Visibility and Resolution Enhancement of Fourth-Order Ghost Interference with Thermal Light

A scheme for fourth-order double-slit ghost interference with a pseudo-thermal light source is proposed. It is shown that not only can the visibility be dramatically enhanced compared to the third-order case, but also higher resolution is demonstrated if we scan two of three reference detectors in opposite directions with the same speed, meanwhile another two in identical directions where the speed of one reference detector is twice the other. The results show that the visibility and resolution improvement of the fourth-order ghost interference fringe can be applied to the Nth-order ghost imaging.

Poly(vinylidene fluoride) Modified Commercial Paper as a Separator with Enhanced Thermal Stability and Electrolyte Affinity for Lithium-ion Battery

Commercial paper is of great potential as a ready-made substrate to make battery separator due to superior electrolyte affinity of cellulose.Nevertheless,the direct utilization of commercial paper as a separator is impracticable because of its micro-sized holes between coarse cellulose fibers,which might induce short circuits.Herein,a novel reinforced composite separator is proposed by modifying commercial paper(CP)with highdielectric polymer poly(vinylidene fluoride)(PVDF)via a vacuum filtration method.The paper substrate enables excellent electrolyte wettability and high ionic conductivity of the CP-PVDF composite separator due to the superior electrolyte affinity of cellulose molecule.Meanwhile,the strong hydrogen bonds between F atoms in PVDF and H atoms in the-OH groups of cellulose endow the separator with high thermal stability and mechanical strength.Moreover,the CP-PVDF exhibits outstanding interfacial compatibility toward Li metal anode and guarantees the prominent cycle durability of symmetric Li/Li cells up to 600 h.As a result,the LiFePO_(4)/Li cells assembled with CP-PVDF separator show dramatic rate performance with high discharge capacity of 113.7 m Ah g^(-1),and prolonged cycle life at 5 C.This work indicates that the paper-based composite membranes possess great potential for high-safety and electrochemical performance batteries.

Semi-empirical estimation for enhancing negative thermal expansion in PbTiO_(3)-based perovskites

Generally,most materials expand when heated and contract when cooled,whereas negative thermal expansion(NTE)materials are very rare.As a typical NTE material,PbTiO_(3) and related compounds have drawn particular interest in recent years.The discovery of an enhanced NTE system in PbTiO_(3) is beneficial to deepen our understanding of its mechanism and regulate its properties.At present,the method of discriminating an enhanced NTE material based on PbTiO_(3) is not universal.Here,we propose a semi-empirical method through evaluating the average lattice distortion in related systems to estimate the relative coefficient of thermal expansion conveniently.The rationality of the method was verified by the analysis of the 0.6PbTiO_(3)-0.4Bi(Ga_(x)Fe_(1-x))O_(3) system.So far,all PbTiO_(3)-based compounds with enhanced NTE conform well to this method.This method provides the possibility to find more enhanced NTE PbTiO_(3)-based materials.

Thermal Conductance of Cu and Carbon Nanotube Interface Enhanced by a Graphene Layer

Thermal conduetances between Cu and graphene covered carbon nanotubes （gCNTs） are calculated by molecular dynamics simulations. The results show that the thermal conductance is about ten times larger than that of Cu- CNT interface. The enhanced thermal conductance is due to the larger contact area introduced by the graphene layer and the stronger thermal transfer ability of the Cu-gCNT interface. From the linear increasing thermal conductance with the increasing total contact area, an effective contact area of such an interface can be defined.

Improving Heat Transfer in Parabolic Trough Solar Collectors by Magnetic Nanofluids

A parabolic trough solar collector(PTSC)converts solar radiation into thermal energy.However,low thermal efficiency of PTSC poses a hindrance to the deployment of solar thermal power plants.Thermal performance of PTSC is enhanced in this study by incorporating magnetic nanoparticles into the working fluid.The circular receiver pipe,with dimensions of 66 mm diameter,2 mm thickness,and 24 m length,is exposed to uniform temperature and velocity conditions.The working fluid,Therminol-66,is supplemented with Fe3O4 magnetic nanoparticles at concentrations ranging from 1%to 4%.The findings demonstrate that the inclusion of nanoparticles increases the convective heat transfer coefficient(HTC)of the PTSC,with higher nanoparticle volume fractions leading to greater heat transfer but increased pressure drop.The thermal enhancement factor(TEF)of the PTSC is positively affected by the volume fraction of nanoparticles,both with and without a magnetic field.Notably,the scenario with a 4%nanoparticle volume fraction and a magnetic field strength of 250 G exhibits the highest TEF,indicating superior thermal performance.These findings offer potential avenues for improving the efficiency of PTSCs in solar thermal plants by introducing magnetic nanoparticles into the working fluid.

