Abstract A model of irreversible Carnot-like power plant with n Carnot-like cycles is optimized. The irreversibilities of each cycle are: finite rate heat transfer between the working fluid and the external heat sources, internal dissipation of the working fluid, and heat leak between reservoirs; is extended to two or more of this combined model. Applying the Bellman’ Principle, we find the optimal recurrence relations for the allocation of the heat exchangers for thes power plants. The optimal allocation or effectiveness is determined by two design rules, applied alternatively: internal thermal conductance fixed or areas fixed. The optimal recurrence relations obtained for this combined model are invariant to the power and efficiency and to the heat transfer law.

Resumen Se optimiza un modelo de planta de potencia irreversible con n ciclos tipo Carnot. Las irreversibilidades de cada uno de los ciclos son: transferencia finita de calor entre el fluido de trabajo y los depósitos de temperatura, disipación del fluido de trabajo y fuga de calor entre ambos depósitos; es extendido a dos o más de este ciclo combinado. Aplicando el Principio de Bellman, encontramos las relaciones de recurrencia óptimas para la dimensión y efectividad de los intercambiadores de calor para modelo combinado. La óptima dimensión y efectividad se determina mediante dos reglas de diseño, aplicadas alternativamente: conductancias térmicas restringidas ó área total constante. Las relaciones óptimas para la dimensión ó efectividad obtenidas para este modelo combinado son invariantes a la potencia y eficiencia y a la ley de transferencia de calor.

A test bench was conceived in order to determine experimentally the flow coefficient [C V] for process control valves, operating with compressible fluids, under established regulations by the standards ANSI/ISA-75.02-1996 and ANSI/ISA-75.01.01-2002. This test bench is used to verify the calibration of valves with continually variable opening, after they have been repaired. The measurements in the test bench allow establishing the C V of these valves for various opening percentages. It was necessary to go through the C V equation for compressible fluids, to proceed with the flow sensor selection. This equation was obtained under similarity conditions by the equality of Euler numbers between prototype and model (test specimen). It is also described the electronic instrumentation for measuring flow, temperature and pressure difference, the design and the development of electronic circuits which control the instrumentation, and the algorithms for the operation and acquisition of measurements.

In this work we include, for the Carnot cycle, irreversibilities of linear finite rate of heat transfers between the heat engine and its reservoirs, heat leak between the reservoirs and internal dissipations of the working fluid. A first optimization of the power output, the efficiency and ecological function of an irreversible Carnot cycle, with respect to: internal temperature ratio, time ratio for the heat exchange and the allocation ratio of the heat exchangers; is performed. For the second and third optimizations, the optimum values for the time ratio and internal temperature ratio are substituted into the equation of power and, then, the optimizations with respect to the cost and effectiveness ratio of the heat exchangers are performed. Finally, a criterion of partial optimization for the class of irreversible Carnot engines is herein presented.

The design and assembly of a mechanism to bend schedule 80 stainless steel pipe up to 1½ in nominal diameter is presented. The use of a relatively small hydraulic actuator, coupled with a toothed wheel to produce the bending torque, is a novel approach to the process. The bending method uses two arms and a radius block in order to accomplish the bending. The hydraulic power consumption in the machine is very small (750 W, 3.4 MPa, 11.4 in/min). The strongest restriction upon the design is that it could be manufactured in small shops, with a cost low enough to be profitable even for a small production volume.

Se presenta el diseño y construcción de un mecanismo para doblar tubo de acero inoxidable, hasta de 1½ pulg de diámetro nominal y cédula 80. El sistema fue ideado para pequeñas industrias, que requieren una producción moderada con bajo costo. Emplea una unidad de potencia hidráulica muy reducida (750 W, 3.4 MPa, 11.4 in/min). Para doblar el tubo se emplea el método de doblado guiado. El par torsor se genera con un mecanismo novedoso de rueda dentada y un actuador lineal hidráulico. El tubo se sujeta a un dado de sujeción y un dado guía permanece fijo; el doblado se forma sobre el perímetro de este dado.

In this work, we consider the class of irreversible Carnot engines that results from combining the characteristics of two models found in the literature: the model in finite time and the model in finite size. The performance of the resulting model, including three irreversibilities, was doubly-optimized in finite time and finite size. The first optimization of power and efficiency, maintaining the thermal conductances fixed, was performed in finite time. Since the optimum time ratio from the first optimization, is the same for both maximum power and maximum efficiency, this means that the model can be newly optimized but now in finite size. Then, the second optimization, maintaining the overall heat transfer coefficient constant, was performed. For both optimizations, analytical expressions for the efficiency that maximizes the power and maximum efficiency were obtained. Changing the order in which partial optimizations were carried out, a remarkable optimal property was obtained: the resources of total contact time and the total area of heat transfer are proportional.

En este trabajo consideramos la clase de ciclos de Carnot irreversible que resultan de combinar las características de dos modelos: Modelo en tiempo finito y Modelo en dimensión finita. El desempeño del modelo resultante fue optimizado dos veces en tiempo finito y dimensión finita. Primero, optimizamos la potencia y la eficiencia en tiempo finito, manteniendo las conductancias térmicas fijas. Como el cociente de tiempos óptimo de la primera optimización es el mismo para potencia máxima y eficiencia máxima lo sustituimos, en las ecuaciones obtenidas, para que el modelo sea nuevamente optimizado pero ahora en dimensión finita. Entonces, la segunda optimización fue realizada, manteniendo el coeficiente global de transferencia de calor fijo. Obtuvimos, en ambas optimizaciones, expresiones analíticas para la eficiencia que maximiza la potencia y la máxima eficiencia. Al cambiar el orden en el cual las optimizaciones parciales fueron realizadas, se obtuvo una propiedad optimal notable: los recursos de tiempo total y área total de transferencia de calor resultan ser proporcionales.

In this paper we analyze a Brayton cycle with external and internal irreversibilities. The external ones come from heat transfer with coun-terflow heat exchangers in the cold and hot sides; the internal irreversibilities are given by the isentropic efficiencies of the compressor and turbine. Optimization is carried out with respect to the pressure ratio and the total inventory of the heat transfer units, using the e-NTU method. We show the analytical expressions for the efficiency that mazimizes work and the optimal allocation (size) of heat exchangers. We also analyze the asymptotic behavior of these expressions. The results obtained extend a Bejan's model and are more general and useful.

En este trabajo analizamos un ciclo Brayton con irreversibilidades externas e internas. Las externas provienen de la transferencia de calor mediante intercambiadores de calor de flujo cruzado de los lados frio y caliente; las irreversibilidades internas son producidas por las eficiencias isoentrópicas del compresor y la turbina. La optimización se realiza con respecto a la razón de presiones y al inventario total del número de unidades de trasferencia de calor, empleando el método e-NTU. Mostramos las expresiones analíticas para la eficiencia que maximiza el trabajo y la dimensión óptima de los intercambiadores de calor. También analizamos el comportamiento asintótico de estas expresiones. Los resultados obtenidos extienden un modelo de Bejan y son más útiles y generales.