Numerical Investigation Of Heat Transfer Research Articles

Experimental and numerical investigation of heat transfer and flow of water-based graphene oxide nanofluid in a double pipe heat exchanger using different artificial neural network models

In this study, a water-based graphene oxide nanofluid was utilized in a counter-current flow double pipe heat exchanger (DPHE). The inner pipe carried the hot fluid (deionized water-based fluid). In the outer pipe, the cold fluid was flown, in which the experiments were performed once for deionized water-based fluid and once for graphene oxide nanofluid. These experiments were conducted at various inlet hot fluid temperatures of 35, 45, and 55 °C, volumetric concentrations of 0.01, 0.055, and 0.1% for nanofluid, and cold fluid flow rates of 14.4, 18.9, and 23.4 ml/s to evaluate the thermohydraulics of the DPHE. The results demonstrated that an increase in the flow rate and concentration of nanoparticles led to an improvement in the heat transfer coefficient (HTC) . It is also observed that inlet hot fluid temperature had a negligible effect on this coefficient compared to the concentration and flow rate. Additionally, the results showed that the friction factor and pressure drop of nanofluid were higher than those of the basefluid and their values were increased by increasing the concentration. The maximum increase compared to the basefluid was 72% for the friction factor and 111%, for the pressure drop. Besides, radial basis function neural network (RBFNN) and multi-layer perceptron neural network (MLPNN) models were designed for estimating the HTC. Both models accurately predicted the coefficient, but the RBFNN model exhibited higher accuracy than the MLPNN model. The results further indicated that the nanofluid outperformed the basefluid in terms of HTC. Due to the exceptionally high thermal conductivity of graphene nanoparticles, the HTC of the nanofluid was improved by up to 85% compared to the basefluid. The optimum value of HTC was achieved at a temperature of 55 °C, a volume concentration of 0.1%, and a flow rate of 23.4 ml/s.

Numerical investigation of heat transfer and pressure drop characteristics on the hot fluid side of the plate-fin precooler under negative pressure conditions

Plate-fin heat exchangers are widely employed in aerospace and many other fields due to the advantage of high efficiency and low resistance. However, they usually operate at atmospheric or high-pressure conditions. In this study, The commercial CFD solver Fluent 16.0 was used to evaluate the overall performance of the plate-fin precooler whose hot fluid is nitrogen under negative pressure and high temperature conditions. The characteristics of the hot fluid flow field inside the precooler with and without fins were investigated. The effect of fin number on the heat transfer and pressure drop characteristics of the hot fluid side was analyzed. Furthermore, the comprehensive performance of the precooler under different pressure conditions was compared quantitatively. The results showed that under negative pressure conditions, the hot fluid flow field features inside the precooler without fins was regular, while that of the precooler with fins took on a “<” shaped flow features, indicating the evolving of thermal boundary layer. It was also found that the comprehensive performance of the precooler did not increase with an increase in the number of fins when the hot fluid was in a low-density and high-speed flow state. Moreover, pressure conditions did not affect the heat transfer performance of the precooler but had a significant impact on the pressure drop performance.

The Numerical Investigations of Heat Transfer and Bubble Behaviors of R22 in Subcooled Flow Boiling in Casing Tubes

