Papers by Diogo Lôndero da Silva
This paper presents an experimental and numerical study to evaluate the thermal-hydraulic perform... more This paper presents an experimental and numerical study to evaluate the thermal-hydraulic performance of light commercial capacity evaporators operating under frosting conditions. A tube-fin heat exchanger was tested on a closed-loop wind-tunnel considering the fan performance. A visual analysis of the frost formation processes was carried out to compare the frost layer morphology in different conditions. A mathematical model was developed and the numerical results were compared with the experimental accumulated mass of frost, air flow rate and cooling capacity, with all the predictions falling within the experimental band of uncertainties. Based on this comparison, a frost density correlation was proposed for a typical range of light commercial refrigeration applications. The results show evaporator cooling capacity reductions up to 40% due to frost formation process. Moreover, the effects of air flow reduction and low conductivity frost layer on the overall thermal resistance were analyzed, when it was found that the former is the main cause of the cooling capacity reduction under frosting conditions.
Florianópolis, 2012
Dedico este trabalho ao apoio dos meus pais José Danilo e Lizete, à amizade do meu irmão Douglas ... more Dedico este trabalho ao apoio dos meus pais José Danilo e Lizete, à amizade do meu irmão Douglas e a companhia e carinho da minha amada Vanina.
Procceedings of the 19th Brazilian Congress of Thermal Sciences and Engineering
Proceedings of the 26th International Congress of Mechanical Engineering, 2021
Frost accretion on a tube-fin evaporator surface raises its thermal and hydraulic resistances, wh... more Frost accretion on a tube-fin evaporator surface raises its thermal and hydraulic resistances, which in turn deteriorates the cooling capacity of the refrigeration system. For this reason, periodic defrost operations are required to recover the initial performance of the system. Most defrost techniques rely on supplying heat to the frost layer. Due to technological and thermodynamic limitations, only part of the heat supply is effectively used to melt the frost built-up on the evaporator, while the rest increases the refrigerator thermal load. Therefore, the amount of heat dissipated, the duration of a defrost operation, and the time between two consecutives defrost operations must be considered for properly designing the defrost system. The present paper assesses, by means of a simulation model that considers the airflow reduction with frost accretion, the effects of evaporator operating and geometric conditions, and defrost cycle parameters on the time-averaged cooling capacity. T...
Chemical engineering transactions, 2021
Fruits and vegetables are fresh products that are highly perishable and refrigeration is widely a... more Fruits and vegetables are fresh products that are highly perishable and refrigeration is widely applied to extend food shelf-life under postharvest conditions. The main phenomena associated with the refrigeration process are heat and mass transfer, which directly influence food decay. For this reason, the objective of this research is to evaluate the thermal and mass profiles of fresh strawberry and lettuce, under refrigeration. Strawberry and lettuce samples were harvested from a hydroponic system and stored at 5 ± 1 °C for 5 days under low relative humidity conditions (50-60 %). In order to correlate the two main phenomena, the mass transfer and cooling kinetics parameters were quantified. The mass loss results demonstrated a greater reduction for lettuce (21.7 %) than for strawberry (16.7 %) samples, which is related to the larger surface to mass ratio of lettuce. The strawberry transpiration rate presented a stable behavior after the first day of storage (1.31 g kg-1 h-1), which...
This work is aimed at the optimal design (i.e. number of transversal and longitudinal tube rows, ... more This work is aimed at the optimal design (i.e. number of transversal and longitudinal tube rows, number of fins) of fan-supplied tube-fin evaporators for light commercial refrigeration applications operating under frosting conditions. Quasi-steady-state algebraic models were put forward for the refrigeration cycle and its components for computing not only the cooling capacity depletion due to the evaporator frosting over time, but also the changes experienced by the evaporating temperature and its effect on the compressor power. Transient, unsteady-state algebraic models were also advanced to account for the temperature and humidity variations inside the refrigerated compartment, and so the compressor runtime. The optimization exercise aiming at system-level energy consumption minimization revealed that, when the evaporator volume and width are held constrained, the lowest energy consumption was achieved for evaporators with evaporators with (36), (44) and (63) (transversal lon...
