Effect of Carbon Particle Seeding As Radiant Absorbent for Enhanced Heat Transfer

2019 ◽  
Author(s):  
Hamed Abedini Najafabadi ◽  
Nesrin Ozalp
Keyword(s):  
Heat Transfer ◽  
Elevated Temperatures ◽  
Radiation Heat Transfer ◽  
Carbon Particle ◽  
Subsequent Treatment ◽  
Working Fluid ◽  
Solar Simulator ◽  
Original Activity ◽  
Carbon Particles ◽  
Solar Reactor

Abstract Carbon particles can be used as catalyst in solar reactors where they serve as radiant absorbent and nucleation sites for the heterogeneous decomposition reaction. Unlike commonly used metal catalysts, carbon catalyst does not have durability problem and high cost. However, in order to achieve sustainable catalytic decomposition of feedstock over carbon catalysts at elevated temperatures, the surface area of the carbon particles must be maintained. A subsequent treatment of deactivated carbon samples with CO2 at about 1000°C would increase the surface and would recover the original activity as catalyst. In solar reactor, carbon particles are directly exposed to the high-flux irradiation providing efficient radiation heat transfer directly to the reaction site. Therefore, one of the key parameters to achieve higher conversion efficiencies in solar reactor is the presence and transport of carbon particles. This paper will present impact of carbon use in enhancing the heat transfer inside a solar reactor radiated by a solar simulator. Flux entering the receiver is determined using Monte Carlo ray tracing (MCRT) method which is coupled with energy balance equations to derive numerical model describing dynamic temperature variation in solar receiver. Simulation results indicated that feeding carbon particles results to lower temperatures for the cavity walls and working fluid compare to the case that no carbon is injected. This finding is in accordance with our experimental results obtained from a cylindrical cavity receiver radiated by a 7 kW solar simulator. The results indicated that heat transfer within the system is highly influenced by the particle size. At particle sizes larger than 450 μm, carbon feeding increases the thermal efficiency of the system.

Effect of Carbon Particle Feeding as Radiant Absorbent for Enhanced Heat Transfer

2021 ◽  
pp. 1-15
Author(s):  
Hamed Abedini ◽  
Nesrin Ozalp
Keyword(s):  
Heat Transfer ◽  
Particle Size ◽  
Temperature Profile ◽  
Energy Absorption ◽  
Carbon Particle ◽  
Carbon Particles ◽  
Solar Reactor ◽  
Simulation Results ◽  
Particle Feeding ◽  
Solar Receiver

Abstract Carbon particles can be used as catalyst in solar reactors where they serve as radiant absorbent and nucleation sites for the heterogeneous decomposition reaction. Unlike commonly used metal catalysts, carbon catalyst does not have durability problem and high cost. However, in order to achieve sustainable catalytic decomposition of feedstock over carbon catalysts at elevated temperatures, the surface area of the carbon particles must be maintained. A subsequent treatment of deactivated carbon samples with CO2 at about 1000 °C would increase the surface and would recover the original activity as catalyst. In a windowed solar reactor, carbon particles are directly exposed to the high flux irradiation providing efficient radiation heat transfer directly to the reaction site. Therefore, one of the key parameters to achieve higher conversion efficiencies in a solar reactor is the presence and transport of carbon particles. In this paper, a transient one-dimensional model is presented to describe effect of carbon particle feeding on energy transport and temperature profile of a cavity-type solar receiver. The model was developed by dividing the receiver into several control volumes and formulating energy balance equations for gas phase, particles, and cavity walls within each control volume. Monte Carlo ray tracing (MCRT) method was used to determine the solar heat absorbed by particles and cavity walls, as well as the radiative exchange between particles and cavity walls. Model accuracy was verified by experimental work using a solar receiver where carbon particles were injected uniformly. Comparison of simulation results with the experimentally measured temperatures at three different locations on cavity receiver wall showed an average deviation of 3.81%. The model was then used to study the effect of carbon particle size and feeding rate on the heat transfer, temperature profile, and energy absorption of the solar receiver. Based on the simulation results, it was found that injection of carbon particles with a size bigger than 500 µm has no significant influence on heat transfer of the system. However, by reducing the particle size lower than 500 µm, temperature uniformity and energy absorption were enhanced.

