thermodynamic efficiency
Recently Published Documents

Abstract Based on meteorological and dust devil intensification observation data in the desert transition zone of the Xiaotang region in the northern margin of the Taklimakan Desert, and combined with GPS sounding in the hinterland of the Taklimakan Desert, this study investigated the improvement and evaluation of the dust devil parameterization scheme. The results indicate that the thermodynamic efficiency of dust devils after improvement was significantly higher than that before improvement, improving the values by 84.7%, 63.9%, 25.6%, 13.3%, 12.5%, 22.7%, 26.6%, 26.9%, and 21.4% for the hourly intervals from 09:00–17:00, respectively. The annual occurrence of dust devils after improvement was 431 times, 55.2% more than before improvement. The correlation coefficients of convective boundary layer height after improvement was 0.96, higher than that before improvement (0.908). After the improvement, the total annual dust emission time was 181.3 h, 95.9% less than that calculated using the day length before improvement, and 31.8% more than that calculated using sunshine time before improvement. After the improvement, the average vertical dust flux of a single dust devil was 0.25 m2/s, 68.8% less than that before improvement. After the improvement, the average annual dust emission from dust devils per square kilometer was 15.3 t/km2, significantly lower than the value of 320.5 t/km2 before the improvement, approximately one-twentieth of the value.

Abstract We study the Stochastic Thermodynamics of cell growth and division using a theoretical framework based on branching processes with resetting. Cell division may be split into two sub-processes: branching, by which a given cell gives birth to an identical copy of itself, and resetting, by which some properties of the daughter cells (such as their size or age) are reset to new values following division. We derive the first and second laws of Stochastic Thermodynamics for this process, and identify separate contributions due to branching and resetting. We apply our framework to well-known models of cell size control, such as the sizer, the timer, and the adder. We show that the entropy production of resetting is negative and that of branching is positive for these models in the regime of exponential growth of the colony. This property suggests an analogy between our model for cell growth and division and heat engines, and the introduction of a thermodynamic efficiency, which quantifies the conversion of one form of entropy production to another.

Abstract This paper considers the main CO2 power cycle configurations based on the Allam and JIHT cycles. In particular, the authors of the article have proposed new configurations of the power cycle. The efficiency of these cycles is studied as a function of the initial temperature and pressure of the working fluid. The thermodynamic efficiency can reach 65–66%. It is shown that the presence of regenerative heat transfer and the properties of supercritical carbon dioxide have a great influence on the thermal efficiency.

In integrated steel plants, the removal of phosphorous normally takes place during the primary basic oxygen furnace (BOF) steelmaking process. Phosphorous is usually introduced to the integrated steelmaking process through blast furnace additions, such as iron ore, coke, sinter, and fluxes. Among the others parameters such as optimizing the charging system, oxygen supply system, oxygen lance parameters of the converter, the flux quality in combination with temperature process control can improve the BOF efficiency of Dephosphorization. Phosphorus partition ratio (LP) is usually used to evaluate the thermodynamic efficiency of the dephosphorization of slags with different compositions in steelmaking processes. However, this parameter is only useful in equilibrium conditions, and it is not accurate when used to evaluate slag efficiency in industrial processes. Because of this, the aim of this work was to study the phosphorus partition ratio estimated from the experimental results in real plant conditions of two different BOF steel plants and compare them with well-known published models. In the present study, data from two steel plants (further Plant A and Plant B) were evaluated applying Healy’s, Suito and Inoui’s, Zhang’s as well as Assis’s equations. The calculated values were compared against measured values.

Abstract Starting from the observation that the reduced state of a system strongly coupled to a bath is, in general, an athermal state, we introduce and study a cyclic battery-charger quantum device that is in thermal equilibrium, or in a ground state, during the charge storing stage. The cycle has four stages: the equilibrium storage stage is interrupted by disconnecting the battery from the charger, then work is extracted from the battery, and then the battery is reconnected with the charger; finally, the system is brought back to equilibrium. At no point during the cycle are the battery-charger correlations artificially erased. We study the case where the battery and charger together comprise a spin-1/2 Ising chain, and show that the main characteristics - the extracted energy and the thermodynamic efficiency - can be enhanced by operating the cycle close to the quantum phase transition point. When the battery is just a single spin, we find that the output work and efficiency show a scaling behavior at criticality and derive the corresponding critical exponents. Due to always present correlations between the battery and the charger, operations that are equivalent from the perspective of the battery can entail different energetic costs for switching the battery-charger coupling. This happens only when the coupling term does not commute with the battery's bare Hamiltonian, and we use this purely quantum leverage to further optimize the performance of the device.

The article presents the results of the analysis of the operation of a heat pump in the system of low-temperature rectification of a propane-butane mixture. High-purity propane is obtained from a propane-butane mixture. A "rectification column-heat pump" system is proposed, which transforms the heat removed during the cooling of the component in the upper part of the column into heat absorbed during heating of the bottoms. In accordance with the energy balance of the system, it has been established that part of the heat pump condensation is not used in the distillation column, but is removed to the environment. The heat pump flow diagram contains one evaporator and two condensers. The operation of the heat pump is evaluated from the standpoint of thermodynamics – by the method of energy analysis of the cycle with R134 and R290 working substances, It has been established that the low thermodynamic efficiency of the heat pump is determined by external irreversible losses in the condensers and the evaporator The advantages of R290 as a working substance of the heat pump have been proved and the required theoretical volumetric capacity of the compressor has been determined.

