View All Items
(1 - 5 of 5)
- Title
- Cavitation and heat transfer over micro pin fins.
- Creator
-
Nayebzadeh, Arash, Peles, Yoav, Chow, Louis, Kassab, Alain, Plawsky, Joel, University of Central Florida
- Abstract / Description
-
With the dramatic increase in the usage of compact yet more powerful electronic devices, advanced cooling technologies are required to maintain delicate electronic components below their maximum allowable temperatures and prevent them from failure. One solution is to use innovative pin finned heat sinks. This research is centered on the evaluation of hydrodynamic cavitation properties downstream pin fins and extended toward single-phase heat transfer enhancement of array of pin fins in...
Show moreWith the dramatic increase in the usage of compact yet more powerful electronic devices, advanced cooling technologies are required to maintain delicate electronic components below their maximum allowable temperatures and prevent them from failure. One solution is to use innovative pin finned heat sinks. This research is centered on the evaluation of hydrodynamic cavitation properties downstream pin fins and extended toward single-phase heat transfer enhancement of array of pin fins in microchannel. In this work, transparent micro-devices capable of local wall temperature measurements were micro fabricated and tested. Various experimental methods, numerical modeling and advanced data processing techniques are presented. Careful study over cavitation phenomena and heat transfer measurement downstream pin fins were performed.Hydrodynamic cavitation downstream a range of micro pillar geometries entrenched in a microchannel were studied. Three modes of cavitation inception were observed and key parameters of cavitation processes, such as cavity length and angle of attachment, were compared among various micro pillar geometries. Cavity angle of attachments were predominantly related to the shape of the micro pillar. Fast Fourier transformation (FFT) analysis of the cavity image intensity revealed transverse cavity shedding frequencies in various geometries and provided an estimation for vortex shedding frequencies.Experimental and numerical heat transfer studies over array of pin fins were carried out to find out the influence of lateral interactions of fluid flow on the enhancement of heat transfer. Local temperature measurements combined with a conjugate fluid flow and heat transfer modeling revealed the underlying heat transfer mechanisms over pin fin arrays.
Show less - Date Issued
- 2019
- Identifier
- CFE0007690, ucf:52407
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007690
- Title
- Investigation of Flow Field Structures in a Rectangular Channel with a Pin Fin Array.
- Creator
-
Tran, Patrick, Kapat, Jayanta, Bhattacharya, Samik, Huang, Helen, University of Central Florida
- Abstract / Description
-
Pin fin arrays are commonly found in heat exchangers, turbine blades, and electronic heat sinks. Fin arrays are extended surfaces that are used as turbulence promoters by inducing horseshoe vortex (HSV) and von Karman vortex (KV) structures. The horseshoe vortex are primarily studied in the leading edge of the blunt body, whereas the KV are formed in the trailing side. This study presents an experimental investigation of flow field structures and pressure loss on staggered pin fin array in...
Show morePin fin arrays are commonly found in heat exchangers, turbine blades, and electronic heat sinks. Fin arrays are extended surfaces that are used as turbulence promoters by inducing horseshoe vortex (HSV) and von Karman vortex (KV) structures. The horseshoe vortex are primarily studied in the leading edge of the blunt body, whereas the KV are formed in the trailing side. This study presents an experimental investigation of flow field structures and pressure loss on staggered pin fin array in the wake region, where KV are dominate. These flow structures increase the local levels turbulence and generate eddies that promote flow mixing, which in turn allows for higher levels of heat transfer. Improvement in heat transfer can increase the efficiency of the heat exchanger by reducing the thermal load and stress on the components which can extended product life. A study of the vortex shedding using a Particle Image Velocimetry (PIV) technique is used to measure flow field using a closed loop vertical water tunnel. A Time Resolved Particle Image Velocimetry (TR-PIV) study for both steady and unsteady flow structures in the fully developed region of a pin fin array at multiple wall normal cross sections are performed. The pin fin array consists of circular pin fins with 8 rows of 7.5 pins in rectangular channel with Reynolds number varying from 10,000 to 20,000. The Pin array is in a staggered configuration with stream wise (Y/D) spacing of 2.5 and span wise (X/D) spacing of 2.5, and height to pin diameter (H/D) of 2. A supplemental computation fluid dynamic (CFD) study is also for comparison with the PIV flow field. The goal of the present study is to determine the major vortex structures that found the flow at different Z/D, quantify parameters that numerical methods are unable to solve, and provide a base line for other parameters that can be used to improve the accuracy of numerical models. The novelty of this work is to provide data and characterize the near the viscous sub layer of Z/D =0.
Show less - Date Issued
- 2019
- Identifier
- CFE0007736, ucf:52446
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007736
- Title
- Improving Turbine Performance: A Contribution to the Understanding of Heat Transfer and Vortical Structures in Staggered Pin Fin Arrays.
- Creator
-
Otto, Marcel, Kapat, Jayanta, Ahmed, Kareem, Bhattacharya, Samik, Kinzel, Michael, Wiegand, Rudolf, University of Central Florida
- Abstract / Description
-
Through the comparison of flow structures, velocity contours, turbulence statistics, and additional flow quantities, the error sources of RANS are qualitatively described. The findings in this work will help gas turbine design engineers to tweak their turbulence models and give guidance on the interpretation of their results. The novelty is the application of the transient TLC method on this type of geometry as well as the near-wall PIV measurements. The advancements in additive manufacturing...
