In this paper, we generalize two new statistical distributions, to improve the ability to model failure rates with non-monotonic, monotonic, and mainly bathtub curve behaviors. We call these distributions Generalized Powered Uniform Distribution and MOE-Powered Uniform. The proposed distributions’ approach is based on incorporating a parameter k in the power of the values of the random variables, which is associated with the Probability Density Function and includes an operator called the Powered Mean. Various statistical and mathematical features focused on reliability analysis are presented and discussed, to make the models attractive to reliability engineering or medicine specialists. We employed the Maximum Likelihood Estimator method to estimate the model parameters and we analyzed its performance through a Monte Carlo simulation study. To demonstrate the flexibility of the proposed approach, a comparative analysis was carried out on four case studies with the proposed MOE-Powered Uniform distribution, which can model failure times as a bathtub curve. The results showed that this new model is more flexible and useful for performing reliability analysis.

In conventional absorption refrigeration systems (ARS), the heat from the condenser is usually rejected by the environment in place to be used in the system, so recuperating this is a good alternative to enhance the system’s performance. For instance, in this paper, an alternative ARS in which LiBr/Water is used as a refrigerant mixture, where part of condensing heat is recovered via the solution heat recovery generator absorption cycle (HR-ARS) was energy and exergy evaluated. The influence of generator, condenser and evaporator temperatures, as well as the efficiency of the solution heat exchanger on the coefficient of performance, exergy performance and exergy destroyed of the HR-ARS system, were analyzed and compared with the traditional ARS system at the same working conditions. The results showed an increase between 5.8%–6.3% on the COP and 3.7%–9.5% in the exergy efficiency when condenser/absorber temperature was reduced from 40°C to 30°C. However, when the evaporation temperature rose from 5°C to 15°C, the COP (coefficient of performance) increased by around 8%, although this could be increased by 2.3%–6.3% if the generator temperature decreases from 100°C to 80°C. Moreover, the COP and exergetic performance for the HR-ARS is more significant at the lowest generator, condenser and evaporator temperatures, as well as at high efficiency in the solution heat exchanger, in comparison to ARS system. Furthermore, the COP and exergy performance for the HR-ARS system was improved by 2.57% to 3.11% and 0.22% to 0.7%, respectively, while the recovering condensation heat for generation is around 1.51%–3.76% lower than with the ARS. It also was found that for all ranges of evaporator and condenser temperatures, the COP for the HR-ARS system is around 3% higher than that obtained with the ARS at the three different generator temperatures here analyzed, while when the solution heat exchanger effectiveness was increased from 0.7–1.0, the total exergy destruction for the HR-ARS resulted be 3.24%–5.01% smaller than the ARS system. Finally, it can be concluded that the components with the most exergy destroyed in the systems (80% to 94%) are the generator and absorber.

El presente trabajo compara las propiedades termodinámicas, del agua saturada y sobrecalentada, obtenidas mediante correlaciones propuestas por dos grupos de autores contra aquellas correlaciones obtenidas por la IAPWS. Además, el COP de un ciclo de refrigeración por absorción es estimado, en el que es empleado como mezcla de trabajo, para distintas efectividades del intercambiador de calor de solución, mediante el uso de dichas correlaciones. Los resultados muestran que, al comparar las propiedades, estimadas por medio de las correlaciones propuestas, contra las obtenidas por la IAPWS, se concluye que hay una buena concordancia entre la mayoría de propiedades bajo estudio. Cuando se utilizan las correlaciones para estimar el COP del ciclo, las correlaciones propuestas por uno de los dos grupos de autores lo estiman muy bien, siendo la máxima desviación de cuando la efectividad del intercambiador de calor de solución es de ; mientras que, si se utilizan las correlaciones propuestas por el otro grupo de autores, la desviación es casi constante, promediando . Finalmente, una ventaja del uso de las correlaciones propuestas por ambos autores, en comparación con las obtenidas por la IAPWS, es que estas resultan de formulaciones de simples polinomios (n 6), lo que las hace más sencillas de programar, así como su posible implementación como herramienta computacional para el cálculo de las propiedades del agua durante el análisis y simulación de sistemas de refrigeración por absorción.

This paper shows an energy and exergy analysis of an ejector-compression refrigeration cycle, in which two heat exchangers are included to the system: 1) between the condenser and liquid separator (IHX-1) and 2) between the condenser and the evaporator (IHX-2), which is an alternative configuration proposed and this configuration is defined as ERC+IHX-1+IHX-2. The effect of evaporation temperature and the heat exchanger effectiveness on the energy and exergy efficiencies and the irreversibilities of each component of the cycle have been analyzed for refrigeration and air conditioning applications. The results show that for the alternative configuration and an effectiveness of IHX-1=80%, it results slightly with a higher COP than when the configurations work with an effectiveness of IHX-2=80%. However, the exergy efficiency increases when the evaporation temperature decreases. The components that show the highest contribution to the irreversibilities in the ERC+IHX-1+IHX-2 configuration are: the condenser, the compressor and the evaporator; whereas that the lowest contribution is due to the expansion valve and IHX-1. In addition, the alternative configuration proposed presents a higher exergetic efficiency and lower irreversibilities than the configurations ERC+IHX-1 y ERC+IHX-2 reported in the literature.