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This study is a systematic review of research on heat transfer analysis in cavities and aims to provide a comprehensive understanding of flow and heat transfer performance in various kinds of cavities with or without the presence of fins, obstacles, cylinders, and baffles. The study also examines the effects of different forces, such as magnetic force, buoyancy force, and thermophoresis effect on heat transfer in cavities. This study also focuses on different types of fluids, such as air, water, nanofluids, and hybrid nanofluids in cavities. Moreover, this review deals with aspects of flow and heat transfer phenomena for only single-phase flows. It discusses various validation techniques used in numerical studies and the different types and sizes of mesh used by researchers. The study is a comprehensive review of 297 research articles, mostly published since 2000, and covers the current progress in the area of heat transfer analysis in cavities. The literature review in this study shows that cavities with obstacles such as fins and rotating cylinders have a significant impact on enhancing heat transfer. Additionally, it is found that the use of nanofluids and hybrid nanofluids has a greater effect on enhancing heat transfer. Lastly, the study suggests future research directions in the field of heat transfer in cavities. This study's findings have significant implications for a range of areas, including electronic cooling, energy storage systems, solar thermal technologies, and nuclear reactor systems. [ABSTRACT FROM AUTHOR]

This work investigates heat transfer and entropy generation of a turbulent flow of an Al2O3–Cu/water hybrid nanofluid in a plain tube (PT) with classical (TPT) and elliptical‑cut twisted tape (TECT) inserts. The heat transfer and pressure drop are investigated numerically at Re (7000–15,000), mass concentration (1–4%), and the inlet temperature of the fluid (300 K). Further, the total entropy generation and Bejan number are examined at Re = 7000 and a mass concentration of 4%. The obtained results indicate that heat transfer can be intensified when inserting classical and elliptical‑cut twisted tape. In addition, an increase in the thermal conductivity of the fluid may cause a slight increase in the heat transfer coefficient. Moreover, heat transfer and thermal performance factors increase when the mass concentration of nanoparticles increases. The Nusselt numbers for TECT and TPT are 1.7 and 1.57 times higher than those for PT, respectively. The Nusselt number and thermal performance factor of hybrid nanofluid are greatest at roughly 195 and 1.9, respectively, showing 3.9% and 7.73% improvement compared to CuO/water nanofluid at Re = 7000. The analysis of the generation of entropy is expressed as a function of thermal and frictional contributions. The results indicate the existence of a minimum entropy generation for each type of tubes for Al2O3–Cu/water hybrid nanofluid. Total entropy generation analysis demonstrates that thermal entropy generation dominates at high heat flux. Moreover, increasing the nanoparticles decreases the generation of total entropy, which is ascribed to the thermal conductivity increment. In addition, the rate of total entropy generation declines as the vortex flow increases. [ABSTRACT FROM AUTHOR]

A numerical investigation is carried out to investigate the transitional flow behaviour of nanofluids flow in an inclined pipe using both single and multi-phase models. Two different nanofluids are considered, and these are Al 2 O 3 –water and TiO 2 –water nanofluids. Moreover, SST κ − ω transitional model is implemented to study the nanofluids flow in inclined pipe. Gravitational force is also adopted by considering Boussinesq approximation in the momentum equation. Results reveal that Buoyancy force play a significant role on the degeneration of heat transfer rate with the increase of Reynolds number for different inclination angles. It indicates that mixed convection has opposite effect on the inclined pipe than the forced convection on the horizontal pipe. Moreover, some deformation of the flow and temperature fields near the upstream region is observed with the increase of inclination angle due to Buoyancy force. [ABSTRACT FROM AUTHOR]

Single and multi-phase numerical simulations are carried out to investigate the heat transfer and entropy generation behaviour of transitional flow of TiO 2 H 2 O nanofluid in a circular pipe. Results reveal that the small diameter of nanoparticles has the highest heat transfer rate for χ = 6% and the TiO 2 -water nanofluid shows higher heat transfer rate using multi-phase model compared to that of the single phase model. Also no optimal Reynolds has been observed which could minimise the total entropy generation. New correlations are proposed to calculate the average Nusselt number using a nonlinear regression analysis with a standard deviation of error of less than 0.5%. [ABSTRACT FROM AUTHOR]

A numerical investigation has been carried out applying single phase approach on turbulent forced convection flow of water based Al2O3 and TiO2 nanofluids flowing through a horizontal circular pipe under uniform heat flux boundary condition applied to the wall. The effect of volume concentrations, Brownian motion and size diameter of nanoparticles on flow and heat transfer have been examined for Reynolds number, Re = 10 × 103 to 100 × 103, Prandtl number, Pr = 7.04 to 20.29, nanoparticle volume concentration, χ = 4% and 6% and nanoparticles size diameter, dp = 10, 20, 30 and 40 nm respectively. Results reveal that the small size of nanoparticles with their Brownian motion has the highest average shear stress ratio, heat transfer rate and thermal performance factor for χ = 6%. Besides, it is found that the heat transfer rate increases as the particle volume concentration and Reynolds number increase with a decrease of nanoparticles size diameter. Moreover, Al2O3–water nanofluid shows a higher heat transfer rate compared to that of TiO2–water nanofluid. Finally, a conclusion has been drawn from the present analysis that the heat transfer performance is more affected by the size diameter and Brownian motion of nanoparticles than the thermal conductivity of nanofluid. Results of the non-dimensional fully developed velocity and turbulent kinetic energy, frictional factor and average Nusselt number for pure fluid (water) as well as the result of average Nusselt number for Al2O3 and TiO2–water nanofluid have been validated with published experimental results as well as with available correlations where a reasonable good agreement has been achieved. [ABSTRACT FROM AUTHOR]

