Conjugate Heat Transfer in Latent Heat Thermal Storage System With Cross Plate Fins

Melting enhancement in triplex-tube latent heat energy storage system using nanoparticles-metal foam combination

Abstract: Phase change material (PCM) energy storage systems have relatively low thermal conductivity values which greatly reduces the systems’ performance. In this study, a compound porous-foam/nanoparticles enhancement technique was used to significantly improve melting of a phase change material (PCM) in a triplex-tube heat exchanger applicable to liquid desiccant air-conditioning systems. A mathematical model that takes into account the non-Darcy effects of porous foam and Brownian motion of nanoparticles was formulated and validated with previous related experimental studies. The influence of nanoparticle volume fraction and metal foam porosity on the instantaneous evolution of the solid-liquid interfaces, distribution of isotherms, and liquid-fraction profile under different temperatures of the heat transfer fluid (HTF) were investigated. Results show that dispersing nanoparticles in the presence of metal foams results in melting time savings of up to 90% depending on the foam structure and volumetric nanoparticle concentration. Although the melting time decreases as the porosity decreases and/or volume fraction increases, high-porosity metal foam with low volume-fraction nanoparticles is recommended. This ensures minimal PCM volume reduction and promotes positive contribution of natural convection during the melting process.

Optimizing fin design for a PCM-based thermal storage device using dynamic Kriging

Abstract: A key challenge in the development of a practical thermal storage device (TSD) is the low thermal conductivity of common phase change materials (PCM). This low conductivity impedes both heat input and extraction. The most common solution is to use conductive metal fins to spread heat through the device. However, optimizing the effectiveness of the container and the fin arrangement is difficult due to the large number of potential design parameters. This paper develops a strategy to make simulation-based optimization process affordable and accurate. First, numerical techniques are designed to accurately and efficiently compute heat and mass transport in a variety of geometries without generating grids to conform to each geometry. This facilitates rapid prototyping and mitigates the expense of individual simulations. Second, a pre-screening process identifies the independent variables with the largest and most nonlinear effect on the objective function in the optimization process, thus narrowing the parameter space. Finally, a dynamic Kriging-based optimization approach constructs a multidimensional response surface using sparse input datasets; the response surface is then used to identify an optimal design. The combination of the above three strategies is shown to result in an approach that can aid in the design of optimal thermal storage devices that rely on a mixture of PCM and metal fins.

Medium- and high-temperature latent and thermochemical heat storage using metals and metallic compounds as heat storage media: A technical review

Abstract: Latent and thermochemical heat storage technologies are receiving increased attention due to their important role in addressing the challenges of variable renewable energy generation and waste heat availability, as well as the mismatch between energy supply and demand in time and space. However, as the operating storage temperature increases, a series of challenging technical problems arise, such as complex heat transfer mechanisms, increased corrosion, material failure, reduced strength, and high-temperature measurement difficulties, especially for metals and metallic compounds as heat storage media. This paper reviews the latest research progress in medium- and high-temperature latent and thermochemical heat storage using metals and metallic compounds as storage media from a technical perspective and provides useful information for researchers and engineers in the field of energy storage. In this paper, the status and challenges of medium- and high-temperature latent and thermochemical heat storage are first introduced, followed by an assessment of metals and metallic compounds as heat storage media in latent and thermochemical heat storage applications. This is followed by a comprehensive review of three key issues associated with medium/high-temperature latent heat storage applications: heat transfer enhancement, stability and corrosion, as well as a discussion of four key issues associated with medium/high-temperature thermochemical heat storage: heat transfer, cycling stability, mechanical property and reactor/system design. Finally, the prospects of medium/high-temperature latent and thermochemical heat storage are summarized.

