Willian Duarte

Federal University of Minas Gerais | UFMG · Departamento de Engenharia Mecânica (DEMEC)

The analysis of the amount of mass in a refrigeration system is directly related to the coefficient of performance of the cycle. The mass inventory of solar-assisted heat pumps is still more relevant because the evaporation temperature varies greatly according to the solar radiation flux. In that way, a mass charge model for DX-SAHP operating with...

The expansion device plays a crucial role in the operation of heat pumps and refrigeration systems, making its study integral to advancements in the fields of refrigeration and heating. Among various expansion devices, the Thermostatic Expansion Valve (TEV) stands out due to its rapid response time and mechanical nature, which grants it high contro...

The aim of this paper is to determine the temporal response of T-type and K-type thermocouples with different coating thicknesses. In applications with high thermal gradients, the thermocouple can experience thermal fatigue caused by its exposure to high temperature levels and severe thermal cycling involving heating and cooling of the sensor. Repe...

The refrigeration industry has been moving towards environmentally friendly refrigerants, and R744 (carbon dioxide) is a potential solution. The use of R744 as a refrigerant has been gaining attention due to its low environmental impact, non-toxic nature, and favorable thermodynamic properties. Despite these advantages, manufacturing small-capacity...

The Montreal Protocol and its amendments have been increasingly restricting the use of refrigerant fluids, considering the significant environmental impact they can cause. However, a large portion of refrigeration and air conditioning units in developing countries like Brazil still operate with R-22, and discarding these equipments solely due to th...

The objective of this work is to present a distributed condenser steady state mathematical model, written in Python language, of a H 2 O/NH 3 /H 2 diffusion and absorption fridge for vaccine storage in regions without electrification. The refrigerator thermal input in ammonia vapor generator set was originally promoted by Joule effect through an 80...

This paper presents the development of a mathematical model for a direct-expansion solar-assisted heat pump (DX-SAHP) operating in steady-state. The mathematical model was implemented using the scientific software EES and using a code written in Python. It was utilized a lumped parameter model for the heat exchangers and a semi-empirical model for...

RESUMO: Para o bom uso do sistema de ar condicionado é necessário o adequado dimensionamento da carga térmica. A carga térmica (taxa de transferência de calor a ser removida do ambiente climatizado) depende de diversos fatores como: as dimensões do ambiente, número de pessoas presentes, condições climáticas, entre outros. Esse cálculo pode ser real...

The high cost of electricity has done that the air condition sector search for alternatives to produce cold efficiently. It is a necessity, especially in Brazil, where 17% of the total electricity consume in residences is due air condition systems. Many studies have presented technical-economic data of heat-pumping and air conditioner systems but t...

An expansion device is one of the key components of heat pump systems. Although in the literature there are several studies that analyze the effect of opening the expansion valve on heat pumps, none of them reported this effect for heat pumps that operate with solar energy. In this study, the mass flow rate characteristics through an expansion devi...

In 2017, electrical air conditioning systems represent an approximate consumption of 20% of the total electrical energy consumed in Brazilian homes. In addition, air conditioning systems may account for 85% of the consumption of residential electric energy in the peak of summer and in commercial establishments approximately 40% of the electric ener...

This review article aims to investigate the arrangements, energy performance, economic viability and environmental impacts of solar assisted heat pumps (SAHP) integrated with renewable energy sources. Such equipments have been the object of recent studies in the area of energy and sustainability as it involves the conversion of solar energy into th...

A use of CO2 operating in a transcritical cycle has been proven for heat pumps is a demonstrably viable and considerably interesting option due to the environmental advantages of CO2 over other refrigerant gases. In order to improve the energy performance of systems that use heat pumps, integrating a type of energy such as renewable geothermal, sol...

The use of heat pumps to heat water instead of electric heaters is a way to reduce energy consumption and consequently greenhouse gas emissions. In this context, carbon dioxide (CO2 or R744) as a refrigerant fluid has drawn the attention of several researchers in the refrigeration field. Several works in the literature evaluated the performance of...

Measuring mass flow rate in refrigeration systems with flow meters can be expensive when taking into account the cost of the equipment itself and the costs related to installation and maintenance. A mode based on Artificial Neural Networks can be used to predict the value of the mass flow, at a low cost, through easily observed and measured paramet...

This work is a theoretical and experimental study about the refrigerant charge inventory in a CO2 Direct Expansion Solar Assisted Heat Pump to heating residential water. The effects of variation in the irradiation levels were analyzed for 72 experimental points, and a mathematical model was developed to predict the amount of refrigerant in several...

In this work, a cascade refrigeration system operating with four different ecological refrigerant pairs was modeled. This system uses R744 (Carbon dioxide) in the low-temperature cycle and operates with R290 (propane), R1234yf (2,3,3,3-tetrafluoropropene), R152a (1,1-difluorethane), and R717 (ammonia) in the high-temperature cycle. Energetic, exerg...

This work presents a study for examining the viability of Solar Geothermal Hybrid Source Heat Pump systems to produce domestic hot water in Brazilian-type climates. The system considered has an open-loop ground-water (aquifer) and an uncovered solar collector that can be used in a separate or connected in series topology. The refrigerant chosen for...

In the past decades, combined solar energy with heat pump systems has been one of the very widespread ways to improve the efficiency of conventional heat pumps. In that way, this paper presents an experimental analysis of the influence of environmental conditions in a small size DX-SAHP operating with CO2 as refrigeration fluid to heat water. The v...

