Increment In Thermal Conductivity Research Articles

Computational analysis of MHD hybrid nanofluid over an inclined cylinder: Variable thermal conductivity and viscosity with buoyancy and radiation effects

Due to their widespread use in engineering, hybrid nanofluids have been the primary focus of mathematical and physical research. Only the improvement of hybrid nanofluids’ variable heat conductivity and viscosity has been considered so far. Hybrid nanofluid flow across an inclined cylinder has many potential uses, including heat transfer and cooling in electrical devices, energy storage, refrigerants, and the automobile industry. Examining the effects of buoyant force, variable viscosity, variable thermal conductivity, mass suction, convective thermal conditions, and a magnetic field on the stagnation point flow of a Al2O3–Cu/H2O hybrid nanofluid in an inclined cylinder is our objective in this work. In order to find solutions to boundary-condition flow-describing partial differential equations, we turn them into ordinary differential equations using similarity transformations. We achieve this by employing a numerical strategy known as the fourth-order Runge–Kutta technique, which incorporates shooting techniques. A graphical representation of the findings emphasizes the influence of many physical parameters on flow dynamics. In addition, we address the influence of drag force and rate of heat transfer on various elements, such as the Biot parameter, magnetic variable, viscosity variable, and thermal conductivity variable. The mixed convection and magnetic parameters cause the velocity profile to rise while the temperature profile falls. The research’s results elucidate the cause behind the rise in thermal contour of hybrid nanofluids, which is seen when there is an increment in thermal conductivity, radiation parameter, and Biot number. The heat transfer rate exhibits a significant increase of 36.87% in the aiding flow scenario when a 2.0 mass suction is applied in conjunction with a 0.01 hybrid nanofluid, as compared to the conventional fluid. In the scenario of opposing flow, the heat transfer rate exhibits a significant increase of 36.96% when compared to that of ordinary fluid. Heat transfer increases 43.00% when Rd increases from 0.1 to 0.5 for both assisting and opposing flow.

Experimental study on preparation and heat transfer efficiency of ethylene glycol/water-based hybrid nanofluids enhanced by graphene oxide/MXene nanoparticles

In this study, the preparation and heat transfer efficiencies of ethylene glycol (EG)/water-based (50:50) hybrid nanofluids were enhanced using graphene oxide (GO)/MXene (1:1) nanoparticles. The stability of the nanofluids was analyzed, and the thermal conductivity and viscosity were tested at 20–60 °C. A correlation equation for the thermal conductivity ratio of the nanofluids was proposed. The heat transfer efficiency of the nanofluids was evaluated using the performance enhancement ratio (PER) and Mouromtseff number (Mo). The prepared EG/water-based GO/MXene nanofluids exhibited good chemical and dispersion stability. The thermal conductivity and viscosity of the nanofluids gradually increased with the GO/MXene dosage. The nanofluid containing 0.3 wt% GO/MXene nanoparticles exhibited the largest thermal conductivity increment of 33.49 % at 60 °C compared with EG/water and maintained the low viscosity. The proposed prediction equation based on the temperature and mass dosage was highly accurate. The PER and Mo demonstrated the suitability of the GO/MXene nanofluids for heat transfer applications.

Radial assembly of graphene nanoplates via ice-template method to construct 3D thermally conductive phase change materials

Phase change material (PCM) with the capacity to store and release substantial thermal energy, has drawn significant attention. However, its large-scale application is still hindered by inadequate thermal management capacity and unsatisfactory thermal conductivity. In this study, graphene nanoplates were assembled into a 3D thermally conductive scaffold using a specialized ice template method. By virtue of the unique growth of ice crystals in radial pattern, a series of multidirectional thermal conduction pathways were successfully constructed within PCM, which has provided microscopically interconnected pathways for thermal transport. Consequently, a remarkable 5.2-fold increment in thermal conductivity (1.365 W m−1 K−1) in comparison to pure paraffin was achieved by incorporating a mere 6 vol% of GNP, which therefore enables excellent thermal cycling stability, remarkable latent heat storage capacity exceeding 175 J/g, together with leak-proof properties even under extended high-temperature conditions. Moreover, the solar-to-thermal energy storage efficiency is up to 85.8 % due to its efficient photothermal effect. This work presents an innovative approach to design PCMs with enhanced thermal conductivity and photothermal efficiency, offering promising applications in advanced thermal storage.

