In order to achieve a lower consumed energy, the performance of a new type of rotating volumetric pump with two profiled rotors (variant I) which is compared with a centrifugal pump (variant II) is presented. The analysis regarding the same flow rate of transported liquid and the same pressure increases points out the conduct of the system at the variation of the key operating parameters. The actual driving power of the rotating volumetric pump is higher stating that is more advantageous in operation. The effective efficiency of the system is improved due to the original constructive solution.
Conventional technologies for the construction of rotating pumps are based on the use of maximum mechanical power [
Considering the problems that existing profiled rotors of rotating pumps have, a new rotating working machine with profiled rotors was proposed in this paper.
A special problem consists in performing a rotating working machine that will transform the energy received at the coupling into potential pressure energy with minimal losses. There are two main criteria for classifying pumps [
1) According to the principle of operation: volumetric pumps and non-volumetric pumps.
2) According to the driving mode: electric pumps, motor pumps and turbo pumps.
In this paper, a comparative analysis between two pumps will be presented, namely, as variants:
1) A rotating volumetric pump with two profiled rotors designed and made by the University Politehnica of Bucharest [
2) A centrifugal pump made by WILO [
As part of a research topic, the performances of the two types of pumps were compared and the results are presented below.
The parameters relevant for the study are the flow rate transported by the machine and the driving power for both variants studied in the paper. In this section, the two studied versions are presented.
For the concept proposed for analysis in this paper (variant I), the rotating piston has the shape of a triangle due to the materials strength (
The fluid in the chamber (1) is taken up by the rotating pistons (6) and transported to the discharge chamber (9).
On the shafts 7 and 8, two toothed wheels are mounted (
a cylindrical gear; thus, the penetration of the pistons 6 from the upper rotor into the cavities 10 from the lower rotor (3) is ensured.
Because the machining cost is high, ordinary CNC machine tools are used by some manufacturers instead of the five-axis CNC machine tools that have very high costs. Therefore, it is necessary to analyze the relationship and transform the corresponding profile of the rotor in different cross-sections [
The outline of the WILO type centrifugal pump (variant II) is presented in
From the pump documentation [
- pump type: HELIX VE 606 RBI;
- flow rate: 5 m3/h = 1.38 × 10−3 m3/s;
- pumping height at 0.75 mH2O;
- temperature of the pumped agent: t = 10˚C;
- maximum pressure: p = 16 bar.
1) for variant I: building with height S + P + 2E + floors 3, 4 removed from Muzeul Zambaccian street, number 15, sector 1, Bucharest, the pump has the characteristics: V ˙ = 1.38 × 10 − 3 m 3 / s , H = 60 mH2O, the driving power will be:
P = V ˙ ⋅ Δ p η I = V ˙ I ⋅ ρ g H I η I [ W ] . (1)
2) for variant II, the WILO-Helix VE type pump is replaced with a rotating volumetric pump with profiled rotors that must pump cold water at the same parameters:
P I I = V ˙ I ⋅ ρ g H I η I I [ W ] . (2)
After a 180˚ rotation the fluid contained in the useful volume Vu, i.e., in the space between the pistons, the lower casing (1) and lower rotor (2), will be sent to the discharge chamber. On a full rotation of the shaft (9), two such volumes will be transported from the suction to the discharge [
V ˙ u = 2 ( π R c 2 2 − π R r 2 2 ) ⋅ l [ m 3 / rot ] . (3)
The casing radius (Rc) is the sum of the rotor radius (Rr) and the piston height (z):
R c = R r + z [ m ] . (4)
it results:
V ˙ u = π l z ( z + 2 R r ) [ m 3 / rot ] . (5)
The fluid volumetric flow rate discharged by a single rotor of length l [m] and speed nr [rot/ min] will be:
V ˙ u = π l z ( z + 2 R r ) ⋅ n r 60 [ m 3 / s ] . (6)
Because the machine has two identical rotors, the fluid flow rate circulated by machine will be:
V ˙ m = 2 V ˙ u = π l z ( z + 2 R r ) ⋅ n r 30 [ m 3 / s ] . (7)
From Relation (5) it can be seen that the flow rate transported by the rotating machine will increase proportionally to the change of the following parameters: l: length of the rotor [m]; z: piston height [m]; Rr: rotor radius [m]; nr: the machine speed [rot/min]. Obviously, a certain ratio must be established between the rotor radius (Rr) and the piston height (z).
It is considered that the rotating machine presented is a volumetric pump that must achieve a pressure increase equal to Δp [N/m2].
In this case, the theoretical driving power of the machine will be given by the relation [
P = V ˙ m ⋅ Δ p [ W ] . (8)
Replacing V ˙ m from Equation (7), one can obtain:
P = π l z ( z + 2 R r ) ⋅ n r 30 ⋅ Δ p [ W ] . (9)
From Equation (7) one can see that the power of the machine varies according to the following parameters:
*Constructive parameters: l: rotor length [m]; Rr: rotor radius [m]; z: the height of the rotating piston [m].
*Functional parameters: nr: machine speed [rpm]; Δp: the increase in pressure achieved by the pump between suction and discharge.
The actual driving power of the rotating volumetric pump will be higher:
P r = P η e [ W ] . (10)
where ηe is the effective efficiency of the pump [
η e = η v ⋅ η m ⋅ η h . (11)
where:
- ηv is the volumetric efficiency of the pump;
- ηm is the mechanical efficiency of the pump;
- ηh is the hydraulic efficiency of the pump.
For the volumetric pump (variant I), in the paper [
η e = η v ⋅ η m ⋅ η h . (12)
where:
- ηv is the volumetric efficiency of the pump(ηv = 0.9);
- ηm is the mechanical efficiency of the pump (ηm = 0.8);
- ηh is the hydraulic efficiency of the pump (ηh = 0.72).
So, for the volumetric pump η = 0.8, and for the centrifugal pump η = 0.51 [
E I I E I = V ˙ I ⋅ Δ p η I I ⋅ η I V ˙ I ⋅ Δ p = η I η I I = 0.8 0.51 = 1.56 . (13)
It can be concluded that the volumetric pump with profiled rotors used will be more advantageous because it leads to an energy saving for its driving.
The influence of the rotor profile on the performance of an original new rotating pump was studied in comparison with a centrifugal pump, highlighting the increase in flow rate achievable using the triangular shape of the rotors. The aspirated fluid is circulated to discharge with minimal energy loss; thus, the motor torque is: M = F ⋅ b ⋅ sin α [ N ⋅ m ] , where F is the force which presses on the
rotating piston, b is the force arm: b = R r + z 2 [ m ] .
The force F will always be perpendicular to the arm, so the angle between the force (F) and the arm (b) is always equal to 90˚. This fact leads to an advantage over piston machines which are variable during 360. As a result, neglecting the friction between the rotor and the casing, the entire engine torque is used to drive the fluid.
The constructive solution presented in the paper has parts only in rotational movement, it has a safe operation and easy maintenance.
The investment for building a pumping installation is not high; this is because, for the rotor’s construction, a computation program is available and their constructions can be made on a computer center with numerical control.
The authors declare no conflicts of interest regarding the publication of this paper.
Fischer-Szava, G., Băran, N., Constantin, M., Oprea, M., Dobre, C., Duiculete, G. and Ibrean, B. (2023) The Advantages of Using Rotating Machines with Profiled Rotors. World Journal of Engineering and Technology, 11, 41-47. https://doi.org/10.4236/wjet.2023.111004