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• Thermal performance evaluation of a perforated pin-fin heatsink. • Analysis of the effect of perforation inclination angle on the outcomes. • The highest PEC was obtained for the perforation inclination angle of 45º. • PEC of the heatsink with γ of 45º was 16.63–11.06% higher than that with γ of 0º. • γ of -15º and 45º provide the lowest frictional and thermal entropy generations. The numerical analysis of water/silver nanofluid (NF) flow in a perforated pin-fin heatsink (PFHS) is performed considering the nanoparticle concentration (φ) of 1% and seven different perforation inclination angles (γ). The configuration with the best hydrothermal performance and the lowest entropy generation rate at different values of Reynolds number (Re) is determined using the two-phase mixture technique. According to the results, the γs of 45º and -45º exhibit the highest heat transfer coefficient (h) and the lowest thermal resistance factor and mean CPU temperature at four studied Re s of 500, 1000, 1500, and 2000. Consequently, the highest hydrothermal performance evaluation criterion (PEC) was obtained for the heatsink with γ of 45º followed by γ of -45º at Re of 500; the increase in Re reduced the PEC due to the pressure drop. PEC of the heatsink with γ of 45º was almost 11.06–16.63% higher than that with γ of 0º. In addition, γ of -15º and 45º provided the lowest frictional and thermal entropy generation rates (S ˙ f r and S ˙ t h) at Re of 1500 and then 2000. S ˙ f r and S ˙ t h for γ of 45º were 1401% and 97% lower than those for γ of 0º at Re =1500. [ABSTRACT FROM AUTHOR]

The aim of this study is to investigate various aspects influencing the entropy production in a twisted double-pipe heat exchanger using two-phase mixture model. A combination of different percentages of CuO nanoparticles (φ =0–3%) in 0.5 wt% Carboxymethyl Cellulose (CMC)-water as a non-Newtonian nanofluid (at 298 K) in the inner tube and water was used as the heating fluid at 308 K at the opposite direction. The simulation outcomes indicated that rising the Re from 500 to 2000 for nanofluid, increased thermal and frictional entropy. On the other hand, raising the φ from 0 to 3% sufficiently lowered the thermal and frictional entropy, which was much more significant in frictional entropy generation rate. For Re =2000, the increase in φ from 0% to 3% caused a decrement in thermal, frictional, and total entropy of 9.2%, 15.3% and 11.8%, respectively. The effect of twisting pitch (2–6 mm) changes on both types of entropy generation also showed that the higher twist pitch resulted in the greater entropy generation, mainly for thermal entropy (24.2%). The results also showed that for all φ , the Bejan number decreased with Re augmentation, and at constant Re , increased with raising φ to some extent. [ABSTRACT FROM AUTHOR]

• Effect of open-ring pin fin arrangement on the heat sink performance is examined. • In-line and staggered arrangements of open-ring pin fins are compared. • Biologically prepared water-silver nanofluid is employed as coolant. • Convective heat transfer coefficient is enhanced by 24.7% in staggered arrangement. • Reduction in frictional entropy generation reaches 14% by adding nanoparticles. Thermal performance of a heat sink having open-ring pin fins (ORPF) and cooled by biologically synthesized silver-water nanofluid is explored in terms of first and second laws of thermodynamics within the present work by focusing on the arrangement of ORPFs, namely the in-line and staggered ones. Influences of four different volumetric fractions of nanoparticles (φ =0–1%) and four different Reynolds numbers (Re =500–2000) on the thermal performance and entropy generation behavior of the nanofluid are numerically evaluated. Outcomes revealed that the convective heat transfer coefficient is improved by up to 71% and 19.3% in the in-line, and 65% and 24.7% in the staggered ORPF configurations, respectively, due to the increment in Re and addition of nanoparticles (at Re =500). Moreover, a decline in the pumping power is noticed by adding φ =1% of nanoparticles at Re =1500, compared to base fluid. The pumping power, on the other hand, is increased by 10.5% at Re =2000 and φ =0% when staggered configuration is considered instead of in-line one. Thermal and frictional entropy generation rates are remarkably reduced by incorporation of nanoparticles. In addition, using staggered ORPF arrangement instead of the in-line one can decrease the frictional and thermal entropy generation rates by up to 17% and 4.4%, respectively, at Re =2000. [ABSTRACT FROM AUTHOR]

