Showing papers by "Arash Karimipour published in 2021"

A review on the properties, preparation, models and stability of hybrid nanofluids to optimize energy consumption

Abstract: These days, the importance of energy consumption has led scientists to optimize thermal devices. One of the solutions proposed for this purpose is using solid nanoparticles to amend the thermal properties of conventional fluids. Adding the nanoparticles into the foundation fluids results in an improvement in the fluid properties (thermal conductivity, viscosity, etc.). Nanofluid (NF) has been drawing attention in various engineering applications in the past decade due to its superior heat transfer characteristics than the conventional working fluid. In recent years, the researchers have focused on adding two or more nanoparticles into foundation fluids, known as hybrid nanoparticles. Hybrid nanofluids (HNFs) suggest a more appropriate heat transfer performance and thermophysical features than the conventional heat transfer fluids (ethylene glycol, water and oil) and even NFs with single nanoparticles. It was proven that HNF can be an alternative to the single NF, since it can provide more heat transfer enhancement, particularly in the context of the solar energy, electromechanical, HVAC, electromechanical and automobile. In the current research, the properties, preparation and stability of HNFs are investigated. Also, some models and correlations for predicting HNFs properties are presented.

Investigation of the effect of adding nano-encapsulated phase change material to water in natural convection inside a rectangular cavity

Abstract: The present simulation aims to investigate adding NEPCM nanoparticles to water in the natural convection inside a cavity by using FVM method and SIMPLE algorithm Nano-encapsulated phase change material (NEPCM) consists of a shell and core with phase change property The NEPCM particles in base fluid have the ability to transfer heat by absorbing and dissipating heat in the liquid-solid phase change state In this study, the energy wall phenomenon due to the phase change of NEPCM core has appeared that the whose energy transfer strength is proportional to the latent heat of NEPCM core and the thickness of the energy wall Moreover, the relationship between the energy wall and the heat transfer rate is payed attention, and the effects of the energy wall parameters including strength, thickness, and event location of energy wall and volume fraction are studied on the energy wall and heat transfer rate According to the obtained results, adding NEPCM to the water enhances its heat transfer up to 48% in order to increase heat capacity of water-NEPCM mixture Also, best heat transfer rate happens when the energy wall is at the center of the cavity Moreover, a relation is presented for the thermal expansion coefficient of NEPCM, which considers the effects of the thermal expansion coefficient of the core and shell material

Effects of examine the phase change material through applying the solar collectors: exergy analysis of an air handling unit equipped with the heat recovery unit

Abstract: Taking into account a share of 42.4% of total energy usage for buildings, utilizing of energy reduction techniques in this sector will be effective. In this article, transient energetic analysis along with the exergetic study of an air handling unit (AHU) equipped with a heat recovery unit (HRU) were examined. The transient analysis was performed in July by developing a program based on the energy/exergy balance equations. The results showed that owing to using the phase change material (PCM), heat exchange diminished by 545 kWh July (8.6% reduction). Owing to using of a heat recovery unit, the cooling load energy demand lowered by 4043 kWh July (10% reduction). Although the irreversibility through the cooling experienced a 20% reduction due to the addition of an HRU, but the total irreversibility decreased by only 0.4%. Integrating the solar system with AHU + HRU led to energy-saving by 1832 kWh (11.6% reduction). Moreover, the total irreversibility reduced by 9% due to using the solar system. Finally, it was found that the solar system accounts for 83.62% of the total irreversibility.

