Keywords

The development of hydrogen energy has attracted global focus, which is greatly concerned with energy and environmental issues. Recently, many countries around the world have deployed hydrogen energy-related technologies. Due to the advantages of low energy consumption and high efficiency, the liquid hydrogen pump is widely valued for liquid hydrogen transferring. The impeller is the most important part of the pump. Considering the cavitation issue, we used an integrated impeller with an inducer and centrifugal impeller to improve the performance.

At present, there is less literature to be investigated. In 2015, Li et al. [1] designed a semi-open integrated impeller for aviation fuel pumps. The performance requirements are 8000 rpm, 77,000 L/h, and the inlet and outlet pressure difference is 0.956 MPa. According to calculations, the pump does not produce cavitation in the operating range, and the efficiency is 65%. And then, they optimized the profile line to improve the performance [2]. Liu et al. [3] optimized the blade wrapping angle. In 2018, Li et al. [4] designed a fuel centrifugal pump with an integrated inducer and impeller influenced by an inlet flow ejector. The pump performance requirements are 1500 L/h, 10678 rpm, 23.07 m. And the simulation efficiency is 69%. The experiment efficiency is 65%. Tian et al. [5] designed an integrated impeller for an aero fuel pump and optimized the centrifugal impeller blade wrapping angle. The pump performance requirements are 3.9 kg/s, 9000 rpm, △P ≥ 80 kPa. And the simulation efficiency is 81.5%.

In this paper, we designed an integrated impeller with an inducer and centrifugal impeller and optimized axial length and outlet angle. By analyzing the flow field pressure and relative liquid flow angle distribution, the structural design of the impeller is determined, and the performance curve is obtained.

1 Preliminary Design of Integrated Impeller

1.1 Performance Parameters

Table 1. Performance parameters
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According to Table 1, the liquid hydrogen integrated impeller is designed as shown in Fig. 1. The impeller has 3 main blades and 3 auxiliary blades.

Fig. 1.
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Closed integral impeller

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1.2 Calculation and Boundary Conditions

Adopt the SST \({\text{k}}-\upomega \) turbulence model and secondary windward space discrete format. The convergence residual is set to 10–5. Set the inlet as pressure boundary condition as 1.3 bar and outlet as volume flow rate boundary as 10 L/s. Set wall roughness as 1.2 μm.

1.3 Results of Preliminary Impeller Design

Table 2. The results of preliminary impeller design
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The results of the preliminary design are shown in Table 2. The efficiency is 89.65%. The flow field pressure and velocity distribution are shown in Fig. 2.

Fig. 2.
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Total pressure and absolute velocity of the preliminary design

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2 Optimization of the Integrated Impeller Structure

2.1 Optimization of the Axial Length

After changing the axial length of the centrifugal impeller from 15 to 40 mm with the interval of 5 mm, we get the calculation results as shown in Fig. 3. When the axial length of the centrifugal impeller is 25 mm, the efficiency is optimal.

Fig. 3.
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Efficiency and head change with the axial length of the centrifugal impeller

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Fig. 4.
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Relative flow angle of each plane when axial length of the centrifugal impeller is 25 mm.

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The relative flow angle contribution is shown in Fig. 4. 20, 35, 45, and 55 mm correspond to the inducer plane, the inlet, the middle, and the outlet plane of the centrifugal impeller. On each plane, with the increase of radius, the circumferential direction velocity increases, and the relative flow angle decreases. At the 20 mm plane, the relative flow angle is about 35° at the roof of the blade and about 18° at the top of the blade. The relative flow angle is consistent with the β angle of the blade design. At the 35 mm plane, the relative flow angle is about 34° at the roof of the blade and about 26° at the top of the blade. The design β angle is 43° and 23°. The low relative flow angle area at the inner diameter is affected by the leading edge of the auxiliary blade. At the 45 mm plane, the relative flow angle is about 39.5° at the roof of the blade and the design β angle is 41.5°. The relative flow angle is about 42.4° at the top of the blade and the design β angle is 24.5°. The β angle of the blade limits the development of fluid flow and the counter-current zone appears. At the 55 mm plane, the relative flow angle is about 45° at the roof of the blade and the design β angle is 32°. At top of the blade, the flow angle is 25°, which is close to the design of β angle 27°. In general, the impeller structure needs to be improved.

2.2 Optimization of the Outlet Angle

The outlet angle affects the pump performance including hydraulic efficiency, and characteristic curve. Six groups of outlet angles are shown in Table 3. And the calculation results are shown as follows.

Table 3. Impeller performance at different outlet angles
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Fig. 5.
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Relative flow angle distribution at different outlet angles

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As shown in Table 3, when selecting a larger outlet angle such as ⑥, the efficiency is highest under the design working conditions. Due to 2.1, the area where the blade angle is not reasonable is between the length of 45 and 55 mm. And the distribution of liquid flow angle at the shaft length section of 45 mm and 55 mm under the condition of six groups of blade shapes was analyzed.

As showed in Fig. 5, in group ①, at 45 mm plane, the liquid flow angles at the root and top of the leaf at 45 mm were about 35° and 24°, and the design β angles of the leaves were 38° and 23°, respectively. The design angle is appropriate. At 55 mm plane, the liquid flow angle at the root and top of the leaf is about 48° and 32°, and the design β angles of the blade are 28° and 23°. It can be seen that the outlet angle setting is too small. In group ②, at 45 mm plane, the design angle is appropriate. At 55 mm plane, the liquid flow angle at the root and top of the leaf is about 40° and 23°, and the design β angles of the blade are 30° and 25°. It can be seen that the outlet angle setting is small but has improved compared to ①. ③, ④, ⑤ is also gradually improving compared to the previous one. In group ⑥, the liquid flow angles at the root and top of the leaf were about 43° and 29° at 45 mm plane, and the design β angles of the leaves were 43° and 28.5°. At 55 mm plane, the liquid flow angle at the root and top of the leaf is about 38° and 33°, and the design β angles of the blade are 38° and 34°. The design outlet angle is appropriate. So we adopt the group ⑥.

3 Results

Fig. 6.
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Impeller performance curve

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The Impeller performance curve is shown in Fig. 6. Under the design flow rate condition of 10 L/s, the impeller efficiency reaches the optimal value of 92.63%, and the head is 167.24 m (Fig. 7).

Fig. 7.
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Total pressure and absolute velocity of the final design

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Finally, the complete structure of the impeller and volute under the design condition was calculated, and the efficiency was 85.69%. The efficiency loss in volutes was 6.9%.

4 Conclusion

The liquid hydrogen pump impeller is designed with an integrated inducer and centrifugal impeller in this paper. After the axial length of the centrifugal impeller and are outlet angle are optimized, simulation is performed on the impeller with the design conditions. Even with the high surface toughness, the impeller efficiency and overall efficiency with the volute shell reach 92.63% and 85.69%, respectively. With the reliable results shown in this paper, our liquid hydrogen pump will build up and test soon, and the test performance will be published. This paper will benefit for the development of the low energy consumption and high efficiency liquid hydrogen pump.