Validity of performance factors used in recent studies on heat transfer enhancement by surface modification or insert devices

2022 ◽  
Vol 186 ◽  
pp. 122431
Author(s):  
Siti Nurul Akmal Yusof ◽  
Nura Mu'az Muhammad ◽  
Wan Mohd Arif Aziz Japar ◽  
Yutaka Asako ◽  
Chungpyo Hong ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Surface Modification ◽  
Heat Transfer Enhancement ◽  
Transfer Enhancement ◽  
Performance Factors

Numerical Simulation of Laminar Flow Heat Transfer Enhancement Using Surface Modification

2014 ◽  
Author(s):  
Abhijit S. Paranjape ◽  
Ninad C. Maniar ◽  
Deval A. Pandya ◽  
Brian H. Dennis
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Surface Modification ◽  
Laminar Flow ◽  
Heat Transfer Enhancement ◽  
Rectangular Channel ◽  
Longitudinal Vortex ◽  
Bottom Wall ◽  
Transfer Enhancement ◽  
Smooth Channel

Heat transfer augmentation techniques have gained great importance in different engineering applications to deal with thermal management issues. In this work, a numerical investigation was carried out to see the effects of a modified surface on the heat transfer enhancement compared to a smooth surface. In the first case, spherical dimple arrays were applied to the surface. The effects were observed for dimples on the bottom wall of a channel for a laminar airflow. The effects of a 21×7 staggered array and a 19×4 inline array on the bottom wall were investigated. In the second case, the heat exchange enhancement in a rectangular channel using longitudinal vortex generators (LVG) for a laminar flow was considered. In both cases, a 3D steady viscous computational fluid dynamics package with an unstructured grid was used to compute the flow and temperature field. The heat transfer characteristics were studied as a function of the Reynolds number based on the hydraulic diameter of the channel. The heat transfer was quantified by computing the surface averaged Nusselt number. The pressure drop and flow characteristics were also calculated. The Nusselt number was compared with that of a smooth channel without surface modification to assess the level of heat transfer enhancement.

scholarly journals Internal Cooling Using Novel Swirl Enhancement Strategies in a Slot Shaped Single Pass Channel

2010 ◽  
Author(s):  
Del Segura ◽  
Sumanta Acharya
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Turbine Blades ◽  
Main Channel ◽  
Internal Cooling ◽  
Transfer Enhancement ◽  
Mean Velocity ◽  
Performance Factors ◽  
Air Temperatures ◽  
Rectangular Channels

Heat transfer results for a given slot shaped channel with a 3:1 aspect ratio are presented using various methods to enhance swirl in the channel including helical shaped-trip-strips and swirl-jets issuing from the side walls. Four different configurations of the swirl jets and one configuration of the helical trip strips were studied. The Reynolds numbers investigated range from 10,000 to 50,000 and are based on the mean velocity of the fluid at the channel inlet, or when swirl-jets are used, the equivalent mass flow rates at the exit of the main channel. Independently these heat transfer enhancement strategies have proven to be effective in either round channels, in the case of swirl jets and helical protrusions, or rectangular channels, in the case of trip strips. A transient technique combined with Duhamel’s superposition theorem was used to obtain the heat transfer coefficient distributions. Narrow-band liquid crystals were used to map the transient surface temperatures and were combined with thermocouples that measured the bulk-air temperatures along the flow path in the main channel. The results for the tests reported in this paper show mean heat transfer enhancement values (Nu/Nuo) greater than 4.5 and low normalized friction factors. Thermal performance factors ranged from 1.1–3.3 for the various configurations studied. These results show significant improvements over other types of heat transfer enhancement methods currently used in the mid-span section of turbine blades.

Validity of Performance Factors Used in Recent Studies On Heat Transfer Enhancement of Nanofluids

2021 ◽  
Author(s):  
Nura Mu'az Muhammad ◽  
Wan Mohd Arif Aziz Japar ◽  
Siti Nurul Akmal Yusof ◽  
Yutaka Asako ◽  
Mohammad Faghri ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Single Phase ◽  
Circular Tube ◽  
Pumping Power ◽  
Transfer Enhancement ◽  
Empirical Correlations ◽  
Transfer Rates ◽  
Performance Factors ◽  
Equal Temperature

Abstract Many previous studies used the performance factors for the evaluation of heat transfer enhancement of nanofluids under the identical pumping power. The validity of the performance factors was not examined yet. The validity of the performance factors used in previous studies examined considered only flows in a circular tube based on the empirical correlations and experimental data. It was found that the performance factors used in the previous studies are not valid for the evaluation of heat transfer enhancement of nanofluids. Furthermore, this paper shows that the direct comparison of heat transfer rates without the assumptions of equal surface area and the equal temperature difference is suitable for the evaluation of heat transfer enhancement of single-phase fluids.

Swirl-Enhanced Internal Cooling of Turbine Blades: Part 1—Radial Flow Entry

2011 ◽  
Author(s):  
Del Segura ◽  
Sumanta Acharya
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Turbine Blades ◽  
Main Channel ◽  
Internal Cooling ◽  
Transfer Enhancement ◽  
Mean Velocity ◽  
Performance Factors ◽  
Air Temperatures ◽  
The Mean

Heat transfer results for a given slot shaped channel with a 3:1 aspect ratio and jets issuing from side walls are presented. Two different jet configurations are used as a means to enhance turbulence in the main flow stream. The Reynolds numbers investigated range from 10,000 to 50,000 and are based on the mean velocity of the fluid at the channel inlet for the slot shaped channel without enhancement, or when swirl-jets are used, the equivalent mass flow rates at the exit of the main channel. Blowing Ratios, defined as the mean side jet velocity verses the mean main channel velocity, ranged from 8.6 to 30.2. This heat transfer enhancement strategy has proven to be effective in round channels. A transient technique combined with Duhamel’s superposition theorem was used to obtain the heat transfer coefficient distributions. Narrow-band liquid crystals were used to map the transient surface temperatures and were combined with thermocouples that measured the center-line air temperatures along the flow path in the main channel. The results of the passage with jet enhancements were compared to the smooth slot channel, without any type of heat transfer enhancements. The tests results reported in this paper show mean heat transfer enhancement values (Nu/Nuo smooth) greater than 4.2 and low normalized friction factors. Thermal performance factors (OTP) ranged from 1.55–3.69 for the various configurations studied. These results show significant improvements over other types of heat transfer enhancement methods currently used in the mid-span section of turbine blades.

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