Potential energy and atomic stability of H2O/CuO nanoparticles flow and heat transfer in non-ideal microchannel via molecular dynamic approach: the Green–Kubo method

Abstract: It is interesting to investigate the number of nanoparticle (NP) and temperature effects on H2O/CuO nanofluid thermal conductivity and the atomic manner in a non-ideal microchannel. The outcomes of the physical features of these structures were supposed using molecular dynamic (MD) method and LAMMPS simulation package. For the study of dynamic properties of nanofluid microchannel system, parameters such as temperature profiles, velocity, density, and potential energy of H2O/CuO atomic structures were calculated. Furthermore, the thermal conductivity of these structures was estimated by the Green–Kubo method in the final step. This simulation shows that nanoparticle number is a crucial parameter in nanofluid movement in a microchannel. Theoretically, via adding CuO nanoparticle to H2O fluid, the maximum rate of velocity, density, temperature, and thermal conductivity of base fluid increases to 0.106 g cm−3, 29.810 A ps−1, 549.217 K, and 0.81 W mK−1 rates, respectively. Moreover, the temperature increase of Cu microchannel increases the rate of density, velocity, temperature, and thermal conductivity of CuO nanofluids.

Using phase change material as an energy-efficient technique to reduce energy demand in air handling unit integrated with absorption chiller and recovery unit–Applicable for high solar-irradiance regions

Abstract: In the Saudi Arabia climate zone, the share of cooling in buildings sector energy usage is 66%. In this study, the main goal is to reduce energy usage in the cooling sector, which was investigated with the introduction of phase change material (PCM) and recovery unit (RU). By incorporation of the enthalpy-porosity technique into the energy equation, the thermal behavior of the PCM-based walls along with the ceiling was modeled transiently throughout the year. Taking into account high solar intensity in Saudi Arabia region, the sol-air temperature was defined to consider the effects of solar irradiance on the building envelopes. To meet the cooling requirements in the building, an air handling unit (AHU) combined with an absorption chiller was used. The annual calculations affirmed that by adding PureTemp (melting temperature of 22-24°C) the heat gain decreased by 7.13% which in turn led to an energy-saving by 47.3 k W h m 2 . Moreover, due to the incorporation of a RU into AHU, the energy demand in AHU was lowered by 63.8 k W h m 2 (equivalent to an 8.38% reduction). Finally, by using the energy-efficient techniques of adding PCM and installing RU, the AHU energy usage was decreased by 14.6% which was equivalent to a 111.1 k W h m 2 . y e a r energy-saving

Application of rotating circular obstacles in improving ferrofluid heat transfer in an enclosure saturated with porous medium subjected to a magnetic field

Abstract: In this paper, the evaluation of the heat transfer rate and fluid flow in an enclosure with rotating circular obstacles has been studied. The enclosure is filled with a porous medium and subjected to the magnetic field. Fe3O4/water nanofluid has been used to simulate the effect of magnetism. The finite volume method has been applied to solve the equations. To velocity–pressure coupling, the SIMPLE algorithm has been applied. The influence of magnetism on the enclosure in the conductive and non-conductive boundaries along the magnetic field has been investigated. The streamlines and isotherm-lines contours in the conductive and non-conductive boundaries along the magnetic field, the dimensionless angular velocities of the circular obstacles, and their direction have been obtained. The results show that the different temperature cases of the circular obstacles and their direction play an essential role in the flow and heat transfer. The highest and lowest heat transfer rates occur in cold circular obstacles and hot circular obstacles, respectively. Also, the composition of the porous medium and the magnetic field show different behaviors at the heat transfer rate.

Atomic rheology analysis of the external magnetic field effects on nanofluid in non-ideal microchannel via molecular dynamic method

Abstract: In the present study, the molecular dynamics method is used to probe the aggregation phenomenon of hybrid nanoparticle within platinum microchannel with pyramidal barriers. In molecular dynamics simulations, argon atoms are described as base fluid particles and for the interaction between these atoms, we use Lennard-Jones potential, while the platinum–platinum and Al2O3 nanoparticles interactions are simulated applying the embedded atom method force field. To analyze the achieved simulation results, some physical parameters such as potential energy, temperature, and distance of nanoparticles center of mass are calculated. The results show external magnetic field decrease the aggregation phenomenon in nanoparticles. Numerically, by adding external magnetic field to simulation box, the COM distance of nanoparticles reaches to 2.7 A and the aggregation time of nanoparticles changes from 1.7 to 2.3 ns. These appropriate effects of external magnetic field from our computational study can be used in the design of heat transfer applications.

