Experimental Investigation of an Evacuated Tube Heat Pipe Solar Collector Using Different Fluids

In the current work, the effect of four different fluids ethylene glycol, ethanol, methanol, and acetone as well as their aqua solutions on the performance of the thermosyphon evacuated tube heat pipe solar collector is investigated. Water is used as a heat transfer fluid with a volume flow rate of 1.95 l/min. Five modules each of three evacuated tube heat pipe solar collectors are used. The thermosyphon heat pipes are manufactured and charged with each working fluid and its aqua solution of volume concentration of 0, 0.25, 0.5, 0.75 and 1.0 respectively.
The performance of the systems is illustrated by the solar collector efficiency and the overall system efficiency. The results showed that pure water gives higher solar collector efficiencies than that of ethylene glycol, ethanol, methanol, and their solutions while acetone gives higher solar collector efficiency than the pure water. Correlation equations for solar collector efficiency in terms of (Tm-T)/G and concentration are deduced. The current results are validated with the previously experimental published correlations.
Nomenclature:
Symbol
Description
Symbol
Description
a, b, o
Constants of Eq. (9)
Qo
Output water energy rate, (kW)
a, b, c
Constants of Eq. (10)
Ti
Inlet or initial water temperature, (°C)
Ac
Solar collector area, (m2)
Tm
Mean water temperature, (°C)
Cp
Specific heat of the water, (kJ/kg °C)
Tf
Final water temperature, (°C)
Ei
Input solar Energy, (kJ)
To
Outlet water temperature, (°C)
Eu
Useful stored energy, (kJ)
ETSWT
Evacuated Tube Solar Water Heater
FR
Removal factor of the collector
T
Ambient temperature (°C)
G
Solar radiation intensity (W/m2)
t
Time, (s)
𝑚̇
Water (HTF) mass flow rate, (kg/s)
UL
Overall heat loss factor
ms
Mass of water in storage tank (kg)
V
Water volume flow rate, (m3/s)
Qi
Input solar energy rate (kW)
x
Volume concentration of heat pipe fluid
Greek Symbols
abbreviation
w
Water density (kg/m3)
HTF
Heat Transfer Fluid
ηc
Collector efficiency
THP
Thermosyphon Heap Pipe
η𝑠
System efficiency
THPECT
Thermosyphon Heap Pipe Evacuated Tube Collector
Introduction
Heat pipes are the most efficient means of transferring heat. They may transfer hundreds of times more energy between two bodies than a solid metal bar