Journal of Heat and Mass Transfer Research
Volume:10 Issue: 1, Winter-Spring 2023

The performance of internal combustion engines can be improved by optimizing fuel spray characteristics. However, high injection pressures and small nozzle diameters in modern fuel injectors result in cavitation flows inside the nozzle, making it difficult to accurately characterize vapor bubble formation and growth. In this review, we explore the influence of cavitation flow on spray formation and examine the effects of geometric and operational factors. We discuss the experimental techniques used to generate a cavitation map and the mathematical models used to describe the behavior and magnitude of the bubble. We also investigate the impact of cavitation on spray properties, including the enhancement of liquid jet fragmentation due to the collapse of cavitation bubbles near the nozzle output. We present a multidimensional cavitation-coupled spray model and discuss the effect of cavitation on spray angle. While experimental work is effective, theoretical analysis can also provide insights into the impact of cavitation flow on spray characteristics. Our review concludes that the spray angle increases during the growing cavitation and super cavitation regimes, but decreases significantly following the cavitation flip. The string cavitation is observed when the position of the needle valve shifts or at a lower needle lift and the spray cone angle increases significantly. Overall, this review provides an inclusive overview of cavitation flow and its influence on spray formation and will aid in the development of more efficient internal combustion engines.

Quenching progression on a flat surface and heat transfer enhancement with an impinging jet over smooth and dimpled surface modification is presented in this manuscript. With rapid advancements in today’s electronic, electrical, and mechanical systems, the need for the removal of the associated heat generation rates is also increasing. Achieving that by jet impingement provides an economical and fast solution. A smooth flat plate is quenched repeatedly from three different initial temperatures of 300,350 and 400° C. The results in terms of re-wetting parameters viz., Re-wetting temperature, and wetting delay are reported. Parallelly, the effect of the hemispherical dimpled (array) surface with a pitch of 3 mm, and diameter of 2 mm with varying depths of 0.5 mm(d/t=10) and 1mm(d/t=5) are studied. The results are then compared to that of a smooth surface. Water is used as a coolant at a temperature of 17 ±2°C. A large deviation in results is reported when the plate surface was subjected to repeated trials due to a change in the metallurgical properties of the surface. The results of a dimple depth of 0.5mm show a higher heat transfer rate as compared to that of both the smooth surface and the dimple depth of 1 mm. A maximum of 40% and a minimum of 26% enhancement in heat transfer rate is reported for dimple depth 0.5mm compared to 1mm. Further, a 59.76% of heat transfer efficiency was recorded for the experimental setup and this efficiency was found to be increasing with an increase in the water pump pressure.

One field of study in microfluidics is the control, trapping, and separation of microparticles suspended in fluid. In recent years, much research has been started in this field. Some of its applications are related to cell handling, viruses, and bacteria detection, checking and analyzing biological cells and DNA molecules, testing water quality, or checking impurities in water. One of the new methods in this field is using Induced-charge electrokinetic phenomena (ICEK) and dielectrophoresis force. In the Induced-charge electrokinetic phenomena, the property of polarization of a conductive surface located in an electric field causes vortices to be created on the conductive plate in the fluid. This conductive plate is called a floating electrode. In the present study, considering the Induced-charge electrokinetic phenomena, the dielectrophoresis force, and creating an outlet on the roof of the microchannel at the place where two vortices of the ICEK phenomenon meet (secondary outlet), the microparticles inside the fluid are separated in the desired ratio. The separation is such that after the microparticles reach the floating electrode, they are trapped in the ICEK flow vortex and separated through a secondary channel, which is placed crosswise and non-coplanar above the main channel. In the present study, yeast microparticles are suspended in a KCl electrolyte solution and injected into the microchannel by a syringe pump. The arbitrary adjustment of the percentage of conduction and separation of microparticles towards the secondary outlet by adjusting the parameters of the applied voltage and fluid inlet velocity to the microchip is one of the innovations of the present study. In the simulation results, we observed that for input velocities (20-120) (µm)/s, respectively, with applied voltages (150-330) V (to create an electric field in the floating electrode), 100% of the particles can be directed towards the secondary-outlet, and separated. To validate the simulation results, the results obtained from the simulation method of the present study have been compared with the results of previous works.