Amidst the background of “double carbon”, energy saving and emission reduction is a popular direction in the current refrigeration industry. Therefore, the research on the boiling heat transfer of gas–liquid two-phase flow is helpful to strengthen the heat transfer and design a more efficient heat exchanger. In this paper, a research method combining numerical simulation and experimental verification is adopted. Firstly, an experimental platform used for the subcooled flow boiling of refrigerant in casing tubes is introduced and experiments are carried out to obtain experimental data, which provides a theoretical basis for the development of numerical simulation and verifies the feasibility of numerical simulation. A numerical model of subcooled flow boiling in R22 was established and the grid independence test was carried out. Based on the simulation results, three factors affecting the boiling heat transfer of R22 are analyzed: First, the boiling heat transfer coefficient of R22 increases with the increase of the mass flow rate of R22, but the increase decreases when the mass flow rate increases from 0.018 kg/s to 0.020 kg/s. Second, the boiling heat transfer coefficient of R22 increases significantly with the increase of hot water flow rate. Third, the influence of R22 subcooling on boiling heat transfer is more complex. When the subcooling is 5 °C and 1 °C, heat transfer can be enhanced; high subcooling at 5 °C can enhance convective heat transfer and low subcooling at 1 °C can accelerate the arrival of saturated boiling. In this paper, three kinds of bubble behaviors affecting heat transfer in supercooled flow boiling, including sliding, polymerization, and bounce are also studied, which provides a basis for further research on heat transfer mechanism of supercooled flow boiling.

Experimental and numerical investigations of heat transfer and flow characteristics during flow boiling in straight and diverging PDMS microchannel

Recent trends of miniaturization and densely packed circuits have necessitated the development of novel cooling methods, especially for emerging fields like flexible microelectronics, biotechnology, and nanotechnology. A polydimethylsiloxane (PDMS) based microchannel flow boiling heat sink can be used for these applications due to its unique properties as such as unique mechanical properties, biocompatibility, optical transparency, etc. PDMS microchannels are fabricated using soft lithography techniques, which involve using a mould to pattern the PDMS material. The mould is created using photolithography, and the PDMS is poured over the mould and cured to create the microchannels. In this study, an effort is made to compare the flow and heat transfer performance of a PDMS microchannel heat sink with different channel shapes, i.e. straight and diverging microchannel heat sinks for different heat flux and mass flux conditions. The PDMS microchannel was fabricated using the soft lithography technique and a flexible laser-induced graphene heater was fabricated and integrated with the developed PDMS microchannel to act as a heat source. Experimentally, the parameters like bubble pattern, pressure drop, exit vapour quality, and corresponding heat transfer coefficient were determined at varying mass and heat flux ranging from 19 to 114 kg m−2s−1 and from 13.3 to 156.6 kW m−2 respectively for both the microchannels. It was observed that the flow in the diverging microchannel is more stable and has a 13% higher heat transfer coefficient value compared to the straight microchannel under similar conditions. Further, a 3D numerical study was carried out to corroborate and elaborate on the results. The heat transfer, flow characteristics, and bubble pattern results show an excellent agreement with experimental results. This work has significant relevance in designing flexible microchannel heat sinks.

Numerical Investigation of Heat Transfer and Pressure Drop Characteristics in a Double Pipe Heat Exchanger with Corrugated Tubes and Rod Baffles at Various Reynolds Numbers

Numerical Investigation of Heat Transfer and Pressure Drop Characteristics in a Double Pipe Heat Exchanger with Corrugated Tubes and Rod Baffles at Various Reynolds Numbers

Numerical Investigations of Heat Transfer and Fluid Flow Characteristics in Microchannels with Bionic Fish-Shaped Ribs

Microchannel cooling technology is an effective method to solve local thermal stacking. In this paper, four innovative microchannels with bionic fish-shaped rib arrangements (CM-O, CM-R, CM-H, and CM-G) are designed by imitating geese and fish clusters. The heat transfer and flow characteristics of the microchannels are simulated numerically at different Reynold’s numbers (Re = 200 − 1600). The liquid water temperature and flow field in the four innovative microchannels with bionic ribs are analyzed. The results show that the ribs’ arrangement has an influence on the thermal performance of microchannels. Compared to the smooth microchannel (CM), the of the Nu microchannels with the bionic fish-shaped ribs increases by 33.00–53.26% while the fave increases by 28.63–34.93% at Re = 1200. The vortices around the ribs are clearly observed which improves the temperature gradient. The performance evaluation criterion (PEC) of CM-H is higher than that of the others. This indicates that the rib arrangement of CM-H is superior for heat dissipation application.