Efficacy of incorporating PCMs into the commercial wall on the energy-saving annual thermal analysis

Abstract: In this study, the efficacy of incorporating phase change material (PCM) into the building walls on the annual heat transfer reduction is examined. First, heat transfer from the base wall (without PCM) was numerically calculated monthly throughout the year. Then, PCM was incorporated into the wall and its heat transfer was calculated. It was found that using PCM in all months is beneficial and the maximum heat transfer reduction is 16.7% and occurs in June. Based on the results, the lower the thermal conductivity, the greater the PCM’s ability to reduce heat transfer. Installation of PCMs such as Enerciel 22, C16–C18, Paraffin $$\left( {{\text{C}}_{18} } \right)$$ and Capric acid (with thermal conductivity of about 0.15 W m−1 K−1) inside the wall reduces heat transfer between the indoor and outdoor space by up to 15% throughout the year. Incorporating PCM of Enerciel 22 in the warm months of the year (June, July, August and September) reduces heat transfer to the room by 15.36%, while, in the colder months of the year, the heat transfer from the interior is reduced by 14.82%. Finally, throughout the year, the heat transfer between the interior and the outdoor is reduced by 14.87% due to the using PCM of Enerciel 22.

Mixed thermomagnetic convection of ferrofluid in a porous cavity equipped with rotating cylinders: LTE and LTNE models

Abstract: In the present study, the impressions of the MHD and porous medium on mixed convection of Fe3O4-water nanofluid in a cavity with rotating cylinders in three different temperature cases with local thermal equilibrium and local thermal non-equilibrium approaches were studied. The effect of the presence of cylinders in three different temperature cases to improve the heat transfer rate was investigated. A finite volume method was used to solve equations. The Richardson, Hartmann, and Darcy numbers ranges are 1 ≤ Ri ≤ 100, 0 ≤ Ha ≤ 30, 0.001 ≤ Da ≤ 0.1, respectively. The volume fraction of nanoparticles varies in the range of 0–3%. The results show that the use of porous media has a beneficial effect on increasing the heat transfer rate, but the combination of the porous medium and the magnetic field can increase or decrease the heat transfer. Also, the most effective and highest heat transfer rate was occurred at Da = 0.01 and Da = 0.1, respectively. In addition, when the cylinders are cold or hot, the highest and lowest heat transfer rates occur, respectively. Finally, it was concluded that the magnetic field could control the fluid flow inside the cavity.

Discrete ordinates thermal radiation with mixed convection to involve nanoparticles absorption, scattering and dispersion along radiation beams through the nanofluid

Abstract: This paper studied a two dimensional fluid flow and heat transfer in a finned open cavity filled by a water/Al2O3 nanofluid. Discrete ordinates (DO) method was used to investigate the effects of nanoparticle absorption and dispersion coefficients on the volumetric radiation rays passing a nanofluid. The employed nanofluid was water (base fluid) and alumina nanoparticles. A relatively, low volume fraction of the nanoparticles was needed for the preparation of the semitransparent medium. The finite volume technique of SIMPLE algorithm was coupled to DO to solve the continuous, momentum, and energy equations. The enclosure inner walls are the gray diffuse emitters and reflectors. As a result, a new dimensionless energy equation was presented in which could involve both effects of mixed convection and thermal radiation of DO based on Reynolds, Prandtl and Planck numbers. The results of the present study are different from previous studies, which neglected the effects of radiation or even considered them with inappropriate radiation method of Rosseland’s approximation for the nanofluid medium.

