An experimental study of immersed thermosiphon heat exchangers for solar domestic hot water systems

The design of immersed thermosiphon heat exchangers used in solar domestic hot water (SDHW) systems was investigated experimentally. A flow visualization tank was designed and constructed to be able to observe the flow of water. Different exchanger designs were tested under normal SDHW operating conditions for Halifax, Nova Scotia. The SDHW system used for the study consisted of a 2.98 m2 solar collector and a 370 L storage tank. Propylene glycol was circulated using a photovoltaic powered pump with a maximum rate of 1.26 L/min at full sun (1000 W/m2).; The effect of increasing hydraulic resistance on the shell side of the exchanger by altering the inlet geometry was determined using availability (or exergy) analysis. The level of stratification within the storage tank was quantified using availability and the impact of stratification on the SDHW system was determined using principles of the first and second laws of thermodynamics. The results from this study were compared to past experiments with similar heat exchanger designs.; Decreasing the heat exchanger inlet area on the shell side was found to decrease the water flow rate and increase the level of stratification. The stored availability was found to be influenced by two factors: the level of stratification and the mean tank temperature. Tanks with poor stratification but high average temperatures were found to have similar availability to tanks with good stratification and low average temperature. The tank availability was related to theoretical maximum and minimum stored availability using the mixing number and stratification number. Both the mixing number and stratification number were found to give a good representation of the level of stratification in the tank. (Abstract shortened by UMI.)...