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.

Carbon Particle Generation and Preliminary Small Particle Heat Exchange Receiver Lab Scale Testing

2013 ◽  
Author(s):  
Lee Frederickson ◽  
Kyle Kitzmiller ◽  
Fletcher Miller
Keyword(s):  
High Temperature ◽  
Heat Exchange ◽  
Natural Gas ◽  
Small Particle ◽  
Carbon Particle ◽  
Solar Flux ◽  
Gas Mixture ◽  
Solar Simulator ◽  
Spherical Cap ◽  
Carbon Particles

High temperature central receivers are on the forefront of concentrating solar power research. Current receivers use liquid cooling and power steam cycles, but new receivers are being designed to power gas turbine engines within a power cycle while operating at a high efficiency. To address this, a lab-scale Small Particle Heat Exchange Receiver (SPHER), a high temperature solar receiver, was built and is currently undergoing testing at the San Diego State University’s (SDSU) Combustion and Solar Energy Laboratory. The final goal is to design, build, and test a full-scale SPHER that can absorb 5 MWth and eventually be used within a Brayton cycle. The SPHER utilizes air mixed with carbon particles generated in the Carbon Particle Generator (CPG) as an absorption medium for the concentrated solar flux. Natural gas and nitrogen are sent to the CPG where the natural gas undergoes pyrolysis to carbon particles and nitrogen is used as the carrier gas. The resulting particle-gas mixture flows out of the vessel and is met with dilution air, which flows to the SPHER. The lab-scale SPHER is an insulated steel vessel with a spherical cap quartz window. For simulating on-sun testing, a solar flux is produced by a solar simulator, which consists of a 15kWe xenon arc lamp, situated vertically, and an ellipsoidal reflector to obtain a focus at the plane of the receiver window. The solar simulator has been shown to produce an output of about 3.25 kWth within a 10 cm diameter aperture. Inside of the SPHER, the carbon particles in the inlet particle-gas mixture absorb radiation from the solar flux. The carbon particles heat the air and eventually oxidize to carbon dioxide, resulting in a clear outlet fluid stream. Since testing was initiated, there have been several changes to the system as we have learned more about the operation. A new extinction tube was designed and built to obtain more accurate mass loading data. Piping and insulation for the CPG and SPHER were improved based on observations between testing periods. The window flange and seal have been redesigned to incorporate window film cooling. These improvements have been made in order to achieve the lab scale SPHER design objective gas outlet flow of 650°C at 5 bar.

A Computational Fluid Dynamics Study on the Effect of Carbon Particle Seeding for the Improvement of Solar Reactor Performance

2010 ◽  
Vol 132 (12) ◽  
Author(s):  
Nesrin Ozalp ◽  
Anoop Kanjirakat
Keyword(s):  
Flow Reactor ◽  
Carbon Particle ◽  
Decomposition Reaction ◽  
Reactor Performance ◽  
Injection Point ◽  
Carbon Particles ◽  
Solar Reactor ◽  
Lagrangian Framework ◽  
Nucleation Sites ◽  
Window Screening

This study focuses on a technique, referred to as “solar cracking” of natural gas for the coproduction of hydrogen and carbon as byproduct with zero emission footprint. Seeding a solar reactor with micron-sized carbon particles increases the conversion efficiency drastically due to the radiation absorbed by the carbon particles and additional nucleation sites formed by carbon particles for heterogeneous decomposition reaction. The present study numerically tries to investigate the above fact by tracking carbon particles in a Lagrangian framework. The results on the effect of particle loading, particle emissivity, injection point location, and effect of using different window screening gases on a flow and temperature distribution inside a confined tornado flow reactor are presented.

