Calcium Carbonate Scale Formation During Subcooled Flow Boiling

1997 ◽  
Vol 119 (4) ◽  
pp. 767-775 ◽  
Author(s):  
S. H. Najibi ◽  
H. Mu¨ller-Steinhagen ◽  
M. Jamialahmadi
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Calcium Carbonate ◽  
Flow Boiling ◽  
Fluid Velocity ◽  
Nucleate Boiling ◽  
Operating Conditions ◽  
Initial Surface ◽  
Subcooled Flow Boiling ◽  
Subcooled Flow

Scale deposition on the heat transfer surfaces from water containing dissolved salts considerably reduces fuel economy and performance of the heat transfer equipment. In general, this problem is more serious during nucleate boiling due to the mechanisms of bubble formation and detachment. In this study, a large number of experiments were performed to determine the effect of fluid velocity, initial surface temperature, and bulk concentration on the rate of calcium carbonate deposition on heat transfer surfaces during subcooled flow boiling. A physically sound prediction model for the deposition process under these operating conditions has been developed which predicts the experimental data with good accuracy. Two previously published models are also discussed and used to predict the experimental data.

Subcooled Flow Boiling Inception and Heat Transfer of Water in a Circular Tube Under Pulsatile Flow

2018 ◽  
Author(s):  
Hongsheng Yuan ◽  
Sichao Tan ◽  
Kun Cheng ◽  
Xiaoli Wu ◽  
Chao Guo ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Steady Flow ◽  
Flow Rate ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Nucleation Site ◽  
Subcooled Flow Boiling ◽  
Average Heat ◽  
Subcooled Flow

The flow rate can fluctuate in offshore nuclear power systems which are exposed to wind and waves, as well as in loops where flow instabilities occur, resulting in different thermal-hydraulic characteristics compared with that under steady flow. Among the thermal-hydraulic characteristics, onset of nucleate boiling (ONB) model determines whether the fluid is boiling, and boiling heat transfer is crucial to equipment performance and safety, both being key issues in subcooled flow boiling. Therefore, an experimental study was conducted to investigate how an imposed periodic flow oscillation affects the boiling inception and heat transfer of subcooled flow boiling of water in a vertical tube. The experiments were conducted under atmospheric pressure with the average flow rate ranging from 96kg/m2s to 287kg/m2s and heat flux ranging from 10kW/m2 to 197kW/m2. The relative pulsatile amplitude range is 0.1–0.3 and pulsatile period range is 10s-30s. Photographic images and thermal parameters such as temperatures and flow rate were recorded. The lack of nucleation site on the heated surface of the test section results in high wall superheat at ONB. The effects of pulsatile amplitude and period on superheat at boiling onset and average heat transfer were analyzed. The results show that the superheat at boiling inception is decreased when the average heat flux is lower than the heat flux at boiling inception of the corresponding steady flow, and the superheat at boiling onset is increased when the average heat flux is higher than the heat flux at boiling onset of the corresponding steady flow. The above effect of flow rate pulsation on superheat increases with increasing amplitude and decreasing period, and the mechanism can be explained by boiling nucleation theory. The lack of large active nucleation site also affects the boiling heat transfer. By comparing the contribution of nucleate boiling to heat transfer with the widely used Cooper’s pool boiling correlation, the subcooled flow boiling was found suppressed by convection. The average heat transfer of both the intermittent flow boiling and the single phase flow is influenced by flow oscillation.

Heat Transfer and Bubble Movement of Double- and Single-Side Heating Subcooled Flow Boiling in Narrow Channels

2005 ◽  
Author(s):  
Liang-Ming Pan ◽  
Chuan He ◽  
Ming-Dao Xin ◽  
Tien-Chien Jen ◽  
Qinghua Chen
Keyword(s):  
Heat Transfer ◽  
Flow Boiling ◽  
Narrow Channel ◽  
Nucleate Boiling ◽  
Bubble Behavior ◽  
Subcooled Flow Boiling ◽  
Narrow Channels ◽  
Subcooled Flow ◽  
Single Side ◽  
Micro Channels

Compared with conventional channels, narrow and micro channels have significant heat transfer enhancement characteristic. With smooth internal surface, such channels can efficiently avoid encrustation at the washing of the high-speed liquid. Moreover, heat transfer elements can be easily assembled. These types of channels have been adopted extensively in many engineering applications, e.g. microelectronic cooling, advanced nuclear reactor, cryogenic, aviation and space technology and thermal engineering. Geometrical size of flow passage-away affects heat exchange of flow boiling, with the result that the bubble in narrow channel acts very different from those in non-narrow channel. This paper experimentally compared the bubble behavior with different heating methods of narrow rectangular channels, and the bubble behavior of subcooled flow boiling of R-12 in the narrow channels both with double side and single heating. Experimental settings are: the heating length of test-section is 400 mm, the cross-section is 35 mm in width and 2mm in gap size, mass flux is 700∼1500 kg.m−2.s−1, the heat flux is 25∼70kW.m−2 and the pressure is 1.3∼2.0 MPa. Comparisons were made on Onset of Nucleate Boiling (ONB) point and bubble characters with various flow patterns. Results revealed that the characteristics of double and single side heating shown good agreement with proper modifications.

