scholarly journals Computational and experimental evaluation of heat transfer intensity in channels of complex configuration for gas flow with different levels of turbulence

2021 ◽  
Vol 2119 (1) ◽  
pp. 012007
Author(s):  
L V Plotnikov ◽  
B P Zhilkin ◽  
Yu M Brodov ◽  
L E Osipov
Keyword(s):  
Heat Transfer ◽  
Cross Sections ◽  
Turbulence Intensity ◽  
Gas Flow ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Measuring Instruments ◽  
Flow Paths ◽  
Experimental Stand ◽  
Urgent Task

Abstract Disclosure of the physical mechanism of the influence of the turbulence intensity of gas flows on the heat transfer level in pipes of different configurations is an urgent task in the field of heat and power engineering. A brief overview of the literature on this topic is given in the article. A description of the boundary conditions for modeling is presented. The main characteristics of the experimental stand and measuring instruments are described. The purpose of this study is to study the effect of the initial turbulence level of a stationary gas flow on the heat transfer intensity in long pipes with different cross sections. The study is carried out using numerical simulation. The simulation results are qualitatively confirmed using experimental data. The values of the local heat transfer coefficient are shown to increase from 5 to 17% with increasing turbulence intensity (from 2 to 10%) in pipes with different cross sections. The heat transfer intensity in a triangular pipe is found to increase up to 30% compared to a round pipe. It is revealed that there is an up to 15% suppression of heat transfer in a square pipe compared to a round pipe. The data obtained may be useful for the design of flow paths and gas exchange systems for power machines and installations.

scholarly journals Nonstationary gas-dynamics and local heat transfer in the output channel of the turbocharger compressor

2019 ◽  
Vol 196 ◽  
pp. 00007 ◽  
Author(s):  
Leonid Plotnikov ◽  
Nikita Grigor'ev ◽  
Nikolaj Kochev
Keyword(s):  
Heat Transfer ◽  
Gas Dynamics ◽  
Gas Flow ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Measuring System ◽  
Rotor Speed ◽  
Outlet Channel ◽  
Thermomechanical Characteristics ◽  
Channel Configuration

Thermomechanical characteristics of the gas flow at the turbocharger compressor outlet largely determine the quality of the intake process in piston engines with boost. The article presents the results of an experimental study of gas-dynamics and heat transfer of gas flows after compression in a turbocharger centrifugal compressor. A brief description of the experimental setup, the configuration of pipes under investigation, the measuring system and the experimental features are given. The studies were carried out on a free compressor, i.e. without considering the piston part. Different conditions in the compressor outlet channel were created by installing special nozzles with different hydraulic resistances. It has been established that the local heat transfer increases from 23 to 46 % with an increase in the turbocharger rotor speed, depending on the outlet channel configuration. It should be noted that an increase in rotor speed is also accompanied by an increase in air flow through the channel. The increase in flow rate was from 10 to 42 %.

Annular Liquid Film Flow Under Local Heating in Microchannel

2005 ◽  
Author(s):  
Elizaveta Ya. Gatapova ◽  
Vladimir V. Kuznetsov ◽  
Oleg A. Kabov ◽  
Jean-Claude Legros
Keyword(s):  
Heat Transfer ◽  
Liquid Film ◽  
Biot Number ◽  
Gas Flow ◽  
Film Flow ◽  
Local Heating ◽  
Local Heat Transfer ◽  
Flow Region ◽  
Local Heat ◽  
Liquid Film Flow

In our previous investigations the formation of liquid bump of locally heated laminar liquid film with co-current gas flow was obtained [1,2]. The evaporation of liquid was left out of account. Heat transfer to the gas phase was approximately specified by a constant Biot number [2,3]. The aim of this work is an investigation of the evaporation effect, the hydrodynamics and the heat transfer of liquid film flow in a channel 0.2–1 mm height. The 2-D model of locally heated liquid film moving under gravity and the action of co-current gas flow with low viscosity in a channel are considered. The channel can be inclined at an angle with respect to horizon. It is supposed that the height of the channel is much less than its width. Surface tension is assumed to depend on temperature. The velocity profiles for gas and liquid regions are found from problem of joint motion of isothermal non-deformable liquid film and gas flow. Using the findings the joint solution of heat transfer and diffusion problem with corresponding boundary condition is calculated. Having the temperature field in the whole of liquid and gas flow region we find a local heat transfer coefficient on the gas-liquid interface and Biot number as a function of flow parameters and spatial variables.

