Optimum Heat Transfer Rate Research Articles

Optimization of Nanofluid Concentration for Energy Intensification in Corrugated Plate Type Heat Exchanger

The overall heat transfer coefficient of the heat exchanger will improve with an increase in the flow rate and concentration of nanofluid. But beyond an optimum nanoparticle concentration, the overall effectiveness seems to decrease due to an increase in pressure drop that consequently leads to an increase in pumping power. The novelty of the present work is to find the optimum concentration of CuO-Water nanofluid that exhibits the optimum heat transfer rate and global minimum pumping power, using both experimental and numerical study. The cold nanofluid and hot water entered the counter currently at 303.15 and 333.15 K respectively in the corrugated plate heat exchanger. It was observed from the experimental and numerical results that the values of overall heat transfer coefficient and pressure drop were increased monotonically (454–710 W/(m2-K) and 6–133 Pa respectively), with the increment in the concentration and flow rates of the nanofluid. Because of this trend, it was challenging to figure out the optimum nanofluid concentration using these parameters. Later, a procedure was presented to obtain an optimum concentration of nanofluid, to reduce the hot stream temperature by 288.15 K. The hydraulic power exhibited a global minimum at an optimum concentration of 0.5 vol% of nanofluid.

Investigating the thermal performance of nano-encapsulated phase change materials-water nanofluid in the presence of a heat source as applied in electronic devices

BackgroundGlobal warming and the human need for power resources in the last decades have highlighted the concerns related to energy saving for long-term applications. Thermal energy-saving systems are an important technique to overcome this issue. MethodsIn the present study, we aim to simulate the performance of a thermal energy-storing system with Nano-Encapsulated Phase Change Materials (NEPCMs) by Computational Fluid Dynamics (CFD). Free convection heat transfer through a square enclosure is numerically simulated, and a hot block is located at pisitions of the enclosure. The simulation is done with the FVM method and SIMPLE algorithm. The analyzed parameters are different Ra numbers (5 × 103 − 105), non-dimensional melting temperatures (0.1 ≤ θf ≤ 0.9), and NEPCM melting intensities (0.01 ≤ χ ≤ 0.03). Significant FindingsT The results revealed that the θf = 0.3 is corresponding to the optimum heat transfer rate, and it is independent of the Ra number. In the case with the highest heat transfer rate, adding NEPCMs to the based fluid caused the heat transfer to improve by 12.5%. Furthermore, in this θf number, uniform heat transfers through the cold walls of the enclosure. A low number of χ also revealed less Nusselt number. Increasing AR in high Ra number improves Nusselt number by 5%.

STUDY ON PARAMETERS IN COUNTER CURRENT DOUBLE PIPE HEAT EXCHANGER APPLYING CIRCULAR TURBULATOR

Many industries dealing with manufacturing and HVAC (heating, ventilation, and air cooling) are rely heavily on thermodynamics principles with respect to heat and mass transfer. The objective of this study is to do optimization to yield optimum heat transfer rate and minimized pressure drop with regard to number of circular turbulator (CT) and water debit on Nusselt number (Nu) in counter current double pipe heat exchanger. This work has applied the classical rule of thermal science dealing with Nusselt number in relation to convection and conduction of heat transfer rate due to temperature effect. The result shows the highest Nu found to be 835.3 at 5 CT and water debit of 9 L/min. The addition of CT number gives effect on fluid current due to vortex generation. This study also investigates the effect of CT number on friction coefficient that the friction coefficient of a heat exchanger in the absence of CT is lower than that in the presence of CT. For any CT number, the friction coefficient is reduced with increasing water debit. The study has also found that the thermal performance ratio has achieved higher values for heat exchanger in the absence of CT.

