Thermodynamic Model of a Screw Compressor

Thermodynamic Model of a Screw Compressor

van Bommel, L.L.

Infante Ferreira, C.A. (mentor)

Mechanical, Maritime and Materials Engineering

Process and Energy (P&E)

2016-08-29

A Compressor Resorption Heat Pump (CRHP) is a potential contribution to energy reduction in applications in which waste streams are upgraded, with limited energy addition, into high value process streams for reuse in industry. Previous research concluded that a CRHP with a wet screw compressor is a suitable option for many applications. An ammonia/water mixture was found to be the most appropriate fit, in terms of thermodynamic behaviour, for such an application. Objective of this thesis was to develop an integration of a geometry model and a thermodynamic model suitable for further optimisation of the wet twin-screw compressor. The integration of the geometry model and the thermodynamic model was carried out in modelling tool Matlab/Simulink, with inclusion of the physical properties of the working fluid. The development of the integrated dynamic model was carried out based on research for a heat pump process with a pre-selected geometry and a homogeneous two-phase fluid. The existing geometry model was transformed from shaft rotation based to time based equations to achieve the dynamic model requirements and the possibility of modelling the process in Simulink. The geometry model provides inputs to the thermodynamic model that dynamically describes the wet twin-screw compressor from the suction phase through compression to the discharge phase. The thermodynamic model requires inclusion of physical properties of the fluid and these were added by importing the physical properties through Refprop via Fluidprop. Mechanical constraints of a wet twin-screw compressor inevitably lead to internal leakage paths that reduce the compressor efficiency. The leakage paths have been included together with factors for friction, flow loss, etc. to represent the process in a more realistic way. The integrated model has been validated with the calculated result by model case A and measured results from the experimental set-up by Zaytsev [1]. A number of variations have been applied to the integrated model as examples of how to evaluate options for improvements. Making use of the developed integrated model parameters can be varied to show the influence on the compressor. The evaluations used a specific set of boundary conditions from previous research, using the geometry specified by Zaytsev [1]. The effects of three input parameters on the output and efficiency were evaluated: rotor length, discharge port area and vapour quality. The main result of the evaluation is that per boundary condition, the inputs from the geometry model have to be adjusted to achieve an optimal design of the twin-screw compressor. Further research to find the optimal design can be done with the help of the model that was developed for this thesis.

screw compressor
CRHP
Compression resorption heat pump
Thermodynamic model screw compressor
compressor heat pump
two phase compressor

http://resolver.tudelft.nl/uuid:5d7963b4-b3fa-40ed-b2f4-7fb1518b7ab8

Student theses

master thesis

(c) 2016 van Bommel, L.L.