Proceedings of International Forum for Green Asia 2017
Special issue of Evergreen - Joint Journal of Novel Carbon Resource Sciences & Green Asia Strategy

P-19

Specific heat capacity of mesoporous silica gel for adsorption
heat pump applications
Md. Amirul Islam,1,2 Kyaw Thu,1,2 Bidyut Baran Saha1,3
1Kyushu University Program for Leading Graduate School, Green Asia Education Center, Kasuga,Fukuoka 816-8580, Japan
2
International Institute for Carbon-Neutral Energy Research (WPI-I2CNER), Kyushu University,
744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan
3Mechanical Engineering Department, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka, JapanAbstract
Silica gel has been extensively employing as an adsorbent in the field of separation process,purification of gases and adsorption heat pump in the last few decades. The specific heat
capacity of such porous materials is a significant controlling parameter in adsorption
characteristics simulation and system design. This research work is focused on the experimental
evaluation of the specific heat capacities of several types of silica gel for adsorption coolingapplications. The apparatus used in this measurement is a heat flux type differential scanningcalorimeter (DSC) from 35°C to 100°C temperature range. The specific heat capacity values
are found 0.85 to 1.10 kJ kg-1 K-1 in the measurement range. No phase transition or thermal
anomaly is encountered within the measurement conditions. It is found that the specific heat
capacity increases with increase in particle size.
adsorbent is not constant instead a function oftemperature. However, detailed analyses ofspecific heat capacity of porous silica gel atvarious temperatures are not available inopen literature. In the present study, thespecific heat capacities of several types ofsilica gel have been measured using a heat
flux type DSC.

1. Introduction
Silica gel has an incompletelydehydrated polymeric structure of colloidal
silicic acid which exhibits an excellent
capacity for adsorption of water. It isfrequently used for commercial purposes like
separation [1], cooling [2-3], dehumidification[4] and recently desalination [5-6]. The
adsorption
refrigeration
technology
employing silica gel is developing in recent
decades because it is environment friendly
and it requires low grade heat source to drive
the system [7-8]. In design and optimization ofsuch adsorption cycles, the specific heat
capacity of the silica gel is one of the key
thermophysical parameter to measure. In
general, higher specific heat capacity of silica
gel decreases the undesired thermal shock
which arises from the heat of adsorption andrapid cooling/heating but higher specific heathinders the performance of adsorption systemsince significant amount of the suppliedenergy is retained by the silica gel. It is
obvious that the adsorption cycles involve
rapid thermal fluctuation due to alternateheating and cooling [9-10]; hence, it is logicalto perceive that specific heat capacity of the

2. Experimental
2.1. Materials

RD (regular density) Silica gel of four
different particle size, type A and type B
silica gels are investigated in this study.
System calibration is carried out using pureindium and α-alumina (Al2O3) powder asstandards.
2.2. Basic components of DSC
The differential scanning calorimeter(DSC) has a typical heat flux cell which isenclosed by a heating block to dissipate heat tothe specimen (S and R) via a constantan discattached to the block. The constantan disc has
two platforms on which the specimen (S) andreference (R) pans are placed.
Severalthermocouples are used to determine thedifferential temperature of interest for the53Proceedings of International Forum for Green Asia 2017
Special issue of Evergreen - Joint Journal of Novel Carbon Resource Sciences & Green Asia Strategy

P-19
Specific Heat Capacity of RD, Type A, Type B and Cu Sputered Silica
Gelprogrammed heating/cooling cycle. The
schematic diagram of the differential scanningcalorimeter is shown in Fig.1. The thermal
analyzer regulates the temperature and provides
an accurate heating rate to the sample and thereference section. The DSC maintains an inert
environment by introducing nitrogen gas at acontrolled flow rate of 50ml/min.
Platforms

Thermal analyzer

SR

Specific Heat Capacity (J/g-K)

1.2

q̇r

Type A Silica Gel
0.6

Type B Silica Gel

455565Temperature ( C)758595The difference of specific heat capacity
between type A and type B silica gel (Fig. 3.)
is due to the pore size variation and physicalstructure.

Thermocouples

Fig. 1. Schematic diagram of the DSC apparatus

5. Conclusion
Specific heat capacity of RD type (fourdifferent particle size), type A and type B
silica gels were measured. RD silica gel oflargest particle size is found to have thehighest specific heat capacity (0.96 to 1.10 kJ
kg-1 K-1) among these six samples. On theother hand, type A silica gel have the lowest
specific heat capacity (0.85 to 0.95 kJ kg-1 K1) in the measured temperature range.
Specific heat capacity has the tendency toincrease gradually with temperature.

3. Experimental procedureAluminum pan of flat geometry andnearly identical weight and size is placed on
S and R to hold sample materials. The sample
is dried in an ordinary oven at 100°C for 10hours and then in a vacuum oven at 100°C for
3 hours to eliminate any water vapor or otherimpurities in the sample. A complete
experiment to measure the specific heat
capacity comprises of blank run, reference
sample (α-Al2O3) run and sample run.

Reference

4. Results and discussion

M.
Suzuki,
Adsorption
Engineering,
Kodansha, 1990.
[2] E. C. Boelman, B. B. Saha, T. Kashiwagi,
ASHRAE Trans. 1995, 101, 358–366.
[3] B. Choudhury, B. B. Saha, P. K. Chatterjee, J.
P. Sarkar, Appl. Energy 2013, 104, 554–567.
[4] A. Myat, K. Thu, N. K. Choon, Appl. Therm.
Eng. 2012, 39, 70–77.
[5] J. W. Wu, E. J. Hu, M. J. Biggs, Chem. Eng.
Res. Des. 2011, 89, 2168–2175.
[6] K. C. Ng, K. Thu, Y. Kim, A. Chakraborty, G.
Amy, Desalination 2013, 308, 161–179.
[7] K. C. Ng, H. T. Chua, C. Y. Chung, C. H. Loke,T. Kashiwagi, 2001, 21.
[8] S. Mitra, P. Kumar, K. Srinivasan, P. Dutta, Int.
J. Refrig. 2015, 58, 186–197.
[9] A. R. M. Rezk, R. K. Al-Dadah, Appl. Energy
2012, 89, 142–149.
[10] M. Z. I. Khan, K. C. A. Alam, B. B. Saha, A.
Akisawa, T. Kashiwagi, Renew. Energy 2008,
33, 88–98.
[1]Specific heat capacity of different
particle size RD Silica gels is shown in Fig.
2. The result clearly indicates that higher
particle size samples have higher specificheat capacity. The reason is due to lack ofhomogeneity of the adsorbent sample withrespecttoHeatparticle
Specific
Capacity ofsize.
RD, Type A, Type B and Cu Sputered SilicaGel
1.2

Specific Heat Capacity (J/g-K)

0.7

Fig. 3. Specific heat capacity of type A and B silica gel

Temperature
control heater

1.1
1.0

0.9
0.8
Largest Particle Size

0.7

Second Large Particle Size
0.6

Third Large Particle Size
Smallest Particle Size

0.5

0.4
450.8

35

q̇s35

0.90.4ComputerTN2 gas

1.00.5TsTr

1.15565
Temperature ( C)

7585

95

Fig. 2. Specific heat capacity of RD silica gel

Email: amirul@phase.cm.kyushu-u.ac.jp

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