• Effect of inlet velocity profile on the performance of a heatsink is examined. • The device performance is studied from the perspective of the first and second laws. • The non-uniform inlet velocity profile leads to better device hydrothermal function. • The non-uniform inlet velocity profile causes a decline in frictional entropy. The prediction of heat transfer characteristics numerically depends on several factors such as the numerical method, the boundary and operating conditions, etc. The present paper investigated the influence of using the uniform and non-uniform inlet velocity profiles on the heat transfer coefficient (h), pumping power (W ˙ p), temperature uniformity (θ), and thermal and frictional entropy generation rates (S ˙ t h and S ˙ f r) in a pin-fin heatsink with silver/water nanofluid (NF) coolant. The numerical study is conducted utilizing the two-phase mixture scheme. The results proved that h is almost the same for two inlet profiles with the maximum deviation of 0.2%. θ and W ˙ p , however, for uniform profile is nearly 2.52–1.86% and 15–26% higher than those for the other case at Reynolds numbers of 500–2000, respectively, indicating a lower temperature uniformity and higher power consumption for uniform velocity profile. The figure of merit was obtained as 1.19–1.36 at Re numbers of 500–2000; indicating the better hydrothermal performance of the non-uniform inlet velocity profile over the other case. In addition, S ˙ t h was almost the same for both cases due to same mean temperature and temperature gradients. However, S ˙ f r for non-uniform profiles was 4.41–8.84% lower than that for other profile at Reynolds numbers of 500–2000. [ABSTRACT FROM AUTHOR]

This research is dedicated to the numerical assessment of the performance of a novel system that uses solar and geothermal energy at the same time, which is capable of heating/cooling the outside air before it enters the air conditioning system of a building and supplying the required electricity for the building. The desired system consists of a photovoltaic/thermal-heat pipe (PVT-heat pipe) unit and an earth-air heat exchanger (EAHE). To cool the outside air in hot seasons of the year, the air is passed through the EAHE system and the exhaust air from building is used to cool the photovoltaic panels. Outside air heating in cold seasons is also possible by passing air through the PVT-heat pipe and EAHE systems. The genetic algorithm-based two-objective optimization is used to determine the necessary conditions to simultaneously maximize the annual useful energy and exergy yields of the hybrid system. The performance metrics of the optimal system are compared with the corresponding values of the PVT-EAHE unit. Outcomes revealed that the annual useful energy output of the PVT-heat pipe-EAHE system (93925.6kWh) is less than the PVT-EAHE system (96448.6kWh), while the PVT-heat pipe-EAHE system is able to produce more exergy (10904.5kWh) than the PVT-EAHE system (10015.5kWh). [ABSTRACT FROM AUTHOR]

In the present work, the aim is to numerically investigate the effect of channel grooving on the energy and exergy efficiencies of a photovoltaic/thermal (PV/T) system. The aqueous suspension of biologically prepared silver nanoparticles is employed as coolant. Two-phase mixture technique and ANSYS Fluent software are used to perform simulations and inspect the influence of Reynolds number (Re), nanomaterial volumetric concentration (φ) and groove pitch (S) on the performance metrics. The considered range for the Re , φ and S was 500–2000, 0–1% and 0–1 m. The ascending trend of thermal, electrical and overall energy efficiencies with boosting φ and Re was reported. In addition, it was seen that the electrical and overall exergy efficiencies augment with boosting φ and Re. Moreover, it was reported that at Re =500 and 1000, the thermal exergy efficiency rises with boosting φ, while for higher Re s the opposite occurs. Finally, the variation pattern of overall energy and exergy efficiencies was ascending-trending. The highest overall energy and exergy efficiencies were found to be 115.73% and 18.34%, respectively, which belonged to the case of φ=1%, Re =2000 and S =0.25 m. [ABSTRACT FROM AUTHOR]