Thermal Property Enhancement of a Novel Shape-Stabilized Sodium Acetate Trihydrate-Acetamide/Expanded Graphite-Based Composite Phase Change Material

Phase change materials(PCMs)are a kind of highly efficient thermal storage materials which have a bright application prospect in many fields such as energy conservation in buildings,waste heat recovery,battery thermal management and so on.Especially inorganic hydrated salt PCMs have received increasing attention from researchers due to their advantages of being inexpensive and non-flammable.However,inorganic hydrated salt PCMs are still limited by the aspects of inappropriate phase change temperature,liquid phase leakage,large supercooling and severe phase separation in the application process.In this work,sodium acetate trihydrate was selected as the basic inorganic PCM,and a novel shape-stabilized composite phase change material(CPCM)with good thermal properties was prepared by adding various functional additives.At first,the sodium acetate trihydrate-acetamide binary mixture was prepared and the melting point was adjusted using acetamide.Then the binary mixture was incorporated into expanded graphite to synthesize a novel shape-stabilized CPCM.The thermophysical properties of the resultant shape-stabilized CPCM were systematically investigated.The microscopic morphology and chemical structure of the obtained shape-stabilized CPCM were characterized and analyzed.The experiment results pointed out that acetamide could effectively lower the melting point of sodium acetate trihydrate.The obtained shape-stabilized CPCM modified with additional 18%(mass fraction)acetamide and 12%(mass fraction)expanded graphite exhibited good shape stability and thermophysical characteristics:a low supercooling degree of 1.75℃and an appropriate melting temperature of 40.77℃were obtained;the latent heat of 151.64 kJ/kg and thermal conductivity of 1.411 W/(m·K)were also satisfactory.Moreover,after 50accelerated melting-freezing cycles,the obtained shape-stabilized CPCM represented good thermal reliability.

Enhanced heat transfer in a heat exchanger square-duct with discrete V-finned tape inserts

The article presents an experimental and numerical study on thermal performance enhancement in a constant heatfluxed square-duct inserted diagonally with 45° discrete V-finned tapes(DFT).The experiments were carried out by varying the airflow rate through the tested square duct with DFT inserts for Reynolds number from 4000 to 25000.The effect of the DFT with V-tip pointing upstream at various relative fin heights and pitches on heat transfer and pressure drop characteristics was experimentally investigated.Both the heat transfer and pressure drop were presented in terms of Nusselt number and friction factor respectively.Several V-finned tape characteristics were introduced such as fin- to duct-height ratio or blockage ratio(R_B=e/H = 0.075,0.1,0.15 and 0.2),fin pitch to duct height ratio(R_P= P/H=0.5,1.0,1.5 and 2.0) and fin attack angle,α = 45°.The experimental results reveal that the heat transfer and friction factor values with DFT inserts increase with the increment of R_B but the decrease of R_P.The inserted square-duct at R_B = 0.2 and R_P = 0.5 provides the highest heat transfer and friction factor while the one with R_B= 0.1 and R_P= 1.5 yields the highest thermal performance.Also,a numerical simulation was conducted to investigate the flow structure and heat transfer mechanism inside the tested duct with DFT inserts.