Enhanced thermal conductivity of plasma generated ZnO–MgO based hybrid nanofluids: An experimental study

Hybrid nanofluids (HNFs) of metallic oxide-based nanoparticles (NPs) have been prepared in different basefluids (BFs) employing the thermal plasma technique. NPs of ZnO–MgO were directly dispersed into pristine coolant, engine oil, distilled water (DW), and coconut oil. Plasma was generated between two identical electrodes applying 8.0 kV at the ambient conditions and proved economically viable in preparing stable HNFs. X-ray Diffractometry (XRD) showed ZnO and MgO NPs possessed hexagonal and cubic crystal structures, respectively. The band gap is calculated through UV-visible spectroscopy. The thermal conductivity (TC) of the HNFs has been measured using a thermal conductivity analyzer based on the transient hot wire method. The band gaps of pristine coolant and its HNFs were obtained to be 3.35 eV and 3.33 eV, respectively. In engine oil and its HNFs, band gaps of 3.16 eV and 3.02 eV have been extracted. There appears to be a slight reduction in band gap for coolant and engine oil-based HNFs. The band gap value of coconut oil-based HNFs was 4.05 eV, which showed a higher value than the pristine coconut oil-based HNFs (3.95 eV). The band gap calculated in the case of DW-based HNFs was 3.79 eV. TC of HNFs with volume concentration of 0.019 % for DW, 0.020 % for coolant, 0.016 % for engine oil, and 0.017 % for coconut oil were tested between 20 and 60 °C. An increase in TC was observed with the rise in temperature of the HNFs. Maximum increment in TC was observed at 60 °C for coolant-based HNFs, which was 19 %, followed by DW (18%), coconut oil (18%), and engine oil (16%), respectively. DW-based HNFs can be used as a coolant and optical filter for optoelectronics devices like photovoltaic cells for better performance. The study underscores precise control of NPs size as pivotal for band gap influence. HNFs hold promise as the next-gen heat transfer fluids (HTFs), revolutionizing thermal conductivity across industries. This research lays a firm foundation for plasma-synthesized HNFs' application in enhanced heat transfer and optoelectronic devices. Coolant-based HNFs excel in thermal conductivity, addressing heat transfer challenges.

Entropy generation of thermophysical properties on heat and mass transfer pulsatile flow of non-Newtonian nanofluid

Purpose The purpose of this study is to investigate the effects of entropy generation of some embedded thermophysical properties on heat and mass transfer of pulsatile flow of non-Newtonian nanofluid flows between two porous parallel plates in the presence of Lorentz force are taken into account in this research. Design/methodology/approach The governing partial differential equations (PDEs) were nondimensionalized using suitable nondimensional quantities to transform the PDEs into a system of coupled nonlinear PDEs. The resulting equations are solved using the spectral relaxation method due to the effectiveness and accuracy of the method. The obtained velocity and temperature profiles are used to compute the entropy generation rate and Bejan number. The influence of various flow parameters on the velocity, temperature, entropy generation rate and Bejan number are discussed graphically. Findings The results indicate that the energy losses can be minimized in the system by choosing appropriate values for pertinent parameters; when thermal conductivity is increasing, this leads to the depreciation of entropy generation, and while this increment in thermal conductivity appreciates the Bejan number, the Eckert number on entropy generation and Bejan number, the graph shows that each time of increase in Eckert will lead to rising of entropy generation while this increase shows a reduction in Bejan number. To shed more light, these results were further demonstrated graphically. The current research was very well supported by prior literature works. Originality/value All results are presented graphically, and the results in this article are anticipated to be helpful in the area of engineering.

Experimental investigation of a biomass-derived nanofluid with enhanced thermal conductivity as a green, sustainable heat-transfer medium and qualitative comparison via mathematical modelling.

