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

2008 ◽  
Author(s):  
Pedro Dinis Gaspar ◽  
L. C. Carrilho Gonc¸alves ◽  
R. A. Pitarma
Keyword(s):  
Air Temperature ◽  
Mass Flow ◽  
Air Flow ◽  
Three Dimensional ◽  
Food Products ◽  
Ambient Air ◽  
Air Velocity ◽  
Air Curtain ◽  
Numerical Predictions ◽  
Thermal Entrainment

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.° 3 of EN 441 Standard (Tamb = 25 °C, φamb = 60%; νamb = 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.

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

2010 ◽  
Author(s):  
Pedro Dinis Gaspar ◽  
L. C. Carrilho Gonc¸alves ◽  
Xiao Ge
Keyword(s):  
Thermal Behaviour ◽  
Air Temperature ◽  
Thermal Performance ◽  
Air Flow ◽  
Experimental Tests ◽  
Ambient Air ◽  
Air Velocity ◽  
Cfd Modelling ◽  
Air Curtain ◽  
Numerical Predictions

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.

scholarly journals Performance of solar dryer chamber used for convective drying of sponge-cotton

2014 ◽  
Vol 18 (suppl.2) ◽  
pp. 451-462 ◽  
Author(s):  
Walid Aissa ◽  
Mostafa El-Sallak ◽  
Ahmed Elhakem
Keyword(s):  
Mass Flow Rate ◽  
Air Temperature ◽  
Mass Flow ◽  
Flow Rate ◽  
Air Flow ◽  
Ambient Air ◽  
Moisture Ratio ◽  
Convective Drying ◽  
Solar Dryer ◽  
Air Temperatures

Solar dryer chamber is designed and operated for five days of July 2008. Drying experiments are conducted for sponge-cotton; as a reference drying material in the ranges between 35.0 to 49.5?C of ambient air temperature, 35.2 to 69.8 ?C drying air temperature, 30 to 1258 W/m2 solar radiation and 0.016 to 0.08 kg/s drying air flow rate. For each experiment, the mass flow rate of the air remained constant throughout the day. The variation of moisture ratio, drying rate, overall dryer efficiency, and temperature distribution along the dryer chamber for various drying air temperatures and air flow rates are discussed. The results indicated that drying air temperature is the main factor in controlling the drying process and that air mass flow rate has remarkable influence on overall drying performance. For the period of operation, the dryer attained an average temperature of 53.68?C with a standard deviation of 8.49?C within a 12-h period from 7:00 h to 19:00 h. The results of this study indicated that the present drying system has overall efficiency between 1.85 and 18.6 % during drying experiments. Empirical correlations of temperature lapse and moisture ratio in the dryer chamber are found to satisfactorily describe the drying curves of sponge-cotton material which may form the basis for the development of solar dryer design charts.

Evaluation of the influence of ambient air temperature and air velocity on mortar cement durability using a forced convection solar dryer

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Younes Bahammou ◽  
Mounir Kouhila ◽  
Haytem Moussaoui ◽  
Hamza Lamsyehe ◽  
Zakaria Tagnamas ◽  
...  
Keyword(s):  
Environmental Factors ◽  
Forced Convection ◽  
Air Temperature ◽  
Building Materials ◽  
Ambient Air ◽  
Physical Significance ◽  
Drying Process ◽  
Air Velocity ◽  
Content Type ◽  
Ambient Air Temperature

PurposeThis work aims to study the hydrothermal behavior of mortar cement toward certain environmental factors (ambient air temperature and air velocity) based on its drying kinetics data. The objective is to provide a better understanding and controlling the stability of mortar structures, which integrate the sorption phenomenon, drying process, air pressure and intrinsic characteristics. This leads to predict the comportment of mortar structures in relation with main environmental factors and minimize the risk of cracking mortar structures at an early age.Design/methodology/approachThermokinetic study was carried out in natural and forced convection solar drying at three temperatures 20, 30 and 40°C and three air velocities (1, 3 and 5 m.s-1). The empirical and semiempirical models tested successfully describe the drying kinetics of mortar. These models simulate the drying process of water absorbed by capillarity, which is the most common humidity transfer mechanism in building materials and contain parameters with physical significance, which integrate the effect of several environmental factors and intrinsic characteristics of mortar structures.FindingsThe models simulate the drying process of water absorbed by capillarity, which is the most common humidity transfer mechanism in building materials and contain parameters with physical significance, which integrate the effect of several environmental factors and intrinsic characteristics of mortar structures. The average activation energy obtained expressed the temperature effect on the mortar diffusivity. The drying constant and the diffusion coefficient can be used to predict the influence of these environmental factors on the drying behavior of various building materials and therefore on their durability.Originality/valueEvaluation of the effect of several environmental factors and intrinsic characteristics of mortar structures on their durability.

