Structural design and performance analysis of external gear pump for high viscosity polymer pumping

Abstract

High-viscosity gear pumps are key equipment for transporting highly viscous polymer media, and their performance is significantly influenced by the coupling effect of medium viscosity and operational parameters. To address the issues of low pumping efficiency and insufficient equipment stability in the preparation process of aerospace composite materials, this study analyzes the fluid pumping characteristics of composites and the gear pump structure under high-viscosity conditions. A universal high-viscosity external gear pump suitable for GNP2200 aerospace composite preparation was designed, with design calculations performed on the core structure to determine key parameters. Experimental tests were conducted to evaluate the pump’s power under varying rotational speeds and medium viscosities. Theoretical calculations and simulation comparisons of the rotational speed were carried out across three viscosity ranges. In addition, volumetric efficiency, energy efficiency, and overall efficiency were computed based on actual working conditions, and the relationship between the dynamic viscosity of the medium and efficiency was analyzed via simulation to comprehensively evaluate the pump’s performance. The results indicate that the pumping capacity is closely related to medium viscosity, and the consistency between simulation and theoretical results validates the rationality of the structural design. When the dynamic viscosity is below 5000 cP, the pump achieves a maximum no-load efficiency of 98.5% and a minimum of 87.0%. Maintaining the speed within the range of 65–90 r/min leads to higher pumping efficiency, extended service life, and improved operational performance. This study provides theoretical and practical insights for the optimized design of high-viscosity gear pumps.

Introduction

High-viscosity pumps represent an ideal solution for conveying highly viscous liquids and find extensive applications. The fluid media handled during operation are predominantly polymers, characterized by elevated temperatures and high viscosity. These properties impose stringent requirements on the structural design of gear pumps. Within industries such as petroleum, chemical engineering, daily chemicals, and pharmaceuticals, raw materials, intermediates, and final products often exist as highly viscous fluids. The pressurization and transfer of these fluids to meet production demands rely heavily on high-viscosity gear pumps as core equipment. Enterprises typically favor high-viscosity gear pumps characterized by simple working principles, reliable operational stability, and high efficiency. Performance requirements are particularly rigorous for applications involving the conveyance of high-viscosity polymers in the defense and military sectors^1,2.

Currently, although numerous enterprises have developed gear pumps suitable for high-viscosity fluid transportation, persistent deficiencies in design and testing methodologies result in unresolved challenges regarding key component design, material selection, leakage prevention, and noise control. Consequently, high-viscosity gear pumps utilized in petrochemical, textile, and consumer goods industries frequently fail to meet operational requirements. Globally, core technologies for high-viscosity gear pumps remain predominantly mastered by few industrialized nations, forcing most countries to rely on manufacturing technically inferior gear oil pumps. This technological disparity is particularly critical for military applications where extreme demands for efficiency, reliability, and service life create strategic dependencies due to limited access to core technologies. Yao³ conducted comprehensive analysis of gear pump status and development, demonstrating that addressing severe trapped oil pressure shocks requires focused investigation of influencing factors; practical noise control techniques must be developed for unloading measures; and systematic optimization of gear parameter selection processes is essential for reducing flow pulsation. Their research further proposes employing variable analysis for targeted pump investigation, where secondary design utilization of gear parameter variations enables performance enhancement through continuous optimization. By integrating practical scenario analysis with persistent refinement practices, this approach facilitates more reliable future development of gear pump technologies.

