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1.
A numerical study of the effects of the number and distribution of fins on the storage characteristics of a cylindrical latent heat energy storage system (LHESS) was conducted. Due to the low thermal conductivity of phase change materials (PCMs) used in LHESS, fins were added to the system to increase the rate of heat transfer and charging. Finite elements were used to implement the developed numerical method needed to study and solve for the phase change heat transfer (melting of PCM) encountered in a LHESS during charging. The effective heat capacity method was applied in order to account for the large amount of latent energy stored during melting of the PCM and the moving interface between the solid and liquid phases. The effects of increasing the number and distribution of fins on the melting rate of the PCM were studied for configurations having between 0 and 27 fins for heat transfer fluid (HTF) velocities of 0.05 and 0.5?m/s. Results show that the overall heat transfer rate to the PCM increases with an increase in the number of fins irrespective of the HTF velocity. It was also observed that the total amount of energy stored after 12?h increases nearly linearly with the addition of fins up to 12 fins; further addition of fins increasing the total energy stored by ever smaller amounts. 相似文献
2.
The melting process of industrial grade paraffin wax inside a shell-and-tube storage is analyzed by means of numerical simulation
and experimental results. For this purpose, the enthalpy porosity method is extended by a continuous liquid fraction function.
The extended method is tested using results gained from a gallium melt test inside a rectangular enclosure. 相似文献
3.
A numerical analysis of transient heat transfer during the flow of a melt in a cylindrical mould is presented. The analysis includes thermal resistance at the melt-mould interface, and axial conduction inside both melt and mould. Energy equations are formulated in a domain that expands continuously due to the advance of the melt inside the empty mould, and solved by the finite difference method using a time-stepping procedure. Calculations are compared to existing analytic results. It is found that axial conduction in the melt can significantly influence the rate of heat loss from the flowing melt, and that analytic approximations, which neglect axial conduction, may give erroneous predictions for the rate of heat loss. 相似文献
4.
An experimental investigation has been made of thermal characteristics of a rectangular, annular single-phase natural circulation
loop with the inner tube filled with a solid–liquid phase change material (PCM) under cyclic pulsating heat load. A rectangular,
annular loop of 150 cm in height and 75 cm in width was constructed with an annular gap of 0.6 cm, within which water was
filled. The inner tube of the annular loop was filled with a PCM (n-Eicosene) or air. Under the cyclic pulsating heat load, temperature field within the water-filled annular loop with PCM-
or air-filled inner tube was found to evolve into a steady periodic variation for the range of parameters considered. The
water temperature and/or its fluctuating amplitude along the heated or cooled sections of the loop with the PCM-filled inner
tube were found to be markedly lower than those measured in the loop with the air-filled inner tube under the identical conditions.
On the other hand, along the insulated sections of the loop a somewhat minute difference in temporal variations of the water
temperatures exists between the loops with PCM- and air-filled inner tube. In addition, at the outer wall along the cooled
section, a time-periodic variation of temperature was detected in synchronizing with the pulsating heat load. Parametric effects
of varying amplitude and time-period of the pulsating heat input, as well as of varying the inlet coolant temperature of the
cooling jacket were investigated.
Received on 30 June 2000
The authors are grateful for the support for this study from National Science Council of Republic of China in Taiwan under
the Project Nos. NSC87-2212-E006-054 and NSC88-2212-E006-022. 相似文献
5.
This paper discusses the results of numerical and experimental study of an encapsulated cool thermal energy storage system.
The storage system is a cylindrical storage tank filled with phase change material encapsulated in spherical container, placed
in a refrigeration loop. A simulation program was developed to evaluate the temperature histories of the heat transfer fluid
and the phase change material at any axial location during the charging period. The present analysis aims at studying the
influence of the inlet heat transfer fluid temperature and porosity on system performance. An experimental setup was designed
and constructed to conduct the experiments. The results of the model were validated by comparison with experimental results
of temperature profiles for different inlet heat transfer fluid temperatures and porosity. The results are in good agreement
with the experimental results. The results reported are much useful for designing cool thermal energy storage systems. 相似文献
6.
