Experimentally investigating effects of gap size and injection flowrate on heat transfer and boiling characteristics for the downward facing wall heating

2015 ◽  
Vol 90 ◽  
pp. 774-781 ◽  
Author(s):  
J.W. Chen ◽  
T.J. Chuang ◽  
Y.M. Ferng
Keyword(s):  
Heat Transfer ◽  
Gap Size ◽  
Wall Heating

Influence of coated surfaces and gap size on boiling heat transfer of deionized water

2020 ◽  
Vol 42 (3) ◽  
Author(s):  
Jéssica Martha Nunes ◽  
Reinaldo Rodrigues de Souza ◽  
Alessandro Roger Rodrigues ◽  
Mohammad Reza Safaei ◽  
Elaine Maria Cardoso
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Deionized Water ◽  
Gap Size ◽  
Coated Surfaces

Development of Cooling System for a Large Area at High Heat Flux by Using Flow Boiling in Narrow Channels

2009 ◽  
Author(s):  
Shinichi Miura ◽  
Yukihiro Inada ◽  
Yasuhisa Shinmoto ◽  
Haruhiko Ohta
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Flow Rate ◽  
Mass Velocity ◽  
Cooling System ◽  
Volumetric Flow Rate ◽  
High Heat ◽  
High Heat Flux ◽  
Gap Size ◽  
Heated Channel

Advance of an electronic technology has caused the increase of heat generation density for semiconductors densely integrated. Thermal management becomes more important, and a cooling system for high heat flux is required. It is extremely effective to such a demand using flow boiling heat transfer because of its high heat removal ability. To develop the cooling system for a large area at high heat flux, the cold plate structure of narrow channels with auxiliary unheated channel for additional liquid supply was devised and confirmed its validity by experiments. A large surface of 150mm in heated length and 30mm in width with grooves of an apex angle of 90 deg, 0.5mm depth and 1mm in pitch was employed. A structure of narrow rectangular heated channel between parallel plates with an unheated auxiliary channel was employed and the heat transfer characteristics were examined by using water for different combinations of gap sizes and volumetric flow rates. Five different liquid distribution modes were tested and their data were compared. The values of CHF larger than 1.9×106W/m2 for gap size of 2mm under mass velocity based on total volumetric flow rate and on the cross section area of main heated channel 720kg/m2s or 1.7×106W/m2 for gap size of 5mm under 290kg/m2s were obtained under total volumetric flow rate 4.5×10−5m3/s regardless of the liquid distribution modes. Under several conditions, the extensions of dry-patches were observed at the upstream location of the main heated channel resulting burnout not at the downstream but at the upstream. High values of CHF larger than 2×106W/m2 were obtained only for gap size of 2mm. The result indicates that higher mass velocity in the main heated channel is more effective for the increase in CHF. It was clarified that there is optimum flow rate distribution to obtain the highest values of CHF. For gap size of 2mm, high heat transfer coefficient as much as 7.4×104W/m2K were obtained at heat flux 1.5×106W/m2 under mass velocity 720kg/m2s based on total volumetric flow rate and on the cross section area of main heated channel. Also to obtain high heat transfer coefficient, it is more useful to supply the cooling liquid from the auxiliary unheated channel for additional liquid supply in the transverse direction perpendicular to the flow in the main heated channel.

The Characteristics of Porous Solar Wall Heating System with Localized UFAD

2012 ◽  
Vol 178-181 ◽  
pp. 237-243
Author(s):  
Li Ouyang ◽  
Wei Liu
Keyword(s):  
Heat Transfer ◽  
Porous Medium ◽  
Saturated Porous Medium ◽  
Flow Characteristics ◽  
Heating System ◽  
Physical Models ◽  
Air Distribution ◽  
Cable System ◽  
Wall Heating ◽  
Solar Wall

In this paper, the physical models of the porous solar wall heating system with localized underfloor air distribution (UFAD) are established. Based on Brinkman-Forchheimer Extended Darcy and energy two-equation models for saturated porous medium, the influences of the structure of underfloor space on the heat transfer and flow characteristics of the system are simulated, analyzed and compared.The results show that the underfloor space with rational partition is good for improving the heat transfer and flow characteristics of system, and maintaining the cable system in the underfloor space.

Near-Wall RANS Modelling in LES of Heat Transfer in Backward-Facing Step Flows Under Conditions of Constant and Variable Fluid Properties

2010 ◽  
Author(s):  
S. Jakirlic´ ◽  
B. Kniesner
Keyword(s):  
Heat Transfer ◽  
Temperature Fields ◽  
Large Temperature ◽  
Backward Facing Step ◽  
Local Flow ◽  
Wall Heating ◽  
Variable Fluid Properties ◽  
Fluid Properties ◽  
Flow Domain ◽  
Near Wall