Regarding the design and performance optimization of high-viscosity gear pumps, Ko et al.⁴ studied the development of electric diesel pumps for commercial vehicles. They modeled the fuel supply system on diesel engines to analyze the workload of the injection pump and fuel supply rate. The diesel pump met the engine’s fuel pressure and flow requirements while consuming only 48.3% of the energy required by an engine-driven pump. Yoon et al.⁵ employed the submerged solid method to investigate gear pump efficiency and mass flow rate by varying pump speed and the clearance between the gear tip and the housing, but did not study the effects of pressure and rotational speed on the pump. Lunev et al.⁶ analyzed the cavitation behavior of gear pumps based on Henry’s Law. They found that if the liquid is more viscous, the time the liquid volume spends under negative pressure is shorter, resulting in significantly less dissolved air escaping than the amount that would escape at a given pressure. Chen Qi et al.⁷, to support the development of high-performance, high-viscosity gear pumps, constructed a multi-objective optimization design mathematical model based on the working conditions, application scenarios, and processing requirements of high-viscosity gear pumps. They used the constrained variable metric method for optimization calculations, and comparisons between calculation results and experiments verified the correctness of the established mathematical model. Akhmedova et al.⁸ studied the impact of high-viscosity food media on the performance of rotary pumps. Using experimental data, they found that the input power for pumping high-viscosity media is proportional to the rotor speed. Li Yulong et al.⁹ researched gear pumps for aerospace applications, they derived a formula for the volumetric efficiency of gear pumps, Simultaneously, by estimating the finite meshing points of the driven or driving gear, they proposed a new contact ratio coefficient formula suitable for both undercut and standard gears. By optimizing the fundamental parameters of the gear pair, including module, number of teeth, addendum coefficient, pressure angle, and displacement coefficient, they addressed the issue of declining volumetric efficiency while ensuring minimal pump weight and space launch costs. Fadlalla et al.¹⁰ conducted an experimental study on the operational performance of airlift pumps handling non-Newtonian fluids. They performed a series of experiments using a 31.75 mm airlift pump to pump xanthan gum aqueous solutions across a wide range of inlet air flow rates (6–140 SLPM). Xanthan gum concentrations ranged from 0.05 to 0.60 wt% (corresponding to viscosities between 10 and 1000 cP). They analyzed the effect of viscosity changes on liquid flow rate and pump efficiency, discovering that increasing viscosity significantly impacts transient void fraction distribution and accelerates the slug-to-churn transition. Li Minghao et al.¹¹ proposed an innovative vane pump design. This design utilizes the synchronous movement of upper and lower vanes on the rotor to regulate the chamber volumes on both sides, thereby facilitating efficient fluid transfer. Unlike previous studies, the vane pump faces challenges with dynamic contact between the vanes and rotor due to its unique structure. A viscous wall strategy was employed to address the fluid dynamics challenges at contact points, significantly improving the accuracy of performance predictions. Lee et al.¹² performed numerical simulations using the Moving Dynamic Mesh (MDM) technique in the commercial CFD software FLUENT to better understand unsteady flow characteristics within the pump. They investigated the effects of rotor gap size and rotor speed on flow characteristics, particularly the temporal variations in velocity and pressure fields.

However, the aforementioned studies have not provided detailed research on how to reliably investigate the pumping capacity of pumps through experiments in the field of aerospace composite material preparation, so as to design a highly efficient and reliable high-viscosity gear pump. How to pump these special high-viscosity polymers in combination with practical working conditions remains a challenging issue. The development, manufacturing, and optimized design of high-viscosity gear pumps are therefore particularly important. In response to the production requirements of composite materials in the aerospace sector, this paper analyzes the structural characteristics of high-viscosity gear pumps and designs a GNP2200 high-viscosity external gear pump. Key parameters of the pump structure were determined, and the rotational speed and volumetric efficiency of the pump were evaluated through calculation and simulation analysis. The performance of the high-viscosity gear pump was assessed, validating the rationality and applicability of its design.

Methods and designs

Design requirements for high-viscosity gear pumps

In addition to their application in aerospace composite manufacturing, high-viscosity pumps are also pivotal components in the production and processing of polymers for the textile, petrochemical, and consumer goods industries, with substantial demand. Designing large-scale, high-viscosity pumps that are reliable and stable in operation remains a major priority within these sectors. Consequently, the continuous optimization of their structural design has remained an active research focus. Driven by industry-defined performance parameters for high-viscosity gear pumps, we have developed a suitable pump design tailored to these requirements. The specific parameters provided by the enterprise are as follows:

Flow rate less than 291.5 m³/h, pressure differential less than 25 MPa, rotational speed less than 600 rpm, medium temperature inside the pump 0–80 °C, medium viscosity inside the pump less than 5000 cP, displacement: 50–12,000 cm³/rev, motor power 37 kW.

Since the working fluid is a high-viscosity polymer, the medium must be kept warm during transportation to reduce flow resistance, while ensuring good pump sealing. The external leakage index for the gear pump is required to approach zero leakage.

