Thermal Performance Enhancement Research Articles

Enhanced Thermal Performance of Composite Phase Change Materials Based on Hybrid Graphene Aerogels for Thermal Energy Storage.

Thermal conductivity and latent heat are crucial performance parameters for phase change materials (PCMs) in thermal energy storage. To enhance the thermal performance of PCMs, with the help of graphene oxide (GO) acting as a dispersing agent, well-defined hybrid graphene aerogels (HGAs) with a three-dimensional (3D) porous structure were successfully synthesized by hydrothermal reaction of GO and graphene nanoplatelets (GNPs). GNPs, dispersing uniformly along the interconnecting graphene network, acted as thermal conductive fillers and supporting materials. Palmitic acid (PA) was impregnated into the HGA by vacuum forces. It was found that the thermal conductivity of the PA/HGA was enhanced without compromising heat storage capacity. Compared with PA, the PA/HGA with 4.2 wt% GNPs exhibited enhanced thermal conductivity of 2.1 W/mK and high latent heat of 206.2 J/g simultaneously. The PA/HGA with good thermal performance has potential applications in thermal energy storage.

Enhancement of thermal transport performance in microscale spiral-channel cooling cores

Enhancement of thermal transport performance in microscale spiral-channel cooling cores

Experimental study on synergistic enhancement of thermal performance of a closed two-phase thermosyphon by a TiO2 nanofluid doped with Al2O3

The heat transfer performance of two-phase closed thermosyphon solar collectors (TPCTs) can be improved by adding nanoparticles to the conventional working fluid, but it is necessary to ensure good rheological properties while improving the heat transfer performance. Therefore, spherical (TiO2) nanoparticles with good rheological properties and rod-shaped (Al2O3) nanoparticles with high thermal conductivity were mixed and applied to the TPCT. First, the effects of individual factors such as the concentration of nanoparticles and the operating parameters on the thermal performance of the TPCT were investigated and a regression analysis was performed. Then, the joint effect of inclination angle and filling ratio on the thermal performance of TPCT was further investigated by orthogonal experiment. The results show that doping TiO2 with Al2O3 can further improve the thermal performance of TPCT. For the volume concentration of 0.6% of nanoparticles, filling ratio of 50% and inclination angle of 80°, the best heat transfer performance of TPCT was achieved. Compared with the deionized water (DW), the thermal resistance of the single (TiO2–H2O) and hybrid (Al2O3+TiO2–H2O) nanofluid TPCT is reduced by 10.7% and 13.4%, the thermal efficiency is increased by 11.0% and 13.7%, and the equivalent heat transfer coefficient is increased by 16.2% and 18.7%, respectively.

Thermal performance enhancement of basin-type solar still coupled with mini solar pond and shallow solar pond in closed-cycle mode

ABSTRACT Solar desalination is an appropriate and cost-effective technology for water distillation which requires solar energy as a heat source. Based on the previous studies, the effect of basin water depth of solar still coupled with shallow solar pond has not been performed yet. The optimum frequency of external heat supply to solar still during off-sunshine hours has been found missing in literature. The objective of present study is to enhance the nocturnal distillate productivity of solar still and is accomplished by increasing the basin water temperature during off-sunshine hours. The variation in basin water depth of modified solar still on the distiller output is studied. The individual and combined effects of shallow solar pond and mini solar pond integrated to solar still on the performance of still are studied. To achieve this, the solar still coupled with shallow solar pond in closed cycle mode (heat transfer through heat exchanger) and continuous flow mode (8 a.m. to 8 p.m.) are tested at various basin water depth of 4–7 cm. Further, the solar still with optimum basin water depth is integrated with shallow pond in continuous flow mode (8 a.m. to 8 p.m.) and mini pond in two-batch frequency mode (12 a.m. to 2 a.m. and 4 a.m. to 6 a.m.). A total cumulative distillate output of 3.5 kg/m2, 3.08 kg/m2, 3.18 kg/m2 and 2.96 kg/m2 with an enhancement of 2.94%, 14.5%, 20.85% and 16% was obtained for modified solar still (still integrated with shallow pond) with basin water depth of 4 cm, 5 cm, 6 cm and 7 cm respectively as compared to reference solar still. The cumulative productivity of 4.6 kg/m2 was obtained for modified still (still integrated with shallow pond and mini pond) with an enhancement of 43.75% over reference solar still.