Two backward-facing step (BFS) flow configurations associated with the heat transfer under the conditions of constant and variable fluid properties were investigated computationally by means of LES and a zonal Hybrid LES/RANS (HLR) method. The latter scheme couples a RANS (Reynolds-Averaged Navier-Stokes) model with large-eddy simulation (LES) within a two-layer framework. A differential near-wall eddy-viscosity model resolves the wall layer and the LES model the remainder of the flow domain. As an introductory heat-transfer case a fully-developed channel flow at Re number Rem = 24000 (DNS: Abe et al., 2004) was computed. In both presently investigated BFS cases the flow is subjected to increasingly enhanced wall heating. Whereas the first considered case (ReH = 28000, ER = 1.25), treated experimentally by Vogel and Eaton (1985) - reference LES is due to Keating et al., 2004, deals with a passive scalar transport, the high-intensity heat flux introduced into the flow domain through the step wall in the second investigated configuration (ReH = 5540, ER = 1.5; reference LES by Avancha and Pletcher, 2002; corresponding isothermal experiment by Kasagi and Matsunaga, 1995) leads to large temperature gradients causing a strong variation of the flow properties. An important feature of the latter flow is a substantial increase of the friction coefficient magnitude with the wall heating intensification in both the flow reversal and recovery region, associated with the local flow acceleration in the immediate wall vicinity. The results obtained by the present simulations with respect to the mean velocity and temperature fields, friction factor and Stanton number variations follow closely the reference experimental and LES databases.

Flow Boiling Heat Transfer and Flow Pattern in Rectangular Channel of Mini-Gap

2004 ◽  
Author(s):  
Yang Yang ◽  
Yasunobu Fujita
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Annular Flow ◽  
Flow Boiling ◽  
Flow Patterns ◽  
Gap Size ◽  
Vapor Quality ◽  
Micro Channels ◽  
Mini Channels

Flow boiling in micro- and mini-channels has attracted much attention in recent years. But the phenomena is such confined channels have not been fully understood and explained. Some conclusions reached by different authors are even contradictory. The present research is trying to study some aspects of flow boiling in mini- and micro-channels. In the present paper boiling heat transfer and two-phase flow patterns in rectangular narrow channels were studied. The gap size of the channel was varied as 2, 1, 0.5 and 0.2 mm with the channel width and length being kept at 20 mm and 100 mm, respectively. In the present mini- and micro-channels, four flow patterns were identified; bubbly, intermittent, wavy and annular flow. They can be also divided into several sub-flow patterns. Flow patterns showed strong channel gap size dependence. Smaller gap size deleted bubbly flow, thus induced simpler flow patterns to shift the annular flow at lower vapor quality. The channels can be divided into two groups depending on the gap size; the larger gap group of 2 and 1 mm, and the smaller gap group of 0.5 and 0.2 mm. The larger gap group showed similar heat transfer behavior as conventional size of tubes. The smaller gap group indicated some peculiar phenomena. Heat transfer coefficient in the smaller gap group was relatively high in the low quality region. Then heat transfer coefficient decreased monotonously with increasing vapor quality. This behavior was considered attributable to the micro-bubble generation in the channel corners and an early partial dryout of thin liquid film. Thus the relationship between heat transfer coefficient and flow pattern should be carefully pursued in micro- and mini-channels to develop heat transfer correlations based on flow patterns.

Heat Transfer and Friction Factor Correlations for Solar Air Heater With Gap in V-Rib With Symmetrical Gap and Staggered Ribs

2019 ◽  
Vol 12 (3) ◽  
Author(s):  
Sumer Singh Patel ◽  
Atul Lanjewar
Keyword(s):  
Heat Transfer ◽  
Friction Factor ◽  
Smooth Surface ◽  
Heat Transfer Analysis ◽  
Operating Parameters ◽  
Solar Air Heater ◽  
Gap Size ◽  
Maximum Enhancement ◽  
Air Heater ◽  
Relative Roughness

Abstract The present experimental study is concerned with heat transfer analysis of air flowing in solar air heater duct with a gap in V-rib with symmetrical gap and staggered ribs geometry. The investigated parameters are Reynolds number (Re) of 4000–14,000, relative roughness pitch (p/e) of 12, relative roughness height (e/Dh) of 0.043, angle of attack (α) of 60 deg, relative staggered rib pitch (p′/p) of 0.65, relative gap size (g/e) of 4, relative staggered rib size (r/e) of 4, relative gap position of additional gap in each symmetrical rib elements (d/w) of 0.65, relative gap size of additional gap in each symmetrical rib elements (g′/e) of 1, number of main gaps (Ng) of 1, 2, 3, 4, and number of additional gap (ng) varying from 1 to 5. Fourteen roughened absorber plates were tested. The maximum enhancement in Nusselt number (Nu) and friction factor (f) was 2.34 and 2.79 times that of smooth surface corresponding to the number of main gaps (Ng) of 4 with the number of additional gaps (ng) of 4. The performance of the gap in V-rib with symmetrical gap and staggered rib geometry has been compared with the existing latest V-rib geometry and smooth surface. The proposed gap in V-rib with symmetrical gap and staggered ribs geometry has a better performance than the existing latest V-rib geometry. The following correlations have been developed for heat transfer and friction factor in terms of roughness and operating parameters. Heat transfer:Nur=0.0073(Re)0.9788(Ng)0.2790(ng)0.0184exp[−0.1678(ln(Ng))2]exp[−0.0129(ln(ng))2] Friction factor:fr=0.0477(Re)−0.0678(Ng)0.5919(ng)−0.0562exp[−0.4922(ln(Ng))2]exp[−0.0487(ln(ng))2]

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