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The primary objective of this study is to conduct a practical investigation of heat transfer (HT) and friction factor (f) characteristics within a double pipe heat exchanger (DPHE) configured in a counter-flow arrangement. To achieve this, a novel approach involving twisted tape (TT) with dimple inserts accompanied by adjacent holes working fluid is water implemented. This dimples, characterized by their concave geometry, are strategically employed to augment the heat exchange process while concurrently mitigating any adverse impact on fluid pressure. A pivotal facet of this study centered on examining the influence of dimple diameter, as well as a consistent dimple-to-depth ratio (D/H), on both heat transfer efficiency and friction factor. The performance of TT inserts featuring diverse diameter (D) = 2, 4 and 6 mm is meticulously scrutinized in terms of their impact on heat transfer and friction factor characteristics. The outcomes of the study furnished intriguing insights. It is observed that the diameter of the dimples wielded a discernible encouragement on friction factor, revealing a direct correlation. The maximum rate of friction factor is recorded at a 2 mm dimple diameter configuration. When evaluating Nusselt number (Nu) and performance evaluation criteria (PEC), it is revealed that the most favorable results is achieved with the 4 mm dimple diameter configuration. Drawing upon these empirical findings, a significant conclusion can be drawn. Utilization of twisted tape inserts adorned at dimples is a practical, efficient and economically viable approach to heighten HT efficiency within heat exchangers. By optimizing dimple diameter and adhering to a consistent diameter-to-depth ratio, substantial improvements in HT capabilities can be harnessed without disproportionately compromising fluid pressure. This innovative methodology holds the potential to revolutionize heat exchanger design, offering an avenue to enhance HT efficiency with practical and cost-effective solutions. [ABSTRACT FROM AUTHOR]

The high energy consumption of water bath heaters in city gate stations due to heating the passing gas is always a significant concern. A suggested approach is to apply a shell and tube heat exchanger to raise efficiency or utilize heat losses. This study first examined the impact of the geometrical parameters of a heat exchanger, e.g., baffle cut, baffle number, tube pitch, and tube diameter, on heat transfer, pressure drop, and exchanger price as objective functions and estimated the optimal point of the exchanger's geometry based on the TOPSIS algorithm. Then, the feasibility of replacing a shell and tube exchanger with a water bath heater in city gate stations was probed. The shell and tube exchanger was simulated and analyzed by Ansys Fluent software. The results showed that increases in the baffle cut from 20 to 50%, tube pitch from 1.3 to 1.9, and tube diameter from 21.3 mm to 42.2 mm reduced heat transfer by 10, 3, and 7% and pressure drop by 9, 10 and 11%, respectively, while a surge in the number of baffles from 2 to 5 raised pressure drop and heat transfer by 14 and 12%, respectively. The outcomes associated with the economic analysis of replacing an exchanger revealed that this replacement decreased fuel consumption and led to reduced contamination, on the one hand, and cost conservation, on the other hand, such that the net present value index zeroed in less than 5 years. [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]

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]

Aiming at the gas steam cycle system with partial load operation throughout the year, the influence of adding a gas turbine inlet temperature regulating heat exchanger on the energy efficiency of the combined cycle was analyzed based on the variation curve of the combined cycle partial load performance with inlet temperature of similar models provided in the literature. Taking the hot water temperature of the inlet temperature regulator designed for a certain gas steam cycle thermal power plant as the experimental testing conditions, and under the same inlet heater resistance limit conditions, the comprehensive performance of two types of gas–water heat exchangers using three-dimensional deformation tubes and composite steel aluminum fin tubes was tested and compared for analysis. Based on the performance characteristics and experimental calculation results of three-dimensional deformation tube heat exchangers, a new type of gas turbine inlet temperature regulator using three-dimensional deformation tubes was designed based on the local climate conditions and partial load operation characteristics of a thermal power plant. And the heating and cooling conditions of the gas turbine inlet temperature regulating device were discussed and analyzed for the typical operating conditions throughout the year. The conclusions obtained can provide reference for the selection of gas turbine inlet temperature regulators by power plant engineering technicians and the engineering application of this innovative gas turbine inlet temperature regulator. [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]

The thermal efficiency of heat exchangers, heat sinks, solar heaters, etc., could be optimized by improving the heat transfer in the system without increasing the exergy destruction. It is important to consider pressure loss as well as heat transfer enhancement to increase overall energy efficiency. One of the most effective methods to increase heat transmission with minimal pressure drop penalty is by deploying vortex generators. In this paper, a detailed review of the synergy angle, angle of attack, friction factor, Nusselt number, flow configuration, Reynolds number, and the impact of geometry of the vortex generators on the enhancement of heat transfer and exergy is presented. The principles of field synergy and exergy are utilized to predict the thermo-hydraulic performance of the vortex generators. Different geometries of vortex generators such as rectangular, delta, trapezoidal winglets, and other novel geometries of vortex generators are installed in varied flow configurations and analyzed based on field synergy and exergy principles which were not the matter of interest in review papers in the past. [ABSTRACT FROM AUTHOR]