Experimental investigation of the hydrothermal aspects of water–Fe 3 O 4 nanofluid inside a twisted tube

Abstract: The impetus of this experimental investigation is to analyze the laminar forced convection of water-based nanofluid (NF) including Fe3O4 nanoparticles inside a twisted tube. The impacts of NF concentration (0% < $$ \varphi $$ < 2%), Reynolds number (500 < $$ {\text{Re}} $$ < 2000) and twist pitch (10–100 mm) on the average Nusselt number ( $$ \overline{\text{Nu}} $$ ), friction factor, and overall hydrothermal performance indicator are assessed, and the results are compared with those of the plain tube. It was found that the $$ \overline{\text{Nu}} $$ of NF rises with boosting $$ \varphi $$ and $$ {\text{Re}} $$ , while it declines with boosting twist pitch. In addition, it was found that the rise of $$ \varphi $$ causes a rise in the friction factor, while it diminishes with the rise of $$ {\text{Re}} $$ and twist pitch. Moreover, the results depicted that the overall hydrothermal performance of NF in the twisted tube is superior to that of the water in the plain tube. The best overall hydrothermal performance of the NF occurred at $$ \varphi $$ = 2%, $$ {\text{Re}} $$ = 2000 and twist pitch = 10 mm.

Numerical investigation of magnetic field on forced convection heat transfer and entropy generation in a microchannel with trapezoidal ribs

Abstract: In this study, the effects of adding trapezoidal ribs to microchannel on functionalized multi-walled nano-tubes/water nanofluid heat transfer are examined. The dimensionless slip coefficient (0–0.1...

Effects of Brownian motions and thermophoresis diffusions on the hematocrit and LDL concentration/diameter of pulsatile non-Newtonian blood in abdominal aortic aneurysm

Abstract: LDL concentration is believed to be responsible for plaque formation that leads to atherosclerotic cardiovascular disease. We conducted this study to investigate the effects of hematocrits and LDL diameters on LDL concentration on the wall of an abdominal aortic aneurysm (AAA). The blood flow was considered to be a pulsatile and non-Newtonian flow whose viscosity was a function of hematocrits and strain rate. Lumen, Brownian, and thermophoresis diffusions were analyzed in LDL concentration. The results demonstrated that adding thermophoresis diffusion increases LDL concentration. Moreover, among three types of LDLs, including small LDLs, intermediate LDLs, and large LDLs, small LDLs were the ones with the highest concentration at the wall of the aneurysm. Furthermore, the effects of vorticity on diffusions were examined; it could be noted that the maximum Brownian diffusion appeared in vorticity places. Our results indicated that Brownian diffusion declines as hematocrit reaches 45% whereas thermophoresis diffusion increases. The current simulation investigated the effects of hematocrits, vorticity, Brownian, and thermophoresis diffusions on LDL concentration on the wall. Three types of LDL were taken into account for investigation of the effects of the diameter and reference concentration on LDL concentration. The outcomes of this study could be summarized as the following: the maximum amount of the wall shear stress appeared at 0.2T and at the upstream end of the AAA; moreover, thermophoresis diffusion increased small LDL concentration by 26% on the wall for hematocrit 45%.

Numerical study on the performance of a homogeneous charge compression ignition engine fueled with different blends of biodiesel

Abstract: The increasing need for fossil fuels along with their limited resources and also environmental concerns caused by pollution from internal combustion engines have always led researchers to improve the technology. The use of homogeneous compression ignition combustion technology as well as alternative fuel sources such as biodiesel is proposed as a novel and promising solution to achieve goals including improving efficiency and reducing environmental pollutants specifically NOx and CO2 that are emerging in the industry. In this study, the effect of using different blends of diesel/biodiesel fuel on thermal performance along with output pollution of a homogeneous fuel compression ignition engine is investigated. The fuels range from B00 to B40, and parameters such as engine thermal efficiency, maximum cylinder pressure and exhaust emissions have been evaluated. The results show retarded and reduced maximum pressure with a decrease in engine thermal efficiency, a reduction in NOx and CO2 emissions and an increase in CO emissions, while the mass fraction of biodiesel in the fuel composition is increased. Moreover, in the investigated engine, the B20 is considered as the optimum composition with a reduction of 4.2% in maximum cylinder pressure, 5% in thermal efficiency and 26% in NOx emissions compared to B00.

