Ricardo T. Páez-Hernández

Dynamic robustness and thermodynamic optimization in a non-endoreversible Curzon-Ahlborn engine

Abstract In this work we analyze the stability of a non-endoreversible Curzon–Ahlborn engine, taking into account the engines implicit time delays. When comparing the systems dynamic stability with its thermodynamic properties (efficiency and power output), we find that the temperature ratio τ = T 2/T 1 (T 1 > T 2 being the temperatures of the external heat reservoirs) represents a trade-off between stability and energetic properties. This result is in agreement with previous studies of the endoreversible Curzon–Ahlborn engine. The only dierence is that, in the non-endoreversible case, τ can only increase up to R (with R < 1, a parameter measuring the degree of internal irreversibilities), while in the endoreversible case it can grow up to one. Finally, we demonstrate that the total time delay does not destabilize the system steady-state, regardless of its length, and thus it does not seem to play a role in the dynamic-thermodynamic property trade-off.

Local Stability Analysis of a Thermo-Economic Model of a Chambadal-Novikov-Curzon-Ahlborn Heat Engine

In this work we present a local stability analysis of the thermo-economic model of an irreversible heat engine working at maximum power conditions. The thermo-economic model is based on the maximization of a benefit function which is defined by the ratio of the power output and the total cost involved in the plant’s performance. Our study shows that, after a small perturbation, the system decays exponentially to the steady state determined by two different relaxation times. In particular, we show that the relaxation times are function of the temperature ratio τ = T2/T1 (T1 > T2), the cost function ƒ and the parameter R (a parameter related to the degree of internal irreversibilities). We observe that the stability of the system improves as τ increases whereas for changes in ƒ and R, the stability properties are characterized by a rapid decay along the fast eigendirection as ƒ increases and R decreases. Finally, we discuss our results in the context of energetic properties.

General Properties for an Agrawal Thermal Engine

Abstract This paper presents a general property of endoreversible thermal engines known as the Semisum property previously studied in a finite-time thermodynamics context for a Curzon–Ahlborn (CA) engine but now extended to a simplified version of the CA engine studied by Agrawal in 2009 (A simplified version of the Curzon–Ahlborn engine, European Journal of Physics 30 (2009), 1173). By building the Ecological function, proposed by Angulo-Brown (An ecological optimization criterion for finite-time heat engines, Journal of Applied Physics 69 (1991), 7465–7469) in 1991, and considering two heat transfer laws an analytical expression is obtained for efficiency and power output which depends only on the heat reservoirs’ temperature. When comparing the existing efficiency values of real power plants and the theoretical efficiencies obtained in this work, it is observed that the Semisum property is satisfied. Moreover, for the Newton and the Dulong–Petit heat transfer laws the existence of the g function is demonstrated and we confirm that in a Carnot-type thermal engine there is a general property independent of the heat transfer law used between the thermal reservoirs and the working substance.

Dynamic and Thermodynamic Properties of a CA Engine with Non-Instantaneous Adiabats

This paper presents an analysis of a Curzon and Alhborn thermal engine model where both internal irreversibilities and non-instantaneous adiabatic branches are considered, operating with maximum ecological function and maximum power output regimes. Its thermodynamic properties are shown, and an analysis of its local dynamic stability is performed. The results derived are compared throughout the work with the results obtained previously for a case in which the adiabatic branches were assumed as instantaneous. The results indicate a better performance for thermodynamic properties in the model with instantaneous adiabatic branches, whereas there is an improvement in robustness in the case where non-instantaneous adiabatic branches are considered.

Comparative Performance Analysis of a Simplified Curzon-Ahlborn Engine

This paper presents a finite-time thermodynamic optimization based on three different optimization criteria: Maximum Power Output (MP), Maximum Efficient Power (MEP), and Maximum Power Density (MPD), for a simplified Curzon-Ahlborn engine that was first proposed by Agrawal. The results obtained for the MP are compared with those obtained using MEP and MPD criteria. The results show that when a Newton heat transfer law is used, the efficiency values of the engine working in the MP regime are lower than the efficiency values (τ) obtained with the MEP and MPD regimes for all values of the parameter τ=T2/T1, where T1 and T2 are the hot and cold temperatures of the engine reservoirs (T2<T1), respectively. However, when a Dulong-Petit heat transfer law is used, the efficiency values of the engine working at MEP are larger than those obtained with the MP and the MPD regimes for all values of τ. Notably, when 0<τ<0.68, the efficiency values for the MP regime are larger than those obtained with the MPD regime. Also, when 0.68<τ<1, the efficiency values for the aforementioned regimes are similar. Importantly, the parameter τ plays a crucial role in the engine performance, providing guidance during the design of real power plants.

