Search

This review presents a comprehensive exploration of the advancements in polymer composites, focusing on their performance, manufacturing processes, recycling techniques, and sustainable practices. With the increasing demand for high-performance materials in various industries, including aerospace, automotive, and construction, polymer composites have emerged as a pivotal solution, offering unparalleled strength, durability, and lightweight properties. This review explores the essential characteristics of polymer composite materials and blends, highlighting the synergy between various matrices and reinforcements that lead to improved material properties. Significant emphasis is given to high-performance composites, where the integration of innovative materials and additives has led to revolutionary applications. By examining the material properties and performance, this review highlights the capabilities of polymer composites to meet rigorous requirements in special cases and extreme conditions. Furthermore, it explores the environmental impact of these materials, promoting sustainable practices throughout their lifecycle. The critical role of recycling in the manufacturing process is dissected to unveil strategies that not only mitigate environmental harm but also promote the circular economy in the composite industry. It addresses both the challenges and opportunities presented by these materials, offering insights into future directions for research and application. [ABSTRACT FROM AUTHOR]

The heat transfer capacity of a convectional heat exchanger needs to be increased to minimize size and cost. Inserts are a promising way to enhance heat transfer at a bearable penalty in pressure drop. The objective of this study is to evaluate experimentally the thermal-hydraulic characteristics of a heat exchanger tube inserted with a novel alternatively twisted swirl generator (ATSG) tape. The experimental data has been collected for nine distinct combinations of ATSG tapes, includes the tapes with three twist angles (45°, 60°, and 90°) and three twist ratios (3, 4 and 5) for Reynolds numbers of 4,000 to 20,000. The use of ATSG tapes resulted in a considerable improvement in heat transfer rate compared to simple twisted tapes (TT). Over the range evaluated, heat transfer coefficient, pressure drop and thermal performance factor (TPF) with ATSG tapes in a tube are, respectively, 1.57–1.82, 1.58–2.54, and 1.22–1.46 times to that of simple TT in a tube. The maximum TPF achieved is 1.52 for ATSG tape with twist ratio of 3 and twist angle of 90°. The TPF for any combination of ATSG tapes is greater than one, which signifies that it is an efficient approach. [ABSTRACT FROM AUTHOR]

Drying of agricultural food products is one of the most attractive and cost-effective applications of solar energy. The solar dryer is less reliable due to the intermittent nature of solar energy. This shortcoming can be overcome to some extent by storing solar energy. Information on sensible and latent heat storage materials and systems is spread widely in the literature. In this paper, we try to gather information about the previous and current research works in the field of thermal energy storage technology for solar air heater and dryer. The relative studies are classified on the basis of the type of storage material used in solar dryers, i.e. phase change material (PCM), rock, water, etc. Several designs of solar dryers with different heat storage materials were proposed by researchers. Recent studies focused on PCMs such as Paraffin and salt hydrate, due to their high heat storage capacity per unit volume. [ABSTRACT FROM AUTHOR]

Abstract: In view of above present investigation is planned with the following. The present investigation has been carried out with the following objectives: [(1)] To study performance of packed bed solar air heater for high porosity range and for different shapes of matrices. [(2)] Development of correlations for heat transfer coefficient and friction factor for packed bed solar air heater and its comparison with conventional design. [(3)] Exergy analysis of packed bed solar air heater. The present study involved outdoor experimental work for generation of heat transfer and friction data for flow in a packed bed solar air heater at different mass flow rates of air for various porosities and shapes of matrices. Data is also collected for conventional smooth duct under similar operating conditions for ensuring accuracy of experimental data. Six matrices had been tested for seven values of flow rates corresponding to flow Reynolds number of about 1000–4700 and data is collected under steady state condition. Ranges of parameters covered in this experimental investigation are as follows: Reynolds number, Re=1000–4700 Porosity, P=0.9614–0.9984 Number of layers, n=3–6 It is found that in the entire range of Reynolds number, Colburn factor decreases with an increase of packing Reynolds number and volumetric heat transfer increased monotonically with a decrease in porosity. Also from the various matrices studied hexagonal shaped matrix performed lowest of all other matrices. Square shaped matrix performed best amongst the matrices studied. Following correlations have been developed for Colburn factor and friction factor in terms of porosity and operating parameters: [Copyright &y& Elsevier]

