Near-Field Radiative Energy Exchange Analysis of Nanospheres and Nanorods:Space Waste Heat Recovery Device Design

[摘要] In the present study, a theoretical method for sphere-to-sphere radiative heat exchange isimplemented for silica, lithium fluoride, and arsenic triselenide nanospheres of equal andunequal radii. The method is extended to approximate a sphere-to-plane geometric configurationvia an asymptotic method. The asymptotic method calls for an iterative process by which theradiative exchange is continuously calculated up to convergence as the radii of one microsphereis increased. These results are compared to previously published theoretical approximations andexperimental data.A theoretical method for cylinder-to-cylinder radiative heat exchange is formulated. Themethod utilizes a modified version of the numerical method for near-field sphere-to-sphereradiative exchange. Modifications were made to the numerical procedure to make it applicable tocylindrical geometry of nanorods. Nanorods investigated had length to diameter ratios of 3: Iand 7:1. The heat exchange of nanorods is plotted vs. gap to assess the impact of near-fieldradiative transfer as gap decreases. Graphical results of energy vs. nanorod radii are alsopresented. A nanorod-to-plane configuration is estimated utilizing a nanorod asymptoticiimethod. The nanorod-to-nanorod method approximates a nanorod-to-plane geometricconfiguration when one nanorod radii is held constant, and the second nanorod radii is iterativelyincreased until the corresponding radiative exchange converges.A theoretical method for cylinder-to-cylinder radiative heat exchange is formulated byutilizing a sphere approximation method. The sphere approximation method calls for dividingthe cylinders into smaller connected spheres and applying a previously published numericalmethod for near-field sphere-to-sphere radiative exchange. The overall radiative powerexchange is obtained by an additive ray tracing assumption. These results are compared toresults produced by a rigorous cylinder-to-cylinder radiative heat exchange method. The heatexchange of nanorods is plotted vs. gap to assess the impact of near-field radiative transfer asgap decreases. The unit sphere method is applied to nanorod configurations having length todiameter ratios of 3: 1, 5: 1, 7: 1. Graphical results of energy vs. nanorod radii are presented. Ananoradii/gap dimensionless relationship caused by geometric effects is found and related topower for nanorods of different aspect ratios and temperatures. A V -shaped configuration isconsidered with the results plotted for heat exchange vs. angle. An assessment of the number ofspheres required to produce an accurate approximation of the V -shaped configuration ofnanorods is presented. An error analysis of this method based on a ray blocking assumptionfrom neighboring spheres is discussed.An analysis is presented of a new device that utilizes near-field radiative heat transferincorporated with pyroelectric materials to convert spacecraft waste heat to electrical energy. Abackground of pyroelectric material devices is presented to show the background as applied tothis application. Near-field plane-to-plane radiative heat exchange is implemented forcalculation of the near-field radiative heat exchange within the device. The numerical method isiiibased upon an asymptotic approximation shown in previous work for sphere-to-sphere. Onesphere is iteratively increased with the radiative heat exchange continuously calculated untilconvergence, whereby, the geometric configuration approaches plane-to-sphere. Bysuperimposing this method on multiple spheres, the plane-to-plane approximation is achieved.This procedure is applied for silica and lithium fluoride coated planes. Near-field radiative heattransfer results expected in the spacecraft device are presented.

[发布机构] Rice University

[效力级别] engineering