Pure Base Fluid Research Articles

Experimental analysis of saturated pool boiling of acetone and isopropanol with added surfactant sodium lauryl sulfate over aluminum surface

AbstractThe present article reports a detailed experimental study to know the effect of adding surfactants to different base fluids. For this purpose, an aqueous solution of different concentrations of surfactant with base fluids was formed and then heated at varying heat flux in a pool boiling apparatus. Acetone and isopropanol have been used as base/boiling fluids with anionic surfactant sodium lauryl sulfate (SLS) of 200, 400, 600, 800, and 1000 PPM concentration. The data obtained by heating surfactant‐based fluids has been compared to the data of heating pure base fluids to establish the role of surfactants and the importance of surfactant concentration, that is, critical micelle concentration (CMC) in pool boiling augmentation. CMC value was found in the case of pool boiling of acetone with an SLS concentration of 400 PPM. However, the CMC value is found to be a lower value of SLS concentration of 200 PPM in the pool boiling process of isopropanol. Therefore, it is interesting to investigate the possible causes of such heat transfer phenomena with different values of surfactant concentration. Variations in heat flux change the degree of superheat of the aluminum heater substrate. The heat transfer performance is studied, and finally, a semi‐empirical correlation is proposed to know the heat transfer coefficient and its dependency over the concentration of surfactant.

Effects of Knudsen numbers on natural convection patterns of nanofluids with a sub-continuous lattice Boltzmann model

To investigate effects of particle sizes on natural convection of nanofluids, nanoparticle sizes together with mean free paths in solid and fluid phases are used to define two Knudsen numbers Knd,s and Knd,f, respectively. These two Knudsen numbers are further applied to build the new effective conductivity and viscosity models, which include non-linear effects of both Knudsen numbers and volume fractions. A sub-continuous non-dimensional lattice Boltzmann model is built to compute the velocity and temperature fields. Effective thermal conductivity and base fluid conductivity based Nusselt numbers are compared. Heat flux enhancement ratios relative to pure base fluid are calculated. Nusselt numbers and enhancement ratios in wide ranges of key governing parameters over 10−6≤Knd,f≤104, 103≤Raf,L≤106, and 10−3≤ϕs≤10−1 are plotted. The optimal governing parameters and corresponding nanoparticle sizes are obtained from the full maps. The changes of heat transfer patterns with varying Knudsen numbers are also illustrated by temperature and streamline fields. Results agree with various experimental and simulation results. Also, the present sub-continuous models and simulation results provide a correlation with all parameters for practical engineering applications of nanofluids with effects of particle sizes.

Effect of various multiple strip inserts and nanofluids on the thermal–hydraulic performances of parabolic trough collectors

The thermal performance of the parabolic trough collectors can be improved by the use of swirl generator inserts added to the solar receiver. These inserts help improve the energy capture from the internal receiver walls and reduce the external wall thermal losses. If nanoparticles are added to the heat transfer fluid of the solar receiver tube, then this also increases the output working fluid temperature thereby reducing the outer wall’s temperature. The main objective of the current study is to assess the effect of various straight strip shapes with and without nanofluids. Four different strip arrangements were considered; large conical-shape strips, small conical-shape strips, rectangular-shape strips and elliptical-shape strips. All of these configurations were then also tested in 6% of SiO2 nanoparticles mixed in Therminol® VP-1 (TO) forming the nanofluid. Results showed that the straight large conical strips lead to the maximum enhancement in the Nusselt number (up to 57.49% for the pure base fluid and up to 62.53% for the nanofluid). The thermal efficiency improvement for this optimal configuration with nanofluid was found to be 15.41% with a thermal loss reduction of around 26%. A similar trend was found for the thermal exergy efficiency which showed an improvement of 15.32% for this optimal configuration with the use of nanofluid.

