Influence of Shrinkage on Phase Change Material-based Thermal Rectifiers

Thermal rectifiers have recently emerged as a field of interest because of their potential application in a wide-ranging field. Thermal rectifiers can be employed to shield heat-sensitive electronics components, building thermal management and thermal energy conversion. A thermal rectifier allows heat transfer in a preferred direction while curtailing heat transfer in the reverse direction. Recently, the thermal conductivity differential of Phase Change Materials (PCMs) in their different states has been employed to develop thermal rectifiers. However, these studies are limited to analyzing the effect of change in the thermal conductivity alone, neglecting the influence of change in other thermophysical properties. The difference in PCM density in different states leads to the development of void volume upon phase transition, which can significantly alter thermal rectification. Therefore, this study analyzes the interdependent influence of thermal conductivity and density on thermal rectification under a wide range of temperature biases. The presence of void volume under reverse bias augments thermal rectification, whereas it has an adverse effect when developed under the forward bias. A criterion is developed to identify when the influence of density negates that of thermal conductivity, which requires the design of the thermal rectifier to be altered. Furthermore, optimization criteria and expressions for optimal thermal rectification are developed, incorporating the influence of both thermal conductivity and density

Influence of Natural Convection on Design of Thermal Diodes

Thermal diode, analogous to the electrical diode, is an emerging field of interest due to its potential application in thermal management, thermal shielding, and thermal circuits. Application of Phase Change Material (PCM) is among the different approaches proposed and analyzed to achieve high thermal rectification. However, these studies often limit the analysis to conduction heat transfer and neglect advection. In the present study, the influence of natural convection on conventional single PCM-based thermal diodes' thermal rectification has been analyzed. Natural convection enhances heat transfer in the inverse direction of gravity, augmenting thermal rectification of diodes with preferential flow in the opposite direction of gravity, whereas adversely affecting the performance of thermal diodes with preferential heat flow in the direction of gravity. Therefore, the design of thermal diode with preferential flow in gravity direction is modified to limit natural convection via the use of metal foam and baffles. The non-phase change material in a thermal diode with preferential flow in the direction inverse to the gravity is replaced with phase change material augmenting the natural convection because of the increase in length. The modified designs led to a mean thermal rectification enhancement of approximately 85% and 1275% in thermal diodes with preferential towards gravity and inverse to the gravity directions, respectively. A thermal rectification of more than 50 is achieved in a modified thermal rectifier for preferential flow in the direction inverse to the gravity

Artificial neural network-Genetic algorithm optimized graded metal foam

The effective utilization of renewable energy directly correlates to efficient performance of integrated energy storage system. The efficiency of Thermal Energy Storage (TES) systems strongly correlates with the heat transfer rate during phase change processes. Heterogeneous metal foams which allow augmenting heat transfer without compromising the thermal capacity suffers from high manufacturing cost. A series of homogeneous metal foams stacked is employable to reap advantages associated with heterogeneous metal foam at a similar manufacturing cost as homogeneous metal foam. The present study focuses on optimizing the porosity distribution of graded metal foam to augment the performance of the TES system. The unidirectional phase change process, observed particularly during solidification, acts as a bottleneck. Therefore, the present study focuses on augmenting unidirectional phase-change processes. The present study discusses the influence of PCM and metal foam thermophysical properties and operational characteristics of the TES system on heat transfer augmentation in different graded metal foams. A numerical model is developed to quantify the influence of graded metal foam on heat transfer rate, which is used to train an Artificial Neural Network (ANN) model. The porosity distribution has been optimized using a Genetic algorithm, which employs the ANN model to ascertain heat transfer rate for different graded metal foams. The optimal distribution has been found to be 93.7% and 96.3% for two-layer graded metal foam and 92.8%, 95%, and 97.2% for three-layer graded metal foam, which augments heat transfer by 1160% and 1185%, respectively

Design, Development, and Testing of a Low-Concentration Vanadium Redox Flow Battery

The purpose of this paper is to highlight the design, development, and testing of a low-concentration vanadium redox flow battery (VRFB). The low-cost implementation has a 7 cm × 7 cm active membrane area and an electrolyte volume of 450 mL for each positive and negative electrolyte. The electrolyte concentration is approximately 0.066 M vanadium. An H-cell for performing electrolysis with the electrolytes is developed, and the process and method for creating the electrolyte for this low-concentration implementation are described and documented. The maximum power density and energy efficiency of the battery among tests between 500 and 800 mA are 1.32 W/L and 28.51%, respectively. Results are presented in terms of polarization curves, charge/discharge cycles, and voltage, coulombic, and energy efficiencies. Adaptation of a COMSOL Multiphysics model is implemented to compare the computational performance figures and the results of our VRFB implementation. The numerical results agree with experimentation, and differences in the results can be attributed to the losses present in the experimental tests. The proposed battery and design are intended to investigate the performance and feasibility of a low-concentration VRFB. The ultimate long-term objective of this research is the development of a novel, costeffective, and safe redox flow battery using hydrogen peroxide as one of the electrolytes