A. A. Vyatkin A. A. Ivanova V. G. Kozlov 《Journal of Applied Mechanics and Technical Physics》2016,57(2):344-351
This paper describes the thermal convection and heat transfer in a cylindrical fluid layer rotating around a horizontal axis, with various constant temperatures set at the layer boundaries. The influence of the rotational speed of the cylindrical fluid layer on the convective heat transfer in this layer is studied. The study results are presented as functions of dimensionless parameters that characterize the action of two convective mechanisms: centrifugal and thermal-oscillatory. It is shown that, with low rotational speed, the heat transfer is determined by quasistationary gravitational convection. 相似文献
7.
Khalid N. Alammar 《Heat and Mass Transfer》2006,42(9):861-866
Using the standard k–ε turbulence model, a two-dimensional turbulent pipe flow was simulated with and without square cavities. Effect of cavity aspect ratio on flow and heat transfer characteristics was investigated. Uncertainty was approximated through experimental validation and grid independence. The simulation revealed circulation inside the cavities. Cavity boundaries were shown to contribute significantly toward turbulence production. Cavity presence was shown to enhance overall heat transfer through the wall, while increasing pressure drop significantly across the pipe. It was predicted that cavities with higher aspect ratio enhance heat transfer more while increasing pressure drop. 相似文献
8.
The three-dimensional velocity fluctuation effects on heat transfer enhancement were experimentally investigated using a wind tunnel system and cylinders placed upstream of the test section in the wind tunnel. The cylinders with different diameters were used as turbulators to generate vortical flow motions with three-dimensional velocity fluctuations. A heated plate, part of the tunnel wall, was placed far downstream of the cylinders such that it was subjected mainly to flows with velocity fluctuations but with negligible steady vortical motions. These studies included three-component velocity measurements to characterize the near-wall and cross-section velocity fields and to obtain the turbulent kinetic energy. The temperatures were measured by thermocouples on the heated plate to obtain the convection heat transfer coefficients and the Nusselt numbers. Results indicate that the heat transfer was enhanced by the velocity fluctuations, which is attributed to the modification of boundary layer velocity profiles without the modification of boundary layer thickness. The resulting normalized Nusselt number was approximately a parabolic function of a dimensionless parameter, the product of Reynolds number and normalized turbulent kinetic energy. 相似文献
9.
3D numerical simulation on fluid flow and heat transfer characteristics in multistage heat exchanger with slit fins 总被引:1,自引:0,他引:1
In this paper, a numerical investigation is performed for three-stage heat exchangers with plain plate fins and slit fins
respectively, with a three-dimensional laminar conjugated model. The tubes are arranged in a staggered way, and heat conduction
in fins is considered. In order to save the computer resource and speed up the numerical simulation, the numerical modeling
is carried out stage by stage. In order to avoid the large pressure drop penalty in enhancing heat transfer, a slit fin is
presented with the strip arrangement of “front coarse and rear dense” along the flow direction. The numerical simulation shows
that, compared to the plain plate fin heat exchanger, the increase in the heat transfer in the slit fin heat exchanger is
higher than that of the pressure drop, which proves the excellent performance of this slit fin. The fluid flow and heat transfer
performance along the stages is also provided. 相似文献
10.
11.
A fluidic oscillator can produce self-induced and self-sustaining oscillating jet by fluid supply without moving parts. This device has attracted research interest in heat and mass transfer enhancement in recent years. In the current study, a double-feedback fluidic oscillator was numerically investigated based on three-dimensional unsteady Reynolds-averaged Navier-Stokes equations (3D-URANS) while the operating fluid is an incompressible flow. Then, the results were validated with experimental data by two-dimensional time-resolved particle image velocimetry (2D-TR-PIV) and thermographic phosphor thermometry (TPT) for the velocity and temperature field, respectively. A grid sensitivity study was done by comparison of instantaneous and time-averaged flow fields. Additionally, the proper orthogonal decomposition (POD) method was used to find the phase information of the oscillating jet, and fast Fourier transform (FFT) analysis was used to find the frequency of the oscillating jet to validate the numerical results. The effect of the working fluid was also studied. Finally, in order to determine the effect of the Reynolds number on heat transfer enhancement, the Q-criterion was calculated to provide detailed insight into the oscillating mechanism. The results show that the non-dimensional frequency of oscillation is independent of either the working fluid or mass flow rate. Additionally, for a given fluid, increasing Re causes strong vortices and increases the frequency of oscillation. However, the convection heat transfer did not change significantly when varying the mass flow rate because the convection velocity of vortices increases as the mass flow rate is enhanced. A comparison with a free jet reveals that the oscillating jet in a channel is useful in terms of covering a larger area. 相似文献
12.
