Heat Thermal Energy Storage Media Research Articles

Experimental Investigation on Solar Water Heater Integrated with Thermal Battery Using Phase Change Material and Porous Media

Evacuated tube heat pipe solar collector as a passive solar water heating system is a simple, reliable, and cost-effective way to capture the sun’s thermal energy to supply hot water to homes. In the proposed system, the manifold is reshaped to a tank and filled with phase change materials (PCM) and porous media, which the PCM acts as a latent heat thermal energy storage medium. In order to increase the heat flux from the heat pipe to the PCM and overcome the low thermal conductivity of the PCM, porous media is used. The porous media is connected to the heat pipe condenser to collect the heat and distribute it uniformly throughout the PCM filling the pores. This design of the manifold acts as a heat storage tank or thermal battery. Another pipe in the tank transfers heat from the PCM to the water. Experiments were conducted in 2 modes: charging/discharging and periodic draw-off. The results demonstrated that this thermal battery design could provide homes with the hot water they require on sunny days, while it needs an auxiliary heater or larger solar collector to provide enough hot water on rainy/cloudy days. Considering the solar radiation fluctuation, the efficiency of the thermal battery is 50% ± 9.3%. The thermal battery can warm up the cold water higher than the operating temperature on a sunny day (more than 120 L per day at 38 °C). Using porous media provides better heat distribution in the PCM.

Economic Feasibility of Thermal Energy Storage-Integrated Concentrating Solar Power Plants

Concentrating solar power (CSP) is a high-potential renewable energy source that can leverage various thermal applications. CSP plant development has therefore become a global trend. However, the designing of a CSP plant for a given solar resource condition and financial situation is still a work in progress. This study aims to develop a mathematical model to analyze the levelized cost of electricity (LCOE) of Thermal Energy Storage (TES)-integrated CSP plants in such circumstances. The developed model presents an LCOE variation for 18 different CSP configurations with TES incorporated for Rankine, Brayton, and combined power generation cycles, under regular TES materials and nano-enhanced TES materials. The model then recommends the most economical CSP plant arrangement. Within the scope of this study, it was found that the best configuration for electricity generation is a solar power tower with nano-enhanced phase change materials as the latent heat thermal energy storage medium that runs on the combined cycle. This returns an LCOE of 7.63 ct/kWh with a 22.70% CSP plant efficiency. The most favorable option in 50 MW plants is the combined cycle with a regular TES medium, which has an LCOE of 7.72 ct/kWh with a 22.14% CSP plant efficiency.

Regulation of the output temperature in a novel water heating system using solid graphite as sensible heat thermal energy storage medium: Effects of water tank

The quality of output temperature is one of the key parameters for the reliability of water heating system. In this work a simulation work was done to regulate the output temperature in a novel water heating system using solid graphite as thermal energy storage medium. The effects of water tank on the quality of output temperature was considered. Two different strategies were thus considered: (i) single tank system, and (ii) double-tank system. And two different working conditions were analyzed: (i) standard design condition, and (ii) demand change conditions. The results showed that the application of water tanks can reduce the standard deviation of output temperature by 68.49% and 68.81% under the standard design condition, respectively. And the improvement is highly related to the capacity of hot water tank. For the demand change condition, the regulation strategy was carried out based on the criterion of heat power equilibrium. The results showed that the single tank system will deteriorate the reliability of water heating for demand change condition, though it can reduce the oscillation of the output temperature. For the double-tank system, a two-step adjustment method was applied. The results showed that the average output temperature can be quite close to the target value when demand ratio changes to 0.8 and 0.9. And the standard deviation of temperature has also reduced by 24.19% and 63.06%, respectively.

Molten Salt/Metal Foam/Graphene Nanoparticle Phase Change Composites for Thermal Energy Storage

The binary and ternary mixtures of nitrates are desirable phase change materials (PCMs) as latent heat thermal energy storage media for solar energy applications. In this study, graphene oxide was ...

Lowered total solidification time and increased discharge rate of reduced graphene oxide-solar salt composites: Potential for deployment in latent heat thermal energy storage system

Solar salt is a useful energy storage medium and a heat transfer fluid for concentrated solar thermal applications. The present work explores the use of reduced graphene oxide (rGO) nanostructures as an additive to solar salt, to improve its thermophysical properties. Reduced graphene oxide nanostructures at weight fractions of 0.125 wt% and 0.5 wt% were added to the solar salt, leading to rGO-solar salt composites. The thermophysical characterization experiments revealed that the specific heat in the 0.5 wt% rGO-solar salt nanocomposite was elevated by 6% over the temperature range of 50–270 °C. The time required for complete solidification of 0.125 wt% and 0.5 wt% was reduced by 43% and 49%. In the discharge cycle, the heat transfer rate was amplified by 90% and 138% respectively for 0.125 wt% and 0.5 wt% rGO-solar salt nanocomposites, attributable to thermal conductivity enhancement, specific heat augmentation and heterogeneous nucleation. Thus, rGO-solar salt composites are suitable for use as latent heat thermal energy storage medium in solar thermal applications.

Investigation of exergy and yield of a passive solar water desalination system with a parabolic concentrator incorporated with latent heat storage medium

In the present study, two solar stills were assembled and experienced to evaluate the yield and energy performance of an improved passive solar desalination system compared to a conventional one. The improved still is incorporated with a latent heat thermal energy storage medium and a parabolic solar concentrator. A parabolic solar concentrator was added to concentrate and increase the amount of solar irradiance absorbed by the still basin. Paraffin wax was applied as phase change material (PCM) in the solar still bottom plate. In the current study also, the effect of impure water profundity inside the still on still’s accumulated yield have been assessed. The following study involved a mathematical analysis for calculation of the exergetic proficiency as an efficient tool for the optimization, and yield evaluation of any energy systems and solar stills as well. Experimental research conducted in steady days of summer and winter at six different values of impure water profundity inside the solar still basin. The salinity of the impure water tested was about 3000–5000ppm, while the salinity for the resulted drinkable water was about 550–500ppm. The performed outcomes revealed that during summer, exergetic efficiency is higher than its qualified value in winter with approximately (10–15%) for the same water profundity. Results also disclosed that, the exergetic efficiency is higher when the water profundity in the basin is lower with approximately (6–9%). The experimental findings reveals that, the solar still with PCM and parabolic concentrator is higher in the daily freshwater yield in summer with an amount of (55–65%) and in winter with an amount of (35–45%) compared to the usual solar based still. The current work performed during January 2016 as a winter season, and July 2016 as a summer season from 8:00am to 6:00pm under the climate conditions of Tanta city-Egypt.