Two-Dimensional Effects on the Response of Packed Bed Regenerators

1989 ◽  
Vol 111 (2) ◽  
pp. 328-336 ◽  
Author(s):  
J. A. Khan ◽  
D. E. Beasley
Keyword(s):  
Heat Transfer ◽  
Void Fraction ◽  
Transient Response ◽  
Packed Bed ◽  
Wall Effect ◽  
Heat Transfer Fluid ◽  
Fluid Temperature ◽  
Two Dimensional ◽  
Dimensional Effects ◽  
Wide Range

Packed beds have a wide range of applications as heat transfer and energy storage devices. Employed as a regenerator, a packed bed is subject to the flow of a heat transfer fluid, which alternately stores and recovers energy from a packing of discrete particles. The flow direction reverses during the addition and removal of energy. The nature of a packing of discrete particles in a container is such that variations in the resistance to flow and in the void fraction occur across the cross section of the packing. Particularly, the region of the bed near the boundary of the container has a markedly reduced resistance to flow. In addition, the wall effect on the packing geometry changes the void fraction in the near-wall region. The purpose of the present study is to quantify the two-dimensional effects of nonuniform void fraction, velocity, and temperature distributions in a packed bed regenerator on the dynamic and steady periodic behavior. A two-dimensional numerical model of the transient response of a packed bed subject to the flow of a heat transfer fluid has been developed and verified through comparison with measured responses. The model includes the effects of nonuniform velocity and porosity in the bed, and the effects of axial and radial thermal dispersion. The results of the present computations are compared with one-dimensional transient periodic results to demonstrate the two-dimensional effects on the transient response of a packed bed regenerator to a step change in fluid temperature. The classical dimensionless parameters, such as reduced length and reduced time, are not sufficient to characterize the two-dimensional transient nature of a packed bed regenerator. This study identifies the range of bed-to-particle-diameter ratios over which the transient response is significantly influenced by the wall effect on void fraction and flow.

Thermal Storage and Heat Transfer in Phase Change Material Outside a Circular Tube with Axial Variation of the Heat Transfer Fluid Temperature

1999 ◽  
Vol 121 (3) ◽  
pp. 145-149 ◽  
Author(s):  
Zhu Yingqiu ◽  
Zhang Yinping ◽  
Jiang Yi ◽  
Kang Yanbing
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Phase Change Material ◽  
Circular Tube ◽  
Thermal Storage ◽  
Heat Transfer Fluid ◽  
Fluid Temperature ◽  
Design And Optimization ◽  
Wide Range ◽  
Change Material

A theoretical model is developed to analyze the thermal storage and heat transfer characteristics in a phase change material outside a circular tube with heat transfer fluid inside the tube. A new method, the alternative iteration between temperature and thermal resistance method, is presented to analyze the variation of the phase change radius, the axial temperature variation in the heat transfer fluid and the thermal storage in the circular tube. Dimensionless formulae are developed using theoretical and numerical analysis. The present solutions agree well with those in the literature. The dimensionless correlations are not limited to one condition, so they provide a basis for tube heat transfer design and optimization over a wide range of conditions.

Heat and Mass Transfer in an Incompressible Turbulent Boundary Layer

1972 ◽  
Vol 94 (1) ◽  
pp. 23-28 ◽  
Author(s):  
E. Brundrett ◽  
W. B. Nicoll ◽  
A. B. Strong
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Mass Transfer ◽  
Porous Plate ◽  
Mixing Length ◽  
Two Dimensional ◽  
Transfer Data ◽  
Incompressible Turbulent Boundary Layer ◽  
Wide Range ◽  
Incompressible Boundary

The van Driest damped mixing length has been extended to account for the effects of mass transfer through a porous plate into a turbulent, two-dimensional incompressible boundary layer. The present mixing length is continuous from the wall through to the inner-law region of the flow, and although empirical, has been shown to predict wall shear stress and heat transfer data for a wide range of blowing rates.

A 3-D Model Simulation of High Temperature Solar Cavity Receiver

2017 ◽  
Author(s):  
Huayi Feng ◽  
Yanping Zhang ◽  
Chongzhe Zou
Keyword(s):  
Heat Transfer ◽  
Radiation Intensity ◽  
Large Scale ◽  
Model Simulation ◽  
Heat Transfer Fluid ◽  
Working Fluid ◽  
Outlet Temperature ◽  
Fluid Temperature ◽  
Heat Transfer Efficiency ◽  
Direct Normal Irradiance

In this paper, a 3-D numerical model is proposed to investigate the capability of generating high operating temperature for a modified solar cavity receiver in large-scale dish Stirling system. The proposed model aims to evaluate the influence of radiation intensity on the cavity receiver performance. The properties of the heat transfer fluid in the pipe and heat transfer losses of the receiver are investigated by varying the direct normal irradiance from 400W/m2 to 1000W/m2. The temperature of heat transfer fluid, as well as the effect of radiation intensity on the heat transfer losses have been critically presented and discussed. The simulation results reveal that the heat transfer fluid temperature and thermal efficiency of the receiver are significantly influenced by different radiation flux. With the increase of radiation intensity, the efficiency of the receiver will firstly increase, then drops after reaching the highest point. The outlet working fluid temperature of the pipe will be increased consistently. The results of the simulations show that the designed cylindrical receiver used in dish Stirling system is capable to achieve the targeted outlet temperature and heat transfer efficiency, with an acceptable pressure drop.

