scholarly journals Intensification of heat transfer between heat exchange surfaces at low RE values

2015 ◽  
Vol 36 (3) ◽  
pp. 331-344
Author(s):  
Jozef Cernecky ◽  
Zuzana Brodnianska ◽  
Jan Koniar
Keyword(s):  
Heat Transfer ◽  
Heat Exchange ◽  
Friction Coefficient ◽  
Holographic Interferometry ◽  
Temperature Fields ◽  
Pressure Losses ◽  
Interferometry Method ◽  
Transfer Parameters ◽  
Holographic Interferometry Method ◽  
Quantitative Evaluations

Abstract This contribution deals with the heat transfer parameters and pressure losses in heat exchange sets with six geometrical arrangements at low Re values (Re from 476 to 2926). Geometrical arrangements were characterised by the h/H ratio ranging from 0.2 to 1.0. The experiments used the holographic interferometry method in real time. This method enables visible and quantitative evaluations of images of temperature fields in the examined heat exchange. These images are used to determine the local and mean heat transfer parameters. The obtained data were used to determine the Colburn j-factor and the friction coefficient f. The measured values show that by using the profiled heat exchange surfaces and inserting regulating tubes, an intensification of heat transfer (increase of Num, and/or j) was achieved. However, pressure losses recorded a significant increase (increase of f).

The Research of Temperature Fields in the Proximity of a Bundle of Heated Pipes Arranged Above Each Other

2017 ◽  
Vol 139 (8) ◽  
Author(s):  
Jozef Cernecky ◽  
Zuzana Brodnianska ◽  
Przemysław Błasiak ◽  
Jan Koniar
Keyword(s):  
Heat Transfer ◽  
Cfd Simulation ◽  
Temperature Fields ◽  
Horizontal Shift ◽  
Geometric Conditions ◽  
Interferometry Method ◽  
Computational Fluid Dynamics Cfd ◽  
Transfer Parameters ◽  
C 50 ◽  
The Impact

The paper deals with the research of temperature fields in the proximity of heated pipes arranged above each other in a natural air convection. The holographic interferometry method was used for the visualization of temperature fields. The experiments were made with pipes, diameter of 20 mm, length 200 mm, spacing two-dimensional (2D) at surface temperatures of 40 °C, 50 °C, and 60 °C, with the vertical arrangement of the pipes as well as with the horizontal shift of their centers by 1/4D and 1/2D (on a surface temperature of 50 °C). Temperature profiles were determined from the experimentally obtained images of temperature fields, and local parameters of heat transfer were calculated. Under the same marginal and geometric conditions, computational fluid dynamics (CFD) simulations of temperature fields were performed as well, while the results (temperature fields, local and mean parameters of heat transfer) were also calculated for various distances between the pipe centers (1D, 2D, and 3D). From the obtained experimental results and CFD simulation results, it is possible to observe the impact of the arrangement and spacing of pipes on heat transfer parameters. The achieved results imply the change in the spacing of the pipes has a greater impact on heat transfer parameters in the bundle of heated pipes located above each other than a moderate horizontal shift of their centers.

The Effect of Regulating Elements on Convective Heat Transfer along Shaped Heat Exchange Surfaces

2013 ◽  
Vol 34 (1) ◽  
pp. 5-16 ◽  
Author(s):  
Jozef Cernecky ◽  
Jan Koniar ◽  
Zuzana Brodnianska
Keyword(s):  
Heat Transfer ◽  
Heat Exchange ◽  
Cfd Simulation ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Temperature Fields ◽  
Transfer Coefficients ◽  
Heat Transfer Intensification ◽  
Heat Transfer Coefficients ◽  
Forced Air

Abstract The paper deals with a study of the effect of regulating elements on local values of heat transfer coefficients along shaped heat exchange surfaces with forced air convection. The use of combined methods of heat transfer intensification, i.e. a combination of regulating elements with appropriately shaped heat exchange areas seems to be highly effective. The study focused on the analysis of local values of heat transfer coefficients in indicated cuts, in distances expressed as a ratio x/s for 0; 0.33; 0.66 and 1. As can be seen from our findings, in given conditions the regulating elements can increase the values of local heat transfer coefficients along shaped heat exchange surfaces. An optical method of holographic interferometry was used for the experimental research into temperature fields in the vicinity of heat exchange surfaces. The obtained values correspond very well with those of local heat transfer coefficients αx, recorded in a CFD simulation.

