This collaborative, EArly-concept Grants for Exploratory Research (EAGER), research project focuses on a design concept that may allow energy harvesting from waste heat, by converting the heat to electrical energy. The vision of the research is to use heat pipes, in particular so-called oscillating heat pipes (OHP). Inside an OHP, a series of serpentine-arranged mini-channels exist that are partially filled with a working fluid. There has been limited, if any, research in the area of energy-harvesting through the use of heat pipes. Heat pipes provide salient mechanical work within their structure due to vapor expansion and fluid flow. This research aims to harvest this internal work by augmenting the OHP heat transfer to the environment through utilization of a specially designed energy harvesting system that enables generation of electrical work through a piezoelectric effect, namely thermally-actuated piezoelectric transduction (TPT). This research project will contribute to better understanding of the physics and application of TPT, improved understanding of piezoelectric-materials, energy-harvesting using OHPs. This research will bridge research perspectives and approaches from the thermal/fluid sciences and power generation. Potential applications for these devices are numerous, especially for waste heat recovery and/or renewable power generation. The technology and basic science derived can result in: off-grid power generation for communications devices (e.g., third world country cellular phone charging and defense applications), more energy-efficient electronics packaging schemes, and new opportunities for high heat flux thermal energy harvesting. Geothermal temperature gradients may also be exploited for constant, renewable power generation via the implementation of ultra-large OHP/TPT systems or OHP/TPTs aligned in-series. This collaborative project will support both graduate and undergraduate researchers that have been traditionally underrepresented.
The OHP has yet to be investigated as a means to destabilize natural temperature gradients for the purpose of establishing a Stirling cycle, nor has it been investigated as a means for power generation. A unique opportunity for using TPT is atop a flat-plate oscillating heat pipe (OHP) - a device that effectively transfers heat via cyclic phase change of an internal working fluid - giving rise to an oscillatory temperature field on its surface. The research will investigate the use of both TPT and OHPs for combined 1) power generation/energy harvesting, and 2) highly-efficient heat transfer. To accomplish this, a unique energy harvester, which is directly attached to the OHP surface, will be designed and will consist of a micro-sized heat sink, encapsulated gas and suspended, spring-resisted piezoelectric material. An aggressive schedule of well-designed experiments is planned to determine how the effectiveness of TPT depends on OHP and energy harvester design. A highly-coupled set of governing equations will be defined and solved by joining common OHP thermo/fluidic models with the constitutive equations of piezoelectric materials. Numerical multi-physics software will be utilized to simulate the convective air flow in the energy harvester and electricity generation inherent to the proposed method for OHP-integrated TPT. The mechanical response and fatigue of various piezoelectric materials for TPT will be evaluated. Thermoelectricity generation via the proposed OHP/TPT is a unique and potentially transformative approach to enthalpy-to-electricity conversion as the OHP/TPT can efficiently transfer heat from one location to another (with ultra-high thermal conductivity) while also generating power.