Abstract: Thermal performance of the four identical trapezoidal cavity absorbers for linear Fresnel reflecting solar device were studied and compared. The absorbers were designed for operating in conjunction with a prototype Fresnel solar reflector. Rectangular and round pipe sections were used as absorber by placing in the trapezoidal cavity. The absorber pipes were coated with ordinary dull black board paint and black nickel selective surface. The bottom of the cavity was provided with plane glass to allow the solar radiation to be reflected from the Fresnel reflector. The other three sides of the cavity absorber were insulated to reduce heat loss. Thermal performance of the Fresnel reflecting concentrator with each trapezoidal cavity absorber was studied experimentally at different concentration ratio of the reflector. The study revealed that the thermal efficiency was influenced by the concentration ratio and selective surface coating on the absorber. The thermal efficiency decreased with the increase in the concentration ratio of the Fresnel reflecting collector. The selective surface coated absorber had a significant advantage in terms of superior thermal performance as compared to ordinary black painted absorber. The round pipe (multi-tube) receiver had higher surface area to absorb solar energy as compared to rectangular pipe receiver. Thermal efficiency of the solar device with round pipe absorber was found higher (up to 8%) as compared to rectangular pipe absorber. [Copyright &y& Elsevier]

Abstract: There should be minimum heat loss from the absorber to achieve better efficiency of the solar collector. Overall heat loss coefficients of the trapezoidal cavity absorber with rectangular and round pipe were studied in the laboratory. Two identical rectangular pipe absorbers (section size: 100×23mm, thickness: 2.5mm and length 2170mm) and two round pipe absorbers (a set of six mild steel round tubes of 16mm diameter and 2.5mm thickness brazed together in single layer making 100mm width) were fabricated. A rectangular and a round pipe were painted with ordinary mat black paint (emissivity at 100°C=0.91) and one pipe of each type was coated with black nickel selective surface (emissivity at 100°C=0.17). Overall heat loss coefficient of the absorber was studied by circulating hot oil through it at different temperatures. The heat loss coefficient was increased with the absorber temperature. The heat loss coefficients for ordinary black coated and selective surface coated round pipe absorbers were varied from 3.5 to 7.5W/m2/°C and 2.7–5.8W/m2/°C respectively. The rectangular pipe section has marginally higher heat loss coefficients as compared to round pipe absorber. Selective surface coating on the absorbers reduced heat loss coefficient significantly by 20–30% as compared to ordinary black coating. The double glass cover also reduced heat loss coefficient by 10–15% as compared to single glass cover. The overall heat loss coefficients were also estimated analytically by parallel plate correlation and cavity correlations. The trend of variation of estimated heat loss coefficients by both methods was similar to experimental values. However, estimated values by cavity correlation were closure and uniformly distributed at all temperature range. [Copyright &y& Elsevier]

The experimental and numerical analysis is arranged to evaluate thermal hydraulic performance analysis with entropy generation on nanofluid flow in helical screw inserts in the tube with single and double strip and different twist ratios (TRs) in laminar flow. Single strip insert is also compared with double strip of helical screw inserts. Maximum enhancement of 421% in the values of Nusselt number is found with double strip helical screw insert in the flow of nanofluid at 1.5 of TR and 300 of Re as compared with plain tube inflow of water. Correlations are generated for Nu and f. Entropy production number is found lower value with double strip inserts than single strip helical screw inserts at low value of twist ratio in the flow of nanofluid than water. Thermal performance factor is achieved higher values with double strip insert at all flow rates at 2.5 of TR than single strip inserts, whereas found maximum value of 2.38 with double strip insert at twist ratio of 2.5 and Reynolds number of 300 in the flow of nanofluid. Optimum design of double strip inserts attained low entropy production number and higher value of thermal performance factor in the flow of nanofluid. [ABSTRACT FROM AUTHOR]

Abstract: In order to verify and solve the problem of NOx and PM emissions, it is necessary to directly observe the internal combustion chamber of a diesel engine. Many studies have been performed in recent years to verify the macroscopic and microscopic behavior of the injected fuel spray because observing it is not easy due to the difficulties of the experiment. Researchers have investigated the spray characteristics for various diesel injector nozzles over a wide range of temperatures and pressure, but there is lack of evaluation for the spray characteristics for biodiesel. At a time when rapid rise of fuel prices and depleting hydrocarbon resources of the world have forced us to look for alternative fuels biodiesel produced by transesterification of non-edible vegetable oils is promising to be an important additive/substitute to petro diesel. Biodiesel being an oxygenated and sulfur-free fuel leads to more complete combustion and lower emissions. But, the energy content or net calorific value of biodiesel is less than that of diesel fuel; also it has higher viscosity and density, than diesel fuel. A considerable improvement in these properties can be obtained by mixing diesel and biodiesel and then using the blends. Biodiesel and biodiesel/petro diesel blends, with their higher lubricity levels, are increasingly being utilized as an alternative. Present paper analyzed the correlation of injection parameters that will affect the spray characteristics of biodiesel. Observations for analyzing the effect of injection parameters on spray cone angle, break up length and fuel penetration were made. Finally the performance and emissions tests were studied. Atomization and vaporization of fuel are greatly influenced by viscosity and density of fuel and these properties are temperature dependent. Thus fuel inlet temperature plays a very important role in fuel atomization process. At higher temperature viscosity of fuel decreases which enhances the atomization of biofuels. [Copyright &y& Elsevier]

