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.

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 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.

An Experimental Investigation of the Rib Surface-Averaged Heat Transfer Coefficient in a Rib-Roughened Square Passage

1997 ◽  
Vol 119 (2) ◽  
pp. 381-389 ◽  
Author(s):  
M. E. Taslim ◽  
C. M. Wadsworth
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Thermal Performance ◽  
Blockage Ratio ◽  
Transfer Coefficients ◽  
Height Ratio ◽  
Average Heat ◽  
Heat Transfer Coefficients ◽  
The Heat Transfer Coefficient

Turbine blade cooling, a common practice in modern aircraft engines, is accomplished, among other methods, by passing the cooling air through an often serpentine passage in the core of the blade. Furthermore, to enhance the heat transfer coefficient, these passages are roughened with rib-shaped turbulence promoters (turbulators). Considerable data are available on the heat transfer coefficient on the passage surface between the ribs. However, the heat transfer coefficients on the surface of the ribs themselves have not been investigated to the same extent. In small aircraft engines with small cooling passages and relatively large ribs, the rib surfaces comprise a large portion of the passage heat transfer area. Therefore, an accurate account of the heat transfer coefficient on the rib surfaces is critical in the overall design of the blade cooling system. The objective of this experimental investigation was to conduct a series of 13 tests to measure the rib surface-averaged heat transfer coefficient, hrib, in a square duct roughened with staggered 90 deg ribs. To investigate the effects that blockage ratio, e/Dh and pitch-to-height ratio, S/e, have on hrib and passage friction factor, three rib geometries corresponding to blockage ratios of 0.133, 0.167, and 0.25 were tested for pitch-to-height ratios of 5, 7, 8.5, and 10. Comparisons were made between the rib average heat transfer coefficient and that on the wall surface between two ribs, hfloor, reported previously. Heat transfer coefficients of the upstream-most rib and that of a typical rib located in the middle of the rib-roughened region of the passage wall were also compared. It is concluded that: 1 The rib average heat transfer coefficient is much higher than that for the area between the ribs; 2 similar to the heat transfer coefficient on the surface between the ribs, the average rib heat transfer coefficient increases with the blockage ratio; 3 a pitch-to-height ratios of 8.5 consistently produced the highest rib average heat transfer coefficients amongst all tested; 4 under otherwise identical conditions, ribs in upstream-most position produced lower heat transfer coefficients than the midchannel positions, 5 the upstream-most rib average heat transfer coefficients decreased with the blockage ratio; and 6 thermal performance decreased with increased blockage ratio. While a pitch-to-height ratio of 8.5 and 10 had the highest thermal performance for the smallest rib geometry, thermal performance of high blockage ribs did not change significantly with the pitch-to-height ratio.

Preliminary studies of the loss of heat from leaves under conditions of free and forced convection

1965 ◽  
Vol 13 (2) ◽  
pp. 153 ◽  
Author(s):  
GI Pearman
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Wind Tunnel ◽  
Transfer Coefficient ◽  
Convective Heat Transfer ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Free And Forced Convection ◽  
Wind Velocities ◽  
The Heat Transfer Coefficient

An account is given of techniques and methods used in measurement of convective heat transfer from leaves of the succulent Carpobrotus. Heat transfer was studied under still air conditions and in wind (in a specially constructed wind-tunnel) up to velocities of 300 cm sec-1. A correlation was demonstrated between experimentally obtained values of heat transfer coefficients and theoretical values calculated from empirical formulae. At wind velocities of 300 cm sec-1 the heat transfer coefficient for Carpobrotus was increased to seven times its value still air.

Natural Heat Transfer Coefficients of Chicken Drum Shaped Bodies

2005 ◽  
Vol 1 (3) ◽  
Author(s):  
Michael Ngadi ◽  
Julian N. Ikediala
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Correlation Equation ◽  
Deep Fat Frying ◽  
Heat Transfer Correlation ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Increasing Temperature ◽  
The Heat Transfer Coefficient

Average heat transfer coefficients of chicken drum shaped bodies were estimated using aluminum chicken drum shaped models. Three model drum sizes namely small, medium and large, and three frying oil viscosities for three temperature differences were used. Estimated heat transfer coefficients were in the range from 67 to 163 W/m²K. Increasing temperature difference increased heat transfer coefficient. Conversely, increasing the size of the chicken drum model bodies and oil viscosities decreased the heat transfer coefficient. A heat transfer correlation equation between average Nu and Ra was derived. The methodology developed in this study could be used to estimate heat transfer coefficients of chicken drum during deep-fat frying.

Study on Heat Transfer and Flow Behavior of Mini-Tube Bank for Micro Heat Exchanger

2006 ◽  
Author(s):  
Y. Koizumi ◽  
T. Okuyama ◽  
H. Ohtake
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Flow Behavior ◽  
Flow State ◽  
Wake Region ◽  
Tube Bank ◽  
Disturbed Condition ◽  
The Heat Transfer Coefficient

