Eventos Anais de eventos
ENCIT 2022
19th Brazilian Congress of Thermal Sciences and Engineering
Nucleate pool boiling of Carbon Dioxide on a horizontal and vertical surface
Submission Author:
Rafael Boschini Albuquerque Passarella , SC
Co-Authors:
Rafael Boschini Albuquerque Passarella, Thaís Ferreira, Adonis Menezes, Júlio Passos
Presenter: Júlio Passos
doi://10.26678/ABCM.ENCIT2022.CIT22-0676
Abstract
The nucleate boiling has as main characteristic the transfer of high heat fluxes to small temperature differences between the heating surface and the refrigerant fluid. This makes it possible to design heat exchangers with smaller dimensions due to the high heat transfer coefficients. As an example, the flooded evaporators used in the refrigeration and air conditioning industry can be mentioned. Carbon dioxide (CO2) - when treated as a refrigerant fluid is called R-744 - is a natural, abundant, inexpensive, non-toxic and non-flammable fluid, which is harmful to health only at high concentrations (above 1000 ppm in air). After the Vienna Convention (in 1987) and the increasingly concern with the damage caused by the CFCs on the Ozone layer, the Montreal Protocol was created, pressing member countries to progressively eliminate the use of substances that may damage this layer. In this context, CO2 resurged as an alternative to the synthetic refrigerants, because it not only has zero Ozone Depletion Potential (ODP) and negligible Global Warming Potential (GWP), but if obtained through the Carbon Capture and Storage (CCS) technique, its use can alleviate the effect of fossil fuels to the global warming. However, experimental data for nucleate boiling are scarce in the open literature. Thus, in order to comprehend the behavior of carbon dioxide (working fluid) during nucleate boiling, this study will present experimental results concerning the heat transfer coefficient during nucleate pool boiling on the end of a copper block horizontally and vertically oriented. Power is supplied to the copper block and to the test section, at the end of the copper block in contact with the pool liquid, by means of two cartridge electrical resistances of 10 ohms each, embedded in the copper block. The dimensions of the end surface of the copper block are 10 mm width and 30 mm height, when vertically oriented. Using the Fourier law and measuring nine points of temperature in the copper block, at three plan cross sections, at different distances from the end, and three points per section, the temperature of the test section was calculated and the boiling curve plotted. Test conditions include a pressure of 28 bar and heat fluxes from 1.26 kW/m² to the critical heat flux. The experimental heat transfer coefficient and critical heat flux are compared with values predicted by models in the literature.
Keywords
pool boiling, Nucleated Boiling, Carbon dioxide, R744 (CO2)
