Esa Utriainen

Evaluation of the Cross Corrugated and Some Other Candidate Heat Transfer Surfaces for Microturbine Recuperators

To achieve high thermal efficiencies, 30 percent and higher, for small gas turbines a recuperator is mandatory. As the recuperator represents 25–30 percent of the overall machine cost, efforts are now being focused on establishing new low-cost recuperator concepts for gas turbine engines. In this paper the cross corrugated (CC), also called chevron pattern, heat transfer surface is reviewed to assess its thermal and hydraulic performance and compare it to some other candidate surfaces for a 50 kW microturbine. The surfaces may be categorized into three primary surface types and one plate-fin type. Design calculations of a recuperator heat transfer matrix using these surfaces enable direct comparison of the recuperator matrix volumes, weights and dimensions. It is concluded that the CC surface has great potential for use in recuperators of the future. (Less)

Numerical analysis of a primary surface trapezoidal cross wavy duct

A three‐dimensional numerical study was conducted to assess the hydraulic and heat transfer performance of a primary surface type heat exchanger surface, called the trapezoidal cross wavy (TCW) duct. This duct is similar to the ducts being used in compact recuperators manufactured by Solar Turbines Inc. The governing equations, i.e. the mass conservation equation, Navier‐Stokes equations and the energy equation, are solved numerically by a finite volume method for boundary fitted coordinates. Periodic boundary conditions are imposed in the main flow direction. In this particular case laminar convective flow and heat transfer prevail. Owing to the complex geometry a complicated secondary flow pattern appears in the cross‐sectional planes. Details of the recuperator ducts and the numerical method, as well as relevant results, are presented. The overall results are also compared with corresponding results (i.e. Nu numbers, friction factors) of straight ducts with various cross‐sectional shapes.

Computational Analysis of Pin-Fin Arrays Effects on Internal Heat Transfer Enhancement of a Blade Tip Wall

Cooling methods are strongly needed for the turbine blade tips to ensure a long durability and safe operation. Improving the internal convective cooling is therefore required to increase the blade tip life. A common way to cool the tip is to use serpentine passages with 180-deg turns under the blade tip cap. In this paper, enhanced heat transfer of a blade tip cap has been investigated numerically. The computational models consist of a two-pass channel with a 180-deg turn and various arrays of pin fins mounted on the tip cap, and a smooth two-pass channel. The inlet Reynolds number is ranging from 100,000 to 600,000. The computations are 3D, steady, incompressible, and nonrotating. Details of the 3D fluid flow and heat transfer over the tip walls are presented. The effects of pin-fin height, diameter, and pitches on the heat transfer enhancement on the blade tip walls are observed. The overall performances of ten models are compared and evaluated. It is found that due to the combination of turning, impingement, and pin-fin crossflow, the heat transfer coefficient of the pin-finned tip is a factor of 2.67 higher than that of a smooth tip. This augmentation is achieved at the expense of a penalty of pressure drop around 30%. Results show that the intensity of heat transfer enhancement depends upon pin-fin configuration and arrangement. It is suggested that pin fins could be used to enhance the blade tip heat transfer and cooling.

A Comparison of Some Heat Transfer Surfaces for Small Gas Turbine Recuperators

For small gas turbines a recuperator is mandatory to achieve high thermal efficiencies, 30 percent and higher. As the recuperator represents 25–30 percent of the overall machine cost, efforts are now being focused on establishing new low cost recuperator concepts for gas turbine engines. In this paper a comparison of four different heat transfer surfaces is performed for a recuperator for a representative 50 kW micro turbine. Two standard methods of comparison, the so-called volume goodness factor and the flow area goodness factor, were used to choose several promising heat transfer surfaces for design calculations of a recuperator heat transfer matrix. Thus a direct comparison of recuperator matrix dimensions, volume and weight is possible for the selected surfaces. The hydraulic diameter is equal for all surfaces thus only their thermohydraulic performances are compared. In this paper details of the heat transfer surface geometries as well as the resulting recuperator matrix dimensions, volumes and weights are presented.Copyright

