Drying Kinetics of Building Materials: Brief Theory and Experimental Evaluation

2016 ◽  
Vol 7 ◽  
pp. 114-127 ◽  
Author(s):  
E. Barreira ◽  
J.M.P.Q. Delgado
Keyword(s):  
Experimental Evaluation ◽  
Building Materials ◽  
Molecular Diffusion ◽  
Moisture Transfer ◽  
Drying Kinetics ◽  
Drying Process ◽  
Drying Time ◽  
Surface Moisture ◽  
First Order Kinetics ◽  
Kinetics Of

The effect of moisture in buildings is normally related with damage, which may occur due to the presence of moisture itself or due to its evaporation. The drying process plays an important role in the available moisture, both inside the material or at its surface. This paper presents the results of an experimental evaluation of the drying kinetics, considering both surface and bulk moisture transfer. Two different specimens were used: External Thermal Insulation Composite Systems (ETICS) to study surface moisture transfer and Autoclaved Cellular Concrete (ACC) to analyse the bulk moisture transfer. For both samples the drying kinetics was assessed considering different environment conditions (air temperature and humidity). Five different first-order kinetics models, available in the literature, were adjusted to describe the drying process and estimate the equilibrium moisture content of ETICS and ACC.The results point that Logarithmic and Midilli models allow the best fit and that the drying time constant is strongly affected by the moisture transfer phenomenon (at surface or bulk) and by the drying air conditions. It was also estimated the apparent molecular diffusion coefficient for ACC and its variation with temperature.

Drying Kinetics Evaluation of Solid Red Bricks

2015 ◽  
Vol 3 ◽  
pp. 119-134
Author(s):  
E. Barreira ◽  
J.M.P.Q. Delgado ◽  
V.P. de Freitas
Keyword(s):  
Moisture Content ◽  
Molecular Diffusion ◽  
Moisture Transfer ◽  
Drying Kinetics ◽  
Drying Process ◽  
Drying Time ◽  
First Order ◽  
First Order Kinetics ◽  
Kinetics Of ◽  
Best Fit

Moisture is one of the most deteriorating factors of buildings. The moisture content depends on hygroscopic equilibrium between buildings materials and environment, which is determined by the drying and wetting rate of masonry. So, the moisture content is not only determined by the water that is absorbed by the material, but also by the amount of water that is evaporated under favourable conditions, which is described by the drying process.This work presents the results of an experimental evaluation of the drying kinetics of solid red brick, considering the bulk moisture transfer. The drying kinetics was assessed considering different environment conditions (air temperature and humidity). The experimental results showed that the drying flux is extremely dependent of temperature and relative humidity in the first stage of the drying process. The values obtained were between 0.025 kg/m2h (T=15oC and RH=80%) and 0.135 kg/m2h (T=30oC and RH=50%), for the worst and better drying ambient conditions.Different first-order kinetics models, available in the literature, were adjusted to describe the drying process and estimate the equilibrium moisture content of the samples. The results point that Midilli et al. model allows the best fit and that the drying time constant is strongly affected by the drying air conditions. It was also estimated the apparent molecular diffusion coefficient for solid red brick samples and its variation with temperature.

Experimental Evaluation and Kinetic Analysis of Direct-Contact Ultrasonic Fabric Drying Process

2020 ◽  
Vol 13 (2) ◽  
Author(s):  
Chang Peng ◽  
Saeed Moghaddam
Keyword(s):  
Direct Contact ◽  
Ultrasonic Transducer ◽  
Gaussian Model ◽  
Weibull Model ◽  
Drying Kinetics ◽  
Energy Prices ◽  
Drying Process ◽  
Liquid Form ◽  
Drying Time ◽  
Kinetics Of

