Small Heat Flux Research Articles

Turbulent Flow and Heat Transfer Characteristics of Non-Newtonian Impinging Jets on a Flat Plate

In the present work, a numerical analysis of non-Newtonian impinging jets on a flat plate subjected to a constant heat flux is carried out under turbulent flow conditions. By employing the power-law constitutive model to describe the jet’s non-Newtonian behavior, simulations have been performed for two (2D) and three-dimensional (3D) jet flow conditions. For turbulence simulation, SST- $$k\omega$$ turbulence model has been used coupled with continuity and energy equations. Dimensional results have been obtained by varying the inflow conditions 0.5–1.4 m/s and at a constant heat flux of 5000 W/m2. To instill the influences of shear thinning, Newtonian, and shear-thickening fluids, the range of power-law indices (n) is varied from 0.6 to 1.6. The results of the simulations infer that the pseudoplastics fluids are more efficient than Newtonian and dilatant fluids. Increasing power law shows efficacy of the fluids to cool the surface decreases as is observed by the average values of the Nusselt number on the target. It is found that there is a small difference in the final average temperature of the plate after cooling with different fluids, but that owes it to the small heat flux used in the present analysis. It is observed that the higher the velocity of the jet, the better is the cooling. Finally, the energy-saving capabilities of the jets are characterized by altering the rheological characteristics of the jets.

Development of a Miniature Loop Heat Pipe for High Heat Flux Devices and Evaluation of Its Heat Transport Performance

This paper describes the design, fabrication, and the heat transfer performance of a miniature loop heat pipe (mLHP) aiming for cooling a small and high heat flux devices. For the design process, a one-dimensional numerical model was developed. Based on the numerical model, an mLHP was fabricated. The mLHP comprises an evaporator (15×16×t3 mm3), a condenser (12×12.5×t2 mm3) and transport lines (O.D.=1.6 mm, L=100 mm). The mLHP uses Shirasu porous glass (SPG) as a wick and is mainly made of stainless steel. The heat transport performance was investigated in horizontal attitude, anti-gravity (top heat mode) and gravity-assisted (bottom heat mode) with working fluid of water. When the condenser was dissipated by natural air convection, the mLHP performed 5-W (20-W/cm2) heat transport at 170-℃ heat source temperature in horizontal attitude. The thermal resistance was 7.9℃/W. In the bottom heat mode, the lowest thermal resistance of 2.6℃/W was obtained due to the gravity assist. Additionally, the mLHP was tested under the condition that the evaporator side was kept horizontal but the condenser side was bent upwards by 90 degree around the middle of transport lines. Consequently, in low heat load condition the bent mLHP showed the same performance with the bottom heat mode, but shifted to the horizontal mode as the heat load increased. Thus, the heat transport performance was comprehensively investigated for considering various uses.

Burning dynamics and in-depth flame spread of wood cribs in large compartment fires

Wood cribs pervade the fire research literature as the chosen fuel load for testing within the built environment. As such, the underpinning knowledge of fire behaviour in compartments was developed from experiments using wood cribs in small compartments. Despite the apparent incomparability of porous fuel-beds such as cribs to real solid fuels in the built environment, the role of the fuel mass transfer number (“B-Number”) in defining the compartment fire dynamics has received little attention. In the case of large open-plan compartments, the burning processes are strongly dependant on the relationship of the fuel nature and compartment geometry. To address these limitations, the physical processes in-depth and external to a spreading wood crib fire in a compartment are examined. A theory to couple these processes to a compartment is proposed and analogised into the classical “Emmons problem”, leading to a definition of a total mass transfer number for a wood crib. Comparing the theory against data from a large-scale experiment shows that the wood crib approximates steady-state burning in two regimes: a fuel-bed-controlled regime and a momentum-controlled regime. The fuel-bed-controlled regime occurs when the burning and spread rates are governed by the processes internal to the crib, and the fire behaviour is therefore defined by the crib geometry. This regime is characterised by a fire that travels or grows slowly, with small external heat fluxes. The momentum-controlled regime occurs when the fire is fully-developed and the external heat fluxes are very large. Burning rates are controlled by the residence time, with the compartment fire dynamics defined by complex transport processes associated with the momentum-driven flows external to the crib. Transitions from the fuel-bed-controlled regime to the momentum-controlled regime are driven by accelerations in the flame spread rate along the surface of the crib leading to an additional energy input mechanism that is used to raise the in-depth flame spread rate of the crib. It is hypothesised that the burning mechanisms of fuels with large mass transfer numbers, such as non-charring plastics, diverge significantly from wood cribs, and therefore extrapolating test data from wood cribs fires in compartments to real fuels must be done with extreme caution. Thus, the nature of the fuel is an important and unavoidable consideration when studying the fire dynamics of large open-plan compartments.