Numerical investigation of heat transfer and entropy generation in serpentine microchannel on the battery cooling plate using hydrophobic wall and nanofluid

Battery cooling is essential in electronic devices since the performance of batteries is negatively influenced by the increase in temperature of batteries. This paper investigates the significance of a serpentine microchannel that is situated on the surface of the battery. The nanofluid flow and thermal behavior are simulated through numerical methods in the serpentine microchannel and battery surface. The results confirmed that the present nanofluid is able to increase heat transfer between serpentine microchannel and battery by up to 20 %. Moreover, the most effective parameter on the heat transfer improvement was the Reynolds number so when the Reynolds number varies from 25 to 150 the heat transfer increased from 6.34 to 12.75. More importantly, the hydrophobic walls of microchannels lead to a 14.4 % enhancement in heat transfer compared with a conventional wall.

Numerical investigation of heat transfer and pressure drop characteristics of flow boiling in manifold microchannels with a simple multiphase model

The Manifold Microchannel (MMC) heat sink is an emerging micro-scale electronic cooling technology with high heat dissipation potential and application prospects. This paper numerically studied the subcooled flow boiling in MMC heat sinks. The feasibility of using the Mixture multiphase flow model to simulate the subcooled flow boiling in the MMC heat sink is validated. As the vapor-liquid interfaces are not reconstructed in this model, less computational resources are needed compared with other multiphase models. The results show that at constant channel width, the maximum and average temperatures of the MMC decrease with the increase of the microchannel aspect ratio. For cases with an inlet velocity of 0.35 m/s, the average wall temperature decreases from 388.53 K to 374.26 K when the aspect ratio increases from 6.67 to 16.67. The difference between the maximum and the minimum temperature on the heated surface increases with the increase of channel aspect ratio, resulting in an uneven temperature distribution. The thickness of temperature boundary layer near the divider is thicker than that near the heated base at low aspect ratio. Low pressure drops are obtained for cases with high aspect ratios due to the increase in cross-sectional area. The pressure drop of MMC with aspect ratio of 6.67 is nearly twice of the case with aspect ratio of 16.67. Although the Mixture model could not characterize the bubble shapes, the numerical results are similar to those obtained by the VOF model and the experimental visual results. A complex case of subcooled flow boiling in Z-type MMC with a hotspot heat flux of 800 W/cm2 is also conducted using the whole computational domain. Mal-distributions of mass flux, wall temperature and vapor void fraction are observed for this complicated problem. The difference between the maximum and the minimum temperatures is about 12 K. The Mixture model is more suitable to obtain reasonable numerical results of flow boiling in complex MMC with much less computational resource.

Numerical investigation of heat transfer in the presences of thermo‐cross diffusion gradients on flow over a curved geometry

AbstractHere, we examine the behavior of micropolar fluids as they travel through a curved stretching surface. We integrate thermo‐diffusion and diffusion‐thermo effects into the temperature and concentration equations to study the impact of cross‐diffusion gradients on velocities, temperatures, and concentrations. The equations governing the flow are nonlinear, thus by applying practical similarity transformations, we obtain a system of nonlinear ordinary differential equations that can be solved. Using the Runge–Kutta numerical procedure, we are able to determine an answer to the modified system. The profiles of velocity, concentration, and temperature are shown, along with the influence of non‐dimensional parameters on those variables. The skin friction coefficient, as well as the Nusselt and Sherwood numbers, is computed numerically, and their fluctuations as a function of various parameters are investigated. The implications of these findings for engineering and industry are greater.

