Microscale solid-state thermal diodes enabling ambient temperature thermal circuits for energy applications

Abstract

Thermal diodes, or devices that transport thermal energy asymmetrically, analogous to electrical diodes, hold promise for thermal energy harvesting and conservation, as well as for phononics or information processing. The junction of a phase change material and phase invariant material can form a thermal diode; however, there are limited constituent materials available for a given target temperature, particularly near ambient. In this work, we demonstrate that a micro and nanoporous polystyrene foam can house a paraffin-based phase change material, fused to PMMA, to produce mechanically robust, solid-state thermal diodes capable of ambient operation with Young's moduli larger than 11.5 MPa and 55.2 MPa above and below the melting transition point, respectively. Moreover, the composites show significant changes in thermal conductivity above and below the melting point of the constituent paraffin and rectification that is well-described by our previous theory and the Maxwell-Eucken model. Maximum thermal rectifications range from 1.18 to 1.34. We show that such devices perform reliably enough to operate in thermal diode bridges, dynamic thermal circuits capable of transforming oscillating temperature inputs into single polarity temperature differences - analogous to an electrical diode bridge with widespread implications for transient thermal energy harvesting and conservation. Overall, our approach yields mechanically robust, solid-state thermal diodes capable of engineering design from a mathematical model of phase change and thermal transport, with implications for energy harvesting.

Microencapsulation of 1-hexadecanol as a phase change material with reversible thermochromic properties

“…One of the prospective techniques for storing thermal energy is the application of phase change materials (PCMs). [5][6][7] Owing to their high capacity for the reversible storage of thermal energy, PCMs have been used in a variety of applications including solar energy storage, building temperature control, waste heat recovery, and fabric thermoregulation.…”

Engineering the Thermal Conductivity of Functional Phase‐Change Materials for Heat Energy Conversion, Storage, and Utilization

“…NTC thermal‐switching materials are widely studied in phase change thermal diodes, such as paraffin (eicosane, octadecane, hexadecane, etc. ), PEG, and crystalline polyethylene (PE) fiber .…”

“…However, these two chosen PCMs possess similar decreasing thermal conductivity trends, which restricted the effective temperature region of the thermal rectification. Another solid‐state thermal diode was fabricated from the paraffin‐polystyrene foam hybrid and phase invariant material (PMMA) by Wang et al, which could attain a maximum thermal rectification of 1.38 under a steady state conditions analysis. They also investigated unsteady state conditions by designing and fabricating a thermal diode bridge circuit that was analog to an electrical diode bridge circuit.…”

“…b) The setup for measuring a thermal diode bridge circuit, in which the arrow symbols represent the preferential direction for the heat flow (top) and the closed circuit and open circuit represent the experimental, thermal diode bridge outputs as a function of time from the input temperature oscillations (bottom). a,b) Reproduced with permission . Copyright 2017, Royal Society of Chemistry.…”

Electron-Transfer-Induced Thermal and Thermoelectric Rectification

“…In molecular environments where heat conduction is dominated by vibrational (phononic) energy transfer, thermal rectification may result from nonlinear coupling, that is, anharmonicity, and the breaking of symmetry. Such phenomena have been the focus of significant theoretical and experimental examination [9][10][11][12][13][14][15]. Phononic heat conduction has been discussed as a possible mechanism for the operation of thermal components such as thermal transistors [16][17][18], thermal memory [19], and thermal logic gates [20].…”