• Performance of a heat exchanger with converging sinusoidal wall is examined. • Two-phase mixture model is used to perform the simulations. • Biologically prepared water-silver nanofluid is used as the coolant. • The use of converging wavy wall entails a 407-439% increase in entropy generation. • Using converging wavy wall improves overall performance up to the Reynolds 1000. The cooling performance of biological water-silver nanofluid (NF) in three double-pipe heat exchangers with converging sinusoidal inner wall (SCDHX), converging inner wall (CDHX), and plain inner wall (PDHX) was examined numerically using the first and second laws of thermodynamics. The two-phase mixture model is employed to conduct the simulations. Based on the results, the sinusoidal wall increases the flow mixing, and thereby the convective heat transfer coefficient in SCDHX enhances by 50% and 18% over the PDHX type for Re s of 500 and 2000, respectively. Moreover, the highest NF frictional entropy generation rate (S ˙ f , m , c) was obtained for SCDHX; 67% and 80% higher than those for CDHX and PDHX, respectively. The efficiency criteria ratio (η) of SCDHX was obtained as roughly 1.1 for Re s of 500 and 1000, which is 27.27% higher than that for CDHX type. Also, the efficiency criteria ratio of SCDHX over the CDHX was in the range of 1.21-1.41. Besides, a robust soft computing, namely the Gaussian process regression (GPR) approach, was proposed to accurately estimate the total entropy of cold NF, the total entropy of hot NF, and the performance ratio based on the nanoparticle concentration and Reynolds number. [ABSTRACT FROM AUTHOR]

Enhancing the performance of latent heat storage systems is vital for optimizing energy conservation, reducing operational costs, and supporting the transition to a more resilient and sustainable energy infrastructure. In the current numerical research, the aim is to simultaneously use the rotation of the middle tube and the eccentricity of the inner hot tube to improve the melting performance of a triplex-tube latent heat energy storage system. In this system, the phase change material (PCM) is placed in the middle tube and the flow of hot water passes through the inner and outer tubes. The counterclockwise rotation speed of the middle tube is considered constant and equal to 1 rpm, while the eccentricity value (e) and angle (θ) are changed in the ranges of 1–8 mm and 0–315°, respectively. Numerical simulations were conducted using Computational Fluid Dynamics (CFD) techniques implemented through Ansys Fluent 19.1 software. Examining the results of the numerical simulations revealed that the simultaneous use of the middle tube rotation and the eccentricity of inner wall does not always lead to an improvement of the melting performance of the system. Among the investigated cases, the lowest melting time, which is equal to 425.5 s and is 11.9 % lower than the value belonging to the concentric system, occurs in the case of e=4 mm and θ=315°. Also, it was found that the PCM average temperature in this case is 3.55 K lower than the concentric system.

The present paper deals with 3D numerical analysis of a battery thermal management system (TMS) including the Phase Change Material (PCM). The TSM comprises three annular fins located around the battery considering the tip clearance (TC) space between the fin tips and the alumina enclosure. The calculations were performed for four cases with different TCs (1.5 mm, 1 mm, 0.5 mm, and 0 mm). The entropy generation analysis was performed to determine the locations of the geometry with highest frictional and thermal irreversibilities. The results showed that the application of TC leads to improve the PCM free convection and thereby enhance the heat transfer rate. So that there is an optimum TC (0.5 mm) in which the highest heat transfer rate and lowest PCM melting time is obtained. Moreover, the magnitude of frictional entropy generation rate is much lower than that of the thermal term. For accurate estimation of the liquid fraction, fractional and thermal entropy generation rates, a new ensemble machine learning (ML), namely Gradient Boosting Decision Tree (GBDT), was developed based on the fin tip and flow time parameters as input features. The outcomes of ML-based simulation exhibited promising performance for the precision prediction of three understudy targets. [ABSTRACT FROM AUTHOR]

