Thermodynamics and Fluid Mechanics of a Closed Blade Cascade Wind Tunnel for Organic Vapors

Abstract

The organic Rankine cycle (ORC) offers great potential for waste heat recovery and use of low-temperature sources for power generation. However, the ORC thermal efficiency is limited by the relatively low-temperature level, and it is, therefore, of major importance to design ORC components with high efficiencies and minimized losses. The use of organic fluids creates new challenges for turbine design, due to dense gas behavior and the low speed of sound. The design and performance predictions for steam and gas turbines have been initially based on measurements and numerical simulations of flow through two-dimensional cascades of blades. In case of ORC turbines and related fluids, such an approach requires the use of a specially designed closed cascade wind tunnel. In this contribution the design and process engineering of a continuous running wind tunnel for organic vapors is presented. The wind tunnel can be operated with heavy weight organic working fluids within a broad range of pressure and temperature levels. For this reason, the use of classical design rules for atmospheric wind tunnels is limited. The thermodynamic cycle process in the closed wind tunnel is modeled, and simulated by means of a professional power plant analysis tool, including a database for the ORC fluid properties under consideration. The wind tunnel is designed as a pressure vessel system and this leads to significant challenges particular for the employed wide angle diffuser, settling chamber, and nozzle. Detailed computational fluid dynamics (CFD) was performed in order to optimize the important wind tunnel sections.

CFD-supported data reduction of hot-wire anemometry signals for compressible organic vapor flows

“…Relation (12) states that the "true" rms-values are systematically higher than the measured ones. For hot-wires with l << , there is no need to correct the data.…”

“…To check the assumptions made for deriving the correction correlation (12), the experimentally obtained behavior of the turbulent length scales  and  were compared with the outcome of a direct numerical simulation using the same thermodynamic initial state as done in the grid experiments, see Figure 11. Although the numerical simulation covered a decay with larger length scales, the same behavior as observed in the experiments was found.…”

“…For instance, the measured turbulent intensities were Tu = 3.03 % and 3.34 % for the probes with l = 4 mm and l = 1 mm for an integral length of about  ≈ 3 mm. Using correlation (12), the ratio between the two values for Tu would be expected to be 0.88. In contrast, experimentally, a ratio of 3.03/3.34 = 0.91 was found.…”

“…It permits the investigation of organic vapor flows at elevated temperature and pressure levels as representative of ORC power system applications. More details on the test facility CLOWT and its working principle can be found in previous publications [10][11][12][13]. Figure 1.a shows the entire test rig with the centrifugal compressor (blue colored), the basic test section with 2.5 m total length containing a second nozzle, the calibration test section (with cross area 50 mm x 100 mm), and a diffuser, Figure 1.b.…”

Bayesian inference of thermodynamic models from vapor flow experiments

“…The facility is designed to operate with several gases, including air, CO 2 , and organic fluids. At the Münster University of Applied Sciences, the Closed Loop Organic Wind Tunnel (CLOWT), a closed-loop continuous-running wind tunnel, is currently under construction [32,33]. The facility aims at investigating the flow around simple nozzle geometries, as well as turbine blade cascades, and it is designed to operate with fluoroketone Novec TM 649 (CF 3 CF 2 C(O)CF(CF 3 ) 2 ).…”