Natural Convection-Radiation Heat Transfer in Rectangular Cavity With the Presence of Participating Media

2010 ◽  
Author(s):  
Behnam Moghadassian ◽  
Farshad Kowsary ◽  
Hamed Gholamian
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Radiation Heat Transfer ◽  
Flow Characteristics ◽  
Simple Algorithm ◽  
Great Accuracy ◽  
Working Fluid ◽  
Participating Media ◽  
Nusselt Numbers ◽  
Different Temperatures

The problem of natural convection radiation with the presence of participating fluid in a tilted square cavity has been investigated numerically. Two vertical walls are at uniform different temperatures while the others are adiabatic. The working fluid is taken as grey, absorbing, emitting and non-scattering. The finite volume method is used to solve the dimensionless governing equations and SIMPLE algorithm is applied for pressure velocity coupling. The radiative heat flux gradient is estimated by finding radiative intensities from the radiative transfer equation (RTE). A very recent method, called the QL method, is utilized to solve RTE. In this study the effects of the inclination angle, Rayleigh number and optical thickness on the heat transfer and flow characteristics are studied. A great accuracy in the results was observed in the prediction of flow contours and average radiative and convective Nusselt numbers at walls.

Investigation of Lightweight Space Radiator Design for Low and No Gravity Environments

2011 ◽  
Author(s):  
Virginia Bieger ◽  
Jian Ma
Keyword(s):  
Heat Transfer ◽  
Heat Pipe ◽  
Liquid Droplet ◽  
Radiation Heat Transfer ◽  
Construction Materials ◽  
Carbon Composite ◽  
Liquid Sheet ◽  
Working Fluid ◽  
Working Fluids ◽  
Fin Design

Space heat rejection is heavily relying on radiator subsystem, which is only depended on pure radiation heat transfer and typical convection is not available. Increased efficiency coupled with reduced mass is of strategic importance in space thermal system. This paper reviews the existing individual aspects of lightweight space radiator subsystem designs under low and no gravity environments, i.e. working fluids, fin design, or optimization, based on standard construction materials. In addition, new concept approaches using latest technologies and their challenges are also investigated in this study. Common designs include heat pipe, liquid sheet, and liquid droplet radiators, the latter two being more conceptual than functional. Most technological advances have been made in the materials of construction and optimization areas while using the traditional heat pipe design since 1960s. Carbon composites are the most promising material for construction, as they possess a good heat transfer rate while minimizing the weight of the system. Working fluids selection has more to do with the operational temperature range than the system design, though construction materials must be taken into account when selecting a working fluid. Fin design is the least reported on, but the general consensus is triangular fins are the best option for minimizing weight while increasing surface area for radiation. Based on the review of current research, the most promising design would be a carbon composite heat pipe with a working fluid of liquid water or ammonia and triangular fins.

Carbon Particle Generation and Lab-Scale Small Particle Heat Exchange Receiver Experimentation and Modeling

2014 ◽  
Author(s):  
Lee Frederickson ◽  
Mario Leoni ◽  
Fletcher Miller
Keyword(s):  
Heat Exchange ◽  
Computer Model ◽  
Small Particle ◽  
Carbon Nanoparticles ◽  
Carbon Particle ◽  
Rankine Cycle ◽  
Gas Temperature ◽  
Solar Simulator ◽  
Ansys Fluent ◽  
Carbon Particles

