Harvest Ambient Heat via Constraint-Shaped Phase-Change Cycles: Micro $ΔT$, Subcooled Liquid, and Liquid-Only Compression

Abstract: Conventional heat engines require two reservoirs; their efficiency is bounded by the Carnot limit. In a well-defined theoretical framework where the working fluid undergoes phase change in the presence of asymmetric constraints, that limit does not apply: the appropriate description is constraint-reshaped entropy distributions $P_{\infty}(S;λ)$. We give \emph{one} complete \emph{theoretical} design: micro temperature difference (1--2\,$^\circ$C), subcooled liquid, liquid-only compression, and asymmetric constraint phase change (R134a). The cycle absorbs heat from a \textbf{single} heat source (the environment; $q_{\mathrm{in}} = 0.9\,\mathrm{kJ}/\mathrm{kg}$ per cycle), delivers net useful work ($w_{\mathrm{net}} = +0.514\,\mathrm{kJ}/\mathrm{kg}$), and uses only standard components. The analysis is rigorous: energy and mass balance are closed; all property data are from NIST and are reproducible at the cited URL. We show that, within this framework, this constitutes single-heat-source power generation.