Heat transfer and flow behavior in the mini tube bank were examined. The tube bank was composed of 1 mm diameter nickel wires and a 30 mm wide × 15 mm high flow channel. Experiments were performed in the range of the rod Re = 5 ~ 430 by using water. Numerical analyses were also conducted with the commercial CFD code STAR-CD. The heat transfer coefficient after the second row was lower than first row's one. The flow visualization results indicated that the wake region was stagnant when the Reynolds number was low. This flow stagnation seemed to cause the heat transfer coefficient deterioration in the tube bank. As the Reynolds number was increased, the flow state in the wake region gradually changed from the stagnant condition to the more disturbed condition. The deeper the row was, the more disturbed the wake was. The heat transfer coefficient began to recover to the first row value at certain Reynolds number. The recovery started from the most downstream row; fifth row in the present experiments and was propagated to the upstream row. The Reynolds number when the recovery was initiated decreased as the spacing between rods was increased. The analytical results of the STAR-CD code supported the experimental results. When the wake was stagnant, the heat transfer coefficient distribution around the rear rod, i.e. the rod in the wake, showed a large dip in the front region of the rod. It was considered that this dip caused the heat transfer coefficient decrease after the second row observed in the experiments.

Heat Flux Reduction From Film Cooling and Correlation of Heat Transfer Coefficients From Thermographic Measurements at Engine Like Conditions

2002 ◽  
Author(s):  
S. Baldauf ◽  
M. Scheurlen ◽  
A. Schulz ◽  
S. Wittig
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Film Cooling ◽  
Transfer Coefficients ◽  
Average Heat ◽  
Heat Transfer Coefficients ◽  
New Correlation ◽  
The Heat Transfer Coefficient

Heat transfer coefficients and the resulting heat flux reduction due to film cooling on a flat plate downstream a row of cylindrical holes are investigated. Highly resolved two dimensional heat transfer coefficient distributions were measured by means of infrared thermography and carefully corrected for local internal testplate conduction and radiation effects [1]. These locally acquired data are processed to lateral average heat transfer coefficients for a quantitative assessment. A wide range variation of the flow parameters blowing rate and density ratio as well as the geometrical parameters streamwise ejection angle and hole spacing is examined. The effects of these dominating parameters on the heat transfer augmentation from film cooling are discussed and interpreted with the help of highly resolved surface results of effectiveness and heat transfer coefficients presented earlier [2]. A new method of evaluating the heat flux reduction from film cooling is presented. From a combination of the lateral average of both the adiabatic effectiveness and the heat transfer coefficient, the lateral average heat flux reduction is processed according to the new method. The discussion of the total effect of film cooling by means of the heat flux reduction reveals important characteristics and constraints of discrete hole ejection. The complete heat transfer data of all measurements are used as basis for a new correlation of lateral average heat transfer coefficients. This correlation combines the effects of all the dominating parameters. It yields a prediction of the heat transfer coefficient from the ejection position to far downstream, including effects of extreme blowing angles and hole spacing. The new correlation has a modular structure to allow for future inclusion of additional parameters. Together with the correlation of the adiabatic effectiveness it provides an immediate determination of the streamwise heat flux reduction distribution of cylindrical hole film cooling configurations.

Performances of falling film evaporators on whole milk and a comparison with performance on skim milk

1997 ◽  
Vol 64 (1) ◽  
pp. 57-67 ◽  
Author(s):  
R. SELWYN JEBSON ◽  
HONG CHEN
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Skim Milk ◽  
Falling Film ◽  
Transfer Coefficients ◽  
Liquid Loading ◽  
Heat Transfer Coefficients ◽  
Whole Milk ◽  
The Heat Transfer Coefficient

The performances of falling film evaporators used in the New Zealand dairy industry for concentrating whole milk were evaluated by determining kg steam used/kg water evaporated, and the heat transfer coefficient of each pass in the evaporators. A specially written computer program was used to calculate the results. The heat transfer coefficients varied from 0·3 to 3·0 kW/m2K, and the steam consumption from 0·10 to 0·39 kg steam/kg evaporation, depending on the number of effects. The steam consumptions for whole and skim milk were similar. The momentum of the vapours passing down the tubes, the temperature difference across the tubes, the viscosity of the feed and the liquid loading were found to be the main factors controlling the heat transfer coefficient. A correlation between the heat transfer coefficient and these factors is presented, and other factors likely to have an influence on the performance are discussed. The correlation is compared with that obtained for skim milk.

scholarly journals Endwall Heat Transfer in a Vane Cascade Passage and in a Curved Duct

1989 ◽  
Author(s):  
M. T. Boyle ◽  
K. V. Hoose
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Suction Side ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Steel Strips ◽  
Surface Heat Transfer Coefficient ◽  
Duct Geometry

Measurements of endwall heat transfer coefficient have been made for flow through a vane cascade passage and a similarly shaped duct. The purpose of this work is to evaluate the usefulness of the duct shape for modelling cascade endwall heat transfer. The Reynolds number for the cascade experiment is 5.4 × 105 based on chord. For the duct geometry the inlet velocity is adjusted in order to match the Reynolds number based on the pitch dimension. Thin stainless steel strips mounted on the endwall make up a large flat resistance heater. The temperature distribution over the heater surface is measured with 156 resistance temperature sensors. Surface heat transfer coefficient is obtained in the vicinity of each sensor by a local energy balance. The results are presented so as to show clearly the effect of secondary flow on endwall heat transfer. Except in the entrance plane region, the qualities of the cascade endwall Stanton number distribution compare well with the duct endwall measurements. The duct endwall heat transfer coefficients are everywhere greater than for the cascade passage endwall. The effect of a counter-clockwise rotating vortex in the suction side corner is shown clearly for both geometries.

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.

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