Heat Transfer Enhancement in Square Ducts With V-Shaped Ribs of Various Angles

2002 ◽  
Author(s):  
Rongguang Jia ◽  
Arash Saidi ◽  
Bengt Sunde´n
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Enhancement ◽  
Experimental Studies ◽  
Eddy Diffusivity ◽  
Heat Fluxes ◽  
Secondary Flows ◽  
Turbulent Heat ◽  
Transfer Enhancement ◽  
Transfer Coefficients

Experimental studies have revealed that both downstream and upstream pointing V-shaped ribs result in better heat transfer enhancement than transverse straight ribs of the same geometry. Secondary flows induced by the angled ribs are believed to be responsible for this higher heat transfer enhancement. Further investigations are needed to understand this. In the present study, the heat and fluid flow in V-shaped-ribbed ducts is numerically simulated by a multi-block 3D solver, which is based on solving the Navier-Stokes and energy equations in conjunction with a low-Reynolds number k-ε turbulence model. The Reynolds turbulent stresses are computed with an explicit algebraic stress model (EASM), while turbulent heat fluxes are calculated with a simple eddy diffusivity model (SED). Firstly, the simulation results of transverse straight ribs are validated against the experimental data, for both velocity and heat transfer coefficients. Then, the results of different rib angles (45° and 90°) and Reynolds number (15,000–30,000) are compared to determine the goodness of different rib orientations. Detailed velocity and thermal field results have been used to explain the effects of the inclined ribs and the mechanisms of heat transfer enhancement.

Regional Heat Transfer and Pressure Drop in Two-Pass and Three-Pass Flow Passages With 180-Degree Sharp Turns

1989 ◽  
Author(s):  
M. K. Chyu
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Reynolds Number ◽  
Heat Transfer Enhancement ◽  
Pressure Loss ◽  
Secondary Flows ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
Pressure Loss Coefficient ◽  
Single Turn

The heat transfer distributions for flow passing through a two-pass (one-turn) and a three-pass (two-turn) passages with 180-degree sharp turns are studied by using the analogous naphthalene mass transfer technique. Both passages have square cross-section and length-to-height ratio of 8. The passage surface, including top wall, side walls and partition walls, is divided into 26 segments for the two-pass passage and 40 segments for the three-pass passage. Mass transfer results are presented for each segment along with regional and overall averages. The very non-uniform mass transfer coefficients measured around a sharp 180-degree turn exhibit the effects of flow separation, reattachment and impingement, in addition to secondary flows. Results of the three-pass passage indicate that heat transfer characteristics around the second turn is virtually the same as that around the first turn. This may imply that, in a multiple-pass passage, heat transfer at the first turn has already reached the thermally developed (periodic) condition. Over the entire two-pass passage, the heat transfer enhancement induced by the single-turn is about 45% to 65% of the fully developed values in a straight channel. Such a heat transfer enhancement decreases with an increase in Reynolds number. In addition, overall heat transfer of the three-pass passage is approximately 15% higher than that of the two-pass one. This 15% increase appears to be Reynolds number independent. The pressure loss induced by the sharp turns is found to be very significant. Within the present testing range, the pressure loss coefficient for both passages varies significantly with the Reynolds number.

Heat Transfer Enhancement in Square Ducts With V-Shaped Ribs

2003 ◽  
Vol 125 (4) ◽  
pp. 788-791 ◽  
Author(s):  
Rongguang Jia, ◽  
Arash Saidi, and ◽  
Bengt Sunden
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Stokes Equations ◽  
Eddy Diffusivity ◽  
Heat Fluxes ◽  
Navier Stokes ◽  
Turbulent Heat ◽  
Transfer Enhancement ◽  
Navier Stokes Equations ◽  
Square Ducts

This paper concerns a numerical investigation of the heat and fluid flow in V-shaped ribbed ducts. The Navier-Stokes equations and the energy equation are solved in conjunction with a low Reynolds number k–ε turbulence model. The Reynolds turbulent stresses are computed with an explicit algebraic stress model (EASM) while the turbulent heat fluxes are calculated with a simple eddy diffusivity model (SED). Detailed velocity and thermal field results have been used to explain the effects of the V-shaped ribs and the mechanisms of the heat transfer enhancement.

