enhanced heat transfer in small diameter packed beds
TRANSCRIPT
![Page 1: Enhanced heat transfer in small diameter packed beds](https://reader030.vdocuments.net/reader030/viewer/2022012209/61df09a2a4d7b01a104791e3/html5/thumbnails/1.jpg)
Challenge the future
Delft University of Technology
Enhanced heat transfer in small diameter packed beds
C. T’Joen, J.R. van Ommen, M. Rohde
![Page 2: Enhanced heat transfer in small diameter packed beds](https://reader030.vdocuments.net/reader030/viewer/2022012209/61df09a2a4d7b01a104791e3/html5/thumbnails/2.jpg)
2 | 20
Challenge the future
Delft University of Technology
• Packed bed = “stacking of particles within a confinement” • Stacking can be ordered (e.g. FCC, BCC) or random • Different particle shape / size distribution possible
• Focus here: “small” random packed beds of spherical particles
• Applications:
• Catalytic chemical (multi-tubular) reactors: e.g. Fischer-Tropsch process, the production of phthalic anhydride and terephthaldehyde and the epoxidation of ethylene oxide
• Nuclear reactors: pebble bed reactor (VHTR)
Introduction: packed beds
![Page 3: Enhanced heat transfer in small diameter packed beds](https://reader030.vdocuments.net/reader030/viewer/2022012209/61df09a2a4d7b01a104791e3/html5/thumbnails/3.jpg)
3 | 20
Challenge the future
Delft University of Technology
• Advantages: • High specific surface area (+porous sphere) • Easy to construct and maintain • Option to refill ‘online’ (VHTR)
• Disadvantages:
• Complex structure: heat/mass transfer? • Flow bypass near the wall: ‘local ordening’ • High pressure drop • Hot spots in the near wall zone
Introduction: packed beds
![Page 4: Enhanced heat transfer in small diameter packed beds](https://reader030.vdocuments.net/reader030/viewer/2022012209/61df09a2a4d7b01a104791e3/html5/thumbnails/4.jpg)
4 | 20
Challenge the future
Delft University of Technology
• Complex interaction between different heat transfer modes: • Conduction: sphere-sphere, within the sphere • Convection: complex geometry, wakes, flow bypass, hot spots • Radiation: sphere to bed, bed to wall • Mass transfer: chemical reactions
• Different scales:
• Inside the spheres • Inside the bed
Packed bed thermo-hydraulics
![Page 5: Enhanced heat transfer in small diameter packed beds](https://reader030.vdocuments.net/reader030/viewer/2022012209/61df09a2a4d7b01a104791e3/html5/thumbnails/5.jpg)
5 | 20
Challenge the future
Delft University of Technology
Packed bed thermo-hydraulics
![Page 6: Enhanced heat transfer in small diameter packed beds](https://reader030.vdocuments.net/reader030/viewer/2022012209/61df09a2a4d7b01a104791e3/html5/thumbnails/6.jpg)
6 | 20
Challenge the future
Delft University of Technology
• Complex interaction between different heat transfer modes: • Conduction: sphere-sphere, within the sphere • Convection: complex geometry, wakes, flow bypass, hot spots • Radiation: sphere to bed, bed to wall • Mass transfer: chemical reactions
• Different scales: • Inside the spheres • Inside the bed
• Difficult to model! • Current approaches: porous media ↔ 3D CFD?
Packed bed thermo-hydraulics
![Page 7: Enhanced heat transfer in small diameter packed beds](https://reader030.vdocuments.net/reader030/viewer/2022012209/61df09a2a4d7b01a104791e3/html5/thumbnails/7.jpg)
7 | 20
Challenge the future
Delft University of Technology
• Measure for the local amount of ‘void’ • Near the wall: ‘local ordening’
• More open structure • Results in flow bypass, ‘channeling’
• Strong impact on bed thermo-hydraulics
• Effect increases as bed becomes smaller
• Dbed ~ 20-50 x Dsphere
Porosity
![Page 8: Enhanced heat transfer in small diameter packed beds](https://reader030.vdocuments.net/reader030/viewer/2022012209/61df09a2a4d7b01a104791e3/html5/thumbnails/8.jpg)
8 | 20
Challenge the future
Delft University of Technology
• Various techniques exist: gamma beam attenuation used @ DUT • Provide radially averaged porosity data • Can be modified to provide axial data
• Measure for the local amount of ‘void’
0 1 2 3 4 5 6 7 8 90
0.2
0.4
0.6
0.8
1
Distance From Wall (Pebble Diameters)
Radi
al V
oid
Frac
tion
ε r(r
)
Near wall zone Centre region
Measuring porosity profiles?
