To investigate the heat transfer from enhanced evaporation surfaces, various structured tubes, particularly with re-entrant cavities, and one smooth reference surface were tested in the pool boiling mode using the hydrocarbon propane as working fluid. The tubes are made of carbon steel ST35.8. As experimental parameters saturation temperatures between 253 K and 293 K and heat fluxes in the range from 2 kW/m2 to 100 kW/m2 are employed. For the visualization of the boiling phenomena and the two-phase flow from the tube surfaces a test rig is employed with a high speed video system. An empirical correlation has been generated to describe the experimental results.Compared with the smooth reference tube, the structured surfaces with re-entrant cavities show distinct improvements of the heat transfer performance. Particularly for low and medium heat fluxes (q < 40 kW/m2), higher heat transfer coefficients of factors up to 3 were observed.

Pool boiling experiments have been carried out on a smooth and an enhanced tube, employing sub-surface tunnels, with pure propane, pure iso-butane and two mixtures of propane and iso-butane as working fluids. It is found that, the enhanced tube suffers much more severe heat transfer degradation in boiling of mixtures than the smooth tube. This substantial degradation of boiling heat transfer is thought to be due to the malfunction of the sub-surface tunnels which is supported by some very special bubble behaviors observed in boiling of mixtures on the enhanced tube, e.g. the sharp turn of bubble curvature near the wall, the generation of small bubbles, the jets of small bubbles on the bottom surface, etc.. The measured bubble dynamics data also prove that the amount of vapor generated in boiling of mixtures is lower than that in boiling of pure components.

Experimental investigations are presented of enhanced evaporation tubes with re-entrant cavities operating in the pool boiling mode under saturation conditions of the working fluid propane.The heat transfer coefficients of the evaporator tubes are determined for different heat fluxes and saturation temperatures. The boiling phenomena are qualitatively visualized by means of high speed video technique and the quantitative evaluations of the high speed videos, e.g. the determination of the bubble departure diameter, the bubble generation frequency, are carried out for low heat fluxes using digital image processing methods. The high speed hardware including the illumination system and the applied digital image processing (digital filtering, Fourier-frequency-analysis and correlation technique) are described. Both, the qualitative and quantitative data of the high speed visualization are discussed.

Experimental investigations are carried out to obtain more information about the heat and especially the mass transfer phenomena concerning evaporation of water from a prototype evaporation surface for low consumption and electric motor vehicles. One prototype evaporator with various structured surface coverings of different materials is tested. The basic test section consists of an industrial prototype evaporator with fine longitudinal re-entrant grooves. The test conditions of the air temperature and the air humidity vary between 20 °C and 40 °C and 20 % and 40 % respectively. The heat fluxes range from 430 W/m2 to 1175 W/m2. Water is used as working fluid. Results of the prototype evaporator and three different structures of different material properties, covering the surface of the prototype, are presented in this paper. First results show a good heat transfer from the evaporation surface to the air flow above the surface.

Flow boiling heat transfer in small-sized channels employed in compact heat exchangers is attracting increasing attention with the progressing miniaturization in many industrial fields. Experiments have been conducted to investigate the heat transfer and the pressure drop in narrow channels (rectangular channels with 2×4 mm and 0.5×2 mm (width × depth)). The working fluid is deionized water. The flow rate is 100 up to 700 kg/m2s at exit atmospheric pressure. By means of video-camera, flow boiling phenomena were observed as well. Three flow patterns, i.e. bubbly flow, slug flow and annular flow, could be distinguished. Based on the present single-phase flow experimental results the flow boiling pressure drop was compared with the Lockhart-Martinelli correlation, and ±30% deviation from Lockhart-Martinelli was found.

