Propylene Glycol-water Mixtures Research Articles

Determination of fluorescence quantum yields and decay times of NADH and FAD in water–alcohol mixtures: The analysis of radiative and nonradiative relaxation pathways

Combined studies on fluorescence quantum yield of coenzymes NADH and FAD in water–methanol, water–ethanol and water–propylene glycol mixtures and on time-resolved fluorescence of these molecules under excitation at 450 and 355 nm by means of time-correlated single photon counting (TCSPC) method have been carried out. A novel model that allowed to separate the contributions from several excited state relaxation mechanisms to fluorescence dynamics in the pico- and nanosecond time domains and to fluorescence quantum yield was developed and used for analysis of experimental data. The results indicated the existence of at least two different nonradiative relaxation mechanisms in NADH and FAD: a relatively slow nanosecond and a much faster picosecond ones. The analysis suggested that the increase of NADH fluorescence quantum yield with all alcohols concentration occurred mainly due to relatively slow nanosecond non-radiative and radiative relaxation mechanisms related with the change of conformation distributions, while the picosecond fluorescence quenching was found to have practically the same and conformation-insensitive value in water–monohydric alcohol mixtures. Similar conclusion was made for NADH in water–propylene glycol solutions where however a moderate decrease of the picosecond quenching rate was determined at high propylene glycol concentrations that was attributed to a slowdown of picosecond quenching under high viscosity conditions. In the case of FAD the analysis suggested that the dramatic rise of fluorescence quantum yield with alcohol concentration was mostly due to the conformation-sensitive picosecond quenching. This conclusion supports the known mechanism of the picosecond fluorescence quenching in FAD through electron transfer reaction in the π-stacked conformation between isoalloxazine and adenine moieties. Radiative decay times in NADH and FAD were estimated from experimental data and found to be about 10 ns and 20–30 ns, respectively.

Polarised fluorescence in FAD excited at 355 and 450 nm in water–propylene glycol solutions

Time-resolved polarised fluorescence in flavin adenine dinucleotide (FAD) in water–propylene glycol mixtures has been studied as a function of propylene glycol concentration using the TCSPC technique. The fluorescence was excited by picosecond laser pulses either at 450 nm or at 355 nm, the wavelengths that belong to the first and second FAD absorption bands, respectively. The global fit procedure was used for the determination of fluorescence decay times, corresponding weighting coefficients, initial anisotropy and rotational diffusion time from experiment. The experimental data manifested a double-exponential decay in the whole range of propylene glycol concentrations with the decay times τ 1 , τ 2 and weighting coefficients a 1 , a 2 . The coefficients a 1 and a 2 and the corresponding relative fluorescence quantum yields Q ( 1 ) r e l and Q ( 2 ) r e l were shown to change dramatically with addition of propylene glycol to the solution and demonstrated the domination of contribution of longer decay time at medium and high propylene glycol concentrations. The rotational diffusion time τ r o t manifested a sharp rise, up to 40 times with propylene glycol concentration that was practically proportional to solution viscosity. The initial anisotropy was determined to be equal to r 0 = 0.35 ± 0.03 and r 0 = 0.25 ± 0.02 under excitation at 450 nm and 355 nm, respectively. The dependence of fluorescence parameters on the solution viscosity and polarity was discussed taking into account FAD conformation distributions.

Entropy Generation and Statistical Analysis of MHD Hybrid Nanofluid Unsteady Squeezing Flow between Two Parallel Rotating Plates with Activation Energy

