Heat transfer in a recirculation zone at steady-state and oscillating conditions - the back facing step test case

Steady state and transient heat transfer is a very important aspect of any combustion process. To properly simulate gas to wall heat transfer in a turbulent flow, an accurate prediction of the flow and the thermal boundary layer is required. A typical gas turbine combustion chamber flow presents similarities with the academic backward facing step case, especially in the near wall regions where the heat transfer phenomena take place. For this reason, due to its simple geometry and the availability of well documented experiments, the backward facing step with wall heat transfer represents an interesting validation case. Results of steady-state and transient calculations with the use of various turbulence models are compared here with available experimental data

Application of Fractal Grids in Industrial Low-Swirl combustion

Fractal-grid-generated turbulence is a successful technique to significantly increase the reaction rate in the center of a low-swirl flame. Previous results (Verbeek et al. Combust. Flame 162(1), 129–143, 2015) are promising, but the experiments are only performed using natural gas at a single equivalence ratio and flow rate. In industry, the need arises to adapt gas turbines to a wider range of fuels, such as biogas and syngas. To simulate these other fuels, natural gas is enriched with up to 30 % hydrogen (molar based). By means of planar OH-LIF, the turbulent flame speed is assessed. It is shown that the beneficial effect of fractal-grid-generated turbulence remains upon hydrogen enrichment. The fractal grids enhance the combustion in an energy efficient way, irrespective of the hydrogen fraction. Moreover, the characteristic linear relation of the normalized local consumption speed versus the normalized rms velocity holds for the investigated range, with an increasing coefficient upon hydrogen enrichment. For industry, a wide operability range is essential to operate at part load, therefore the lean stability limit is investigated, as well. It is shown that fractal grids increase the lean stability limit, i.e., the adiabatic flame temperature at which blow off occurs, by 50 K, compared to a standard grid. Increasing the bulk flow significantly increases the lean stability limit and the difference between the two investigated grid types increases upon hydrogen enrichment. Hydrogen addition results in a decrease in the lean stability limit, regardless of the grid. A positive correlation was found between the adiabatic flame temperature at blow-off and the rms velocity at the flame brush. The outcome of the presented study provides, despite a slightly increased lean stability limit, a promising prospect for the application of fractal grids in industrial low-swirl combustion

Thermal entrance effects in a thermoacoustic stacked screen regenerator

Thermoacoustic cryocoolers are of raising interest because they are cost effective and reliable. The underlying heat pumping process occurs in the regenerator, where a sound wave interacts with a solid matrix material. Stacked screens are frequently used to build regenerators for thermoacoustic applications because of their favorable thermal properties and vast mesh sizes. One dimensional codes are commonly used for estimating the performance of thermoacoustic cryocoolers. While these codes are a useful tool in thermoacoustic device design, they do not incorporate entrance effects at the extremities of the regenerator or the resulting convective effects. In this paper these effects are investigated by means of a full Navier-Stokes solution of the flow and heat transfer in a geometrical reduced model of a regenerator. It is shown that convective effects play a role at low pressure amplitudes. A convection driven heat pumping process occurring at the extremities of the regenerator is described. Furthermore, a geometrical study is conducted to estimate the optimal opening of the stacked screen for ideal heat transfer

Immune reactivity in relationto cytomegalovirusinfection after allogeneic bone marrow transplantation

Contains fulltext : 4445.pdf (publisher's version ) (Open Access

Cytomegalovirus immunity in allogeneic marrow grafting

Contains fulltext : 4452.pdf (publisher's version ) (Open Access