CFD Analysis of Flow and Heat Transfer in a Novel Heat Sink for Electronic Devices

2010 ◽  
Author(s):  
Bladimir Ramos-Alvarado ◽  
Peiwen Li ◽  
Hong Liu ◽  
Abel Hernandez-Guerrero
Keyword(s):  
Heat Transfer ◽  
Power Consumption ◽  
Heat Sink ◽  
Electronics Cooling ◽  
Flow Channel ◽  
Heat Sinks ◽  
Temperature Fields ◽  
Pumping Power ◽  
Pressure Losses ◽  
Channel Configuration

Novel flow channel configurations in heat sinks for electronics cooling were proposed in this paper. Computational analyses were carried out to better understand the heat transfer performance, the uniformity of temperature fields of the heat sinking surface, as well as the pressure losses and pumping power in the operation of heat sinks. Comparison of the overall performance regarding to temperature uniformity on the heat sink surface and pumping power consumption was made for heat sinks having novel flow channel configurations and having traditional flow channel configurations. It has been found that the novel flow channel configuration dramatically reduces the pressure loss in the flow field. Giving the same pumping power consumption of an electronics cooling process, the temperature difference on surface of the heat sink which has novel flow channel configuration can be much lower than that of the heat sinks which have traditional flow channel configurations.

Based on the Matrix of Silicon Nanocrystals a Modeling Study of Thermo-hydraulic Properties of Micro-channel Heat Transfer Elements

2021 ◽  
Vol 19 (3) ◽  
pp. 38-45
Author(s):  
Forat H. Alsultany ◽  
Qasim S. Kadhim
Keyword(s):  
Heat Transfer ◽  
Heat Exchange ◽  
Thermal Stabilization ◽  
Specific Power ◽  
Heat Sources ◽  
Ambient Temperatures ◽  
Pressure Losses ◽  
Geometric Configurations ◽  
Wide Range ◽  
The Matrix

The construction of a heat exchange element based on a matrix of silicon whiskers for thermal stabilization systems of miniature heat sources with specific power up to 100 W/cm2 operating over a wide range of ambient temperatures is proposed. Based on the developed mathematical model of convective heat transfer in a microchannel compact heat exchanger with a developed heat exchange surface, numerical simulation of the hydrodynamics and heat transfer processes for various configurations of microchannel insertions was carried out. Fields of pressures, flow velocities, coolant temperatures and matrix from silicon single crystals have been obtained in a wide range of coolant flow rates, criteria dependencies for the Nusselt number and pressure losses of various geometric configurations of heat exchangers have been determined. Critical operation modes are investigated; optimization directions are proposed. According to the developed technology, prototypes for testing have been manufactured.

The Effect of Heat Transfer Area Roughness on Heat Transfer Enhancement by Forced Convection

2014 ◽  
Vol 136 (4) ◽  
Author(s):  
Jozef Cernecky ◽  
Jan Koniar ◽  
Zuzana Brodnianska
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Forced Convection ◽  
Holographic Interferometry ◽  
Temperature Fields ◽  
Heat Transfer Area ◽  
Transfer Enhancement ◽  
Nusselt Numbers ◽  
Air Convection ◽  
Forced Air

The paper deals with the visualization of temperature fields in the vicinity of profiled heat transfer surfaces and a subsequent analysis of local values of Nusselt numbers by forced air convection in an experimental channel. Holographic interferometry was used for visualizing the temperature fields. Experiments were carried out at Re 462 up to 2338 at the distances between heat transfer surfaces of 0.025 m and 0.035 m. Temperature contours were determined from the obtained images of holographic interferograms of temperature fields and the local values of Nusselt numbers along the profiled surface for x/s = 0 up to x/s = 1.25 were calculated from them. A significant effect of the profiled surface on the local values of Nusselt numbers can be observed from the obtained results.

scholarly journals Investigation of Nailed Timber Connections Using the Laser Interferometry Method

2018 ◽  
Vol 26 (4) ◽  
pp. 32-38
Author(s):  
Mykola Savytskyi ◽  
Svitlana Shekhorkina ◽  
Alexander Kesariiskyi ◽  
Valeriy Kondrashchenko ◽  
Stanislav Dukát
Keyword(s):  
Holographic Interferometry ◽  
Laser Interferometry ◽  
Element Model ◽  
Optimum Conditions ◽  
Stress Strain ◽  
Strain Behavior ◽  
Interferometry Method ◽  
Timber Connections ◽  
Holographic Interferometry Method ◽  
Laser Holographic Interferometry

Abstract The paper presents an adapted methodology of laser holographic interferometry for an investigation of the stress-strain state of nailed timber connections. During the study the possibility of detecting local deformations in the connection were verified. The optimum conditions for fixing the samples and the loading ranges to ensure an optimal interference pattern were determined. An investigation of the peculiarities of the interaction between the elements and the stress-strain behavior of nailed timber connections was performed. The experimental data obtained on the stress-strain behavior of a nailed timber connection using the laser holographic interferometry method have sufficient repeatability between different series and can also be used as a criterion verification for a finite-element model.

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