Transfer Process Research Articles

Turning Waste into Treasure: Utilizing Environment-Pollutant Graphite Tailings as Photocatalyst for Photocatalytic Building Materials

Graphite tailings, as solid waste residuals from graphite extraction and refinement, pose serious risks to the surrounding ecological environment and the safety of residents’ lives. However, it is desirable but challenging how to rationalize the utilization of graphite tailings and further to develop their functionality. Herein, we demonstrate a "turning waste into treasure" strategy: capitalizing on the characteristics of graphite tailings in visible light absorption and rich metal catalytic sites, graphite tailings are employed as photocatalysts and fine aggregates to manufacture photocatalytic building materials, achieving sustainable use. Tailings powder from Luobei, Heilongjiang Province is selected as the photocatalyst, we discover that it exhibits photocatalytic degradation capability for methylene blue (MB) in water under visible-light irradiation: the degradation rates reach 70% within one hour and near-complete degradation within two hours, accompanying good recyclability. Structural analysis reveals that the graphite tailings are enriched with Fe2O3 and TiO2. They are capable of forming type-II heterojunction that enable efficient charge separation and transfer processes, transmitting photogenerated electrons to the active catalytic site to accomplish the photocatalytic degradation of MB. Moreover, other tailings, such as those from Jixi, also achieve photocatalytic degradation of MB, and cement specimens made with graphite tailings also bespoke photocatalytic degradation performance. This work is to provide solutions for the reuse of graphite tailings in the field of functional building materials, and to explore the feasibility of transforming graphite tailings from industrial solid waste to photocatalytic building materials.

Exploring photophysical behavior and fullerene-induced quenching in difluoroboron flavanone [formula omitted]-diketonates for application in organic electronic devices: Experimental and theoretical analysis

The photophysical properties of two difluoroboron flavanone β-diketonates (DK1 and DK2) and their interaction with fullerene (C60) in toluene solution and spin-coated films were investigated using time-correlated single-photon counting, absorption spectroscopy, and steady-state fluorescence spectroscopy. In molecular crystal, the complexes exhibited red-shifted absorption and emission relative to their spectra in solution. Additionally, both complexes displayed bi-exponential decay behavior in time-resolved fluorescence measurements, indicating their capability to form both H and J types of aggregates in the solid state. The introduction of C60 resulted in significant fluorescence quenching and reduced excited-state lifetimes for both complexes. This quenching, observed in both solution and spin-coated films, was primarily driven by photo-induced electron transfer (PET) processes, underscoring the potential of these complexes as donors in fullerene-based heterojunction organic solar cells. To elucidate the process of aggregate formation and the impacts of different dimerization types within the crystalline structure of the complexes, first-principles calculations using Density Functional Theory (DFT) and time-dependent density functional theory (TD-DFT) were performed. We also employed DFT to explore various DK configurations on the fullerene surface, evaluating intermolecular distances and formation energies. These calculations highlighted the energetically favourable gap between the low-lying LUMO levels of the complexes and C60, confirming their suitability for such applications.

Thermal-Hydraulic Characteristics of an Earth Air Heat Exchanger: An experimental analysis

