Individual Row Heat Transfer in a Crossflow In-Line Tube Bank

1964 ◽  
Vol 86 (2) ◽  
pp. 143-148 ◽  
Author(s):  
C. P. Welch ◽  
H. N. Fairchild
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Flow ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Tube Bank ◽  
Number Range ◽  
Heat Transfer Coefficients ◽  
Reynolds Number Range ◽  
Tube Banks

Individual row heat-transfer coefficients are presented for air flowing across 10-row in-line tube banks at close back spacings with heat flow from air to tube. The Reynolds number range covered is approximately 1000 to 20,000 with heat fluxes of 640 Btu/hr-sq ft to 12,500 Btu/hr-sq ft. The effect of both tube row number and Reynolds number is shown. These effects are different for tangent (tubes touching in direction of airflow) and nontangent tubes.

Heat Transfer to Mercury Flowing In-Line Through a Bundle of Circular Rods

1964 ◽  
Vol 86 (2) ◽  
pp. 180-186 ◽  
Author(s):  
M. W. Maresca ◽  
O. E. Dwyer
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Turbulent Flow ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Number Range ◽  
Heat Transfer Coefficients ◽  
Turbulent Flow Regime ◽  
Measuring Surface ◽  
Theoretical Predictions

Experimental results were obtained for the case of in-line flow of mercury through an unbaffled bundle of circular rods, and they were compared with theoretical predictions. The bundle consisted of 13 one-half-in-dia rods arranged in an equilateral triangular pattern, the pitch:diameter ratio being 1.750. Measurements were taken only on the central rod. Six different rods were tested. All rods in the bundle were electrically heated to provide equal and uniform heat fluxes throughout the bundle. The rods were of the Calrod type. The test rods had copper sheaths with fine thermocouples imbedded below the surface for measuring surface temperatures. Some rods were plated with a layer of nickel, followed by a very thin layer of copper, to provide “wetting” conditions, while others were chromeplated to provide “nonwetting” conditions. Heat-transfer coefficients were obtained under the following conditions: (a) Prandtl number, 0.02; (b) Reynolds number range, 7500 to 200,000; (c) Peclet number range, 150 to 4000; (d) “Wetting” versus “nonwetting”; (e) Both transition and fully established flow; (f) Variation of Lf/De ratio from 4 to 46. The precision of the results is estimated to be within 2 to 3 percent. An interesting finding, consistent with earlier predictions, was that the Nusselt number, under fully established turbulent-flow conditions, remained essentially constant, at the lower end of the turbulent flow regime, until a Reynolds number of about 40,000 was reached.

Prediction of Heat Transfer Coefficients in Gas Flow Normal to Finned and Smooth Tube Banks

1981 ◽  
Vol 103 (4) ◽  
pp. 705-714 ◽  
Author(s):  
J. C. Biery
Keyword(s):  
Heat Transfer ◽  
Gas Flow ◽  
Finned Tube ◽  
Smooth Tube ◽  
Transfer Coefficients ◽  
Tube Bank ◽  
Finned Tubes ◽  
Heat Transfer Coefficients ◽  
High Reynolds ◽  
Tube Banks

A new method is presented to predict heat transfer coefficients for gas flow normal to smooth and finned tube tanks with triangular pitch. A transformation from the actual tube bank to an equivalent equilateral triangular pitch infinite smooth tube bank (ETP-I-STB) is made. A function of Ch(Ch = NSTNPR2/3NRe0.4) versus (Xt D0)Δ, ratio of transverse pitch to tube diameter for the ETP-I-STB, was developed. The Ch for the equivalent ETP-I-STP then applies to the actual tube bank. The method works with circular finned tubes, smooth tubes, continuous finned tubes, and segmented finned tubes with any triangular pitch. Also, fair predictions were made for in-line tubes with high Reynolds numbers.

