Mass Fraction Of Nanoparticles Research Articles

Enhancement of Mechanical Properties and Microstructure of Aluminium alloy AA2024 By adding TiO2 Nanoparticles

Modern engineering applications, especially in the automotive and aerospace industries, require essential and appealing properties such as lightweight with high strength and resistance. The key objective of the present study is to investigate the effect of TiO2 nanoparticles on the microstructure, impact strength, hardness and wear resistance of the stir cast aluminum alloy AA2024, An aluminium alloy was reinforced with different mass fractions (0 %, 2.5 %, 5 %, 7.5 %) of titanium dioxide nanoparticles by stir casting followed by solution annealing at 500°C for 3 h, quenching in water and aging at 175°C for 3 h. Results showed that regular morphology and fine grain size of primary AA2024 particles are achieved after the addition of 2.5 wt.% TiO2 compared to the sample without the addition of nanoparticles composite. In addition, it was found that adding nanoparticles increased energy absorption, and this effect is improved by increasing impact strength by adding nanoparticles, the impact strength increased from 5 j/m2 to 7 j/m2 at 5%. At the same time, the increase of nanoparticles effect decreases the mass losses (increase in wear resistance). With a weight fraction of 5 wt.% TiO2, the alloy exhibits the highest value of hardness.

Preparation and Properties of Thermoregulated Seaweed Fibers Based on Magnetic Paraffin wax@calcium Carbonate Microcapsules

In order to enhance the application of thermoregulated materials, magnetic phase change microcapsules were prepared using a self-assembly method. Paraffin wax was chosen for its fine thermoregulation properties as the core material, while Fe3O4 nanoparticles doped in calcium carbonate served as the hybrid shell material. The microcapsules were then blended with sodium alginate and processed into seaweed fibers through wet spinning. The microstructure, thermal, and magnetic properties of the microcapsules were analyzed using scanning electron microscopy, energy dispersive X-ray spectroscopy, a laser particle size analyzer, an X-ray diffractometer, a differential scanning calorimeter, a thermogravimetric analyzer, and a vibrating sample magnetometer. The thermoregulation of the fibers was evaluated using a thermal infrared imager. The results indicated that the microcapsules had a uniform size distribution and good thermal properties. When the mass fraction of Fe3O4 nanoparticles was 8%, the microcapsules exhibited a saturation magnetization of 2.44 emu/g and an enthalpy value of 94.25 J/g, indicating effective phase change and magnetic properties. Furthermore, the thermoregulated seaweed fibers showed a high enthalpy value of 19.8 J/g with fine shape, offering potential for developing multifunctional fiber products.

Heat transfer analysis and melting behavior of nano composite phase change materials (NCPCMs) in a reverse flow solar air heater

This paper presents a CFD investigation on heat transfer analysis and melting behavior of Nanocomposite Phase Change Materials (NCPCMs) in a Reverse Flow Solar Air Heater (RFSAH). Semicircular tubes filled with PCM are embedded on the top surface of the absorber plate. The study was conducted with three different nanoparticles (CuO, Al2O3, Fe3O4) based NCPCMs at three concentrations of 0.1, 0.2, and 0.3 % by weight. The constant geometrical parameters such as pitch ratio (P/e = 6), height ratio (e/Dh=0.1571), and Reynolds number (Re = 5000) is considered for this study. A 2-D transient numerical analysis using the RNG k-ε turbulence model is performed for the melting behavior of NCPCMs inside the semicylindrical tubes. The incorporation of nanoparticles into the base PCM enhances thermal conductivity but reduces the latent heat of NCPCMs. Thus, it is observed that NCPCMs have a faster melting rate. The CuO based NCPCM shows a more quick and uniform phase transition compared to the Fe3O4, and Al2O3 based NCPCMs and reached their peak value at a higher mass fraction of 0.3. Furthermore, the heat transfer and melting fraction improves with increasing in mass fraction of nanoparticles. The phase transition process of CuO based NCPCM is approximately 1.9 times, and 1.01 times, 1.03 times faster as compared to the base PCM, and Fe3O4, Al2O3 based NCPCMs respectively.

