Passive Temperature Moderation Using Multi-Transformation Phase
Change Materials (MTPCM) in Tropical Desert Climate
Ravindra Kumar*, Rohitash Kumar, Manoj Kumar Mishra, Brij Bala Tak,
Pramod Kumar Sharma, and P.K. Khatri
Defence Laboratory Jodhpur ( Rajasthan )
India – 342011
ABSTRACT: In present study, a new phase change material(PCM) , based on binary system of
heavy fatty acids have been developed to act as passive temperature moderator in hot tropical
climates in non air conditioned buildings, structures, vehicles , public transport system etc.
Differential calorimetric studies reveal presence of major phase transformation peak in temperature
range 36-38 0C with latent heat 150-160 J/g and trace of second phase at 38-40 0C. The new
material overcome the problem of poor solidification during hot night shown by commercially
available hydrated salt based PCMs. The material filled in Aluminum/ HDPE panel has been used
as an internal lining, for passive temperature moderation in a real size prototype cabin at Jodhpur
(Rajasthan) in India. It has performed well during whole summer by maintaining passive melting
(during day) - solidification (during night) cycle and restricting inside temperature below 400C .
Keywords: Passive cooling, Phase change material, MTPCM, Latent heat.
1.0 INTRODUCTION:
Phase change materials are being utilized world over for various applications like
solar & waste heat storage1-7, electronic cooling 8, transient thermal management during time
varying work loads on electronics9etc. PCM have also been utilized for energy saving in buildings
in cold countries.10-11 Off late PCM has been utilized by Mozheveiov et. al.12 for temperature
moderation of a real size room using calcium chloride hexa hydrate as PCM. They have
demonstrated that temperature moderation in 20-30 0C and a 24 hour melting (during day) solidification (during night) cycle is possible with Calcium chloride hexa hydrate as PCM in
desert conditions of Israel.
In tropical regions like Thar Desert in India, very severe heat condition prevails in the
month of May and June. The ambient temperature remains in the range of 46-500C for 5-6 hrs of
the day ( 12:00 to 18:00 Hrs ). The temperature of surfaces directly exposed to sun rises to 70720C. Temperature inside confined spaces like non air conditioned buildings, structures and public
transport systems may rise to above 50 0C. In such conditions, temperature moderation using phase
change materials is very attractive preposition to save electric power required for cooling.
Hydrated salt based PCM tried by Mozheveiov et. al.12 is not suitable for hotter regions as they do
not solidify by ambient cooling during night.
In present study, special PCM have been developed by making solid solution of binary
and ternary systems of heavy fatty acids. Out of various systems studied , the binary system of
Palmitic – lauric acid shows presence of multiple numbers of hypo/hyper eutectic tunable phases.
* Author for communication
E Mail : rka_dlj @ rediffmail.com
1
One composition in this system has been tailored to absorb maximum heat during day time by
melting near human body temperature (35-38 0C). The kinetics of phase reversal has been
accelerated by introducing traces of high temperature phase to ensure completion of PCM
solidification in 6-8 hrs of ambient cooling during hot desert night in the temperature range of 3235 0C.
The material, when used as internal lining in a prototype real size cabin has provided
moderation of temperature by 10-15 0C. The material has worked well through out the summer
season by maintaining melting (during day) - solidification (during night) cycles. Present paper
discusses details of the study.
2.0 MATERIALS AND METHODS: Chemicals of Loba / Merck make (AR grade) have been
used in the study to prepare various compositions of PCM by melting and solution making.
Thermal properties namely phase change temperature and latent heat associated with each
transformation were studied using differential scanning calorimeter make M/s Water USA,
model: Q10 . Phase reversal kinetics and cyclic stability was studied in programmable
environmental chamber make M/s CM equipment Bangalore. Optimized composition of PCM
was filled in aluminum panel of size 7.5 cm width X 4.0 cm thickness and varied lengths.
A prototype cabin of inner dimensions of 240cm X 180 cm X 120 cm was
fabricated using medium density fiber board (MDF) as outer walls and MTPCM filled aluminum
panel as internal lining. The quantity of PCM required was decided based on total heat flow
during day through 1/2” thick MDF panel. Complete PCM solidification by ambient cooling
during night was ensured by maintaining natural air convection from three windows provided in
the cabin. The temperature profiles of outer and inner surface of cabin was monitored through out
the summer season using probe type digital / IR thermometer.
