Transient Pool Boiling Under Self Pressurized Systems

2003 ◽  
Author(s):  
Ahmed ElGafy ◽  
Khalid Lafdi
Keyword(s):  
Heat Flux ◽  
Pool Boiling ◽  
Saturation Temperature ◽  
Heating Surface ◽  
Working Fluid ◽  
Atmospheric Conditions ◽  
Transient Conditions ◽  
System Pressure ◽  
The Mean ◽  
The Heat Transfer Coefficient

An experimental investigation of the transient pool boiling under self-pressurized systems is presented in this work. A vertical cylindrical heating surface of known surface roughness is used. Test runs are carried out on a closed vessel to attain self-pressurized system while water is utilized as the working fluid. Two glass windows are opened in the test vessel to observe the phenomenon. The increasing pressure and the consequent variable difference between the mean heating surface temperature and the saturation temperature corresponding to the system pressure are measured during each of the test runs. The runs cover an input heat flux from (40 × 103 to 80 × 103 W/m2) over a pressure range from the atmospheric to 5.5 bars. For transient conditions, an empirical correlation to relate the heat transfer coefficient to both heat flux and pressure is obtained. Also, a comparative study is performed between the present work and a previous work under steady state atmospheric conditions.

scholarly journals Optimization of thermo-hydraulic characteristics of solar cavity receiver under concentrated heat flux

2019 ◽  
Vol 103 (1) ◽  
pp. 003685041987590
Author(s):  
Yun Hao ◽  
Yueshe Wang
Keyword(s):  
Heat Flux ◽  
Heating Surface ◽  
Flow Distribution ◽  
Working Fluid ◽  
Stable Operation ◽  
Hydraulic Characteristics ◽  
Spot Center ◽  
Research Findings ◽  
High Temperature Steam ◽  
Better Than

It is important to study the effects of heat flux on the thermo-hydraulic characteristics in a solar cavity receiver because of the non-uniform radiation flux temporally and spatially. In this article, we presented a mathematical model of thermo-hydraulic characteristics of a solar cavity receiver, considering the effect of heat flux distribution on the energy transfer (radiation–conduction–convection). Using the model, the thermo-hydraulic characteristics under high concentrated heat flux were studied and then optimized the characteristics from two aspects: tube diameter (22, 27, 32, and 38 mm) and connection structure of the heating surface (H-type, central inlet/outlet, and vertical U-type). It was found that flow distribution changed smoothly at the diameter of 27 mm with the increase of the heat flux; when the diameter of tubes at the certain distance (1.6 σHF) from the spot center was replaced by 38 mm, the thermo-hydraulic characteristics were improved. For the evaporating surfaces, the thermo-hydraulic characteristics of working fluid (water) with the central inlet/outlet connection structure were better than those of the H-type connection structure. For the surperheated surfaces, the vertical U-type connection structure was applied to obtain the high temperature steam. These research findings are helpful for the safe and stable operation of the whole solar power system.

Subcooled Boiling in the Ultrasonic Field (on Cause of MEB Generation)

2009 ◽  
Author(s):  
Fumio Inagaki ◽  
Koichi Suzuki ◽  
Chungpyo Hong
Keyword(s):  
Heat Flux ◽  
Aqueous Solutions ◽  
Ultrasonic Vibration ◽  
Pool Boiling ◽  
Atmospheric Condition ◽  
Heating Surface ◽  
Ultrasonic Field ◽  
Subcooled Boiling ◽  
Maximum Heat ◽  
Maximum Heat Flux

Subcooled quasi-pool boiling for water, ethanol aqueous solutions of 10wt% and 50wt% and ethanol in ultrasonic field is performed for the upward flat heating surface of copper block with 10mm in diameter under the atmospheric condition. Tested liquid subcooling is 15K, 20K and 25K for water and aqueous solutions of ethanol and 20K, 30K and 40K for 100wt% ethanol. At 20K of liquid subcooling for water and ethanol aqueous solutions, no microbubble emission boiling (MEB) has been observed in quasi-pool boiling. Even if MEB occurred, the heat flux does not increase and it turns easily to film boiling. In ultrasonic field, MEB occurs remarkably and the heat flux increases higher than the ordinary critical heat flux as observed in highly subcooled boiling. The experimental results show that the ultrasonic vibration introduces the instability of interface of liquid and vapor and accelerate MEB at 20K of liquid subcooling for water and aqueous solutions of ethanol. At 15K of liquid subcooling for water and aqueous solutions, no effect of ultrasonic vibration is observed. At 25K of liquid subcooling, the ultrasonic vibration extends MEB region to higher superheat of heating surface for aqueous solutions of ethanol. The maximum heat flux in MEB decreases with increasing of ethanol concentration and becomes CHF for 100wt% ethanol. No effect of ultrasonic vibration on boiling is observed for the 100wt% ethanol in the present experiments.

