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.

Nonboiling Heat Transfer and Friction of Air/Water Mist Flow in a Square Duct With Orthogonal Ribs

2017 ◽  
Vol 9 (4) ◽  
Author(s):  
Yi-Hsuan Huang ◽  
Chiao-Hsin Chen ◽  
Yao-Hsien Liu
Keyword(s):  
Heat Transfer ◽  
Liquid Film ◽  
Heat Transfer Enhancement ◽  
Film Formation ◽  
Heated Surface ◽  
Air Flow ◽  
Water Mist ◽  
Air Cooling ◽  
Transfer Enhancement ◽  
Mist Flow

Heat transfer of air/water mist flow in a single-side heated vertical duct was experimentally investigated. The mist flow was produced by introducing fine dispersed water droplets into the air stream, and the water–air mass flow ratios were up to 15%. The Reynolds numbers of the air flow were 7900, 16,000, and 24,000. The rib spacing-to-height ratios were 10 and 20 in the current study. Mist flow cooling achieved higher heat transfer rates mainly because of the droplet deposition and liquid film formation on the heated surface. The heat transfer enhancement on the smooth surface by the mist flow was 4–6 times as high as the air flow. On the ribbed surface, a smaller rib spacing of 10 was preferred for air cooling, since the heat transfer enhancement by the flow reattachment was better utilized. However, the rib-induced secondary flow blew away the liquid films on the surface, and the heat transfer enhancement was degraded near the reattachment region for the mist cooling. A larger rib spacing-to-height ratio of 20 thus achieved higher heat transfer because of the liquid film formation beyond the reattachment region. The heat transfer enhancement on the ribbed surface using mist flow was 2.5–3.5 times as high as the air flow. The friction factor of the mist flow was two times as high as the air flow in the ribbed duct.

Non-Boiling Heat Transfer of Air/Water Mist Flow in a Square Duct With Orthogonal Ribs

2016 ◽  
Author(s):  
Yi-Hsuan Huang ◽  
Chiao-Hsin Chen ◽  
Yao-Hsien Liu
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Heated Surface ◽  
Air Flow ◽  
Liquid Films ◽  
Water Mist ◽  
Transfer Enhancement ◽  
Square Duct ◽  
Flow Mixing ◽  
Mist Flow

Heat transfer of mist flow in a rib-roughened square duct was experimentally determined using infrared thermography. The mist flow was generated by introducing fine dispersed water droplets into the air stream. A constant heat flux was applied to the surface during the test and the surface temperature was kept below the boiling point. The heat transfer measurement was performed on a heated surface located inside a vertical square duct with a hydraulic diameter of 4cm. The air/water mist flow was carried upward by air flow from a blower placed at the bottom of the duct. The flow passed through a flow straightener and entered the heated region of the square duct. The Reynolds numbers of the carrier fluid were 7900, 16000 and 24000. The results showed that mist flow cooling achieved higher heat transfer rates compared to the air cooling. Thin liquid films formed on the heated surface by the mist flow and the evaporation from the droplets and liquid film contributed to a higher heat removal rate. The heat transfer enhancement on the smooth surface by the mist flow was 4 to 6 times higher compared to the air flow. Rib turbulators were typically applied in channel walls for heat transfer enhancement in gas turbine blades or heat exchangers. Ribs caused flow reattachment and promoted flow mixing. The higher Nusselt number induced by flow reattachment can be visualized using infrared thermography. For the ribbed case, the heat transfer contours were reported based the regions between ribs. Square brass ribs were used and the rib height-to-hydraulic diameter ratio was 0.05. The rib pitch-to-height ratios were 10 and 20 in the current study. For the mist flow in the ribbed duct, the intense flow mixing and secondary flow caused by the ribs blew away liquid films on the surface. The heat transfer enhancement near the reattachment region was mainly influenced by the droplet impingement on the surface. In the ribbed duct, the heat transfer enhancement from using the mist flow was 2.5 to 3.5 times higher compared to the air flow.

