High-Power Heat Transfer in Supercritical Fluids

2021 ◽  
pp. 424-450
Author(s):  
Pavel V. Skripov ◽  
Aleksandr D. Yampol'skiy ◽  
Sergey B. Rutin
Keyword(s):  
Heat Transfer ◽  
Supercritical Fluids ◽  
Large Scale ◽  
Spatial Scales ◽  
Conductive Heat ◽  
Operating Pressure ◽  
Transfer Mode ◽  
Stationary Heat Transfer ◽  
Heat Loads ◽  
Insight Into

Non-stationary heat transfer in supercritical fluids at relatively small temporal and spatial scales was studied experimentally. The aim of the study was to clarify the peculiarities of conductive heat transfer mode at significant heat loads. An unexpected stepwise decrease in the instant heat transfer coefficient has been revealed in the course of crossing the vicinity of the critical temperature along the supercritical isobar. This means that the peaks of isobaric heat capacity and excess thermal conductivity, which are known from stationary measurements, do not affect the experimental results. It is assumed that the action of considerable gradient in temperature and the presence of heat-transfer surface in pulse heated system can serve as factors that suppress large-scale fluctuations, leading to a “smoothing” the critical enhancement of the thermophysical properties. As an important consequence, this study gives new insight into selection of the operating pressure of supercritical heat transfer agent.

Heat Transfer in Supercritical Fluids

2017 ◽  
pp. 271-291 ◽  
Author(s):  
Sergey B. Rutin ◽  
Aleksandr D. Yampol'skiy ◽  
Pavel V. Skripov
Keyword(s):  
Heat Transfer ◽  
Supercritical Fluids ◽  
Critical Pressure ◽  
Small Time ◽  
Heat Transfer Agent ◽  
Operating Pressure ◽  
Layer Region ◽  
Stationary Heat Transfer ◽  
Conduction Mode ◽  
Heat Loads

Results of experimental study of non-stationary heat transfer in supercritical fluids, which were obtained using the method of controlled pulse heating of low-inertia wire probe, are discussed. The aim of this study was to clarify the peculiarities of heat conduction mode at significant heat loads. A threshold decrease in the “instant” heat transfer coefficient, the more pronounced the closer the pressure value to critical pressure, has been found, as well as the absence of impact of the isobaric heat capacity peak known from stationary measurements on the experimental results. These results give new insights into selection of the operating pressure of supercritical heat transfer agent. Small time and spatial scale in the experiments (units of millisecond and units of micrometer) in combination with high-power heat release (up to 20 MW/m2) makes it possible to associate the results with the behavior of boundary layer region of heat transfer agent.

Introduction

1978 ◽  
Vol 288 (1355) ◽  
pp. 385-386
Keyword(s):  
Heat Transfer ◽  
Lower Mantle ◽  
Large Scale ◽  
Radiative Heat ◽  
Reasonable Doubt ◽  
Mantle Flow ◽  
Conductive Heat ◽  
Mantle Material ◽  
Radiative Processes ◽  
The Earth

During the last fifteen years, three major developments have influenced thinking on temperature distributions within the Earth and on the origin of magmas. Perhaps the most important was the recognition that large scale plate movements which have occurred at the Earth’s surface require large scale counterflow of mantle material in the solid state. The thermal diffusivity of mantle rocks and the scale of mantle flow are such that even if the flow velocity is as low as 1 mm/a, the temperature distribution within the Earth is governed by convective, rather than conductive, transfer of heat. This has meant that the majority of thermal models of the Earth’s interior have had to be discarded as irrelevant; nearly all were based on assumptions of conductive heat transfer with a transition downwards to radiative processes. It was a feature of these models that they all gave rather high temperatures in the lower mantle; indeed, in order to keep the lower mantle below its melting temperature it was commonly necessary both to invoke radiative heat transfer and to postulate concentration of nearly all the radioactive heat production in the upper few hundred kilometres. Today the approach is very different. Conductive calculations are thought to be appropriate for only the outermost part of the mantle — that part which is incorporated in the surface plates; below the plates and at their margins, which are zones of localized up welling or downward motion, temperatures are related to the circulating motions within the mantle. It is not clear at present how deep these motions extend; beyond reasonable doubt to 700 km, but possibly over the full depth of the mantle. Remaining constraints on the distribution of heat-producing elements are largely chemical rather than physical.

scholarly journals Modeling of Loop Heat Pipe Thermal Performance

2021 ◽  
Vol 81 (1) ◽  
pp. 41-72
Author(s):  
Inès Gabsi ◽  
Samah Maalej ◽  
Mohamed Chaker Zaghdoudi
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Heat Pipe ◽  
Loop Heat Pipe ◽  
Conductive Heat ◽  
Steady State Operation ◽  
Evaporation Heat ◽  
Compensation Chamber ◽  
Heat Loads ◽  
Good Agreement

The present work deals with the heat transfer performance of a copper-water loop heat pipe (LHP) with a flat oval evaporator in steady-state operation. Modeling the heat transfer in the evaporator was particularly studied, and the evaporation heat transfer coefficient was determined from a dimensionless correlation developed based on experimental data from the literature. The model was based on steady-state energy balance equations for each LHP component. The model results were compared to the experimental ones for various heat loads, cooling temperatures, and elevations, and a good agreement was obtained. Finally, a parametric study was conducted to show the effects of different key parameters, such as the axial conductive heat leaks between the evaporator and the compensation chamber cases, the capillary structure porosity and material, and the groove dimensions.