Thermal performance enhancement of a new dual-PCM heat sink using two-objective optimization

Phase change materials (PCMs) can effectively improve the performance of electronic heat sinks especially when subjected to intermittent heat loads. PCMs however brings some shortcomings such as increased size of component, and slowed heat rejection during the discharging, which urged the inevitability in development of optimized design. This study presents the results of the two-objective shape optimization of a new dual-PCM heat sink. The cooling phenomenon is analysed with thorough and realistic consideration of heat loss through the fin tips to the ambient, as well as heat transfer between the PCM and the air above it. Natural convection of liquid PCM and its volume variation during phase change transition are taken into account. Two-objective optimizations are performed to maximize the heat sink operational time in the charging process and minimize the discharging time, for three critical temperatures of 50 °C, 65°C, and 80 °C. Response Surface Methodology (RSM) is utilized to attain this goal. The fin thickness, the fin height, the width of ducts and the base thickness are selected as design parameters. The optimum volumetric percentages of PCM are found to be 80.50%, 76.94% and 74.81% for set point temperatures (SPTs) of 50 °C, 65 °C, and 80 °C, respectively. The optimized designs for three SPTs deliver charging periods up to 7% longer and discharging periods up to 4.2% shorter than the reference geometry. Furthermore, total volume of the heat sink is decreased up to 23% due to current optimizations, signifying a favourable compact design.

Innovative measures for thermal performance enhancement of single well-based deep geothermal systems: existing solutions and some viable options

Innovative measures for thermal performance enhancement of single well-based deep geothermal systems: existing solutions and some viable options

Remarkable enhancement in thermal performance of polypropylene carbonate by using exfoliated boron nitride nanosheets

Biodegradable polymers are expected to replace traditional petroleum-derived polymers to meet environmental needs. However, its poor heat resistance limits its wide use. Intensive efforts have been taken to enhance the heat resistance, but the results are less than satisfactory and involve complicated steps. In this work, a facile carboxymethylcellulose-boron nitride nanosheets (CMC-BNNS) are used to realize the heat resistance enhancement modification of biodegradable poly (propylene carbonate) (PPC). Sodium carboxymethylcellulose (CMC-Na) is used to exfoliate and functionalize hexagonal boron nitride (h-BN) for the first time. The obtained CMC-BNNS with a uniform size after differential centrifugation can be stably dispersed in water and organic solvents. Benefit from the surface multifunctional group and 2D splinting effect of CMC-BNNS, the resultant PPC/CMC-BNNS composites not only possess superior heat resistance, but also display better thermal conductivity and dynamic mechanical properties compared with PPC/BN composites. The glass transition temperature (Tg) of the of PPC/CMC-BNNS composites with 2.5 wt% CMC-BNNS loading content greatly increases to 39.19 °C from 27.39 °C of neat PPC. This work provides a novel route for exfoliating 2D materials and heat resistance modification of biodegradable polymers.

Experimental Investigation of Integrated Energy Storage on Thermal Performance Enhancement of Evacuated Glass-Thermal Absorber Tube Collector (EGATC) for Air Heating Application

Thermal energy storage (TES) in solar thermal application assist to increase the performance and efficiency of the solar thermal collector system. Various technique has been developed to enhance TES performance such as using water and PCM as energy storage material. Type of material selection and design arrangement also contribute to the performance of solar thermal collector. The aim of this research is to enhance the thermal performance of energy storage on Evacuated Glass-Thermal Absorber Tube Collector (EGATC) for air heating application. The performance study has been conducted to measure the outlet temperature and energy storage rates as per indoor setup under the artificial solar radiation on the effect of parameters such as inner absorber surface area air contact (perforated fins), outer absorber selective coating surface, outer absorber wall thickness, double layer non vacuum glass tube, single layer transparent outer glass tube and single layer thin film inner glass tube. The results showed that the performance of temperature outlet, energy store and energy buffer increase at wind speed 0.9 m/s, zero (0) perforated fin, non-coating outer absorber and 2mm outer absorber wall thickness. It was also demonstrated that a double layer vacuum glass tube showed a better thermal performance enhancement compared with double layer non-vacuum glass tube, single layer transparent outer glass tube and single layer thin film inner glass tube. This concluded that EGATC performance can be increase with those respective parameters.

