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The miniaturization of electronic devices without compromising their heat dissipation capacities is the main concern due to the rapid evolution in power industries and engineering fields. The conventional methods of cooling or heating the devices are changed and old tactics of using conventional fluids for heat dissipation are replaced with nanofluids of strong thermal efficiency. In the present context, the experimental as well as theoretical studies of nanofluids (Cu–H2O/Al2O3–H2O) flow inside the wavy and microchannels are elucidated and discussed for different physical conditions. It is found that the use of Cu–H2O/Al2O3–H2O nanofluid improves the thermal efficiency of heat exchangers. The complex shapes and sizes of heat exchangers such as multilayer heat exchangers, heat exchangers with twisted and square shapes and multijet heat exchangers are considered effective coolants as compared with straight microchannel heat exchangers. The use of Cu–H2O/Al2O3–H2O nanofluids improves the overall heat transfer efficacy of electronic devices, and it is considered a promising coolant for various applications including aerospace (spacecraft and satellites), automobile (cooling the engines and power management in electric vehicles), renewable energy (solar plants), microelectronic devices (heat dissipation through the microprocessor and cooling the other components of devices) and modern heat exchangers of engineering domains. [ABSTRACT FROM AUTHOR]

The potential of hybrid nanofluids to boost thermal efficiency of heat exchanger systems is the focus of this review study. The primary focus is on addressing the associated issues of nanoparticle clumping, system obstruction, and reduced efficacy of heat exchanger due to increased fluid thickness. Accordingly, this review intends to demonstrate the innovative practices (experimentally and theoretically) that helps improving the heat transfer and thermal performance of heat exchangers. In this regard, a critical analysis is conducted to appraise the experimental and numerical simulations, which introduce the impact of different nanoparticle concentrations and compositions on heat exchanger thermal performance. The findings of this review has shown that the hybrid nanofluid of CuO–Cu/water has the greatest thermal performance factor (1.065), following Al2O3–Cu/water (1.055), and Cu–TiO2/water (1.039). Also, the utilization of turbulator heat exchangers has enabled improving the thermal performance by 126 % with a 6 % rise in volume fraction at the maximum Reynolds number. This study underlines the need for further research into novel nanomaterial combinations, fine-tuning of fluid characteristic, and comprehensive stability assessments to enhance the utilization of hybrid nanofluids in heat exchanger systems. Finally, discussions of limitations associated with such systems and proposed potential solutions will lead to a valuable contribution in the possible future development of cost-effective heat exchanger systems. [ABSTRACT FROM AUTHOR]

A nanofluid is a solution of nanoparticles with diameters fewer than 100 nanometers suspended in a base fluid such as water, ethylene glycol, or oil. In the nanofluid, these nanoparticles are suspended. The goal of this research is to look at the functioning of a twin-pipe heat exchanger that uses counter flow arrangements and two different nanofluids as cooling fluids. Alkaline water is a basic fluid made up of silicon carbide (SiC) and carbon nanotubes (CNT). The goal of this research was to see how different compositions of SiC and CNT nanoparticles dispersed in water affected the heat transfer capacities of a twin pipe heat exchanger developed with a counterflow arrangement. The flow rate of the nanofluid and the particle volume concentration of alkaline water were (0.02) and (0.04), respectively. Fluids with constant intake temperatures of 60°C for water and 30°C for nanofluid flow at the same input velocity via a heat exchanger. Both fluids are traveling at the same rate. According to the findings, nanofluid absorbs more heat than water at a range of flow speeds. Because of the improved thermal properties of nanoscale fluids, this results in increased thermal efficiency in heat exchangers. [ABSTRACT FROM AUTHOR]

The heat transfer improvement and the increase of heat exchangers’ efficiency represent a very important issue in the energy field. Many research projects have focused on the use of fluids with high thermal conductivity such as nanofluids. In this case, hybrid nanofluids, are a new class of nanofluids with good heat transfer characteristics. The present work falls within this framework and involves a numerical study to examine the influence of two oil-based hybrid nanofluids, Al2O3-MWCNT and MgOMWCNT, with different volume concentrations and inlet flow rates. More to the point, the impact of different nanoparticle ratio and the location of hybrid nanofluid in a laminar flow of two-pipe counter-current heat exchanger have been investigated. In virtue of which, the results illustrate that increasing the volume concentration of nanoparticles and the flow rate of the hybrid nanofluid has a positive impact on improving the heat transfer rate. Therefore, the improvement in heat transfer rate reached 77.8% for Al2O3-MWCNT/oil hybrid nanofluid and 59.5% for MgO-MWCNT/oil hybrid nanofluid. Similarly, the study has also revealed that the preferred nanoparticles ratio for Al2O3-MWCNT/oil hybrid nanofluid is in the order of (25:75) and its circulation in the inner tube as a hot fluid makes it possible to improve the thermal performance of the considered two-tube heat exchanger to a greater advantage. [ABSTRACT FROM AUTHOR]

Nanofluids represent a novel category of advanced heat transfer fluids composed of nanoparticles within a size range of 1-20 nm dispersed in a base fluid such as water. Contemporary research predominantly focuses on incorporating nanoparticles like Al2O3 and ZnO into the water at a 0.1% volume fraction to create nanofluids. Recent investigations aim to optimize thermal performance by introducing nanoparticles into the base fluids and inducing turbulence through various macro-inserts. Key factors influencing heat exchanger efficiency enhancement include geometric parameters, thermal conductivity and volume fraction. This study endeavours to analyse the thermal and fluid flow characteristics of a proposed nanofluid, augmenting thermal transfer through computational simulations and experimental validation, achieving an error margin of 3%-5%. The impact of rectangular micro inserts, with dimensions of 4 cm in height and longitudinal spacings of 5 cm and 11.5 cm, on the heat transfer rate is examined to enhance fluid flow turbulence. Results indicate that among different geometric profiles, the insert with a spacing of 11.5 cm demonstrates superior performance, yielding higher heat transfer rates and Nusselt numbers. This research holds significant implications for various industries including thermal, power, aviation, space and automotive sectors, particularly in the utilization of concentric tube heat exchangers across diverse applications. By exploring novel geometrical and fluid domains within heat exchangers, this study unveils promising avenues for enhancing the heat transfer efficiency compared to conventional methods, highlighting the potential for further investigation into alternative materials and configurations for heat elimination enhancement. [ABSTRACT FROM AUTHOR]

Hybrid nanofluids are emerging as an alternative to conventional heat transfer fluids and nanofluids for improving the thermal efficiency of heat exchanging devices synergistically due to their outstanding thermophysical properties associated because of the dispersion of different types of nanoparticles as compared to mono nanofluids. This will help in optimizing fluid characteristics in different flow regimes for several applications. However, enhancing the thermal energy efficiency of heat exchangers is challenging owing to the deprived stability of hybrid nanofluids at greater volume concentrations. This work concentrated on the synthesizing, thermophysical depiction, and thermal performance estimation of stable water-based Cu-graphene hybrid nanofluids using very low volume concentrations of Cu and graphene hybrid nanostructures. Cu-graphene hybrid nanofluid was successfully synthesized by dispersing the synthesized Cu and graphene nanostructures (keeping the Cu concentration constant at 0.04 vol % and varying the graphene concentration from 0.01 to 0.1 vol %) in water. Hybrid nanofluids display excellent stability against aggregation for up to 7 weeks, as proven by higher zeta potential values. Thermophysical characteristics of the prepared hybrid nanofluids were effectively measured. The thermal conductivity of Cu-graphene hybrid nanofluids shows exceptional enrichment (~ 35%) at minimal concentrations of hybrid nanostructures. Viscosity of the water-based hybrid nanofluids shows remarkable enhancement as compared to water and represents the increasing trend in viscosity of the base fluid with respect to the increase in concentration of hybrid nanostructures. The thermal and rheological properties of hybrid nanofluids are effectively validated with existing theoretical models. In addition, the specific heat and pumping power of Cu-graphene hybrid nanofluids with respect to the volume concentration of hybrid nanostructures are calculated using the existing theoretical equations. A figure of merit (FOM) analysis was conducted for the synthesized hybrid nanofluids to gauge thermal efficiency and evaluate the applicability of these hybrid nanofluids under laminar and turbulent flow conditions. [ABSTRACT FROM AUTHOR]

