JOURNAL OF HEAT AND MASS TRANSFER RESEARCH
Year:2024 | Volume:11 | Issue:2|Papers Count:12

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.

In this study, we examined the effects of diffusive heating, Hall current, and radiation absorption on the magnetohydrodynamic (MHD) mixed convective flow of a viscous, incompressible, electrically conducting Casson fluid along an inclined porous plate. This flow occurs in the presence of thermal radiation and chemical reactions. Using a perturbation approach, we derived solutions for the non-dimensional equations. Within the boundary layer, we analyzed how various non-dimensional factors influence the velocities, temperatures, and concentrations of the fluid. Additionally, computational analyses were conducted to explore the impact of relevant factors on the shear stress rate and the rates of heat and mass transfer. As the Hall and radiation absorption parameters increase, the velocity and temperature of the fluid also increase. Conversely, when the diffusive heating parameters increase, the fluid velocity and temperature exhibit opposite trends. Additionally, as thermal radiation increases, the temperature tends to decrease. Increasing the permeability factor reduces the skin friction coefficient, but increasing the thermal and mass Grashof numbers has the opposite effect. A higher Prandtl number leads to an increase in the Nusselt number. Lastly, the Sherwood number decreases as the amount of absorbed radiation increases.

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 were conducted in Kashan, Iran, located at coordinates 34°06' N 51°23' 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.

The engine fin is an essential component that significantly impacts the cooling system'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.

In this paper, the effect of buoyancy force on the temperature change of the phase change materials which has been encapsulated in two pipes in a channel, is simulated numerically using Boussinesq approximation. An application of this topic is in air-conditioning, which uses ice in the pipes as PCM for coolant and the aim is calculating the PCM discharging time. The unsteady governing equations including continuity, momentum and energy in the fluid flow and phase change material for laminar flow regime, have been solved by the well-known SIMPLE method. The needed time to phase change material reach the inlet temperature of the fluid flow has been obtained and compared to the results of the lumped temperature assumption. The results show that the discharging time is 4,000 for Gr=5,000 and 70,000 for Gr=200,000. It is 25,000 for kr=0.5 and 34,000 for kr=1.5. Also, it is 11,000 for Cpr=103 and 28,000 for Cpr=104. Finally, it has been concluded that due to the fine mixing of PCM because of buoyancy force, the results are so closed to the results of the lumped temperature assumption for PCM.

The Runge-Kutta method combined with the shooting technique is used to solve the numerical results of the theoretical model for the electrically conducting micropolar fluid through two parallel plates in the presence of a heat source or sink and first-order chemical reactions in the flow heat and mass transfer equations. This work encourages us to use the Homotopy analysis approach to develop semi-analytical solutions for dimensionless velocity, dimensionless microrotation, dimensionless temperature, and dimensionless concentration. The answers are used to produce the analytical approximations of the physical characteristics, such as the skin friction factor, Nusselt number, and Sherwood number. Additionally, tabular values for the physical parameters, such as the skin friction factor, Nusselt number, and Sherwood number, are provided. Graphs are also used to illustrate how characterizing parameters behave. We found a high correlation between the semi-analytical and numerical findings of this study when we compared our semi-analytical works with the earlier studies. Compared to the prior method, this approach to the model is simpler, and it may be readily extended to find semi-analytical solutions to other MHD and EMHD fluid flow issues in the physical sciences and engineering.

The main purpose of this article is to provide a critical analysis of published research on these heat transfer surfaces. Important experimental methods and numerical procedures are explained, and many types of vortex generators are described. The phenomenon of flow attributed to vortex generators mounted, connected, pierced, or placed inside surfaces that transmit heat was also examined. In addition, recommendations for applying vortex generator (VGs) technology to improve air-side heat transfer are provided, as well as information on the thermal performance of newly proposed VG heat transfer surfaces. The performance of air-side heating surfaces can often be significantly improved through the use of vortex generators. However, their effectiveness can be greatly affected by many factors, including fluid flow rate, pipe geometry (diameter, shape, pitch, in-line or staggered configuration), fin type, and geometry of the vortex generator (height, length, shape, angle of attack, etc.). Circular fin-tube heat exchangers generally perform worse in terms of thermal-hydraulic efficiency than flat-tube-fin and oval-tube-fin heat-exchanging devices, and more recently, suggested vortex generators. Most current heat exchanger optimization methods focus only on thermal-hydraulic performance.