The pipe layout design has a great effect on the thermal-hydraulic characteristics of earth air heat exchanger (EAHE) systems. So, in the current study proposed four new buried pipe design configurations; low to high to low, high to low to high, spiral, and circular, in addition to the straight or uniform for comparison. These five configurations are tested and analyzed experimentally depending on the thermo-hydraulic performance for summer cooling requirements with variation of Re in the range of 18041 – 40843. The results show that changing the uniform design of the EAHE with fixed pipe length enhances both the heat transfer process and pressure loss values. At the same operating conditions, the circular design has the best performance compared to the other ones. For all pipe shapes, the cooling effect increases with the increase of air Re. The thermal- hydraulic performance of the circular design pipe is higher than that of the other pipe designs. The highest coefficient of performance (COP) average values that can be obtained at Re = 18041 is 3.05 for circular shape and enhances by 48.08 % compared to uniform shape. The effectiveness of EAHE with circular shape is improved by about 3.52 % compared to uniform shape at Re = 18041. Spiral design is optimum design based on the Nu value which reaches about 48 with enhancement 12.56% and 0.34 % compared to uniform and circular shapes respectively, at Re = 40843. The hydrothermal performance factor is highest in the case of circular shape with value about 21.9 at Re = 21257. By increasing Re, the drawbacks of the increasing in the total entropy generation are reflected negatively on the exergy efficiency. The specific cost of the circular shape at Re = 40843 is the optimum value by about 0.7 $/W. Spiral and circular shapes have a decrease of CO2 emissions less than uniform shape by percentage varied from 2.93 % to 13.84% for decrease in the Re from 21257 to 40843. It is concluded that using EAHE with four new shapes is highly efficient in increasing cooling capacity and energy consumption in buildings.

Dynamic analysis of the bubble's spatiotemporal evolution on a microheater under microsecond pulse heating

Transient heating of liquids upon a microheater surface manifests an exceedingly rapid temperature escalation, inducing a pronounced superheating at the onset of nucleation. Rare study focuses on the spatiotemporal behavior of subcooled boiling bubbles on a thin-film microheater surface. The present study experimentally explores the subcooled pool boiling heat transfer process on a platinum thin-film microheater with dimensions of 1000 μm × 1000 μm under microsecond pulse heating conditions. The visualized results indicate that three typical heat transfer regimes related to various heating scenarios can be identified, including the single-phase, nucleate boiling and film boiling heat transfer regimes. Consequently, the boiling incipience moment and the corresponding average microheater temperature are meticulously discussed and compared with analogous scholarly contributions. Moreover, the rapid bubble lifecycle involving nucleation, growth, coalescence and collapse within approximate 130 μs under microsecond pulse heating is captured and detailly analyzed. At lower heat flux, the boiling process is distinctly classified into five phases: (I) single-phase heat transfer, (II) isolated bubbles nucleation, growth and coalescence, (III) formation and growth of vapor blanket, (IV) shrinkage and collapse of vapor blanket, followed by (V) microbubbles condensation. As the vapor blanket nearly envelops the microheater completely, the temperature dramatically surges, with the increase rate markedly surpassing that observed during phase II. When further raising the heat flux, the regrowth of main bubble locating at the central area can be observed. Meanwhile, the nucleation and growth of numerous microbubbles in the peripheral zones after the collapse of vapor blanket are identified.

Eletrochemical evaluation of a sensor modified with tucumã biochar for analysis of environmental samples

In this study, a carbon paste electrode modified with tucumã biochar (EPCM/TB) was produced for the determination of pyridine in industrial effluents. To develop the methodology, different paste proportions were evaluated, and a proportion of 40:30:30 (m/m/m) of graphite:tucumã biochar:binder was selected. Cyclic voltammetry was used to characterize the charge and mass transfer process of the electrochemical system; the reaction occurred with the transfer of two electrons. The reaction was irreversible and controlled by diffusion. The experimental variables such as the supporting electrolyte, pH and instrumental parameters of the differential pulse voltammetry (DPV) technique were evaluated. After the optimization of these parameters, four analytical curves were constructed using DPV to calculate the matrix effect (ME). The analytical curves in the presence of the matrix showed good linearity for the three effluents, with R2 values of 0.991, 0.997 and 0995. The limits of detection (LODs) for effluents 1, 2 and 3 were 34.9, 5.5 and 36.8 nmol/L, respectively. The limits of quantification (LOQs) for effluents 1, 2 and 3 were 116.6 nmol/L, 18.4 nmol/L and 122.6 nmol/L, respectively. The MEs of the three effluent samples showed values above 50.0 %, indicating strong MEs; therefore, the quantification of pyridine was performed using the matrix curves. The method had recoveries close to 100 % for the three effluents. The repeatability and reproducibility studies of the method provided RSD% values below 5 %; therefore, the method has potential application in the quantification of pyridine in textile effluents.