Heat Transfer Experiments of Mini-Tube Bank

2009 ◽  
Author(s):  
Yutaka Ebihara ◽  
Atsushi Katsuta ◽  
Yasuo Koizumi ◽  
Hiroyasu Ohtake
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Test Section ◽  
Square Lattice ◽  
Test Fluid ◽  
Wake Region ◽  
Transfer Coefficients ◽  
Tube Bank ◽  
Heat Transfer Coefficients ◽  
The Difference

Heat transfer and flow behavior in the mini rod bank were examined. The tubes are simulated with a 1 mm diameter nickel wire. The tube bank was composed of the 5×5 square-lattice array and the 5×5 staggered array. The tube banks were arranged in the flow channel of 30 mm wide or 15 mm wide, 15 mm high and 480 mm long. Water was used as the test fluid. A flow rate was varied in the range of the Reynolds number Re = uD/ν of 1 ∼ 800, where D is the tube diameter. The approaching velocity of fluid in the channel was in the range of 0.0036 m/s ∼ 0.68 m/s. Experiments were performed at atmospheric pressure. The measured heat transfer coefficients of the rows after the second row were lower than those of the first row and the difference between those increased as the Reynolds number was increased. The difference turned to decrease around Reynolds number = 50 in the 15 mm wide test section experiments of the square–lattice array and around Reynolds number = 200 in the 30 mm wide test section experiments of the staggered array. The heat transfer coefficients reached back to the first row value around Re = 400 in the former experiments. It was confirmed through the present results and the previous results that the heat transfer in the rear rows is deteriorated by the flow stagnation in the wake region of the preceding rod and the deterioration is recovered as the Reynolds number is increased since the wake region becomes disturbed.

Flow and Heat Transfer of Micro-Tube Bank

2010 ◽  
Author(s):  
Yasuo Koizumi ◽  
Atsushi Katsuta ◽  
Hiroyasu Ohtake
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Transfer Coefficients ◽  
Tube Bank ◽  
Heat Transfer Coefficients ◽  
Line Array ◽  
The Difference ◽  
The Heat Transfer Coefficient

Heat transfer and flow behavior in a mini-tube bank was examined. The tube bank was simulated with wires of 1 mm diameter. The wires were arranged in the 5×5 in-line array and the 5×5 staggered array with the arranging pitch = 3. Experiments were performed in the range of the tube Reynolds number Re = 4 ∼ 3,500. Numerical analyses were also performed with the commercial CFD code of STAR-CD. The heat transfer coefficient of the tube of the first row was well expressed with the existing heat transfer correlations. In the case of the in-line array, unlike usual sized tube banks, the measured heat transfer coefficients of the tubes after the second row were lower than those of the first row and the difference between those increased as the Reynolds number was increased. At approximately Reynolds number ≃ 50, the difference turned to decrease; the heat transfer coefficients initiate to recover to the first row value. Then, the heat transfer coefficient in the rear row became larger at approximately Re ≃ 1,000 than that of the first row. In the case of the staggered array, the decrease in the heat transfer coefficient in the rear row was smaller than that in the case of the in-line array. The recovery of the heat transfer coefficient to the first row value started at a little bit lower Reynolds number and it exceeded the first row value at approximately Re ≃ 700. The flow visualization results and also the STAR-CD analytical results indicated that when the Reynolds number was low, the wake region of the preceding tube was stagnant. This flow stagnation caused the heat transfer deterioration in the front part of the rear tube, which resulted in the lower heat transfer coefficient of the rear tube than that of the first row. As the Reynolds number was increased, the flow state in the wake region changed from the stagnant condition to the more disturbed condition by periodical shedding of the Karman vortex. This change caused the recovery of the heat transfer in the front region of the rear tube, which resulted in the recovery of the heat transfer coefficient of the rear tube.

Single-Phase Heat Transfer of R245fa + Lubricant Oil Mixtures Inside Horizontal Smooth and Microfin Tubes

2019 ◽  
Vol 27 (02) ◽  
pp. 1950020
Author(s):  
Yufei Liu ◽  
Kazuhide Watanabe ◽  
Daisuke Jige ◽  
Norihiro Inoue
Keyword(s):  
Heat Transfer ◽  
Single Phase ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Number Range ◽  
Heat Transfer Coefficients ◽  
Lubricant Oil ◽  
Oil Mixtures ◽  
Oil Concentration ◽  
Microfin Tubes