Researchers and engineers are actively working on enhancing the efficiency of heat exchangers in engineering applications by developing novel designs, exploring new materials, and utilizing nanofluids. Three kinds of nanofluids with varying concentrations are investigated in this paper. The objective is to assess the performance of N‐shaped double‐pipe heat exchanger used in thermoelectric power plants. The performance has been evaluated using COMSOL Multiphysics software. The findings show that higher nanofluid concentrations resulted in elevated heat transfer coefficients and improved efficiency of N‐shape double pipe heat exchanger. The analysis revealed that a mere 1% rise in the volume fraction of nanofluids enhanced the efficiency of the heat exchanger on average 23% when compared to the base fluid (water). In comparison to the N‐shape double pipe (Inconel 625) heat exchangers, the N‐shape double pipe (copper) heat exchangers appear to be more efficient. The introduction of nanoparticles has a notable impact on the heat transfer coefficients. Specifically, within an N‐shaped double pipe (copper) heat exchanger, the inclusion of a 1% volume fraction results in a 2.09% enhancement in the heat transfer coefficient for Al2O3/water, a 1.3% improvement for Fe3O4/water, and a 1.15% increase for TiO2/water. It also exposed that adding 1% Al2O3/water led to a significant 0.623% increase in effectiveness, while TiO2/water showed a 0.259% rise, and Fe3O4/water exhibited a 0.375% improvement. Moreover, increasing the Reynolds number enhances the Nusselt number for Al2O3/water and Fe3O4/water nanofluids by 55.22%, and for TiO2/water by 54.60% at a 6% volume concentration, leading to additional increases in exchanger efficiency. Therefore, the augmentation in nanofluid concentration leads to a reduction in the temperature pinch points both at the intake and outflow. This observation suggests that nanofluids exhibit a superior ability compared to conventional fluids when it comes to effectively lowering temperatures. [ABSTRACT FROM AUTHOR]

This paper studies how the correlation with the Nusselt number affects the final result of the efficiency, ε, and exergy efficiency, ηex, of a chevron-type gasketed plate heat exchanger, which is installed in a typical small solar installation dedicated to single-family housing; the solar fluid is a TiO2:SiO2/EG:DI hybrid nanofluid with concentrations from 0% to 1.5% vol. The experimental model assumes constant flow of the solar fluid and varies on the domestic hot water side—from 3 lpm to 6 lpm. The inlet temperatures are 30 °C and 60 °C on the cold and hot sides of the heat exchanger, respectively. Of the six analysed correlations that showed similar trends, it is concluded that for the assumed flow conditions, geometry, and chevron angle of the plate heat exchanger, one model is the most accurate. The largest difference between the ηex values for a given concentration is 3.4%, so the exergy efficiency is not affected by the chosen Nusselt model by very much. However, the choice of correlation with the Nusselt number significantly affects the efficiency, ε; the difference between the values obtained within a given concentration is more than 40% and depends on the Reynolds number and flow. Most research discusses the scenario with the nanofluid as a coolant. This paper considers the opposite situation in which the solar fluid is a hotter working medium that transfers heat to domestic hot water installation. [ABSTRACT FROM AUTHOR]

The present paper presents a numerical investigation of heat transfer in an exchanger fitted with a modified conical-shaped turbulator containing water/Fe2O3 nanofluid. The study aims to address the critical need for improved heat exchanger efficiency, a vital component in various industries, including the chemical, power generation, and food industries. The work focuses on achieving enhanced heat transfer performance within a smaller volume, a primary goal of modern technology and industrial processes. The innovation in this study lies in the design and analysis of a novel conical turbulator, which has not been explored extensively in the context of heat exchangers fitted with nanofluids. Unlike traditional methods, which often rely on active or semi-active means to enhance heat transfer, this research introduces a passive approach through the incorporation of turbulators. Specifically, the study investigates the use of perforated cone-shaped turbulators in conjunction with nanofluids to boost heat transfer performance. The research employs state-of-the-art computational fluid dynamics (CFD) models, allowing for a comprehensive evaluation of the turbulator's performance across a wide range of Reynolds numbers (Re = 4000–20,000). It further examines the influence of various turbulator parameters, nanoparticle content, and geometry on heat transfer efficiency. Key findings indicate that the modified turbulator exhibits exceptional performance, increasing Nusselt numbers by 3.4–5.4 times and friction coefficients by 2.3–1.8 times compared to smooth pipes. Particularly noteworthy is the 92 % increase in the Nusselt number achieved with a mere 2 % increase in the Fe2O3 nanoparticle content. The present study introduces a novel passive heat transfer enhancement method using perforated cone-shaped turbulators and nanofluids, filling a significant gap in existing research. The innovative turbulator design and its substantial performance improvements offer promising prospects for achieving higher heat exchanger efficiency, making it a valuable contribution to thermal systems and heat transfer engineering. [ABSTRACT FROM AUTHOR]

In this study, we aim to investigate the heat transfer and flow characteristics of diverse hybrid nanofluids (CuO-ZnO-Water, EG-Water, CuO-EG-Water, SiO2-EG-Water, and Al2O3-EG-Water) as coolants across eight discrete inlet velocities in a shell and tube heat exchanger. Various materials (copper, stainless steel, titanium, and carbon steel) have been employed for the tubing to optimize system performance. The impact of Reynolds number concerning hybrid nanofluids on Nusselt number and friction factor was assessed in this research. The results of the numerical simulations are found to agree well with experimental results within an average deviation of 1.8%. The results indicated the superior heat transfer capabilities of the hybrid nanofluid compared to the base fluid across all conditions. The outcomes revealed the superior heat transfer capabilities of the CuO-ZnO-Water hybrid nanofluid under all tested conditions. When employing CuO-ZnO-Water as a coolant, a substantial increase of over 9% in temperature reduction was observed, as opposed to the approximately 6% attained by other hybrid nanofluids at a lower velocity of 0.5 m/s. Notably, higher Reynolds numbers corresponded to increased Nusselt numbers and decreased friction factors. The decline percentage of the friction factor was 43% at Reynolds number ranging between 10,000 to 40,000. We emphasize the imperative need to optimize nanoparticle types for crafting hybrid nanofluids to enhance the performance of industrial heat exchangers and their coolant efficiency. Ultimately, the utilization of hybrid nanofluids in conjunction with shell and tube heat exchanger systems has yielded a notable enhancement in the overall thermal efficiency of these systems. [ABSTRACT FROM AUTHOR]

