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

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

The seawater heat exchangers with helical baffles have

been widely applied in natural gas liquefaction plants.

Background

Background

Problems

Heterogeneous

condensation

complex flowing &

heat exchanging

properties

lack of mature

design experience

Inner Structure

External Structure

design

failure

Designed with reference to traditional methods.

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

Flow and Heat

Transfer Model

User

Interface

Simulation

Approach

Property

Calculation Method

Algorithm

Design

Flow and Heat

Transfer Model

User

Interface

Simulation

Seawater Properties Calculation

IAPWS-2008 is used in the simulation.

Salinity: 0%-9% Temprature: 0℃-100℃

Developmets of seawater property calculation:

PSS-78 EOS-80 IAPWS-95 IAPWS-2008

Accuracy：low high Range：small large

IAPW-2008 Model Look-up-table

Density

Dynamic viscosity

specific heat

Fast Property Calculation for

Mixed Refrigerant

Methods:

Traditional mix proportion

Fitting calculation of the traditional

mixture properties based on

GERG-2008

Extensions for other proportion

Test:

Precision: Max Error<2%

Average Error<0.5%

Speed: 104 times faster than GERG

Approach

Property

Calculation Method

Algorithm

Design

Flow and Heat

Transfer Model

User

Interface

Simulation

Algorithm Design

Control units

Energy balance equations:

Control units are divided according to the number of baffles(k).

Subcooling and superheated sections should be calculated separately.

Superheated Subcooling Two-phase

1 2 3 …... k k+1 k+2

Algorithm Design

Gas phase fraction

calculation

Shell-side heat

transfer coefficient

calculation

Local heat transfer

coefficient calculation

Property calculation

functions

Inlet and outlet

temperature

Inlet and outlet

enthalpy

Thermal load

calculationLMTD calculation

Length and heat

transfer area

calculation

Pressure drop

calculation

Heat exchanger

segmentation

Calculation flow chart for each section

Algorithm Design

Design Module Check Module

Approach

Property

Calculation Method

Algorithm

Design

Flow and Heat

Transfer Model

User

Interface

Simulation

Heat transfer equations

wR,m wR, wR, wR, )( TFKQ

otubetube wR, fLnF

odf o

oio

o

tube

tube

i

oi

i

wR,121

1

ff

f

f

fr

K

out w,inr,

in w,outr,

out w,inr,in w,outr,

min

max

minmax

wR,m

TT

TTln

TTTT

ΔT

ΔTln

ΔTΔTΔT

Heat transfer equations

Tube-side heat transfer coefficient ：

Shelll-side heat transfer coefficient ：

Heat Transfer Calculation

2.0

i

8.0

wi 15.27326.231395d

wT

1

33

,sat , ,sat , ,sat , ,sat , lg0.25 ' '

1 2

,sat , 0

10 0.655R l R l R g R l

o

R l

g hY Y

qd

0.8 0.3

1 20.023 Re PrMo Y Y

d

Single phase

Two-phase

Tube-side pressure drop:

Shell-side pressure drop:

Two-phase multiplier for two-phase fluid:

Pressure Drop Calculation

nptrLi PNFPPP )(

2

2u

d

lPL

23

2uPr

25.1

2uPn

Re

64

25.0Re

3164.0

Re<2000

Re>2000

e

sshellideal

D

DufP 22

2

L PPtp

2

2

L

11

tttt XX

C

2.3)ln(11.0 GXC tt

Approach

Property

Calculation Method

Algorithm

Design

Flow and Heat

Transfer Model

User

Interface

Simulation

Software framework

Thermal

Parameters Input

Structure

Parameters Input

Design Calculation

Check Calculation

Structure

Parameters Output

Thermal

Parameters Output

Check the

Design Results

Refrigerants Choice

Units Setup

Tube Type Choice

Fast Property

Calclation Model

Tube-side Flow and Heat

Transfer Model

Shell-side Flow and Heat

Transfer Model

Externally Threaded

Tube Model

Coupling of Shell Side

and Tube Side

Design

Check

Input Module Calculation Module Output Module

Toolbar

Menu

status bar

Main

interface

Viewtree Input/output

User Interface

Input

Output

Input Overview

Warning messages

Results (table)

Results (chart)

Calculation Mode

Refrigerant

Thermal parameters

Structural parameters

Main components

Additional conditions

Main interface

Choose Defined Mix refrigerant Define Mix refrigerant

Seawater salinity

Refrigerant Properties

User Interface

Structural parameters

User Interface

Excel

Print

Results (table)

User Interface

Choose parameters Change the range

1pass

2passes

4passes

Results (chart)

Parameters showed

Tube side coefficient 、temperature

Shell side coefficient 、temperature、

pressure、quality

Whole coefficient、heat flux

User Interface

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！