Visualization of Convective Boiling Heat Transfer in Single Micro-Conduits With Different Shapes of Cross Sections

2005 ◽  
Author(s):  
Tzu-Hsiang Yen ◽  
Masahiro Shoji ◽  
Fumio Takemura ◽  
Yuji Suzuki ◽  
Nobuhide Kasagi
Keyword(s):  
Heat Transfer ◽  
Flow Pattern ◽  
Cross Sections ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Flow Patterns ◽  
Transfer Coefficients ◽  
Convective Boiling ◽  
Heat Transfer Coefficients ◽  
Square Microchannel

Visualization experiments of convective boiling in transparent single micro conduits with the same hydraulic diameter but different cross sections are carried out with simultaneous measurement of local heat transfer coefficients and pressure losses. Two different cross sections with the same similar hydraulic diameters are applied: A circular microtube of 210μm in diameter and a square microchannel of 214μm × 214μm cross section. ITO/Ag thin film of 100 nm is sputtered on the outer surface of the conduits for the direct joule heating. The convective boiling shows some periodic variation of different flow patterns in both square and circular conduits. These flow patterns include bubbly, plug, slug, annular and capillary flows. The capillary flow pattern is the independent liquid droplets moving in the flow direction and very rarely observed in conventional tubes. The reason of such variation of flow patterns is that confined spaces limit the bubble growth in radial direction. So the nucleation bubble grows in both upstream and downstream and makes the flow pattern varies radically. The square microchannel conduit has more simple flow pattern variation, more nucleation bubbles and larger local heat transfer coefficients at lower vapor quality. It is due to that corners of the square microchannel act as helps nucleation cavities. Corners also promotes the formation of liquid film and the contact line between liquid and wall, which can stabilize the flow field. Local heat transfer coefficients decrease with increasing local vapor qualities. Local heat transfer coefficients increase with increasing boiling number but have their maximum value when boiling number reaches critical value. Such peculiar heat transfer characteristics can also be explained by the visualization results.

Darryl E. Metzger Memorial Session Paper: Surface Heat Transfer From a Three-Pass Blade Cooling Passage Simulator

1995 ◽  
Vol 117 (4) ◽  
pp. 650-656 ◽  
Author(s):  
M. K. Chyu ◽  
V. Natarajan
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Cross Sections ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Test Model ◽  
Flow Area ◽  
Blade Cooling ◽  
Sharp Turn ◽  
Cooling Passage

Using an analogous mass transfer system based on naphthalene sublimation, the present research focuses on investigating the local heat transfer characteristics from three-pass smooth and turbulated blade cooling passages. To simulate the actual passage geometry, the test model is incorporated with trapezoidal cross sections including variable passage sizes. Measured local mass transfer results reveal strong evidence of velocity redistribution over the trapezoidal flow area. Elevated mass transfer always exists in the vicinity of a sharp turn. However, in the present study, one of the most notable mass transfer increases is perceived in the third pass, downstream to the second turn, where the flow area is reduced severely. Overall, the combined effects of the three-pass and two sharp turns virtually double the mass transfer as compared to its straight counterpart with fully developed, turbulent flow. With a pitch-to-height ratio equal to 10 and 90 deg orientation, the rib turbulators produce approximately an additional 30 percent of overall mass transfer enhancement in comparison to the smooth case. Locally, rib-induced enhancement varies with different surfaces and passes. The greatest enhancement lies on the first pass, about 40 percent; the other two passes are comparable, less than 20 percent.

Thermo-Fluidic Characteristics in a Cross-Linked Silicon Microchannel Heat Sink

2007 ◽  
Author(s):  
R. Muwanga ◽  
I. Hassan
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Cross Sections ◽  
Heat Sink ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Working Fluid ◽  
Microchannel Heat Sink ◽  
Significant Difference ◽  
The Cross

This paper presents the flow and heat transfer characteristics in a cross-linked silicon microchannel heat sink. The heat sink is composed of 45 channels, 270 μm wide × 285 μm tall in a silicon substrate formed via deep reactive ion etching. A detailed discussion of the pressure drop data reduction is described, including characterization of the channel cross-sections and methods to account for inlet and exit loss coefficients. No significant difference is observed in the pressure drop measurements between the cross-linked and standard heat sinks flowing air and water. The use of un-encapsulated liquid crystal thermography was successfully utilized to obtain local heat transfer data with FC-72 as the working fluid. The heat transfer results show inflections in the thermal profile due to the cross-links.

