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Raquel da Cunha Ribeiro da Silva

Bio: Raquel da Cunha Ribeiro da Silva is an academic researcher from State University of Campinas. The author has contributed to research in topics: Nusselt number & Frost. The author has an hindex of 1, co-authored 6 publications receiving 38 citations.

Papers
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Journal ArticleDOI
TL;DR: In this article, the authors presented the results of a numerical study validated by experimental measurements on the solidification of PCM along a horizontal tube by using the boundary immobilization technique.

49 citations

Journal ArticleDOI
TL;DR: In this article, an experimental and numerical investigation where the emphasis was placed on obtaining empirical correlation for the Nusselt number was carried out, and some experimental results of the frost thickness around every cylinder in a triangular arrangement are presented, an estimated experimental correlation to find Nusselst number.
Abstract: An experimental study was reported earlier on the development of frost formation by humid flow passing over the cylinder. In this study, dimensionless correlations used in previous experimental data, and reported empirical correlations of the Nusselt number, were used. This paper reports results of an experimental and numerical investigation where the emphasis was placed on obtaining empirical correlation for the Nusselt number. In this work some experimental results of the frost thickness around every cylinder in a triangular arrangement are presented, an estimated experimental correlation to find Nusselt number. This correlation is based on the experimental measurements in a wind tunnel situated in the Laboratory of Thermal storage and Fluids in the Mechanical Engineering Faculty at Unicamp. A numerical study is performed to study the frost formation in the cylindrical system.

1 citations

Journal ArticleDOI
14 Aug 2013
TL;DR: In this article, the authors evaluated numerically some of the parameters involved in modeling the process of frost formation over a cold cylinder surface subject to the flow of humid air, and employed a one-dimensional transient formulation based upon the local volume averaging technique.
Abstract: This paper evaluates numerically some of the parameters involved in modeling the process of frost formation over a cold cylinder surface subject to the flow of humid air. The model employs one-dimensional transient formulation based upon the local volume averaging technique. Was utilized for numerical predictions the empirical Nusselt correlation from the literature, obtained in experimental studies on frost formation phenomena of frost grow over a cold cylinder surface. To predict frosting process a numerical solution was utilized, and a new correlation for Nusselt number based on the experimental correlation of Kim was estimated. For the new Nusselt correlation an optimization method that adjusts the numerical solution of modeling the frost formation process with experimental results of the frost layer thickness was used. The calculation procedure allows the estimation of the parameter K of equation. The modeling process was validated by comparison with available experimental data.
Journal ArticleDOI
TL;DR: In this paper , a numerical experimental analysis was performed to understand the formation process of porous ice in flat plates with different surface treatments and parameters, and the results showed that application of a coating allowed a significant reduction on the frost formation process contributing to the improvement of thermal efficiency and performance of refrigeration systems.
Abstract: The frost growth on cold surfaces in evaporators is an undesirable phenomenon which becomes a problem for the thermal efficiency of the refrigeration systems because the ice layer acts as a thermal insulation, drastically reducing the rate of heat transfer in the system. Its accumulation implies an increase in energy demand and a decrease in the performance of various components involved in the refrigeration process, reducing its efficiency and making it necessary to periodically remove the frost, resulting in expenses for the defrost process. In the present work, a numerical-experimental analysis was performed in order to understand the formation process of porous ice in flat plates with different surface treatments and parameters. This understanding is of utmost importance to minimize the formation of porous ice on cold surfaces and improve equipment efficiency and performance. In this context, a low-cost experimental apparatus was developed, enabling an experimental analysis of the phenomenon under study. The environmental conditions evaluated are the temperature of the cold surface, room temperature, humidity, and air velocity. The material of the surfaces under study are aluminum, copper, and brass with different surface finishes, designated as smooth, grooved (hydrophilic), and varnished (hydrophobic). The numerical-experimental analysis demonstrates measurements and simulations of the thickness, surface temperature, and growth rate of the porous ice layer as a function of the elapsed time. The numerical results were in good agreement with the experimental results, indicating that the varnished surface, with hydrophobic characteristics, presents greater difficulty in providing the phenomenon. Therefore, the results showed that application of a coating allowed a significant reduction on the frost formation process contributing to the improvement of thermal efficiency and performance of refrigeration systems.
Journal ArticleDOI
TL;DR: In this paper, a new correlation for Nusselt number based on the experimental correlation of Kim was estimated, and an optimization method that adjusts the numerical solution of modeling the frost formation process with experimental results of the frost layer thickness was used.
Abstract: This paper evaluates numerically some of the parameters involved in modeling the process of frost formation over a cold cylinder surface subject to the flow of humid air. Was utilized for numerical predictions the empirical Nusselt correlation from the literature, obtained in experimental studies on frost formation phenomena of frost grow over a cold cylinder surface. To predict frosting process a numerical solution was utilized, and a new correlation for Nusselt number based on the experimental correlation of Kim was estimated. For the new Nusselt correlation an optimization method that adjusts the numerical solution of modeling the frost formation process with experimental results of the frost layer thickness was used. The calculation procedure allows the estimation of the parameter K of equation. The modeling process was validated by comparison with available experimental data.

