Thermo-Hydraulic Performance of Heated Tube with Twisted Delta Winglet Swirler Insert: A Numerical Simulation

Among the various methods for enhancing heat transfer in a heat exchanger, a passive method of inserting a continuous swirler inside a heated tube provides a secondary flow along the fluid that reduces the thickness of the thermal boundary layer, thus increasing the efficiency of convection heat transfer performance. The research’s primary goal is to conserve energy, materials, and money by operating efficient heat exchanger equipment. However, the continuous swirler along the fluid flow creates a persistent obstruction, which amplifies the friction factor and increases the working fluid’s energy loss. As a result, this research presented the twisted delta winglet swirler (TDWS), a new design of a decaying swirler that uses delta winglets twisted to 180° to produce a swirling flow along the tube. The swirler comprises four twisted delta winglets arranged in a circle with a diameter 6% smaller than the tube and a length of L/D=2.2. It was placed at the entrance to a heated tube test section with a diameter of 0.016 m and a length of L/D=93.75. The Reynolds Stress Model was used to simulate the flow domain with a water-ethylene glycol mixture was chosen as the working fluid. TDWS transformed the uniform inlet flow from potential energy to high kinetic energy, resulting in a high intensity of swirling flow downstream of the circular tube up to L/D=46.88 before decaying and reaching a steady state. Compared to other decaying swirlers, TDWS obtained one of the lowest relative friction factors, 1.36, with this flow. The maximum global relative Nusselt number increased by only 11% because this value considered the area where the flow reached a steady state. Since the TDWS is a decaying swirler, the thermal-hydraulic performance reached unity along the tube. However, the optimal performance of TDWS in the plain tube with a length of L/D=93.75 can be found if the dimension or geometric configuration of the TDWS is modified, or two or more TDWS may be placed in an array orientation

Numerical Simulation of Heat Transfer Performance of Water: Ethylene Glycol Mixture (W:EG) Through Turbine-Like Decaying Flow Swirler

The propeller-type swirler has been mentioned several times in the literature as one of the decaying flow swirlers designed to improve heat transfer performance while maintaining a low friction factor. However, the distance travelled by swirling flow varies according to the swirler’s design configuration. As a result, the purpose of this paper is to investigate the heat transfer performance and friction factor of a new turbine-like decaying flow swirler (TDS). The distance traversed and decays downstream the tube by the created swirling flow will then be determined. The TDS is a rigid turbine or compressor consist of four twisted blades at 172.2° set at the entrance of a fully developed 1.5 m tube with a dimensionless length (L/D) of 93.75. A 60:40% water and ethylene glycol mixture was employed as a working fluid for the turbulent flow with Reynolds numbers ranging from 4583 to 35,000. The results indicate that the maximum relative heat transfer is 1.16 and the highest relative friction factor is 1.47 at the lowest Reynolds number tested. For Reynolds numbers less than and equal to 10,136, the thermal hydraulic performance achieved unity. The obtained relative heat transfer is deemed to be poor in comparison to several publications. The swirl flow finally entirely decays after L/D = 70.32 after being visualised through the vortex core and cross-sectional plane of the tube, contributing to a reduced heat transfer performance. In conclusion, TDS performance can be optimised for a lower dimensionless length using the same design configuration, or the design configuration should be modified to increase the generated swirl flow intensity

Effect of diameter, twist angle, and blade count on the thermal-hydraulic performance of a decaying twisted swirler

Inserting a decaying swirler into a heat exchanger has been shown to improve heat transfer with minimal effect on the friction factor. The study analyses the effect of diameter, twist angle, and blade count on the thermal-hydraulic performance of a Decaying Twisted Swirler (DTS) in a horizontally heated tube. The diameter, twist angle, and DTS's blade count are examined for 13.5 mm–15.5 mm with a 0.5 mm interval, 0°–360° with a 60° gap, and 2 to 6 blades, respectively. The Nusselt number, friction factor, and thermal-hydraulic performance are examined for Reynolds numbers between 4583 and 35000. The relative Nusselt number and friction factor increase as DTS diameter and twist angle increase, reaching a maximum value at Re = 4583. Despite this, the relative Nusselt number dispersed as the blade count increased. The relative friction factor increases as the blade count increases. Maximum relative Nusselt number and friction factor reached 1.64 and 3.25, respectively with DTS's 15.5 mm diameter, 360° angle, and 4 blades. Nonetheless, the thermal-hydraulic performance is greatest when the DTS has a diameter of 15.5 mm, a twist angle of 180°, and 2 blades with 1.17

Numerical analysis of SiO2 nanofluid performance in serpentine PEMFC cooling plate