Effect of WC addition on microstructure and properties of laser melting deposited Ti6Al4V

Titanium alloys are generally characterized by low surface hardness, poor thermal conductivity, high friction coefficients and susceptibility to adhesive wear, which significantly hinder their industrial applications. To address this issue, we enhance the wear resistance of titanium alloys by incorporating nano WC particles. However, the optimal amount of WC to be added to titanium alloys remains unexplored. In this study, we prepared Ti6Al4V-xWC (wt%) (x = 0, 10, 20) coatings on Ti6Al4V substrates using laser melting deposition, specifically examining the effects of WC content on the microstructure and properties of the coating. The experimental findings indicate that the introduction of WC particles resulted in the formation of a TiC reinforced phase within the composite coating which promoted the equiaxialization of lamellae α phase. The hardness of the coatings increased significantly with the increase of the mass fraction of WC nanoparticles. Notably, the Ti6Al4V-10WC and Ti6Al4V-20WC coatings exhibited wear resistance that was 2.5 and 3.4 times greater, respectively, compared to the Ti6Al4V coatings. This enhancement in wear resistance can be attributed to the reinforcing phase (TiC) formed by the addition of WC. This experiment demonstrates a viable approach to improving the wear resistance of the Ti6Al4V titanium alloy through surface treatment.

Experimental research of convective heat transfer between nanofluids and high-temperature dense granite in deep geothermal reservoirs

Global warming is increasing as CO2 emissions from the use of conventional fossil fuels continue to rise. The development of geothermal energy is gradually becoming the key to the sustainable development of human society in the future. Enhancing the heat transfer performance of circulating heat transfer fluids is one of the effective means to efficiently exploit deep geothermal resources. In this study, a self-developed circulating heat exchange experimental setup was established. The convection heat transfer characteristics of nanofluids in high-temperature rocks were experimentally investigated. Al2O3 nanofluid and CuO nanofluid were used as the working medium for heat transfer in high temperature granite samples. The effects of the Reynolds number (1000–6000) and parameters such as nanoparticle type (CuO & Al2O3), size (20 nm & 40 nm) and mass fraction (0 wt%-2wt%) on the heat transfer intensity were analyzed. The effect of nanoparticle accumulation on the rock surface on the local heat transfer strength was also investigated. The results indicate that the increase of Reynolds number enhances the heat transfer strength of nanofluids in rocks. Nanofluid containing 20 nm Al2O3 nanoparticles has better heat transfer performance in rock than nanofluid containing 20 nm CuO nanoparticles. Meanwhile, the heat transfer performance of nanofluid containing 20 nm Al2O3 nanoparticles in rock is better than that of nanofluid containing 40 nm Al2O3 nanoparticles. The heat transfer intensity increases and then decreases as the nanoparticle mass fraction increases. The heat transfer coefficient at Reynolds number 6000 is 52.2 % higher than that of water. For nanofluids and water, the local heat transfer intensity decreases with increasing distance from the inlet. Meanwhile, accumulation of nanoparticles on rock surfaces during convective heat transfer enhances heat transfer intensity. The results show that nanofluids have the potential to be applied to deep geothermal resource extraction. This paper provides data and technical support for the application of nanomaterials in medium and deep geothermal systems to enhance heat transfer efficiency.

Experimental study and analysis of CO2 and SO2 absorption in various water-based nanofluids by response surface methodology