• Nanofluid flow in a twisted tube with variable twist pitch is investigated numerically. • The non-Newtonian water-CMC/CuO nanofluid is considered as coolant. • Two-phase mixture model is used to perform the simulations. • The GEP scheme is adopted to simulate the performance metrics. • Using variable twist pitch entails an increase in the nanofluid performance. A 3-D numerical investigation is performed to evaluate the effect of variable twist pitch on the hydrothermal behavior and entropy generation features of non-Newtonian water-CMC/CuO nanofluid (NF) flow inside a twisted tube with a square cross-section. Three twisted tubes with a length of 500 mm, each of which has 3 twists, are considered. The first tube (Case I) has a constant twist pitch of 100 mm, while the twist pitch of Case II (150.0, 127.5, 100.8, 74.2, and 47.5 mm) and Case III (190, 144.6, 97.9, 51.3, and 6.2 mm) are variable. The simulations are performed using the two-phase mixture method considering different nanoparticle concentrations (ϕs) of 0–3% and Reynolds numbers (Res) of 600–1500. Based on the results, the highest and lowest overall hydrothermal performance was obtained for Case II and Case I, respectively. Moreover, the lowest ratios of thermal and frictional entropies of NF flow in the twisted tube to those of the plain tube were obtained for Case II. As another novelty of the current work, an evolutionary machine learning approach, namely, gene expression programming (GEP), was adopted to simulate the first law and second law performances of the NF in Case III. [ABSTRACT FROM AUTHOR]

This study explores the impact of tube rotation on the melting performance of a multi-tube latent heat energy storage system through numerical analysis. The system involves a phase change material (PCM) contained within a tube, which absorbs heat from hot water flowing through a tube surrounding the PCM, as well as two tubes enveloped by the PCM. The investigation considers the angle between the line connecting the centers of the two inner tubes and the horizon (α = 0°, 45°, 90°, and 135°), along with the direction of rotation of inner tubes. Results are compared with data from scenarios involving only outer tube rotation and stationary systems. Temporal variations in temperature and liquid fraction contours, along with the temporal evolution of average temperature and average liquid fraction of PCM are presented. It was determined that for each α, the melting performance varied from best to worst across the system configurations as follows: the system with all three rotating tubes, the system with only the outer rotating tube, and the stationary system. The minimum time required to complete PCM melting for cases at α = 0°, 45°, 90°, and 135° is respectively 44.92 %, 42.11 %, 41.32 %, and 40.62 % less than that of the stationary system.

The aim of this numerical investigation is to evaluate the laminar forced convection of biologically synthesized water-silver nanofluid through a heat sink (HS) filled with porous foam (PHS) using first and second laws of thermodynamics. The impacts of inlet velocity (V=0.5–3 m·s−1) and volume fraction of nanofluid (φ=0–1%) on the performance metrics of HS are assessed and the outcomes are compared with those of the non-porous HS (NHS). The outcomes revealed that for both the PHS and NHS, the increase of Vcauses an intensification in convection coefficient, pumping power, and entropy generation due to fluid friction, while the maximum CPU temperature, thermal resistance, and entropy generation due to the heat transfer reduces by boosting V. Also, it was found that the augmentation of Vresults in intensification in convection coefficient, pumping power, overall hydrothermal performance, and frictional entropy generation, while the opposite is true for maximum CPU temperature, thermal resistance, and thermal entropy generation. Furthermore, it was reported that, except for φ = 0.5%, the overall hydrothermal performance of NHS is better than that of PHS, while PHS has better second-law performance than NHS in all the studied cases. Also, it can be concluded that the best hydrothermal performance for PHS belongs to φ = 1% and V = 0.5 m·s−1, while for NHS, these values are 1% and 2 m·s−1.

•Numerical study of using ultrasonic wave for thermal management of CPUs.•Effect of constant and variable transducer power distribution is examined.•Case#A and Case#B are different in 3 transducer locations on a wall of heatsink.•PEC for Case#A is higher than unity (1.31) only under constant power scenario.•Ṡfrand Ṡthfor Case#A is higher and lower than those for Case#B.