scholarly journals Heat transfer in shallow caves: influence of turbulent convection

2021 ◽  
Vol 2116 (1) ◽  
pp. 012027
Author(s):  
B Qaddah ◽  
L Soucasse ◽  
F Doumenc ◽  
S Mergui ◽  
P Rivière ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Large Scale ◽  
Heat Diffusion ◽  
Scale Model ◽  
Conductive Heat ◽  
Turbulent Structures ◽  
External Temperature ◽  
Eddy Simulation ◽  
Cave Paintings ◽  
Large Scale Flow

Abstract The enhancement of the conservation conditions of cave paintings requires a detailed understanding of heat transfer in such cavities. This article presents a numerical investigation of turbulent free convection in a parallelepipedic cavity. Non-homogeneous wall temperatures are prescribed from a large-scale model taking into account external temperature fluctuations damped by heat diffusion in the rock massif above the cavity. Large Eddy Simulation is performed to solve the turbulent flow fields for a given wall temperature field corresponding to a Rayleigh number of 8.5 x 109. The outcomes of the model are analysed in terms of statistical mean. Results show complex large scale flow patterns with regions of high turbulent intensity. The Q-criterion is used to identify turbulent structures for an instantaneous flow field. Then we analyse the spatial distribution of the conductive heat flux at the walls to locate the regions with intense convection. We show that the conductive flux smaller than the wall-to-wall radiative flux in the major part of the cavity, and close to its value at some spots.

scholarly journals Analytical Solution of Problems about the Radiative and Radiative–Conductive Stationary Heat Transfer in a Medium with an Arbitrary Dependence of the Scattering and Absorption on Frequency Boundary Conditions

Energies ◽  
2021 ◽  
Vol 14 (19) ◽  
pp. 6339
Author(s):  
Eugene Shamparov ◽  
Sergey Rode ◽  
Anatoly Bugrimov ◽  
Inna Zhagrina
Keyword(s):  
Heat Transfer ◽  
Analytical Solution ◽  
Outer Boundary ◽  
Radiant Heat ◽  
Conductive Heat Transfer ◽  
Radiant Heat Transfer ◽  
Conductive Heat ◽  
Parallel Surfaces ◽  
Arbitrary Frequency ◽  
Stationary Heat Transfer

We defined a method for the analytical solution of problems on stationary radiative and radiative–conductive heat transfer in a medium with an arbitrary frequency dependence of absorption and scattering near its boundary. We obtained formulas for the heat conductance of the remote surface and the thickness of the radiative–conductive relaxation of the medium. We determined characteristics of radiant heat transfer from the medium to free space such as the radiation spectrum, the radiation temperature and the medium outer boundary temperature. In addition, we solved the problem on the radiative–conductive heat transfer from one of two parallel surfaces to another with a medium between them.

scholarly journals Drying of algae by various drying methods

2018 ◽  
Author(s):  
Bhaskar Thorat ◽  
Bhaumik Bheda ◽  
Manoj Shinde ◽  
Rajaram Ghadge
Keyword(s):  
Heat Transfer ◽  
Crucial Role ◽  
High Performance ◽  
Conductive Heat Transfer ◽  
Drying Methods ◽  
Conductive Heat ◽  
Heat Transfer Mode ◽  
Sun Drying ◽  
Transfer Mode

Algae drying was carried out using Vacuum Tray Dryer and an Innovative Solar Conduction Dryer. Algae was dried in a Vacuum Tray Dryer at 60°C under varied pressure conditions and makes use of specially designed double condenser system. The open sun drying and solar conduction dryer (SCD) was also used for algae drying. Comparison between open sun drying and solar conduction dryer were done and it was found that the solar conduction dryer gives high performance than the open sun drying. It was also found that, the conductive heat transfer mode plays a crucial role in the solar conduction dryer. Keywords: Vaccum Dryer; Solar Conduction Dryer; Algal Drying

INFLUENCE OF HEAT TREATMENT OF MOUNTAIN MASSIVE ON TEMPERATURE MODE OF GEOTHERMAL CIRCULATION SYSTEM

2018 ◽  
pp. 44-50
Author(s):  
Yu. P. Morozov
Keyword(s):  
Heat Transfer ◽  
Operating Time ◽  
Fluid Motion ◽  
Coolant Temperature ◽  
Circulation System ◽  
Thermal Processes ◽  
Temperature Mode ◽  
Heat Influx ◽  
Stationary Heat Transfer

Based on the solution of the problem of non-stationary heat transfer during fluid motion in underground permeable layers, dependence was obtained to determine the operating time of the geothermal circulation system in the regime of constant and falling temperatures. It has been established that for a thickness of the layer H <4 m, the influence of heat influxes at = 0.99 and = 0.5 is practically the same, but for a thickness of the layer H> 5 m, the influence of heat inflows depends significantly on temperature. At a thickness of the permeable formation H> 20 m, the heat transfer at = 0.99 has virtually no effect on the thermal processes in the permeable formation, but at = 0.5 the heat influx, depending on the speed of movement, can be from 50 to 90%. Only at H> 50 m, the effect of heat influx significantly decreases and amounts, depending on the filtration rate, from 50 to 10%. The thermal effect of the rock mass with its thickness of more than 10 m, the distance between the discharge circuit and operation, as well as the speed of the coolant have almost no effect on the determination of the operating time of the GCS in constant temperature mode. During operation of the GCS at a dimensionless coolant temperature = 0.5, the velocity of the coolant is significant. With an increase in the speed of the coolant in two times, the error changes by 1.5 times.

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