Experiment and predicted model study of resuspended nanofluid pool boiling heat transfer under electric field

In the pool boiling, the deposition of nanoparticles leads to the instability of boiling heat transfer of nanofluids. While, electric field can actively control the movement of nanoparticles. Therefore, the nanoparticle resuspension behavior, boiling heat transfer of resuspended nanofluid and prediction models for boiling heat transfer of resuspended nanofluid under the electric field were studied in the present study. Concretely, the heat transfer performance under the coupling effect between electric field and resuspended nanofluid was discussed. Besides, pool boiling and critical heat flux (CHF) prediction model were proposed to research the heat transfer variation caused by the movement of nanoparticles under electric field. It is found that the nanoparticles can be resuspended by electric field, and the boiling heat transfer of resuspended nanofluid under electric field is significantly enhanced when comparing to the pure base fluid. However, there exists an optimal concentration for the best enhanced effect. Besides, the enhancement of heat transfer results from the heat exchange by nanoparticles, the reduced surface tension of gas-liquid interface and the thermal conductivity enhancement effect. The predicted curves of model agree well with the experimental data. Meanwhile, the models comprehensively consider the effect of heat exchange by nanoparticles, surface tension and thermal conductivity

Natural convective heat transfer investigation of nanofluids affected by electrical field with periodically changed direction

Nanofluids with excellent thermal properties have significant advantages in the heat transfer enhancement. While, nanoparticles are easily deposited on the heat transfer interface or electrode after long-term running, which causes serious heat transfer instability. Therefore, the resuspension and natural convective heat transfer of nanofluids affected by electrical field with periodically changed direction were studied in the present study. Specifically, the variation of deposited nanoparticle layer on heat transfer surface was observed. Meanwhile, the resuspended nanofluid heat transfer characteristics were analyzed. Furthermore, mechanism of nanoparticle resuspension and heat transfer performance of resuspended nanofluid were also discussed. It is found that nanoparticles could be resuspended stably by electrical field with periodically changed direction. Meanwhile, the heat transfer performance of resuspended nanofluid under electrical field is significantly enhanced when compared to the pure base fluid, which is increased with the improvement of voltage, concentration, and direction switching time. The mechanism analysis shows that the deposited nanoparticles are resuspended by the driven of upward electric forces and drag of basefluid, and limit in a certain range by the periodically changed electrical field. Besides, A dimensionless heat transfer prediction model of nanofluid affected by electrical field with periodically changed direction was proposed, which has an acceptable reliability.

Convective heat transfer performance of thermal oil-based nanofluids in a high-temperature thermohydraulic loop

Enhancing the performance of heat transfer fluids (HTF) is a key target for improving the efficiency of many industrial processes. Employing nanofluids for this purpose, by dispersing nanoparticles into the initial HTF to improve its thermo-physical properties, is one possible way to increase its heat transfer capacity. However, testing these properties at high temperature is not always easy. An experimental setup consisting of a thermohydraulic loop for high-temperature heat transfer measurements was developed in this work. The accuracy and repeatability of the measurements taken in the heat transfer loop were ensured. A nanofluid consisting of a commercial thermal oil, doped with Sn nanoparticles at 1 wt% and olive oil surfactant used to enhance colloidal stability, was tested and compared to the results obtained for the base fluid and the base fluid/stabiliser mixture employing their experimentally measured thermo-physical properties. The nanofluid generally enhanced the convective heat transfer coefficient in relation to the base fluid with enhancements of up to 7.23% at 200 °C and 9.43% at 140 °C vs. the pure base fluid.

Thermal performance analysis of a 1–5 TEMA E shell and coil heat exchanger operating with SWCNT–water nanofluid with varied nanoparticle concentration

Single-walled carbon nanotube–water nanofluids were tested in a 1–5 TEMA E shell and coil heat exchanger. Cold nanofluid, flowing inside the coil, was heated by hot water flowing in the shell side. Volumetric fraction of nanoparticles, inlet temperature of nanofluid, and mass flow rate of nanofluids ranged from 0 to 0.21%, 2.3 to 23.4 °C, and 40 to 90 g/s, respectively. For a given Reynolds number, at the coil side, pure base fluid (φ = 0%) performed better than low-concentration nanofluid samples (φ = 0.035% and 0.053%) and was nearly equivalent to the nanofluid of highest concentration, φ = 0.21%. The thermal conductivity enhancement factor of the nanofluid ranged from 0 to 0.2 and to 0.45, at inlet temperatures of 30 °C and 50 °C, respectively. It is believed to work in favor of a better performance of the nanofluid samples. On the other hand, the unusual (literature-wise) low temperature of the nanofluid further amplified the enhancement of the nanofluid viscosity, with a reduction effect on the Reynolds number. Besides, other thermal resistances of the heat exchanger work toward an attenuation of the enhancement effect that nanoparticles may have in the heat exchanger performance.

