Sonic Limit Research Articles

Ruido en el contexto de crisis social

Noise is a way to go beyond sonic and social limits in social crisis contexts. This essay is about screams content and manifestations in three marches to support Ayotzinapa᾿s case, framed in human rights violations and antisystemic social processes. It combines ethnography with semiotics, the first to describe the expressions and the second to locate its significance. In some streets of Guadalajara in the year 2014 there was possibility for the collective ecstatic (to leave itself) in each scream, because the high volume and the rabid expressions of the indignation prevailed, and echoed the characteristic sounds of the social movement emerged by this case. Screams content was about State’s social power decadence, public education tension, people politics, and Iguala’s aberrant event.

Analytical Investigation of the Heat-Transfer Limits of a Novel Solar Loop-Heat Pipe Employing a Mini-Channel Evaporator

This paper presents an analytical investigation of heat-transfer limits of a novel solar loop-heat pipe developed for space heating and domestic hot water use. In the loop-heat pipe, the condensate liquid returns to the evaporator via small specially designed holes, using a mini-channel evaporator. The study considered the commonly known heat-transfer limits of loop-heat pipes, namely, the viscous, sonic, entrainment, boiling and heat-transfer limits due to the two-phase pressure drop in the loop. The analysis considered the main factors that affect the limits in the mini-channel evaporator: the operating temperature, mini-channel aspect ratio, evaporator length, evaporator inclination angle, evaporator-to-condenser height difference and the dimension of the holes. It was found that the entrainment is the main governing limit of the system operation. With the specified loop design and operational conditions, the solar loop-heat pipe can achieve a heat-transport capacity of 725 W. The analytical model presented in this study can be used to optimise the heat-transfer capacity of the novel solar loop-heat pipe.

Performance Limits of Oscillating Heat Pipes: Theory and Validation

Oscillating heat pipes have been the subject of significant research since 1990, but to allow their entry into broad application, it is important to understand their operational limitations. This paper presents analytical and experimental investigations of the various performance limits of oscillating heat pipes. The Bond number limit, vapor inertia limit, heat flux limit, viscous limit, sonic limit, and limitations on heated length are discussed in detail and developed with analytical tools for prediction. These limits are then tested against experimental studies. It is found that the Bond number coefficient can be as high as 2.4–2.74, rather than the typically reported 1.8–2.0. The established vapor inertia, heat flux, viscous, and sonic limits show good agreement with published experimental data sets, as well as controlled experiments run specifically to test these limits. Finally, it was determined that longer evaporator lengths result in a reduction of overall heat transport capability. An analytical approach is presented to predict this performance loss, showing good agreement with experimental results.

The Nature of Turbulence in the LITTLE THINGS Dwarf Irregular Galaxies

Abstract We present probability density functions and higher order (skewness and kurtosis) analyses of the galaxy-wide and spatially resolved distributions of H i column density in the LITTLE THINGS sample of dwarf irregular galaxies. This analysis follows that of Burkhart et al. for the Small Magellanic Cloud (SMC). About 60% of our sample have galaxy-wide values of kurtosis that are similar to that found for the SMC, with a range up to much higher values, and kurtosis increases with integrated star formation rate. Kurtosis and skewness were calculated for radial annuli and for a grid of 32 pixel × 32 pixel kernels across each galaxy. For most galaxies, kurtosis correlates with skewness. For about half of the galaxies, there is a trend of increasing kurtosis with radius. The range of kurtosis and skewness values is modeled by small variations in the Mach number close to the sonic limit and by conversion of H i to molecules at high column density. The maximum H i column densities decrease with increasing radius in a way that suggests molecules are forming in the weak-field limit, where H2 formation balances photodissociation in optically thin gas at the edges of clouds.