Squeezing flow is a flow where the material is squeezed out or disfigured within two parallel plates. Such flow is beneficial in various fields, for instance, in welding engineering and rheometry. The current study investigates the squeezing flow of a hybrid nanofluid (propylene glycol–water mixture combined with paraffin wax–sand) between two parallel plates with activation energy and entropy generation. The governing equations are converted into ordinary differential equations using appropriate similarity transformations. The shooting strategy (combined with Runge–Kutta fourth order method) is applied to solve these transformed equations. The results of the conducted parametric study are explained and revealed in graphs. This study uses a statistical tool (correlation coefficient) to illustrate the impact of the relevant parameters on the engineering parameters of interest, such as the surface friction factor at both plates. This study concludes that the squeezing number intensifies the velocity profiles, and the rotating parameter decreases the fluid velocity. In addition, the magnetic field, rotation parameter, and nanoparticle volumetric parameter have a strong negative relationship with the friction factor at the lower plate. Furthermore, heat source has a strong negative relationship with heat transfer rate near the lower plate, and a strong positive correlation with the same phenomena near the upper plate. In conclusion, the current study reveals that the entropy generation is increased with the Brinkman number and reduced with the squeezing parameter. Moreover, the results of the current study verify and show a decent agreement with the data from earlier published research outcomes.

Squeezed flow of polyethylene glycol and water based hybrid nanofluid over a magnetized sensor surface: A statistical approach

Hybrid liquids having better energy transportation properties comparative to mono-fluids. Such materials have appliances in distinct areas like military equipment and solar collectors. When thermal radiation and heat source are significant, nothing is known on a comparative analysis between the dynamics of chemically reactive polyethylene glycol and water-zirconia nanofluid and polyethylene glycol and water-zirconia‑magnesium oxide hybrid nanofluid over a permeable sensor surface. The results are presented in two cases: hybrid nanofluid (propylene glycol-water mixture + zirconia+ magnesium oxide) and nanofluid (propylene glycol-water mixture + zirconia), using the Runge-Kutta fourth-order based shooting method. The squeezed flow index parameter reduces both fluid temperature and velocity, according to the study's main findings. When the squeezed flow index parameter is increased, the surface drag force decreases at a rate of 0.47936 (in the case of hybrid nanofluid). There is also a significant positive relationship between two parameters (chemical reaction and Schmidt number) and mass transmission rate. Both parameters are increasing at 0.870459 and 0.886875, respectively. Furthermore, it is discovered that the magnetic field improves fluid velocity (due to the squeezing of the upper plate) and heat transfer rate decreases at a rate of 1.50787 as the heat source parameter increases.

Energy Analysis of Concentrated Photovoltaic/Thermal Panels with Nanofluids

In this study, a prototype system was established for location heating application and electricity generation through utilizing two concentrated photovoltaic thermal panels (CPV/T) possessing flat surface receivers connected in series with each other. The purpose of the system is to supply the heating needs of a room in winter season and to meet the electricity requirement of the equipment used in this system. In the analysis of the installed system, different refrigerants (10% mono propylene glycol + 90% water and 0.5% Al2O3-water nanofluid) were tested at three different flow rates (0.4 m3/h, 0.5 m3/h, 0.6 m3/h). Throughout the experiments, the fan-coil air outlet temperature used to heat the room was adjusted to 35 °C with an inverter and a process control device. The results attained from the experiments carried out using different fluids throughout different months and days (April-May) have demonstrated that the thermal and electrical efficiencies of the system are found to be in good agreement with each other when evaluated in terms of the fluids utilized. The highest electrical energy recovery was found as 268 W at 0.6 m3/h flow rate for propylene glycol-water mixture and 194 W at 0.5 m3/h flow rate for nanomixture. The total thermal energy efficiency for the system using different fluids was found to be around 22%. The total thermal energy gain of the system was also calculated as 2312 W at 0.6 m3/h for the propylene glycol mixture and 2041 W at 0.5 m3/h for the nanomixture.

