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Heat transfer deterioration in thermal systems significantly limits the efficiency and practicality of these systems. This review explores state-of-the-art studies on the use of nanofluids (NFs) in various tubular heat exchangers (HEXs), addressing their influence on overcoming the limitations. It discusses the fundamentals of HEXs and NFs, including design criteria, heat transfer mechanisms and thermal transport properties. This work compiles effective thermal conductivity and viscosity correlations under diverse conditions and evaluates NF performance in reactor, flat and helical coiled tube, twisted tube, U-tube and finned tube-based HEXs. Results revealed substantial improvements in system efficiency, with SiC–MWCNT/water NFs achieving 99.9 % absorbance in solar collectors and Ag–rGO/water and Ag–ZnO/silicon oil NFs enhancing efficiency by 210 % and 240 %, respectively. Water–alumina NFs increased convective heat transfer rates and friction factors in flat tube HEXs by 123.6 % and 210 %, respectively. Helical coil exchangers exhibited a pressure drop of 47.35 % with MWCNT/water NFs and a 69.62 % rise in heat transfer coefficient with polyaniline–water NFs. This review suggests that optimising HEX efficiency depends on the strategic use of NFs and finned-tube designs. It also highlights the significance of selecting suitable source materials for NFs, the corresponding health risks, disposal and waste management. Economic viability depends on using optimal flow parameters, including temperature, concentration of nanoparticles, system compactness and installation and running costs. Finally, this review concludes with insights into existing challenges and prospects in thermohydraulic, environmental and economic aspects, pointing to future developments in engineered fluids and their commercial applications. [Display omitted] • The study explores the potential of nanofluids to enhance heat transfer in various tubular heat exchangers. • Strategic use of nanofluids and finned-tube designs can optimise heat transfer efficiency. • Nanofluids improve safety in reactors due to lower cooling activity and self-healing properties. • Turbulent flow conditions within heat exchangers significantly improved heat transfer. [ABSTRACT FROM AUTHOR]

Algal biofuels are intriguingly a renewable energy source that could partially substitute fossil fuels, but further research is required to optimise the growth parameters and establish competitive large-scale cultivation systems. Algal growth is directly dependent on momentum, heat, and mass transfer within the photobioreactor and environmental conditions. Therefore, in this computational study, the heat transfer between the thin-layer cascade (TLC) reactor and its surrounding was reported based on static (location and reactor geometry) and dynamic (air temperature, solar irradiance, and wind velocity) parameters. The resulting model was validated using experimental data. The Nusselt number and the monthly average water temperature were computed to investigate the heat transfer phenomena between the TLC reactor and atmosphere. In addition, a novel corelation was used to estimate the evaporative losses from the TLC reactor. The effect of geometric properties (inclination angle of the reactor, water depth, and channel width) was evaluated on heat transfer. Results showed that heat transfer rate and the optimum water temperature for algal growth were significantly affected by hydrodynamics, environmental conditions, and reactor design. Water temperature decreased with the increase in channel width, water depth, and slope angle of the reactor. Furthermore, algal productivity declined with the increase in the amount of evaporated water. [ABSTRACT FROM AUTHOR]

Malodorous emissions from industrial and household sewage systems cause harmful effects on nearby human populations and the environment. Eco-friendly malodor removing systems utilize bacteria to control unpleasant odors from sewage systems. Heat transfer is a vital factor in industrial system designs because microorganisms require an optimum water temperature to function efficiently. A numerical study was conducted to estimate the heat transfer rate in the water basin of a malodor removing system. Flow-deflecting baffles were utilized to reduce heat loss in the basin. Heat transfer was reduced by installing a rotating drum to increase gas dissolution by an improved liquid circulation. The average and local heat transfer coefficients, Nusselt number, and temperature distribution were evaluated to estimate heat loss in the water basin. This study proposes an empirical relation to generalize the numerical results for calculating heat transfer rates. Results showed that using baffles and rotating drum reduced heat transfer in the basin. Furthermore, the heat transfer coefficient was increased by raising the superficial gas velocity and bubble size. [ABSTRACT FROM AUTHOR]

Considerable prime global energy is used in the transport sector. Significant energy is lost to overcome the internal friction of engines in transport vehicles. Journal bearings are crucial tribo-pairs and passive components that cause energy loss. Frictional losses increase extensively during the warm-up period of an engine due to high lubricant viscosity. Recent tribological developments have shown that surface textures can be a potential solution to reduce friction. A numerical investigation is performed to evaluate the effect of surface texture on the frictional and lubrication performance of a journal bearing at varying thermal operating conditions in an internal combustion engine. Temperature variations during engine warm-up are considered with oil rheology to observe texture-based improvements. Surface texture substantially reduces frictional energy loss during engine warm-up. Eight different monograde and multigrade engine oils are considered, and consistency is observed in texture-based improved outcomes. [ABSTRACT FROM AUTHOR]

This paper presents a novel empirical correlation to estimate the heat transfer in raceway ponds for different pond sizes and depths. The correlation involves the calculation of Nusselt number. Heat transfer in outdoor raceway ponds was modeled with the effects of pond design, hydrodynamics, and environmental conditions. Monthly average water temperature, Nusselt number, and Prandtl number were used to examine the heat transfer phenomena between pond and its surroundings. A novel relation was also employed to estimate the amount of monthly evaporated water from the raceway ponds. Different aspect ratios, pond depths, and paddle wheel rotational speeds were considered to evaluate the effect of pond geometry and turbulent mixing on heat transfer. The use of empirical relation is an effective approach in designing raceway ponds to estimate heat loss in ponds. Algal productivity decreased with increasing amount of evaporated water. Moreover, the environmental conditions, pond design, and turbulent mixing significantly affected the heat transfer rate and the optimum water temperature for algal growth. [ABSTRACT FROM AUTHOR]