ELECTROHYDRODYNAMIC MINI FLAT HEAT PIPE FOR ADVANCED ELECTRONICS COOLING

Mini-grooved flat heat pipe with small size, compact structure, high thermal conductivity, and close contact with chips is very promising to be applied for electronic devices cooling under small space and high heat flux condition. However, capillary limit always restricts the heat transfer capacity of heat pipe. Adopting electrohydrodynamic (EHD) technology with simple structure, sensitive control, and low-energy consumption to the heat pipe can lower the reliance of heat pipe on capillary force and improve the heat transfer performance of heat pipe. In this paper, a one-dimensional mathematical model is established for mini-grooved flat heat pipe under dielectrophoretic force to study the working fluid flow and heat transfer along axial direction under EHD effect. The performance of mini-grooved flat heat pipe under different electric field intensity and electrodes distribution is analyzed. It is found that adding electric field to the mini-grooved flat heat pipe can lessen the demand for capillary force on the heat pipe, reduce the required working fluid filling amount, improve the wall temperature uniformity, and enlarge the range of negative working inclined angle, which enhances the heat transfer performance of heat pipe significantly. Under the electric field intensity 5 kV·mm-1, the critical input heat of Case 1 heat pipe is 4.8 times higher than that without electric field. And, when electrodes are arranged at the whole heat pipe with Case 2 convex gradient V-type grooved wick, the heat transfer performance of heat pipe is optimal. Considering the practical condition, fabricating sloped grooved heat pipe under EHD is more convenient. However, the electric field intensity cannot be larger than 5.5 kV·mm-1 in case of reaching entrainment limit and electrical properties of working fluid being destroyed.

Enhanced pool boiling heat transfer on soft liquid metal surface

Pool boiling is a high-efficient energy transfer method through the gas-liquid phase transition. It has the characteristics of small heat transfer temperature difference and high heat flux density. The current enhancement of boiling heat transfer is realized mainly through modifying the solid heating surface. So far, there has been no report on the study of pool boiling heat transfer on soft surfaces. Therefore, in this work the pool boiling heat transfer performances of ethanol on the copper surface and soft liquid metal surface are investigated experimentally. The experimental results indicate that soft surface can effectively reduce the wall superheat corresponding to the onset of boiling (ONB). In saturation boiling, the superheat of the wall surface at ONB is reduced by nearly 12 ℃, while the heat transfer coefficient is improved by 149%. It is found that soft surface enhances pool boiling heat transfer performance significantly by increasing nucleate site density, reducing the bubble departure diameter, and increasing bubble departure frequency. Unlike the copper surface, the soft surface deforms elastically under the action of the vertical component of surface tension <i>γ</i><sub>lv</sub>sin<i>θ</i> at the three-phase contact line of the vapor bubble. From the perspective of surface energy analysis, the difference in surface energy Δ<i>E</i><sub>LM</sub> between before and after bubble departure on soft liquid metal surface is smaller than in smooth surface Δ<i>E</i><sub>CS</sub>. The potential barrier of the soft surface is smaller than of the copper surface, and the buoyancy required for bubble separation is small, and the bubble is easy to separate. Elastocapillary wave and bubble jet phenomenon on the soft surface are observed particularly, which are generated on liquid metal under the action of elastic restoring force. The fluctuation of elastocapillary wave contributes to the enhancement of heat and mass transfer in thermal boundary layer and the generation of residual nucleation site. The residual bubble grows up rapidly and coalesces with the rising large bubble, forming bubble jet phenomenon. Elastocapillary wave and bubble jet contribute to the enhancement of pool boiling heat transfer on soft liquid metal surface.

