Heat Transfer From a Small Heated Region to R-113 and FC-72

1989 ◽  
Vol 111 (4) ◽  
pp. 1053-1059 ◽  
Author(s):  
K. R. Samant ◽  
T. W. Simon
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Quartz Substrate ◽  
Rectangular Channel ◽  
Nucleate Boiling ◽  
Decomposition Temperature ◽  
Large Temperature ◽  
Resistance Thermometer ◽  
Maximum Heat ◽  
Heater Element

An experimental investigation of heat transfer from a small heated patch to a subcooled, fully developed turbulent flow is conducted. The test patch, approximately 0.25 mm long and 2.0 mm wide, is located on the floor of a small rectangular channel through which a coolant (R-113 or FC-72) is circulated. A thin film of Nichrome deposited on a quartz substrate serves as an integrated heater element and resistance thermometer. The maximum achievable heat flux with R-113, limited by the thermal decomposition temperature of the fluid, is 2.04 MW/m2 at a bulk velocity of 1.8 m/s and a high wall superheat of 80° C. The results obtained with FC-72 show large temperature excursions at the onset of nucleate boiling and a boiling hysteresis near the onset of nucleate boiling. These effects decrease with increasing velocity and/or subcooling. The heat flux at departure from nucleate boiling increases with increasing velocity and/or subcooling. A maximum heat flux of 4.26 MW/m2 at departure from nucleate boiling is observed.

Experimental Investigation of an Evaporator Enhanced With a Micro-Porous Structure in a Two-Phase Thermosyphon Loop

2008 ◽  
Author(s):  
Richard Furberg ◽  
Rahmatollah Khodabandeh ◽  
Bjo¨rn Palm ◽  
Shanghua Li ◽  
Muhammet Toprak ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Rectangular Channel ◽  
Large Diameter ◽  
Nucleate Boiling ◽  
Nano Particles ◽  
Working Fluid ◽  
Two Phase ◽  
Maximum Heat ◽  
Maximum Heat Transfer

Following is an experimental study of six different evaporators in a closed two-phase thermosyphon loop system, where the influence of various evaporator dimensions and surfaces was investigated. The evaporators featured a 30 mm long rectangular channel with hydraulic diameters ranging from 1.2–2.7 mm. The heat transfer surface of one of the tested evaporators was enhanced with copper nano-particles, dendritically connected into an ordered micro-porous three dimensional network structure. To facilitate high speed video visualization of the two-phase flow in the evaporator channel, a transparent polycarbonate window was attached to the front of the evaporators. Refrigerant 134A was used as a working fluid and the tests were conducted at 6.5 bar. The tests showed that increasing channel diameters generally performed better. The three largest evaporator channels exhibited comparable performance, with a maximum heat transfer coefficient of about 2.2 W/(cm2K) at a heat flux of 30–35 W/cm2 and a critical heat flux of around 50 W/cm2. Isolated bubbles characterized the flow regime at peak performance for the large diameter channels, while confined bubbles and chaotic churn flow typified the evaporators with small diameters. In line with previous pool boiling experiments, the nucleate boiling mechanism was significantly enhanced, up to 4 times, by the nano- and micro-porous enhancement structure.

High Heat Flux Phase Change on Silicon Wick Structures

2012 ◽  
Author(s):  
Qingjun Cai ◽  
Avijit Bhunia ◽  
Yuan Zhao
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Phase Change ◽  
Test Chamber ◽  
Nucleate Boiling ◽  
High Heat ◽  
High Heat Flux ◽  
Maximum Heat ◽  
Wick Structure ◽  
Silicon Pillars

Silicon is the major material in IC manufacture. It has high thermal conductivity and is compatible with precision micro-fabrication. It also has decent thermal expansion coefficient to most semiconductor materials. These characteristics make it an ideally underlying material for fabricating micro/mini heat pipes and their wick structures. In this paper, we focus our research investigations on high heat flux phase change capacity of the silicon wick structures. The experimental wick sample is composed of silicon pillars 320μm in height and 30 ∼ 100μm in diameter. In a stainless steel test chamber, synchronized visualizations and measurements are performed to crosscheck experimental phenomena and data. Using the mono-wick structure with large silicon pillar of 100μm in diameter, the phase change on the silicon wick structure reaches its maximum heat flux at 1,130W/cm2 over a 2mm×2mm heating area. The wick structure can fully utilize the wick pump capability to supply liquid from all 360° directions to the center heating area. In contrast, the large heating area and fine silicon pillars 10μm in diameter significantly reduces liquid transport capability and suppresses generation of nucleate boiling. As a result, phase change completely relies on evaporation, and the CHF of the wick structure is reduced to 180W/cm2. An analytical model based on high heat flux phase change of mono-porous wick structures indicates that heat transfer capability is subjected to the ratio between the wick particle radius and the heater dimensions, as well as vapor occupation ratio of the porous volume. In contrast, phase change heat transfer coefficients of the wick structures essentially reflect material properties of wick structure and mechanism of two-phase interactions within wick structures.

