Fin Surface Research Articles

Enhancement of the cooling by mixed convection of a CPU using a rotating heat sink: Numerical study

The technological progress made in recent years has driven electronic apparatus to become not only more efficient and work faster but also considerably smaller in weight and size. Furthermore, the power densities of these devices have known an impressive increase. However, the challenge for the electronic industry is the lifetime device improvement by controlling the adequate removal of their excess heat. The use of more efficient cooling systems is, therefore, crucial in order to ensure durable device functionality. In this work, computational simulation was carried out to study the enhancement cooling process mixed convection of an electronic component (CPU mounted in a motherboard) using a new design of a heat exchanger by combining the heat sink (the finned surface) and the fan in a single component, this allows more heat to be moved faster and with less energy than a conventional cooler. Three radial heat sinks (HS18, HS24 and HS36) are considered depending on circumferential fin numbers ( n = 18, 24 and 36). The effect of Reynolds number, heat flux and rotational velocity is investigated, and the optimum comprehensive performance was determined. The results reveal the cooling performance turns out to be better for heat sink with n = 36. The rotational velocity operates a significant effect on the temperature field only for values below than 900 rpm. We also found that the improvement in the Nusselt number and its percentage enhancement is intensified with increased rotational velocity and decreased with heat flux. A bigger Ω and ReΩ meant a more obvious heat transfer enhancement (NuΩ/Nu0) in the case of smaller Q, but (NuΩ/Nu0) decreased with increasing Q.

Research on anti-frosting potential of air source heat pump evaporator in hot-summer and cold-winter zone

In this paper, the performance curve of a heat pump evaporator under critical frosting conditions was fitted. The functional relationship between the refrigerant evaporation temperature and the absolute air humidity ratio was obtained. In addition, the transfer unit model of the air source heat pump (ASHP) evaporator was established. The inlet air temperature, humidity ratio, velocity, fin pitch, and row number of evaporators were considered as input parameters. The anti-frosting potential of the heat transfer unit was simulated under critical frosting conditions. The results showed that, based on the heating potential of moist air unit mass under critical frosting conditions, the heating potential is at its minimum at an air humidity ratio of 3.39 g/kga. The maximum difference between the minimum temperature on the fin surface and the refrigerant evaporation temperature was found to be only 0.06 °C. The study findings highlighted that controlling the refrigerant evaporation temperature above the critical frosting temperature is an important method to prevent the evaporator from frosting. Under a low temperature environment, with the increase in the fin pitch and the inlet air velocity, the anti-frosting regulation performance of the two tube rows evaporator was found to improve compared to the single tube case. The aim behind increasing the inlet air velocity is to increase the heat transfer temperature difference between the inlet air and the critical frosting conditions. After optimizing the evaporator’s structural and operational parameters, the evaporator’s fin pitch is set according to the ambient air temperature. This was successful in meeting the requirement that the evaporator does not frost most of the time. Moreover, by adjusting the inlet air velocity, the evaporator will not frost at other times. In hot-summer and cold-winter zone, the operation of the ASHP evaporator with no frost can be achieved.

Thermal distribution analysis of rectangular fin considering multiboiling heat transfer modes

AbstractIn this investigation, a numerical method is used to compute the thermal distribution analysis of a rectangular fin with surface emissivity and internal heat generation. Here, the thermal conductivity, heat generation, emissivity at the surface, and coefficient of heat transfer depend on temperature linearly. The role of four distinct multiboiling heat transfer modes such as laminar film boiling (condensation), laminar convection, turbulent convection, and nucleate boiling are discussed in detail and the corresponding outcomes are displayed graphically. Isolated (insulated) and convective tip boundary conditions for the fin tip are employed in this study. The solution is obtained using shooting technique involving Runge Kutta Fehlberg method. It is emphasized that the thermal distribution shows a diminishing trend for the convective tip condition compared to the insulated tip. In addition to this, it is illustrated that laminar film boiling and laminar convection are two effective modes of heat transfer in comparison with turbulent convection and nucleate boiling for a finned surface in boiling liquids. The study on fin efficiency shows that fin efficiency increases with the increase in internal heat generation number.

