# ESS Seminar Cryogenic Design of HeH 2 Heat

- Slides: 45

ESS Seminar Cryogenic Design of He-H 2 Heat Exchanger for CMS • Cryogenics for HTS Cables in Korea 15 min • Standard Counter-Flow Design 10 min • Proposed Cross-Flow Design 15 min May 12, 2016 Ho-Myung CHANG Hong Ik University, Seoul, KOREA (On sabbatical leave at ESS)

Cryogenics for HTS Cables Ø Why Superconducting (HTS) Cables? • Efficiency Less transmission loss (Cryogenic Cooling? ) • Environment Less CO 2 emission (Cryogenic Cooling? ) • Power density More energy per unit area (Yes) LN 2 flow

Cryogenics for HTS Cables Ø 15 Years of HTS Transmission Cables in KOREA R&D (DAPAS) Commissioning (KETEP) Commercialization (KEPCO)

Cryogenics for HTS Cables Ø Jeju Project (154 k. V AC, 1 km) – Completed in March 2016 • Transmission Grid in Juju Island • 3 Phase in 3 Cryostats (2 Go’s + 1 Return) • Started 6 month-operation (March-Sept, 2016)

Cryogenics for HTS Cables Ø A World Record in HTS Cable LIPA (AMSC+Nexans) 138 k. V 610 m Jeju (KEPCO+LS) 154 k. V 1 km

Cryogenics for HTS Cables Ø Cryogenic Refrigeration of HTS Cables Decompression of LN 2 Stirling Cryocoolers 1. 5~2 k. W @ 70 K Brayton Refrigerator 2~10 k. W @ 70 K

Cryogenics for HTS Cables Ø Refrigeration Cycle (He or Ne) Gas Cycle Ø Three Key Issues • Refrigerators • Heat Exchangers • LN 2 Circulation Ø Coolant Cycle (LN 2) Liquid Cycle

Cryogenics for HTS Cables Ø Important Design Issue – Possibility of LN 2 Freeze-out • Need for Long-Length HTS Cables (1~3 km) → Required Cold LN 2 Supply near Freezing Temperature (63. 4 K) • Practical Fluctuation of Thermal Load and/or Operating Condition • Stoppage of LN 2 Flow due to Freeze-out → Hazard of Disastrous Accident followed by a Loss of HTS Cooling

Cryogenics for HTS Cables Ø Existing Anti-Freezing Schemes (Taiyo Nippon Sanso, CEC, 2012) • Refrigeration Cycle with High-Pressure Cooling ⇒ Penalty in thermodynamic efficiency • Tube-in-Bath HX ⇒ Low effectiveness He • LN Two-stage HX ⇒ Penalty of large DP

Cryogenics for HTS Cables Ø New Proposal of Anti-Freezing Scheme (Chang et al. , Cryogenics, 2013)

Cryogenics for HTS Cables Ø Fabrication of PFHX’s for Experiment Counter-Flow HX 2 -Pass Cross-Flow HX

Cryogenics for HTS Cables Ø Experimental Set-up (Chang et al. , Cryogenics, 2013) • Counter-Flow vs. 2 -Pass Cross-Flow • Gas He - LN Pool and GM Cooler (SHI 500 B) - Temperature Control by a Heater - Generation of Freezing Condition • Liquid N 2 - Compressed Liquid at ~ 0. 4 MPa - Constant Inlet Temperature (77. 5 K) • Silicon Diode T Sensors • He Flowmeter • Electronic Scale for LN 2 flow rate

Cryogenics for HTS Cables Ø Apparatus and Procedure

Cryogenics for HTS Cables Ø Experimental Results (Chang et al. , Cryogenics, 2013) Heater Power Temperature Flow Rate

Cryogenics for HTS Cables Ø Application of 2 -Pass Cross-Flow HX • Based on the proven robustness to temporary freezing conditions • Effective reduction of the freeze-out risk of LN 2 • Compact design for He-He HX (10 k. W Brayton refrigerator) and He-LN 2 HX

Cryogenics for HTS Cables Ø Modified HX Design (Chang et al. , Physics Procedia, 2015)

Cryogenics for HTS Cables Ø Fabrication and Leak Test Completed (2015) Dong. Hwa Entec Co. (KOREA)

ESS Seminar Cryogenic Design of He-H 2 Heat Exchanger for CMS • Cryogenics for HTS Cables in Korea • Standard Counter-Flow Design • Proposed Cross-Flow Design

Standard Counter-Flow Design Ø He-H 2 Heat Exchanger at 15 -20 K • A Key Component of ESS Target CMS (Cryogenic Moderator System) • Thermal Interface between and • Maximum Heat ~ 30 k. W Cold Gas He (Refrigerator – TMCP) Warm Liquid H 2 (Cooling Circuit – CMS) ⇒ Largest HX at 15 -20 K (Jurns, 8 March 2016)

Standard Counter-Flow Design Ø Given Conditions (ESS-0034501, 24 Aug 2015) • Capacity Max Cooling Power • Cold Fluid GHe (Refrigerant) • Warm Fluid LH 2 (Coolant) • Geometry Max Height

