Heat Transfer Rate Research Articles

Thermal-Fluid study of curved tubes in cross-flow

Three-dimensional simulations have been performed to investigate thermal performance by the external surface of curved circular tubes provided with concave and convex curvatures. The simulations were performed in Ansys-fluent software and results has been validated against the available results. The tubes were placed in a uni-directional free stream of air at a Reynolds number of 35000 which is within subcritical range for circular tube. The heat transfer capabilities of curved tubes have been compared with that of a straight tube of same diameter and height. A constant-heat-flux condition over the external surface has been used. The curved tubes have been designed such that it has vertical extensions at the end and curvatures at the middle section with curvature ratios of 0.075, 0.15, 0.225 and 0.3. Plots of coefficients of pressure, drag and lift, Nusselt number, heat transfer ratio and contours of pathlines were utilized to investigate the thermal behaviour around the tube surface. Results show the highest augmenting thermal performance exhibited by convex curved tube with curvature ratio 0.15 followed by curvature ratio of 0.225. Other reasonably better augmented heat transfer exhibited by concave curved tube with curvature ratio of 0.3. The present study also identifies augmenting, mitigating and insignificant zones around the tubes based on heat transfer rates. The results show an improvement in heat transfer when curved tube is used instead of straight tube which can be utilised in waste heat recovery recuperators.

Influence of MHD Flow on Shrinking Sheet with Partial Slip and Heat Generation at Stagnation Point

Fluid dynamics encompasses the fundamental principles of continuity, momentum, and energy conservation, which are applied through mathematical models like the Navier-Stokes equations. These equations are essential for describing how fluid properties like velocity, pressure, and density change in response to forces and environmental conditions. Thus, this study attempted to explore the characteristics of flow and heat transfer of a shrinking sheet in magnetohydrodynamics (MHD), along with the effect of partial slip and heat generation on the system. We employ a similarity transformation technique for turning the governing partial differential equations into ordinary differential equations. These equations are solved numerically through shooting method in Maple, and the results are compared to the previous research. The analysis shows that the suction parameter and velocity slip parameter have an increasing effect on both the skin friction rate and the heat transfer rate. In the meantime, the heat transfer rate decreases as the parameter increases for the heat generation, magnetic parameter, Eckert number and thermal slip parameter. The bvp4c solver in MATLAB is implemented to conduct a stability analysis and determine the physically feasible solution. According to our research, the stability of the solution occurs only in the first solution.

Numerical study of unsteady thin film flow and heat transfer of power-law tetra hybrid nanofluid with velocity slip over a stretching sheet using engine oil

This paper explores the effects of velocity slip and power-law nanofluid flow on tetrahybrid nanofluids across a stretching sheet. Tetrahybrid nanofluids, which combine four distinct nanoparticles Ag, SiO2, CuO, and ZnO with engine oil as the base fluid, are investigated for their potential to enhance thermal performance. Engine oil plays a critical role in reducing friction and wear in mechanical systems by forming a protective layer on components such as cylinders, pistons, and bearings. Using MATLAB’s bvp4c, the study solves a set of ordinary differential equations derived from boundary layer equations, applying appropriate similarity transformations. It is observed that two unique velocity profiles intersect at a specific location, which shifts away from the stretching sheet as the velocity slip parameter increases. The findings indicate that tetrahybrid nanofluids offer superior heat transfer rates compared to standard nanofluids, showing improvements of 7.43, 6.27, and 5.35% over hybrid and tri-hybrid nanofluids, respectively. This study provides graphical representations of how various parameters, including the Prandtl number, power-law index, slip parameter, magnetic field parameter, and Reynolds number, affect temperature and velocity profiles. It is revealed that increasing the value of the solid volume fraction causes the tetrahybrid nanofluid velocity to decrease and its temperature to rise. The innovation of this work lies in its detailed examination of tetrahybrid nanofluids, extending beyond earlier research on simpler nanofluids and offering valuable insights for advanced thermal management solutions.