This presentation attempts to give a historical review of heat pipe science and technology up to the present state. In a first part, a brief introduction is given into design, operation and performance limits of heat pipes and closed two-phase thermosyphons. In a second part, the historic development of closed two-phase thermosyphons and heat pipes is highlighted. It includes the history of the International Heat Pipe Conference (IHPC) series, whose 40 years anniversary we are celebrating this year. A list of overview reports and textbooks is given. A large section of this second part deals with major inventions and developments from the origins to our time. Here one can see, rather compressed and certainly not fully complete, the multitude of heat pipe/thermosyphon designs which have been developed to solve a great variety of thermal control tasks. It has also been tried to classify the numerous members of the heat pipe family in the form of a table of passive liquid-vapour heat transfer devices. The third part of the presentation deals with applications. From five of the many application fields, some selected examples are given: thermosyphons for permafrost stabilization and deicing; heat pipe/thermosyphon heat exchangers; cooling of electric and electronic devices and components; liquid metal heat pipes for temperature calibration, material treatment and solar applications; (open and closed) two-phase thermosyphons for passive nuclear safety systems.

Covers advancements in spacecraft and tactical and strategic missile systems, including subsystem design and application, mission design and analysis, materials and structures, developments in space sciences, space processing and manufacturing, space operations, and applications of space technologies to other fields.

Dry (solid) sorption systems are attractive competitors to wet (liquid) sorption systems in providing useful cold and/or useful heat. Among the dry sorption systems, those based on the absorption/desorption of hydrogen in/from metal alloys reveal advantageous features, and this has stirred up the interest of researchers already since the 1970s. In recent years, many attempts have been made to develop metal hydride based heating and cooling systems. Of special interest was and is the possibility to utilize low temperature heat (waste heat, solar heat) to drive those systems. Major applications are seen in air-conditioning and heat supply for buildings and in air-conditioning of automobiles. In this paper, the research and development work on metal hydride based heating and cooling systems is reviewed which has been published in the last three decades. Emphasis is given primarily to cooling/air-conditioning. The objectives are to provide the fundamental understanding of metal hydride based heating and cooling systems and to give useful guidelines regarding various design parameters. The operation principles of various types of systems are explained and the importance of the metal hydride reaction bed heat and mass transfer characteristics is stressed. Possible ways for improving the coefficient of performance and specific cooling capacity are discussed. Besides a brief characterization of many experimental and theoretical investigations, the worldwide status of the development of metal hydride based heating and cooling systems is summarized in a tabular form.

This paper presents a feasibility study of a single-stage metal hydride heat pump (SS-MHHP) working on the crossed van't Hoff line concept. The consequence of crossed van't Hoff line SS-MHHP is to utilize the enthalpy of formation of the refrigeration alloy for driving the system. The performance of this system is predicted by solving the unsteady, two dimensional- mathematical model in an annular cylindrical configuration using the finite volume method. Two different hydride alloy pairs are employed, namely, V0.846Ti0.104Fe0.05 / Fe0.9Mn0.1Ti and V0.855Ti0.095Fe0.05 / MmNi(4.7)Al(0.3) (regeneration alloy / refrigeration alloy). The influences of heat source (T-D) and refrigeration (T-C) temperatures on the amount of hydrogen transfer between paired reactors, coefficient of performance (COP) and specific cooling power (SCP) of the system are studied. For the selected range of operating temperatures, the performance of the crossed van't Hoff line SS-MHHP is compared with the conventional SS-MHHP; a maximum improvement in COP of about 60 % is found. For the selected hydride pairs V0.846Ti0.104Fe0.05 / Fe0.9Mn0.1Ti and V0.855Ti0.095Fe0.05 / MmNi(4.7)Al(0.3), the optimum operating temperatures are found to be 373/303/291 K (heat source/heat sink/refrigeration temperatures) and 400/303/283 K, respectively. At the optimum operating temperatures, the COP and SCP are found to be 0.89 and 30.8 W/kg total system (including reactor mass) mass, for the V0.846Ti0.104Fe0.05 / Fe0.9Mn0.1Ti hydride pair, while for the V0.855Ti0.095Fe0.05 / MmNi(4.7)Al(0.3) hydride pair the COP and SCP are 0.86 and 30.3 W/kg total system mass.

工质热物性显著影响脉动热管的流动与传热特性.本文通过理论计算及实验研究,定性分析了工质热物性对临界直径、毛细滞后阻力、启动运行及传热极限等方面的影响.研究表明,为保证脉动热管的运行性能,在设计阶段应综合考虑工质、管材及管径大小等因素.首先,根据使用场合的热流密度及运行温度高低合理选取工质种类;然后,选用合适的管壁材料,尽可能减少液塞与管壁之间前、后接触角不同引起的毛细滞后阻力;最后,确定管内直径范围.本文工作旨在为脉动热管的设计和选用提供一些依据和参考.