In this laboratory study, an attempt has been made to explore the details of the effect of an ultrasonic field on the melting behavior of pure phase change materials (PCMs) and nano-enhanced PCMs using images recorded with digital and thermal cameras. A 50/50 mixture of beeswax and coconut oil was employed as the pure PCM and the copper oxide nanoparticles were used to improve the thermal aspects of the pure PCM. Three different mass concentrations i.e., (1 %, 2 %, and 4 %) were considered for nanoparticles. The required ultrasonic field was generated using two stainless steel 27 kHz 40 W piezoelectric transducers. It was revealed that the application of ultrasonic field to the pure PCM and nano-enhanced PCM containing 1 %, 2 %, and 4 % of nanoparticles reduces their complete melting time by 58.33 %, 60.00 %, 61.39 % and 64.44 %, respectively. The images taken with the digital and thermal cameras confirmed that agitation oscillating fluid motion and cavitation are two mechanisms that definitely contribute to the improvement of PCM melting characteristics in the presence of ultrasonic field.

Purpose This paper aims to numerically investigate the heat transfer and entropy generation characteristics of water-based hybrid nanofluid in natural convection flow inside a concentric horizontal annulus.Design/methodology/approach The hybrid nanofluid is prepared by suspending tetramethylammonium hydroxide-coated Fe3O4 (magnetite) nanoparticles and gum arabic (GA)-coated carbon nanotubes (CNTs) in water. The effects of nanoparticle volume concentration and Rayleigh number on the streamlines, isotherms, average Nusselt number and the thermal, frictional and total entropy generation rates are investigated comprehensively.Findings Results show the advantageous effect of hybrid nanofluid on the average Nusselt number. Furthermore, the study of entropy generation shows the increment of both frictional and thermal entropy generation rates by increasing Fe3O4 and CNT concentrations at various Rayleigh numbers. Increasing Rayleigh number from 103 to 105, at Fe3O4 concentration of 0.9 per cent and CNT concentration of 1.35 per cent, increases the average Nusselt number, thermal entropy generation rate and frictional entropy generation rate by 224.95, 224.65 and 155.25 per cent, respectively. Moreover, increasing the Fe3O4 concentration from 0.5 to 0.9 per cent, at Rayleigh number of 105 and CNT concentration of 1.35 per cent, intensifies the average Nusselt number, thermal entropy generation rate and frictional entropy generation rate by 18.36, 22.78 and 72.7 per cent, respectively.Originality/value To the best knowledge of the authors, there are not any archival publications considering the detailed behaviour of the natural convective heat transfer and entropy generation of hybrid nanofluid in a concentric annulus. [ABSTRACT FROM AUTHOR]

The influence of ultrasound on the rheological behavior of new phase change material (PCM) is investigated. The PCMs are made from natural biological materials containing silicon carbide (SiC) nanoparticles or expanded graphite (EG) powders with weight fractions of 0, 0.05, 0.1, and 0.2 %. The rheological behavior of PCM composites is tested by a rheometer with shear rates of 10 up to 250 rpm. Surveys showed the smallest PCMs' viscosity at shear rates over 100 rpm is obtained for the highest sonication time. Results depict an ignorable change in the dynamic viscosity of PCMs with shear rate, and the shear thinning behavior reduces the PCMs' viscosity by raising the shear rate by 10–140 rpm. Results for EG/PCM and SiC/PCM composites showed non-Newtonian behavior at low shear rates. However, steadiness in viscosity at a shear rate higher than 140 rpm is observed for the Newtonian behavior of PCMs. The other outstanding consequence of this study is the development of novel robust machine learning, namely CatBoost, to simulate the rheological behavior of understudy nano-PCMs based on the weight fraction, sonication time, and shear rate. The multigene genetic programming (MGGP) as a comparative model is adopted to validate the primary model and provide a relationship for estimating the viscosity of each nano-PCMs. Simulation results revealed the superiority of the CatBoost (PCM-EG: R = 0.978 and RMSE = 1.739 mPa·s; PCM-SiC: R = 0.996 and RMSE = 0.374 mPa·s) to the MGGP (PCM-EG: R = 0.967 and RMSE = 2.103 mPa·s; PCM-SiC: R = 0.992 and RMSE = 2.368) in PCM composites.

