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Improvements in miniaturization and boosting the thermal performance of energy conservation systems call for innovative techniques to enhance heat transfer. Heat transfer enhancement methods have attracted a great deal of attention in the industrial sector due to their ability to provide energy savings, encourage the proper use of energy sources, and increase the economic efficiency of thermal systems. These methods are categorized into active, passive, and compound techniques. This article reviews recent passive heat transfer enhancement techniques, since they are reliable, cost-effective, and they do not require any extra power to promote the energy conversion systems’ thermal efficiency when compared to the active methods. In the passive approaches, various components are applied to the heat transfer/working fluid flow path to improve the heat transfer rate. The passive heat transfer enhancement methods studied in this article include inserts (twisted tapes, conical strips, baffles, winglets), extended surfaces (fins), porous materials, coil/helical/spiral tubes, rough surfaces (corrugated/ribbed surfaces), and nanofluids (mono and hybrid nanofluids).

To investigate the impacts of using nano-enhanced phase change materials on the thermal performance of a borehole heat exchanger in the summer season, a three-dimensional numerical model of a borehole heat exchanger is created in the present work. Seven nanoparticles including Cu, CuO, Al2O3, TiO2, SiO2, multi-wall carbon nanotube, and graphene are added to the Paraffin. Considering the highest melting rate and lowest outlet temperature, the selected nano-enhanced phase change material is evaluated in terms of volume fraction (0.05, 0.10, 0.15, 0.20) and then the shape (sphere, brick, cylinder, platelet, blade) of its nanoparticles. Based on the results, the Paraffin containing Cu and SiO2 nanoparticles are found to be the best and worst ones in thermal performance improvement, respectively. Moreover, it is indicated that the increase in the volume fraction of Cu nanoparticles could enhance markedly the melting rate, being 0.20 the most favorable value which increased up to 55% the thermal conductivity of the nano-enhanced phase change material compared to the pure phase change material. Furthermore, the blade shape is by far the most appropriate shape of the Cu nanoparticles by considering about 85% melting of the nano-enhanced phase change material.

In this numerical study, 4 types of hybrid nanofluid, including Ag-MgO/water, TiO2-Cu/water, Al2O3-CuO/water, and Fe3O4-multi-wall carbon nanotube/water, have been considered potential working fluid in a single U-tube borehole heat exchanger. The selected hybrid nanofluid is then analyzed by changing the volume fraction and the Reynolds number. Based on the numerical results, Ag-MgO/water hybrid nanofluid is chosen as the most favorable heat carrier fluid, among others, considering its superior effectiveness, minor pressure drop, and appropriate thermal resistance compared to the pure water. Moreover, it was indicated that all cases of Ag-MgO/water hybrid nanofluid at various volume fractions (from 0.05 to 0.20) and Reynolds numbers (from 3200 to 6200) could achieve better effectiveness and lower thermal resistances, but higher pressure drops compared to the corresponding cases of pure water. Nevertheless, all the evaluated hybrid nanofluids present lower coefficient of performance (COP)-improvement than unity which means that applying them as working fluid is not economically viable because of having higher pressure drop than the heat transfer enhancement.

PurposeThis study aimed at developing and testing a model to evaluate employee performance in Isfahan municipality.Design/methodology/approachA mixed-method design is applied in this study. To extract the model, a semi-structured interview based on the thematic analysis approach was employed. The qualitative data were obtained using a researcher-made questionnaire from a sample of 12 municipal experts selected based on purposive sampling. In the quantitative phase, the sample consisted of 76 managers and interim managers. The validity of the questionnaire was determined by the content validity index, while the structural validity was tested based on structural equation modeling using SmartPLS software. The reliability of the questionnaire was confirmed using Cronbach's alpha and composite reliability indices.FindingsThe factors obtained in the qualitative model included performance evaluation criteria, the desired time interval for performance evaluation, results announcement, performance evaluation approach, performance evaluation method and evaluator-related variables. There should have been an agreement between evaluators and those who were evaluated in all components of the model. In the quantitative section, performance evaluation criteria, evaluators, the evaluation method and time interval were confirmed with coefficients of 0.871, 0.815, 0.646 and 0.615, respectively.Practical implicationsThe novelty of this study is that it uses a mixed-method research approach to extract a performance evaluation model that is specific to the Isfahan municipality.Originality/valueThe novelty of this study is that it uses a mixed-method research approach to extract a performance evaluation model that is specific to the Isfahan municipality.

The present work deals with modeling coating characteristics of yttria-stabilized zirconia such as deposition efficiency, adhesion strength, surface roughness, and hardness in plasma spray process. Here, the process factors are input power, primary gas flow rate, stand-off distance, powder feed rate, and carrier gas flow rate. Firstly, a number of 32 experiments were conducted based on rotatable central composite design of experiments. Then, adaptive neuro-fuzzy inference system was used to correlate mapping relationships between plasma spray factors and mentioned coating properties. After examination of various network structures, results showed that the one with a number of two triangular membership function predicts the coating properties with the lowest root mean square error. Therefore, the developed model was used to determine the effect of plasma spray factors on mentioned characteristics according to graphs which were plotted through the proposed model.

