Flexural Performance of PVA Reinforced ECC Beams: Numerical and Parametric Studies

Engineered cementitious composite (ECC) refers to the group of cementitious mixtures possessing the strainhardening and crack control abilities. In this research, the mechanical performance of ECC beams will be investigated with respect to the effect of aggregate size and amount, by employing nonlinear finite element method. The validity of the models were verified with the experimental results of the ECC beams under monotonic loading. Based on the numerical analysis method,nonlinear parametric study was then conducted to evaluate the influences of various parameters on the flexural stress and flexural deflection of ECC beams. A new models that accounts for the ECC aggregate content (AC), ECC compressive strength (fECC), and maximum aggregate size (Dmax) parameters are proposed. The analytical results obtained from the proposed models were compared with experimental results obtained from 57 ECC beam tests previously published. The simulation results indicated that when increase the aggregate size and content no definite trend in flexural strength is observed and the ductility of ECC is negatively influenced by the increase of aggregate size and content. Also, the ECC beams revealed enhancement in terms of flexural stress, strain, and midspan deflection when compared with the reference beam (microsilica MSC), where, the average improvement percentage of the specimens were 45%, 1242%, and 1427.15%,respectively. These results are quite similar to that of the experimental results, which provides that the finite element model is in accordance with the desirable flexural behaviour of the ECC beams. Furthermore, the proposed models can be used to predict the flexural behaviour of ECC beams with great accuracy

Experimental and Numerical Investigation of Heat Transfer Augmentation Using Al2o3-Ethylene Glycol Nanofluids Under Turbulent Flows in a Flat Tube

A study of computational fluid dynamics has been conducted to study the characteristics of the heat transfer and friction factor of Al2O3/Ethylene glycol-water nanofluid flowing inside flat tube. The three dimensional realizable k?e turbulent model with an enhanced wall treatment was utilized. The evaluation of the overall performance of the tested tube was predicated on the thermo-hydrodynamic performance index. The obtained results showed that the difference in behaviour depending on the parameter that has been selected to compare the nanofluid with the base fluid. In addition, the friction factor and the heat transfer coefficient increases with an increase of the nanoparticles volume concentration at the same Reynolds number. The penalty of pressure drop is negligible with an increase of the volume concentration of nanoparticles. Conventional correlations that have been used in turbulent flow regime to predict average heat transfer and friction factor are Dittus-Boelter and Blasius correlations, for tubes are also valid for the tested nanofluids which consider that the nanofluids have a homogeneous fluid behaviour

Flexural behavior of concrete beams reinforced with different types of fibers

Enhanced tensile properties of fiber reinforced concrete make it suitable for strengthening of reinforced concrete elements due to their superior corrosion resistance and high tensile strength properties. Recently, the use of fibers as strengthening material has increased motivating the development of numerical tools for the design of this type of intervention technique. This paper presents numerical analysis results carried out on a set of concrete beams reinforced with short fibers. To this purpose, a database of experimental results was collected from an available literature. A reliable and simple three-dimensional Finite Element (FE) model was defined. The linear and nonlinear behavior of all materials was adequately modeled by employing appropriate constitutive laws in the numerical simulations. To simulate the fiber reinforced concrete cracking tensile behavior an approach grounded on the solid basis of micromechanics was used. The results reveal that the developed models can accurately capture the performance and predict the load-carrying capacity of such reinforced concrete members. Furthermore, a parametric study is conducted using the validated models to investigate the effect of fiber material type, fiber volume fraction, and concrete compressive strength on the performance of concrete beams

An Experimental Determination of Thermal Conductivity and Electrical Conductivity of Bio Glycol Based Al2O3 Nanofluids and Development of New Correlation

Nanofluid, as a kind of new engineered material consisting of nanometer-sized additives and base fluids, has attracted great attention from investigators for its superior thermal properties and many potential applications. In this paper, the thermal conductivity, dispersion stability and electrical conductivity of 100% bioglycol (BG) based nanofluids containing Al2O3 nanoparticles were studied in a temperature range of 30 to 80 °C. Nanofluids with 0.1, 0.3, 0.5, 0.7, and 1% volume concentrations were prepared using the two-step method without using surfactant. The nanofluids demonstrated excellent stability over this temperature range after using long-term sonication. A new correlation has been developed for the thermal conductivity of nanofluids as a function of temperature and particle volume concentration. This study also revealed that the thermal conductivity enhancement of bio glycol (BG), ethylene glycol (EG) and propylene glycol (PG) of 1.0% volume concentration at 30 °C was 17%, 9% and 3.6% respectively. However, the increment in temperature reacts inversely to the thermo-electrical conductivity (TEC) ratio. The maximum value of TEC is 9.5 at 0.5% volume concentrations and temperature of 30 °C

