scholarly journals Numerical Study on Heat Transfer Performance in Packed Bed

Energies ◽  
2019 ◽  
Vol 12 (3) ◽  
pp. 414 ◽  
Author(s):  
Shicheng Wang ◽  
Chenyi Xu ◽  
Wei Liu ◽  
Zhichun Liu
Keyword(s):  
Heat Transfer ◽  
Thermal Resistance ◽  
Transfer Process ◽  
Heat Transfer Performance ◽  
Numerical Study ◽  
Continuous Phase ◽  
Heat Transfer Process ◽  
Packed Beds ◽  
Transfer Performance ◽  
Entransy Dissipation

Packed beds are widely used in industries and it is of great significance to enhance the heat transfer between gas and solid states inside the bed. In this paper, numerical simulation method is adopted to investigate the heat transfer principle in the bed at particle scale, and to develop the direct enhanced heat transfer methods in packed beds. The gas is treated as continuous phase and solved by Computational Fluid Dynamics (CFD), while the particles are treated as discrete phase and solved by the Discrete Element Method (DEM); taking entransy dissipation to evaluate the heat transfer process. Considering the overall performance and entransy dissipation, the results show that, compared with the uniform particle size distribution, radial distribution of multiparticle size can effectively improve the heat transfer performance because it optimizes the velocity and temperature field, reduces the equivalent thermal resistance of convection heat transfer process, and the temperature of outlet gas increases significantly, which indicates the heat quality of the gas has been greatly improved. The increase in distribution thickness obviously enhances heat transfer performance without reducing the equivalent thermal resistance in the bed. The result is of great importance for guiding practical engineering applications.

scholarly journals Effect of the Inclination Angle on the Steady-State Heat Transfer Performance of a Thermosyphon

2019 ◽  
Vol 9 (16) ◽  
pp. 3324
Author(s):  
Wu ◽  
Zhang ◽  
Li ◽  
Xu
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Thermal Resistance ◽  
Inclination Angle ◽  
Heat Transfer Performance ◽  
Heat Transfer Process ◽  
Transfer Performance ◽  
Steady State Heat ◽  
Predicted Values ◽  
Steady State Heat Transfer

A two-phase closed thermosyphon is an efficient heat transfer element. The heat transfer process of this type of thermosyphon includes conduction and convective heat transfer accompanied by phase changes. Variations in the inclination angle of a thermosyphon affect the steady-state heat transfer performance of the device. Therefore, the inclination angle is an important factor affecting the performance of a thermosyphon. In this paper, an equation for the actual heating area variations with respect to the inclination angle is deduced, and a model for the areal thermal resistance of a thermosyphon is proposed by analyzing the main influence mechanisms of the inclination angle on the heat transfer process. The experimental results show that the areal thermal resistance, which accounts for the effect of the actual heating area, does not change with respect to the inclination angle and exhibits a linear relationship with the heat transfer rate. The thermal resistance equation is fit according to the experimental data when the inclination angle of the thermosyphon is vertically oriented (90°), and the predicted values of the thermosyphon’s thermal resistance are obtained when the thermosyphon is inclined. The deviations between the experimental data and predicted values are less than ±0.05. Therefore, the theoretical equation can accurately predict the thermosyphon’s thermal resistance at different inclination angles.

Heat Transfer Performance for Helium Gas Flowing in a Minichannel With Different Inner Diameters

2021 ◽  
Author(s):  
Feng Xu ◽  
Qiusheng Liu ◽  
Makoto Shibahara
Keyword(s):  
Heat Transfer ◽  
Transfer Process ◽  
Heat Transfer Performance ◽  
Heat Transfer Process ◽  
Transfer Performance ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Wide Range ◽  
Helium Gas ◽  
Inner Diameter

Abstract The high heat load on the first wall of the helium cooled blanket is removed by tube flow of helium gas. Heat transfer augmentation is considered to be acquired by downsizing of channels. Therefore, this paper experimentally studied the influence of inner diameter on the heat transfer performance of helium gas flowing in a minichannel. The helium gas flowed in the small platinum tubes with the inner diameters of 0.8 mm and 1.8 mm, respectively. The heat generation rate of the tube was controlled by a heat input subsystem and raised with an exponential equation. The surface temperature and heat flux of the tubes were obtained under a wide range of e-folding time at different flow velocities. The heat transfer coefficients of different inner diameter tubes were compared at the same conditions. The heat transfer performance of the 0.8 mm-diameter tube was compared with a classical correlation. The experimental results showed that the heat transfer performance in the minichannel is better than a conventional large-diameter tube. The heat transfer coefficients of the 0.8 mm-diameter tube were higher than those of the 1.8 mm-diameter tube. The heat transfer process was enhanced with reducing the inner diameter of the minichannel. The heat transfer process was divided into two parts including transient and quasi-steady-state regions.

