Development of UV Reactor Design Code using Potential Flow

Theory and MSSS

Jeong-Gyu Bak, Hyosun Kim28 Feb. 2018

IUVA America Conference 2018

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IUVA America Conference 28 Feb 2018Acknowledgements

Neotec UV Inc.Woochul Hwang, Chief engineer

Hanyang Univ.Prof. Jinsoo Cho, Dept. of ME.

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IUVA America Conference 28 Feb 2018Outline

Introduction

Object

UV-CFD

- Potential Flow

- UV Radiation Model

- Dose Calculation

Case Study1

Case Study2

Summary

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IUVA America Conference 28 Feb 2018Introduction

Potential Flow Code. Early CFD codes based on potential flow theory were developed foraerodynamic/hydrodynamic fields from the late 1960s to early 1970s

These codes were replaced with higher order method subsequently

It’s considered as an old method, but is still used in preliminary design Less computational time(get results in few seconds)

Formula 1 Motor Racing CFD Trends 1990-2010 illustrated by Hanna & Parry, 2011.

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IUVA America Conference 28 Feb 2018Introduction

Role of CFD in UV Reactor Design – Pros. Detailed flow behavior and fluence distribution in the reactor Study on interaction of hydraulics, optics, and microbial inactivation kinetics easily

Enabling efficient and effective design of a UV reactor

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IUVA America Conference 28 Feb 2018Introduction

Role of CFD in UV Reactor Design – Cons. Computational cost is still expensive.

- Few hours for small systems1) and,- Few weeks for large systems2) using a modern workstation.

Not suitable for initial design (system sizing) due to computational time.

Mesh creation effort increases in large and complex UV system.

Convergence is impossible in some cases (due to unsteadiness).

1) Close conduit reactor (4 lamps) using 4-core Xeon E5-1620V4 workstation 2) Open channel reactor (32 lamps) using 48-core Xeon E5-2690V3 cluster

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IUVA America Conference 28 Feb 2018Objective

Research Motivation and Objective Apply/modify the potential code for UV analysis Developing UV system sizing (design) code that requires less computation time.

Finding a correction factor for reliable results.

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IUVA America Conference 28 Feb 2018UV-CFD

Modeling Approach

Preparation of aGeometric Model

Hydraulic Calculation

UVRadiation

Calculation

Dose Calculation

RED(Reduction Equivalent Dose)

- SRS1)

- RANS2)

- Euler- Potential

- MPSS3)

- MSSS4)

- LSI5)

- DO6)

- Bolton UVCalc

1) Scale-Resolving Simulation (eg. LES)2) Reynolds Averaged Navier-Stokes3) Multiple Point Source Summation4) Multiple Segment Source Summation5) Line Source Integration Model6) Discrete Ordinate Model

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IUVA America Conference 28 Feb 2018Potential Flow

Major Characteristics/Assumptions Linearized flow equation: simple implementation of a computer code. A series of singularities as sources, sinks, vortexes and doubletsare used to model the flow.

Inviscid Steady

𝜕𝜕𝜕𝜕𝑡𝑡

= 0

Irrotational flow field

∇ × 𝑉𝑉 = 0

Incompressible

∇ � 𝑉𝑉 = 0“Flow around circular cylinder” by Thierry Dugnolleis licensed under CC0 by 1.0

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IUVA America Conference 28 Feb 2018UV Radiation Model

Multiple Segment Source Summation Calculation of the UV irradiance proposed by Liu et al1).

Necessary to parallel computation to reduce the computation timein large problems (eg. more than 10 lamps)

𝑠𝑠1 + 𝑠𝑠2 + 𝑠𝑠3 = 𝑟𝑟1 tan 𝜃𝜃1

+𝑟𝑟2𝑛𝑛𝑎𝑎 sin𝜃𝜃1

𝑛𝑛𝑞𝑞 1 − 𝑛𝑛𝑎𝑎2𝑛𝑛𝑞𝑞2

sin2 𝜃𝜃1

+ 𝑟𝑟3𝑛𝑛𝑎𝑎 sin𝜃𝜃1

𝑛𝑛𝑤𝑤 1 − 𝑛𝑛𝑎𝑎2𝑛𝑛𝑤𝑤2

sin2 𝜃𝜃1

𝐼𝐼𝑗𝑗 = (1− 𝑅𝑅1)(1− 𝑅𝑅2)⁄𝑃𝑃 𝐽𝐽

4𝜋𝜋(𝑙𝑙1 + 𝑙𝑙2 + 𝑙𝑙3)2 𝑇𝑇𝑤𝑤𝑙𝑙30.01𝑇𝑇𝑞𝑞

𝑙𝑙20.01𝐴𝐴𝑓𝑓 cos𝜃𝜃1

𝐴𝐴𝑓𝑓 =(𝑙𝑙1 + 𝑙𝑙2 + 𝑙𝑙3)2∆𝜃𝜃 cos𝜃𝜃1

𝑟𝑟(ℎ2 − ℎ1)

Where,

1) Liu, D., Ducoste, J. J., Jin, S., and Linden, K. (2004). Evaluation of alternative fluence rate distribution models. Journal of Water Supply: Research and Technology – AQUA, 53(6):391-408.