Cited by
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Journal ArticleDOI
TL;DR: In this paper, the effect of number of inner tubes as a geometrical parameter during charging process was investigated and the consequences of increasing operational parameters including the HTF mass flow rate and inlet temperature were studied.

154 citations

Journal ArticleDOI
TL;DR: In this paper, the authors assumed that there is no slip velocity between nanoparticles and paraffin and used FVM to show the treatment of NEPCM during melting and for verification, previous article was tested.

151 citations

Journal ArticleDOI
TL;DR: In this article, a comprehensive review of cold storage technologies using solid-liquid phase change materials is presented, and the key issues to be solved in further research on cold storage technology are proposed.

100 citations

Journal ArticleDOI
TL;DR: In this paper, a comparative thermal performance assessment is reported for vertical and horizontal orientation of shell and tube type Latent Heat Storage Unit (LHSU) using stearic acid (melting point of 55.7-56.6°C) and water as Heat Transfer Fluid (HTF).
Abstract: A comparative thermal performance assessment is reported for vertical and horizontal orientation of shell and tube type Latent Heat Storage Unit (LHSU) using stearic acid (melting point of 55.7–56.6 °C) as Phase Change Material (PCM) and water as Heat Transfer Fluid (HTF). Total 45 thermocouples are used in radial, axial and angular directions to measure the temperature distribution in the PCM. In horizontal LHSU, temperature in the upper half of the horizontal diametric plane reaches the melting point faster due to natural convection. As a result, the upper half melts earlier than the lower half. In order to demonstrate the motion of solid-liquid interface, liquid fraction contours are presented. For vertical LHSU, melting front moves in a conical fashion around the vertical plane with faster melting at upper axial locations. Experimental analysis suggests that horizontal LHSU is better for part load operation as compared to vertical LHSU, as it requires lesser time to melt half of the PCM mass. Energy storage/retrieval rate during melting and solidification is also compared for both the LHSU configurations.

73 citations

Journal ArticleDOI
TL;DR: An attempt is made to assess the performance of multiple PCM based thermal storage systems by carrying out a comprehensive review of available literature on the topic.
Abstract: Latent heat thermal storage (LHTS) systems employing phase change materials (PCMs) offer several advantages compared to sensible heat storage units. However, they exhibit an inherent poor thermal performance owing to poor heat transfer, poor thermal conductivity of PCMs, and so on. Methods such as replacing single PCMs with multiple PCMs, addition of fins, micro/macro/nano-encapsulated composite PCMs and dispersion of high conductivity particles to PCMs have been suggested and studied in the past by different authors as a means for performance enhancement of LHTS systems. While extensive literature is available on the last three methods, studies on multiple PCMs are very limited. It is rather difficult at this stage to conclude on the benefits and merits/demerits of the method, given the limited data available in the open literature. Therefore, there is a need for consolidation and compilation of the existing literature to understand and assess the performance of LHTS units operating with multiple PCMs. An attempt is made in this paper to assess the performance of multiple PCM based thermal storage systems by carrying out a comprehensive review of available literature on the topic. Studies have evinced that single PCM units replaced with multiple PCMs offered superior performance with enhanced charging/discharging rates and better energy/exergy efficiencies. Also, past investigations reveal optimal melting temperatures of PCMs, optimal melting temperature difference between PCMs, optimal mass and so on to obtain an optimal performance of multiple PCM systems. Relevant published data were compared and discussed to understand the research trend over the years. Discussions were extended covering the challenges involved with multiple PCMs highlighting the scope for further research. An overall summary based on the survey has been presented for a concise understanding of key findings published in the open literature.

65 citations