Optimization of the effect of Prandtl number, inclination angle, magnetic field, and Richardson number on double-diffusive mixed convection flow in a rectangular domain

The effect of Prandtl number (Pr), inclination of the cavity (γ), magnetic field (Ha), and Richardson number (Ri) on double-diffusive mixed convection is numerically investigated. The study aims to understand and optimize all the selected parameters effect on heat and species transfer and fluid flow. The best combination of the selected parameter and their level for the optimum performance of the cavity is determined by the Taguchi method. The significance of the parameters considered is determined using the analysis of variance (ANOVA) method. The governing equations are solved using FVM based SIMPLE algorithm technique. Contour plots are used to present the numerical results. The combination of the factor levels for the optimum heat and mass transfer rate is found from the Taguchi analysis as Pr = 7.0, Ha = 0, γ = 60°, and Ri = 10. From the numerical analysis, the value of the average Nu and average Sh for the optimum combination is found as 27.35 and 34.79 respectively. From the ANOVA result, it is found that the Pr and γ have 47.74% and 25.49% contribution on average Nu and 47.41% and 25.59% contribution on average Sh respectively.

Thermal magneto-hydrodynamics in a ventilated porous enclosure

The present study examines mixed convection in a ventilated cavity saturated with porous substance and heated at the right-bottom and top-left corners under the influence of uniform magnetic field applied externally. The analysis is carried out numerically using in-house CFD code. Five different heating configurations are analyzed. The effects of pertinent parameters such as Reynolds number (Re = 1–1000), Richardson number (Ri = 0.1–100), Darcy number (Da = 10−7–10−3), Hartmann number (Ha = 1–100), angle of magnetic field ( $$ \gamma $$ = 0–180°) and porosity (e = 0.1–1.0), on the flow and temperature fields are examined for the search of the appropriate configuration yielding optimum heat transfer rate. Furthermore, heat transfer characterization at different heating configurations and parametric combinations is assessed.

Fork-shaped constructal fin array design a better alternative for heat and mass transfer augmentation under dry, partially wet and fully wet conditions

In actual practical situations, the evaporator fins of refrigeration and air-conditioning apparatuses may operate under dry, fully wet or partially wet conditions. Thus in the present study, the optimum design of an array of constructal fork shaped fins operating under partially wet conditions has been determined by using a linear variation of the humidity ratio of saturated air with the corresponding fin surface temperature. The point of separation between the dry and wet portions may be located either in the stem or branch part of the fin and hence, two cases having different governing equations and boundary conditions are analysed in the current study. The optimisation study is done by maximising the total heat transfer rate of the fin array and un-finned surface and the constraints are imposed in such a way that fin material limitations, minimum fin gap requirements as well as space limitations in the radial direction are taken into account. For obtaining the optimum condition, a swarm based meta heuristic algorithm called Firefly algorithm has been employed. Arrays of fork-shaped fin having two and three numbers of branches are analysed in the present study and a comparative study is done with the rectangular fin array. For more compact evaporators, it would be more preferable to select the fin array that results in larger optimum heat transfer rate as well as that having a smaller total length of each fin. An important finding is that the array of fork–shaped fins with two branches give higher optimum heat transfer rate than that from the rectangular fin array in all the cases of different operating conditions. However, no advantage with respect to either higher optimum heat transfer rate or smaller fin length is obtained when the number of branches of fork shaped fins is increased from two to three.

CFD simulation for evaluation of optimum heat transfer rate in a heat exchanger of an internal combustion engine

Heat exchanger is an essential component of an engine cooling system. Radiators are compact heat exchangers used to transfer the heat absorbed from engine to the cooling media. The jacket cooling water gets cooled and re-circulated into system after exchanging the heat with cooling water in a heat exchanger. Conventional fluids like water, oil, ethylene glycol, etc. possess less heat transfer performance; therefore, it is essential to have a compact and effective heat transfer system to obtain the required heat transfer. A reduction in energy consumption is possible by improving the performance of heat exchanging systems and incorporating various heat transfer enhancement techniques. In this paper, the heat transfer rate using nano-sized ferrofluid with and without magnetization is analysed using CFD simulation and compared with the experimental values obtained from a heat exchanger using water as base fluid. The heat transfer rate is measured using different combinations by varying the percentage of nano particles and by introduction of different magnetic intensity (gauss) on to the ferrofluid. The optimum heat transfer rate and efficiency of heat exchanger is calculated with the different combinations and the values are compared with the values of CFD simulation. CFD simulation was undertaken for water alone as cooling media and for water with ferro particle addition from 2% to 5%. The difference in temperature observed to be similar with experimental values. The deviation is within the acceptable limit and therefore the experimental findings are validated. The experiment was conducted on a parallel flow heat exchanger with water alone as cooling media, water with varying percentage of ferro fluid and water with varying magnetic intensity on ferrofluid. Percentage of ferro particles added up to where the optimum temperature difference could be obtained and the magnetic intensity also varied up to the optimum value.

