Journal of Heat and Mass Transfer Research
https://jhmtr.semnan.ac.ir/
Journal of Heat and Mass Transfer Researchendaily1Sat, 01 Jun 2024 00:00:00 +0330Sat, 01 Jun 2024 00:00:00 +0330Experimental Investigation of the Hybrid Nanoparticles into the LiCl Liquid Desiccant as Nanofluid on the Efficiency of Absorption Dehumidification System
https://jhmtr.semnan.ac.ir/article_8488.html
In this study, to increase the heat and mass transfer coefficients in the system, a combination of liquid desiccant such as lithium chloride (LiCl) and hybrid nanoparticles of multi-walled carbon nanotubes (CNT-MW) Aluminum Oxide (Al2O3) and silicon oxide (SiO2) has been used. Poly-Vinyl Pyrrolidone (PVP) surface activator or surfactant has been used for complete stability of hybrid nanoparticles in lithium chloride (LiCl) desiccant solution and liquid water. By the experimental data, heat and mass transfer coefficients in the system have been determined in a relational way for different combinations of nanoparticles and adsorbents. The effect of important parameters such as air flow intensity and desiccant liquid, air temperature and humidity, temperature and composition of incoming desiccant liquid nanofluid on the efficiency of the system has been studied. And from there the exergy analysis of the system has been done. In this way, the best operating conditions for the better performance of the system containing liquid desiccant nanofluid have been determined.The results of this research have clearly shown that, changes in the air humidity and temperature have been increased by adding the hybrid nanoparticles to LiCl/H2O liquid desiccant.&nbsp; In this regard, the mass transfer rate has been improved from 3.41% to 28.3% and the heat transfer rate has been improved from 4.18% to 29.11%. So, the average improvement has been 23.23% and 22.22%, respectively. Adding hybrid nanoparticles to LiCl/H2O liquid desiccant has increased the mass transfer coefficient from 17.42% to 29.26% and the heat transfer coefficient from 19.83% to 33.55%. Therefore, according to these results, the average value of improvement in mass and heat transfer coefficients has been about 22.73% and 26.51%, respectively.Physical Overview of the Instability in Laminar Wall-Bounded Flows of Newtonian Fluids at Subcritical Reynolds Numbers
https://jhmtr.semnan.ac.ir/article_8491.html
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). 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. Generally, the scaling proved to be in the form of Ac = O(Reg) for Newtonian fluids where Re is the Reynolds number, g &le; -1, and Ac is the critical perturbation amplitude. 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.Mathematical Modeling for Vacuum Infrared Radiation Drying of Pyinkado (Xylia Xylocarpa)
https://jhmtr.semnan.ac.ir/article_8415.html
The main goal is to build a mathematical model to describe the heat and moisture transfer process and experiment to determine the appropriate vacuum drying mode for Pyinkado wood material. According to the objective above, research has been conducted using the infrared vacuum drying method for Pyinkado, and a mathematical model has been developed to represent the heat and moisture transfer processes during the drying process. Solve mathematical models using the finite element method. Comsol Multiphysics software is used to simulate the drying process. Results are shown through images and temperature and humidity distribution charts. Experimental results recorded the distribution of temperature and humidity during the vacuum drying process of Pyinkado, compared with results calculated from a mathematical model with profiles and trends consistent with the drying experiment. The largest average error when drying using the infrared radiation vacuum method is less than 5%. Determine the appropriate technological parameters for the vacuum drying process of wood with a thickness of 50 mm. The parameters are as follows: drying temperature Ts = 58.9 &deg;C, pressure p = 0.2 bar, and infrared radiation intensity Phn = 625&ndash; 641 W/m2.Numerical Studies on the Effect of Different Obstruction Geometries on Performance of Rectangular Channel Air Heaters
https://jhmtr.semnan.ac.ir/article_8591.html
Air heaters have poor thermal efficiency. Flow obstructions improve the efficiency of the air heater by enhancing heat transfer and disrupting the formation of the laminar sub-layer. In the present study, a rectangular channel of aspect ratio 6 and obstructions of various geometry (triangular, rectangular, and arc (or semi-circular)) are used with a longitudinal pitch (Pl/e) of 4, transverse pitch (Pt/b) of 2 ratios for Reynolds Number (Re) from 5000 to 20000. Various performance parameters such as Nusselt Number (Nu), Friction factor (f), and Thermal Enhancement Factor (TEF) were analyzed for the above conditions using Computational Fluid Dynamics (CFD) to compare the thermohydraulic performance of air heaters with various obstruction geometries. Maximum TEF of 1.27, 1.08, and 1.05 are obtained at Re = 5000 for delta, rectangular, and arc flow obstructions, respectively. Delta flow obstructions are superior to arc and rectangular shapes for the investigated range of Reynolds numbers.The Behavior of Heat Flow and Temperature under Quantum-Relativistic Conditions
https://jhmtr.semnan.ac.ir/article_8616.html