The absorption of acidic gases in the oil and gas industries is important due to their toxicity and corrosive effects. Recently, the application of nanofluids based on aqueous or organic solvents as absorbents has been examined by a variety of researchers. In this study, a single bubble column was exploited to study the effect of water-based nanofluids on the absorption processes of SO2 and CO2 using response surface methodology (RSM) based on Box-Behnken three-level experiment design. With this in mind, CO2 and SO2 are separately injected at the bottom of a bubble column filled with one of the nanofluids: Al2O3-water, SiO2-water, or ZnO-water for each experiment. Then, the rate of SO2 or CO2 absorption in the nanofluids has been elucidated. The effect of important parameters including the weight fraction of the nanoparticles (NPs) (0.01, 0.055, and 0.1 wt.%), gas–liquid contact time (150, 300, and 450 s), and the diameter of nozzle for gas injection (0.46, 0.57, and 0.68 mm) have been studied. Results revealed that the maximum molar flux of both gases was observed in the ZnO-water nanofluid, followed by the SiO2-water nanofluid. In addition, increasing the nanoparticle mass fraction and the bubble size causes the molar flux to rise. However, increasing the gas–liquid contact time causes the molar flux of the mentioned gases to decrease. Finally, a set of the accurate equations has been proposed to predict the molar flux of SO2 and CO2 in the various nanofluids assessed in this work.

Investigation of the Photothermal Performance of the Composite Scaffold Containing Light-Heat-Sensitive Nanomaterial SiO2@Fe3O4

The objective of this investigation was to fabricate a photothermally responsive composite bone scaffold aimed at facilitating bone tissue regeneration and remedying bone defects via mild thermal stimulation. The photothermal-sensitive nanomaterial SiO2 coated Fe3O4 (SiO2@Fe3O4), synthesized through the hydrolysis–condensation process of tetraethyl orthosilicate (TEOS), displayed a uniform distribution of SiO2 coating, effectively preventing the aggregation of Fe3O4 particles within the scaffold matrix. The composite scaffold containing 5% mass fraction of photothermal-sensitive nanoparticles exhibited evenly dispersed microstructural porosity, a compressive strength of 5.722 MPa, and a water contact angle of 58.3°, satisfying the mechanical property requisites of cancellous bone while demonstrating notable hydrophilic characteristics. Upon exposure to near-infrared light at ambient temperature, the 5% composite scaffold underwent a temperature elevation of 3–6 °C within 40–45 s, attaining a temperature range (40–43 °C) conducive to fostering osteogenic differentiation. Experimental findings validated that the SiO2@Fe3O4/polyvinyl alcohol (PVA)/hydroxyapatite (HA)/polycaprolactone (PCL)/β-tricalcium phosphate (β-TCP) bone scaffold showcased outstanding mechanical and photothermal attributes, thereby presenting a pioneering avenue for advancing bone tissue cell proliferation and addressing bone defect rehabilitation.

Improving the emission properties of graphene–carbon nanotube hybrid nanostructures through functionalization with BaO nanoparticles and laser treatment

This paper presents the manufacturing technology of hybrid nanostructures based on a buffer layer of reduced graphene oxide (rGO) flakes with vertical single-walled carbon nanotubes (SWCNTs) and their bundles functionalized with BaO nanoparticles. Using density functional theory (DFT) calculations, supercells of rGO/SWCNT/BaO films were constructed and the patterns of the electron work function were revealed. It has been demonstrated that the electron work function is influenced by both the mass fraction of BaO nanoparticles and the inter-tube distance. Branched carbon nanostructure was formed using a pulsed laser irradiation. Fragmentation of BaO nanoparticles on the carbon surface was achieved. It was shown that after laser treatment, Ba(NO3)2 particles up to 200 nm in size were fragmented into smaller BaO nanoparticles with sizes of a few nanometers, covering the nanotubes. The field emission current–voltage characteristics (CVCs) were measured and showed a 42-fold increase in emission current compared to the nanostructure without BaO functionalization and laser treatment. BaO-functionalized hybrid carbon nanostructures are predicted to be efficient field cathodes, with a current density of at least 2 A/cm2, for use in X-ray tubes, field emission displays, and vacuum microwave devices.

