“…The gain-phase plots suggest that the hex acts like a low-pass filter i.e., the gain decreases with increasing frequency. We observe that for all values of u¯ considered in this study, the starting value of |HTF| is less than 1, 23–25 and it decreases with increasing u¯. Figure 4.(a) |HTF| and (b) Φ(HTF) obtained from numerical simulations, for d = 3 mm, h g = 0.3 mm and different mean velocities, u¯.…”
One of the major concerns in the operability of power generation systems is their susceptibility to combustion instabilities. In this work, we explore whether a heat exchanger, an integral component of a domestic boiler, can be made to act as a passive controller that suppresses combustion instabilities. The combustor is modelled as a quarterwave resonator (1-D, open at one end, closed at the other) with a compact heat source inside, which is modelled by a time-lag law. The heat exchanger is modelled as an array of tubes with bias flow and is placed near the closed end of the resonator, causing it to behave like a cavity-backed slit plate: an effective acoustic absorber. For simplicity and ease of analysis, we treat the physical processes of heat transfer and acoustic scattering occurring at the heat exchanger as two individual processes separated by an infinitesimal distance. The aeroacoustic response of the tube array is modelled using a quasi-steady approach and the heat transfer across the heat exchanger is modelled by assuming it to be a heat sink. Unsteady numerical simulations were carried out to obtain the heat exchanger transfer function, which is the response of the heat transfer at heat exchanger to upstream velocity perturbations. Combining the aeroacoustic response and the heat exchanger transfer function, in the limit of the distance between these processes tending to zero, gives the net influence of the heat exchanger. Other parameters of interest are the heat source location and the cavity length (the distance between the tube array and the closed end). We then construct stability maps for the first resonant mode of the aforementioned combustor configuration, for various parameter combinations. Our model predicts that stability can be achieved for a wide range of parameters.
“…The gain-phase plots suggest that the hex acts like a low-pass filter i.e., the gain decreases with increasing frequency. We observe that for all values of u¯ considered in this study, the starting value of |HTF| is less than 1, 23–25 and it decreases with increasing u¯. Figure 4.(a) |HTF| and (b) Φ(HTF) obtained from numerical simulations, for d = 3 mm, h g = 0.3 mm and different mean velocities, u¯.…”
One of the major concerns in the operability of power generation systems is their susceptibility to combustion instabilities. In this work, we explore whether a heat exchanger, an integral component of a domestic boiler, can be made to act as a passive controller that suppresses combustion instabilities. The combustor is modelled as a quarterwave resonator (1-D, open at one end, closed at the other) with a compact heat source inside, which is modelled by a time-lag law. The heat exchanger is modelled as an array of tubes with bias flow and is placed near the closed end of the resonator, causing it to behave like a cavity-backed slit plate: an effective acoustic absorber. For simplicity and ease of analysis, we treat the physical processes of heat transfer and acoustic scattering occurring at the heat exchanger as two individual processes separated by an infinitesimal distance. The aeroacoustic response of the tube array is modelled using a quasi-steady approach and the heat transfer across the heat exchanger is modelled by assuming it to be a heat sink. Unsteady numerical simulations were carried out to obtain the heat exchanger transfer function, which is the response of the heat transfer at heat exchanger to upstream velocity perturbations. Combining the aeroacoustic response and the heat exchanger transfer function, in the limit of the distance between these processes tending to zero, gives the net influence of the heat exchanger. Other parameters of interest are the heat source location and the cavity length (the distance between the tube array and the closed end). We then construct stability maps for the first resonant mode of the aforementioned combustor configuration, for various parameter combinations. Our model predicts that stability can be achieved for a wide range of parameters.
“…This will allow us to account for the influence of the high temperature at the outlet end, which affects the phase of the reflection coefficient and, consequently, the model predictions of the oscillation frequency. We will also infer the parameters of more complex thermoacoustic models derived via system identification based on high-fidelity numerical simulations [13] in order to assess systematic model error (epistemic error). Another improvement will come from replacing regression with a more robust and quantitatively informative technique in order to provide uncertainty estimates also for the acoustic and thermoacoustic parameters.…”
We combine a thermoacoustic experiment with a thermoacoustic reduced order model using Bayesian inference to accurately learn the parameters of the model, rendering it predictive. The experiment is a vertical Rijke tube containing an electric heater. The heater drives a base flow via natural convection, and thermoacoustic oscillations via velocity-driven heat release fluctuations. The decay rates and frequencies of these oscillations are measured every few seconds by acoustically forcing the system via a loudspeaker placed at the bottom of the tube. More than 320,000 temperature measurements are used to compute state and parameters of the base flow model using the Ensemble Kalman Filter. A wave-based network model is then used to describe the acoustics inside the tube. We balance momentum and energy at the boundary between two adjacent elements, and model the viscous and thermal dissipation mechanisms in the boundary layer and at the heater and thermocouple locations. Finally, we tune the parameters of two different thermoacoustic models on an experimental dataset that comprises more than 40,000 experiments. This study shows that, with thorough Bayesian inference, a qualitative model can become quantitatively accurate, without overfitting, as long as it contains the most influential physical phenomena.
“…The heat transfer parameter of pulsated flow in wave channel was studied by [32][33][34]. Other studies focused on the hydrodynamics and heat transfer such as [35][36][37][38][39]. The use of nanofluids with pulsed flow was studied by [40][41][42][43][44][45][46][47][48] where wave and corrugated channel were used during these studies.…”
In this numerical study, the heat transfers of two types of fuels, namely kerosene and gasoline, were studied within a wavy channel with pulsed flow. The CFD module at COMSOL Multiphysics was used in this study. Several variables were used and applied to both types of fuel and compared between them. These variables included the values of Reynolds numbers between 200 to 800, as well as several values of Strouhal Numbers between 0 to 0.25. Different variable values were also used for the wavy channel, including the wave numbers (0, 2, 4, 6, 8, 10) as well as variable values of the wave amplitude (0, 0.1, 0.2, 0.3). Through this study, it was observed that as Strouhal Numbers increase, there is an increase in the Nusselt Number value. It was also observed that as the number of waves increases, there is an improvement in the heat transfer values. The numerical results showed that the values of heat transfer improved with an increase in the amplitude of the wave..
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