Proton exchange membrane fuel cell (PEMFC) is among the potential substitute to current conventional internal combustion engine (ICE) in the automotive sector due to its efficient conversion efficiency and environmental friendly. However, thermal management issues in PEMFC needs to be addressed as excessive heat in PEMFC can deteriorate its performance as well as causing dehydration to the membrane. In this study, an advanced coolant of SiO2 nanofluids was numerically studied and effect in term of the heat transfer and fluid flow behavior in a single PEMFC cooling plate is investigated. The study simulated SiO2 nanofluids in a serpentine PEMFC cooling plate. The simulation is conducted at a low volume concentrations of 0.1, 0.3 and 0.5 % of SiO2 in water and water: Ethylene Glycol (W:EG) of 60:40 as base fluids. In this serpentine cooling plate design of PEMFC, a constant heat flux is applied to mimic the actual application of PEMFC. Upon completion of the study, heat transfer and fluid flow shows that the heat transfer coefficient of 0.5 vol. % of SiO2 nanofluids has improved by 3.5 % at Reynold (Re) number of 400 as compared to the base fluid of water with an acceptable pumping power increment

Heat transfer and pressure drop of water based hybrid Al2O3:SiO2 nanofluids in cooling plate of PEMFC

A Proton Electrolyte Membrane fuel cells (PEMFC) is considered to be a viable alternative to Internal Combustion Engines (ICEs) in automotive applications due to the key advantages in thermal management system. The main duty of thermal management system is to maintain the desirable temperature, with a uniform temperature distribution across the stack and its individual membranes. In this paper, the thermal enhancement for two types of PEMFC cooling plates were analysed and presented. The hybrid Al?O?:SiO? was used as coolant in distributor cooling plate. The study focuses on water based 0.5% volume concentration of single Al?O? , single SiO? nanofluids, hybrid Al?O?:SiO nanofluids with mixture ratio of 10:90 and 50:50. The effect of different ratios of nanofluids to heat transfer enhancement and fluid flow in Reynold number range of 400 to 2000 was observed. A 3D computational fluid dynamic (CFD) was developed based on distributor cooling plates using Ansys 16.0. Positive heat transfer enhancement was obtained where the 10:90 Al?O?:SiO? nanofluids has the highest heat transfer coefficient as compared to other nanofluids used. However, all nanofluids experienced higher pressure drop. Therefore, the advantage ratio was used to analyze the effect of both heat transfer enhancements and pressure drop demerits for nanofluids adoption. The results concluded that 10:90 Al?O?:SiO? hybrid nanofluid is the most feasible candidate followed by 50:50 Al?O?:SiO? Al?O? hybrid nanofluids up to fluid flow of Re1000. The positive results implied that hybrid Al?O?:SiO? nanofluids do improve the single nanofluids behaviour and has a better potential for future applications in PEMFC thermal management

Corrosion Performance of Nanopaint for Automotive Application

Nanostructured coating that possessed high density of grain boundaries enable excellent physical coverage of the coated surface against corrosion and mechanical problems compared to the larger grain size of particles found in conventional paint. The current study focusses on the effect of SiO2 and TiO2 nanoparticles as additive in acrylic automotive paint for corrosion. The new paint namely nanopaints was prepared at three different concentrations. The nanopaint were characterized using Electro-chemical test and the open circuit potential (OCP) is recorded. Electrochemical test in a saltwater solution method also used to determine the potential of nanopaint concentration on automotive surfaces. The results reveal that nanoparticle additive provide better corrosion rate as compared to the original basecoat. The optimum anticorrosion behaviour for both TiO2 and SiO2 nanopaints were achieved at weight percentage of 1.5 wt% and 1.0 wt%, respectively. Therefore, the nanopaint has potential to provide better corrosion performance for automotive surface application

Water : Ethylene glycol properties alteration upon dispersion of Al2O3 and SiO2 nanoparticles

Proton exchange membrane fuel cell (PEMFC) seems to be a popular option as a green energy carrier due to its high efficiency and pollutant-free operation. However, the slight temperature difference between the working temperature and surroundings requires innovation in cooling strategy. Active thermal management strategy is limited due to the larger space requirement. Alternatively, utilizing nanofluids as coolant as the passive cooling strategy tends to be a viable quick fix. In this research, thermophysical properties of Al2O3:SiO2 hybrid nanofluids in the base fluid of water: Ethylene Glycol (EG) were discussed comprehensively concerning alterations made in thermal conductivity, dynamic viscosity, and electrical conductivity properties. There were four mixture ratios of 0.5% volume concentration of hybrid nanofluids considered ranging from 10:90, 30:70, 50:50, and 70:30 Al2O3:SiO2. Upon completion of the study, there is an improvement of 9.8% shown in 10:90 Al2O3:SiO2 hybrid nanofluids for thermal conductivity measured at 60°C in comparison to the base fluid. Meanwhile, 10:90 Al2O3:SiO2 hybrid nanofluids are also favorable with the lowest values of viscosity as compared to other mixture ratios resulting in lower parasitic loss. Electrical conductivity on the other hand also showed an increment in 10:90 Al2O3:SiO2 hybrid nanofluids as compared to base fluid and other mixture ratios