Performance Comparison of Propylene Glycol-Water and Ethylene Glycol-Water Mixtures as Engine Coolants in a Flat-Tube Automobile Radiator

This study aims at evaluating and comparing the thermal performance of five different engine coolants employed in an experimental engine cooling system with a flat-tube louvered-fin automobile radiator. For this purpose, a PLC-controlled test system was set up. The system could maintain the temperatures of the air and coolant at the radiator inlet, the speed of the air and flow rate of the coolant at the required values during the tests. The tested coolants were pure wa-ter, 30/70 ethylene glycol (EG)/water, 30/70 propylene glycol (PG)/water, 50/50 EG/water and 50/50 PG/water mixtures. In all tests, the coolant temperature at the radiator inlet was kept at 90°C, while the coolant flow rate was varied between 0.10–0.25 l/s with 0.05 l/s increments. Furthermore, the air temperature at the ra-diator inlet was kept at 25, 30 and 35°C, and the air speed passing over the radia-tor was varied between 1–4 m/s with 1 m/s increments. The thermal performance of the radiator was evaluated by locating the measured coolant flow rate and coolant inlet/outlet temperatures into the conservation of energy equation. It was found that water yielded the highest radiator heat rejection rates. Compared with water, 30/70 EG/water, 50/50 EG/water, 30/70 PG/water, 50/50 PG/water mix-tures yielded on average 3.50%, 7.89%, 8.28%, 11.46% lower radiator heat rejec-tion rates, respectively. Since PG has some advantages over EG such as lower cost and toxicity, PG mixtures can be employed as antifreeze instead of EG mix-tures in expense of a slight decrease in the thermal performance.

Effectiveness of some New Water Based Insecticides Against Locust and Grasshoppers Applied As LV and ULV Spray Techniques in Egypt فاعلية بعض المبيدات ذات القاعده المائية على الجراد و النطاطات عند تطبيقها بتقنية الحجوم الصغيره والمتناهية فى الصغر فى جمهورية مصر العربية

Efficacy of five water based insecticides on Schistocerca gregaria (Forskal), Locusta migratoria (Linnaeus),and multiple grasshoppers species applied as low volume (LV) and Ultralow volume (ULV) were tested. Obtained data indicated that descending order of insecticides efficacy were as follow: chlorpyrifos, thiamethoxam + chlorantraniliprole, spinetoram + methoxyfenozide, chlorantraniliprole then pyridalyl, in case of S. gregaria both spinetoram + methoxyfenozide and chlorantraniliprole were quite similar. Concerning spray characteristics, the effectiveness of spraying tested water based pesticides diluted with 30% Propylene glycol water mixture as ULV spray technique was obvious, where the droplets size, relative span, and number of droplets per cm2 were suitable for locust control.

Chemical composition, antioxidant activity, standardization and kinetics of production of water-propylene glycol extracts of medicinal plants

Water-propylene glycol extracts of medicinal plants are widely used as active components in therapeutic and cosmetic products for external use. However, sparse data on the extracting efficiency of water-propylene glycol mixtures and chemical composition of water-propylene glycol extracts of plant raw materials are available in the scientific literature. Usually the manufacturer documentation also provides information about characteristics of the products that are not related to their biological activity. The results of HPLC/MS/MS study of Matricaria chamomilla L. flowers have shown that water-propylene glycol and water-ethanol extracts are similar in the composition of phenolic compounds: the dominant compounds of water-propylene glycol extract of Matricaria chamomilla L. flowers are apigenin and its glycosides (apigenin-7-glucoside, apigenin-7-O-6-O-malonyl-D-glycoside, apigenin-7-acetylglycoside, acetyl-malonyl-apigenin-7-O-glycoside), as well as 5,4’-dioxy-3,6,7,3’-tetramethoxyflavone, cis- and trans-forms of 2-O-glucopyranoside 2-hydroxy-4-methoxycoric acid, 7-methoxycumarin. Spectral and analytical characteristics in the UV-visible range of the spectra of water-propylene glycol extracts of a number of medicinal plants most often used in the cosmetic industry were studied to reveal extracts with the highest protective properties against UV radiation in A and B areas (extracts of Salvia officinalis L. leaves, Matricaria chamomilla L. flowers, Achillea millefolium L. grass), free radicals (extracts of Camellia sinensis L. leaves, Hypericum perforatum L. herb), and the highest content of flavonoids (extracts of Hypericum perforatum L. herb, leaves of Salvia officinalis L.) were revealed. When extracting raw materials from the same batch, the optical density at a wavelength of 270 nm is associated with the content of flavonoids, antioxidants and dry matter by a functional relationship, which is very convenient for rapid control of extraction processes in order to obtain a product with reproducible characteristics. Formulas for calculating the content of antioxidants in extracts using the DPPH method in comparison with standard samples of rutin and gallic acid are derived. Interpretation of data on the antioxidant content in different extracts in comparison with other analytical parameters are also presented. Demonstrated high repeatability of the shape of the spectral curves of Matricaria chamomilla L. flowers extract, observed regardless of the source of raw materials can be used in combination with the individuality of the curve shape of the extracts of raw materials of different types as one of the authenticity criteria. The proposed UV-spectrometric method was used to study the dynamics of Matricaria chamomilla L. flower extraction under different process parameters (temperature, propylene glycol/water ratio in the extractant). It is shown that extraction of raw materials with 50% water-propylene glycol for 4 h at a temperature of 50°C is optimal.