Heat transfer enhancement of bioglycol/water based TiO2 and SiO2 nanofluids in a flat tube with twin twisted tapes

The research on heat transfer has been receiving important attention since long time ago and has found applications in several areas such as the cooling of electronic devices, manufacturing systems and solar energy systems. The effective passive methods for heat transfer augmentation are the additive technique for nanofluid and swirl flow devices, are acquiring great attention in order to enhance the thermal performance of the heat exchangers. Among the swirl flow devices which are used to create swirl or secondary flow, twisted-tape inserts are very popular because of their good thermal performance. The increasing demand for more efficient heat transfer fluids in many applications has been led to enhance heat transfer to meet the cooling challenge necessary. Nanofluid is a relatively new engineering material consisting of the nanometre-sized additives and base fluids, has gained extensive attention due to its role in improving the efficiency of thermal systems. Although, there are many studies of nanofluids with different types of base fluid such as water, Ethylene glycol (EG) and Propylene glycol (PG), there are very limited studies of using nanofluids with BioGlycol as a base fluid. While, BioGlycol (BG) showed more advantages compared to water Ethylene glycol (EG) and Propylene glycol (PG), for instance, a much lower freezing point and higher boiling point than water, provided lower viscosity compared to Propylene glycol (PG) and Ethylene glycol (EG), has greater thermal stability while possessing similar or better thermophysical properties compared to Propylene and Ethylene glycols and non-toxic renewable sourced fluid. The aim of the present study is to evaluate the heat transfer coefficient and pressure drop of BioGlycol/Water based TiO2 and SiO2 nanofluids for flow in a flat tube and with twin twisted tapes experimentally and numerically. For this evaluation, the thermophysical properties of TiO2 and SiO2 nanofluids are prepared at different volume concentrations and temperatures. A test rig was fabricated with the facility to heat the liquid by wrapping with two nichrome heaters on the flat tube with an option to insert the twisted tapes. Experiments are carried out to determine the Nusselt number and friction factor with BioGlycol/water of (20/80)% mixture ratio by volume based TiO2 and SiO2 nanofluids at (30, 50 and 70oC) in the turbulent range of Reynolds number (Re) for flow in a flat tube and with twin twisted tapes. The maximum enhancement in the heat transfer was 28.2% for 1.0% TiO2 nanofluids at Re = 21,194 and temperature 50oC. However, the maximum heat transfer enhancement was 29.3% of SiO2 nanofluids with 2.0% volume concentrations at Re = 21,169. It can be stated that the heat transfer enhancement depends on the nanoparticles concentration and operating temperature of the nanofluid. An increase in the Nusselt number and friction factor with a decrease in twist ratio for BioGlycol/water and nanofluids was observed from the experiments. The maximum heat transfer enhancement of SiO2 at 2.0% volume concentration and 50oC with counter twisted tapes (CTT-5) and co-counter twisted tapes (COT-5) with twist ratio of 5 were up to 129% and 113% respectively higher than the flat tube of BioGlycol/water. Furthermore, using the TiO2 nanofluid with 1.0% volume concentration at 50oC with (CTT-5) and (COT-5) gave the maximum heat transfer enhancement up to 124% and 106% respectively higher than the flat tube of BioGlycol/water. For the case of plain tubes, it is preferable to have the flow of TiO2 and SiO2 nanofluids at 1.0% and 2.0% volume concentrations, respectively. Meanwhile, for the nanofluid flow with twisted tapes, it is recommended to use the twist ratio of 5. The use of TiO2 nanofluid with twisted tapes is preferable for volume concentrations up to 1.0%. However, the use of SiO2 nanofluid with twisted tapes is not recommended due to the lower thermal enhancement index compared to the nanofluid flow in plain tubes

Computational Fluid Dynamics Study of Heat Transfer Enhancement in a Circular Tube using Nanofluid

A study of computational fluid dynamics has been conducted to study the characteristics of the heat transfer and friction factor of CuO/water & Al2O3/water nanofluid flowing inside straight tube. The three dimensional realizable k-e turbulent model with enhanced wall treatment was utilized. As well as were used Temperature dependent thermophysical properties of nanofluid and water. The evaluation of the overall performance of the tested tube was predicated on the thermo-hydrodynamic performance index. The obtained result showed that the difference in behaviour depending on the parameter that has been selected to compare the nanolfuid with the base fluid. In addition, the friction factor anf the heat transfer coefficient increases with an increase of the nanoparticles volume concentration at the same Reynolds number