3.0 RESULTS & DISCUSSION:
Automatic phase reversal ( solidification ) of PCM by ambient cooling during
night is an essential condition for PCM application for passive temperature moderation of
buildings, vehicles and structures. In tropical regions, this has to be completed in 6-8 hrs
(01:00-08:00 Hrs.) during early morning when ambient temperature is in the range 32 -350C.
Use of low melting point PCM like hexa hydrated calcium chloride (M.P.: 29300C) as used by Mozheveiov et. al.15, although desirable from human comfort criteria, is ruled
out in such a harsh climatic condition of tropical regions. Next best option, although not so
comfortable is to use a PCM with phase change temperature near to human body temperature
(36-37 0C). One such material, Zinc nitrate hexa hydrate having melting point in the temperature
range 35-360 C was tried in the present study. However, the material was not solidifying during
night due to requirement of high degree of under cooling for solidification (phase reversal
temperature < 250 C). Addition of 1-1.5 % Boric acid as extrinsic heterogeneous nucleating
agent, although, improves the solidification temperature to 30 0C, but still not able to ensure
complete phase reversal during night. Separation of nucleating agents after few cycles due to
density difference, hygroscopic nature and incongruent melting- solidification behavior were
other factors making hydrated salts unsuitable for passive cooling in tropical desert.
Seeing these limitations of hydrated salts, fatty acids were studied for their
suitability in hot desert climate. Out of various binary/ternary systems studied, lauric acid, Palmetic acid binary system was found promising. During differential scanning analysis the
system shows, depending on composition, presence of multi transformation peaks, 1 to 4 in
numbers (Fig.1), in 34-60 0C temperature range. The number and position of the peaks can be
2
tailored to some extent by controlling composition to alter heat absorption and phase reversal
behavior for different applications.
Sample: pala80
Size: 2.7200 mg
FIG.1. DSC CURVE OF LAURIC - PALMITIC BINARY SYSTEM SHOWING
DSC
TUNABLE
MULTIPLE TRANSFORMATIONSDSC
File: C:\TA\Data\DSC\laupametic\pala80.003
Operator: Rohitash Kumar
Run Date: 16-Dec-2008 16:27
Instrument: DSC Q10 V9.7 Build 291
Comment: heating cooling rate 5 deg/min
6
Sample: pala90
Size: 3.5300 mg
File: C:\TA\Data\DSC\laupametic\pala90.003
Operator: Rohitash Kumar
Run Date: 18-Dec-2008 14:36
Instrument: DSC Q10 V9.7 Build 291
Comment: heating cooling rate 5 deg/min
6
30.47°C
34.07°C
4
4
2
H e a t F lo w ( W /g )
H e a t F lo w (W /g )
2
31.70°C
150.4J/g
0
34.87°C
152.6J/g
34.80°C
153.4J/g
0
35.83°C
160.4J/g
-2
-2
-4
37.79°C
37.85°C
Sample: pala25
Size: 2.3000 mg
-6
-20
DSC
0
Comment:
Exo Up heating cooling rate 5 deg/min
20
40
Temperature (°C)
42.33°C
File: C:\TA\Data\DSC\laupametic\pala25.004
Operator: Rohitash Kumar
Run Date: 12-Dec-2008
10:34
60
80
Instrument: DSC Q10 V9.7 Build 291
Universal V4.2E TA Instruments
3
Sample: laric 25%, palmitic75%
Size: 6.7000
-4 mg
-20 cooling method
Method: heating
0
20
DSC
40
Temperature (°C)
Exo Up
File: C:\TA\Data\DSC\exp data\lapasevfiv.001
Operator: Rohitash Kumar
60 14:59
80
Run Date: 01-Jan-2007
Universal V4.2E TA Instruments
Instrument: DSC Q10 V9.7 Build 291
15
49.05°C
47.44°C
2
10
37.65°C
183.8J/g
31.00°C
37.47°C
184.6J/g
0
5
H e a t F lo w ( m W )
H e a t F lo w ( W /g )
1
48.49°C
180.1J/g
0
56.53°C
36.11°C
185.0J/g
35.81°C
40.62°C
-1
-5
34.67°C
43.51°C
54.62°C
56.76°C
-2
Exo Up
-20
0
20
40
Temperature (°C)
60
80
Universal V4.2E TA Instruments
3
-10
Exo Up
39.05°C
-20
0
20
40
Temperature (°C)
60
80
Universal V4.3A TA Instruments
In present study the material was tailored in such a way (composition is under
Indian patent, application no. 2258/DEL/2007) that it absorbs heat near human body temperature
in temperature range 35-380C. The material also has minor phase change peak at 36.9 0C (Fig 2).
