Heat Transfer Analysis of a Novel Pressurized Air Receiver for Concentrated Solar Power via Combined Cycles

2009 ◽  
Vol 1 (4) ◽  
Author(s):  
I. Hischier ◽  
D. Hess ◽  
W. Lipiński ◽  
M. Modest ◽  
A. Steinfeld
Keyword(s):  
Heat Transfer ◽  
Thermal Efficiency ◽  
Porous Ceramic ◽  
Conservation Equation ◽  
Heat Transfer Analysis ◽  
Operational Parameters ◽  
Small Aperture ◽  
Solar Absorber ◽  
Energy Conservation Equation ◽  
Combined Cycles

A novel design of a high-temperature pressurized solar air receiver for power generation via combined Brayton–Rankine cycles is proposed. It consists of an annular reticulate porous ceramic (RPC) bounded by two concentric cylinders. The inner cylinder, which serves as the solar absorber, has a cavity-type configuration and a small aperture for the access of concentrated solar radiation. Absorbed heat is transferred by conduction, radiation, and convection to the pressurized air flowing across the RPC. A 2D steady-state energy conservation equation coupling the three modes of heat transfer is formulated and solved by the finite volume technique and by applying the Rosseland diffusion, P1, and Monte Carlo radiation methods. Key results include the temperature distribution and thermal efficiency as a function of the geometrical and operational parameters. For a solar concentration ratio of 3000 suns, the outlet air temperature reaches 1000°C at 10 bars, yielding a thermal efficiency of 78%.

Heat Transfer Analysis of a Novel Pressurized Air Receiver for Concentrated Solar Power Via Combined Cycles

2009 ◽  
Author(s):  
Illias Hischier ◽  
Daniel Hess ◽  
Wojciech Lipin´ski ◽  
Michael Modest ◽  
Aldo Steinfeld
Keyword(s):  
Heat Transfer ◽  
Thermal Efficiency ◽  
Porous Ceramic ◽  
Conservation Equation ◽  
Heat Transfer Analysis ◽  
Operational Parameters ◽  
Small Aperture ◽  
Solar Absorber ◽  
Energy Conservation Equation ◽  
Combined Cycles

A novel design of a high-temperature pressurized solar air receiver for power generation via combined Brayton-Rankine cycles is proposed. It consists of an annular reticulate porous ceramic (RPC) bounded by two concentric cylinders. The inner cylinder, which serves as the solar absorber, has a cavity-type configuration and a small aperture for the access of concentrated solar radiation. Absorbed heat is transferred by conduction, radiation, and convection to the pressurized air flowing across the RPC. A 2D steady-state energy conservation equation coupling the three modes of heat transfer is formulated and solved by the finite volume technique and by applying the Rosseland diffusion, P1, and Monte Carlo radiation methods. Key results include the temperature distribution and the thermal efficiency as a function of the geometrical and operational parameters. For a solar concentration ratio of 3000 suns, the outlet air temperature reaches 1000°C at 10 bars, yielding a thermal efficiency of 78%.

Design Studies for a Solar Reactor Based on a Simple Radiative Heat Exchange Model

2005 ◽  
Vol 127 (3) ◽  
pp. 425-429 ◽  
Author(s):  
C. Wieckert
Keyword(s):  
Heat Transfer ◽  
Solar Power ◽  
Radiation Heat Transfer ◽  
Heat Transfer Analysis ◽  
Physical Parameters ◽  
Concentrated Solar Power ◽  
Radiation Heat ◽  
Small Aperture ◽  
Lower Cavity ◽  
Solar Reactor

A high-temperature solar chemical reactor for the processing of solids is scaled up from a laboratory scale (5kW concentrated solar power input) to a pilot scale (200kW). The chosen design features two cavities in series: An upper cavity has a small aperture to let in concentrated solar power coming from the top. It serves as the solar receiver, radiant absorber, and radiant emitter to a lower cavity. The lower cavity is a well-insulated enclosure. It is subjected to thermal radiation from the upper cavity and serves in our application as the reaction chamber for a mixture of ZnO and carbon. Important insight for the definition of the geometrical parameters of the pilot reactor has been generated by a radiation heat transfer analysis based on the radiosity enclosure theory. The steady-state model accounts for radiation heat transfer within the solar reactor including reradiation losses through the reactor aperture, wall losses due to thermal conduction and heat consumption by the endothermic chemical reaction. Key results include temperatures of the different reactor walls and the thermal efficiency of the reactor as a function of the major geometrical and physical parameters. The model, hence, allows for a fast estimate of the influence of these parameters on the reactor performance.