Heat transfer to proximal cylinders in hypersonic flow

Uncontrolled atmospheric entry of meteors, satellites, and spacecraft components often leads to their partial or complete demise. In this destructive process, driven by hypersonic ablation, reentry objects fragment, interact, and alter each other's aerothermal environment. The effect of these interactions on the heat transfer to the fragments has not been investigated, despite the heat transfer's importance in hypersonic ablation and reentry demise. This study focuses on the numerical investigation of heat transfer to proximal circular cylinders in a thermochemically frozen flow and in two dimensions. First, binary body configurations at Mach numbers 2, 4, and 8 revealed that the heat load and peak heat transfer can be augmented for either or both proximal bodies by +20% to −90% of an isolated body. Second, different clusters of five proximal bodies showed that the heat load to any given body can range from +40% to −90% of an isolated body. Moreover, the average heat load in a cluster is found to vary between +20% and −60% of an isolated body. Intuitively, clusters which are thin in the direction perpendicular to free-stream velocity and long in the direction parallel to the free-stream velocity have their cluster-averaged heat load reduced. In contrast, thick and thin clusters, in directions perpendicular and parallel to the free-stream velocity, are subject to an increased cluster-averaged heat load.

Numerical investigation of heat transfer and parameter coupling characteristics for Spider web microchannel topological structure

Numerical investigation of heat transfer and parameter coupling characteristics for Spider web microchannel topological structure

Numerical investigation of heat transfer and fluid flow characteristics of ternary nanofluids through convergent and divergent channels.

The characteristics of nanomaterials have garnered significant attention in recent research on natural and forced convection. This study focuses on the forced convection characteristics of ternary nanofluids within convergent and divergent channels. The ternary nanofluid comprises titanium oxide (TiO2), zinc oxide (ZnO), and silver suspended in water, which serves as the base fluid. Using COMSOL Multiphysics 6.0, a reliable software for finite element analysis, numerical simulations were conducted for steady and incompressible two-dimensional flow. Reynolds numbers varying from 100 to 800 were employed to investigate forced convection. Additionally, we explored aspect ratios (channel height divided by the height of the convergent or divergent section) of -0.4, -0.2, 0, 0.2, and 0.4. Our findings revealed that only at aspect ratio a = 0.4 did the average outlet temperature increase as the Reynolds number rose, while other aspect ratios exhibited decreasing average temperatures with declining Reynolds numbers. Moreover, as the Reynolds number increased from 100 to 800 and the total volume fraction of the ternary nanofluids ranged from 0.003 to 0.15, there was a significant 100% enhancement in the average Nusselt number. For clarity, this article briefly presents essential information, such as the study's numerical nature, fluid properties (constant-property fluid), and the methodology (COMSOL Multiphysics 6.0, finite element analysis). Key conclusions are highlighted to enable readers to grasp the main outcomes at a glance. These details are also adequately covered in the manuscript to facilitate a comprehensive understanding of the research. The utilization of this emerging phenomenon holds immense potential in various applications, ranging from the development of highly efficient heat exchangers to the optimization of thermal energy systems. This phenomenon can be harnessed in scenarios in which effective cost management in thermal production is a critical consideration.

3D Numerical Investigation of Heat Transfer of Infants in the Indoor Environment

This study aimed to investigate the heat transfer around the infant surface in the indoor environment based on computational fluid dynamics analysis. A three-dimensional numerical model containing a virtual infant manikin was developed in COMSOL software. The high-quality geometry model of the infant was obtained using three-dimensional body scanning technology. Governing fluid flow and energy equations were solved along with the low Re k–ε turbulence model. Real-scale measurements were carried out to determine the accuracy of the developed numerical model. Good agreement was found between the simulation results and the experimental data. The results showed that, at room temperature of 21oC, the convective heat transfer coefficient was 64.2% greater than the radiative heat transfer coefficient, which demonstrated that the convective heat transfer was the main approach for heat exchange between the infant and its surrounding environment. Moreover, the largest convective heat transfer coefficients were observed at the forearm and calf, indicating the importance of the additional thermal protection at these regions. The findings will be beneficial to provide some instructions on infant thermal care for caregivers.

