Pedro Dinis Gaspar

Detailed CFD modelling of open refrigerated display cabinets

A comprehensive and detailed computational fluid dynamics (CFDs) modelling of air flow and heat transfer in an open refrigerated display cabinet (ORDC) is performed in this study. The physical-mathematical model considers the flow through the internal ducts, across fans and evaporator, and includes the thermal response of food products. The air humidity effect and thermal radiation heat transfer between surfaces are taken into account. Experimental tests were performed to characterize the phenomena near physical extremities and to validate the numerical predictions of air temperature, relative humidity, and velocity. Numerical and experimental results comparison reveals the predictive capabilities of the computational model for the optimized conception and development of this type of equipments. Numerical predictions are used to propose geometrical and functional parametric studies that improve thermal performance of the ORDC and consequently food safety.

Three-Dimensional CFD Modelling and Analysis of the Thermal Entrainment in Open Refrigerated Display Cabinets

This study presents a three-dimensional Computational Fluid Dynamics (CFD) simulation of the air flow pattern and the temperature distribution in a refrigerated display cabinet. The thermal entrainment is evaluated by the variations of the mass flow rate and thermal power along and across the air curtain considering the numerical predictions of abovementioned properties. The evaluation on the ambient air velocity for the three-dimensional (3D) effects in the pattern of this type of turbulent air flow is obtained. Additionally, it is verified that the longitudinal air flow oscillations and the length extremity effects have a considerable influence in the overall thermal performance of the equipment. The non uniform distribution of the air temperature and velocity throughout the re-circulated air curtain determine the temperature differences in the linear display space and inside the food products, affecting the refrigeration power of display cabinets. The numerical predictions have been validated by comparison with experimental tests performed in accordance with the climatic class n.o 3 of EN 441 Standard (Tamb = 25 oC, φamb = 60%; vamb = 0,2 m s -1 ). These tests were conducted using the point measuring technique for the air temperature, air relative humidity and air velocity throughout the air curtain, the display area of conservation of food products and nearby the inlets/outlets of the air mass flow.

CFD parametric studies for global performance improvement of open refrigerated display cabinets

A detailed CFD modelling of an open refrigerated display cabinet has been formulated in a previous study. Some modifications are introduced in order to perform parametric studies dealing with low-cost geometrical and functional characteristics for improvement of the global performance and energy efficiency. The parametric studies are devoted to the analysis of the thermal response and behaviour inside the food conservation space influenced by (1) air flow rate through the evaporator heat exchanger; (2) air curtain behaviour; (3) hole dimensions and distribution of the back panel; (4) discharge and return grilles angles; and (5) flow deflectors inside the internal duct. The analysis of the numerical predictions from the parametric studies allows the development of an optimized model for the conception of an open refrigerated display cabinet with a more adequate configuration. The numerical predictions of the optimized model show lower product temperature and reduced electrical energy consumption, allowing the improvement of the food safety and the energy rationalization of the refrigeration equipment.

Influence of Ambient Air Velocity Orientation in Thermal Behaviour of Open Refrigerated Display Cabinets

Open refrigerated display cabinets (ORDCs) suffer alterations of their thermal behaviour and of its performance due to variations of ambient air conditions (air temperature, relative humidity and velocity magnitude and orientation). Some factors interfere and affect the re-circulated air curtain behaviour and thus the equipment’s overall thermal performance. Examples of these factors are the location of air conditioning system discharge grilles, air mass flows originated by pressure differences due to openings to surroundings, and ambient air flow instabilities due to consumers’ passage nearby the frontal opening of the display cabinet, among others. This work performs a three-dimensional (3D) Computational Fluid Dynamics (CFD) modelling of air flow and heat transfer in an ORDC. The influence of ambient air velocity orientation in performance of the re-circulated air curtain is evaluated. A CFD parametric study is developed considering the ambient air orientation parallel, oblique and perpendicular to the frontal opening plane of the equipment. The 3D effects of ambient air velocity orientation are determined through the analysis of air temperature and velocity inside the equipment as well as along and across the air curtain. The longitudinal air flow oscillations and length extremity effects are analyzed, having a considerable influence in the overall thermal performance of the equipment. Experimental tests following EN-ISO Standard 23953 were conducted for climatic class n.er 3 (Tamb = 25 °C, φamb = 60%) in order to characterize the phenomena near inlets, outlets and physical borders. Moreover, experimental data is used to prescribe boundary conditions as well as to validate numerical predictions of temperature and velocity distributions.Copyright

Handbook of research on advances and applications in refrigeration systems and technologies

In recent years, the sustainability and safety of perishable foods has become a major consumer concern, and refrigeration systems play an important role in the processing, distribution, and storage of such foods. To improve the efficiency of food preservation technologies, it is necessary to explore new technological and scientific advances both in materials and processes. The Handbook of Research on Advances and Applications in Refrigeration Systems and Technologies gathers state-of-the-art research related to thermal performance and energy-efficiency. Covering a diverse array of subjects-from the challenges of surface-area frost-formation on evaporators to the carbon footprint of refrigerant chemicals-this publication provides a broad insight into the optimization of cold-supply chains and serves as an essential reference text for undergraduate students, practicing engineers, researchers, educators, and policymakers.