RELAP5-3D Sensitivity Studies of Incorporating Axial Boron Gradients Into a Heater Tube Experiment for Pool Boiling CHF Testing in TREAT

2020 ◽  
Author(s):  
Richard Hernandez ◽  
Nicholas R. Brown ◽  
Charles P. Folsom ◽  
Nicolas E. Woolstenhulme ◽  
Colby B. Jensen
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
National Laboratory ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Coupling Factor ◽  
Design Parameters ◽  
Coolant Temperature ◽  
Axial Region ◽  
Maximum Heat

Abstract Nuclear reactor designs are governed by postulated accident events that may occur during their operational lifetime. One type of incident is a reactivity-initiated accident (RIA), during which a sudden surge of power in the fuel components within the core may result in the latter exceeding its cooling capabilities. This could lead to a departure from nucleate boiling (DNB) event which results in a significant decrease in heat transfer capabilities. Preventing the occurrence of a DNB crisis requires a fundamental understanding of the cladding-to-coolant heat transfer under fast transient conditions, as well as the governing hydrodynamic and design parameters that influence when the critical heat flux (CHF) will be exceeded. Presently, large uncertainties in computer models used to predict CHF have led to conservative safety limits governing light-water reactor (LWR) designs. The Idaho National Laboratory (INL) is currently leading a combined effort that takes advantage of the restart of the Transient Reactor Test (TREAT) facility, to better understand the mechanism of CHF under in-pile pool boiling conditions. The goal of this laboratory directed project is to use the unique capabilities of TREAT coupled with a non-fueled nuclear heated borated stainless-steel 304 tube experiment within an experimental capsule. The borated tube will induce CHF in the surrounding coolant when subjected to a power pulse within the TREAT. The impacts of rapid surface heating effects as well as radiation-induced surface activation (RISA) will be experimentally investigated. This feature is a continuation to previous thermal hydraulics analysis that was conducted to inform on a test matrix for the design of the borated heater experiment. The borated tube was used in place of a solid rod so that the center axial region can be instrumented to allow for better experimental analysis. Therefore, it is desirable to design this rodlet so that the maximum heat flux occurs at the center of the axial length of the rod. The work presented here analyzes the potential to integrate axial boron gradients within this tube to shape its power curve. Several generic axial power shapes were initially considered. Natural boron concentrations between 0.1–2.0 wt.% were analyzed and a power coupling factor (PCF) was calculated for each. A self-shielding study was conducted to develop radial power profiles for several boron concentrations. These were then applied to three different power pulses to determine how these two parameters influence the chosen axial heat flux curve. Variations in the initial coolant temperature were investigated. Lastly, how the shape of the generic curve is affected following a DNB event was also studied. Two different CHF cases were included within the scope of this analyses; one during which CHF was exceeding along the entire axial region of the rod, and another where the former occurred at the center region only. The behavior of the curve overtime was investigated.

Boiling Heat Transfer Characteristics of Staggered-array Water Impinging Jets on Hot Steel Plate

2018 ◽  
Vol 140 (3) ◽  
Author(s):  
Sang Gun Lee ◽  
Jin Sub Kim ◽  
Dong Hwan Shin ◽  
Jungho Lee
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Surface Temperature ◽  
Boiling Heat Transfer ◽  
Steel Plate ◽  
Nucleate Boiling ◽  
Impinging Jets ◽  
Heat Transfer Characteristics ◽  
Maximum Heat ◽  
Maximum Heat Flux