![Page 9: Enhanced heat transfer in small diameter packed beds](https://reader030.vdocuments.net/reader030/viewer/2022012209/61df09a2a4d7b01a104791e3/html5/thumbnails/9.jpg)
9 | 20
Challenge the future
Delft University of Technology
Simulating random beds?
• Generating a true random bed? • Numerical models:
• Monte Carlo rejection method •Discrete Element Method • Overlap removal method (in-house code, G. Auwerda)
• Good agreement with data!
0 1 2 3 4 5 6 7 8 90
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Distance From Wall (Pebble Diameters)
Radi
al V
oid
Frac
tion
ε r(r
)
ExperimentDEMMC RejectionRemoving Overlaps
![Page 10: Enhanced heat transfer in small diameter packed beds](https://reader030.vdocuments.net/reader030/viewer/2022012209/61df09a2a4d7b01a104791e3/html5/thumbnails/10.jpg)
10 | 20
Challenge the future
Delft University of Technology
Simulating flow and heat transfer?
• Using both commercial and open-source CFD tools • Fluidity (Imperial College London) and Openfoam • Benchmark done for flow and heat transfer: CSP with N = 1
source: Romkes et al., 2003
![Page 11: Enhanced heat transfer in small diameter packed beds](https://reader030.vdocuments.net/reader030/viewer/2022012209/61df09a2a4d7b01a104791e3/html5/thumbnails/11.jpg)
11 | 20
Challenge the future
Delft University of Technology
Benchmarking the codes
• Using both commercial and open-source CFD tools • Fluidity (Imperial College London) and Openfoam • Benchmark done for flow and heat transfer : CSP with N = 1
![Page 12: Enhanced heat transfer in small diameter packed beds](https://reader030.vdocuments.net/reader030/viewer/2022012209/61df09a2a4d7b01a104791e3/html5/thumbnails/12.jpg)
12 | 20
Challenge the future
Delft University of Technology
Benchmarking the codes
• Model inter-comparison (NRG:DNS, TUD:LES) • Triple periodic domain with inter-pebble gaps • Diagnostics: velocity field (domain mean and rms, plus probes)
Source: Shams et al. (NRG)
![Page 13: Enhanced heat transfer in small diameter packed beds](https://reader030.vdocuments.net/reader030/viewer/2022012209/61df09a2a4d7b01a104791e3/html5/thumbnails/13.jpg)
13 | 20
Challenge the future
Delft University of Technology
Benchmarking the codes
• Model inter-comparison (NRG:DNS, TUD:LES) • Triple periodic domain with inter-pebble gaps • Diagnostics: velocity field (domain mean and rms, plus probes)
Source: Pavlidis et al. (DUT)
![Page 14: Enhanced heat transfer in small diameter packed beds](https://reader030.vdocuments.net/reader030/viewer/2022012209/61df09a2a4d7b01a104791e3/html5/thumbnails/14.jpg)
14 | 20
Challenge the future
Delft University of Technology
A Structured Tube for Gas-Liquid Reactions Tubular reactor
Random packing (Dumped particles)
Structured packing (Channel network)
Different phenomena, at different length scales: complex interaction
Reaction-diffusion, film transport resistances
Objective: decouple phenomena optimize performance
Length ~101 m Radius
~10-2 m
G + L
Catalyst ~10-3 m
G + L
Heat transport/transfer, bypassing, G/L contact, G/L distribution
G/L flow, ΔP, dispersion, RTD
D. Vervloet, F. Kapteijn, J. Nijenhuis, J.R. van Ommen
![Page 15: Enhanced heat transfer in small diameter packed beds](https://reader030.vdocuments.net/reader030/viewer/2022012209/61df09a2a4d7b01a104791e3/html5/thumbnails/15.jpg)
15 | 20
Challenge the future
Delft University of Technology
A Structured Tube for Gas-Liquid Reactions
(~ 2 x)
Random Structured G + L
G + L
A randomly packed bed can be replaced by stacking corrugated and flat plates
Pressure drop 20
ΔP /
L (k
Pa m
-1)
(~ 0.1 x) U
ov (k
W m
-2 K
-1)
0
Heat transfer wall 1
0
Random Struct.