scholarly journals An experimental study on the subcooled flow boiling pressure drop of R141b in the system of two microchannels

2021 ◽  
Vol 2119 (1) ◽  
pp. 012053
Author(s):  
A. S. Shamirzaev
Keyword(s):  
Experimental Data ◽  
Experimental Study ◽  
Heat Flux ◽  
Pressure Drop ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Copper Block ◽  
Subcooled Flow Boiling ◽  
Subcooled Flow ◽  
Boiling Incipience

Abstract An experimental study of the pressure drop under subcooled flow boiling of the refrigerant R141b in a system with two slotted microchannels was carried out. A copper block with two microchannels 2 mm wide, 0.4 mm deep, and 16 mm long was used as an experimental section for testing. The mass flow rate varied in the range from 1 to 4 g/s, the initial subcooling from 20°C to 50°C. Experimental data show a significant decrease in the pressure drop when the critical heat flux is reached. The experimental data are compared with the model known from the literature. Experimental data show that the occurrence of nucleate boiling incipience at subcooled boiling corresponds to a larger heat flux than that given by the recommended correlation.

Flow Morphology and Heat Transfer During Subcooled Flow Nucleate Boiling of HFE-7000 in Microchannels

2008 ◽  
Author(s):  
Chih-Jung Kuo ◽  
Yoav Peles
Keyword(s):  
Heat Transfer ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Transfer Coefficients ◽  
Subcooled Flow Boiling ◽  
Heat Transfer Coefficients ◽  
Subcooled Flow ◽  
Hydraulic Conditions ◽  
Parallel Microchannels ◽  
Bubble Agitation

Flow boiling was experimentally studied in parallel microchannels using coolant HFE-7000. Subcooled nucleate boiling was achieved under various thermal-hydraulic conditions for mass velocities ranging from G = 164 kg/m2·s to G = 3025 kg/m2·s. Local surface temperatures were measured and flow visualizations were conducted to obtain flow morphologies, boiling curves, and heat transfer coefficients during boiling process. It was found that heat transfer was significantly enhanced during subcooled flow boiling by bubble agitation of the liquid.

scholarly journals Convective flow boiling heat transfer in an annular space: N-heptane/water case in a bubbly sub-cooled flow

2020 ◽  
Vol 3 (2) ◽  
pp. 33
Author(s):  
M. M. Sarafraz ◽  
H. Arya
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Flow Rate ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Heating Surface ◽  
Nucleate Boiling ◽  
Subcooled Flow Boiling ◽  
Subcooled Flow ◽  
Flow Boiling Heat Transfer

The subcooled flow boiling heat transfer characteristics of n-heptane and water is conducted for an upward flow inside the vertical annulus with an inner gap of 30 mm, in different heat fluxes up to 132kW.m-2, subcooling max.:30C, flow rate: 1.5 to 3.5lit.min-1 under the atmospheric pressure. The measured data indicate that the subcooled flow boiling heat transfer coefficient significantly increases with increasing liquid flow rate and heat flux and slightly decreases with decreasing the subcooling level. Although results demonstrate that subcooling is the most effective operation parameter on onset of nucleate boiling such that with decreasing the subcooling level, the inception heat flux significantly decreases. Besides, recorded results from the visualization of flow show that the mean diameter of the bubbles departing from the heating surface decreases slightly with increasing the flow rate and slightly decreases with decreasing the subcooling level. Meanwhile, comparisons of the present heat transfer data for n-heptane and water in the same annulus and with some existing correlations are investigated. Results of comparisons reveal an excellent agreement between experimental data and those of calculated by Chen Type model and Gungor–Winterton predicting correlation.

Heat Transfer Characteristics in Partial Boiling, Fully Developed Boiling, and Significant Void Flow Regions of Subcooled Flow Boiling

1998 ◽  
Vol 120 (2) ◽  
pp. 395-401 ◽  
Author(s):  
S. G. Kandlikar
Keyword(s):  
Heat Transfer ◽  
Single Phase ◽  
Flow Boiling ◽  
Saturation Temperature ◽  
Nucleate Boiling ◽  
Vapor Generation ◽  
Subcooled Flow Boiling ◽  
Liquid Saturation ◽  
Subcooled Flow ◽  
The Heat Transfer Coefficient

Subcooled flow boiling covers the region beginning from the location where the wall temperature exceeds the local liquid saturation temperature to the location where the thermodynamic quality reaches zero, corresponding to the saturated liquid state. Three locations in the subcooled flow have been identified by earlier investigators as the onset of nucleate boiling, the point of net vapor generation, and the location where x = 0 is attained from enthalpy balance equations. The heat transfer regions are identified as the single-phase heat transfer prior to ONB, partial boiling (PB), and fully developed boiling (FDB). A new region is identified here as the significant void flow (SVF) region. Available models for predicting the heat transfer coefficient in different regions are evaluated and new models are developed based on our current understanding. The results are compared with some of the experimental data available in the literature.

