scholarly journals Performance of Universal Reciprocating Heat-Engine Cycle with Variable Specific Heats Ratio of Working Fluid

Entropy ◽  
2020 ◽  
Vol 22 (4) ◽  
pp. 397 ◽  
Author(s):  
Lingen Chen ◽  
Yanlin Ge ◽  
Chang Liu ◽  
Huijun Feng ◽  
Giulio Lorenzini
Keyword(s):  
Finite Time ◽  
Heat Engine ◽  
Nonlinear Function ◽  
Working Fluid ◽  
Cycle Model ◽  
Specific Heats ◽  
Power Outputs ◽  
Internal Irreversibility ◽  
Heat Engine Cycle ◽  
Engine Cycle

Considering the finite time characteristic, heat transfer loss, friction loss and internal irreversibility loss, an air standard reciprocating heat-engine cycle model is founded by using finite time thermodynamics. The cycle model, which consists of two endothermic processes, two exothermic processes and two adiabatic processes, is well generalized. The performance parameters, including the power output and efficiency (PAE), are obtained. The PAE versus compression ratio relations are obtained by numerical computation. The impacts of variable specific heats ratio (SHR) of working fluid (WF) on universal cycle performances are analyzed and various special cycles are also discussed. The results include the PAE performance characteristics of various special cycles (including Miller, Dual, Atkinson, Brayton, Diesel and Otto cycles) when the SHR of WF is constant and variable (including the SHR varied with linear function (LF) and nonlinear function (NLF) of WF temperature). The maximum power outputs and the corresponding optimal compression ratios, as well as the maximum efficiencies and the corresponding optimal compression ratios for various special cycles with three SHR models are compared.

Thermodynamic Optimization Characteristics of a Type I Absorption Heat Pump within Finite Time

2012 ◽  
Vol 204-208 ◽  
pp. 4250-4253
Author(s):  
Xi Ling Zhao ◽  
Yan Li ◽  
Lin Fu
Keyword(s):  
Heat Pump ◽  
Finite Time ◽  
System Performance ◽  
Heat Engine ◽  
Type I ◽  
Absorption Heat Pump ◽  
Friction Heat ◽  
Internal Irreversibility ◽  
Heat Engine Cycle ◽  
Engine Cycle

The absorption heat pump was studied with finite time thermodynamics. A four reservoirs model of absorption heat pump which is treated as an irreversible Carnot heat pump driven by an irreversible Carnot heat engine was established considering the heat resistance and the irreversibility of the internal cycle. A generalized optimization relationship between the main parameters and the corresponding conditions were derived. It is show that, two internal irreversibility parameters, the heat engine cycle and the heat pump cycle has different effects on system performance, and the reduction of the friction, heat loss, and internal dissipations of the equivalent heat pump cycle are more important than its reduction of heat engine cycle.

Thermodynamic Analysis of Waste-Heat Thermoelectric Generators

1997 ◽  
Vol 25 (3) ◽  
pp. 197-204
Author(s):  
Mamdouh el Haj Assad
Keyword(s):  
Thermodynamic Analysis ◽  
Finite Time ◽  
Thermoelectric Generator ◽  
Waste Heat ◽  
Heat Engine ◽  
Thermoelectric Generators ◽  
The Real ◽  
Dimensional Parameters ◽  
Heat Engine Cycle ◽  
Engine Cycle

A thermodynamic analysis of a real waste-heat thermoelectric generator is investigated. The thermoelectric generator is considered as a heat engine cycle process with internal irreversibilities. The efficiency of the thermoelectric generator is expressed in terms of two non-dimensional parameters which are to be optimized. A finite-time thermodynamic analysis is used to optimize the temperatures of the hot and cold junctions of the real thermoelectric generator. A comparison between ideal and real waste-heat thermoelectric generators is demonstrated.

Closed-Cycle OTEC Systems

1994 ◽  
Author(s):  
William H. Avery ◽  
Chih Wu
Keyword(s):  
Thermal Equilibrium ◽  
Constant Pressure ◽  
Cold Water ◽  
Heat Engine ◽  
Heat Removal ◽  
Working Fluid ◽  
Closed Cycle ◽  
Work Done ◽  
Heat Engine Cycle ◽  
Design Pressure