Heat Transfer Rate Optimisation of Ionanofluid Based Heat Sink Using ANSYS

Heat dissipation of various electrical and electronic devices has been a significant concern in the current years of modernisation. Many researchers proved that a liquid-cooled microchannel heat sink (MCHS) is an effective way of removing high heat load. Due to ionic liquids’ unique properties such as negligible volatility, non-flammability, high thermal stability, and ionic conductivity, this liquid is combined with nanofluids to synthesise a new class of potential fluids termed Ionanofluids (ionic liquid-based nanofluids). In this research, a numerical simulation of fluid flow and heat transfer characteristics of MWCNT (Multiwalled Carbon Nanotubes) based Ionanofluids as a coolant in a rectangular-shaped microchannel heat sink is analysed. The Two-step method is used for preparing the studied Ionanofluids consisting of 0.5 wt.% of MWCNT nanoparticles ultra-sonicated with a mixture of propylene glycol and 1-Butyl-3-methylimidazolium chloride ([Bmim][Cl]-ionic liquid) fluids. Copper micro channelled heat sink comprising 1 m channel height, 25 μm of channel diameter, and 0.7 m channel width is modelled and simulated with ANSYS-Fluent. The results showed that the heat transfer coefficient increases about 11.4% while the thermal resistance decreases about 15.18% by using the proposed ionanofluids with the concentration of 0.5 wt.% at Re=2000 compared with that of an MCHS with propylene glycol. Moreover, the pressure drop along the studied MCHS increased up to a maximum of 30 kPa for higher heat gradients. Ionanofluids decreased the thermal resistance and temperature difference between the heated surface of the MCHS and Ionanofluids inlet to a greater extent when validated with pure base fluid and previous studies. From the simulated results, a better cooling performance is observed with Ionanofluids compared to pure propylene glycol (PG) for the proposed microchannel heat sink.

Enhancing and attenuating heat transfer characteristics for circulating flows of nanofluids within rectangular enclosures

Due to wide applications of nanofluids to designs of thermal engineering systems, the free convection participated by nanofluids inside rectangular enclosures has been intensively investigated. Generally, rightward-traveling heat transfer across a rectangular enclosure is enhanced when a pure base fluid is replaced with a nanofluid. Amid numerous dedicated literature studies of such a phenomenon, a somewhat anomalous behavior for at least four types of nanofluids has been unreported. Here we have numerically discovered this behavior in terms of averaged Nusselt number versus the nanoparticle volume fraction parameterized in enclosure-geometry Aspect ratio and Rayleigh number. At AR ≥ 2.5 and Ra = 104, a regime, in which the average Nusselt number may enhance or diminish as the nanoparticle volume fraction increases, has unexpectedly emerged. Furthermore, as the aspect ratio increases, the average Nusselt number features mildly zigzag performances at large Rayleigh numbers. Being validated with simulation results, mechanisms that govern the emergence of such phenomena are also identified. Our study may benefit future investigations that desire to understand heat-transfer mechanisms of nanofluids and to optimize heat-transfer characteristics for various thermal systems.

A Review on Titanium Dioxide Based Nanofluids: Synthesis and Stabilizing Techniques in Both “Pure (Single System) and Mixed (Hybrid System) Base Fluids”

Nanofluids have been an attractive field of study due to its important effect on enhancing the thermal conductivity when used in heat transfer applications. Titanium dioxide based nanofluid specifically has been a focus of study due to its distinguished properties as it results in a very good heat transfer enhancement with low viscosity and low-pressure drop while maintaining a very good stability of dispersion for a long time. Also, Titanium dioxide is relatively cheap and non-toxic so using it as a nanofluid will be more economical and safer in many industries. This review represents the most recent synthesis methods of titanium dioxide based nanofluid in both pure and Mixed (hybrid system) base fluids along with the analysis of its properties and the outcome findings. All of which will be discussed in this paper coherently and thoroughly which will be a good reference and makes it easier for other researchers to investigate and choose the suitable synthesis conditions that give them the required nanofluid properties and stability.