Correction to: Thermal performance enhancement of shell and helical coil heat exchanger using MWCNTs/water nanofluid

Correction to: Thermal performance enhancement of shell and helical coil heat exchanger using MWCNTs/water nanofluid

Thermo-hydraulic Performance Analysis of Al2O3/water Nanofluid Flow in a Tube Extended by Twisted Tape

In this numerical study, heat transfer characteristics and hydrodynamical analysis have been performed for a circular tube inserted with twisted tape, which has different twisted pitch ratios (TPR=0, 50, 100, and 200). As a working fluid Al2O3/water nanofluid is used which has different volumetric concentrations (0.0≤φ≤3.0 vol. %). The numerical analysis has been carried out under the constant wall heat flux (q′′) of 4357 W/m2 for laminar flow ranging the Reynolds (Re) number from 1000 to 2000. According to numerical results, the highest average Nusselt number (Nu) and average Darcy friction factor (ff) have realized in twisted pitch ratio (TPR) 50. The reason is that when the twisted pitch ratio gradually decreases, stronger secondary flows and a higher velocity can be obtained. When compared with water, the highest Nu for TPR=50 has been obtained at φ=3.0 vol. % concentration as 61.15%. Also, when compared with TPR=0, the highest thermal performance enhancement (TPE) was realized at φ=3.0 vol. % concentration and Re=2000 conditions as 61.15% for TPR=50. Keywords: CFD Convective heat transfer Laminar flow Al2O3/water Twisted tape

Dynamic heat transfer characteristics of gravity heat pipe with heat storage

For the thermal performance enhancement of electronic components under intermittent high heat load, this paper proposes a gravity heat pipe with heat storage (GHPHS) that couples the advantages of GHPs and latent heat storage (LHS) units. A three-dimensional heat transfer model of GHPHS is developed and numerically studied, focusing on the comparison with traditional GHPs. Furthermore, the effects of the position and fin number of LHS units as well as the type and filling rate of phase change materials (PCMs) are investigated. The results indicate that the average heat source temperature reduces by 48.4 % and the maximum temperature duration shortens by 50 % with adding LHS units into GHPs, which can reduce the transient heat load shock and enhance the overall temperature uniformity. Moreover, the closer the LHS units is to heat sources, the better the temperature uniformity of GHPs is. When gallium is the PCM, the maximum heat source temperature reduces by 26 % when compared with the paraffin, and the increase in PCM fill rate facilitates a delay in the onset of maximum temperature and enhances the temperature uniformity. The fin number significantly affects the competition mechanisms between heat convection and conduction during the melting and solidification. As the fin number increases from 38 to 150, the maximum temperature of heat sources decreases by 29.7 % and the overall temperature uniformity of GHPs increases by 31.7 %. However, there is a limit to the influence of fin number on the thermal enhancement of GHPHSs.

An Overview of Heat Transfer Enhancement Based Upon Nanoparticles Influenced By Induced Magnetic Field with Slip Condition Via Finite Element Strategy

Abstract The mathematical model of heat generation and dissipation during thermal energy transmission employing nanoparticles in a Newtonian medium is investigated. Dimensionless boundary layer equations with correlations for titanium dioxide, copper oxide, and aluminium oxide are solved by the finite element method. Parameters are varied to analyze their impact on the flow fields. Various numerical experiments are performed consecutively to explore the phenomenon of thermal performance of the combination fluid. A remarkable enhancement in thermal performance is noticed when solid structures are dispersed in the working fluid. The Biot number determines the convective nature of the boundary. When the Biot number is increased, the fluid temperature decreases significantly. Among copper oxide, aluminium oxide, and titanium oxide nanoparticles, copper oxide nanoparticles are found to be the most effective thermal enhancers.

Thermal performance enhancement of shell and helical coil heat exchanger using MWCNTs/water nanofluid

Thermal performance enhancement of shell and helical coil heat exchanger using MWCNTs/water nanofluid

On the thermal performance enhancement of spiral-coil energy piles with a thermal recovery system

The pile foundation designed to ensure building stability when equipped with heat exchanger pipes to harvest geothermal energy is called an energy pile. Ground Source Heat Pump (GSHP) systems combined with energy piles have been used and developed as sustainable and efficient HVAC systems. Energy piles suffer from cold or heat accumulation in and around the pile, degrading their long-term performance. The current study seeks to alleviate this problem by proposing a thermal recovery system. The proposed system circulates ambient air in the pile foundation to extract the accumulated heat. A three-dimensional transient computational fluid dynamics model of the GSHP system coupled with the energy pile and the suggested recovery system is developed. This model is then used to investigate the effect of the various design parameters on the performance of the system and to determine the optimum system parameters. It is demonstrated that the maximum provided cooling load of the system with the proposed recovery system is 50% higher than the conventional system without the recovery. Moreover, the fifteen-year average COPannual of the system with double Ground-Air Heat Exchanger (GAHE) pipes and the system with one GAHE pipe is 30% and 16% more than the system without recovery.