The effect of staggered-array water impinging jets on boiling heat transfer was investigated by a simultaneous measurement between boiling visualization and heat transfer characteristics. The boiling phenomena of staggered-array impinging jets on hot steel plate were visualized by 4K UHD video camera. The surface temperature and heat flux on hot steel plate was determined by solving 2-D inverse heat conduction problem, which was measured by the flat-plate heat flux gauge. The experiment was made at jet Reynolds number of Re = 5,000 and the jet-to-jet distance of staggered-array jets of S/Dn = 10. Complex flow interaction of staggered-array impinging jets exhibited hexagonal flow pattern like as honey-comb. The calculated surface heat transfer profiles show a good agreement with the corresponding boiling visualization. The peak of heat flux accords with the location which nucleate boiling is occurred at. In early stage, the positions of maximum heat flux locate at the stagnation point of each jet as the relatively low surface temperature is shown at their positions. At the elapsed time of 10 s, the flat shape of heat flux profile is formed in the hexagonal area where the interacting flow uniformly cools down the wetted surface. After that, the wetted area continuously enlarges with time and the maximum heat flux is observed at its peripheral. These results point out that the flow interaction of staggered-array jets effectively cools down the closer area around jets and also show an expansion of nucleate boiling and suppression of film boiling during water jet cooling on hot steel plate. [This work was supported by the KETEP grant funded by the Ministry of Trade, Industry & Energy, Korea (Grant No. 20142010102910).]

Microporous Coatings to Maximize Pool Boiling Heat Transfer of Saturated R-123 and Water

2015 ◽  
Vol 137 (8) ◽  
Author(s):  
Joo Han Kim ◽  
Ajay Gurung ◽  
Miguel Amaya ◽  
Sang Muk Kwark ◽  
Seung M. You
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Boiling Heat Transfer ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Transfer Coefficients ◽  
Maximum Heat ◽  
Microporous Coating ◽  
Plain Surface ◽  
Improved Performance

The present research is an experimental study for the enhancement of boiling heat transfer using microporous coatings. Two types of coatings are investigated: one that is bonded using epoxy and the other by soldering. Effects on pool boiling performance were investigated, of different metal particle sizes of the epoxy-based coating, on R-123 refrigerants, and on water. All boiling tests were performed with 1 cm × 1 cm test heaters in the horizontal, upward-facing orientation in saturated conditions at atmospheric pressure and under increasing heat flux. The surface enhanced by the epoxy-based microporous coatings significantly augmented both nucleate boiling heat transfer coefficients and critical heat flux (CHF) of R-123 relative to those of a plain surface. However, for water, with the same microporous coating, boiling performance did not improve as much, and thermal resistance of the epoxy component limited the maximum heat flux that could be applied. Therefore, for water, to seek improved performance, the solder-based microporous coating was applied. This thermally conductive microporous coating, TCMC, greatly enhanced the boiling performance of water relative to the plain surface, increasing the heat transfer coefficient up to ∼5.6 times, and doubling the CHF.

Jet Impingement Boiling From a Circular Free-Surface Jet During Quenching: Part 1—Single-Phase Jet

2001 ◽  
Vol 123 (5) ◽  
pp. 901-910 ◽  
Author(s):  
David E. Hall ◽  
Frank P. Incropera ◽  
Raymond Viskanta
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Free Surface ◽  
Boiling Heat Transfer ◽  
Single Phase ◽  
Jet Impingement ◽  
Nucleate Boiling ◽  
Transient Temperature ◽  
Spatial Distributions ◽  
Maximum Heat

This paper reports results from an experimental study of boiling heat transfer during quenching of a cylindrical copper disk by a subcooled, circular, free-surface water jet. The disk was heated to approximately 650°C, and as quenching occurred, transient temperature measurements were taken at discrete locations near the surface and applied as boundary conditions in a conduction model to deduce transient heat flux distributions at the surface. Results are presented in the form of heat flux distributions and boiling curves for radial locations varying from the stagnation point to ten nozzle diameters for jet velocities between 2.0 and 4.0 m/s 11,300⩽Red⩽22,600. Data for nucleate boiling in the stagnation region and spatial distributions of maximum heat flux are presented and are in good agreement with correlations developed from steady-state experiments. Spatial distributions of minimum film boiling temperatures and heat fluxes are also reported and reveal a fundamental dependence on jet deflection and streamwise location. A companion paper (Hall et al., 2001) describes single-phase and boiling heat transfer measurements from a two-phase (water-air), free-surface, circular jet produced by injecting air bubbles into the jet upstream of the nozzle exit.

