffisiënte word bereken deur middle van die wiskundige model en korrelasies wat in literatuur geidentifiseer is. Vloeistof parameters is geëvalueer met eksperimenteel bepaalde temperature en massa-vloei tempos. Die gevolglike hitte-oordrag koëffisiënt profiles is vergelyk met eksperimentele profiele om die hipotese dat die bestaande korrelasies nie die binne-pyp hitte-oordrag koëffisiënte akkuraat voorspel nie, te bevestig. Die eksperimenteel bepaalde koëffisiënte is gekorreleer en die gegenereerde korrelasies, saam met geïdentifiseerde twee-fase hitte-oordrag koëffisiënt korrelasies, word gebruik in 'n wiskundige model om teoretiese koëffisiënt profiele te genereer. Dit word dan vergelyk met die eksperimenteel bepaalde hitteoordrag koëffisiënte om die akkuraatheid van voorspelling te toon. Tekortkominge in die teoretiese en eksperimentele model word geïdentifiseer en aanbevelings gemaak om hulle aan te spreek in die toekoms.

The research facility at the University of Manchester in the Morton Laboratory is a full scale replica of an industrial sized natural circulation thermosyphon reboiler, which comprises 50 tubes of 3 m length and 25.4 mm OD. The facility is operated under vacuum. Water is used as the process fluid and condensing steam is the heating source. Experimental datasets were obtained for the reboiler and have been presented in the form of profile plots of feed rate, fluid recirculation, recirculation ratio and vapour quality. The data elucidate the effect of pressure [0.1 to 1.0 bar] and heat duties [78 to 930 kW] on the performance of the reboiler. Three distinct modes of operation have been observed. Mode one is defined as a flow-induced instability or geysering (low heat duty) and exists below a definite transitional point that is independent of process pressure. Mode two is a region of stable operation that occurs above the threshold of the flow-induced instability, while mode three, which is defined as the heat-induced instability (density-wave instability), is pressure dependent obtained at high duties and is characterised by violent oscillations. These instability thresholds represent the lower and upper limits of operation of the reboiler. The region of stable operation is enveloped between the two limits and is very dependent on process pressure as it progressively becomes smaller as the vacuum becomes lower. These studies led to unique experimental observations, which revealed the existence of intermittent reversed flow in the entire loop. The use of throttling in the heat-induced unstable region to return to stable operation tends to be over a narrow range, outside of which the sole way to regain stability is to lower the heat load or increase the process pressure. In the region of flow-induced instability, throttling the fluid at the inlet is useless and actually makes the situation worse. These instabilities are alleviated by increasing the heat load.

The Next Generation Nuclear Plant (NGNP) will most likely produce electricity and process heat, with both being considered for hydrogen production. To capture nuclear process heat, and transport it to a distant industrial facility requires a high temperature system of heat exchangers, pumps and/or compressors. The heat transfer system is particularly challenging not only due to the elevated temperatures (up to ∼ 1300K) and industrial scale power transport (≥50 MW), but also due to a potentially large separation distance between the nuclear and industrial plants (100+m) dictated by safety and licensing mandates. The work reported here is the preliminary analysis of two-phase thermosyphon heat transfer performance with alkali metals. A thermosyphon is a device for transporting heat from one point to another with quite extraordinary properties. In contrast to single-phased forced convective heat transfer via ‘pumping a fluid’, a thermosyphon (also called a wickless heat pipe) transfers heat through the vaporization / condensing process. The condensate is further returned to the hot source by gravity, i.e. without any requirement of pumps or compressors. With this mode of heat transfer, the thermosyphon has the capability to transport heat at high rates over appreciable distances, virtually isothermally and without any requirement for external pumping devices. Two-phase heat transfer by a thermosyphon has the advantage of high enthalpy transport that includes the sensible heat of the liquid, the latent heat of vaporization, and vapor superheat. In contrast, single-phase forced convection transports only the sensible heat of the fluid. Additionally, vapor-phase velocities within a thermosyphon are much greater than single-phase liquid velocities within a forced convective loop. Thermosyphon performance can be limited by the sonic limit (choking) of vapor flow and/or by condensate entrainment. Proper thermosyphon requires analysis of both.