In this study, bio-based carbon nanospheres (CNSs) were synthesized from lignocellulosic-rich groundnut skin (Arachis hypogaea) and tested for their practical application in nanofluids (NFs) for enhanced heat transfer. The CNSs were characterized using various techniques, including FESEM, EDS, XRD, Raman spectroscopy, zeta potential analysis, and FTIR. Thermal conductivity (TC) and viscosity measurements were conducted using transient plane source (TPS) technique with a Hot Disk thermal analyser and discovery hybrid rheometer, respectively. The nanoparticles (NPs) were dispersed in two base fluids: ethylene glycol (EG) and a 60 : 40 mixture of deionized water (DI) and EG. Optimization studies were performed by varying the stirring and measurement times to improve TC values. The results showed that when a power source of 40 mW was applied at a high concentration of nanoparticles (i.e., 0.1 wt%), there was a 91.9% increment in thermal conductivity (TC) compared to the base fluid EG. DI-EG-based nanofluids (NFs) exhibited enhancements of up to 45% compared to the base fluid DI-EG (60 : 40), with a heating power of 80 mW and concentration of 0.1 wt%. These results demonstrated significant TC improvements with NP incorporation. Further experiments were performed by varying the temperature in the range of 30-80 °C with readings taken for every 10 °C increase, which showed a direct relation with the TC values. At 80 °C, EG-based NFs showed increments of 77%, 111.49%, 139.67% and 175% at 0.01, 0.02, 0.05 and 0.1 wt% concentrations of NPs, respectively. It was also found that with the increase in the concentration of NPs, viscosity increased, whereas an increase in the temperature led to a decrease in viscosity. The CNS nanofluid exhibited a Newtonian behaviour with the nanoparticle concentration and temperature, resulting in an approximately 114% enhancement compared to the base fluid when the concentration of CNSs was 0.1 wt% at 30 °C but decreased by up to 18% when the temperature was increased to 90 °C. Using appropriate mathematical models for assessing thermophysical quantities, it was discovered that the model values and experimental values correspond reasonably well. Our method thus validates our experimental results and deepens the understanding of the mechanisms behind enhancing thermal conductivity in biomass-derived nanofluids. In summary, our work advances sustainable nanomaterial synthesis, providing a new solution for boosting thermal conductivity while maintaining environmental integrity, thereby inspiring further research and innovation in this field.

Thermoresponsive Shape Memory Polymer Based on Polylactic Acid/Styrene-Butadiene-Styrene Blends with Different Inorganic Metal Fillers

In this study, polylactic acid (PLA) blended with 30 wt% styrene-butadiene-styrene (SBS) (70PLA/30SBS) was added with different fillers; Erbium Oxide (Er2O3), Halloysite Nanotubes (HNT) and Tungsten Carbide (WC2) to investigate the effect of the filler on the shape fixity (Rf) and shape recovery (Rr) at different deformation and recovery times, rheological and morphological properties. The tubular structure of HNT led to the reduction of Rf when immersed longer during the deformation phase. Meanwhile, the presence of Er2O3 improved the Rr and Rr with longer deformation and recovery times, respectively. The blend with HNT has the highest viscosity while the blend with 70PLA/30SBS-Er2O3 indicated lower viscosity than the unfilled blend. All filled blends indicated the sea-island structure with the SBS droplets in PLA continuous phase. The elements identification made on the surface of the samples illustrates that the fillers were well-distributed in 70PLA/30SBS blends. The insignificant improvement of shape memory in the presence of the thermal conductive fillers due to the dominance of the restriction of chain motion due to the presence of fillers compared with increment of thermal conductivity at low filler loading.

On the oxygen vacancy annealing in air plasma sprayed yttria‐stabilized zirconia thermal barrier coatings

AbstractYttria‐stabilized zirconia (t’‐YSZ) thermal barrier coatings (TBCs) were deposited by air plasma spraying (APS) using commercial purity and high‐purity feedstock powders. The coatings were subjected to short‐term, low‐temperature annealing (500–1200°C for 30 min). Significant structural changes were observed by X‐ray diffraction and Raman spectroscopy. These changes were attributed to annihilation of excess oxygen vacancies created by the process. APS induces partial reduction of YSZ due to the reducing potential of the high‐temperature and hydrogen‐rich plasma environment. Laser flash thermal conductivity, impulse excitation elastic modulus, and dilatometric measurements show significant changes in the YSZ during the short‐term low‐temperature thermal exposure, concurrent to the vacancy annealing. The results were analyzed in terms of the coating chemistry and the processing environment. High‐purity coatings exhibited larger increment in thermal conductivity and elastic modulus than commercial purity coatings.