In view of the current global energy situation, increasing the efficiency of heat exchangers can contribute significantly to reducing energy consumption and greenhouse gas emissions. In this study, the effects of nanofluids (SiO2/Water) prepared at different fluid flow rates and different volumetric concentrations (vol.%0.1-0.2-0.3) on three heat exchangers (Shell and Tube, Double Pipe, Plate) with the same capacity were investigated experimentally and statistically. It was concluded that there was an increase of 47% in effectiveness and 87.3% in NTU value with the increase in the volumetric concentrations of nanofluids and fluid flow rate. With the use of nanofluids, it was observed that entropy production decreased by up to 56.08%. The results obtained were analyzed using Response Surface Methodology (RSM) and mathematical models were created and the prediction capabilities of the models were 98% and above. Entropy minimization was performed using statistical methods and it was statistically determined that plate heat exchangers give better results among heat exchangers with the same capacity. It is concluded that the entropy production is minimum when the fluid flow rate is 2 lpm, the volumetric concentration is 0.3% and a plate heat exchanger is used. This study has provided a different and comprehensive perspective on heat exchangers, and it is thought that it will give many ideas to researchers working in this field. [ABSTRACT FROM AUTHOR]

Improvements in heat exchanger thermal efficiency are crucial for achieving energy use and cost reductions. The use of nanofluids and the rotation of the exchanger inner tube may enhance heat transfer and exchanger efficiency. In this work, after having performed experiments on such a heat exchanger, a three dimensional numerical model was developed to simulate the transitional forced convection flow of a horizontal double-tube heat exchanger, with the aim of obtaining insight into the effects of the inner tube rotation, fluid flow rate and type of nanofluid employed. It was found that an increase in the nanoparticle concentration up to 3% increased the exchanger efficiency. Al2O3, Al2O3-Cu and Cu-water nanofluids were studied, with the Cu-water being the fluid with the best performance (19.33% improvement). Heat transfer was enhanced with inner tube rotation up to 500 rpm (41.2%). Nevertheless, pressure drop and friction values were increased due to both phenomena, leading to higher pumping power values for the operation of the heat exchanger. Hence, a balance between the performance and pumping power increase must be considered when modifications are made on a heat exchanger. The development of the numerical model might help in further optimizing, redesigning and scaling up heat exchangers. [ABSTRACT FROM AUTHOR]

In recent times, the field of nanotechnology has been instrumental in driving significant breakthroughs in heat transport. These technological breakthroughs have shown their significance in improving the efficiency of heat exchangers, such as thermal pipes, microfluidic structures, and electronic components that depend on effective heat transfer processes. This study aims to explore innovative methods for enhancing heat transfer effectiveness. The present investigation focuses on the two-dimensional, incompressible, electrically conducting ternary liquid flow between two parallel porous plates in a microchannel. This has been considered with the convective boundary conditions employing the thermophoretic particle deposition phenomena. The numerical results of the mathematical, physical problem entailed a similar solution employed with the RKF-45 method. The stimulus of these process-sensitive non-dimensional parameters has been discussed and presented graphically with validation of the published results. The velocity profiles decline as increment in S 1 and M F whereas the thermal profile lessens with the augmentation in Biot numbers Bi 1 and Bi 2 . Moreover, the study emphasizes that the mass and thermal energy distribution rates exhibit a reduction when the solid volume percentage, thermophoretic constraints, and the existence of a porous medium increase. The ramifications of these discoveries are significant in terms of the design and optimization of microfluidic devices and thermal exchangers. The findings are visually shown using illustrations, offering valuable insights into the intricate relationships among the variables under investigation. [ABSTRACT FROM AUTHOR]

The present study investigates the effects of using a magnetic field on the flow field and heat transfer of ferromagnetic Fe3O4/H2O nanofluid considering two-phase model for nanofluid in heat exchanger equipped with helical ribs. Three methods are employed to enhance the thermal efficiency of heat exchanger, as employing of corrugations, utilizing nanofluid as heat transfer fluid, and employing the magnetic field. The performance evaluation criteria index (PEC) is employed to analyze the thermal-hydraulic characteristics of the heat exchanger. The main aim is to achieve an optimum model with the highest performance evaluation criteria value. Usaging of corrugated heat exchanger or nanofluid can increase the average Nusselt number and friction factor in the tube sharply. Also, it is understood that the presence of a magnetic field has a significant effect on the heat transfer enhancement inside the heat exchanger. The model with magnetic field of 600 G has the highest Nusselt number ratio among all studied models, which is followed with 400 G, 200 G, and 0 magnetic fields, respectively. Furthermore the effects of different corrugation heights, widths, and pitches have been studied. Finally, usage of the novel corrugated heat exchanger with 14 mm corrugation heights, 9 mm rib width, and 12.5 mm blade pitches filled with nanofluid, and under a magnetic field of 600 G it suggested as the most efficient configuration. Also, at the Reynolds number of 4,000, the highest performance evaluation criteria values are achieved. [ABSTRACT FROM AUTHOR]

In this paper, the simultaneous impacts of using nanofluid and ultrasonic vibrations in a double-pipe heat exchanger are experimentally investigated. The vibrating heat exchanger is designed so that the ultrasonic waves with the power of 60 watts and frequency of 40 kHz are applied to its body at equal length distances in a uniform and effective manner. Water-based Al2O3 nanofluid is used in this research. The available empirical correlation has been used to confirm the accuracy of the measurements and validate the results. The effective thermal parameters have been tested in three cases using water, nanofluids, and ultrasonic-excited nanofluids as the working flow of the double-pipe heat exchanger. These tests have been performed in a relatively wide range of flow rate (113–257 lh−1), Reynolds number (3230–7431), inlet hot fluid temperature (40–60 °C), and nanoparticle volume fraction (0.4–0.8%). The results indicate the positive effect of adding nanoparticles and applying ultrasonic vibrations, especially at higher inlet hot fluid temperatures and higher nanofluids concentrations. The nanoparticles are more effective at high-flow rates, whereas the ultrasonic vibration is highlighted at low-flow rates. Also, the effectiveness-NTU analysis carried out for the current heat exchanger shows that using nanofluid and ultrasonic-excited nanofluid instead of water can increase the efficiency of the thermal system up to 18.3% and 42.3%, respectively. [ABSTRACT FROM AUTHOR]

Activation energy can be elaborated as the minimal energy required to start a certain chemical reaction. The concept of this energy was first presented by Arrhenius in the year 1889 and was later used in the oil reservoir industry, emulsion of water, geothermal as well as chemical engineering and food processing. This study relates to the impacts of mass transfer caused by temperature differences (Soret) and heat transport due to concentration gradient (Dufour) in a Carreau model with nanofluids (NFs), mixed convection and a magnetic field past a stretched sheet. Moreover, thermal radiation and activation energy with new mass flux constraints are presumed. All chemical science specifications of nanofluid are measured as constant. As a result of the motion of nanofluid particles, the fluid temperature and concentration are inspected, with some physical description. A system of coupled partial differential frameworks is used mathematically to formulate the physical model. A numerical scheme named the Runge–Kutta (R-K) approach along with the shooting technique are used to solve the obtained equations to a high degree of accuracy. The MATLAB R2022b software is used for the graphical presentation of the solution. The temperature of the nanofluid encompasses a quicker rate within the efficiency of a Dufour number. An intensifying thermal trend is observed for thermophoresis and the Brownian motion parameter. The Soret effect causes a decline in the fluid concentration, and the opposite trend is observed for rising activation energy. In addition, the local Nusselt number increases with the Prandtl number. Further, the comparative outcomes for drag force are established, with satisfying agreement with the existing literature. The results acquired here are anticipated to be applied to improving heat exchanger thermal efficiency to maintain thermal balancing control in compact heat density equipment and devices. [ABSTRACT FROM AUTHOR]