Combined Reaction System for NH3 Decomposition and CO2 Methanation Using Hydrogen Permeable Membrane Reactor in 1D Model Analysis

In a previous study, we developed an integrated reaction system combining NH3 decomposition and CO2 methanation within a membrane reactor, significantly enhancing reactor performance through efficient H2 separation. Ru/Ba/γ-Al2O3 and Ru/ZrO2 were employed as catalysts for each reaction. To ensure the accuracy and reliability of our results, they were validated through 1D models using FlexPDE Professional Version 7.21/W64 software. Key parameters such as reactor arrangement, catalyst bed positioning, overall heat transfer coefficient, rate constants, and H2 permeance were investigated to optimize system efficiency. The study revealed that positioning the NH3 decomposition on the shell side and CO2 methanation on the tube side resulted in a better performance. Additionally, shifting the methanation catalyst bed downward by approximately one-eighth (10 mm from 80 mm) achieves the highest CO2 conversion. A sensitivity analysis identified the rate constant of the NH3 decomposition catalyst and the H2 permeance of the membrane as the most influential factors in enhancing CO2 conversion. This highlights the priority of improving membrane H2 permeance and catalytic activity for NH3 decomposition to maximize system efficiency.

Studies of a Mechanically Pumped Two-Phase Loop with a Pressure-Controlled Accumulator Under Pulsed Evaporator Heat Loads

As avionics become more power dense, electronic device cooling has become a significant barrier to aircraft integration. A mechanically pumped two-phase loop (MPTL) is a thermal subsystem that enables near isothermal evaporator operation, which is desirable for electronics cooling. The goal of this study was to integrate an MPTL with a pressure-controlled accumulator and model a predictive control technique to demonstrate improvements for transient, isothermal evaporator operation for MPTLs under pulsed evaporator heat loads. The model predictive controller enables active control of MPTL compressible volume, which has not been demonstrated for pulsed evaporator heat loads. Experimental data were collected to validate a representative numerical model. A pressure-controlled accumulator was added to an MPTL to experimentally characterize the system thermodynamic response for three pulsed evaporator heat loads. Two statistical methods were used to assess the numerical model agreement with the experimental results. Under pulsed evaporator heat loads, the mean percent error agreed within 3.45% and the mean average percent error agreed within 0.74% for the three pulsed evaporator heat loads. Finally, a traditional proportional–integral (PI) controller and an advanced model predictive controller were developed and integrated into the validated numerical model. Both control methods were evaluated for an expanded set of evaporator heat load profiles to analyze transient behavior. For evaporator heat profiles with high heat transfer rates, the model predictive controller can maintain a target ±2 K refrigerant temperature at the evaporator exit throughout the evaporator heat load duration, whereas the PI-controlled MPTL cannot. Through this work, active control of a pressure-controlled accumulator within an MPTL is shown to improve refrigerant isothermal (±2 K) operation when compared to a traditional control technique.

Numerical Investigation of a Heat Exchanger with Annular Fins for Cryocooler Application

In this paper, the heat transfer characteristics of a typical hot heat exchanger used in pulse tube cryocooler have been numerically investigated. The numerical simulation is performed with the help of the commercial tool Ansys Fluent® to study the effect of different shapes and sizes of fins on the rate of heat transfer. The major parameters of the analysis include the diameter and pitch of the fins, the oscillating temperature at the inlet and outlet of the heat exchanger, and its operating frequency. A numerical investigation is conducted for the annular fin to illustrate its effect on the rate of heat transfer by calculating its Nusselt number and heat transfer coefficient. The effect of with fin and without fin on temperature and pressure variations has been studied for different angles in a cycle. The vortex development mechanisms within the gap between fins have been analyzed and compared with the vortex development mechanisms without fin. Results will be helpful for better design of heat exchangers for cryocoolers.

Exploring the Effects of Open-Air Cooling on the Formation of Microstructure in Cast A356 Aluminum Alloy

