Studies on Fluid-to-Fluid Modeling of Critical Heat Flux in a Helically-Coiled Tube

2012 ◽  
Vol 588-589 ◽  
pp. 1777-1780 ◽  
Author(s):  
Lu Zhi Tan ◽  
Ji Tian Han ◽  
Chang Nian Chen ◽  
Peng Cheng Dou
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Mass Flux ◽  
High Mass ◽  
Coiled Tube ◽  
Fluid Modeling ◽  
Modeling Approaches ◽  
Flow Parameters ◽  
Helically Coiled Tube ◽  
R 134A

An experimental study on critical heat flux (CHF) in a helically-coiled tube cooled with R-134a has been completed in order to assess present fluid-to-fluid modeling approaches. The investigated range of flow parameters for R-134a was: pressure from 0.2 to 0.5 MPa, mass flux values from 50 to 1500 kg m-2 s-1 and inlet quality from -0.2 to 0.1. The CHF data of R-134a have been compared with that of water by applying the Ahmad and the Katto modeling. The water equivalent CHF data translated from R-134a CHF data by using the two modeling approaches have shown a good agreement with the actual water CHF data from previous studies when mass flux exceeds 600 kg m-2 s-1. The results indicate that both the Ahmad and the Katto modeling can be applied only for the high mass flux conditions in helically-coiled tubes.

Comparison of Critical Heat Flux for R-134a Flow Boiling in a Horizontal Straight Tube and a Helically-Coiled Tube

2012 ◽  
Vol 588-589 ◽  
pp. 1813-1816
Author(s):  
Lu Zhi Tan ◽  
Ji Tian Han ◽  
Chang Nian Chen ◽  
Peng Cheng Dou
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Mass Flux ◽  
Flow Boiling ◽  
Experimental Studies ◽  
Working Fluid ◽  
Straight Tube ◽  
Coiled Tube ◽  
Helically Coiled Tube ◽  
R 134A

Experimental studies on critical heat flux (CHF) have been conducted in a uniformly heated horizontal straight tube and helically-coiled tube respectively with R-134a as the working fluid. The helically-coiled tube has the same heated length and inner diameter with the straight tube and experiments were performed under the following conditions: pressure from 0.4 to 2.5 MPa, mass flux values from 80 to 1500 kg m-2 s-1, inlet quality from -0.23 to 0.28 and critical quality from 0.65 to 0.86. The CHF data of the helically-coiled tube have been compared with that of the straight tube. The results show that the helically-coiled tube gets significant improvement in the CHF values vs. the straight tube under the same conditions and the degree of improvement depends on the mass flux, system pressure, inlet quality and critical quality.

Experimental study on critical heat flux during flow boiling of R134a in a vertical helically coiled tube

2020 ◽  
Vol 234 (15) ◽  
pp. 3094-3101
Author(s):  
Xiaojuan Niu ◽  
Huaijie Yuan ◽  
Liang Zhao
Keyword(s):  
Experimental Study ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Wall Temperature ◽  
Mass Flux ◽  
Flow Boiling ◽  
Vapor Quality ◽  
Coiled Tube ◽  
Helically Coiled Tube ◽  
System Pressure

This paper carried out an experimental study on the critical heat flux during flow boiling of R134a in a vertical helically coiled tube. The length, inner diameter, coil diameter, and pitch of the test tube were 1.85 m, 8 mm, 205 mm, and 25 mm, respectively. Experiments cover the mass flux range of 190–400 kg·m−2·s−1, heat flux of 15–55 kW·m−2, inlet pressure of 0.8–1.1 MPa, and inlet vapor quality of 0.01–0.35. The effects of critical heat flux identification method, mass flux, system pressure, and inlet vapor quality on critical heat flux were presented. The critical heat flux obtained by the wall temperature rise method was larger than that obtained by the wall temperature oscillation method. The deviation of the critical heat flux corresponding to two methods, including wall temperature rises sharply above 10 ℃ and wall temperature drastic oscillation, was about 20% under the present experimental conditions. The critical heat flux increased with mass flux while it decreased with the inlet vapor quality and pressure. The experiment data were compared with four existing empirical correlations. A new correlation is proposed for critical heat flux prediction in vertical helical tubes.