The heat losses are mainly affects on the performance of cavity receiver of solar concentrator. In this paper, the experimental and numerical study is carried out for different heat losses from cylindrical cavity receiver of 0.35 m cavity diameter and 0.55 m opening diameter with wind skirt. The total and convection losses are studied experimentally to no wind conditions for the temperature range of 60 °C to 80 °C at 0°, 25°, 50°, 75° and 90° inclination angle of cavity receiver .The experimental set up mainly consists of cylindrical cavity receiver which is insulated with glass wool insulation to reduce the heat losses from outside surface.. The numerical analysis was carried out with Fluent Computational Fluid Dynamics (CFD) software, to study connective heat losses for no wind condition. The numerical results are compared with experimental results and found good agreement with maximum deviation of 13%. The effect of inclination angle of cavity receiver on total losses & convection losses shows that as the inclination angle increases from 0o to 90o, both losses decreased due to decreased in convective zone into the cavity receiver. The effect of operating temperature of cavity shows that as the temperature of cavity receiver increases, the total and convective losses goes on increasing. The present results are also compared to the convective losses obtained from M. Prakash. The convective loss from M. Prakash shows nearest prediction to both experimental and numerical results.

Flow of aluminum oxide/water nanofluid is numerically investigated in a heat exchanger at different densities of solid nanoparticles and Reynolds numbers. The behavior of heat transfer in laminar flow of single-phase nanofluid are explored at various volume fractions of oxide aluminum (0%, 2%, 4%, 6%) and Reynolds numbers (5, 15, 25, and 40) using a finite volume method. The main purpose is to study the flow behavior of nanofluid and its heat transfer in a shell and tube heat exchanger with tube banks of the elliptical cross-section with different angles of attack. The results of this study indicate that an increase in the velocity of flow enhances the heat transfer coefficient, resulting in a more uniform temperature distribution. In addition, increase of angle of attack leads to a higher velocity of the fluid flow between the tubes. At higher Reynolds numbers, more remarkable entropy reduction is observed with increasing nanoparticle volume fraction. Depending on its volume fraction, addition of solid nanoparticles at a constant Reynolds number amplifies the flow velocity components and reduces the temperature gradient. The Nusselt number can increase up to 17% in Reynolds number of 5 for all tube banks depending on the volume fraction and angle of attack, which is up to 23% for Re = 40. Therefore, the amount of shell-side friction coefficient increases by 25 to 35% for Re = 5 to 40. For all designs, the increase in the friction coefficient due to angle of attack is less important than the variations of nanofluid volume fractions.

The cooling process of parts in limited spaces is of great interest to researchers due to its many applications in industries such as electronics. Therefore, achieving the best performance of such systems has always been one of the challenges facing researchers. Due to this necessity, in the present simulation via the lattice Boltzmann method (LBM), the cooling of two hot semi-cylinders via magnetohydrodynamics (MHD) free convection has been interrogated. The novelty of the available study compared to antecedent studies is the effect of a magnetic field (MF) in different types and heat absorption for cooling two hot objects embedded within a triangular enclosure comprising non-Newtonian ferrofluid, which has not been studied so far. The accuracy of the obtained results was guaranteed via the validation of the written code in comparison with other studies qualitatively and quantitatively. Based on the results, To have a larger the Nusselt (Nu) value, at the highest Rayleigh (Ra) value, it is sufficient to decline the fluid power-law (PL) index, heat absorption index and the Hartmann (Ha) value. The reduction of in the mean Nu value due to rise of the Ha value for the shear thinning fluid is about 59%, while it is about 38% and 21% for the Newtonian and the shear thickening fluids, respectively. The existence of heat absorption, in addition to reducing the Nu value by about 75% in highest value, for the shear thinning fluid, results in a decrease in the value of thermal performance index (ITP), which is very insignificant for the shear thickening fluid at Ha=60. The predominance of conduction over convection is the result of enhancing the PL index, which diminishes the effect of type and power of MF. For Ra=104, due to low convection effects, changing the type of MF is ineffective, while for Ra=106, this effect is highest. By changing the angle of inclination of the chamber and changing the arrangement of hot objects on the walls of the cavity, by changing the flow patterns, the thermal characteristics of the system can be strongly affected. In all cases, the trend of the ITP changes is in accordance with the trend of the mean Nu changes, which exhibits that HT has the largest share to production entropy (PE).