Cooling of a Heated Surface by Mist Flow

1994 ◽  
Vol 116 (1) ◽  
pp. 167-172 ◽  
Author(s):  
S. L. Lee ◽  
Z. H. Yang ◽  
Y. Hsyua
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Liquid Film ◽  
Heated Surface ◽  
High Heat ◽  
Dynamic Interaction ◽  
High Heat Flux ◽  
Steady Temperature ◽  
Mist Flow ◽  
High Level

Cooling requirements in modern industrial applications, such as the removal of heat from electronic equipments, often demand the simultaneous attainment of a high heat flux and a low and relatively uniform and steady temperature of the heated surface to be cooled. The conventional single-phase convection cooling obviously cannot be expected to function adequately, since the heat flux there is directly proportional to the temperature difference between the heated surface and the surrounding medium. To maintain a high heat flux, the temperature of the heated surface usually must be kept at a high level. An attractive alternative is cooling by a spray, which takes advantage of the significant latent heat of evaporation of the liquid. However, in conventional industrial spray coolings, such as in the case of the cooling tower of a power plant, the temperature of the heated surface usually remains relatively high and is nonuniform and unsteady containing numerous flashy hot spots. In order to optimize the performance of the spray cooling of a heated surface by a mist flow, a clear understanding is required of (1) the dynamic interaction between the droplets and the carrier fluid and (2) the thermal reception of the droplets at the heated surface. It is the dynamic interaction between the phases that is causing the droplets to deposit onto the heated surface. The thermal reception at the heated wall develops mass and heat transfer leading to the mode of cooling of the heated surface. In the present study, an experimental investigation was made of the combination of the dynamic depositional behavior of droplets in a water droplet-air mist flow with the use of a specially designed particle-sizing two-dimensional laser-Doppler anemometer. Also, the heat transfer characteristics at the heated surface were investigated in relation to droplet deposition on the heated surface for wide ranges of droplet size, droplet concentration, mist flow velocity, and heat flux. It was discovered that over a certain suitable range of combination of these parameters, a superbly effective cooling scheme could be established by the evaporation on the outside surface of an ultrathin liquid film. Such a film was formed on the heated surface by the continuous deposition of fine droplets from the mist flow. Under these conditions, the heat flux is primarily related to the evaporation of the ultrathin liquid film on the heated surface and thus depends less on the temperature difference between the heated surf ace and the ambient mist flow. The heated surface is quenched to a low, relatively uniform and steady temperature at a very high level of heat flux. Heat transfer enhancement as high as seven times has been found so far. This effective heat transfer scheme is here termed mist cooling.

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.

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.

scholarly journals Time Averaged and Fluctuating Heat Transfer Measurements in an Atomising Mist Jet Nozzle

2009 ◽  
Author(s):  
Oisn F. P. Lyons ◽  
Darina B. Murray ◽  
Gerard Byrne ◽  
Tim Persoons
Keyword(s):  
Heat Transfer ◽  
Internal Structure ◽  
Research Group ◽  
Single Phase ◽  
Water Mist ◽  
Phase Behaviour ◽  
Heat Transfer Characteristics ◽  
Air Jets ◽  
Mist Flow ◽  
Jet Nozzle

Much is already known about the heat transfer characteristics of impinging air jets, and they are widely used in many engineering applications. There currently exist many correlations describing such characteristics. However, the complex internal structure of many nozzles can lead these to produce results which deviate from those predicted by correlations. One such nozzle is currently used in this research group to produce a water mist flow and this paper describes the experimental characteristics of its single phase behaviour.

Enhancement of heat transfer in a square channel by roughened surfaces in rib-elements and turbulent flow manipulation

2017 ◽  
Vol 27 (7) ◽  
pp. 1571-1595 ◽  
Author(s):  
Jian Liu ◽  
Gongnan Xie ◽  
Bengt Ake Sunden ◽  
Lei Wang ◽  
Martin Andersson
Keyword(s):  
Heat Transfer ◽  
Turbulent Flow ◽  
Research Work ◽  
Flow Characteristics ◽  
High Heat ◽  
The Novel ◽  
Content Type ◽  
Flat Surfaces ◽  
Square Channel ◽  
High Heat Transfer

Purpose The purpose of this paper is to augment heat transfer rates of traditional rib-elements with minimal pressure drop penalties. Design/methodology/approach The novel geometries in the present research are conventional cylindrical ribs with rounded transitions to the adjacent flat surfaces and with modifications at their bases. All turbulent fluid flow and heat transfer results are presented using computation fluid dynamics with a validated v2f turbulence closure model. Turbulent flow characteristics and heat transfer performances in square channels with improved ribbed structures are numerically analyzed in this research work. Findings Based on the results, it is found that rounded transition cylindrical ribs have a large advantage over the conventional ribs in both enhancing heat transfer and reducing pressure loss penalty. In addition, cylindrical ribs increase the flow impingement at the upstream of the ribs, which will effectively increase the high heat transfer areas. The design of rounded transition cylindrical ribs and grooves will be an effective way to improve heat transfer enhancement and overall thermal performance of internal channels within blade cooling. Originality/value The novel geometries in this research are conventional cylindrical ribs with rounded transitions to the adjacent flat surfaces and with modifications at their bases. The combination of cylindrical ribs and grooves to manipulate the turbulent flow.

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.

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