Heat Transfer Enhancement For PCM Thermal Energy Storage in Triplex Tube Heat Exchanger
Abduljalil. A. Al-Abidi1,2, Sohif. Mat1, K. Sopian1, M.Y. Sulaiman1 , Abdulrahman. Th. Mohammad1 1
Solar Energy Research Institute, National University of Malaysia, Bangi, Selangor, Malaysia 2
Department of HVAC Engineering, Sana’a Community College, Sana’a, Yemen
Address correspondence to
Abduljalil A. Al-abidi, Solar Energy Research Institute, National
University of Malaysia, 43000 Bangi, Selangor, Malaysia, E-mail:
[email protected] Tel:+ 60156135676 , Fax: + 60389214593,
ABSTRACT Thermal energy storage is critical for reducing the discrepancy between energy supply and energy demand, as well as for improving the efficiency of solar thermal energy systems. Among the different types of thermal energy storage, phase change materials (PCM) thermal energy storage has gained significant attention recently because of its high energy density per unit mass/volume at nearly constant temperature. This study experimentally investigates the using of a triplex tube heat exchanger (TTHX) with PCM in the middle tube as the thermal energy storage to power a liquid desiccant air conditioning system. Four longitudinal fins were welded to each of the inner and middle tubes as a heat transfer enhancement in the TTHX to improve the thermal performance of the thermal energy storage. The average temperature of the PCM during the melting process in the TTHX with and without fins was compared. The PCM temperature gradients in the angular direction were analyzed to study the effect of the natural convection in the melting process of the thermal storage. The energy storage efficiency of the TTHX was determined. Results indicated that there was a considerable enhancement in the melting rate by using fins in the TTHX thermal storage. The PCM melting time is reduced to 86 % by increasing of the inlet HTF. The average heat storage efficiency calculated from experimental data for all the PCMs is 71.8%, meaning that 28.2% of the heat actually was lost.
INTRODUCTION In the last three decades, numerous researchers have intensively studied phase change materials (PCMs) in thermal energy storage because of their high thermal energy densities per unit volume/mass and their availability in different fields of engineering with wide temperature ranges. The use of PCM thermal energy storage is recommended to improve energy efficiency and to reduce the discrepancy between the energy supply and demand of solar thermal energy applications. Among the different types of thermal energy storage, PCM thermal storage promises performance and reliability, with the advantages of high storage density and almost constant thermal energy. They offer the ability to absorb and store large quantities of thermal energy through the endothermic melt process[1].
Most PCMs have limited applications because of their low thermal conductivity. Thermal energy storage leads to prolonged melting and solidification. Numerous studies focused on the heat transfer enhancement technique, which deals with the improvement of such poor PCM characteristics, including the utilization of finned tubes[2-4], insertion of a metal matrix into the PCM, application of multi-tube heat exchangers[4], utilization of bubble agitation in PCMs, application of PCM dispersed with high conductivity particles, and using microencapsulated PCMs [5]. Al-Abidi et al.[3] experimentally investigated the PCM melting process in the middle tube of a triplex tube heat exchanger (TTHX). They studied three heating approaches to melt the PCM: an inside heating method, an outside heating method, and heating at both sides. The charging process totally depended on the solar heating. Temperature distributions in three directions were studied. They reported that heating both sides of the middle tube is preferable because the low heat transfer fluid (HTF) inlet temperature is used, and the PCM melting time was reduced in contrast to the melting time of the other methods. Jian-you [6] used triplex concentric tubes with PCM filling in the middle tube, where the charging process in the outside tube came from the inside tube.
