Effect of flow instability on flow boiling friction pressure drop in parallel micro-channels

2018 ◽  
Vol 97 ◽  
pp. 64-71 ◽  
Author(s):  
Xuejiao Li ◽  
Li Jia ◽  
Chao Dang ◽  
Zhoujian An ◽  
Qian Huang
Keyword(s):  
Pressure Drop ◽  
Flow Instability ◽  
Flow Boiling ◽  
Micro Channels ◽  
Friction Pressure ◽  
Friction Pressure Drop

Experimental Studies of Adiabatic Flow Boiling in Fractal-Like Branching Micro-Channels

2008 ◽  
Author(s):  
Brian J. Daniels ◽  
James A. Liburdy ◽  
Deborah V. Pence
Keyword(s):  
Pressure Drop ◽  
Void Fraction ◽  
Flow Boiling ◽  
Experimental Studies ◽  
Channel Length ◽  
Channel Height ◽  
Channel Network ◽  
Adiabatic Flow ◽  
Numerical Predictions ◽  
Micro Channels

Experimental results of adiabatic boiling of water flowing through a fractal-like branching microchannel network are presented and compared to numerical simulations for identical flow conditions. The fractal-like branching channel network had channel length and width ratios between adjacent branching levels of 0.7071, a total flow length of 18 mm, a channel height of 150 μm and a terminal channel width of 100 μm. The channels were DRIE etched into a silicon disk and pyrex was anodically bonded to the silicon to form the channel top and allowed visualization of the flow within the channels. The water flowed from the center of the disk where the inlet was laser cut through the silicon to the periphery of the disc. The flow rates ranged from 100 to 225 g/min and the inlet subcooling levels varied from 0.5 to 6 °C. Pressure drop across the channel as well as void fraction in each branching level were measured for each of the test conditions. The measured pressure drop ranged from 20 to 90 kPa, and the measured void fraction ranged from 0.3 to 0.9. The pressure drop results agree well with the numerical predictions. The measured void fraction results followed the same trends as the numerical results.

Two-Phase Void Fraction and Pressure Drop in Horizontal Crossflow Across a Tube Bundle

1998 ◽  
Vol 120 (1) ◽  
pp. 140-145 ◽  
Author(s):  
G. P. Xu ◽  
K. W. Tou ◽  
C. P. Tso
Keyword(s):  
Pressure Drop ◽  
Void Fraction ◽  
Mass Velocity ◽  
Flow Model ◽  
Tube Bundle ◽  
Diameter Ratio ◽  
Two Phase ◽  
Friction Pressure ◽  
Oil Flow ◽  
Friction Pressure Drop

Void fraction and friction pressure drop measurements were made for an adiabatic, horizontal two-phase flow of air-water, air-oil across a horizontal in-line, 5 × 20 tube bundle with pitch-to-diameter ratio, P/D, of 1.28. For both air-water and air-oil flow, the experimental results showed that the average void fraction were less than the values predicted by a homogenous flow model, but were well correlated with the Martinelli parameter Xtt and liquid-only Froude number FrLO. The two-phase friction multiplier data exhibited an effect of flow pattern and mass velocity, and they could be well-correlated with the Martinelli parameter.

Experimental Study of Flow Patterns, Pressure Drop and Flow Instabilities in Parallel Rectangular Minichannels

2004 ◽  
Author(s):  
Prabhu Balasubramanian ◽  
Satish G. Kandlikar
Keyword(s):  
Pressure Drop ◽  
High Speed ◽  
Flow Instability ◽  
Flow Boiling ◽  
Pressure Fluctuations ◽  
Flow Patterns ◽  
Flow Instabilities ◽  
Stable Operation ◽  
Phase System ◽  
High Heat Flux

