Thermal performance analysis of a co-axial evacuated tube collector with single and two-phase flow consideration under North-eastern India climatic condition

The standard condition for evaluation of solar heating system considers solar insolation of 1000 W/m2 which provides a good estimation of the performance of the system, but not able to predict a realistic situation due to the fluctuating behaviour of solar insolation. Therefore, an attempt is made t...
Ausführliche Beschreibung

The standard condition for evaluation of solar heating system considers solar insolation of 1000 W/m2 which provides a good estimation of the performance of the system, but not able to predict a realistic situation due to the fluctuating behaviour of solar insolation. Therefore, an attempt is made to simulate a practical condition for a solar heating system by varying solar radiation throughout the day as well as months of a year. Hourly solar insolation data are collected from web-based resource PVGIS for the region of Silchar, a north-eastern location in India. The results revealed that the temperature profile of the working fluid in the Evacuated Tube Collector is non-linear and the rise in temperature is more in the months of November-March than April-October. The outlet temperature is highest for the month of February and lowest in June which signifies that the system can be practically applicable in this region for water heating purpose, as it produces a higher temperature in winter days. Also, the daily analysis shows the efficiency of the system is very low during the morning and evening hours. Moreover, there is a possibility of obtaining a two-phase flow in the outer pipe under certain circumstances and this production of vapour is accompanied by a reduction in efficiency. The analysis shows that with radiation being fixed, inlet temperature and mass flow rate are the most dominant factors for two-phase flow. Present model also suggests an optimum mass flow rate beyond which the flow becomes two-phase and not desirable. Ausführliche Beschreibung