Heat Transfer Enhancement Techniques Research Articles

Impacts of double rotating cylinders on the forced convection of hybrid nanofluid in a bifurcating channel with partly porous layers

Impacts of using double rotating cylinders and partly porous layers in the bifurcating channels on the hydro-thermal performance were numerically assessed. Hybrid nanoparticles were used in water and finite element method was selected as the solver. Effects of Reynolds number, rotational speeds of the cylinders and their locations in the bifurcating channels, porous layer sizes and nanoparticle solid volume fractions on the hydro-thermal performance features were explored. The contribution of different hot wall parts was changed with varying Reynolds number and rotational velocity of the cylinders. Depending upon the rotational direction of the cylinders, the vortex occurrence and size at the bifurcations change significantly. Heat transfer considering all hot walls rise with higher rotational speeds in both directions. The amount of improvement in the heat transfer rate becomes 25% and 19% with varying speeds of the cylinders as compared to motionless cylinders. The pressure coefficient reduces with increasing the second cylinder speed in clockwise direction and this is favorable for thermal performance since the heat transfer also increases. The overall impact of the varying horizontal locations of the cylinders on the heat transfer rate is slight. The separated zones at the branching depends on the porous layer sizes. The overall heat transfer behavior becomes opposite when varying the sizes of the porous layers in the horizontal and vertical channels. By using nanoparticles in the base fluid, 35.75% improvement in the heat transfer rate is achieved for vertical wall at Re = 350 while pressure drop coefficient rises by about 8.5%. The overall improvement in the heat transfer rate by using nanofluid is 26%. Owing to diverse use of bifurcating channels in thermal engineering from fuel cells to electronic cooling, the proposed methods of heat transfer enhancement techniques can be considered simultaneously for effective control the thermal performance of those systems.

Enhanced power plant air-cooled condensers using auto-fluttering reeds

Air-cooled condensers offer a pathway to decreasing the water consumption associated with electricity production, but dry-cooled plants suffer from lower efficiencies than those of conventional systems. One approach to increasing the performance of air-cooled condensers is to employ heat transfer enhancement techniques. Many enhancement devices have been proposed, but they have not been evaluated in air-cooled condensers at relevant scales. One promising low-cost air-side enhancement approach is the use of auto-fluttering reeds, which increase the vorticity of the flow and result in higher heat transfer coefficients. This work investigates the use of auto-fluttering reeds in a dry-cooled Rankine cycle power plant experimentally and numerically. The experimental results quantify the pressure drop and heat transfer characteristics of the enhanced condensers, which are then incorporated into a detailed model to assess performance at the system level. The air-cooled condenser geometry is also optimized to determine the maximum efficiency with and without the reeds. The results show that auto-fluttering reeds could improve the system performance in retrofit applications and may have some economic benefits in new dry-cooled power plants.

Review on Heat Transfer Enhancement by Rectangular Fin

Heat generation of engineering appliances has bad effect in handling the system can cause the trouble, short life cycle of machines, frequent maintenance requirements and low reliability of systems. The passive cooling technique has been widely used to solve such problems. This review work summarizes the heat transfer enhancement technique in a rectangular fin with economic way. So many research about the enhancement of heat transfer by rectangular fins experimentally and numerically and found very significant result. In this review, various types of rectangular fin structures are studied simultaneously. It is revealed through reviewing the related literature that the highest value of equivalent heat transfer enhancement is found the increase in average heat transfer performance of inverted triangular notched fin 50.51% as compared with plane rectangular fin and the perforated fin total heat transfer rate increased by 38.9% compared to regular fin. Furthermore, by reduction of the optimal fin spacing, heat flux can be changed by 20% in standard rectangular fin when compared with regular fin spacing. Also cooling performance of the inclined rectangular fin with 60° of tilt angle is seen to be as 6% higher than solid rectangular fin. This article can be considered as a benchmark in the practical application for enhances the heat transfer rates.

A review of SPSAH and DPSAH characteristics by variation of fluid profile in the duct

The thermal performance of solar air heaters can be enhanced by increasing the rate of heat transfer. The thermal performance of DPSAH is higher than that of SPSAH based on the study of various researchers. Many researchers have studied the performance analysis of solar air heaters with various heat transfer enhancement techniques like using fins, corrugated absorber plate, packed bed, generating turbulence to the flow. By using ribs of different geometrical shapes and sizes attached to the absorber plate turbulence increases which in turn increases the thermal and thermo-hydraulic performances of the solar air heater. The paper presents the study of the research carried on various processes used to increase turbulence and so thermal performance of SPSAH and DPSAH.

