A numerical study of air preheater leakage

Drapaca

et al. 2017

Entropy

Leakage through microscale or nanoscale cracks is usually hard to observe, difficult to control, and causes significant economic loss. In the present research, the leakage in a pipe was evaluated by the virtual entropy generation (VEG) method. In virtual entropy generation method, the "measured entropy generation" is forced to follow the "experimental second law of thermodynamics". Taking the leakage as the source virtual entropy generation, a new pipe leakage evaluation criterion was analytically derived, which indicates that the mass leakage rate should be smaller than the pressure drop rate inside a pipe. A numerical study based on computational fluid dynamics showed the existence of an unrealistic virtual entropy generation at a high mass leakage rate. Finally, the new criterion was used in the evaluation of leakage available in the literature. These results could be useful for leakage control or industry criteria design in the future.

Section: Evaluation Of Leakagementioning

confidence: 99%

Leakage Evaluation by Virtual Entropy Generation (VEG) Method

Drapaca

et al. 2017

Entropy

Proceedings of the Institution of Mechanical Engineers, Part A:

“…Maharaj et al. 27 presented an analytical and numerical study (two-dimensional CFD) to quantify direct leakage for a Ljungström air preheater that was assumed to be similar to flow through an orifice. Zhang et al.…”

Section: Introductionmentioning

confidence: 99%

Modification of rotary air preheater toward achieving extended life-span utilizing porous media approach: A case study

Hajebzadeh¹,

Ansari²

2021

The main goal of this study is to achieve the extended operating life of the rotary regenerative air pre-heater (Ljungström) of Bandar Abbas power plant by modifying operational parameters by decreasing the corrosion. To achieve this goal, a three-dimensional CFD simulation of the Ljungström is carried out, utilizing the thermal non-equilibrium porous media model. Temperatures are validated against measured data from the power plant with a maximum relative error of 5.54% on the Celsius scale, and mass flow rates are validated with a maximum relative error of −5.25%. The effect of the Ljungström key parameters including the rotational speed, cold layer material, inlet air/flue gas temperature, and mass flow rate, are analyzed in presence of leakages and neglecting it, using porous media approach. The leakage effect is investigated considering radial and axial/peripheral clearances. Finally, a simulation is performed by applying feasible improved parameters extracted from the above analyses considering the effect of all parameters together in presence of leakages, which shows a 6.14% improvement in the Ljungström effectiveness, reducing the total leakage to about one-third of the actual model and eliminating any corrosion.

“…Their results showed that the cold end leakage could significantly reduce the flue gas temperature, whereas the hot end leakage has less effect on the flue gas temperature. Maharaj et al [19] established a simplified flow path model for numerical calculation of direct air leakage. It is found that the results calculated by empirical formula are lower than the simulated values due to the ignorance of the gradual change of the gap size along the radial direction.…”

Section: Introductionmentioning

confidence: 99%

Experimental and Numerical Investigations on the Local Direct Leakage Process of Rotary Regenerative Air Preheater

Zhu

et al. 2020

Applied Sciences

An inherent defect of the operating rotary air preheaters (RAPH) is known as leakage, which seriously hinders the efficient and safe operation of RAPH. It is significant for the estimation of the direct leakage to determine the effects of different structure parameters of sealing sheets and different operation parameters of a RAPH. A direct leakage set-up was built and a three-dimensional numerical model was established to explore the local direct air leaking process of rotary regenerative air preheater and study the effects of geometrical and operational parameters on the leakage. The numerical simulation using the transition k-kl-ω turbulence model was verified by the experimental results. The results show that the local direct air leakage mainly depends on the total pressure difference between the two sides of the seal instead of the one-side pressure. The air leakage can be significantly reduced by narrowing the leakage gap. The increase in the number of sealing sheets can reduce the air leakage own to the increase in the leakage resistance. The increase in the spacing between the adjacent sealing sheets can enlarge the recirculation zone and increase the energy loss of mainstream, greatly reducing the local direct air leakage. Due to the different size recirculation zone formation and streamline curvature induced by sealing sheet, the effect of bending angle on the direct air leakage varies. To obtain lower leakage rate, it is recommended for the rotor of tri-sectional air preheater to pass through flue gas section, secondary-air section, and primary-air section in sequence.