Numerous studies reported that the heat transfer between the HTF and the PCM with embedded fins in the PCM can be improved by increasing the heat transfer area. Different fin configurations, including external and internal fins (circular, longitudinal, and rectangular), are applied to PCMs. Agyenim et al.[7] used circular and longitudinal fin heat transfer enhancements to achieve the complete melting of erythritol as a PCM thermal storage to power an absorption-type air-conditioning system. The main objective of these techniques was to melt the PCM through the solar energy availability in European countries where the sunshine is less than 8 h. They reported that the longitudinal fin thermal energy storage systems are suitable for charging and discharging in a concentric tube PCM system, because they achieved the best charging performance with insignificant subcooling during discharge. Bauer [8] developed an analytical model to investigate the effective utilization of fins in LHTES; he studied the solidification times of PCM using two geometries; the first geometry is a plane wall and the second geometry is a tube surrounded by the PCM-fin arrangement. Mosaffa et al.[9] presented a two-dimensional analytical model to study the solidification process of a PCM in a shell and tube heat exchanger with radial fins; they reported the PCM solidified more quickly in the cylindrical shell storage than in the rectangular storage. In addition, the solid fraction of the PCM increases more quickly when the cell aspect ratio is small. Ismail et al.[10] investigated numerically and experimentally the effect of fin design parameters such as fin length, fin thickness, number of fins, and the aspect ratio of the annular space on the complete solidification, solidified mass fraction, and the total stored energy of the PCM. Al-Abidi et al.[11] introduced external and internal fins to the TTHX as a heat transfer-enhancement technique. They numerically investigated the effect of different design and operation parameters such as the fin length, fin thickness, number of fins, and PCM geometries, as well as the TTHX materials and Stefan number, on the melting process. The result indicated that the melting time for the eight-cell PCM unit geometries was reduced to 34.7% compared with that of the triplex tube without fins.
Triple tube concentric heat changer with PCM in the middle tubes increases the heat-transfer area, consequently improving the heat transfer relative to that of the double pipe concentric heat exchanger. In addition, the time required for total melting and the inlet temperature for the heat transfer fluid (HTF) is reduced. The current study experimentally investigates the using of TTHX with PCM in the middle tube as the thermal energy storage to power a liquid desiccant air conditioning system. Moreover, the effect of longitudinal fins welded to each of the inner and middle tubes as a heat transfer enhancement in the TTHX to improve the thermal performance of the thermal energy storage is studied.
EXPERIMENTAL TEST AND PROCEDURE Physical model Figure 1 shows the physical configuration of the TTHX, which has an inner tube radius ri of 25.4 mm with a thickness of 1.2 mm. The middle tube radius rm and the outer tube radius ro were 75 and 100 mm, respectively, with a 2 mm thickness. Copper pipes were used to ensure high thermal conductivity. The outer and inner tubes were used for the HTF (water), whereas the middle tube was used for the PCM that is based on a commercially available material, Rubitherm GmbH (RT82). The PCM physical properties such as the melting temperature, solidification temperature, as well as the latent heat of fusion of RT82, were independently investigated by analyzing a 20.29mg sample of RT82 using a Differential Scanning Calorimeter (DSC). The thermophysical properties of RT82 as reported by the manufacturer are shown in Table 1, whereas the independent investigation by the authors is reported in Table 2.