To address the issue of low efficiency in cooling heat exchangers at the deeper ends of mine fans, we propose a micro-unit approach for arranging the cooling water flow path within the heat exchanger. This method involves subdividing the heat exchanger into micro heat transfer units and determining the heat transfer characteristics of each individual unit through theoretical calculations and software simulations. Utilizing a computer program, these micro units are systematically arranged and combined to exhaust all possible cooling water flow paths. The ultimate objective is to derive the optimal structural arrangement of the cooling water flow path within the heat exchanger, with the goal of achieving the most efficient heat transfer effect. The findings reveal that the optimized structure, obtained through the micro-unit optimization method, achieves an average air outlet temperature of 311.65 K. This temperature is lower than that of the typical current-flow structure (311.88 K) and the typical counter-flow structure (311.68 K), indicating a superior heat transfer effect. Further examination demonstrates that the average air outlet temperature across all counter-flow structures is 311.68 K, which is notably lower than the average air outlet temperature of 311.90 K observed in the current-flow structure. This highlights the enhanced heat transfer effectiveness of the counter-flow structure. This novel method for optimizing the heat exchanger flow path applies the concept of finite element analysis to the optimization process, reducing computational and experimental costs. This approach is significant for improving the efficiency of heat exchangers. [ABSTRACT FROM AUTHOR]

The present research utilizes an inverse 3D CFD technique, coupled with the least squares approach and laboratory temperature readings, to predict the suitable turbulence flow model and unknown heat transfer rates within a cubic hot box. This enclosure features four cylindrical horizontal tubes arranged in a diamond configuration, functioning as heaters to generate heat within the space. Furthermore, the heat dissipation from each tube, flow field and temperature contours are also established. The energy equation for tubes and the governing equations for air are solved by coupling. The present estimates are obtained assuming a constant heat transfer rate. The range of the Rayleigh number is from 60,294 to 76,824. Testing various turbulence models revealed that the zero-equation turbulence model reduces the root mean square discrepancy between the simulated thermal behavior and laboratory outcomes compared to other methodologies. To verify the chosen flow model’s accuracy, the Nusselt numbers and flow field distributions aress compared with existing correlations and interferometer photographs. The maximum errors between the estimates of heat loss and heat transfer rate and the corresponding values from previous studies are 44 and 28% for St = 0.036, 34 and 3% for St = 0.045, and 37 and 18% for St = 0.054. To assess the impact of tube surface and spacing on the flow field model, calculation results are compared with those from four square-arranged tubes, revealing a lack of existing studies on this specific investigation. [ABSTRACT FROM AUTHOR]

This study examines the turbulent heat transfer characteristics of Al2O3–Cu hybrid nanofluids in circular ducts with triangular rib configurations. Numerical simulations were conducted for a 25 cm long, -cm high duct with walls maintained at 313 K. Hybrid nanofluids enter at 298 K, with triangular ribs on the internal surface at three attack angles (45°, 60°, and 90°) spaced 20 mm apart. Al2O3–Cu/H2O hybrid nanofluids at concentrations of 0.1–2 vol.% were investigated for Reynolds numbers between 20,000 and 60,000. The study aimed to determine the optimal rib configuration and nanofluid concentration for enhancing heat transfer while minimizing friction losses. Key findings include: (1) the 60° rib configuration produced the highest local heat transfer coefficient, with the maximum occurring at the rib centers. (2) Increasing nanofluid concentration and Reynolds number enhanced heat transfer but reduced skin friction. (3) The optimal performance was achieved with 2 vol.% Al2O3–Cu at Re = 60,000. (4) Velocity contours revealed larger recirculation zones for 60° ribs compared to 45° and 90° configurations. (5) Turbulent kinetic energy was highest for 60° ribs, contributing to enhanced thermal performance. These findings have implications for improving the efficiency of heat exchangers, cooling systems, and other thermal management applications. [ABSTRACT FROM AUTHOR]