In this article, two computational frameworks are presented for the numerical simulation of flow and heat transfer under the effects of natural convection phenomena in a field containing water-copper Nano-fluid and including porous media. The first is a CFD model which is built based on accurate algorithms for spatial derivatives and time integration. The spatial derivatives have been calculated using first-order upwind and second-order central differencing approaches. Also, time integration is performed using the fourth-order Runge-Kutta method. In the second, a parametric reduced order model is developed to compute the whole flow field under the effects of some important parameters such as Darcy number and Rayleigh number. This model is constructed based on POD-snapshots method. The POD modes are calculated by the solution of an eigenvalues problem. The calculated eigenfunctions are POD modes which are ranked using energy-based criteria based on the total kinetic energy of the flow field. This approach leads to the development of a reduced-order model that can be used as a surrogate model of the CFD high-order approach. The results obtained from the reduced order model show relatively good agreements under variations of some important parameters such as Darcy and Rayleigh numbers and nanoparticles density on the flow and thermal fields with the benchmark DNS data. Also, from the results, it is concluded that the surrogate model has very small values of errors (order of 10-4 ~ 10-6) and the time spent on calculations is less than 10% of the time required for direct numerical simulation.

A 2-D computational analysis of heat transfer augmentation and fluid flow characteristics with B-shaped and D-shaped artificial roughness has been carried out under the Reynolds number (Re) range from 4000-20000. Comparing the predictions of different turbulence models with experimental results available in the literature, the renormalization group k-Ɛ (RNG) turbulence model is selected for the present study. A detailed analysis of heat transfer variation was done using various geometrical parameters such as four different pitch (P) values of 10, 15, 20, and 25 mm corresponding to pitch ratio (P/e) of 11.111, 16.666, 22.222, and 27.777 respectively, at constant height (e) of 0.9 mm. The highest value of Nusselt number (Nu) improvement reached up to 2.264 times and 21.91 times at P/e of 11.111 for B-shape and D-shape roughness respectively for Re of 20000 as compared to the smooth channel. A significant enhancement of heat transfer is predicted in the present simulation and the maximum Thermohydraulic Performance Parameter (THPP) attained up to 1.47 for B-shaped roughness. The novelty of the proposed model appears as present numerical findings offer better performance compared to existing research.

The manufacturing process of heating systems involves incorporating various heat exchangers, each with distinct characteristics. Among these, the helical heat exchanger stands out due to its space-efficient design and enhanced heat transfer rate compared to other variants. Recently, heat exchangers have witnessed novel nanofluid explorations aiming to replace conventional working fluids. Nanofluids possess unique properties that hold the potential for substantial improvements, consequently influencing the efficiency of heat exchangers employing them. The effectiveness of these heat exchangers is intrinsically tied to the properties of the employed nanofluids. Recent years have witnessed remarkable strides in comprehending the distinct traits exhibited by diverse nanofluids. This comprehensive study amalgamates findings from multiple investigations focused on helical-tube heat exchangers utilizing nanofluids as the primary medium. Notably, it underscores the existence of varying conclusions and perspectives among different researchers. This variance arises from the complexity of nanofluid behavior and its interactions within heat exchangers. Consequently, the efficacy of helical heat exchangers leveraging nanofluids hinges on the specifics of the chosen nanofluid and its characteristics. This subject continues to stimulate vigorous research and discussions among scholars. In summation, the dynamic landscape of heat exchanger innovation has brought the spotlight onto helical heat exchangers and their integration with nanofluids, showcasing the intricate interplay between fluid properties and efficient heat exchange.

