Using ANNs to approach to the energy performance for a small refrigeration system working with R134a and two alternative lower GWP mixtures

In this paper, an artificial neural network application to model a small refrigeration system is presented. The main objective of this study is an energy comparison of three refrigerants: R134a, R450A and R513A. The application of the artificial neural network was designed to model individually three typical energy parameters: the cooling capacity, the power consumption and the coefficient of performance, as a function of the evaporating temperature and the condensing temperature. Each model was validated using a technique called cross-validation, producing minimum relative errors of for the cooling capacity and the coefficient of performance, while 0.05 for the power consumption. Based on the appropriate validation results, computer simulations were performed to build 3D color surfaces. After inspecting these 3D color surfaces, it was concluded that R450A presented a slightly lower cooling capacity than R134a, actually a 10% reduction in the cooling capacity was estimated. Similar results were observed for the power consumption, that is, R450A had about 10% less power consumption than the other two refrigerants. On the other hand, it was observed that R134a and R513A presented very similar energy behaviors. With respect the COP, it was concluded that all three refrigerants showed a very similar behavior. After the analysis performed with the artificial neural networks and the use of 3D surface color, it was concluded that R450A and R513A are appropriate refrigerants to replace R134a in the short term in applications at medium evaporating temperature

Overview of low GWP mixtures for the replacement of HFC refrigerants: R134a, R404A and R410A

The current European F-gas regulation establishes restrictions in the use of fluoride refrigerants with a high global warming potential (GWP) in applications of refrigeration and air conditioning (RAC) systems. Moreover, a gradual limitation on the GWP weight of the fluoride refrigerants placed on the market is ongoing and will end with approximately one-fifth of today's offer. In this context, many of the RAC systems operate with refrigerants R134a, R404A, and R410A that have GWP values of 1300, 3943 and 2088, respectively, are being forced to be replaced by environmentally friendly alternatives, like hydrofluoroolefin (HFO) refrigerants and their mixtures with hydrofluorocarbons (HFC), which can be designed to present intermediate characteristics and become the ideal candidate many RAC applications. This work presents the most recent HFC/HFO/HC/R744 refrigerant mixture options for an alternative to the refrigerants mentiond above and compares their energetic and performance with the early developed mixture prototypes

Experimental exergy analysis of R513A to replace R134a in a small capacity refrigeration system

The replacement of HFCs using lower GWP refrigerants in the coming years is a priority to reduce the predicted climate change. The exergy analysis of vapor compression systems can help to identify the feasibility of alternative fluids in existing installations and the potential to improve them. In this sense, this paper presents an exergy analysis of an experimental setup which operates with R134a and the alternative HFO/HFC mixture R513A. The evaporating temperature is ranges between −15 °C and 5 °C, while the condensing temperature is set at 30 °C and 35 °C. In this analysis, the highest amount of exergy destruction rate is obtained at the compressor, followed by the evaporator. The maximum exergy efficiencies are observed at the condenser and the thermostatic expansion device. Finally, the average global exergy efficiency of R513A when replaced R134a in this refrigeration experimental setup is 0.4% higher (absolute difference), and with respect to the components, there is only slight reduction in efficiency in the condenser using R513A. Therefore, the R513A replacement is acceptable according to the second law of thermodynamics

Experimental study of R1234yf as a drop-in replacement for R134a in a domestic refrigerator

This paper presents an experimental study for three identical domestic refrigerators using R1234yf as a drop-in replacement for R134a. An alternative methodology was proposed to estimate the optimal mass charge for R1234yf; with the use of such methodology, new evidences were sought on the thermal behavior of the refrigerator compartments as well as at the heat exchangers. Additionally, energy performance for both refrigerants was measured, and, finally, a TEWI analysis was conducted. For the type of refrigerator evaluated, results showed that R1234yf presented an average (for the 3 refrigerators) of 0.4 °C for the fresh food compartment, and 1.2 °C for the freezer, among different charges with respect to R134a. The optimal charge for R1234yf was 92.2 g, which is about 7.8% lower than the one for R134a, which represents a small increase of 4% in energy consumption in comparison to R134a. Finally, the TEWI analysis for the R1234yf was 1.07% higher than the R134a.We thank Universidad de Guanajuato for the support in the realization of this research. We also want to thank the Company Honeywell (through Marco García) for the donation of the refrigerant R1234yf, and to acknowledge the support of Mabe TyP in the performing of the tests. The authors wish to thank to Montoro Sanjosé Carlos Rubín for their support in the editing of the English-language version of this paper