Investigation on the heat transfer characteristics of propylene glycol–water mixture in the shell side of a spiral‐wound heat exchanger

AbstractThe heat transfer characteristics of propylene glycol–water (PG–W) mixture (10%, 20%, and 30% propylene glycol) on the shell side of a spiral‐wound heat exchanger (SWHE) were investigated experimentally. Among the SWHE selected, there are 18 twined tubes with a diameter of 8 mm. PG–W mixture is on the shell side and water is on the tube side. The results show that the heat transfer coefficient of PG–W mixture flowing downwards is higher than upwards under countercurrent conditions. The heat transfer coefficient decreases with the increasing of concentration of PG–W mixture. When the inclination angle of the SWHE is 90°, the heat transfer coefficient of PG–W mixture is the largest; and when the inclination angle is less than 90°, the heat transfer coefficient decreases with the decrease of inclination angle. The inclination angle has a great effect on the heat transfer coefficient at a high concentration. The fitting correlation equations between Nu, Re, Pr, and inclination angles of SWHE are established.

Shear flow behavior and dynamic viscosity of few-layer graphene nanofluids based on propylene glycol-water mixture

We report the shear flow behavior of few layer graphene (FLG) based nanofluids produced with a commercial mixture of water and propylene glycol and three nonionic surfactants, Triton X-100, Pluronic® P123, and Gum Arabic respectively. The flow properties of these nanofluids were experimentally investigated between 283.15 and 323.15 K and for FLG content from 0.05 to 0.5 wt%. The nanofluids were subjected to different experiments, at rest at fixed temperature, under steady shear flow at fixed temperature and under temperature ramp at fixed shear rate in order to evaluate their stability and behavior under shear and temperature influence. These results were compared and correlated to visual aspect of the samples at the end of measurements. This experimental study evidences that the temperature, the shearing and the shearing duration have an important influence on the stability under shear of nanofluids in function of concentration and surfactant used. Finally, for all stable nanofluids under shear, the dynamic viscosity evolution of nanofluids with temperature is correlated to Vogel-Fulcher-Tammann model.

Synthesis and thickening properties of copolymers of acrylic acid and alkoxy(С12-С14)oligoethylene glycol methacrylates

Samples of hydrophobically modifi ed polyacrylic acid containing 1% of alkoxy(С12-С14)oligoethylene glycol methacrylate units have been synthesized by free radical precipitation polymerization. The infl uence of the length of ethoxylated spacer of macromonomers and neutralization degree of carboxylic groups on thickening properties of obtained polymers in water and waterpropylene glycol mixtures at diff erent temperatures has been determined.