Temperature Distribution of Hot Air Flow in Heating Zone for Drying Application

2014 ◽  
Vol 627 ◽  
pp. 153-157
Author(s):  
Nawadee Srisiriwat ◽  
Chananchai Wutthithanyawat
Keyword(s):  
Temperature Distribution ◽  
Air Temperature ◽  
Power Supply ◽  
Air Flow ◽  
Heating Zone ◽  
Velocity Control ◽  
Rectangular Duct ◽  
Air Velocity ◽  
Hot Air ◽  
Set Up

The temperature distribution of hot air flow in heating zone of a rectangular duct has been investigated for drying application. The experimental set-up consists of a heater and a fan to generate the hot air flow in the range of temperature from 40 to 100°C and the range of air velocity between 1.20 and 1.57 m/s. An increase of the heater power supply increases the hot air temperature in the heating zone while an increase of air velocity forced by fan decreases the initial temperature at the same power supply provided to generate the hot air flow. The temperature distribution shows that the hot air temperature after transferring through air duct decreases with an increase of the length of the rectangular duct. These results are very important for the air flow temperature and velocity control strategy to apply for heating zone design in the drying process.

scholarly journals Off-Design Performances of an Organic Rankine Cycle for Waste Heat Recovery from Gas Turbines

Energies ◽  
2020 ◽  
Vol 13 (5) ◽  
pp. 1105 ◽  
Author(s):  
Carlo Carcasci ◽  
Lapo Cheli ◽  
Pietro Lubello ◽  
Lorenzo Winchler
Keyword(s):  
Gas Turbine ◽  
Mass Flow Rate ◽  
Air Temperature ◽  
Mass Flow ◽  
Flow Rate ◽  
Power Output ◽  
Organic Rankine Cycle ◽  
Rankine Cycle ◽  
Ambient Air ◽  
Air Mass

This paper presents an off-design analysis of a gas turbine Organic Rankine Cycle (ORC) combined cycle. Combustion turbine performances are significantly affected by fluctuations in ambient conditions, leading to relevant variations in the exhaust gases’ mass flow rate and temperature. The effects of the variation of ambient air temperature have been considered in the simulation of the topper cycle and of the condenser in the bottomer one. Analyses have been performed for different working fluids (toluene, benzene and cyclopentane) and control systems have been introduced on critical parameters, such as oil temperature and air mass flow rate at the condenser fan. Results have highlighted similar power outputs for cycles based on benzene and toluene, while differences as high as 34% have been found for cyclopentane. The power output trend with ambient temperature has been found to be influenced by slope discontinuities in gas turbine exhaust mass flow rate and temperature and by the upper limit imposed on the air mass flow rate at the condenser as well, suggesting the importance of a correct sizing of the component in the design phase. Overall, benzene-based cycle power output has been found to vary between 4518 kW and 3346 kW in the ambient air temperature range considered.

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

2009 ◽  
Author(s):  
Pedro Dinis Gaspar ◽  
L. C. Carrilho Gonc¸alves ◽  
Andreas Vo¨geli
Keyword(s):  
Heat Transfer ◽  
Porous Medium ◽  
Unit Length ◽  
Experimental Tests ◽  
Cfd Modeling ◽  
Air Velocity ◽  
Conservation Area ◽  
Air Curtain ◽  
Numerical Predictions ◽  
Back Panel

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.

scholarly journals Numerical Simulation of Thermal-Hydrodynamic Behavior within Solar Air Collector

2018 ◽  
Vol 24 (3) ◽  
pp. 29
Author(s):  
Mustafa T. Mustafa ◽  
Ayad T. Mustafa
Keyword(s):  
Three Dimensional ◽  
Ambient Air ◽  
Heat Energy ◽  
Air Velocity ◽  
Hydrodynamic Behavior ◽  
Ansys Fluent ◽  
Velocity Increase ◽  
Air Temperatures ◽  
Solar Air Collector ◽  
Simulation Results

Solar collectors, in general, are utilized to convert the solar energy into heat energy, where it is employed to generate electricity. The non-concentrating solar collector with a circular shape was adopted in the present study. Ambient air is heated under a translucent roof where buoyant air is drawn from outside periphery towards the collector center (tower base). The present study is aimed to predict and visualize the thermal-hydrodynamic behavior for airflow under inclined roof of the solar air collector, SAC. Three-dimensional of the SAC model using the re-normalization group, RNG, k−ε turbulence viscus model is simulated. The simulation was carried out by using ANSYS-FLUENT 14.5. The simulation results demonstrated that at same insolation; airflow, ground and air temperatures increase when the collector radius decreases towards the collector center. The ground temperature and air velocity increase, while airflow temperature decreases when the inclination angle increases from 0° to 20° due to changing in airflow movement. More decreasing in airflow temperature has been occurred when the inlet height increases from 0.1m to 0.25m. The simulation results were validated by comparing with the experimental data. In conclusions, the obtained results showed the capability of producing warm airflow to generate electricity in Baghdad city.    

