Conference Agenda

A Roots Blower is rotary type of positive displacement machine. The clearance gaps between the rotors and the housing are the main reason for volumetric inefficiency, and therefore gaps are required to be minimised. Improvements can be done by minimising leakage flows using different configurations of rotor tip shapes for which prediction tool is beneficial rather than manual numerical simulations. Also, the shape optimization tools play an important role in finding the optimal solution for design changes. To study design-conceptualization, the fluent-adjoint solver in conjunction with RBF morph technology will be used. The coupling of both technologies is known as adjoint-sculpting which uses the prior estimation of effect of shape change based on the Observable target from Fluent-adjoint and use of RBF fluid morphing technology to accommodate those changes. The RBF morph is advantageous because it does not need any re-meshing of fluid volume and maintains the same quality as base volume mesh. To study the optimization method used for Positive displacement machines, 2D simplified Roots blower is considered. The methodology will be compared with the manual CFD results of different shapes of rotor tip. Following this, the variation in observables and different shape of tips will be explored. The results from this study will be helpful for compressors technology to implement the rotor tip shape design change which will save time and resources with respect to manual CFD calculations.

In the race to fight climate change and live sustainably, heat pumps are becoming increasingly popular due to their ability to efficiently deliver heat using electricity. However, heat pump performance degrades at low ambient conditions, making implementation challenging in very cold climates. The introduction of vapor injection (VI) has been seen in experimental research to improve capacity and coefficient of performance (COP), especially at low ambient conditions with heat pumps. While the performance of such compressors is heavily researched, the industry still has no standardized practices for characterizing their performance. Currently, there are standard practices for testing VI compressors according to ASHRAE 23 and EN 13771 but these rating standards do not provide guidance on the selection of test points and the fitting of data. Empirical models, such as AHRI Standard 540’s 10-coefficient model, exist for fitting the data of non-VI compressors, but there is no equivalent model established for VI compressors. In order to incorporate the effects of additional varying parameters such as injection pressure, compressor frequency, superheat, and ambient temperature, new techniques for sampling and fitting data will be necessary since a fully empirical polynomial approach would require far too many tests and variables. This paper reviews the current practices/methods for compressor test sampling and performance mapping in academia for both VI and non-VI compressors. Accurate and reliable compressor performance mapping for VI will be important for the design and implementation of such compressors in HVAC equipment in the coming years. The authors are engaged in a multi-year research program funded by the Department of Energy and future work will include the construction of a compressor test stand that will be used to evaluate best practices for testing and characterizing VI compressor performance.

Future carbon-free industrial processes require electrified steam generation methods, e.g., high-temperature heat pumps (HTHP). Alternatively, mechanical vapor recompression (MVR) may be used to recover waste heat or waste steam. This research combines HTHP and MVR by implementing an MVR rotary lobe blower as the first stage compressor in a two-stage 400 kW R-718 HTHP with a total temperature lift of 50 K and an evaporation temperature of 80 °C. Before assembling the R-718 HTHP, the liquid-injected rotary lobe blower was tested in an R-718 compressor performance test stand. This paper focuses on the design of the test stand and the performance test results for different shaft speeds, pressure ratios, and suction pressures. The test results are compared to the initial manufacturer’s coefficient-based correlation, which is then modified to fit the experimental data. The updated model predicts the compressor’s behavior in the R-718 HTHP regarding cooling capacity, efficiency, and COP.

A novel mechanism that can be adapted for use as a compressor or as an expander is described. A test cell to measure performance as an expander is described and results of testing under various heat load conditions are presented. Some results of detailed modelling of performance as a compressor are presented in the form of graphs of isentropic and volumetric efficiency plotted against pressure ratio and pressure difference. These are compared and contrasted with equivalent graphs for conventional types of compressor. This comparison is used to demonstrate how the novel concept combines the benefits of both reciprocating and screw compressors and expanders. Proposals for future development of this work are suggested, with some possible new applications for the novel concept. This paper is part of a series of presentations and extends work presented at previous conferences, including the Herrick Compressor Conference in 2022. This paper includes performance data that has not previously been published and the discussion explores some explanations for the differences between the novel concept and conventional compressors.

Compressors are the major energy consumption components in vapor compression systems, drawing much research effort in reducing carbon emissions. The isothermal compressor integrates the compressor chamber and gas cooler to achieve near isothermal compression, reaching up to 30% energy reduction compared to the traditional isentropic compression work. This paper presents a detailed isothermal compressor model combined with a generalized liquid piston model to account for the carbon dioxide (CO₂) isothermal compression process. The model is established based on MATLAB environment. The model uses the real experimental data as boundary conditions and initial settings, which also considers the CO₂ solubility in liquid piston (mineral oil) for designing, optimizing and customizing the compression chambers. The validation was carried out with experimental data using a prototype with 3.5 kW capacity. The results have demonstrated the accuracy of the dynamic model (6.2% relative error for chamber pressure and 0.5 K deviation for chamber temperature), which provide a guideline for designing and customizing the isothermal compression cycle.