Energetic and Exergetic Performances of Plate Heat Exchanger Using Brine-Based Hybrid Nanofluid for Milk Chilling Application

Theoretical study on the energetic and exergetic performances of a counter-flow corrugated plate heat exchanger using hybrid nanofluids for the milk chilling application has been done in the present investigation. Magnesia-silver and Alumina-silver nanoparticles have been dispersed in the ethylene glycol–water mixture and propylene glycol–water mixture (20:80 brine solutions) with different particle volume concentration separately. Effect of particle volume concentration and flow rate of the hybrid nanofluid on the heat transfer rate, convective, and overall heat transfer coefficients, mass flow rate of milk, pressure drop, pumping power, entropy generation rate, second law efficiency, irreversibility, irreversibility distribution ratio, non-dimensional exergy (NDE) destruction, and performance index have been studied. It has been observed that heat transfer rate, convective and overall heat transfer coefficients, pressure drop, pumping power, irreversibility, entropy generation rate, second law efficiency, and milk flow rate increase; while NDE destruction, performance index, and irreversibility distribution ratio decrease with the hybrid nanofluid flow rate and the volume concentration of the nanofluid. Within studied ranges, the hybrid nanofluid yields the maximum improvement of heat transfer rate and convective heat transfer coefficient of about 1.6% and 9.4%, respectively, compared to base fluid. It has also been found that silver + alumina shows slightly better performance improvement and hence hybrid nanofluid is recommended as a suitable alternative for the milk chilling units.

Influence of the base fluid on the thermo-physical properties of PV/T nanofluids with surfactant

Nanofluids have become widely used in different applications. One of these applications, it may be used in Photovoltaic/Thermal PV/T systems, as there is many research that works to determine the best type of nanofluids for this important application. In this study, differences in the thermo-physical properties of three types of nanofluids were emphasized, which used nano-SiC as additive and cetyl-trichromyl ammonium bromide as surfactant. Water was mixed with 35% ethylene glycol, and with 35% of propylene glycol. The study aims to find the best base fluid for use in solar PV/T applications.The increase in density and viscosity of all studied nanofluids was evident as well as the superiority of the density of ethylene glycol water mixture (for the tested temperature range, nano-EG-water density was higher than nano-water and nano-PG-water densities by 15.51% and 0.066%, respectively compared to water). The propylene glycol-water mixture has higher viscosity than the other two nanofluids (it was higher than nano-water and nano-EG-water viscosities by 16.066% and 0.212%, respectively compared to water). The thermal conductivity of the three nanofluids was close to each other in the studied temperatures region. Glycol solutions were more stable than water when ultra-shaking hours were from four to six hours.

Potential heat transfer enhancement of functionalized graphene nanoplatelet dispersions in a propylene glycol-water mixture. Thermophysical profile

Abstract The thermal conductivity of the heat transfer fluids commonly used in industrial processes is a major concern in the continuous searching of their performance improvement. During last decades, dispersions of high thermal conductivity nanoparticles in conventional fluids, nanofluids, have received increasingly attention to achieve this aim. The thermophysical properties, not commonly available in the literature, are necessary to describe their thermo-fluid behaviour. Thus, characterization studies become necessary to evaluate the potential heat transfer enhancements. This work presents the thermophysical profile according to the properties with a noticeable influence on the heat transfer capability of different functionalized graphene nanoplatelet dispersions (0.25, 0.50, 0.75 and 1.0) wt% in a propylene glycol-water mixture at (30:70)% mass ratio, usually employed in thermal facilities. Initially, nanofluid stability was investigated optimizing the pH value by analysing zeta potential measurements. Then, densities, heat capacities, thermal conductivities, and dynamic viscosities were experimentally determined throughout the temperature range from (293.15 to 323.15) K. Density was studied by using a pycnometric technique and results were used to analyze the isobaric thermal expansivity behaviour. A differential scanning calorimeter was utilized to obtain heat capacities and thermal conductivities were measured for the nanopowder, base fluid and nanofluids through devices based on the guarded heat flow meter method and the transient hot wire technique. Furthermore, rheological behaviour was analysed by means of a rotational rheometer with cone-plate geometry. Conductivity enhancements up to 16% with respect to base fluid were achieved. Finally, potential enhancements of heat transfer performance in laminar and turbulent flow were investigated through an analysis of different figures of merit based on the experimental results.