Central receivers being installed in recent commercial CSP plants are liquid-cooled and power a steam turbine in a Rankine cycle. San Diego State University’s (SDSU) Combustion and Solar Energy Laboratory has built and is testing a lab-scale Small Particle Heat Exchange Receiver (SPHER). The SPHER is an air-cooled central receiver that is designed to power a gas turbine in a Brayton cycle. The SPHER uses carbon nanoparticles suspended in air as an absorption medium. The carbon nanoparticles should oxidize by the outlet of the SPHER, which is currently designed to operate at 5 bar absolute with an exit gas temperature above 1000°C. Carbon particles are generated from hydrocarbon pyrolysis in the carbon particle generator (CPG). The particles are mixed at the outlet of the CPG with dilution air and the mixture is sent to the SPHER. As the gas-particle mixture flows through the SPHER, radiation entering the SPHER from the solar simulator is absorbed by the carbon particles, which transfer heat to the gas suspension and eventually oxidize, resulting in a clear gas stream at the outlet. Particle mass loading is measured using a laser opacity measurement combined with a Mie calculation, while particle size distribution is determined by scanning electron microscopy and a diesel particulate scatterometer prior to entering the SPHER. In predicting the performance of the system, computer models have been set up in CHEMKIN-PRO for the CPG and in ANSYS Fluent for the SPHER, which is coupled with VeGaS ray trace code for the solar simulator. Initial experimentation has resulted in temperatures above 850°C with around a 50K temperature difference when particles are present in the air flow. The CPG computer model has been used to estimate performance trends while the SPHER computer model has been run for conditions to match those expected from future experimentation.

Harvesting Nanoscale Radiation Heat Transfer With Pyroelectric Materials

2009 ◽  
Author(s):  
Jin Fang ◽  
Hugo Frederich ◽  
Laurent Pilon
Keyword(s):  
Heat Transfer ◽  
Energy Transfer ◽  
Energy Conversion ◽  
Electromagnetic Waves ◽  
Waste Heat ◽  
Radiation Heat Transfer ◽  
Low Frequency ◽  
Working Fluid ◽  
Radiation Heat ◽  
New Device

Pyroelectric energy conversion offers a novel, direct energy-conversion technology by transforming time-dependent temperature directly into electricity. It makes use of the pyroelectric effect to create a flow of charge to or from the surface of a material as a result of heating or cooling. However, existing pyroelectric energy converter can only operate at low frequency due to relatively low heat transfer rate between the pyroelectric materials and the working fluid subjected to oscillatory fluid flow between hot and cold sources. On the other hand, energy transfer by thermal radiation between two semi-infinite solids can be enhanced by several orders of magnitude as the gap separating them reduces to subwavelength size thanks to interference and tunneling of electromagnetic waves across the gap. This paper proposes a novel way to harvest nanoscale radiation heat transfer for direct pyroelectric energy conversion of waste heat into electricity. A new device is investigated numerically by accurately modeling nanoscale radiation heat transfer between the pyroelectric materials and hot and cold surfaces. Performance of the pyroelectric converter is predicted at various frequencies. The result shows that rapid energy transfer and higher operating frequency can be achieved to increase efficiency and power density.

Experimental study of thermohydraulic characteristics and irreversibility analysis of novel axial corrugated tube with spring tape inserts

2020 ◽  
Vol 92 (3) ◽  
pp. 30901
Author(s):  
Suvanjan Bhattacharyya ◽  
Debraj Sarkar ◽  
Ulavathi Shettar Mahabaleshwar ◽  
Manoj K. Soni ◽  
M. Mohanraj
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Thermal Performance ◽  
Working Fluid ◽  
The Novel ◽  
Heat Exchanger Tube ◽  
Heat Transfer Augmentation ◽  
Corrugated Tube ◽  
The Impact ◽  
Exchanger Tube

The current study experimentally investigates the heat transfer augmentation on the novel axial corrugated heat exchanger tube in which the spring tape is introduced. Air (Pr = 0.707) is used as a working fluid. In order to augment the thermohydraulic performance, a corrugated tube with inserts is offered. The experimental study is further extended by varying the important parameters like spring ratio (y = 1.5, 2.0, 2.5) and Reynolds number (Re = 10 000–52 000). The angular pitch between the two neighboring corrugations and the angle of the corrugation is kept constant through the experiments at β = 1200 and α = 600 respectively, while two different corrugations heights (h) are analyzed. While increasing the corrugation height and decreasing the spring ratio, the impact of the swirling effect improves the thermal performance of the system. The maximum thermal performance is obtained when the corrugation height is h = 0.2 and spring ratio y = 1.5. Eventually, correlations for predicting friction factor (f) and Nusselt number (Nu) are developed.

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