Cryogenic Engineering Lab. 팀 3 김경중, 박창기 Current researches in Cryogenic Engineering Laboratory

Major research areas 2 Refrigerator  Magnetic refrigerator  Pulse tube refrigerator  Mixed refrigerant Joule-Thomson refrigerator Space cryogenics  No vent filling  Line chill-down  Space cryogenics

Refrigerator 3

Magnetic refrigerator 4  Application of the magnetocaloric effect  High thermodynamic efficiency : reversible process  Use of solid magnetic refrigerant

Pulse tube refrigerator 5  Solid expander replaced by gas expander, orifice and reservoir  Similar to Stirling cycle

Joule Thomson cryocooler 6  Simple construction  High operation reliability  Application  Cooling infrared sensors  Cryosurgery  LNG liquefaction Heat exchanger

Cryogenic Engineering Lab. Efficiency improvement of BOG re-liquefaction cycle by using phase separator and exergy analysis 박창기

Contents 8 Problem definition Introduction Exergy analysis

BOG (Boil-off gas) Problem definition LNG Evaporation Heat inleak LNG evaporation because of heak in-leak from environment Pressure increase in the tank Venting of the evaporated NG Liquefaction of the evaporated NG

Efficiency definition of BOG re-liquefaction cycle

BOG liquefaction cycle Introduction C A HX V C: Compressor A: Aftercooler HX: Heat exchanger V: Joule-Thompson valve V

Introduction 12 BOG liquefaction cycle with phase separator Phase separator Mixer C A HX V V C: Compressor A: Aftercooler HX: Heat exchanger V: Joule-Thompson valve

Freezing point of NFMR Mole fraction 고체 액체 기체 삼중점임계점  Freezing point problem is solved by mixing several refrigerants C. Lee, J. Yoo, J. Lee, S. Jeong, "Visualization of the solid–liquid equilibria for non-flammable mixed refrigerants", Cryogenics, 75, pp , 2016.

Efficiency analysis at various conditions Ar : R14 : R218 = 0.3 : 0.2 : 0.5 LP150 kPa HP2700 kPa Specific work consumption Phase separating temperature - Without phase separatorWith phase separator LP200 kPa HP2800 kPa Specific work consumption Phase separating temperature 300 K 6.5 % 100 kW

Exergy analysis about the results Without phase separator HX Useful effect Total exergy input = 1548 kW

Exergy analysis about the results With 300 K phase separator HX Useful effect Total exergy input = 1448 kW

Conclusion Phase separator Mixed refrigerant Freezing point measurement

Space cryogenics 18

No-vent filling 19 Supply tank Receiver tank Vent Unexpected momentum International space station Space vehicle Technologies On-orbit technology Cryogenic propellant storage technology Fluid transfer technology NVF  Reduction Space Launch Vehicle mass  Difficulty of vent filling under micro-gravity condition

Transfer line chill-down 20  Indispensable process of undertaking cryogenic mission and establishing a normally operated cryogenic system  Less cryogenic liquid consumption  Shorter chill-down time Ref.

Cryogenic expander 21  Generally key component of cryocooler  Enthalpy reduction without entropy change  Reduction boil-off gas (BOG) of cryogenic propellant

Cryogenic Engineering Lab. Analytic model of No-vent Filling (NVF) 김경중

General filling method Problem definition Cryogen Vent Injection Cryogen Normal gravity Cryogen Micro-gravity Fuzzy liquid-vapor interface Unwanted momentum generation Limitation

Problem definition Previous research  Variables study  Experiment for liquid nitrogen(LN 2 ) and liquid hydrogen(LH 2 )  Experiment for variables change(wall temperature, liquid temperature, mass flow rate and pressurization pressure)  Analysis  Equilibrium model  Optimized model for specific experimental device  Non-dimensional map to find feasible initial condition Previous model can predict NVF result, but NVF process Process predictable model independent on experimental device is needed.

NVF processes Introduction 2. Pressurization due to tank cool down 3. Pressure equilibrium due to condensation and evaporation balance 1. Pressurization due to flash evaporation 123

Experimental apparatus Transfer line Supply tank Receiver tank

Analysis Wall coordinate 1 2 n n-1 n-2 … Top bulk Bottom bulk Convection Conduction

Analysis Evaporation Flash evaporationPool boiling YesNo P receiver <P sat Nucleate boilingFilm boiling YesNo receiverReceiver tank satSaturation state LeidenfrostLeidenfrost point

Analysis Condensation No condensation Condensation by heat transfer Yes No Yes No P receiver >P sat T v >T in receiverReceiver tank satSaturation state vVapor inIncoming

Results and discussions Comparison  Bottom temperature tendency 30 caseT wall [K]T supply [K]P supply [kPa] Requirement of axial conduction of bottom

Results and discussions Comparison  Middle temperature tendency 31 caseT wall [K]T supply [K]P supply [kPa] Conduction (wall coordinate) is reliable.

Results and discussions Comparison  Pressure tendency 32 caseT wall [K]T supply [K]P supply [kPa] Well-predicted pressure overshoot

33

Appendix

Principle of JT refrigerator 35

NFMR(Non-flammable mixed refrigerants) Comparison with FMR  Lower isothermal enthalpy difference  No risk of explosion and flammability

Exergy analysis about the results Ar : R14 : R218 = 0.3 : 0.2 : 0.5 A A B B C C With phase separator A: Total flow B: Vapor fraction after phase separating C: Liquid fraction after phase separating 240 K

Exergy analysis about the results Ar : R14 : R218 = 0.3 : 0.2 : 0.5 A A B B C C Refrigerant Mass flow [kg/s] Ar2.15 R R Mass flow [kg/s] Mass flow [kg/s] Refrigerant Mass flow [kg/s] Ar2.06 R R With 300 K phase separator Without phase separator Sum Sum21.2

Exergy analysis about the results Ar : R14 : R218 = 0.3 : 0.2 : 0.5 With 300 K phase separator Without phase separator 5335 kW 4679 kW 656 kW

Temperature profile in HX T2T2 T1T1 Venkatarathnam, Gadhiraju. Cryogenic mixed refrigerant processes. Ed. Klaus D. Timmerhaus. New York: Springer, Exergy loss during heat transfer