Chebyshev Collocation Spectral Method for Three-Dimensional Transient Coupled Radiative–Conductive Heat Transfer

2012 ◽  
Vol 134 (9) ◽  
Author(s):  
Ya-Song Sun ◽  
Jing Ma ◽  
Ben-Wen Li
Keyword(s):  
Heat Transfer ◽  
Spectral Method ◽  
Three Dimensional ◽  
Conservation Equation ◽  
Conductive Heat Transfer ◽  
Discrete Ordinates ◽  
Conductive Heat ◽  
Chebyshev Collocation ◽  
Energy Conservation Equation ◽  
Collocation Spectral Method

Abstract A Chebyshev collocation spectral method (CSM) is presented to solve transient coupled radiative and conductive heat transfer in three-dimensional absorbing, emitting, and scattering medium in Cartesian coordinates. The walls of the enclosures are considered to be opaque, diffuse, and gray and have specified temperature boundary conditions. The CSM is adopted to solve both the radiative transfer equation (RTE) and energy conservation equation in spatial domain, and the discrete ordinates method (DOM) is used for angular discretization of RTE. The exponential convergence characteristic of the CSM for transient coupled radiative and conductive heat transfer is studied. The results using the CSM show very satisfactory calculations comparing with available results in the literature. Based on this method, the effects of various parameters, such as the scattering albedo, the conduction–radiation parameter, the wall emissivity, and the optical thickness, are analyzed.

Computational Heat Transfer Analysis of the Effect of Skirts on the Performance of Third-World Cookstoves

2009 ◽  
Vol 1 (4) ◽  
Author(s):  
Alex Wohlgemuth ◽  
Sandip Mazumder ◽  
Dale Andreatta
Keyword(s):  
Heat Transfer ◽  
Thermal Efficiency ◽  
Third World ◽  
Heat Transfer Analysis ◽  
Vertical Position ◽  
Dynamics Model ◽  
Unknown Parameters ◽  
Insulating Layer ◽  
Computational Predictions

In many developing countries, natural gas, wood, or biomass fired cookstoves find prolific usage. Skirts, placed around the cookpot, have been proposed as a means to improve the thermal efficiency. However, use of skirts has shown conflicting results, and the role of skirts is poorly understood. In this study, a computational heat transfer analysis of a generic third-world cookstove is conducted with the goal to understand the effect of various skirt-related parameters on the overall heat transfer characteristics and thermal efficiency. A computational fluid dynamics model, including turbulence and heat transfer by all three modes, was created. The model was first validated against the experimental data, also collected as part of this study. Unknown parameters in the model were calibrated to better match the experimental observations. Subsequently, the model was explored to study the effects of several skirt-related parameters. These include the vertical position of the skirt, the width of the gap between the skirt and the cookpot, and the thermal conductivity of the skirt (insulating versus conducting material). The computational predictions suggest that the skirt must either be made out of an insulating material or insulated on the outer surface by a backing insulating layer for it to provide maximum benefits. It was also found that it must be placed at an optimum distance away from the cookpot and aligned with the mouth of the cookstove chimney for maximum thermal efficiency. An optimum set of conditions obtained through this computational analysis resulted in an increase in the thermal efficiency from 20.7% to 28.7%.

Sub-Grid Filtering Model for Multiphase Heat Transfer With Immersed Tubes

2014 ◽  
Author(s):  
William A. Lane ◽  
Emily M. Ryan ◽  
Avik Sarkar ◽  
Sankaran Sundaresan
Keyword(s):  
Heat Transfer ◽  
Solid Phase ◽  
Constitutive Relations ◽  
Conservation Equation ◽  
Coarse Grid ◽  
Computational Grids ◽  
Constitutive Function ◽  
Flow Simulations ◽  
Energy Conservation Equation ◽  
Functional Forms

Adequately resolving the hydrodynamics and heat transfer in gas-solid flow simulations typically requires computational grids on the order of 1–10 particle diameters. This requirement is not feasible for most full-scale applications. To overcome these impracticalities, we consider a sub-grid filtering approach where the microscopic heat transfer mechanisms are approximated through coarse grid simulations using constitutive relations. Using the open source CFD code Multiphase Flow with Interphase Exchanges (MFIX), we simulate a periodic unit cell domain with immersed horizontal heat transfer cylinders under varying solid-phase fractions and temperatures. The simulation results are averaged over the domain and are used to fit functional forms describing relations between the flow properties and input conditions. The result is a constitutive function that is added as a source term to the solid-phase energy conservation equation to approximate the effective heat transfer between the cylinders and flow with coarse grid simulations.