In this article, the effect and behaviour of ultra-high-velocity heat motion are described. The ultra-high velocity of heat conduction in a system composed of particles in gas form is viewed as the motion of particles that aligns with the principles of thermodynamics, the theory of relativity, and quantum physics theory. An alternative method for ultra-high velocity heat conduction has been developed and explained. This method has been achieved by using the Lowrance invariant of the microscopic environment in Makowski spacetime, hence both quantum and relativistic concepts are used, presenting a quantum-relativistic environment. The average number of field quanta has been obtained based on the relativistic effect, which is connected with the constituent mass of particles and determines the density matrix of a quantum oscillator. The presented relativistic heat conduction model is theoretically consistent with many important laws of physics and provides a more accurate representation of heat conduction in many technologically important situations.Analysis of Mixed Convection inside an Enclosure in the Presence of a Rotating Grooved Cylinder
https://jhmtr.semnan.ac.ir/article_8638.html
In the present study, mixed convective heat transfer inside a square enclosure in the presence of a rotating cylinder with various numbers of grooves is presented. Effects of counterclockwise and clockwise rotations with non-dimensional rotating speeds (RS) in the range from -1000 to 1000 are studied for different radius ratios (R) of 0.1, 0.2, and 0.3. Computations are carried out for Rayleigh numbers 103, 104, and 105 using the finite volume approach. The obtained results are validated against the available data for an empty enclosure (in the absence of a cylinder) as the reference case and also for an enclosure with a rotating smooth cylinder. It is demonstrated that for a specific value of the Rayleigh number, increasing the radius ratio enhances the thermal performance inside the enclosure regardless of the groove number and rotating speed. Increasing the Rayleigh number attenuates the roles of rotating speed and radius ratio, gradually. It is concluded that among all cases, the case with counterclockwise rotating smooth cylinder and among the grooved cases, Case 5 with three grooves provide the maximum heat transfer enhancements.Artificial Neural Network Approaches for Predicting the Heat Transfer in a Mini-Channel Heatsink with Alumina/Water Nanofluid
https://jhmtr.semnan.ac.ir/article_8643.html
This work uses artificial neural networks to evaluate heat transfer in a mini-channel heatsink using an alumina/water nanofluid. The multi-layer perceptron (MLP) and radial basis function (RBF) neural networks are employed for the modeling. To apply the artificial neural network analysis, 60 data of experimental works are utilized. The outcomes depicted that the simulated annealing (SA) technique significantly increased the performance of the RBF network, although the optimal MLP structure was discovered by trial and error. The optimized RBF network carried over more data with less than 2% errors as compared to the MLP. While the results of the MLP network showed that the average relative error for the test data set was 2.0496%, this value was 1.417% for the RBF network. The modeling time is a significant determining element when choosing the optimal technique. The RBF network optimization took longer than 60 minutes, even though all MLP structures were run 100 times in less than 15 minutes. In summary, artificial neural networks are effective instruments for simulating these kinds of processes, and their application can save a lot of time-consuming experimentation. Additionally, the RBF network outperforms the MLP in terms of precision while requiring less processing time.Entropy Generation of Two Immiscible Fluid Flow of Couple-Stress and Viscous Liquid in a Vertical Wavy Porous Space
https://jhmtr.semnan.ac.ir/article_8612.html
The purpose of this research is to examine the entropy generation analysis of two immiscible MHD fluid flows in a vertical wavy channel with travelling thermal waves and porous space when subjected to an external magnetic field. Region-I is occupied with a couple-stress liquid, while region-II is with viscous liquid. The wall channels are maintained at different temperatures and concentrations. The governing flow equations are derived by taking into account the presence of both a mean part and a perturbed part in the solution. Long wave approximation, which contributes to the wall waviness, is used to derive the solution of the perturbed part. The R-K 4th-order method is employed together with the shooting technique to solve the resultant system of coupled and non-linear ordinary differential equations. The results are presented graphically for the distribution of velocity, heat, and concentration, entropy generation, Bejan number, shear stress, Nusselt number, and Sherwood number for arising parameters, Hartmann number, Brinkman number, porous parameter, couple-stress parameters, waviness parameter, Schmidt number, and Soret number and are discussed. As the couple stress fluid parameter, Grashoff number, and heat generation/absorption increase, the velocity distribution rises. Temperature drops as the porosity parameter and Hartmann number increase. With a rise in the Soret and Schmidt numbers, concentration reduces. Entropy generation decreases with the Hartmann number, porous parameter, and chemical reaction parameter and increases with the Brinkman number. The numerical solutions obtained are compared with previously published work to validate the model, and the results exhibit a remarkable agreement.Experimental Heat Transfer Analysis of Helical Coiled Tubes on the Basis of Variation in Curvature Ratio and Geometry
https://jhmtr.semnan.ac.ir/article_8625.html
