High Heat Transfer Fluid Research Articles

Experimental study in a compound parabolic solar concentrator with different configurations of thermal energy storage system

ABSTRACT This study explores the integration of thermal energy storage (TES) systems with solar water heating systems to increase their utilization time. While solar water heating systems are effective for low-temperature applications, they become less efficient at higher heat transfer fluid (HTF) temperatures. To solve this problem, the study suggests combining a compound parabolic concentrator (CPC) solar collector with a TES system to improve heat transfer rates and minimize heat loss. The study examines the effect of different mass flow rates and HTF inlet temperatures on the integrated system's performance, evaluating energy efficiency, exergy efficiency, and overall loss coefficient. The results reveal that the six-phase change materials (PCMs) configuration achieves the highest intercept line efficiency of 72%, with a heat transfer rate 1.7 times higher than that of the single PCM configuration. Moreover, the exergy analysis shows superior performance compared to commonly used flat collectors. Overall, the proposed CPC solar collector integrated with a TES system is suitable for low-temperature applications with an inlet HTF temperature not exceeding 65°C.

Parametric studies on solidification of phase change material inside a cylindrical container toward achieving optimal energy efficiency

AbstractFifty percentage of the energy consumption inside any building is utilized for space cooling purposes. Energy storage through phase change material (PCM) is a viable option to fulfill the cooling energy requirements. The PCM is usually stored inside multiple containers/packets. However, the PCM's low thermal conductivity is a fundamental problem that delays the solidification time and can be accelerated through the nanoparticle addition and higher heat transfer fluid (HTF) flow rate. The recent advancement in nanoparticles opens an opportunity to enhance the heat transfer characteristics of the PCM. Therefore, a detailed parametric analysis is carried out for the PCM inside a cylindrical container to analyze the impact of thermal conductivity (“k”) enhancement through nanoparticle addition and the external surface heat transfer coefficient (“h”) on the solidification time reduction of the Water and RT21 PCM. It is concluded from the results that while utilizing gaseous HTF, it is better to increase the surface “h” rather than increasing the “k” of the PCM. On the other hand, for liquid HTF, “k” value played a significant role in solidification time reduction than increasing the “h” value. A considerate amount of solidification time reduction is possible through nanoenhanced RT21 and water PCM. This study will help the researchers/engineers design an energy efficient storage material toward achieving sustainability.

Numerical simulation of a metal hydride tank with LaNi4.25Al0.75 using a novel kinetic model at constant flows

Tritium as the fuel of fusion reactor must be stored in a metal hydride (MH) tank at a desired absorbing rate. This requirement must be fulfilled by proper design of the MH tank, which can be assisted by numerical simulation. In this work, a numerical model is proposed to couple hydrogen absorption kinetics and the heat and mass transfer of the MH tank. A novel kinetic model at constant flows for the gas-solid reaction is developed to analyze the complex hydrogen absorption kinetics of a MH at different pressures, which is the core of the numerical model. Kinetic analysis is performed to obtain the hydrogen absorption rate equation of LaNi4.25Al0.75, which has two stages upon the increase of pressure. The numerical model, after being well verified by our experimental data, is used to predict the hydrogen absorption performance of a double-layered annulus MH tank filled by LaNi4.25Al0.75. The predicted results indicate that a thinner LaNi4.25Al0.75 layer and higher heat transfer fluid (HTF) velocity can improve the heat transfer of the MH tank effectively, thereby enhancing the hydrogen absorption performance. When the layer thickness and HTF velocity is 3 mm and 25 m s−1, the double-layered annulus MH tank can meet the target of absorbing 5 mol of hydrogen for 60 min at 1.87 NL min−1. This designed MH tank with LaNi4.25Al0.75 can provide a reference for tritium storage in fusion reactors.

Effective Separation of a Water in Oil Emulsion from a Direct Contact Latent Heat Storage System

The problem of emulsification between Phase Change Material (PCM) and Heat Transfer Fluid (HTF) in direct contact latent heat storage systems has been reported in various studies. This issue causes the PCM to flow out of the storage tank and crystallize at unwanted locations and thus presents a major limitation for the proper operation of such systems. These anomalies become more pronounced when high HTF flow rates are employed with the aim to achieve fast heat transfer rates. The goal of this paper is to find a method which will enable the fast separation of the formed emulsion and thus the uninterrupted operation of the storage unit. In this study, three separation methods were examined and the use of superhydrophobic filters was chosen as the best candidate for the demulsification of the PCM and HTF mixtures. The filter was produced by processing of a melamine sponge with different superhydrophobic adhesives and was tested with emulsions closely resembling the ones formed in a real direct contact setup. The superhydrophobic filter obtained, was able to separate the emulsions effectively while presenting a very high permeability (up to 1,194,980 kg h−1 m−2 bar−1). This is the first time the use of a superhydrophobic sponge has been investigated in the context of demulsification in direct contact latent heat storage.

Thermal behavior of latent thermal energy storage unit using two phase change materials: Effects of HTF inlet temperature

This work presents a numerical study of the thermal behavior of shell-and-tube latent thermal energy storage (LTES) unit using two phase change materials (PCMs). The heat transfer fluid (HTF) flow through the inner tube and transfer the heat to PCMs. First, a mathematical model is developed based on the enthalpy formulation and solved through the governing equations. Second, the effects of HTF inlet temperature on the unsteady temperature evolution of PCMs, the total energy stored evolution as well as the total melting time is studied. Numerical results show that for all HTF inlet temperature, melting rate of PCM1 is the fastest and that of PCM2 is the slowest; increasing the HTF inlet temperature considerably increases the temperature evolution of PCMs. The maximum energy stored is observed in PCM2 with high melting temperature and high specific heat; heat storage capacity is large for high HTF inlet temperature. When the HTF inlet temperature increases from 338K to 353K, decreasing degree of melting time of PCM2 is the biggest from 1870s to 490s, which reduces about 73.8%; decreasing degree of melting time of PCM1 is the smallest from 530s to 270s, which reduces about 49.1%.

A novel triple-sleeve energy storage exchanger and its application in an environmental control system

Phase change material (PCM) based on thermal energy storage (TES) for Heating, Ventilation and Air Conditioning applications can involve thermal storage at various temperatures associated with heating and cooling processes. In this paper, a novel TES heat exchanger called triple-sleeve energy storage exchanger (TRESE) is firstly introduced. Based on the TRESE, a proposed novel environmental control system (ECS) is detailed. The ECS can be operated in eight modes so as to be adaptive to various weather conditions all year around. Finally, an experimental study on the TRESE operating performance is reported. The influences of the temperature and mass flow rate of heat transfer fluid (HTF) on heat storage performance are experimentally investigated. The experimental results indicate that the amount of heat storage at a high HTF temperature is more than that at a low temperature. In addition, heat storage period at a low HTF mass flow rate and temperature is much longer than that at a high mass flow rate and temperature.