Experimental apparatus
Thermal energy storage systems using the triplex concentric tube heat exchanger with and without internal and external fins were fabricated to investigate the heat transfer enhancement on the thermal performance of the PCM thermal storage. Figure 2 shows a schematic diagram of the experimental apparatus, which includes the TTHX without fins, the TTHX with fins, hot-water circulation pumps, evacuated tube solar collectors, charging storage tank with electric heater, rotameter for measuring the flow rate, electronic controller, and manual shut-off valve. Figure 3 shows the. TTHX section consisting of three horizontally mounted concentric tubes with lengths of 500 mm. The inner tube was extended to approximately 300 mm from the entrance to ensure that the flow would be fully developed. Two tubes with 32 mm diameter were welded eccentrically to the outer tube from above and below at the entrance and exit of the HTF to deliver the hot water in to and out of the outer tubes. The physical geometrical parameters of the TTHX are mentioned in the physical model section. The inner and outer tubes are used to hold the HTF (water), and the middle tube is filled with 5.6 kg of liquid PCM (RT 82). Four longitudinal fins (fin pitch of 42mm,length of 480mm,and thickness of 1mm)welded to each of the inner and middle tubes for the TTHX with internal-external fins as shown in Figure 3. Fifteen thermocouples emerged in the PCM every 10 mm in the radial and different angular directions. The thermocouples were located 100 mm from the entrance of the HTF tube in the thermal storage, as shown in Figure 1 and Figure 3. Two thermocouples were installed at the inlet and outlet of the HTF tube to measure the inlet and outlet temperatures of the HTF. The data monitoring system was comprised of K-type thermocouples (measured at 0.5% accuracy), a data logger, and a personal computer to measure the temperatures in the PCM thermal storage. HTF flow rate was measured using a rotameter (measured at 5% accuracy). Seventy millimetre-thick glass wool insulation was wrapped around the TTHX to decrease heat loss and to insulate the surface. The hot water used in the charging process was delivered from a central heating station at the Green Technology Park at the Solar
Research Energy Institute, National University of Malaysia, as shown in Figure 2. This heating station was designed to deliver the hot water required by various solar thermal systems. The central heating station consists of 300 evacuated tube solar collectors with three 200-L storage tanks. One storage tank was used for the current application. Charging started when the storage tank temperature reached a temperature of 90 °C.
RESULTS AND DISCUSSION To charge the PCM thermal storage with a steady state HTF inlet temperature, different experimental studies were carried out. The charging process to melt the PCM depended on the electrical heat sources. Heating up of the storage tank was conducted by a solar heating source until the required temperature was achieved. Then, the electric heater, controlled by a thermostat, was run to maintain a constant inlet temperature. The average temperature of the PCM based on the 15 thermocouple readings embedded in the PCM thermal storage entrance as shown in Figure 3.
Comparison of temperature profiles for TTHX with and without fins Figure 4 shows the PCM average temperature versus time for the TTHX with and without fins during the melting process. The temperature profile indicated that there is no significant difference in the average PCM temperatures at the early time of melting when the conduction mechanism dominated the heat transfer process. After 10 min of melting, the average temperature of the TTHX with internalexternal fins was higher than the TTHX without fins. The curves show that the TTHX with fins recorded a shorter complete melt time after 60 min., whereas the TTHX without fins consumed a longer time. Complete melting in the TTHX without fins was approximately 100 min or more.
Angular temperature variation for thermal energy storage In this study, temperature measurements along the angular directions were considered to investigate the effect of the natural convection of the thermal storage. The angular direction starts from 0° clockwise to 157.5° for the TTHX with fins and from 0° clockwise to 180° for the TTHX without fins, as shown in Figure 5. The angular average temperature-variation readings were taken from thermocouples at the same angles (22.5°, 67.5°, 112.5°, and 157.5°) for the TTHX with fins and at angles (0°, 45°, 90°, 135°, and 180°) for the TTHX without fins. Figure 6 shows the average temperature variations along angular directions for the melting processes. These averages measurements are collected from different thermocouple readings in different locations at the thermal storage entrance. The average temperature was the same in the earlier part of the heating process, as well as at the final stage of the melting process of the PCM for the TTHX without fins. The highest temperature was observed at ϴ = 0° because of the buoyancy-driven natural convection during the phase transition process of the PCM. The reason is that the hot liquid PCM was squeezed up into the upper part of the thermal storage. There were no significant differences in the average temperature for all angular directions. This is attributed to the natural convection in the top region of the thermal storage as well as the vortex at the bottom side of the thermal storage. The highest average temperature was recorded at ϴ = 157.5° for the TTHX with fins, which were located at the bottom of the thermal storage; this is attributed to the good thermal diffusion in this part, followed by ϴ = 112.5°. There was no significant difference in the average temperature observed at ϴ = 67.5° and ϴ = 22.5°. The average temperature occurred at ϴ = 22.5° and ϴ = 67.5°, which were less than ϴ = 112.5°, ϴ = 157.5°. This is may be because that the upper part was affected by the entrance disturbance. The flow was disturbed by changing the flow path from the 32-mm inlet pipe to the outer tube. The other
source that affected the heat diffusion in this part was the location of the outer tube inlet pipe, which was not centered but was soldered at the left side, as shown in the Figure 3.