Simultaneous 1D hybrid fs/ps rotational CARS, phosphor thermometry, and CH* imaging to study transient near-wall heat transfer processes

Near-wall transient heat transfer and flame–wall interaction (FWI) are topics of great importance in the development of downsized internal combustion (IC) engines and gas turbine technology. In this work we perform measurements using 1D hybrid fs/ps rotational CARS (HRCARS), thermographic phosphors (TGP) and CH* imaging in an optically-accessible chamber designed to study transient near-wall heat transfer processes relevant to IC engine operation. HRCARS provides single-shot gas-phase temperatures (40 µm spatial resolution and up to 3 mm wall-normal distances), while thermographic phosphors measures wall temperature and CH* measures the flame front position. These simultaneous measurements are used to resolve thermal boundary layer (TBL) development and associated gaseous heat loss for three important processes of gas–wall interactions: (1) an unburned-gas polytropic compression process, (2) FWI, and (3) post-flame and gas expansion processes. During a mild polytropic compression process, measurements emphasize that even a relatively small wall heat flux (≤5 kW/m2) yields an appreciable temperature stratification through a developing TBL. During FWI, thermal gradients induced by the flame are resolved within the TBL. Gases closest to the wall (y<0.2 mm) continue to experience thermal loading from polytropic compression until the flame is within ∼1.4 mm from the wall. Immediately afterwards, the wall first senses the flame as the wall temperature begins to increase. During FWI, gas temperatures up to 1150 K impinge on the wall, producing peak wall heat fluxes (620 kW/m2) and the wall temperature increases (ΔTwall=14 K). Gaseous heat loss in the post-flame gas occurs rapidly at the wall, yielding a TBL of colder gases extending from the wall as wall heat flux slowly decreases. HRCARS further captures the rapid cooling of gases in the TBL and core-gas during the mild expansion and exhaust process.

Simulation and visualization experiment on the liquid nitrogen boiling behaviors during the quenching and recovery process of YBCO tapes

The resistance Superconducting Fault Current Limiter (RSFCL) using YBCO tape is supposed to be of great potential in the high voltage power grids. The fast recovery rate after quenching is the safety guarantee of the electric system to prevent the subsequent fault current shocks. However, the transient heat transfer and local boiling bubble behaviors of liquid nitrogen (LN2) highly affecting the recovery rate are seldom revealed, especially for the disc structure RSFCL with tiny channels. In this work, the boiling heat transfer characteristics during the quenching and recovery process of a YBCO tape in LN2 bath were studied. A 3-D CFD model based on a local part of a typical RSFCL with disc structure was first built to reveal the transient heat transfer coefficient, cooling curve, gas phase volume and temperature distribution that cannot be measured in experiments. The visualization experiment for verification and observation on bubble distribution was conducted with a high-speed camera. Results show that the boiling bubbles generate immediately as quenching starts, film boiling can form quickly within in 0.035 s on the tape surface. The bubble motion behaviour is severely affected by the layout of the Teflon framework. The bubbles detachment from the upper surface of the tape is more frequent than that from the lower surface of the tape, causing inhomogeneous temperature distribution along the tape. Since the recovery is mainly under the film boiling with small heat flux, even a single YBCO tape needs about 2.5 s to return to 77.7 K from 162 K, which means it is impossible to reclose the YBCO tape within 2 s after the quenching cutting off, especially for practical large RSFCL systems with longer recovery time. Besides, there are bubbles still remaining in the system after 5 s when the temperature has recovered to 77.7 K. The remaining gas would change the dielectric field and induce a risk of electric breakdown under the next large impulse current, which should be considered in the safe operation of RSFCL.