Numerical Study of Flow and Heat Transfer in Novel Structure Packed Beds

2009 ◽  
Author(s):  
Jian Yang ◽  
Qiuwang Wang ◽  
Min Zeng
Keyword(s):  
Heat Transfer ◽  
Particle Shape ◽  
Heat Transfer Performance ◽  
Numerical Study ◽  
Particle Model ◽  
Physical Parameters ◽  
Packed Beds ◽  
Transfer Performance ◽  
Flow And Heat Transfer ◽  
Better Than

A forced convection heat transfer inside micro pores of structure packed beds with spherical or ellipsoidal particles are numerically studied in this paper. Three-dimensional Navier-Stokes equations and RNG k-ε turbulence model with scalable wall function are adopted for present computations. The effects of packing form and particle shape are carefully studied and the flow and heat transfer performances in uniform and nonuniform packed beds are also compared in detail. The macroscopic hydrodynamic and heat transfer results are obtained from micro pore cells by using integrating method. The results show that, with the same physical parameters, the pressure drops in structure packed beds are much lower than those in randomly packed beds while the overall heat transfer efficiencies (except SC packing) are much higher. The traditional correlations of flow and heat transfer extracted from randomly packings are unavailable for structured packings, and some modified correlations are obtained. Furthermore, it finds that, with the same particle shape (sphere), the overall heat transfer performance of SC packing is better than that of BCC packing. With the same packing form (BCC), the overall heat transfer performance of spherical particle model is better than that of ellipsoidal particle model and with the same particle shape and packing form (BCC packing with sphere), the overall heat transfer performance of uniform packing is better than that of non-uniform packing.

scholarly journals Numerical assessment on heat transfer performance of double-layered oblique fins microchannel heat sink with Al2O3 nanofluid

2021 ◽  
pp. 142-142
Author(s):  
Ji Choong ◽  
Kok Yu ◽  
Mohd Abdullah
Keyword(s):  
Heat Transfer ◽  
Thermal Resistance ◽  
Heat Sink ◽  
Heat Transfer Performance ◽  
Volume Fraction ◽  
Numerical Study ◽  
Al2o3 Nanoparticles ◽  
Microchannel Heat Sink ◽  
Transfer Performance ◽  
Primary Channel

This paper demonstrates a numerical study on heat transfer characteristics of laminar flow in a double-layered oblique finned heat sink using nanofluids with Al2O3 nanoparticles. Microchannel heat sink with primary channel width of 0.5 mm with aspect ratio of 3 is employed. Instead of having conventional straight fins, oblique fins with narrow secondary channels are used. In this numerical study, single-phase fluid model with conjugate heat transfer is considered. The numerical modelling was first validated with existing data for double-layered conventional microchannel heat sink having water (base fluid) as the working fluid. Numerical investigations on oblique finned microchannel heat sink were then conducted for flow rates ranging from 3?10-7 to 15?10-7 m3/s, equivalent to primary channel inlet velocity in between 0.2 and 1.0 m/s. It was found that double-layered oblique finned configuration yields better heat transfer performance, inferred by the lower overall thermal resistance obtained as compared with that of double-layered conventional heat sink. Employing double-layered oblique finned heat sink, the heat transfer performance could be further enhanced, by using nanoparticles that are added into water-based fluid. It is found that the reduction of overall thermal resistance is proportional to the volume fraction of nanoparticles. Using cross flow double-layered oblique finned configuration, the largest reduction in the overall thermal resistance can reach up to 25%, by using nanofluids with 4% volume fraction of Al2O3 nanoparticles.

Numerical Study on the Effect of Inner Tube Position on Heat Transfer Process in Self-Recuperative Radiant Tube

2011 ◽  
Vol 228-229 ◽  
pp. 676-680 ◽  
Author(s):  
Ye Tian ◽  
Xun Liang Liu ◽  
Zhi Wen
Keyword(s):  
Heat Transfer ◽  
Transfer Process ◽  
Numerical Study ◽  
Flame Temperature ◽  
Three Dimensional ◽  
Mathematic Model ◽  
Heat Transfer Process ◽  
Bulk Temperature ◽  
Radiant Tube ◽  
Peak Value

A three-dimensional mathematic model is developed for a 100kw single-end recuperative radiant tube and the simulation is performed with the CFD software FLUENT. Also it is used to investigate the effect of distance between combustion chamber exit and inner tube on heat transfer process. The results suggest that the peak value of combustion flame temperature drops along with the increasing of distance, which leads to low NOX discharging. Also radiant tube surface bulk temperature decreases, which causes radiant tube heating performance losses.

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.

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