Source Temperature Ratio Research Articles

Power and Thermal Efficiency Optimization of an Irreversible Steady-Flow Lenoir Cycle.

Using finite time thermodynamic theory, an irreversible steady-flow Lenoir cycle model is established, and expressions of power output and thermal efficiency for the model are derived. Through numerical calculations, with the different fixed total heat conductances () of two heat exchangers, the maximum powers (), the maximum thermal efficiencies (), and the corresponding optimal heat conductance distribution ratios () and () are obtained. The effects of the internal irreversibility are analyzed. The results show that, when the heat conductances of the hot- and cold-side heat exchangers are constants, the corresponding power output and thermal efficiency are constant values. When the heat source temperature ratio () and the effectivenesses of the heat exchangers increase, the corresponding power output and thermal efficiency increase. When the heat conductance distributions are the optimal values, the characteristic relationships of and are parabolic-like ones. When is given, with the increase in , the , , , and increase. When is given, with the increase in , and increase, while and decrease.

Thermo-Ecological Analysis of Irreversible Dual-Miller Cycle (DMC) Engine Based on the Ecological Coefficient of Performance (ECOP) Criterion

In this paper, an ecological-based numerical analysis and optimization have been carried out for an air-standard irreversible Dual-Miller cycle engine with late inlet valve closing version using the ecological coefficient of performance (ECOP) criterion which covers finite rate of heat transfer, heat leak and internal irreversibilities. A detailed computational analysis has been performed in order to examine the general and optimum performances of the cycle. The results obtained based on ECOP function are compared with a different ecological function and with the maximum power output conditions. The consequences of ECOP, ecological function and maximum power output conditions are acquired based on the compression ratio, cut-off ratio, pressure ratio, Miller cycle ratio, source temperature ratio and internal irreversibility parameter. The influences of these parameters on the optimum performances are examined in detail.

Thermo-ecological performance analyses and optimizations of irreversible gas cycle engines

This paper reports ecological performance analyses and optimization of irreversible gas cycle engines such as Joule–Brayton cycle (JB), Atkinson cycle (AC), Otto cycle (OC), Diesel cycle (DC), Miller cycle (MC), Dual-Atkinson cycle (DAC), Dual-Diesel cycle (DDC), Dual-Miller cycle (DMC) engines based on the ecological coefficient of performance (ECOP) criterion which covers internal irreversibility, heat leak and finite-rate of heat transfer. Comprehensive computational analyses have been conducted to investigate the global and optimal performances of the gas cycle engines. The results obtained based on the ECOP criterion are compared with a different ecological function which is named as the ecologic objective-function and with the maximum power output conditions. The results have been acquired introducing the compression ratio, cut-off ratio, pressure ratio, air recharging ratio, source temperature ratio and internal irreversibility parameter. The changes of cycle performances with respect to these parameters are examined and demonstrated with figures.

Performance optimization of an air-standard irreversible dual-atkinson cycle engine based on the ecological coefficient of performance criterion.

This paper presents an ecological performance analysis and optimization for an air-standard irreversible Dual-Atkinson cycle (DAC) based on the ecological coefficient of performance (ECOP) criterion which includes internal irreversibilities, heat leak, and finite-rate of heat transfer. A comprehensive numerical analysis has been realized so as to investigate the global and optimal performances of the cycle. The results obtained based on the ECOP criterion are compared with a different ecological function which is named as the ecologic objective-function and with the maximum power output conditions. The results have been attained introducing the compression ratio, cut-off ratio, pressure ratio, Atkinson cycle ratio, source temperature ratio, and internal irreversibility parameter. The change of cycle performance with respect to these parameters is investigated and graphically presented.

The new thermo-ecological performance optimization of an irreversible three-heat-source absorption heat pump

The new thermo-ecological performance optimization of an absorption heat pump operating between three temperature levels with the losses of heat resistance, internal irreversibility and leakage is analyzed by taking the ecological coefficient of performance (ECOP) as an objective function. The new thermo-ecological criterion takes into account the first and second law of thermodynamics and is defined as the heating rate per unit loss rate of availability. The ecological coefficient of performance has been expressed and maximized in terms of the temperatures of the working fluid in the main components of the system. The corresponding optimal temperatures and other optimum performance parameters have been derived analytically, and the effects of the internal irreversibility, the heat leakage coefficient and the source temperature ratio on the global and optimal performances are discussed. The obtained results may provide a general theoretical tool for the ecological design of absorption heat pumps.

