scholarly journals EVALUATION OF CONVECTIVE HEAT AND MASS TRANSFER COEFFICIENTS FOR DIFFERENT PRODUCTS IN A NEW NATURAL CONVECTION SOLAR DRYER

2010 ◽  
Vol 33 (4) ◽  
pp. 345-362
Author(s):  
Sh. Shams El-Din ◽  
M. Habib ◽  
A. El-Hanafy ◽  
Kh. Ramzy
Keyword(s):  
Mass Transfer ◽  
Natural Convection ◽  
Heat And Mass Transfer ◽  
Convective Heat ◽  
Transfer Coefficients ◽  
Mass Transfer Coefficients ◽  
Solar Dryer

Empirical Evaluation of Convective Heat and Moisture Transport Coefficients in Porous Cotton Medium

2002 ◽  
Vol 124 (3) ◽  
pp. 530-537 ◽  
Author(s):  
Kamel Ghali ◽  
Nesreen Ghaddar ◽  
Byron Jones
Keyword(s):  
Mass Transfer ◽  
Heat And Mass Transfer ◽  
Convective Heat ◽  
Transport Coefficients ◽  
Model Parameters ◽  
Moisture Uptake ◽  
Transfer Coefficients ◽  
Mass Transfer Coefficients ◽  
Air Penetration ◽  
Heat And Moisture

The air penetration within a porous clothing system on a moving human being is an important physical process that considerably affects the heat and moisture resistance of the textile material. This effect of the coupled convection heat and mass exchange within the clothing system is experimentally investigated and theoretically modeled to determine the heat and mass transfer coefficients between the air penetrating the void space and the solid fiber as a function of the velocity of penetrating air. Experiments were conducted inside environmentally controlled chambers to measure the transient moisture uptake of untreated cotton fabric samples as well as the outer fabric temperature using an infrared pyrometer. The moisture uptake was conducted at three different volumetric flow rates of 0.0067, 0.018 and 0.045 m3/sec/m2 of fabric area to represent airflow penetrations that could result from slow, medium, and vigorous walking, respectively. The theoretical analysis is based on a two-node adsorption model of the fibrous medium. A set of four coupled differential equations were derived describing time-dependent convective heat and mass transfer between the penetrating air and the solid fiber in terms of relevant unknown transport coefficients. The unknown model parameters were adjusted to fit the experimental data. The outer heat and mass transfer coefficients were found to increase with the air penetration flow rate.

scholarly journals Numerical Study of the Drying of Cassava Roots Chips Using an Indirect Solar Dryer in Natural Convection

2021 ◽  
Vol 3 (1) ◽  
pp. 138-157
Author(s):  
Merlin Simo-Tagne ◽  
Ablain Tagne Tagne ◽  
Macmanus Chinenye Ndukwu ◽  
Lyes Bennamoun ◽  
Marcel Brice Obounou Akong ◽  
...  
Keyword(s):  
Mass Transfer ◽  
Natural Convection ◽  
Heat And Mass Transfer ◽  
Numerical Study ◽  
Transfer Coefficients ◽  
Drying Time ◽  
The Core ◽  
Cassava Root ◽  
Solar Dryer ◽  
Theoretical Results

In this work, an indirect solar dryer for drying cassava root chips was modelled and experimentally validated using the environmental conditions of Yaoundé in Cameroon and Yamoussoukro in Ivory Coast. The dryers were operational in natural convection mode. Resolution of the equations was achieved by finite differences and the 4th order of Runge–Kutta methods. A model was proposed for performing heat and mass transfer using thermophysical properties of cassava roots, and the obtained results were satisfactory for all conditions, with moisture content difference of less than 0.2 kg/kg between the experimental and theoretical results. The model showed that the core of the product takes more time to dry, which always prolongs the drying duration. The heat and mass transfer coefficients vary during the entire process of solar drying. The drying kinetics vary during the drying with values lower than 1.2 × 10−4 kg/(kg.s). The great gradients of humidity were observed in the thickness of the sample with a regular distribution of the temperature each drying time in the thickness of the sample.

scholarly journals Drying and Heating Processes in Arbitrarily Shaped Clay Materials Using Lumped Phenomenological Modeling

Energies ◽  
2021 ◽  
Vol 14 (14) ◽  
pp. 4294
Author(s):  
Elisiane S. Lima ◽  
João M. P. Q. Delgado ◽  
Ana S. Guimarães ◽  
Wanderson M. P. B. Lima ◽  
Ivonete B. Santos ◽  
...  
Keyword(s):  
Mass Transfer ◽  
Relative Humidity ◽  
Heat And Mass Transfer ◽  
Convective Heat ◽  
Transport Coefficients ◽  
Ceramic Materials ◽  
Raw Material ◽  
Transfer Coefficients ◽  
Mass Transfer Coefficients ◽  
Mass Transfers

This work aims to study the drying of clay ceramic materials with arbitrary shapes theoretically. Advanced phenomenological mathematical models based on lumped analysis and their exact solutions are presented to predict the heat and mass transfers in the porous material and estimate the transport coefficients. Application has been made in hollow ceramic bricks. Different simulations were carried out to evaluate the effect of drying air conditions (relative humidity and speed) under conditions of forced and natural convection. The transient results of the moisture content and temperature of the brick, and the convective heat and mass transfer coefficients are presented, discussed and compared with experimental data, obtaining a good agreement. It was found that the lower the relative humidity is and the higher the speed of the drying air is, the higher the convective heat and mass transfer coefficients are at the surface of the brick and in the holes, and the faster the moisture removal material and heating is. Based on the predicted results, the best conditions for brick drying were given. The idea is to increase the quality of the brick after the process, to reduce the waste of raw material and energy consumption in the process.

The Experimental Investigation of Steam Condensation With Non-Condensable Gas Under Natural Convection

2018 ◽  
Author(s):  
Xizhen Ma ◽  
Wen Fu ◽  
Haijun Jia ◽  
Peiyue Li ◽  
Jun Li
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
High Pressure ◽  
Natural Convection ◽  
Heat And Mass Transfer ◽  
Vertical Wall ◽  
Experimental System ◽  
Steam Condensation ◽  
Transfer Coefficients ◽  
Calculation Results

The non-condensable gas is used to keep the pressure stable in the steam-gas pressurizer. The processes of heat and mass transfer during steam condensation in the presence of non-condensable gas play an important role and the thermal hydraulic characteristics in the pressurizer is particularly complicated due to the non-condensable gas. The effects of non-condensable gas on the process of heat and mass transfer during steam condensation were experimental investigated. A steam condensation experimental system under high pressure and natural convection was built and nitrogen was chosen in the experiments. The steam and nitrogen were considered in thermal equilibrium and shared the same temperature in the vessel under natural convection. In the experiments, the factors, for instance, pressure, mass fraction of nitrogen, subcooling of wall and the distribution of nitrogen in the steam, had been taken into account. The rate of heat transfer of steam condensation on the vertical wall with nitrogen was obtained and the heat transfer coefficients were also calculated. The characteristics curve of heat and mass transfer during steam condensation with non-condensable gas under high pressure were obtained and an empirical correlation was introduced to calculated to heat transfer coefficient of steam condensation with nitrogen which the calculation results showed great agreement with the experimental data.

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