Efficiency and cost optimization of offset Plate-Fin heat exchanger

Plate-fin heat exchangers, are also called compact heat exchangers. Due to their small size, compared to other heat exchangers they are user friendly which allow greater flexibility in plant architecture. The heat exchanger is made by stacking up fin surfaces which are separated by a sheet. With the increase in the area of the offset fin structure, the heat transfer also increases. But on the other end total annual cost and entropy generation is also affected by geometric variables. In the present work, seven geometric variables of the heat exchanger are investigated for the optimization of effectiveness, total annual cost and entropy generation minimization. Genetic algorithm is implemented for the optimization. Finally, parametric analysis is also performed to investigate the effect of design variables on the optimized results.

New Host Record for Nerocila fluviatilis (Crustacea, Isopoda) and First Data on Its Abundance and Size, with Updated Geographic Distribution and Hosts

Nerocila fluviatilis Schiœdte and Meinert 1881 (Isopoda, Cymothoidea, Cymothoidae) is reported for the first time for a new host order of host, Mugil liza Valenciennes, 1836 (Actinopterygii, Mugiliformes, Mugilidae). Fish were collected in a coastal Atlantic lagoon in eastern Uruguay, Laguna de Rocha, and parasites were consistently restricted to the surface of caudal, anal, and paired fins. All stages of N. fluviatilis were found. Data on prevalence (6%), mean intensity of infestation (5.2), and size are provided for the first time for all stages of N. fluviatilis. An updated account of the geographic distribution and hosts of the isopod is given.

Significance of non-Fourier heat conduction in the thermal analysis of a wet semi-spherical fin with internal heat generation

The transient temperature distribution of a wet semi-spherical porous fin with convection, internal heat generation, and radiation is researched using a non-Fourier heat conduction (NFHC) model. A mathematical model for transient heat transfer in a dehumidifying environment is developed from the non-Fourier law and the corresponding governing equation is formulated. This equation is subjected to nondimensionalization using suitable dimensionless terms and is further solved by employing the finite difference method (FDM). A substantial deviation in thermal response by considering non-Fourier law under unsteady heat transmission has been analyzed graphically with the influence of various nondimensional parameters on the dry and wetted fins surface. The examination reveals the notable difference in temperature variation between the dry and wetted fins surfaces. Some important key results of the research analysis include that the transient thermal distribution through the fin decrease as the magnitude of the convective, wet porous and radiation-conduction parameters develop. For higher generating numbers, thermal distribution will be higher. The temperature in the hyperbolic model increases after some time in the existence of relaxation time and the temperature in a non-Fourier model flow in the form of a thermal wave.

A novel temperature prediction method without using energy equation based on physics-informed neural network (PINN): A case study on plate- circular/square pin-fin heat sinks

This study introduces a new physics-informed neural networks (PINN)-based prediction method to determine the temperature pattern of fluid and fins when flow passes over plate-circular/ plate-square pin fin heat sinks (PCPFHS / PSPFHS). The proposed method is based on calculating the velocity pattern on the fins' surface. For this target, a training algorithm based on the feed-forward neural network (FNN) (110 layers of learnable weights and 16 neurons in each layer), a nonlinear activation function (rectified linear unit, "ReLU") and the Adam method for optimization is used. The training algorithm is fed by transient large eddy simulation (LES) results at every 0.01 s time step for the total physical time of 100 s. According to the input parameter type, the training:validation ratio is varied between 70:30 and 90:10 in order to keep the coefficient of determination (R2) at its maximum. The automatic differentiation employed the forward accumulation approach to reduce calculation costs, while the transient training matrix fed the neural network. The adaptive gradient (AdaGrad) method is also to improve convergence process and its speed up. Based on the developed calculation tools, the temperature pattern for the flow and over the fins are calculated according to the energy balance on the fin surface and the transient pattern of velocity predicted by PINN. After careful validation with experimental data and sensitivity analysis on the number of neurons and layers, the thermal behavior of PCPFHS and PSPFHS are determined using the conduction heat transfer equation inside the fins via the finite element method and by assuming a heat balance between the fins' surface and airflow. As a result of the proposed method, it is possible to reduce the number of equations in the calculation process of these parameters. According to the results, it is found that PSPFHS has an average Nusselt number which is 9.63% greater than the one in PCPFHS. However, compared to PCPFHS, PSPFHS shows a -17.78% reduced vorticity ratio at Re = 4,865. The results indicated that, for long calculation times (for instance, at 2,000 s physical time), the PINN method reduces calculation costs up to 35% compared to the technique that directly solves the energy conservation in the whole domain.