Performance study of ground heat exchanger based on thermal conductivity of hybrid soil

The need for renewable energy sources has grown as the world has significantly changed, and fossil fuels have been used extensively in global perspective. As a result, renewable energy has replaced fossil fuels in many places around the world because it is better for the environment. Geothermal energy is the most efficient way to heat and cool space from all renewable energy sources. Geothermal renewable energy, in particular from ground heat exchangers (GHE), has enormous potential for use in construction (building). In order for the GHE to function appropriately (efficiently), it is critical (better) to have sufficient quantities of backfilling material. This material is used to fill the gap between the soil surrounding. The heat transfer rate from the air to the soil, which is controlled by thermal characteristics of the soil near the GHE pipe, determines the thermal performance of the GHE. Using some backfilling materials that have been thermally improved, the thermal properties of the soil around the GHE pipe can be improved as well. Therefore, the current study examines the impact of hybrid soils without moisture on the GHE performance. The hybrid soils comprise of two components: native soil and bentonite. A thermal property analyzer was used to measure the thermal conductivity of the hybrid soil. According to the study, compared to other grain sizes, native soil with a grain size of 2.0 to 2.5mm has the highest thermal conductivity value at 20% bentonite, which is 0.331 W/m.K. The effectiveness of the GHE system was assessed using a mathematical model, demonstrating that the GHE has significantly reduces temperatures along pipes with length of 0 to 16m. In a nutshell, once the thermal conductivity of hybrid soil increases, the performance of GHE will improve

Electro-thermal characteristics of hybrid TiO2-SiO2 nanofluid coolants in an electrically-active system

hermal management in an electrically-active system is a challenging engineering branch due to the critical requirement for rapid cooling rates with inhibition of electrical discharge. A Polymer Electrolyte Membrane Fuel Cell (PEMFC) is an example of a system that needs both conditions to be critically fulfilled. The use of conventional deionised water with low electrical conductivity as the cooling fluid ensures insignificant electrical potential losses but large thermal capacities can only be achieved with a significant penalty to the PEMFC system size. Formulation of nanofluid coolants has been highly successful for systems working under normal environments, but research towards new nanofluid coolants for active electrical systems are relatively new. This paper reports a fundamental investigation on the electrical and thermal behaviours of a hybrid 1%v TiOz-SiOz(at 50:50 ratio) nanofluid dispersed in 60:40 water/ethylene glycol solution. A test bench consisting of a heated rectangular channel combined with continuous electrical supply at 0.7 V and 3 A nominal current was developed to simulate the operating conditions of a PEMFC stack cooling. The test variables are the heater temperature and Reynolds number (300 to 700) of the coolants. The cooling profiles and changes in electrical properties of the system and coolants were analysed. Significant increase in cooling rates were achieved by the hybrid nanofluids (200% to 250%) compared to water and water/ethylene glycol coolants. The electrica analysis indicates that the power drop is low for water and water/ethylene glycol but drops rapidly in an exponential profile (between 15% to 45%) which also leads to a visible increase in the electrical conductivity of the nanofluids coolants. As such, further research is needed to reduce the apparent electrical discharge problem before a suitable nanofluid coolant can be developed for electrically-active systems

The characteristics of hybrid Al2O3:SiO2 nanofluids in cooling plate of PEMFC

A Proton Electrolyte Membrane fuel cells (PEMFC) is considered to be a viable alternatives to Internal Combustion Engines (ICEs) in automotive applications due to the key advantages in thermal management system. The main duty of thermal management system is to maintain the desirable temperature, with a uniform temperature distribution across the stack and.its.individual membranes. In this paper, the thermal enhancement of a PEMFC cooling plate was analysed and presented. The hybrid Al2O3:SiO2 was used as coolant in distributor cooling plate. The study focuses on water based 0.5% volume concentration of single Al2O3, single SiO2 nanofluids, hybrid Al2O3:SiO nanofluids with mixture ratio of 10:90, 20:80, 50:50, 60:40 and 90:10. The effect of different ratios of nanofluids to heat transfer enhancement and fluid flow in Reynold number range of 400 to 2000 was observed. A 3D computational fluid dynamic (CFD) was developed based on distributor cooling plates using Ansys 16.0. Positive heat transfer enhancement was obtained where the 10:90 Al2O3:SiO2 nanofluids has the highest heat transfer coefficient as compared to other nanofluids used. However, all nanofluids experienced higher pressure drop. Therefore, the advantage ratio was used to analyze the effect of both heat transfer enhancements and pressure drop demerits for nanofluids adoption. The results concluded that 10:90 Al2O3:SiO2 hybrid nanofluid is the most feasible candidate up to fluid flow of Re1000. The positive results implied that hybrid Al2O3:SiO2 nanofluids do improve the single nanofluids behaviour and has a better potential for future applications in PEMFC thermal management