A novel optimal constructal fork-shaped fin array design to ascertain thermo-heightened performance under dehumidifying conditions

The current work deals with the design and analysis of an array of constructal fork-shaped fins attached to a circular tube and operating under fully wet condition. For the mass transport process, a linear relation is adopted between the humidity ratio of saturated air and the corresponding fin surface temperature. After obtaining temperature distribution analytically, a metaheuristic optimization technique is adopted to maximize the net heat transfer rate of the fin array and un-finned surface imposing certain constraints. The constraints are taken such that the radial space limitations, fin material limitations as well minimum fin gap considerations are taken into account. As the present problem involves a large number of design parameters as well as the interrelated constraints, Particle Swarm Optimization technique has been employed for determining the optimum condition. The proposed theoretical analysis has been performed for different operating conditions and the results have been compared with the corresponding rectangular fin array. From the analysis, it has been found that optimum fork–shaped fin array with two branches gives higher heat transfer rate than the corresponding optimum rectangular fin array. For a typical situation (fin volume 0.0005 m3, air relative humidity 70%, ambient temperature 30 °C, base temperature 5 °C, convective heat transfer coefficient 20Wm-2 K−1, fin material thermal conductivity 236 Wm-1 K−1 and minimum gap between fins 0.002 m), optimum fork-shaped array with two branches gives 59.58% higher heat transfer rate than that of the optimum rectangular fin array. In certain cases, though the difference in heat transfer rate between optimum fork–shaped fin array with two branches and the corresponding optimum rectangular fin array is small, but the total fin length for the former case is found to be lower and thus fork shaped fin array with two branches is a better option than the rectangular fin array. However, no benefit in terms of either higher optimum heat transfer rate or lower total fin length is obtained by increasing the number of branches of the fork shaped fins beyond two.

Thermal characteristics of CPU cooling by using a novel porous heat sink and nanofluids

In this paper, different heat sinks are investigated to improve CPU cooling experimentally. Different types of copper heat sinks including a novel “porous heat sink” are proposed and compared to obtain the optimum heat transfer rate. Water and Al2O3/water nanofluids (40 nm) in two different volume fractions (0.1 and 0.2 vol.% from 40-nm nanoparticles) are used as heat transfer fluid to cool the CPU. Different flow rates are also examined in the experimental study. The Nusselt number, wall temperature, thermal resistance and LMTD temperature have been analyzed for a wide range of parameters of the heat sinks. Also, the effect of geometry, heat transfer fluid, input power and flow rate on the heat transfer rate is reported. The result shows that the geometry of the heat sink has an important effect on the thermal performance of the system. The rate of heat transfer in the proposed novel porous heat sink is larger than the other cases. The Nusselt number in the porous heat sink by using nanofluids is 2.2 times larger than the heat sink with an inline pattern.

Heat Transfer and Friction Factor Characteristics in Twisted Square Ducts

The present work experimental and numerical investigations have been carried out to study friction factor and heat transfer characteristics of twisted square ducts. Experiments were conducted for different velocities of air under constant heat flux condition, twist ratio is equal to 6.12 and also Reynolds number varied from 8000 to 30000. The experimental analysis has been carried out and the experimentation is completely based upon design of experiments to get the optimum heat transfer rate and minimize pressure drop. The results of friction factor, Nusselt number and thermal performance factor are presented. Twisted square duct shows relatively higher heat transfer and optimum pressure drop compared to plain square duct. The experimental results shows that Nusselt number for the twisted square duct is about 1.89 times above that for the plain square duct while friction factor is 2.29 times higher (f/fo= 2.29). Thermal performance (enhancement ratio) of the twisted square duct is 1.41. In this work Numeric simulations were calculated by using the CFD software package ANSYS 18.2 FLUENT has been used. Heat transfer and numerical flow behaviors such as temperature, friction factor contours of the are also reported. Hence it is concluded that square duct with twist ratio 6.12 gives highest heat transfer and thermal performance due to lowest friction loss indicating promising device of the twisted square duct.