Standard Counter-Flow Design Ø Properties of He at 1. 9 MPa (NIST REFPROP 9. 1)

Standard Counter-Flow Design Ø Properties of para-H 2 at 1. 5 MPa (NIST REFPROP 9. 1)

Standard Counter-Flow Design Ø Thermal Conductivity of Aluminum (Woodcraft, Cryogenics, 2005)

Standard Counter-Flow Design Ø Effectiveness-NTU Method • (Averaged) Variable specific heat • Ratio of capacity rates • Number of Transfer Unit (NTU) • Effectiveness (e) • e -NTU relation (Counter-flows)

Standard Counter-Flow Design Ø Standard Counter-Flow HX 20 K 20. 5 K 19. 87 K 18 K 19. 21 K 17 K 18. 52 K 16 K 17. 78 K 15 K 17 K HX 1 HX 2 HX 3 HX 4 HX 5

Standard Counter-Flow Design Ø Plate-Fin Heat Exchangers (PFHX) • Widely used in cryogenic systems • Brazed aluminum fins and plates • Compactness (Large surface area / volume) • Design flexibility ⇒ Counter-flows, Cross-flows, Multi-streams etc.

Standard Counter-Flow Design Ø Geometric Parameters of PFHX

Standard Counter-Flow Design Ø Geometric Parameters of PFHX Total surface area (per stream) Free flow area (per stream) Fin / Total surface area Hydraulic diameter

Standard Counter-Flow Design Ø Engineering Correlations (Barron, 1999) Mass flux Reynolds number Colburn j-factor (plane fins) Friction factor (plane fins) Heat transfer coefficient Pressure drop Fin parameter Fin efficiency Surface effectiveness Overall heat transfer coefficient Number of Transfer Unit (NTU)

Standard Counter-Flow Design

Standard Counter-Flow Design Ø Final Design • Required NTU • Dimension • Estimated NTU • Inlets / Exits 0. 4 m (L) x 0. 4 m (W) x 1. 6 m (H) (H = 0. 1 m + 1. 4 m + 0. 1 m) Diagonal array for uniform flows Non-Uniform Flows Cold Layer Warm Layer

Standard Counter-Flow Design Ø Final Design

ESS Seminar Cryogenic Design of He-H 2 Heat Exchanger for CMS • Cryogenics for HTS Cables in Korea • Standard Counter-Flow Design • Proposed Cross-Flow Design

Proposed Cross-Flow Design Ø Important Design Issue – Possibility of LH 2 Freeze-out LH 2 Cycle • Design LH 2 Temperature Close to Freezing Temperature (14. 3 K) • Coldest He Temperature Lower than 15 K • Temperature Fluctuation Due to Unsteady or Variable Beam Power • Stoppage of LH 2 Flow Hazard of Disastrous Accident

Proposed Cross-Flow Design Ø Design Concept

Proposed Cross-Flow Design • Counter-Flow HX • Cross-Flow HX (Both Unmixed) • At Colder HX’s ⇒ Larger DT between fluids ⇒ Lower e (Effectiveness) ⇒ Smaller DNTU

Proposed Cross-Flow Design

Proposed Cross-Flow Design Ø 1 -Pass vs. 2 -Pass Cross-Flows HX 1 HX 2 HX 3

Proposed Cross-Flow Design Ø Combined HX of Counter-Flow and 2 -Pass Cross-Flow

Standard Counter-Flow Design

Proposed Cross-Flow Design Ø Final Design • Required NTU • Dimension 0. 4 m (L) x 0. 4 m (W) x 1. 8 m (H) H = 0. 1 m + 0. 7 m (counter) + 0. 1 m + 0. 4 m (2 -pass cross) + 0. 1 m • Estimated NTU • Structure 2 -Pass Cross-Flows + Counter-Flows Straight Passage for LH 2 Diagonal (Inlets / Exits) Array Cold Layer Warm Layer

Proposed Cross-Flow Design Ø Final Design

Proposed Cross-Flow Design Ø Results and Discussion • Overall HX Size Increase by 10~15% for the same performance • Freeze-out Hazard Could be significantly reduced • Flow Distribution Basically uniform • Pressure Drop (DP) Same for warm (H 2) layers Slightly more for cold (He) layers • Axial Conduction Negligible (d. T/dx ~ 3 K/m) Even smaller in cross-flows • Fin Types Larger U and Larger DP • TMCP Cycle Possibly a more efficient cycle Cold Layer Warm Layer

Proposed Cross-Flow Design Ø Thermodynamic Structure of Brayton Refrigeration Cycles ESS TMCP

Summary Ø Cryogenic Research for HTS Transmission Cables in KOREA Ø He-H 2 Heat Exchanger at 15 -20 K for ESS CMS • Standard Counter-Flow Design 0. 4 m x 1. 6 m • Modified Cross-Flow Design 0. 4 m x 1. 8 m (~15% Larger) ⇒ Reduced risk of freeze-out, No additional DP of LH 2, Efficient TMCP cycle (? )

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