An Investigation of Flow, Heat Transfer Characteristic of Annular Flow and Critical Heat Flux in Vertical Upward Round Tube

2006 ◽  
Author(s):  
Fan Pu ◽  
Suizheng Qiu ◽  
Guanghui Su ◽  
Dounan Jia
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Liquid Film ◽  
Critical Heat Flux ◽  
Heat Transfer Characteristic ◽  
Annular Flow ◽  
Transfer Characteristic ◽  
Round Tube

The term annular flow is used to describe the configuration of vapor-liquid flow in which part of the liquid travels as a film on the wall and the rest is entrained as drops by the vapor core in the center of the channel. The objective of this paper is to develop a hydrodynamic model for vertical upward annular flow. A separated flow model is developed and the conservations of Mass, Momentum, Energy, entrainment rate correlation in wide range of conditions and interfacial frictional correlation are used to research the flow and heat transfer characteristic of annular flow. The liquid film thickness, liquid film mass flow rate, two-phase heat transfer coefficient pressure along axial position, local velocity profiles along radial position are predicted theoretically. The influence of the mass flux, heat flux on liquid film thickness, heat transfer coefficient etc. are investigated in detail. The critical heat flux are also predicted in vertical upward round tube according to the theory that the dryout in vertical annular flow emerges at the point where the film is depleted due to the integrating result of entrainment, deposition and evaporation. The influence of mass flux, inlet mass quality and tube diameter on critical heat flux is also predicted in this paper. Finally the predicted result of critical heat flux is compared with experimental data, and the theoretical CHF values are higher than that of experimental data, with error within 30%.

Experimental Investigation on Critical Heat Flux in Horizontal Tube

2018 ◽  
Author(s):  
Peng Chuanxin ◽  
Zan Yuanfeng
Keyword(s):  
Experimental Data ◽  
Heat Flux ◽  
Liquid Film ◽  
Critical Heat Flux ◽  
Annular Flow ◽  
Horizontal Tube ◽  
Lookup Table ◽  
Low Flow ◽  
Round Tube ◽  
Boiling Crisis

The critical heat flux (CHF) in horizontal tube under low flow condition is investigated in this paper. It is found that the boiling crisis occurs at the upper surface of the horizontal tube. According to the exit quality and flow pattern, the category of boiling crisis in the horizontal tube under low flow is considered to be Dryout. The prediction results of Bowring correlation and Lookup table are much larger than the experimental data. Because the Bowring correlation and Lookup table are proposed for the CHF prediction of vertical round tube. The distribution of liquid film in horizontal annular flow is asymmetrical due to gravity. The non-uniform distribution of the liquid film reduces the CHF.

Flow Behavior and Flow Boiling Heat Transfer in Thin-Rectangular Mini-Channels

2008 ◽  
Author(s):  
Yasuo Koizumi ◽  
Hiroyasu Ohtake ◽  
Tomonari Yamada
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Flow Pattern ◽  
Critical Heat Flux ◽  
Boiling Heat Transfer ◽  
Annular Flow ◽  
Flow Channel ◽  
Heat Transfer Surface ◽  
Liquid Slug ◽  
Flux Condition

Boiling heat transfer of thin-rectangular channels of the width of 10 mm has been examined. The height of the flow channel was in a range from 0.6 mm to 0.4 mm. Experimental fluid was water. Bubbly flow, slug flow, semi annular flow and annular flow were observed. The flow pattern transition agreed well with the Baker flow pattern map for the usual sized flow path. The critical heat flux was lower than the value of the usual sized flow channel. The Koizumi and Ueda method predicted well the trend of the critical heat flux of the present experiments. At the critical heat flux condition, the heat transfer surface was covered by liquid slug, a large bubble pushed away the liquid slug, a dry area was formed on the heat transfer surface and then liquid slug came around to cover the heat transfer surface again. This process repeated rapidly. Following this observation, a heat transfer surface temperature calculation model at the critical heat flux condition was proposed. The calculated result re produced the experimental result.

