Radiative Heat Transfer and Fluid Flow

Simulation in a Solar Reactor

Luiz Felipe de Oliveira Campos, Escola de Química, UFRJ;

Luiz Fernando Lopes Rodrigues Silva(*), DEQ, Escola de Química, UFRJ;

Paulo L. C. Lage, LTFD, Programa de Engenharia Química, COPPE/UFRJ

(*) lflopes@eq.ufrj.br

PRESENTATION TOPICS

• Motivation and Introduction;

• Problem Description;

• Simulations;

• Results;

• Conclusion and next steps.

Motivation

• Main current energy source: Fossil fuels

• World oil reserves: 1200 billion barrels (2005)[1]

• World natural gas reserves: 180 trillion m3 (2004)[1]

• Oil: 80 million barrels/day 41 years [2]

• Natural gas: 7.36 billion m3 /day 67 years [2]

• Energy comsumption x Energy demand

[1] Kalogirou, S. – Solar Energy Engineering : Processes and Systems, 2009.

[2]Goswami, Y.D. - Energy: the burning issue, 2007.

Motivation

Global temperature since 1850

Kalogirou, S. – Solar Energy Engineering : Processes and Systems, 2009.

Motivation

CO2 levels in the last 1000 years

Kalogirou, S. – Solar Energy Engineering : Processes and Systems, 2009.

Introduction

• Renewable energy: less pollution

• Wind energy

• Biomass

• Geothermal

• Ocean Energy

• Biggest Investors[3]: China, EUA and Europe

• Brazil?

[3] Jeremy Von Loon – Bloomberg Business Week , 2010.

Abreu, S.L. – Solar Energy Resource Assessment in Brazil using Radiative Transfer Model

Problem Description

• “An improved engineering design of a solar chemical reactor

for the thermal dissociation of ZnO at above 2000K is

presented. It features a rotating cavity receiver lined with

ZnO particles that are held by centrifugal force (...).

Concentrated solar radiation enters the cavity through a

3mm thick quartz window, wich is mounted on a water colled

aluminum ring and integrated to the front face of the cavity

via a conical frustum that contains a 60 mm diameter

aperture.”

Schunk et al; 2008 – A Receiver-Reactor for the Solar Thermal Dissociation of ZnO.

Solar reactor

scheme

(1)Cavity;

(2)Aperture;

(3)Quartz window;

(4)Rotating Drum;

(5)Actuation;

(6) Insulation;

(7)Dynamic feeder;

(8)Product outlet port;

(9)Rotary joint;

(10)Cooling Fluids

Problem Description

• Dynamic feeder: Spread of ZnO particles

• Rotating Cavity: Reaction

• Outlet port: Quenching section

• Injecton of Ar: Quartz window protection

Simulations

• Schunk et al; 2008: Optimal flow configuration without

radiative heat transport considerations

• Analysis: Radiative heat transfer effects on the flow,

considering surface radiation (non participating media)

• Monte Carlo simulation with gray difusive surfaces in ANSYS

CFX 12.1 using the SST turbulence model and the thermal

model with the automatic wall treatment and the Kader’s law-

of-the-wall

Simulations – Boundary Conditions

• Fluid: Argon as Ideal gas, fed at 900 K.

• Inlet1: 0.384 Kg/s

• Inlet 2: 0.12 Kg/s

• Outlet: 0 Pa relative pressure (reference pressure: 105 Pa)

• Rotating Cavity: 2000 K

• Frustum: 900 K

• Window: irradiation of 5000 suns modeled by blackbody at

3064 K

• Feeder/Rotatory joint: Adiabatic

Inlet1, Inlet 2, Frustum, Feeder/Rotatory Joint, Cavity

Results – Mesh Analysis

Horizontal Line: L , Vertical Line: r

Convergence: Achieved for a number of rays greater than 10 milion.

Number of rays used: 40 milion

Results – Mesh Analysis

Results – Mesh Analysis

Results

Results

Results

Results - Comparison

Velocity w profiles:

Black/White – Without radiation;

Schunk et al.

Colored – With radiation

Results - Comparison

Temperature profiles:

Black/White – Without radiation ;

Schunk et al.

Colored – With radiation

Results

• Experimental observations made by Schunk et al.

• Cavity temperature: 1807 K – 1907 K

• Zn condensation over the window was observed

• Particles deposition at the outlet port

Conclusions

• Radiative heat transfer affects significantly the temperature

and velocity profiles.

• Better agreement with experimental observations.

• Absence of vortices in the frustum region can avoid particles

to be dragged to the window better protection.

• Radiation should’ve been accounted for geometry analysis.

Next Steps

• Reaction analysis.

• Particle tracking.

• Heat losses to the environment.