scholarly journals Analysis of Heat Transfer Mechanism for Shelf Vacuum Freeze-Drying Equipment

2014 ◽  
Vol 2014 ◽  
pp. 1-7 ◽  
Author(s):  
Hong-Ping Cheng ◽  
Shian-Min Tsai ◽  
Chin-Chi Cheng
Keyword(s):  
Heat Transfer ◽  
Heat Exchange ◽  
Low Temperature ◽  
Temperature Gradient ◽  
Freeze Drying ◽  
Heat Transfer Fluid ◽  
Processing Temperature ◽  
Fluid Temperature ◽  
Three Dimension ◽  
Flow Rates

Vacuum freeze-drying technology is applicable to the process of high heat-sensitive products. Due to the long drying period and extremely low processing temperature and pressure, the uniform and efficiency of heat transfer fluid temperature in shelf are critical for product quality. Therefore, in this study, the commercial computer fluid dynamics (CFD) software, FLUENT, was utilized for three-dimension numerical simulation of the shelf vacuum freeze-drying process. The influences of different inlet and outlet positions for shelves on the uniformity of the flow rate and temperature were discussed. Moreover, it explored the impacts on the temperature gradient of shelves after heat exchange of different flow rates and low temperature materials. In order to reduce the developing time and optimize the design, the various secondary refrigerants in different plies of shelves were investigated. According to the effect of heat exchange between different flow rates and low temperature layer material shelves on the temperature gradient of shelves surface, the minimum temperature gradient was 20 L/min, and the maximum was 2.5 L/min.

A Natural Convection Fin with a Solution-Determined Nonmonotonically Varying Heat Transfer Coefficient

1981 ◽  
Vol 103 (2) ◽  
pp. 218-225 ◽  
Author(s):  
E. M. Sparrow ◽  
S. Acharya
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Natural Convection ◽  
Transfer Coefficient ◽  
First Principles ◽  
Numerical Solutions ◽  
Flow Direction ◽  
Operating Conditions ◽  
Fluid Temperature ◽  
Wide Range

A conjugate conduction-convection analysis has been made for a vertical plate fin which exchanges heat with its fluid environment by natural convection. The analysis is based on a first-principles approach whereby the heat conduction equation for the fin is solved simultaneously with the conservation equations for mass, momentum, and energy in the fluid boundary layer adjacent to the fin. The natural convection heat transfer coefficient is not specified in advance but is one of the results of the numerical solutions. For a wide range of operating conditions, the local heat transfer coefficients were found not to decrease monotonically in the flow direction, as is usual. Rather, the coefficient decreased at first, attained a minimum, and then increased with increasing downstream distance. This behavior was attributed to an enhanced buoyancy resulting from an increase in the wall-to-fluid temperature difference along the streamwise direction. To supplement the first-principles analysis, results were also obtained from a simple adaptation of the conventional fin model.

Dynamic Performance Analysis of Large-Scale Packed Bed Truncated Conical Thermal Energy Storage

2019 ◽  
Author(s):  
Shobhana Singh ◽  
Kim Sørensen
Keyword(s):  
Energy Storage ◽  
Large Scale ◽  
Storage System ◽  
Transient Behavior ◽  
Packed Bed ◽  
Energy Storage System ◽  
Heat Transfer Fluid ◽  
Design Parameters ◽  
Wide Range ◽  
Dynamic Performance Analysis

Abstract In the present paper, a high-temperature packed bed energy storage system of volume 175,000m3 is numerically investigated. The system is a underground packed bed of truncated conical shape, which comprises of rocks as a storage medium and air as a heat transfer fluid. A one-dimensional, two-phase model is developed to simulate the transient behavior of the storage. The developed model is used to conduct a parametric study with a wide range of design parameters to investigate the change in performance during both charging and discharging operation. Results show that the model satisfactorily predicts the dynamic behavior, and the truncated conical shaped storage with a rock diameter of 3cm, insulation thickness up to 0.6m and charging-discharging rate of 553kg/s leads to lower thermal losses and higher energy efficiencies. The paper provides useful insight into the transient performance and efficiency of a large-scale packed bed energy storage system within the range of parameters investigated.

Numerical Study of Thermochemical Storage Using Ca(OH)2/CaO: High Temperature Applications

2016 ◽  
Author(s):  
Qasim A. Ranjha ◽  
Nasser Vahedi ◽  
Alparslan Oztekin
Keyword(s):  
Heat Transfer ◽  
Energy Storage ◽  
Thermal Energy ◽  
Thermal Energy Storage ◽  
Numerical Study ◽  
Storage System ◽  
Packed Bed ◽  
Heat Transfer Fluid ◽  
Operational Parameters ◽  
Storage And Retrieval

Thermal energy storage by reversible gas-solid reaction has been selected as a thermochemical energy storage system. Simulations are conducted to investigate the dehydration of Ca(OH)2 and the hydration of CaO for thermal energy storage and retrieval, respectively. The rectangular packed bed is heated indirectly by air used as a heat transfer fluid (HTF) while the steam is transferred through the upper side of the bed. Transient mass transport and heat transfer equations coupled with chemical kinetics equations for a two dimensional geometry have been solved using finite element method. Numerical results have been validated by comparing against results of previous measurements and simulations. The effect of geometrical and operational parameters including the material properties on overall storage and retrieval process has been investigated. The co-current and counter-current flow arrangements for steam and heat transfer fluid have been considered.

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