An examination of evacuated tube collectors in comparison to direct flow and heat pipe for the purpose of solar water heating

ABSTRACT

Solar thermal collectors are quite popular in water heating applications. When attempting to comprehend the benefits and drawbacks of various collector designs, it is essential to compare them. This makes choosing the technology best suited for a particular environment and application easier. This study compares and contrasts the direct flow and heat pipe evacuated tube collectors (ETCs) utilized in solar water heaters. Experiments were carried out on a test bench with two ETCs linked in series under standard settings. Early optical studies revealed that both ETCs have features that were comparable to one another. A thermal performance evaluation was conducted on bright, intermittently cloudy, and gloomy days. The heat pipe ETC started up more quickly and had a daily efficiency of approximately 20% greater than that of the direct flow ETC, with peak efficiencies of 0.72 and 0.58, respectively, on a clear sunny day. However, on overcast days with intermittent sun irradiation, the direct flow ETC’s large thermal capacity gave 10–15% higher net energy gain. It was observed that the heat pipe ETC experienced a larger drop in heat transfer rate of over 60% when irradiance decreased from 1000 to 500 W/m² due to clouds, compared to only 45% for the direct flow ETC. However, the heat pipe recovered faster when irradiation returned to higher levels. The findings indicate that direct flow and heat pipe ETCs have distinct variances in their thermal performance in both the transient and steady-state states. When these features are understood, it is possible to make an informed decision about the ideal solar collector design based on the application’s needs and the environment.

KEYWORDS:

• Solar thermal collectors
• evacuated tubes
• comparative analysis
• performance testing
• solar water heating

Abbreviation

Abbreviation	=	Definition
CFD	=	Computational Fluid Dynamics
CV	=	Centrifugal Volute
DASCs	=	Direct Absorption Solar Collectors
EG	=	Ethylene Glycol
ETC	=	Evacuated Tube Collector
ETC-DF	=	Direct Flow Evacuated Tube Collector
ETC-HP	=	Heat Pipe Evacuated Tube Collector
HVAC	=	Heating, Ventilation, and Air Conditioning
IEC	=	International Electrotechnical Commission
MgO	=	Magnesium Oxide
MWCNT	=	Multi-Walled Carbon Nanotubes
PCM	=	Phase Change Material
PPR	=	Polypropylene Random
PVT-TEG	=	Photovoltaic-Thermal-Thermoelectric Generator
RTD	=	Resistance Temperature Detector
TES	=	Thermal Energy Storage

Disclosure statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Supplemental material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/15567036.2024.2375750

Additional information

Notes on contributors

Vijayakumar Palanivel

Vijayakumar Palanivel an Indian citizen born in Namakkal, Tamil Nadu, obtained his doctoral degree in Solar Energy from Anna University, Chennai. With approximately 11 years of teaching experience, he currently serves as an Assistant Professor in the Department of Aeronautical Engineering at Nehru Institute of Technology (Autonomous), Coimbatore. His areas of interest include Solar Energy, Nanofluids, Internal Combustion Engines, and Energy Conservation and Management.

Arunkumar Munimathan

ArunKumar Munimathan is a citizen of India, born in Dharmapuri, Tamil Nadu, India. He obtained his Doctoral research in the area of Thermal Engineering at Anna University Chennai, India. He has about 10 years of teaching experience and presently working as an Associate Professor in the Department of Mechatronics Engineering, Hindusthan College of Engineering and Technology (Autonomous), Coimbatore. His areas of interests are Solar Energy, alternative fuels, emission control, Heat Transfer.