Regional Heat Transfer in Two-Pass and Three-Pass Passages With 180-deg Sharp Turns

1991 ◽  
Vol 113 (1) ◽  
pp. 63-70 ◽  
Author(s):  
M. K. Chyu
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Reynolds Number ◽  
Heat Transfer Enhancement ◽  
Pressure Loss ◽  
Secondary Flows ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
Pressure Loss Coefficient ◽  
Single Turn

The heat transfer distributions for flow passing through two-pass (one-turn) and three-pass (two-turn) passages with 180-deg sharp turns are studied by using the analogous naphthalene mass transfer technique. Both passages have square cross section and length-to-height ratio of 8. The passage surface, including top wall, side walls, and partition walls, is divided into 26 segments for the two-pass passage and 40 segments for the three-pass passage. Mass transfer results are presented for each segment along with regional and overall averages. The very nonuniform mass transfer coefficients measured around a sharp 180-deg turn exhibit the effects of flow separation, reattachment, and impingement, in addition to secondary flows. Results for the three-pass passage indicate that heat transfer characteristics around the second turn are virtually the same as those around the first turn. This may imply that, in a multiple-pass passage, heat transfer at the first turn has already reached the thermally developed (periodic) condition. Over the entire two-pass passage, the heat transfer enhancement induced by the single-turn is about 45 to 65 percent of the fully developed values in a straight channel. Such a heat transfer enhancement decreases with an increase in Reynolds number. In addition, overall heat transfer of the three-pass passage is approximately 15 percent higher than that of the two-pass one. This 15 percent increase appears to be Reynolds number independent. The pressure loss induced by the sharp turns is found to be very significant. Within the present testing range, the pressure loss coefficient for both passages is Reynolds number dependent.

scholarly journals Effect of Integrating Metal Wire Mesh with Spray Injection for Liquid Piston Gas Compression

Energies ◽  
2021 ◽  
Vol 14 (13) ◽  
pp. 3723
Author(s):  
Barah Ahn ◽  
Vikram C. Patil ◽  
Paul I. Ro
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Enhancement ◽  
Metal Wire ◽  
Wire Mesh ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Gas Compression ◽  
Liquid Piston

Heat transfer enhancement techniques used in liquid piston gas compression can contribute to improving the efficiency of compressed air energy storage systems by achieving a near-isothermal compression process. This work examines the effectiveness of a simultaneous use of two proven heat transfer enhancement techniques, metal wire mesh inserts and spray injection methods, in liquid piston gas compression. By varying the dimension of the inserts and the pressure of the spray, a comparative study was performed to explore the plausibility of additional improvement. The addition of an insert can help abating the temperature rise when the insert does not take much space or when the spray flowrate is low. At higher pressure, however, the addition of spacious inserts can lead to less efficient temperature abatement. This is because inserts can distract the free-fall of droplets and hinder their speed. In order to analytically account for the compromised cooling effects of droplets, Reynolds number, Nusselt number, and heat transfer coefficients of droplets are estimated under the test conditions. Reynolds number of a free-falling droplet can be more than 1000 times that of a stationary droplet, which results in 3.95 to 4.22 times differences in heat transfer coefficients.

Heat Transfer Enhancement in a Rectangular (AR = 3:1) Channel With V-Shaped Dimples

2012 ◽  
Vol 135 (1) ◽  
Author(s):  
C. Neil Jordan ◽  
Lesley M. Wright
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Liquid Crystal ◽  
Pressure Drop ◽  
Heat Transfer Enhancement ◽  
Thermal Performance ◽  
Secondary Flows ◽  
Transfer Enhancement ◽  
Reduced Pressure

