IEA SHC Task 42 / ECES Annex 29 WG A1: Engineering and Processing of PCMs, TCMs and Sorption Materials

An overview on the recent results on the engineering and characterization of sorption materials, PCMs and TCMs investigated in the working group WG A1 "Engineering and processing of TES materials" of IEA SHC Task 42 / ECES Annex 29 (Task 4229) entitled "Compact Thermal Energy Storage" is presented

Design and feasibility of high temperature shell and tube latent heat thermal energy storage system for solar thermal power plants

© 2016 Elsevier Ltd. A simple shell and tube heat exchanger provides a straightforward design for near-term integration of latent heat thermal energy storage (LHTES) systems in concentrated solar thermal-tower (CST-tower) plants, but currently there is no literature available for this configuration in the 286-565 °C temperature range. Therefore, the primary objective of this work is to evaluate the potential of this configuration for CST-tower plants. In addition, a proper design method of this storage configuration should simultaneously account for the effects of geometric parameters and the number of modules. The present work optimizes these parameters for market ready phase change materials (PCM) that are suitable in the aforementioned temperature range. This optimization consisted of fixing the PCM volume while varying the other geometric parameters (namely, L, L/d, R/ro) simultaneously over a wide range. The goal was to achieve the highest amount of total stored/delivered energy with a minimum heat transfer surface area. This analysis revealed that there was an optimum area between 36 and 63 m2GJ-1(or 0.12-0.22 m2kWhth-1), depending on the PCM employed. This optimum surface area can be obtained with several combinations of geometric parameters, but only certain combinations were found to achieve the highest total stored/delivered energy. The charging and discharging efficiency for the selected PCMs was found to be ~99% and 75-85%, respectively. Using the optimized designs, the cost of this shell and tube LHTES system was found to vary between 27 and 170 US$ kWhth-1, which indicates that with further development it may be competitive with conventional sensible storage systems (e.g. two-tank molten salts)

Performance of a Low Profile, Concentrating Solar Thermal Collector for Industrial Process Heating Applications

Recent studies have demonstrated that solar heat has a critical role to play in providing heat for industrial processes. In the present work, the thermal performance of a novel low profile concentrating solar thermal collector as a means to replace gas usage by mounting it on the rooftop of factories is investigated. The proposed collector incorporates an internal linear tracking system that concentrates beam radiation during a large part of a sunny day without external or rotational motion. The configuration presented here is suitable for an industrial metal process heating (drying and cleaning) application. In this paper, the annual behavior of the collector has been simulated for this application with TRNSYS (Transient System Simulation Tool) software in order to study its performance and economic feasibility. The annual solar fraction and economic metrics were used as selection criteria among design options (e.g. varying the solar array, storage tank sizes, and control methods). Assuming a constant thermal load of 260 kWh per day, the optimal total area of the collectors was calculated to be 200 m² for this application. Overall, the results show that, for the meteorological data of Sydney, the proposed concentrating collector can reach a solar fraction of 53%, while achieving positive economic returns. A preliminary economic analysis of this system indicates that a government subsidy of 50% of the capital equipment will reduce the payback period to 11 years. Due to the fact that solar-derived industrial heat production is an emerging market, further research and economies of scale could potentially be expected to drastically improve the economic viability of these types of systems going forward

A Thermal Stability Study of the Urea-Sodium Nitrate Eutectic Mixture as a PCM

ACTInternational audienceThe eutectic mixture formed by urea and sodium nitrate has been previously identified as a PCM candidate by the authors for heating and domestic hot water storage applications. It presents a melting point of 86 °C, a melting enthalpy of 172 J/g and a price around 0.9 euro/kg. In a previous work of some of the authors, the thermal stability of the eutectic mixture was preliminarily evaluated using an accelerated thermal cycling test that comprised 210 thermal cycles. Under the experimental conditions applied, the PCMs showed a stable behaviour. The main objective of the present work is to evaluate the stability of the mixture for longer periods of use under conditions representative of actual applications. Thermal degradation segregation will be assessed experimentally close to operation conditions

Standardization of PCM characterization via DSC

This work investigates the influence of particle size on crystallization behaviour of microencapsulated and emulsified n-octadecane using differential scanning calorimetry (DSC) and laser diffraction. Analyses of microcapsules show a stepwise decrease of nucleation temperature (from 26 °C to 14 °C) with decreasing particle size (from 300 μm to 3 μm). Further reduction of particle size in emulsions (< 0.2 μm) results in a slight decrease of nucleation temperature (<2 °K). Analyses of cooling thermograms of emulsions show two peaks, a minor peak around 8-9 °C and a major peak, which onset nucleation temperature Tc is influenced substantially by the lipophilic character of the surfactants (Tc varies between 13 °C and 22 °C).The minor peak is attributed to the transition from rotator to stable crystal phase and its signal increases with decreasing particle size