“…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¯.…”
Section: Heat Exchanger Modellingmentioning
confidence: 74%
“…Typical gain-phase plots of HTF of a hex are shown in 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 jHTFj is less than 1, [23][24][25] and it decreases with increasing " u. Given the HTF, we can now construct aQ Àû relationship, similar to that of a heat source, from equation 5asQ…”
Section: Htf ¼Qmentioning
confidence: 99%
“…From equations (12), (13), (23) and (24), we can evaluate the elements of the total scattering matrix of the hex as 34…”
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¯.…”
Section: Heat Exchanger Modellingmentioning
confidence: 74%
“…Typical gain-phase plots of HTF of a hex are shown in 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 jHTFj is less than 1, [23][24][25] and it decreases with increasing " u. Given the HTF, we can now construct aQ Àû relationship, similar to that of a heat source, from equation 5asQ…”
Section: Htf ¼Qmentioning
confidence: 99%
“…From equations (12), (13), (23) and (24), we can evaluate the elements of the total scattering matrix of the hex as 34…”
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.
“…He attempted to suppress FIV by weakening vortex shedding and decreasing drag. Witte et al [125] numerically studied the effect of heat transfer for a cylinder at subcritical flow at a Reynolds number of 3900. They used DNS and LES techniques and simulated 2D flow for pulsating laminar flow at Re = 0.4, 4.0, and 40.…”
Section: Flow Over Heated Single Cylindermentioning
This study is an effort to encapsulate the fundamentals and major findings in the area of fluid-solid interaction, particularly the flow-induced vibrations (FIV). Periodic flow separation and vortex shedding stretching downstream induce dynamic fluid forces on the bluff body and results in oscillatory motion of the body. The motion is generally referred to as flow-induced vibrations. FIV is a dynamic phenomenon as the motion, or the vibration of the body is subjected to the continuously changing fluid forces. Sometimes FIV is modeled as forced vibrations to mimic the vibration response due to the fluid forces. FIV is a deep concern of engineers for the design of modern heat exchangers, particularly the shell-and-tube type, as it is the major cause for the tube failures. Effect of important parameters such as Reynolds number, spacing ratio, damping coefficient, mass ratio and reduced velocity on the vibration characteristics (such as Strouhal number, vortex shedding, vibration frequency and amplitude, etc.) is summarized. Flow over a bluff body with wakes developed has been studied widely in the past decades. Several review articles are available in the literature on the area of vortex shedding and FIV. None of them, however, discusses the cases of FIV with heat transfer. In particular systems, FIV is often coupled to heat transfer, e.g., in nuclear power plants, FIV causes wear and tear to heat exchangers, which can eventually lead to catastrophic failure. As the circular shape is the most common shape for tubes and pipes encountered in practice, this review will only focus on the FIV of circular cylinders. In this attempt, FIV of single and multiple cylinders in staggered arrangement, including tandem and side-by-side arrangement is summarized for heated and unheated cylinder(s) in the one- and two-degree of freedom. The review also synthesizes the effect of fouling on heat transfer and flow characteristics. Finally, research prospects for heated circular cylinders are also stated.
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