Nanofluids are generally utilized in providing cooling, lubrication phenomenon, and controlling the thermophysical properties of the working fluid. In this paper, nanoparticles of Al2O3 are added to the base fluid, which flows through the counterflow arrangement in a turbulent flow condition. The fluids employed are ethylbenzene and water, which have differing velocities on both the tube and the shell side of the cylinders. A shell tube-type heat exchanger is used to examine flow characteristics, friction loss, and energy transfer as they pertain to the transmission of thermal energy. The findings of the proposed method showed that the efficiency of a heat exchanger could be significantly improved by the number, direction, and spacing of baffles. With the inclusion of nanoparticles of 1% volume, the flow property, friction property, and heat transfer rate can be considerably improved. As a result, the Nusselt number and Peclet numbers have been increased to 261 and 9.14 E +5. For a mass flow rate of 0.5 kg/sec, the overall heat transfer coefficient has also been increased to a maximum value of 13464. The heat transfer rate of the present investigation with nanoparticle addition is 4.63% higher than the Dittus–Boelter correlation. The friction factor is also decreased by about 17.5% and 11.9% compared to the Gnielinski and Blasius correlation. The value of the friction factor for the present investigation was found to be 0.0376. It is hence revealed that a suitable proportion of nanoparticles along with the base fluids can make remarkable changes in heat transfer and flow behavior of the entire system. [ABSTRACT FROM AUTHOR]

The most common type of heat exchanger used in a variety of industrial applications is the shell-and-tube heat exchanger (STHE). In this work, the impact of graphene nanoplate (GNP)/water nanofluids at 0.01 wt.%, 0.03 wt.%, and 0.06 wt.% on the thermal efficiency, thermal performance factor, pressure drop, overall heat transfer, convective heat transfer coefficient (CVHTC), and heat transfer characteristics of a shell-and-tube heat exchanger was examined. For these experiments, a new STHE was designed and built. The novelty of this study is the use of GNPs/water nanofluids in this new STHE for the first time and the fully experimental investigation of the attributes of nanofluids. GNP properties were analysed and confirmed using analyses including XRD and TEM. Zeta potential, DLS, and camera images were used to examine the stability of nanofluids at various periods. The zeta potential of the nanofluids was lower than -27.8 mV, confirming the good stability of GNP/water nanofluids. The results illustrated that the experimental data for distilled water had a reasonably good agreement with Sieder-Tate correlation. The maximum enhancement in the CVHTC of nanofluid with 0.06 wt.% of GNP, was equal to 910 (W/m2K), an increase of 22.47%. Also, the efficiency of the heat exchanger for nanofluid at 0.06 wt.% improved by 8.88% compared with that of the base fluid. The heat transfer rate of the nanofluid at maximum concentration and volume flow rate was 3915 (J/kg.K), an improvement of 15.65% over the base fluid. The pressure drops increased as the flow rate and concentration of the nanofluid increased. Although increasing the pressure drop in tubes would increase the CVHTC, it would also increase the power consumption of the pump. In conclusion, nanofluid at 0.06 wt.% had good performance. [ABSTRACT FROM AUTHOR]

The improvement of the efficiency of heat exchangers has always been one of the most critical concerns of industry. Pulsating heat pipes are a new and high-efficiency technology in the field of heat transfer. Pulsating heat pipes are widely used in solar water heaters, solar water desalination systems, etc. In this study, the effect of different nanofluids on the performance of heat pipes was investigated. ZrO2/SiO2 nanocomposites were tested under functionalized and non-functionalized states in a pulsating heat pipe. For this purpose, the heat pipe was charged with each nanofluid at concentrations of 0.25, 0.5, and 1 g L−1, and the thermal resistance of the pipe was compared as an output parameter. The thermal resistance for different nanofluids was defined and compared at different input powers of the evaporator and a constant filling ratio of 50%. The obtained results showed that nanofluids as a working fluid could improve the heat transfer of pulsating heat pipe compared to the working fluid of water and reduce the thermal resistance. The nanofluid with a concentration of 0.25 g L−1 exhibited the best performance. In this case, the resistance of pulsating heat pipe at some fluxes was decreased up to 48%. [ABSTRACT FROM AUTHOR]

The present work focuses on a numerical investigation of nanofilms' (water/copper and water/aluminium) evaporation inside a heat exchanger by mixed convection flowing down on one channel plate. The channel was composed of two parallel vertical plates. The wetted plate was heated while the other plate was maintained isothermal and dry. The impact of the dispersion of different types of nanoparticles in the liquid film and their volume fraction in mass and heat exchange and the evaporation process has been analysed in this work. The results show that an increase of the nanoparticle inlet volume fraction enhances the efficiency of evaporation in heat exchangers. It is shown that an enhancement of 22% in evaporation rate has been recorded when the inlet nanoparticle volume fraction is elevated by 5%. The results show that the water–copper nanofluid had higher evaporation rate compared to water–aluminium nanofluid. [ABSTRACT FROM AUTHOR]

In this study, the heat transfer and flow characteristics of TiO2‐H2O nanofluids with TiO2 mass fractions of 0.0, 0.1, 0.3, and 0.5 wt.% in corrugated and smooth double‐pipe heat exchangers were compared using numerical simulations. The results demonstrated that TiO2‐H2O nanofluids effectively enhanced the heat transfer compared to deionized water, and that the heat exchange capacity gradually increased with the TiO2 mass fraction. The corrugated pipe heat exchanger disturbed the fluid flow on both the shell side and pipe side, breaking the boundary layer and creating vortices in the corrugated zone. This provided a higher heat transfer capability than the smooth double‐pipe heat exchanger, but also increased the fluid flow resistance in the pipe. In general, the use of nanofluids and corrugated pipes was found to significantly improve the heat transfer efficiency of the double‐pipe heat exchanger. [ABSTRACT FROM AUTHOR]

In this research, the effect of using GO/ water nanofluid as a coolant fluid in an isothermal heat transfer system was studied. At first, to evaluate the atomic bond, chemical, and surface structure of the nanoparticles, XRD-FTIR and FESEM tests were used. Two-step method was used to prepared nanofluid then DLS test was utilized to examine the stability of the nanofluid. Thermal conductivity and the dynamic viscosity were measured experimentally from 25 to 75 ℃ and volume fractions of 0–0.15%. The maximum improvement in thermal conductivity is 11.2% at 0.15% and 75 ℃. Also The dynamic viscosity increased. The validity and uncertainty of the test results were examined. The heat transfer and turbulent flow of the nanofluid under a constant temperature boundary condition were investigated between 6000 and 18,700 Reynolds numbers. Various parameters such as the pressure drop, friction factor, convection heat transfer coefficient, and Nusselt number of the turbulent flow were evaluated. According to the results, the greatest increase in the convection heat transfer coefficient of the nanofluid was 34.7% compared to that of the base fluid. Also, the greatest enhancement in the friction factor was 9.64%. It can be stated that the improvement of the convection heat transfer coefficient dominantly affects the pressure drop so this nanofluid can be used as a coolant fluid in industrial systems. [ABSTRACT FROM AUTHOR]

