scholarly journals Comparative study of flow condensation in conventional and small diameter tubes

2012 ◽  
Vol 33 (2) ◽  
pp. 67-83 ◽  
Author(s):  
Dariusz Mikielewicz ◽  
Rafał Andrzejczyk
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Flow Structure ◽  
Annular Flow ◽  
Flow Boiling ◽  
Small Diameter ◽  
Bubble Generation ◽  
Flow Condensation ◽  
The Heat Transfer Coefficient

Abstract Flow boiling and flow condensation are often regarded as two opposite or symmetrical phenomena. Their description however with a single correlation has yet to be suggested. In the case of flow boiling in minichannels there is mostly encountered the annular flow structure, where the bubble generation is not present. Similar picture holds for the case of inside tube condensation, where annular flow structure predominates. In such case the heat transfer coefficient is primarily dependent on the convective mechanism. In the paper a method developed earlier by the first author is applied to calculations of heat transfer coefficient for inside tube condensation. The method has been verified using experimental data from literature on several fluids in different microchannels and compared to three well established correlations for calculations of heat transfer coefficient in flow condensation. It clearly stems from the results presented here that the flow condensation can be modeled in terms of appropriately devised pressure drop.

Analytical Modeling of Annular Flow Boiling Heat Transfer in Mini- and Microchannel Heat Sinks

2010 ◽  
Vol 132 (4) ◽  
Author(s):  
A. Megahed ◽  
I. Hassan
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Analytical Model ◽  
Boiling Heat Transfer ◽  
Annular Flow ◽  
Flow Boiling ◽  
Heat Sinks ◽  
Flow Boiling Heat Transfer ◽  
The Heat Transfer Coefficient

An analytical model is proposed to predict the flow boiling heat transfer coefficient in the annular flow regime in mini- and microchannel heat sinks based on the separated model. The modeling procedure includes a formulation for determining the heat transfer coefficient based on the wall shear stress and the local thermophysical characteristics of the fluid based on the Reynolds’ analogy. The frictional and acceleration pressure gradients within the channel are incorporated into the present model to provide a better representation of the flow conditions. The model is validated against collected data sets from the literature produced by different authors under different experimental conditions, different fluids, and with mini- and microchannels of hydraulic diameters falling within the range of 92–1440 μm. The accuracy between the experimental and predicted results is achieved with a mean absolute error of 10%. The present analytical model can correctly predict the different trends of the heat transfer coefficient reported in the literature as a function of the exit quality. The predicted two-phase heat transfer coefficient is found to be very sensitive to changes in mass flux and saturation temperature. However, it is found to be mildly sensitive to the change in heat flux.

Transient Heat Transfer During Cryogenic Chilldown

2005 ◽  
Author(s):  
Jelliffe Jackson ◽  
Jun Liao ◽  
James F. Klausner ◽  
Renwei Mei
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Flow Structure ◽  
Flow Boiling ◽  
Superconducting Magnets ◽  
Nucleate Boiling ◽  
Transient Heat Transfer ◽  
Boiling Regime ◽  
The Heat Transfer Coefficient

Cryogenic fluids have found many practical applications in today’s world, from cooling superconducting magnets to fueling launch vehicles. In many of these applications the cryogenic fluid is initially introduced into piping systems that are in excess of 150 degrees Kelvin higher than the fluid. This leads to voracious evaporation of the fluid and significant pressure fluctuations, which is accompanied by thermal contraction of system components. This process is known as chilldown, and although it was first investigated more than 4 decades ago, very little data are available on the momentum and energy transport during this transient process. Consequently, the development of predictive models for the pressure drop and heat transfer coefficient has been hampered. In order to address this deficiency, an experimental facility has been constructed that enables the flow structure to be observed while temperatures and pressures at various locations are measured. This study focuses on the inverse numerical procedure used to extract the transient heat transfer coefficient information from the data collected; this information is then used to evaluate the performance of various correlations for heat transfer coefficient in the flow boiling regime. The method developed utilizes flow structure information and temperature measurements, in conjunction with numerical computations for the temperature field within the tube wall, to calculate the heat transfer coefficient. This approach allows the transition point between the film boiling regime and the nucleate boiling regime to be determined, and it also elucidates the variation of the heat transfer coefficient along the circumference of a horizontal tube, with the heat transfer on upper portion being significantly smaller than that at the bottom.