Experimental Study of Forced Convective Heat Transfer in a Coiled Flow Inverter Using TiO2–Water Nanofluids

The curved geometry of a coiled flow inverter (CFI) promotes chaotic mixing through a combination of coils and bends. Besides the heat exchanger geometry, the heat transfer can be enhanced by improving the thermophysical properties of the working fluid. In this work, aqueous solutions of dispersed TiO2 nanometer-sized particles (i.e., nanofluids) were prepared and characterized, and their effects on heat transfer were experimentally investigated in a CFI heat exchanger inserted in a forced convective thermal loop. The physical and transport properties of the nanofluids were measured within the temperature and volume concentration domains. The convective heat transfer coefficients were obtained at Reynolds numbers (NRe) and TiO2 nanoparticle volume concentrations ranging from 1400 to 9500 and 0–1.5 v/v%, respectively. The Nusselt number (NNu) in the CFI containing 1.0 v/v% nanofluid was 41–52% higher than in the CFI containing pure base fluid (i.e., water), while the 1.5 v/v% nanofluid increased the NNu by 4–8% compared to water. Two new correlations to predict the NNu of TiO2–water nanofluids in the CFI at Reynolds numbers of 1400 ≤ NRe ≤ 9500 and nanoparticle volume concentrations ranges of 0.2–1.0 v/v% and 0.2–1.5 v/v% are proposed.

Comparative performance assessment of different absorber tube geometries for parabolic trough solar collector using nanofluid

Parabolic trough collector is the most mature and widely deployed concentrated solar power technology with temperature ranging from 325 to 700 K. In this study, three different absorber tube geometries (smooth absorber tube, absorber tube with twisted tape insert and tube with longitudinal fins) of commercially available LS-2 collector are modeled and investigated using engineering equation solver. The objective of this study is to present a numerical comparative analysis of the available thermal enhancement techniques. Comprehensive energetic and exergetic performance of different tube geometry configurations using Al2O3/water as a heat transfer fluid has been compared to assess the nature of exergy destruction due to the fluid’s pressure, due to the heat transfer between sun and the receiver wall and due to the temperature difference between receiver wall and heat transfer fluid temperature. Furthermore, pure base fluid (water) along with the nanofluid is used to evaluate the system’s performance (thermal efficiency, exergetic efficiency, heat transfer coefficient, receiver temperature, pressure drop, pumping work demand and friction factor). Smooth absorber tube with pure base fluid is the reference case, while five cases (smooth tube with nanofluid, tube with pure water and fins inserted, tube with nanofluid and fins inserted, tube with pure water and twisted tape inserted, tube with nanofluid and twisted tape inserted) are investigated. Thermal efficiency of absorber tube with twisted tape insert and nanofluid is almost 72.26%, followed by tube with internal fins (72.10%), while smooth absorber tube has nearly 71.09%. Heat transfer coefficient of twisted tape inserted tube with nanofluid and longitudinal fins tube with nanofluid is greater than smooth absorber tube to almost 118.23% and 103.26%, respectively. The emphasis is also given to the pressure drop of the examined cases as it depends up on the friction factor of the absorber tubes. The use of nanofluid and twisted tape inserts leads to higher thermal enhancement, followed by the nanofluid and internal fins inserted tube. The nanoparticle concentration is also varied to investigate its effect on different performance parameters of the system.

Hybrid nanoparticle swirl flow due to presence of turbulator within a tube

The goal of the current attempt is to offer a new effective turbulator for increasing performance of a thermal system. Incorporating hybrid nanopowders makes thermal treatment better than pure base fluid. A boundary layer is destroyed with insertion of turbulator, and a greater pressure drop will be reported. As revolution of swirl flow device deteriorates, frictional resistance reduces and secondary flow becomes weaker. An inlet velocity can enhance the temperature gradient, but with the cost of a greater pressure loss. Nanoparticles can transport easier with a rise in Re and interaction with wall increases which disturbs the boundary layer.