Characterization of the Specific Electrical Energy Consumption of Agrifood Industries in the Central Region of Portugal

This paper provides a characterization of the electrical energy consumption of agrifood industries located in the central region of Portugal that use refrigeration systems to ensure the food safety. The study is based on the result analysis of survey data and energy characteristics of the participating companies. The agrifood industries included in the survey belong to the following sector: meat, dairy, horticultural, distribution and wine. The comparison of energy indicators for the specific electrical energy consumption of companies of a sector and between sectors is analysed and discussed, providing reference levels for the energy performance of agrifood industries. Since the agrifood sector accounts for high level of energy consumption, the energy performance level knowledge can promote the rational use of energy as well as helping on the decision making of practice measures for the improvement of the energy efficiency.

Dependency of Air Curtain Performance on Discharge Air Velocity (Grille and Back Panel) in Open Refrigerated Display Cabinets

This study performs a Computational Fluid Dynamics (CFD) modeling of air flow and heat transfer of an open refrigerated display cabinet in order to evaluate the influence of the discharge air velocity on the performance of its recirculated air curtain. The physical-mathematical model considers the flow through the internal ducts, across the fans and the evaporator, and also the thermal response of food products. The fan boundary condition is modeled in order to vary the air velocity at the discharge grille. The back panel perforation is modeled as a porous medium. The density and dimension of the back panel perforation variation is modeled by the Darcy’s law with the Forchheimer extension, varying the viscous and inertial resistance coefficients of the porous medium, based on its porosity, permeability, air velocity and pressure loss coefficient. Experimental tests were conducted to characterize the phenomena near the physical borders and to prescribe boundary conditions as well as to validate the numerical predictions on the temperature, relative humidity and velocity distributions. The numerical results show that the lowest average temperature in the conservation area of the display cabinet is achieved at a discharge air grille velocity of 1.15 ms−1 . This value is lower than the experimental one, 1.51 ms−1 , measured on the real equipment. The absence of a velocity component in the third dimension, which can destabilize the air curtain, is assumed to be the reason for this discrepancy. The profiles of the numerical predictions of the air curtain indicate that in the optimum case the air curtain is not so stable to bear big disturbances from outside. In order to increase the thermal performance and to reduce the energy consumption of these equipments, it’s not recommended to run the re-circulated air curtain velocity below 1.15 ms−1 . For each CFD model, the values and directions of the air mass flow rate and heat transfer across the re-circulated air curtain by unit length are predicted and compared with the experimental ones in order to evaluate its thermal energy gains and losses.Copyright

Characterization Of The Specific Energy Consumption Of Electricity In The Portuguese Sausage Industry

The sausage is an ancient food type that is nowadays considered as a delicatessen. Sausages are categorized within the deli sector as meat sub products. It is a food product preferred by consumers due to its nutritional value and organoleptic characteristics (wide range of flavours and textures). There are many types of sausages, with around 1200 different varieties (according to German classification), classified into types according to different criteria such as types of ingredients, consistency, and preparation (raw, cooked, pre-cooked, dry). In the UK, 196,152 metric tons of sausages were consumed during 2011, valued in

Specific Electrical Energy Consumption and CO2 Emissions Assessment of Agrifood Industries in the Central Region of Portugal

1.2 billion, while in the US this value was around

Criteria Assessment of Energy Carrier Systems Sustainability

20.4 billion two years before. The heating and cooling processes during sausage production are indispensable technologies to ensure both the specific organoleptic characteristics and properties conservation through time. This paper characterizes the production process and the energy consumption of sausages processing industry in Portugal (20 industries) and discusses the average specific energy consumption (SEC) of electricity and its standard deviation. The average value of this indicator for the sample was 660 kWhe/ton raw material. The energy consumption of this type of industry is mainly that of electricity (82%). Several electricity savings, estimated at 23.9%, can be achieved by implementing simple practice measures in the refrigeration systems.