Numerical investigation of heat transfer &amp; hall effects on MHD nanofluid flow past over an oscillating plate with radiation

The effects of convective heat generation and the oscillatory motion of a plate in the presence of MHD, Alumina nanofluid flow, thermal radiation, and Hall current are considered. The plate oscillates harmonically in its axes with uniform temperature. The dimensional equations have to be changed into non-dimensional equations with a set of dimensionless parameters. The Laplace transformation technique is utilized to get an exact solution. The possessions of velocity and temperature are analyzed with several parameters like Prandtl number (Pr), Grashof number (Gr), Hall parameter (m), magnetic parameter (M), radiation (R), solid volume fraction(ᵠ), phase angle(ω).The influence of primary and secondary velocity is discussed by the graph. It is observed that the increment of Hall parameter (m) diminishes the primary velocity, an increment of Grashof number leads to an increase in both velocities, and increasing solid volume fraction raises the temperature. The Nusselt number and skin friction coefficient values have expressed in the table. It is apparent that an increment of radiation increased the value of the Nusselt number and also an increment of phase angle value diminished the skin friction coefficient value.

Numerical Investigation of Heat Transfer in Open Microchannel Heat Sinks With Transverse Ribs for High Heat Flux Dissipation

As one of the key components of the nuclear fusion reactor, the target of divertor directly faces huge heating power from fusion plasma, and thus its capability to withstand high heat flux is of essential importance for the stability and safety operation of fusion devices. The divertor target needs to meet the heat dissipation requirements of up to 20 MW/m2 heat loads in future fusion reactors. Herein, we proposed an open microchannel heat sink with transverse ribs (OMHS-TR) to enhance the heat transfer of W/Cu flat-type mock-ups. The fluid flow and heat transfer characteristics of OMHS-TR were numerically investigated, and the effect of the number of transverse ribs (TR) was studied under the operational conditions with a mass flux of 30 L/min and a heat flux of 20 MW/m2. The numerical results demonstrated that OMHS-TR shows significant enhanced heat transfer performance with 19.6 K reduction in average wall temperature, 30.6 K reduction in maximum surface temperature, and ~ 44% increment of Nusselt number when compared with those of open microchannels without TR. However, TR also leads to high-flow disturbances and blocking-flow effect, which increases the pressure drop. The heat transfer coefficient and pressure drop of OMHS-TR increase with the increase in the number of TR. This study may provide some insights for high heat flux dissipation on the target plate of the divertor.

Numerical Investigation of heat transfer and pressure drop in shell and tube heat exchangers with segmental and helical baffles

Numerical Investigation of heat transfer and pressure drop in shell and tube heat exchangers with segmental and helical baffles

Numerical investigation of heat transfer and fluid motion in air inflatable textiles: Effect of thickness, surface emissivity and ambient temperature

Air inflatable textile has attracted increasing attention due to the advantage of light, cheap, environmentally friendly and low thermal conductivity. While its thermal insulation is still not yet well understood since the complex interior heat and mass transfer under various thickness and ambient conditions. In this work, a three-dimensional model was developed to investigate the fluid motion and heat transfer in both air inflatable and fiber-filled textiles. The coupled conduction, convection and radiation were modelled by CFD approach. The experimental and numerical results were compared to verify the proposed model. Good agreements were found with the average difference in surface temperature and heat flux less than 2.54% and 9.95%, respectively. Then the effect of various parameters including thickness, surface emissivity and ambient temperature on heat flux, thermal resistance and fluid flow behavior was further analyzed. The simulated interior velocity and temperature distribution suggested that the higher thickness (≥10 mm) was not favorable for better thermal insulation when the air was adopted as thermal insulation layer. Because more available space for air movement would accelerate thermal convection and result in the deteriorated thermal insulation. In addition, inner surface layer with lower emissivity could effectively suppress the thermal radiation in air inflatable textiles and was beneficial to increase the thermal insulation. Besides, the thermal insulation of fiber-filled textile was nearly unaffected when lower ambient temperature was applied, while that of air inflatable textiles significantly decreased due to the aggravated convective heat and flow transfer under large temperature difference.

