Abstract
The purpose of this study was to experimentally investigate the thermal performance and operating characteristics of various heat pipe working fluids in evacuated tube solar collectors. Heat pipe efficiency was evaluated by calculating the solar collector efficiency value when using four types of working fluids: water, ethanol, flutec-pp9 and methyl acetate under the same operating conditions on an indoor experiment apparatus. The experimental conditions were as follows: The inclination angle of the evacuated tube solar collectors were 20°, 40° and 60° from the normal basis. The mass flow rate into the manifold of the evacuated tubular solar collector was 0.3 kg/min. The heat flux on the collector surface was 870 W/m2. The results showed that, at an angle of incidence of 40°, the values of \({\text{F}}_{\text{R}} \left( {\tau \alpha } \right)\) and \({\text{F}}_{\text{R}} {\text{U}}_{\text{L}}\) with methyl acetate as the working fluid were 0.6572 and −2.0086, respectively, with water they were 0.6636 and −1.8457, respectively, ethanol they were 0.6147 and −0.6353, respectively, and with flutec-pp9 they were 0.525, and −3.2313, respectively.
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Abbreviations
- A c :
-
Collector area (m2)
- C p :
-
Specific heat (J/kg °C)
- \(\dot{m}\) :
-
Mass flow rate (kg/s)
- Q u :
-
Useful energy gain (W)
- \(\tau \alpha\) :
-
Transmittance–absorptance product
- F R :
-
Heat removal factor
- U L :
-
Overall heat transfer coefficient (W/m2 °C)
- G T :
-
Irradiation on a collector surface (W/m2)
- \(\eta\) :
-
Solar collector efficiency (−)
- T :
-
Temperature (°C)
- T ap :
-
Absorber plate temperature (°C)
- T a :
-
Ambient temperature (°C)
- T i :
-
Inlet temperature (°C)
- T o :
-
Outlet temperature (°C)
- M :
-
Merit number (kW/m2)
- \(\rho_{l}\) :
-
Density of the liquid (kg/m3)
- \(\sigma_{l}\) :
-
Surface tension (N/m × 102)
- \(\mu_{l}\) :
-
Viscosity of the liquid (cP)
- \(L\) :
-
Enthalpy of vaporization (kJ/kg)
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Acknowledgements
This research was supported by a Grant (Code 15IFIP-B065893-03) from the Industrial Facilities & Infrastructure Research Program funded by the Ministry of Land, Infrastructure and Transport of the Korean government.
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Joo, HJ., Kwak, HY. Experimental analysis of thermal performance according to heat pipe working fluids for evacuated tube solar collector. Heat Mass Transfer 53, 3267–3275 (2017). https://doi.org/10.1007/s00231-017-2029-0
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DOI: https://doi.org/10.1007/s00231-017-2029-0