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Test system established and experimental research on latent thermal energy storage unit performed

For the purpose of research on latent thermal energy storage unit, test system has been established, containing the latent heat storage unit coupled with existing renewable energy system.  Test system was implemented in the Laboratory for Thermal Measurements of the Department of Thermodynamics and Energy Engineering at the University of Rijeka, Faculty of Engineering.

A vertical shell-and-tube latent heat storage unit was designed, consisting of 19 flat finned tubes, each containing 8 longitudinal fins, offset by 45° angle. Heat transfer inside the unit occurs between the heat transfer fluid (HTF) and the phase-change material (PCM, paraffin RT 25), the latter enabling latent heat of melting to be stored.

The system consists of 18 kW water-water heat pump, two 300 l inertial tanks, HTF piping system and test zone with hydraulic regulation of HTF inlet temperature and measuring equipment.

Part of the latent heat storage unit secondary heating/cooling circuit with regulation equipment

A series of measurements for melting and solidification processes of phase-change material has been performed for various water inlet temperatures. For investigations regarding melting, water inlet temperatures varied from 37 to 42 °C, and for investigations regarding solidification, water inlet temperatures varied from 7 to 13 °C.

Modification of the test line and experimental research on fin-and-tube heat exchangers performed

Within the project objective Enhancement of the heat exchanger energy efficiency by investigating optimal operating conditions, test line for heat exchangers has been modified and experimental research of influence of operating conditions on heat transfer in fin-and-tube heat exchangers has been performed.

Test line has been modified and   two fin-and-tube heat exchangers have been installed into the system.

In heat exchangers test zones, measurement sensors for air and water inlet and outlet temperatures, anemometers for air velocity measurements both in front of and behind the heat exchangers in the air duct, as well as differential pressure gauges for pressure drop measurements have been set up.

Fin-and-tube heat exchangers and installed measuring equipment

Measurements have been performed for even and uneven air inlet velocity profiles for selected mass flow rates and various water flow rates ranging from 800 to 3100 kg/h. Also, measurements have been performed for various water inlet temperatures ranging from 40 to 60 °C.

Test system for microchannel fin-and-tube heat exchanger established and experimental research performed

Based on the project proposal and equipment acquired, a test system for experimental research of the influence of heat exchanger geometry on heat transfer, equipped with measurement sensors and senders, has been established.

Test system for experimental research has been established in the Laboratory for Thermal Measurements at the University of Rijeka, Faculty of Engineering. An open type air tunnel is used. The test system consists of air conditioning unit, air ducts, working fluid pipe system and test zone in which examined heat exchangers are integrated.

Test zone on the air side of the heat exchanger has been equipped with temperature sensors field, both in front of and behind the heat exchanger, set of four hot-wire anemometers for air velocity measurements in front of and behind the heat exchanger, as well as with a differential pressure gauge for measurements of air pressure drop through the heat exchanger. An additional pressure gauge has been connected to an orifice plate to determine air flow rates in the test zone.

On the water side, a secondary heating/cooling circuit has been built, with all additional control equipment and fittings.

A modular data acquisition system, for experimental data collecting and storing, has been connected to the test system.

Experimental research on the microchannel fin-and-tube heat exchanger has been performed for a wide range of air and water inlet temperatures and velocities. Measurements have been performed for air inlet velocities ranging from 0.5 to 5 m/s and water inlet velocities ranging from 0.05 to 1 m/s. Air and water inlet temperatures  were between 2 to 67 °C.

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Velocity and differential pressure measuring sensors