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You searched for +publisher:"Kansas State University" +contributor:("Amy R. Betz"). Showing records 1 – 3 of 3 total matches.

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Kansas State University

1. Li, Nanxi. High-pressure pool boiling and physical insight of engineered surfaces.

Degree: PhD, Department of Mechanical and Nuclear Engineering, 2017, Kansas State University

Boiling is a very effective way of heat transfer due to the latent heat of vaporization. Large amount of heat can be removed as bubbles form and leave the heated surface. Boiling heat transfer has lots of applications both in our daily lives and in the industry. The performance of boiling can be described with two important parameters, i.e. the heat transfer coefficient (HTC) and the critical heat flux (CHF). Enhancing the performance of boiling will greatly increase the efficiency of thermal systems, decrease the size of heat exchangers, and improve the safety of thermal facilities. Boiling heat transfer is an extremely complex process. After over a century of research, the mechanism for the HTC and CHF enhancement is still elusive. Previous research has demonstrated that fluid properties, system pressures, surface properties, and heater properties etc. have huge impact on the performance of boiling. Numerous methods, both active and passive, have been developed to enhance boiling heat transfer. In this work, the effect of pressure was investigated on a plain copper substrate from atmospheric pressure to 45 psig. Boiling heat transfer performance enhancement was then investigated on Teflon© coated copper surfaces, and graphene oxide coated copper surfaces under various system pressures. It was found that both HTC and CHF increases with the system pressure on all three types of surfaces. Enhancement of HTC on the Teflon© coated copper surface is contributed by the decrease in wettability. It is also hypothesized that the enhancement in both HTC and CHF on the graphene oxide coated surface is due to pinning from micro and nanostructures in the graphene oxide coating or non-homogeneous wettability. Condensation and freezing experiments were conducted on engineered surfaces in order to further characterize the pinning effect of non-homogeneous wettability and micro/nano structure of the surface. Advisors/Committee Members: Amy R. Betz.

Subjects/Keywords: Pool boiling; High pressure; Wettability; Engineered surfaces

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APA (6th Edition):

Li, N. (2017). High-pressure pool boiling and physical insight of engineered surfaces. (Doctoral Dissertation). Kansas State University. Retrieved from http://hdl.handle.net/2097/35561

Chicago Manual of Style (16th Edition):

Li, Nanxi. “High-pressure pool boiling and physical insight of engineered surfaces.” 2017. Doctoral Dissertation, Kansas State University. Accessed January 24, 2021. http://hdl.handle.net/2097/35561.

MLA Handbook (7th Edition):

Li, Nanxi. “High-pressure pool boiling and physical insight of engineered surfaces.” 2017. Web. 24 Jan 2021.

Vancouver:

Li N. High-pressure pool boiling and physical insight of engineered surfaces. [Internet] [Doctoral dissertation]. Kansas State University; 2017. [cited 2021 Jan 24]. Available from: http://hdl.handle.net/2097/35561.

Council of Science Editors:

Li N. High-pressure pool boiling and physical insight of engineered surfaces. [Doctoral Dissertation]. Kansas State University; 2017. Available from: http://hdl.handle.net/2097/35561


Kansas State University

2. 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 (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

3. Van Dyke, Alexander Scott. Frost nucleation and growth on hydrophilic, hydrophobic, and biphilic surfaces.

Degree: MS, Department of Mechanical and Nuclear Engineering, 2015, Kansas State University

The purpose of this research was to test if biphilic surfaces mitigate frost and ice formation. Frost, which forms when humid air comes into contact with a surface that is below the dew point and freezing temperature of water, hinders engineering systems such as aeronautics, refrigeration systems, and wind turbines. Most previous research has investigated increasingly superhydrophobic materials to delay frost formation; however, these materials are dependent on fluctuating operating conditions and surface roughness. Therefore, the hypothesis for this research was that a biphilic surface would slow the frost formation process and create a less dense frost layer, and water vapor would preferentially condense on hydrophilic areas, thus controlling where nucleation initially occurs. Preferential nucleation can control the size, shape, and location of frost nucleation. To fabricate biphilic surfaces, a hydrophobic material was coated on a silicon wafer, and a pattern of hydrophobic material was removed using photolithography to reveal hydrophilic silicon-oxide. Circles were patterned at various pitches and diameters. The heat sink was comprised of two parts: a solid bottom half and a finned upper half. Half of the heat sink was placed inside a polyethylene base for insulation. Tests were conducted in quiescent air at room temperature, 22 °C, and two relative humidities, 30% and 60%. Substrate temperatures were held constant throughout all tests. All tests showed a trend that biphilic surfaces suppress freezing temperature more effectively than plain hydrophilic or hydrophobic surfaces; however, no difference between pattern orientation or size was noticed for maximum freezing temperature. However, the biphilic patterns did affect other aspects such as time to freezing and volume of water on the surface. These effects are from the patterns altering the nucleation and coalescence behavior of condensation. Advisors/Committee Members: Amy R. Betz.

Subjects/Keywords: Frost formation; Biphilic; Nucleation; Phase change heat transfer; Surface enhancement; Mechanical Engineering (0548)

…at Kansas State University, Manhattan, KS, was used to fabricate the mixed surfaces. A… …Kansas State University, where they were made biphilic. The silicon wafers were placed in a… 

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

APA (6th Edition):

Van Dyke, A. S. (2015). Frost nucleation and growth on hydrophilic, hydrophobic, and biphilic surfaces. (Masters Thesis). Kansas State University. Retrieved from http://hdl.handle.net/2097/19105

Chicago Manual of Style (16th Edition):

Van Dyke, Alexander Scott. “Frost nucleation and growth on hydrophilic, hydrophobic, and biphilic surfaces.” 2015. Masters Thesis, Kansas State University. Accessed January 24, 2021. http://hdl.handle.net/2097/19105.

MLA Handbook (7th Edition):

Van Dyke, Alexander Scott. “Frost nucleation and growth on hydrophilic, hydrophobic, and biphilic surfaces.” 2015. Web. 24 Jan 2021.

Vancouver:

Van Dyke AS. Frost nucleation and growth on hydrophilic, hydrophobic, and biphilic surfaces. [Internet] [Masters thesis]. Kansas State University; 2015. [cited 2021 Jan 24]. Available from: http://hdl.handle.net/2097/19105.

Council of Science Editors:

Van Dyke AS. Frost nucleation and growth on hydrophilic, hydrophobic, and biphilic surfaces. [Masters Thesis]. Kansas State University; 2015. Available from: http://hdl.handle.net/2097/19105

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