Diapositiva 1 · 2020-02-12 · 13th International Conference MULTIPHASE FLOW IN INDUSTRIAL PLANTS...

13th International Conference

MULTIPHASE FLOW IN INDUSTRIAL PLANTS

MFIP 2014

Davide DEL COL, Marco AZZOLIN, Alberto BISETTO and Stefano BORTOLIN

Department of Industrial Engineering

University of Padova

A PREDICTING METHOD OF FRICTIONAL PRESSURE DROP

DURING TWO-PHASE FLOW IN SMALL DIAMETER CHANNELS

1



Outline

2

Introduction and motivation

New database

Description of the test rig

Experimental technique

Description of the model and comparison with

experimental data

Conclusions



Introduction

3

Two-phase flow in minichannels is widely present

in evaporators and condensers.

Pressure drop have a strong influence

on the two-phase heat transfer

It is crucial to have reliable pressure drop prediction methods

for two-phase heat transfer modeling and optimization

Increasing interest in refrigerants possessing low GWP

due also to growing number of regulations and laws

In 2012 the European Commission

proposed to cut F-gas emissions

by two-thirds by 2030

European Union’s F-gas regulations:

from 2017 automotive

air-conditioning GWP < 150



New Database

4

The new pressure drop database is obtained from

experimental tests with

Natural

refrigerant R290 (propane)

HFO R1234ze(E)

Mixtures R32/R1234ze(E)

Fluid Mass velocity [kg m-2 s-1] Pressure [bar] Saturation temperature [°C]

R1234ze(E) 200-400-600-800 7.7 40.1

R290 200-400-600-800 14 41

R32/R1234ze(E)

0.23/0.77

400 13.8 36.7-47.6

R32/R1234ze(E)

0.5/0.5

200-400-600 18 36.3-43.7

Experimental test conditions


MULTIPHASE FLOW IN INDUSTRIAL PLANTS 5

R32/R1234ze(E) Mixture

17.7 bar

43.1 °C

35.6 °C

Composition by mass R32/R1234ze(E) 0.5/0.5

T_dew 43.1°C

T_bubble 35.6°C

T_glide 7.5°C

Temperature given at 17.7 bar

Fluid properties calculated with NIST Refprop 9.1 using for the mixing parameters the KW2

model with tuned parameters as recommended by Akasaka (2013)



Test apparatus

6

DP Test Section

INTERNAL

DIAMETER

di = 0.96 mm

INNER SURFACE

ROUGHNESS

Ra = 1.3 µm

ABIABATIC

TWO-PHASE FLOW



Test Rig

7

PS pre-sector MF mechanical filter PV pressure vessel TV valve CFM Coriolis-effect mass flow meter PV pressure vessel FD filter drier P pressure transducer T thermocouple DP differential pressure transducer



Experimental technique

8

enters as subcooled liquid

enters as superheated vapor

Refrigerant

,

, ,

water water water PS

in MS in PSref

m c Th h

m

, ( , )in PSh f P T

1234, , R zex f P h X

ADIABATIC

,in MS L

V L

h hx

h h

For

PURE FLUIDS

For

MIXTURES



0,001

0,010

0,100

100 1000 10000 100000

FR

ICT

ION

FA

CT

OR

[ / ]

Re [ / ]

Blasius

Churchill

R290 Liquid

R290 vapor

R32 R1234ze 23/77% liquid

R32 R1234ze 50/50% liquid

R1234ze liquid

R1234ze vapor

Single Phase Friction Factor

Re [/]

Fric

tio

n F

acto

r [/

]

9

22

hD pf

G L

In order to validate the

data acquisition and to

gain a critical insight into

the test section hydraulic

performance

Friction Factor Definition



Del Col et al. (2013) model

10

The Del Col et al. model (IJHMT, 2013) suggested the following equation to

predict two-phase frictional pressure drop during annular or mist flow (JG >

2.5) in minichannels

If JG < 2.5 the authors proposed to use the same equation, fixing a minimum

value for ϕ2LO equal to 1.

22 2

,

2 LOLO LO

f f LO h L

f Gdp dp

dz dz D

The liquid-only friction factor is evaluated as

RR = 2Ra/Dh

RR is the relative roughness of the tube.

0.2

0.046 0.7

LO LOf Re RR X



Del Col et al. (2013) model

11

0.006

0.008

0.01

0.012

0.014

0.016

0.018

0.02

0.022

0 2000 4000 6000 8000 10000

f LO

[/]

ReLO [/]

CAVALLINI ET AL. SMOOTH

CAVALLINI AT AL. ROUGH

PRESENT MODEL

0

0

.2

0

.

.2

2

5

0,

1, 3500

0.0461 , 3500

0.7

0.046 0.7

0.7

0.046 35000.0

46

LO

LO LO

LO

LOLO L

LO

O

LO

if Re Re

X

f Re R

if Re

f Reif Re Re

RR

f RRf R

R X

e

Re+LO 3500

If ReLO is small RR does not affect the pressure losses, so fLO is evaluated as in a smooth

tube. If ReLO increases RR starts to influence the friction factor, the more the bigger is ReLO,

and fLO tends to the one evaluated for rough tubes.

RR = 0.005

comparison with previous model



0

50

100

150

200

250

300

350

400

0 50 100 150 200 250 300 350 400

(dp

/dz) f

,CA

LC

[kP

a m

-1]

(dp/dz)f,EXP [kPa m-1]

R32/R1234ze 50/50%

R32/R1234ze 23/77%

R290

R1234ze

+20%

-20%

Comparison with the model

(dp/dz)f,EXP [kPa m-1]

(dp/d

z) f

,CA

LC [kP

a m

-1]

Fluid eAB [%] eR [%] σN [%]

R1234ze(E) 8.6 -6.1 7.7

R290 10.3 -8 12

R32/R1234ze(E) 3.8 -1.5 4.8



Conclusions

For most applications alternatives to high GWP synthetic refrigerants

could be found in natural refrigerants, HFOs or mixtures.

A model to predict frictional pressure drop during two-phase flow in small

diameter channels has been tested against an updated database which

includes different fluids R1234ze(E) (HFO), propane (HC), and a mixture of

R32/R1234ze(E) (mixture of HFC and HFO).

The present two-phase pressure drop database is satisfactorily predicted

by the model, with a total mean absolute deviation equal to 7.6%, a mean

average deviation equal to -5.2% and a standard deviation of 8.2%.

This model is a useful and reliable tool to design compact heat

exchangers using minichannels where the prediction of the two-phase

pressure drop is a crucial issue.

13



Thank you

for your attention

[email protected]

http://www.dii.unipd.it/en/sustainable-thermal-energy-technologies

Università degli Studi di Padova

Dipartimento di Ingegneria Industriale

14

Diapositiva 1 · 2020-02-12 · 13th International Conference MULTIPHASE FLOW IN INDUSTRIAL PLANTS...

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Transcript of Diapositiva 1 · 2020-02-12 · 13th International Conference MULTIPHASE FLOW IN INDUSTRIAL PLANTS...