HTF inlet temperatures influences Figure 7 shows the temperature contours of the TTHX with fins for PCM thermal energy storage at t =30 min for HTF inlet temperatures of 85°C, 90°C, 95°C, and 100°C. The charging of the PCM under different HTF inlet temperatures was performed at an 8.3 kg/min mass flow rate. The minimum temperature required to achieve PCM melting, which was above the PCM melting temperature, was the basis for the HTF inlet temperature values. The temperature readings were based on the thermocouples embedded in the PCM thermal storage entrance, and from linear interpolation between these points. Figure 7 shows that the heat conduction mechanism dominated the heat transfer process when the HTF inlet temperature was 85°C after 30 min. When the HTF inlet temperature increased to 90°C and 95°C the PCM average temperature increased specially in the lower part of the thermal storage due to good thermal diffusion. The PCM was totally melted when the HTF inlet temperature increased to 100°C, where the natural convection accelerated the PCM melting process. The total melting times of the PCM were reduced to 86 % by increasing the inlet HTF temperature from 85°C to 100°C.
Thermal energy storage efficiency Figure 8 displays the inlet and outlet temperatures of the HTF, as well as the average temperature of the PCM temperature versus time for the TTHX with fins. The average charging temperatures of the PCM melting were 87°C with an 10.8 kg/min mass flow rate. It was observed for all melting tests that the PCM temperature increased rapidly initially, during the sensible heating period
of the melting process. As the phase transitions started, the difference between the inlet and outlet temperatures was constant for a long period of time until the melting process for the PCM was complete. Figure 9 illustrates the average temperature of the PCM, as well as the outlet and inlet temperatures of the HTF versus time for the TTHX with fins during the discharging process. The average HTF inlet temperature for discharging was 63°C with an 4.848 kg/min mass flow rate. It was noted for the solidification process that the PCM temperature decreased initially, during the sensible cooling period of the freezing process. As the phase transitions completed, the difference between the outlet and inlet temperatures was decreased until the freezing process for the PCM was complete. The energy consumed for the PCM charging include the sensible heating process to heat up the PCM from the initial temperature ( usually ambient temperature), latent heat of fusion for the PCM, and sensible heating after the melting temperature of the PCM. The other components related to heating consumed for thermal storage structure and heat transfer fluid. The total energy deliver to the system that generated in the thermal energy station either it is from renewable energy or waste energy conveyed by the HTF (water) so the energy input to the system can be determined by the following equation.
̇
(
)
(1)
where Qch is the energy to melt the whole PCM during charging period which translated from the storage tank, mch is the HTF mass flow rate, cpw is the specific heat of the HTF (water).
During discharging, the purpose is to recover heat from the solidifying PCM, so that the total enthalpy received from the PCM is the product energy content. But the energy release considered for the application depended on the application temperature required, in our application, the minimum temperature required to operate the liquid desiccant is about 60ºC-70 ºC. The maximum energy release from the thermal storage can be written as this formula.
( ̇
)
(2)
where Qdis is the energy which collected by HTF form PCM during the discharge period and transferred to the load. mdis is the HTF mass flow rate. PCM thermal energy storage efficiency was studied for TTHX with fins. The efficiency is defined as a ratio of the real heat retrieved by the HTF during the PCM solidification to the heat extracted from the HTF during PCM melting process that can be stored in the PCM. For viewing the total process energy, the overall efficiency of the thermal storage can be written as [12].