Performance analysis of heat pipe radiator unit for space nuclear power reactor

Heat pipe radiator, featured with remarkable advantages in heat transfer efficiency and inherent safety with small specific mass and little weight, are widely adopted to the heat-rejection system for space nuclear power reactors. In this paper, physical and numerical models are developed to obtain the startup and transient behaviors of radiator unit with a potassium (K) heat pipe covered by fin under space environment. The heat transfer limit theory is adopted as criteria for heat pipe operation success. Numerical results indicated that according to the internal vapor flow regimes, the K heat pipe startup could be divided into three distinct stages. The K heat pipe started up from frozen state successful and rapidly until the expected operation state is reached. Among the different heat transfer limits, only the sonic limit due to choked flow restricts the K heat pipe during the second stage. Overall, for the heat-rejection system of space nuclear power reactor, the heat pipe radiator unit can effectively radiated waste heat to the space environment in 5min and responses fast under transient conditions.

Влияние основных ограничивающих факторов на пределы теплопереноса в тепловых трубах с различными теплоносителями

Aluminium and copper heat pipes with grooved and metal fibrous capillary structure are high effective heat transfer devices. They are used in different cooling systems of electronic equipment like a LED modules, microprocessors, receive-transmit modules and so on. However, thus heat pipes have heat transfer limitations. There are few types of these limitations: hydraulic limitation, boiling limitation, liquid entrainment by vapor flow and sonic limitation. There is necessity to know which one of these limitations is determinant for heat pipe due to design process. At a present article calculations of maximum heat transfer ability represented. All these calculations were made for LED cooling by using heat pipes with grooved and metal fibrous capillary structures. Pentane, acetone, isobutane and water were used as a coolants. It was shown that the main operation limit for axial grooved heat pipe, which determinate maximum heat transfer ability due to inclination angle for location of cooling zone higher than evaporation zone case, is entrainment limit for pentane and acetone coolants. Nevertheless, for isobutane coolant the main limitation is a boiling limit. However, for heat pipes with metal fibrous capillary structure the main limitation is a capillary limit. This limitation was a determinant for all calculated coolants: water, pentane and acetone. For high porosity range of capillary structure, capillary limit transfer to sonic limit for heat pipes with water, that means that the vapor velocity increases to sonic velocity and can’t grow any more. Due to this, coolant cant in a needed quantity infill condensation zone and the last one drained. For heat pipes with acetone and pentane, capillary limit transfer to boiling limit. All calculations were made for vapor temperature equal to 50°C, and for porosity range from 30% to 90%.

Thermal–structural analysis of the platelet heat-pipe-cooled leading edge of hypersonic vehicle

One of the main challenges for the hypersonic vehicle is its thermal protection, more specifically, the cooling of its leading edge. To investigate the feasibility of a platelet heat-pipe-cooled leading edge structure, thermal/stress distributions for steady-state flight conditions are calculated numerically. Studies are carried on for IN718/Na, C-103/Na and T-111/Li compatible material combinations of heat pipe under nominal operations and a central heat pipe failure cases, and the influence of wall thickness on the design robustness is also investigated. And the heat transfer limits (the sonic limit, the capillary limit and the boiling limit) are also computed to check the operation of platelet heat pipes. The results indicate that, with a 15mm leading edge radius and a wall thickness of 0.5mm, C-103/Na and T-111/Li combinations of heat pipe is capable of withstanding both nominal and failure conditions for Mach 8 and Mach 10 flight respectively.

Heat transfer capability simulation of high-temperature heat pipe in supersonic vehicle leading edge applications

A numerical method is proposed to determine the heat transfer capability of the high-temperature heat pipe and the stagnation temperature with supersonic vehicle leading edge applications. The finite element method is employed here to perform the temperature field simulation. Without considering the heat transfer limitations of the heat pipe, such as capillary limit and sonic limit, both numerical and experimental results indicate that equivalent high thermal conductivity method is a reasonable way to simulate the heat transfer capability of the high-temperature heat pipe in preliminary design of a heat-pipe-cooled leading edge. Several important parameters’ effects on the thermal protection performance are also numerically investigated.

