Carbon Nanotube Arrays for Enhanced Thermal Interfaces to Thermoelectric Modules

摘要

Thermoelectric (TE) materials exploit the Seebeck effect in which an electric potential is generated from a supplied temperature gradient. The power output is a direct function of the magnitude of the temperature gradient applied across the TE module; therefore ideal thermal properties of the interfaces between the TE module and its respective heat source and sink are crucial for generating maximum power. Fundamentally, these interfaces act as a significant barrier to heat flow both to and from the TE module. Primarily due to increased surface contact area and inherently low diffusive thermal resistance, carbon nanotube (CNT) arrays are known to provide low thermal interface resistance. In this study, vertically aligned CNT arrays are synthesized on copper and graphitic foils. The substrate foils are first coated with a five-layer metal stack, where iron is the primary catalyst. They are subsequently subjected to microwave plasma chemical vapor deposition (MPCVD) to synthesize CNTs on one or both sides of the foil, which becomes an insertable thermal interface material (TIM) for TE modules. The thermal performance of the CNT array is evaluated using two methods. First, the thermal performance of the CNT array is evaluated by measuring the efficiency of a standard bismuth-telluride TE module with the CNT TIM applied. Experiments indicate that a copper foil coated on both sides with CNTs increases TE power generation by 60% relative to the absence of a TIM and by 25% relative to a bare copper foil. Data from the photoacoustic (PA) technique indicate that the thermal interface resistance decreases due to the presence of CNTs, reaching a minimum of 17 mm~2 K/W for a double-sided CNT film on copper. However, CNT arrays on graphitic foil showed no decrease in thermal interface resistance.