In this work, a simulation model was developed to predict the thermal performance and discharge temperature of a heat pump and compare with the experimental data. In this analysis a lumped model will be used for each component of the system. The effect of various parameters, including collector area, storage volume, solar radiation, windy speed, an...

Abstract. One way to reduce electricity consumption is to use heat pumps assisted by solar energy instead of electric heaters. Several studies were found using solar-assisted heat pumps that use either a thermostatic expansion valve or an electronic expansion valve, but there is a few work on solar-assisted heat pumps using capillary tubes despite...

The present work is a theoretical/experimental study about the fluid mass charge in a direct expansion solar assisted heat pump (DX-SAHP), for the supply of domestic hot water. The heat pump operates in the transcritical cycle, with carbon dioxide as the refrigerant. CO2 is a natural fluid that has an ozone depletion potential (ODP) equal to zero a...

Due to more stringent environmental legislation over the years, the automotive sector seeks alternatives to reduce the emission of pollutants. The air conditioning system consumes a good deal of energy from the combustion engine. This work presents a comparative analysis of conventional and an air conditioning with water-cooled condenser using R134...

In recent years, the international community has been continuously encouraged the development of new vapor compression refrigeration systems, that operate with ecological refrigerants, to replace systems with non-ecological refrigerants. In view of this need, this paper presents a mathematical model of a small cooling capacity vapor compression ref...

This paper presents a steady-state model of a vapor compression refrigeration system (VCRS) that produces 1200 l of chilled water (5 °C) for an indirect expansion air-conditioning system (IEACS) and 600 l of hot water (40 °C) for bath. The proposed model was used to design a VCRS with reduced geometric structure and to compare the environmental, en...

This work presents a study for examining the viability of Solar Geothermal Hybrid Source Heat Pump systems toproduce domestic hot water in Brazilian climates. The system considered has an open loop ground underground (aquifer)water and an uncovered solar collector that can be use separately or connected in series topology. The refrigerant chosenfor...

This paper presents the development of a numerical, iterative and nonisentropic model for the thermodynamic processes of a reciprocating compressor of a refrigeration system operating at steady state. The mathematical model was implemented using the scientific software Engineering Equation Solver (EES) and it is based on the application of the ener...

In a Direct Expansion Solar Assisted Heat Pump (DX-SAHP), a valuable part of the energy is provided from solar radiation. The solar radiation can fluctuate during the day affecting the performance of the system. The impact of a fixed opening in the expansion device on the system performance is not well known, especially for a small-size solar assis...

One option to reduce the energy consumption to produce domestic hot water is to replace the electrical heaters by direct expansion solar assisted heat pumps. Although, there are many studies on the performance of this system, there are few studies on economic analysis of the equipment. In this paper, an economic analysis comparing the payback of he...

An important step during a project of a heat pump system is choosing a more suitable refrigerant. This paper presents a comparative study among refrigerants for a small direct expansion solar assisted heat pump (DX-SAHP). The mathematical model used in this study is presented in detail and validated from an experimental setup. The R134a is the refe...

Energy use is one of the main indicators for the economic and social development of a country, reflecting directly in the quality of life of the population. The expansion of energy use together with the depletion of fossil resources and the poor efficiency of energy systems have led many countries in recent years to invest in renewable energy sourc...

Heating water through of heat pump has a reduced consumption of electric energy due to the use of the energy available in the environment. This work explores the lack of studies of direct expansion solar assisted heat pump (DX-SAHP) using refrigerants with low Global Warming Potential (GWP). The numeric model proposed uses a lumped parameter model...

Energy use is one of the main indicators for the economic and social development of a country, reflecting directly in the quality of life of the population. The expansion of energy use together with the depletion of fossil resources and the poor efficiency of energy systems have led many countries in recent years to invest in renewable energy sourc...

This study is developed to evaluate the possibility of R1234yf to be a drop-in replacement for a pre-designed system with R134a, including the characterization of control system in a vapor compression system. The control algorithms are required for regulating the refrigerant flow rate into the evaporator and their control parameters depend intrinsi...

Abstract. With the increasing demand and cost of Brazilian electric energy, alternatives for the production of energy from renewable sources, among them solar, have been investigated. This work presents a literature review on this topic, focusing on photovoltaic energy and the use of reversible hydroelectric plants. It includes a case study of OPV...

Abstract. Gaps between stationary and rotating parts are inevitable in turbomachines. The leakage flow between the rotor-stator gaps of the high pressure region to the low pressure region can be reduced using seals. The most commonly used seals or seals in turbines are those of the brush seal type, seal oring, grooves, retainer, felt, gaskets, mech...

Abstract. There are several studies that compare the performance of R-134a and R-1234yf, but no yet for a direct expansion solar assisted heat pump (DX-SAHP). This theoretical analysis was made using lumped models for heat exchangers and a black box model for the hermetic R134a compressor. This modeling was validated using experimental results from...

Resumo: A compressão de vapor é a principal maneira de se obter efeito refrigerante. Embora sua eficiência seja alta, o uso dos fluidos refrigerantes (CFC e HFC) contribuem para o aquecimento global e o custo da energia para o acionamento de compressores é crescente. As dificuldades mencionadas mostram que é necessário o conhecimento mais apurado d...

Este artigo apresenta um modelo matemático físico, para um compressor alternativo operando em regime permanente. Para o desenvolvimento deste modelo, o compressor foi dividido em três volumes de controle: região pré-compressão, câmara de compressão, e região pós-compressão. Na câmara de compressão foram utilizados métodos numericos juntamente com r...