scholarly journals A comparative study of different heat transfer enhancement mechanisms in a partially porous pipe

2021 ◽  
Vol 3 (10) ◽  
Author(s):  
Nima Fallah Jouybari ◽  
Majid Eshagh Nimvari ◽  
Wennan Zhang
Keyword(s):  
Heat Transfer ◽  
Porous Media ◽  
Porous Material ◽  
Porous Layer ◽  
Heat Transfer Performance ◽  
Pipe Wall ◽  
Critical Role ◽  
Flow In Porous Media ◽  
Turbulent Regime ◽  
Transfer Performance

AbstractThe effect of porous material position on the heat transfer inside a pipe working in a turbulent regime is studied here to obtain a detailed understanding of the heat transfer enchantment mechanisms in different porous substrate positions. To this end, an in-house Fortran code is developed to solve the governing equations using the finite volume method and SIMPLE algorithm. Turbulent flow in porous media is modeled using a modified version of k–ε model. The flow field and heat transfer inside the partially filled pipe are investigated for the two cases of central and boundary configurations. The porous and flow characteristics including Reynolds number, Darcy number, the conductivity ratios of solid to fluid and the thickness of inserted porous layer are varied and the heat transfer performance is studied in different cases. It is observed that two entirely different phenomena enhance the heat transfer in central and boundary configurations. While the channeling of fluid between the porous media and the pipe wall highly affects the heat transfer performance in the former, the thermal conductivity of porous media plays a highly critical role in the latter configuration. It is shown that, for the same filling ratio, inserting the porous layer at the core of the pipe is more effective than placing it at the wall. Investigating porous materials with different solid conductivities revealed that covering the pipe wall with a porous material is justified only for solid matrixes with high thermal conductivities.

scholarly journals Numerical study of flow patterns and heat transfer in mini twisted oval tubes

2015 ◽  
Vol 26 (12) ◽  
pp. 1550140 ◽  
Author(s):  
Amin Ebrahimi ◽  
Ehsan Roohi
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Performance ◽  
Numerical Study ◽  
Critical Role ◽  
Reynolds Numbers ◽  
Flow Patterns ◽  
Working Fluid ◽  
Transfer Performance ◽  
Temperature Dependent ◽  
Overall Performance

Flow patterns and heat transfer inside mini twisted oval tubes (TOTs) heated by constant-temperature walls are numerically investigated. Different configurations of tubes are simulated using water as the working fluid with temperature-dependent thermo-physical properties at Reynolds numbers ranging between 500 and 1100. After validating the numerical method with the published correlations and available experimental results, the performance of TOTs is compared to a smooth circular tube. The overall performance of TOTs is evaluated by investigating the thermal-hydraulic performance and the results are analyzed in terms of the field synergy principle and entropy generation. Enhanced heat transfer performance for TOTs is observed at the expense of a higher pressure drop. Additionally, the secondary flow generated by the tube-wall twist is concluded to play a critical role in the augmentation of convective heat transfer, and consequently, better heat transfer performance. It is also observed that the improvement of synergy between velocity and temperature gradient and lower irreversibility cause heat transfer enhancement for TOTs.

scholarly journals Analysis of Heat Transfer Characteristics of a GnP Aqueous Nanofluid through a Double-Tube Heat Exchanger

Nanomaterials ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 844
Author(s):  
Uxía Calviño ◽  
Javier P. Vallejo ◽  
Matthias H. Buschmann ◽  
José Fernández-Seara ◽  
Luis Lugo
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Heat Transfer Performance ◽  
Turbulent Regime ◽  
Transfer Performance ◽  
Transfer Coefficients ◽  
Scanning Calorimetry ◽  
Tube Heat Exchanger

The thermal properties of graphene have proved to be exceptional and are partly maintained in its multi-layered form, graphene nanoplatelets (GnP). Since these carbon-based nanostructures are hydrophobic, functionalization is needed in order to assess their long-term stability in aqueous suspensions. In this study, the convective heat transfer performance of a polycarboxylate chemically modified GnP dispersion in water at 0.50 wt% is experimentally analyzed. After designing the nanofluid, dynamic viscosity, thermal conductivity, isobaric heat capacity and density are measured using rotational rheometry, the transient hot-wire technique, differential scanning calorimetry and vibrating U-tube methods, respectively, in a wide temperature range. The whole analysis of thermophysical and rheological properties is validated by two laboratories. Afterward, an experimental facility is used to evaluate the heat transfer performance in a turbulent regime. Convective heat transfer coefficients are obtained using the thermal resistances method, reaching enhancements for the nanofluid of up to 13%. The reported improvements are achieved without clear enhancements in the nanofluid thermal conductivity. Finally, dimensionless analyses are carried out by employing the Nusselt and Péclet numbers and Darcy friction factor.

