Heat and Mass Transfer in Shrimp Hot-Air Drying: Experimental Evaluation and Numerical Simulation

Abstract

Shrimp is one of the most popular and widely consumed seafood products worldwide. It is highly perishable due to its high moisture content. Thus, dehydration is commonly used to extend its shelf life, mostly via air drying, leading to a temperature increase, moisture removal, and matrix shrinkage. In this study, a mathematical model was developed to describe the changes in moisture and temperature distribution in shrimp during hot-air drying. The model considered the heat and mass transfer in an irregular-shaped computational domain and was solved using the finite element method. Convective heat and mass transfer coefficients (57.0-62.9 W/m²∙K and 0.007-0.008 m/s, respectively) and the moisture effective diffusion coefficient (6.5 × 10^-10-8.5 × 10^-10 m²/s) were determined experimentally and numerically. The shrimp temperature and moisture numerical solution were validated using a cabinet dryer with a forced air circulation at 60 and 70 °C. The model predictions demonstrated close agreement with the experimental data (R2≥ 0.95 for all conditions) and revealed three distinct drying stages: initial warming up, constant drying rate, and falling drying rate at the end. Initially, the shrimp temperature increased from 25 °C to around 46 °C and 53 °C for the process at 60 °C and 70 °C. Thus, it presented a constant drying rate, around 0.04 kg/kg min at 60 °C and 0.05 kg/kg min at 70 °C. During this stage, the process is controlled by the heat transferred from the surroundings. Subsequently, the internal resistance to mass transfer becomes the dominant factor, leading to a decrease in the drying rate and an increase in temperatures. A numerical analysis indicated that considering the irregular shape of the shrimp provides more realistic moisture and temperature profiles compared to the simplified finite cylinder geometry. Furthermore, a sensitivity analysis was performed using the validated model to assess the impact of the mass and heat transfer parameters and relative humidity inside the cavity on the drying process. The proposed model accurately described the drying, allowing the further evaluation of the quality and safety aspects and optimizing the process.

Keywords: CFD; food preservation; mathematical modeling; seafood.

Figure 1

(a) Schematic representation of experimental device; (b) illustrations of the shrimp sample, computational domain with the heat and mass transport mechanisms considered in the model, and the mesh used in the numerical solution.

Figure 2

(a) Aluminum object used for h_T estimation; (b) experimental data of aluminum temperature (points) and the fit of Equation 12 (black line). The dashed lines indicate the experimental air temperature.

Figure 3

Influences of the number of elements on the calculated moisture content in the center of the shrimp (X_db,c) during drying at 60 °C.

Figure 4

Moisture content (left side) and mid-layer temperature (right side) curves obtained experimentally (dots) and predicted by the mathematical model (continuous lines) during shrimp drying at 60 °C (a) and 70 °C (b). Values were calculated using a computational domain discretized with a maximum element size of 1 mm.

Figure 5

(a) Total drying rate (dX_db/dt, continuous lines) and temperature (T, dotted lines) of the shrimp as a function of the moisture content (X_db) over drying at 60 °C (blue) and 70 °C (red). (b) Average heat flux transferred to the shrimp via convection ($q_{conv}^{″}$, continuous lines) and evaporative heat flux ($q_{evap}^{″}$, dotted lines) in the shrimp surface over-drying at 60 °C (blue) and 70 °C (red). Numerical results used computational domain discretized with a maximum element size of 1 mm.

Figure 6

Temperature profiles (T) in the mid-layer of the shrimp during the drying at 60 °C calculated using a computational domain discretized with a maximum element size of 1 mm.

Figure 7

Moisture content profiles (X_db) in mid-layer of the shrimp during the drying at 60 °C calculated using a computational domain discretized with a maximum element size of 1 mm.

Figure 8

(a) Numerical solution for moisture and temperature distribution in the shrimp after 180 min of drying at 60 °C for cylindrical-shaped and irregular-shaped computational domains. (b) Moisture content and mid-layer temperature curves (black lines—irregular shape, red lines—cylindrical shape). Values were obtained with computational domain discretized with a maximum element size of 1 mm.

Figure 9

Temperature (T) and moisture (X_db) kinetics resulting from parametric analysis of (a) diffusion coefficient (D), (b) convective transfer coefficients (h_T and h_m), and (c) relative humidity of air (RH) during shrimp drying at 60 °C. Numerical results obtained using a computational domain with a maximum element size of 1 mm.