scholarly journals Determination of Limiting Heat Flux for The Inception of Nucleate Boiling Regime for Crude Oils

2021 ◽  
Vol 85 (2) ◽  
pp. 115-127
Author(s):  
Obaid ur Rehman ◽  
Marappa Gounder Ramasamy ◽  
Nor Erniza M Rozali ◽  
Umesh B. Deshannavar
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Nucleate Boiling ◽  
Crude Oils ◽  
Bulk Temperature ◽  
Maximum Heat ◽  
Maximum Heat Transfer ◽  
Accuracy Of Results

Finding the limiting heat flux above which nucleate boiling starts and below which forced convective heat transfer exists is a crucial task for the accuracy of results from crude oil fouling tests. In this study, crude oils from two sources were tested at bulk temperatures of 100, 120 and 140 °C and different velocities. Heat transfer coefficient increased gradually with bulk temperature indicated lowering of the viscosity at high temperatures which promoted turbulence and enhanced heat transfer. The velocity effects were similar to that of bulk temperatures on maximum heat transfer coefficient while less heat flux was required to achieve the same surface temperature at lower velocities. Deshannavar and Ramasamy’s model to predict maximum heat flux was compared with experimental results and a poor estimation was observed for the crude oils tested.

Near-Wall Microlayer Evaporation Analysis and Experimental Study of Nucleate Pool Boiling on Inclined Surfaces

1998 ◽  
Vol 120 (3) ◽  
pp. 641-653 ◽  
Author(s):  
G. F. Naterer ◽  
W. Hendradjit ◽  
K. J. Ahn ◽  
J. E. S. Venart
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heating Surface ◽  
Nucleate Boiling ◽  
Inclined Surfaces ◽  
Wide Range ◽  
Model Predictions ◽  
Microlayer Evaporation ◽  
Near Wall

Boiling heat transfer from inclined surfaces is examined and an analytical model of bubble growth and nucleate boiling is presented. The model predicts the average heat flux during nucleate boiling by considering alternating near-wall liquid and vapor periods. It expresses the heat flux in terms of the bubble departure diameter, frequency and duration of contact with the heating surface. Experiments were conducted over a wide range of upward and downward-facing surface orientations and the results were compared to model predictions. More active microlayer agitation and mixing along the surface as well as more frequent bubble sweeps along the heating surface provide the key reasons for more effective heat transfer with downward facing surfaces as compared to upward facing cases. Additional aspects of the role of surface inclination on boiling dynamics are quantified and discussed.

Boiling Heat Transfer and Critical Heat Flux Enhancement of Upward- and Downward-Facing Heater in Nanofluids

2013 ◽  
Vol 135 (7) ◽  
Author(s):  
Muhamad Zuhairi Sulaiman ◽  
Masahiro Takamura ◽  
Kazuki Nakahashi ◽  
Tomio Okawa
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Boiling Heat Transfer ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Flux Enhancement ◽  
Optimum Configuration ◽  
Wall Superheat ◽  
Nucleate Boiling Heat Transfer

Boiling heat transfer (BHT) and critical heat flux (CHF) performance were experimentally studied for saturated pool boiling of water-based nanofluids. In present experimental works, copper heaters of 20 mm diameter with titanium-oxide (TiO2) nanocoated surface were produced in pool boiling of nanofluid. Experiments were performed in both upward and downward facing nanofluid coated heater surface. TiO2 nanoparticle was used with concentration ranging from 0.004 until 0.4 kg/m3 and boiling time of tb = 1, 3, 10, 20, 40, and 60 mins. Distilled water was used to observed BHT and CHF performance of different nanofluids boiling time and concentration configurations. Nucleate boiling heat transfer observed to deteriorate in upward facing heater, however; in contrast effect of enhancement for downward. Maximum enhancements of CHF for upward- and downward-facing heater are 2.1 and 1.9 times, respectively. Reduction of mean contact angle demonstrate enhancement on the critical heat flux for both upward-facing and downward-facing heater configuration. However, nucleate boiling heat transfer shows inconsistency in similar concentration with sequence of boiling time. For both downward- and upward-facing nanocoated heater's BHT and CHF, the optimum configuration denotes by C = 400 kg/m3 with tb = 1 min which shows the best increment of boiling curve trend with lowest wall superheat ΔT = 25 K and critical heat flux enhancement of 2.02 times.

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