An indoor experimental investigation of the thermal performance of a TPLT-based natural circulation steam generator as applied to PTC systems

• An indoor TPTL natural circulation steam generation system was designed and tested.
• System performance was studied with an emphasis on the evaporator (i.e., receiver).
• Two types of flow instabilities, backflow and bi-directional flow, were observed.
• Effects of the flow instability on thermal performance of the system were analyzed.

An indoor experimental setup of a two-phase loop thermosyphon (TPLT)-based natural circulation steam generator, as applied to parabolic trough solar collector for medium temperature steam generation was proposed. Thermal performance of the TPLT steam generation system, especially the receiver, was investigated experimentally. Relatively low two–phase heat transfer coefficients, 263.03 and 265.03 W/m2 K for two selected steam discharging pressures, were obtained in the receiver for such horizontally-arranged TPLT system. Two types of flow instability, i.e., backflow and bi-directional flow, were observed in the TPLT system. The effects of flow instability on thermal performance of the TPLT steam generation system were analyzed. The results showed that isothermality of the system could be improved due to the presence of both unstable flow conditions. The improved isothermality, however, finally resulted in a lower thermal efficiency. At the steam discharging pressure of 0.15 MPa, heat transfer coefficient was increased by 20.07% and was decreased by 0.40% for the bi-directional flow and backflow patterns, respectively.