Pool boiling performance of 3D-printed reentrant microchannels structures

This study developed reentrant microchannels structures (RMS) by the Selective Laser Melting (SLM) technique for pool boiling enhancement. The 3D-printed reentrant microchannels structures were of parallel Ω-shaped reentrant channels with rough wall surfaces, which were built of bronze powder. Pool boiling tests of the RMS were conducted in deionized water in both saturated and subcooled boiling conditions with two liquid subcoolings of 15°C and 30°C. The pool boiling enhancement was explored by the comparison of a solid plain surface as benchmark. It was found that the reentrant microchannels structures reduced the wall superheat for onset of nucleation boiling (ONB) considerably, and generally present a 10% to 330% enhancement in boiling heat transfer coefficients over the plain surface in subcooled boiling conditions. The enhancement can be attributed to that the reentrant microchannels structures contributed to significant increase in active nucleation sites, enlarged surface area for heat exchange, and more liquid replenishment for surface rewetting. The boiling heat transfer coefficients of RMS generally exhibited a rapid decline at small heat fluxes region, then maintained to be more or less stable or increased slightly at moderate to high heat flux regions, and lastly decreased slightly at high heat flux region. The boiling heat transfer of RMS can be enhanced remarkably in the subcooled boiling tests.

High-quality textured SnSe thin films for self-powered, rapid-response photothermoelectric application

Abstract Tin selenide (SnSe) has attracted great attention in thermoelectrics (TE) thanks to its record high figure of merit (ZT) discovered in single crystal (SC). However, the practical application of SnSe SC is limited due to its extreme growth condition. With the development of flexible integrated electronics, using flexible polycrystalline TE films to substitute rigid SC becomes a main trend. Nevertheless, large resistances of TE films restrict their application as power devices. Here, self-powered SnSe-based photothermoelectric (PTE) detectors are demonstrated. The PTE detectors are sensitive to wide-spectrum and exhibit higher responsivity and respnse speed comparing with SC, due to the small heating volume, small conductive heat flux and large dissipation content of thin films. High-quality (400)-textured SnSe polycrystalline thin films are one-step synthesized by chemical vapor deposition. In-situ in-plane TE measurement shows that the obtained SnSe films possess a dimensionless ZT of 0.15 and a power factor of 0.322 mW m−1 K−2 at 550 K, showing SC level TE performance at low temperatures.

The Role of Clouds and Surface Heat Fluxes in the Maintenance of the 2013–2016 Northeast Pacific Marine Heatwave

AbstractStarting in late 2013, the Northeast (NE) Pacific Ocean experienced anomalously warm sea surface temperatures (SSTs) that persisted for over 2 years. This marine heatwave, known as “the Blob,” produced many devastating ecological impacts with socioeconomic implications for coastal communities. The warm waters observed during the NE Pacific 2013/2016 marine heatwave altered the surface energy balance and disrupted ocean–atmosphere interactions in the region. In principle, ocean–atmosphere interactions following the formation of the marine heatwave could have perpetuated warm SSTs through a positive SST‐cloud feedback. The actual situation was more complicated. While reanalysis data show a decrease in boundary layer cloud fraction and an increase in downward shortwave radiative flux at the surface coincident with warm SSTs, this was accompanied by an increase in longwave radiative fluxes at the surface, as well as an increase in sensible and latent heat fluxes out of the ocean mixed layer. The result is a small negative net heat flux anomaly (compared to the anomalies of the individual terms contributing to the net heat flux). This provides new information about the midlatitude ocean–atmosphere system while it was in a perturbed state. More specifically, a mixed layer heat budget reveals that anomalies in both the atmospheric and oceanic processes offset each other such that the anomalously warm SSTs persisted for multiple years. The results show how the atmosphere–ocean system in the NE Pacific is able to maintain itself in an anomalous state for an extended period of time.