Enhancement of Single-Phase Refrigerant Mixture (R-407C) Flow in Meso-Scale Heat Exchangers Using Micro-Coils

2007 ◽  
Author(s):  
Yasir M. Shariff ◽  
T. S. Ravigururajan
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Single Phase ◽  
Heat Transfer Performance ◽  
Reynolds Numbers ◽  
Working Fluid ◽  
Mixture Flow ◽  
Refrigerant Mixture ◽  
R 134A ◽  
The Heat Transfer Coefficient

Experimental results from single-phase refrigerant mixture flow in smooth and micro-coil enhanced meso-channels are presented. R-407C — a mixture of R-32 (23%)/R-125 (25%)/R-134a (52%) — is used as the working fluid and different micro-coils are used in conjunction with two meso-channels (2.78mm and 3.97 mm) to obtain distinct roughness parameters. The flow was varied over a range of Reynolds numbers and experiments were conducted over a heat flux range of 2 to 11 kW/m2. The heat transfer coefficient was found to be dependent on both the heat flux as well as mass flux levels. Results show that heat transfer characteristics are comparable to R-113, and that micro-coil inserts enhanced the heat transfer performance compared to the performance in smooth meso-channels.

Two Phase Heat Transfer of Ammonia in a Mini/Micro Channel

2010 ◽  
Author(s):  
M. Hamayun Maqbool ◽  
Bjo¨rn Palm ◽  
R. Khodabandeh ◽  
Rashid Ali
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Mass Flux ◽  
Experimental Results ◽  
Working Fluid ◽  
Internal Diameter ◽  
Vapour Quality ◽  
The Heat Transfer Coefficient

Experiments have been performed to investigate heat transfer in a circular vertical mini channel made of stainless steel (AISI 316) with internal diameter of 1.70 mm and a uniformly heated length of 245 mm using ammonia as working fluid. The experiments are conducted for a heat flux range of 15 to 350 kW/m2 and mass flux range of 100 to 500 kg/m2s. The effects of heat flux, mass flux and vapour quality on the heat transfer coefficient are explored in detail. The experimental results show that the heat transfer coefficient increases with imposed wall heat flux while mass flux and vapour quality have no considerable effect. Experimental results are compared to predictive methods available in the literature for boiling heat transfer. The correlations of Cooper et al. [1] and Shah [3] are in good agreement with our experimental data.

Simulation of Heat Flux Effect in Straight Heat Pipe as Passive Residual Heat Removal System in Light Water Reactor Using RELAP5 Mod 3.2

2016 ◽  
Vol 819 ◽  
pp. 122-126 ◽  
Author(s):  
M. Hadi Kusuma ◽  
Nandy Putra ◽  
Surip Widodo ◽  
Anhar Riza Antariksawan
Keyword(s):  
Heat Flux ◽  
Heat Pipe ◽  
Saturation Temperature ◽  
Heat Removal ◽  
Working Fluid ◽  
Steady State Condition ◽  
Set Up ◽  
Heat Removal System ◽  
Removal System ◽  
Residual Heat

Heat pipe is considered being used as a passive system to remove residual heat that generated from reactor core when incident occur or from spent fuel pool. The present research is aimed to studying the characteristics of straight heat pipe as passive residual heat removal system. As an initial step, a numerical simulation was conducted to simulate the best experimental design set up being prepared for the next step of the research. The objective is to get the thermal hydraulic characteristic due to variation of heat flux of heat source. The thermal hydraulic RELAP5 MOD 3.2 code is used to simulate and analyze the straight heat pipe characteristics. Variations of heat flux are 1567 Watt/m2, 3134 Watt/m2, 4701 Watt/m2, 6269 Watt/m2, and 7837 Watt/m2. Water as working fluid is heated on evaporation section with filling ratio 60%. Environmental air with variation 5 m/s and 10 m/s of velocity are used as external cooler. Straight heat pipe used in the simulation is wickless with 0.1 m of diameter and 6 m of length. The results show that higher heat flux given to the evaporator section will lead to more rapid heat transfer and achievement of steady state condition. The increasing of heat flux leads to an increase of evaporation of the working fluid and of pressure built in the heat pipe affecting higher saturation temperature of working fluid. Heat flux loading must consider the velocity of air as heat removal in the condenser to prevent dry out phenomenon in the evaporator. Based on the results, given the experimental set-up, the optimum range of experimental parameters could be determined.