Preparation and rheological properties of highly stable bidisperse magnetorheological fluids

The utilization of magnetic nanofluids as the base carrier liquid proves to be an effective strategy for enhancing the stability of magnetorheological fluids. However, the preparation method for bidispersed magnetorheological fluids still deserves further investigation. In this study, Fe3O4 nanoparticles were synthesized through chemical co-precipitation, and aviation hydraulic oil-based magnetic nanofluids were prepared using myristic acid as a surfactant. Micron-sized particles, modified with the same surfactant, were dispersed into the magnetic nanofluids, resulting in a novel bidisperse magnetorheological fluid (C-MRFF). The coated particles underwent physical phase analysis and magnetic property testing through an x-ray diffractometer, Fourier infrared spectrometer, transmission electron microscope, scanning electron microscope, and vibrating sample magnetometer. Due to the addition of nanoparticles, C-MRFFs exhibited superior stability to micron-sized particle-based magnetorheological fluids. They demonstrated the best sedimentation stability and redispersibility at a 9% mass fraction of nanoparticles. Thanks to the protection of the micron-sized particle surface coating, C-MRFFs displayed superior sedimentation stability to traditional bidisperse magnetorheological fluids over a wide temperature range. The magnetorheological properties of C-MRFFs were studied. The results indicated that the yield stress of C-MRFFs increased with increasing magnetic field strength or decreasing temperature. The increase in the mass fraction of nanoparticles was beneficial to the increase in yield stress until severe settling of C-MRFFs occurred. In comparison to micron-sized particle-based magnetorheological fluids, C-MRFFs exhibited higher yield stresses. Although the yield stress of C-MRFFs was slightly lower than that of traditional bidisperse magnetorheological fluids due to the surface coating of larger particles, they exhibited stronger shear resistance over a wide temperature range.

Experimental investigation on the stability and heat transfer enhancement of phase change materials composited with nanoparticles and metal foams

Conventional phase change materials (PCMs) possess the challenge of low thermal conductivity, which hinders the energy exchange rate and storage efficiency. PCMs composited nanoparticles and metal foams have been a proven solution to enhance the thermal characteristics of PCMs. In this work, three enhanced PCM composites including nanoparticle/paraffin, metal-foam/paraffin and nanoparticle/metal-foam/paraffin were prepared using fusion blending and vacuum impregnation method. The effects of different nanoparticles with different mass fractions on the stability and heat storage and release characteristics of nanoparticle/paraffin were investigated. Compared with paraffin, the melting time and solidification time of nano-metal/paraffin are reduced by a maximum of 30.18 % and 43.15 %, respectively. In addition, the effect of pore density of metal foam on natural convective heat transfer process was evaluated. The results showed that the stability in descending order is as follows: nano‑aluminum, nano‑copper and nano‑silver. The optimal mass fraction of nanoparticles with good stability was 1.5 wt% (copper), 1.0 wt% (silver), 1.5 wt% (aluminum), respectively. The metal foam makes the internal temperature distribution of PCMs more uniform in the heat transfer process, while inhibiting the convective heat transfer process. With the increase of pore density, the effect on natural convection heat transfer process rises. When the PPI (pores per linear inch) of foamed metal is greater than 40, the natural convection process can be inhibited, obviously. The foam metal has a more significant effect on the heat transfer performance of nanoparticle/metal-foam/paraffin than that of the nanoparticles. The economic benefits of nanoparticle/paraffin, metal-foam/paraffin and nanoparticle and metal foam composite phase change materials are progressively decrease, with MFP being suitable for applications with high economic budgets.

Aqueous Theta-Phase Aluminum Oxide Nanofluid for Energy Applications: Experimental Study on Thermal Conductivity

The use of nanofluids in energy systems allows for increasing efficiency and developing more economic systems. Alumina-water is one of the most common nanofluids used but little information is available about the aqueous theta-phase aluminum oxide. Given the lack of thermal conductivity data for this nanofluid, in this research, this property is experimentally evaluated. Nanofluid is prepared using the two-step method, employing a magnetic stirrer and a sonication bath. A high-precision sensor is employed for measuring thermal conductivity, using the method of transient hot wire. The thermal conductivity measurements for the base fluid (water) are compared with data provided by NIST. Nanoparticle mass fraction in the nanofluid is increased from 1 to 10% and the temperature from 22.1 to 59.3 °C. Three sonication times (1.5, 4 and 16.5 h) are used. A strong dependence between the thermal conductivity and the temperature and nanoparticles concentration has been found, while the sonication time has a negligible influence on the thermal conductivity in the range of times tested. A correlation to obtain the thermal conductivity of the water-based nanofluid using theta-phase aluminum oxide has been developed, including nanoparticle volume concentration and temperature. An excellent agreement is obtained between predicted and experimental data.