Measurement of the microlayer characteristics in the whole range of nucleate boiling for water by laser interferometry

During nucleate boiling, a thin liquid film (microlayer) is formed beneath a boiling bubble when the bubble undergoes rapid growth/expansion. The linear distribution of the microlayer has been previously confirmed, and its crest shape has been observed in the isolated bubble region of nucleate boiling. However, the microlayer behavior in larger heat flux regions up to critical heat flux has not yet been elucidated. In this study, to further understand the microlayer structure in the whole heat flux range of nucleate boiling, microlayer configuration was measured using laser interferometry. Water was adopted as the test fluid, and it is confirmed that the microlayer can be observed over a whole range of nucleate boiling containing the critical heat flux point. It is also confirmed that the deformation of the microlayer from axisymmetric shape was caused by complicated, irregular bubble motions such as bubble coalescence, which was observed for relatively higher heat flux. The crest shape of the microlayer, which appears near the periphery of its maximum diameter under relatively smaller heat flux, was not observed at a relatively higher heat flux. Finally, it is confirmed that heat flux does not obviously influence the thickness distribution of the initial microlayer.

Experimental and Numerical Study of Double-Pipe Evaporators Designed for CO2 Transcritical Systems

The performance of a CO2 double-pipe evaporator was studied through experiments and a simulation model that was established by the steady-state distribution parameter method and experimentally verified while using a CO2 transcritical water‒water heat pump system. The effects of different operating parameters on heat transfer performance were studied over a range of evaporation temperatures (−5 to 5 °C), mass velocity (100‒600 kg/m2s), and heat flux (5000‒15,000 W/m2). It was found that the dryout quality increased at a small evaporation temperature, a large mass velocity, and a small heat flux. The simulation yield means relative error (RE) of heat transfer for the evaporation temperature and that of the CO2 pressure drop for the chilled water inlet temperature were 5.21% and 3.78%, respectively. The effect of tube diameter on the performance of CO2 double-pipe evaporator is probed through simulations. At the same time, this paper defines a parameter α , which is the proportion of the pre-dryout region to the whole heat transfer region. A larger α value is desirable. A further theoretical basis is provided for designing an efficient and compact CO2 evaporator.

Topology optimization of liquid-cooled microchannel heat sinks: An experimental and numerical study

Electronics cooling is always a critical challenge for its small profile and high heat flux. Various microchannel heat sinks have been proposed in literature to achieve reliable and energy efficient cooling effect. They are mainly different patterned fin shapes originated from researchers’ experience. In this paper, we present the process of designing liquid-cooled microchannel heat sink fin geometries based on a numerical method, topology optimization. The optimization model is developed to find designs that satisfy heat transfer requirement with low pressure drop penalty. It is implemented based on a derived accurate 2D model with minimizing pressure drop as objective and average junction temperature as a constraint. Parameter study for different velocities and junction temperature constraints is performed. The optimized structures are then post processed under geometry constraints and analyzed by 3D CFD simulation. Size optimization is implemented on conventional straight channel heat sinks, which serve as the benchmark cases. Moreover, an experimental test loop is built to validate the 3D simulation of topology optimized heat sinks and straight channel heat sinks. The performance comparison shows that the topology optimized heat sinks could save up to 50.9% pumping power under the same thermal performance requirement. Detailed CFD analysis is then engaged to examine their thermohydraulic characteristics and reveal the reasons for their superior performance.

Low Mach number limit for the full compressible Navier–Stokes equations with Cattaneo’s heat transfer law

In this paper, we study the low Mach number limit for the full compressible Navier–Stokes equations with Cattaneo’s heat transfer law. It is rigorously justified that, in the framework of classical solutions with small density, temperature and heat flux variations, the solutions of the full compressible Navier–Stokes equations with Cattaneo’s heat transfer law converge to that of the incompressible Navier–Stokes equations as the Mach number tends to zero.