Enhanced Internal Heat Transfer on the Tip-Wall in a Rectangular Two-Pass Channel (AR = 1:2) by Pin-Fin Arrays

To improve gas turbine performance, the operating temperature has been increased continuously. However, the heat transferred to the turbine blade is substantially increased as the turbine inlet temperature is increased. Cooling methods are therefore much needed for the turbine blades to ensure a long durability and safe operation. The blade tip region is exposed to the hot gas flows and is difficult to cool. A common way to cool the tip is to use serpentine passages with a 180° turn under the blade tip cap taking advantage of the three-dimensional turning effect and impingement. Increasing internal convective cooling is however required to increase the blade tip life. In this article, enhanced heat transfer of a blade tip has been investigated numerically. The computational models consist of a two-pass channel with a 180° turn and arrays of pin-fins mounted on the tip-cap, and a smooth two-pass channel. Inlet Reynolds numbers range from 100,000 to 600,000. The computations are 3-D, steady, and incompressible. The detailed 3-D fluid flow and heat transfer over the tip surfaces are presented. The overall performance of the two models is evaluated. It is found that due to the combination of turning, impingement, and pin-fin crossflow the heat transfer coefficient of the pin-finned tip might be a factor of 1.84 higher than that of a smooth tip. This augmentation is achieved at the expense of a penalty of pressure drop around 35%. It is suggested that the pin-fins could be used to enhance blade tip heat transfer and cooling.

Film-Cooling Performance of a Turbine Vane Suction Side: The Showerhead Effect on Film-Cooling Hole Placement for Cylindrical and Fan-Shaped Holes

In this paper, the transient IR-thermography method is used to investigate the effect of showerhead cooling on the film-cooling performance of the suction side of a turbine guide vane working under ...

Towards Efficient CFD-Simulations of Engine LikeTurbine Guide Vane Film Cooling

It is well known that the efficiency of a gas turbine can be increased by using higher combustion temperatures and that this demands improved cooling. This study focuses on strategies to decrease t ...

Window Temperature Impact on IR Thermography for Heat Transfer Measurements

Using time-resolved temperature measurements obtained through IR thermography, the film cooling effectiveness and heat transfer coefficient can be determined simultaneously from a single test for the entire observed surface. This is a type of test ideally suited for studying the heat load and cooling configuration efficiency on a gas turbine blade or guide vane. As shown in this paper, accurate measurements require special care to be taken of the window material and temperature. This issue stems from the non-unity internal transmittance of the window through which the test article is observed, coupled with the unusual feature of the test rig window in this kind of setup frequently being heated at a faster rate than the test object during a test. It is exasperated by the strong coupling between the two parameters being sought, making the output sensitive to small changes in the input. Approaches for measuring the window temperature are outlined and uncertainty estimates in the determination of the heat transfer coefficient and film cooling effectiveness given as 23% and 0.08, respectively.

Recuperators in Gas Turbine Systems

The application of recuperators in advanced thermodynamic cycles is growing due to stronger demands of low emissions of pollutants and the necessity of improving the cycle efficiency of power plants to reduce the fuel consumption.This paper covers applications and types of heat exchangers used in gas turbine units. The trends of research and development are brought up and the future need for research and development is discussed. Material aspects are covered to some extent.Attempts to achieve compact heat exchangers for these applications are also discussed. With the increasing pressure ratio in the gas turbine cycle, large pressure differences between the hot and cold sides exist. This has to be accounted for.The applicability of CFD (Computational Fluid Dynamics) is discussed and a CFD–approach is presented for a specific recuperator. This recuperator has narrow wavy ducts with complex cross-sections and the hydraulic diameter is so small that laminar flow prevails. The thermal-hydraulic performance is of major concern.Copyright

Film-Cooling Performance of Multiple Arrays of Cylindrical and Fan-Shaped Holes

Experimental investigations are performed on the suction side of a cooled turbineguide vane. Transient IR thermography is used to evaluate film cooling performanceof cylindrical and fan-shaped hole ...