A Novel Image Formation Model for Descattering.

In the field of image descattering, the image formation models employed for restoration approaches are often simplified. In these models, scattering distribution is uniform in homogeneous media when transmission is fixed. Through specifically designed experiments, we discover that scattering exhibits non-uniform characteristics even in homogeneous media. Neglecting non-uniform scattering in these models limits their accuracy in representing scattering distribution, resulting in existing image descattering approaches inadequate. To tackle these issues, this paper proposes a novel image formation model for image descattering, considering more physical parameters, such as zenith angle, azimuth angle, scattering phase function, and camera focal length. Our model describes the light transfer process in scattering media more accurately. For image descattering, we introduce corresponding algorithms for parameter estimation in our model and simultaneous restoration from degraded images. Experimental evaluations demonstrate the effectiveness of our proposed model in various tasks, including physical parameter estimation, pure-scattering removal, image dehazing, and underwater image restoration. In terms of calculating parameters, our results are close to the real values; in terms of underwater image restoration, our work outperforms the state-of-art methods; in terms of image dehazing, our work promotes the performance of existing methods by replacing previous models with our model.

Construction and verification of distributed hydrothermal coupling model in the source area of the Yangtze River

Study regionThe source area of the Yangtze River, a typical catchment in the cryosphere on the Tibet Plateau, was used to develop and validate a distributed hydrothermal coupling model. Study focusClimate change has caused significant changes in hydrological processes in the cryosphere, and related research has become hot topic. The source area of the Yangtze River (SAYR) is a key catchment for studies of hydrological processes in the cryosphere, which contains widespread glacier, snow, and permafrost. However, the current hydrological modeling of the SAYR rarely depicts the process of glacier/snow and permafrost runoff from the perspective of coupled water and heat transfer, resulting in distortion of simulations of hydrological processes. Therefore, we developed a distributed hydrothermal coupling model, namely WEP-SAYR, based on the WEP-L (Water and energy transfer process in large river basins) model by introducing modules for glacier and snow melt and permafrost freezing and thawing. New hydrological insights for the regionIn the WEP-SAYR model, the soil hydrothermal transfer equations were improved, and a freezing point equation for permafrost was introduced. In addition, the glacier and snow meltwater processes were described using the temperature index model. Compared to previously applied models, the WEP-SAYR portrays in more detail glacier/snow melting, dynamic changes in permafrost water and heat coupling, and runoff dynamics, with physically meaningful and easily accessible model parameters. The model can describe the soil temperature and moisture changes in soil layers at different depths from 0 to 140cm. Moreover, the model has a good accuracy in simulating the daily/monthly runoff and evaporation. The Nash-Sutcliffe efficiency exceeded 0.75, and the relative error was controlled within ±20%. The results showed that the WEP-SAYR model balances the efficiency of hydrological simulation in large scale catchments and the accurate portrayal of the cryosphere elements, which provides a reference for hydrological analysis of other catchments in the cryosphere.

Carbon dioxide capture in sodium carbonate solution: Mass transfer kinetics and DTAC surfactant enhancement mechanism