Local Heat Transfer Coefficient of Flow Boiling in Microchannels With Artificial Reentrant Cavities

2007 ◽  
Author(s):  
Chih-Jung Kuo ◽  
Yoav Peles
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Flow Boiling ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Bubble Generation ◽  
Parallel Microchannels

Flow boiling in parallel microchannels with structured reentrant cavities was experimental studied. Flow patterns, boiling inceptions and heat transfer coefficients were obtained and studied for G = 83 kg/m2-s to G = 303 kg/m2-s and heat fluxes up to 643 W/cm2. The heat transfer coefficient-mass velocity and quality relations had been analyzed to identify boiling mechanism. Comparisons of the performance of the enhanced and plain-wall microchannels had also been made. The microchannels with reentrant cavities were shown to promote nucleation of bubbles and to support significantly better reproducibility and uniformity of bubble generation.

Correlations and Theory for Microchannel Condensation

2008 ◽  
Author(s):  
Qian Su ◽  
Guang Xu Yu ◽  
Hua Sheng Wang ◽  
John W. Rose
Keyword(s):  
Heat Transfer ◽  
Surface Tension ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Theoretical Approach ◽  
Annular Flow ◽  
Fair Agreement ◽  
Calculation Methods ◽  
Fluid Property ◽  
The Heat Transfer Coefficient

In recent years several correlations have been proposed for calculating the heat-transfer coefficient during condensation in circular and non-circular channels of typical dimension around 1 mm where surface tension effects are important and correlations for larger diameter channels are inappropriate. A wholly theoretical approach applicable to annular flow has also been proposed. The correlations are all based on data for R134a, while the theory is applicable to any fluid. In this paper comparisons are made between the correlations for R134a and ammonia; plots based on theory are also included. Fair agreement is seen between all calculation methods for R134a but wide differences are seen for ammonia indicating that the correlations, based only on one fluid, do not capture the fluid property dependence accurately.

Study on Flow Boiling Heat Transfer of Carbon Dioxide With PAG-Type Lubricating Oil in Pre-Dryout Region Inside Horizontal Tube

2010 ◽  
Author(s):  
Chaobin Dang ◽  
Minxia Li ◽  
Eiji Hihara
Keyword(s):  
Heat Transfer ◽  
Carbon Dioxide ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Mass Flux ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Flow Boiling Heat Transfer ◽  
The Heat Transfer Coefficient

In this study, the boiling heat transfer coefficients of carbon dioxide with a PAG-type lubricating oil entrained from 0 to 5 wt% in a horizontally placed smooth tube with an inner diameter of 2 mm were experimentally investigated under the following operating conditions: mass fluxes from 170 to 320 kg/m2s, heat fluxes from 4.5 to 36 kW/m2, and a saturation temperature of 15 °C. The results show that for a low oil concentration of approximately 0.5% to 1%, no further deterioration of the heat transfer coefficient was observed at higher oil concentrations in spite of a significant decrement of the heat transfer coefficient compared to that under an oil-free condition. The heat flux still had a positive influence on the heat transfer coefficient in low quality regions. However, no obvious influence was observed in high quality regions, which implies that nucleate boiling dominates in the low quality region whereas it is suppressed in the high quality regions. Unlike the mass flux under an oil-free condition, mass flux has a significant influence on the heat transfer coefficient, with a maximum increase of 50% in the heat transfer. On the basis of our experimental measurements of the flow boiling heat transfer of carbon dioxide under wide experimental conditions, a flow boiling heat transfer model for horizontal tubes has been proposed for a mixture of CO2 and polyalkylene glycol (PAG oil) in the pre-dryout region, with consideration of the thermodynamic properties of the mixture. The surface tension and viscosity of the mixture were particularly taken into account. New factors were introduced into the correlation to reflect the suppressive effects of the mass flux and the oil on both the nucleate boiling. It is shown that the calculated results can depict the influence of the mass flux and the heat flux on both nucleate boiling and convection boiling.

scholarly journals Experimental Investigation of Flow Condensation in Microgravity

2013 ◽  
Author(s):  
Hyoungsoon Lee ◽  
Ilchung Park ◽  
Christopher Konishi ◽  
Issam Mudawar ◽  
Rochelle I. May ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Dissipation ◽  
Flow Boiling ◽  
Condensation Heat Transfer ◽  
Interfacial Structure ◽  
Sensible Heat ◽  
Two Phase ◽  
The Heat Transfer Coefficient