Thermal and Economic Analysis of Gas Turbine Using Inlet Air Cooling System

A basic goal of operation management is to successfully complete the life cycle of power systems, with optimum output against minimal input. This document intends calculating both, the performance and the life cycle cost of a gas turbine fitted with an inlet air cooling mechanism. Correspondingly, both a thermodynamic and an economic model are drawn up, to present options towards computing the cooling loads and the life cycle costs. The primary observations indicate that around 120MWh of power is derived from gas turbine power plants incorporating the cooling mechanism, compared to 96.6 MWh for units without the mechanism, while the life cycle cost is lower for units incorporating the cooling process. This indicates benefits in having the mechanism incorporated in the architecture of a gas turbine

Experimental Investigation of Turbulent Heat Transfer by Counter and Co-Swirling Flow in a Flat Tube Fitted with Twin Twisted Tapes

The use of inserts has gained extensive attention due to their role in improving the efficiency of thermal systems. In this study, an experimental investigation was conducted to explore the effect of twin counter and co-twisted tapes on heat transfer rate (Nu), friction factor (f) and thermal enhancement index (η). The twin counter twisted tapes (CTT) and twin co-twisted tapes (CoTT) were used as swirl flow generators in a test section. The tests were conducted using the CTT and CoTT with three different twist ratios (H/D) = 5, 10 and 15) for Reynolds numbers range between 7200 and 32,400 under uniform heat flux conditions. The results show that Nusselt number (Nu), friction factor (f) and thermal enhancement index (η) increase with decreasing twist ratio (H/D) and the CTT is more efficient than the CoTT for heat transfer enhancement. Within the scope of this study, heat transfer rates in the flat tube fitted with the CTT are around 22.5% and 61% higher than those with the CoTT and plain flat tube, respectively. The maximum thermal enhancement index (η) obtained at the constant flow rate by the CTT with H/D = 5, 10 and 15, are 1.58, 1.44 and 1.15 respectively, while those obtained using the CoTT with the same range of H/D are 1.43, 1.19 and 1.04, respectively. Furthermore, the empirical correlations of the heat transfer (Nu), friction factor (f) and thermal enhancement index (η) are also reported

Experimental and Numerical investigation of Heat transfer enhancement using Al2O3-Ethylene Glycol/Water Nanofluids in Straight Channel

A study of computational fluid dynamics has been conducted to study the characteristics of the heat transfer and friction factor of Al2O3/Ethylene glycol-water nanofluid flowing in straight channel. The three dimensional realizable k– turbulent model with enhanced wall treatment was utilized. As well as were used Temperature dependent thermophysical properties of nanofluid and water. The evaluation of the overall performance of the tested channel was predicated on the thermo-hydrodynamic performance index. The obtained results showed that the difference in behaviour depending on the parameter that has been selected to compare the nanofluid with the base fluid. In addition, the friction factor and the heat transfer coefficient increases with an increase of the nanoparticles volume concentration at the same Reynolds number. The penalty of pressure drop is negligible with an increase of the volume concentration of nanoparticles. Conventional correlations that have been used in turbulent flow regime to predict average heat transfer and friction factor are Dittus-Boelter and Blasius correlations, for channel are also valid for the tested nanofluids which consider that the nanofluids have a homogeneous fluid behave

Experimental Investigation of Thermal Conductivity and Electrical Conductivity of BioGlycol - Water Mixture Based Al2O3 Nanofluid

Nanofluid as a new brand of cooling fluid consisting of nanometer-sized particles dispersed in base fluid. In this study, the thermal conductivity and electrical conductivity of BioGlycol (BG)–water (W) mixed nanofluids containing Al2O3 nanoparticles were studied. Nanofluids with 0.5 to 2.0% concentrations were prepared by the two-step method. The nanofluids demonstrated excellent stability over the temperature range of 30 to 80 °C after using the long term sonication process. Comparisons of the experimental data with many existing models illustrated that they do not display good agreement. Therefore, a new nonlinear model has been developed with 5% maximum deviation for the thermal conductivity of nanofluids as a function of temperature and volume concentration. The results of BG:W mixtures have displayed improvement in thermal performance of 7.5% in comparison with Propylene glycol (PG):W in similar circumstances. The thermal conductivity of nanofluid increased as a function of volume concentration and temperature. The maximum thermal conductivity enhancement using 40:60% (BG:W) mixture ratio was twice as high as 60:40% in the same conditions. Electrical conductivity was observed to decrease as the volume concentration increased. Thermo-electrical conductivity ratio (TEC) has been evaluated theoretically based on thermal and electrical conductivity results