Thermal Energy Exchange between Carbon Nanotube Arrays and Air - PowerPoint PPT Presentation

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Thermal Energy Exchange between Carbon Nanotube Arrays and Air

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  1. Integrated Carbon Nanotube Microfin Architectures Kordás K et al., 2007 Factors Affecting Thermal Energy Transfer at Nanotube-Air Interface Molecular Simulation of Heat Flow between of CN and Air Schematic of CN & air system with heat source & heat sink Typical steady state temperature profile -Q Air atoms (22% O2 + 78% N2) +Q Carbon nanotube (10,10) chair • Air flow through the carbon nanotube array • Interfacial thermal resistance at air-carbon nanotube interface • Fin-array geometry (spacing, width, height of fins, …) • Carbon nanotube length, forest density. • Temperature drop at the interface due to interfacial thermal resistance • In the air heat flow is diffusive Scattering Mechanism Role of Adsorption Energy G=0.90MW/m2K at P=10atm & G=0.44MW/m2K at P=5atm interfacial thermal Conductance, G surface coverage,  residence time,  specular diffusive G~0.1MW/m2K at 300K & P=1atm ~ 250 nm thick layer of air • Low adsorption energy  specular scattering • High adsorption energy  diffusive scattering • Significant role of the adsorption energy parameter Molecular Flow through CN Array: Drag Force Kapitza Length & Critical Length for CN-Air System Schematic of CN & Air System with for Flow Simulations Drag Force vs. Velocity • Significant interfacial thermal resistance is an important limiting factor for the heat flow between nanotubes and gases • Continuum fluid flow description severely overestimates the drag force Conclusions Molecular Flow through CN Array: Mechanism and Design Guidance • The nanotube-air interfacial thermal conductance is about 0.1 MW/m2K at room temperature and atmospheric pressure, corresponding to 250 nm thick layer of air. The conductance strongly depends on interaction parameters. • The air flow through carbon nanotube array can be well described by the free molecular flow theory. The flowing air can only pass through an array of no more than 400 carbon nanotubes in series. • Our findings suggest that the arrays should be in islands containing ~ 100×100 tubes arrays separated by larger spaces with bare surfaces for maximizing thermal energy exchange. Velocity profile Design guidance Acknowledgements: Supported by the gift from the Intel Corporation and by the New York State Interconnect Focus Center at RPI. • Free molecular flow is the flow mechanism • Mean free path >> tube size • ~100x100 islands of carbon nanotubes Thermal Energy Exchange between Carbon Nanotube Arrays and Air Ming Hu, Sergei Shenogin, Pawel Keblinski, New York State Interconnect Focus Center and Rensselaer Nanotechnology Center, RPI, Troy, NY 12180, Nachiket Raravikar Intel Corporation, Chandler, AZ 85226