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Beyond Beta: Systemic Experimental Investigation of Plastic Heat Generation.
Abstract not provided.
Plastic Heat Exchangers with High Conductance
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Microwave assisted heating of plastic waste: Effect of plastic/susceptor (SiC) contacting patterns
We discuss plastic accumulation as a growing sustainability challenge. Most plastics are thermally inert at room temperature, requiring high temperatures for depolymerization. In the quest for developing sustainable plastic upcycling, we investigate silicon carbide (SiC) as microwave absorbing susceptors for reaching depolymerization temperatures. We utilize three SiC topologies – particles, hot-pressed plastic films containing SiC particles, and monoliths. SiC particles of >0.5 mm in diameter can provide heating rates approaching ~200 °C/min at modest powers. Still, physically mixed plastic-susceptor beds suffer from density differences, causing non-uniform contact during plastic softening and melting. Hot-pressed plastic films containing SiC particles allow uniform plastic-susceptor contact but suffer from slow heating as only a single layer of susceptors exists between polymer layers. SiC monoliths mitigate these challenges by preferentially dissipating the microwaves and rapidly heating the plastics independently of polymeric properties.
Adiabatic Heating in Modular Plasticity Models
Plastic deformations in metals are dissipative. Some fraction of the dissipated mechanical energy (plastic work) is converted into thermal energy and serves as a heat source. In cases where the heat cannot be readily transferred to the environment, the local temperature will increase thereby producing variations in mechanical behaviors associated with temperature-dependent properties (e.g. thermal softening due to decreasing yield strengths). This issue is often referred to as "adiabatic heating as an adiabatic temperature condition corresponds to the limiting case where no heat transfer takes place. The impact of converting plastic work into heat on the mechanical response of metals has been long studied. Nonetheless, it still remains an issue. For instance, with respect to ductile failure, the second Sandia Fracture Challenge noted that accounting for plastic heat generation was necessary for predictions under dynamic loading conditions. Furthermore, both experimental and modeling efforts continue to be pursued to better describe and understand the effect of plastic work conversion into heat on structural responses. Noting the need for capturing plastic work conversion into heat in structural analyses, a simple and fairly traditional representation of these responses has been added into existing modular plasticity models in the Library of Advanced Materials for Engineering (LAME). Here, these capabilities are briefly described with the underlying theory and numerical implementation discussed in Sections 2 and 3, respectively. Examples of syntax are given in Section 4 and some verification exercises are found in Section 5. Simple structural analyses are presented in Section 6 to briefly highlight the impact of these features and concluding thoughts are given.
Thermal transport in semicrystalline polyethylene by molecular dynamics simulation
Recent research has highlighted the potential to achieve high-thermal-conductivity polymers by aligning their molecular chains. Combined with other merits, such as low-cost, corrosion resistance, and light weight, such polymers are attractive for heat transfer applications. Due to their quasi-one-dimensional structural nature, the understanding on the thermal transport in those ultra-drawn semicrystalline polymer fibers or films is still lacking. Here, we built the ideal repeating units of semicrystalline polyethylene and studied their dependence of thermal conductivity on different crystallinity and interlamellar topology using the molecular dynamics simulations. We found that the conventional models, such as the Choy-Young's model, the series model, and Takayanagi's model, cannot accurately predict the thermal conductivity of the quasi-one-dimensional semicrystalline polyethylene. A modified Takayanagi's model was proposed to explain the dependence of thermal conductivity on the bridge number at intermediate and high crystallinity. We also analyzed the heat transfer pathways and demonstrated the substantial role of interlamellar bridges in the thermal transport in the semicrystalline polyethylene. Lastly, our work could contribute to the understanding of the structure–property relationship in semicrystalline polymers and shed some light on the development of plastic heat sinks and thermal management in flexible electronics.
Conversion of Plastic Work to Heat: A full-field study of thermomechanical coupling
This project targeted a full-field understanding of the conversion of plastic work into heat using advanced diagnostics (digital image correlation, DIC, combined with infrared, IR, imaging). This understanding will act as a catalyst for reformulating the prevalent simplistic model, which will ultimately transform Sandia's ability to design for and predict thermomechanical behavior, impacting national security applications including nuclear weapon assessments of accident scenarios. Tensile 304L stainless steel dogbones are pulled in tension at quasi-static rates until failure and full-field deformation and temperature data are captured, while accounting for thermal losses. The IR temperature fields are mapped onto the DIC coordinate system (Lagrangian formulation). The resultant fields are used to calculate the Taylor-Quinney coefficient, β, at two strain rates rates (0.002 s -1 and 0.08 s -1 ) and two temperatures (room temperature, RT, and 250°C).
