Local and mean heat-transfer fora turbulent flow of nonboiling water in a tube with high heat loads

Atomic Energy ◽  
1961 ◽  
Vol 8 (3) ◽  
pp. 221-224 ◽  
Author(s):  
V. V. Yakovlev
Keyword(s):  
Heat Transfer ◽  
Turbulent Flow ◽  
High Heat ◽  
Heat Loads

On Calculating Heat Transfer and Pressure Drop of Supercritical-Pressure Coolants

2016 ◽  
Vol 2 (3) ◽  
Author(s):  
Vladimir A. Kurganov ◽  
Yuri A. Zeigarnik ◽  
Irina V. Maslakova
Keyword(s):  
Heat Transfer ◽  
Turbulent Flow ◽  
Thermophysical Properties ◽  
High Heat ◽  
Supercritical Pressure ◽  
Heat Transfer Deterioration ◽  
Normal Heat ◽  
Turbulent Flow Structure ◽  
Heat Loads

Specific features of thermophysical properties of single-phase supercritical-pressure (SCP) coolants and typical ranges of their thermodynamic state that determine heat-transfer regularities are presented. A brief analysis of the existing concepts on SCP-coolants heat transfer under turbulent flow in tube is given. Typical features of normal and deteriorated heat-transfer regimes are described. The simple classification of deteriorated heat-transfer regimes at high heat loads that make it possible to distinguish the causes and appraise a degree of heat-transfer deterioration danger is proposed. The results from the studies of the hydraulic-resistance structure under the regimes of normal and deteriorated heat transfer are considered and the conditions, when a one-dimensional (1-D) (homogeneous) flow model can be used in hydraulic calculations, are revealed. Using sounding measurements data, the interrelation between heat-transfer deterioration and radical changes in the averaged turbulent flow structure due to fluid thermal acceleration and Archimedes forces effects is analyzed. The recommendations on calculating normal heat transfer with an account of refined standards on thermophysical properties of water and carbon dioxide are presented. The review and analysis of the existing criteria for forecasting heat-transfer deterioration and assessing the boundaries of the normal heat-transfer range are given, and the correlations for describing deteriorated heat transfer are presented.

Normal and Deteriorated Heat Transfer Under Heating Turbulent Supercritical Pressure Coolants Flows in Round Tubes

2021 ◽  
pp. 494-532
Author(s):  
Vladimir A. Kurganov ◽  
Yury A. Zeigarnik ◽  
Irina V. Maslakova
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Turbulent Flow ◽  
Thermophysical Properties ◽  
High Heat ◽  
Supercritical Pressure ◽  
Drop Method ◽  
New Correlation ◽  
Normal Heat ◽  
Heat Loads

Heat transfer to a turbulent flow of supercritical pressure (SCP) fluids under intense heating conditions is considered. The problem of heat transfer deteriorating under high heat loads and the reasons of its origination are analyzed. The results of hydraulic measurements in a flow and its structure using “two pressure drop” method and sounding technique in the regimes of normal and deteriorated heat transfer are presented. The existed correlations on normal heat transfer are analyzed and assessed as to their accuracy. It is pointed out that all the correlations developed using “old” thermophysical properties existed before implementing IAWPS-97 must be corrected. Respective recommendations on this problem and the new correlation for normal heat transfer are presented.

Enhancement of heat transfer in a square channel by roughened surfaces in rib-elements and turbulent flow manipulation

2017 ◽  
Vol 27 (7) ◽  
pp. 1571-1595 ◽  
Author(s):  
Jian Liu ◽  
Gongnan Xie ◽  
Bengt Ake Sunden ◽  
Lei Wang ◽  
Martin Andersson
Keyword(s):  
Heat Transfer ◽  
Turbulent Flow ◽  
Research Work ◽  
Flow Characteristics ◽  
High Heat ◽  
The Novel ◽  
Content Type ◽  
Flat Surfaces ◽  
Square Channel ◽  
High Heat Transfer

Purpose The purpose of this paper is to augment heat transfer rates of traditional rib-elements with minimal pressure drop penalties. Design/methodology/approach The novel geometries in the present research are conventional cylindrical ribs with rounded transitions to the adjacent flat surfaces and with modifications at their bases. All turbulent fluid flow and heat transfer results are presented using computation fluid dynamics with a validated v2f turbulence closure model. Turbulent flow characteristics and heat transfer performances in square channels with improved ribbed structures are numerically analyzed in this research work. Findings Based on the results, it is found that rounded transition cylindrical ribs have a large advantage over the conventional ribs in both enhancing heat transfer and reducing pressure loss penalty. In addition, cylindrical ribs increase the flow impingement at the upstream of the ribs, which will effectively increase the high heat transfer areas. The design of rounded transition cylindrical ribs and grooves will be an effective way to improve heat transfer enhancement and overall thermal performance of internal channels within blade cooling. Originality/value The novel geometries in this research are conventional cylindrical ribs with rounded transitions to the adjacent flat surfaces and with modifications at their bases. The combination of cylindrical ribs and grooves to manipulate the turbulent flow.