Effects of hot electron inertia on electron-acoustic solitons and double layers

The propagation of arbitrary amplitude electron-acoustic solitons and double layers is investigated in a plasma containing cold positive ions, cool adiabatic and hot isothermal electrons, with the retention of full inertial effects for all species. For analytical tractability, the resulting Sagdeev pseudopotential is expressed in terms of the hot electron density, rather than the electrostatic potential. The existence domains for Mach numbers and hot electron densities clearly show that both rarefactive and compressive solitons can exist. Soliton limitations come from the cool electron sonic point, followed by the hot electron sonic point, until a range of rarefactive double layers occurs. Increasing the relative cool electron density further yields a switch to compressive double layers, which ends when the model assumptions break down. These qualitative results are but little influenced by variations in compositional parameters. A comparison with a Boltzmann distribution for the hot electrons shows that only the cool electron sonic point limit remains, giving higher maximum Mach numbers but similar densities, and a restricted range in relative hot electron density before the model assumptions are exceeded. The Boltzmann distribution can reproduce neither the double layer solutions nor the switch in rarefactive/compressive character or negative/positive polarity.

Thermocapillary phenomena and performance limitations of a wickless heat pipe in microgravity.

A counterintuitive, thermocapillary-induced limit to heat- pipe performance was observed that is not predicted by current thermal-fluid models. Heat pipes operate under a number of physical constraints including the capillary, boiling, sonic, and entrainment limits that fundamentally affect their performance. Temperature gradients near the heated end may be high enough to generate significant Marangoni forces that oppose the return flow of liquid from the cold end. These forces are believed to exacerbate dry out conditions and force the capillary limit to be reached prematurely. Using a combination of image and thermal data from experiments conducted on the International Space Station with a transparent heat pipe, we show that in the presence of significant Marangoni forces, dry out is not the initial mechanism limiting performance, but that the physical cause is exactly the opposite behavior: flooding of the hot end with liquid. The observed effect is a consequence of the competition between capillary and Marangoni-induced forces. The temperature signature of flooding is virtually identical to dry out, making diagnosis difficult without direct visual observation of the vapor-liquid interface.

Heat transfer characteristics and limitations analysis of heat-pipe-cooled thermal protection structure

The theories of heat transfer, thermodynamics and fluid dynamics are employed to develop the coupled heat transfer analytical methods for the heat-pipe-cooled thermal protection structure (HPC TPS), and a three-dimensional numerical method considering the sonic limit of heat pipe is proposed. To verify the calculation correctness, computations are carried out for a typical heat pipe and the results agree well with experimental data. Then, the heat transfer characteristics and limitations of HPC TPS are mainly studied. The studies indicate that the use of heat pipe can reduce the temperature at high heat flux region of structure efficiently. However, there is a frozen startup period before the heat pipe reaching a steady operating state, and the sonic limit will be a restriction on the heat transfer capability. Thus, the effects of frozen startup must be considered for the design of HPC TPS. The simulation model and numerical method proposed in this paper can predict the heat transfer characteristics of HPC TPS quickly and exactly, and the results will provide important references for the design or performance evaluation of HPC TPS.

Analytical study of the heat transfer limits of a novel loop heat pipe system

A novel loop heat pipe system was designed for use in solar hot water heating and an analytical model was developed to investigate its thermal performance and determine six major limits to system operation, i.e. capillary limit, entrainment limit, viscous limit, boiling limit, sonic limit, and filled liquid mass limit. Relations among the limits and several associated parameters, i.e. the heat pipe operating temperature, wicks type, heat pipe diameter, and height difference between the absorbing pipes array and condenser (heat exchanger), were established through a comprehensive analyses. It was found that the levels of capillary, entrainment, viscous, sonic, and filled liquid mass limits increased with the increasing temperature; however, the boiling limit was in the adverse trend. It was also found that the mesh screen wicks were able to obtain a higher capillary limit than sintered powder wicks, whilst other limits remained same. Larger pipe diameters would lead to higher operating limits. The height difference between the condenser (heat exchanger) and absorbing pipes (absorber) was the most important factor impacting on heat transfer capacities of the system, and largely affected the capillary limit of the system. It was noted when the pipe (inner) diameter increased to 5.6 mm or above, the governing limit of the system switched from entrainment to capillary. Relationship between the system governing limit, i.e. capillary limit, and the above addressed parameters were analysed. Adequate system configuration and operating conditions were suggested, which were summarized as follows: 6 mm of pipe inner diameter with mesh screen wicks, 58°C of heat pipe operating temperature, and 1.3 m height difference between absorber and condenser (heat exchanger). Copyright © 2010 John Wiley & Sons, Ltd.

