| 1. |
- Gong, S., et al.
(författare)
-
Orientation effect on heat transfer coefficient of a downward surface for flow boiling in a rectangular channel under low flow rate
- 2020
-
Ingår i: International Journal of Heat and Mass Transfer. - : Elsevier. - 0017-9310 .- 1879-2189. ; 153
-
Tidskriftsartikel (refereegranskat)abstract
- Natural convection boiling in channel with Arc-Shaped will be encountered in the IVR-ERVC (In-Vessel Retention measure by External Reactor Vessel Cooling) system in nuclear power plant under severe accident. The flow and heat transfer characters in this situation is simulated by flow boiling of deionized water in an inclined rectangular channel under low flow rates. This paper aims to separate various parameters (such as orientation, mass flow rate and inlet quality, etc.) to investigate their individual effects on heat transfer coefficient (HTC) in a rectangular channel with cross section of 17 mm × 10 mm. By using a preheater at the inlet of the rectangular channel, the inlet quality could be controlled and the two-phase flow situation could be observed before the fluids entering into the main heater region on one side of the channel wall in downstream. Thus the characteristics of HTC on the main heater could be investigated at different flow patterns. The channel orientations vary from 15 to 90°, the mass flow rates vary from 110 to 288 kg/(m2s) and the qualities vary from 0.003 to 0.036, respectively. Experimental results show that the mass flow rate and quality effects on the HTC are very weak in this study. However, the orientation angle effect on HTC shows an transition region within 45°~60°, while it slowly changes when the orientation angle is smaller than 45° and bigger than 60°. Such tendency could be well formulated by the error function. Compared with different empirical formulas of saturated boiling HTC, it is found that the Liu & Winterton correlation can well predict the experimental HTC results in 90° orientation channel. Based on such correlation and coupled with the error function, a new model was developed by considering the orientation effect, which has an error of ±15% comparing with the experimental data.
|
|
| 2. |
- Zhu, Y. -C, et al.
(författare)
-
Experimental Study of Critical Heat Flux on a Graphite Film
- 2020
-
Ingår i: Kung Cheng Je Wu Li Hsueh Pao/Journal of Engineering Thermophysics. - : Science Press. - 0253-231X. ; 41:3, s. 643-647
-
Tidskriftsartikel (refereegranskat)abstract
- Saturated pool boiling experiment with heater surfaces of smooth graphite films was conducted under atmospheric pressure, and the deionized water was used as working fluid. The test results showed that the graphite film began to expand and fracture in some parts of the surface as the heat flux reached 1.83 MW/m2. Then the expanded area enlarged and the resistance of the graphite film rapidly increased with the increase of the heat flux, until the whole film was expanded and the surface was ruptured uniformly under a heat flux of 2.40 MW/m2, while the resistance increased slowly during this process. Ultimately, the graphite film was burned out at a heat flux of 3.17 MW/m2. Consequently, the critical heat flux of the graphite film could be enhanced by an adaptively expanding processing with an enhancement ratio of 73%. The visualization results through a high-speed camera showed that compared with the smooth surface, the quantity of nucleation was greater, the bubble departure diameter was smaller, and the bubble departure frequency was higher on an expanded graphite surface under the same heat flux condition.
|
|
| 3. |
- Li, X., et al.
(författare)
-
Flow Pattern Identification of Porous Media Based on Signal Feature Extraction and SVM
- 2022
-
Ingår i: Kung Cheng Je Wu Li Hsueh Pao/Journal of Engineering Thermophysics. - : Science Press. - 0253-231X. ; 43:11, s. 2957-2965
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, the visualization experiment of gas-liquid two-phase flow in porous media is carried out. The typical flow patterns of bubbly flow, slug flow and annular flow are photographed by high-speed camera, and the corresponding differential pressure fluctuation signals are measured and recorded, Using probability density function (PDF) and power spectral density (PSD) curves, the time-domain and frequency-domain characteristics of differential pressure signals corresponding to each flow pattern are analyzed, and the quantitative characteristic parameters are introduced to construct the characteristic vector reflecting the time-frequency characteristics of differential pressure signals. A two-phase flow pattern identification method in porous media based on support vector machine (SVM) is proposed. The results show that the overall recognition rate of the three flow patterns measured by the method is 98.18%, which can provide a new technical support for the on-line recognition of gas-liquid two-phase flow patterns in porous media.
|
|
| 4. |
- Liu, J., et al.
(författare)
-
Linear stability of a fluid mud–water interface under surface linear long travelling wave based on the Floquet theory
- 2021
-
Ingår i: European journal of mechanics. B, Fluids. - : Elsevier BV. - 0997-7546 .- 1873-7390. ; 86, s. 37-48
-
Tidskriftsartikel (refereegranskat)abstract
- The Floquet theory is combined with the unsteady Orr–Sommerfeld equations for the first time to model the linear stability of a fluid mud–water interface under the influence of a linear long travelling wave (or linear shallow water wave). The modelling results reveal three instability modes that could appear on the fluid mud–water surface: the Kelvin–Helmholtz (K–H) and finite-wavelength (F-W) instabilities, which are also present in steady two-layer systems, and parametric instability, which is only seen in periodic problems. The growth rate of the parametric instability is generally small, but it affects the growth rate curves of the other two instabilities. The K–H and F-W instabilities are found to be dominant, and each plays an important role in determining the evolution of the fluid mud–water interface. Both the K–H and F-W instabilities grow with increasing water depth and decreasing wave period as well as with decreasing thickness and density of the mud layer. However, they exhibit distinct dependencies on the fluid mud-to-water viscosity ratio and compete near the critical conditions. For unstable flow near the critical conditions, the K–H instability dominates over the F-W instability at a low viscosity ratio and vice versa at a high viscosity ratio, while for unstable flow far beyond the critical conditions, the K–H instability is dominant regardless of the viscosity ratio. These results are practically instructive for waterway and harbour construction and protection since they provide valuable insights into the early dynamics of the instability mechanisms of the fluid mud–water interface.
|
|