Modeling and combined application of the modified NSGA-II and TOPSIS to optimize a refrigerant-to-air multi-pass louvered fin-and-flat tube condenser

In the present work, the performance of a refrigerant-to-air multi-pass louvered fin-and-flat tube condenser is optimized without changing the condenser dimensions include length, width and depth. In order to achieve this aim, a one dimensional finite element model is developed to predict the condenser performance. The developed model is then used for optimization procedure after validating by the experimental data. The modified NSGA-II approach is applied to maximize heat transfer rate (Q) and minimize entropy generation number (Ns), refrigerant pressure drop (ΔPref) and air pressure drop (ΔPair) as the objective functions. The non-dominated optimum design points are then plotted and trade-off optimum points are obtained using the Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) and Nearest to the Ideal Point (NIP) method. Comparing the results of four-objective optimization with the results of separately run three and two-objective optimization problems reveals that Q and Ns can be used interchangeably. An independent two-objective optimization of Q and ΔPref results in heat transfer rate increase of about 4% and refrigerant pressure drop reduction of about 85%. In addition, the calculations show that in this case the effectiveness of the optimized condenser increases 3.3% in comparison with the base line condenser. Also, the results of sensitivity analysis of change in the optimum heat transfer rate and refrigerant pressure drop with change in the decision variables are reported.

Numerical Analysis of the Effects of Selected Geometrical Parameters and Fluid Properties on MHD Natural Convection Flow in an Inclined Elliptic Porous Enclosure with Localized Heating

Magnetohydrodynamic (MHD) natural convection flow and associated heat convection in an oriented elliptic enclosure has been investigated with numerical simulations. A magnetic field was applied to the cylindrical wall of the configuration, the top and bottom walls of the enclosure were circumferentially cooled and heated, respectively, while the extreme ends along the cross‐section of the elliptic duct were considered adiabatic. The full governing equations in terms of continuity, momentum, and energy transport were transformed into nondimensional form and solved numerically using finite difference method adopting Gauss–Seidel iteration technique. The selected geometrical parameters and flow properties considered for the study were eccentricity (0, 0.2, 0.4, 0.6, and 0.8), angle of inclination (0°, 30°, 60°, and 90°), Hartmann number (0, 25, and 50), Grashof number (104, 105, and 106), and Darcy number (10−3, 10−4, and 10−5). The Prandtl number was held constant at 0.7. Numerical results were presented by velocity distributions as well as heat transfer characteristics in terms of local and average Nusselt numbers (i.e., rate of heat transfer). The optimum heat transfer rate was attained at e value of 0.8. Also, the heat transfer rate increased significantly between the angles of inclination 58° and 90°. In addition, Hartmann number increased with decreased heat transfer rate and flow circulation. A strong flow circulation (in terms of velocity distribution) was observed with increased Grashof and Darcy numbers. The combination of the geometric and fluid properties therefore can be used to regulate the circulation and heat transfer characteristics of the flow in the enclosure.

Experimental studies on parallel wavy channel heat exchangers with varying channel inclination angles

Experimental studies were performed on corrugated plate heat exchangers. The corrugated plates’ channel inclination angles for the parallel plates were varied from 0° to 80° in increments of 20° in order to experimentally determine the configuration with the optimum heat transfer rate. The channel spacing was kept constant. The media used in both the hot and the cold channels were water. The temperatures of the two media between which heat was exchanged were 25.4°C for cold water and 38°C for hot water. The flow in the heat exchangers was parallel with both the fluids entering from the same side. The flow rate of the hot water was kept constant while that of the cold water was varied. The heat exchangers consisted of ten channels, five for hot water and five for cold water. It was found that the rate of heat transfer increases for all the plate inclination angles as the flow rate of cold water is increased. The overall heat transfer coefficient was observed to be the highest for the 20° inclination angle. The low flow rates of the hot and cold fluids make it a unique study, as the two fluids get more time for heat transfer. The 20° channel inclination angle also has the highest average thermal length. Based on the results, correlations between Nusselt number and Reynolds number were developed.