Influence of High Mainstream Turbulence on Leading Edge Heat Transfer

1991 ◽  
Vol 113 (4) ◽  
pp. 843-850 ◽  
Author(s):  
A. B. Mehendale ◽  
J. C. Han ◽  
S. Ou
Keyword(s):  
Heat Transfer ◽  
Turbulence Intensity ◽  
Leading Edge ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Turbulence Decay ◽  
High Turbulence

The influence of high mainstream turbulence on leading edge heat transfer was studied. High mainstream turbulence was produced by a bar grid (Tu = 3.3–5.1 percent), passive grid (Tu = 7.6–9.7 percent), and jet grid (Tu = 12.9–15.2 percent). Experiments were performed using a blunt body with a semicylinder leading edge and flat sidewalls. The mainstream Reynolds numbers based on leading edge diameter were 25,000, 40,000, and 100,000. Spanwise and streamwise distributions of local heat transfer coefficients on the leading edge and flat sidewall were obtained. The results indicate that the leading edge heat transfer increases significantly with increasing mainstream turbulence intensity, but the effect diminishes at the end of the flat sidewall because of turbulence decay. Stagnation point heat transfer results for high turbulence intensity flows agree with the Lowery and Vachon correlation, but the overall heat transfer results for the leading edge quarter-cylinder region are higher than their overall correlation for the entire circular cylinder region. High mainstream turbulence tends not to shift the location of the separation-reattachment region. The reattachment heat transfer results are about the same regardless of mainstream turbulence levels and are much higher than the turbulent flat plate correlation.

The Transition From Turbulent to Laminar Gas Flow in a Heated Pipe

1970 ◽  
Vol 92 (4) ◽  
pp. 569-579 ◽  
Author(s):  
C. A. Bankston
Keyword(s):  
Heat Transfer ◽  
Gas Flow ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Local Heat ◽  
Heat Fluxes ◽  
External Boundary ◽  
Transfer Coefficients ◽  
Adiabatic Flow ◽  
Heat Transfer Coefficients

Experimental results are reported on the heat transfer and fluid friction of heated hydrogen and helium gas flows undergoing transition from turbulent to laminar flow in a circular tube. The entering Reynolds numbers range from 2350 to 12,500 and the nondimensional heat-flux parameter ranges from 0.0021 to 0.0061. Local heat-transfer coefficients and friction factors are obtained, and the flow transition, which is evident in these results, is verified at small heat fluxes by measuring directly the turbulence intensity at the center line with a hot-wire anemometer. At large heat fluxes, laminarization is found to occur at local bulk Reynolds numbers well in excess of the minimum number for fully turbulent adiabatic flow, and the resulting heat-transfer coefficients are much lower than those associated with fully turbulent flow at the same Reynolds number. The relation between laminarization in heated tubes and in severely accelerated external boundary layers is investigated and some similarities are noted. The acceleration and pressure-gradient parameters used to predict boundary-layer laminarization are modified for tube flow and used to correlate the initiation and completion of laminarization in the heated tube.

Experimental research into the methods for controlling the thermal-mechanical characteristics of pulsating gas flows in the intake system of a turbocharged engine model

2021 ◽  
pp. 146808742098736
Author(s):  
Leonid V Plotnikov
Keyword(s):  
Heat Transfer ◽  
Gas Dynamics ◽  
Gas Flow ◽  
Mechanical Characteristics ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Gas Flows ◽  
Intake System ◽  
Instantaneous Values ◽  
Technical Solutions

It is a relevant objective in thermal physics and piston engine construction to develop technical solutions for controlling the gas dynamics and heat exchange of gas flows in the intake system of turbocharged engines in order to improve performance. The article presents other authors’ data on the improvement of processes in the gas exchange systems of piston engines. It also provides a description of experimental set-ups, instruments, measurement tools and research methods for establishing the thermal-mechanical characteristics of pulsating flows in the intake system of a turbocharged engine. The instantaneous values of the gas flow rate and the local heat transfer coefficient were determined using the measured results by applying a constant temperature hot-wire anemometer (H-WA). The article describes technical solutions for influencing the gas dynamics and heat exchange of gas flows by stabilising and turbulising the flow. The regularities of changes in the instantaneous values of the flow velocity, pressure and the local heat transfer coefficient in time for a pulsating gas flow with different intake system configurations are obtained. It is shown that the installation of a levelling grid in the compressor outlet channel leads to the stabilisation of the flow and the suppression of heat transfer in the engine intake system by an average of 15% compared to the base system. It was found that the presence of a channel with grooves in the intake system leads to flow turbulisation and the intensification of heat transfer in the intake system by an average of 25%.

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