ENCIT2012-347 UNSTEADY COMPRESSIBLE HEAT TRANSFER IN SUPERCRITICAL FLUIDS - PDF
Leonardo Santos de Brito Alves, UFF, Brazil
Abstract: We demonstrate that the currently accepted expression for the piston effect relaxation time is incorrect and obtain its correct form. Comparisons with results available in the literature are carried out for validation purposes. This discovery, reported here for the first time, has important consequences for the design of thermo-acoustic experiments.
Keywords:Piston Effect; Compressible Flow; Supercritical Fluids.
Presentation Schedule: Thursday, 14:40-15:00. Session: HMT3. Presenter: Leonardo Santos de Brito Alves.
ENCIT2012-279 HEAT CONDUCTION ANALYTICAL SOLUTIONS TO BE APPLIED IN BOUNDARY CONDITIONS OBTAINED FROM DISCRETE DATA - PDF
Ana Paula Fernandes, Gilmar Guimarães, UFU, Brazil
Abstract: Analytical solutions have varied uses. One is to provide solutions that can be used in verification of numerical methods. Another is to provide relatively simple forms of exact solutions that can be used in estimating parameters, thus, it is possible to reduce computation time in comparison with numerical methods. In this paper, an alternative procedure is presented. Here is used a hybrid solution based on Green's function and real characteristics (discrete data) of the boundary conditions.
Keywords:Heat conduction; analytical solutions; discrete data.
Presentation Schedule: Thursday, 14:20-14:40. Session: HMT3. Presenter: Ana Paula Fernandes.
ENCIT2012-049 EXPERIMENTAL EVALUATION OF THE CONVECTIVE AND THE CONJUGATE COOLING OF A PROTRUDING HEATER IN A DUCT - PDF
Bruna Rafaella Loiola, Carlos Alberto Carrasco Altemani, Unicamp, Brazil
Abstract: Experiments were performed to investigate the conjugate forced convection-conduction cooling of a protruding heater mounted on the lower (substrate) plate of a rectangular duct. The heater was an Aluminum rectangular block heated by means of electric power dissipation in an embedded resistance. Airflow was forced in the duct with the hydraulic diameter Reynolds number (ReD) in the range from 2,000 to 6,000. Effects of the substrate plate thermal conductivity on the heater conjugate cooling were obtained from measurements with two distinct plates: a Plexiglas plate and an Aluminum plate. The results were expressed in terms of the adiabatic Nusselt number (Nuad) and the conjugate coefficient (g+11), both as functions of ReD. The direct convective heat loss from the heater surfaces to the airflow was described by the adiabatic Nusselt number. The conjugate cooling, encompassing the heater direct convective loss to the airflow and the conduction loss to the substrate plate was described by a single conjugate coefficient g+11.
Keywords:conjugate heat transfer; adiabatic Nusselt number; conjugate coefficient; experimental investigation.
Presentation Schedule: Thursday, 15:20-15:40. Session: HMT3. Presenter: Bruna Rafaella Loiola.
ENCIT2012-010 STUDYING OF THERMAL CONTACT RESISTANCE AND UNCERTAINTY ANALYSIS IN THERMAL PROPERTIES ESTIMATION OF METALLIC MATERIALS - PDF
Luís Felipe dos Santos Carollo, Ana Lúcia Fernandes de Lima e Silva, Sandro Metrevelle Marcondes de Lima e Silva, FEI, Brazil
Abstract: A study of the thermal contact resistance and the uncertainty analysis that happens in the simultaneous estimation of thermal conductivity and volumetric heat capacity is presented. The purpose of performing this work is the lack of information in published papers when experimental procedures are carried out. Several experimental papers do not present these analyses, which are indispensable of the experimental viewpoint, and when these influences are taking into account, only values are presented; in other words, how the analyses were carried out and what method was used are not explained. So, the analyses in the present work are done in an one-dimensional experiment, where a symmetric assembly is applied. The sample is located between the resistive heater and the insulation. The thermal contact resistance is calculated by considering two influences: the first is the gap between the resistive heater and the sample, and the second is the kapton layer of the resistive heater. Good results are obtained in this analysis, because these influences result in a temperature difference around 0.2 ºC, which is equal to the uncertainty of the thermocouple. The uncertainty analysis is based on the uncertainty propagation procedure by pondering the thermal contact resistance, experimental, and numerical errors. The uncertanty analysis is satisfactory, because the obtained result is lower than 5 \%.
