Powering nanobots with body heat

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Journal of Special Topics
P1_9 Powering Nanobots with Body Heat
A. S. Dulay, R. A. Boadle, E. Wigfield Department of Physics and Astronomy, University of Leicester, Leicester, LE1 7RH. November 27, 2009 Abstract
This article discusses the feasibility of using variations in the human body temperature to power a medical nanobot. It is found that thermal energy gained from a Carnot cycle processis not -9 sufficient to power a typical nanobot. A typical medical nanobot requires 1x10 W, the model -17 outlined here finds that the maximum power a nanobot can gain is 5.7x10 W. Under normal -19 circumstances the power gain is only 9.8x10 W. Thus it is concluded that this process is not sufficient to act as the sole power source for such a nanobot.

Introduction Nanorobotics refers to themainly hypothetical discipline of building robots on the nanometre scale. Nanobots are still very much in a research and development phase [1], for example, a sensor only 1.5nm across has been developed capable of counting individual molecules in a chemical sample. One of the first uses for nanobots is likely to be for medical applications where they may be used to find and destroy cancer cells [2].How the nanobots produce the energy required to function is one of the key areas of development in nanobot design. This article discusses an idea for generating power by utilising internal body heat. The Human Power Source The example nanobot considered in this model has a volume of 2.7x10-17m3, this diameter is an approximation based on a published medical nanobot design [3]. As a nanobot travelsin the bloodstream it will experience temperature changes of several Kelvin as it moves from the body core to the extremities. Temperature differences such as this are utilised in Carnot-cycle heat engines which extract work from temperature gradients. In a reversible Carnotcycle, changes in temperature cause gas to expand or contract in a closed chamber driving a piston to do work on itssurroundings. A Carnot-engine’s efficiency, η, where T1 is the maximum temperature and T2 is the minimum temperature, is, �� = 1 − ��2 .
1

��

(1)

The power output of an ideal Carnot engine is given by �� =
∆T�������� �� η ��

(2)

where V is the volume of the nanobot’s thermal sink, CVol is the volumetric heat capacity of the substance used as a thermal sink, in this case water , ∆�� isthe temperature difference experienced, where ∆�� = ��1 − ��2 and t is the duration of the temperature change. For this model, it is assumed that the nanobot will not lose any heat through radiation to its surroundings.

1

P1_9 Powering Nanobots with Thermal Power November 27, 2009.

When the nanobot is at the core of the body, starting its cycle at the heart, the temperature is generallyagreed to be 310K (37oC) [4]. As a nanobot circulates around the body, a journey taking approximately 60s [5], it will undergo temperature changes depending on the various organs it passes through. The largest temperature gradient would be for a nanobot passing through a male’s testes where T1=310K and T2=307K [5]. Where CVol=4.186kJ.kg-1.K-1[6], the volume as stated earlier, V=2.7x10-17m3 , ∆��=3Kand t=60s, η =0.01 calculated from (1). Using (2), the maximum power output for the nanobot under these circumstances is 5.7x10-17W. Typically, nanobots such as the example robot would be used for arterial work close to the core of the body, and therefore would only undergo slight temperature changes of 0.4K[7], using previous values for V and Cvol and η =0.0013, in this case the maximum poweroutput given by (2) is 9.8x1019 W. In a very extreme case such as hyperthermia where the human body undergoes heat stroke, the core body temperature rises to 315K within a period of 10minutes. Where T1=315, T2=310K, V=2.7x10-17m3, CVol=4.186kJ.kg-1.K-1, ∆��=5K and t=600s, η=0.016 (2) giving a maximum power output of 1.5x10-17W. This produces less power than the Nanobot Power Requirements A medical...
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