Experimental investigation of thermal performance of novel cold plate design used in a Li-ion pouch-type battery

• Thermal performance of serpentine tube and mini channel cold plates are compared. • Transient average battery temperature change is examined at the various conditions. • The effect of cold plate design on the battery temperature homogeneity is studied. • Low fluid inlet temperatures adversely affect battery temperature uniformity. The world's tendency towards electric vehicles has accelerated and the thermal management of them are critical part of the actual studies. Liquid-based cooling is known as the most common one among other cooling techniques. However, there is still need on the use of various heat transfer enhancement techniques to reduce the maximum temperature and maintain homogenous temperatures. This study experimentally investigated thermal performance of water-cooled cold plates used in thermal management of batteries by using conventional serpentine tube and a novel mini channel designs including a lithium-ion phosphate battery under certain discharge rates from 1C to 5C. Experiments are conducted for different water flow rates from 0.1 to 1.1 L/min as the coolant with inlet temperatures from 15 to 35 °C. Experimental results show that lower coolant inlet temperature causes the largest maximum temperature difference on battery surface. The use of mini channel cold plate resulted in 5.7 °C reduction in the maximum average battery surface temperature compared to serpentine one. Battery surface temperature homogeneity is improved up to 40% for operating conditions for mini channel cold plate usage. Thus, enhancement on thermal performance of proposed new mini channel cold plate is accomplished by temperature measurements.

An integrated optimization methodology for heat transfer enhancement: A case study on nanofluid flow in a pipe equipped with inserts

A hybrid approach that combines Multi-objective Optimization (MOO) and Multiple-criteria Decision-making (MCDM) techniques has been introduced in the present paper for heat transfer augmentation in pipes. The combination of two passive heat transfer enhancement techniques namely the nanofluid and insert employment have been applied in the representative problem. In this context, the performance of water-based CuO,Fe3O4, and CNT-Fe3O4 nanofluids and two different inserts as twisted tape (TT) and wire coil (WC) were evaluated and their optimum design and flow parameters were determined. The methodology introduced here has two major parts. Firstly, a MOO study was conducted employing the experimentally obtained correlations for the Nusselt number (Nu) and the friction factor (f) as objective functions. The optimum values of the selected design parameters (the Reynolds number (Re), nanoparticle volume fraction ((ϕ)), twist ratio (h/d), wire coil pitch ratio (p/d), and the Prandtl number (Pr)) that maximizes Nu while minimizing f were found as Pareto front. Secondly, the Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) method was used to help decision-makers making an optimal choice among the Pareto optimal solutions that meet their requirements. In the MCDM problems, two criteria (Nu and f) and fifteen alternatives were evaluated for each case. A sensitivity analysis was also conducted by changing the weights of criteria. It was found that the combination of TT and CNT-Fe3O4 with the values of design parameters (Re; ϕ; h/d; Pr)=(20,000; 0.27%; 10; 5.50) exhibited the best thermal-hydraulic performance for the equal weights of criteria.

ANALYSIS OF HEAT TRANSFER MECHANISMS IN THE SOLIDIFICATION OF PCM WITH DIFFERENT PASSIVE ENHANCEMENT TECHNIQUES FOR FREE COOLING APPLICATIONS

The continuous increase in the level of green-house gas emissions and the depletion of fossil fuels are identified as the major driving forces behind efforts to effectively utilize different sources of renewable energy. Free cooling concept is gaining importance in building cooling applications. The medium which is used to store energy is Phase Change Material. Among the phase change materials available commercial PCM is of great use. The only drawback with the PCM is its thermal conductivity is very low. Various heat-transfer enhancement techniques between the phase change material (PCM) and the heat transfer fluid (HTF) were tried by researchers. Passive enhancement techniques are very simple and gives good heat transfer enhancement which decreases the solidification time and increases the solidification rate. In the present work two types of passive enhancement techniques like increasing the roughness of the heat transfer surface and dimples over the heat transfer surface were tried and it has been observed that the dimpled surface will provide better results compared to rough surface over normal surface. Overall there is decrease in solidification time of 37 min. and increase in solidification rate of 19.37% with dimpled surface over normal surface.

