Experimental Investigation of the Performance of a Hermetic Screw-Expander Organic Rankine Cycle

Abstract

Abstract:In this study, the authors experimentally investigate the performance of the organic Rankine cycle (ORC) and screw expander under the influence of supply pressure and pressure ratio over the expander. Three tests were performed with expander pressure ratios of 2. 4-3.5, 3.0-4.6, and 3.3-6.1, which cover the over-expansion and under-expansion operating modes. The test results show a maximum expander isentropic efficiency of 72.4% and a relative cycle efficiency of 10.5% at an evaporation temperature of 101 °C and condensation temperature of 45 °C. At a given pressure ratio over the expander, a higher supply pressure to the expander causes a higher expander isentropic efficiency and higher cycle efficiency in the over-expansion mode. However, in the under-expansion mode, the higher supply pressure results in a lower expander isentropic efficiency and adversely affects the cycle efficiency. The results also show that under the condition of operation at a given pressure ratio, a higher supply pressure yields a larger power output owing to the increased mass flow rate at the higher supply pressure. The study results demonstrate that a screw-expander ORC can be operated with a wide range of heat sources and heat sinks with satisfactory cycle efficiency.

Design and preliminary results of a 20-kW transcritical organic Rankine cycle with a screw expander for low-grade waste heat recovery

“…A cooling tower with a capacity of 200 RT was used for heat rejection in the TRC system. The details of the heat and cooling sources were described in a previous study [8].…”

“…Evidence suggests that the thermal efficiency of an ORC system in a subcritical state is typically lower than 10% [7][8][9][10][11]. However, the transcritical ORC is more attractive for low-grade heat recovery because of the low exergy loss [12].…”

Rankine Cycles, Modeling and Control

“…The overall efficiency for a turbine will vary and is dependent on pressure ratio over the turbine as well as supply pressure. The curve will typically peak at a specific pressure ratio depending on the pump and pressure supply [7]. This was considered as a minor issue, hence a new model was not built.…”

Design and experimental investigation of the cogenerative domestic micro power plant with ORC system

“…Głównym tematem badań różnego typu ekspanderów jest poprawa ich sprawności. Prace w tym zakresie są prowadzone zarówno na drodze badań eksperymentalnych [3][4][5] jak i obliczeń numerycznych [6][7][8]. Prace nad ekspanderami są prowadzone również w IMP PAN w Gdańsku.…”