Effective Mass Transfer Coefficient Research Articles

Efficient estimation of gas exchange and respiration kinetics in apple using pathlength-resolved GASMAS

Optimization of controlled atmosphere (CA) storage of pome fruit crucially depends on understanding of respiratory gas exchange. Different fruit properties are involved in describing gas transfer and respiration kinetics, which can vary between cultivars, fruit batches and individual fruit. Determination of these properties currently requires a combination of different time-consuming techniques and data analysis procedures. This study introduces a more efficient single method for O2 gas exchange characterization of fruit based on the non-destructive pathlength-resolved GASMAS (gas in scattering media absorption spectroscopy) technique. GASMAS was used to measure the absolute intercellular O2 concentration in fruit of different apple cultivars (Malus x domestica Borkh.) with distinct porosity including 'Jonagold', 'Braeburn', and 'Nicoter'. To resolve the ambiguity between variation in pathlength and O2 concentration inherent to GASMAS, the pathlength travelled through pores cavities was quantified through a second GASMAS measurement at the absorption line of H2O vapour. Dynamic experiments were then performed in which the fruit was subjected to varying external O2 concentrations while measuring the internal O2 response. The observed dynamic profiles of external and internal O2 concentration were fitted with a lumped -respiration model to estimate the effective mass transfer coefficient, maximum respiration rate and Michaelis Menten constant of intact fruit. The model showed a good fit (R2>0.95) with the measured data and reliable estimates for the model parameters. The proposed method provides a novel and more efficient way to estimate the gas exchange properties of fruit that are essential for optimizing CA storage conditions. Future challenges for the proposed method are with applications to other gasses such as CO2 and ethylene.

Analysis of mass transfer characteristics in a planar solid oxide fuel cell with a chaotic flow channel

The flow channel design is crucial for the heat and mass transfer of reactants in a solid oxide fuel cell (SOFC), which ultimately affects the overall performance of the cell. To improve the gas transport characteristics and temperature uniformity, a chaotic flow channel with orthogonal corrugation is adopted for the design of a planar SOFC stack, and the influence of different wave parameters is evaluated. The results show that the chaotic flow channel induces secondary flow through the superposition of orthogonal waves, which reduces the low-oxygen region and enhances the local electrochemical reaction. The output power is improved in the chaotic flow channel by increasing the amplitude or decreasing the wavelength. The output power density with amplitude of 0.3 mm and wavelength of 1.2 mm at 0.5 V is increased by about 25.16 %. Meanwhile, the effective mass transfer coefficient and mass transfer efficiency is enhanced by 148 % and 378 %, respectively. Additionally, the chaotic structure improves the uniformity of oxygen and temperature. This study helps to improve the understanding of the gas transport processes within the flow channel and provides a basis for the design and optimization of SOFC flow channels.

Drying Kinetics and Mass Transfer Characteristics of Walnut under Hot Air Drying

This study was conducted to investigate the drying kinetics and internal and external mass transfer characteristics of walnuts for an understanding of the drying mechanism. The drying characteristics, mass transfer characteristics, and color of walnut during hot air drying (HAD) were investigated under different initial moisture content (IMC) (0.35, 0.39, and 0.43 g water/g wet mass) and drying temperatures (50, 60, 70, and 80 °C). The results indicated that the IMC and drying temperature both have significant effects on the drying process of walnut, showing the higher the IMC, the longer the preheating time, the smaller the effective moisture diffusivity (Deff) and mass transfer coefficient (hm), and the longer the drying time, but reverse results for drying temperature. The values of Deff and hm for walnut ranged from 4.94 × 10−10 to 1.44 × 10−9 m2/s and 1.24 × 10−7 to 3.90 × 10−7 m/s, respectively. The values of activation energy for moisture diffusion and mass transfer ranged from 21.56 to 23.35 kJ/mol and 28.92 to 33.43 kJ/mol, respectively. Multivariate linear prediction models were also established for estimating the Deff and hm as a function of the HAD process parameters. The drying temperature has a greater effect on the walnut kernel lightness than the IMC. The Verma et al model could be used to describe the HAD process of the walnut. The findings contribute to the understanding of moisture transfer mechanisms in walnuts and have practical value for the evaluation and improvement of drying systems.