Experimental study on heat transfer performance of new gravity heat pipe in geothermal utilization

In this paper, a set of heat pipe performance testing device is built for a new gravity heat pipe with internal tubes, fins and charged with CO2 liquid and nano-fluids mixtures. The influence of the length to diameter ratio of the heat pipe, the different cold and heat source temperature and the flow rate of the cold and heat loop on the heat transfer performance of the heat pipe is discussed, respectively.The results show that, for the heat pipe itself, the heat pipe has a good heat transfer performance when it has a smaller ratio of length to diameter. The increase of the heat source temperature is the main factor affecting the equivalent heat transfer coefficient of the heat pipe. With the ratio of water flow increase,whether the heat or the cold flux,it has the same effect on the heat transfer rate of heat pipe. The increase of the flow rate strengthens the performance of heat pipe. It is worth noting that, change of the cold source temperature should be referred to the heat source temperature, it will be a better effect with small heat flux density. When the heat source temperature is higher, the lower the cold source temperature, the greater the heat loss and the poor heat transfer performance of the heat pipe.

A Review of the Geological Constraints on the Conductive Boundary Layer at the Base of the Hydrothermal System at Mid‐Ocean Ridges

AbstractModels of high‐temperature hydrothermal systems at intermediate‐ to fast‐spreading mid‐ocean ridges have a conductive boundary layer (CBL) separating the magmatic heat source from the convecting hydrothermal fluid. Paleo‐CBLs preserved in the geological record provide a means to test theoretical models of the thermal, mechanical, and petrological evolution of this boundary. CBLs occur as metamorphic contact aureoles at or near the dike‐gabbro boundary where axial magma lenses (now plutonic rocks) intruded into the basal dikes, leading to their transformation into low permeability granulite and hornblende hornfels at &gt;800 °C. Paleo‐CBLs are well documented in the Troodos and Oman ophiolites, and evidence of similar lithologies has been found at every location where the dike‐gabbro transition has been mapped and/or sampled in modern fast‐spreading crust (Hess and Pito Deeps, IODP Hole 1256D). Evaluation of the geothermometers used in studies of the thermal evolution of the CBL shows a lack of consistency that can be understood in terms of compositional controls. Peak temperatures are &gt;900 °C in all areas at the base of the CBL, leading to partial melting, stoping, and disaggregation that facilitates thinning from below as required to maintain the high heat fluxes necessary to drive active black smoker systems. However, such thin CBLs are not the norm; steady state conditions must have thicker CBLs and smaller heat fluxes. In turn, global estimates of properties such as chemical fluxes for normal hydrothermal conditions may lead to substantially different element/heat fluxes than those based on active systems.

Computational examination of two-phase microchannel heat transfer correlations with conjugate heat spreading

Microchannel flow boiling is an attractive thermal management strategy for ever-growing volumetric heat dissipation demands associated with electronic systems. Due to difficulties related to measurement at the microscales, the majority of researchers have chosen to study relatively simple situations with uniform heat flux. However, many applications involve local hotspots which give rise to highly non-uniform heat flux and temperature gradients due to heat spreading. This necessitates the consideration of conjugate heat transfer for accurate analysis.The current work is aimed at investigating conjugate heat transfer in a two-phase microchannel array. Experimental data was collected on R134a flow boiling heat transfer for very small hydraulic diameter (<100 µm) silicon microchannels with very high heat fluxes (>1 kW cm−2) applied via platinum strip heaters with a footprint size of 1 cm × 1 mm. The collected experimental data was then combined with detailed computational modeling utilizing finite element modeling with COMSOL Multiphysics and MATLAB to examine the applicability of five published heat transfer correlations for use in determining local heat transfer coefficients. A two-phase correlation from Agostini and Bontemps, developed for markedly different test parameters, provided the best computational agreement with an RMS temperature difference from experiment of 3.3 °C and a predicted peak perimeter-averaged heat transfer coefficient of 116 MW m−2 K−1. Modeling confirms the presence of highly non-uniform local heat flux and correspondingly non-uniform local heat transfer coefficient. The results of this study make clear the need for better micro-scale two-phase correlations developed to predict local heat transfer coefficients at these small scales and high local heat fluxes.

