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You searched for subject:(Critical Pressure Coefficient). Showing records 1 – 2 of 2 total matches.

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Kansas State University

1. Dahariya, Smreeti. High-pressure pool-boiling heat transfer enhancement and mechanism on engineered surfaces.

Degree: PhD, Department of Mechanical and Nuclear Engineering, 2020, Kansas State University

Boiling has received considerable attention in the technology advancement of electronics cooling for high-performance computing applications. Two-phase cooling has an advantage over a single-phase cooling in the high heat removal rate with a small thermal gradient due to the latent heat of vaporization. Many surface modifications have been done in the past including surface roughness, mixed wettability and, porous wick copper play a crucial role in the liquid-vapor phase change heat transfer. However, the mechanisms of high-pressure pool-boiling heat transfer enhancement due to surface modifications has not been well studied or understood. The properties of water, such as the latent heat of vaporization, surface tension, the difference in specific volume of liquid and vapor, decrease at high-pressure. High-pressure pool-boiling heat transfer enhancement is studied fundamentally on various engineered surfaces. The boiling tests are performed at a maximum pressure of 90 psig (620.5 kPa) and then compared to results at 0 psig (0 kPa). The results indicate that the pressure influences the boiling performance through changes in bubble dynamics. The bubble departure diameter, bubble departure frequency, and the active nucleation sites change with pressure. The pool-boiling heat transfer enhancement of a Teflon© coated surface is also experimentally tested, using water as the working fluid. The boiling results are compared with a plain surface at two different pressures, 30 and 45 psig. The maximum heat transfer enhancement is found at the low heat fluxes. At high heat fluxes, a negligible effect is observed in HTC. The primary reasons for the HTC enhancement at low heat fluxes are active nucleation sites at low wall superheat and bubble departure size. The Teflon© coated surface promotes nucleation because of the lower surface energy requirement. The boiling results are also obtained for wick surfaces. The wick surfaces are fabricated using a sintering process. The boiling results are compared with a plain surface. The reasons for enhancements in the pool-boiling performance are primarily due to increased bubble generation, higher bubble release frequency, reduced thermal-hydraulic length modulation, and enhanced thermal conductivity due to the sintered wick layer. The analysis suggests that the Rayleigh-critical wavelength decreases by 4.67 % of varying pressure, which may cause the bubble pinning between the gaps of sintered particles and avoids the bubble coalescence. Changes in the pitch distance indicate that a liquid-vapor phase separation happens at the solid/liquid interface, which impacts the heat-transfer performance significantly. Similarly, the role of the high-pressure over the wicking layer is further analyzed and studied. It is found that the critical flow length, λu reduces by three times with 200 μm particles. The results suggest that the porous wick layer provides a capillary-assist to liquid flow effect, and delays the surface dry out. The surface modification and the pressure amplify the boiling heat… Advisors/Committee Members: Amy R. Betz.

Subjects/Keywords: Critical Heat Flux; Heat Transfer Coefficient; Thermal-Hydraulic; Rayleigh-Critical Wavelength; Pinning Mechanism; Capillary Pressure

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Dahariya, S. (2020). High-pressure pool-boiling heat transfer enhancement and mechanism on engineered surfaces. (Doctoral Dissertation). Kansas State University. Retrieved from http://hdl.handle.net/2097/40311

Chicago Manual of Style (16th Edition):

Dahariya, Smreeti. “High-pressure pool-boiling heat transfer enhancement and mechanism on engineered surfaces.” 2020. Doctoral Dissertation, Kansas State University. Accessed January 24, 2021. http://hdl.handle.net/2097/40311.

MLA Handbook (7th Edition):

Dahariya, Smreeti. “High-pressure pool-boiling heat transfer enhancement and mechanism on engineered surfaces.” 2020. Web. 24 Jan 2021.

Vancouver:

Dahariya S. High-pressure pool-boiling heat transfer enhancement and mechanism on engineered surfaces. [Internet] [Doctoral dissertation]. Kansas State University; 2020. [cited 2021 Jan 24]. Available from: http://hdl.handle.net/2097/40311.