Abstract The trend in miniaturization of power electronic components requires the development of new robust and passive cooling methods to meet increased heat flux demands. Conventional heat sinks encounter inherent shortcomings due to heat spreading resistance of the heat sink baseplate particularly in natural convection heat sinks used to cool small localized heat sources. Heat pipes embedded within the base of heat sinks can be used to improve spreading performance but are limited by the ability to conduct heat into and out of the heat pipes. In the current study, a small, naturally aspirated two-phase thermosyphon heat sink was developed and characterized experimentally. The proposed architecture integrates all thermosyphon components into one compact device, where the evaporator, riser and the downcomer are incorporated at the heat sink base. The downcomer also serves as the condenser within the base of a vertical finned natural convection heat sink. The side-heated evaporator consists of an array mini-channels configuration which can operate in either pool boiling or flow boiling configuration, which allows the thermosyphon heat sink to operate in either reflux mode or looped mode, respectively. Experiments were carried out using HFE 7000 as the working fluid. The effect of the of input power on the thermal performance is examined for both modes for powers ranging from 10 to 80 W. Results demonstrate that this approach significantly reduces the spreading resistance resulting in a net improvement which can be traded-off for a decrease the overall size or weight of the heat sink.

Abstract Thermosyphon cooling systems represent the future of datacenter cooling, and electronics cooling in general, as they provide high thermal performance, reliability and energy efficiency, as well as capture the heat at high temperatures suitable for many heat reuse applications. On the other hand, the design of passive two-phase thermosyphons is extremely challenging because of the complex physics involved in the boiling and condensation processes; in particular, the most important challenge is to accurately predict the flow rate in the thermosyphon and thus the thermal performance. This paper presents an experimental validation to assess the predictive capabilities of JJ Cooling Innovation’s thermosyphon simulator against one independent data set that includes a wide range of operating conditions and system sizes, i.e. thermosyphon data for server-level cooling gathered at Nokia Bell Labs. Comparison between test data and simulated results show good agreement, confirming that the simulator accurately predicts heat transfer performance and pressure drops in each individual component of a thermosyphon cooling system (cold plate, riser, evaporator, downcomer (with no fitting parameters), and eventually a liquid accumulator) coupled with operational characteristics and flow regimes. In addition, the simulator is able to design a single loop thermosyphon (e.g. for cooling a single server’s processor), as shown in this study, but also able to model more complex cooling architectures, where many thermosyphons at server-level and rack-level have to operate in parallel (e.g. for cooling an entire server rack). This task will be performed as future work.

Abstract This paper advances the state-of-the-art in novel passive two-phase systems for more efficient cooling of datacenters and telecom central offices compared to the traditional air-based cooling solutions (e.g. aisle-based containment systems). The proposed passive two-phase technology uses numerous server-level thermosyphons to dissipate the heat generated by critical components, such as central processing units, accelerators, etc., with the flexibility of selecting the rack-level and room-level cooling elements depending on the deployment scenarios. The main goal of this paper is to experimentally investigate the thermal performance and maximum heat removal capability of a server-level thermosyphon for cooling compact servers. The experimental apparatus, built at Nokia Bell Labs, incorporates a single 7-cm high liquid-cooled thermosyphon that fits within a 2U server (smaller form factors can be achieved by a proper design that would further reduce the thermosyphon’s height). The heat source is represented by a pseudo-chip, composed of six parallel cartridge heaters installed in a copper block that incorporates local temperature measurements and is able of dissipating a total power of ≈ 500 W over a footprint area of 3.5 cm × 3.5 cm (corresponding heat flux of ≈ 41 W/cm2). Steady-state experiments were carried out at various heat loads up to 240 W (corresponding heat flux of ≈ 20 W/cm2), filling ratios and secondary side inlet conditions (coolant temperatures and mass flow rates), using R1234ze(E) and deionized water as the working fluids on the primary and secondary side, respectively. Test results demonstrate high heat transfer performance of the server-level thermosyphon over a wide range of conditions, and operating points are identified and classified into an operational map. Thermosyphon-based cooling systems across multiple length scales can significantly improve operation in terms of lowering energy consumption, allowing for higher hardware density, increased processing speed and reliability.

