Thermal modeling and optimization of a thermally matched energy harvester

Abstract

The interest in energy harvesting devices has grown with the development of wireless sensors requiring small amounts of energy to function. The present article addresses the thermal investigation of a coupled piezoelectric and bimetal-based heat engine. The thermal energy harvester in question converts low-grade heat flows into electrical charges by achieving a two-step conversion mechanism for which the key point is the ability to maintain a significant thermal gradient without any heat sink. Many studies have previously focused on the electrical properties of this innovative device for energy harvesting but until now, no thermal modeling has been able to describe the device specificities or improve its thermal performances. The research reported in this paper focuses on the modeling of the harvester using an equivalent electrical circuit approach. It is shown that the knowledge of the thermal properties inside the device and a good comprehension of its heat exchange with the surrounding play a key role in the optimization procedure. To validate the thermal modeling, finite element analyses as well as experimental measurements on a hot plate were carried out and the techniques were compared. The proposed model provided a practical guideline for improving the generator design to obtain a thermally matched energy harvester that can function over a wide range of hot source temperatures for the same bimetal. A direct application of this study has been implemented on scaled structures to maintain an important temperature difference between the cold surface and the hot reservoir. Using the equations of the thermal model, predictions of the thermal properties were evaluated depending on the scaling factor and solutions for future thermal improvements are presented.

An Energy Harvester with Temperature Threshold Triggered Cycling Generation for Thermal Event Autonomous Monitoring

“…There are three ways of heat transfer [ 1 ]: heat conduction, heat convection, and heat radiation. For this device, heat conduction plays a significant role in the process of the bimetallic cantilever absorbing heat to separate from the generation cantilever, because the better the heat conduction performance, the faster the bimetallic cantilever responds to the heat event.…”

“…Wireless sensor networks (WSN) need a huge number of sensing nodes for unattended monitoring to undesired events like industrial equipment failure, human health problem, and environmental disaster, etc. [ 1 ]. Many sensor nodes working in the field suffer the common problem of insufficient on-site power supply.…”

Dynamic model of a novel thermogravity rotary actuator for solar energy harvesting

“…The article 7 presented the electrical modeling and optimization of bimetallic strip and piezoceramics thermal energy harvesters, which were used in two steps to convert thermal gradients into electricity up to 20 V. The developed electrical model based on lumped parameter model was implemented in SPICE for simulation of device performance analysis in different working phases. In Reference 8, the thermal modeling of a coupled piezoelectric and bimetallic‐based heat engine based on equivalent electrical circuit approach was presented. The developed model was validated using the finite element analysis and empirical measurements.…”

Coupling of PZT Thin Films with Bimetallic Strip Heat Engines for Thermal Energy Harvesting

“…Energy harvesting using piezoelectric [ 1 , 2 , 3 , 4 , 5 , 6 ], thermal [ 7 , 8 , 9 ] or electrostatic [ 10 ] conversion is pursued as an alternative to batteries for the power supply of wireless sensor nodes. Nowadays, emerging sensor nodes have lower and lower consumptions and emerging energy harvesting systems are able to provide enough energy to power them.…”

“…This device is based on a two-step conversion mechanism: a thermo-mechanical conversion by a bimetallic strip followed by an electro-mechanical conversion thanks to a piezoelectric membrane placed on the bimetal. This configuration, first proposed by Skotnicki in [ 11 ], has been widely studied in the literature [ 1 , 2 , 3 , 4 ].…”