Simultaneous enhancement in thermal conductivity and heat storage capability of hexadecylamine/SiO2 for thermal energy storage

Hexadecylamine (HDA) was encapsulated into SiO2 nano-shell to enhance the heat transfer rate without deteriorating the heat storage capability by a simple, environmentally benign, and cost-effective method. The investigation on the thermal properties of HDA/SiO2 ss-CPCM demonstrated that a good trade-off between latent heat capability and thermal conductivity increment was achieved. The SiO2 shell promoted the thermal conductivity and hence increased the heat transfer rate. The heat transfer rate of HDA/SiO2 ss-CPCM was enhanced during both the heating and cooling processes. It took 554 s and 454 s for the composite to vary from 40 °C to 78 °C and from 78 °C to 40 °C, <659 s and 538 s for the pure HDA. Its thermal conductivity (0.2304 W m−1 K−1) is about 200 % of that of the pristine HDA when modified with 5.1 wt% SiO2. Besides, the composite achieved an exciting latent heat capacity with a crystallization enthalpy of 210.8 J g−1 and a melting enthalpy of 214.9 J g−1. The values were a good approximation to those of pristine HDA (227.6 J g−1 and 224.3 J g−1). It also illustrated excellent thermal stability and reliability after undergoing 100 heating/cooling cycles. HDA/SiO2 ss-CPCM with good thermal properties can be applied in the field of thermal energy storage.

Enhanced flexibility and thermal conductivity of HfC decorated carbon nanofiber mats

Future-generation spacecraft components allude discovery of novel materials that can withstand extreme environments (>2000 °C). The combined effect of ultra-high temperature ceramics (UHTCs) and carbon fibers (Cf) can satisfy the demanding requirements of aerospace applications. A novel, hybrid, and flexible hafnium carbide (HfC)-decorated carbon nanofiber (Cnf) mat was fabricated via electrospinning. Enhanced thermal stability of the flexible HfC decorated Cnf over Cnf can be elucidated from the 20-fold increment in thermal conductivity and the onset of degradation at higher temperatures (840 °C). Successful integration of multi-layered sandwich lattice using in-housed fabricated HfC decorated Cnf showed retention of the fibrous structure even after extreme spark plasma sintering (SPS) process at 1850 °C. Fabricating a similar multi-layered structure using procured Cf was unsuccessful due to bundled agglomeration and micron-sized fibers. High-load indentation suggests that HfC decorated Cnf interlayer is stronger (∼2.3 times) than the parent UHTC with no cracking at the interface. Compared with the HfC matrix, the indentation-damaged area at the interface reduced up to ∼56% due to toughening mechanisms such as Cnf, fiber pull-out and bridging. The synthesized HfC decorated Cnf mat is proposed as an ultra-thin filler material for joining similar or dissimilar UHTCs while maintaining similar chemistry and better mechanical integrity at the interface. The findings insinuate a new paradigm in designing hybrid and flexible ceramic-containing materials for thermal protection systems (TPS) of future-generation spacecraft components that can mitigate failure in extreme environments (>2000 °C).

Synthesis and Characterization of Titania–MXene-Based Phase Change Material for Sustainable Thermal Energy Storage

PLUCISE A82 (PW82) is considered one of the best phase change materials as it is economical, commercially viable, and eco-friendly. Unless there is a great need to optimize the number of parameters to investigate encapsulated PCMs with good performance, for the effective and practical applications of organic phase change materials, it is required to enhance their thermal conductivity. In this study, efforts were made to increase the thermal properties of phase change materials by seeding different nanoparticles. The direct synthesis method, in which the mixing of nanoparticles in paraffin wax (PW82) takes place, is used for the production of NEPCM. Differential scanning calorimeter and heat conduction experiments were used to evaluate the effect of variable concentration of nano-encapsulation on thermal storage and heat conduction characteristics of nano-enhanced PCM. The thermal storage feasibility was also determined. In this study, titania (TiO2), Ti3C2/MXene was mixed in PW82 in 0.1, 0.2, and 0.3 wt.%. The investigation was also carried out for hybrid nano-enhanced PCM in a hybrid combination of (TiO2), and Ti3C2 (MXene) in PW82, used in wt.% concentration of 0.1, 0.2, and 0.3. Doping of titania and MXene improves the specific heat capacity of PCM. For doping of 0.3 wt.% of TiO2–Ti3C2 in PCM, the specific heat is improved to 41.3%. A maximum increment in thermal conductivity of 15.6% is found for doping of TiO2–Ti3C2 0.3 wt.%. The dissociation temperature of this prepared nano-enhanced PCM increases by ~6% for 0.3 wt.% weight fraction. Therefore, this study demonstrates that the doping of TiO2 and Ti3C2 with PW82 to form a new class of NEPCMs has significant scope to enhance the thermal storage capacity of organic paraffin.