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IUVA America Conference 28 Feb 2018Dose calculation

Lagrangian Particle Tracking Method Assume pathogen as particles

Accumulate the dose at each position along the particle path

Using MS2 dose response curve by collimated beam test

1) USEPA. (2006). Ultraviolet Disinfection Guidance Manual for the Final Long Term2 Enhanced Surface Water Treatment Rule; EPA office of Water: Wasington, DC, USA.

𝐷𝐷𝑝𝑝 = �𝑝𝑝𝐼𝐼 𝑑𝑑𝑑𝑑

Instantaneous dose

Accumulated dose

log 𝐼𝐼 = −log101𝑛𝑛0

�𝑝𝑝=1

𝑛𝑛0

( ⁄𝑁𝑁 𝑁𝑁0)𝑝𝑝

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IUVA America Conference 28 Feb 2018Case Study[1]

Close Conduit Reactor Lab scale pilot UV reactor with 125W (UVC 41W) 4 LP lamps

Only comparison with 3D RANS1) and 2D potential flow

Flow

Computational mesh(upper: potential flow, lower: RANS)

1) Solver: Ansys CFX- Turbulent model: k-w SST- Number of particles: 3000

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IUVA America Conference 28 Feb 2018Case Study[1]

Velocity and UV Intensity Velocity: show the different patterns due to equations (idle vs real flow)

UV intensity: same value and patterns

UV Intensity [W m-2] @ UVT 85%(upper: potential flow, lower: RANS)

Velocity [m s-1](upper: potential flow, lower: RANS)

Unit: [W m-2] = 0.1 [mW cm-2]

Flow

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IUVA America Conference 28 Feb 2018Case Study[1]

Particle tracking Particle tracks never cross each other in a potential flow case.

Uniformly distributed in the entire reactor chamber.

Unit: [J m-2] = 0.1 [mJ cm-2]

Particle track by potential flow (colored by dose) Particle track by RANS (colored by dose)

Unit: [J m-2] = 0.1 [mJ cm-2]

Flow

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IUVA America Conference 28 Feb 2018Case Study[1]

UV Dose Delivery Potential flow predicts 1.4 times higher RED1) than that of RANS

In the potential flow cases, dose distributions are more uniform.

y=1.4275xR2=0.9937

1) RED: Reduction Equivalent DoseDelivery Dose Prediction: Potential Flow vs. RANS

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IUVA America Conference 28 Feb 2018Case Study[1]

Comparison of Computation Time Potential code with MSSS approach can reduce computation time

by 60 times in the presented model.

By potential flow code- 9 cases- General desktop computer (4 cores)

Total 5 hours

By RANS code (Ansys CFX)- 9 cases- Mini cluster (24 cores)

Total 30 min. 2 cpu core hours. 120 cpu core hours.

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IUVA America Conference 28 Feb 2018Case Study[2]

Parallel Flow Open Channel Pilot reactor based on Neotec NOL-H series

With 8 LP Lamps (320 W) per module, 4 modules were used.

Comparison with RANS and potential flow

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IUVA America Conference 28 Feb 2018Case Study[2]

Velocity and UV Intensity Flow is more uniform in the potential flow case, but velocity is slightly faster.

UV intensity show the same values and patterns in both cases.

UV Intensity [W m-2] @ UVT 73.7%(upper: potential flow, lower: RANS)

Velocity [m s-1](upper: potential flow, lower: RANS)

Unit: [W m-2] = 0.1 [mW cm-2]

Unit: [W m-2] = 0.1 [mW cm-2]

Unit: [m s-1]

Unit: [m s-1]Flow

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IUVA America Conference 28 Feb 2018Case Study[2]

UV Dose Delivery Potential flow predicts 0.9 times lower RED1) than that of RANS. In the potential flow case, it shows the locally high dose delivery value, because there is no mixing.

y=0.9299xR2=0.9885

Delivery Dose Prediction: Potential Flow vs. RANS

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IUVA America Conference 28 Feb 2018Case Study[2]

By potential flow code- 5 cases- General desktop computer (4 cores)

Total 3 weeks

By RANS code (Ansys CFX)- 5 cases- Mini cluster (48 cores)

Total 50 min.

Comparison of Computation Time Potential code with MSSS approach can reduce computation time

by 7260 times in the presented model.

3.3 cpu core hours. 24192 cpu core hours.

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IUVA America Conference 28 Feb 2018Summary

Combination of Potential Flow and MSSS It shows 1.4 times higher RED values in closed conduit type reactor,and 0.9 times lower RED values in open channel type reactor.

Further studies are required for finding the multiplier (correction factor) for various reactor types.

Potential flow code can be used for initial UV system sizing, and proto-type design as the time required for an analysis is significantly less.

THANK YOU

Jeong-Gyu Bak, Hyosun Kim28 Feb. 2018

IUVA America Conference 2018