Flow boiling heat transfer characteristics of 1,1,1,2-tetrafluoroethane (R134a) were experimentally investigated in a horizontal stainless steel mini tube. The inner diameter of the test tube is 1.3 mm, and the tube wall thickness is 0.1 mm. Local heat transfer coefficients are obtained over a range of vapor qualities up to 0.8, mass fluxes from (310 to 860) kg.m(-2).s(-1), heat fluxes from (21 to 50) kW.m(-2), and saturation pressures from (0.65 to 0.75) MPa. The dependences of heat transfer coefficients on mass flux, heat flux, saturation pressure, and vapor quality are demonstrated. On the basis of ail available model in recent literature, potential heat transfer mechanisms are also analyzed.

The structural and operational characteristics between two kinds of pulsating heat pipes(PHPs) were compared.It is revealed that the flat plate type PHPs with square channels has two structural characteristics distinct different from the circle tube type PHPs,such as the sharp angled edges and the transverse heat balance effects through the thin wall between two neighboring channels,which contributed to the distinct operational characteristics.Experiments show that in the horizontal and vertical top heat modes,both type PHPs have the same optimum filling ratio ranging from 40% to 70%;in the vertical bottom heat mode,the circle tube type PHPs has an optimum filling ratio ranging from 30% to 70%,while the flat plate type PHPs with square channels has an optimum filling ratio of about 15%.

In the recent past, Pulsating Heat Pipes (PHPs) have attracted the attention of many researchers as viable candidates for enhanced heat transfer through passive two-phase heat transfer mechanism. Although a complete theoretical understanding of operational characteristics of this device is not yet achieved, there are many emerging niche applications, ranging from electronics thermal management to compact heat exchangers. For a better theoretical understanding, it is vital to generate experimental data under various operating boundary conditions. In this background, this paper presents an experimental study on two flat plate closed loop pulsating heat pipes in a thermal spreader configuration. Both are made of aluminum with overall size 180×120×3 mm3; one structure having 40 parallel square channels with cross-section 2×2 mm2, while the second with 66 parallel square channels with cross-section 1×1 mm2. The working fluid employed was Ethanol. Some peculiar performance trends, in comparison with circular channel devices, have been observed which are attributed to the sharp angled corners of the channels. The influence of various operating parameters, including volumetric filling ratio of the working fluid, input heat flux and operating orientation, on the thermo-hydrodynamic performance, was investigated. Successful operation at all orientations with respect to gravity was also achieved. In terms of applications, this paper explores the possibility of embedded pulsating heat pipe as an integrated structure or heat spreader, so as to render higher overall thermal conductance to the host substrate.

This paper presents an experimental study including visualization on a flat plate closed loop pulsating heat pipes.It consists of a total of 40 channels with square cross section(2 mm×2 mm,165 mm long) machined directly on an aluminum plate(180 mm×120 mm×3 mm) covered by a transparent plate.The working fluid employed is ethanol.As a result,various flow patterns and their transitions are observed and found to be related to the fluid fill ratio,input heat load and the device orientation.Also the operational characteristics and working mechanism are discussed.

In order to understand the heat transfer mechanism of the looped pulsating heat pipe with different working fluids,wind cooled a vertical looped pulsating heat pipe was investigated on an experimental setup with three working fluids:R123,ethanol and water.Different thermal resistances and their varying trends under different heat loads and fill ratios of the pulsating heat pipe using different working fluids were measured.It is found that the startup characteristics and thermal resistances are related to the properties of the working fluids including the saturation temperature,specific heat,latent heat of vaporization and the variation of pressure with temperature for saturated vapor.Different property has different effect on different working conditions,which determines the easiness to start pulsation and reveals the thermal resistance variation tendency with the change of heat load.

In order to understand the heat transfer mechanism of the looped pulsating heat pipe with different working fluids, wind cooled a vertical looped pulsating heat pipe was investigated on an experimental setup with three working fluids: R123, ethanol and water. Different thermal resistances and their varying trends under different heat loads and fill ratios of the pulsating heat pipe using different working fluids were measured. It is found that the startup characteristics and thermal resistances are related to the properties of the working fluids including the saturation temperature, specific heat, latent heat of vaporization and the variation of pressure with temperature for saturated vapor. Different property has different effect on different working conditions, which determines the easiness to start pulsation and reveals the thermal resistance variation tendency with the change of heat load.

