Page 60 - MASHRAE 35th Anniversary

to the ambient and the worst cooling effect is distilled water. Few researchers explored the performance of hydrocarbons and freon refrigerant as working fluid in thermosyphon. Ma et al. (2017) investigated the performance of a two-phase closed thermosyphon (TPCT) charged with eight working fluids, R134a, R601, R245fa, R600a, R1234ze, R152a, R245fa/R152a and R601/R245fa. Meanwhile, Kuznetso et al. (2016) was examined the performance between R-22 and R134a as the working fluids for the two-phase thermosyphon.
On the other hand, some researchers also inspected thermosyphon system using ETC (Ersöz 2016; Jahangiri Mamouri et al. 2014). Ersoz Mustafa Ali (2016) was investigated the effects of using six working fluids, hexane, petroleum ether, chloroform, acetone, methanol and ethanol with thermosyphon heat pipe with three different air velocities as 2, 3 and 4 m/s. Ersoz Mustafa Ali (2016) was found that hexane has lowest energy and exergy efficiency for air velocity of 2, 3 and 4 m/s. Meanwhile Acetone demonstrated the highest energy efficiency for air velocity of 2 and 3 m/s and highest exergy efficiency for air velocity at 2 m/s. On the other hand, Chloroform revealed the high energy efficiency for air velocity at 4 m/s and high exergy efficiency for air velocity at 3 and 4 m/s. S. Jahangiri Mamouri et al. (2014) also study in the effect of using thermosyphon heat pipes and vacuum glass on the performance of solar still. This study only uses desalinated water as the working fluid.
Refer to all previous studies on thermosyphon, no researchers is use refrigerant as a working fluid with evacuated tube collector (ETC) and there are only few studies on using the ETC in thermosyphon system. However, they only concentrate on different working fluid with different velocities, series effects and combinations parallel to U pipes and performance of solar still while using only desalinated water as a working fluid. In this study, the refrigerants and several working fluids circulated in two phases closed loop thermosyphon solar drying system with evacuated tube collector at different pressure. The objectives are to investigate the closed loop thermosyphon efficiency and to identify the best working fluids for the system.
DESCRIPTION OF EXPERIMENTAL SETUP
All the experiments were conducted in Bandar Baru Bangi, Malaysia which is located at latitude :
The liquid-based solar collector is connected to the heat exchanger through upriser and downcomer pipe, forming a closed loop system. The drying processes are carried out in the drying chamber whereby the drying materials are protected from the direct sunlight. The drying chamber is equipped with the heat exchanger where the heat source for drying process is originated from blower fan which is installed at the outlet opening of drying cabinet to promote an even circulation of drying air. Generally, the proposed thermosyphon solar drying system comprises of two
circulation loops which are the working fluid circulated in the closed thermosyphon loop and the hot air flow inside the drying chamber. The working fluid flow is driven by natural convection through density differences due to fluid phase changes in thermosyphon loop. On the other hand, airflow is driven by force convection using a blower fan mounted on the top opening of the drying chamber. The performance of TSDS is tested with parallel connection of U- pipe in the evacuated tube as shown in Fig. 2. The performance of water, ethanol, R134a and R600a as the phase change working fluid are also investigated with different quantity of evacuated tube. Therefore, there is a total of four experiments involve in this works which comprise the difference number of evacuated tubes.
Figure 1 Schematic of Themosyphon Solar Drying System (TSDS)
longtitude:101.7571° E. The proposed thermosyphon drying system consist of two parts, drying chamber and 4 sets of
2.9619° N and
ETCs solar collectors as shown in Fig. 1.
2
Figure 2 Parallel collector.
U-pipe connection
in evacuated tube
Measuring Points
Several measuring devices and instruments are installed to measure the parameters required for the performance evaluation of TCDC as shown in Fig. 3. Instantaneous solar radiation was measured using a pyranometer. The pyranometer was positioned at the inclination angle of solar collector, which is 40 degrees to the horizontal. Thermocouples Type-K were used to measure the fluid temperature and air temperature inside the thermosyphon loop and drying chamber respectively. The voltage signals from the pyranometer and thermocouples were recorded with 1s interval using a multi-channel data logger. The