• Thermal efficiency of Ti3C2Tx MXene nanofluid in a pin-fin heat sink is evaluated. • Experimental and numerical analysis on the hydrothermal performance of nanofluid. • Utilising MXene nanofluid resulted in a significant thermal performance improvement. • A small increase in coolant pumping power was observed. MXenes are an eco-friendly innovative type of graphene-like nanomaterials and are proven to exhibit remarkable thermal, electrical, mechanical and optical properties. This study is aimed at evaluating the thermal efficiency of novel Ti 3 C 2 T x MXene-based nanofluid in a pin-fin heat sink was via experimental and numerical analyses. The aqueous-based 2D Ti 3 C 2 T x MXene nanofluid was synthesised in a two-step process, followed by their characterisation and experimental testing. For the numerical analysis, the forced convection of the nanofluid was simulated through multiphase Lagrangian–Eulerian approximation by incorporating the interphase interactions of Brownian motion, thermophoresis, drag and Saffman lift forces, gravity, virtual mass and pressure gradient-induced forces. The thermal performance of the MXene nanofluids was assessed in terms of log mean temperature difference, average Nusselt number, local temperature and local Nusselt number distribution at the base of the heat sink and thermal contours. Their fluid flow characteristics were probed by analysing the coolant pumping power, flow streamlines distribution and performance evaluation criteria of the heat sink. Results demonstrated that utilising the MXene-based coolant resulted in a significant average Nusselt number enhancement at the expense of a small increase in coolant pumping power. Maximum improvements of 29.8 and 40.5% in the average Nusselt number were observed for nanoparticle concentrations of 0.013 vol% and 0.027 vol% respectively. [Display omitted] [ABSTRACT FROM AUTHOR]

This manuscript is aimed at investigating the thermohydraulic characteristics of Al 2 O 3 − Cu /water hybrid nanofluid in a micro pin-fin heat sink by implementing a multiphase Lagrangian–Eulerian approach. In modelling the nanofluid the influence of slip mechanisms i.e. Saffman lift and drag force, Brownian motion, gravity, virtual mass, thermophoresis and pressure gradient-induced force is included. In addition, the fin efficiency of the nanofluid cooled sharp and streamlined fin configurations is probed by analysing diamond, circular and elliptical fins arranged in the staggered assembly. Spherical shaped hybrid nanoparticles of 15 nm are studied for the particle volume fraction of 1%. The performance of heat sinks is evaluated by analysing the quantitative parameters including log mean temperature difference, average (Nu avg) and surface (Nu s) Nusselt number. Besides, the flow streamlines, thermal and vorticity contours represent the qualitative depiction of flow and thermal distributions. Results demonstrate that utilising nanofluid optimises Nu avg enhancement to maximum values of 25.14%, 19.65% and 24% for diamond, circular and elliptical fins, respectively. The thermal efficiency of nanofluid is highest across the upstream fins and it diminishes towards the downstream fins. At the highest pressure drop, the fin efficiency of the studied fin configurations is in the order of circular, elliptical and diamond fins. Unlabelled Image • Performance of Al 2 O 3 − Cu / water is investigated in a micro pin fin heat sink. • Hybrid nanofluid is simulated by using a multiphase discrete phase model. • The fin efficiency of diamond, circular and elliptical fins is analysed. • The streamlined fin shapes reduce wake width and promote heat transfer enhancement. • Heat sink with the diamond fins showed maximum Nusselt number enhancement of 25.14%. [ABSTRACT FROM AUTHOR]

• Manufacturing and thermal applications of the lattice structure have been discussed in detail. • Four classes of materials (polymers, ceramics, liquid resins and, metals and alloys) are considered for the detailed review. • Pressure drop is not significant for lattice structure, unlike metallic foams. • Thermo-hydraulic performance of the thermal systems is improved. Lattice structures are a class of cellular materials with enhanced thermomechanical properties compared with their counterpart cellular materials such as foams. They have recently attracted researchers towards implementation in various engineering applications due to their diverse fabrication techniques driven by the advancement in additive manufacturing technology. This article reviews the four classes of materials (polymers, ceramics, liquid resins, and metals and alloys) used to fabricate the various lattice structures employed in different thermal applications. Firstly, the classification and description of the lattice structures are concluded, along with their applications in several domains in general and particularly in thermal systems. Secondly, the materials and fabrication techniques used for lattice structure manufacturing are briefly reviewed. Thirdly, extensive literature analysis is carried out on the heat transfer characteristics of numerous categories of lattice structures. Results revealed that lattice structures are the most promising media to enhance the thermo-hydraulic performance of heat-transferring systems in terms of augmenting the heat transfer rate and reducing the pressure drop. Meanwhile, some of its designs increase its thermal resistance, suitable for application in energy storage systems. On the basis of critical analysis of the fabrication, characterization and applications, several important conclusions are presented, along with the future research directions, to fill the gap in this area of research. [Display omitted] [ABSTRACT FROM AUTHOR]