Show moreThrough the comparison of flow structures, velocity contours, turbulence statistics, and additional flow quantities, the error sources of RANS are qualitatively described. The findings in this work will help gas turbine design engineers to tweak their turbulence models and give guidance on the interpretation of their results. The novelty is the application of the transient TLC method on this type of geometry as well as the near-wall PIV measurements. The advancements in additive manufacturing disrupt the classic turbine cooling development for casted airfoils. More and more complicated shapes and cooling schemes are possible. Nonetheless, a detailed physical understanding of fundamental cases - as provided in this study - is required for physics-based optimization of cooling designs.
Show less - Date Issued
- 2019
- Identifier
- CFE0007848, ucf:52803
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007848
- Title
- PRESSURE DROP AND ENDWALL HEAT TRANSFER EFFECTS OF POROUS TURBULATORS IN A RECTANGULAR CHANNEL.
- Creator
-
Pent, Jared, Kapat, Jay, University of Central Florida
- Abstract / Description
-
This study examines the local and averaged endwall heat transfer effects of a staggered array of porous pin fins within a rectangular channel. The porous pin fins were made from aluminum and had a pore density of 10 pores per inch (PPI). The pressure drop through the channel was also determined for several flow rates and presented in terms of the friction factor. Local heat transfer coefficients on the endwall were measured using Thermochromic Liquid Crystal (TLC) sheets recorded with a...
Show moreThis study examines the local and averaged endwall heat transfer effects of a staggered array of porous pin fins within a rectangular channel. The porous pin fins were made from aluminum and had a pore density of 10 pores per inch (PPI). The pressure drop through the channel was also determined for several flow rates and presented in terms of the friction factor. Local heat transfer coefficients on the endwall were measured using Thermochromic Liquid Crystal (TLC) sheets recorded with a charge-coupled device (CCD) camera. Static and total pressure measurements were taken at the entrance and exit of the test section to determine the overall pressure drop through the channel and explain the heat transfer trends through the channel. Results are presented for Reynolds numbers between 25000 and 130000 and a blockage ratio (blocked channel area divided by open channel area) of 50%. All results were compared to the corresponding results obtained using solid pins. All experiments were carried out in a 150 mm by 500 mm channel with an X/D of 1.72, a Y/D of 2.0, and a Z/D of 1.72 for the porous pins. It was found that for the range of Reynold's numbers tested in this study, the porous pin array consistently resulted in a larger friction factor, and therefore greater losses than a geometrically similar array of solid pins. The friction factors for the solid pin array were between 9.5 and 10.5, similar to the results found in the literature. For the porous pins, however, the friction factors were significantly increased as the Reynold's number increased, reaching as high as 15.3 at the highest Reynold's number tested. The heat transfer enhancement for the porous pins was found to be between 150 and 170% while the solid pins resulted in a heat transfer enhancement between 190 and 230%.
Show less - Date Issued
- 2009
- Identifier
- CFE0002819, ucf:48085
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0002819
- Title
- Investigation of Novel Fin Structures Enhancing Micro Heat Sink Thermal Performance.
- Creator
-
Ismayilov, Fuad, Peles, Yoav, Kassab, Alain, Putnam, Shawn, Akturk, Ali, University of Central Florida
- Abstract / Description
-
Operating temperature in electronics applications is continuously increasing. Therefore, for the past few decades, high heat flux removing micro heat sinks are investigated in terms of heat transfer effectiveness. This study generally concentrates on improving the passive heat transfer techniques. Micro heat sinks used in experiments are fabricated using MEMS techniques. Resistance temperature detectors, RTDs, were used for temperature measurements. The experimental data was obtained for...
Show moreOperating temperature in electronics applications is continuously increasing. Therefore, for the past few decades, high heat flux removing micro heat sinks are investigated in terms of heat transfer effectiveness. This study generally concentrates on improving the passive heat transfer techniques. Micro heat sinks used in experiments are fabricated using MEMS techniques. Resistance temperature detectors, RTDs, were used for temperature measurements. The experimental data was obtained for single and two phase flow regions; however, only single phase flow results were considered in numerical simulations. Numerical validations were performed on the micro heat sinks, including cylinder and hydrofoil shaped pin fins. Following the validation phase, optimization has been performed to further improve the hydraulic and thermal performance. DOE study showed that the chord length and leading edge size of the hydrofoil pin fin are significant contributors to the thermal performance. The ranges of geometrical variables were identified and fed into multi-objective optimization cycles implementing the multi-objective genetic algorithm. The optimization objectives were to minimize pumping requirements while enhancing the local and global heat transfer effectiveness over the surface of the heater in single phase flow environment. A broad range of geometries were obtained with an acceptable tradeoff between thermal and hydraulic performance for low Reynolds number. Additionally, tandem geometries were investigated and showed that higher heat transfer effectiveness could be obtained with acceptable pumping power requirements. The importance of such optimization studies before the experimental testing is highlighted, and novel geometries are presented for further experimental investigations. Thermal performance improvement of 28% was obtained via implementing proposed geometries with only a 12% pressure drop increase. Local heat transfer optimization, aiming to decrease the local temperatures were also performed using doublet pin fin configurations. Results showed that tandem hydrofoils could control the flow with minimum pressure drops while reaching the desired low local temperatures.
Show less - Date Issued
- 2019
- Identifier
- CFE0007821, ucf:52828
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007821