Improvement of carbon fiber/phenolic composite properties by low-loading graphene oxide and SiO2 nanoparticles

As an ablative thermal protection material, the mechanical properties and ablative resistance of carbon fiber/phenolic (C-Ph) composite should be improved to meet the high requirements in deep space exploration. Herein, the properties of C-Ph composites were improved by the synergistic effect of low-concentration graphene oxide (GO) solution and low mass fraction of SiO2 nanoparticles. Compared to the unmodified C-Ph composite, the compressive strength of the modified composites was increased by 40.75 % and the linear and mass ablation rates were reduced by 17.78 % and 43.95 %, respectively. The introduction of GO effectively improved the interfacial bonding between the fiber and phenolic resin. Meanwhile, the uniformly dispersed SiO2 nanoparticles resisted the applied loads, thus synergistically enhancing the mechanical properties of the composites. In terms of improving ablation resistance, GO promoted the graphitization of fibers and enhanced the stability of the char layer. Concurrently, SiO2 nanoparticles reacted with the carbon matrix under high temperatures to form ablation-resistant SiC, thus synergistically enhancing the ablative properties of the composite.

Study on the active cooling effect and convective heat transfer performance inside the rail

In order to study the impact of different influencing factors on the active cooling effect of electromagnetic rail. The effects of the flow velocity of cooling medium, the geometric shape of the cooling channel, the cooling water inlet temperature and the nanoparticle mass fraction on the cooling effect of rail are experimentally investigated. The results indicate that increasing the flow velocity of cooling medium can enhance the heat transfer effect. But when the flow velocity exceeds 2 m/s, further increasing the flow velocity has little effect on enhancing heat transfer, and the correlation between the Nusselt number and the Reynolds number has been obtained and expressed as Nu=0.316Pr1/3Re0.530. Among the three cooling channel geometries studied in this article, square channel has the best cooling effect. The inlet temperature of cooling water has little effect on the convective heat transfer coefficient, but has a significant impact on the thermal equilibrium temperature of the rail. The mass concentration of nanoparticles has a significant impact on the cooling effect of the rail. The larger the mass fraction of nanoparticles, the greater the convective heat transfer coefficient, and the lower the rail peak temperature after reaching thermal equilibrium. However, if the concentration of nanoparticles continues to increase, the effect of enhancing heat transfer will gradually weaken.

Experimental study on the heat transfer performance of liquid metal high-temperature oscillating heat pipes with diamond nanoparticles

In order to realize effcient thermal dissipation at high temperatures, diamond nanoparticles were added in the sodium–potassium (NaK) alloy liquid metal high-temperature oscillating heat pipes (LMHOHPs) to improve the heat transfer performance. The NaK alloy with different mass fractions (0 wt%, 0.25 wt%, 0.50 wt%, 0.75 wt%, 1.00 wt%) of diamond nanoparticles was used as the working fluids. Under the input power of 2000–3500 W and the inclination angle of 0°, 30°, 60°, and 90°, the start-up characteristics and heat transfer performance of LMHOHPs after adding diamond nanoparticles were measured and analyzed. The results showed that after adding diamond nanoparticles, the LMHOHP started more smoothly and could effectively promote the unidirectional circulation flow of the working fluid. The enhancement effects of diamond nanoparticles were more obvious at low input powers. When the inclination angle was 0°, nanoparticles generally presented an enhancement effect. In this study, there was an optimal nanoparticle concentration of 0.50 wt%, which enhanced the heat transfer performance under all the investigated conditions. When the nanoparticle concentration was 0.75 % and the inclination angle was 30°, the maximum enhancement rate of 15.41 % was reached at the input power was 2250 W.

