Abstract
Thermodynamically isolated systems normally relax to equilibria characterized by single temperatures; however, in recent years several systems have been identified that challenge this presumption, demonstrating stationary temperature gradients at equilibrium. These temperature gradients, most pronounced in systems involving epicatalysis, can be explained via an underappreciated symmetry in the Van ’t Hoff equation.
Acknowledgment
The author thanks M. W. Anderson, T. Herrinton, G. Levy, D. Miller, and W. F. Sheehan for their comments and insights. Figures were prepared by S. Grubb and C. Ibarra. The author is indebted to the two anonymous reviewers whose critical comments greatly improved the paper.
Appendix
This appendix describes a device designed to accentuate STGs. Its underlying effects have been corroborated by experiments, and it is currently the subject of laboratory research and development [48].
The STG device consists of two narrowly spaced parallel epicatalytic surfaces (S1 and S2) that are differentially active with respect to a dimeric gas AB (Fig. 7). S1 preferentially dissociates the dimer endothermically (AB +
Surfaces S1 and S2 are separated by a small gap (width
The device’s areal power density should scale as
The temperature differential
Thermal shorting between S1 and S2 should be minimized. Radiative heat backflow from S2 to S1 is inevitable if
Radiative and conductive heat backflows appear manageable, but gas convection is unavoidable because it is precisely gas flow that cycles chemical energy between S1 and S2. Detailed analysis and numerical simulations [53] indicate that, for most room-temperature STG designs, convection dominates heat transfer (and thermal shorting), whereas at high temperatures radiation does. Analysis and simulations also indicate that sizable stationary temperature differences should be achievable. For example, it is predicted that a 1-micron thick cavity containing hydrogen-bonded dimers (e. g., methanol, formic acid) might attain temperature differences of
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