The effect of lubricant oil on the single-phase heat transfer of R245fa inside horizontal smooth and microfin tubes was experimentally investigated. Tests were conducted using a horizontal smooth tube with an inner diameter of 8.32[Formula: see text]mm and two microfin tubes with equivalent diameters of 8.9 and 8.7[Formula: see text]mm, fin height of 0.12 and 0.18[Formula: see text]mm, and number of fins of 65 and 85, respectively. The heat transfer coefficients were measured for pure R245fa and R245fa + lubricant oil mixture in the Reynolds number range of 2000–10000, heat fluxes of 5 and 10[Formula: see text]kWm[Formula: see text], and refrigerant temperatures of 30∘C and 45∘C at the test section inlet. Oil concentration was varied at 1, 2 and 5[Formula: see text]wt.%. The results showed that the heat transfer of pure R245fa agreed well with previous correlations. However, the heat transfer coefficients of the R245fa + lubricant oil mixtures were lower than those of the pure R245fa, and decreased with an increase in oil concentration for both smooth and microfin tubes. The reduction in heat transfer was more marked for the HF tube than for the smooth and LF tubes. For the HF tube, the decrease in heat transfer was apparently more pronounced at higher oil concentrations from 2 to 5[Formula: see text]wt.% owing to immiscibility between the oil and refrigerant.

Study on Heat Transfer and Flow Analysis of 5×5 and 5×1 Mini-Tube Bank of Micro Heat Exchanger

2007 ◽  
Author(s):  
M. Arai ◽  
Y. Koizumi ◽  
H. Ohtake
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Flow State ◽  
Wake Region ◽  
Transfer Coefficients ◽  
Tube Bank ◽  
Heat Transfer Coefficients ◽  
The Heat Transfer Coefficient

Heat transfer and flow behavior in the mini rod bank were examined. The tube bank was simulated with 5 wires of 1 mm diameter. The wires were arranged on the center line of the flow channel of 30 mm wide, 15 mm high and 300 mm long. The pitch between wires were varied from 1.5 mm to 9 mm. Experiments were performed in the range of the rod Re = 1 ∼ 400, i.e. the flow velocity in the channel was in the range of 0.0036 m/s ∼ 0.34 m/s. The measured heat transfer coefficients of the first row were a little bit higher than, rather close to, the predicted values by the correlations. The heat transfer coefficients after the second row were lower than those of the first row. The difference between those increased as the Reynolds number was increased. Around Reynolds number = 100, the difference turned to decrease. After the occurrence of the heat transfer coefficient recovery in the rows after the second row, the deeper the row was, the larger the heat transfer coefficient was. The flow visualization results and the analytical results by the STAR-CD code indicated that when the Reynolds number was low, the wake region of the preceding rod was stagnant. This flow stagnation caused the heat transfer coefficient deterioration around the stagnation point of the rear rod. As the Reynolds number was increased, the flow state in the wake region changed from the stagnant condition to the more disturbed condition by periodical shedding of the Karman vortex from the preceding rod. This agitation of the wake region by the vortices caused the recovery of the deteriorated heat transfer coefficients. The deeper the row was, the more disturbed the wake flow state was. The measured average heat transfer coefficients of the tube bank agreed well with the analytical results by the STAR-CD code. The measured and the analyzed results were close to the predicted values by correlations.

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.

scholarly journals Pool Boiling Heat Transfer Coefficients in Mixtures of Water and Glycerin

Processes ◽  
2021 ◽  
Vol 9 (5) ◽  
pp. 830
Author(s):  
Viktor Vajc ◽  
Radek Šulc ◽  
Martin Dostál
Keyword(s):  
Heat Transfer ◽  
Dynamic Method ◽  
Water Mass ◽  
Heat Fluxes ◽  
Static Method ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Mean Relative Error ◽  
Mixture Effects ◽  
Mass Fractions

Heat transfer coefficients were investigated for saturated nucleate pool boiling of binary mixtures of water and glycerin at atmospheric pressure in a wide range of concentrations and heat fluxes. Mixtures with water mass fractions from 100% to 40% were boiled on a horizontal flat copper surface at heat fluxes from about 25 up to 270kWm−2. Experiments were carried out by static and dynamic method of measurement. Results of the static method show that the impact of mixture effects on heat transfer coefficient cannot be neglected and ideal heat transfer coefficient has to be corrected for all investigated concentrations and heat fluxes. Experimental data are correlated with the empirical correlation α=0.59q0.714+0.130ωw with mean relative error of 6%. Taking mixture effects into account, data are also successfully correlated with the combination of Stephan and Abdelsalam (1980) and Schlünder (1982) correlations with mean relative error of about 15%. Recommended coefficients of Schlünder correlation C0=1 and βL=2×10−4ms−1 were found to be acceptable for all investigated mixtures. The dynamic method was developed for fast measurement of heat transfer coefficients at continuous change of composition of boiling mixture. The dynamic method was tested for water–glycerin mixtures with water mass fractions from 70% down to 35%. Results of the dynamic method were found to be comparable with the static method. For water–glycerin mixtures with higher water mass fractions, precise temperature measurements are needed.