Account of Temperature Change at Calibration of Air Flow Sensor

2018 ◽  
Vol 7 (3.19) ◽  
pp. 158
Author(s):  
Yu. A. Kryukov ◽  
M A. Mikheev ◽  
T Е. Golovchenko ◽  
V V. Ivanov ◽  
L K. Lytkin
Keyword(s):  
Temperature Change ◽  
Air Temperature ◽  
Mass Flow ◽  
Air Flow ◽  
Equation System ◽  
Flow Sensor ◽  
Strain Gauges ◽  
System Of Equations ◽  
Measuring Bridge ◽  
Circuit Resistance

The article describes of temperature change consideration during the calibration of air flow sensor for a car engine. The sensor uses a blade made of elastic material with strain gauges applied to the front and the back surfaces, the deformation of which is measured and recalculated into a mass flow of air. They suggested the system of equations whose solution makes it possible to determine the mass flow rate and air temperature according to the known signal values at the measuring bridge output and the measuring circuit resistance. The coefficients of equation system are determined during calibration and then are recorded into the memory of the microcontroller sensor.  

Effects of Dry Chilling on the Microflora on Beef Carcasses at a Canadian Beef Packing Plant

2016 ◽  
Vol 79 (4) ◽  
pp. 538-543 ◽  
Author(s):  
Y. LIU ◽  
M. K. YOUSSEF ◽  
X. YANG
Keyword(s):  
Escherichia Coli ◽  
Relative Humidity ◽  
Air Temperature ◽  
Ambient Air ◽  
Indicator Organisms ◽  
Air Velocity ◽  
E Coli ◽  
Beef Carcasses ◽  
Significant Difference

ABSTRACT The aim of this study was to determine the course of effects on the microflora on beef carcasses of a commercial dry chilling process in which carcasses were dry chilled for 3 days. Groups of 25 carcasses selected at random were sampled when the chilling process commenced and after the carcasses were chilled for 1, 2, 4, 6, 8, 24, and 67 h for determination of the numbers of aerobes, coliforms, and Escherichia coli. The temperatures of the surfaces and the thickest part of the hip (deep leg) of carcasses, as well as the ambient air conditions, including air temperature, velocity, and relative humidity (RH), were monitored throughout the chilling process. The chiller was operated at 0°C with an off-coil RH of 88%. The air velocity was 1.65 m/s when the chiller was loaded. The initial RH levels of the air in the vicinity of carcasses varied with the locations of carcasses in the chiller and decreased rapidly during the first hour of chilling. The average times for shoulder surfaces, rump surfaces, and the deep leg of carcasses to reach 7°C were 13.6 ± 3.1, 16.0 ± 2.4 and 32.4 ± 3.2 h, respectively. The numbers of aerobes, coliforms, and E. coli on carcasses before chilling were 5.33 ± 0.42, 1.95 ± 0.77, 1.42 ± 0.78 log CFU/4,000 cm2, respectively. The number of aerobes on carcasses was reduced by 1 log unit each in the first hour of chilling and in the subsequent 23 h of chilling. There was no significant difference (P > 0.05) between the numbers of aerobes recovered from carcasses after 24 and 67 h of chilling. The total numbers (log CFU/100,000 cm2) on carcasses before chilling and after the first hour of chilling were 3.86 and 2.24 for coliforms and 3.30 and 2.04 for E. coli. The subsequent 23 h of chilling reduced the numbers of both groups of organisms by a further log unit. No coliforms or E. coli were recovered after 67 h of chilling. The findings show that the chilling regime investigated in this study resulted in significant reductions of all three groups of indicator organisms.

The Effect of New Pouring Precooling Concrete on Lower Layer Concrete in Different Seasons

2013 ◽  
Vol 663 ◽  
pp. 60-64
Author(s):  
Kai Ping Tian ◽  
Bai Lin Xu ◽  
Yao Ying Huang ◽  
Yi Hong Zhou ◽  
Yue Mei Ding
Keyword(s):  
High Temperature ◽  
Surface Temperature ◽  
Air Temperature ◽  
Lower Layer ◽  
Three Dimensional ◽  
Concrete Block ◽  
Ambient Air ◽  
Ambient Air Temperature ◽  
Different Seasons ◽  
Three Dimensional Finite Element

Based on massive concrete block in practical engineering, the effect of new pouring precooling concrete on lower layer concrete in different seasons was simulated by using three-dimensional finite element simulation program of non-steady temperature field, and the temperature changes near the surface of lower layer concrete have been analyzed detailedly. It is indicated that, there is obvious “cold strike” effect of new pouring precooling concrete on lower layer concrete in summer, the effect in autumn followed by, and there is also the effect in spring but not obvious. In winter, as ambient air temperature is very low, there is not “cold strike” effect and the lower layer concrete temperature gradually recovery after pouring new concrete. Because actual concrete pouring deck surface maintenance is often not in place, the surface temperature of the pouring deck, which is greatly influenced by ambient air temperature and solar radiation, is very high in high temperature seasons. At the moment, the “cold strike” effect of new pouring precooling concrete on lower layer concrete is very obvious and likely to lead to the crack of the concrete. Hence, it is suggested that, after finish pouring of concrete and final set of concrete, sprinkling water or flowing water maintenance should be carried out in high temperature seasons, such as summer and autumn; before pouring the concrete, it is better to take measures, like spray and sprinkling water, to reduce the surface temperature of lower layer concrete, and try to avoid starting pouring concrete at midday.

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