Stability and Thermal Conductivity of Mono and Hybrid Nanoparticles Dispersion in Double-End Capped PAG Lubricant

Stable nanolubricant mixtures are interrelated with thermal conductivity enhancement, thus improving heat transfer performance in automotive air conditioning (AAC) systems. This paper studies the stability and thermal conductivity of double-end capped polyalkylene glycol (PAG)-based nanolubricants specially designed for R1234yf refrigerant. Mono nanolubricants (Al2O3/PAG and SiO2/PAG) and hybrid nanolubricants (Al2O3–SiO2/PAG) were prepared using a two-step preparation method at different volume concentrations of 0.01 to 0.05%. The stability of these nanolubricants was observed by visual, UV-Vis spectrophotometer, and zeta potential. Thermal conductivity (k) was measured from 30 to 70 °C using a C-Therm thermal properties analyser. The results from the stability analysis show that all nanolubricants were confirmed in excellent stability conditions for more than six months with minimum visual sedimentation, more than 70% concentration ratio, and zeta potentials greater than 60 mV. The Al2O3–SiO2/PAG samples recorded the highest values of thermal conductivity increment, followed by the Al2O3/PAG and SiO2/PAG samples with 2.0%, 1.7%, and 1.5% enhancement. Hybrid nanolubricants have been shown to have greater potential in the AAC system because of their excellent stability and better property enhancement in thermal conductivity.

Evaluation of groundwater pumping impact on the thermal conductivity of neighboring ground source heat exchangers

This study evaluates the correlation between groundwater velocity and the thermal conductivity and heat exchange performance of the ground source heat exchangers. The groundwater was extracted from un-grouted water well, which is located beside the drilled ground source heat exchangers (GHEs), to make artificial groundwater velocity in the region. The thermal response tests were carried out for three GHEs, which were drilled around the water well at different distances at the test site in Yamagata City, Northern Japan. During the tests, the pumping rate varied from 0 (no pumping) to 200 L/min in three steps and at two days intervals. The hydrothermal parameters of the ground around the GHEs were estimated for the GHEs and each step of pumping rate using a script in MATLAB software and with the help of the moving line source (MLS) method. This method can estimate the groundwater velocity and the effective thermal conductivity of the soil for different pumping rates to study the effect of the pumping on the neighboring GHEs. As a result, the thermal conductivity was improved by pumping groundwater in all GHEs. The rate of pumping had a direct relation with the improvement level and higher rate of pumping caused higher amount of thermal conductivity improvement. Moreover, this study showed that the location of the GHE around the pumping point does not effect on the level of thermal conductivity increment. Therefore, there was no correlation between the distance of the GHE and pumping well and the closest GHE was not necessarily experienced highest impact.

Reaction-induced phase separation towards in situ network in epoxy resins for simultaneously improving thermal conductivity and fire safety

Simultaneously improving the thermal conductivity and fire safety of the polymeric thermal management materials (PTMMs) still remains a challenge. In this work, through reaction-induced phase separation (RIPS), co-continuous networks were in situ formed between polyetherimide (PEI) and epoxy resin (EP) cured with either commercially available 4,4′-diaminodiphenyl sulfone (DDS) or the synthesized bis(4-aminophenyl) phenylphosphonate (BAPP). Boron nitride nanosheets (BNNSs) were selectively localized in the interfacial region between the EP-rich and PEI-rich phases as the thermally conductive fillers; therefore the thermally conductive networks were constructed. BNNSs and BAPP simultaneously endowed the composites with enhanced thermal conductivity and expected fire safety. In detail, the EPBAPP/PEI/BNNS composite with barely 1 wt% BNNSs showed a thermal conductivity increment over 67%; and both the heat and smoke release were greatly suppressed in cone calorimetry: the peak heat release rate (PHRR) reduced by 58%, total heat release (THR) by 56% and total smoke production (TSP) by 46%, compared with the reference. The successful application of the RIPS method in constructing in situ thermally conductive networks provided promising perspectives for designing versatile PTMMs.