Flow Boiling Heat Transfer From Plain and Microporous Coated Surfaces in Subcooled FC-72

2001 ◽  
Vol 123 (5) ◽  
pp. 918-925 ◽  
Author(s):  
K. N. Rainey ◽  
G. Li ◽  
S. M. You
Keyword(s):  
Flow Boiling ◽  
Fluid Velocity ◽  
Nucleate Boiling ◽  
Subcooled Flow Boiling ◽  
Copper Surfaces ◽  
Fluid Velocities ◽  
Subcooled Flow ◽  
Microporous Coating ◽  
Coated Surfaces ◽  
Enhanced Boiling

The present research is an experimental study of subcooled flow boiling behavior using flat, microporous-enhanced square heater surfaces in pure FC-72. Two 1-cm2 copper surfaces, one highly polished (plain) and one microporous coated, were flush-mounted into a 12.7 mm square, horizontal flow channel. Testing was performed for fluid velocities ranging from 0.5 to 4 m/s (Reynolds numbers from 18,700 to 174,500) and pure subcooling levels from 4 to 20 K. Results showed both surfaces’ nucleate flow boiling curves collapsed to one line showing insensitivity to fluid velocity and subcooling. The log-log slope of the microporous surface nucleate boiling curves was lower than the plain surface due to the conductive thermal resistance of the microporous coating layer. Both, increased fluid velocity and subcooling, increase the CHF values for both surfaces, however, the already enhanced boiling characteristics of the microporous coating appear dominant and require higher fluid velocities to provide additional enhancement of CHF to the microporous surface.

Experimental Study About ONB and Subcooled Boiling Heat Transfer

2004 ◽  
Author(s):  
Changhong Peng ◽  
Aye Myint ◽  
Yun Guo ◽  
Dounan Jia
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Single Phase ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Bulk Temperature ◽  
Subcooled Boiling ◽  
Subcooled Flow Boiling ◽  
Subcooled Flow ◽  
Vertical Annuli

Water subcooled boiling heat transfer were experimentally investigated in the vertical annuli with narrow gap. Subcooled flow boiling covers the region from the location where the bubbles forms on the wall to the location where the bulk temperature reaches saturated temperature. Three locations in the subcooled flow boiling have been identified by the earlier researcher as the onset of nucleate boiling (ONB), the beginning of fully developed boiling, the location where the thermodynamic quality is zero that is attained from the enthalpy balance equation. The heat transfer regions are identified as single-phase heat transfer prior to ONB, partial boiling (PB) and fully developed boiling (FDB). In this study, the available models for predicting heat transfer in the different regions and the modified correlation can predict our experimental data.

Subcooled Flow Boiling With Sintered Porous Coatings in Small Channel

2010 ◽  
Author(s):  
Yan Sun ◽  
Li Zhang ◽  
Hong Xu ◽  
Dongmei Ji
Keyword(s):  
Heat Transfer ◽  
Flow Boiling ◽  
Heating Surface ◽  
Nucleate Boiling ◽  
Working Fluid ◽  
Polished Surface ◽  
Subcooled Flow Boiling ◽  
Porous Coatings ◽  
Small Channel ◽  
Subcooled Flow

Heat transfer characteristics from sintered microporous coating surfaces are experimentally investigated for subcooled flow boiling in the horizontal, rectangular small channel with the low aspect ratio. The channel has a hydraulic diameter of 1.98 mm and a heated length of 150 mm. Experiments are conducted at atmospheric pressure with fully-degassed deionized water as the working fluid. The liquid mass flux ranges from 93.6 to 187.1 kg/m2s, and the inlet subcooling ranges from 30 to 70 K. The heating surface of the channel is covered with the copper microporous coatings to enhance the nucleate boiling heat transfer. Four coatings sintered with differently sized particles are tested to reveal influences of microporous parameters and identify the optimum structure. A smooth (highly polished) surface is also tested as reference. Although few studies have been performed to quantify the heat transfer enhancement contributed by combining internal porous coatings and small channels, this combination has promising applications in many areas such as air conditioning, chip cooling, refrigeration systems, and many others involving compact heat exchangers.

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