Sodium carbonate solvent absorbent has been widely studied for CO2 reduction to deal with global warming because of its green, low cost, and non-corrosive advantages. However, in the application of sodium carbonate as an absorbent for CO2 capture, there is no unified cognition of the mass transfer process, which leads to the lack of guidance for the industrial large-scale process. Moreover, the mechanism of mass transfer enhancement of surfactants, which can effectively improve the mass transfer performance, has not been effectively explored in the literature. Based on this, this paper firstly adopts the molecular dynamics method to analyze the solution characteristics after surfactant addition and optimize the surfactant. Subsequently, a classical dissolved oxygen test method was used to measure the gas-liquid mass transfer coefficient for CO2 absorption into sodium carbonate solution. And based on this mass transfer coefficient measurement method, the mass transfer process of sodium carbonate solution with surfactant was analyzed. The results showed that the sodium carbonate solution with 5 wt% concentration and 10 wt% concentration at 30 °C did not satisfy the pseudo first-order fast chemical reaction kinetics assumption. To improve CO2 absorption mass transfer rate, dodecyl trimethyl ammonium chloride (DTAC) surfactant was introduced, which was improved by 119 % compared with non-enhanced solvent at 5 wt% concentration solution, and the assumption of pseudo first order fast chemical reaction was satisfied. After the introduction of surfactant, the barrier effect decreased the liquid phase mass transfer coefficient, but the Marangoni effect happened in the 5 wt% concentration of sodium carbonate solution, which enhanced the liquid-phase mass-transfer coefficient. This finding reveals the mechanism of mass transfer promotion of sodium carbonate by the surfactant DTAC, which is of great engineering significance for the application in the field of decarbonization after the introduction of surfactant.

The interfacial charge change enhanced by Pr0.6Sm0.4Co0.8Mn0.2O3 activated peroxymonosulfate was used for the efficient degradation of tetracycline under the nanoscale domain limiting and distance effect

In this work, an improved sol-gel method was used to prepare a series of Co-infused PrSmMnO3 perovskites (Pr0.6Sm0.4Co1-XMnXO3, PSCM) to rapidly activate peroxymonosulfate (PMS) for efficient degradation of tetracycline (TC). The experimental results showed that the degradation efficiency of the PSCM-82/PMS system for TC in the pH 2-11 range was close to 100%. The nanoscale domain-limiting and distance effect of PSCM under different activators were discussed, and the catalytic mechanism of the non-radical electron transfer pathway in the PSCM-82/PMS system was proposed. After the optimization of the DFT calculation, it can be seen that the dCo-Mn-Co range of the PSCM-82 material is 9.8 - 9.9 Å. The molecular size of PMS is 9.9 Å, which precisely matches the dCo-Mn-Co range of the material. Moreover, the distance between molecular sizes was relatively minimal, and the interface charge transfer was enhanced by both the confinement and distance effects. This promotes a fast catalytic reaction and an optimal degradation rate. During this process, PMS molecules were adsorbed by the active metal sites on the surface of PSCM-82, resulting in a large amount of interfacial charge transfer. This allows a strong coupling between the PMS and the catalyst, resulting in a reaction surface with high redox potential. According to the results of density functional theory (DFT) calculation, quenching experiment, electron paramagnetic resonance (EPR) experiment and electrochemical research, it can be concluded that the main degradation pathway of TC is realized through the direct electron transfer process.

Enhanced Chirality Transfer in Self‐Assembled Nanocomposites Powered by A Trace Amount of Chiral Dimeric Molecules

Chiral‐selective self‐assembly has markedly advanced the development of chiral materials. While the Sergeant and Soldiers principle allows for chirality amplification, it necessitates precise shape‐matching between chiral and achiral molecules, leading to a low chirality transfer efficiency—where one chiral molecule influences the chirality of a limited number of achiral molecules. Here, we show that this efficiency can be markedly enhanced by introducing chiral dimeric molecules. In this work, a single chiral molecule can control the chirality of up to 200 achiral molecules and even direct the assembly of inorganic nanoparticles into chiral nanocomposites through a sequential chirality transfer process. Moreover, this approach exhibits remarkable robustness, operating effectively without necessitating a precise match between chiral and achiral molecules. Consequently, using the same chiral molecules at an exceptionally low molar fraction (0.5 mol%) allows for the chiral‐selective assembly of achiral molecules over a broad spectrum, regardless of their packing habits, thus facilitating the creation of otherwise inaccessible chiral materials with modulated chiroptical properties. Last but not least, even a trace amount of chiral molecules can enhance the elastic modulus of the self‐assembled nanocomposites by a factor of eight.