During phase reversal initial nuclei of solid start forming at comparatively higher temperature of
35.90C. These nuclei facilitate further solidification. The overall kinetics of solidification is thus
accelerated and gets completed in 6-8 hrs in ambient temperature range of 32-350C available
during night. The experiment in controlled temperature chamber confirms complete phase
reversal in 6-8 hrs.
Unlike in hydrated salt system , the second phase in new material is intrinsic in nature
and hence no separation of phases takes place. This improves the material stability. No
significant deterioration in thermal properties has been observed even up to 5000 cycles of
melting and solidification.
.
Sample: pala67
Size: 3.5800 mg
FIG.2
File: C:\TA\Data\DSC\laupametic\pa
DSC CURVE OF DESERT TUNED
MTPCM-37 la67.004
Operator: Rohitash Kumar
DSC
Run Date: 24-Dec-2008 11:30
Instrument: DSC Q10 V9.7 Build 291
Comment: heating cooling rate 0.5 deg/min
0.6
33.65°C
34.90°C
0.4
Start of Phase
reversal at 35.9 0C
H e a t F lo w (W /g )
0.2
35.48°C
156.8J/g
30.63°C
35.90°C
0.0
40.87°C
35.49°C
154.9J/g
39.92°C
-0.2
Traces of high
temp. phase
-0.4
-0.6
Exo Up
36.92°C
15
20
25
30
35
Temperature (°C)
4
40
45
50
Universal V4.2E TA Instruments
The optimized composition of MTPCM was filled in rectangular aluminum pipes/ HDPE
container and used as internal lining in a prototype cabin. Temperature profile of cabin (sun
exposed outer roof and inside) on a typical summer day is shown in fig.3. Maximum inside
temperature of the cabin remains below 40 0C through out the day while roof temperature
exposed to sun goes to more than 700C. In similar conditions, the inside temperature of another
cabin with out PCM lining goes to more than 50oC. The door and windows of the cabin was kept
open during night to facilitate automatic phase reversal by natural air flow . The experiment was
repeated through out summer (one week data given in table 1) and the performance in terms of
holding inside maximum temperature below 400C was maintained.
TABLE.1 PERFORMANCE OF PCM COOLED CABIN OVER A WEEK
Time
5-6-08
6-6-08
7-6-08
8-6-08
9-6-08
10-6-08
11-6-08
12-6-08
14:00
15:00
13:00
15:30
14:30
15:00
15:30
14:30
Solar induced surface
Temperature on
Out side roof (0C )
54.2
59.8
54.8
64.2
67.9
65.0
54.5
61.0
T E M P E R A T U R E (O C )
Date
Temperature(maximum)
in center of shelter
(0C)
37.9
38.1
37.6
38.2
38.2
38.0
37.3
37.5
Ambient Temp.
75
70
65
60
55
50
45
40
35
30
25
Solar Induced Temp.
Temp. in a confined
space
MTPCM moderated
Temp.
1 3 5 7 9 11 13 15 17 19 21 23
TIME OF DAY(00:00Hrs.)
FIG. 3 TEMPERATURE PROFILE OF CABIN HAVING PCM
INNER LINING
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4.0 CONCLUSIONS :
In tropical regions, during summer, temperature inside confined spaces in non
A/C buildings and public transport systems rises to intolerable levels of 50-550C. Passive
temperature moderation using PCM is attractive to save electrical power. However,
conventional PCM like calcium chloride hexa hydrate can not be utilized in extreme hot
climates due to poor solidification by ambient cooling in night. In present study we have
developed a new PCM based on organic alloying in binary system of fatty acids. The
material has been tailored in such a manner that it starts absorbing environmental heat in
day time when temperature exceeds human body temperature. Phase reversal kinetic of
new material has been enhanced by introducing traces of high temperature phase as
intrinsic nuclei to facilitate further solidification of major phase. PCM filled aluminum
panels, when used as internal lining, does not allow internal temperature of a prototype
cabin to rise above 400C through out the extreme summer. The new PCM was completing
melting (day) – solidification (night) cycle with diurnal cycle of hot desert. The material
can be helpful in various applications involving passive temperature moderation in non
air conditioned buildings, power saving in cooling and providing cooling backups during
power failures.
5.0 ACKNOWLEDGEMENT:
Authors are thankful to Dr N.K.Jain Director Defence laboratory Jodhpur for
consistent guidance and encouragement in carrying out this work.
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