Abstract: Artificial roughness in the form of ribs is a convenient method for enhancing thermal performance of solar air heaters. This paper presents the experimental investigation of heat transfer and friction factor characteristics of a rectangular duct roughened with W-shaped ribs arranged at an inclination with respect to the flow direction on its underside on one broad wall. W ribs have been tested both pointing in downstream W-down and upstream W-up to the flow. The range of parameters for this study has been decided on the basis of practical considerations of the system and operating conditions. The duct has a width to height ratio (W/H) of 8.0, relative roughness pitch (p/e) of 10, relative roughness height (e/Dh ) of 0.03375 and angle of attack of flow (α) of 30–75°. The air flow rate corresponds to Reynolds number between 2300–14,000. The heat transfer and friction factor results have been compared with those for smooth duct under similar flow and thermal boundary condition and thermo-hydraulic performance has been investigated. Thermo-hydraulic performance comparison for different angle of attack of flow shows that W-down arrangement with angle of attack of flow as 60° gives best thermo-hydraulic performance. In addition heat transfer and friction factor correlations have been developed. [Copyright &y& Elsevier]

Abstract: Artificial roughness in form of ribs is convenient method for enhancement of heat transfer coefficient in solar air heater. This paper presents experimental investigation of heat transfer and friction factor characteristics of rectangular duct roughened with W-shaped ribs on its underside on one broad wall arranged at an inclination with respect to flow direction. Range of parameters for this study has been decided on basis of practical considerations of system and operating conditions. Duct has width to height ratio (W/H) of 8.0, relative roughness pitch (p/e) of 10, relative roughness height (e/D h) 0.018–0.03375 and angle of attack of flow (α) 30–75°. Air flow rate corresponds to Reynolds number between 2300–14,000. Heat transfer and friction factor results have been compared with those for smooth duct under similar flow and thermal boundary condition to determine thermo-hydraulic performance. Correlations have been developed for heat transfer coefficient and friction factor for roughened duct. [Copyright &y& Elsevier]

Abstract: Due to depletion of fossil fuel, bio-fuels have generated a significant interest as an alternative fuel for the future. The use of bio-fuels to fuel gas turbine seems a viable solution for the problems of decreasing fossil-fuel reserves and environmental concerns. Bio-fuels are alternative fuels, made from renewable sources and having environmental benefit. In recent years, the desire for energy independence, foreseen depletion of nonrenewable fuel resources, fluctuating petroleum fuel costs, the necessity of stimulating agriculture based economy, and the reality of climate change have created an interest in the development of bio-fuels. The application of bio-fuels in automobiles and heating applications is increasing day by day. Therefore the use of these fuels in gas turbines would extend this application to aviation field. The impact of costly petroleum-based aviation fuel on the environment is harmful. So the development of alternative fuels in aviation is important and useful. The use of liquid and gaseous fuels from biomass will help to fulfill the Kyoto targets concerning global warming emissions. In addition, to reduce exhaust emission waste gases and syngas, etc., could be used as a potential gas turbine fuel. The term bio-fuel is referred to alternative fuel which is produced from biomass. Such fuels include bio-diesel, bio-ethanol, bio-methanol, pyrolysis oil, biogas, synthetic gas (dimethyl ether), hydrogen, etc. The bio-ethanol and bio-methanol are petrol additive/substitute. Bio-diesel is an environment friendly alternative liquid fuel for the diesel/aviation fuel. The gas turbine develops steady flame during its combustion; this feature gives a flexibility to use alternative fuels. Therefore so the use of different bio-fuels in gas turbine has been investigated by a good number of researchers. The suitability and modifications in the existing systems are also recommended. [Copyright &y& Elsevier]

Abstract: An experimental investigation has been carried out to study the heat transfer and friction characteristics in solar air heater by using discrete W-shaped roughness on one broad wall of solar air heater with an aspect ratio of 8:1, the roughened wall being heated while the remaining three walls are insulated. The experiment encompassed Reynolds number (Re) range from 3000 to 15,000, relative roughness height (e/Dh ) in the range of 0.0168–0.0338, relative roughness pitch (p/e) 10 and the angle of attack (α) in the range of 30–75°. The effect of parameters on the heat transfer and friction are compared with the result of smooth duct under similar flow conditions. Correlations for heat transfer and friction have been developed as a function of roughness and flow parameters. [Copyright &y& Elsevier]