The influence of curvature ratio (CR) within helical tubes on secondary flows and subsequent enhancement of heat transfer is well-established. Furthermore, the interaction between the shell fluid and the helical tube is recognized as pivotal in this regard. In this paper, the impact of varying CR and coil geometry on the performance of heat exchangers (HEs) through experimental heat transfer analysis conducted on five distinct coils viz., straight helical (ϴ= 90&deg;), conical (ϴ= 70&deg;,50&deg;,30&deg;), and spiral (ϴ= 0&deg;) configurations have been studied. Moreover, correlations for modified effectiveness are proposed for all HEs. The Reynolds number range chosen for the analysis spans from 3700 to 20000, encompassing laminar and turbulent flow regimes of the coil hot water. The optimal HE is identified based on thermal and hydrodynamic parameters, including hot water temperature difference, effectiveness, modified effectiveness, rate of heat transfer, pressure drops of coil, shell fluids, and pumping power. Observations reveal that helical cone coil heat exchangers (HCCHEs) demonstrate superior thermal and hydrodynamic characteristics when the fluid flow aligns with increasing CR. Notably, for both laminar and turbulent flows, the highest hot water temperature difference, effectiveness and rate of heat transfer are observed for ϴ= 30&deg; HCCHE, while the lowest values are attributed to ϴ= 90&deg; HE. Tube side Nusselt numbers, pressure drops and friction factors show agreement with predictions of researchers. The analysis reveals that the coil fluid pressure drop is maximal for ϴ =0&deg; HE, whereas the maximum shell fluid pressure drop is encountered for ϴ =90&deg; HE. Furthermore, the highest pumping power per unit heat transfer area for coil and shell fluids are noted for ϴ= 0&deg; HE and ϴ= 90&deg;HE, respectively, while ϴ= 30&deg; HCCHE exhibits comparable performance to the remaining HEs within the specified parameter range, establishing its optimality.Influences of Gyrotactic Microorganisms and Nonlinear Mixed Bio-convection on Hybrid Nanofluid Flow over an Inclined Extending Plate with Porous Effects
https://jhmtr.semnan.ac.ir/article_8626.html
This study investigates nonlinear mixed convective hybrid nanofluid flow over a spongy and inclined stretching surface. There are numerous applications of nonlinear convection especially it is pivotal in predicting weather patterns accurately and optimizing heat transfer for efficient electronic and industrial cooling systems. The flow is also influenced by porous behavior of the plate and presence of the microorganisms. Main emphasis is given to analyze the influence of thermal and mass Grashof numbers for its nonlinear nature upon flow system. The equations that administered the flow system are converted to dimensionless notations by using suitable variables. Homotopy analysis approach has used for solution of modeled equations. It has perceived in this work that, fluid velocity declines with upsurge in inertial factor, permeability parameter, volume fraction and magnetic factor. Thermal profiles upsurge with growth in Brownian, thermophoresis factors, Eckert number and weaken with Prandtl number. Concentration of fluid increases with progression in thermophoresis factor and drops with greater values of Schmidt number and Brownian factor. Density number has declined with growth in Peclet, bioconvective Lewis numbers and inclination angle. Over the range &lt;=Nb, Nt, Ec&lt;= the heat transfer rate jumps from 1.8057 to 2.1332 in case of Nb , from 1.8057 to 2.1968 in case of Nt and it jumps from 1.8057 2.3177 in case of Ec that shows maximum heat transfer rate in case of variations in Eckert number.Effect of Activation Energy on Magnetized Couple Stress Fluid over an Inclined Stretching Permeable Cylinder
https://jhmtr.semnan.ac.ir/article_8627.html
Activation energy is of considerable significance in diverse applications such as chemical kinetics, catalyst development, enzymes, semiconductors and systems sensitive to temperature, such as chemical reactors and engines. The objective of this research is to investigate the influence of activation energy on a magnetized couple stress fluid over an inclined stretching permeable cylinder in a non-Darcy porous medium. The effects of cross-diffusion and stratified mixed convection are also considered in fluid model. The boundary layer equations, which describe the flow, have been converted into dimensionless form through suitable transformable variables. Subsequently, these transformed equations are solved using fourth order Runge-Kutta mechanism along with shooting technique. The outcomes comprises visual depictions and comprehensive explanations demonstrating the influence of relevant variables on thermal, concentration and velocity fields. Observations reveal that the concentration profile is directly influenced by the Forchheimer number and activation energy parameter, whereas both temperature and concentration fields decrease with elevated thermal and solutal stratification parameters. Additionally, numerical outcomes for the skin-friction coefficient, Nusselt number and Sherwood number are presented in tabular form.Improving Engine Cooling Performance through Slotted Fin Design: A Steady-State Thermal Analysis Study
https://jhmtr.semnan.ac.ir/article_8632.html
The engine fin is an essential component that significantly impacts the cooling system&#039;s effectiveness and overall performance. Although the engine fin is used to dissipate heat generated, an attempt to enhance the effective surface area for the fin needs to be addressed. This research aims to enhance the effectiveness of engine cooling systems through the fin design, which may involve incorporating slots to expand the surface area and improve overall efficiency. The analysis involved two fin geometries, rectangular and cylindrical fins, made of Aluminum 1100 material. The design models are created using the computer-aided design software PTC CREO Parametric 6.0., and steady state thermal analysis and modal analysis were performed using ANSYS 2023 R1. The steady-state thermal analysis results indicate that the slotted cylindrical fin design demonstrated the highest heat transfer rate compared to the conventional fin design. The results from this study are expected to provide valuable performance in improving heat dissipation.Chemical Reactions on MHD Couple Stress Fluids towards Stretchable Inclined Cylinder.
