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A sublimation heat engine.

ABSTRACT: Heat engines are based on the physical realization of a thermodynamic cycle, most famously the liquid-vapour Rankine cycle used for steam engines. Here we present a sublimation heat engine, which can convert temperature differences into mechanical work via the Leidenfrost effect. Through controlled experiments, quantified by a hydrodynamic model, we show that levitating dry-ice blocks rotate on hot turbine-like surfaces at a rate controlled by the turbine geometry, temperature difference and solid material properties. The rotational motion of the dry-ice loads is converted into electric power by coupling to a magnetic coil system. We extend our concept to liquid loads, generalizing the realization of the new engine to both sublimation and the instantaneous vapourization of liquids. Our results support the feasibility of low-friction in situ energy harvesting from both liquids and ices. Our concept is potentially relevant in challenging situations such as deep drilling, outer space exploration or micro-mechanical manipulation.

SUBMITTER: Wells GG

PROVIDER: S-EPMC4366496 | biostudies-literature | 2015 Mar

REPOSITORIES: biostudies-literature

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A sublimation heat engine.

Wells Gary G GG Ledesma-Aguilar Rodrigo R McHale Glen G Sefiane Khellil K

Nature communications 20150303

Heat engines are based on the physical realization of a thermodynamic cycle, most famously the liquid-vapour Rankine cycle used for steam engines. Here we present a sublimation heat engine, which can convert temperature differences into mechanical work via the Leidenfrost effect. Through controlled experiments, quantified by a hydrodynamic model, we show that levitating dry-ice blocks rotate on hot turbine-like surfaces at a rate controlled by the turbine geometry, temperature difference and sol ...[more]

PMID: 25731669

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Project description:Laser and photocell quantum heat engines (QHEs) are powered by thermal light and governed by the laws of quantum thermodynamics. To appreciate the deep connection between quantum mechanics and thermodynamics we need only recall that in 1901 Planck introduced the quantum of action to calculate the entropy of thermal light, and in 1905 Einstein's studies of the entropy of thermal light led him to introduce the photon. Then in 1917, he discovered stimulated emission by using detailed balance arguments. Half a century later, Scovil and Schulz-DuBois applied detailed balance ideas to show that maser photons were produced with Carnot quantum efficiency (see Fig. 1A). Furthermore, Shockley and Quiesser invoked detailed balance to obtain the efficiency of a photocell illuminated by "hot" thermal light (see Fig. 2A). To understand this detailed balance limit, we note that in the QHE, the incident light excites electrons, which can then deliver useful work to a load. However, the efficiency is limited by radiative recombination in which the excited electrons are returned to the ground state. But it has been proven that radiatively induced quantum coherence can break detailed balance and yield lasing without inversion. Here we show that noise-induced coherence enables us to break detailed balance and get more power out of a laser or photocell QHE. Surprisingly, this coherence can be induced by the same noisy (thermal) emission and absorption processes that drive the QHE (see Fig. 3A). Furthermore, this noise-induced coherence can be robust against environmental decoherence.Fig. 1.(A) Schematic of a laser pumped by hot photons at temperature T(h) (energy source, blue) and by cold photons at temperature T(c) (entropy sink, red). The laser emits photons (green) such that at threshold the laser photon energy and pump photon energy is related by Carnot efficiency (4). (B) Schematic of atoms inside the cavity. Lower level b is coupled to the excited states a and ?. The laser power is governed by the average number of hot and cold thermal photons, and . (C) Same as B but lower b level is replaced by two states b(1) and b(2), which can double the power when there is coherence between the levels.Fig. 2.(A) Schematic of a photocell consisting of quantum dots sandwiched between p and n doped semiconductors. Open circuit voltage and solar photon energy ??(h) are related by the Carnot efficiency factor where T(c) is the ambient and T(h) is the solar temperature. (B) Schematic of a quantum dot solar cell in which state b is coupled to a via, e.g., solar radiation and coupled to the valence band reservoir state ? via optical phonons. The electrons in conduction band reservoir state ? pass to state ? via an external circuit, which contains the load. (C) Same as B but lower level b is replaced by two states b(1) and b(2), and when coherently prepared can double the output power.Fig. 3.(A) Photocell current j = ??(??) (laser photon flux P(l)/?(?(l))) (in arbitrary units) generated by the photovoltaic cell QHE (laser QHE) of Fig. 1C (Fig. 2C) as a function of maximum work (in electron volts) done by electron (laser photon) E(?) - E(?) + kT(c) log(?(??)/?(??)) with full (red line), partial (brown line), and no quantum interference (blue line). (B) Power of a photocell of Fig. 2C as a function of voltage for different decoherence rates , 100?(1c). Upper curve indicates power acquired from the sun.

Project description:About 500 experimental heat transfer data taken from the open literature and relevant to the most thermally solicited area (i.e., the throat region) of liquid rocket engine thrust chambers, are collected and manipulated. This collection is the outcome of a thorough and exhaustive survey of the available experimental data of hot-fire tests produced to date. Among the test cases reported in the literature, only those with a throat heat transfer that is not affected by laminar flow, evident soot deposition, or intended non-uniform propellant injection are collected. The heat transfer is typically measured in terms of wall heat flux and temperature. Sometimes the heat transfer coefficient, which is a combination of these two terms, is provided. Each collected heat transfer measurement is supplied with data relevant to the specific operative condition of the considered test case, as well as the configuration of the adopted thrust chamber and propellant injector. Among the different considered propellant combinations, most of the experiments are made burning oxygen-hydrogen or oxygen-kerosene. Experiments made using mildly heated and compressed air, although not a rocket propellant, are also considered because of their relevance to the problem of interest. The collected dataset, called the primary dataset, is numerically elaborated to create a secondary dataset that is more thorough and consistent than the primary one. In fact, also thanks to the adoption of a suitable hot-gas flow modeling, the secondary dataset contains elaborated data that are not always available in the selected open-literature as well as the non-dimensional numbers that are associated with the heat transfer and are typically used in regression rules, like the Nusselt and the Stanton numbers. The datasets presented in this manuscript are discussed and used to find heat transfer regressions in the research manuscript "Overview and analysis of the experimentally measured throat heat transfer in liquid rocket engine thrust chambers", Acta Astronaut. 184 (2021), 46-58 [1].

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A sublimation heat engine.

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A sublimation heat engine.

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