Abstract Over the past two decades, due to the rising energy prices and growing awareness about climate change, significant efforts have been devoted to reducing the energy consumption of various home appliances. However, the energy efficiency of clothes dryers has little improvement. Recent innovations in the direct-contact ultrasonic fabric drying technique offer new opportunities for energy saving. In this technique, high-frequency mechanical vibrations generated by the ultrasonic transducer are utilized to atomize water from a fabric in the liquid form, which demonstrates great potential for reducing energy use and drying time of the fabric drying process. Here, for the first time, fabric drying kinetics under different direct-contact ultrasonic drying conditions were investigated experimentally and analytically. The drying processes of four kinds of fabrics were experimentally tested under different ultrasonic transducer vibration frequency (115, 135, and 155 kHz) and input power (1.2, 2.5, and 4.4 W) conditions. According to the experimental data, five different kinds of models were applied to quantify the drying kinetics of fabrics during direct-contact ultrasonic drying. The models not only incorporated the transducer parameters but also the parameters related to the nature of fabric. Our evaluation results of model prediction performance demonstrated that the two empirical models, i.e., the Weibull model and the Gaussian model, were superior to the three semi-theoretical models for anticipating the drying kinetics of fabrics under direct-contact ultrasonic drying. Furthermore, the Weibull model is more suitable for practical energy-efficient direct-contact ultrasonic fabric drying applications compared with the Gaussian model.

scholarly journals Drying kinetics and effective diffusion of buckwheat grains

2020 ◽  
Vol 44 ◽  
Author(s):  
Valdiney Cambuy Siqueira ◽  
Rafael Araújo Leite ◽  
Geraldo Acácio Mabasso ◽  
Elton Aparecido Siqueira Martins ◽  
Wellytton Darci Quequeto ◽  
...  
Keyword(s):  
Effective Diffusion ◽  
Information Criterion ◽  
Drying Kinetics ◽  
Drying Rate ◽  
Linear Regression Method ◽  
Drying Process ◽  
Food Sector ◽  
Drying Time ◽  
Air Speed ◽  
Kinetics Of

ABSTRACT Buckwheat has become important in the food sector as its flour does not contain gluten. Since buckwheat is a relatively new crop in the agricultural environment, there is little information available regarding its processing. Drying is one of the most important post-harvest stages of buckwheat. The aim of the present study was to describe the drying process of buckwheat grains. Buckwheat grains with a moisture content of 0.41 ± 0.01 (dry basis, d.b.) were harvested, followed by drying in an experimental dryer at the temperatures of 40, 50, 60, 70, and 80 °C, at an air speed of 0.8 m s-1. The drying rate was determined, and the mathematical models generally employed to describe the drying process of several agricultural products were fitted to the experimentally obtained data. Model selection was based on the Gauss-Newton non-linear regression method and was complemented by Akaike Information Criterion and Schwarz’s Bayesian Information Criterion. It was concluded that the drying rate increased with an increase in temperature and decreased with an increase in drying time. It is recommended to use the Midilli model to represent the drying kinetics of buckwheat grains at the temperatures of 40, 60, and 70 °C, while the Approximation of diffusion model is recommended for the temperatures of 50 and 80 °C. The magnitudes of effective diffusion coefficients ranged from 1.8990 × 10-11 m2 s-1 to 17.8831 × 10-11 m2 s-1. The activation energy required to initiate the drying process was determined to be 49.75 kJ mol-1.

Wetting and Drying of External Surfaces with ETICS Systems

2013 ◽  
Vol 334-335 ◽  
pp. 343-348 ◽  
Author(s):  
E. Barreira ◽  
João M.P.Q. Delgado ◽  
V.P. de Freitas
Keyword(s):  
Building Materials ◽  
Drying Kinetics ◽  
Linear Type ◽  
Drying Time ◽  
First Order Kinetics ◽  
Air Temperatures ◽  
Proposed Model ◽  
Insulation Systems ◽  
Drying Conditions ◽  
Type Power

Moisture is one of the most deteriorating factors of buildings. The deteriorating effect of moisture occurs mainly during the drying phase, and appropriate parameters of the drying kinetics are required for the building materials. Environmental factors, such as air temperature and air humidity affect drying. An experimental campaign was performed to investigate the drying performance of External Thermal Insulation Systems (ETICS). Drying kinetics was examined at three air temperatures, four solar orientations and two different air humidities. A first-order kinetics model was obtained, in which the drying time constant was a function of the drying conditions, and the equilibrium material moisture content was described by several different models, such as linear type, power type, exponential type, Arrhenius type and Logarithmic type. The parameters of the proposed model were found to be affected strongly by the material and the drying air conditions.