Council of Science Editors:

Dahariya S. High-pressure pool-boiling heat transfer enhancement and mechanism on engineered surfaces. [Doctoral Dissertation]. Kansas State University; 2020. Available from: http://hdl.handle.net/2097/40311


University of North Texas

2. Altalidi, Sulaiman Saleh. Two-Phase Spray Cooling with HFC-134a and HFO-1234yf for Thermal Management of Automotive Power Electronics using Practical Enhanced Surfaces.

Degree: 2017, University of North Texas

The objective of this research was to investigate the performance of two-phase spray cooling with HFC-134a and HFO-1234yf refrigerants using practical enhanced heat transfer surfaces. Results of the study were expected to provide a quantitative spray cooling performance comparison with working fluids representing the current and next-generation mobile air conditioning refrigerants, and demonstrate the feasibility of this approach as an alternative active cooling technology for the thermal management of high heat flux power electronics (i.e., IGBTs) in electric-drive vehicles. Potential benefits of two-phase spray cooling include achieving more efficient and reliable operation, as well as compact and lightweight system design that would lead to cost reduction. The experimental work involved testing of four different enhanced boiling surfaces in comparison to a plain reference surface, using a commercial pressure-atomizing spray nozzle at a range of liquid flow rates for each refrigerant to determine the spray cooling performance with respect to heat transfer coefficient (HTC) and critical heat flux (CHF). The heater surfaces were prepared using dual-stage electroplating, brush coating, sanding, and particle blasting, all featuring "practical" room temperature processes that do not require specialized equipment. Based on the obtained results, HFC-134a provided a better heat transfer performance through higher HTC and CHF values compared to HFO-1234yf at all tested surfaces and flow rates. While majority of the tested surfaces provided comparable HTC and modestly higher CHF values compared to the reference surface, one of the enhanced surfaces offered significant heat transfer enhancement. Advisors/Committee Members: Bostanci, Huseyin, Shenoda, Michael, Wang, Shuping.

Subjects/Keywords: Spray cooling; Enhanced surface; Critical heat flux (CHF); Heat transfer coefficient (HTC); refrigerants; Temperature; Pressure; Experiment; electronics.

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Altalidi, S. S. (2017). Two-Phase Spray Cooling with HFC-134a and HFO-1234yf for Thermal Management of Automotive Power Electronics using Practical Enhanced Surfaces. (Thesis). University of North Texas. Retrieved from https://digital.library.unt.edu/ark:/67531/metadc1011876/

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Chicago Manual of Style (16th Edition):

Altalidi, Sulaiman Saleh. “Two-Phase Spray Cooling with HFC-134a and HFO-1234yf for Thermal Management of Automotive Power Electronics using Practical Enhanced Surfaces.” 2017. Thesis, University of North Texas. Accessed January 24, 2021. https://digital.library.unt.edu/ark:/67531/metadc1011876/.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

MLA Handbook (7th Edition):

Altalidi, Sulaiman Saleh. “Two-Phase Spray Cooling with HFC-134a and HFO-1234yf for Thermal Management of Automotive Power Electronics using Practical Enhanced Surfaces.” 2017. Web. 24 Jan 2021.

Vancouver:

Altalidi SS. Two-Phase Spray Cooling with HFC-134a and HFO-1234yf for Thermal Management of Automotive Power Electronics using Practical Enhanced Surfaces. [Internet] [Thesis]. University of North Texas; 2017. [cited 2021 Jan 24]. Available from: https://digital.library.unt.edu/ark:/67531/metadc1011876/.

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

Council of Science Editors:

Altalidi SS. Two-Phase Spray Cooling with HFC-134a and HFO-1234yf for Thermal Management of Automotive Power Electronics using Practical Enhanced Surfaces. [Thesis]. University of North Texas; 2017. Available from: https://digital.library.unt.edu/ark:/67531/metadc1011876/

Note: this citation may be lacking information needed for this citation format:
Not specified: Masters Thesis or Doctoral Dissertation

.