Structural design of high-viscosity gear pump

The main structure of the high-viscosity gear pump consists of the pump body, driving shaft, driving gear, driven shaft, driven gear, bearings, sealing mechanism, and other components. The key structural design and selection criteria are as follows:

Pump body design

Generally, the heavier the pump housing, the higher its temperature and pressure resistance. Since the pumped medium is a high-viscosity polymer in a high-temperature molten state, it tends to solidify upon cooling. Therefore, the medium must be maintained at a certain temperature to reduce flow resistance. For this reason, the pump body and cover adopt a jacketed structure. Additionally, to facilitate machining and assembly, the pump body is composed of three plates: a middle plate tightly fitted to the outer diameters of the gears and bearings, and front and rear side plates assembled on both sides of the pump body to restrict axial movement of the gears and bearings.

This high-viscosity gear pump is primarily used in the chemical industry, where the conveyed medium is highly corrosive. The pump body material is cast from 3Cr13 stainless steel and subjected to aging treatment, ensuring excellent corrosion resistance, high strength, and wear resistance.

Gear and shaft structure design

To achieve a compact structure, improve gear meshing performance, and avoid undercutting, modified gears are employed. The gears and shafts are designed as separate components. However, to ensure rotational precision, the driving shaft with the driving gear and the driven shaft with the driven gear are processed using an integrated machining technique during gear grinding. The outer diameter of the shaft at the gear installation position is designed as Φ110 mm.

Both the gears and shafts are made of 3Cr13 stainless steel and undergo quenching and tempering treatment, providing not only corrosion resistance but also excellent comprehensive mechanical properties, including high strength and toughness, to ensure long-term stable operation.

(1) Determination of Gear Module

According to Reference¹³, the displacement of gear pumps has conventionally been calculated using the formula Q = 2πkzBm². However, significant errors occur when this formula is applied to profile shifted gear pumps. Since the tooth thickness varies at different points along the involute tooth profile, the tooth thickness s' at the pitch circle during gear mesh is determined by s' = s(r'/r) − 2r' (invα' − invα), where: r represents the gear reference circle radius (r = mz/2); r' denotes the gear pitch circle radius; s is the tooth thickness on the reference circle of the profile shifted gear; α indicates the standard pressure angle (typically α = 20°); z represents the number of gear teeth; and m signifies the gear module. Considering that in practical design of profile shifted gears and calculation of nominal gear dimensions, the tooth flank clearance is typically neglected (i.e., designed under zero-backlash conditions) for computational simplicity, and based on the zero-backlash meshing condition for profile shifted transmission, the displacement calculation formula for high-viscosity gear pumps becomes:

1

where, Q denotes the pump displacement; k represents the displacement compensation coefficient, with a value range of 1.06–1.115; z₁ is the number of teeth on the driving gear; m stands for the gear module; h_a* indicates the addendum coefficient; z_Σ refers to the total number of teeth of meshing gears; α denotes the standard pitch circle pressure angle; α₁₂ represents the meshing angle of gears; x_Σ is the sum of gear modification coefficients; B signifies the tooth width (mm). Typically, high-viscosity pumps feature greater tooth widths, where the ratio of tooth width B to pitch circle diameter equals 1.42, that is B = 1.42 mz.

Consequently, the gear module is calculated as:

2

Since the two meshing gears in a high-viscosity pump are identical, the above equation can be simplified as:

3

(2) Gear displacement coefficient

To achieve higher displacement per revolution in high-viscosity pumps, larger gear modules (m) and fewer teeth (z) are typically selected. However, a low tooth count increases the risk of undercutting and interference. To prevent undercutting, a positive modification coefficient (profile shift) is generally applied.

The minimum number of teeth required to avoid undercutting during gear machining is given by:

4

The minimum modification coefficient is expressed as:

5

where h_a^∗ denotes the gear addendum coefficient and z represents the number of teeth.