Heat exchanger studies have been conducted for several decades since the beginning of the development of heat transfer theories due to their widespread use in various industries. The ongoing research topics include heat exchanger efficiency, design parameter optimization, material development, and heat transfer technology exploration. Research has been continued to evolve nanofluid compositions, concentrations, and operating conditions that affect heat exchanger efficiency. They have used hybrid nanofluids in heat exchangers, which contain multiple types of nanoparticles or nanoparticles with additional additives, as hybrid nanofluids improve thermal performance. As a result, the development and optimization of hybrid nanofluids as a working medium in heat exchangers are gaining popularity, and the use of hybrid nanofluids in heat exchangers has already drawn a lot of interest as a viable strategy in industrial sectors. Therefore, such a surge of interest in using hybrid nanofluids in heat exchangers has resulted in a significant body of literature on this. In this review paper, the authors aim to incorporate the findings of these studies and offer a thorough evaluation of the state-of-the-art research on the application of hybrid nanofluids in various types of heat exchangers. This review provides a synopsis of the published literature on the efficacy of heat exchangers utilizing hybrid nanofluid. The researchers have also encountered and documented several challenges, including stability and aggregation, improving thermal conductivity, fluid flow characteristics, corrosion and material compatibility, cost and scalability, and determining the ideal size and shape of nanoparticles while considering environmental and health concerns. In addition, this review identifies research gaps in preventing agglomeration, ensuring nanoparticle dispersion, optimizing fluid composition to minimize flow effects, exploring and identifying materials compatible with hybrid nanofluids, investigating cost-effective methods for hybrid nanofluid production, and addressing scalability issues for widespread implementation in industrial heat exchangers. This review paper will be a valuable resource for researchers and practitioners seeking to overcome these challenges and advance the field of hybrid nanofluids for heat exchanger applications. [ABSTRACT FROM AUTHOR]

The need to improve the heat transfer rate in various industries due to its increasing growth, the need to use new turbulators, and the simultaneous use of hybrid nanofluids with them as new methods are inevitable. In this paper, studies are done to analyze the exergy efficiency of ternary hybrid nanofluid flow in a heat exchanger with novel compound twisted turbulator and helical blades. System is under magnetic field from top to bottom in four different values which are related with four different Hartmann numbers (Ha = 50, 100, 200 and 400). The optimization is carried out due to fulfilling the highest exergy efficiency value. According to numerical results, in all the studied Reynolds numbers, the exergy efficiency values of systems with turbulator are more than the basic system. The combined system has well increased the exergy efficiency in the whole range of studied Reynolds numbers and can be introduced as the optimal geometry in the present work. The combination with counterclockwise direction of blades and clockwise direction of twisted tape is more efficient than the system with clockwise blades and twisted tape. Adding helical blades and increasing their number leads to increased exergy efficiency. The highest exergy efficiency according to the PEC index is related to the twisted rotating bar with hemispherical surface barriers, which increases by 7% in Re = 12,000. [ABSTRACT FROM AUTHOR]

Featured Application: Cooling of Power Electronic Devices, Electromechanical Machines, Thermoelectric Devices, and Bioengineering Applications. The capabilities of nanofluids in boosting the heat transfer features of thermal, electrical and power electronic devices have widely been explored. The increasing need of different industries for heat exchangers with high efficiency and small dimensions has been considered by various researchers and is one of the focus topics of the present study. In the present study, forced convective heat transfer of an ethylene glycol/magnesium oxide-multiwalled carbon nanotube (EG/MgO-MWCNT) hybrid nanofluid (HNF) as single-phase flow in a heat exchanger (HE) with elliptical corrugated tubes is investigated. Three-dimensional multiphase governing equations are solved numerically using the control volume approach and a validated numerical model in good agreement with the literature. The range of Reynolds numbers (Re) 50 < Re < 1000 corresponds to laminar flow. Optimization is carried out by evaluation of various parameters to reach an optimal case with the maximum Nusselt number (Nu) and minimum pressure drop. The use of hybrid nanofluid results in a greater output temperature, a higher Nusselt number, and a bigger pressure drop, according to the findings. A similar pattern is obtained by increasing the volume fraction of nanoparticles. The results indicate that the power of the pump is increased when EG/MgO-MWCNT HNFs are employed. Furthermore, the thermal entropy generation reduces, and the frictional entropy generation increases with the volume fraction of nanoparticles and Re number. The results show that frictional and thermal entropy generations intersect by increasing the Re number, indicating that frictional entropy generation can overcome other effective parameters. This study concludes that the EG/MgO-MWCNT HNF with a volume fraction (VF) of 0.4% is proposed as the best-case scenario among all those considered. [ABSTRACT FROM AUTHOR]

The aim of the present work is to investigate the role of Al2O3/water nanofluid and the geometric parameters of flow in heat transfer, pressure drop and heat exchanger efficiency. By applying periodic conditions, the flow and heat transfer of Al2O3/water nanofluid inside a tube has been investigated at the presence of heat transfer enhancer and under the influence of constant wall temperature. The turbulent flow regime and Reynolds numbers are considered to be in the range of 2000–10,000. Computational fluid dynamics software has been applied to model the governing differential equations using baffles with heights of 2, 4 and 6 mm and pitchs p/d = 0.5, 1, 2 and nanofluid with volume fractions of 1 and 2. The results of numerical modeling show that using rectangular baffle inside the pipe increases heat transfer compared to a simple pipe. As can be seen, adding nanoparticles to the base fluid increases heat transfer and by increasing the volume percentage of the nanofluid, the Nusselt number and heat transfer also increase. Moreover, increasing the volume percentage of nanoparticles from 1 to 2% increases the thermal efficiency in the heat exchanger with and without baffle. As the Reynolds number increases, the heat efficiency coefficient of the baffleless heat exchanger decreases when the Reynolds number is more than 2000. However, in the heat exchanger with baffle, increasing the Reynolds number decreases the thermal efficiency initially and then, for the Reynolds number more than 3500, an increase in thermal efficiency is illustrated. The results of the present study can be used for cooling process and heat transfer in large-scale heat exchangers and integrated circuits. [ABSTRACT FROM AUTHOR]

For enhancing the heat transfer efficiency of heat exchanger, silica-water (SiO 2 -H 2 O) nanofluids were used as a working medium in this study. Further, the effects of tube structure, twisted tape hole spacing, and hole shape on the flow and heat exchange characteristics of nanofluids in the tube were systematically researched by numerical simulation. The results displayed that a triangular tube exhibited larger flow resistance, better heat transfer effect and more comprehensive performance compared to the round tube. The conclusion also showed that the highest comprehensive evaluation index (PEC) was obtained by producing open circular holes on the twisted tape. The usage of porous twisted tape, nanofluids, and triangular tube could significantly improve the system economy and enhance the heat exchange ability. At the same time, the flow in the tube was disordered and accompanied with the increase in entropy. The maximum improvement of heat exchange efficiency of nanofluids in round tube and triangular tube with porous twisted tape was 74.80 and 55.97%, respectively. [Display omitted] • Effects of different hole shapes in twisted tape on forced convection are studied. • Effects of hole spacing in twisted tape on forced convection are studied. • Tube with round hole twisted tape shows the best heat transfer performance. • Round tube and porous twisted tape can improve heat transfer by 74.80% at most. [ABSTRACT FROM AUTHOR]