Modification of waste tire pyrolytic oil as base fluid for synthetic lube oil blending and production: waste tire utilization approach

This study provides an environmentally friendly process for the production of waste tire pyrolytic oil from fast pyrolysis for use in lube oil production. The produced waste tire pyrolytic oil was further distilled to provide an almost pure base fluid for production of lube oil. The distilled pyrolytic oil was further transformed to lube oil via polyol synthesis. Characterization of the distilled pyrolytic oil from waste tire pyrolysis shows that the oil after distillation contained 2.04 g/100 g of Aliphatic hydrocarbons, 1.96 g/100 g of naphthalene, and 5.99 g/100 g of paraffin. The synthetic base fluid was blended with additive to obtain the desired lube oil. Based on the results obtained, the properties of the produced lubricant fall within the acceptable criteria for standard lube oils/commercial lubricants. Six different blends (A–F) were produced using varied percentages of the selected additives and the base fluid, however, sample C gave the best lube oil blend considering its average density (0.97 kg/L), average viscosity which compares favourably with ISO viscosity (68 mm2/s) of class 68 oil at 40 °C with a flash point above 200 °C.

Theoretical Study of the Film Boiling Heat Transfer of Different Nanofluids on the Vertical Heated Surface

The use of boiling nanofluids for cooling high-temperature perorating surfaces allows intensifying considerably the process of cooling by increasing the heat transfer coefficient nanofluid compared to the pure base fluid. A significant influence on the intensity of heat transfer during the boiling of nanofluid will turn out properties of nanoparticles and their concentration in the base fluid, under heating of base fluid to saturation temperature. In this study, the mathematical model of the numerical solution and the results of the simulation calculation of characteristics of film boiling of Al2O3, CuO, ZnO, TiO2, ZrO2 and SiO2 water nanofluid for various nanoparticles concentration φ∞ of (0.1, 0.2, 0.3, 0.4, and 0.5) Water nanofluid on the vertical heated wall were presented. The theoretical results obtained allow us to estimate the influence of physical properties of nanofluids on heat and mass transfer during cooling low-temperature surfaces. It is shown that the greatest impact on the processes heat and mass transfer during film boiling nanofluids overheating of the wall depended upon the ratio of temperatures, Brownian diffusion, and concentration of nanoparticles in a base fluid. Also, the results showed that the use of nanofluids as coolants for heat exchange equipment in the mode of supercritical heat exchange increases the heat transfer and accelerate the process of cooling high-temperature surfaces. Increasing the concentration of nanoparticles in the nanofluids will contribute to a greater increase in heat transfer in the supercritical heat transfer due to the low thermal capacity of steam compared to that fluid conductivity. While increasing the nanoparticle concentration will lead to an increase in the effective viscosity of the nanofluids.

Approaches to Graphene, Carbon Nanotube and Carbon nanohorn, Synthesis, Properties and Applications

By far the most important members of carbon-based materials family, are graphene, Carbon Nanotube (CNT) and Carbon Nanohorn (CNH). Thanks to their outstanding features and effective applications, have been broadly researched in recent times. Numerous ways have been proposed to synthesize graphene, CNT and CNH. This paper presents an overview of approaches to graphene, CNT and CNH synthesis, properties and applications. Most of the ways to create graphene is related to Hummer's method. Thanks to the exclusive electrical and thermal properties of graphene, it has been applied to build batteries, gas and vapor sensors, and elimination of numerous pollutants from water. Also, this review involves the conventional definition of the carbon nanotubes growth mechanism. Undoubtedly, an expert interpretation of nanotube growth at the atomic scale is one of the major challenges to improve nanotubes bulk synthesis procedure. In fact, a controlled growth may lead to get the ideal form of nanotube. Moreover, carbon nanohorn is a new member of single-graphene tubules family with a diameter of 3-6 nm and a length 35-45 nm. According to the latest reports, a new fluid including carbon nanohorns and ethylene glycol can be used for solar energy applications. Carbon nanohorns have an important role in increasing sunlight absorption as for the pure base fluid. Nanohorn spectral characteristics are far more interesting than those of amorphous carbon for the exclusive application. They can be used in important industries such as gas sensors, drug delivery, detecting some food borne contaminants.

