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| Author(s): |
Daniel Felipe Sempértegui Tapia
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | São Carlos. |
| Institution: | Universidade de São Paulo (USP). Escola de Engenharia de São Carlos (EESC/SBD) |
| Defense date: | 2016-03-23 |
| Examining board members: |
Gherhardt Ribatski;
Jader Riso Barbosa Junior;
José Maria Saiz Jabardo;
Alexandre Kupka da Silva;
Jurandir Itizo Yanagihara
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| Advisor: | Gherhardt Ribatski |
| Abstract | |
The present thesis concerns an experimental study on the effects of cross-sectional geometry and low GWP refrigerants on the thermal-hydraulic performance for convective boiling inside micro-scale channels. Experimental results for heat transfer coefficient and pressure drop gradient during convective boiling were obtained for circular, square and triangular channels for the fluid R134a. The evaluated channels present the same external perimeter and equivalent diameters of 1.1, 0.977 and 0.835 mm, respectively. In the case of the circular geometry, experimental results were also acquired for the HFOs R1234ze(E) and R1234yf and the hydrocarbon R600a (isobutane), which are fluids with low GWP and null ODP. Experiments were performed for a wide range of heat fluxes and mass velocities, saturation temperatures of 31 and 41°C and vapor qualities up to 0.95. The experimental data were carefully analyzed and discussed based on a parametrical analysis focusing on the effect of the cross-sectional geometry and the working fluid. Subsequently, the experimental data were compared against the most quoted predictive methods from literature. In general, it was verified that none of the predictive methods were able to accurately capture the experimental trends of the overall database. So, new predictive methods for the pressure drop and heat transfer coefficient were developed based on the broad database obtained in the present study. The proposed methods provided satisfactory results not only for the experimental database used for its development, but also for independent databases collected in the literature. Additionally, based on the data obtained in the present study and a performance analysis taken into account pressure drop, heat transfer coefficient and the channel packing factor, triangular cross sectional geometry is recommended for heat sinks. (AU) | |
| FAPESP's process: | 10/17605-4 - Experimental analysis of the effect of the microchannel geometry on the two-phase flow pattern, heat transfer coefficient and pressure drop during convective boiling. |
| Grantee: | Daniel Felipe Sempértegui Tapia |
| Support Opportunities: | Scholarships in Brazil - Doctorate |