SIMULATION OF THE SEAWATER HEAT EXCHANGER WITH HELICAL BAFFLES Qingnan Huang Shanghai Jiao Tong University, China
Outlines Background Simulation Methods Property Calculation Method Algorithm Design Flow and Heat Transfer Model User Interface Conclusions
Background The seawater heat exchangers with helical baffles have been widely applied in natural gas liquefaction plants. Characteristics: Helical baffles Spiral flow in shell side Mixed refrigerant in shell side Seawater in tube side Advantages: Good performance in shell side Small pressure drop in shell side Less possibility for scaling Smaller bundle vibration
Background Designed with reference to traditional methods. External Structure Heterogeneous condensation complex flowing & heat exchanging properties lack of mature design experience Problems design failure Inner Structure
Background Specific factors ignored in traditional methods Heat transfer and mass transfer in the shell-side Properties of refrigerants change along the shell. Seawater properties are different from pure water. The structure of helical baffles Accurate design calculation method for the seawater heat exchangers with helical baffles is necessary.
Approach Property Calculation Method Algorithm Design Simulation Flow and Heat Transfer Model User Interface
Approach Property Calculation Method Algorithm Design Simulation Flow and Heat Transfer Model User Interface
Seawater Properties Calculation Developmets of seawater property calculation: PSS-78 EOS-80 IAPWS-95 IAPWS-2008 Accuracy:low high Range:small large IAPWS-2008 is used in the simulation. Salinity: 0%-9% Temprature: 0-100 Density Dynamic viscosity specific heat IAPW-2008 Model Look-up-table
Fast Property Calculation for Mixed Refrigerant Methods: Test: Traditional mix proportion Fitting calculation of the traditional mixture properties based on GERG-2008 Extensions for other proportion Precision: Max Error<2% Speed: Average Error<0.5% 10 4 times faster than GERG
Approach Property Calculation Method Algorithm Design Simulation Flow and Heat Transfer Model User Interface
Algorithm Design Control units Control units are divided according to the number of baffles(k). Subcooling and superheated sections should be calculated separately. 1 2 3... k k+1 k+2 Superheated Two-phase Subcooling Energy balance equations:
Algorithm Design Heat exchanger segmentation Gas phase fraction calculation Property calculation functions Inlet and outlet temperature Shell-side heat transfer coefficient calculation Local heat transfer coefficient calculation Inlet and outlet enthalpy Thermal load calculation LMTD calculation Length and heat transfer area calculation Pressure drop calculation Calculation flow chart for each section
Algorithm Design Design Module Check Module
Approach Property Calculation Method Algorithm Design Simulation Flow and Heat Transfer Model User Interface
Heat transfer equations Heat transfer equations Q K F ( T R, w R, w R, w m) R, w F n R, w tubeltube fo ΔT K m R, w R, w ΔTmax ΔT ΔTmax ln ΔT 1 i min fo r i fi f o d o min Tr,out Tw, in Tr,in Tw, out Tr,out Tw, in ln T T 1 tube tube r,in 2f o w, out 1 f o fi o
Heat Transfer Calculation Tube-side heat transfer coefficient : 0.8 w 1395 23.26T w 273. 0. 2 i 15 d i Shelll-side heat transfer coefficient : Single phase 0.023 Re Pr d M 0.8 0.3 o Y1 Y2 Two-phase o 1 3 3 0.25 R,sat, l R,sat, l R,sat, g gr,sat, lh lg ' ' Y1 Y2 R,sat, lqd0 10 0.655
Pressure Drop Calculation Tube-side pressure drop: P L P ( P P ) F N Shell-side pressure drop: i l u d 2 2 L r u P r 3 2 t 2 p P n u P n 1.5 2 2 64 Re 0.3164 0.25 Re Re<2000 Re>2000 P ideal 2 f u shell 2 D D s e Two-phase multiplier for two-phase fluid: P tp P 2 L 2 L 1 C 1 X tt X tt 2 C 0.11ln( X G) 3.2 tt
Approach Property Calculation Method Algorithm Design Simulation Flow and Heat Transfer Model User Interface
Software framework Input Module Calculation Module Output Module Design Thermal Parameters Input Design Calculation Structure Parameters Output Refrigerants Choice Units Setup Tube Type Choice Check Structure Parameters Input Externally Threaded Tube Model Fast Property Calclation Model Tube-side Flow and Heat Transfer Model Coupling of Shell Side and Tube Side Shell-side Flow and Heat Transfer Model Check Calculation Check the Design Results Thermal Parameters Output
User Interface Main interface Input Menu Calculation Mode Refrigerant Toolbar Main interface Thermal parameters Structural parameters Main components Additional conditions Output Input Overview Warning messages Results (table) Results (chart) Viewtree Input/output status bar
User Interface Refrigerant Properties Seawater salinity Choose Defined Mix refrigerant Define Mix refrigerant
Structural parameters User Interface
Print User Interface Results (table) Excel
User Interface Results (chart) 1pass 2passes Parameters showed Tube side Shell side Whole coefficient temperature coefficient temperature pressure quality coefficient heat flux 4passes Choose parameters Change the range
Conclusions 1) A segmentation parameters model is developed, which could reflect heat transfer and mass transfer in the shell side 2) The IAPWS-2008 method is used for the seawater properties and a fast property calculation is built for the shell side. 3) Considering the influence of the helical baffle structure, the modified two-phase heat transfer and pressure drop correlations are developed. 4) A design software framework is set up and a friendly graphic user interface is developed. 5) The method can be used to study the influence of heat exchanger structures and to guide for the seawater heat exchanger design.
Thank you!