The lightweight composition, non-magnetic nature, and machinability of aluminum alloy A356 make it an important material in many industries due to its significant mechanical properties such as strength, ductility, fatigue resistance, and castability. Aluminium alloy forms an oxide layer when exposed to air. The microstructure of this alloy plays a critical role in determining its mechanical behavior. This study utilized aluminum alloy A356, composed of 92.05% aluminum, 7% silicon, 0.35% magnesium, 0.20% copper, 0.10% manganese, and 0.10% zinc. This alloy exhibits extremely high corrosion resistance, similar to stainless steel, with a melting point of 650°C. The study examines multi- component (mainly Al with Si) A356 containing small amounts of Mg, Cu, Mn, and Zn for their complex microstructural behavior. It includes observations using techniques such as optical microscopy and X-ray diffraction (XRD). This research was carried out to investigate different areas of the same metal’s microstructure and to discover the influence of cooling rates during the solidification process. The findings revealed that there are dissimilarities between the central parts and outer areas, as well as similarities between the two side portions. Also, this study highlights processing conditions’ impact on the material response while looking at heat transfer rate effects during solid-state transformation. The findings of this study highlight the presence of distinct microstructures (dendritic and equiaxed structures) across different sections of the cast Aluminum alloy A356. These findings contribute to a better understanding of the microstructure-property relationship of Aluminum alloy A356, assisting in improvising design and manufacturing processes for enhanced performance.

Experimental studies on heat transfer performance of a heat exchanger with drilled twisted tape inserts

Experimental studies on heat transfer performance of a heat exchanger with drilled twisted tape inserts

Mathematical molding and heat transfer in MHD blood base hybrid nanofluid on a moving extensible surface

AbstractThis work explores the heat transfer properties and mathematical modeling of blood‐based hybrid nanofluid flow on a moving extensible surface in magnetohydrodynamic (MHD) flow. For the first time, this model is treated semi numerical with the influence of viscous dissipation. Blood, a complex biological fluid, is added to the nanoparticles aluminum oxide and copper as a base fluid for the formation of hybrid nanofluid. We formulate the governing partial differential equations assuming laminar, incompressible, and steady‐state flow. Applying the appropriate similarity transformation, a nonlinear system of ODEs is obtained from the recommended system of PDEs. Semi numerical simulations are utilized to analyze the effects of the flow and heat transfer characteristics of the including Eckert number, thermal radiation, magnetic field, couple stress parameter, and volume fraction of nanoparticles. The findings show that the magnetic factor, thermal radiation, and Eckert number significantly increase the rates of heat transfer, furthermore, the velocity field of hybrid nanofluid is decreasing with the increasing of couple stress, magnetic field, and nanoparticles volume friction, while skin friction is increasing with the increasing of couple stress, magnetic field, and nanoparticles volume friction. This work opens up new possibilities for optimizing heat transfer processes in biomedical applications involving blood flow by shedding light on the intricate interactions between surface stretching, hybrid nanofluid properties, and magnetic field effects.

Improvement of Heat Conduction in Triply Periodic Minimal Surface Heat Sinks Filled with Phase Change Materials

Recently phase change materials (PCMs) have received significant attention in the field of thermal management and energy storage systems. However, the thermal performance of PCMs is restricted by their low thermal conductivity. Triply periodic minimal surface (TPMS) is a novel surface with high strength, high specific surface area, and high connectivity, which can be applied in PCM heat sinks to enhance the local heat transfer rate. In this study, a topology optimization method for TPMS structures applied in PCM heat sinks with the objective of least dissipation of heat transport potential capacity is proposed. The optimized structure has a higher volume fraction of metal material near the heating surface while lower in the region away from the heating surface. Furthermore, the optimized structure accelerates the advancement of the melting interface. With a constant heat flux on the heating surface, the average temperature of the heating surface can be reduced by about 30 K compared to the uniform TPMS structure.

Magnetohydrodynamic Effects on Double Diffusion of Non‐Newtonian Hybrid Nanofluid in Circular Eccentric Annuli

ABSTRACTThe numerical investigation conducted in this study focuses on the heat and mass transfer in magnetohydrodynamic non‐Newtonian power‐law fluid flow of temperature‐dependent Al2O3–Fe3O4–water hybrid nanofluid within cylindrical annuli across four different eccentricities. This type of problem finds widespread application in various engineering contexts, where hybrid non‐Newtonian fluids offer enhanced efficiency for cooling and insulation purposes. In this configuration, the inner circle of the geometry is hot while the outer circle is cold, with the nanofluid filling the space between the cylinders. The governing equations are simulated using the Galerkin weighted residual finite element method. Various parameters are controlled in the study, including the Rayleigh number ranging from to , power‐law index ranging from to , nanoparticle volume fraction ranging from to , Hartmann number ranging from to , Buoyancy ratio ranging from to , and Lewis number ranging from to , in addition to the fixed Prandtl number (6.8377). The study presents visualizations such as streamlines, isotherms, and iso‐concentration contours, along with the assessment of heat and mass transfer rates expressed in terms of Nusselt and Sherwood numbers. The findings reveal that the heat transfer rate increases with higher nanoparticle volume fraction, Rayleigh number, and Buoyancy ratio. Similarly, the mass transfer rate is enhanced with increased Rayleigh number, Lewis number, and power‐law index. Notably, elevating the power‐law index leads to a decrease of 50.1% in the local Nusselt number and 52.4% in the local Sherwood number, respectively. With and , increasing from to raises and .