Numerical analysis of heat transfer from perforated fins of an induction motor housing

The major goal of this research article is to demonstrate how perforation on the fin surface of an induction motor’s housing improves cooling performance. Heat transfer study was also conducted between traditional fins and the suggested perforated fins housing. An Induction Motor (IM) overheats as a result of continuous operation, raising its temperature, lowering its performance and shortening its lifespan. The innovative designs and development of fins are necessary for effective cooling and enhancing the thermal performance of IM. In the present work, the thermal analysis of induction motor is carried out by means of providing the perforations on existing fins and varying perforation size from 4 mm to 10 mm diameters and number of perforation from 20 to 11, on fins and observed the steady state heat transfer and temperature variation. In this regard, the half part of IM is modelled because of symmetry and steady state thermal analysis is carried out for un-finned, solid fins and perforated fins using ANSYS software. Results show that, more reduction in temperature on the surface of IM is observed in case of perforated fins having 11 perforations of 10 mm diameter, as compared to the other cases.

Investigative Study of Solidification and Melting of Stearic Acid in Triplex Pipe with Perforated Fin Surface

The energy storage capacity of latent heat thermal energy storage systems is high therefore these systems are efficient among all other thermal heat storage. This study experimentally investigates the charging and solidification of stearic acid (C18H36O2) in the finned triplex pipe heat exchanger with holes on the fin surface. The melting and discharging of stearic acid are carried out at steady inlet heat transfer fluid (HTF) i.e., water temperature. This study also investigates the result of the change in HTF flow rate on solidification and melting of phase change material. Finally, the study focuses on the comparison of average effectiveness for finned triplex tube heat exchanger and finned triplex tube with cylindrical holes on fin surface with rates of 0.33 and 0.43 Kg/s. The results showed that the average effectiveness with a finned triplex tube with a perforated fin surface is 4% more than that of a finned triplex tube at 0.33 Kg/s whereas it is 5 % more at 0.43 Kg/s during the charging process. On the other side during discharging process average effectiveness is 14 % more at 0.33 Kg/s and 11 % at 0.43 Kg/s.

Condensation on a Vertical Plate With Sinusoidal Microfins

Abstract A theoretically based, approximate solution for condensation on horizontal, microfinned tubes has been used as a basis to obtain a relation between heat flux and vapor-surface temperature difference for condensation on a vertical plate with sinusoidal microfins. The earlier result was in excellent agreement with experimental data with regard to magnitudes of the heat-transfer coefficient, dependence on fin and tube dimensions, and for a range of fluids with widely different properties. The new equation for condensation on a vertical plate with sinusoidal microfins takes account of the vertical gravity force and the lateral surface tension-induced pressure gradient over the curved fin surface. The equation reduces to the Nusselt result when fin height is zero and to simple area enhancement of the Nusselt result when surface tension is set to zero. Comparisons are made with experimental data for condensation of nitrogen on a vertical surface with sinusoidal microfins.

Heat Transfer Intensification by Means of Convex-Strip Around Tube in Fin and Tube Heat Exchanger with Field Synergy Principle

Fin and tube is a compact heat exchanger, have been widely used in various engineering fields such as heating, ventilation, air conditioning, and refrigeration systems. An example, indoor and outdoor air-conditioning, the air is used as one of the heat exchanger media. However, over 90% of the total thermal resistance from air to liquid lies on the airside. Therefore, the reduction of thermal resistance should be made to increase heat transfer. This study is intended to investigate the effect of enhancing convex-strip surface to heat transfer and friction characteristic on the heat exchanger. Three-dimensional modeling of the convex fin and the plain fin was conducted on a constant tube temperature of 106℃. Tube with the configuration of the six staggered strands on the odd tube and five rows on the even tube is determined. The velocity variation in the fin gap is assessed under the Reynolds number range between 3,438 to 15,926. The enhancement of four convex-strips around the tube on the fin surface can generate the value of the field synergy angle on fluid flow. The simulation results also show that the improvement of convection heat transfer coefficient value in convex-strip fin with staggered configuration is 15.39% higher than plain-fin.