Experimental and numerical investigation of heat transfer by water spray injection into pressurized gas atmospheres

Better realization of isothermal changes of state can be seen as a decisive general prerequisite for the improvement of reachable overall efficiencies of compressors, power plants or Stirling engines. The injection of water during a compression or expansion stroke is a promising method for approximating isothermal change of state, as there is a big potential of high heat transfer rates in comparison to traditional cooling and heating methods through walls. Water injection into atmospheres of nitrogen and helium up to 18 bar is investigated in an experimental setup varying initial temperature difference between injected water and gas temperatures and by varying the injection pressure, injection time or the gas type. It is shown that thermal resistance remains relatively independent of the temperature difference but strongly depends on the injection pressure difference. Transferred heat and heat flow rise with the pressure of the gas atmospheres. Numerical simulations are conducted along an expansion stroke and lead to the result that the delivered work can reach 94.2% of the isothermal course. By water injection with preheated water with a low initial temperature difference of 55 K, the expansion can deliver the same amount or even higher amount of work as the isothermal case. • Water spray injection in nitrogen and helium atmospheres pressurized up to 18 bar. • New calculation method of thermal resistances during spray injection. • Injection pressure has the highest impact on thermal resistance. • Monatomic gas helium is favourable compared to diatomic gas nitrogen. • Simulations of expansion with water injection get close to an isothermal curve.

Numerical investigation of heat transfer in helical tubes modified with aluminum oxide nanofluid and modeling of data obtained by artificial neural network

The purpose of this study is to investigate the computational fluid dynamics to find the effects of Reynolds number, different volume fractions of aluminum oxide nanofluid and different heat fluxes in heat transfer performance (Nusselt number) in a helical tube. This simulation was investigated at Reynolds number range 2000 and 10,000 and volumetric fraction range 1% and 4% of aluminum oxide nanofluid and constant heat fluxes of 4000–6000 W/m2. The single-phase model was used to model the nanofluid and the feasible k-ε model was used to simulate the turbulent flow. Then, perceptron artificial neural networks with the Levenberg–Marquardt algorithm were used to predict the Nusselt number such that input parameters include Reynolds number, nanoparticle volume fraction and output or target was considered Nusselt number for the network. The results show that with increasing the volume fraction of aluminum oxide nanofluid and Reynolds number, the Nusselt number increases by about 20.35%. Also, by increasing the constant heat flux from 4000–6000 W/m2, the Nusselt number increases by 18.75%. The results of the artificial neural network show that the topology 2-10-1 is very successful in predicting the Nusselt number so that the minimum mean squared error for the data allocated to the training and validation sections were 0.024449627 and 0.117025052, respectively, which are obtained under optimal epochs 19 and 9. The value of the correlation coefficient obtained in predicting the Nusselt number is 0.944416302.

Comparative study of solar air heater (SAH) roughened with transverse ribs of NACA 0020 in forward and reverse direction

Experimental and Numerical investigation of heat transfer and fluid flow characteristics is carried out for SAH duct (aspect ratio, W/H = 10:1) with transverse ribs of different cross-sections (square, semi-circular and symmetric half NACA 0020 in both forward and reverse orientations) on one of its broad wall. Solutions are obtained using SIMPLE algorithm for coupling of pressure and velocity, while for discretization of momentum and energy equations upwind scheme of second order is used in commercial ANSYS software. Nusselt number ( Nu ) and friction factor (f) are evaluated for Reynolds number (Re) ranging from 6000 to 18000, fixed relative roughness pitch (P/e = 12) and relative roughness height (e/D = 0.05). The highest value of ( Nu ) is found for ribs of semi-circular cross-section while minimum (f) is observed for forward oriented symmetric half NACA 0020. The highest thermo-hydraulic performance parameter is achieved at Re = 6000 with symmetric half NACA 0020 rib roughness when used in reverse orientation. Contours plots of temperature, velocity streamlines and pressure variation yielded important results for understanding the physical phenomenon inside the SAH. The numerical outcomes are validated with experimental results.