Unique Analysis for Cascaded Rectangular–Triangular Fins with Convection–Radiation Transport

A double-differential transform method has been used to analyze a cascaded rectangular–triangular fin losing heat by simultaneous convection and radiation to its surroundings. The base of the fin is heated by convection by a hot fluid at a uniform temperature. The thermal conductivity of the fin material assumed to be a linear function of temperature. An exact analytical solution is developed for a pure convection cascaded rectangular–triangular fin of constant thermal conductivity. Results are presented for the temperature distribution for a range of dimensionless parameters governing the problem. Both single- and two-material cascaded rectangular–triangular fins are analyzed. An optimization study has been performed to establish data for optimum heat transfer rate, cold fluid Biot number, fin efficiency, and fin effectiveness. If properly designed, a cascaded rectangular–triangular fin can be more effective than a rectangular or a triangular fin.

Experimental study of the effects of a transversal air-flow deflector in electronics air-cooling

This paper presents an experimental investigation of the influence of a transversal flow deflector on the cooling of a heated block mounted on a flat plate. The deflector is inclined and therefore it guides the air flow to the upper surface of the block. This configuration is simulating the air-cooling of a rectangular integrated circuit or a current converter mounted on an electronic card. The electronic component is assumed dissipating low heat power, as such, air forced convection is still a sufficient cooling way even without fan or heat sink on the component. The measurements are given by hot and cold wires anemometers and by an InfraRed camera. The results give details of the effects of the deflection on the hydrodynamic and the thermal fields on and over the block for different inclination angles. They show that the deviation caused by the deflector may significantly enhance the heat transfer from the component. Deflection is also able to avoid local overheating of the electronic component. Optimum heat transfer rate and homogenised temperature are shown to be obtained with an inclination angle α=30°.

Natural convection in a porous trapezoidal enclosure with magneto-hydrodynamic effect

The effects of magnetic force, acting vertically downward on natural convection within a porous trapezoidal enclosure saturated with an electrically conducting fluid have been investigated numerically. The bottom wall of the enclosure is subjected to a constant hot temperature and the top wall experiences a constant cold temperature whereas the remaining sidewalls are kept adiabatic. The physical problems are represented mathematically by different sets of governing equations along with the corresponding boundary conditions. By using Galerkin weighted residual method of finite element formulation, the non-dimensional governing equations are discritized. For natural convection in a porous medium the influential parameters are the modified Rayleigh number Ram, the fluid Rayleigh number Raf , the inclination angle of the sidewalls of the cavity γ, the rotational angle of the enclosure Φ and the Hartmann number Ha, through which different thermo-fluid characteristics inside the enclosure are obtained. In the present study, the obtained results are presented in terms of streamlines, isotherms and average Nusselt number along the hot wall. The result shows that with increasing Ha, the diffusive heat transfer become prominent even though the modified Rayleigh number increases. Optimum heat transfer rate is obtained at higher values of Ram in the absence of magnetic force.

Performance and optimization analysis of a constructal T-shaped fin subject to variable thermal conductivity and convective heat transfer coefficient

In the present study, an exercise has been devoted to establish an analytical model for thermal performance and optimization of a constructal fin subject to variable thermal conductivity of fin material and convective heat transfer coefficient over the fin surface. For the adaptation of these considerations, the governing energy equation for the stem as well as the flange becomes nonlinear. A new analytical scheme based on the Adomian decomposition method has been established for the solution process. As the present study is an analytic, it can be extended to the analysis for determining the optimum dimensions of fins satisfying either the maximization of rate of heat transfer for a given fin volume or the minimization of fin volume for a desired heat transfer rate. From the results, it can be highlighted that the present model predicts the fin performance always an under value in comparison with that the published results whereas the optimum heat transfer rate determined by using the present analysis gives an over value. The effect of different geometric and thermophysical parameters on both the fin performance and optimization has been studied. For a comparative study, the present and published results are executed for a wide range of thermogeometric parameters.