Energies, 2021
Modern refrigerators are equipped with fan-supplied evaporators often tailor-made to mitigate the... more Modern refrigerators are equipped with fan-supplied evaporators often tailor-made to mitigate the impacts of frost accretion, not only in terms of frost blocking, which depletes the cooling capacity and therefore the refrigerator coefficient of performance (COP), but also to allow optimal defrosting, thereby avoiding the undesired consequences of condensate retention and additional thermal loads. Evaporator design for frosting conditions can be done either empirically through trial-and-error approaches or using simulation models suitable to predict the distribution of the frost mass along the finned coil. Albeit the former is mandatory for robustness verification prior to product approval, it has been advocated that the latter speeds up the design process and reduces the costs of the engineering undertaking. Therefore, this article is aimed at summarizing the required foundations for the design of efficient evaporators and defrosting systems with minimized performance impacts due to...
Journal of Food Engineering, 2021
Abstract The main phenomena involved in the food refrigeration process are heat and mass transfer... more Abstract The main phenomena involved in the food refrigeration process are heat and mass transfer. In this context, the aim of this study was to evaluate the influence of refrigeration system parameters on food quality during postharvest storage. Experiments were conducted where the mean air temperature, air temperature fluctuation, air velocity, thermal oscillation period and humidity ratio were controlled, to quantify the food mass transfer, cooling rates and sensorial acceptance. The food sample under evaluation was lettuce packed in perforated polyethylene bags. A standardized test (IEC 63169:2020) was performed under the same experimental conditions for comparison. Food cooling rate was influenced by air velocity and a gradual increase (0.1–1.1 °C) in food temperature was observed during storage. A temperature increase from 3.0 to 7.0 °C, raised the mass loss of the food by 8.8%, which was directly influenced by the driving force provided by the humidity. Higher temperature fluctuations led to negative results in the sensorial analysis, with less freshness and higher consumption rejection.
Proceedings of the 25th International Congress of Mechanical Engineering, 2019
Journal of the Brazilian Society of Mechanical Sciences and Engineering, 2018
This work is focused on the optimal sizing of fan-supplied tube-fin evaporators for light commerc... more This work is focused on the optimal sizing of fan-supplied tube-fin evaporators for light commercial refrigerators operating under frosting conditions. Quasi-steady-state algebraic models were put forward for the refrigeration cycle and its components for computing not only the cooling capacity depletion due to the evaporator frosting over time, but also the changes experienced by the evaporating temperature and its effect on the compression power. Transient algebraic models were also advanced to account for the temperature and humidity variations inside the refrigerated compartment, and so the compressor runtime. Both component-level and system-level optimization exercises were performed for sizing the evaporator. The former was focused on the local entropy generation minimization, considering the irreversibilities due to heat transfer, mass transfer and pressure drop that take place at the evaporator, whereas the latter was aimed at the overall energy consumption of the refrigerator, including not only the compression power, but also the heat dissipation within the refrigerated compartment by the defrost heater and the evaporator fan. Notwithstanding the time-averaged cooling capacity and the evaporator envelope have been held constrained, the component-level and the system-level optimization procedures led to different evaporator designs.
Journal of the Brazilian Society of Mechanical Sciences and Engineering, 2019
Proceeding of 3rd Thermal and Fluids Engineering Conference (TFEC), 2018
Procceedings of the 16th Brazilian Congress of Thermal Sciences and Engineering, 2016
In the past decades, it has been observed a remarkable increase in the global production of vehic... more In the past decades, it has been observed a remarkable increase in the global production of vehicles. This situation is more noticeable in developing countries, like Brazil, where the annual production of cars has almost quadrupled since 1990. Many of these automobiles are equipped with mobile airconditioning (MAC) systems in order to improve the comfort and security of the vehicle occupants. In contrast to these positive characteristics, the MAC systems are also responsible for greenhouse gas emissions and an average increase of 7.5% on the fuel consumption. Due to environmental regulations, and vehicular efficiency programs, the automotive industry has been researching alternative fluid refrigerants and new technologies to minimize the environmental impact of MAC systems. Considering this scenario, the aim of this paper is to review the main features of MAC systems currently in use and identify the main Research and Development and Innovation (R&D&I) activities related to MAC systems that can be used on the Brazilian Market. The literature review indicates that energy efficiency improvements can be obtained by more efficient compressors, high performance heat exchangers, reduction of passenger cabin thermal load, design based on the thermal comfort analysis, improvements based on alternative cycles and reutilization of the waste heat.
