1,720,968 research outputs found
Energy performance of water strip modules for industrial heating in real operation conditions: Steady-state and CFD analyses
Full text linkThe objective of this study is the theoretical evaluation of the energy performance of a radiant strips heating system fed with hot water by varying the operating conditions. First, the convective coefficients and the heating power (both convective and radiant parts) of the heating system are evaluated in steady-state conditions by simulating heat exchange similar to real operating conditions (such as the presence of a ventilation system, the opening of doors, windows, or skylights, etc.), in comparison with the nominal data. To carry out this preliminary assessment, different references in the scientific literature are considered with respect to experimental measurements and numerical simulations for similar applications. The steady-state analysis revealed that the increase in the overall yield of the heating strips, compared to the data measured according to the EN 14,037 standard, is in the order of 30%. Afterward, a CFD analysis is reported to dynamically study the effect of the above-mentioned typical situations of real operation of the system in industrial sheds. The CFD analysis confirms that the presence of constant air exchange leads to an improvement of more than 30% in the performance of the water strip system. The main conclusion is that designing the water strip system following the EN 14,037 standard probably will oversize the industrial heating plant
Numerical analysis of the effects of the structure shape and orientation of kelvin cell porous structures during air forced convection
Full text linkIn recent years, in order to counteract the growth of environmental pollution and the contemporary scarcity of various energy sources, researchers have proposed innovative and efficient solutions for heat transfer applications. Extended surfaces, which can involve the use of fins, open cell metal foams, etc., have been demonstrated to be promising solutions. Open cell metal foams consist of structs intersecting at nodes resulting in stochastic oriented cells. Periodic metal foams have also attracted great interest. These structures are made of a single cell unit periodically replicated. Kelvin cells and Weaire–Phelan ones are two conventional elementary unit cells. In this paper, a numerical model is developed and validated, aiming at analysing the thermal and hydraulic behaviors of modified Kelvin cell-based metal foams during air forced convection. Constant porosity (0.9) and pore density (40 PPI) were adopted. Five different geometrical configurations (one cylindrical and four elliptical) and four orientations (0–15–30–45◦ ) of the struts with respect to the main air flow direction were investigated. The inlet air velocities varied between 0.5 and 4 m s−1 . Interesting results were obtained and discussed in terms of pressure drops, heat transfer coefficients, and pumping power per area density
Thermal storage based on phase change materials (PCMs) for refrigerated transport and distribution applications along the cold chain: A review
Full text linkFoodstuff has to be transported from where it is produced or packaged to the market. It is important to control the temperature and humidity of the delivered food to minimize the waste and ensure customer satisfaction. At the same time, unfortunately, the transport sector is among the polluting sectors. Therefore, innovative solutions have been proposed such as the adoption of Latent Thermal Energy Storage (LTES) systems based on Phase Change Materials (PCMs) to control the food temperature. Such systems minimize the fuel consumption and thereby reduce the emission. LTES systems rely on the phase change process to absorb and store heat in a more sustainable way while ensuring a nearly constant temperature for the foodstuff while being transported. Hence, we first present a general overview of the application of PCMs at low temperatures. Then, the literature on the adoption of PCMs in the refrigerated transport sector is critically surveyed. Different proposals offered in the literature..
Does COVID-19 Impact Less on Post-stroke Aphasia? This Is Not the Case
Full text linkBackground: The coronavirus disease 2019 (COVID-19) pandemic has greatly affected people’s mental health resulting in severe psychological consequences. One of the leading causes of long-term disability worldwide is aphasia. The language changes experienced by a person with aphasia (PWA) often have a sudden and long-lasting negative impact on social interaction, quality of life, and emotional wellbeing. The main aim of this study was to investigate the impact of COVID-19 on the different psychosocial dimensions which affect PWA. Methods: This retrospective study included 73 PWA and 81 elderly matched controls. All patients were in the chronic phase. They were all discharged from rehabilitation services, which left them with different degrees of language deficits (i.e., severe vs. mild vs. moderate). All participants were administered the hospital anxiety and depression scale (HADS) through an online survey. PWA also took part in the stroke and aphasia quality of life scale questionnaire (SAQOL-39). Results: Although the comparison between two different time points [one month before (T0) and one month after the lockdown (T1)] led to a significant increase in depression and anxiety symptoms in both groups (PWA vs. control), lower rates of depression and anxiety were found in PWA compared to the healthy group. Significant deterioration was also present in PWA in the communication and psychosocial scales of the SAQOL-39 test, which correlated with the observed changes in the psychological domains. Interestingly, the results were not significantly influenced by the degree of aphasia severity. Similarly, in both groups, none of the demographic variables (gender, age, and educational level) significantly affected the scores in the different subscales. Conclusions: This evidence which, at first glance, seems to suggest that PWA have been partially spared from the impact of COVID-19, actually masks a dramatic situation that has always characterized this population. Indeed, given that PWA already live in a state of social isolation and emotional instability, these conditions might have, paradoxically, limited the effects of the coronavirus. However, as our results showed a deterioration in the emotional state and communication skills of our patients, possible solutions are discussed in order to prevent further decline of their cognitive abilities
Approximate and CFD energy performance analyses of industrial heating by water strip modules – Part 1
Full text linkCFD analyses for the development of an innovative latent thermal energy storage for food transportation
Full text linkThe transportation of perishable products is a crucial activity that must be carefully managed along the cold chain. The refrigerated transport aims at ensuring the suitable transportation conditions by maintaining the desired temperature level in the refrigerated compartment. Moreover, the carriage of perishable fresh foodstuffs calls for additional precautions due to the intrinsic metabolic activity of fresh foods which causes them to be highly temperature sensitive. About 30% of fresh products perishes on the route due to the loss of suitable temperature values. Recently, scientists have been focusing their efforts on the development of innovative solutions, which ensure a proper refrigerated products distribution and transportation in a more environmental-friendly and cost-effective way. Hence, in this work, a novel concept of a Latent Thermal Energy Storage (LTES) system consisting of an insulation layer of poly-urethane foam wrapping a second one of Phase Change Material (PCM) is proposed. In particular, the thermal performance is investigated by running numerical CFD analyses in Ansys Fluent. The effect of different product loads (25%-50%-75%) is studied. Besides, the contributions of the heat respiration and diverse food pre-cooling temperatures on the system performance are also analysed. For the long-distance route no door openings nor additional heat infiltrations are considered
3D numerical simulation of a novel ventilated roof: thermal performance analysis and fluid flow behavior
No full textThis paper presents a numerical simulation of a ventilated roof based on a novel plastic support especially designed to reduce the solar heat gains by improving the airflow distribution as compared to a traditional one. In order to evaluate the benefits of the new configuration, a 3 D numerical model was developed allowing for a deep understanding of the airflow distribution inside the ventilated roof channels. The simulations were performed by varying the solar irradiance from 600 to 1000 W m−2 assuming buoyancy-driven airflow. The investigation was conducted by comparing the new proposed ventilated roof assembly to the traditional layouts. In particular, two roof types were considered as benchmarks: an insulated roof and a non-insulated one. When compared to the traditional ones, the results revealed that the innovative ventilated roof led to a great reduction (up to 70%) of the total amount of solar heat gains for all the simulated scenarios
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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