Performance evaluation of helical coils as a passive heat transfer enhancement technique under flow condensation by use of entropy generation analysis

Current research focuses on the performance of helically coiled tubes as a passive heat transfer enhancement technique for R134a flow condensation from an entropy generation perspective. Similar to other enhancement techniques, helical coils, are accompanied by pressure drop as a penalty, diminishing their performance, so that these coils are of lower performance compared to straight tubes where the increase in entropy generation due to pressure drop overcomes the decrease in entropy generation due to enhanced heat transfer. Unlike previous studies that have largely investigated heat transfer and pressure drop characteristics of helical coils regardless of their performance, this study employs entropy generation analysis as an effective method to distinguish flow and geometrical conditions at which helical coils are of lower entropy, i.e. higher performance, compared to straight tubes. The findings reveal that, for both helical and straight tubes, entropy generation is enhanced as tube diameter, mass velocity, vapor quality, and wall heat flux increase and saturation temperature decreases. Additionally, applying helical coils within wider ranges of mass velocities can be justified at lower values of tube (≤8.3 mm) and coil diameters (≤200 mm), saturation temperatures (≤40 °C), and vapor quality (≤0.6), and at higher values of wall heat flux (≥15 kW/m2). These results substantiate that employing helical coils in lieu of straight tubes is not justifiable always (for all flow and geometrical conditions) although they are of superior heat transfer performance compared to straight tubes.

Thermal Energy Storage and Heat Transfer of Nano-Enhanced Phase Change Material (NePCM) in a Shell and Tube Thermal Energy Storage (TES) Unit with a Partial Layer of Eccentric Copper Foam.

Thermal energy storage units conventionally have the drawback of slow charging response. Thus, heat transfer enhancement techniques are required to reduce charging time. Using nanoadditives is a promising approach to enhance the heat transfer and energy storage response time of materials that store heat by undergoing a reversible phase change, so-called phase change materials. In the present study, a combination of such materials enhanced with the addition of nanometer-scale graphene oxide particles (called nano-enhanced phase change materials) and a layer of a copper foam is proposed to improve the thermal performance of a shell-and-tube latent heat thermal energy storage (LHTES) unit filled with capric acid. Both graphene oxide and copper nanoparticles were tested as the nanometer-scale additives. A geometrically nonuniform layer of copper foam was placed over the hot tube inside the unit. The metal foam layer can improve heat transfer with an increase of the composite thermal conductivity. However, it suppressed the natural convection flows and could reduce heat transfer in the molten regions. Thus, a metal foam layer with a nonuniform shape can maximize thermal conductivity in conduction-dominant regions and minimize its adverse impacts on natural convection flows. The heat transfer was modeled using partial differential equations for conservations of momentum and heat. The finite element method was used to solve the partial differential equations. A backward differential formula was used to control the accuracy and convergence of the solution automatically. Mesh adaptation was applied to increase the mesh resolution at the interface between phases and improve the quality and stability of the solution. The impact of the eccentricity and porosity of the metal foam layer and the volume fraction of nanoparticles on the energy storage and the thermal performance of the LHTES unit was addressed. The layer of the metal foam notably improves the response time of the LHTES unit, and a 10% eccentricity of the porous layer toward the bottom improved the response time of the LHTES unit by 50%. The presence of nanoadditives could reduce the response time (melting time) of the LHTES unit by 12%, and copper nanoparticles were slightly better than graphene oxide particles in terms of heat transfer enhancement. The design parameters of the eccentricity, porosity, and volume fraction of nanoparticles had minimal impact on the thermal energy storage capacity of the LHTES unit, while their impact on the melting time (response time) was significant. Thus, a combination of the enhancement method could practically reduce the thermal charging time of an LHTES unit without a significant increase in its size.

Investigation of storage rotation effect on phase change material charging process in latent heat thermal energy storage system

Applying Phase Change Materials (PCMs) in Thermal Energy Storage (TES) systems is an appropriate method to utilize renewable energies, more efficiently. Due to the low thermal conductivity of the PCMs, the application of active and passive heat transfer enhancement techniques is increasing. In this study, a double-pipe Latent Heat Thermal Energy Storage (LHTES) System in which the annulus is filled with PCM is considered and storage rotation method is suggested as an active heat augmentation technique to accelerate the charging process of the systems. Different scenarios are considered for rotations, including constant speed and step-by-step rotation methods. The charging process of a LHTES system is simulated numerically considering 2-D model, and the effect of different scenarios of the storage rotation is investigated on charging time. The results show that rotating the storage with constant rotational speed has a slight positive effect on complete melting process time (maximum reduction of 3.45%), however 15.5% reduction in charging time can be achieved compared to the fixed mode by applying step-by-step rotation scenario which is related to the case with two opposite direction rotations and 180 angle difference between the stop steps.