Performance analysis of a longitudinal fin under the influence of magnetic field using differential transform method with Pade approximant

AbstractThe temperature distribution in a longitudinal fin with magnetic field due to conductive‐convective‐radiative heat transfer is debriefed in this research article. Thermal properties of the fin material, such as thermal conductivity and heat transfer coefficient, have been considered to vary non‐linearly with local temperature whereas surface emissivity has been taken to be constant. The main governing equation of the current model is developed with the aid of Fourier's law of heat conduction, exponentially temperature‐dependent thermal conductivity, Maxwell expression for the effect of the magnetic field, and power‐law temperature‐dependent heat transfer coefficient. This equation is converted into a non‐dimensional form using dimensionless variables and then traced out numerically with the assist of Runge‐Kutta Fehlberg's fourth‐fifth method. Also, the transformed nonlinear energy equation is solved using a DTM‐Pade approximant, yielding an approximate closed‐form solution. The findings of the analytical and numerical investigation are depicted graphically. The outcomes have divulged that the convective and radiative parameters significantly decrease the temperature distribution and improve convective cooling from the fin surface. The rise in the Hartmann number is responsible for the decreasing of the temperature distribution and it aids in accelerating heat transfer.

Numerical Simulations of the Flow Dynamics in a Tube with Inclined Fins Using Open-Source Software

Finned tubes increase the convective heat transfer in heat exchangers, reducing the total energy consumption of integrated industrial processes. Due to its stability and robustness, Computational Fluid Dynamics (CFD) commercial software is generally utilized for analyzing complex systems; however, its licensing is expensive. Nowadays, open-source software is a viable substitute for proprietary software. This work presents a CFD analysis of the hydrodynamics of a finned tube using the OpenFOAM and SALOME Meca platforms. The results are compared with experimental data and CFD using the commercial software Fluent, both previously reported in the open literature. This work studies the fluid flow pattern around a tube with six 45-degree-angled fins, and the working fluid, air, is considered as an incompressible fluid. Special attention is paid to calculating the pressure coefficient distribution for the internal and external surfaces of the inclined fins. Open-source platforms allow researchers to visualize how the airflow interacts with the cylinder and the fin surfaces to form a fluid structure, formerly known as a horseshoe vortex system. The findings of the analysis of flow dynamics in the channel between inclined fins and in the wake help explain the results obtained in experimental tests and are relevant for the configuration of a bank of tubes with inclined fins.

Motion mechanism and thrust characteristics of amphibious robots with long fin fluctuation for propulsion on hard level ground

This paper presents the principle of motion, mechanical modeling and key characteristics of the propulsive force of a new flexible-fin traveling wave propulsion mechanism used in an amphibious robot. Firstly, the form of motion and the basic propulsion principle of traveling wave propulsion of flexible fins on the ground are described. During fluctuation of the flexible fins, the relative motion between the outermost contact line on the fin surface and the ground generates the propulsive force of forward motion and the lateral force along the fin surface. Based on the laws of flexible-fin fluctuation kinematics and the basic principles of friction mechanics, the propulsion mechanics model of flexible fins during traveling wave propulsion on the ground is established. By numerically solving the propulsive force equation, the relationship between the propulsive force of the flexible fin and the motion parameters of the fin surface can be obtained. Numerical calculations combined with the results of experimental tests reveal that the flexible-fin propulsive force shows periodic variations within one fluctuation period of the fin surface, and the variation period is related to the number of waves present on the fin surface. The wavenumber on the fin surface has a large impact on the fluctuation amplitude of the propulsive force. In the range of 1.6–1.9 waves on the fin surface, the average propulsive force is the most ideal, while in the range of fin-surface inclinations less than 50° and fluctuation amplitudes greater than 30°, the propulsive force of the flexible fin is the ideal parameter range. This research provides theoretical support for the design of a flexible-fin traveling wave propulsion mechanism.