This paper reviews the latest findings on instability and subcritical transition to turbulence in wall-bounded flows (i.e., pipe Poiseuille flow, plane channel flow, and plane Couette flow). Among the non-Newtonian fluids, viscoelastic and viscoplastic fluids were investigated. The main focus was on the early stage of transitional flow and the appearance of coherent structures. The scaling of threshold disturbance amplitude for the onset of natural transition was discussed. In addition, the transition of Newtonian fluids was compared with that of non-Newtonian fluids. Accordingly, the scaling for the transition of viscoelastic (i.e., highly elastic) fluid can be shown as Ac=O(Wig), where Wi is the Weissenberg number, g≤-1 is a scaling constant, and Ac is the critical perturbation amplitude. Moreover, the viscoelastic fluid flow at high Re numbers (i.e., Re>>1) is more stable than the Newtonian fluid flow in terms of the critical disturbance magnitude. Interestingly, the scaling for instability of viscoplastic fluid can be read as Rec=O(Bib), where Bi is the Bingham number and b≤1 is a constant. It was noted that exploration of perturbations like vortices, streaks, and traveling waves together with their amplitudes could clarify the instability and transition process. Hence, this paper focused on physical behavior and realizations of the transitional flow. Finally, a summary of consequential implications and some open issues for future works were presented and discussed.

In this study, a novel design was proposed for enhancing heat transfer in a channel with metal foam, corrugated walls, and hybrid nanofluids. The numerical analysis of hybrid nanofluids (MWCNTs+TiO2) with DW (distillate water) as the base fluid was performed in a channel with triangular corrugations and open metal foam. The mass fractions of hybrid nanofluids (mixture of DW and MWCNTs+TiO2) were set at 0.025%, 0.05%, and 0.075%. The effects of metal foam porosity and PPI (pore density), as well as different Reynolds numbers (ranging from 7000 to 13000), on thermal performance were investigated. The results showed that the heat transfer enhancement with metal foam increased by 130% for all hybrid nanofluids. Moreover, the heat transfer enhancement in metal foam with a porosity of 0.9 was 9.8% higher than that of metal foam with a porosity of 0.99. Additionally, quadratic correlations for the average Nusselt number (Nua) were proposed for all hybrid nanofluids, taking into account PPI, porosity, and Reynolds numbers as variables. Finally, the optimum values of Nua for all hybrid nanofluids were determined, providing valuable insights for optimizing the heat transfer performance in this configuration.

The present study aimed to investigate the effects of the semi-circular cut twisted tape insert in tube type heat exchangers. The study selected twist ratios of 4.5, 5.5, and 6.5mm, and cut diameters of 5mm, 8mm, and 11mm. The Reynolds number ranged from 4000-16000. The study quantitatively demonstrated the impacts of cut diameter and twist ratio in terms of Nusselt number, friction factor, and thermal performance factor. The aforementioned output parameters were employed as metrics to assess the efficacy of the twisted tape insert. The obtained results reveal that smaller twist generates extra swirl which intensifies heat transfer. Also, as the diameter of the cut increases Nusselt number increases. In a quantitative analysis, it was observed that when Re=4000, the plain twisted tapes with y=4.5, 5.5, and 6.5 exhibited maximum thermal performance factors of 1.36, 1.32, and 1.21, respectively. On the other hand, for the modified twisted tapes (having a cut diameter of 11mm), the values were higher, measuring 1.84, 1.77, and 1.68 for the same respective ‘y’ values.