Keywords:thermal contact resistance; uncertainty analysis; thermal properties estimation; heat conduction.
Presentation Schedule: Thursday, 16:20-16:40. Session: HMT3. Presenter: Sandro Metrevelle Marcondes de Lima e Silva.
ENCIT2012-046 ENHANCEMENT OF THE CONVECTIVE COOLING OF TWO HEATERS IN A RECTANGULAR DUCT BY IMPINGING JETS - PDF
Ismael de Marchi Neto, Carlos Alberto Carrasco Altemani, Unicamp, Brazil
Abstract: A numerical investigation was performed to compare two alternative configurations for the convective air cooling of two heaters flush mounted on the lower horizontal wall of a rectangular duct. One configuration consisted of duct flow with uniform airflow velocity and temperature at the duct inlet and the heaters were located in the flow entrance region. In the other, the cooling was obtained by impinging air jets exiting with uniform velocity and temperature from two square holes on the upper duct wall just above the heaters. The simulations were performed under steady state conditions considering the three dimensional flow region of each configuration, where the conservation equations were solved. The results were presented in the form of the adiabatic Nusselt number and a dimensionless pressure drop for both configurations, in the range of the duct Reynolds number from 500 to 9,000.
Keywords:Impinging jets; convective cooling; flush heaters; forced convection; pumping power.
Presentation Schedule: Thursday, 15:40-16:00. Session: HMT3. Presenter: Ismael de Marchi Neto.
ENCIT2012-401 NUCLEATE BOILING OF HFE7100 ON NANOSTRUCTURED SURFACES - PDF
Reinaldo Rodrigues Souza, Elaine Maria Cardoso, Julio César Passos, UFSC, Brazil
Abstract: The aim of this study was to analyze the effect of nanostructured surfaces on the nucleate boiling of HFE7100, at saturation temperature and atmospheric pressure. The nanostructure investigated consisted of nanoparticles of maghemite, deposited on a copper disc substrate with two different roughness values. The results obtained with the nanostructure were compared with experimental results for the smooth and rough substrates. An increase in the heat transfer coefficient was observed for the substrate with maghemite deposition and for all gap sizes tested.
Keywords:Confined Nucleate Boiling; Nanostructures; Maghemite; Heat Transfer Coefficient.
Presentation Schedule: Thursday, 15:00-15:20. Session: HMT3. Presenter: Reinaldo Rodrigues de Souza.
ENCIT2012-324 ANALYSIS OF STEADY-STATE HEAT DISSIPATION IN SHORT HORIZONTAL RECTANGULAR FIN ARRAY - PDF
Vilson Altair Silva, Lorenzo Alfonso Caliari de Neves Gomes, Carlos Adriano Corrêa Ribeiro, Ana Lúcia Fernandes de Lima e Silva, Sandro Metrevelle Marcondes de Lima e Silva, FEI, Brazil
Abstract: In this work the process of heat transfer by natural convection was analyzed in rectangular finned heatsinks for different geometrical configurations. To study these configurations, different heatsinks were manufactured by varying the geometrical parameters fin spacing, height and number of fins. One essential parameter to be studied in heatsinks is the determination of the mean convection heat transfer coefficient, h. In order to obtain h, heatsinks were heated uniformly in their bottom surfaces and, through a system of data acquisition, the temperatures of the base and the top of the fin were measured in each heatsink. Several values of h were obtained over a temperature range between 20°C and 120°C. The results were compared with results obtained from empirical correlations found in literature. The results of h presented differences smaller than 5\% for some of the heatsinks. The temperature on the top of the fin was compared with the temperature obtained by numerical and analytical solutions. Furthermore, the temperature field in function of time was calculated numerically by using the commercial software ANSYS CFX12.0®. The temperature profiles, calculated numerically on the base and on the top of the fin, were compared with the experimental temperatures and the maximum difference was lower than 2\%.
Keywords:Heatsinks; Convection Heat Transfer Coefficient; Natural Convection; CFX; Experimental and Numerical Methods.
Presentation Schedule: Thursday, 16:00-16:20. Session: HMT3. Presenter: Vilson Altair da Silva.