Rheological Behavior of Air in the Two-Pass Solar Collector

This study pivoted on the flow behavior of air streams across solar air collectors provided with wooden baffles under the absorber plates. The two-pass system was used for both flat and finned surfaces. The von Kármán momentum integral and Blasius equations were solved with the help of PDPE and ODE45 techniques. The solution was assumed to be a part of the initial value problem (IVP). The energy analysis of both solar air collectors was carried out using the Hottel–Whillier–Bliss equation (HWB) equation. The Sankey diagram was used for energy distribution across the solar collectors. The gray box modeling approach was adopted to comprehend the airflow behavior across the channel. The objective of this study is to examine the intrinsic behavior of the proposed design. The displacement of boundary to compensate for the momentum of air stream (θt) decreased by 31.25%–62.50% with an increase in mass flow rate (m)˙of 24.69%–49.38% for the flat plate collector (FPC). Similarly, the shear stress posed by the absorber plate (τw) dropped by 15.89%–37.20% with the augmentation of the mass flow rate. The momentum thickness for the flat plate with triangular fin (FPTF) increased relatively by 31.25%, compared to FPC at 8.10 g·s−1. The estimated value of collector efficiency (ηI) FPTF soared up by 4%–11.51% when it was juxtaposed against the corresponding values derived for FPC. The wall shear stress near the absorber plate followed that of a second-order Gaussian model. It was noticed in this study that the addition of the fin slowed down the shear effect and the momentum defect of airstream at the same mass flow rate.

Airside Thermal Performance of Louvered Fin Flat-Tube Heat Exchangers with Different Redirection Louvers

The performance of heat exchangers is severely limited by airside thermal resistance. The effect of redirection louvers (RLs) on the airside thermal performance of a compact flat-tube louvered fin heat exchanger was investigated. A steady-state 3D numerical analysis was conducted for different fin configurations by varying the number of RLs (NRL = 1, 2, 3, and 5). Conjugate heat transfer analysis was performed at the low Re (50–450) for domestic and transport air-conditioning applications. Geometric parameters such as louver pitch, louver angle, fin pitch, and flow depth were set as 1.7 mm, 27°, 1.2 mm, and 20 mm, respectively. The effective heat transfer fin surface areas of different fin configurations were also kept identical for a comparative analysis. The influence of the RLs on the airside thermal–hydraulic performance was analysed by exploring the local and average Nusselt numbers, pressure drop, Colburn j factor, friction factor f, performance evaluation criteria (PEC), and flow efficiency of different fin configurations. The numerical results revealed that the asymmetric fin configuration with two RLs (NRL = 2) showed the best heat transfer performance for the entire Re range. It resulted in a 33% higher average Nusselt number, causing a 24% higher pressure drop compared to NRL=5. At low flow velocities (Re < 75), NRL = 3 showed better PEC; however, at high flow velocities (Re > 75), NRL = 1 outperformed other fin configurations. Finally, it was noted that increasing the number of RLs reduced the amplitude of the wavy-shaped flow formed between the neighbouring louvered fin, consequently deteriorating the flow efficiency.

Experimental and numerical investigation on frosting of finned-tube heat exchanger considering droplet impingement

Air source heat pumps are prone to frosting under low-temperature, and high-humidity conditions. Frosting in finned-tube heat exchangers increases their heat transfer and airflow resistances. Moreover, it leads to reductions in the evaporation and condensation temperatures of the unit, increased energy consumption, working performance deterioration, and even shutdown. Therefore, it is necessary to simulate the frost formation process, in order to provide a reference for frost-prevention design of finned-tube heat exchangers in cold, high- humidity areas. However, fin microchannel frosting is a complex process that involves heat and mass transfer. It is difficult to describe the frost layer formation process completely. This is, especially true for droplet formation during nucleation. This paper describes the mass transfer process that occurs during nucleation via a droplet impingement model and uses the enthalpy porosity method to solve the solidification problem. Air-source heat pump frosting tests performed in the enthalpy difference laboratory verify the numerical methods. It is determined that the model in this paper can simulate the frost growth process more comprehensively and accurately than a mathematical model that does not consider droplet formation. Then, the effects of the mass transfer rate, air temperature, humidity, inlet velocity, and fin surface temperature on the finned-tube heat exchanger frosting process are described. Frost growth is related positively to the rate at which water vapor impacts the fin surface. The frost is thickest when the moist air temperature range is between 1 °C and 3 °C. Moreover, the frost density varies little when the wet air temperature is above 0 °C. The variation of frost density and frost thickness shows an opposite trend under the wind speed factor.