A novel battery thermal management system based on P type triply periodic minimal surface

As an effective cooling method, liquid-cooled battery thermal management system (BTMS) is crucial to maintain the performance of the battery packs. Triply periodic minimal surface (TPMS) is a mathematically described surface with large surface area and tortuous regions. These features allow the TPMS-based structures to be used as the internal filling structures of the heat exchangers for thermal performance improvement. In this study, the TPMS-based internal filling structures in the liquid-cooled BTMS are proposed. The results demonstrate that the cooling performance and temperature consistency of the battery module can be enhanced by filling the TPMS-based structures in the cooling channel. Compared with the conventional straight tube, at the inlet flow rate of 0.003 kg/s, the maximum temperature and temperature difference of the battery module in the BTMS with the sheet structure decrease by 9.0% and 59.8%, respectively. In addition, the gradient sheet structure is designed to alleviate the temperature gradient of the coolant in the flow direction. The results illustrate that the temperature difference of the battery module in the gradient sheet structure decreases by 15.7% than that in the uniform sheet structures (c = ±0.5). This study can provide a new approach for thermal performance enhancement of the liquid-cooled BTMS.

Experimental Investigations of Thermophysical Properties and Convective Heat Transfer of Al2O3 and CuO Nanofluids in a Copper Tube: Proposing New Correlations

The performance of the Alumina/water and copper oxide/water nanofluids in a heat exchanger is experimentally investigated for particle weight concentrations ranging from 0.02 wt% to 0.5 wt%. The alumina/water and copper oxide/water nanofluids were prepared using two-step methods in an aqueous solution with 0.01 wt% CTAB (Cetyl Trimethyl Ammonium Bromide) as a surfactant at different concentrations and were characterized using HRTEM (High-Resolution Transmission Electron Microscopy) technique. Laminar forced convective heat transfer analysis using alumina and copper oxide nanoparticles suspended in water in a circular horizontal tube under constant heat flux boundary conditions was performed. The effect of various flow conditions and weight concentrations in the local heat transfer coefficient and pressure drop of both the nanofluids were investigated. Reynolds number varied from 1275 to 2200. Results show that 12.7 & 14.5 % thermal performance enhancement was observed with 0.5 wt% of Al2O3 and CuO nanofluids. Maximum, 50.62 % enhancement was observed in the average heat transfer coefficient by Al2O3 nanofluids, whereas 52.74 % was observed using CuO nanofluids using 0.5 wt% concentrations of the nanofluids and at Reynolds number of 2200. Correlations were proposed for thermal conductivity, viscosity, and Nusselt number for both the nanofluids with the maximum and minimum deviations of ±9 % and ±10 %, respectively.

Investigation of the Heat Transfer and Pressure Drop in Tubes with Transverse Ribs of Zigzag Configurations

Heat transfer through tube walls can be promoted using a ribbed tube configuration. Most of the ribs used in previous reports have equal height along the tube length. In this numerical study, we investigate the heat transfer and pressure drop in a transverse ribbed tube where ribs of unequal heights are mounted such that the tops of the ribs form a zigzag shape. Four configurations were studied. Each configuration had a set of two neighboring ribs of different heights. The set was repeated along the tube length to form a zigzag shape. The rib height ratios, e2/e1, of the four sets were 0.25, 0.5, 0.75, and 1.0. The ratios of the height of the taller rib, pitch, and width to the tube diameter were kept constant at values of e1/d = 0.1, p/d = 1.0, and w/d = 0.05, respectively. The Reynolds number ranged from 10,000 to 60,000, while the Prandtl number ranged from 0.71 to 7.0. The results from the k-ε and k-ω models were first validated and compared with the experimental results of smooth and ribbed tubes. The two models showed comparable results, with the k-ε showing slightly better performance and was thus selected to perform the current study. It was found that the average Nusselt number increases along with increases in the rib height ratio, Prandtl number, and Reynolds number. The friction factor changed exponentially with the rib height ratio, while the Reynolds number showed a minor effect. At the same pumping power, a maximum thermal performance enhancement of approximately 8% was achieved at rib height ratios of 0.25 and 0.5. The rib height ratio of 0.5 has an advantage over that of 0.25 as it has a higher average Nusselt number. Two correlations were introduced to estimate the Nusselt number and friction factor for the current ribbed tube of zigzag configurations.