Studying the Effect of Porosity of Porous Layer Coating on the Performance of the Horizontal Tubular Falling Film Evaporator

2021 ◽  
Author(s):  
Alaa Adel Ibrahim ◽  
Hassan Elgamal ◽  
Ahmed M. Nagib Elmekawy
Keyword(s):  
Heat Transfer ◽  
Porous Media ◽  
Numerical Simulations ◽  
Thermal Performance ◽  
Heat Transfer Performance ◽  
Transfer Performance ◽  
Falling Film ◽  
Film Evaporator ◽  
Porosity Ratio ◽  
Layer Coating

Abstract Through the recent decades, many studies have focused on finding efficient methods to enhance the heat transfer performance in heat exchangers. Therefore, using porous media attracted many researchers, as it is such a simple, efficient, and low-cost technique in enlarging the surface contact area of heat transfer through the fluid pass. Nevertheless, there is little work associated with using porous media to enhance the thermal performance of falling film evaporators. The present study seeks to discuss numerically the liquid flow behaviour over falling film evaporator tubes in the case of bare tubes and tubes with porous layer coating. The two-dimensional multi-phase numerical simulations are also carried out in order to investigate the effect of the porosity ratio of the porous medium added to the tubes in the heat transfer performance. Furthermore, deducing the way to select a decent porosity ratio to be used to get the best thermal performance is demonstrated through the study. Time-averaged results gained from the numerical simulations have been compared to those of bare-tube falling film evaporator to observe much higher heat transfer performance represented in the average surface Nusselt number (Nu) which increased by 3 times.

Experimental Investigation of Heat Transfer Performance of Different Nanofluids Using Automobile Radiator

2015 ◽  
Vol 787 ◽  
pp. 212-216 ◽  
Author(s):  
S. Senthilraja ◽  
K.C.K. Vijayakumar ◽  
R. Gangadevi
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Performance ◽  
Convection Heat Transfer ◽  
Test Fluid ◽  
Turbulent Regime ◽  
Transfer Performance ◽  
Fluid Flow Rate ◽  
Nanoparticle Concentration ◽  
Heat Transfer Fluids ◽  
Better Than

TIn this present study, the forced convection heat transfer performance of different fluids, namely, Al2O3-water, and CuO-water nanofluid has been studied experimentally in an automobile radiator. Three different concentration of nanofluid in the range of 0-1.0 vol.% have been prepared by addition of Al2O3and CuO nanoparticles into water. The test fluid flow rate can be varied in the range of 2 l/min to 5 l/min to have a fully turbulent regime. Obtained results demonstrate that the fluid circulating rate can improve the heat transfer performance. The heat transfer performance of CuO-water nanofluid was found better than the other heat transfer fluids. Furthermore, the Nusselt number is found to increase with the increase in the nanoparticle concentration and nanofluid velocity.

Pilot-Scale System With Particle-Based Heat Transfer Fluids for Concentrated Solar Power Applications

2020 ◽  
Author(s):  
Christopher A. Bonino ◽  
Joshua Hlebak ◽  
Nicholas Baldasaro ◽  
Dennis Gilmore
Keyword(s):  
Heat Transfer ◽  
Large Scale ◽  
Heat Transfer Performance ◽  
High Efficiency ◽  
Solar Power ◽  
Critical Role ◽  
Heat Transfer Fluid ◽  
Process Unit ◽  
Transfer Performance ◽  
Concentrated Solar Power

Abstract Concentrated solar power (CSP) is a promising large-scale, renewable power generation and energy storage technology, yet limited by the material properties of the heat transfer fluid. Current CSP plants use molten salts, which degrade above 600°C and freeze below 220°C. A dry, particle-based heat transfer fluid (pHTF) can operate up to and above 1,000°C, enabling high-efficiency power cycles, which may enhance CSP’s commercial competitiveness. Demonstration of the flow and heat-transfer performance of the pHTF in a scalable process is thereby critical to assess the feasibility for this technology. In this study, we report on a first-of-a-kind pilot system to evaluate heat transfer to/from a densely flowing pHTF. This process unit circulates the pHTF at flowrates up to 1 tonne/h. Thermal energy is transferred to the pHTF as it flows through an electrically heated pipe. A fluidization gas in the heated zone enhances the wall-to-pHTF heat transfer rate. We found that the introduction of gas mixtures with thermal conductivities 4.6 times greater than that of air led to a 65% increase in the heat transfer coefficient compared to fluidization by air alone. In addition to the fluidization gas, the particle size also plays a critical role in heat transfer performance. Particles with an average diameter of 270 μm contributed to heat transfer coefficients that were up to 25% greater than the performance of other particles of the same composition in size range of 65 to 350 μm. The considerations for the design of an on-sun system are also discussed. Moreover, the collective work demonstrates the promise of this unique design in solar applications.

Sign in / Sign up

Export Citation Format

Share Document