Modeling the Structure and Diffusion of Porous Layers

The aim of this work is to develop an adsorber with a fixed bed of adsorbent and a mathematical model of the adsorption bed. On the basis of the theory of fractal clusters, an equation for calculating the layer porosity that takes into account the average cluster radius, the fractal dimension of the cluster structure and the anisotropy index of the adsorbent layer is proposed. The adsorption mechanism in the layer was established, and the proportionality coefficients were estimated based on the tetrahedral packing of grains in the layer. Based on the analysis of the movement of the carrier through the adsorption layer and its deformation, an equation that describes the change in the porosity of the granular layer when the water flow moves through it, depending on the proportionality coefficients, is proposed. An equation that made it possible to calculate the change in the porosity of the layer in comparison with the porosity of the stationary stacking was obtained. An effective design for the adsorber that made it possible to increase the efficiency of using the structure of porous adsorption layers was developed. Equations of the heat and mass transfer taking into account the granule shape coefficient, effective diffusion coefficient and mass transfer coefficient were derived. These equations establish the relationship between the average distance between active centers on the adsorption surface and the degree of filling of the adsorption surface with the adsorbed component.

Numerical analysis of the heat and mass transfer process in absorbers using water and lithium bromide

This study aimed to simulate the heat and mass transfer process of a spiral tubular Lithium Bromide/Water (LiBr/H2O) absorber based on a non-linear mathematical model developed in MATLAB program, using an iterative numerical method and experimental data from the literature for calibration and validation. For this, the absorber was simplified as a descending film flat plate and the simulation considered three different cases of cooling water temperature variation: 21.5°C, 23.5°C, 25.6°C. The effective mass transfer coefficient, Kef, was obtained from the literature, and the overall heat transfer coefficient, U, was calculated using the overall thermal resistance within the absorber. The distributions for the temperature and concentration of the solution and cooling water, obtained by the model, showed good agreement when compared to the literature. It was found that the heat and mass transfer increased when varying the absorber length up to 14.25 m, and from this value on, they remained nearly constant. Increasing the mass flow rate of the cooling water inlet decreases the temperature and concentration of the LiBr/H2O. In addition, copper and aluminum proved to be more suitable for use in the absorber tube than stainless steel.

Flow characteristics analysis and performance evaluation of a novel rotary proton exchange membrane fuel cell

This paper proposes a new type of rotary proton exchange membrane fuel cell (R-PEMFC) and its simulation model is established and verified based on experimental data. Then the effects of different rotational angular speeds (RASs) on reactant flow characteristics and electrochemical reactions are investigated. Also, the key quantitative indexes, such as average value, uniformity index and effective mass transfer coefficient (EMTC) are adopted, while combining the polarization curve and net power to estimate the comprehensive R-PEMFC performance. The results indicate that the R-PEMFC effectively ameliorates uneven distribution and improves the transmission capability and output performance. Compared with the static state (0 rpm), the EMTC and maximum power density are enhanced by 65.86 % and 8.51 % respectively at the RAS of 1080 rpm, and the net power density can reach 5316 W·m−2.

An analytical model to decompose mass transfer and chemical process contributions to molecular iodine release from aqueous phase under severe accident conditions

Radioactive iodine is a representative fission product to be quantified for the safety assessment of nuclear facilities. In integral severe accident analysis codes, the iodine behavior is usually described by a multi-physical model of iodine chemistry in aqueous phase under radiation field and mass transfer through gas-liquid interface. The focus of studies on iodine source term evaluations using the combination approach is usually put on the chemical aspect, but each contribution to the iodine amount released to the environment has not been decomposed so far. In this study, we attempted the decomposition by revising the two-film theory of molecular-iodine mass transfer. The model involves an effective overall mass transfer coefficient to consider the iodine chemistry. The decomposition was performed by regarding the coefficient as a product of two functions of pH and the overall mass transfer coefficient for molecular iodine. The procedure was applied to the EPICUR experiment and suppression chamber in BWR.

Solid-liquid extraction of chlorogenic acid from Eucommia ulmoides Oliver leaves: Kinetic and mass transfer studies

Chlorogenic acid is an important natural active compound in Eucommia ulmoides Oliver leaves. A second-order kinetic model was considered applicable for the solid-liquid extraction process and revealed the positive effects of reducing the particle size, increasing the liquid-solid ratio and temperature on accelerating the extraction rate and increasing the equilibrium yield. An empirical model on the studied variables was developed to predict the extraction process and its feasibility was verified. The activation energy was 19.67 kJ mol−1. The mass transfer process was investigated based on Fick’s second law, where the extraction rate depends on the internal diffusion of the compound and the internal resistance was the main factor affecting the extraction process. Temperature and liquid-solid ratio significantly changed the effective diffusion coefficient and mass transfer coefficient in different ways, and the Biot number was related to the liquid-solid ratio. Overall, these findings provided fundamental datas and theoretical guidances for the extraction of chlorogenic acid.

