# Numerical Design and Laboratory Testing of Encapsulated PCM Panels for PCM-Air Heat Exchangers
## 2 Methods
### Laboratory Testing  
To evaluate the fabricated panel, it is important to analyse (a) the effect of inlet temperature on melting and solidification stages; (b) the effect of airflow on charging and discharging; (c) the effects of the distance between panels; (d) the energy exchanged between air and panel during charging and discharging and (e) the charging and discharging time. The design of the new panel surface was not focused on the behaviour of attachment and detachment at the boundary layer. Instead, the overall heat transfer was the variable of interest. Furthermore, the test is intended to confirm and validate the numerical design. As a result, the methodology of previous works found on literature [14; 16; 17], where thermocouples are attached to the test surface were used. Thus, three tests evaluated the new design and compared it with the existing and a flat panel. The first test analysed the heat transfer with different panel gaps, the second test investigated the pressure drop and the third test studied the melting and solidifying process. The following summarises the experimental steps. 1. Laboratory test 1: Investigation of heat transfer and pressure drop of one panel with different gaps between panels. 1. A test rig consisting in a variable fan, rectangular ducts and a test section was mounted to evaluate the heat transfer of new and the existing panel, (Figure 2); 2. Each half of panel was filled with a potting compound and a resistance wire; 3. A power supply of 13.5 W heated each panel and 14 thermocouples measured the surface temperature of the panels every 10 s; 4. One thermocouple before and 3 after the test section measured the increase in air temperature every 10 s; 5. Three different airspeeds were tested (0.5, 1.0 and 1.5 m/s or Re \(\cong\) 2000, 4100 and 6061, respectively) at three different gaps (8, 9 and 10 mm gap). Each test finished after the steady state was achieved for at least 30 min;* With panel surface and air temperature data acquired, the heat of convection was calculated through energy balance and the Nusselt number was estimated. * To validate the results acquired on the rig, a smooth panel with the same gaps and airspeed was simulated with ANSYS Fluent. The Nusselt number estimated in the test was validated by [PERSON]'s correlation (Equation (10);
* Results of pressure drop and heat transfer from the smooth panel were used to estimate the Thermal Enhancement Factor (TEF);
* The optimum configuration considering heat transfer and efficiency was used in the second experiment. * Laboratory test 2 (Figure 6a): Pressure drop along 1, 2 and 3 TB
* A test rig consisting in a fan and rectangular ducts was mounted to measure the pressure drop of 1, 2 and 3 thermal batteries for existing and new TB. * The airflow of the tests varied between 50-150 L/s with steps of 20 L/s;
* The test was concluded when the pressure drop for new and existing panels was tested for 1, 2 and 3 TB. * Laboratory test 3 (Figure 6b): Melting and solidifying process of 1 and 2 TB Ws tested to compare the efficiency between the existing and the new panel. The energy balance from the airside was applied to evaluate the charging and discharging process as well as the time necessary. * A test rig consisting in a fan, rectangular ducts and a cooling/heating source with a control system able to provide stable temperature during charging and discharging tests (charging setpoint of 15 \({}^{\circ}\)C and heating setpoint of 30 \({}^{\circ}\)C adjusted on the cooling/heating source (Hybrid Thermal Mixing Low Temperature Hot Water: HTM LTHW [27]));
* The existing and new panels were filled and sealed with the PCM CrodaTherm\({}^{\text{TM}}\) 24 [28];
* One thermocouple before and 2 after the test section measured the air temperature every 15 s; two thermocouples was judged to be enough as the variation between them was small.