An experimental investigation of a scaled-down and simplified laboratory model of a transformer cooling system is presented and discussed in this paper. The overall goal of this work was to obtain experimental data for validating cost-effective approximate mathematical models, used in investigations aimed at the development of numerical methods for assessing the operating limits of current transformers and optimizing the designs of next-generation transformers. The laboratory model used in this work was a vertical, single-phase, closed-loop thermosyphon operating with water as the working fluid. The steady and unsteady behaviors of this closed-loop thermosyphon were established and investigated using the following series of power inputs: 50 W, 125 W, 200 W, 125 W, and 50 W. Each of these levels of power input was maintained until steady-state conditions were achieved; and then the excursion to the adjacent power level (up or down, depending on the position in the aforementioned series) was effected. The corresponding experimental results are presented and discussed in this paper. The steady-state experiments with water as the working fluid are used to obtain valuable benchmarking results and also reliable initial conditions for the unsteady experiments. The experiments with excursions from one power level to an adjacent one provide novel results pertaining to unsteady operation of closed-loop thermosyphons. Another novel feature of this work is a demonstration that a simple lumped-parameter formulation can yield good predictions of the overall unsteady behavior of closed-loop thermosyphon systems akin to those used for cooling transformers.

A solar thermal-driven multiple-effect thermosyphon distillation (METD) system is proposed for waste-water treatment. The METD system consists of a series of cascaded thermosyphons that are connected by embedding the condenser section of each thermosyphon in the evaporator section of the following device. The input thermal energy is supplied by a solar collector integrated with a latent heat thermal energy storage unit. A thermal network model is developed to predict the heat transfer rates through the METD system and distilled water production rates. METD systems with various number of effects and hot end temperatures are investigated. It is found that the ratio of distilled water production to the input thermal energy increases by increasing the number of effects with no dependence on the hot end temperature. Quantitatively, a METD system with 5 effects can produce 11 kg of fresh water per hour with an input heat of 1.4 kW.

Thaw subsidence and frost heave are two different hazards to pipelines in arctic regions. The former is due to the thawing of permafrost induced by a warm pipeline, while the latter is resulted from a cold buried pipeline that causes ice lens growth upon freezing in the direction of heat loss. Some pipelines may be operated in a wide temperature range and thus subjected to both types of threats. Two-phase closed thermosyphons have been employed extensively in Arctic projects to protect the permafrost from thawing. The thermosyphons’ response as a “thermo-diode” is the key to this technology. This paper presents a finite element analysis (FEA) based feasibility study for using thermosyphons with pipelines in arctic regions to reduce the potential for frost heave. There are two major challenges in the numerical simulation. One is the efficient modeling of a thermosyphons which works as a heat pump in winter and stops working in summer. This study proposes an anisotropic conduction model that simplifies the thermal-fluid processes within the thermosyphon without overwhelming computational cost. The other challenge is the frost heave modeling, which was recently achieved based on the framework of the porosity rate function. New developments involved in this paper include the extended application to permafrost and transient temperature boundary conditions. The outcome of this work proves the value of using thermosyphons with pipelines that transfer both cold product. The method introduced here can also be used to optimize the design of new infrastructure and pipelines in permafrost, as well as to assess how thermosyphons work as a mitigation method in existing projects that are affected by frost heave.

A closed loop two-phase thermosyphon has been modeled based on earlier experimental and numerical studies by Mukherjee and Mudawar [1, 2]. Unlike conventional thermosyphons in which the heat dissipating device is submerged in a pool of liquid coolant, the current system uses a flow boiling arrangement. The advantage is that for a given boiling surface area, the critical heat flux (CHF) can be increased. Parametric studies with respect to adiabatic section flow areas, boiler section flow area, and system height were performed. The maximum practical heat flux that is attainable is predicted, as well as other flow parameters such as mass flow rate, flow velocities and fluid quality existing the boiler. Performance enhancements relative to the original system, may be possible by introducing a divergent cross sectional area in the boiler section that increases the system mass flow rate. It can also, however, reduce the flow velocity in certain sections of the boiler, tending to reduce the boiler CHF. Experimental studies are recommended to determine if an actual improvement can be realized.

Thermosyphons are an artificial ground-freezing technique that has been used to stabilize permafrost since the 1960s. The largest engineered structure that uses thermosyphons to maintain frozen ground is the Trans Alaska Pipeline, and it has over 124,000 thermosyphons along its approximately 1300 km route. In passive mode, thermosyphons extract heat from the soil and transfer it to the environment when the air temperature is colder than the ground temperature. This passive technology can promote ground cooling during cold winter months. To address the growing need for maintaining frozen ground as air temperatures increase, we investigated a solar-powered refrigeration unit that could operate a thermosyphon (nonpassive) during temperatures above freezing. Our tests showed that energy generated from the solar array can operate the refrigeration unit and activate the hybrid thermosyphon to artificially cool the soil when air temperatures are above freezing. This technology can be used to expand the application of thermosyphon technology to freeze ground or maintain permafrost, particularly in locations with limited access to line power.