Dynamic neural networks to analyze the behavior of phase change materials embedded in building envelopes

Abstract: Heat transfer during melting and solidifying processes in phase change materials, is a highly non-linear phenomenon. Artificial Neural Networks seem a suitable approach to deal with highly non-linear processes. The present work uses dynamic neural networks to simulate the behavior of a phase change material layer of a building envelope, which typically are under strongly varying conditions, with temperatures and heat fluxes changing at different rates inside a wide range of values. In the present work, the experimental procedure to obtain the training dataset is explained; then, an ANN is trained using experimental data, together with additional data related to the thermal behavior of PCMs; finally, generalization of the ANN is analyzed, and the results are evaluated. Initial training attempts, show a perfect match between experimental data and simulation results of the neural networks, with absolute mean errors below the accuracy of the fluximeters. However, when analyzing the simulations carried out with data different to those used to train the networks, the results differ strongly to those expected. This means that neural networks seem to have a bad generalization when dealing with phase change materials under strongly varying conditions, probably due to the high variability of the input data, and the strongly non-linear behavior of phase change processes.

A fixed grid numerical modelling methodology for convection-diffusion mushy region phase-change problems

Abstract: An enthalpy formulation based fixed grid methodology is developed for the numerical solution of convection-diffusion controlled mushy region phase-change problems. The basic feature of the proposed method lies in the representation of the latent heat of evolution, and of the flow in the solid-liquid mushy zone, by suitably chosen sources. There is complete freedom within the methodology for the definition of such sources so that a variety of phase-change situations can be modelled. A test problem of freezing in a thermal cavity under natural convection is used to demonstrate an application of the method.

Transient cooling of electronics using phase change material (PCM)-based heat sinks

Abstract: Use of a phase change material (PCM)-based heat sink in transient thermal management of plastic quad flat package (QFP) electronic devices was investigated experimentally and numerically. Results show that increased power inputs enhance the melting rate as well as the thermal performance of the PCM-based heat sinks until the PCM is fully melted. A three-dimensional computational fluid dynamics model was proposed to simulate the problem and demonstrated good agreement with experimental data. Results indicate the potential for PCM-based heat sinks for use in intermittent-use devices.

Cooling of mobile electronic devices using phase change materials

Abstract: An experimental study is conducted on the cooling of mobile electronic devices, such as personal digital assistants (PDAs) and wearable computers, using a heat storage unit (HSU) filled with the phase change material (PCM) of n-eicosane inside the device. The high latent heat of n-eicosane in the HSU absorbs the heat dissipation from the chips and can maintain the chip temperature below the allowable service temperature of 50 °C for 2 h of transient operations of the PDA. The heat dissipation of the chips inside a PDA and the orientation of the HSU are experimentally investigated in this paper. It was found that different orientation of the HSU inside the PDA could affect significantly the temperature distribution.

Experimental investigations on phase change material based finned heat sinks for electronic equipment cooling

Abstract: This paper reports the results of an experimental investigation of the performance of finned heat sinks filled with phase change materials for thermal management of portable electronic devices. The phase change material (PCM) used in this study is n-eicosane and is placed inside a heat sink made of aluminium. Aluminium acts as thermal conductivity enhancer (TCE), as the thermal conductivity of the PCM is very low. The heat sink acts as an energy storage and a heat-spreading module. Studies are conducted for heat sinks on which a uniform heat load is applied for the unfinned and finned cases. The test section considered in all cases in the present work is a 80 × 62 mm 2 base with TCE height of 25 mm. A 60 × 42 mm 2 plate heater with 2 mm thickness is used to mimic the heat generation in electronic chips. Heat sinks with pin fin and plate fin geometries having the same volume fraction of the TCE are used. The effect of different types of fins for different power level (ranging from 2 to 7 W) in enhancing the operating time for different set point temperatures and on the duration of latent heating phase were explored in this study. The results indicate that the operational performance of portable electronic device can be significantly improved by the use of fins in heat sinks filled with PCM.

Experimental and numerical studies on performance of PCM-based heat sink with different configurations of internal fins

Abstract: This paper presents both experimental and numerical investigations on the application of a PCM-based heat sink for the purpose of thermal management. A comparison was carried out between heat sink with and without phase change material (PCM). The effects of various parameters such as power levels, number of fins, fin height and fin thickness were studied. The results showed that increasing the number of fins and fin height resulted in an appreciable increase in overall thermal performance. Increasing the fin thickness only gave a slight improvement. There was an optimum fin thickness, above which the heat sink performance showed no further improvement. Increasing the power level input, as expected, increased the melting rate of the PCM. In all cases, heat conduction was the primary mode of heat transfer at the initial stage of melting. At the later stage, free convection played a more crucial role in enhancing the melting of the PCM.