Nanofluids have made a breakthrough contribution toward maximizing the efficiency of heat exchangers. Consequently, graphene nanofluids have attracted significant attention, as they yield the best heat‐transfer enhancement among all nanofluids; however, graphene is highly expensive, and further studies on hybrid graphene nanofluids are required to optimize costs. Research has been performed on the performance of pure graphene nanofluids, though little has been conducted on hybrid graphene nanofluids. Therefore, we investigated the hydrodynamic and convective heat‐transfer performance of graphene‐titanium dioxide composite (GTNC) nanofluid in a micro‐heat exchanger, and compared the results with the performance of pure graphene and pure titanium dioxide nanofluids under similar conditions. Herein, we report the synthesis of GTNC using our novel green micro‐synthesis technique and the preparation of graphene, titanium dioxide, and GTNC nanofluids using a two‐step method at three concentrations (0.02~0.08 wt%) using a surfactant. Furthermore, the stability and thermo‐physical properties of nanofluids were investigated, and nanofluids were studied for their effect on the performance of a counter‐current laminar flow micro‐heat exchanger at different flow rates (Re = 750‐1460). Findings show that thermal conductivity enhancement of GTNC nanofluid and pure graphene nanofluid at the highest mass fraction (0.08%) was 25.8% and 31.6%, respectively, while the maximum enhancement of convective heat‐transfer coefficient was 64.6% and 87%, respectively. These results indicate that hybrid GTNC nanofluid showed proximate thermal performance and stability level to graphene nanofluid with 50% less graphene content, which improves the economics of the process. [ABSTRACT FROM AUTHOR]

Numerical analysis is carried out on heat transfer performance of industrial-length double-tube heat exchanger, by using hybrid nanofluid as a coolant with the effect of external magnetic field. The double-tube heat exchanger contains two tubes, namely inner and outer, and has lengths of 1.39 m and 1.03 m, respectively. The hot oil passes into the outer tube, and the coolant (hybrid nanofluid) passes into the inner tube. Two types of hybrid nanofluids are used for this investigation: (a) CNT-Al2O3/water and (b) CNT-Fe3O4/water. Volume fraction and Reynolds number are considered as 0.1% to 0.5% and 800 to 2400, respectively. This study is carried out with mixture model wherein the equations are solved with control volume approach combined with second-order upwind scheme. Results indicate that Nusselt number is found higher for CNT-Fe3O4/water hybrid nanofluid in the presence of magnetic field. On using hybrid nanofluid, higher thermal efficiency and better performance index of heat exchanger are achieved. The effectiveness increased nearly ~ 30% at higher Reynolds number with Ha = 20. About 40% better performance index is achieved at lower Reynolds number for CNT-Fe3O4/water when compared with CNT-Al2O3/water hybrid nanofluid. Increment in thermal efficiency of heat exchanger is improved almost 30% by increasing the Reynolds number. [ABSTRACT FROM AUTHOR]

The thermal efficiency of the heat exchanger is substantial in chemical and mechanical systems. The presence of the non-homogeny magnetic field considerably enhances the heat rate of nanofluid stream. In this exploration, the presence of the non-uniform magnetic intensity on the heat rate of nanofluid stream is noted inside the 1 8 0 ∘ elbow pipe. FVM is used to model the flow characteristics and temperature distribution through the 1 8 0 ∘ elbow pipe. Our major focus is to demonstrate the main influences of the non-uniform FHD on flow stream and heat transfer of nanofluid in various inlet velocities and magnetic intensities. Achieved outcomes display that growing the magnetic intensity from 1e + 6 to 4e + 6 enhances the average Nusselt number about 30%. Our findings show that increasing the inlet velocity to Re = 100 decreases the magnetic effects about 17% on the heat transfer growth. [ABSTRACT FROM AUTHOR]

U-tubes are nowadays widely used in large industries, especially in heat exchangers, as well as solar absorbers. Optimizing and increasing the thermal efficiency of heat exchangers reduces fossil fuel consumption and costs savings. A comparative experimental study was conducted on friction factor, and heat transfer of oil-based nanofluids flow (CuO and Fe 3 O 4 with 0.5%, 1%, and 2% mass concentrations) inside inclined U-tube at 0°, 30°, 60°, and 90° inclination angles under constant heat flux. The nanofluids prepared in two steps method by dispersing nanoparticles in SN-500 base oil. The tests were performed in five different flow rates. The results showed that compared to the base fluid, using nanoparticles increased the friction factor and convective heat transfer coefficient. According to the results, it was found that the highest heat transfer rate belonged to 0.5% CuO and 1% Fe 3 O 4 , and the maximum increase in Nusselt number for nanofluids happened at 30° inclination angles. Finally, it was found that the Fe 3 O 4 nanofluid with 1% concentration had the highest value among all the test nanofluids samples in horizontal and inclined modes. Unlabelled Image • Thermo-hydraulic properties of oil-based nanofluids have been studied in U-tubes. • 0.5% CuO and 1.0% Fe3O4 nanofluids have the highest Nusselt number. • CuO nanofluids show anti-wear properties and reduce the friction factor. • Fe3O4 nanofluid with a 1% concentration has the highest thermal performance index. • Maximum increase in Nusselt number happens at 30° inclination angle. [ABSTRACT FROM AUTHOR]

In the current research, viscosity and thermal conductivity of hybrid Cu/CNTs water-based nanofluids were investigated at various concentrations of nanofluid and temperatures. The results demonstrated that although increasing the concentration leads to enhance the thermal conduction coefficient and viscosity, the increase in temperature followed the expected results of increasing thermal conductivity and decreasing viscosity. For the objective of evaluating the function of the U-shaped heat exchanger system, exergy variations concerning different operation conditions of three nanofluid concentrations (0.1, 0.2, and 0.5%) and three different pitches of the spiral strip (2, 3, and 4) were considered. The results showed that in all cases, a rise in Reynolds number would increase heat transfer. Additionally, the presence of a spiral strip resulted in much more increase in turbulent flow; subsequently, an impressive effect on the thermal performance can be obtained. The findings of the exergy efficiency for the U-shaped heat exchanger using hybrid nanofluid in different scenarios indicated that it is improved to 9–17%, and exergy improvement with the ratio of 4 is 23–26% and, for the ratio of 4, obtained 10–12.7%. For predicting the exergy efficiency of the heat exchanger, the designed neural network presented a three-layer model (one input layer, one hidden layer, and one output layer) containing seven neurons in the hidden layer and the leading algorithm of backpropagation Levenberg–Marquardt that anticipates the behavior of the system with a precision of R2 = 0.9967. The investigation of error distribution indicated that the model follows a normal distribution. [ABSTRACT FROM AUTHOR]