An alternative to ribs for internal heat transfer enhancement of gas turbine airfoils is dimpled depressions. Relative to ribs, dimples incur a reduced pressure drop, which can increase the overall thermal performance of the channel. This experimental investigation measures detailed Nusselt number ratio distributions obtained from an array of V-shaped dimples (δ/D = 0.30). Although the V-shaped dimple array is derived from a traditional hemispherical dimple array, the V-shaped dimples are arranged in an in-line pattern. The resulting spacing of the V-shaped dimples is 3.2D in both the streamwise and spanwise directions. A single wide wall of a rectangular channel (AR = 3:1) is lined with V-shaped dimples. The channel Reynolds number ranges from 10,000–40,000. Detailed Nusselt number ratios are obtained using both a transient liquid crystal technique and a newly developed transient temperature sensitive paint (TSP) technique. Therefore, the TSP technique is not only validated against a baseline geometry (smooth channel), but it is also validated against a more established technique. Measurements indicate that the proposed V-shaped dimple design is a promising alternative to traditional ribs or hemispherical dimples. At lower Reynolds numbers, the V-shaped dimples display heat transfer and friction behavior similar to traditional dimples. However, as the Reynolds number increases to 30,000 and 40,000, secondary flows developed in the V-shaped concavities further enhance the heat transfer from the dimpled surface (similar to angled and V-shaped rib induced secondary flows). This additional enhancement is obtained with only a marginal increase in the pressure drop. Therefore, as the Reynolds number within the channel increases, the thermal performance also increases. While this trend has been confirmed with both the transient TSP and liquid crystal techniques, TSP is shown to have limited capabilities when acquiring highly resolved detailed heat transfer coefficient distributions.

Falling Film Evaporation of Water on Horizontal Configured Tube Bundles

2010 ◽  
Author(s):  
Wei Li ◽  
Xiaoyu Wu ◽  
Zhong Luo
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Enhancement ◽  
Inlet Temperature ◽  
Falling Film ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
Film Evaporation ◽  
Tube Bundles ◽  
Falling Film Evaporation

This paper reports an experimental study on falling film evaporation of water on 6-row horizontal configured tube bundles in a vacuum. Three types of configured tubes, Turbo-CAB-19fpi and −26fpi, Korodense, including smooth tubes for reference, were tested in a range of film Reynolds number from about 10 to 110. Results show that as the falling film Reynolds number increases, falling film evaporation goes from tubes partial dryout regime to fully wet regime; the mean heat transfer coefficients reach peak values in the transition point. Turbo-CAB tubes have the best heat transfer enhancement of falling film evaporation in both regimes, but Korodense tubes’ overall performances are better when tubes are fully wet. The inlet temperature of heating water has hardly any effects on the heat transfer, but the evaporation pressure has controversial effects. A correlation with errors within 10% was also developed to predict the heat transfer enhancement capacity.

Experimental Investigation on Heat Transfer and Pressure Drop of Nanodiamond-Engine Oil Nanofluid in a Microfin Tube

2010 ◽  
Author(s):  
M. A. Akhavan-Behabadi ◽  
M. Ghazvini ◽  
E. Rasouli
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Heat Transfer Enhancement ◽  
Convection Heat Transfer ◽  
Heat Fluxes ◽  
Engine Oil ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Nusselt Numbers

In this study, the effect of adding nanodiamond powder as an additive to engine oil on laminar flow heat transfer enhancement and pressure drop increasing is experimentally investigated. The plain and microfin tubes were used as the test sections and were heated by an electrical coil heater to produce constant heat fluxes. Thermal conductivity and heat capacity of nanofluids were measured for different volume fractions and temperatures. Convection heat transfer coefficients and Nusselt numbers of nanofluids were obtained for different nanoparticle concentrations as well as various Peclet and Reynolds numbers. Experimental results show the enhancement of heat transfer due to the nanoparticles presence. Furthermore, the effect of particle concentration on pressure drop was studied for different heat fluxes. Finally, the performance evaluation of both nanofluid and microfin tube from the point view of heat transfer enhancement and pressure drop increasing is done.

Channel Height Effect on Heat Transfer and Friction in a Dimpled Passage

1999 ◽  
Author(s):  
H. K. Moon ◽  
T. O’Connell ◽  
B. Glezer
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Enhancement ◽  
Channel Height ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
Entry Length ◽  
Heat Transfer Coefficients ◽  
Friction Factors ◽  
Smooth Channel