scholarly journals Systematic heat transfer measurements in highly viscous binary fluids

2021 ◽  
Author(s):  
Ann-Christin Fleer ◽  
Markus Richter ◽  
Roland Span
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Volatile Component ◽  
Test Tube ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Low Viscosity ◽  
The Heat Transfer Coefficient

AbstractInvestigations of flow boiling in highly viscous fluids show that heat transfer mechanisms in such fluids are different from those in fluids of low viscosity like refrigerants or water. To gain a better understanding, a modified standard apparatus was developed; it was specifically designed for fluids of high viscosity up to 1000 Pa∙s and enables heat transfer measurements with a single horizontal test tube over a wide range of heat fluxes. Here, we present measurements of the heat transfer coefficient at pool boiling conditions in highly viscous binary mixtures of three different polydimethylsiloxanes (PDMS) and n-pentane, which is the volatile component in the mixture. Systematic measurements were carried out to investigate pool boiling in mixtures with a focus on the temperature, the viscosity of the non-volatile component and the fraction of the volatile component on the heat transfer coefficient. Furthermore, copper test tubes with polished and sanded surfaces were used to evaluate the influence of the surface structure on the heat transfer coefficient. The results show that viscosity and composition of the mixture have the strongest effect on the heat transfer coefficient in highly viscous mixtures, whereby the viscosity of the mixture depends on the base viscosity of the used PDMS, on the concentration of n-pentane in the mixture, and on the temperature. For nucleate boiling, the influence of the surface structure of the test tube is less pronounced than observed in boiling experiments with pure fluids of low viscosity, but the relative enhancement of the heat transfer coefficient is still significant. In particular for mixtures with high concentrations of the volatile component and at high pool temperature, heat transfer coefficients increase with heat flux until they reach a maximum. At further increased heat fluxes the heat transfer coefficients decrease again. Observed temperature differences between heating surface and pool are much larger than for boiling fluids with low viscosity. Temperature differences up to 137 K (for a mixture containing 5% n-pentane by mass at a heat flux of 13.6 kW/m2) were measured.

The Effects of Nucleate Boiling Versus Film Boiling on Heat Transfer in Power Boiler Tubes

1962 ◽  
Vol 84 (4) ◽  
pp. 365-371 ◽  
Author(s):  
H. S. Swenson ◽  
J. R. Carver ◽  
G. Szoeke
Keyword(s):  
Heat Transfer ◽  
Nucleate Boiling ◽  
Steel Tube ◽  
Heat Fluxes ◽  
Inside Surface ◽  
Film Boiling ◽  
Stainless Steel Tube ◽  
Transfer Coefficients ◽  
Steam Quality ◽  
Heat Transfer Coefficients

In large, subcritical pressure, once-through power boilers heat is transferred to steam and water mixtures ranging in steam quality from zero per cent at the bottom of the furnace to 100 per cent at the top. In order to provide design information for this type of boiler, heat-transfer coefficients for forced convection film boiling were determined for water at 3000 psia flowing upward in a vertical stainless-steel tube, AISI Type 304, having an inside diameter of 0.408 inches and a heated length of 6 feet. Heat fluxes ranged between 90,000 and 180,000 Btu/hr-sq ft and were obtained by electrical resistance heating of the tube. The operation of the experimental equipment was controlled so that nucleate boiling, transition boiling, and stable film boiling occurred simultaneously in different zones of the tube. The film boiling data were correlated with a modified form of the equation Nu = a a(Re)m(Pr)n using steam properties evaluated at inside surface temperature. Results of a second series of heat-transfer tests with tubes having a helical rib on the inside surface showed that nucleate boiling could be maintained to much higher steam qualities with that type of tube than with a smooth-bore tube.

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