Experimental Investigation of Heat Transfer Augmentation by Different Jet Impingement Hole Shapes Under Maximum Crossflow

2016 ◽  
Author(s):  
Prashant Singh ◽  
Bharath Viswanath Ravi ◽  
Srinath Ekkad
Keyword(s):  
Heat Transfer ◽  
Liquid Crystal ◽  
Jet Impingement ◽  
High Heat ◽  
Absolute Pressure ◽  
Target Plate ◽  
Heat Transfer Augmentation ◽  
Plate Spacing ◽  
High Heat Transfer ◽  
Heat Loads

To achieve higher overall efficiency in gas turbine engines, hot gas path components are subjected to high heat transfer loads due to higher turbine inlet temperatures. Jet impingement has been extensively used especially as an internal cooling technique in the leading edge and mid-chord region of first stage vanes, which are subjected to highest heat loads. With the advent of additive manufacturing methods such as Direct Metal Laser Sintering (DMLS), designers are not limited to designing round or race track holes for impingement. The present study is focused on exploring new jet hole shapes, in an arrangement, typical of mid-chord region in a double wall cooling configuration. Transient liquid crystal experiments are carried out to study heat transfer augmentation by jet impingement on smooth target where the spent air is allowed to exit in one direction, thus imposing maximum crossflow condition. The averaged Reynolds number (based on jet hydraulic diameter) is varied from 2500 to 10000. The jet plate has a square array of jets with 7 jets in one row (total number of jets = 49), featuring hole shapes — Racetrack and V, where the baseline case is the round hole. The non-dimensional streamwise (x/dj) and spanwise (y/dj) spacing is 6 and the normalized jet-to-target-plate spacing (z/dj) is 4 and the nozzle aspect ratio (L/dj) is also 4. The criteria for the hole shape design was to keep the effective area of different hole shapes to be the same, which resulted in slightly different hydraulic diameters. The jet-to-target plate spacing (z) has been adjusted accordingly so as to maintain a uniform z/dj of 4, across all three configurations studied. Heat transfer coefficients are measured using a transient Liquid Crystal technique employing a one-dimensional semi-infinite model. Flow experiments are carried out to measure static pressures in the plenum chamber, to calculate the discharge coefficient, for a range of plenum absolute pressure-to-ambient pressure ratios. Detailed normalized Nusselt number contours have been presented, to identify the regions of high heat transfer augmentation locally, so as to help the designers in the organization of jet hole shapes and their patterns in an airfoil depending upon the active heat loads.

Effects of High Heating Loads on Unsteady Flow and Heat Transfer in a Cooling Passage With a Staggered Array of Pin Fins

2019 ◽  
Author(s):  
Chien-Shing Lee ◽  
Tom I.-P. Shih ◽  
Kenneth M. Bryden ◽  
Richard A. Dennis
Keyword(s):  
Heat Transfer ◽  
Unsteady Flow ◽  
Heat Load ◽  
High Heat ◽  
Flow And Heat Transfer ◽  
Pin Fins ◽  
Flow Mechanisms ◽  
Cooling Passage ◽  
Cooling Air ◽  
Heat Loads

Abstract Time-accurate 3-D CFD simulations based on the SST-SAS turbulence model were performed to study the effects of heat load on the unsteady flow and heat transfer in a cooling duct with a staggered array of short pin fins. For this duct, the static pressure at its exit is maintained at 25 bars, and the cooling air that enters has a temperature of 673 K with a flow rate that produces a Reynolds number of 25,000. To examine the effects of heat load, the following isothermal wall temperatures were studied: 678 K, 873 K, 1073 K, and 1,273 K, which give rises to heat loads that range from 15 kW/m2 to 1.5 MW/m2. Results obtained show high heat loads to cause considerable changes in the temperature of the cooling flow along the duct, which causes significant changes in density and velocity as well as viscosity and thermal conductivity. These changes along the duct were found to affect the locations where unsteady flow separation take place around the pin fins, the magnitude of the vorticity shed in the wakes, and the shedding Strouhal number. These unsteady flow mechanisms in turn strongly affect the nature of the surface heat transfer. A correlation formula for the heat transfer, which accounts for the effects of heat loads, was developed.

Boiling of Water at Sub-Atmospheric Conditions With Enhanced Structures

2005 ◽  
Author(s):  
Aniruddha Pal ◽  
Yogendra Joshi
Keyword(s):  
Heat Transfer ◽  
Electronics Cooling ◽  
High Heat ◽  
Maximum Temperature ◽  
Working Fluid ◽  
Atmospheric Conditions ◽  
Liquid Cooling ◽  
High Heat Transfer ◽  
Heat Loads ◽  
Very High

Liquid cooling with phase change is a very attractive option for thermal management of electronics because of the very high heat transfer coefficients achievable. Two-phase liquid cooling can be implemented in a thermosyphon loop, which has an evaporator, where heat is absorbed from the source during boiling of the working fluid, and a condenser, where the absorbed heat is rejected. Water is a preferred working fluid for boiling heat transfer due to its excellent thermal properties. Using water at sub-atmospheric conditions helps in initiation of boiling at low temperatures, which is necessary for electronics cooling applications, often limiting the maximum temperature to 85°C for silicon devices. Past studies have also shown that using boiling enhancement structures improve heat transfer by lowering the incipience overshoot, increasing heat flux and reducing evaporator volume. However, detailed study on the effects of enhancement structures and sub-atmospheric saturation conditions on the boiling of water in a compact thermosyphon loop is lacking in the literature. The objective of this study is to understand the boiling phenomena under the above-mentioned conditions and to investigate their effectiveness in electronics cooling applications. Experiments were carried out in a thermosyphon setup at 9.7, 15 and 21 kPa saturation pressures for two different enhancement structure geometries at varying heat loads (1–170 W). The experimental investigation showed that very high heat fluxes (≥ 80 W/cm2) can be achieved by boiling at sub-atmospheric pressures with enhancement structures. It is observed that with decreasing system pressure, the surface temperature also decreased for all the heat loads. The surface temperatures attained were well below the acceptable value of 85° C for all the cases.

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