Thermal transport in porous graphene with coupling effect of nanopore shape and defect concentration

Thermal conductivity of porous graphene can be affected by defect concentration, nanopore shape and distribution, and it is hard to clarify the effects due to the correlation of those factors. In this work, molecular dynamics simulation is used to compare the thermal conductivity of graphene with three shapes of regularly arranged nanopores. The results prove the dominant role of defect concentration under certain circumstances in reducing thermal conductivity, while the coupling effect of nanopore shape should be noticed. When the atoms at the local phonon scattering area around each nanopore are properly removed, the abnormal increment of thermal conductivity can be detected with the increase of defect concentration. Heat flux vector angles can effectively characterize the local phonon scattering area, which can be used to describe the effect of nanopore shape. The coupling effect of defect concentration and pore shape with similar heat flux path is clarified according to this process. By adjusting vertex angle of triangle defect, there is a balanced state of the effect factors between the variation of defect concentration and the same phonon scattering area. It provides a possible way to describe the weighing factors of the coupling effect. The results suggest a feasible approach to optimize and regulate thermal properties of porous graphene in nanodevice.

Computational analysis of heat transfer augmentation and thermodynamic irreversibility of hybrid nanofluids in a tube fitted with classical and elliptical‑cut twisted tape inserts

This work investigates heat transfer and entropy generation of a turbulent flow of an Al2O3–Cu/water hybrid nanofluid in a plain tube (PT) with classical (TPT) and elliptical‑cut twisted tape (TECT) inserts. The heat transfer and pressure drop are investigated numerically at Re (7000–15,000), mass concentration (1–4%), and the inlet temperature of the fluid (300 K). Further, the total entropy generation and Bejan number are examined at Re = 7000 and a mass concentration of 4%. The obtained results indicate that heat transfer can be intensified when inserting classical and elliptical‑cut twisted tape. In addition, an increase in the thermal conductivity of the fluid may cause a slight increase in the heat transfer coefficient. Moreover, heat transfer and thermal performance factors increase when the mass concentration of nanoparticles increases. The Nusselt numbers for TECT and TPT are 1.7 and 1.57 times higher than those for PT, respectively. The Nusselt number and thermal performance factor of hybrid nanofluid are greatest at roughly 195 and 1.9, respectively, showing 3.9% and 7.73% improvement compared to CuO/water nanofluid at Re = 7000. The analysis of the generation of entropy is expressed as a function of thermal and frictional contributions. The results indicate the existence of a minimum entropy generation for each type of tubes for Al2O3–Cu/water hybrid nanofluid. Total entropy generation analysis demonstrates that thermal entropy generation dominates at high heat flux. Moreover, increasing the nanoparticles decreases the generation of total entropy, which is ascribed to the thermal conductivity increment. In addition, the rate of total entropy generation declines as the vortex flow increases.

Influence of graphite nano powder on ethylene propylene diene monomer/paraffin wax phase change material composite: Shape stability and thermal applications

In present research, ethylene propylene diene monomer (EPDM) impregnation in liquid paraffin wax (PW) phase change material (PCM) has been accomplished for PCM shape stabilization which is of great importance in various thermal energy storage applications. Otherwise stated, EPDM rubber was mixed with specific amount of Benzoyl peroxide as a crosslink agent using two-roll mill along with hot press at 160 °C for 15 min and subsequently graphite nano powder was added to enhance extremely low PCM thermal conductivity. Afterwards, fabricated EPDM/Graphite composites have been impregnated in melted PW PCM at 120 °C for 24 h. Findings have demonstrated that, by graphite percentage increment, EPDM cross-links amount has been declined and as a consequence, swelling rate along with PW PCM content has been increased. As expected, 20 wt% graphite addition to EPDM matrix has led to thermal conductivity increment by 120 %. In addition, for all EPDM/Graphite/PW PCM composite systems, leakage amount was <1 % which is desirable for thermal energy storage applications. Furthermore, according to swelling and leakage findings, EPDM/Graphite/PW PCM composite which contains 72.5 wt% PW (EWG24), was selected as an adequate system and thermal analysis results have shown that EWG24 had highest phase change enthalpy with suitable thermal efficiency improvement (45 %). Finally, Time-Temperature history analysis has depicted that EWG24 optimum system had 28 % further heat storage compared to its corresponding EG24 composite. Ultimately, performance time has been improved by 60 % compared to graphite-free PCM system, which makes EPDM/PW PCM/Graphite composite an adequate candidate for various thermal storage applications.

