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