Exhaust Gas Heat Recovery for an ORC: A Case Study

This work aims at developing a heat exchanger (HEX) sizing approach considering the need to maximize the heat recovery within the limitations of pressure drop and space. The application consists in the recovery of the energy contained in exhaust gases coming from an internal combustion engine (ICE). Two heat exchanger geometries are selected as case studies. The design approach involves the application of design of experiments (DOE) techniques and computational fluid dynamics (CFD) simulations. DOE techniques are used to observe the influence of some selected parameters (factors) in the design of the heat exchangers, and CFD simulations are carried out to determine the performance of the heat exchanger. The information obtained is used to determine local Nusselt number correlations that are used for the design of the heat exchangers

Advanced Exergy Analysis of an Integrated SOFC-Adsorption Refrigeration Power System

In this chapter, an exergy analysis applied to a solid oxide fuel cell (SOFC)/vapor adsorption refrigeration (VAR) system is presented. The influences of four significant parameters (current density, inlet fuel temperature, fuel utilization and steam-to-carbon ratio) on the exergy efficiency of both the SOFC stack and the SOFC-VAR system are investigated. In order to do so, a mathematical model is constructed in Engineering Equation Solver (EES) software to generate the simulations. The analysis shows that the calculated exergy efficiency is around 8% lower than the energy efficiency for both cases. Moreover, it is found that most of the causes of irreversibilities in the system are due to electronic and ionic conduction in the components. It is also shown that the exergy efficiency is substantially sensitive to fuel inlet temperature, which is evidenced by a bending-over behavior. Finally, in accordance with the calculated efficiency defects, the main exergy destructions are present in the heat exchangers, the SOFC, the afterburner and the generator

The Cross-Cultural Adaptation of International Medical Graduates to General Practice in New Zealand

This study demonstrates that occupational success is an important factor in the adaptation of highly skilled migrants to host societies, as seen through the experiences of the international medical graduates (IMGs) who came to New Zealand and became general practitioners (GPs). New Zealand is reliant on IMGs to support and deliver quality health care to its population: IMGs constitute over 40% of the current medical workforce. The central contributions of this thesis are to three distinct discourses on the experiences of migrants. The first contribution is an investigation and critical analysis of the experiences of IMGs who came to practise medicine in New Zealand. During the course of analysing the primary data, and relating it to existing literature, it was observed there was a lack of a model that captured the essence of the specific acculturation of highly skilled migrants such as IMGs. Therefore, the second contribution is the development of a concise integrated framework - the Integrated Framework for Acculturative Research (IFAR), for the study of highly skilled migrants’ acculturation to new environments. The experiences of the IMGs who came to New Zealand have been used to develop and discuss the application of the IFAR to cross-cultural adaptation research. There is an historical component to these narratives as the IMGs in this research spanned nearly five decades of acculturation into New Zealand society. The third contribution is in the domain of qualitative research, where email interviews (e-interviews) have been used to gather data within the context of ethnography. While there has been significant literature, theories and models developed about cross-cultural and intercultural adaptation of migrants into host nations, there are gaps in the understanding of the experiences of highly skilled migrants, who are different from other types of migrants, given their predispositions and higher levels of human capital such as education and work experience. There is an emerging literature on this subject, to which this study adds. The IMGs in this study used their human capital to become medical practitioners in New Zealand, achieving their main motivation for migrating in the first place. The reasons the IMGs stated for migration are consistent with existing literature on ‘push’ and ‘pull’ factors; however for all of them, the primary reason was to pursue their medical careers in New Zealand. After arrival, most of them had to do additional training before they were allowed to practise independently. The medical training ranged from those required to achieve the registration of the Medical Council of New Zealand (MCNZ), to those needed to achieve the Fellowship of the Royal New Zealand College of General Practitioners (RNZCGP). The participants noted several challenges during their training period, including a lack of clear information on what was required; having to prove their ability despite many years of experience as medical practitioners; dealing with poor teachers for some; having to travel long distances to attend training seminars; and for a few, dealing with financial constraints. However, they all overcame such challenges and became successful independent GPs. Their age, pre-migration human capital, and post-migration motivation were essential in initiating their desired occupations in New Zealand. These three success factors are supported by emerging literature on highly skilled migrants. The early participants initially worked in hospital settings before choosing general practice. Some left because they experienced issues in the hospital environment such as tensions with local colleagues, and the need to work long unfriendly hours. All participants noted that the reasons for choosing general practice included their desire to work more closely with communities and to experience a greater variety of medicine. Additionally, many reported that the flexibility of working in general practice gave them a better work/life balance that allowed them to do other things within the community and outside of their general practice. Female participants noted that general practice was more conducive when raising a family, compared to hospital-based specialties. These are the strengths of general practice that are well documented in literature. While the participants did not note any major ongoing challenges, some reported being frustrated with the poor links between primary and secondary health care that impacted on the timely care of their patients. With an increase in chronic conditions and mental health issues, coupled with an ageing population, many participants reported that they needed more time and frequent consultations to treat certain patients. Given New Zealand’s co-payment system, participants reported having to consider the appropriate levels of care for patients with chronic conditions so as not to financially overburden them. For participants working in rural and economically deprived areas, there were other social factors that affected their medical practice, such as the high levels of family violence, sexual health issues, teenage pregnancies and substance abuse. These issues are supported by current literature regarding health and society in New Zealand. Despite the challenges they faced, all the IMGs planned on continuing to work in general practice in New Zealand for the foreseeable future. Migrants’ pledge of continuing in their chosen occupations in host nations can be a very good indicator of acculturation and integration. The MCNZ reported that nearly two-thirds of all IMGs left New Zealand two years post-registration. However, retention rates improved significantly once IMGs obtained their vocational registration. Occupational continuity sheds light on immigrants’ level of acculturation because it establishes that they are comfortable living among the hosts, and working in their chosen professions. This study demonstrates that occupational success is a key prerequisite to continuity and long-term integration into host societies. As highly skilled migrants, they could have gone to almost any country but they chose New Zealand. They remain here, having forged their medical careers and a lifestyle of their choosing. They now consider New Zealand their home, at least until they enter a different stage of their lives

