Similarity criteria of an autonomous pumping system and their impact on energy efficiency indicators

Abstract

Introduction. The authors have formulated a system of equations to describe the liquid flowing in a self-contained pumping system (SPS) that has a centrifugal pump (CP). To solve the problem, it is necessary to take into account a change in static pressure, features of the hydraulic resistance of pipes, and the influence of temperature. The authors have shown that the flow under study has two similarity criteria in the case of a certain characteristic flow rate. The authors have also assessed their influence on the energy efficiency values of a basic hydraulic circuit. Materials and methods. The authors make a hydraulic analysis of an SPS that has pump 1K 50-32-125, whose characteristics are presented in the technical specification. A mathematical model, based on the Bernoulli equation for an unsteady flow, was developed to solve the problem. Results. The authors solve the non-steady problem of pumping liquid through the central heating system into the SPS if the liquid level is variable in the self-similar (quadratic) resistance range. For the case when Str = 0 and Str is the analogue of the Strouhal number, the authors find the analytical expression of pumping time for the pre-set amount of liquid and the value of criterion Θ (a dimensionless complex value linking the difference between the head in the central heating system and the initial static head in the event of zero supply, the steepness of the pressure characteristic and the hydraulic resistance of the circuit). The results of the hydraulic analysis of SPS that has pump 1K 50-32-125 and different pipeline diameters, technical parameters characteristic of self-contained water supply and sanitation systems are presented. Power consumption value E is identified for water pumping. This value is used to assess the energy efficiency of water supply and sewerage systems. Conclusions. The authors have found that the values of the similarity criterion Θ increase together with the pipeline diameter, while efficiency decreases and the energy consumption value improves. Under the conditions under consideration, it is advisable to focus on a change in the value of E rather than efficiency, when energy efficiency is assessed in the process of selecting equipment.