The use of phase change heat transfer in parallel minichannels and microchannels is one of the solutions proposed for cooling high heat flux systems. The increase in pressure drop in a two phase system is one of the problems, that need to be studied in detail before proceeding to any design phase. The pressure drop fluctuations in a network of parallel channels connected by a common head need to be addressed for stable operation of flow boiling systems. The current work focuses on studying the pressure-drop fluctuations and flow instabilities in a set of six parallel rectangular minichannels, each with 333 μm hydraulic diameter. Demonized and degassed water was used for all the experiments. Pressure fluctuations are recorded and signal analysis is performed to find the dominant frequencies and their amplitudes. These pressure fluctuations are then mapped to their corresponding flow patterns observed using a high speed camera. The results help us to relate pressure fluctuations to different flow characteristics, and their effect on flow instability.

Experimental Studies of Pressure Drop and Flow Instability in Evaporative Micro-Channels

2008 ◽  
Author(s):  
Hee Joon Lee ◽  
Dongyao Liu ◽  
Shi-Chune Yao
Keyword(s):  
Pressure Drop ◽  
Flow Instability ◽  
Experimental Studies ◽  
Bond Number ◽  
Effective Length ◽  
Instability Criterion ◽  
Micro Channel ◽  
Micro Channels ◽  
Wide Range ◽  
Channel Systems

Experiments were conducted on evaporative micro-channel systems of water, containing 48 parallel channels of 353 μm hydraulic diameter. The general correlation of two-phase pressure drop for an initial design purpose of evaporative micro-channel systems reported in [1] has been validated. For the water boiling in micro-channels, flow instability was observed. The instability criterion, proposed by Kandlikar [2], is able to predict the water experimental results. However, further examination of his criterion revealed that it can not predict the results of Brutin and Tadrist’s data of n-pentane. This is because the Bond number of water is 0.01, but 0.33 for n-pentane. As a result, the growing bubble of n-pentane may not cover the whole length of the micro-channel. A general expression of the effective length of squeezed bubbles in micro-channel was established for fluids at a wide range of Bond number. Using this proposed effective length, the Brutin and Tadrist’s experimental instability data can also be predicted satisfactorily.

Experimental Investigation on Flow Instability in a Single Vertical Microtube

2015 ◽  
Author(s):  
Qian You ◽  
Ibrahim Hassan ◽  
Lyes Kadem
Keyword(s):  
Heat Flux ◽  
Pressure Drop ◽  
Mass Flux ◽  
Flow Instability ◽  
Flow Boiling ◽  
Flow Direction ◽  
Density Wave ◽  
Mass Fluxes ◽  
Flow Oscillations ◽  
Flow Directions

The experiments are conducted to study the flow boiling instability in a single microtube with 0.889 mm hydraulic diameter in vertical upward and downward flow directions (VU and VD). The subcooled dielectric liquid FC-72 is driven at mass fluxes varying from 700 to 1400 kg/m2·s, and the heat flux uniformly applied on the microtube surface is up to 9.6 W/cm2. The onsets of flow oscillations (OFIs) in both flow directions are observed. Their oscillation types and characteristics are presented as well. The effects of mass flux and heat flux on flow instability in vertical flow directions are discussed. The results show that as the mass flux increases, the OFI occurrence is postponed, and the compounded oscillation types (Ledinegg, pressure drop and density wave oscillations) turn to pressure drop type dominant. At low mass fluxes, the OFI appears earlier in VD than in VU due to the buoyancy force impeded the bubble discharging. As the mass flux increases, the OFI appearance in VD is close to the ones in VU and its flow oscillations tend to be re-stabilized. After OFIs appeared at a given mass flux, with more heat flux added, the density wave oscillation type in VU becomes more active. However, at a constant mass flux, as the heat flux increases, the flow instability in VD becomes “stable” which may be due to the rapid flow pattern change, and this kind of “stable” is not expected because the local dryout may accompany. Hence, the microtube with vertical upward flow direction (VU) performs better from flow boiling instability point of view.

Sign in / Sign up

Export Citation Format

Share Document