摘要:

A Carnot-like irreversible power cycle is analyzed under maximum per-unit-time efficiency conditions. The model includes finite-rate heat transfers between the working fluid and the external heat reservoirs, heat leak between heat reservoirs, and internal dissipations of the working fluid. We present the results for the optimum distribution of the external and internal thermal heat conductances and the optimum area allocation ratio in terms of a dimensionless price parameter, the engine temperature ratio, and the internal irreversibility factor. The calculated optimized efficiencies agree with observed values for real power plants. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122023

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Direct evidence for freezing in two relaxor ferroelectrics,PbMg1/3Nb2/3O3andPbSc1/2Ta1/2O3,at a certain temperatureTf≠0 Kwas obtained from the temperature dependence of the maximum relaxation time,&tgr;max.It was shown that&tgr;max(T)follows the Vo¨gel–Fulcher (VF) law, and tends toward infinity as temperature approachesTf.The freezing temperatureTfderived from&tgr;max(T)coincides with the value ofTfobtained from the fit of frequency, &ohgr;, dependence of the temperature,Tmax,of the dielectric permittivity maximum to the same VF law. Thus, this result solves the controversy that the VF law for&ohgr;(Tmax)may not correspond to the freezing of the spectrum. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122024

出版商:AIP    

年代:1998

数据来源: AIP