A Mathematical Modeling Method on Micro Heat Pipe with a Trapezium-Grooved Wick Structure

With heat flux increasing and cooling space decreasing in the products in microelectronics and chemical engineering, micro heat pipe has become an ideal heat radiator for products with high heat flux. Through analyzing the factors influencing the structure, strength and heat transfer limits of circular micro heat pipe with trapezium-grooved wick structure, the heat transfer models are established in this paper, including the models of viscous limit, sonic limit, entrainment limit, capillary limit, condensing limit, boiling limit, continuous flow limit and frozen startup limit. The study lays a powerful theoretical foundation for the design and manufacture of circular micro heat pipe with a trapezium-grooved wick structure.

Phase change heat transfer device for process heat applications

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 ∼1300 K) 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 thermal 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.

Shocks versus kinks in a discrete model of displacive phase transitions

We consider dynamics of phase boundaries in a bistable one-dimensional lattice with harmonic long-range interactions. Using Fourier transform and Wiener-Hopf technique, we construct traveling wave solutions that represent both subsonic phase boundaries (kinks) and intersonic ones (shocks). We derive the kinetic relation for kinks that provides a needed closure for the continuum theory. We show that the different structure of the roots of the dispersion relation in the case of shocks introduces an additional free parameter in these solutions, which thus do not require a kinetic relation on the macroscopic level. The case of ferromagnetic second-neighbor interactions is analyzed in detail. We show that the model parameters have a significant effect on the existence, structure, and stability of the traveling waves, as well as their behavior near the sonic limit.

Space reactor power systems with no single point failures

Nuclear reactor power systems could revolutionize space exploration and support human outpost on the moon and Mars. This paper reviews various energy conversion technologies for use in space reactor power systems and provides estimates of the system's net efficiency and specific power, and the specific area of the radiator. The suitable combinations of the energy conversion technologies and the nuclear reactors, classified based on the coolant type and cooling method, for best system performance and highest specific power, are also discussed. In addition, a number of power system concepts with both static and dynamic energy conversion, but with no single point failures in reactor cooling, energy conversion and heat rejection, and for nominal electrical powers up to 110 kW e, are presented. The first two power systems employ reactors cooled with lithium and sodium heat pipes, SiGe thermoelectric (TE) and alkali-metal thermal-to-electric conversion (AMTEC), and potassium heat pipes radiators. The reactors heat pipes operate at a fraction of the prevailing capillary or sonic limit, and in the case of a multiple heat pipes failure, those in the adjacent modules remove the additional heat load, thus maintaining the reactor adequately cooled and the power system operating at a reduced power. The third power system employs SiGe TE converters and a liquid metal cooled reactor with a divided core into six sectors that are neurotically and thermally coupled, but hydraulically decoupled. Each sector has a separate energy conversion loop, a heat rejection loop, and a rubidium heat pipes radiator panel. When a core sector experiences a loss-of-coolant, the fission power of the reactor is reduced, and that generated in the sector in question is removed by the circulating coolant in the adjacent sectors. The fourth power system employs a gas cooled reactor with a core divided into three identical sectors, and each sector is coupled to a separate Closed Brayton Cycle (CBC) loop with He–Xe binary mixture (40 g/mol) working fluid, a secondary loop with circulating liquid Nak-78, and two water heat pipes radiator panels.

Liquid Metal Loop and Heat Pipe Radiator for Space Reactor Power Systems

This paper presents four radiator configurations that could be stowed in the launch bay of the DELTA-IV Heavy vehicle and have effective areas of 69.1 to 350 m 2 . The radiator for a space reactor power system with a lithium-cooled sectored compact reactor and thermoelectric converters has an effective area of 203 m 2 and lowest specific mass. The sectored compact reactor and thermoelectric converters system generates ∼114 kWe for 7-10 years. The radiator consists of six panels, each having a forward, fixed segment and two rear, deployable segments, and rejects heat into space using rubidium heat pipes with carbon-carbon armor and fins. The D-shaped heat pipes operate below 50 % of the prevailing sonic or capillary limit. The radiator operates at a constant pressure drop of 12 kPa and inlet and exit temperatures of 780 and 755 K. Investigated are the effects on the radiator's specific mass and lithium inventory of 1) tapering and changing width of coolant channels, 2) thermal-hydraulically coupling the panel segments in parallel, and 3) using perforated dividers between inlet- and exit-channels. The radiator with perforated dividers has a wet specific mass of 6.82 kg/m 2 , a liquid-lithium inventory of 179.3 liters, and a stowed height of 8 m.