International Journal of Refrigeration, 2018
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service... more This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Highlights Optimal defrost of fan-supplied tube-fin evaporators is investigated Numerical models are used to predict the operation between defrost cycles Optimal time to defrost is identified based on the on-off cycle efficiency Operating conditions, defrost power and evaporator geometry are evaluated
Applied Thermal Engineering, 2017
In refrigeration applications, frost build-up on the evaporator surfaces depletes the thermalhydr... more In refrigeration applications, frost build-up on the evaporator surfaces depletes the thermalhydraulic performance due to an increase in the thermal resistance and the blockage of the air flow. These negative effects depend not only on the total amount of frost, but also on the frost morphology that affects the density and, therefore, the thermal conductivity of the frost layer. In this paper, the studies of frost accretion on fan-supplied tube-fin evaporators carried out in previous works are advanced to investigate the effects of the frost morphology on the thermalhydraulic performance of fan-supplied evaporators. A visual inspection of the frost deposition was carried out to characterize the frost morphologies under different operating conditions. Moreover, a mathematical model was used to figure out how the operating conditions and the geometric parameters affect the cooling capacity and the pressure drop. The visualization confirmed that the operating conditions have a strong effect on the in-situ frost morphology. In addition, the numerical results not only illustrate the impact of the frost morphology on the evaporator performance, but also point out that the number of defrost operations may be reduced if a proper heat exchanger design is adopted.
International Journal of Refrigeration, 2009
This paper outlines an algebraic model for simulating the transcritical expansion of carbon dioxi... more This paper outlines an algebraic model for simulating the transcritical expansion of carbon dioxide through adiabatic capillary tubes. The model was put forward based on the analytical solution of the momentum conservation equation assuming an isenthalpic expansion process. The theoretical model predictions were compared with 66 experimental data points covering different operating conditions and tube geometries. A good agreement between the experimental and calculated mass flow rates was achieved, with more than 94% of the data points lying within an error band of AE10%.
International Journal of Refrigeration, 2009
This paper advances a study of the transcritical expansion of carbon dioxide (R-744, CO 2) throug... more This paper advances a study of the transcritical expansion of carbon dioxide (R-744, CO 2) through adiabatic capillary tubes. The influence of both operating conditions (inlet and exit pressures, inlet temperature) and tube geometry (capillary diameter and tube length) on the CO 2 mass flow rate was experimentally evaluated using a purpose-built testing facility with a strict control of the measured variables. A dimensionless correlation to predict the refrigerant mass flow rate as a function of tube geometry and operating conditions was developed. In addition, a theoretical model was put forward based on the mass, energy and momentum conservation principles. The model results were compared with experimental data, when it was found that the model predicts 95% of the measured refrigerant mass flow rate within an error band of AE10%. The model was also employed to advance the knowledge about the transcritical carbon dioxide flow through adiabatic capillary tubes.
International Journal of Refrigeration, 2011
An experimental and theoretical study of the diabatic flow of carbon dioxide through lateral capi... more An experimental and theoretical study of the diabatic flow of carbon dioxide through lateral capillary tube suction line heat exchangers is outlined. The influence of both operating conditions (capillary tube inlet and outlet pressures, capillary tube inlet temperature and suction line inlet temperature) and tube geometry (heat exchanger length and position, suction line diameter and capillary tube length) on the heat and mass flow rates was experimentally evaluated using a purpose-built testing facility. In total, 75 tests were carried out with heat fluxes spanning from 1 to 11 kW m À2 and refrigerant mass flow rates ranging from 12 to 26 kg h À1. In addition, the mathematical model of Hermes et al. (2008) was adapted to run with carbon dioxide as working fluid. The model was validated against experimental data, and a good agreement between the experimental and calculated mass flow rates was achieved with 85% and 98% of the data points being within AE5% and AE10% error bounds, respectively.
Uploads
Papers by Diogo Lôndero da Silva