Critical Heat Flux in Horizontal Tube Bundles in Vertical Crossflow of R113

1992 ◽  
Vol 114 (1) ◽  
pp. 179-184 ◽  
Author(s):  
K. M. Leroux ◽  
M. K. Jensen
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Mass Flux ◽  
Horizontal Tube ◽  
High Mass ◽  
Intermediate Mass ◽  
Average Value ◽  
Mass Fluxes ◽  
Local Quality ◽  
Low Mass

The critical heat flux (CHF) on a single tube in a horizontal bundle subject to an upward crossflow of R113 has been studied in three bundle geometries. Effects of local quality, mass flux, pressure, and bundle geometry on the CHF were investigated. The shapes of the CHF-quality curves display three distinct patterns, which progress from one to another as mass flux increases. At low mass fluxes, the CHF data monotonically decreased with increasing quality. At intermediate mass fluxes with increasing quality, the CHF data initially decreased to a relative minimum, then increased to a relative maximum, and finally began to decrease again as the higher qualities were reached. At high mass fluxes, as quality increased, the CHF rose gradually from the zero quality value to a maximum and then began to decrease. For all mass fluxes, the zero-quality CHF points clustered around an average value, which varied slightly with test section geometry. Mechanisms for the CHF condition are suggested.

Experimental Investigation on Flow Characteristics of Supercritical CO2 in a Helically Coiled Tube

2013 ◽  
Vol 368-370 ◽  
pp. 631-635
Author(s):  
Shu Xiang Wang ◽  
Wei Zhang ◽  
Jin Liang Xu
Keyword(s):  
Heat Flux ◽  
Fluid Flow ◽  
Mass Flux ◽  
Flow Characteristics ◽  
Experimental Investigations ◽  
Coiled Tube ◽  
Frictional Pressure Drop ◽  
Helically Coiled Tube ◽  
Coil Diameter ◽  
Fluid Flow Characteristics

Under the background of global warming, carbon dioxide among natural refrigerants has attracted considerable attention as an alternative refrigerant. In the present study, experimental investigations of the fluid flow characteristic of supercritical CO2in a helically coiled tube with the inner diameter 9.0 mm, coil diameter 283 mm and coil pitch 32 mm were carried out. Both frictional pressure drop and friction factor were obtained under the pressure of 8.0 MPa, mass flux from 0 to 600 kg/m2s and inner heat flux from 0 to 20 kW/m2. The results indicate that inner wall heat flux and mass flux had significant effects on fluid flow characteristics. The study provides experimental data that could be used for the design and development of more efficient exchangers for refrigeration conditioning, heat pump and some other systems.

Convective Boiling Heat Transfer and Pressure Drop Characteristics of R134a in a Microfinned Helically Coiled Tube

2005 ◽  
Author(s):  
Wenzhi Cui ◽  
Longjian Li ◽  
Mingdao Xin ◽  
Qinghua Chen ◽  
Quan Liao ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Pressure Drop ◽  
Mass Flux ◽  
Boiling Heat Transfer ◽  
Annular Flow ◽  
Convective Boiling ◽  
Coiled Tube ◽  
Frictional Pressure Drop ◽  
Helically Coiled Tube

The main purpose of this paper was to experimentally study the heat transfer and pressure drop characteristics of refrigerant R134a boiling inside a new geometry microfin helically coiled tube. Experiments were performed in a range of mass quality from 0.05 up to 0.9, mass velocity 70 ∼ 380 kg/m2s and heat flux 2.0 ∼ 21.8 kW/m2. The local and average convective boiling heat transfer coefficients were reported in this paper, which were found to be dependent on both of mass flux and heat flux. Compared with corresponding smooth helically coiled tube, the microfin helically coiled tube could enhance the convective boiling heat transfer very well. The enhancement factor was up to 2.2 with the variety of mass flux and heat flux. Heat transfer in annular flow was specially studied. A flow boiling heat transfer correlation was presented for the annular flow regime, which had a mean deviation of 9.1%. The frictional pressure drop values were obtained by subtracting acceleration pressure drop and gravitational pressure drop from the measured total pressure drop. The frictional pressure drop data can be well correlated by Lockhart-Martinelli parameter. Considering the corresponding flow regimes, i.e., stratified and annular flow, two frictional pressure drop correlations were proposed, and showed a good agreement with the respective experimental data.

