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

Sung-Wei Hsu,Hsiao-Wei Chiang,Chih-Wei Yen

doi:10.3390/en7096172

Sung-Wei Hsu, Hsiao-Wei Chiang + Show 1 more

Open Access

https://doi.org/10.3390/en7096172

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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.

Highlights

The approach of burning fossil fuels to obtain heat for use in thermal processes or power for mechanical drivers has been employed for centuries
To determine the effects of the supply pressures on the expander, and the pressure ratios over it on the performances of both the screw expander and the organic Rankine cycle (ORC) cycle, the following three tests were intentionally performed by regulating the heat input and heat rejection: (1) Test 1: The temperature of the hot water was regulated to be in the range of 85–122 C and the flow rate of the coolant water was fixed at 400 LPM
ORC is used for heat energy conversion, the evaporation pressure and condensation pressure of circulating working fluid will change to meet the condition of heat source and heat sink

Summary

Introduction

The approach of burning fossil fuels to obtain heat for use in thermal processes or power for mechanical drivers has been employed for centuries. This burning process produces carbon dioxide, which is a greenhouse gas and is harmful to the environment as it contributes to problems such as air pollution, global warming, and climate change. In order to resolve these problems, i.e., to mitigate greenhouse gas emissions and fossil fuel depletion, much effort has been made toward using industrial waste heat and renewable energies for producing electricity. A variety of low-grade heat sources, such as flue gas, hot water produced during thermal processes, and waste steam, are rejected to the environment because they have comparatively low energy availability and are not very economical. In which the expander pressure ratios were set to 3.3–6.1, 3.0–4.6, and 2.4–3.5 to investigate their effects on the expander performance, system cycle efficiency, and power output

System Description

Theoretical Modeling

Results and Discussion

Summary and Conclusions