Numerical Study on the Influence of Variable Section-Enhanced Mass Transfer Flow Field Design on PEMFC Performance Based on Underrib Convection Flow

The optimal design of variable section is a flow field optimization method that changes the pressure of the reacting gas in the flow channel by setting up a contraction surface in the flow channel, which is effective in improving many aspects of the proton exchange membrane fuel cell (PEMFC) performance. However, there are also problems such as uneven oxygen distribution in some of the flow channels, and the current density and net output power are not significantly improved. To find a balance among gas transfer efficiency, drainage capacity, uniformity of current density distribution, and output performance, this paper investigates the design of a variable cross-section-enhanced mass transfer flow field for PEMFC flow channel contraction by establishing a three-dimensional numerical model, starting from the sidewall width direction and the bottom height direction of the flow channel cross-section dimensions, in order to assess the effects of variable cross-section contraction at the bottom and sidewalls of the flow channel on the cell performance. The polarization curves, mass transfer capacity, current density distribution, and net output power of the variable cross-section contraction flow field are analyzed and compared with the straight flow field. On this basis, the optimum size parameters and operating parameter combinations are determined. Variable cross-sectional contraction flow field improves PEMFC output performance. The contraction of the variable cross-section contraction flow field at the sidewalls effectively improves reactive gas transfer efficiency and drainage capacity, improves current density distribution, and increases the net output power of the PEMFC. In particular, the sidewall contraction flow field has a 9.0% increase in power density, a 6.45% increase in the effective mass transfer coefficient (EMTC), a 6.52% increase in uniformity of current density distribution, and a 6.05% net power increment compared to the straight flow field, respectively. The best output performance, the highest oxygen concentration, and the lowest water concentration are achieved with a combination of parameters: number of sidewall contractions N = 6 , length L f = 6 mm , and width W f = 1.2 mm . And a wide range of air stoichiometry ratios are applied when the contraction of the variable cross-section contraction flow field is located at the sidewalls. Increasing the cathode stoichiometry ratio from 10 to 50 increased the cell power density by 25.5% and from 50 to 90 increased the cell power density by 9.5%. The simulation results can provide theoretical basis for the application of variable section flow field design for practical PEMFC.

Mass transfer parameters and quality characteristics of aonla slices under refractance window drying

This study investigates the effects of refractance window (RW) drying process parameters on mass transfer and quality characteristics of dried aonla slices. RW drying of aonla slices was carried out at three levels of water temperature (75, 82 and 90 °C) and slice thickness (2, 4 and 6 mm). In terms of quality characterization, the total phenolic content, ascorbic acid content, and browning index were determined. Higher retention of ascorbic acid (64.49 ± 0.34%) and phenolic content (37.84 ± 0.08 mg GAE/g dry matter) was found at 90 and 82 °C water temperature, respectively with inconsequential variation in browning index. Mass transfer parameters such as Biot number, effective moisture diffusivity and mass transfer coefficient were estimated using Dincer and Dost model. Effective moisture diffusivity during drying varied from 4.27 × 10−10 to 1.09 × 10−09 m2s−1 and Biot number was observed to be in the range of 0.268 to 8.666 for different drying conditions. XRD pattern suggested that RW dried aonla slices had semi-crystalline structure. The changes in crystalline structure to amorphous was pronounced more at high water temperature. It was also revealed by the disintegration of cell wall/membrane and connecting surfaces, which resulted into smooth and flaky microstructures with sharp edges. The gamut of crystallite size was obtained as 49.12 ± 0.26 to 99.12 ± 1.19 nm. The presence of bound water after completion of drying was represented by FTIR peaks centered around 3577 cm−1. The infrared spectroscopy of RW dried aonla postulated that peak intensity of absorption bands negligibly changed with varying processing conditions, but minor peak shift was observed. This study elucidates the suitability of RW drying for retention of heat-sensitive compounds in food produce such as aonla with better quality retention and morphological characteristics.