Investigating heat exchanger tube performance: second law efficiency analysis of a novel combination of two heat transfer enhancement techniques

AbstractIn the study, the focus was on evaluating the second law efficiency of a heat exchanger tube operating under continuous heat flux and turbulent flow conditions. The evaluation involved the use of a hybrid GnP and Fe3O4 and modified coiled wire as passive heat transfer enhancement techniques. The primary objective was to investigate the impact of these combined techniques on thermal and hydraulic performance, entropy generation number, Bejan number and second law efficiency. To achieve this, different mass fractions of GnP and Fe3O4 nanoparticles were used in the hybrid nanofluid, along with two forms of modified coiled wire: barrel type and hourglass type. The experimental results indicated that the utilization of hybrid nanofluids and modified helical inserts led to a noticeable improvement in the second law efficiency of the heat exchanger tube. However, it was observed that the differences in entropy generation number and Bejan number between the barrel and hourglass types were not significant, mainly due to higher frictional losses associated with the latter. The highest recorded second law efficiency was 0.416, while the lowest entropy generation number was 0.118. These values were achieved through the combined use of GnP and Fe3O4 with a mass fraction of 0.4% and a barrel-type coiled wire insert with a pitch ratio of 0.5.

Impact of nanoparticle agglomeration on thermal conductivity of molten salt based nanofluids: Insights from molecular dynamics and lattice Boltzmann methods

The nanoparticle aggregation has significant influence on heat transfer properties. The contradictions between different researches exist and the underlying mechanisms of heat conduction remain unclear. To address these issues, the thermal conductivity of solar salt-SiO2 nanofluids in the non-aggregated and aggregated states was investigated, based on the combination of the advantages of molecular dynamics (MD) in revealing physical insights and lattice Boltzmann method (LBM) in simulating properties for complex structures. LBM models were simplified on the basic of MD results. Different heat transfer physics in nanofluids at nanoscale and mesoscale were compared. The results show that the thermal conductivity of aggregated nanofluid is higher than the non-aggregated nanofluid. By analyzing the diffusion coefficient, number density and vibrational density of states, we found that the previous hypotheses (such as Brownian motion, interfacial layer and interfacial thermal resistance) cannot explain the enhanced thermal conductivity induced by the nanoparticle agglomeration. The heat transfer mechanisms of aggregated nanofluid were further analyzed from new perspectives, i.e., the contributions of different material components and fluctuation modes to heat flux. It is found that the nanoparticle aggregation leads to the nanoparticle contribution increase, indicating the formation of low thermal resistance channels within the aggregates. The heat conduction contributed by collision decreases in the aggregated state, while that contributed by potential energy increases. Moreover, the thermal conductivity of aggregated nanofluid is negatively correlated with temperature, aggregate size and fractal dimension of agglomerates, and positively correlated with mass fraction of nanoparticles, degree of agglomeration, and backbone length of each aggregate.

Regulating droplet impact dynamics of nanoparticle suspension: Phenomena, mechanisms, and implications

Droplet impact on solid substrates is a ubiquitous phenomenon in nature, agriculture, and industrial processes, playing a crucial role in numerous applications including self-cleaning, pesticide utilization, and inkjet printing. As a promising technique, adding nanoparticles into simple fluids to form nanofluids can effectively manipulate droplet impact behaviors. However, a comprehensive understanding of how nanoparticles modify the droplet impact dynamics, especially on the nanoscale, is still far from being fully explored. Hence, in this work, through the combined effort of molecular dynamics simulations and theoretical analysis, we elaborate on the influences of nanoparticles on droplet impact process. Using simple droplets as a control, we summarize four typical droplet impact modes and reveal how nanoparticles alter the impact behaviors of droplets, taking into account the key parameters including substrate wettability, impact velocity, volume fraction, and mass fraction of nanoparticles. We also demonstrate that with appropriate modifications, the theoretical/empirical models to predict the maximum contact diameter and the occurrence of breakup for simple droplets still hold to predict those of nanofluid droplets. Our findings and results enhance the understanding of the impact of nanoparticles on the droplet impact dynamics, with promising possibilities for various applications where regulating droplet impact behaviors is desired.