Integral treatment for forced convection heat and mass transfer of nanofluids over linear stretching sheet

An integral treatment is proposed for the analysis of the forced convection flow of a nanofluid over a stretching sheet. The obtained results agree well with the numerical results. The results of the presented solution provide an analytic solution, which can be conveniently used in engineering applications. Four types of nanoparticles, i.e., alumina （Al2O3）, silicon dioxide （Si02）, silver （Ag）, and copper （Cu）, dispersed in the base fluid of water are examined. The analytical results show that an increase in the volume fraction of nanoparticles increases the thickness of the thermal boundary layer. The reduced Nusselt number is a decreasing function of the volume fraction of nanoparticles. ＇ Key words nanofluid, integral method, stretching sheet, analytical solution, thermal enhancement

Wet-resilient graphene aerogel for thermal conductivity enhancement in polymer nanocomposites

Three-dimensional(3 D)graphene-based aerogels have significant potential for adsorption,sensors,and thermal management applications.However,their practical applications are limited by their disorganized structure and ultra-low resilience after compression.Some methods can realize a well-aligned structure,however,they involve high costs and complex technology.Herein,a 3 D graphene hybrid aerogel with an anisotropic open-cell and well-oriented structure is realized by unidirectional freeze casting,which combines the‘soft’(e.g.graphene oxide,Tween-80)and‘hard’(e.g.graphene assembly)components to realize full recovery after flattening.A graphene aerogel annealed at a moderate temperature(200℃)can possess superhydrophilicity and outstanding wet-resilience properties,including after being pressed under40 MPa.Furthermore,the graphene aerogel annealed at a high temperature of 1500℃exhibits excellent thermal conductivity enhancement efficiency in polydimethylsiloxane(PDMS).The resultant nanocomposites clearly demonstrate anisotropic thermal conductivity and promising applications as thermal interface materials.This strategy offers new insights into the design and fabrication of 3 D multifunctional graphene aerogels.

Uniform, fast, and reliable CMOS compatible resistive switching memory

Resistive switching random access memory(RRAM) is considered as one of the potential candidates for next-generation memory. However, obtaining an RRAM device with comprehensively excellent performance, such as high retention and endurance, low variations, as well as CMOS compatibility, etc., is still an open question. In this work, we introduce an insert TaO_(x) layer into HfO_(x)-based RRAM to optimize the device performance. Attributing to robust filament formed in the TaO_(x) layer by a forming operation, the local-field and thermal enhanced effect and interface modulation has been implemented simultaneously. Consequently, the RRAM device features large windows(> 10^(3)), fast switching speed(-10 ns), steady retention(> 72h), high endurance(> 10^(8) cycles), and excellent uniformity of both cycle-to-cycle and device-to-device. These results indicate that inserting the TaO_(x) layer can significantly improve HfO_(x)-based device performance, providing a constructive approach for the practical application of RRAM.

A state-of-the-art review on shallow geothermal ventilation systems with thermal performance enhancement-system classifications,advanced technologies and applications

Geothermal energy with abundance and large quantity can partially cover building heating/cooling loads and promote the carbon-neutrality transitions.Shallow geothermal ventilation(SGV)system,with a little initial in-vestment cost,is one of promising technologies to partly replace the conventional air-conditioning system for air pre-cooling/pre-heating.This paper reviews applications of SGV system for improving thermal performance over latest two decades,which mainly includes the reclassification of SGV system,coupling with other advanced energy-saving technologies,application potentials for building cooling/heating under various weather conditions.Heat transfer mechanism and mathematical modelling techniques have been reviewed,together with in-depth analysis on current research trends,existing limitations,and recommendations of SGV system.Phase change materials,with considerable latent energy density,can stabilize the thermal performance with high reliability.The review identifies that optimization designs and advanced approaches need to be investigated to address the existing urgent issues of SGV system(e.g.,large land occupation,difficulty in centralized collection of condensate water timely for horizontal buried pipe,bacteria growth,polluted supply air,and high construction cost for ver-tical buried pipe).A plenty of studies show that the SGV system could greatly expand the application scope and improve system energy efficiency by combining with other energy-saving technologies.This paper will provide some guidelines for the scientific researchers and engineers to keep track on recent advancements and research trends of SGV system for the building thermal performance enhancement and pave path for future research works.

A technique for enhancing the thermal stability of hydrogen-loaded fiber Bragg grating

Heat treatment with the presence of hydrogen (H2) that react with GeE' centers (Ge≡) at high temperature will weaken the refractive index modulation of grating fabricated in hydrogen-loaded normal germanosilicate fiber. Pre-annealing treatment of the above fiber was demonstrated to be able to enhance the grating's thermal stability effectively. 0.37-nm blue-shift of the reflected Bragg wavelength was observed.