(3) Tooth Tip Thickness

For high-viscosity gear pumps, the tooth tip thickness must be appropriately designed as it significantly affects the internal leakage of the pump. An insufficient tooth tip thickness reduces volumetric efficiency and weakens the tooth tip strength, leading to poor wear resistance. Conversely, an excessive thickness increases friction between the gear and pump housing, adversely affecting pump efficiency¹⁴. The tooth tip thickness for high-viscosity gear pumps can be estimated using the following empirical formula:

6

where p denotes the pump outlet pressure (MPa); δ₂ represents the radial clearance between gears; u indicates the dynamic viscosity of the medium (cP); z₀ is the number of teeth in contact with the pump housing; V signifies the circumferential velocity at gear tip.

(4) Gear Contact Ratio

During operation, the high-viscosity gear pump forms two isolated chambers within the housing—the suction chamber and discharge chamber—enabling fluid transfer. In gear design for such pumps, the contact ratio (ε) must exceed 1 (typically maintained between 1.05 and 1.15) to ensure smooth and reliable operation¹⁵. Considering potential undercutting effects, the contact ratio is calculated as:

7

where d_b represents the base circle diameter (mm); d_f denotes the root circle diameter; h_f indicates the radial difference between pitch circle and root circle (mm); α₁₂ is the working pressure angle; m stands for gear module (mm).

Additionally, as high-viscosity gear pumps typically require continuous discharge, maintaining a contact ratio (ε) greater than 1 is essential. However, this inevitably leads to oil trapping phenomena during operation. To mitigate this issue, relief grooves are conventionally machined symmetrically on the pump cover. In this study, an asymmetric relief groove configuration is proposed: a tapered relief groove on the suction side and a rectangular relief groove on the discharge side. Furthermore, the groove depth in high-viscosity pumps is designed to be greater than that in standard hydraulic pumps.

Seal selection

The sealing performance is critical for ensuring safe and reliable operation of high-viscosity gear pumps, particularly in chemical industry applications. The quality of sealing directly affects the pump’s service life and operational performance. In this design, a double mechanical seal is adopted at the input shaft end, which offers reliable sealing performance with minimal leakage, extended service life, low power loss, and negligible wear on the shaft or sleeve.

Bearing selection

Bearings represent one of the core components in high-viscosity gear pumps, and their service life significantly determines the overall pump durability. Although high-viscosity gear pumps generally operate at relatively low rotational speeds, the high viscosity of the conveyed medium increases the likelihood of fluid entrapment and elevates pumping pressure, thereby imposing greater loads on bearings. To ensure smooth operation, precision Class D rolling bearings are selected, which exhibit superior mechanical properties, extended service life, convenient maintenance, reliable performance, excellent starting characteristics, and high load capacity at moderate speeds.

In summary, considering the specific application requirements and design parameters of gear pumps, the structure of the GNP2200 external gear high-viscosity pump is illustrated in Fig. 1. The pump dimensions are 806 mm × 512 mm × 830 mm (L × W × H). The main components include: pump housing, driving shaft, driving gear, driven shaft, driven gear, bearings, sealing assembly, oil cup, end cover, relief valve, and other accessories. The basic design parameters of high viscosity gear pump gears are shown in Table 1.

Fig. 1.

Structural configuration of the high-viscosity gear pump.

Table 1.

Fundamental design parameters of gears for GNP2200 high-viscosity gear pump.

Parameter	Symbol	Value	Unit
Number of teeth	z	15	–
Module	m	12	mm
Pressure angle	α	20	(°)
Addendum coefficient	ha*	1.1	–
Bottom clearance coefficient	c*	0.15	–
Profile shift coefficient	x	0.18	–
Face width	B	252	mm
Contact ratio	ε	1.1	–
Center distance	a	184	mm

Experimental testing and statistical analysis

The hydraulic circuit diagram of the high-viscosity gear pump is shown in Fig. 2. When the motor is started, it drives the gear pump. The high-viscosity medium is pumped from the storage tank and passes through a pressure sensor and a flow meter. By adjusting the opening of the throttle valve, the pressure of the system circuit can be gradually increased. At each stable pressure point, data from all sensors are collected to evaluate the performance of the pump under different pressures. This circuit is designed to test the performance of the gear pump—primarily focusing on flow rate, volumetric efficiency, and input power—under varying outlet pressures, rotational speeds, and oil temperatures.

Fig. 2.

The hydraulic circuit diagram of the high-viscosity gear pump.