scholarly journals Drying kinetics of mango fruit using tray and oven dryer

2020 ◽  
Vol 3 (2) ◽  
pp. 51
Author(s):  
Nurhasmanina Norhadi ◽  
Ammar Mohd Akhir ◽  
Nor Roslina Rosli ◽  
Farid Mulana
Keyword(s):  
Moisture Content ◽  
Drying Kinetics ◽  
Drying Rate ◽  
Airflow Rate ◽  
Drying Process ◽  
Air Velocity ◽  
Mango Fruit ◽  
Drying Time ◽  
Different Temperatures ◽  
Kinetics Of

Drying is generally used to increase the shelf life of food products. In this context, mango fruit is used as a sample for the drying process because of its high commercial value and particularly high moisture content. The mango was sliced into few batches of sample with a size of 20 mm × 30 mm × 5 mm each. The experiments were conducted using tray and oven dryer at different temperatures of 40, 50 and 60 °C with a steady airflow rate of 1.3 m/s. The objectives are to study the effect of drying time, temperature and air velocity towards drying of mango fruit, to compare the physical characteristics of mango sample after drying and to determine the best drying kinetics model fitted to each tray and oven dryer. The results showed that the increase in drying time, temperature and air velocity would reduce the moisture content while at the same time, drying rate increased significantly. Tray dryer was found to be more effective than oven dryer because of higher drying rate with better product quality and appearance at the end. Furthermore, the gathered data were fitted into few widely used drying mathematical models and it was found that Henderson and Pabis model at 60°C is best suited for tray dryer whereas Page model at 40 °C is the best for oven dryer.

scholarly journals Kinetics of heat and moisture exchange and method for calculating the duration of the convective drying process of natural leather

2020 ◽  
Vol 65 (4) ◽  
pp. 464-475
Author(s):  
A. I. Alshansky ◽  
A. L. Klimentyev
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Drying Kinetics ◽  
Drying Process ◽  
Drying Time ◽  
Moisture Exchange ◽  
Kinetics Of ◽  
The Heat Transfer Coefficient

Methods for processing experimental data based on generalized variables of the drying process, which characterize the most general patterns of drying in a period of decreasing speed, are considered. A method for processing experimental data based on the expanded level of drying kinetics is presented, which allows obtaining all dependencies for calculating the main parameters of the drying process. Equations are given for determining the densities of heat fluxes, the intensity of moisture evaporation, the temperature of the material, and the duration of drying for the period of falling speed. A dependence is given for calculating the Rebinder number, which establishes a relationship between moisture exchange and heat exchange for the second drying period. The values of all the coefficients in the equation for the Nusselt heat transfer criterion, which are necessary for determining the heat transfer coefficients, have been established. Calculations of the heat transfer coefficient for a number of modes of natural leather drying are presented. On the basis of the method for calculating the drying kinetics developed by B.S. Sazhin, an equation was established to determine the drying time of leather, which describes the entire drying process, including both drying periods. This method of calculating the kinetics of drying contains a minimum number of coefficients determined empirically, which reduces the amount of work at processing these experiments and the number of necessary experiments. The main constants in the criterial heat transfer equation for determining the heat transfer coefficient have been determined. Verification of the reliability of all obtained equations and comparison of the calculated and experimental values for all parameters of the drying kinetics are given. The obtained results of the study of drying natural leathers make it possible to control the technological process, preventing overdrying of the leather, disturbing the temperature regime, which leads to a reduction in energy costs for drying.

scholarly journals The Effect of Vacuum Impregnation Pretreatment on Air-Drying Kinetics of Pears

2020 ◽  
Vol 8 (11) ◽  
pp. 2248-2254
Author(s):  
Şeyma Uysal ◽  
Fikret Pazır
Keyword(s):  
Effective Diffusion ◽  
Solution Concentration ◽  
Drying Kinetics ◽  
Vacuum Impregnation ◽  
Drying Process ◽  
Drying Time ◽  
Air Drying ◽  
Pyrus Communis L ◽  
Experimental Values ◽  
Kinetics Of

