Heber Sugo

New Highly Thermally Conductive Thermal Storage Media

With the overall aim of storing and delivering heat at >600 °C, miscibility gap alloys (MGA) in the systems C-Al, C-Mg and C-Cu were manufactured and characterised. Samples within all three systems were able to be manufactured in which small particles of the active phase (Al, Mg or Cu, respectively) were able to be encapsulated within a graphite matrix at high volume fraction. No signs of compound formation, solid solution or oxidation were discovered using X-ray diffraction and scanning electron microscope analysis. All three systems are therefore worthy of further study.

Scaling Up Miscibility Gap Alloy Thermal Storage Materials

Miscibility gap alloys (MGAs) are a new thermal storage technology that utilises the latent heat of fusion of metals. MGAs encapsulate the liquid phase while maintaining high thermal conductivity, resulting in a safe and effective method of thermal storage. In order to develop MGA to a stage where it can be useful in an industry setting, production and size need to be enlarged greatly. This study attempts several methods of increasing the size of MGA storage blocks. The resulting C-Zn MGA storage blocks have a volume of 0.58 L, which are capable of storing 0.34 MJ of highly dispatchable thermal energy.

Thermal Capacitors Made From Miscibility Gap Alloys (MGAs)

The current paper addresses the thermal characterisation of Miscibility Gap Alloys (MGAs). These novel materials combine two immiscible metallic phases with different melting temperatures. The fusible phase (i.e. the phase with a lower melting temperature) acts as a phase change material that stores latent heat (in addition to sensible heat) thus optimising energy storage capacity. The second phase forms an enclosure and prevents the leakage of liquid material. Due to the high inherent thermal conductivity of metals, MGAs exhibit excellent thermal conduction in comparison to traditional phase change materials such as hydrate salts or paraffin. The combination of high energy storage and fast heat transfer makes MGA uniquely suited for use as thermal capacitors in applications like space heating, concentrated power generation or temperature stabilisation of sensitive equipment. The current paper determines the thermal properties of MGAs using Lattice Monte Carlo analysis combined with micro-computed tomography imaging.

Miscibility Gap Alloys: A New Thermal Energy Storage Solution

The status of miscibility gap alloys (MGA), which have demonstrated excellent characteristics for thermal storage applications over a wide range of temperatures, is reviewed. MGA remain macroscopically solid whilst delivering latent heat from embedded metal particles supplemented by the sensible heat of the whole material. Heat can be delivered rapidly due to very high thermal conductivity leading to modular solid storage designs which can act as solar boilers for direct steam CSP or other applications. Progress in the manufacture, alloy design and a demonstration of 1.5 kW steam turbine generator with integrated MGA storage unit are briefly described.

Preparation of lanthanum hexaboride cathodes for thermionic energy generation

Due to low work function, high melting point and superior chemical stability at high temperatures, lanthanum hexaboride (LaB6) has great potential as a thermionic emitter in renewable energy applications. The main challenge is to synthesise these hexaborides at lower temperatures without any post-synthesis cleaning treatments. In this present work, we investigated several techniques to prepare pure lanthanum hexaboride using different blends of lanthanum oxide (La2O3)boron (B), La2O3-B-carbon (C), La2O3-boron carbide (B4C) blends, respectively. The starting powders for each blend were mixed by milling for 20 to 30 min and pressed as pellets. Additionally, several samples of La2O3-boron blends were prepared by high-energy milling (HEM) for 16 hours. Subsequently, the pellets were placed in a tube furnace at different temperatures under a moderate vacuum to undergo solid state reactions. The synthesised products were investigated for the structural, morphological and thermionic properties using X-ray diffraction (XRD), scanning electron microscope (SEM), electron dispersive spectroscopy (EDS) and a Schottky apparatus. We are able to synthesis pure LaB6 at comparably lower temperatures via all the investigated methods. Pure LaB6 is found to be synthesised as low as 1250 °C via the method using high-energy milling. XRD and SEM analyses revealed that LaB6 prepared using these methods were nanocrystalline. Thermionic emission measurements show that pure LaB6 is found to possess a low Richardson work function of 2.64 eV making it suitable for producing high current density cathodes.