Experimental measurements of thermal–hydraulic performance of aluminum-foam water-to-air heat exchangers for a HVAC application

In this paper, thermal and hydraulic performance of in-house made prototypes of water-to-air heat exchangers are experimentally investigated and compared to those of a compact heat exchanger, used in a commercial fan-coil. The prototypes are built replacing the fins with aluminum foam surfaces characterized by a large porosity, higher than 96%. In order to evaluate the performance of the foam-based heat exchangers in a real-scale application, the geometry of the prototypes was based on that of the reference model and, moreover, experimental tests were performed placing the heat exchangers within the commercial cabinet, under the same fan power. Different bonding techniques were also tested to couple metal foams to copper tubes. Results show that similar hydraulic performance can be obtained with the foam-based heat exchangers, if compared to the commercial device. However, the large foam porosity accounts for a lower value of the surface-to-volume ratio of the aluminum foam media, thus yielding a strong penalty, up to 60%, of the heat transfer rate with respect to that of the conventional finned surface. Moreover, experimental results highlight how the bonding technique and the foam packaging have a strong influence on the contact thermal resistance and, consequently, on the overall heat transfer coefficient. Epoxy bonding allows to increase the thermal performance of the heat exchanger, if compared to press fitting, between 15% and 110%. In conclusion, results presented in this paper suggest that metal foams can be considered as a potential alternative to fins in water-to-air heat exchangers only if the foam-tube bonding is obtained by welding or brazing.

Performance study of spiral finned tubes on heat transfer and wake flow structure

Heat exchangers have been widely utilised in many industrial and residential sectors. In this paper, the turbulent flow of a heat exchanger with spiral finned tubes (SFT) is numerically simulated using a large eddy simulation (LES), which outperforms existing two-equation solvers in finding the details of flow structure around bluff bodies. This work aims to find the coherent structures around spiral fins using the Q-criteria and to obtain flow topologies playing an important role to improve the heat transfer of spiral finned tubes. The SFT shows three primary flow regions representing various vortex structures. The study also observes how turbulent flow changes with different Reynolds numbers and how turbulent coherent structure changes with varying Nu numbers on the fin surface. The result shows that the correlation coefficient reaches 0.81 by examining the correlation of the Nu number and the Q values over the time series at each sampling point. In addition, the modal information of temperature variation is estimated using dynamic mode decomposition analysis. The dynamic mode of temperature shows highly consistent with the Q criterion distribution.

Evaluation of flow and thermal characteristics for flow through a wall-confined array of pin-fins using large-eddy simulation

In the present work, the flow and thermal characteristics for flow through a wall-confined array of pin-fins are studied using large-eddy simulation (LES). The geometry considered here resembles the trailing-edge portion of a early-stage gas-turbine blade. The wall-confined array of low-aspect ratio cylindrical fins are arranged in a staggered manner, and the direction of the coolant is perpendicular to the axis of the fins. The analysis is performed for a fixed spacing between the fins and for a Reynolds number of 5900. In view of the actual running conditions, large temperature differences, ranging from 25∘C to 300∘C, are considered between the walls and the coolant. Together with this, the effect of higher pressure, ranging from 5 bar to 10 bar, on the cooling performance is analyzed. The numerical solver used is thoroughly validated with the reference experimental and LES data available in the literature. A detailed investigation of the mechanism for heating of the fluid, transport, and diffusion of the heat flux is presented by analyzing Nusselt number, turbulent heat fluxes and vorticity contours. It is observed that, an increase in Nusselt number is due to encapsulation of small-scale vortices around the pin-fin surfaces and a decrease in Nusselt number downstream is due to the lower frequency of high-energy vortex. The localized Nusselt number is higher over the fin surfaces compared to end-walls, and the base vortex is responsible for higher energy extraction at the junction of the pin-fin and the end-walls and its effect increases downstream. The spanwise component of velocity is responsible for localized mixing than the remaining two components, and the coolant gets heated inside the recirculation zone and diffusion of which occurs mostly at the free shear layer. The analysis of higher pressure and temperature difference shows higher Nusselt number at high pressure, whereas higher heat flux at lower pressure.