A review on effect of various artificial roughness on heat transfer enhancement in a channel flow

Heat transfer improvement plays a vital role in several industrial applications as well as in the transportation sector such as gas turbines, heat exchangers, various cooling devices, and combustor liners. The extensive research to enhance the heat transfer rate in various sectors has been carried out to achieve the objectives such as (i) to increase the system efficiency, (ii) to reduce thermal load, (ii) to reduce consumption of non-renewable energy, (iii) to reduce the production of emission, (iv) to develop new green technologies, (v) to lower energy prices for the consumer. The heat transfer in various sectors has been carried out by adopting three different ways (i) increasing the surface area of the heat transfer systems, (ii) enhancing the fluid properties, (iii) by adding extra surface on the heat transferring surface. This article aims to deliver a comprehensive review of the current research on heat transfer enhancement techniques by using artificial roughness elements such as rib tarbulator, fin, and dimple. It includes various types of rib tarbulators, fins, and dimples used for heat transfer enhancement of gas turbine blades of the power plant, combustion liners as well as solar air heaters. The physical mechanism responsible for heat transfer enhancement in various artificial roughness elements has been discussed and compared. The challenges and difficulties associated with the heat transfer techniques have been discussed. The parameters such as dimple depth, channel height to dimple imprint diameter, pitch, the density of artificial roughness element, arrangement of artificial roughness, relative roughness pitch, relative roughness height, angle of attack on flow, mass flow rate, Reynolds number on thermal performance, thermohydraulic performance, flow structure, friction characteristics have been studied and compared. From the comprehensive review, it may be recommended that the teardrop shape dimple can be used for further enhancement of heat transfer as compared to other artificial roughness elements. In the future, this teardrop may be used to enhance the heat transfer in the solar thermal system and some other relevant thermal systems.

Effect of geometrical parameters on entropy generation during R134a boiling flow inside unique internally grooved tubes: Experimental approach

Generally, using heat transfer enhancement techniques in heat exchangers always accompanies frictional pressure drop amplification; entropy generation analysis is a suitable technique to investigate the heat transfer and pressure drop together. In this study, the effects of tube's geometrical parameters and flow conditions on entropy generation during two-phase boiling flow of R134a refrigerant in horizontal internally grooved tubes are experimentally investigated. The experimental tests are conducted in a wide range of operating conditions, including mass flux of 16.5–105 kg/m2s, vapor quality of 0.06–0.98, and heat flux of 3.5–25 kW/m2. Test evaporator tubes are made up of copper of 20 mm inner diameter with nine types of discrete inclined grooves on the tubes' internal wall surface. The results represent that using the grooved tubes is desirable for the majority of test conditions except for mass fluxes between 20 and 80 kg/m2s at vapor qualities higher than about 0.4–0.5. The ratio of groove pitch length to groove width within the geometrical parameters has the most notable effect on the total entropy generation. Besides, a new correlation is developed for entropy generation of R134a evaporating flow inside internally grooved tubes with discrete inclined grooves.

Experimental Study of Heat Transfer Enhancement by Turbulence Generator in Side Pipe

The enhancement of heat transfer exchangers is an important matter of concern for achieving more efficient thermal energy conversion systems. The use of modified twisted tape (TT) inserts as a passive heat transfer augmentation technique is an efficient way of improving heat transfer. Twisted tape insert is one of the passive heat transfer enhancement techniques that are widely used in various applications for heat transfer, such as air conditioning and cooling systems, heat recovery systems, Processes, procedures for food and milk, plants for chemical processes. To increase the heat transfer rate of the tubular heat exchanger, in this study a small-scale experimental setup was performed. The heat improvement of the heat exchanger is done using twisted tape inserts with a twist ratio (y=5.5). The effects of two-dimensional parameters namely Nusselt number & friction factor on tubular heat exchanger effectiveness are studied. The turbulent flow was generated by the insertion into the test pipe of the twisted tape inserts, producing a high turbulence rate in the pipe, resulting in an increase in turbulence. And hence the enhancement of heat transfer and drop in pressure. The length and width of the insert were 1000 mm and 21.5 mm respectively. The diameter of the test pipe outside & inside is 23 mm and 22 mm respectively. The length of the test section is 2000 mm. The study is carried out for the Reynold number regime (500-6500). The results show that The maximum enhancement for Nu number at Re 500 was 32% that of the plain tube.

