Effects of large computational time steps on the computed turbulence were investigated using a fully implicit method. In turbulent channel flow computations the largest computational time step in wall units which led to accurate prediction of turbulence statistics was determined. Turbulence fluctuations could not be sustained if the computational time step was near or larger than the Kolmogorov time scale.

Effects of the computational time step on numerical solutions for turbulent flow

Organic Rankine cycle design and performance comparison based on experimental database

A study on heat and mass transfer behaviour on porous medium embedded in a square annulus is conducted. The inner surface wall is considered to have a cool temperature Tc while the outer surface is...

Dufour and Soret effects on square porous annulus

Performance characteristics of a 200-kW organic Rankine cycle system in a steel processing plant

Thermoeconomic analysis of a biogas-fueled micro-gas turbine with a bottoming organic Rankine cycle for a sewage sludge and food waste treatment plant in the Republic of Korea

The heat/mass transfer analogy for a simulated turbine blade

The secondary flows, including passage and other vortices in a turbine cascade cause significant aerodynamic losses and thermal gradients. Leading-edge modification of the blade has drawn considerable attention as it has been shown to reduce the secondary flows. However, the heat transfer performance of a leading-edge modified blade has not been investigated thoroughly. Since a fillet at the leading edge blade is reported to reduce the aerodynamic loss significantly, the naphthalene sublimation technique with a fillet geometry is used to study local heat (mass) transfer performance in a simulated turbine cascade. The present paper compares Sherwood number distributions on an endwall with a simple blade and a similar blade having modified leading-edge by adding a fillet. With the modified blades, a horseshoe vortex is not observed and the passage vortex is delayed or not observed for different turbulence intensities. However, near the blade trailing edge the passage vortex has gained as much strength as with the simple blade for low turbulence intensity. Near the leading edge on the pressure and the suction surface, higher mass transfer regions are observed with the fillets. Apparently the corner vortices are intensified with the leading-edge modified blade.Copyright © 2005 by ASME

Influence of blade leading edge geometry on turbine endwall heat(mass) transfer

There has recently been a growing interest in sustainable energy converters. One such technology is the organic Rankine cycle, which uses conventional turbine technology with a low temperature waste heat source. A 200 kW organic Rankine cycle system was designed for waste heat recovery application using R245fa as a working fluid. A radial type turbine with 15,000 rpm was employed to generate more than 200 kW with an expansion ratio of 9. Since R245fa has Ma = 1 at low velocity of the working fluid (about 1/3 of air sound of speed) at about 100°C, it reaches supersonic flow conditions easily with small pressure expansion. To avoid supersonic flow conditions in the turbine, the expansion ratio was evenly divided and applied to two turbine stages. Two radial type rotors were placed in the back-to-back layout in a single shaft. The inlet temperature of the turbine was about 124°C, and the inlet pressure was about 2 MPa. The designed turbine was fully tested in the 200 kW ORC system using the design conditions. It succeeded in generating more than 200 kW with R245fa. The performance of the turbine was validated with the experimental results and CFD analysis. Herein, the design procedure and performance evaluation of the ORC turbine was described using R245fa.

Development of a 200 kW ORC radial turbine for waste heat recovery

An experimental system is designed, constructed, and operated to make local measurements of heat transfer from constant-temperature surfaces in a linear turbine cascade. The system includes a number of embedded heaters and a control system to maintain the turbine blades and end walls in the cascade at a uniform temperature. A five-axis measurement system is used to determine temperature profiles normal to the pressure and suction sides of the blades and to the end wall. Extrapolating these measurements close to the surface, the local heat transfer is calculated using Fourier's law. The system has been tested in the laboratory, and results are shown for the temperature distributions above the surfaces and for the local variations in the Nusselt number on the different surfaces in the cascade. The system can also be used to study the heat and mass transfer analogy as considerable data are available for mass transfer results with similar geometries.

Heat Transfer Study in a Linear Turbine Cascade Using a Thermal Boundary Layer Measurement Technique

Heat transfer rates from a surface can be determined from the slope of the temperature profile measured with a thermocouple wire traversing within a boundary layer. However, accuracy of such measurement can suffer due to flow distortion and conduction through the thermocouple wire. The present numerical study consists of two parts—a 2D simulation of flow distortion due to a cylinder in cross flow near a solid wall and a 3D simulation defined as a fin problem to calculate the thermal profile measurement error due to conduction through the thermocouple wires. Results show that the measured temperature is lower than the true temperature resulting in a 5% under-prediction of local heat transfer coefficient. A parametric study shows that low thermal conductivity thermocouple (E type) with a small wire diameter (76 micron) is desirable to reduce the measurement error in local Nusselt number.

S. Han

Papers

The heat/mass transfer analogy for a simulated turbine blade

Influence of blade leading edge geometry on turbine endwall heat(mass) transfer

Development of a 200 kW ORC radial turbine for waste heat recovery

Heat Transfer Study in a Linear Turbine Cascade Using a Thermal Boundary Layer Measurement Technique

Numerical simulation of thermal boundary layer profile measurement