During the experiment, the medium temperature is first maintained at a specific value, and the drive motor speed is fixed. Then, by progressively adjusting the throttle valve in the circuit, different loads are applied to systematically increase the pump’s outlet pressure. At each stable pressure condition, the data acquisition system synchronously records readings from the pressure sensor, flow meter, speed/torque sensor, and temperature sensor—namely, the pump’s outlet pressure, actual output flow rate, input shaft speed and torque, and oil temperature. After real-time collection and storage, these raw data are used to calculate key pump performance indicators, including theoretical flow rate, volumetric efficiency, input power, and overall efficiency. Finally, performance curves of the pump under different pressures and temperatures are plotted.

Experimental tests were conducted on the high-viscosity gear pump under realistic operating conditions to measure the input shaft power under combinations of temperature (25–40 °C), pressure (1.0 MPa, 1.5 MPa, 2.0 MPa), pump speed (50, 100, 150, 200, 250, 300 r/min), and medium viscosity (150–1000 cP, 1000–3000 cP, 3000–5000 cP, 5000–8000 cP). The measured input power data were plotted using MATLAB, as shown in Fig. 3a–c.

Fig. 3.

Experimental data relationship between high viscosity gear pump speed and input shaft power under different pressures and medium viscosities.

The experimental values in Fig. 3a–c clearly indicate a positive correlation between pump speed and input power under the same delivery pressure. Higher viscosity of the transported medium also leads to greater input power. The discrepancies between the experimental data under various conditions and the enterprise requirements ranged from 3.2 to 4.7%. These observations are consistent with the calculated input shaft power from the design analysis of the GNP2200 high-viscosity gear pump. Although the computational results are slightly conservative, the error remains below 10% compared to the enterprise standard data. This margin of error meets the practical engineering requirements for aerospace composite production and demonstrates the operational reliability of the designed GNP2200 high-viscosity gear pump.

Performance analysis of high-viscosity pumps

The pumping capacity, as a primary performance parameter for pump evaluation, is fundamentally determined by rotational speed, volumetric efficiency, and energy efficiency in high-viscosity gear pumps¹⁶. Insufficient rotational speed leads to severe internal leakage, resulting in diminished volumetric efficiency. Conversely, excessive speed may cause medium expulsion from tooth spaces when inlet pressure is inadequate, creating cavities at the tooth base that increase suction resistance. This condition manifests as inadequate oil supply, cavitation, elevated vibration, and noise generation. Furthermore, high rotational speeds amplify axial/radial clearances and meshing gaps, while intense shear-induced heating from rapid operation causes dramatic temperature rises in high-viscosity media—collectively reducing pump efficiency and potentially compromising normal operation¹⁷. The operational efficiency of high-viscosity gear pumps directly governs their pumping capacity, with higher efficiency correlating to superior performance.

Pump rotational speed

High-viscosity gear pumps typically operate at relatively low speeds, primarily dictated by process requirements and material characteristics. The rotational speed for three operational phases can be estimated using the following empirical formulae¹⁸:

For media with kinematic viscosity ranging 1000–3000 mm²/s, the minimum pump speed is given by:

8

where V represent the minimum circumferential velocity of the high-viscosity gear pump, which can be derived from the above equation as:

9

For media with kinematic viscosity ranging from 3000 to 8000 mm²/s, the minimum pump speed is given by:

10

Similarly, defining V as the minimum circumferential velocity of the high-viscosity gear pump, the equation transforms to:

11

When handling media with kinematic viscosity between 0 and 5000 mm²/s, the maximum pump speed is determined by:

12

Similarly, defining V as the minimum circumferential velocity of the high-viscosity gear pump, the equation transforms to:

13

where p denotes the outlet pressure (MPa); v represents the kinematic viscosity of the medium (mm²/s); d_a is the tip circle diameter (mm).

Pump volumetric efficiency

During operation of the high-viscosity gear pump, the volume of high-viscosity medium transported per revolution (V₀) can be approximated as the difference between two cylindrical volumes based on gear kinematics¹⁹:

14

where V₀ is the displaced volume per revolution; dₐ is the tip circle diameter; d is the pitch circle diameter, B is the tooth width.

For external gear pumps with identical gears, the theoretical flow rate (Q₀) under ideal leak-free conditions is:

15

where Q₀ is the oretical flow rate; n is the rotational speed.