Investigation on Silver Modification of Different Shaped Filler on the Heat Conduction Performance Improvement for Silicone Elastomer

The continuous miniaturization and multi-function of electronic devices have put forward high requirements for the effective removal of the heat generated in the system. Developing thermally conductive polymer composite-based thermal interface materials is becoming the research hotspot. In addition to the usually concerned intrinsic thermal conductivity of the filler itself, surface modification is one of the important ways to form an effective heat conduction pathway and improve the overall thermal conductivity of materials. In this work, we used silicon rubber as the polymer matrix and achieved the thermal conductivity increment via various fillers with different shapes. The adopted fillers are spherical aluminum oxide (Al2O3), linear carbon fiber and boron nitride sheets, which can be considered as zero-dimensional (0D), one-dimensional (1D), and two-dimensional (2D) fillers respectively. We also prepared the silver-modified fillers and investigated the influence on the formation of heat conduction pathways and interfacial thermal resistance of different shaped fillers. An obvious increment in thermal conductivity of the composite with silver-modified fillers was observed compared to the composite with pristine fillers. Furthermore, through the practical thermal management performance investigation, we found the thermal conductivity increment did improve the actual heat transfer performance of composite elastomers functioning as thermal interface materials

Energetic, exergetic, and thermoeconomic analyses of different nanoparticles-added lubricants in a heat pump water heater

The heat pumps are frequently used in domestic and industrial applications for hot water supply. The present paper aims to thermodynamically investigate the impacts of the nanoparticle-addition into the lubricants on the energetic, exergetic, and thermoeconomic aspects of a heat pump. In the experiments, air to the water heat pump is separately charged with various metal oxide-based nanoparticles (Al 2 O 3 , CuO, and TiO 2 )-added oils at a constant mass fraction of 0.5%. Polyolester (POE) and 134a are used as a lubricant, and refrigerant, respectively. The mass flow rates of the water passed through the condenser are varied from 10 to 25 g/s with an interval of 5 g/s. In the results, it is observed that the thermal conductivity value noteworthy increases with the presence of nanoparticles in POE. The highest increment in thermal conductivity is found to be 39% for POE + CuO in comparison with that of pure POE. Furthermore, with nanoparticles addition, it is noticed that the COP value generally improves, and the highest improvement for COP value is noticed to be 8% for POE + TiO 2 nanolubricant at the mass flow of 25 g/s. Furthermore, exergy efficiency enhances by 3.6%, 1.8%, and 4.5% for POE + Al 2 O 3 , POE + CuO, and POE + TiO 2 , respectively. The lowest heating cost is calculated to be 3.465 ¢/kWh at 20 g/s flow rate for POE + Al 2 O 3 . In conclusion, this paper clearly reports that usage of nanoparticles along with lubricants is presenting better energetic, exergetic, and thermoeconomic results rather than the usage of lubricant alone in the heat pumps.

Role of magnesium chloride in the performance and phase composition of lead glass sludge foam

In the present work, different MgCl2 dosages were admixed with lead glass sludge (LGS) to evaluate their effects on the performance of the produced LGS-foam at different elevated temperatures. The results revealed that adding MgCl2 caused a negative impact on the bloating process, including porosity and volume expansion reduction, as well as bulk density and thermal conductivity increment. This was associated with the high affinity of magnesium for enhancing the crystallization of LGS through the formation of diopside and cristobalite minerals. Moreover, the speed up of softening temperature of LGS using MgCl2 makes LGS completely softened before full dissociation of CaCO3, decreasing gas entrapping inside the softened LGS. Nevertheless, the use of MgCl2 decreased the free Pb inside LGS through thermal/chlorination process.