Chemoselective Dehydrogenation and Hetero-Arylation of Amides via Radical Translocation Enabled by Photoexcited Triplet Ketone Catalysis.

We herein report the chemoselective dehydrogenation and heteroarylation of amides through photoexcited triplet ketone catalysis. Under mild reaction conditions, the generated aryl radical through the halogen atom transfer (XAT) process further undergoes an intramolecular 1,5-HAT event to generate an α-amido alkyl radical, which then intercepted with either cobalt or a reduced cyano arene radical leads to dehydrogenated and heteroarylated products, respectively, in good yields.

Reduction of 4‐Nitrophenol Catalyzed by Gold Nanoclusters with Aggregation‐Induced‐Emission: Emission Intensity Correlated Activity and Mechanistic Exploration

AbstractThiolate‐protected Au nanoclusters (NCs) have developed as a promising class of model catalysts to achieve fundamental understanding of metal nanocatalysis. Whereas, the packing mode of peripheral ligand on metal core is changeful in the reaction medium and show elusive impact on catalytic activity. In this work, using glutathione (GSH) protected Au NCs (Au@GSH NCs) with aggregation‐induced‐emission (AIE) characteristics as model catalyst for the hydrogenation of 4‐nitrophenol (4‐NP), photoluminescence (PL) intensity correlated catalytic activity of Au@GSH NCs was successfully mediated by the addition of Ag+ in the preparation or poor solvent in the reaction medium, showing a relationship of “as one falls, another rises.” Au NCs with intense PL implied a dense packing of peripheral ligand, which hampered the accessibility of active site and thus exhibited slowest catalytic reaction kinetics of the reduction of 4‐NP and vice versa. Based on this methodology, a case study of the effect of salt additives on the catalytic activity is carried out, different mechanisms are distinguished by the change in the PL intensity, and with the combination of diagnostic deuterium isotope experiments, it has been demonstrated that the proton from water solvent is involved in the reaction and that the proton transfer process is the rate‐determining step, the contribution of ionic additives to the hydrogen bonding network determines their effect on the reaction kinetics. The correlation between PL intensity and catalytic activity of Au NCs could provide an efficient way to design highly active Au NC catalysts and give a new insight to understand the unique optoelectronic properties of Au NCs and reaction mechanism.

Design and experimental demonstration of functional devices for energy manipulation in new analog acoustic computers

The development of new analog computers based on analog signals of electromagnetic or elastic waves has become a hot research topic in recent years. In this Letter, based on the concept of quantum state transfer, we study the process of energy transfer between acoustic cavities. Through the transformation from the temporal domain to the spatial domain, we further study the process of energy transfer between acoustic waveguides, and then we realize the applications of energy distributors and limiters in the acoustic system, which are the functional devices of wireless communication technology in new analog acoustic computers. We both simulationlly and experimentally demonstrate the effectiveness of the two applications. The energy distributor and limiter we proposed have the advantages of a relatively wide operating frequency range and adjustability. Our work shows the transfer mechanism of acoustic energy between different structures, which increases its potential application value in new analog acoustic computers.

Picosecond Pulse Radiolysis Observation of the Formation and Spur Kinetics of Hydrated Electrons in Sodium Dodecyl Sulfate-Water-Cyclohexane-Hexanol Quaternary Microemulsions.

The observation of electron transfer and solvation processes in liquid-liquid multiphase systems is of great challenge, especially at the interface. In this study, the formation and spur kinetics of hydrated electrons (eaq-) were investigated in sodium dodecyl sulfate-water-cyclohexane-hexanol microemulsions with ω values (nwater/nsurfactant) from 18 to 48 using picosecond pulse radiolysis coupled with pulse-probe UV-vis spectroscopy. Interestingly, a relatively slow formation of eaq- was observed, corresponding to the electron transfer from the oil phase to water pools. The evolution curves of eaq- were simulated by using a simplified consecutive reaction model. It demonstrated that the electrons generated in the oil phase are solvated in the water pools of the microemulsions at a close rate. Surprisingly, the addition of NaNO3 could accelerate electron transfer into water pools. The decays of eaq- in the microemulsions were significantly slower than that in pure water and accelerated with increasing water content, indicating the absence of a nanoconfinement effect.