Impact of Dual Phase Lag on Natural Convection Flow in a Porous Vertical Channel in the Presence of Periodic Boundary

ABSTRACTThe dual‐phase‐lag (DPL) heat conduction model is utilized in this research to analyze the fluid flow of viscous fluid passing through a porous vertical channel with periodic boundary conditions. Periodic heating is subjected to the channel boundary. Equations regarding the model, including the momentum and energy equations, in which the DPL term is incorporated, all in dimensional form, are stated and are being transformed to their dimensionless form, then solved analytically by undetermined coefficients and variation of parameters. The actual expressions of temperature and velocity, as well as the heat transfer rate and skin friction, are determined. The effects of the DPL parameters, suction/injection, Prandtl number, heat source/sink, and Strouhal number on the dimensionless temperature and velocity profiles are demonstrated using graphs that are constructed with the aid of MATLAB. It was found during the investigation that the introduction of the DPL model, together with suction/injection in the channel, enhances the velocity and fluid temperature within the channel. Also, the decreasing effect of temperature gradient phase lag on fluid temperature and velocity conversed with that of heat flux phase lag. As an important contribution, the discovery of the effects of the phase‐lag parameters of the DPL model and suction/injection on fluid temperature and velocity would significantly help researchers advance the design of electrical and electronic systems.

Grooved single-channel dual media tank thermal energy storage systems to improve overall thermal performance: Numerical analysis

In this study, a numerical analysis of a single-channel structured dual media tank (DMT) thermal energy storage (TES) system is done to investigate the effect of grooves on thermo-hydraulic performance. Due to computational complexity, a single channel is considered, and results are validated by the numerical results of other studies. The study encompasses the analysis of unsteady temperature distribution, heat transfer coefficient, and friction factor by varying the groove size ratio with the diameter of the pebbles. The φ ratio (grooves diameter/pebbles diameter) is varied from 3.15 to 4.73, and the effect of the Re for different widths of the channel is studied. The numerical result reveals a 50 % increase in heat transfer coefficient when φ is varied from 3.15 to 4.73 at a Reynolds number of 22.4. Similarly, a small variation in the frictional factor can be observed. amounts to 22 % while keeping a Reynolds number of 22.4 and a diameter ratio (φ) ranging from 3.15 to 4.73. Furthermore, research is done on how Reynolds number affects volumetric heat transfer (ℎv). The results indicate a 31 % decrease in ℎv at φ = 3.15. on the other hand, a larger value of φ is observed to result in a lesser drop in ℎv. Additionally, the computation performance improvement factor (PEF) shows greater values for φ = 3.15, indicating that the ideal groove diameter to achieve maximum heat transfer rate and minimum pressure drop is smaller.

Comparative study of geometric characteristics of microcapillaries for chemical reactions

In this paper, a comprehensive comparative study of various geometrical characteristics of microcapillaries used for chemical reactions is carried out. Three main shapes of microcapillaries are considered: serpentine, fractal and lobular. The focus is on how microcapillary geometry affects key parameters of the reaction process, including reactant mixing efficiency, flow distribution, heat transfer, and reaction rate. Optimization of these parameters is critical to improve the performance of chemical processes at the microscale. COMSOL Multiphysics software was used for the simulations, which enabled the evaluation of hydrodynamic characteristics such as Reynolds number, mixing coefficients and temperature distribution profile. The study also includes calculations of criteria used to quantify the efficiency of reagent mixing. In addition to numerical modeling, experiments were conducted, the results of which were used to verify the obtained calculated data. This improved the accuracy and reliability of the conclusions. The results of the study show that the choice of microcapillary geometry has a significant influence on the hydrodynamic parameters of the flow and, consequently, on the overall efficiency of chemical reactions. For example, serpentine geometry may provide better mixing in the early stages of the reaction, whereas a brush-like shape may be optimal for long-term processes with high heat transfer rates. The conclusions of this work provide practical recommendations for the choice of microcapillary geometry depending on the specifics of the chemical reaction. Using the example of acetone self-condensation, a suitable geometry, lobular, was identified. The recommendations are aimed at increasing productivity, improving the quality of reaction products and reducing energy costs.