Like other manufacturing processes, plasma spraying also has a non-linear behavior due to contribution of many coating parameters. This characteristic makes finding optimal factor combination difficult. Hence, the problem can be solved through effective and strategic statistical methods integrated with systematic experimental data. The purpose of this paper is to study the tribological and mechanical performance of coated surface deduced by plasma spraying process. Taguchi experimental design and analysis of variances (ANOVA) were used to investigate the influence of plasma spraying factors (spraying layers, accelerating voltage, arc current, travel speed, stand-off distance, powder feed rate, carrier gas flow rate, and primary gas flow rate) on oxidant percent and hardness. To find optimal combination of factors to reach maximum oxidation and hardness, gray relational analysis (GRA) coupled with principal component analysis (PCA) are applied on experimental data. Here, the PCA is used to find the most appropriate weighing factors necessary for construction gray relational grade. Results indicated that stand-off-distance is the most significant factor having the greatest influence on gray relational grade, followed by powder feed rate, traverse speed, spraying layers, and primary gas flow rate. Furthermore, GRA coupled with PCA can effectively acquire the optimal combination of plasma spraying parameters and the proposed approach can be a useful tool to increase the coating performance.

Spinal cord injury (SCI) is a critical neurological condition that may impair motor, sensory, and autonomous functions. At the cellular level, inflammation, impairment of axonal regeneration, and neuronal death are responsible for SCI-related complications. Regarding the high mortality and morbidity rates associated with SCI, there is a need for effective treatment. Despite advances in SCI repair, an optimal treatment for complete recovery after SCI has not been found so far. Therefore, an effective strategy is needed to promote neuronal regeneration and repair after SCI. In recent years, regenerative treatments have become a potential option for achieving improved functional recovery after SCI by promoting the growth of new neurons, protecting surviving neurons, and preventing additional damage to the spinal cord. Transplantation of cells and cells-derived extracellular vesicles (EVs) can be effective for SCI recovery. However, there are some limitations and challenges related to cell-based strategies. Ethical concerns and limited efficacy due to the low survival rate, immune rejection, and tumor formation are limitations of cell-based therapies. Using EVs is a helpful strategy to overcome these limitations. It should be considered that short half-life, poor accumulation, rapid clearance, and difficulty in targeting specific tissues are limitations of EVs-based therapies. Hydrogel-encapsulated exosomes have overcome these limitations by enhancing the efficacy of exosomes through maintaining their bioactivity, protecting EVs from rapid clearance, and facilitating the sustained release of EVs at the target site. These hydrogel-encapsulated EVs can promote neuroregeneration through improving functional recovery, reducing inflammation, and enhancing neuronal regeneration after SCI. This review aims to provide an overview of the current research status, challenges, and future clinical opportunities of hydrogel-encapsulated EVs in the treatment of SCI.

In this study Fe (III)-doped TiO 2 nanoparticles were synthesized by sol–gel method at two atomic ratio of Fe/Ti, 0.006 and 0.034 percent. Then the photoactivity of them was investigated on degradation of phenol under UV (<380 nm) irradiation and visible light (>380 nm). Results showed that at appropriate atomic ratio of Fe to Ti (% 0.034) photoactivity of Fe(III)–doped TiO 2 nanoparticles increased. In addition, the effects of various operational parameters on photocatalytic degradation, such as pH, initial concentration of phenol and amount of photocatalyst were examined and optimized. At all different initial concentration, highest degradation efficiency occurred at pH = 3 and 0.5 g/L Fe(III)–doped TiO 2 dosage. With increase in initial concentration of phenol, photocatalytic degradation efficiency decreased. Photoactivity of Fe (III)-doped TiO 2 under UV irradiation and visible light at optimal condition (pH = 3 and catalyst dosage = and 0.5 g/L) was compared with P25 TiO 2 nanoparticles. Results showed that photoactivity of Fe(III)-doped TiO 2 under visible light was more than P25 TiO 2 photoactivity, but it was less than P25 TiO 2 photoactivity under UV irradiation. Also efficiency of UV irradiation alone and amount of phenol adsorption on Fe(III)-doped TiO 2 at dark condition was investigated.

Geothermal energy systems can help in achieving an environmentally friendly and more efficient energy utilization, as well as enhanced power generation and building heating/cooling, thereby making energy systems more sustainable. The role of the backfill material, which fills the space between a pipe and the surrounding soil, is important in the operation of ground heat exchangers. Among the review articles on parameters affecting ground heat exchanger performance published over the past eight years, only two discuss types of backfill materials, even though the importance of these materials is significant. However, no review has yet been published exclusively on the kinds of backfill materials used in ground heat exchangers. This article addresses this need by providing a comprehensive review of a variety of types of backfill materials and their effects on ground heat exchanger performance. For organizational purposes, the backfill materials are divided into two categories: conventional backfill materials (pure and mixed materials) and modern backfill materials (improved phase change materials). Both categories are described in detail. It is shown that bentonite has been used considerably as a conventional backfill material in ground heat exchangers, followed by silica sand and coarse/fine sand. Moreover, acid and shape-stabilized phase change materials have been applied mostly as modern backfill materials in ground heat exchangers. It is observed, generally, that conventional backfill materials are used more than modern backfill materials in ground heat exchangers. It should be noted that the data covered in this study are not from all the articles published in the last eight years, but rather from a subset based on specific criteria (i.e., English-language papers published in reputable journals). These articles were published by authors from numerous countries. The results may, as a consequence, have some corresponding limitations, but these are likely to be minor.