Flow behaviour of suspensions of functionalized graphene nanoplatelets in propylene glycol–water mixtures

The low thermal conductivity of the fluids usually used in heat exchange processes (water, oils, glycols…) has proved to be one of the limiting factors in improving their heat transfer performance. These traditional fluids enhance their thermal capabilities by dispersing nano-sized particles with high thermal conductivity, as many researches have revealed in the last decades. Although the thermal conductivity of nanofluids has centred the interest of the heat transfer community, the rheological behaviour of the resulting dispersions is very influential in the heat transfer process, pressure drops and pumping powers. In this work, different samples of functionalized graphene nanoplatelets dispersed into two different binary mixtures of propylene glycol and water at 10:90wt% and 30:70wt% have been analysed by using a DHR-2 rotational rheometer equipped with concentric cylinder geometry. Firstly, the flow curves for Krytox GPL102 oil, pure propylene glycol, and the two binary mixtures of propylene glycol and water used as base fluids were experimentally obtained. These values were used to check our experimental procedure finding a good agreement between them and those reported and well known in the literature, with an absolute average deviation of 2.0%. Then, the viscosity-shear rate curves in the temperature range from 278.15 to 323.15K were obtained for the different graphene nanofluid sets. Furthermore, a new equation was proposed in this work to describe the viscosity dependence on both the temperature and the nanoparticles volume concentration of graphene nanoplatelet nanofluids with an absolute average deviation with respect to our experimental data lower than 2%. Additionally, oscillatory tests of the samples were performed observing pseudoplastic behaviour for the nanofluids at lower angular frequencies.

Analysis of the impact of different operating conditions on the performance of a reversible heat pump with domestic hot water production

This paper presents the mathematical modeling of a liquid-to-water heat pump with scroll compressor, brazed plate heat exchangers, additionally built-in liquid-vapor heat exchanger (LVHX) and a desuperheater for domestic hot water (DHW) production. The refrigerant is the zeotropic mixture R407C and the liquid used in the outdoor loop is a propylene-glycol water mixture. Developed mathematical model is validated on experimental data and used as a tool for the heat pump analysis. Simulation results are obtained for the effect of the degree of superheat at the evaporator outlet, the subcooling degree at the condenser outlet, the effect of using or not the LVHX and the effect of using or not the desuperheater for DHW for typical operating conditions of liquid-to-water heat pumps (EN-14,511-2, 2011) in the cooling and heating modes (low and medium temperature applications). Results show that the effect of the degree of superheat or the decision on the suitability of using or not a LVHX may be different for heat pumps that include or not a desuperheater for DHW. In particular, if DHW is a priority, the use of a LVHX is recommended because it leads to higher COP (or EER) values as well as to higher DHW heating powers.

Novel hybrid nanofluid with tunable specific heat and thermal conductivity: Characterization and performance assessment for energy related applications

The utilization of heat transfer fluids with improved specific heat and thermal conductivity will be beneficial for enhanced energy collection in solar thermal systems. Accordingly, hybrid nanofluids comprising ZnO nanoparticles and encapsulated paraffin wax in propylene glycol-water mixture were prepared and characterized. The influence of encapsulated paraffin wax concentration (4–16 wt. %) and ZnO nanoparticle concentration (0–2 vol %) revealed that the thermal conductivity and specific heat could be improved to a maximum of 10.4% and 18.7% respectively, in comparison with those of propylene glycol-water mixture, at their appropriate concentrations. The presence of ZnO nanoparticles was found to influence the phase change characteristics of encapsulated paraffin wax, in such a way that the latent heat due to phase change was increased at an optimum concentration of ZnO nanoparticle concentration. While the maximum enhancement in overall heat transfer coefficient of 15.37% was obtained for the hybrid nanofluid sample that had both thermal conductivity and specific heat higher than the base fluid, the maximum enhancement in heat transfer rate (13.54%) was obtained for the hybrid nanofluid that had 18.65% enhancement in specific heat. The results of present investigation reveal the potential of hybrid nanofluids for energy management.