(3)
̇
̇
(
)
(
)
(4)
Table 3 indicated the energy efficiency of the TTHX with fins. The total amount of heat energy retrieved was 8314 kW during the freezing process, accounting for 71.8% of the heat extracted from the HTF during the melting process. The remaining 28.2% of the total energy charged was sensible subcooled heat from 27 ºC to 63ºC and the amount of heat lost.
CONCLUSIONS A triplex tube heat exchanger was experimentally investigated as latent heat thermal energy storage. The middle tube was filled with PCM, whereas the inner and outer tubes were used for HTF. Heat transfer enhancement techniques by using fins embedded in the PCM in the TTHX was investigated experimentally. The average temperature of the PCM during the melting process in the TTHX with and without fins was compared. The PCM temperature gradients in the angular direction were analyzed to study the effect of the natural convection in the melting process of the PCM. The effect of the HTF inlet temperature on the thermal energy storage effectiveness was studied. Results indicated that there was a considerable enhancement in the melting rate by using fins in the TTHX thermal storage. The average heat storage efficiency calculated from experimental data for all the PCMs is 71.8%.
NOMENCLATURE Q
heat energy (kW)
m
mass flow rate (kg/s)
cp
specific heat (kJ/kg.K)
T
temperature(ºC)
Greek Symbols η
energy efficiency
Subscripts in
inlet
out
outlet
ch
charging
dis
discharging
w
water
REFERENCES [1] Howard, J, A., and Walsh, P.A., An experimental investigation of heat transfer enhancement mechanisms in microencapsulated phase change material slurry flows. Heat Transfer Engineering, vol. 34, no. 2-3, pp. 223–234, 2013. [2] Al-Abidi, A. A., Mat, S., Sopian, K., Sulaiman, M.Y., and Mohammad, A. Th. Experimental study of melting and solidification of PCM in a triplex tube heat exchanger with fins. Energy and Buildings, vol. 68, Part A, pp. 33-41, 2014. [3] Al-Abidi, A. A., Mat, S., Sopian, K., Sulaiman, M.Y., and Mohammad, A. Th., Experimental study of PCM melting in triplex tube thermal energy storage for liquid desiccant air conditioning system. Energy and Buildings, vol. 60, pp. 270-279, 2013. [4] Parry, A. J., Eames, V.C., and Agyenim, F.B., Modeling of thermal energy storage shell-and-tube heat exchanger. Heat Transfer Engineering, vol. 35, no. 1, pp. 1–14, 2014. [5] Zhao, Z., Hao, R., and Shi, Y., Parametric analysis of enhanced heat transfer for laminar flow of microencapsulated phase change suspension in a circular tube with constant wall temperature. Heat Transfer Engineering, vol. 29, no. 1, pp. 97–106, 2008. [6] Jian-you, L., Numerical and experimental investigation for heat transfer in triplex concentric tube with phase change material for thermal energy storage, Solar. Energy, vol. 82, no. 1, pp. 977–985, 2008. [7] Agyenim, F., Eames, P., and Smyth, M., A comparison of heat transfer enhancement in a medium temperature thermal energy storage heat exchanger using fins, Solar Energy, vol. 83, no. 9, pp. 1509-1520, 2009.
