1,720,958 research outputs found
Filtered reciprocity functional approach to estimate internal heat transfer coefficients in 2D cylindrical domains using infrared thermography
No full textPerformance estimation of heat exchanger apparatuses requires a proper knowledge of the thermo-fluid dynamic interaction between fluid and device. One of the aspects to take into account is related to the estimation of the internal convective heat transfer coefficient. This requires the knowledge of the internal temperature and the internal wall heat flux, although these quantities are complicated to be measured. Therefore, the use of inverse problem techniques may be very useful for estimating these quantities. This approach deals with the estimation of the local internal properties, given some external temperature measurements, possibly by means of contactless experimental methodologies (i.e. infrared camera imaging). The solution strategy here presented, for a 2D model, is based on the Reciprocity Functional approach (RF), which requires the solution of two auxiliary problems that are solved, in this paper, by means of the Classical Integral Transform Technique (CITT). The RF approach coupled with CITT, presents some advantages over other techniques since its solution is completely analytical and therefore computationally fast, and it does not require any numerical simulation. Moreover, it deals with the noise content of the experimental data, filtering it and overcoming the documented limits of the classical RF approach. This original method, named Filtered Reciprocity Functional (FRF) approach, was applied to different test cases using simulated measurements, and the results were compared to both the exact and the reconstruct solutions obtained by the Truncated Singular Value Decomposition (TSVD) method, showing a good agreement. Finally, the FRF approach was applied to an experimental case in order to test its robustness when dealing with real data
Local heat flux estimation inside tubes through conjugate gradient method with adjoint operator: application to the pulsating heat pipes case
No full textPurposeThe purpose of this paper is to apply the conjugate gradient (CG) method, together with the adjoint operator (AO) to the pulsating heat pipe problem, including some quite interesting experimental results. The CG method, together with the AO, was able to estimate the unknown functions more efficiently than the other techniques presented in this paper. The estimation of local heat transfer coefficients, rather than the global ones, in pulsating heat pipes is a relatively new subject and presenting a robust, efficient and self-regularized inverse tool to estimate it, supported also by some experimental results, is the main purpose of this paper. To also increase the visibility and the general use of the paper to the heat transfer community, the authors include, as supplemental material, all numerical and experimental data used in this paper. Design/methodology/approachThe approach was established on the solution of the inverse heat conduction problem in the wall by using as starting data the temperature measurements on the outer surface. The procedure is based on the CG method with AO. The here proposed approach was first verified adopting synthetic data and then it was validated with real cases regarding pulsating heat pipes. FindingsAn original fast methodology to estimate local convective heat flux is proposed. The procedure has been validated both numerically and experimentally. The procedure has been compared to other classical methods presenting some peculiar benefits. Practical implicationsThe approach is suitable for pulsating heat pipes performance evaluation because these devices present a local heat flux distribution characterized by an important variation both in time and in space as a result of the complex flow patterns that are generated in this type of devices. Originality/valueThe procedure here proposed shows these benefits: it affords a general model of the heat conduction problem that is effortlessly customized for the particular case, it can be applied also to large datasets and it presents reduced computational expense
Internal heat transfer coefficient estimation in three-dimensional ducts through the reciprocity functional approach - An analytical approach and validation with experimental data
No full textIn the current paper it is presented and tested an innovative method for estimating internal heat transfer coefficients in ducts adopting only thermal measurements acquired on the external wall surface. This approach is based on the reciprocity functional analysis, which is a powerful non-intrusive inverse problem technique. The adoption of this technique is promising since it avoids intrusive measurements, it is fully non-iterative and the computational time and cost are very limited. In this paper, it is presented an extension of the classical reciprocity functional methodology in the sense that a fully analytical expression, obtained by the integral transform technique, is developed for estimating the internal heat transfer coefficient in a three-dimensional problem. Such methodology, avoiding the solution of linear systems, reduces the computational costs that are massive when the traditional approaches are applied to three dimensional problems. The proposed procedure is first validated adopting synthetic temperature data and then tested using real temperature measurements acquired by an infrared camera. The results highlight that the methodology is able to recover the unknown functions in a very short computational time with a good accuracy
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Characterisation of the heat transfer in displaced enhancement devices by means of inverse problem approach applied to IR images
No full textDisplaced enhancement devices are inserts positioned inside pipes that increase the heat transfer rate. This study presents an original application of an inverse analysis technique to experimental infrared temperature data to estimate the local convective heat flux for forced convection flow in a pipe in which this kind of device is present. Butterfly-shaped inserts have been investigated to determine their local and global thermal performance. The insert produces a distortion in the velocity profile that causes an irregular distribution of the wall heat flux along the circumferential coordinate. Several studies have investigated displaced enhancement devices, but they generally considered only the overall heat transfer performance. The present work aims to fill this gap by presenting and testing an experimental procedure for estimating the local convective heat flux in pipes equipped with this type of insert. The experimental results obtained in the present investigation are useful for the design of heat exchangers for processes in which product temperature must be carefully controlled (e.g. pharmaceutical and food industries). These types of devices induce significant spatial variation of the heat flux, and quantitative data of this aspect is of primary importance
Variations on the Author
Get PDF“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
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
- …