Numerical Study on Performance of Flat Tube with Water Based Copper Oxide Nanofluids

Abstract The aim of the present study is to perform numerical analysis on the performance of a flat tube with copper oxide nanofluids. The nanofluid was passed through a virtual 3D model of a flat tube. Advantages of using nanofluids instead of pure base fluid were evaluated. The thermophysical properties of the nanofluid were calculated using correlations (function of temperature and volumetric concentration nanoparticles) developed from experimental work. It was observed that the heat transfer performance of a flat tube increased with increase in particle concentration, temperature and Reynolds number. The pressure drop across flat tube increased with increasing volumetric concentration of nanoparticle and Reynolds number

Numerical investigation of direct absorption solar collectors (DASC), based on carbon-nanohorn nanofluids, for low temperature applications

Direct absorption solar collector (DASC) have recently attracted increasing interest in combination with some new absorbing fluids, obtained through the suspension of nanoparticles in water or other liquids (nanofluids). A volumetric direct absorption in a solar collector is in principle more convenient than a superficial indirect one, assuring a temperature distribution whose peak is internal to the fluid instead and not on the external surface, as in superficial one, thus promising lower heat losses. Nanofluids, i.e. fluids with a suspension of nanoparticles, such as the carbon nanohorns we choose as case study, can be considered a good and innovative family of absorbing fluids, due to their higher absorption coefficient than the pure base fluid and to their high stability under moderate temperature gradients. In this paper, we focus on the application of direct volumetric absorption by nanofluids for civil applications, which have a typical operative temperature lower than 100 °C. A DASC using nanofluids with different nanoparticle concentrations is compared to a commercially available indirect vacuum tube solar collector. The comparison is made between simulated performance of the DASC and the nominal performance of the commercial collector. The simulations are made with a CFD model, that leverages original experimental measurements of the optical properties of the considered nanofluid. It is shown that the DASC concept is more convenient in case of higher heat losses, i.e. in case of a high transmittance solar collector or of very high temperature of the heated fluid. It is also underlined the importance of balancing the heat absorption and heat transport function of the fluid. The simulations of the first considered design reveals, in fact, that the thermal field does not completely develop in the pipe, due to the large pipe diameter in relation to the flow and to the low heat losses, thus producing a low bulk temperature. The addition of a compound parabolic concentrator (CPC) and the adoption of an annular pipe (triple tube) improve the performance in terms of average bulk temperature, though not matching yet the surface reference collector in terms of efficiency.

Pumping power and heat transfer rate of converging microchannel heat sinks: errors associated with the temperature dependency of nanofluids

To find the sensitivity and dependence degree of the numerical simulation predictions on the property variations arising from the temperature gradients, a 3D conjugate heat transfer of Al2O3–water nanofluid convecting through rectangular microchannel heat sinks (MCHS) is considered in the present study. The Koo–Kleinstreuer–Li model is adopted to capture the temperature-dependent nature of thermophysical properties of the working nanofluid compared to the pure fluid (i.e., water). Both straight and width-tapered flow passages are studied using finite volume method within the laminar flow regime to see how sensitive are the predictions to the temperature dependency of the thermophysical properties for both the pure base fluid and nanofluid. Results show that the constant property assumption obtains unrealistic results up to 140% for the Reynolds number, which may mislead in predicting the flow regime (laminar/turbulent). The constant property approach predicts the convection heat transfer coefficient and the pumping power, respectively, 31% lower and 33% higher than those of the temperature-dependent property approach. In addition, the present study concludes that the MCHS should be simulated based on the temperature-dependent thermophysical property approach to be more realistic, especially for converging flow passages due to high-temperature gradients and for nanofluids for their induced temperature-dependent properties. The last two issues induced each other and increase the deviation of the predictions based on the constant property assumption. Finally, because of underestimating the heat transfer rate and overestimating the pumping power, the MCHS would be over-designed if one adopts the constant property assumption for conceptual design and the MCHS would perform under inefficient and off-design conditions.

Optical and dielectric properties of ethylene glycol-based nanofluids containing nanodiamonds with various purities

The work reports on the characterization of optical and dielectric properties of nanofluids consisting in pure nanodiamonds suspended in ethylene glycol. The study is carried out at four concentrations within the range from 0.01 to 0.1 wt%, and for two different types of nanodiamond powders, differing each other in the purity of the diamond phase (87% or 97%). Optical extinction, even at the investigated extremely low concentrations, results significantly increased in the colloids with respect to the pure base fluid, while the refractive index at 589.3 nm remains practically unchanged. Dielectric properties of nanofluids are related with the content of nanodiamonds particles. While the complex permittivity of tested samples is dependent on a small extent, the electrical conductivity is strongly affected by the increase of nanodiamond concentration.