Moisture diffusion modelling and effect of microwave vacuum drying on drying kinetics and quality of yam

Microwave vacuum drying (MVD) is a rapid drying method, which can achieve a good balance between drying rate and quality. In the present work, the effects of MVD processes on the quality, drying kinetics, and moisture diffusion of yam (Dioscorea opposita L.) were investigated. Results indicated that the loss of moisture in the MVD of yam slices mainly occurred in the stage with a constant and decreasing speed. When the moisture content of the dry base was decreased to about 1.3 g/g (dry basis, D.B.), it began to enter the deceleration phase. The effective moisture diffusivity (Deff) and mass transfer coefficient (km) increased following the power, loading amount at one time, and vacuum (pressure drop). The established equation of these parameters described well this variation law. Furthermore, a neural network model was established to predict the change in moisture content in the drying process, and the law of moisture diffusion was described. In terms of quality, the contribution ranked from high to low was loading, power, and pressure. Increasing the microwave power, loading, and maintaining a high vacuum degree could reduce energy consumption and ensure quality, thus improving the economic feasibility of microwave vacuum in the drying process.

An engineered biochar for treatment of selenite contaminated water: Mass transfer characteristics in fixed bed adsorption

Biochar composites have been gaining attention in recent years as a promising and cost-effective material for wastewater treatment. In the present study, a novel procedure was developed to create a biochar (BC) composite impregnated with binary zinc (Zn) and iron (Fe) oxides (denoted as ZnFeBC). The procedure was optimized to enhance selenite, Se(IV), adsorption performance of the ZnFeBC composite. The modified biochar composite had excellent pore characteristics with a specific surface area of 854 m2/g. The maximum Se(IV) adsorption capacity of an unary Zn-loaded biochar composite was 520 µg/g, which significantly increased to 4,100 µg/g after the iron oxide impregnation. Isotherm experiments suggested that the adsorption process was likely through homogeneous monolayer adsorption. The ZnFeBC composite exhibited excellent performance over a broad range of pH values, with the highest Se(IV) adsorption capacities observed at lower pH values (maximums at pH 3). X-ray absorption near edge structure spectroscopy (XANES) indicated that the redox reaction of Se oxyanions did not occur during the adsorption process. ZnFeBC was successfully used to remove Se(IV) from a mining lake water matrix in a fixed-bed adsorption system. Additionally, a mass transfer model optimizing effective diffusion and external mass transfer coefficients was developed to comprehensively assess the adsorption system. Overall, ZnFeBC exhibited great potential as an adsorbent for treating Se(IV) contaminated waters and the developed mass transfer model is useful for scaling up fixed-bed adsorption systems.

Evaluation of drying kinetics of carrot and thermal characteristics of natural and forced convection indirect solar dryer

The thermal characteristics of natural (setup-A) and forced (setup-B) convection indirect solar dryers were evaluated and compared by drying carrot slices. Several modifications were made to setup-A to promote setup-B, including a trapezoidal tunnel, and central processing unit fans which were powered by photovoltaic panels. From the experimental solution, the performance terminologies and the drying characteristics of the carrot were examined. The actual rate of heat supplied to setup-A was 705.64 W and setup-B was 789.55 W. In the respective tests, collectors had an average efficiency of 56.84% and 68.74%. Accordingly, the drying efficiencies for the same were 7.5% and 9.55%, respectively. As a result of the aforementioned calculations, activation energy, effective diffusion coefficient, mass and heat transfer coefficients for setup-A and setup-B were 42.71 kJ/mol and 37.85 kJ/mol, 6.32 × 10−9 m2/s and 7.25 × 10−9 m2/s, 0.0055 m/s and 0.0065 m/s, and 6.32 W/m2 K and 7.25 W/m2 K, respectively. The setup-B showed a better effective moisture extraction rate and energy consumption. Characteristic relationships between moisture content vs diffusion, heat and mass transport coefficients were derived. Uncertainty estimations were performed to verify the precision of the findings.