In practical operation, clearance between gears/pump housing and pressure differential (Δp) between inlet/outlet inevitably cause leakage (Q_L) and backflow, reducing actual flow rate²⁰.

The relationship between leakage, pressure differential, and medium viscosity (ν) can be expressed as:

16

where λ is an exponential coefficient, empirically determined as λ = 0.35.

Since the high-viscosity media transported by high-viscosity gear pumps typically exhibit non-Newtonian fluid behavior, their rheological properties are significantly influenced by temperature, pressure, stress, and strain rate. The viscosity can be empirically modeled using the power-law equation²¹:

17

where γ represents the shear rate, T denotes the temperature of the high-viscosity medium (K or °C), b is the temperature-viscosity coefficient, which is medium-dependent.

Assuming the shear rate is proportional to the gear’s rotational speed (γ ∝ n), then:

18

Combining Eqs. (16) and (18), the volumetric leakage flow rate (QL) of the pump can be derived as:

19

where K_L is the leakage coefficient at , , (K_L = 30.5 cm³/min); , , represents the random comparative characteristic parameters.

Thus, the volumetric efficiency of the high-viscosity gear pump is expressed as:

20

Energy efficiency analysis of the pump

The total power of the high-viscosity gear pump consists of the energy delivered to the medium and the energy dissipated due to internal friction during transport. Thus, the total power is given by:

21

22

The frictional power loss can be expressed as:

23

Based on the power-law viscosity model,

24

The frictional power loss can be expressed as:

25

where K_f (K_f = 4.9 × 10^–4 kW) is the power consumption coefficient of the gear pump at n = n⁰, T = T⁰. n⁰, T⁰, are the random comparative characteristic parameters (n = 1).

The energy efficiency (η) of the gear pump is then given by:

26

Overall pump efficiency

The overall efficiency of the high-viscosity gear pump is determined by both its volumetric efficiency and energy efficiency, and can be expressed as:

27

Result analysis

Analysis of the relationship between medium viscosity and rotational speed

Based on the performance requirements and actual working conditions of the high-viscosity gear pump, the maximum and minimum rotational speeds, as well as the variations in gear circumferential velocity, were calculated for different medium viscosity ranges of the GNP2200 high-viscosity gear pump under a pressure differential of 5 MPa and an operating temperature of 45 °C, using the aforementioned empirical formulas. To more intuitively demonstrate and validate the relationship between medium viscosity and rotational speed, MATLAB software was employed to conduct a comparative analysis between simulation data (obtained under near-actual working conditions) and the corresponding calculated values. The results of the simulation and calculations are presented in Figs. 4, 5, 6, 7, 8 and 9.

Fig. 4.

Relationship between minimum pump speed and medium viscosity at kinematic viscosities of 1000–3000 mm²/s.

Fig. 5.

Relationship between minimum pump speed and medium viscosity at kinematic viscosities of 3000–8000 mm²/s.

Fig. 6.

Correlation between gear tip circumferential velocity and medium viscosity at minimum pump speed (kinematic viscosity range: 1000–3000 mm²/s).

Fig. 7.

Correlation between gear tip circumferential velocity and medium viscosity at minimum pump speed (kinematic viscosity range: 3000–8000 mm²/s).

Fig. 8.

Relationship between maximum pump speed and medium viscosity at kinematic viscosities of 0–5000 mm²/s.

Fig. 9.

Relationship between gear tip circumferential velocity and medium viscosity at maximum pump speed (kinematic viscosity range: 0–5000 mm²/s).

As illustrated in Figs. 4, 5, 6, 7, 8 and 9, the simulation results of the high-viscosity gear pump are in good agreement with the calculated values. The rotational speed of the pump decreases as the kinematic viscosity of the medium increases, accompanied by a corresponding reduction in the circumferential velocity at the gear tip. This behavior is attributed to the increased flow resistance caused by the poor fluidity of high-viscosity media and their slower flow in the gaps, which intensifies the frictional resistance between the gears and the medium. Consequently, the overall pumping resistance increases, making it difficult for the pump to maintain its normal speed. As the rotational speed declines due to rising resistance, the pumping capacity is also reduced. If the rotational speed is forcibly increased to an excessive level, vacuum cavities may form inside the pump, leading to insufficient suction or even dry running. This condition results in localized heating and heat accumulation, which can ultimately cause pump failure. Therefore, selecting an appropriate operating speed according to the viscosity of the pumped medium is essential not only for operational safety but also for improving pumping efficiency.

