scholarly journals Measurement of Heat Transfer and Flow Resistance for a Packed Bed of Horticultural Products with the Implementation of a Single Blow Technique

Processes ◽  
2021 ◽  
Vol 9 (12) ◽  
pp. 2151
Author(s):  
Adam Łapiński ◽  
Kamil Śmierciew ◽  
Huiming Zou ◽  
Dariusz Butrymowicz
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Flow Resistance ◽  
Convective Heat Transfer Coefficient ◽  
Packed Bed ◽  
Turbulent Intensity ◽  
Turbulent Fluctuation ◽  
Air Velocity ◽  
Horticultural Products

This paper provides the practical implementation of the single blow technique as an effective approach of average convective heat transfer coefficient measurement for a packed bed of horticultural products. The measurement approach was positively validated for the case of a packed bed of balls. The presented results cover heat transfer coefficient results for carrots stored in packed beds for two various arrangements (regular and irregular) and bed of apples under conditions of various turbulent intensity at the inlet to the bed. The turbulent intensity (defined as the ratio of the root mean square of the turbulent fluctuation of the air velocity to the mean air velocity) varied from 0.02 to 0.14. The applied velocity ranges for the tests refers to the conventional storage conditions. The heat transfer correlations were proposed based on the obtained results for each arrangement. It was demonstrated that due to flow laminarization inside the bed, the turbulence intensity has no significant effect on heat transfer inside the bed. Heat transfer enhancement of up to 25% was demonstrated for the case of the irregular carrot arrangement in the tested bed. The flow resistance correlations were additionally proposed for the tested beds. It was demonstrated that the product arrangement does not produce an important effect on the pressure drop.

scholarly journals Experimental study of the convective heat transfer coefficient in a packed bed at low Reynolds numbers

2014 ◽  
Vol 18 (2) ◽  
pp. 443-450 ◽  
Author(s):  
Souad Messai ◽  
Ganaoui El ◽  
Jalila Sghaier ◽  
Ali Belghith
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Convective Heat Transfer Coefficient ◽  
Packed Bed ◽  
Bed Temperature ◽  
Proposed Model

An experimental study to evaluate the convective heat transfer coefficient in a cylindrical packed bed of spherical porous alumina particles is investigated. The task consists in proposing a semi-empirical model to avoid excessive instrumentation and time consumption. The measurement of the bed temperature associated to a simple energy balances led to calculate the gas to particle heat transfer coefficient using a logarithmic mean temperature difference method. These experiments were performed at atmospheric pressure. The operating fluid is humid air. The gas velocity and temperature ranged from 1.7-3 m/s and 120-158?C, respectively. The data obtained was compared with the correlations reported in the literature. It is shown that the proposed model is in reasonable agreement with the correlation of Ranz and Marshall. Despite, many researches on experimental investigations of heat transfer coefficient in packed beds at low and average temperature are proposed, few studies presented calculation of convective heat transfer coefficient at high temperature (above 120?C). A possible application of the proposed model is drying and combustion.

scholarly journals Dynamics of convective hot air drying of filiform Lagenaria siceraria

2013 ◽  
Vol 19 (4) ◽  
pp. 485-492 ◽  
Author(s):  
Aishi Zhu ◽  
Kai Xia
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Convective Heat Transfer Coefficient ◽  
Lagenaria Siceraria ◽  
Drying Process ◽  
Air Velocity ◽  
Drying Temperature ◽  
Hot Air

In this study, a laboratory convective hot air dryer was used for the thin-layer drying of filiform Lagenaria siceraria and the influences of the drying temperature and air velocity on the drying process were investigated. The drying temperature and the air velocity were varied in the range of 60-80?C and 0.6-1.04 m?s-1, respectively. The experimental data of moisture ratio of filiform Lagenaria siceraria were used to fit the mathematical models, and the dynamics parameters such as convective heat transfer coefficient ? and mass transfer coefficient kH were calculated. The results showed that the drying temperature and air velocity influenced the drying process significantly. The Logarithmic model showed the best fit to experimental drying data. It was also found that, the air velocity and the drying temperature influence notable on both of the convective heat transfer coefficient ? and the mass transfer coefficient kH. With the increase of hot air velocity from 0.423 to 1.120 ms-1, the values of ? varied from 111.3 to 157.7 W?m-2?K-1, the values of kH varied from 13.12 to 18.58 g?m-2? s-1??H-1. With the increase of air temperature from 60 to 80?C, the values of ? varied between 150.2 and 156.9 W?m-2?K-1, the values of kH varied between 18.26 and 18.75 g?m-2?s-1??H-1.

Calculation of Convective and Radiative Heat Transfer Coefficient Using Thermography During a Physical Exercise

2020 ◽  
Author(s):  
Sathish K. Gurupatham ◽  
Priyanka Velumani ◽  
Revathy Vaidhya
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Human Body ◽  
Radiative Heat Transfer ◽  
Radiative Heat ◽  
Convective Heat Transfer Coefficient ◽  
Transfer Coefficients ◽  
Air Velocity ◽  
Heat Transfer Coefficients

Abstract A detailed model of human thermoregulation and a numerical algorithm to predict thermal comfort is a novel field of research and has wide applications in the auto/transportation industry and in the heating, ventilating, and air-conditioning (HVAC) industry. Anatomically specific convective and radiative heat transfer coefficients for the human body will be required to understand the human thermal physiological and comfort models. It necessitates to create hygienic and thermally comfortable spaces for the best productivity of the users. The physiological nature of thermal comfort during a transient condition such as a physical exercise or travel in an automobile are not yet well understood. In this paper, thermography has been applied to measure the convective and radiative heat transfer coefficients which has not been done before. Three different recovery processes were considered after the running of a human model on a treadmill with a range of speeds starting from 2 miles/hour to 10 miles/hour for stretch of twenty minutes. The recovery process included, (a) fan-assisted cooling with an air velocity of 0.5 m/s for 30 minutes, (b) fan-assisted cooling with an air velocity of 1.5 m/s for 30 minutes, and (c) natural cooling with no assistance of fan for 30 minutes. Thermal images were taken for forehead, trunk, arms, hands, legs of the models and the convective heat transfer coefficient and radiative heat transfer coefficient were calculated. The human models included both male and female, and belonged to two different age groups of less than 15 and above 40 with a total of 24 participants. The results show that though the temperatures, measured using thermography, for various parts of the human body changed locally, the overall calculated radiative heat transfer coefficients matched with the ASHRAE handbook values, and the calculated convective heat transfer coefficient increased with the increase of air velocity, while the models cooled down after the workout. Interestingly, the skin temperature decreased, initially, as the exercise progressed. After the completion of exercise, the skin temperature exhibited a quick rise during the recovery period with a subsequent decrease in the temperature, later. This trend was the same with all different age groups and sex of the models. The results also confirm that thermal images can be relied on for calculating the convective and radiative heat transfer coefficients of the human body to determine the heat transfer rate.

Sign in / Sign up

Export Citation Format

Share Document