A local synergy angle of velocity, temperature and pressure fields for enhancement of comprehensive heat transfer performance

The field synergy principles for convective heat transfer and flow resistance are integrated in this study. A local three-field synergy angle of velocity, temperature and pressure fields is proposed to evaluate the local comprehensive performance of heat transfer and pumping power consumption. The angle is based on the polar angle of a plot with dot products of velocity and enthalpy/total pressure gradients, respectively, as coordinates. The polar angle is then shifted by the observation that the enhancement of heat transfer rate at the cost of pumping power decreases from the second quadrant to the forth quadrant. The application of the synergy angle is demonstrated by examples of flow and heat transfer in channels with different fin structures. Inspired by the distribution of the synergy angle, Airfoil-Rect fin and Rhom-Rect fin structures are designed, which can improve the heat transfer rate with constraints of pumping power consumption. The present study provides a possible approach for heat transfer enhancement.

Entropy, thermal, and mass transportation optimization of magnetohydrodynamic power-law nanofluid over stretched sheet with chemical reaction effect

The power-law nanofluid’s heat and mass transmission over a stretched surface with magnetic field, entropy optimization, and chemical reaction effects is the main focus of the present study. The governing partial differential equations are reduced using similarity transformation into ODEs (ordinary differential equations), which are then numerically solved with the help of the Keller box and finite difference techniques. A substantial evaluation is conducted using the controlling flow factors, which include the Eckert number, chemical reaction factor, Brownian motion parameter, thermophoresis number, power-law index (n), and generalized Prandtl number (Pr), on the fluid velocity profile, flowing fluid temperature, and concentration profile. A decrease in the velocity profile is observed when the chemical reaction process is accelerated, leading to heat absorption. However, when the power-law parameter increases, the fluid’s temperature decreases, and the velocity profile increases at specific values of viscous dissipation (Ec = 0.1) and chemical reaction (γ = 0.01). The values of the coefficient of skin friction (Cf), Sherwood factor (Shx), and reduced local Nusselt number (Nux are also computed and presented in the form of a table for the generalized Prandtl number (Pr = 7.0). The coefficient of skin friction and mass transfer and heat transfer rates are quantitatively compared with those in the literature for particular circumstances, and the results demonstrate good agreement with each other. This research offers insightful information for designing and improving systems that use nanofluids exposed to external magnetic fields, which has ramifications in many technical uses, including heat exchange systems based on nanofluids and thermal management systems.

Application of waste fly ash and graphite powder used as backfill materials in vertical ground heat exchangers

Backfill material plays a significant role in heat transfer between the ground heat exchangers (GHEs) and surrounding soil. Fly ash is the fine ash wasted from coal combustion in thermal power plants, which may cause a serious of problems including air, water and soil pollution. To fully utilize the waste resources and improve the thermal performance of backfill material, a method of using waste fly ash and graphite powder is proposed, and the feasibility of using them as backfill material is investigated via laboratory and field test, in which the economic aspect is taken into consideration. The results indicate that the highest thermal conductivity of thermally enhanced backfill material could be increased to 2.391 W/(m·K) via laboratory test, with a growth rate of 23.69%, in which the mass ratio of graphite reaches 10% meanwhile guaranteeing the workability of fresh mortar. Heat transfer rates could be enhanced by 27.22% compared with traditional backfill material of natural sand via field test, corresponding to a highest heat transfer rate of 55.80 W/m. The economical value could be achieved through the lower cost of raw material and the reduction of drilling depth.