A device and technique to measure the heat transfer limit of a planar heat pipe wick

Heat pipes are increasingly being utilized in applications for cooling electronics such as micro-processors. Heat pipes afford a very high heat transfer rate with only a small temperature difference between the heat source and heat sink. However, heat pipes have several operating limits, known as heat transfer limits, that can cause a severe reduction in the heat transfer rate and lead to catastrophic failure of the micro-processor. Two of these limits, known and the capillary limit and boiling limit are primarily a function of the heat pipe wick. In the present work, we developed a test apparatus and technique to determine the heat transfer limit of a planar heat pipe wick. The advantage of this apparatus and technique is a quantifiable measurement of the wick’s heat transfer limit without being confounded by other operating limit mechanisms such as the viscous or sonic limits. The apparatus and technique also yields the wick’s effective thermal conductivity. The apparatus is compatible with many of the low temperature heat pipe working fluids such as water or methanol, can be operated in any orientation with respect to the gravity vector, accounts for parasitic heat losses, provides for flow visualization studies, and is adaptable to a wide range of wick thicknesses.

“SAIRS” — Scalable Amtec Integrated Reactor space power System

Conceptual Designs of three, 111 kWe, Scalable AMTEC Integrated Reactor Space Power Systems (SAIRS) are developed. These systems employ fast-spectrum reactors cooled by sodium (Na) heat pipes, C-C armored, potassium (K) heat pipes radiators, and Alkali Metal Thermal-To-Electric Conversion (AMTEC) units. The reactor Na- and the radiator K-heat pipes operate at <47% of their prevailing capillary and/or sonic limit. The reactor core is comprised of 60 modules, each has 3 UN fuel pins with rhenium (Re) cladding brazed to a central Na/Mo-14%Re heat pipe of the same OD (1.5 cm). Although heavy, Re is compatible with UN fuel and an effective Spectral Shift Absorber (SSA) that ensures reactor's sub-criticality when fully submerged in wet sand or water, following a launch abort accident. Each of the 6 radiator panels in SAIRS has 6 double-vapor-cavity potassium heat pipes for removing the rejected heat from one of six AMTEC blocks. Each block consists of either 3 or 4 Na-AMTEC units that are heated by ten reactor Na-heat pipes. The AMTEC unit measures 410 × 594 × 115 mm in outside dimensions and weights 44.3 kg. These units are connected in series in 3 or 4 parallel strings for redundancy, while providing a terminal voltage of 400 V DC. At an AMTEC cold side temperature of 700 K and reactor exit temperatures of 1202 K, 1176 K and 1133 K, the nominal efficiencies of the three SAIRS options are 27.3%, 26.9% and 22.7% respectively, resulting in low system masses. The Na-AMTEC units in SAIRS operate at 64–86% of their peak electrical powers, providing for up to 14–36% passive load-following increase in demand without actively increasing the reactor power. The three SAIRS options are identical, except in the efficiency and the number (18 or 24) and electrical connections of Na-AMTEC units, and have alphas ≤30.5 kg/kWe and total heights and major diameters of ≤6 m and ≤4 m, respectively.

Nonlinear Hodge maps

We consider maps between Riemannian manifolds in which the map is a stationary point of the nonlinear Hodge energy. The variational equations of this functional form a quasilinear, nondiagonal, nonuniformly elliptic system which models certain kinds of compressible flow. Conditions are found under which singular sets of prescribed dimension cannot occur. Various degrees of smoothness are proven for the sonic limit, high-dimensional flow, and flow having nonzero vorticity. The gradient flow of solutions is estimated. Implications for other quasilinear field theories are suggested.