Efficiency Improvement of Miniaturized Heat Exchangers

Micro heat exchangers have been revealed to be efficient devices for improved heat transfer due to short heat transfer distances and increased surface-to-volume ratios. Further augmentation of the heat transfer behaviour within microstructured devices can be achieved with heat transfer enhancement techniques, and more precisely for this study, with passive enhancement techniques. Pin fin geometries influence the flow path and, therefore, were chosen as the option for further improvement of the heat transfer performance. The augmentation of heat transfer with micro heat exchangers was performed with the consideration of an improved heat transfer behaviour, and with additional pressure losses due to the change of flow path (pin fin geometries). To capture the impact of the heat transfer, as well as the impact of additional pressure losses, an assessment method should be considered. The overall exergy loss method can be applied to micro heat exchangers, and serves as a simple assessment for characterization. Experimental investigations with micro heat exchanger structures were performed to evaluate the assessment method and its importance. The heat transfer enhancement was experimentally investigated with microstructured pin fin geometries to understand the impact on pressure loss behaviour with air.

Review on heat transfer enhancement of phase-change materials using expanded graphite for thermal energy storage and thermal management

Phase-change materials (PCMs) are particularly attractive for latent heat storage because they provide a high energy storage density at a constant temperature, which corresponds to the phase transition temperature of the material. Various techniques have been introduced to enhance the thermal conductivity of PCMs. Expanded graphite (EG) is a common thermal enhancer because of its high thermal conductivity, low density, and chemical inertness. This paper provides a brief introduction of several common techniques for heat transfer enhancement and EG preparation. The present review focuses on studies that examined the preparation and characterization of EG/PCM composites, as well as the simulations and applications of EG/PCM composites in thermal management and thermal energy storage systems. Solution, melt-blending, impregnation, and compression methods are used to prepare the binary system which only contains PCMs and EG. Melt-blending, hot-pressing, impregnation, polymerization, sol-gel, and piercing-solidifying incuber methods are used to prepare the ternary system, which contains PCMs, EG, and matrix. The simulation and application data confirm that EG has obvious heat transfer reinforcement effects in thermal management and thermal energy storage systems.

Computational-analytical simulation of microsystems in process intensification

Heat and mass transfer enhancement techniques, either passive or active, have an important role in the more general goal of process intensification in modern engineering developments. In this context, the study of transport phenomena at the nano- and micro-scales aims far beyond the plain miniaturization of devices, being mainly directed towards process efficiency improvement and lower energy and raw materials consumption. The analysis of heat and mass transfer at such scales has required the development or extension of both theoretical and experimental methodologies. In light of the inherent multiscale nature of microfluidic devices, classical fully numerical methodologies often require large refined meshes with associated costly computations. A hybrid numerical-analytical approach for the analysis of microfluidic and thermal micro-systems is here reviewed, which includes a computational-analytical integral transform method for partial differential direct problems, that, together with mixed symbolic-numerical computations, lead to robust cost-effective algorithms for micro-scale transport phenomena analysis. Examples of this hybrid approach in selected applications are then examined more closely, including micro-reactors for continuous biodiesel synthesis with multiple reactive interfaces and three-dimensional thermal micro-devices with solid-fluid thermal conjugation.

An experimental investigation on bubbles departure characteristics during sub-cooled flow boiling in a vertical U-shaped channel utilizing high-speed photography