Sustainability

The use of an internal heat exchanger in vapor compression refrigeration systems of one stage is a common practice because it helps to increase the cooling capacity in the evaporator. Furthermore, the use of refrigerants with low global warming potential is becoming more frequent due to environmental regulations worldwide. Thus, this paper presents an evaluation of the improvement produced by the inclusion of an internal heat exchanger cycle (IHXC) in an experimental installation from the viewpoint of exergy, economic and environmental through to exergy, exergoeconomics, and Specific Life Cycle Climate Performance (SLCCP) studies. The tests were conducted using R1234ze(E) as a replacement alternative to R134a in three evaporating temperature conditions: 4 °C, 9 °C, and 14 °C. Comparisons were made considering R134a in BRC mode versus R1234ze(E) in BRC and IHXC modes. Results show that a lower environmental impact is produced by an evaporating temperature of 14 °C with a reduction in SLCCP of 13.3% using IHXC and R1234ze(E). Moreover, the highest increase in exergy efficiency was observed for an evaporating temperature of 4 °C, with this increase being 9%, while the lowest increase in the total cost rate was observed for the same evaporating temperature, being 12.3% and 21.2% for BRC and IHXC modes using R1234ze(E), respectivelyMDPI Academic Open Access Publishinghttps://www.mdpi.com/2071-1050/14/10/600

Thermal Simulation of the Fresh Food Compartment in a Domestic Refrigerator

In the field of domestic refrigeration, it is important to look for methods that can be used to simulate, and, thus, improve the thermal behavior of the fresh food compartment. In this sense, this study proposes some methods to model the thermal behavior of this compartment when the shelves’ positions are changed. Temperature measurements at specific locations in this compartment were obtained. Several shelf position combinations were performed to use three 2D interpolation methods in order to simulate the temperature mean and the temperature variance. The methods used were: Lagrange’s interpolation, cubic spline interpolation and bilinear interpolation. Two validation points were chosen to verify the proposed methods. By comparing the experimental results with the computer simulations, it was possible to conclude that the method of Lagrange’s interpolation provided values that were not close to the real measured values. On the other hand, it was observed that the method of bilinear interpolation offered the best results, estimating values which were very close to the actual experimental measurements. These interpolation methods were used to build color thermal graphs that can be used to find some of the most appropriate shelf position combinations in this type of refrigerator. By inspection of these thermal graphs, it can be seen that the lowest average temperature was obtained when one shelf was located at 24.5 cm while the second shelf was located at 29.5 cm measured from the top of the compartment. In the same way, it can be seen that the minimum temperature variance was obtained when only one shelf was inside the compartment and this shelf was located at 29.5 cm

Desarrollo de un modelo físico para una instalación de producción de frío por compresión de vapor utilizando el refrigerante R134A. Validación experimental y aplicación para la simulación energética

Este trabajo doctoral esta enfocado al desarrollo de un modelo físico que permita simular el comportamiento de una instalación de producción de frío por compresión de vapor, partiendo de las condiciones y requerimientos de funcionamiento. El modelo tiene un grado alto de fiabilidad y puede ser usado en la simulación del comportamiento de la instalación, y de esta manera predecir un mejor funcionamiento encaminado a la operación energéticamente eficiente del sistema u otras aplicaciones. Por lo tanto, los objetivos generales planteados en esta tesis son: desarrollo y validación del modelo físico capaz de predecir el comportamiento estacionario de la instalación, y la aplicación del modelo para la simulación energética con el fin de ayudar a encontrar las condiciones de operación que optimicen el funcionamiento energético de la instalación