Nucleate Pool Boiling Heat Transfer of R134a and R134a-PVE Lubricant Mixtures on Smooth and Five Enhanced Tubes

2010 ◽  
Vol 132 (11) ◽  
Author(s):  
Wen-Tao Ji ◽  
Ding-Cai Zhang ◽  
Nan Feng ◽  
Jian-Fei Guo ◽  
Mitsuharu Numata ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Boiling Heat Transfer ◽  
Pool Boiling ◽  
Saturation Temperature ◽  
Transfer Coefficients ◽  
Pool Boiling Heat Transfer ◽  
Heat Transfer Coefficients ◽  
Enhanced Tubes ◽  
Mass Fractions

Pool boiling heat transfer coefficients of R134a with different lubricant mass fractions for one smooth tube and five enhanced tubes were tested at a saturation temperature of 6°C. The lubricant used was polyvinyl ether. The lubrication mass fractions were 0.25%, 0.5%, 1.0%, 2.0%, 3.0%, 5.0%, 7.0%, and 10.0%, respectively. Within the tested heat flux range, from 9000 W/m2 to 90,000 W/m2, the lubricant generally has a different influence on pool boiling heat transfer of these six tubes.

scholarly journals PREDICTING OF STEAM CONDENSATION HEAT TRANSFER COEFFICIENT IN HORIZONTAL FLATTENED TUBE

2020 ◽  
Vol 24 (06) ◽  
pp. 115-126
Author(s):  
Mohammed Ghazi M. Kamil ◽  
◽  
Muna Sabah Kassim ◽  
Louay Abd Alazez Mahdi ◽  
◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Saturation Temperature ◽  
Condensation Heat Transfer ◽  
Uniform Heat Flux ◽  
Steam Condensation ◽  
The Heat Transfer Coefficient ◽  
Condensation Heat Transfer Coefficient

The heat transfer coefficient of steam condensation has a significant role in the performance of air-cooled heat exchangers. The purpose of this work is to predict the local/average local steam condensation heat transfer coefficient inside the horizontal flattened tube under vacuum conditions using numerous correlations that were developed by some researches which have been conducted under specified conditions. The results from these correlations have been compared with experimental data of Davies, therefore more investigate for the values are necessary to improve or/and validate the existing correlations. The effect of such parameters like the uniform heat flux and saturation temperature also have been studied on the local steam condensation heat transfer coefficient as the results show that the heat transfer coefficient decrease as the heat flux increase, while it increases as the steam saturated temperature increase.

Convective Boiling of R-22 in a Flat Aluminum Multi-Minichannel Tube With Dh = 1.4 mm

2008 ◽  
Author(s):  
Nae-Hyun Kim ◽  
Wang-Kyu Oh ◽  
Jung-Ho Ham ◽  
Do-Young Kim ◽  
Tae-Ryong Shin
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Mass Flux ◽  
Saturation Temperature ◽  
High Mass ◽  
High Heat Flux ◽  
Convective Boiling ◽  
The Heat Transfer Coefficient

Convective boiling heat transfer coefficients of R-22 were obtained in a flat extruded aluminum tube with Dh = 1.41 mm. The test range covered mass flux from 100 to 600 kg/m2 s, heat flux from 5 to 15 kW/m2 and saturation temperature from 5°C to 15°C. The heat transfer coefficient curve shows a decreasing trend after a certain quality (critical quality). The critical quality decreases as the heat flux increases, and as the mass flux decreases. The early dryout at a high heat flux results in a unique ‘cross-over’ of the heat transfer coefficient curves. The heat transfer coefficient increases as the mass flux increases. At a low quality region, however, the effect of mass flux is not prominent. The heat transfer coefficient increases as the saturation temperature increases. The effect of saturation temperature, however, diminishes as the heat flux decreases. Both the Shah and the Kandlikar correlations underpredict the low mass flux and overpredict the high mass flux data.

Pool boiling performance of oxide nanofluid on a downward-facing heating surface

Kerntechnik ◽  
2022 ◽  
Vol 0 (0) ◽  
Author(s):  
Zhibo Zhang ◽  
Huai-En Hsieh ◽  
Yuan Gao ◽  
Shiqi Wang ◽  
Jia Gao ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Surface Roughness ◽  
Stainless Steel ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Critical Heat Flux ◽  
Pool Boiling ◽  
Heating Surface ◽  
Nano Particles

Abstract In this study, the pool boiling performance of oxide nanofluid was investigated, the heating surface is a 5 × 30 mm stainless steel heating surface. Three kinds of nanofluids were selected to explore their critical heat flux (CHF) and heat transfer coefficient (HTC), which were TiO2, SiO2, Al2O3. We observed that these nanofluids enhanced CHF compared to R·O water, and Al2O3 case has the most significant enhancement (up to 66.7%), furthermore, the HTC was also enhanced. The number of bubbles in nanofluid case was relatively less than that in R·O water case, but the bubbles were much larger. The heating surface was characterized and it was found that there were nano-particles deposited, and surface roughness decreased. The wettability also decreased with the increase in CHF.

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