Role of gradients and vortexes on suitable location of discrete heat sources on a sinusoidal-wall microchannel

Abstract: The idea of using the compact device with higher heat transfer potential has encouraged researchers to use microchannels. Creating sinusoidal walls is a technique leading to better effectiveness an...

Liquid Paraffin Thermal Conductivity with Additives Tungsten Trioxide Nanoparticles: Synthesis and Propose a New Composed Approach of Fuzzy Logic/Artificial Neural Network

Abstract: A nanofluid (Nf), which contains tungsten trioxide, WO3, nanoparticles as solid-particles distributed in liquid paraffin, is produced. A set-up is provided to experimentally measure the thermal conductivity (TC) of this mixture at various mass fractions and temperatures. Further, two universal approximators of fuzzy logic (FL) and artificial neural network (ANN) are presented to predict the TC of this mixture. The present work’s novelty can be presented as: prepare a WO3/paraffin nanofluid, measure it's TC, and develop a novel statistical/numerical model of FL compared with ANN. As it can be seen, temperature and concentration effects positively on nanofluid TC. Moreover, ANN and fuzzy models show suitable precisions; however, the interpolation capability of the proposed fuzzy model outperforms ANN at non-trained inputs.

Comparison of Nusselt number and stream function in tall and narrow enclosures in the mixed convection of hybrid nanofluid

Abstract: In this research, the average Nusselt number in tall and narrow enclosures in the presence of mixed convection of a water-based nanofluid (H2O–Cu–TiO2) is determined and compared. The effect of quantities such as Richardson number of 0.01–100, the volume fractions of 0–2% and geometric shape of the enclosure on average Nusselt number and maximum value of flow function is numerically investigated. The FVM and SIMPLER algorithm are used for resolving the nonlinear equations. According to numerical results, for all the Richardson number and two tall and narrow enclosures, the average Nusselt number rises with growing the nanoparticles volume fractions. Comparison of the tall and narrow enclosures shows that for obtaining the highest heat transfer, by growing the nanoparticles volume fractions under similar conditions, it is better to use tall enclosures for large Richardson number and narrow enclosures for small Richardson number. The highest enhancement of the average Nusselt number with increasing the nanoparticles volume fractions for narrow enclosures was 10.44% at the Ri = 0.01. Whereas in the tall enclosures, the highest increase in the average Nusselt number was 14.51% at Ri = 100. For all the Richardson number and two tall and narrow enclosures, the maximum flow function value of the nanoparticles increases with increasing volume fractions. This increase in small Richardson number is greater than in large Richardson number.

A new correlation for predicting the thermal conductivity of liquid refrigerants

Abstract: The material ability to conduct the heat transfer is called thermal conductivity which is defined by Fourier's equation. Thermodynamic data on environmentally acceptable refrigerants have maximum interest for industries to optimize and design equipment of refrigeration such as exchangers and heat compressors. Because source empirical findings are not applicable for all temperature ranges in industries, correlation approaches are usually preferred. In this research, a novel simple correlation has been developed to predict the thermal conductivity of liquid refrigerants using regression approaches. The variance analysis was applied to study the rationality of regression model. Around 15,874 experimental data of 27 refrigerants were examined to obtain the main effects between the independent parameters. Independent parameters are temperature, boiling and reduced temperatures. The calculations show that the accuracy of the proposed correlation using the average absolute relative deviation (AARD) and root mean square deviation has priority over the previous relations. The results indicated that the AARD of the proposed model is 1.1% which is 68% lower than of the most accurate previous model (Latini–Sotte).