According to the severe global warming and increasing demand for freshwater worldwide, different sustainable solutions for supplying water have been considered. Solar desalination is a promising method to convert saline and brackish water resources to distilled water. Solar stills are one of the simple solar desalination methods and have low costs compared to similar solar-powered methods. However, the low distillation capacity and vast distillation area requirements present a challenge for further development of this technique. The application of novel materials that enhance the heat and mass transfer rate in solar stills can be a suitable approach for performance enhancement. In the current review, the most recent advancements according to the novel materials that enhance the distillation rate of the solar stills will be discussed and reviewed concisely. The investigated novel materials in the current review includes different types of natural materials that have been proposed by researchers. Finally, concluding points and future study suggestions will be presented to the researchers. The current review provides the researchers with the most recent advances in the integration of novel materials with conventional solar stills for heat and mass transfer enhancement.

The moving blades in a circular path have many industrial applications, in more modern turbo machines, such as jet engine compressors, the flow conditions are completely incompressible. On the other hand, the 2D study of the flow around these blades, which shows many characteristics of the flow and simplifies the matter, is usually unavoidable. In this regard, the simulation methods LES and RANS, in order to simulate the flow around the NACA0012 airfoil, different modes of fixed and rotating airfoil with different angles of attack and 3D impeller mode have been implemented. The lift coefficient, drag coefficient, torque, and mass flow of S-A, RNG, SST, RSM, and LES models are compared. The net mass rate will be different in the above methods. In RANS methods, the value of the net mass rate is negative; that is, loss of mass rate occurs, but in the LES method, the value of the net mass rate is positive. The highest net mass rate is related to the LES method, and in RANS models, the reverse flow is observed. According to the results, the effects of body forces in energy equation or thermal dissipation under circular motion are important in comparison with experimental data. A comparison of fixed and rotating airfoil lift coefficient diagrams with the LES model shows that the lift coefficient in a fixed airfoil is two times relative to a rotating airfoil. Also, the torque on the impeller, compared with different turbulent models, varies from  88381 to 172116.

Photovoltaic/thermal (PV/T) is a solution for solar energy conversion devices to increase their efficiency. One of the challenges of PV/T is maintaining the temperature at optimal working conditions. Various studies have been conducted to improve PV/T performance, one of which is through the design of thermal collectors on PV/T. In this study, Computational Fluid Dynamics (CFD) simulations were conducted using four different types of channels: circular, hexagonal, semi-circular, and square. The channels were made with the same tube cross-sectional area and mass flow rate of 0.0016 m2 and 0.0096 kg/s, respectively. The simulation results show that the circular channel numerically gives the lowest PV cell temperature, 317.95 K, with an electrical efficiency of 14.70% and a thermal efficiency of 44.18%. This is because the water velocity in the circular channel can be faster than the other channels.  The circular channel has a thinner boundary layer, so the velocity is maximized, and the heat transfer rate increases.

Mixed convection within a ventilated square cavity with a baffle at the bottom wall and heating elements at the side walls has been analyzed. The inlet opening has been set at the bottom of the left wall, while the exit opening is put at the bottom of the right wall. Considering air (Pr = 0.71), dimensionless and steady form of mass, momentum and energy equations are solved by implementing proper boundary conditions with the help of the Galerkin method-based finite element scheme. Maintaining pure mixed convection (Ri = 1), baffle length is changed from 0 to 0.95L, and heater location is varied from 0.1L to 0.7L across Re = 10 to 1000. Qualitative changes of the domain are observed with the help of streamlining and isothermal plots. For quantitative comparison, average temperature, Nusselt number, pressure drop and performance index have been considered. The counteracting effects of the increase in Nusselt number and pressure drop are accounted for together with the help of the performance index, which yielded the most economical and optimum baffle height and heater location. The final evaluation shows that the optimum length of the baffle and the position of the heaters can perform most effectively in the range of Re = 20 – 400.

The paper studies the occurrence of kinetic phase transitions in porous media with thermodynamic phase transitions, which affect filtration flow through permeability or viscosity: in the simplest case, permeability is a step function of local temperature. The dependence of phase boundary under stationary heating and cooling processes has features that are concerned with the non-linearity of Stefan condition. These features result in limited stability of filtration flow. Calculations show that there exist critical temperatures in the vicinity of those stationary filtration flow becomes impossible due to the thermal interaction of phase transition and advection processes. The solutions form two branches; one of those is stable, and the other is unstable; the connection between the branches is a critical point. Several different setups are considered: flat and cylindrical channels, melting of the porous carcass, and crystallization of flowing liquid. Critical conditions for these cases are obtained in the form of approximate formulas that can be used to calculate heat transfer in thermal engineering units, including heat accumulators.