Critical Southern Ocean climate model biases traced to atmospheric model cloud errors

The Southern Ocean is a pivotal component of the global climate system yet it is poorly represented in climate models, with significant biases in upper-ocean temperatures, clouds and winds. Combining Atmospheric and Coupled Model Inter-comparison Project (AMIP5/CMIP5) simulations, with observations and equilibrium heat budget theory, we show that across the CMIP5 ensemble variations in sea surface temperature biases in the 40–60°S Southern Ocean are primarily caused by AMIP5 atmospheric model net surface flux bias variations, linked to cloud-related short-wave errors. Equilibration of the biases involves local coupled sea surface temperature bias feedbacks onto the surface heat flux components. In combination with wind feedbacks, these biases adversely modify upper-ocean thermal structure. Most AMIP5 atmospheric models that exhibit small net heat flux biases appear to achieve this through compensating errors. We demonstrate that targeted developments to cloud-related parameterisations provide a route to better represent the Southern Ocean in climate models and projections.

ОСОБЛИВОСТІ ЗМІНИ ТЕПЛОФІЗИЧНИХ ВЛАСТИВОСТЕЙ НАДКРИТИЧНОЇ ВОДИ ПІД ЧАС ТЕЧІЇ В КРУГЛИХ ТРУБАХ, ЩО ОБІГРІВАЮТЬСЯ

Для процесу течії надкритичної води в каналі, що обігрівається, проведено дослідження особливостей просторового розподілу фізичних властивостей води, зумовлених їх істотною температурною залежністю, характерною для надкритичних середовищ у ділянці псевдофазового переходу. На основі комп'ютерного моделювання розв'язано задачу тепломасоперенесення у вертикальній круглій трубі під час висхідного руху в ній води надкритичних параметрів. Показано, що характер розподілу властивостей теплоносія у поздовжньому перетині труби певною мірою визначається рухом в ньому фронту псевдофазового переходу. Проаналізовано вплив величини густини теплового потоку, що підводиться до стінки труби, на положення границь початку і кінця зони псевдофазового переходу і на пов'язані з цим особливості просторової зміни фізичних властивостей теплоносія. Наведено результати СFD моделювання з розподілу уздовж довжини труби, що обігрівається, таких властивостей надкритичної води, як густина, динамічна в'язкість, коефіцієнт теплопровідності і питома теплоємність. Виконано зіставлення особливостей розподілу зазначених властивостей, розрахованих за температурою на стінці труби і на її осі. Досліджено характер зміни питомої теплоємності по радіусу труби і проаналізовано вплив рівня теплового потоку, що підводиться, на положення максимуму теплоємності в різних поперечних перетинах каналу.

Seasonal and Interannual Variations of Sea Ice Mass Balance From the Central Arctic to the Greenland Sea

AbstractThe seasonal evolution of sea ice mass balance between the Central Arctic and Fram Strait, as well as the underlying driving forces, remain largely unknown because of a lack of observations. In this study, two and three buoys were deployed in the Central Arctic during the summers of 2010 and 2012, respectively. It was established that basal ice growth commenced between mid‐October and early December. Annual basal ice growth, ranging from 0.21 to 1.14 m, was determined mainly by initial ice thickness, air temperature, and oceanic heat flux during winter. An analytic thermodynamic model indicated that climate warming reduces the winter growth rate of thin ice more than for thick ice because of the weak thermal inertia of the former. Oceanic heat flux during the freezing season was 2–4 W m−2, which accounted for 18–31% of the basal ice energy balance. We identified two mechanisms that modified the oceanic heat flux, i.e., solar energy absorbed by the upper ocean during summer, and interaction with warm waters south of Fram Strait; the latter resulted in basal ice melt, even in winter. In summer 2010, ice loss in the Central Arctic was considerable, which led to increased oceanic heat flux into winter and delayed ice growth. The Transpolar Drift Stream was relatively weak in summer 2013. This reduced sea ice advection out of the Arctic Ocean, and it restrained ice melt because of the cool atmospheric conditions, weakened albedo feedback, and relatively small oceanic heat flux in the north.