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

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

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

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

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

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

Thermal conductivity and dynamic viscosity of mono and hybrid organic- and synthetic-based nanofluids: A critical review

Thermal conductivity and dynamic viscosity are two critical properties of nanofluids that indicate their heat transfer performance and flow. Nanofluids are prepared by dispersing mono or several organic or synthetic nanoparticles in selected base fluids to form mono or hybrid nanofluids. The qualitative and quantitative stability measurement of nanofluids will then be addressed, followed by a detailed discussion on how the dispersion of nanoparticles in water (W), ethylene glycol (EG), and themixture of W:EG 60:40%by volume affects the thermal conductivity and dynamic viscosity ratio. The data comparison demonstrated that the thermal conductivity ratio increases with increasing normalized concentrations, the bulk temperature of nanofluids, and the smaller nanoparticle size. The dynamic viscosity ratio is multiplied by the normalized concentration increase. Nevertheless, as the bulk temperature climbed from 0 to 80°C, the dynamic viscosity ratio was scattered, and the dynamic viscosity ratio trend dropped with increasing particle size. While the majority of nanofluids enhanced thermal conductivity ratio by 20%, adding carbon-based nanoparticles to synthetic nanofluid increased it by less than 10%. The disadvantage of nanofluids is that they multiply the dynamic viscosity ratio of all nanofluids, which increase power consumption and reduces the efficiency of any mechanical system