The present research is devoted to the numerical study of the effect of ultrasonic waves emitted from an ultrasonic transducer on the melting performance of a double-pipe latent heat exchanger system (LHS). In the considered LHSs, hot water passes through the inner tube and the phase change material (PCM) located in the annulus melts by taking heat from the water. The performance of the LHS systems including the ultrasonic waves were compared with the performance of common LHS systems in both horizontal and vertical situations. In contrast to conventional methods for enhancing the heat transfer, integration of ultrasonic source with LHS is the novelty of current research. It is followed by evaluating the effect of transduce position and power on thermal energy absorption. The ultrasonic transducers were installed in various positions to find the most suitable location for improving the heat transfer. The melting time of PCM decreased up to 56.63 % and 74.59 % by applying the ultrasonic field for horizontal and vertical LHS, respectively. In addition, the effect of the transducer power on the performance of the best horizontal and vertical LHS cases was investigated. It was found that the increase in the transducer power from 20 W to 150 W is associated with a decrease up to 40.83 % in the charging time of PCM. The obtained improvement of heat charging of LHS can be attributed to the intensifying the convective heat transfer through ultrasonic field.

•Thermal interaction between water and paraffin at natural convection is explored.•Size of inner tank can change the direction of heat flux vectors.•Nugrows by 23% and drops by 53% with step increase of Rain side heating.•For bottom heating, Nualong bottom wall is 2.45 times compared to side heating.•Bottom heating is recommended for effective thermal interaction of the two fluids.

•Two ejector heat pump/humidification-dehumidification cycles were studied.•The ejector cycle with two HDH units has lower pumping power.•The cycle with two HDH units has highest recovery ratio and exergy efficiency.•The ejector cycle with one HDH has lower capital costs and lower water cost.•The same water cost for both cycles is obtained at electricity cost of 0.10 $/kWh.

•Energy and exergy performances of a hybrid vortex tube-TEG system is investigated.•Multi-objective optimization is sued to maximize the hybrid system performance.•Cold fraction and efficiency of vortex tube are considered as decision variables.•Annual average first-law efficiency of the optimal PV/T system is 0.03442.•Annual amount of CO2mitigation by using the hybrid system is 8.55 tons.

•Effect of nanoadditive shape on the concentrating PV/T performance is examined.•Both the first-law and second-law performance metrics are considered.•Studies nanoadditive shapes are platelet, brick, blade, cylindrical and spherical.•The highest overall efficiency of the PV/T device belongs to the platelet nanofluid.•The lowest entropy generation belongs to the PV/T device with platelet nanofluid.

This study focuses on the thermal and frictional entropy generation characteristics of phase change material (PCM) in a triplex tube latent heat storage unit which is a promising technique for thermal management of lithium-ion batteries. Four different wavy structures for the triplex tube heat exchanger with variable waviness are considered, namely Case 1 to 4. Regarding the numerical analysis, the variations in mean temperature and liquid fraction of PCM are first revealed and presented where the crossflow heat transfer fluid in the system is considered water. Furthermore, thermal and frictional entropy generation rates in local and global means are separately discussed for both charging and discharging processes. The results showed that the difference in mean temperature and melting rates among the cases are more noticeable at the end of the process due to intensified natural convection, and Case 3 has 240 s (12.3%) shorter melting time compared to Case 1 and 4. Although solidification rates have similar trends in all cases, the solidification time is different, e.g., it is 110 s (5.2%) shorter in Case 4, compared to Case 1. The entropy generation trends are relatively similar during the solidification, while they are noticeably different in the melting process due to effect of liquid PCM flow.