Time-dependent heat transfer analysis of ellipsoidal protruded microchannel with multiple pulsating jets

Comparing with continuous jets inside microchannel, the heat removal capacity is enhanced by introducing protrusions or pulsating jets individually. Therefore, the preferred heat transfer enhancement and satisfactory thermal performance are investigated after taking both advantages of unsteady properties and ellipsoid protrusions simultaneously in this work. Especially, phase difference, Δφ, as a pivotal parameter, is applied in multiple pulsating jets. The total mass flow rate in microchannel, temperature fluctuation on heated wall, thermal and flow resistance are therefore varied. The largest fluctuation of mass flow rate is achieved when the phase difference between each adjacent jet inlets at Δφ = 0∙π, while the smallest at 0.75∙π, and the temperature distribution of the target wall correspondingly fluctuates. The heat transfer enhancement is most prominent at 0.75∙π. The increment in heat transfer is close to that of flow resistance at Δφ = 0.50∙π, 0.75∙π and 1∙π. The thermal performance TP firstly increases and then decreases with Δφ, and reaches the maximum value at 0.75∙π. Furthermore, due to the phase difference, each jet becomes the one with the highest velocity among all jets periodically, weakening adverse effect of cross flow and suppressing the drift phenomenon effectively. This is exactly the mechanism for heat transfer enhancement of unsteady multiple jets with velocity phase difference in ellipsoid protrusion microchannel.

Experimental investigation of a volumetric solar collector using natural extract of Azadirachta Indica based heat transfer fluids

Volumetric absorption solar collectors (VASC) have recently shown better photo-thermal performance than conventional solar collectors. The present study describes a novel idea for thermal performance enhancement of Volumetric absorption solar collector system using natural extract of Azadirachta Indica leaves in ethanol as heat transfer fluid (HTF) for the very first time. The optical characterization of Azadirachta Indica leaves extract was carried out using a UV–Vis spectrophotometer, which shows the first absorbance peak around 353 nm and second peak at 671 nm showing full use of visible spectrum. The real outdoor experiments showed a maximum temperature rise of 9 ℃ and a thermal efficiency enhancement of 30.4% using Azadirachta Indica based heat transfer fluids compared to the base fluid water. Furthermore, the tested heat transfer fluids were found to be very stable with no sign of agglomeration/sedimentation for 30 days. Economic analysis of natural extract based volumetric absorption solar collector system was found to be highly economical compared to flat plate solar collector with the same dimensions.

ZrO2 and MxOy (M= La, Ce, and Nb) synergistically reinforced porous cordierite ceramics synthesized via a facile solid-state reaction

In an attempt to enhance the sintering and mechanical performance of porous cordierite ceramics (Mg2Al4Si5O18) as support materials for vehicle exhaust catalysts, ZrO2 and MxOy (M = La, Ce, and Nb) were simultaneously introduced into cordierite sintered at 1350 °C for 4 h. Then, the reinforced function of ZrO2 and MxOy on the properties of porous cordierite ceramics was systematically evaluated, especially for the sample co-doped with ZrO2 and La2O3. The results displayed a distinct enhancement in mechanical and thermal performance, and the cold compressive strength increased from 72.74 to 158.59 MPa as well as thermal conductivity ranged from 1.66 to 2.01 W m−1 K−1, respectively. It is found that ZrO2 facilitated activation sintering introduced via lattice distortion in cordierite and La2O3 accelerated the formation of cordierite and ZrSiO4 microcrystalline through the low-temperature liquid phase. The synergic effect between ZrO2 and La2O3, therefore, had a significant role in the reinforced mechanical and thermal performance of porous cordierite ceramics. This work not only offers a feasible strengthening strategy, but also expands the possibilities for building high-performance structural and functional ceramics.