Thermal Storage of Nitrate Salts as Phase Change Materials (PCMs)

Abstract

This study presents the energy storage potential of nitrate salts for specific applications in energy systems that use renewable resources. For this, the thermal, chemical, and morphological characterization of 11 samples of nitrate salts as phase change materials (PCM) was conducted. Specifically, sodium nitrate (NaNO3), sodium nitrite (NaNO2), and potassium nitrate (KNO3) were considered as base materials; and various binary and ternary mixtures were evaluated. For the evaluation of the materials, differential Fourier transform infrared spectroscopy (FTIR), scanning calorimetry (DSC), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM) to identify the temperature and enthalpy of phase change, thermal stability, microstructure, and the identification of functional groups were applied. Among the relevant results, sodium nitrite presented the highest phase change enthalpy of 220.7 J/g, and the mixture of 50% NaNO3 and 50% NaNO2 presented an enthalpy of 185.6 J/g with a phase change start and end temperature of 228.4 and 238.6 °C, respectively. This result indicates that sodium nitrite mixtures allow the thermal storage capacity of PCMs to increase. In conclusion, these materials are suitable for medium and high-temperature thermal energy storage systems due to their thermal and chemical stability, and high thermal storage capacity.

Development of 3D ZnO-CNT Support Structures Impregnated with Inorganic Salts

“…5) confirm the thermal stability of the structure impregnated with NaNO 3 and are in accordance with the literature data [68]. The melting enthalpy decreases from 58.03 J/g (for the first heating cycle) to 56.09 J/g (for the last heating cycle), due to an increase in the heat flux demonstrating that NaNO 3 is impregnated into the 3D structure [57,69,70]. Recrystallization enthalpy is around −58 ÷ −59 J/g (Figure S2).…”

“…NaNO 3 and KNO 3 are among the most widely used inorganic PCMs, with melting points suitable for thermal energy storage applications. Moreover, combination of these salts presents advantages such as high energy density, high heat capacity, low cost, thermal stability [57].…”

Characterization of a latent thermal energy storage heat exchanger using a charging time energy fraction method with a heat loss model

“…Pure salts with high storage capacity, low cost and low environmental impact are developed as potential candidate for thermal energy storage of solar energy or industrial process heat [95]. Nitrates and their binary or ternary eutectic mixtures with desirable characteristics such as negligible supercooling, chemical stability are considered PCMs for the temperature range of 200-300 °C [95,96]. In the thermal oil circuit, the temperature is measured by Pt100 resistance thermometers class A with an accuracy of ±(0,15 + 0,002.T[°C]).…”

“…For the latent heat of fusion 100 kJ/kg is used as indicated in the work of Tamme et al [95]. This value lies in between the value found by Orozco et al [96] (92 kJ/kg) and given by Mohamed et al [98] and Vogel et al [99] (107 kJ/kg).…”

“…𝑅 𝑥,𝑤𝑎𝑙𝑙 and 𝑅 𝑦,𝑤𝑎𝑙𝑙𝑃𝐶𝑀 are the thermal resistance between adjacent control volumes in the x and y direction, respectively. For modelling purposes the specific heat in the liquid region is considered temperature independent and 1.673 kJ/kg.K is used as proposed by D'Aguanno et al [97], while for the specific heat in the solid region 1.35 kJ/kg.K is used as an average of the values found in the work of Tamme et al [95] and Orozco et al [96]. In the work of Vogel et al [99] this value is also used.…”