In this paper, the hydriding kinetics of LaNi5, LaNi4.7Al0.3 and LmNi4.91Sn0.15 is presented. Experiments were carried out by maintaining the pressure ratio (supply pressure to equilibrium pressure at the mid-point of the pressure–concentration–isotherm) equal to 2 and by maintaining nearly isothermal reaction conditions. Two widely used reaction kinetics models, namely Johnson–Mehl–Avrami (JMA) model and Jander diffusion model (JDM) are considered for the analysis. Two JMA models are considered; in the first model, the order of the reaction is assumed as unit and in the second model, the rate constant is calculated by estimating the order by fitting the reaction kinetics data with a reaction kinetics equation. The activation energy and pre-exponential constants of the above-mentioned alloys are estimated by constructing the Arrhenius plot. Activation energies estimated from the different models are compared and the accurate values of activation energy for the different alloys are determined by comparing the reaction kinetics data obtained from the models with the experimental data. The rate-controlling step of the hydriding reaction is obtained for all the alloys investigated.

Adopting R123,water and alcohol as the working medium,the effect of inclination angle and liquid filling ratio on heat transfer performance of pulsating heat pipes(PHPs) were studied on the PHP test rig consisted of 40 elbows bent by fine copper tubes with inner diameter of 1 mm and 2 mm.Results show that the average evaporating temperature increases as the inclination angle varies from +90° to-90°under the same heat load,and the effect of inclination angle on operational performance is obvious under low load.For multi-elbow tubular pulsating heat pipes,the gravity still affects the heat transfer performance,while its effect decreases with the increase of heat load and the decrease of the inner diameter.Optimal range of liquid filling ratio is influenced by inner diameter,heating mode,heat load and working fluid and so on.For engineering application,the liquid filling ratio can be approximately taken as 55% of the total volume inside the tube.

This paper presents an experimental study on the operational limitation of closed loop pulsating heat pipes (CLPHPs), which consist of a total of 40 copper tubes with 1 mm and 2 mm inner diameter, respectively. R123 was employed as the working fluid with filling ratios of 30%, 50% and 70%, respectively. Three operational orientations were investigated, viz. vertical bottom heated, horizontal heated and vertical top heated orientations. The effects of inner diameter, operational orientation, filling ratio and heat input flux on thermal performance and performance limitation were investigated. The results show that for the CLPHP with 2 mm ID tubes the best performance existed in the vertical orientation with heating at the bottom, while for the CLPHP with 1 mm ID tubes, orientation played almost no role. A filling ratio of 50% was optimum for both CLPHPs to obtain best performances in all orientations. The CLPHPs were operated till a performance limit characterized by serious evaporator overheating (dry-out) occurred. Rather high heat loads could be accommodated. Dry-out heat fluxes in the vertical bottom heat mode were about 1242 W/cm2 (1 mm ID) and 430 W/cm2 (2 mm ID) for axial heat transport, and about 32 W/cm2 (1 mm ID) and 24 W/cm2 (2 mm ID) for radial heat input, always with respect to the inner tube diameter.

In order to improve hydrogen storage properties of Mg, the intermetallic compound LaNi5 and the catalysts Ti, V have been applied to synthesise Mg-based nanostructured composites by ball milling. All samples have been ball milled with milling times up to 40h and have been tested by means of pressure-concentration isotherms (PCIs) and reaction kinetics. In addition, X-ray diffraction (XRD) has been employed for structure investigation. According to the PCI results, Mg2Ni has been formed in the samples with 15 and 35wt.% LaNi5 by prolonged ball milling. The improvement of reaction kinetics is more significant with more content of LaNi5, however, the storage capacities are degraded. The hydrogen storage properties of Mg have been further enhanced by additional catalysts of Ti and V. The Mg-based composites can desorb hydrogen at 245°C with reasonable reaction rate. Desorption occurs even at a low temperature of 185°C, however, with an extremely slow desorption rate.