P. Zhang
1
e-mail: zhangp@sjtu.edu.cn
Z. W. Ma
R. Z. Wang
Institute of Refrigeration and Cryogenics,
Shanghai Jiao Tong University,
Shanghai 200240, China
Experimental Investigation of the
Hydraulic and Thermal
Performance of a Phase Change
Material Slurry in the Heat
Exchangers
The application of phase change material slurry to the refrigeration and air conditioning
system opens a new way for energy saving and reduction of the quantity of refrigerant in
the system involved because it can serve as both the energy storage and the transporta-
tion media in the secondary loop, which is responsible for distributing the cooling power.
In the present study, the experimental investigations of the forced flow and heat transfer
characteristics of tetrabutylammonium bromide (TBAB) clathrate hydrate slurry (CHS)
in both the plate heat exchanger (PHE) and the double-tube heat exchanger (DHE) are
carried out. It is found out that the pressure drop in the PHE is about 3.0–50.0 kPa at the
flow rate of 2.5–13.0 L/min 0.15–0.78 m
3
/ hand is about 1.0–27.0 kPa at the flow rate
of 3.0–14.0 L/min 0.18–0.84 m
3
/ h in the DHE, which is nearly 2 times of that of the
chilled water. The overall heat transfer coefficient is in the range of 2500–5000
W / m
2
K for TBAB CHS in the PHE and is about 1500–3500 W / m
2
K in the DHE,
which are both higher than that of TBAB aqueous solution flow because of the involve-
ment of the phase change of TBAB CHS.
DOI: 10.1115/1.4003666
Keywords: phase change slurry, pressure drop, heat transfer, clathrate hydrate slurry
1 Introduction
The application of phase change material slurries PCSs as the
“functional thermal fluids,” including ice slurry, micro-emulsion,
micro-encapsulation, etc., was considered to be very promising
for thermal energy transportation and heat transfer enhancement
in many applications 1. The usage of these phase change slurries
as the secondary refrigerants in air conditioning system can have
such advantages as energy conservation, financial cost reduction
for system operation, and charging amount of the refrigerant re-
duction, accordingly reducing the emission of the chlorofluorocar-
bons CFCs and hydrochlorofluorocarbon HCFCs.
As for the secondary refrigerants, ice slurry, phase change ma-
terial PCM micro-emulsion, and micro-encapsulated PCM are
often employed. The drawbacks of applying ice slurry as the re-
frigerant are that its generation often involves an intensive energy-
consuming process since the subcooling is always needed and the
temperature range of ice slurry around 0 ° C is much lower than
that needed for air conditioning in the temperature range of
5–12°C. Thus, the energy efficiency of ice slurry secondary re-
frigeration system is not high. The aggregation of PCM micro-
emulsion after many thermal cycles may cause the clogging in the
pipe. For the micro-encapsulated PCM, the durability and the deg-
radation of the performance prevent its long-term application
when it is subject to the shear force by pumping.
In recent years, a kind of new phase change slurry, which can
be used as both cold energy storage and transportation media,
tetrabutylammonium bromide CH
3
CH
2
3
4
NBr, TBAB clath-
rate hydrate slurry CHS, was proposed and studied by the re-
searchers in NKK Corporation 2–5 in Japan. The clathrate hy-
drate crystals are dispersing in the aqueous solution to form a kind
of suspension. It was shown that TBAB CHS had a high cold
storage capacity, which was about 2–4 times of that of cold water
in the temperature range of 5–12°C and it had excellent thermo-
physical properties, which were very favorable for application as
the secondary refrigerant. The TBAB CHS has been practically
applied to the cold storage air conditioning system, however, the
flow and heat transfer characteristics in the heat exchanger are not
yet fully characterized, which are apparently important and nec-
essary for the system design and operation. The application of
TBAB CHS requires that the flow and heat transfer characteristics
in the heat exchangers should be well understood because the cold
storage and retrieval are generally accomplished through the func-
tionality of the heat exchangers.
In the present study, the experimental investigations of the flow
and heat transfer characteristics of TBAB CHS in the heat ex-
changers are carried out. Two types of the heat exchangers, plate
heat exchanger PHE and double-tube heat exchanger DHE,
which are widely used in the refrigeration and air conditioning
systems, were employed in the experiments. The pressure drops
and heat transfer coefficients of TBAB CHS with different volume
fractions flowing through heat exchangers were experimentally
measured in order to understand the hydraulic and thermal perfor-
mance of CHS in heat exchangers.
2 Thermophysical Properties of TBAB CHS
TBAB aqueous solution can form two types of semiclathrate
hydrates with different hydration numbers regarding the initial
concentration and different thermal conditions. Water molecules
form a clathrate cage as “host,” however, it is semiclathrate struc-
ture as the Br
-
in TBAB is bound to water molecules through
hydrogen bonds to form the cage with water molecules together
1
Corresponding author.
Manuscript received September 29, 2010; final manuscript received February 14,
2011; published online April 1, 2011. Assoc. Editor: Zahid Ayub.
Journal of Thermal Science and Engineering Applications MARCH 2011, Vol. 3 / 011004-1
Copyright © 2011 by ASME
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