Investigations on Solidification and Melting Processes of the Solar Salt Mixture in Evacuated and Non-Evacuated Receiver Tubes

Valeria Russo (), Giuseppe Napoli, Francesco Rovense (), Primo Di Ascenzi, Gianremo Giorgi, Luigi Mongibello, Carmine Cancro, Gabriele Ciniglio and Walter Gaggioli ()
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Valeria Russo: ENEA Casaccia Research Centre, Via Anguillarese, 301, 00123 Rome, Italy
Giuseppe Napoli: ENEA Casaccia Research Centre, Via Anguillarese, 301, 00123 Rome, Italy
Francesco Rovense: ENEA Casaccia Research Centre, Via Anguillarese, 301, 00123 Rome, Italy
Primo Di Ascenzi: ENEA Casaccia Research Centre, Via Anguillarese, 301, 00123 Rome, Italy
Gianremo Giorgi: ENEA Casaccia Research Centre, Via Anguillarese, 301, 00123 Rome, Italy
Luigi Mongibello: ENEA Portici Research Centre, P.le Enrico Fermi, 1, 80055 Portici, Italy
Carmine Cancro: ENEA Portici Research Centre, P.le Enrico Fermi, 1, 80055 Portici, Italy
Gabriele Ciniglio: ENEA Portici Research Centre, P.le Enrico Fermi, 1, 80055 Portici, Italy
Walter Gaggioli: ENEA Casaccia Research Centre, Via Anguillarese, 301, 00123 Rome, Italy

Energies, 2025, vol. 18, issue 17, 1-24

Abstract: Parabolic trough collector (PTC) plants that use solar salt as a heat transfer fluid face operational challenges due to the salt’s relatively high solidification temperature of around 240 °C, which can compromise reliability if solidification occurs within receiver tubes or piping. While electric tracing cables are typically used to heat piping, they cannot be installed on PTC receivers due to the presence of external glass covers. As an alternative, impedance heating can be employed, applying voltage directly to the steel receivers, which act as resistive heaters. This study presents experimental results on the phase-change behavior of solar salt within receivers, focusing on melting and solidification times. Tests were conducted using two dedicated receivers under vacuum and non-vacuum conditions. Under vacuum, complete melting was achieved at 4.5 V and 1.43 kW in 5.5 h, while solidification from 270 °C took about 4 h, progressing inward from the tube connections. For non-evacuated receivers, 7 V and 3.2 kW were needed for melting in 5.6 h, and solidification at 270 °C was completed in 1.45 h. These outcomes illustrate that non-evacuated tubes require nearly twice the power and have a 2.8-fold increase in heat loss rate, offering quantitative guidance for vacuum loss detection in PTC systems.

Keywords: binary molten salt; receiver tube; parabolic trough collector (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2025
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