Furthermore, experimental observations indicate that both medium viscosity and rotational speed collectively influence the temperature rise of the pump. On one hand, when handling high-viscosity fluids, the inherently poor mobility and slower interstitial flow of the medium reduce the convective heat dissipation efficiency across the pump surface, promoting heat accumulation. On the other hand, although operating at a higher rotational speed under fixed conditions can enhance flow rate, it also exacerbates internal shear friction between the gear meshing surfaces and the medium, generating additional heat. The combined effect (rather than a causal relationship) of these two factors contributes significantly to pump heating. Excessive temperature rise may lead to medium degradation, thermal deformation of components, and other issues, ultimately adversely affecting the operational efficiency and service life of the pump.

Analysis of the relationship between medium viscosity and pumping efficiency

Based on theoretical analysis, the total efficiency of the high-viscosity pump was simulated under no-load conditions with a medium dynamic viscosity below 5000 cP and at four different rotational speeds: 45 r/min, 65 r/min, 90 r/min, and 110 r/min. The variation curve of the total efficiency is illustrated in Fig. 10.

Fig. 10.

Pumping efficiency versus dynamic viscosity of the working fluid in the high-viscosity gear pump.

As analyzed from Fig. 10, the pump achieves a maximum efficiency of 98.5% and a minimum efficiency of 87.0% under no-load conditions. Notably, the overall pumping efficiency exhibits an increasing trend with the rise in medium dynamic viscosity. Furthermore, when the medium dynamic viscosity exceeds 2000 cP, the pumping efficiency is relatively higher at around 90 r/min. Conversely, when the viscosity is below 2000 cP, higher efficiency is observed at approximately 110 r/min. However, this speed approaches the critical maximum limit of the pump. Under full-load operation, prolonged high-speed conditions may significantly compromise the mechanical strength of pump components. Therefore, sustained high-speed operation should be avoided to ensure durability. For optimal performance and extended service life, it is recommended to maintain the pump speed within the range of 65 r/min to 90 r/min when handling media with a dynamic viscosity below 5000 cP. This operational range ensures higher pumping efficiency while enhancing reliability and longevity.

Conclusions

The high-viscosity external gear pump designed in this study features a simple structure and broad applicability, making it suitable for deployment across multiple industries in China including petroleum, chemical, textile, and food processing.

Through calculation and simulation, the basic performance of this high-viscosity gear pump has been verified. Analysis indicates that the kinematic viscosity of the medium has a notable influence on the pump’s rotational speed. Under certain conditions, higher medium viscosity leads to an appropriate reduction in rotational speed, which also affects the pumping efficiency of the high-viscosity gear pump. Under no-load conditions, the pump achieves a maximum efficiency of 98.5% and a minimum efficiency of 87.0%. Analysis and simulation results demonstrate that maintaining the rotational speed within the range of 65 r/min to 90 r/min not only ensures high pumping efficiency but also reduces gear meshing impact and bearing load. Furthermore, efficient operation under these conditions helps control temperature rise. These favorable comprehensive characteristics contribute to reduced wear and fatigue of key components, thereby potentially extending the service life of the pump.

The computational results show good agreement with simulation data, confirming the rationality of the structural design for this high-viscosity pump. These findings provide valuable theoretical guidance for future research and development of high-viscosity gear pumps.

Author contributions

B. Z., S. conceived the idea, collected data, analyzed data, wrote the article; Y. C., Y. supervised the article and funding acquisition; and all authors discussed the results and approved the article.

Funding

The authors extend their appreciation to China Academy of Machinery Science & Technology Qingdao Branch Co., LTD. for finding this research work through the Key Technology Research and Industrialization Demonstration Projects in Qingdao, China (Grant No. 24-3-2-qljh-1-gx), and the Key R&D Program Project of Shandong Province, China (Grant No. 2024CXPT038).

Data availability

The research data is provided within the manuscript.

Declarations

Competing interests

The authors declare no competing interests.