CONDENSATION AND FLOW BOILING HEAT TRANSFER OF HYDROCARBONS IN MINICHANNELS Stefano Bortolin, Marco Azzolin, Arianna Berto, Davide Del Col Department of Industrial Engineering University of Padova Padova, Italy Workshop on Heat Pumps for Low-GWP Refrigerants – December 7, 2020
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CONDENSATION AND FLOW BOILING HEAT TRANSFER OF … · 2020. 12. 15. · • Condensation HTCs and adiabatic two-phase pressure drop have been measured with propane (R290) and propylene
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CONDENSATION AND FLOW BOILING HEAT TRANSFER OF HYDROCARBONS IN MINICHANNELS
Stefano Bortolin, Marco Azzolin,Arianna Berto, Davide Del Col
Department of Industrial EngineeringUniversity of Padova
Padova, Italy
Workshop on Heat Pumps for Low-GWP Refrigerants – December 7, 2020
Outline
2
▪ Introduction
▪ Description of the test facility
▪ Pressure drop measurements
▪ Condensation heat transfer coefficients
▪ Condensation performance and condenser charge evaluation
▪ Flow boiling heat transfer coefficients
▪ Applications: minichannels shell-and-tube condenser and evaporator
▪ Conclusions
Introduction
3
• In the last years, international organizations undertook some actions aimed at
HFCs phase-down:➢ F-gas Regulation (No 517/2014) of the European Union
➢ The Kigali Amendment to the Montreal Protocol (United Nations, 2016)
• The heat pump market continues to prosper in EU countries:
(19th EurObserv’ER Report):➢ At least 4 million HPs were sold in 2018
➢ Reversible air-air HPs still dominate EU market with 3.5 million systems sold in 2018
➢ The air-water HP market increased by 21.5% between 2017 and 2018
• Alternatives to the high GWP fluids currently employed in heat pumps (e.g.
R134a, R410A) must be investigated.
• The GWP100-years is lower than 4 for propane and propylene.
• The major issue related to a wide utilization of HCs is due to their flammability.
Introduction
• Hydrocarbons (HCs) present favorable thermodynamic and transport propertiesthat make them attractive for use in heat pumps.
• Refrigerant charge in heat pumps accumulates in the components (e.g. heatexchangers) where the liquid phase is present.
• Because of HCs flammability it is therefore essential to decrease the volume ofheat exchangers.
• Minichannel technology is a viable solution to reduce refrigerants charge.
• In the scientific literature, it is possible to find only few experimental data takenduring condensation/vaporization of HC refrigerants and the majority of them weretaken inside conventional channels (6-8 mm) or inside plate heat exchangers.
• Propane heat pumps can be used to produce hot water in residential buildings.
• Propane (R290) and propylene (R1270) can be also considered alternatives toR404A in commercial refrigeration and to R134a in R134a/CO2 cascaderefrigeration plants.
Experimental test rig
5
Pressure drop tests – Experimental technique
6
R290 - R1270
,
, ,
water water water PS
in MS in PSref
m c Th h
m
= −
, ( , )in PSh f p T=( ),, in MSx f p h=
ADIABATIC
enters as subcooled liquid
enters as superheated vapor
0.96 mm internal diameter
7
Adiabatic pressure drop
0
50
100
150
200
0 50 100 150 200
CA
LC
. P
RE
SS
UR
E G
RA
DIE
NT
[kP
a m
-1]
EXP. PRESSURE GRADIENT [kPa m-1]
Del Col et al. (2013a)
Friedel (1979)
Müller-Steinhagen and Heck (1986)
Zhang and Webb (2001)
-20%
+20%
Propane Propylene
Cavallini et al.
(2009)
40 °C saturation temperature
0.96 mm diameter channel
Del Col et al. IJR 47, 2014
Del Col et al. IJR 83, 2017
R290
R1270
Test section for HTC measurement
8
0.96 mm internal diameter
REFRIGERANT
Hole for wall
thermocouple
WATER
Heat transfer – Experimental technique
9
• Local heat transfer coefficient HTC
( )( )
in
r LG
q zx z x
m h= −
• Local vapor quality x(z)
( )( )
( ) ( )HTC
sat wall
q zz
d T z T z=
− ( )
( ),
d
d
w
w p w
T zq z m c
z= −
( )satT z by pressure measurement ( )wallT z directly measured