[8] Bauer, T., Approximate analytical solutions for the solidification of PCMs in fin geometries using effective thermophysical properties, International Journal of Heat and Mass Transfer, vol. 54, no. 23-24, pp. 4923–4930, 2011. [9] Mosaffa, A. H., Talati, F., Basirat Tabrizi, H. and Rosen, M. A., Analytical modeling of pcm solidification in a shell and tube finned thermal storage for air conditioning systems. Energy and Buildings vol. 49, PP. 356–361, 2012. [10] Ismail K.A.R., Alves, C.L.F., and Modesto, M.S., Numerical and experimental study on the solidification of PCM around a vertical axially finned isothermal cylinder. Applied Thermal Engineering vol. 2, no. 1, PP.53–77, 2001. [11] Al-Abidi, A. A., Mat, S., Sopian, K., Sulaiman, M.Y., and Mohammad, A. Th., Internal and external fin heat transfer enhancement technique for latent heat thermal energy storage in triplex tube heat exchangers. Applied Thermal Engineering. vol. 53, no. 1, PP.147-56, 2013. [12] Rezaei, M., Anisur, M. R., Mahfuz, M. H., Kibria, M. A., Saidur, R., and R.Metselaar, I. H. S. C., Performance and cost analysis of phase change materials with different melting temperatures in heating systems. Energy. vol.53, pp. 173-178, 2013.
Table 1.Thermophysical properties of the (RT 82 ) PCM. Properties
RT82
Density of PCM, solid,ρs (kg/m3)
950
Density of PCM, liquid, ρl (kg/m3)
770
Specific heat of PCM, Cp (J/kg K)
2000
Latent heat of fusion, L (J/kg)
176000
Melting temperature, Tm (°C)
77-82
Thermal conductivity, k (W/m.K)
0.2
Thermal expansion coefficient (1/K)
0.001
Dynamic Viscosity,
0.03499
(kg/m.s)
Table 2 Reported mean and standard uncertainty of the PCM thermal properties Melting process
Solidification process
Onset point Peak point
Heat of fusion
Onset point
Peak Point
Heat of Fusion
(°C)
(°C)
(KJ/kg)
(°C)
(°C)
(KJ/kg)
70.12± .15
82.18
201.64
81.86
78.16
207.81
± 0.05
±1.39
±0.03
±0.10
±1.36
Table 3 Energy stored and released with energy efficiency for TTHX with fin Properties
Unit
Values
Charging energy
kW
11322
Retrieved energy
kW
8136
PCM thermal efficiency
(%)
71.8
List of Figure Captions Fig. 1 The physical configuration of the TTHX Fig. 2 Schematic diagram of the experimental apparatus includes evacuated tube solar collector (1), TTHX
with fin(2), TTHX without fin(3), hot-water circulation pumps (4,7), electronic
controller(5), charging storage tank with electric heater (6), rotameter(8), thermocouples(9),data logger(10), personal computer(11),pressure gauge(12),air vent(13), and manual shut off valve (14 ). Fig. 3 Fig.3 Schematic diagram of the TTHX; (a) cross section of TTHX, (b) longitudinal section of TTHX. Fig. 4 PCM average temperature for TTHX with and without fins Fig. 5 Thermocouples location, (a) TTHX with fins, (b) TTHX without fins Fig. 6 Average temperatures recorded in the angular direction for the thermal storage, (a) TTHX without fin, (b) TTHX with fins. Fig. 7 HTF inlet temperature effect on the PCM melting time 8.3 kg/min at t= 30 min,(a) 85°C , (b) 90°C, (c) 95°C, (d) 100°C. Fig. 8 Melting process for the TTHX with mass flow rates of 10.8 kg/s, an average HTF inlet temperature 87°C. Fig. 9 Solidification process for the TTHX with mass flow rates of 4.848 kg/s, an average HTF inlet temperature 63°C
Figure 1 The physical configuration of the TTHX
Figure 2 Schematic diagram of the experimental apparatus includes evacuated tube solar collector (1), TTHX with fin(2), TTHX without fin(3), hot-water circulation pumps (4,7), electronic controller(5), charging storage tank with electric heater (6), rotameter(8), thermocouples(9),data logger(10), personal computer(11),pressure gauge(12),air vent(13), and manual shut off valve (14 ).
(a) ri Fin
5
8 12 13 14 15
rm
6
7
910 11
500 mm 480 mm
ɸ
4 3 2 1
200 ɸ 150 ɸ 50.8
Flow direction
Fig.2
r o Thermocouples locations
Figure 3 Schematic diagram of the TTHX; (a) cross section of TTHX, (b) longitudinal section of TTHX.
