Title: P.M.Pavel and M.Constantinescu.
1Romanian Academy of Science Institute of Physical
Chemistry Ilie Murgulescu Spl. Independentei
202, 060021 Bucharest,
HEAT TRANSFER OF A NANOCOMPOSITE PCM-EPOXY HEAT
STORE
P.M.Pavel and M.Constantinescu. ICF-AR Ilie
Murgulescu Bucuresti
Importance of energy storage in PCM and
objectives
Advantages of using PCM-epoxy materials
- Energy storage aims to reduce the conventional
energy consumtion with a direct impact on CO2
emissions. - In order to achieve this it is necessary
- to find new materials with superior performances
- to eliminate the existent material disadvantages
- The PCM-epoxi nano-composite materials obtained
as cross-linked three dimensional structures are
attractive for space heating and cooling of
buildings able to reduce the space and costs for
containerization. - Modeling the heat transfer in the obtained
nanocomposites PCM-epoxi in order to dimensionate
the real buildings. - Taking into account the application in a passive
or active heating or cooling and their needs ,
the suitable material and its geometry will be
used. Geometric form of the material is
application dependant.
Physico-chemical -Phase change temperature
in the required domain -High latent heat of
phase change and caloric capacity -High
thermal conductivity addition of C or Al powder
-Low undercooling -Low volume changes
-Reversible phase transition -Good physical
and chemical stability Kinetical -High
nucleation and crystal grow velocity Economical
-low cost -Reciclability
-Non-toxicity
In experiments were used 1. TES tixotropic
module TESMt 88 Na2SO4-10H2O ? 5 Na2B4O7-10H2O
? 7 SiO2 (encapsulated in a polyethylene
sphere) 2. TES reticulated module(PCM-epoxy)
TESMr 66 Na2SO4-10H2O ? 3,7 Na2B4O7-10H2O ?
30(epoxy resin)1 Carbon black1CaCO3) Starting
with the experimental heat transfer results
concerning the heat transfer in a PCM-epoxy
module, a theoretical model for heat transfer in
a spherical geometry has been developed using the
Megerlin and Goodmann methods. An approximate
formula for the solidification time was deduced
and used on the experimental data. This applies
satisfactory to heat transfer with phase change
in a cross-linked three dimensional polymer
structure.
Material characterization and testing
SEM micrographs for Glauber epoxy
DSC Glauber-epoxyad
DSC Glauber
Thermal Transfer Experiments with Fusion for TES
with PCM
1. Thermal loading experiments in air at constant
temperature for TESM
Experimental results
Thermal loading in air at Tct
Thermal loading set-up for TESM at constant
temperature.
Thermal loading in air with convection.
Discharging in air with convection
PC
The heat transfer coefficient at thermal loading
in air with convection is h ?acaDa(Tin -
Tout)/4?rw2Tw-(Tin Tout)/2 where rw
and Tw are the radius and the temperature at the
surface of TESM ?a, ca, Da, are the density,
specifical heat and the air flow rate, and Tin
and Tout the air temperatures at the entrance and
respectively out of.
1.Experimental cell 2.Spherical
module 3.Termocouple 4. Data taker 5. Resistance
for air heating 6.Measure instrument
(A) 7.Electrical source 8.Compressor 9.Air flow
meter
Thermal cycling setup of the TES modules in air
with convection
Model and Solution for Inward Fusion of TESM
One dimensional spherical geometry for
inward fusion Assumptions 1. The composite
medium is isotropic and homogeneous. 2. The
composite medium is at the fusion temperature at
initial moment. 3. Overall volume change due to
phase change is negligible. 4. Physical
properties are independent of temperature. 5. The
solid-liquid interface is clearly defined the
PCM has a well-defined fusion temperature. 6.
Heat conduction is the only mode of heat-transfer
in the liquid phase natural convection is
assumed to be absent. Model Equations Ste????l?R,R
f???Rf? ? ?2?l?R,Rf???R2 ? ?2?R????l?R,Rf???R? ?l?
1,Rf? ? 0 ?l?RRf,Rf? ? 1 ? ? dRf?d? ?
???l?R,Rf???R?R?Rf? Ste?Fo R r/rw Rf
rf/rw ? (T ? Tw)/ (Tf ? Tw) Fo ?lt/r2w Ste
cl(Tf?Tw)/? Perturbation Solution ?l?R,Rf, Ste) ?
?0?R,Rf? ? Ste?1?R,Rf? ? Ste2?2?R,Rf? ? ... ??Rf,
Ste) ? ?0?Rf? ? Ste?1?Rf? ? Ste2?2?Rf? Method
of strained coordinates for Perturbation
Solution ? ?(R,Rf) ? ?(Rf,Rf) R ? ?i1?
Stei ?i(?,?) Rf ? ?i1? Stei ?i(?,?) After
change variables (R,Rf) ? (?,?) on obtain from
?lorry, Ste) ?1(?,?) ? 0, ?2(?,?) ? 0,
?3(?,?) ? 0 from extern boundary condition,
R1 ?(R1,Rf) 1 ?i(1,?) 0 ?(Rf1) 1 ?i(1,
1) 0 ???/?R?R1 1 ???i/????1 0 from
inward boundary s-l conditions, R Rf ?0???,??
1 ?1???,?? 0 ?2???,?? 0
?dRf?d???d??d?? ?(?????)(????R)??? and from
heat conduction equation in liquid
phase Ste?(?????)(d?/dRf) ? (?????)(????Rf)??(???
??)(????R)??? (?2????2)(????R)2 ?
???????(?2???R2) ? 2?R????????????R? Yields for
non-dimensional position of inward boundary s-l
Rf Rf ? Ste(1 ?)/(6?) Ste2(22? 3)(1
?)/(360?3) and for the energy balance at inward
boundary s-l form d?/d? ?1 ? Ste?d?1(?,?)?d??
? Ste???1(?,?)??????? ? Ste2?d?2(?,?)?d?? ?
Ste2???2(?,?)???????? ? Ste2? d?1(?,?)?d?????1(?,?
)??????? ?????0??,????????? The non-dimensional
time of fusion are obtained by integred last
equation ? ?3(1 ?)2 2(1 ?)3?/6 ? Ste(1
?)2/3 Ste2(1 ?)2/(180?2) with ? a solution of
Rf equation.
Thermal loading for TESM.
Thermal cycling in air with convection
TESMt Tw external, Tcinternal Ta50oC
TESMr Twexternal, Tc internal, Ta50oC
TESMr 1.external 2. internal.
TESMt 1.external 2. internal
CONCLUSIONS 1.These materials present good
mechanical, thermal and chemical properties
suitable for building materials. They can be used
for different applications in active or pasive
systems, depending on their melting
temperature.The geometry used depends also on
their melting temperature and on the chosen
application. 2.The thermal transfer coefficients
at loading/discharging in air with convection
have close values for both TESM proving that they
have a similar thermal behavior. 3. The loading
times in the experiments of loading at constant
temperature are similar for both TESM, leading to
the same conclusion regarding the thermal
behavior. 4.The mathematical model and the
obtained solution gives the possibility to
correlate the variables with the dimensionless
criteria and approximate in acceptable limits the
experimental values.
Results for Inward Fusion of TESM
solidification times
TESMt 1at50oC 2 at 46oC
TESMr 1 at50oC 2 at 46oC