The aim of this study is to determine the effect of nanoparticle concentration (φ) and temperature on the thermal conductivity of polyethylene glycol (PEG)-carbon dot nanofluid (NF). The considered range for temperature and φis 20-60 ºC and 0-7%, respectively. The results indicated an ascending trend of NF thermal conductivity with boosting both temperature and φ. The percentage of increase in thermal conductivity of NF with temperature and φcompared to the base fluid was in the range of 7.23-13.43% and 75.08-85.17%, respectively. Moreover, two efficient data-driven approaches, namely Multi-variate linear regression (MLR) and response surface methodology (RSM) schemes were developed to simulate the thermal conductivity of the PEG-carbon dot NF and fit the predictive relationships. The outcomes of modeling revealed that RSM model (R=0.984 and RMSE=0.013 W/m.K), due to taking into account the interaction between volume fraction and temperature, yielded more accuracy than MLR (R=0.960 and RMSE=0.021 W/m.K).

The present study examines the effect of the number of objective functions on the optimal performance of an exhaust air heat recovery unit including a building integrated photovoltaic/thermal unit (BIPV-T) and a heat recovery wheel (HRW). The unit is able to precool/preheat the outdoor air and generate electricity. Four objective functions are introduced to optimize the performance of the system from energy, energy, economic and environmental perspectives and all the possible single-objective, two-objective, three-objective and four-objective optimizations are conducted and the results are compared. Seven geometrical and operating variables consisting of the width, depth, and length of the BIPV-T channel, air mass flow rate, and rotational speed, length, and depth of the HRW unit are chosen as the decision parameters. The outcomes revealed that if a designer expects the examined unit to supply the entire energy and exergy required by building and the production of extra energy and exergy is worthless, then the optimization of unit performance based on the maximization of the amount of undischarged CO2(Scenario 2) will be the best and the most effective scenario for the single-objective optimization of the unit.

•Critical review of previous studies on the performance of PTSCs with turbulators.•Comparison of previous studies on PTSCs using Nuav/Nuav,0, fav/fav,0and PEC.•Identifying the most optimum turbulators.•Combination of optimum geometries of corrugated channels and channels with obstacles.•Introducing a novel and optimal PTSC.

•Two novel designs of the hybrid exhaust air heat recovery unit are proposed.•Both designs consist of a photovoltaic/thermal system and a rotary heat exchanger.•In the hot/cold season, both designs heat/cool the air and generate electricity.•From an energy viewpoint, it is better for air to enter rotary unit for preheating.•From an exergy viewpoint, it is better for air to enter BPT first and then the SRX.

•Study on a vertical double-tube LHS unit with variable sinusoidal wavy channels.•Performance evaluation of the unit in both melting and solidification mechanisms.•Present the advantages of targeted aggregation of the waves inside the unit.•Reduce the melting and solidification times by 70.8% and 42.8%, respectively.•Analyse the effect of HTF inlet temperature and Reynolds number.

• Second law aspects of hybrid nanofluid in a MCHS whit porous fins are examined. • The water based silver/graphene hybrid nanofluid is used as coolant. • Frictional entropy generation augments by boosting the nanoparticle concentration. • By rising the flow rate, thermal entropy generation declines. • Artificial neural network is employed to obtain a model for the entropy generation. This paper evaluates the characteristic of second law of thermodynamic, including Bejan number and entropy generation for hybrid nanofluid containing graphene-silver nanofluid through a MCHS whit porous fins. Finite-volume technique is utilized to solve the governing equations. To simulate the problem, different porous medium thicknesses, nanoparticle concentrations, and inlet mass flow rates are used while the heat flux remains constant. The minimum values of the frictional and thermal entropy generation are 5 × 10−4 and 6.25 × 10−2, while the maximum values are 3.2 × 10−4 and 9.75 × 10−2. With increasing nanoparticle concentration up to 0.06% wt at constant porous thickness t p =200 µm, frictional entropy generation rises up by 3 × 10−5 and heat transfer rate go up while, thermal entropy generation decreases by 1.5 × 10−2. In addition, by doubling the input mass flow rate and reaching 0.02% at constant nanoparticle concentration (0.06%), thermal entropy generation decreases by 2 × 10−2 while the frictional entropy generation increases by 2.4 × 10−4. The minimum magnitude of Bejan number is 0.994. This show that the irreversibility is derived significantly from thermal entropy generation rate. Finally, an artificial neural network is employed to obtain a model for entropy generation. [ABSTRACT FROM AUTHOR]