Random Struct.
![Page 16: Enhanced heat transfer in small diameter packed beds](https://reader030.vdocuments.net/reader030/viewer/2022012209/61df09a2a4d7b01a104791e3/html5/thumbnails/16.jpg)
16 | 20
Challenge the future
Delft University of Technology
Experimental results (packed bed vs structured packing): • Superior pressure drop • Superior heat transfer • Flatter temperature profiles • Comparable mass transfer
Modelling of Fischer-Tropsch reactor (1-D) based on these parameters: • Much higher selecitivity
for C5+!
A Structured Tube for Gas-Liquid Reactions
![Page 17: Enhanced heat transfer in small diameter packed beds](https://reader030.vdocuments.net/reader030/viewer/2022012209/61df09a2a4d7b01a104791e3/html5/thumbnails/17.jpg)
17 | 20
Challenge the future
Delft University of Technology
• New proposal to STW-OTP: looking for partners (input)!
• Goal: further optimise small packed random beds with ‘smarter’ walls and particles for single phase fluids
• Smart walls: reduce porosity variation but with good heat transfer →dimples, grooves, combinations?
• Smart particles: use varying particle sizes or non spherical shapes to dampen porosity oscillations
• Method: combined experimental and numerical (2 PhD): experiments will be used to validate 3D CFD (OpenFoam)
Outlook: further improvements?
![Page 18: Enhanced heat transfer in small diameter packed beds](https://reader030.vdocuments.net/reader030/viewer/2022012209/61df09a2a4d7b01a104791e3/html5/thumbnails/18.jpg)
18 | 20
Challenge the future
Delft University of Technology
Experimental section • Design experimental HT setup • Validation experiments (tube flow) • First heat transfer test cases
(groove and a dimple case)
• Experimental parameter study: heat transfer and pressure drop, porosity profiles…
Proposed project outline
Numerical section • Set up Openfoam code (RANS, LES) • Code benchmarking • Code validation: test case data
(groove and dimple)
• Optimization (e.g. surrogate methods) using ‘Design of Experiments’
Design guidelines for optimized systems
![Page 19: Enhanced heat transfer in small diameter packed beds](https://reader030.vdocuments.net/reader030/viewer/2022012209/61df09a2a4d7b01a104791e3/html5/thumbnails/19.jpg)
19 | 20
Challenge the future
Delft University of Technology
• Project team: 2 sections of Delft University of Technology • ‘Product and Process Engineering’ (PPE): J. R. van Ommen • ‘Physics of Nuclear reactors’ (PNR): C. T’Joen, M. Rohde
• Large expertise available:
• Large experimental facilities + computational cluster • Expertise in heat transfer and fluid flow experiments • Measurement setup for local porosity profiles • CFD + experimental benchmark data for packed beds (PNR, PPE) • VHTR projects on neutronics (PNR, EU project) • Structured tube project for Fischer Tropsch (PPE)
Project framework
![Page 20: Enhanced heat transfer in small diameter packed beds](https://reader030.vdocuments.net/reader030/viewer/2022012209/61df09a2a4d7b01a104791e3/html5/thumbnails/20.jpg)
20 | 20
Challenge the future
Delft University of Technology
Conclusions
• Packed bed thermo-hydraulics are very complex due to the interaction of different heat/mass transfer mechanisms, on different scales and the complex random geometry.
• An overview was presented of current activities at DUT related to packed bed thermo-hydraulics (experimental and computational)
• A new STW research proposal is being drafted by PNR/PPE (DUT), goal: to further optimise small packed random beds with ‘smarter’ walls and particles for single phase fluids, providing new design guidelines
![Page 21: Enhanced heat transfer in small diameter packed beds](https://reader030.vdocuments.net/reader030/viewer/2022012209/61df09a2a4d7b01a104791e3/html5/thumbnails/21.jpg)
Challenge the future
Delft University of Technology
Enhanced heat transfer in small diameter packed beds
C. T’Joen, J.R. van Ommen, M. Rohde