Future manned missions to Mars are expected to greatly increase the space vehicle’s size, weight, and heat dissipation requirements. An effective means to reducing both size and weight is to replace single-phase thermal management systems with two-phase counterparts that capitalize upon both latent and sensible heat of the coolant rather than sensible heat alone. This shift is expected to yield orders of magnitude enhancements in flow boiling and condensation heat transfer coefficients. A major challenge to this shift is a lack of reliable tools for accurate prediction of two-phase pressure drop and heat transfer coefficient in reduced gravity. Developing such tools will require a sophisticated experimental facility to enable investigators to perform both flow boiling and condensation experiments in microgravity in pursuit of reliable databases. This study will discuss the development of the Flow Boiling and Condensation Experiment (FBCE) for the International Space Station (ISS), which was initiated in 2012 in collaboration between Purdue University and NASA Glenn Research Center. This facility was recently tested in parabolic flight to acquire condensation data for FC-72 in microgravity, aided by high-speed video analysis of interfacial structure of the condensation film. The condensation is achieved by rejecting heat to a counter flow of water, and experiments were performed at different mass velocities of FC-72 and water and different FC-72 inlet qualities. It is shown that the film flow varies from smooth-laminar to wavy-laminar and ultimately turbulent with increasing FC-72 mass velocity. The heat transfer coefficient is highest near the inlet of the condensation tube, where the film is thinnest, and decreases monotonically along the tube, except for high FC-72 mass velocities, where the heat transfer coefficient is enhanced downstream. This enhancement is attributed to both turbulence and increased interfacial waviness. One-ge correlations are shown to predict the average condensation heat transfer coefficient with varying degrees of success, and a recent correlation is identified for its superior predictive capability, evidenced by a mean absolute error of 21.7%.

Flow Boiling Heat Transfer Coefficient of DI-Water/SiO2 Nanofluid Inside a 1.1 mm Round Microchannel

2015 ◽  
Author(s):  
Tiago A. Moreira ◽  
Francisco J. do Nascimento ◽  
Gherhardt Ribatski
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Single Phase ◽  
Flow Boiling ◽  
Volumetric Concentration ◽  
Nanoparticle Layer ◽  
Flow Boiling Heat Transfer ◽  
Before And After ◽  
The Heat Transfer Coefficient

The scope of the present paper is the evaluation of the heat transfer coefficient during flow boiling of DI-water/silica nanofluid inside a 1.1 mm ID tube. The experiments were performed for nanoparticles and DI-water with both having thermal conductivities of the same order of magnitude (kDI-water = 0.6 W/mK, ksilica = 1.4 W/mK). So, it was possible investigating the effect of the nanoparticles on the heat transfer coefficient under condition of negligible thermal conductivity enhancement. Experiments were carried out for mass velocities of 200, 400 and 600 kg/m2s, heat fluxes from 60 kW/m2 to 350 kW/m2 and nanoparticles volumetric concentration of 0.001%, 0.01% and 0.1%. Moreover, flow boiling heat transfer data under similar experimental conditions were obtained for DI-water without nanoparticles before and after performing each nanofluid test. The experiments were performed at the same test section according to the following sequence: i) DI-water, ii) 0.001% vol. nanofluid, iii) DI-water, iv) 0.01% vol. nanofluid, v) DI-water, vi) 0.1% vol. nanofluid, and vii) DI-water. Such procedure was adopted in order to evaluate the influence of the deposition of nanoparticles at each concentration on the heat transfer coefficient. For single-phase flow the HTC decreases as the experiments were performed. The thermal resistance due to deposition of nanoparticles is relevant to the heat transfer coefficient for single-phase flow of nanofluids inside microchannels. The flow boiling HTC decreases with increasing the nanoparticle volumetric concentration from a concentration of 0.001%. Based on the flow boiling HTC behaviors for tests with pure DI-water before and after the nanofluid tests, the fact that the HTC decreases with increasing the nanoparticle volumetric concentration is not explained only by the deposition on the surface of a nanoparticle layer. Tests for pure DI-water before the tests of nanofluids (BBN condition) and after all the nanofluids tests (ABN 0.1% condition) presents similar heat transfer coefficients, despite the deposition of a nanoparticle layer on the surface.

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