Experimental study on the dynamic wetting of silica nanofluids

Nanofluids are recently discovered nanomaterials with improved thermophysical properties that can enhance the efficiency and reliability of heat transfer systems. Their relevant properties for describing heat transfer, thin film flows, droplet impingements, or microfluidics are surface tension and wettability. A thorough investigation on this topic of research is crucial to understand the root cause of the factors affecting the degree of wetting of nanofluids on solid surfaces. In the present work, silica (SiO2) nanofluids with different mass fractions and types of surfactants based on deionized water were prepared using a simple and cheap two-step method. The effect of surface tension changes on the lateral friction force of the nanofluid was studied using a solid–liquid interface lateral friction force detection system. According to the findings, an increase in the mass fraction of silica nanoparticles led to the larger surface tension of the nanofluid, resulting in a linear decrease in the lateral friction of the latter on the hydrophobic surface of PDMS. The use of ionic surfactants as dispersants caused a dramatic decrease in surface tension and static angle of SiO2 nanofluid (by 20% and 30% after adding SDS and by 40% and 50% after adding CTAB, respectively). This exerted a noticeable impact on the lateral friction force of the fluid. On the contrary, polymeric surfactants (NaPSS) had a small effect on the lateral friction of SiO2 nanofluid. Meanwhile, the lateral friction after stable motion differed from the maximum static friction to a small extent.

Investigation on the Effects of Nanorefrigerants in a Combined Cycle of Ejector Refrigeration Cycle and Kalina Cycle

Abstract The main objective of this study is to carry out the thermodynamic analysis of a new power/refrigeration combined cycle which consists of an ejector refrigeration cycle (ERC) and a Kalina cycle. In ERC, nanorefrigerants are used as the working fluid. Used nanorefrigerants are homogenous mixtures of different base refrigerants (R134a, R152a, and R290) and nanoparticles (TiO2 and Al2O3) with 0–5 wt% nanoparticle concentration. The effects of variation in system operational parameters (nanoparticle mass fraction, evaporator pressure, condenser pressure) on energy efficiency and exergy efficiency of the combined cycle are reported. Additionally, net power production, refrigeration capacity, heat input to the combined cycle, and their exergy contents are given for the case of TiO2/R290 nanorefrigerant use in ERC. This study is the first ERC analysis in which the effect of R152a and R290 base refrigerants and TiO2 nanoparticle use on ERC performance is investigated. The results show that as the nanoparticle concentration and evaporator pressure increase and condenser pressure decreases, the energy and exergy efficiencies of the cycle increase. Under all the considered operational conditions of the combined cycle, the highest efficiency results are obtained for R290 and the lowest for R134a-based refrigerants.

Heat collection characteristics of nanofluids in direct absorption solar collector with built-in rotors

As for the uneven heating of the working medium in direct absorption solar collector (DASC),this paper proposed the method of optimizing the flow pattern in DASC by inserting combined rotors into the collector tube to improve the heat collection performance. The working medium used in this paper is Chinese ink nanofluid. The heat collection performance of the collector was studied, and the enhanced mechanism was explained through simulations. Results demonstrated that inserting rotors improved the temperature rise rate in the circuit, and the temperature of the medium after inserting rotors increased by about 56 % compared with that before inserting rotors when the mass fraction of nanoparticles was 0.2 %. In some cases, a small number of rotors can achieve an enhancement effect similar to that of enormous rotors, and improve the economic performance of the system. The numerical simulation results showed that the high-temperature medium in the plain tube is concentrated near the light side, while the medium in the centre and backlight side of the tube cannot easily absorb solar radiation. After rotors were inserted into the tube, the back-side and light-side media were displaced and mixed by the turbulence of rotors, which can improve heat collection.