The Effect of Inlet Orifice on Critical Heat Flux and Flow Boiling Heat Transfer in Single Horizontal Microtube

2013 ◽  
Author(s):  
Yanfeng Fan ◽  
Ibrahim Hassan
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Critical Heat Flux ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Saturation Pressure ◽  
Working Fluid ◽  
Flow Boiling Heat Transfer

Flow oscillation is a crucial issue for the development of flow boiling heat transfer in the applications. Inlet orifice has been proven be an option to eliminate the oscillation. However, the effects of inlet orifice on critical heat flux and flow boiling heat transfer coefficient are lack of study. In this work, the effects of inlet restriction on critical heat flux and heat transfer coefficient in single horizontal microtube under uniform heating condition is experimentally investigated using FC-72 as working fluid. A stainless steel microtube with an inner diameter of 889 μm is selected as main microtube. Two smaller microtubes are assembled at the inlet of main microtube to achieve the restriction configurations of 50% and 20% area ratios. The experimental measurement is carried out at mass fluxes ranging from 160–870 kg/m2·s and heat fluxes varying from 6–170 kW/m2. Two saturation pressures, 10 and 45 kPa, are tested. The experimental results of critical heat flux and two phase heat transfer coefficient obtained in the microtube without orifice are compared with the existing correlations. The addition of an orifice does not enhance the normal critical heat flux but increases the premature critical heat flux. In aspect of heat transfer, the orifice shows improvement on heat transfer coefficient at low mass flux and high saturation pressure.

Effect of Heat Flux on Droplet Entrainment Using Annular Flow Dryout Model

2010 ◽  
Author(s):  
Masroor Ahmad ◽  
Evgeniy Burlutskiy ◽  
Simon P. Walker ◽  
Geoffrey F. Hewitt
Keyword(s):  
Experimental Data ◽  
Heat Flux ◽  
High Pressure ◽  
Liquid Film ◽  
Annular Flow ◽  
High Pressures ◽  
Droplet Entrainment ◽  
Annular Film ◽  
Low Pressures ◽  
Flow Experiments

Annular film dryout depends upon the competition of entrainment, deposition and evaporation processes between the droplet-laden core and wall liquid film. In this paper, effect of heat flux on droplet entrainment is analyzed by modeling different low and high pressure diabatic annular flow experiments numerically using an annular flow dryout model (AFM). Overall, the AFM predicted the experimental data reasonably accurately. It is concluded that at high pressures increasing heat flux may enhance net entrainment considerably but this effect diminishes at low pressures.

scholarly journals Наножидкости для энергетики: механизм влияния диспергентов на тепловые параметры и кризисные явления при кипении

2020 ◽  
Vol 90 (2) ◽  
pp. 175
Author(s):  
В.Н. Морару ◽  
Б.И. Бондаренко ◽  
С.В. Сидоренко ◽  
Д.В. Комыш
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Critical Heat Flux ◽  
Direct Current ◽  
Sedimentation Stability ◽  
Boiling Crisis ◽  
Transfer Parameters ◽  
The Heat Transfer Coefficient

Abstract: The effect of dispersants organic (CTAB) and inorganic nature (sodium pyrophosphate and sodium silicate) on the critical heat flux (CHF) and heat-transfer coefficient (HTC) of boiling various aqueous nanofluids (NFs) under conditions of free convection is studied. It has been established that the addition of ionic dispersants to aluminosilicate NFs, increasing their aggregative and sedimentation stability, as a rule, worsens their heat-transfer parameters during boiling, causing a sudden pre-crisis heater burnout in a test unit powered by direct current. The mechanism of the phenomenon is revealed. On the contrary, the addition of dispersants and surfactants to carbon-containing NFs with high thermal conductivity, improving their stability, at the same time increases the heat transfer coefficient during boiling of NFs, but also cause pre-crisis heater burnout in the case of direct current heating. The effect of dispersants on crisis phenomena during boiling of water and NFs is analyzed and the causes of sudden pre-crisis heater burnout have been elucidated. Several mechanisms have been proposed for interpreting the observed effects, from which the expediency of using alternating heating current and non-ionic, non-foaming surfactants and dispersants to avoid an early onset of the boiling crisis in order to achieve higher values of the critical heat flux and the heat transfer coefficient during the NFs boiling.

Sign in / Sign up

Export Citation Format

Share Document