The Enhancement of Spray Cooling Performance in Nucleate and Transition Boiling Regimes by Using Saline Water Containing Dissolved Carbon Dioxide

2019 ◽  
Vol 12 (2) ◽  
Author(s):  
Lily Das ◽  
B. Munshi ◽  
S. S. Mohapatra
Keyword(s):  
Heat Transfer ◽  
Transfer Rate ◽  
Saline Water ◽  
Removal Rate ◽  
Heat Removal ◽  
Spray Cooling ◽  
High Heat ◽  
Vapor Bubbles ◽  
Dissolved Carbon ◽  
Dissolved Carbon Dioxide

Abstract In the current work, by using various additives, the spray cooling in the transition boiling regime is significantly augmented due to the vapor film instability enhancing, which helps to overcome the disadvantages reported in the open literature for the attainment of high heat flux in the aforesaid boiling regime. Saline water containing dissolved carbon dioxide produces two favorable conditions for high heat transfer rate: (1) controlled vapor bubble nucleation and (2) low entrapped vapor bubbles coalescence rate. These phenomena are the parameters defining the step-up in the heat transfer rate. Systematic spray cooling (from 900 °C) experiments were conducted on a 6-mm thick AISI 304 steel plate (100 mm × 100 mm). The heat transfer analysis indicates that the heat removal rate in case of soda added water depicts an increasing trend with the rising of the soda concentration up to 40% in water, and further increment in soda water concentration declines the heat removal rate due to the formation of the uncontrolled vapor bubbles undergoing early coalescence. In case of salt added carbonated water spray cooling, the quenching performance indicates step-up in critical heat flux up to 1.7 MW/m2. In addition to the above, the spray cooling performance of the above-stated coolant is compared with other potential coolants such as soda–surfactant–water, soda–alcohol–water and soda–salt–surfactant–water mixtures.

Application of Mahalanobis-Taguchi system and design of experiments to reduce the field failures of splined shafts

2014 ◽  
Vol 31 (6) ◽  
pp. 681-697 ◽  
Author(s):  
Boby John
Keyword(s):  
Heat Transfer ◽  
Design Of Experiments ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Removal Rate ◽  
Heat Removal ◽  
Induction Hardening ◽  
Raw Material ◽  
Hardness Profile ◽  
Content Type

Purpose – The purpose of this paper is to develop a methodology to reduce the field failures of splined shafts. The paper also demonstrates the application of Mahalanobis-Taguchi system (MTS) for identifying the optimum hardness profile to avoid failures. Design/methodology/approach – Through the usage profile analysis and comparison between the failed and good shafts, the major reason for shaft failure was identified as hardness variation. Then MTS approach was used to identify the optimum hardness profile for the shafts. An experiment was designed with power, feed and the gap between inductor and quench ring representing the heat transfer rate, heat removal rate and the time between heat transfer and removal of induction hardening process as factors. Based on experimental results, the optimum combination factors that would reduce the variation around the optimum hardness profile were identified. Findings – The study showed that the shaft failures can be reduced by optimizing the hardness profile of the shafts rather than warning customers on overloading, changing the raw material or investing on machining operation to achieve better shaft finish. The study suggested heat transfer rate, heat removal rate and the time between heat transfer and removal had significant impact on the shaft's hardness profile. The study resulted in reducing the field failures from 0.32 to 0.029 percent. Practical implications – This study provides valuable information on how to identify optimum hardness profile using MTS methodology to reduce shaft failures and how to minimize the variation around the optimum hardness profile using design of experiments. Originality/value – To the best of author's knowledge, no study has been conducted to identify optimum hardness profile using MTS methodology. The study also provides an approach to minimize the variation around a non-linear hardness profile using design of experiments.

scholarly journals Enhancement of Mist Flow Cooling by Using V-Shaped Broken Ribs

Energies ◽  
2019 ◽  
Vol 12 (19) ◽  
pp. 3785
Author(s):  
Kuan-Tzu Huang ◽  
Yao-Hsien Liu
Keyword(s):  
Heat Transfer ◽  
Removal Rate ◽  
Heated Surface ◽  
Heat Removal ◽  
High Heat ◽  
Water Mist ◽  
Droplet Impingement ◽  
Square Channel ◽  
Air Volume ◽  
Mist Flow