Applicability of Heat Mirrors in Reducing Thermal Losses in Concentrating Solar Collectors

2016 ◽  
Author(s):  
Prashant Mahendra ◽  
Vikrant Khullar ◽  
Madhup Mittal
Keyword(s):  
Heat Transfer ◽  
Thermal Efficiency ◽  
Solar Irradiance ◽  
Solar Collector ◽  
Flux Distribution ◽  
Heat Transfer Analysis ◽  
Transfer Model ◽  
Solar Collectors ◽  
Parabolic Trough ◽  
Glass Envelope

Flux distribution around the parabolic trough receiver being typically non-uniform, only a certain portion of the receiver circumference receives the concentrated solar irradiance. However, radiative and convective losses occur across the entire receiver circumference. This paper attempts to introduce the idea employing transparent heat mirror to effectively reduce the heat loss area and thus improve the thermal efficiency of the solar collector. Transparent heat mirror essentially has high transmissivity in the solar irradiance wavelength band and high reflectivity in the mid-infrared region thus it allows the solar irradiance to pass through but reflects the infrared radiation back to the solar selective metal tube. Practically, this could be realized if certain portion of the conventional low iron glass envelope is coated with Sn-In2O3 so that its acts as a heat mirror. In the present study, a parabolic receiver design employing the aforesaid concept has been proposed. Detailed heat transfer model has been formulated. The results of the model were compared with the experimental results of conventional concentrating parabolic trough solar collectors in the literature. It was observed that while maintaining the same external conditions (such as ambient/initial temperatures, wind speed, solar insolation, flow rate, concentration ratio etc.) the heat mirror-based parabolic trough concentrating solar collector has about 3–12% higher thermal efficiency as compared to the conventional parabolic solar collector. Furthermore, steady state heat transfer analysis reveals that depending on the solar flux distribution there is an optimum circumferential angle (θ = θoptimum, where θ is the heat mirror circumferential angle) up to which the glass envelope should be coated with Sn-In2O3. For angles higher than the optimum angle, the collector efficiency tends to decrease owing to increase in optical losses.

scholarly journals A Pressurized High-Flux Solar Reactor for the Thermochemical Gasification of Charcoal Slurry—Two-Phase Flow and Heat Transfer Analysis

2019 ◽  
Vol 142 (5) ◽  
Author(s):  
F. Müller ◽  
A. Steinfeld
Keyword(s):  
Heat Transfer ◽  
Two Phase Flow ◽  
Calculated Data ◽  
Heat Transfer Analysis ◽  
Phase Flow ◽  
Operational Parameters ◽  
Two Phase ◽  
Carbonaceous Particles ◽  
Solar Reactor ◽  
Concentrated Solar Energy

Abstract A pressurized solar reactor for effecting the thermochemical gasification of carbonaceous particles driven by concentrated solar energy is modeled by means of a reacting two-phase flow. The governing mass, momentum, and energy conservation equations are formulated and solved numerically by finite volume computational fluid dynamics (CFD) coupled to a Monte Carlo radiation solver for a nongray absorbing, emitting, and scattering participating medium. Implemented are Langmuir–Hinshelwood kinetic rate expressions and size-dependent properties for charcoal particles undergoing shrinkage as gasification progresses. Validation is accomplished by comparing the numerically calculated data with the experimentally measured temperatures in the range 1283–1546 K, chemical conversions in the range 32–94%, and syngas product H2:CO and CO2:CO molar ratios obtained from testing a 3 kW solar reactor prototype with up to 3718 suns concentrated radiation. The simulation model is applied to identify the predominant heat transfer mechanisms and to analyze the effect of the solar rector's geometry and operational parameters (namely: carbon feeding rate, inert gas flowrate, solar concentration ratio, and total pressure) on the solar reactor's performance indicators given by the carbon molar conversion and the solar-to-fuel energy efficiency. Under optimal conditions, these can reach 94% and 40%, respectively.