The aim of this study was to examine the drying kinetics of pears (Pyrus communis L.) with and without vacuum impregnation and under the different temperature by using tray dryer. Vacuum impregnation were applied to the the pears (15 mm thickness, 65 mm outer and 20 mm inner dimensions respectively) with the conditions of 50⁰ Brix impregnation solution concentration, 225 mbar vacuum pressure and 45 min vacuum time. Drying process was carried out at temperatures of 55, 65 and 75°C. Drying time of non-vacuum impregnated pears was determined 640, 500 and 340 min and vacuum impregnated pears was determined 700, 540 and 560 min respectively. Page, Exponential, Henderson and Pabis, Diffusion Approach were examined for testing the drying kinetics. Experimental values are in accordance with the expected values resulted Page and Difussion models of with and without vacuum impregnated pears. Effective diffusion coefficient (Deff) was varying 2.74×10-11 to 7.31×10-11 m2/s. m2/s with respect to the drying temperatures. The activation energy for the non-vacuum impregnated and vacuum impregnated pears was 32.93 kJ / mol and 24.25 kJ / mol, respectively.

scholarly journals The kinetics of nutritional quality changes during winter jujube slices drying process

2021 ◽  
Vol 13 (1) ◽  
pp. 73-82
Author(s):  
Yubao Niu ◽  
Shiyu Wei ◽  
Huan Liu ◽  
Yongzhen Zang ◽  
Yuxue Cao ◽  
...  
Keyword(s):  
Degradation Kinetics ◽  
Weibull Model ◽  
Reducing Sugar ◽  
Total Acidity ◽  
Drying Process ◽  
Drying Time ◽  
Nutrient Quality ◽  
Air Impingement ◽  
Weibull Models ◽  
Kinetics Of

The purpose of this research is to investigate the kinetics of nutrient quality (Vitamin C (Vc), reducing sugar and total acidity) change of winter jujube slices that under different drying temperatures (55, 60, 65 and 70?) and different air velocities (3, 6 and 9m/s) during the air-impingement drying process. Results showed that the content of Vc, reducing sugar and total acidity decreased with increasing drying time. Furthermore, analysis of variances indicated that the drying temperature, air velocity and time had a significant effect on the loss of Vc, reducing sugar and total acidity (p<0.05). Zero order, first order and Weibull models were used to fit the experimental data, Weibull model was considered as the most suitable one to the degradation kinetics of Vc, reducing sugar and total acidity in dried samples at different temperatures and air velocities. According to the Arrhenius formula, the activation energy of Vc, reducing sugar and total acidity degradation kinetics were 63.78 kJ/mol, 36.48 kJ/mol and 153.51 kJ/mol, respectively. This research can provide some references for enhancing dried products quality in the jujube drying industry.

scholarly journals Mathematical modeling of pequi pulp drying and effective diffusivity determination

2017 ◽  
Vol 21 (7) ◽  
pp. 493-498 ◽  
Author(s):  
Elisabete P. de Sousa ◽  
Rossana M. F. de Figueirêdo ◽  
Josivanda P. Gomes ◽  
Alexandre J. de M. Queiroz ◽  
Deise S. de Castro ◽  
...  
Keyword(s):  
Experimental Data ◽  
Effective Diffusivity ◽  
Drying Kinetics ◽  
Convective Drying ◽  
Drying Time ◽  
Air Speed ◽  
Drying Curves ◽  
Increasing Temperature ◽  
Kinetics Of ◽  
Best Fit

ABSTRACT The aim of this work was to study the drying kinetics of pequi pulp by convective drying at different conditions of temperature (50, 60, 70 and 80 °C) and thickness (0.5, 1.0 and 1.5 cm) at the air speed of 1.0 m s-1, with no addition of adjuvant. The experimental data of pequi pulp drying kinetics were used to plot drying curves and fitted to the models: Midilli, Page, Henderson & Pabis and Newton. Effective diffusivity was calculated using the Fick’s diffusion model for a flat plate. It was found that, with increasing thickness, the drying time increased and, with increasing temperature, the drying time was reduced. The Midilli model showed the best fit to the experimental data of pequi pulp drying at all temperatures and thicknesses, presenting higher coefficients of determination (R2), indicating that this model satisfactorily represents the pequi pulp drying phenomenon. There was a trend of increase in the effective diffusivity with the increase in pulp layer thickness and temperature.

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