Substantial heat transfer enhancement can be achieved by cooling with air/water mist flow because of droplet impingement and liquid film/fragment evaporation on the heated surface, which leads to a high heat-removal rate. An experimental investigation was conducted in a square channel with continuous and broken V-shaped ribs. To generate a mist flow, micro droplets were introduced into the gas stream. The rib angle of attack was 45°, and the rib spacing-to-height ratios were 10 and 20. The air Reynolds number ranged from 7900 to 24,000, and the water-to-air volume flow ratio was less than 0.1%. The net heat inputs ranged from 1.1–3.1 W/cm2 and 3.4–9.4 W/cm2 for the air and mist flow cases, respectively. Because the deposited liquid fragments produced uneven temperature distribution on the heated surface, steady-state infrared thermography was used to visualize the heat transfer distribution. Two to seven times higher heat transfer was attained for the broken ribs when using the mist flow than when using air flow. This increase was mainly attributed to the broken structure, which facilitated liquid transport and enhanced liquid coverage. In addition, the broken ribs produced a smaller friction factor than continuous ribs. The broken structures were beneficial for higher thermal performance in the mist flow.

Optimal Ratio of Heat Removal Rate to Pumping Power for PCM Emulsion Fluids: Low Reynolds Number Limits

2006 ◽  
Author(s):  
P. Maloji ◽  
Y.-X. Tao
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Phase Change ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Removal Rate ◽  
Pure Water ◽  
Heat Removal ◽  
Pumping Power ◽  
Optimal Ratio

There are many applications where high heat transfer removal rate in a limited tight space are required. The applications include mini and micro-scale channels flows in compact heat exchangers. The increase in heat transfer rate often requires the significant increase in fluid velocity and therefore the increase in the pumping power. One option is to utilize Phase Change Materials (PCM). This study contributes to the further understanding of performance enhancement of an improved heat transfer fluid by studying the optimal ratio of heat removal rate to the fluid pumping power. PCMs have the unique characteristics that can increase the thermal capacity of heat transfer fluids by providing latent heat capacity at a temperature different than the melting point of the carrier fluid. The ratio of heat transfer rate (Q) to fluid pumping power (P) is about twice as that for using pure water without PCM particles. The effectiveness factor (compared to water without PCM) is also doubled. It has been observed that as Re decreases the effective factor increases and Q/P ratio increases, which is also true if the concentration of PCM increases. In this experimental study focuses are on the heat transfer enhancement effects for very low Reynolds number (Re < 180 of pure water velocity) and PCM concentration slurry flow of 10% to 20%. Experimental investigations relevant to PCM slurry flows are carried out. Experimental results indicate that PCM slurry's heat transfer coefficient and apparent specific heat are affected significantly by the phase change process and the slurry mass fraction. It is found that the Q/P ratio primarily is a function of Reynolds number.

Thermal Analysis of Plastic Serpentine-Type Microchannel Evaporators

2007 ◽  
Author(s):  
Boris Kosoy ◽  
Mehmet Arik
Keyword(s):  
Heat Transfer ◽  
Removal Rate ◽  
Flow Characteristics ◽  
Heat Removal ◽  
High Heat ◽  
Heat Fluxes ◽  
Working Fluid ◽  
Transfer Coefficients ◽  
High Heat Transfer ◽  
Micro Channels

Recently, microchannel liquid cooling technology showed very high heat transfer coefficients enabling high heat fluxes at allowable wall temperatures. It promises to be a potential solution to high flux electronics. This paper presents result of two related areas in the field of microchannel heat transfer. First, experimental results of serpentine-type fluoroplastic evaporated thermosyphons for microchannel applications are presented. R11 and R113 were used as working fluid, and it was shown that R11 has higher heat removal rate than R113. Flow distribution and flow characteristics (liquid, vapor, mixture etc) are discussed. Later discussion is extended towards key issues in mini and micro channels, and proposed correlations will be discussed. It is our great honor to contribute to Prof. Sadik Kakac symposium to celebrate his 75th birthday. We feel privileged knowing him and learning from his scientific books, papers, and personal discussions. We wish him a happy, healthy, and long life.