The heat transfer enhancement in cooling passages with dimpled (concavity imprinted) surface can be effective for use in heat exchangers and various hot section components (nozzle, blade, combustor liner, etc.), as it provides comparable heat transfer coefficients with considerably less pressure loss relative to protruding ribs. Heat transfer coefficients and friction factors were experimentally investigated in rectangular channels which had concavities (dimples) on one wall. The heat transfer coefficients were measured using a transient thermochromic liquid crystal technique. Relative channel heights (H/d) of 0.37, 0.74, 1.11 and 1.49 were investigated in a Reynolds number range from 12000 to 60000. The heat transfer enhancement (NuHD) on the dimpled wall was approximately constant at a value of 2.1 times that (Nusm) of a smooth channel over 0.37≤H/d≤1.49 in the thermally developed region. The heat transfer enhancement ratio Nu¯HD/Nusm was invariant with Reynolds number. The friction factors (f) in the aerodynamically fully developed region were consistently measured to be around 0.0412 (only 1.6 to 2.0 times that of a smooth channel). The aerodynamic entry length was comparable to that of a typical turbulent flow (Xo/Dh = 20), unlike the thermal entry length on dimpled surface which was much shorter (xo /Dh<9.8). The thermal performance Nu¯HD/Nusm/f/fsm1/3≅1.75 of dimpled surface was superior to that 1.16<Nu¯HD/Nusm/f/fsm1/3<1.60 of continuous ribs, demonstrating that the heat transfer enhancement with concavities can be achieved with a relatively low-pressure penalty. Neither the heat transfer coefficient distribution nor the friction factor exhibited a detectable effect of the channel height within the studied relative height range (0.37≤H/d≤1.49).

Boiling Heat Transfer Enhancement by Controllable Tailoring of the TPL

2010 ◽  
Author(s):  
Alexander Ustinov ◽  
Jovan Mitrovic
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Boiling Heat Transfer ◽  
Heat Fluxes ◽  
Thermal Engineering ◽  
Metallic Ions ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
Treatment Technology ◽  
High Heat Transfer

Novel surface treatment technology was developed in the University of Paderborn in partnership with MiCryon Technik GmbH, Quedlinburg, Germany. The technology allows creation of micro-pin structures, which enhance the boiling heat transfer up to 18 times in comparison with a smooth surface, and provide an independency of the surface superheat on the applied heat flux [1–6]. The micro pins as basic structure elements can be created with the diameters of 0.1 μm to 25 μm at pins density ranging up to 109 pins/cm2. Such pin structures are created by electro-deposition of metallic ions on the basic surface. The microstructure provides for the very first time in thermal engineering a possibility to adjust the available length of the three phase line (TPL) on demand, correspondingly tailoring the shape of a boiling curve. The TPL, formed by the micro pins piercing the vapor-liquid interface, acts as an extremely efficient heat sink, providing high heat transfer coefficients and the constancy of the wall superheat at heat fluxes up to 125 kW/m2. Present article delivers the summary on boiling experiments performed with the novel microstructure, and reveals the quantitative dependencies of the heat transfer enhancement rate on the TPL length, having the pressure and the liquid type as further parameters. A newly discovered phenomenon of the vapor bubble chains formation on microstructured surfaces is discussed as well. Experiments were conducted with the refrigerants R134a, R141b and the fluorocarbon liquid FC-3284 at pressures, ranging between 0.5 bar and 9 bar.

Secondary Flow and its Contribution to Heat Transfer Enhancement in a Blade Cooling Passage With Discrete Ribs

1996 ◽  
Author(s):  
Zhengjun Hu ◽  
Jiarui Shen
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Secondary Flow ◽  
Secondary Flows ◽  
Longitudinal Vortex ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
Blade Cooling ◽  
Discrete Ribs ◽  
Cooling Passage

A detailed map of heat transfer coefficients has been measured in a converging blade cooling passage with 45 deg. discrete ribs on two opposite walls for a range of engine representative Re of 10,000 ∼ 50,000. Flow visualization showed that there were four different types of secondary flow created by the discrete ribs: skewed boundary layer, secondary flow in front of the rib, secondary flow behind the rib, swirling longitudinal vortex flow and for large rib heights there were vortex streets. The origin of these secondary flows and their structure are discussed together with their contribution to the local enhancement of heat transfer. The results were used to understand the mechanism of heat transfer enhancement using secondary flow created by rib turbulators and from this to develop new design methods for improved enhanced heat transfer.

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