Steady-shear rheology and activation thermodynamics of the interpolymer complex between nonionic polymeric surfactant and hydrophobically modified polyacrylic acid in propylene glycol–water mixture

Rheology of the individual polymer solutions and complex polymer mixtures was studied in the temperature range from 30 to −20 °C. Based on the obtained data steady-shear flow properties and thermodynamic parameters of a viscous flow were calculated. Exploiting the flow parameters such as the flow behavior index it was demonstrated that addition of synthesized anionic polymeric surfactant—polyvinyl octanal (PVO) to the polyelectrolyte solution enhanced pseudoplasticity of the obtained liquids at low temperatures. Along with that, the anomalous behavior of the activation enthalpy and activation entropy as a function of temperature was observed for the polyelectrolyte solutions containing PVO. Thus, it was shown that relatively high initial values of ΔH A diminish sharply with an increase in temperature and TΔS A values decrease dramatically below 0 °C. The obtained results were in line with the concept of the critical temperature observed for the strongly associated polymeric systems in water–glycol mixtures. In the light of the findings it was assumed that specific interpolymer association occurs at low temperatures resulting in consequent increase in the values of apparent viscosity and pseudoplasticity of the studied polymeric liquids. It was also suggested that studied system is well suited for the formulation of the thickened aircraft deicing fluids.

New hybrid nanofluid containing encapsulated paraffin wax and sand nanoparticles in propylene glycol-water mixture: Potential heat transfer fluid for energy management

The reduction in specific heat commonly encountered due to the addition of nanoparticles to a heat transfer fluid such as propylene glycol-water mixture, can be overcome by co-dispersing surfactant-encapsulated paraffin wax, leading to formation of a hybrid nanofluid. Experimental investigations have been carried out on the preparation and evaluation of thermophysical properties of a hybrid nanofluid containing pluronic P-123 encapsulated paraffin wax (70–120nm diameter, 1–5wt.%) and sand nanoparticles (1vol%) in propylene glycol-water mixture. The comparison of results of differential scanning calorimetry of pure paraffin wax and encapsulated paraffin wax revealed encapsulation efficiency of 84.4%. The specific heat of hybrid nanofluids monotonously increased with paraffin wax concentration, with 9.1% enhancement in specific heat for hybrid nanofluid containing 5wt.% paraffin wax, in comparison to propylene glycol-water mixture. There exists an optimum paraffin wax concentration (1wt.%) for the hybrid nanofluid at which the combination of various thermophysical properties such as specific heat, thermal conductivity and viscosity are favorable for use as heat transfer fluid. Such a hybrid nanofluid can be used as a substitute for propylene glycol-water mixture in solar thermal systems.

Sand-propylene glycol-water nanofluids for improved solar energy collection

Experiments were carried out on the preparation, thermophysical properties' measurement and application of surfactant-free, sand-propylene glycol-water nanofluids for solar energy collection. Thermal conductivity enhancement of 16.3% and viscosity reduction of 47% were observed for 2 vol % sand-PG-water nanofluid at 28 °C. Microconvection caused by Brownian motion was identified as one of the mechanisms of thermal conductivity enhancement. The relative viscosity of sand-propylene glycol-water nanofluid was less than 1 over a temperature range of 10–60 °C and sand nanoparticle concentration range of 0.5–2 vol %. The lower viscosity of sand-PG-water nanofluids in comparison to that of propylene glycol-water mixture is attributed to non-covalent interactions between sand nanoparticles and propylene glycol, leading to perturbation of hydrogen bonding network. The use of 2 vol % sand-PG-water nanofluid resulted in enhancement of heat transfer and solar energy collection by 16.5%. Our results demonstrate that sand-PG-water nanofluids are suitable for use as heat transfer fluid in solar collectors.