Methods for Monitoring the Temperature of GIS Bus Conductor

2014 ◽  
Vol 687-691 ◽  
pp. 770-773
Author(s):  
Gang Wu ◽  
Long Teng Li ◽  
Yun Feng Peng ◽  
Cheng Wen Zhu ◽  
Yong Liang Zhang
Keyword(s):  
Heat Transfer ◽  
Partial Discharge ◽  
Radiation Heat Transfer ◽  
Conservation Equation ◽  
Heat Radiation ◽  
Radiation Heat ◽  
Energy Conservation Equation ◽  
Heat Transfer Theory ◽  
Calculation Results ◽  
Long Time

The performance of GIS bus is directly linked with its heat radiation and temperature rise, and its long-time overheating may cause partial discharge and bus burn-up, posing a threat to the reliability of power system. This paper, based on heat transfer theory and taking into account convection and radiation heat transfer, builds the energy conservation equation and iteratively calculates the temperatures of the bus conductor and shell. The comparison of the calculation results with experimental data has confirmed the correctness of the calculation.

Semi-empirical heat transfer correlations for turbulent tube flow of liquid metals

2018 ◽  
Vol 28 (1) ◽  
pp. 151-172
Author(s):  
Dawid Taler
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Nusselt Number ◽  
Prandtl Number ◽  
Liquid Metals ◽  
Conservation Equation ◽  
Turbulent Prandtl Number ◽  
Content Type ◽  
Nusselt Numbers ◽  
Energy Conservation Equation

Purpose The purpose of this paper is to develop new semi-empirical heat transfer correlations for turbulent flow of liquid metals in the tubes, and then to compare these correlations with the experimental data. The Prandtl and Reynolds numbers can vary in the ranges: 0.0001 ≤ Pr ≤ 0.1 and 3000 ≤ Re ≤ 106. Design/methodology/approach The energy conservation equation averaged by Reynolds was integrated using the universal velocity profile determined experimentally by Reichardt for the turbulent tube flow and four different models for the turbulent Prandtl number. Turbulent heat transfer in the circular tube was analyzed for a constant heat flux at the inner surface. Some constants in different models for the turbulent Prandtl number were adjusted to obtain good agreement between calculated and experimentally obtained Nusselt numbers. Subsequently, new correlations for the Nusselt number as a function of a Peclet number was proposed for different models of the turbulent Prandtl number. Findings The inclusion of turbulent Prandtl number greater than one and the experimentally determined velocity profile of the fluid in the tube while solving the energy conservation equation improved the compatibility of calculated Nusselt numbers, with Nusselt numbers determined experimentally. The correlations proposed in the paper have a sound theoretical basis and give Nusselt number values that are in good agreement with the experimental data. Research limitations/implications Heat transfer correlations proposed in this paper were derived assuming a constant heat flux at the inner surface of the tube. However, they can also be used for a constant wall temperature, as for the turbulent flow (Re > 3,000), the relative difference between the Nusselt number for uniform wall heat flux and uniform wall temperature is very low. Originality/value Unified, systematic approach to derive correlations for the Nusselt number for liquid metals was proposed in the paper. The Nusselt number was obtained from the solution of the energy conservation equation using the universal velocity profile and eddy diffusivity determined experimentally, and various models for the turbulent Prandtl number. Four different relationships for the Nusselt number proposed in the paper were compared with the experimental data.

Evaluation of the Radiative Heat Flux in Absorbing, Emitting and Linear-Anisotropically Scattering Cylindrical Media

1981 ◽  
Vol 103 (2) ◽  
pp. 350-356 ◽  
Author(s):  
F. H. Azad ◽  
M. F. Modest
Keyword(s):  
Heat Transfer ◽  
Anisotropic Scattering ◽  
Conservation Equation ◽  
Substantial Improvement ◽  
Radial Coordinate ◽  
Differential Approximation ◽  
Approximate Methods ◽  
Radial Temperature ◽  
Conservation Of Energy ◽  
Energy Conservation Equation

The contribution of thermal radiation to heat transfer in an emitting, absorbing and linear-anisotropically scattering medium of one-dimensional cylindrical geometry is investigated. It is assumed that the radial temperature distribution in the medium is known or is found in conjunction with overall conservation of energy. The exact solution results in a first-order integral equation in the radial coordinate which is a substantial improvement over previous formulations developed for nonscattering media. Also, two approximate methods are established and tested for their accuracy. The first method is the differential approximation modified to accommodate linear-anisotropic scattering. The second method consists of an exponential kernel approximation in which the geometric integrand functions are replaced by simple exponential functions. The results presented indicate that in engineering applications either approximate method may be used to accurately model the radiative contribution to overall heat transfer rates, reducing the nonlinear integrodifferential energy conservation equation to a nonlinear differential equation.

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