Mercury removal from aqueous media by aminated polyacrylonitrile beads impregnated with nano-urchin bismuth sulfide particles: Experimental and theoretical analysis under batch and continuous mode

The present study encompasses a thorough analysis of aqueous Hg (II) adsorption using aminated polyacrylonitrile beads incorporated with high-capacity surfactant assisted bismuth sulfide nanoparticles. The porous beads provided effective contact between aqueous Hg and the inorganic nano-adsorbent (PBS2) that was encapsulated in the matrix. The macro-sized beads served as suitable packing material for designing a fixed bed adsorption column for continuous mode analysis without significant pressure build up and offered an easy solid–liquid separation after treatment. A marginal negative zeta potential of the adsorbent beads improved the interaction with Hg2+ facilitating the sorption. The incorporation of amine groups into the polymeric bead surface via amination increased the adsorption capacity further from 83.30 mg/g to 130.00 mg/g (∼56.00%) at 303 K. The associated parameters of batch kinetics (effective pore diffusivity and mass transfer coefficient) were determined using a first principle-based model available in literature. Mercury was chemisorbed via synergistic lone pair interactions of S and N atoms with Hg, leading to formation of coordination bonds (Hg-S and Hg-N). An established mass transfer model was utilized to generate simulated breakthrough curves for the continuous analysis using synthetic feed. Additionally, the adsorption column showed comparable performance using both synthetic and real water samples (synthetically spiked) maintaining high selectivity. The optimized values of axial dispersion coefficient (Ez) and fixed bed mass transfer coefficient (kfb) were estimated and subsequently used for the scale up studies to predict column life. The adsorbent beads were regenerated using 0.05 M EDTA aqueous solution and showed good reusability (>95.00%) after 5 cycles of operation. Overall, this work highlights a reusable Hg adsorbent possessing good selectivity and capacity and simultaneously demonstrating real-field applicability.

Heat and Mass Transfer, Quality, Performance Analysis, and Modeling of Thin Layer Drying Kinetics of Banana Slices

Abstract In this study, experimental works were carried out in three different drying methods named heat exchanger-evacuated tube-assisted drying system (HE-ETADS), greenhouse solar dryer (GHSD), and open sun drying (OSD) to compare thin-layer drying kinetics, concept of mass transfer, and quality assessment of banana slices. Initial moisture content (MC) of banana slices was obtained as 78 ± 2.0% (wb), which decreased to 23.2 ± 2.0% (wb), 25.6 ± 2.0% (wb), and 28.8 ± 2.0% (wb) in all three drying systems, respectively, in 9 h of drying time. Average drying rate was evaluated as 7.89, 7.65, and 7.25 g water/g solid h in HE-ETADS, GHSD, and OSD, respectively. Weibull model (WM) defines thin-layer drying kinetics of banana slices in all three drying processes. Maximum hardness and shrinkage factor of dried banana slices were obtained as 373.6 g and 75%, respectively, in HE-ETADS. Effective moisture diffusivity, activation energy, and mass transfer coefficient were computed as 1.11–2.48 × 10−07 m2 s−1, 30.25 kJ/mole, and 3.21–1.0 × 10−04 m/s, in HE-ETADS. Similarly, in GHSD and OSD, these factors were observed as 1.21–2.34 × 10−07 m2 s−1, 41.25 kJ/mole, 3.15–1.0 × 10−04 m/s and 1.3–2.21 × 10−07 m2 s−1, 56.89 kJ/mole, 3.01–1.0 × 10−04 m/s. Maximum total color changes were noted in OSD. Hence, HE-ETADS can potentially dry high moisture content crops effectively within a minimum drying period.

A novel cathode flow field for PEMFC and its performance analysis

A good flow field design is important to the proton exchange membrane fuel cell (PEMFC) performance, especially under a high current density region, which is dominated by concentration polarization. Motivated by the variable cross-section channel idea, in this study, a novel flow field containing a converging-diverging (C-D) pattern is proposed. A three-dimensional multiphase model is established to study its performance. The numerical results show that it outperforms the conventional straight channel and only depth-variant channel. In the novel flow field the enhanced under land cross flow and higher effective mass transfer coefficient both improve the reactant transport. The effects of operating conditions, like stoichiometric ratio and operating pressure, on cell output performance are studied. It is found that a higher promotion rate can be obtained by increasing the stoichiometric ratio, but increasing the operating pressure has little effect. The droplet dynamic behavior in the C-D channel and straight channel are studied, and the results prove the better drainage capability of the novel flow field.