Prussian Blue Analogue‐Based Materials: Synthesis and Their Application in Peroxymonosulfate Activation for Wastewater Treatment

AbstractPeroxymonosulfate‐(PMS) based advanced oxidation processes (AOPs) are effective in degrading refractory organic pollutants in water. The unique internal chemical tunability of Prussian blue analogues (PBAs), a type of metal–organic framework materials (MOFs), makes them promising catalysts for PMS‐AOPs. However, the pristine PBA is limited in practical application due to its structural instability and easy leaching of metal ions. To this end, various methods have been developed to enhance the recycling and catalytic performance of PBAs. In this paper, the recent advances in the modification and composite strategies of PBA catalysts are systematically reviewed. PBA modification by the regulation of synthesis conditions and postsynthesis treatment, along with composite strategy involving metal and nonmetal‐based materials are introduced. The structural morphology improvement, physical and chemical property adjustment, vacancy design, and crystal surface modulation of PBAs induced by these modification and composite strategies are discussed in depth. In addition, the performance of the modified and composite catalysts to activate PMS for organic pollutant degradation is demonstrated. The radical pathway via SO4•−, •OH, and O2•−, nonradical pathway through 1O2, electron transfer process and high‐valent metal–oxo species, or a combination of radical and nonradical pathways are revealed in PMS‐AOPs with PBAs and their derivatives as catalysts.

A cascade X-ray energy converting approach toward radio-afterglow cancer theranostics.

Leveraging X-rays to initiate prolonged luminescence (radio-afterglow) and stimulate radiodynamic 1O2 production from optical agents provides opportunities for diagnosis and therapy at tissue depths inaccessible to light. However, X-ray-responsive organic luminescent materials are rare due to their intrinsic low X-ray conversion efficiency. Here we report a cascade X-ray energy converting approach to develop organic radio-afterglow nanoprobes (RANPs) for cancer theranostics. RANPs comprise a radiowave absorber that down-converts X-ray energy to emit radioluminescence, which is transferred to a radiosensitizer to produce singlet oxygen (1O2). 1O2 then reacts with a radio-afterglow substrate to generate an active intermediate that simultaneously decomposes to emit radio-afterglow. Through finetuning such a cascade, intraparticle radioluminescence energy transfer and the 1O2 transfer process, RANPs possess tunable wavelengths and long half-lives, and generate radio-afterglow and 1O2 at tissue depths of up to 15 cm. Moreover, we developed a biomarker-activatable nanoprobe (tRANP) that produces a tumour-specific radio-afterglow signal, leading to ultrasensitive detection and the possibility of surgical removal of diminutive tumours (1 mm3) under an X-ray dosage 20 times lower than inorganic materials. The efficient radiodynamic 1O2 generation of tRANP permits complete tumour eradication at an X-ray dosage lower than clinical radiotherapy and a drug dosage one to two orders of magnitude lower than most existing inorganic agents, leading to prolonged survival rates with minimized radiation-related adverse effects. Thus, our work reveals a generic approach to address the lack of organic radiotheranostic materials and provides molecular design towards precision cancer radiotherapy.

MATHEMATICAL MODELING OF THE PROCESS OF SEPARATION OF MIXTURES BY LIQUID EXTRACTION

While designing liquid-phase extraction processes, one of the main conditions is to determine the kinetic characteristics of the exchange processes necessary to determine the flows and masses of the components. Existing mass transfer models describe mass transfer processes on a semi-empirical and empirical basis with a limited range of applications, simplifying the real picture in most cases. In this regard, the development of models that more widely describe the processes of liquid-phase extraction and allow their application is considered one of the important tasks. Based on the generalization of the Chilton-Colborne hydrodynamic analogy in gradient flows and further development of the Landau-Levich boundary layer model, a mathematical model has been developed to determine the mass transfer coefficients in the extraction process in continuous and dispersed phases using minimal experimental data obtained at the stage of hydrodynamic studies

Optical Quantum Control of the Electron Transfer Reactions in Protein Flavodoxin.