Ce-doped MIL-125-NH_(2)coupled Ce^(4+)/Ce^(3+)and Ti^(4+)/Ti^(3+)redox mediators for thermo-enhanced photocatalytic oxidative desulfurization

Photocatalytic oxidative desulfurization(PODS)over efficient earth-abundant catalysts to obtain clean fuel oil is of great importance for the environmental protection.In this work,a series of Ce-doped MIL-125-NH_(2)photocatalysts were successfully prepared via a simple in-situ doping method and exhibited superior PODS performance of dibenzothiophene(DBT)under mild reaction conditions.The 1.0 mol%Ce/MIL-125-NH_(2)catalyst achieved 100%sulfur removal within 22 min at 30℃ under visible light illumination,which is mainly attributed to the high surface area and the formation of Ce-Ti-oxo clusters due to electronic coupling.The valence transformation of Ce^(4+)/Ce^(3+)and Ti^(4+)/Ti^(3+)redox mediators could not only expose abundant Lewis acid sites,but also promote the separation and transfer of photogenerated charges.In addition,increasing the reaction temperature has been demonstrated to be effective in promoting the PODS performance.Additionally,a thermo-enhanced PODS mechanism was proposed over Ce/MIL-125-NH_(2),demonstrating the great potential of thermal energy to promote the desulfurization activity.

Optimization of Dimples in Microchannel Heat Sink with Impinging Jets-Part B： the Influences of Dimple Height and Arrangement

The combination of a microchannel heat sink with impinging jets and dimples(MHSIJD) can effectively improve the flow and heat transfer performance on the cooling surface of electronic devices with very high heat fluxes. Based on the previous work by analysing the effect of dimple radius on the overall performance of MHSIJD, the effects of dimple height and arrangement were numerically analysed. The velocity distribution, pressure drop, and thermal performance of MHSIJD under various dimple heights and arrangements were presented. The results showed that: MHSIJD with higher dimples had better overall performance with dimple radius being fixed; creating a mismatch between the impinging hole and dimple can solve the issue caused by the drift phenomenon; the mismatch between the impinging hole and dimple did not exhibit better overall performance than a well-matched design.

Processing Compressed Expanded Natural Graphite for Phase Change Material Composites

Phase change materials(PCMs)are used in various thermal energy storage applications but are limited by their low thermal conductivity.One method to increase conductivity involves impregnating organic PCMs into highly porous conductive matrix materials.Of these materials,compressed expanded natural graphite(CENG)matrices have received the most attention.Despite this attention,the effect that CENG processing has on PCM saturation and overall matrix thermal conductivity has not been fully investigated.Therefore,the effect of the heat treatment process used to expand intercalated graphite flakes is evaluated here.Higher heat treatment temperatures yielded higher saturation rates and overall saturation at similar matrix porosities.For example,increasing temperature from 300℃to 700℃resulted in approximately 60%-70%increase in pore saturation after 100 minutes of soaking.The exposure time to heat treatment had less of an effect on PCM saturation.The exposure time had negligible effect above 30 min and above 500℃heating temperatures.However,because the expanded graphite was found to oxidize around 700℃,the use of longer exposure time in manufacturing applications can be beneficial if a shortened impregnation time is needed.Heat treatment conditions did not impact thermal conductivity.The composite latent heat of fusion was also reduced approximately proportionally to the PCM mass fraction.A local maximum in axial thermal conductivity was observed at around 83%porosity,which is similar to previous studies.The observed conductivity at this maximum was a factor of 81 times greater than the conductivity of the PCM.

Ultralong afterglow and unity quantum yield from a transparent CsCdCl_(3):Mn crystal

Transparent afterglow crystals are keenly desired for three-dimensional information storage.Herein,CsCdCl3 perovskite crystals were grown by a programmable cool-ing procedure in a hydrothermal reactor.The pristine crystal showed an abnormal optical behavior where the absorption increased by 2.3 folds at high temperature,leading to a fourfold boost of photoluminescence(PL)intensity.After Mn2+dop-ing,the PL quantum yield was improved to nearly unity.Importantly,the doped crystals exhibited an ultralong afterglow up to 12 h after ceasing UV excitation and a high transmittance up to 75%in the visible region.This work brought a new mem-ber to the library of transparent afterglow crystal,opening up many possibilities to advanced applications such as volumetric display and three-dimensional information encryption.