In this paper, the effect of different channel spacing in spiral heat exchanger filled with Cu–ZnO–water hybrid nanofluid was investigated to find the optimum thermal–hydraulic performance. The hot water flow enters into the test section from central aperture of heat exchanger, and the cold hybrid nanofluid flow enters into the test section from the outer aperture of the heat exchanger. The effects of different flow velocities, nanoparticles φ and channel spacing values have been analyzed. Results have been presented on Nusselt number, outlet temperature, pressure drop and PEC. According to the obtained results, channel spacing decrease in constant flow velocity values is more effective than volume fraction increase on outlet temperature improvement. Also, an increase in inlet flow velocity leads to lower heat transfer between cold and hot channels, but the growth of volume fraction can improve the thermal efficiency of the heat exchanger at high velocities. On the other hand, the reduction in channel spacing leads to more pressure drop penalty. Especially for the hot water flow, this behavior reduces the hydraulic performance of heat exchanger. The less the channel spacing, the more the pressure drop. The highest average Nusselt number occurs at a velocity of 0.45 (m s−1) and φ = 4% at a channel spacing of 35 mm. The maximum value of the pressure drop occurs at b = 2.5–5 mm. Besides considering the PEC value, 2% volume fraction is recommended for the spiral heat exchanger. [ABSTRACT FROM AUTHOR]

Optimizing the performance of solar collectors and photovoltaic thermal systems that are used for heating/cooling of building as well as electricity generation will efficiently help to approach zero-energy buildings. For this purpose, improving the efficiency of heat exchangers as the main part of solar collectors and photovoltaic thermal systems is necessary. In this paper, two passive methods are employed to ameliorate the efficiency of heat exchangers. To do this, the effect of using Al2O3/water nanofluid in a heat exchanger tube with a swirling flow turbulator was studied. A numerical simulation was carried out to obtain thermal–hydraulic performance in the tube with eccentric helical screw-tape turbulators. The influences of different parameters including nanoparticles volume fraction and eccentricity of tube insert on the performance of heat exchanger are investigated. The results reveal that the coefficient of heat transfer enhances approximately 4.5 times by using nanofluid at nanoparticles volume fraction of 4% with helical turbulator compared to the plain tube at nanoparticles volume fraction of 0%. It was also found that the value of Performance Evaluation Criterion ameliorates as the nanoparticle loading increases. The maximum value of Performance Evaluation Criterion reached 2.2 at nanoparticles volume fraction of 4%, Reynolds number of 4000 and eccentricity of 3. The results of this study reveal the potential of the suggested technique to enhance various thermal systems including solar collectors. [ABSTRACT FROM AUTHOR]

With the onset of the warm and cold season, the temperature inside the building goes far away from the human comfort condition, so an optimal energy source is needed to reach the desired temperature. Naturally, the earth is a massive source of heat that is easily accessible under the buildings, yards, and squares of the city; therefore, the geothermal heat exchangers can be used in depth of the ground to drain the heat from the earth. In optimizing heat transfer equipment to achieve higher energy efficiency, the focus is on reducing the size of the heat exchanger on the one hand and increasing the intensity of heat transfer area on the other hand. Helical heat exchangers are compact and can be used in geothermal systems to receive energy. In this paper, a conical coil tube geothermal heat exchanger is simulated according to the environmental conditions of Tehran, the capital city of Iran, and the potential of using such system is examined by changing the geometric parameters and operational requirements. The coil diameter, coil pitch and the angle of conic of the helical tube are varied for the heat exchanger buried at a depth of 3 m from the earth surface. The soil temperature profile is obtained from the air temperature data Synoptic Meteorological Station. Design parameters are coil diameter, coil pitch, cone angle, length to width ratio of the fin, number of fins and Reynolds number. Taguchi algorithm is applied to find the best geometric parameters. Finally, different volume fractions of Al 2 O 3 nanoparticles are added to the optimized geometry to enhance the heat transfer rate. Results indicate that the optimized geometry considering thermal-hydraulic performance in the range of this study is θ = 0 ° ,   D c = 1000   m m ,   P c = 60   m m ,   R e = 3000 ,   R = 1   a n d   F n = 6 for cone angle, coil diameter, coil pitch, Reynolds number, length to width ratio of fin and number of fins respectively. Changing the objective to increase heat transfer (Nusselt number) the optimized values alter to θ = 3.14 ° ,   D c = 1000   m m , P c = 80   m m ,   R e = 4993 ,   R = 1.5   a n d   F n = 6 . Heat flux on the surface of the tube increases to 18% for 0.5% volume fraction of nanoparticles. [ABSTRACT FROM AUTHOR]

For increasing the heat transfer efficiency of the tubular heat exchanger, Chinese ink (CI) nanofluid was applied in the built-rotor tube, and the effects of the mass fraction of CI and structures of the rotors were investigated through experiments and numerical simulations. The experimental results indicated that the heat transfer performance improved with an increase in the nanofluid mass fraction and that the nanofluid in the built-in rotor tube produced a better heat transfer enhancement effect than that in a plain tube (PT). The Nu of 0.1% CI nanofluid in the PT increased by 11.12%–13.69%, whereas that in the built-in rotor tube increased by 17.57%–18.94%. The flow pattern and temperature distribution in the tube were studied via numerical simulations. The addition of rotors can make the flow pattern change from an axial flow to a three-dimensional spiral flow. This flow pattern reduces the thickness of the laminar sublayer and the temperature of the medium near the wall, as well as the synergy angle in the tube, which makes nanofluid with good thermophysical properties have a better heat transfer enhancement effect in the built-in rotor tube than in the PT. • Chinese ink nanofluid was first used as a convective heat transfer medium to study its enhanced heat transfer performance. • Experiments showed that nanofluid has better heat transfer enhancement performance in the built-in rotor tube than in a plain tube. • The mechanism of heat transfer enhancement of the nanofluid in the built-in rotor tube was analysed via numerical simulations. [ABSTRACT FROM AUTHOR]

The use of nanofluids has opened new intellectual horizons in improving the performance of heat exchangers. Therefore, in this work an experimental study was conducted for investigating the effect of CuFe 2 O 4 /water nanofluid on the heat transfer rate enhancement in a cross-flow type heat exchanger under turbulent flow conditions. Heat transfer rate were examined at different volume percentages of CuFe 2 O 4 nanoparticle (0≤ φ ≤ 0.9% vol.) with a nominal diameter of 28 nm at three inlet fluid temperatures of 72, 80 and 88 °C, water pump rotational speeds of 2000 rpm and 3000 rpm, and cross-flow fan speeds of 1500, 2000 and 2500 rpm. According to the results, the heat transfer rate in the case of using nanofluids with a volume percentage of 0.1% was significantly higher than that of distilled water in all test conditions. The highest relative increase in the universal heat transfer coefficient (U) equal to 92.3%, compared to the use of water (φ = 0) was obtained at 0.1% vol% of nanoparticles, the lowest temperature of fluid entering the heat exchanger (72 °C), medium pump speed (2000 rpm) and low fan speed (1500 rpm). The maximum Performance Evaluation Criterion (PEC) improvement of 44.46% also occurred at this working condition. [ABSTRACT FROM AUTHOR]