The optical quantum control has been successfully applied in modulating biological processes such as energy transfer and bond isomerization. Among the reactions in realizing biological functions, the electron transfer (ET) process is fundamental; hence, the quantum control over such an ET reaction is of far-reaching significance. Here, we realized optical quantum control over ultrafast ET processes in a protein, flavodoxin, by applying various chirped excitation pulses. We observed the wavepacket dynamics within a dephasing time of less than 1 ps. Within this time window, we found that the ultrafast photoinduced ET reaction can be controlled by different chirped excitations with a rate change by a factor of about 2. Furthermore, the control effect is propagated into the subsequent ultrafast back ET reaction, showing a variation of the BET dynamics with different excitation chirps. The underlying mechanism is the initial wavepacket dynamics; the differently prepared wavepackets with chirped excitation evolve along various pathways, resulting in the changes of ET rates. The successful demonstration of optical quantum control of ultrafast biological ET is significant and opens a new avenue to explore the quantum control of real biological ET reactions.

Visible-Light Organic Photosensitizers Based on 2-(2-Aminophenyl)benzothiazoles for Photocycloaddition Reactions.

We have studied 2-(2-aminophenyl)benzothiazole and related derivatives for their photophysical properties in view of employing them as new and readily tunable organic photocatalysts. Their triplet energies were estimated by DFT calculations to be in the range of 52-57 kcal mol-1, suggesting their suitability for the [2+2] photocycloaddition of unsaturated acyl imidazoles with styrene derivatives. Experimental studies have shown that 2-(2-aminophenyl)benzothiazoles comprising alkylamino groups (NHMe, NHiPr) or the native amino group provide the best photocatalytic results in these visible-light mediated [2+2] reactions without the need of any additives, yielding a range of cyclobutane derivatives. A combined experimental and theoretical approach has provided insights into the underlying triplet-triplet energy transfer process.

Study of Ionanofluids Behavior in PVT Solar Collectors: Determination of Thermal Fields and Characteristic Length by Means of HEATT® Platform

Solar electric and solar thermal energies are often considered as part of the solution to the current energy emergency. The pipes of flat plate solar devices are normally heated by their upper surfaces giving rise to an asymmetric temperature field in the bulk of the fluid, which influences the heat transfer process. In the present work, a study of the characteristic length of tubes, or most efficient distance at which heat transfer occurs, in flat photovoltaic-thermal (PVT) hybrid solar devices has been carried out using three heat transfer fluids: water, [Emim]Ac ionic liquid and ionanofluid of graphene nanoparticles suspended in the former ionic liquid. The mean objective of the study was to know whether the heat transfer occurs in optimal conditions. Experimental measurements have been made on a commercial PVT device, and numerical simulations have been performed using the HEATT® platform to determine the characteristic length of the process. The tests conducted showed a clear improvement in the temperature jump of the fluid inside the collector when INF is used compared to water and ionic liquid and even a higher overall energy efficiency. Electricity generation is not greatly affected by the fluid used, although it is slightly higher when water is used. Slower fluid velocities are recommended if high fluid outlet temperatures are the goal of the application, but this penalizes the overall thermal energy production. The characteristic process length is not typically achieved in parallel tube PVT collectors with ordinary flow rates, which would require a speed, and consequently, a flow rate, about 10 times lower, which penalizes the performance (up to four times), although it increases the fluid outlet temperature by 234%, which can be very interesting in certain applications. Ionanofluids may in the medium term become an alternative to water in flat plates or vacuum solar collectors for applications with temperatures close to or above 100 °C, when their costs will hopefully fall. The results and methodology developed in this work are applicable to solar thermal collectors other than PVT collectors.