Enhancing heat transfer rates while concurrently reducing pressure drop will significantly enhance the energy efficiency of industrial heat exchangers, thereby contributing to a cleaner and more sustainable environment in the future. This study explores the fluid flow of a novel combination solution in a helical heat exchanger under a constant heat flux across various Reynolds numbers (5000–17000) aiming to uncover synergies that enhance heat transfer efficiency while reducing drag for the first time. Two key performance metrics, namely Drag Reduction (DR) and Heat Transfer Enhancement (HTE), along with the thermal effective index, are introduced to evaluate both hydrodynamic and thermal characteristics. Under turbulent conditions, an aqueous solution containing Anionic PAM (100–500 ppm) obtains a noteworthy 43% DR at 500 ppm. Simultaneously, a colloidal solution of nano-SiO2 (500–3000 ppm) in deionized water demonstrates an impressive 47% HTE at 2000 ppm. Furthermore, this study introduces two novel terms, “heat transfer enhancement synergy” and “drag reduction synergy,” marking their debut in the literature. The investigation extends to exploring four Nano-SiO2_PAM combinations which is the novelty of the study, revealing an outstanding 93.3% synergy in HTE. Precisely, at Reynolds 14,000, the synergy between 100 ppm PAM and 2000 ppm SiO2 (named comb.20 as the best combination) attains a remarkable 73.76% in DR, showcasing a noteworthy thermal effectiveness reaching approximately 200%. Even for comb.20, at Reynolds 5000, the synergy achieves a notable 133.33% in DR and 76.22% in HTE, which is quite significant. This result is attributed to a complex formation that elongates the polymer chain due to the presence of nanoparticles around the polymer chain, effectively damping eddies. Furthermore, a novel set of correlations is proposed for the prediction of the Nusselt number of the aforementioned solutions, demonstrating a remarkable agreement with experimental data with a maximum error of 24%.Graphical Abstract: Enhancing heat transfer rates while concurrently reducing pressure drop will significantly enhance the energy efficiency of industrial heat exchangers, thereby contributing to a cleaner and more sustainable environment in the future. This study explores the fluid flow of a novel combination solution in a helical heat exchanger under a constant heat flux across various Reynolds numbers (5000–17000) aiming to uncover synergies that enhance heat transfer efficiency while reducing drag for the first time. Two key performance metrics, namely Drag Reduction (DR) and Heat Transfer Enhancement (HTE), along with the thermal effective index, are introduced to evaluate both hydrodynamic and thermal characteristics. Under turbulent conditions, an aqueous solution containing Anionic PAM (100–500 ppm) obtains a noteworthy 43% DR at 500 ppm. Simultaneously, a colloidal solution of nano-SiO2 (500–3000 ppm) in deionized water demonstrates an impressive 47% HTE at 2000 ppm. Furthermore, this study introduces two novel terms, “heat transfer enhancement synergy” and “drag reduction synergy,” marking their debut in the literature. The investigation extends to exploring four Nano-SiO2_PAM combinations which is the novelty of the study, revealing an outstanding 93.3% synergy in HTE. Precisely, at Reynolds 14,000, the synergy between 100 ppm PAM and 2000 ppm SiO2 (named comb.20 as the best combination) attains a remarkable 73.76% in DR, showcasing a noteworthy thermal effectiveness reaching approximately 200%. Even for comb.20, at Reynolds 5000, the synergy achieves a notable 133.33% in DR and 76.22% in HTE, which is quite significant. This result is attributed to a complex formation that elongates the polymer chain due to the presence of nanoparticles around the polymer chain, effectively damping eddies. Furthermore, a novel set of correlations is proposed for the prediction of the Nusselt number of the aforementioned solutions, demonstrating a remarkable agreement with experimental data with a maximum error of 24%. [ABSTRACT FROM AUTHOR]

The aim of this study was to develop a mathematical model with lumped parameters to investigate the energetic parameters of the heat pump with an internal heat exchanger (IHX). The developed mathematical model is validated with 25 tests using R134a as a working fluid. The results show that the maximum prediction error between the modeled and experimental results for the COP is 7.06%. The main objective of this paper was to investigate the COP value of a heat pump as a function of the efficiency of the internal heat exchanger and present a new equation to calculate the COP value. When the efficiency of IHX was increased from 0.65 to 0.95, the COP value increased by 5.41% under the conditions of minimum evaporation − 20 °C and maximum condensation temperature 90 °C. [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]

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]

This study is aimed to conduct energy, exergy and economic analysis on a network of single-effect absorption chillers. First, the network was analyzed parametrically and then optimized to minimize exergy destruction and annual cost. Multi-objective optimization was performed by implementing a particle swarm optimization algorithm. The case study was conducted on the absorption chiller network in Iranian Marun Petrochemical Company. The results indicated the greatest effects of the solution heat exchanger efficiency and network inlet cooling water temperature on energy and exergy performance coefficients and annual cost. Accordingly, decreasing the network inlet cooling water temperature from 35 to 25 °C increased energy and exergy performance coefficients by 5.3 and 6.2%, respectively, and reduced annual cost by $70,000.00. Besides, increasing solution heat exchanger efficiency from 60 to 80% increased energy and exergy performance coefficients by 5.9 and 2.1%, respectively, and decreased the annual cost by $60,000.00. According to the optimization results, the economic function of the network saved 9.95%, so that if the network works in optimized thermodynamics and economic conditions, the cost decreases by 3.24% compared to the typical manner. [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]

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]

In this paper, for improvement of the performance of shell and tube heat exchanger, the effect of adding circular grooves on the shell of heat exchanger is considered numerically. The grooves are created in different heights but with the same pitch of the coil. The obtained results consist of both qualitative and quantitative data affected by geometrical parameters. According to the numerical results, the groove increases the heat transfer rate up to 5% and does not affect the pressure drop dramatically. By use of Taguchi experimental design and exergy analysis, the performance of the heat exchanger is examined in different working conditions, such as different level of cold inlet temperature, cold fluid flow rate, and groove height (roughness value). The results of this consideration revealed that the heat exchanger thermal efficiency varies from 23 to 49% in various conditions and also both the flow rate and the inlet temperature have the same effect on the exergy losses. The optimum groove height is presented equally to 10 mm. [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]