Experimental results of supercoolers (D4.6)
Creators: name: Schubert, Maike
name: Schmid, Oliver
name: Carbonell, Daniel
Publisher: name: Zenodo
Year: 2022
Subjects: Heat pumps
ice slurry
supercooling
coatings
amorphous
plate heat exchanger

description: This report summarizes the main activities carried out on the eld of supercoolers in the H2020 TRI-HP project.<br> The overall goal of the TRI-HP project is the development of trigeneration systems based on electrically driven<br> natural refrigerant heat pumps coupled with renewable electricity generators (PV). The systems are aiming to<br> provide heating, cooling and electricity to multi-family residential buildings with a self-consumed renewable share<br> of 80 %. One of the systems developed is based on a supercooling ice slurry heat pump. A successful development<br> of such system relies on the development of a heat exchanger that can supercool water to temperatures around<br> −2 °C to −3 °C without forming ice, the so-called supercooler. This report summarizes the development and testing<br> results of such supercoolers.<br> The specific goal of the project on the ice slurry field was to develop a compact and reliable supercooler to be<br> used as an evaporator for a 10 kW heat pump using natural refrigerants heat pumps such as propane and CO2.<br> This goal has been achieved by applying coatings (organic, inorganic or a mixture of them) on very compact flat<br> plates heat exchangers. Results shown in this report show not only the reliability of the operation of supercoolers<br> below 0 °C, but also prove the very ambitious measurable targets established at the project proposal phase, i.e.<br> stable operation with a supercooling degree of 4 K. This achievement represents a significant progress respect<br> state of the art Japanese supercoolers that operate at 2 K supercooling degree. Results achieved within TRIHP<br> represent a ground-breaking progress in Europe where nothing similar has been achieved before. From the<br> authors’ knowledge, the supercoolers tested here are the first operational ones at this capacity range ever develop<br> in Europe. In this deliverable results of icephobic coated and nickel treated heat exchangers are summarized.<br> Six heat exchanger with icephobic coatings were tested at SPF laboratories. As reference, a heat exchanger without<br> any coating and a commercial heat exchanger coated with a ceramic anti-fouling coating was used. For coating<br> comparison, three different chemical families were tested at three different mass flows. Experiments of coated<br> heat exchangers show average supercooling degrees in the range of 3 K to 4 K. The anti-fouling coatings performed<br> worse compared to the reference non coated heat exchangers with an about 70 % lower average supercooling degree.<br> All icephobic coatings improved the supercooling degree respect to the reference non-coated case by 7 % to<br> 44 % at 1000 kg/h. The target of 5 kW supercooling power has been reached with two coatings for a mass ow rate<br> of 1000 kg/h in the water cycle. For a mass flow rate of 2000 kg/h a supercooling power of about 6 kW has been<br> reached for five coatings at a temperature of −2.5 °C and hold constantly for a time span of 3 h. Some coatings<br> could reach lower temperatures at this mass flow but the experimental setup was limited to this supercooling<br> power. Thus, the full potential of these supercoolers in terms of capacity is still to be found. The two coatings<br> performing best in the heat exchanger tests were both from the family class hybrid organic-inorganic silane sol-gel<br> (HOIS). Both coatings showed the best results in the small scale laboratory tests as well.<br> From previous investigations it was found that high phosphorous nickel plating creates a beneficial surface to<br> achieve low temperatures. In order to analyse the potential benefits two different types of plate heat exchanger,<br> i.e. brazed and gasketed, were evaluated. Due to the smaller laboratory setup capacity, the heat exchangers were<br> 25 % smaller compared to those tested using icephobic coatings. As reference, the same heat exchangers were<br> tested without any treatment. The nickel layer shows an increase of the supercooling potential of 7 % for a brazed<br> heat exchanger and a water mass flow of 500 kg/h. For a gasketed heat exchanger of similar capacity, little<br> benefits were observed. An average supercooling power of 2.3 kW was achieved on these experiments due to a<br> lower mass flow and heat transfer surface area compared to the heat exchanger prototypes used for the icephobic<br> coatings experiments.