Phenomenon and Mechanism of Spray Cooling on Nanowire Arrayed and Hybrid Micro/Nanostructured Surfaces

2018 ◽  
Vol 140 (11) ◽  
Author(s):  
Jian-nan Chen ◽  
Rui-na Xu ◽  
Zhen Zhang ◽  
Xue Chen ◽  
Xiao-long Ouyang ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
High Speed ◽  
Spray Cooling ◽  
High Heat ◽  
High Heat Flux ◽  
Transfer Enhancement ◽  
Nanostructured Surfaces ◽  
New Energy ◽  
Dry Out

Enhancing spray cooling with surface structures is a common, effective approach for high heat flux thermal management to guarantee the reliability of many high-power, high-speed electronics and to improve the efficiency of new energy systems. However, the fundamental heat transfer enhancement mechanisms are not well understood especially for nanostructures. Here, we fabricated six groups of nanowire arrayed surfaces with various structures and sizes that show for the first time how these nanostructures enhance the spray cooling by improving the surface wettability and the liquid transport to quickly rewet the surface and avoid dry out. These insights into the nanostructure spray cooling heat transfer enhancement mechanisms are combined with microstructure heat transfer mechanism in integrated microstructure and nanostructure hybrid surface that further enhances the spray cooling heat transfer.

scholarly journals Dissolved Carbon Dioxide Sensing Platform for Freshwater and Saline Water Applications: Characterization and Validation in Aquaculture Environments

Sensors ◽  
2019 ◽  
Vol 19 (24) ◽  
pp. 5513
Author(s):  
J.P. Mendes ◽  
L. Coelho ◽  
B. Kovacs ◽  
J.M.M.M. de Almeida ◽  
C.M. Pereira ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Limit Of Detection ◽  
Saline Water ◽  
Light Emitting Diode ◽  
Limit Of Quantification ◽  
Acid Media ◽  
Dissolved Carbon ◽  
Sensing Platform ◽  
Dissolved Carbon Dioxide ◽  
Colorimetric Indicator

A sensing configuration for the real-time monitoring, detection, and quantification of dissolved carbon dioxide (dCO2) was developed for aquaculture and other applications in freshwater and saline water. A chemical sensing membrane, based on a colorimetric indicator, is combined with multimode optical fiber and a dual wavelength light-emitting diode (LED) to measure the dCO2-induced absorbance changes in a self-referenced ratiometric scheme. The detection and processing were achieved with an embeded solution having a mini spectrometer and microcontroller. For optrode calibration, chemical standard solutions using sodium carbonate in acid media were used. Preliminary results in a laboratory environment showed sensitivity for small added amounts of CO2 (0.25 mg·L−1). Accuracy and response time were not affected by the type of solution, while precision was affected by salinity. Calibration in freshwater showed a limit of detection (LOD) and a limit of quantification (LOQ) of 1.23 and 1.87 mg·L−1, respectively. Results in saline water (2.5%) showed a LOD and LOQ of 1.05 and 1.16 mg·L−1, respectively. Generally, performance was improved when moving from fresh to saline water. Studies on the dynamics of dissolved CO2 in a recirculating shallow raceway system (SRS+RAS) prototype showed higher precision than the tested commercial sensor. The new sensor is a compact and robust device, and unlike other sensors used in aquaculture, stirring is not required for correct and fast detection. Tests performed showed that this new sensor has a fast accurate detection as well as a strong potential for assessing dCO2 dynamics in aquaculture applications.

Dependence of Heat Transfer Coefficient on Porous Structure in Porous Media

2008 ◽  
Author(s):  
Akira Matsui ◽  
Kazuhisa Yuki ◽  
Hidetoshi Hashizume
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Porous Media ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
High Performance ◽  
Heat Removal ◽  
High Heat ◽  
Metal Foams ◽  
High Heat Flux