Performance optimization of three-heat-source irreversible refrigerators based on a new thermo-ecological criterion

This paper presents an optimization study of an irreversible refrigeration absorption system based on a new thermo-ecological criterion. The considered objective function is the ecological coefficient of performance ( ECOP). It takes into account the first and second law of thermodynamics and is defined as the cooling load per unit loss rate of availability. The ecological coefficient of performance has been expressed and maximized according to the temperatures of the working fluid in the main components of the system. The corresponding optimal temperatures and other optimum performance parameters have been derived analytically, and the effects of the internal irreversibility, the heat leakage coefficient and the source temperature ratio on the global and optimal performances are discussed. The results show that the maximum coefficient of performance ( COP) and ecological coefficient of performance ( ECOP) occurs for the same operating conditions.

Thermo-ecological performance optimisation of two stage irreversible refrigerators

The present study investigates the optimal performance of two stage refrigeration system based on thermo-ecological performance criterion. To maximise the ecological performance function, the working fluid temperatures are optimised. The optimal conditions such as cooling load, entropy generation rate and Coefficient of Performance (COP) are arrived analytically. The derived solution provides a general theoretical tool for ecological design of the two stage refrigerators. In this analysis, the effects of irreversibilities such as finite rate of heat transfer and heat leakage on the ecological performance are considered. The study also investigates the effect of intermediate temperature ratio and source temperature ratio on the ecological performance function.

Prediction of the transient and steady temperature distributions in a two-layer composite slab in contact with a plasma: exact closed-form solutions

Plasma heating of a one-dimensional two-layer composite slab with a homogeneously imperfect interface is solved by the method of separation of variable. The plasma is composed of a collisionless presheath and sheath on a wall partially reflecting and secondarily emitting ions and electrons. The heating of the composite slab from the plasma accounting for the presheath and sheath is determined from the kinetic analysis. This work proposes an analytical model to calculate the transient and steady temperature, temperature gradient and heating rate profiles inside the composite slab and provides quantitative results applicable to control the temperature evolution and the melting time of it. The predicted surface temperature of the composite slab as a function of time is found to agree well with a finite difference numerical solution. The effects of reflectivities of the ions and electrons on the wall, electron-to-ion source temperature ratio at the presheath edge, ion-to-electron mass ratio, ion charge number, ion ionization energy, plasma flow work-to-heat conduction ratio, solid thermal conductivity and specific heat ratios of the second-to-first layer, dimensionless second layer thickness, Biot numbers for first and second layers, on the temperature profiles are obtained. The thermal contact resistance between the layers to simulate the heat conduction into the second layer is also discussed.

A close-form solution to predict the total melting time of an ablating slab in contact with a plasma

An exact melt-through time is derived for a one-dimensional heated slab in contact with a plasma when the melted material is immediately removed. The plasma is composed of a collisionless presheath and sheath on a slab, which partially reflects and secondarily emits ions and electrons. The energy transport from plasma to the surface accounting for the presheath and sheath is determined from the kinetic analysis. This work proposes a semi-analytical model to calculate the total melting time of a slab based on a direct integration of the unsteady heat conduction equation, and provides quantitative results applicable to control the total melting time of the slab. The total melting time as a function of plasma parameters and thermophysical properties of the slab are obtained. The predicted energy transmission factor as a function of dimensionless wall potential agrees well with the experimental data. The effects of reflectivities of the ions and electrons on the wall, electron-to-ion source temperature ratio at the presheath edge, charge number, ion-to-electron mass ratio, ionization energy, plasma flow work-to-heat conduction ratios, Stefan number, melting temperature, Biot number and bias voltage on the total melting time of the slab are quantitatively provided in this work.