A comparison of techniques to measure the conversion of plastic work to heat in 304L stainless steel under adiabatic conditions
Not Available
Effects of Convection on Experimental Investigation of Heat Generation During Plastic Deformation.
Abstract not provided.
Effects of Convection on Experimental Investigation of Heat Generation During Plastic Deformation.
Abstract not provided.
Conversion of Plastic Work into Heat in Dynamic Tensile Loading of 304L-VAR Stainless-Steel
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Catalytic Oxidative Upcycling of Plastic Waste and Heat Integration using Chemical Looping Systems
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Plastic damping of Alfvén waves in magnetar flares and delayed afterglow emission
Magnetar flares generate Alfvén waves bouncing in the closed magnetosphere with energy up to ∼10{sup 46} erg. We show that on a timescale of 10 ms the waves are transmitted into the star and form a compressed packet of high energy density. This packet strongly shears the stellar crust and initiates a plastic flow, heating the crust and melting it hundreds of meters below the surface. A fraction of the deposited plastic heat is eventually conducted to the stellar surface, contributing to the surface afterglow months to years after the flare. A large fraction of heat is lost to neutrino emission or conducted into the core of the neutron star.
High Thermal Conductivity Polymer Composites for Low Cost Heat Exchangers
This factsheet describes a project that identified and evaluated commercially available and state-of-the-art polymer-based material options for manufacturing industrial and commercial non-metallic heat exchangers. A heat exchanger concept was also developed and its performance evaluated with heat transfer modeling tools.
Continuous Processing of High Thermal Conductivity Polyethylene Fibers and Sheets
This factsheet describes a project that developed a new, continuous manufacturing process to make high molecular weight, high thermal conductivity polyethylene fibers and sheets to replace metals and ceramics in heat transfer applications.
Ductile Glassy Polymer Networks Capable of Large Plastic Deformation and Heat-Induced Elastic Recovery
Many thermoplastic polymers are ductile by combining strength and large deformations. These deformations are irreversible - known as plastic deformation. Elastomers can deform reversibly but have low strength. To this end, we developed glassy and ductile polyamide networks capable of large plastic deformation (>200% strain) and high strength (~50 MPa tensile strength and ~1500 MPa Young’s modulus), similar to those of polyolefins and Nylon-66. We discovered that hydrogen bonding between meta-phthalamide groups was essential to the ductility. Since these polyamide networks are covalently bonded, we demonstrated their unique durability by repeatable elastic recovery at elevated temperatures, exhibiting indifferent tensile properties in each cycle. Furthermore, when we fixed the strain during the elastic recovery, these polyamide networks actuated stresses of 9–18 MPa, among the highest reported in shape-memory polymer actuators. Here, we envision these ductile, glassy polymer networks as promising alternatives to ductile thermoplastics, given the combined benefit of ductility and durability.
Thermomechanical conversion in metals: dislocation plasticity model evaluation of the Taylor-Quinney coefficient
Using a partitioned-energy thermodynamic framework which assigns energy to that of atomic configurational stored energy of cold work and kinetic-vibrational, in this study we derive an important constraint on the Taylor-Quinney coefficient, which quantifies the fraction of plastic work that is converted into heat during plastic deformation. Associated with the two energy contributions are two separate temperatures – the ordinary temperature for the thermal energy and the effective temperature for the configurational energy. We show that the Taylor-Quinney coefficient is a function of the thermodynamically defined effective temperature that measures the atomic configurational disorder in the material. Finite-element analysis of recently published experiments on the aluminum alloy 6016-T4 [1], using the thermodynamic dislocation theory (TDT), shows good agreement between theory and experiment for both stress-strain behavior and temporal evolution of the temperature. The simulations include both conductive and convective thermal energy loss during the experiments, and significant thermal gradients exist within the simulation results. Computed values of the differential Taylor-Quinney coefficient are also presented and suggest a value which differs between materials and increases with increasing strain.