Flow characterization of a submerged inclined impinging pulse jet

This study investigated flow characteristics associated with a circular pulse-impinging jet on an inclined surface using dye visualization and particle image velocimetry techniques. The experiments are carried out for various pulse frequencies (0.1 < St < 0.9) of the jet, a constant angle of surface inclination (θ = 26°), and fixed surface spacing. The primary objective is to explore the flow dynamics aspect of pulse-inclined impinging jets with respect to the pulse frequency and Reynolds number. The present observation shows that at a certain degree of surface inclination (θ ≈ 28°), the jet momentum drives the entire flow in the downhill direction, which represents the critical angle of inclination. Furthermore, the critical angle of the inclination remains unchanged for both steady and pulse jets. The interaction of the inner and outer shear layers of the jet in the downhill direction highly depends on the pulse frequency, which is indeed triggered by the free jet vortices. In a free jet, the vortex formation and their growth depend on the jet shear layer response (convective acceleration) and the time available for vortex formation (local acceleration). Moreover, the instantaneous jet information reveals that the presence of the growing vortices increases the jet entrainment, and its movement along the surface enhances the mixing (shear stress) between the surrounding and boundary layer fluid. The results show that pulsation at Strouhal Number (St) = 0.44 help develop more coherent and durable vortices impinging on the surface, which is identical to the critical St for free and normal impinging jets. Pulsation near the critical St increases the jet entrainment and mixing between the inner and outer jet shear layers and is responsible for enhancement in the heat transfer rate. The results improve our understanding of heat transfer from pulse-inclined impinging jet and reinforce the existence of a critical St (= 0.44) with an inclined pulsing jet, providing the criteria for maximizing the heat transfer rate.

Analysis of thermophoresis and transpiration impacts on electromagnetic convective non-Darcy radiative flow past a rotating cone

This study presents a comprehensive mathematical model to investigate the intricate transport processes involving transpiration, thermal radiation, and a magnetic field in a viscous, incompressible fluid around a rotating vertical cone. By applying suitable transformations, the governing equations were non-dimensionalized and then solved numerically using the bvp4c method. The resulting velocity, temperature, and concentration profiles were examined under practical boundary conditions, and the findings were found to be in excellent agreement with the existing literature, validating the model's accuracy. The study further explores the influence of various factors, including the thermophoretic coefficient, magnetic field, thermal radiation, transpiration, Forchheimer parameters, and relative differences in temperature and concentration, on the flow characteristics. Additionally, the impact of these parameters on mass and heat transfer rates, represented by the Sherwood and Nusselt numbers with thermophoretic particle deposition velocity Vd* and local Stanton number Str was analyzed. Notably, the study highlights the sensitivity of the wall thermophoretic velocity to changes in physical parameters, which significantly affects the flow behavior under different transpiration parameter values. The findings of this study provide valuable insights into the complex interplay between the governing physical phenomena and offer a robust numerical framework for understanding and predicting the transport processes in rotating vertical cone systems with practical applications in various fields, such as engineering, geophysics, and astrophysics.

Analytical and numerical solutions of squeezing nanofluid flow between parallel plates: A comparison of IRPSM and HPM

The nanofluid flow between two parallel plates has many applications across various fields of engineering. The addition of nanoparticles to conventional fluids can improve the rheological properties of nanofluids, enhance the heat transfer rate, and have other beneficial characteristics. Therefore, a squeezing flow problem between two parallel plates has been investigated in this article. The nanofluid flow is composed of alumina (Al2O3) nanoparticles and water, which is used as a base fluid. This study is featured according to the recommendations of a previous study to implement the improved residual power series method (IRPSM). The mathematical model is presented in the form of partial differential equations (PDEs), which are then transformed into ordinary differential equations (ODEs) by means of similarity variables. The considered problem is solved by two analytical methods called IRPSM, the homotopy perturbation method (HPM), and a numerical method (NDSolve). The residual errors of both applied techniques are compared to verify the validation of a new method. The comparison of both applied analytical techniques is conducted at the 17th order of approximations. From the obtained results, we confirmed that both techniques are in great agreement and have a very close relationship. The results of both methods are compared with the numerical method, and it was found that the absolute error between the IRPSM and numerical techniques is much more significant than the absolute error between the HPM and numerical techniques. Also, we have seen that the residuals of IRPSM are quite significant in terms of less residual errors than those of HPM. We confirmed that the IRPSM is a more powerful method than the HPM in terms of solving such types of mathematical problems.