Fin
Figure 4 PCM average temperature for TTHX with and without fins
(a)
(b)
Figure 5 Thermocouples location, (a) TTHX with fins, (b) TTHX without fins
(a)
(b)
Figure 6 Average temperatures recorded in the angular direction for the thermal storage, (a) TTHX without fin, (b) TTHX with fins.
(a)
(c)
(b)
(d)
Figure 7 HTF inlet temperature effect on the PCM melting time 8.3 kg/min at t= 30 min,(a) 85°C , (b) 90°C, (c) 95°C, (d) 100°C.
T PCM
T in
T out
100
Temperature, ºC
90 80 70 60 50 40 30 0
10
20
30
40
50
60
70
80
Time, min Figure 8 Melting process for the TTHX with mass flow rates of 10.8 kg/s, an average HTF inlet temperature 87°C
T PCM
T out
T in
Temperature, ºC
90 80 70 60 50 40 30 0
50
100
150
200
250
300
Time, min Figure 9 Solidification process for the TTHX with mass flow rates of 4.848 kg/s, an average HTF inlet temperature 63°C
Abduljalil A. Al-Abidi has received his B.Sc. degree in Mechanical Engineering from Sana’a University, Sana’a, Yemen in 1999. In 2003 he has got his master degree in Air Conditioning Engineering from Al-Balqa` Applied University, Salt, Jordan. Currently he is a PhD candidate at the Solar Energy Research Institute, University Kebangsaan Malaysia(UKM) in the field of Renewable Energy. He is a member of World Society of Sustainable Energy Technologies (WSSET). His research interest includes thermal energy storage, phase change material, solar energy, solar thermal cooling system.
Sohif Mat has received his B.Sc. degree in Mechanical Engineering from University of Malaya, Malaysia in 1983. In 1990 he has got his PhD degree in Mechanical Engineering, University of Malaya, Malaysia. He is a principle research fellow at the Solar Energy Research Institute (SERI), University Kebangsaan Malaysia (UKM) in Bangi Malaysia, he is a professor at UKM and the industrial relations coordinator of SERI, UKM. His Research Interest includes renewable energy, PCM, evaporative cooling, solar thermal systems.
Kamaruzzaman Sopian has received his B.Sc. degree in Mechanical Engineering from University of Wisconsin-Madison in 1985 and his master degree and PhD in Energy Resources, Solar Energy form University of Pittsburgh and Mechanical Engineering University of Miami-Coral Gables in 1989 and 1997 respectively. He is professor at the department of Mechanical Engineering, Universiti Kebangsaan Malaysia and he is the director of Solar Energy Research Institute, Universiti Kebangsaan Malaysia. His Research interest includes solar energy, photovoltaic power system, solar thermal systems, and renewable energy in common.
M.Yusof .Sulaiman is a principle research fellow at the solar energy research institute (SERI), National university of Malaysia in Bangi Malaysia. Prior to joining SERI he was a professor at the Physics Department , University Putra Malaysia (UPM) from 1973 until his retirement in 2004. He received his PhD from University of London in 1977 in Nuclear Physics . He has served as the Head of Department of Physics ,UPM and the Dean of Faculty of Science Environmental Studies ,UPM. His current research interests include organic solar cell, photovoltaic and applications and thermal cooling system.
Abdulrahman Th. Mohammad is a PhD student in the Liquid Desiccant AirConditioning System, Solar Energy Research Institute, National University of Malaysia, Malaysia. He received his Bachelor’s degree from the Collage of Military Engineering, Iraq in 1994 and Master’s degree from the same collage in 2002. Currently, he is working as a lecturer in Mechanical Engineering, Baqubah Technical Institute, Iraq. He is published about 25 research papers in international journals and conferences.
