1,721,039 research outputs found
Applicability of silicon micro-finned heat sinks for 500× concentrating photovoltaics systems
No full textIn concentrating photovoltaic (CPV) applications, the sunlight is focused onto solar cells up to thousands of times and, without an adequate cooling system, the cell’s temperature can dangerously raise over the operating temperature range in few seconds. In this study, an investigation on micro-finned heat sink for high concentrating photovoltaics has been conducted. The geometry of the system and the choice of the components play an important role in the thermal management of CPV. The size of cell, as well as the optics, can strongly affect the thermal behaviour of the CPV: the effects of the CPV geometry on the thermal performance of the heat sink are experimentally investigated and discussed in order to design an optimised system for passive cooling. A micro-fin array is developed to handle the heat generated by the cell and the system is studied in different conditions to prove the applicability of this passive solution to the harsh CPV conditions. It has been found that micro-fins are a suitable solution for passive cooling at concentrations up to 500×. Moreover, this kind of solutions shows the potential to achieve high mass-specific power values, proving its competitiveness in mobile or tracked systems, such as CPV
Comparison of methods for estimating the solar cell temperature and their influence in the calculation of the electrical parameters in a HCPV module
Full text linkThe electrical parameters of a multi-junction solar cell are influenced by its operating temperature. Hence, the estimation of the cell temperature of a HCPV module is critical for its electrical characterization. However, measuring the cell temperature of a HCPV module is a complex task due to its unique features. This paper calculates the cell temperature in a HCPV module by using a number of methods to address this important issue. We conducted a comparative study of three methods used to estimate the cell temperature of a HCPV module: the Voc-Isc method, the thermal resistance method and the lineal method. The results show that all of the studied methods can be used to estimate cell temperatures with an acceptable margin of error
Thermal effectiveness and mass usage of horizontal micro-fins under natural convection
Full text linkIn recent times, the micro-technologies have gained prominence in various engineering applications. The micro-technologies are already in use for cooling purposes in several systems, but the information on the thermal performance of micro-fins under natural convective heat transfer conditions is yet limited. The correlations between heat transfer coefficients and fin geometry have already been investigated, but are not sufficient to optimize the design of the micro-finned arrays. For this reason, the present investigation gives an overview of micro-fins behavior taking into account, for the first time, different heat sink metrics: the fin effectiveness and the mass specific heat transfer coefficient. The results of an original experimental investigation are merged with the data available in literature. Natural convective micro-fins are able to achieve overall fin effectivenesses higher than 1.1. Even if not always beneficial in terms of heat transfer, micro-fins are found always positive in terms of the material usage. In this light, micro-fins can be considered advantageous in those applications that require a minimized weight of the heat sinks. Moreover, a limited effect due to the orientation is observed
Experimental comparison of micro-scaled plate-fins and pin-fins under natural convection
Full text linkThe presentwork analyses, for the first time, the heat transfer frompin micro-fins. The scope of the present paper is comparing thermal performance of plate micro-fin and pin micro-fin arrays under natural convection conditionsin air.Two fin geometries are considered: plate and pin fin arrayswith the same thermal exchanging surfaceare tested. The investigation shows that the pin micro-fins can improve the thermal performance compared toplate micro-fin arrays. Indeed, pin micro-fins are found to have higher heat transfer coefficients and lower thermalresistances, as well as a better material usage. This makes pin micro-fins able to achieve both thermal enhancementand weight reduction than plate micro-fins. The radiative heat transfer is also calculated: A new model to determine the radiative view factors of pin fins is proposed and is used in the analysis. The effect of the orientation is considered as well
General correlations among geometry, orientation and thermal performance of natural convective micro-finned heat sinks
Full text linkThe interest in micro-technologies has increased in the last decades, because of the low volumes and high performance granted by their application. Micro-fins can find application in several fields, such as power electronics, concentrating photovoltaics and LED. Although micro-technologies have been widely applied in cooling, there is still a lack of knowledge on the thermal behavior of micro-finned heat sinks under natural convective conditions. In the present study, the correspondences between fin geometries and heat transfer coefficients, as well as the effects of the orientation, are experimentally investigated using silicon micro-finned heat sinks with different geometries. The heat sinks are made of 5 cm × 5 cm squared silicon wafer and the fin height ranges between 0.6 mm and 0.8 mm, the spacing between 0.2 mm and 0.8 mm and the thickness between 0.2 and 0.8 mm. Power loads higher than those considered in previous works are studied. The experimental setup is validated using a software simulation and the Nusselt number correlation available in literature. The influence of the fin thickness on this parameter is analyzed and a modified correlation is proposed. Also, the effect of the radiative heat exchange on the overall heat transfer is considered and commented. An analysis of the uncertainty is conducted and reported too
Plate micro-fins in natural convection: An opportunity for passive concentrating photovoltaic cooling
Full text linkThe raise in temperature is a non-negligible issue for concentrating photovoltaics (CPV), where the sunlight is concentrated up to thousands of times and a large amount of heat is collected on the solar cells. Micro-fins have been identified as one of the most promising solution for CPV cooling: despite its potentials, the number of publications on this subject is still limited. The present paper resumes the state-of-the-art of the research on micro-fins, in order to identify the most convenient fin geometry for CPV applications. The results of the investigation conducted in this work show that, compared to a conventional heat sink, micro-fins can improve the thermal performance and, at the same time, lower the weight of a system. For this reason, they are particularly beneficial for tracked systems, such as CPV, where a reduced weight means a reduced load for the tracker. The heat transfer coefficients measured through an experimental setup are used to predict the performance of a micro-finned CPV system in natural convection: an optimized fin array is found able to enhance the mass specific power up to 50% compared to an unfinned surface
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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