© 1999 Robert A. Freitas Jr. All Rights Reserved.

Robert A. Freitas Jr., Nanomedicine, Volume I: Basic Capabilities, Landes Bioscience, Georgetown, TX, 1999

4.6.6 Temporal Thermal Gradients

On the timescale of nanomachine operations, typically 10^-9-10^-6 sec, the human body provides an essentially isothermal operating regime. However, medical nanorobots circulating in the bloodstream may encounter DT of ~3 K during one circulation time ~60 sec under normal circumstances (Section 8.4.1), a temporal thermal gradient of ~0.1 kelvin/sec, or >10 kelvin/sec at 1 mm tissue depth for a fingertip placed on a 600 K stove. Thermal nanosensors can take independent measurements differing by as much as ~100°C in ~10^-9 sec (e.g., Section 4.6.2), giving a maximum detectable thermal gradient of 10¹¹ kelvins/sec, far in excess of physiological rates.* Detection of the minimum ~1 microkelvin change between two measurements taken 1 sec apart probably represents the minimum practical temperature gradient, ~1 microkelvin/sec. For comparison, the record-holder in the insect world is the eyeless cave beetle Speophyes lucidulus, whose antennae can detect thermal change rates as small as ~3000 microkelvins/sec.⁸¹²

* Heating and cooling rates during ultrasonic cavitation in water exceed ~10⁹ kelvins/sec .⁶²⁵

The extraordinary thermal conductivity of diamond ensures that endogenous nanorobot waste heat is rapidly conducted to the surrounding aqueous medium. For example, a 1 micron³ diamondoid nanorobot generating 10 picowatts of onboard power at its core experiences a temperature differential of ~10^-8 K between core and perimeter (using thermal conductivity K_t = 2000 watts/m-K for diamond⁴⁶⁰), well below minimum detectable limits.

Last updated on 17 February 2003