AERODYNAMICS OF A CASCADE DRYER AND ITS INFLUENCE ON TECHNICAL PARAMETERS

ABSTRACT

The article analyzes the aerodynamics of the air flow in cascade dryers and examines its influence on technical parameters. The air velocity, pressure distribution, turbulence level, and the interrelation of heat and mass transfer processes were studied using both experimental and theoretical methods. The analysis results show that by optimally controlling the air flow in cascade drying systems, it is possible to reduce energy consumption during grain drying, ensure stable moisture removal, and improve product quality. The article also presents conclusions regarding the effects of dryer geometry, air distribution, and operating modes on the technical parameters.

АННОТАЦИЯ

В статье анализируется аэродинамика воздушного потока в каскадных сушилках и рассматривается его влияние на технические параметры. Скорость воздуха, распределение давления, уровень турбулентности, а также взаимосвязь процессов тепло- и массообмена были изучены как экспериментальными, так и теоретическими методами. Результаты анализа показали, что при оптимальном управлении воздушным потоком в каскадных системах сушки можно снизить энергозатраты при сушке зерновых продуктов, обеспечить стабильное удаление влаги и повысить качество продукции. В статье также приведены выводы о влиянии геометрии сушилки, распределения воздуха и режимов работы на технические параметры.

Keywords: cascade dryer, aerodynamics, heat transfer, mass transfer, technical parameters, energy efficiency, moisture removal, grain products.

Ключевые слова: каскадная сушилка, аэродинамика, теплообмен, массообмен, технические параметры, энергоэффективность, удаление влаги, зерновые продукты.

Introduction. The efficient drying of grain products remains a pressing issue in agricultural engineering due to its direct impact on product quality and energy consumption. Cascade dryers are widely used for their high throughput and compact structure, yet the internal airflow dynamics within these systems remain insufficiently understood. This study focuses on the aerodynamics of cascade dryers, aiming to identify how air velocity, pressure distribution, and turbulence affect heat and mass transfer efficiency. The hypothesis is that optimizing airflow distribution can significantly enhance drying performance while reducing energy losses. Theoretical models and experimental analysis are used to explore the interrelation between dryer geometry, airflow parameters, and drying outcomes. Given the increasing demand for energy-efficient technologies in agriculture, this research addresses a highly relevant problem and contributes to the scientific foundation needed to improve dryer design and operation [5].

Materials and method.

In particular, in the proposed cascade dryer, aerodynamic resistance has a significant influence on the technical parameters of the device — such as air consumption, energy usage, heat temperature, material moisture content, drying time, and the uniformity of the dried product. When the resistance is high, the movement of the air flow becomes difficult, which reduces the efficiency of the dryer and leads to additional energy consumption. Conversely, an optimal level of aerodynamic resistance ensures proper air distribution, making the drying process stable and economically efficient [1,4,7].

Therefore, it is of great importance to take aerodynamic resistance into account when determining the structural parameters of the cascade dryer. In this study, the effect of aerodynamic resistance on the technical performance of the dryer is analyzed both theoretically and experimentally, and recommendations for optimal operating conditions are developed based on experimental investigations.

To conduct the experimental research, a physical model of the cascade dryer was developed using the MATLAB software, and an experimental setup was prepared. Figure 1 shows the physical model of the cascade dryer designed for the study.

Figure 1. View of the physical model of the cascade dryer

1 – Body of the cascade vertical dryer, 2 – Support frame, 3 – Fan, 4 – Air heater (calorifier), 5 – Duct with damper for distributing the hot air flow, 6 – Inlet pipe for the material to be dried, 7 – Outlet pipe for the heat carrier (exhaust air), 8 – Discharge pipe for the dried material, 9 – Annular fastener (ring clamp), 10 – Frame for mounting the fan and air heater, 11 – Small cascade nozzle, 12 – Large cascade nozzle.

Results and discussions:

At the initial stage of the study, the aerodynamic resistance of the cascade dryer was determined at the lower and upper limits of the variable parameters.
To carry out the experiments, a centrifugal-type fan was used (maximum capacity Q_max = 150 m³/h, motor power N_dv = 0.3 kW, rotational speed n = 400 rpm), together with a Pitot–Prandtl tube (7.18) (50 mm and 100 mm in length), a metal pipeline (D = 60 mm, L = 1200 mm) for measuring the velocity of dusty gas, and two Pitot–Prandtl tubes with an internal diameter of 7 mm to determine static and dynamic pressures. The Pitot–Prandtl tubes were selected in accordance with State Standard (St) requirements based on the outlet diameter of the fan gas pipe to ensure accurate determination of gas velocity, capacity, and pressure.

Additionally, for comparison of the obtained results, an anemometer VA06–TROTEC electronic measuring device was used (measurement range 1.1 m/s ÷ 50 m/s, error coefficient 0.2%; when the gas velocity exceeds 50 m/s, the error increases up to 5%). To control the velocity of the heat carrier, a damper was installed at the outlet of the air heater (calorifier), forming angles of 0°, 30°, 45°, 60°, and 90°. The ambient temperature was also taken into account during the experiments.

At the initial stage of the study, the aerodynamic resistance losses occurring in the working parts of the device were determined experimentally. Considering the multivariable nature of the experiments, tests were conducted separately for the lower and upper parameter limits, and comparative graphs were constructed. The results were compared with the values calculated using Equation (1), and the corresponding errors were determined [2,3,6].