The effects of plasma characteristics on the melting time at the front surface of a film on a substrate: An exact solution

Plasma heating of a film on a substrate is solved by using the Laplace transform method. The plasma is composed of a collisionless presheath and sheath on an electrically negative bias film partially reflecting and secondly emitting ions and electrons. The heating of the film from the plasma accounting for the presheath and sheath is determined from the kinetic analysis. This work proposes an analytical model to calculate the melting time and heating rate of the front surface of a film on the substrate, and provides quantitative results applicable to control the temperature evolution and the melting time in the film. The predicted surface temperature of the film on the substrate as a function of time is found to agree well with experimental data. The effects of dimensionless bias voltage, reflectivities of the ions and electrons on the wall, electron-to-ion source temperature ratio at the presheath edge, ion-to-electron mass ratio, charge number, plasma flow work-to-heat conduction ratios, substrate-to-film solid thermal conductivity ratios, and film-to-substrate solid specific heat ratios on the melting time and heating rate of the front surface are obtained. The contact Biot number between the film and substrate to simulate the heat conduction into substrate is also discussed. The results show that the melting time is strongly dependent on the plasma parameters and thermal properties of the material.

Ecological coefficient of performance (ECOP) optimization for generalized irreversible Carnot heat engines

A performance analysis and optimization based on a new thermoecological criterion has been performed for a generalized irreversible Carnot heat engine with losses due to heat transfer across finite temperature differences, heat leak and internal irreversibilities. The ratio of the power produced by the engine to the loss rate of availability, which is named ecological coefficient of performance (ECOP), has been taken as an objective function for the optimization. The maximum of the ecological coefficient of performance function and the corresponding optimal conditions have been derived analytically. The effects of internal irreversibilities, heat leakage and source temperature ratio on the global and optimal performances have been investigated. The results are compared with those of the ecological performance criterion in the literature.

The effect of sheath on plasma momentum transport to an electrically biased surface

Ion and electron momentum fluxes transport to a biased workpiece surface in contact with a plasma are systematically and kinetically investigated in this study. Micro-electro-mechanical systems (MEMS), semiconductor technology, plasma etching, spray deposition, sputtering, cutting and surface treatment, etc. are strongly affected by momentum transfer from the plasma to workpiece. In this work, the plasma is composed of a collisionless presheath and sheath on an electrically negative biased surface that partially reflects or secondly emits ions and electrons. The presheath is an ionization region that continuously produces ions to maintain ion loss to the workpiece, while the sheath is a space-charge region that accelerates ions and retards electrons to the negative biased surface. The predicted total momentum flux at the wall including that of the ions and electrons as a function of negative electrically biased voltage is found to agree well with experimental data. The effects of the sheath and plasma parameters such as net current density, ion and electron reflectivities of the wall, ion-to-electron mass ratio, charge number, electron-to-ion source temperature ratio at the presheath edge, on the total momentum flux, ion and electron momentum fluxes, and their components through the sheath to the surface are obtained.

Plasma energy transport to an electrically biased surface

The total energy flux, including ion and electron energy fluxes, transport to a biased surface in contact with a plasma is systematically and analytically investigated in this study. Micro-electro-mechanical systems (MEMS), semiconductor technology, plasma etching, spray deposition, sputtering, cutting and surface treatment, etc. are usually controlled by energy transfer from the plasma to workpiece. In this work, the plasma is composed of a collisionless presheath and sheath on an electrically negative biased workpiece partially reflecting and secondly emitting ions and electrons. The presheath is an ionization region that continuously produces ions to supply ion loss to the surface, while the sheath is a space-charge region that accelerates ions and retards electrons toward the surface. Based on the kinetic analysis, the predicted ion density, velocity and energy transmission factor on the surface are found to agree well with experimental data. The effects of dimensionless ion recombination and electron absorption energies, reflectivities and second emissivities of the ions and electrons on the wall, ion-to-electron mass ratio, charge number, electron-to-ion source temperature ratio at the presheath edge, and net current density on energy fluxes across the sheath are obtained. Energies released from recombination of the ions and electrons on the surface play the most important role in energy transfer to the workpiece. The sheath should be accounted for predicting energy transport to a biased surface.