Experimental performance of proton exchange membrane fuel cell with novel flow fields and numerical investigation of water-gas transport enhancement

The performance of the proton exchange membrane fuel cell (PEMFC) depends on the water-gas transport capacity of flow fields. In this paper, the performance of the designed PEMFC with novel flow fields is tested by experimental methods. The experimental results show that the PEMFC with opposite sinusoidal wave flow field (OSWFF) and intercepted flow field (ICFF) are improved compared to the parallel flow field. The PEMFC with single-inlet OSWFF and ICFF show 19% and 11% performance enhancement at 2.0 A cm−2, respectively. A 3D numerical model for the validation experiment is established to analyze the water-gas transport characteristics of the flow field. The mass transfer performance of ICFF with 3D structural optimization is much better than that of OSWFF with 2D structural optimization, and the effective mass transfer coefficient and efficiency evaluation criterion are improved by 106% and 258%, respectively. The 7% improvement in oxygen uniformity in the dual-inlet mode compared to the single-inlet mode enhances the stability of the electrochemical reaction and the 28% improvement in velocity uniformity, which contributes to the uniform distribution and discharge of liquid water, which in turn enhances the PEMFC performance.

発泡プラスチック系断熱材の表面被覆層が長期断熱性能に及ぼす影響

It is known that the thermal conductivity of insulation foams increases with time due to the emission of the blowing agents from foams and the transfer of the air into them. In this paper, the aging of thermal conductivity in phenolic foam is discussed with measured data and numerical analysis. Measurement of specimens with different thicknesses and surface material conditions are conducted and the aging characteristics are examined. Using the estimation equations of thermal conductivity change, the effective diffusion coefficient and mass transfer coefficient of the blowing agents is obtained by comparing the simulation results and the measured value.

Drying kinetics and shrinkage rate of thin‐sliced pears in different drying stages

AbstractIn this research, the effect of different parameters of a convective hot air dryer on the mass transfer coefficients of thin‐sliced pears in different drying stages is analytically and experimentally investigated. According to the results, in the first stage of drying which begins from the initial moisture content (MC) of 87–57% in this study, the convective heat transfer coefficient, the inlet air temperature and the initial MC of the product had the highest influence on the mass transfer rate of the drying product. In the second drying stage (from 57 to 27% MC), the structure of internal pore of the fruit, the internal MC and the thickness of the cut layers are the most influencing parameters controlling the mass transfer coefficient of the product. In the third region of drying (from MC of 27% to the final MC), the inlet air temperature had the greatest effect on the rate of mass transfer from the product. In this region of drying, increasing the drying temperature from 50 to 60°C at an airflow velocity of 0.5 m/s, yielded increasing the effective diffusion coefficient from 1.19 × 10−7 to 4.09 × 10−7 m/s2. The results of this study showed that increasing the airflow rate in the third stage of drying reduces the effective mass transfer coefficient. The highest effective diffusion coefficient in the third region of drying for thin‐sliced pears was obtained equal to 6.24 × 10−7 m/s2 for drying temperature of 80°C and airflow velocity of 0.5 m/s.Practical ApplicationsPears (Pyrus communis L.) are bell‐shaped fruits that are in the range of green, yellow, brown, red, or a combination of these colors. This useful fruit is rich in potassium, vitamins, and minerals. There are 30 varieties of pears in the world and they are consumed cooked, compote, or raw. The drying process of fruits and vegetables by reducing the moisture of the product, prevents chemical and biochemical spoilage of the product and increases their shelf life. However, some undesirable physical and chemical changes such as discoloration, texture, and nutritional value may also occur during drying, which reduces consumer acceptance. Drying operations usually take place in the final stages and after other operations and lead to the production of the final product.

Numerical Simulation of Heat and Mass Transfer in Sludge Low-Temperature Drying Process.

Based on the sludge mass transfer flux model, this paper conducts a simulation study on the drying characteristics of sludge under low-temperature environment and compares it with the previous experimental results. It is found that when the sludge moisture content is low, the change of its drying curve is basically consistent with the experimental results, but there is a large error when the sludge moisture content is 0.4-0.6. In order to better simulate sludge drying characteristics, a model of cracking and shrinkage coefficients based on sludge moisture content is proposed, and the effective diffusion coefficient and mass transfer coefficient are modified. The maximum error between simulation and experiment is reduced to 23.78%. Based on this model, the sludge drying mechanism was studied. It was found that heat transfer and diffusion played a major role in the initial stage of sludge drying, and diffusion played a major role in sludge drying 30 min later.