Numerical Investigation of Subcooled Boiling Heat Transfer in Helically-Coiled Tube

2020 ◽  
Vol 17 (1) ◽  
pp. 7675-7686
Author(s):  
Luthfi A. F. Haryoko ◽  
Jundika C. Kurnia ◽  
Agus P. Sasmito
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Mass Flux ◽  
Boiling Heat Transfer ◽  
Operating Pressure ◽  
Subcooled Boiling ◽  
Coiled Tube ◽  
Helically Coiled Tube

Subcooled boiling heat transfer in helically-coiled tubes offers better heat transfer performance than any other types of boiling processes due to its ability to capture high heat flux with a relatively low wall superheat. This study investigates turbulent subcooled forced convection boiling performances of water-vapour in a helically-coiled tube with various operating conditions i.e. operating pressure, heat, and mass flux. Developed CFD model is validated against previously published experimental results using the RPI model. The model is developed based on the Eulerian-Eulerian framework coupled with k-ε RNG turbulence model and Standard Wall-Function. A good agreement is found between numerical prediction and experimental counterpart for the bulk fluid temperature and non-dimensional length. The result indicates that the subcooled boiling heat transfer in a helically-coiled tube tends to improve heat transfer coefficient and pressure drop in the domain. Subcooled boiling starts at the inner side of the helically-coiled tube (f=9900) due to the existence of secondary flow that comes from the coil curvature. Heat transfer coefficient and pressure drop increased with increasing heat flux and decreasing mass flux, and operating pressure. This is caused by the bubble movement and convective heat transfer phenomena in a helically-coiled tube. Finally, this study can provide a guideline for future research of the subcooled boiling in a helically-coiled tube.

High mass flux flow boiling and critical heat flux in microscale

2013 ◽  
Vol 65 ◽  
pp. 70-78 ◽  
Author(s):  
Alihan Kaya ◽  
Mehmed Rafet Özdemir ◽  
Ali Koşar
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Mass Flux ◽  
Flow Boiling ◽  
High Mass ◽  
Flux Flow

Influence of Geometry Parameters on Critical Heat Flux in Helically Coiled Tubes: Development of Correlation

2013 ◽  
Vol 353-356 ◽  
pp. 3077-3080
Author(s):  
Cui Lian Ji ◽  
Ji Tian Han ◽  
Chang Nian Chen ◽  
Xia Dong ◽  
Ling Jian Kong
Keyword(s):  
Experimental Data ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Geometrical Parameter ◽  
Vertical Tube ◽  
Coiled Tube ◽  
Helically Coiled Tube ◽  
Tube Geometry

Based on 2006 look-up tables to analysis the effect of pipe diameters on CHF, the correlations are established for horizontal helically coiled tube by introducing equivalent geometrical parameter. According to experimental data, it is found that the correlation is very suitable, and the regularity of horizontal helically coiled tube geometry parameters on CHF tends to be consistent with that of a vertical tube.

Experimental Measurements of Critical Heat Flux in Expanding Microchannel Arrays

2013 ◽  
Vol 135 (10) ◽  
Author(s):  
Mark J. Miner ◽  
Patrick E. Phelan ◽  
Brent A. Odom ◽  
Carlos A. Ortiz
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Mass Flux ◽  
Flow Boiling ◽  
Heat Sinks ◽  
Maximum Heat ◽  
Maximum Heat Flux ◽  
Expansion Angle ◽  
R 134A ◽  
And Performance

The effect of an expanding microchannel cross-section on flow boiling critical heat flux (CHF) is experimentally investigated across four rates of expansion. A pumped-loop apparatus is developed to boil R-134a in an array of microchannels cut into copper; a test section is designed to facilitate interchange of the microchannel specimens, allowing consistency across experiments. An optimum expansion angle allowing maximum heat flux is observed, the location of which increases with the mass flow rate. The boiling number does not indicate any optimum in the range observed, showing a nearly monotonic increase with expansion angle. The familiar increase in critical heat flux with mass flux is observed, though expansion shifts the CHF-mass flux curves in a favorable direction. The existence of an optimum expansion angle confirms an earlier qualitative hypothesis by the authors and suggests that microchannel heat sinks offer opportunities for methodical improvement of flow boiling stability and performance.

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