       (1)

 ΔP — pressure drop, N —number of cascade , L — length of the dryer  μ — Dynamic viscosity of the fluid,  ε — Porosity d_p ​ — particle diameter, ρ — Density of the fluid, Q — Volumetric flow rate, D —pipe or filter diameter, ζ_p.t ​ — local resistance coefficient at the inlet,  α — surface opening coefficient  w — Width of the flow channel  ρ ​ — air density V_c​ — Volume of the chamber, l —length of the tube, d — pipe diameter, ζ_m ​ —Intermediate local resistance, ζ_k ​ — Exit local resistance, v —Flow velocity.

The research results are presented in Table 1 and in Figures 2, 3, and 4.

Table 1.

Resistance coefficient of the working elements of the cascade dryer

Figure 2. Dependence of hydraulic resistance on gas velocity (Q = 0.06 kg/s)

1 – when the device productivity is Q_p = 0.06 kg/s, the number of cascade nozzles is 8 units, and the diameter of the perforated holes is 4 mm; 2 – when the device productivity is Q_p = 0.06 kg/s, the number of cascade nozzles is 8 units, and the diameter of the perforated holes is 4 mm.

Figure 3. Dependence of hydraulic resistance on gas velocity (Q = 0.065 kg/s).

1 – when the device productivity is Q_p = 0.065 kg/s, the number of cascade nozzles is 8 units, and the diameter of the perforated holes is 4 mm; 2 – when the device productivity is Q_p = 0.065 kg/s, the number of cascade nozzles is 8 units, and the diameter of the perforated holes is 4 mm.

Figure 4. Dependence of hydraulic resistance on gas velocity (Q = 0.07 kg/s).

1 – when the device productivity is Q_p = 0.07 kg/s, the number of cascade nozzles is 8 units, and the diameter of the perforated holes is 4 mm; 2 – when the device productivity is Q_p = 0.07 kg/s, the number of cascade nozzles is 8 units, and the diameter of the perforated holes is 4 mm.

From the data presented in Figures 2, 3, and 4, it can be observed that when the gas velocity varies within the range of υ = 5–20 m/s (with an interval of 5 m/s) and the mass flow rate increases from Q = 0.06 to 0.07 kg/s (with an increment of 0.005 kg/s), at the lower load applied to the drum dryer, due to the increase in the bracket step and the number of nozzles, the minimum value of the hydraulic resistance increases from ΔP = 50 to 1399 Pa. At the higher load applied to the drum dryer, with the same increase in bracket step and nozzle number, the maximum value of hydraulic resistance increases from ΔP = 59 to 1500 Pa. It can thus be concluded that the increased structural complexity of the drum dryer leads to an increase in hydraulic resistance, which in turn causes the intensification of the drying process. However, an increase in hydraulic resistance has a negative effect on the device’s productivity. Therefore, when selecting the optimal parameters of the device, it is necessary to take these factors into account.

The graphical dependencies presented in Figures 2, 3, and 4 can be expressed by the following regression equations, determined using the least squares method [1,4]. Karilatsiya chizigi hax palinom chiziqdagi karilatsa nuqtasi qiymati

When the device productivity is Q_p=0.06 kg/s

At lower load:

y = 34,257e^0,1825x            R² = 0,9808                   (2)

At higher load:

y = 43,537e^0,1827x                   R² = 0,9906                   (3)

R – value of the cardinal point on the palindrome line in the line graph above.

When the device productivity is Q_p=0.065 kg/s;

At lower load:

y = 34,257e^0,1825x            R² = 0,9908                   (4)

At higher load:

y = 45,513e^0,1825x            R² = 0,991                     (5)

R – value of the cardinal point on the palindrome line in the line graph above.

When the device productivity is Q_p=0.07 kg/s;

At lower load:

y = 31,257e^0,1825x            R² = 0,9808                   (6)

At higher load:

y = 46,803e^0,1826x            R² = 0,961                     (7)

R – value of the cardinal point on the palindrome line in the line graph above.

As a result of reprocessing the empirical formulas obtained from the study, the hydraulic resistance of the drum dryer can be determined by the following equation, Pa.;

ΔP= 42,5е^0,17υρ                                 (8)

The experimental results differ from the theoretical (calculated) results by up to 4.25% and do not exceed this value.

The quantities in Equation (8) are valid for the ranges v=5–20 m/s and Q_p=0.06–0.07 kg/s

At the second stage of the research, the influence of the cascade heater on mutual heat exchange in the studied process was evaluated to determine the optimal design configuration. Based on the analysis results, the effect of the number of cascades installed in the vertical heater (4, 6, and 8 cascades were selected under the existing drying conditions and placed separately during experiments) on the temperature of the drying agent and the material (wheat was chosen as the drying material) was analyzed, and comparative graphs were constructed.

In these experiments, the temperature of the heat agent entering the cascade heater was set at 60°C.

Table 2.

Experimental results on the effect of the height of the cascade heater on the temperature of wheat. When Q_p=0.06 kg∙s is constant.

Table 3.

Experimental results on the effect of the height of the cascade heater on the temperature of sodium nitrate salt when Q_p=0.065 kg∙s constant

Table 4.

Experimental results on the effect of the height of the cascade heater on the temperature of sodium nitrate salt when Q_p=0.07 kg∙s is constant.

Conclusion. From the results presented in Tables 2, 3, and 4, it can be seen that the effect of the heat carrier descending from a height of 1000 mm on the wheat depends on the number of cascade nozzles. In other words, an increase in the number of nozzles inside the cascade heater enhances the amount of energy received by the heated material from the heat carrier.

However, as the productivity of the heated material increases, the heat exchange process between the agent and the material slows down. This phenomenon can be explained by the thickness of the flow layer. For example:

This indicates that at each value of the variable parameters, the supplied heat carrier transfers more than 40% of its energy to the material.
In addition, a change in the diameter of the perforated holes of the cascade nozzles leads to an increase in aerodynamic resistance inside the heater.

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