• The properties of nanofluid in nanochannel in the presence of surfactant molecules are investigated in rectangular atomic channel. • Water molecules are considered as the base fluid, copper atoms as nanoparticles and CTAB molecules were considered as surfactant. • The Atomic stability of simulated nanofluid don't disrupted by surfactant molecules adding to MD simulation box. • Cu nanoparticles and CTAB molecules adding to base fluid molecules improve their thermal behavior. • MD simulation results which calculated by using the Drieding UFF force, and Charm force fields have similar form. The poor heat transfer properties of the base fluid are the first effective obstacle to improving heat exchangers' efficiency. The key point of using very high conductivity of solid particles (in nanometer dimension) is hundreds of times more than common fluids in heat transfer in the composition of these fluids. Therefore, adding nanoparticles (NPs) to base fluids has been a solution to increase the heat transfer (HT) properties of common energy-carrying fluids. On the other hand, adding surfactants prevents the sedimentation and instability of NPs and improves the thermal performance of nanofluids (NF). So, this study surveyed the thermal properties of water-copper NF with/without surfactant molecules in a rectangular nanochannel using molecular dynamics (MD) simulation. Cetryltrimethylammoniu Bromide (CTAB) molecules were used as surfactants, copper structure as NPs, and water molecules as a base fluid in this simulation. In the present study, the effect of nanochannel wall temperature, copper nanoparticle (NP) size, and force field type (DREIDING, Universal Force-Field (UFF), and CHARM) on thermal conductivity (K nf) of water-copper NF were studied. The results show that as the wall temperature decreased from 80 to 30 K, K nf decreased from 0.783 to 0.753 Wm-1K−1. On the other hand, by increasing the radius of NPs from 0.5 to 2 nm, K nf and heat flux (HF) increase from 0.77 to 0.798 Wm-1K−1 and 5734 to 6352 W.m−2, respectively. One of the important purposes of researchers and engineers in various industries is to increase efficiency and reduce the systems' size. Therefore, it is expected that the results of this study will be effective in many different thermal industries. [ABSTRACT FROM AUTHOR]

In heat transfer area, researches have been carried out over several years for the development of convective heat transfer enhancement (HTE) techniques. For proper optimization of thermal engineering systems in terms of design and operation, not only the heat transfer has to be maximized but also the exegetic efficiency has to be minimized as well. Present study provides a theoretical, numerical, and experimental investigation of the exergy analysis in a double pipe heat exchanger. For this purpose, metal oxide-water nanofluids and twisted tapes (TTs) are considered as the model fluids and turbulators. Results are verified with well-known correlations. The results show that nanofluids and TTs can increase the exergetic efficiency by 30-100% compared to empty tube and water as a base fluid. In addition, the exergetic efficiency increases with increase in nanoparticles concentration and decreases in twist ratio. CuO nanofluid gives better enhancement in exergetic efficiency than others under the same condition. Since the prediction of exergetic efficiency from experimental process is complex and time-consuming process, an ant colony optimization-back propagation (ACOR-BP) artificial neural networks (ANN) model for identification of the relationship, which may exist between the thermal and flow parameters and exergetic efficiency, have been developed. The network input consists of 11 parameters (Cp, nf, Cpbf, pbf, pnf, φ, kbf, knf, µbf, µnf, unf, ubf) that crucially dominate the heat transfer process. The results indicate that ACOK-BP ANN provides a high degree of accuracy and reliability. The proposed ANN model can be used to understand how key parameters affect exergetic efficiency without using extensive numerical modeling or experimental studies. [ABSTRACT FROM AUTHOR]

Today, the optimal use of non-renewable energy sources, reducing pollution, and increasing the efficiency of power-generating cycles are of particular importance. There are several ways to increase the efficiency of gas turbines; one that has recently attracted attention is to use an intercooler. However, the efficiency of the heat exchanger used in intercoolers depends on the type of heat exchanger, the characteristics of the operating fluid and the thermal boundary layers, and the pump speed. Improving the thermophysical properties of the working fluid is a passive method of increasing heat transfer, which has attracted the attention of those researching engineering applications. The current review addresses the latest methods of improving gas turbine efficiency using nanofluids and includes experimental and numerical studies. First, the general principles governing turbines are described, then the commonly used types of heat exchangers are introduced. Finally, studies on the use of nanofluids in heat exchangers are reviewed. The technology of producing nanoparticles that can be used in heat exchangers is also discussed. This review article can provide the reader with comprehensive information on making nanofluids and using them in heat exchangers used as intercoolers. [ABSTRACT FROM AUTHOR]

Heat exchangers are key components in many of the devices seen in our everyday life. They are employed in many applications such as land vehicles, power plants, marine gas turbines, oil refineries, air-conditioning, and domestic water heating. Their operating mechanism depends on providing a flow of thermal energy between two or more mediums of different temperatures. The thermo-economics considerations of such devices have set the need for developing this equipment further, which is very challenging when taking into account the complexity of the operational conditions and expansion limitation of the technology. For such reasons, this work provides a systematic review of the state-of-the-art heat exchanger technology and the progress towards using nanofluids for enhancing their thermal-hydraulic performance. Firstly, the general operational theory of heat exchangers is presented. Then, an in-depth focus on different types of heat exchangers, plate-frame and plate-fin heat exchangers, is presented. Moreover, an introduction to nanofluids developments, thermophysical properties, and their influence on the thermal-hydraulic performance of heat exchangers are also discussed. Thus, the primary purpose of this work is not only to describe the previously published literature, but also to emphasize the important role of nanofluids and how this category of advanced fluids can significantly increase the thermal efficiency of heat exchangers for possible future applications. [ABSTRACT FROM AUTHOR]

The geothermal heat exchanger system is one of the most energy-efficient and environmentally friendly building service systems. In the present study, CuO/water nanofluid was used as the heat transfer fluid to enhance the energy efficiency of the geothermal heat exchangers. A three-dimensional numerical model was employed to investigate the effect of nanoparticle diameter and sphericity on the thermal performance of the geothermal heat exchanger, and it was well validated against the experimental results of nanofluids in the geothermal heat exchangers. The numerical results showed that nanoparticles with a diameter of 5 nm and 50 nm were not recommended for the nanofluids used in the geothermal heat exchangers due to the performance efficiency coefficient lower than 1, and the optimum diameter was 40 nm, which had the highest performance efficiency coefficient (1.004875). Moreover, the spherical particle-based nanofluid was characterized by the 8.55% higher energy efficiency, in comparison to rod-shaped particle-based nanofluid. Therefore, the application of nanofluid in the geothermal heat exchanger can enhance heat transfer, and the proposed optimum particle diameter and sphericity could contribute to higher energy efficiency. [ABSTRACT FROM AUTHOR]

• Benefits deriving from MOHC-based nanofluid adoption in ORCs were investigated. • A numerical model for the assessments of the nanofluid benefits was developed. • Semi-empirical correlations for modelling MOHC desorption behaviour were defined. This paper presents an in-depth investigation of the applications of an innovative nanofluid – suspensions of nanoparticles in a base fluid- in the ORC field, based on a new class of nanoparticles – termed Metal-Organic Heat Carriers (MOHCs) – molecularly engineered to reversibly uptake and release the working fluid molecules in which they are suspended. Unlike standard nanoparticles (i.e. Al 2 O 3 , Al, ...), these MOHCs make it possible to extract additional heat from the endothermic enthalpy of desorption which can be as much as twice the level of the latent heat of vaporization of the pure fluid phase alone. The paper illustrates the development of a numerical model for assessing the MOHC-based nanofluid gain in ORC systems. More specifically, the possible combination of the base fluid R245fa with the nanoparticle MIL101, a robust Metal Organic Heat Carrier, was considered. To properly model the reversible adsorption/desorption process, experimental analyses were carried out to study the uptake of the R245fa in MIL101 at different operating conditions and departing from the experimental results, proper semi-empirical correlations were defined and adopted within the numerical model. The resulting performance of the MIL101/R245fa were compared with those of pure organic fluids, whose cycle was optimized in order to maximize the area-to-power ratio. Promising results were achieved in terms of system efficiency increase and heat exchanger area reduction. [ABSTRACT FROM AUTHOR]