The Rankine closed cycle is a process in which beat is used to evaporate a fluid at constant pressure in a “boiler” or evaporator, from which the vapor enters a piston engine or turbine and expands doing work. The vapor exhaust then enters a vessel where heat is transferred from the vapor to a cooling fluid, causing the vapor to condense to a liquid, which is pumped back to the evaporator to complete the cycle. A layout of the plantship shown in Fig. 1-2. The basic cycle comprises four steps, as shown in the pressure-volume (p—V) diagram of Fig. 4-1. 1. Starting at point a, heat is added to the working fluid in the boiler until the temperature reaches the boiling point at the design pressure, represented by point b. 2. With further heat addition, the liquid vaporizes at constant temperature and pressure, increasing in volume to point c. 3. The high-pressure vapor enters the piston or turbine and expands adiabatically to point d. 4. The low-pressure vapor enters the condenser and, with heat removal at constant pressure, is cooled and liquefied, returning to its original volume at point a. The work done by the cycle is the area enclosed by the points a,b,c,d,a. This is equal to Hc–Hd, where H is the enthalpy of the fluid at the indicated point. The heat transferred in the process is Hc–Ha Thus the efficiency, defined as the ratio of work to heat used, is: . . . efficiency(η)=Hc–Hd/Hc–Ha (4.1.1) . . . Carnot showed that if the heat-engine cycle was conducted so that equilibrium conditions were maintained in the process, that the efficiency was determined solely by the ratio of the temperatures of the working fluid in the evaporator and the condenser. . . . η=TE–Tc/TE (4.1.2) . . . The maximum Carnot efficiency can be attained only for a cycle in which thermal equilibrium exists in each phase of the process; however, for power to be generated a temperature difference must exist between the working fluid in the evaporator and the warm-water heat source, and between the working fluid in the condenser and the cold-water heat sink.

Encoding a Model-Based Display with Dynamic Data

2000 ◽  
Vol 44 (22) ◽  
pp. 579-582 ◽  
Author(s):  
Leo Beltracchi
Keyword(s):  
Nuclear Power ◽  
Power Plants ◽  
Analytical Data ◽  
Heat Engine ◽  
Rankine Cycle ◽  
Direct Perception ◽  
Dynamic Data ◽  
Model Based ◽  
Heat Engine Cycle ◽  
Engine Cycle

A model-based display of the heat engine cycle for a nuclear power plant is defined and illustrated in terms of the thermodynamic first principles used to design the plant. The model-based display is a modified Rankine Cycle, the basic heat engine cycle for power plants. The display is made from measured process variables and the properties of water and presented on a CRT in iconic form, thereby providing a direct perception of the process. This structure of display design is an example of Rasmussen's means-ends hierarchy; starting with the abstract and ending with the specific display. Encoding the display with dynamic data aids operators in monitoring and interpreting the plant during transients and disturbances. Analytical data on the TMI-2 accident is used to illustrate the dynamic coding of the model-based display. The concepts discussed and illustrated are applicable to fossil and nuclear power plants and to other process industries.

Mass Engine Cycle

2014 ◽  
Author(s):  
Mostafa H. Sharqawy
Keyword(s):  
Mass Concentration ◽  
Heat Engine ◽  
Thermodynamic Cycle ◽  
High Mass ◽  
Permeable Membrane ◽  
Thermal Reservoir ◽  
Thermodynamic Conditions ◽  
Heat Engine Cycle ◽  
Positive Work ◽  
Engine Cycle

A new thermodynamic cycle is proposed named mass engine cycle. In the proposed cycle, mass is transferred from a high mass concentration reservoir to the cycle, mass is rejected to a low mass concentration reservoir, and a net positive work is generated. This is similar to heat engine cycles where heat is transferred from a high temperature thermal reservoir (heat source) to the cycle; heat is rejected to a low temperature thermal reservoir (heat sink), and a net positive work is generated. The heat engine cycle uses heat exchangers to transfer heat between the cycle and the thermal reservoirs, while the mass engine cycle uses membrane mass exchangers which transfer mass between the cycle and the mass reservoir. These membrane mass exchangers transfer water through a semi-permeable membrane and reject other substances. The driving force for the mass transfer is the hydrostatic and osmotic pressure differences. Similar to Carnot limit of the thermal efficiency of the heat engine cycle, a theoretical limit is obtained for the proposed mass engine cycle under reversible thermodynamic conditions.

Performance Optimization and Parametric Analysis of a Class of Solar-Driven Heat Engines

2010 ◽  
Author(s):  
Houcheng Zhang ◽  
Lanmei Wu ◽  
Guoxing Lin
Keyword(s):  
Heat Transfer ◽  
Heat Loss ◽  
Performance Optimization ◽  
Solar Collector ◽  
Heat Engine ◽  
Working Fluid ◽  
Convection Heat ◽  
Combined System ◽  
Heat Engines ◽  
Internal Irreversibility

A class of solar-driven heat engines is modeled as a combined system consisting of a solar collector and a unified heat engine, in which muti-irreversibilities including not only the finite rate heat transfer and the internal irreversibility, but also radiation-convection heat loss from the solar collector to the ambience are taken into account. The maximum overall efficiency of the system, the optimal operating temperature of the solar collector, the optimal temperatures of the working fluid and the optimal ratio of heat transfer areas are calculated by using numerical calculation method. The influences of radiation-convection heat loss of the collector and internal irreversibility on the cyclic performances of the solar-driven heat engine system are revealed. The results obtained in the present paper are more general than those in literature and the performance characteristics of several solar-driven heat engines such as Carnot, Brayton, Braysson and so on can be directly derived from them.

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