13.
Meccanica - In the present study, the two-phase gas–liquid convective heat transfer is numerically studied inside uniformly heated wavy micro-tubes in the Taylor flow regime. Both Newtonian... 相似文献
14.
15.
The periodically fully developed laminar heat transfer and fluid flow characteristics inside a two-dimensional wavy channel
in a compact heat exchanger have been numerically investigated. Calculations were performed for Prandtl number 0.7, and Reynolds
number ranging from 100 to 1,100 on non-orthogonal non-staggered grid systems, based on SIMPLER algorithm in the curvilinear
body-fitted coordinates. Effects of wavy heights, lengths, wavy pitches and channel widths on fluid flow and heat transfer
were studied. The results show that overall Nusselt numbers and friction factors increase with the increase of Reynolds numbers.
According to the local Nusselt number distribution along channel wall, the heat transfer may be greatly enhanced due to the
wavy characteristics. In the geometries parameters considered, friction factors and overall Nusselt number always increase
with the increase of wavy heights or channel widths, and with the decrease of wavy lengths or wavy pitches. Especially the
overall Nusselt number significantly increase with the increase of wavy heights or channel widths, where the flow may become
into transition regime with a penalty of strongly increasing in pressure drop.
An erratum to this article can be found at 相似文献
16.
17.
《Experimental Thermal and Fluid Science》2001,24(1-2):1-9
Experimental measurements of the forced convection gas-particle heat transfer coefficient in a packed bed, high-temperature, thermal energy storage system were performed using a custom-made experimental facility. Special attention was paid to the application of uncertainty analysis (a very important concept in experimentation). General and detailed uncertainty analyses were carried out, which identified the choices that were made in the experimental planning and procedure to ensure reliable final results. The experimental data reduction program used the governing equations and the results of the uncertainty analysis while making allowance for media property variations with temperature. Results were correlated in terms of Nusselt number, Prandtl number and Reynolds number and comparisons were made with existing correlations developed with similar storage media. The maximum temperature for the bed was about 1000°C (1830°F) with flue gas as the operating fluid in the storage mode and atmospheric air in the recovery mode. Because most related previous studies were not necessarily focused on high-temperature applications, the published gas-particle heat transfer correlations were obtained at relatively low temperature ranges, generally at room temperature or at temperatures slightly above room temperature. Moreover, only a few of the previously reported correlations associated the results with the corresponding uncertainty margins. The results from this study give a convective gas-particle heat transfer correlation for high-temperature thermal energy storage applications. Also, due to substantial uncertainties normally associated with the measurements of this heat transfer coefficient, it is significant to note that no firm conclusions can be reached on the validity or non-validity of previously reported related correlations for which the uncertainty margins were not reported. 相似文献
18.
The convective heat transfer characteristics in a periodic converging–diverging heat exchanger channel are investigated experimentally.
Experiments were performed for Prandtl number 0.7, for corrugation angle of 30°. In order to determine the channel having
the best performance, the channels also compared by considering the flow area goodness factor. 相似文献
19.
20.
H. A. Attia 《Journal of Applied Mechanics and Technical Physics》2005,46(1):68-76
An unsteady flow and heat transfer to an infinite porous disk rotating in a Reiner—Rivlin non-Newtonian fluid are considered. The effect of the non-Newtonian fluid characteristics and injection (suction) through the disk surface on velocity and temperature distributions and heat transfer is considered. Numerical solutions are obtained over the entire range of the governing parameters.Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 46, No. 1, pp. 85–95, January–February, 2005. 相似文献