The experimental/numerical investigation of variations in strip speed, water shower pattern and water temperature on high-temperature strip cooling rate in hot strip mill

Abstract: Hot-rolled strips are cooled on the run-out table to achieve the customer-required mechanical properties. Cooling reduces the oxidation, which can assist the coiling operation. The ability to obtain a range of mechanical properties from a single steel grade reduces the use of alloying elements (elements added to a metal or an alloy which are incorporated in the metallic structure and change in the properties of the basic alloy) and the size of the slab inventories. So in this paper, the high-temperature steel strip cooling pattern with the temperature of 870 °C and reaching the temperature of 630 °C using water and air is studied. Moreover, the numerical simulation of the high-temperature strip cooling and its cooling method is carried out. The results are compared with the similar sampler ones. The changes of three key parameters such as change in strip speed and its effect on cooling rate, change in pattern and arrangement of water showers and its effects and change in the cooling water temperature are investigated. It was found that the uniformity of the heat distribution inside the strip was increased, but the temperature of the strip was lower than the required temperature. The middle and up surface temperatures of the strip were performed at a speed of 3.48 (m s−1), which showed a very good match with the actual tested sample.

Development of the ANN–KIM composed model to predict the nanofluid energetic thermal conductivity via various types of nano-powders dispersed in oil

Abstract: Artificial neural network/kriging interpolation method optimization method which is evaluated concerned the hybrid nanofluid composed of iron oxide (Fe2O3) and aluminum oxide (Al2O3) nano-powders to improve the thermal properties of 10w40 engine oil at different amounts of volume fraction and temperature. An input-target dataset contains 30 input-target pairs. The proposed model is examined at non-trained inputs throughout the investigated intervals beside the first derivatives of the thermal conductivity with respect to temperature and nanoparticle mass fraction. It can be seen that the obtained results have suitable smoothness and continuity. Accordingly, the kriging method shows the acceptable outcomes through the experimental prediction of Al2O3/Fe2O3 nanoparticles dispersed in 10w40 engine oil.

Convection Inside Nanofluid Cavity with Mixed Partially Boundary Conditions

Abstract: In recent decades, research utilizing numerical schemes dealing with fluid and nanoparticle interaction has been relatively intensive. It is known that CuO nanofluid with a volume fraction of 0.1 and a special thermal boundary condition with heat supplied to part of the wall increases the average Nusselt number for different aspect ratios ranges and for high Rayleigh numbers. Due to its simplicity, stability, accuracy, efficiency, and ease of parallelization, we use the thermal single relaxation time Bhatnagar-Gross-Krook (SRT BGK) mesoscopic approach D2Q9 scheme lattice Boltzmann method in order to solve the coupled Navier–Stokes equations. Convection of CuO nanofluid in a square enclosure with a moderate Rayleigh number of 105 and with new boundary conditions is highlighted. After a successful validation with a simple partial Dirichlet boundary condition, this paper extends the study to deal with linear and sinusoidal thermal boundary conditions applied to part of the wall.

An experimental study on the cooling efficiency of magnetite–water nanofluid in a twisted tube exposed to a rotating magnetic field

Abstract: In this experimental research, the laminar forced convection of water–magnetite nanofluid (NF) in a horizontal twisted tube (TT) is examined under a rotating magnetic field (MF). The findings are compared with those of the plain tube (PT). The influence of nanoadditive concentration ( $$\varphi$$ ), Reynolds number (Re), twist pitch (P) and MF arrangement on the heat transfer, friction factor and overall thermohydraulic features of NF is assessed. The MF consists of two magnets that rotate around the tube. For each of the magnets, three modes of clockwise rotation, counterclockwise rotation and without rotation are considered. The findings showed that the combined use of TT and rotating MF entails an increase in the overall thermohydraulic features of water–magnetite NF. In addition, it was found that the overall thermohydraulic features of NF augment with boosting $$\varphi$$ , while they decline with boosting P and Re. Moreover, it was revealed that the best thermohydraulic features of the water–magnetite NF belonged to the case of $$\varphi$$ = 2%, Re = 500 and P = 10 mm in the presence of a rotating magnetic field resulting from the clockwise rotation of the first magnet and the counterclockwise rotation of the second magnet.