• Impacts of nanoparticle, thermal radiation, and volumetric absorption on PTCP. • Thermal loss is the key factor affecting the PTCE. • Sensible heat absorption is altered by the NVC and type of nanoparticles. • Blended nanoparticles enhance the overall system performance. • Brownian motion and optical features augment the heat transfer enhancement. The photo-thermal conversion performance (PTCP) of water-based nanofluids in a volumetrically heated solar collector (VHSC) is evaluated. The influences of nanoparticle volume concentration (NVC), particle size, Reynolds number, operating temperature, and collector geometry on the PTCP are numerically investigated. The utilization of nanoparticles and improving their concentration is found to enhance the photo-thermal conversion efficiency (PTCE) of the collector by augmenting the energy from the sun of the working fluid due to the radiation-nanoparticle interactions. The PTCE enhancement of Graphite, TiO 2 and Ag nanoparticles dispersed in water is respectively 1.37, 1.33 and 1.29 times better, compared to that of water. This is further augmented by adding MgO nanoparticles to TiO 2 , Graphite and Ag particles, resulting in 1.69, 1.67 and 1.59x improved efficiency. Enhancing the flow rate of the fluids also contributes to the PTCE by reducing the losses of thermal from the collector to the ambient. Besides, the enhanced nanoparticle size increases the overall PTCP as it enables the nanofluid to absorb more solar energy. Enhancing the collector length accelerates the thermal loss to the ambient, as a result the system performance diminishes. It is also regarded that the heat absorption of the nanofluid declines with improving inlet temperature of the working fluid. [ABSTRACT FROM AUTHOR]

Nanofluid-microchannels have gained prominence in recent years as a means of cooling electronic devices; however, nanoparticle deposition remains a challenge. In this paper, a discrete phase model (DPM) is used to study the effects of various forces on nanoparticle deposition of Al 2 O 3 -water nanofluids in a straight microchannel. The results indicate that Brownian motion has a significant impact on nanoparticle deposition. For instance, when Cunningham values vary from 1.2 to 0.2, nanoparticle deposition ratios decrease from 8.69% to 3.41%. When the fluid velocity is <0.6 m/s, the thermophoretic force becomes crucial, whereas Saffman's lift force becomes important when the particle diameter is <10 nm. In addition, gravity and pressure gradient forces can be ignored. Virtual mass and drag forces impact deposition indirectly by changing residence times. Finally, a new correlation has been proposed for calculating particle deposition ratios. • A liquid-based deposition process differs from a gas-based deposition process. • Brownian motion has the greatest impact on nanoparticle deposition. • Thermophoretic and Saffman's lift forces become essential in certain conditions. • A new correlation was developed to determine particle deposition ratios. [ABSTRACT FROM AUTHOR]

Nanofluid-microchannels (NF-MCs) have emerged as an important topic for thermal management of electronic devices. However, deposition of nanoparticles is a tricky problem, and this paper conducts a numerical study to identify the best working conditions to prevent deposition of nanofluids in a microchannel cooling system. According to the findings, large nanoparticles, high velocity, low inlet temperature, high nanoparticle density, low nanofluid density, and high base fluid viscosity are the best working conditions for improving nanofluid stability. However, heat transfer rates and pressure drop must also be taken into account. The nanoparticle deposition rate and average heat transfer coefficient only increase by 2.71% and 0.92% respectively as the heat flux increases from 20 kW/m2 to 100 kW/m2, but the pressure drop decreases by 10.57%. Therefore, changing the heat flux is not the best option. Moreover, the inlet temperature has only a minor effect on the heat transfer coefficient, so it is crucial to balance the pressure drop and nanoparticle deposition when designing systems. [Display omitted] • Liquid-based nanoparticle deposition in a microchannel was studied. • Optimal flow characteristics were obtained to reduce deposition. • Ideal nanofluid properties were selected to delay deposition. • Deposition effect was evaluated by heat transfer and pressure drop comprehensively. [ABSTRACT FROM AUTHOR]

[Display omitted] • Absorption capacity of the heat transfer fluid is enhanced by adding nanoparticles. • Hybrid nanoparticles in the base fluid further improves the solar photothermal conversion. • Larger nanoparticles are beneficial for heat storage and enhancement of solar radiation. • The temperature gain of pure Therminol VP1 is higher than other pure fluids. • The sensible heat storage capacity of the system is augmented by hybrid nanoparticles. The paper numerically investigates the fluid flow and radiative heat transfer behaviour of water-based mono and hybrid nanofluids in a direct absorption solar collector under solar irradiation boundary conditions. The effects of radiation on the heat and flow performance with operating parameters such as the type of nanoparticles, volume concentrations of nanoparticles, nanoparticle size and type of base fluids are investigated. The numerical results reveal that uniform temperature distribution is obtained with an incident radiation of 1029.81 W/m2 and that the collector performance increases with the addition of nanoparticles owing to their higher radiative properties. While the temperature gain for pure water is 5.58 K, it is estimated to be 48.72 K and 51.32 K with the volume concentrations of 70 ppm and 100 ppm for Al + Al 2 O 3 and Al + Graphite nanofluids, respectively. Moreover, the thermal performance of the collector is positively affected by increasing the size of nanoparticle. For example, for Al + Al 2 O 3 nanofluids at 10 ppm volume concentration, the temperature increase is 37.12 K and 42.02 K at 10 nm and 50 nm, respectively. Therefore, hybrid nanofluids can be considered as effective heat transfer fluids to increase the solar radiation absorbability, and subsequently, improve the efficiency and performance of the direct absorption solar collector. [ABSTRACT FROM AUTHOR]