Classified as a passive heat transfer enhancement technique, U-shaped channels are commonly encountered with applications associated with boiling heat transfer such as air conditioning systems, evaporators, and boilers. On the other hand, understanding heat transfer in flow boiling is heavily dependent upon bubbles dynamic behavior, which is influenced by flow and geometrical conditions. In this paper, bubbles departure characteristics are experimentally studied in upward sub-cooled flow boiling of distilled water in a vertical U-shaped channel. The influence of flow conditions, embracing heat flux, mass flux, and inlet sub-cooling on bubbles characteristics, encompassing departure diameter, growth and waiting times, and nucleation frequency, is investigated through conducting 68 experiments. All the experiments are carried out at atmospheric pressure over a Nichrome heating surface installed on the outer wall of the channel, with heat flux, mass flux, and inlet flow temperature in the ranges of 26.1–61.5 kW.m-2, 114–255kg.m-2s-1, and 1 to 8 °C. A high-speed camera is utilized to capture bubbles growth process and departure instance. The results reveal that as wall heat flux increases and mass flux and inlet sub-cooling decrease, bubbles departure diameter and frequency rise, while waiting time declines. Also, lower growth times are detected when wall heat flux and mass flux increase and inlet sub-cooling declines. Two new correlations are developed to predict present and previously published experimental data of departure diameter and nucleation frequency with mean standard deviations of 18.0% and 18.5%, correspondingly.

Applications and technological challenges for heat recovery, storage and utilisation with latent thermal energy storage

Thermal energy storage (TES) technology is considered to have the greatest potential to balance the demand and supply overcoming the intermittency and fluctuation nature of real-world heat sources, making a more flexible, highly efficient and reliable thermal energy system. This article provides a comprehensive state-of-the-art review of latent thermal energy storage (LTES) technology with a particular focus on medium-high temperature phase change materials for heat recovery, storage and utilisation. This review aims to identify potential methods to design and optimise LTES heat exchangers for heat recovery and storage, bridging the knowledge gap between the present studies and future technological developments. The key focuses of current work can be described as follows: (1) Insight into moderate-high temperature phase change materials and thermal conductivity enhancement methods. (2) Various configurations of latent thermal energy storage heat exchangers and relevant heat transfer enhancement techniques (3) Applications of latent thermal energy storage heat exchangers with different thermal sources, including solar energy, industrial waste heat and engine waste heat, are discussed in detail.

A novel method of enhancing convective heat transfer by dynamic controlling rib

New and efficient mixing heat technology is increasingly demanded for many industrial fields. This paper proposed a novel technique of enhancing convective heat transfer by dynamic controlling rib and investigated several cases of vibration rib controlling flow. The study results of heat transfer coefficient, temperature and turbulent intensity indicate that dynamic flow control is an efficient heat transfer enhancement technique. The dynamic flow control breaks through the current enhancement heat transfer technologies such as general stationary rib and other vortex generators, and achieves a better heat transfer effect. Comparing traditional rib technologies, vibration rib does not only increase heat transfer performance but leads a lower flow resistance. More importantly, it can be dynamically adjusted to achieve better flow turbulence. As a conclusion, the enhancement heat transfer performance can be timely dynamically adjusted to meet the different heat transfer demand by changing timely the frequency and amplitude of vibration rib, which achieves the optimization of whole system thermal protection. New enhancing heat transfer technique effectively improve the comprehensive heat transfer performance, and provides a reference for intelligent thermal control protection system

Heat transfer performance of a nanofluid-filled tube with wall corrugations and center-cleared twisted-tape inserts

ABSTRACT We numerically examine the thermal performance of a round tubular heat exchanger featuring a combination of three passive techniques for heat-transfer enhancement: (i) center-cleared twisted-tape inserts, (ii) tube corrugations, and (iii) nanofluids. We consider three geometric tape parameters – the central-clearance width (C), the tape width (W), and the 180° tape pitch (H) – across a range of Reynolds numbers (500 ≤ Re ≤ 1250). For both water and a representative nanofluid (Al2O3-water), increasing W or decreasing C or H is found to increase the heat transfer coefficient at all Re. Switching from water to one of four water-based nanofluids − Al2O3-water, CuO-water, Cu-water, and TiO2-water – is found to improve the heat transfer rate sufficiently to overcome any associated rises in pressure drop, resulting in thermal efficiencies higher than those of water. The highest thermal efficiency coefficient (η = 1.157) occurs with the Cu-water nanofluid at the smallest Re (500), whereas the lowest thermal efficiency coefficient (η = 1.115) occurs with the CuO-water nanofluid at the largest Re (1250). Across the entire Re range, increasing the volume concentration of Al2O3 nanoparticles (from ϕ = 2 to 5%) is found to increase the coefficients of heat transfer and thermal efficiency. This study provides new insight into how the heat transfer capabilities of a tubular heat exchanger can be enhanced by combining center-cleared twisted-tape inserts, tube corrugations and nanofluids.