Detailed heat transfer characteristics of particle-sintered porous media and metal foams are evaluated to specify the important structural parameters suitable for high heat removal. The porous media used in this experiment are particle-sintered porous media made of bronze and SUS316L, and metal foams made of copper and nickel. Cooling water flows into the porous medium opposite to heat flux input loaded by a plasma arcjet. The result indicates that the bronze-particle porous medium of 100μm in pore size shows the highest performance and achieves heat transfer coefficient of 0.035MW/m2K at inlet heat flux 4.6MW/m2. Compared with the heat transfer performance of copper fiber-sintered porous media, the bronze particlesintered ones give lower heat transfer coefficient. However, the stable cooling conditions that the heat transfer coefficient does not depend on the flow velocity, were confirmed even at heat flux of 4.6MW/m2 in case of the bronze particle-sintered media, while not in the case of the copper-fiber sintered media. This signifies the possibility that the bronze-particle sintered media enable much higher heat flux removal of over 10MW/m2, which could be caused by higher permeability of the particle-sintered pore structures. Porous media with high permeability provide high performance of vapor evacuation, which leads to more stable heat removal even under extremely high heat flux. On the other hand, the heat transfer coefficient of the metal foams becomes lower because of the lower capillary and fin effects caused by too high porosity and low effective thermal conductivity. It is concluded that the pore structure having high performance of vapor evacuation as well as the high capillary and high fin effects is appropriate for extremely high heat flux removal of over 10MW/m2.

Numerical Study of Water Droplet Heat Removal and Dynamics During its Impact Onto the Micro-Pillar Array at Elevated Temperature

2018 ◽  
Author(s):  
Beni Mehrdad Shahmohammadi ◽  
Shangzhen Xie ◽  
Jiyun Zhao
Keyword(s):  
Heat Transfer ◽  
Level Set Method ◽  
Level Set ◽  
Solid Surface ◽  
Water Droplet ◽  
Heat Removal ◽  
Spray Cooling ◽  
Optimal Size ◽  
Droplet Dynamics ◽  
Micro Pillars

The spray cooling and heat removal efficiency is one of the important aspect of nuclear thermalhydraulics and safety, especially for passive containment cooling after severe accidents. In order to design and optimize these systems effectively, computer modelling of the underlying mechanism of the liquid drop interaction with the hot solid surface would be necessary. Therefore, completeness, accuracy and reliability of the models that are being used in such sensitive areas are vital to the society and environment. Furthermore, the current powerful computer resources need to be fully exploited, so that the precision and the accuracy of the obtained computational results would be further enhanced. Nowadays, Volume-Of-Fluid (VOF) method is widely used in simulating the droplet dynamics, however these models provide estimations that are different in certain extents compare to the experimental results. In present work, we have used the level-set method to study the droplet dynamics and heat removal when the water droplet impact on the surface with different morphologies. The developed model which is based on the finite element method (FEM) has been benchmarked with previously performed experiments regarding the droplet bouncing on a flat hydrophobic surface; these estimations were in a good agreement with the previously published results. Moreover, hot solid surfaces with presence of micro-pillar has been considered to perform sensitivity study for different sizes of the micro-pillars and water droplets. In addition, it has been found that the heat transfer and droplet dynamic behavior would significantly vary in scenarios when the micro-pillars are presents in compare to a flat solid surface; it is observed that a better droplet spreading can be obtained with optimal size of micro-pillars that are present underneath of the droplet axial trajectory. The present study and the model would add valuable information to the field of heat transfer in aspect of spray cooling by investigating the feasibility of using the level-set method for a better estimation of fluid and heat transfer related results.

The Effect of Porous Material on the Improvement of the Micro-Chip Heat Dissipation

2008 ◽  
Author(s):  
Chyouhwu B. Huang ◽  
Hung-Shyong Chen ◽  
Szu-Ming Wu
Keyword(s):  
Heat Transfer ◽  
Porous Material ◽  
Porous Materials ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Heat Dissipation ◽  
Porous Ceramic ◽  
High Heat ◽  
Force Convection ◽  
Uninterruptible Power

Heat dissipation is a very important subject when dealing with industrial application especially in modern semiconductor related applications. Several techniques have been developed to solve the heat generated problem, such as heat dissipation device in IC packaging, high heat conductivity materials, heat tube, force convection, etc. Porous material is used in this study. Porous material is known to have large interior surface, therefore, with proper force convection; it can easily carry heat away. Micro porous ceramic (porous size: 490 μm) is attached to uninterruptible power supply (UPS) power chips. The increase of the heat dissipation rate improves UPS performance. Heat transfer properties comparisons for power chip with and without micro porous materials attached are studies. Also, heat transfer rate under different fan speeds (force convection) is studied. The results show that, heat transfer increases with the use of micro porous materials, the effectiveness ranges between 2–22%. Also, the heat transfer rate varies with air flow rate, the increase of heat transfer is about 4–6%. The dust effect was also performed; experimental results show that heat transfer rate will not be affected by the accumulated dust if a micro porous material is applied.

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