https://jhmtr.semnan.ac.ir/article_8633.html
This study focuses on exploring the influence of homogeneous and heterogeneous chemical reactions on a couple stress fluids surrounding a permeable inclined stretching cylinder. The impact of a uniform magnetic field and porous media is also considered in the fluid model. It is assumed that the diffusion coefficients for chemical species A and B are of similar magnitudes and that the heat released during the chemical reaction is negligible. The governing partial differential equations (PDEs) are evolved and transformed into ordinary differential equations (ODEs) by using adequate similarity alterations. These ODEs are subsequently solved using the shooting technique in conjunction with the fourth-order Runge-Kutta method, implemented through MATLAB software. Results are presented through graphs and tables depicting the velocity, temperature, and concentration fields. Furthermore, numerical findings for the skin friction coefficient and Nusselt number are discussed. The concentration field experiences a decline as homogeneous-heterogeneous reactions intensify, attributable to the heightened dispersion of concentrations across the system, resulting in a more intricate distribution pattern.Experimental evaluation of the hybrid-bifacial cooling of a PV panel in an arid weather using channel heat exchanger and impingement flow nozzles
https://jhmtr.semnan.ac.ir/article_8641.html
In the current global energy conditions, with a growing concern for carbon emissions, the adoption of renewable energy sources is on the rise. Solar panels have emerged as a highly promising method for electrical-thermal energy generation and are widely employed in both industrial and residential settings. This study focuses on evaluating the impact of cooling on PV panel systems and its effect on electrical and thermal efficiency. A hybrid method utilizing both air and water on the PV panels is examined, and the results are compared to those of a reference panel. The experiments are conducted in Kashan, Iran, located at coordinates 34&deg;06&#039; N 51&deg;23&#039; E, in July 2023. By implementing the proposed cooling method, significant improvements in the maximum daily electrical, thermal, and total efficiencies can be achieved, surpassing 20%, 30%, and 50% respectively. The findings indicate that cooling with water proves more advantageous in terms of thermal energy generation, although it slightly decreases the coefficient of energy due to the additional energy required for water pumping compared to air blowing. Furthermore, the study reveals that bifacial cooling, employing jets to cool both sides of the PV panel, significantly enhances thermal and electrical efficiency, particularly in hot and dry weather conditions.Assessing the Effect of Sediment Deposits on the Performance of Residential Heating Radiators: An Experimental Investigation
https://jhmtr.semnan.ac.ir/article_8642.html
In this investigation, we present pioneering findings on the detrimental effects of sediment deposits on the thermal and hydraulic performance of residential heating radiators, through a novel experimental framework. Our approach, through the systematic introduction of particulate matter into the water circuit, quantifies the real-world impact of sediment accumulation. This methodology fills a significant void in literature with validated experimental data and establishes a method for assessing radiator performance under fouled conditions, adhering to ISO 3148 standards. The experimental results underscore a significant efficiency downturn: sediment presence increased pressure drop by up to 10.5% and reduced surface temperature by as much as 13%. Notably, heat output initially saw a slight increase, only to decrease by up to 28.5% over time, with these effects amplifying at higher inlet temperatures. These findings underscore the urgent need for tailored maintenance strategies to combat sediment-related degradation, offering invaluable insights for the design, maintenance, and optimization of heating systems, beneficial to both industry stakeholders and end-users.