The motivation of the present study is energy generation with thermonuclear fusion. Specifically, it is the attainment of breakeven conditions with a fusionable plasma whereby the output fusion energy is at least equal to the energy expended in creating the plasma and bringing it to fusionable conditions. This objective has eluded the physics community for the past seven decades. It is here suggested that perhaps the reason is that ever-bigger fusion machines are built, which unfortunately have brought results not in line with the expectations, in terms of desired fusion output. The opposite view is taken here, where attention is paid to the energy input, with the objective of minimizing the energy losses. One of the most important losses is a consequence of the limited thermodynamic efficiency of conventional engines that convert heat to work, thus generating the electricity involved in the energy input. This preliminary study shows that the efficiency can be improved if a novel thermodynamic cycle is used with heat recovery and recirculation. No attention is paid in the present study to the applicability of the novel cycle to a working engine but only to its feasibility. After the delineation of the concept, we use a simulation program to confirm that such approach is promising, and the objective of improving the thermodynamic efficiency of conventional heat-engines by at least 10% is realistic. Finally, the economic benefits are quantified of such substantial efficiency improvement on a world-wide scale. Mitigation of the damage to our environment due to the reduced heat rejection is also quantified.

The soma, dendrites and axon of neurons may display calcium-dependent release of transmitters and peptides. Such release is named extrasynaptic for occurring in the absence of synaptic structures. This review describes cooperative actions of three calcium sources on somatic exocytosis. Emphasis is given to the release of serotonin by the classical serotonergic leech Retzius neuron, which has allowed detailed studies of each step between excitation and exoctytosis. Trains of action potentials induce transmembrane calcium entry through L-type channels. If the frequency of action potentials is above 5 Hz, summation of calcium transients upon individual action potentials increases the intracellular calcium concentration to activate calcium–induced calcium release. The amplified calcium wave activates motochondrial ATP synthesis that fuels the transport of vesicles to the plasma membrane. Serotonin that is released activates autoreceptors coupled to phospholipase C. Production of IP3 produces release of calcium that sustains the large-scale exocytosis. The swiss-clock workings of the release machinery for somatic exocytosis has a striking disadvantage. The essential calcium-releasing endoplasmic reticulum that lays between resting vesicles and the plasma membrane becomes an obstacle for the vesicle transport. Such architecture reduces drastically the thermodynamic efficiency of the vesicle transport and elevates its energy cost..

Abstract New electrochemical ammonia (NH3) synthesis technologies are of interest as a complementary route to the Haber-Bosch (HB) process for distributed fertilizer generation, and towards exploiting ammonia as a zero-carbon fuel produced via renewably-sourced electricity.1–4 Apropos of these goals is a surge of fundamental research targeting heterogeneous materials5–7 as electrocatalysts for the nitrogen reduction reaction (N2RR). These systems generally suffer from poor stability and NH3 selectivity; competitive hydrogen evolution reaction (HER) outcompetes N2RR.8 Molecular catalyst systems can be exquisitely tuned and offer an alternative strategy,9 but progress has thus far been thwarted by the same selectivity issue; HER dominates. Herein we describe a tandem catalysis strategy that offers a solution to this puzzle. A molecular complex that can mediate an N2 reduction cycle is partnered with a co-catalyst that interfaces the electrode and an acid to mediate concerted proton-electron transfer (CPET) steps, facilitating N−H bond formation at a favorable applied potential and overall thermodynamic efficiency. Without CPET, certain intermediates of the N2RR cycle would be unreactive via independent electron transfer (ET) or proton transfer (PT) steps, thereby shunting the system. Promisingly, complexes featuring several metals (W, Mo, Os, Fe) achieve N2RR electrocatalysis at the same applied potential in the presence of the CPET mediator, pointing to the generality of this tandem approach.

Solar fuel generation from thermochemical H2O or CO2 splitting is a promising and attractive approach for harvesting fuel without CO2 emissions. Yet, low conversion and high reaction temperature restrict its application. One method of increasing conversion at a lower temperature is to implement oxygen permeable membranes (OPM) into a membrane reactor configuration. This allows for the selective separation of generated oxygen and causes a forward shift in the equilibrium of H2O or CO2 splitting reactions. In this research, solar-driven fuel production via H2O or CO2 splitting with an OPM reactor is modeled in isothermal operation, with an emphasis on the calculation of the theoretical thermodynamic efficiency of the system. In addition to the energy required for the high temperature of the reaction, the energy required for maintaining low oxygen permeate pressure for oxygen removal has a large influence on the overall thermodynamic efficiency. The theoretical first-law thermodynamic efficiency is calculated using separation exergy, an electrochemical O2 pump, and a vacuum pump, which shows a maximum efficiency of 63.8%, 61.7%, and 8.00% for H2O splitting, respectively, and 63.6%, 61.5%, and 16.7% for CO2 splitting, respectively, in a temperature range of 800 °C to 2000 °C. The theoretical second-law thermodynamic efficiency is 55.7% and 65.7% for both H2O splitting and CO2 splitting at 2000 °C. An efficient O2 separation method is extremely crucial to achieve high thermodynamic efficiency, especially in the separation efficiency range of 0–20% and in relatively low reaction temperatures. This research is also applicable in other isothermal H2O or CO2 splitting systems (e.g., chemical cycling) due to similar thermodynamics.