Electromagnetic field produced by a cell phone

The present different types of industrial applications and products make use of electromagnetic energy. One way to this energy, the constitutes the radio frequency (RF), in which radio waves and microwaves are used in telecommunications. The RF emissions can be studied in terms of energy, radiation or electric field; radiation is defined as the energy propagation through space in the form of waves or particles. This electromagnetic radiation can be understood as the set of electric and magnetic waves that move together through space generated by the movement of electrical charges that may take place in a metallic conductive object, such as an antenna. The effects of electromagnetic radiation are so generally imperceptibles, by the above is importance of the study of these waves because of the use and management of mobile devices that go hand in hand with time of use and the dissipated energy and avoid injuries in the health. In this work we present an analysis of the issued electromagnetic radiation from a cell phone. We did measurements with an device electric field measure PCE-EM29. From these measurements, we observe that there an important variation of the electromagnetic field, without cellular signal and with cellular signal, so this we indicate that the electromagnetic waves could damage tissue in the ear and the face region.

Multifractal analysis of seismic geoelectric signals observed prior a earthquake of M6.7

In this work we studied the multifractal spectrum behavior calculated during the presence of a possible seismic electric signal (SES). This signal was detected in geolectrical time series registered prior a seism of M6.7 occurred on October 24, 1993 in México. We calculated the multifractal spectrum by using no overlapping windows of segments of 1 hour. Our results display the singularities spectrum calculated before, during and after possible SES, showing important differences in some parameters like the width and maxima values, among others, in the spectra. Those observations suggest that the physical system has different dynamical features along these processes and possibly as a precursor sign.

Linear Approximation of Efficiency for Similar Non- Endoreversible Cycles to the Carnot Cycle

In the present paper the non-endoreversible Curzon-Ahlborn, Stirling and Ericsson cycles as models of thermal engines are discussed from the viewpoint of finite time thermodynamics. That is, it is propose the existence of a finite time of heat transfer for isothermal processes, but the cycles are analyzed assuming they are not endoreversi‐ ble cycles, through a factor that represents the internal ireversibilities of them, so that the proposed heat engine models have efficiency closer to real engines. Some results of previous papers are used, and from the get expressions for the power output func‐ tion and ecological function a methodology to obtain a linear approximation of effi‐ ciency including adequate parameters are shown, similar to those obtained in that previous paper used. Variable changes are made right, like those used previously.

Razón de Compresión y Aproximaciones Lineales en el Ciclo de Curzon y Ahlborn

Resumen Para el llamado ciclo endorreversible de Curzon y Ahlborn se encuentran aproximaciones lineales para su eficiencia en terminos de la razon de los volumenes maximo y minimo alcanzados durante el ciclo (la razon de compresion), considerando el tiempo de duracion de los procesos adiabaticos. Se analiza el comportamiento de la razon de compresion respecto de la razon de temperaturas de las fuentes fria y caliente. Se encuentra que existe una relacion entre la razon de compresion y la razon de temperaturas de las fuentes fria y caliente, que mejora la eficiencia del modelo utilizado. Tambien se encuentra que una aproximacion a segundo orden debe llevar a un mayor acercamiento entre la eficiencia aproximada y los valores reportados en la literatura. Palabras clave: eficiencia, endorreversibilidad, razon de compresion, ciclos Curzon and Ahlborn Compression Ratio and Linear Approximations in the Curzon and Ahlborn Cycle Abstract Linear approximations of the efficiency as function of maximum and minimum volumes ratio (compression ratio) in the endorreversible Curzon and Ahlborn cycle are found, taking into account the time of duration of the adiabatic processes in this cycle. The performance of the compression ratio versus the temperatures of the cold and hot reservoirs ratio is analyzed. It is found that there exist a relation between compression ratio and temperatures of the cold and hot reservoirs ratio that improve the efficiency of the used model. It is also shown that a second order approximation should give a closer relation between the approximate efficiency and literature values.