Experimental Research on the Similarity of Annular Flow Models and Correlations for the Condensation of R134a at High Mass Flux Inside Vertical and Horizontal Tubes

2009 ◽  
Author(s):  
Ahmet Selim Dalkilic ◽  
Suriyan Laohalertdecha ◽  
Somchai Wongwises
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Flow Rate ◽  
Annular Flow ◽  
Cooling Water ◽  
Transfer Coefficients ◽  
Flow Models ◽  
Heat Transfer Coefficients ◽  
Horizontal Tubes ◽  
Condensation Heat Transfer Coefficient

This paper presents an experimental investigation on the usage of annular flow models and correlations valid especially for horizontal tubes to the downward annular flow in the vertical test section. Condensation experiments are performed at the mass flux of 340 kg m−2s−1 during co-current downward condensation of R134a in a vertical smooth copper tube having inner diameter of 8.1 mm and a length of 500 mm. The saturation temperatures are between 40–50°C, heat fluxes are between 12.8 and 45.36 kW m−2, average qualities are ranging between 0.76–0.95. The experimental apparatus are designed to capable of changing the different operating parameters such as mass flow rate, condensation temperature of refrigerant, cooling water temperature and mass flow rate of cooling water etc and investigate their effect on heat transfer coefficients and pressure drops. Considering Chen et al.’s annular flow theory on the heat transfer coefficients that are independent from tube orientation as long as annular flow exists along the tube length, the average predicted condensation heat transfer coefficient of the refrigerant is determined by means of the annular flow model of Kosky and Staub, and Von Karman universal velocity distribution correlations using interfacial shear stress proposed for horizontal and vertical tubes separately. Some well-known annular flow correlations generally used for horizontal tubes in the literature were compared with experimental condensation heat transfer coefficient obtained from vertical tube data during annular flow conditions in the test section.

Experimental Study on the Flow Regime Identification in the Case of Co-Current Condensation of R134a in a Vertical Smooth Tube

2010 ◽  
Author(s):  
Ahmet Selim Dalkilic ◽  
Somchai Wongwises
Keyword(s):  
Heat Transfer ◽  
Flow Regime ◽  
Flow Rate ◽  
Annular Flow ◽  
Cooling Water ◽  
Test Tube ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Flow Regime Identification ◽  
Flow Regime Maps

The present study investigates an intensive comparison of flow regime maps for the verification of annular condensation flow of R134a checked by sight glasses at the inlet and outlet sections of a vertical smooth copper tube having inner diameter of 8.1 mm and a length of 500 mm. R134a and water are used as working fluids in the tube side and annular side of a double tube heat exchanger, respectively. The experimental apparatus are designed to capable of changing the different operating parameters such as mass flow rate, condensation temperature of refrigerant, cooling water temperature and mass flow rate of cooling water etc. and investigate their effect on heat transfer coefficients and pressure drops. Condensation experiments are performed at the mass flux of 456 kg m−2s−1, the saturation temperature is around 40°C, heat fluxes and average qualities are between 16.16–50.89 kW m−2 and 0.81–0.93 respectively. Considering Chen et al.’s annular flow theory on the heat transfer coefficients that are independent from tube orientation as long as annular flow exists along the tube length, experimental data belong to annular flow inside the test tube are plotted on the various flow regime maps and used in the flow regime identification correlations proposed for two-phase flow in horizontal and vertical tubes separately. In spite of their different operating conditions, Barnea et al., Hewitt and Robertson, Baker, Thome, Kattan et al., Chen et al.’s flow regime maps and Taitel and Dukler’s, Dobson’s, Akbar et al.’s, Breber et al.’s, Cavallini et al.’s, Soliman’s flow pattern correlations from literature are found to be predictive for the annular flow conditions in the test tube.

Experimental Apparatus for Measuring in Tube Condensation Heat Transfer Coefficient and Pressure Drop Using Smooth and Micro-Fin Tubes for HFC Refrigerants

2008 ◽  
Author(s):  
Pradeep A. Patil ◽  
S. N. Sapali
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Condensation Heat Transfer ◽  
Test Facility ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Fin Tube ◽  
Condensation Heat Transfer Coefficient

An experimental test facility is designed and built to calculate condensation heat transfer coefficients and pressure drops for HFC-134a, R-404A, R-407C, R-507A in a smooth and micro-fin tube. The main objective of the experimentation is to investigate the enhancement in condensation heat transfer coefficient and increase in pressure drop using micro-fin tube for different condensing temperatures and further to develop an empirical correlation for heat transfer coefficient and pressure drop, which takes into account the micro-fin tube geometry, variation of condensing temperature and temperature difference (difference between condensing temperature and average temperature of cooling medium). The experimental setup has a facility to vary the different operating parameters such as condensing temperature, cooling water temperature, flow rate of refrigerant and cooling water etc and study their effect on heat transfer coefficients and pressure drops. The hermetically sealed reciprocating compressor is used in the system, thus the effect of lubricating oil on the heat transfer coefficient is taken in to account. This paper reports the detailed description of design and development of the test apparatus, control devices, instrumentation, and the experimental procedure. It also covers the comparative study of experimental apparatus with the existing one from the available literature survey. The condensation and pressure drop of HFC-134a in a smooth tube are measured and obtained the values of condensation heat transfer coefficients for different mass flux and condensing temperatures using modified Wilson plot technique with correlation coefficient above 0.9. The condensation heat transfer coefficient and pressure drop increases with increasing mass flux and decreases with increasing condensing temperature. The results are compared with existing available correlations for validation of test facility. The experimental data points have good association with available correlations except Cavallini-Zecchin Correlation.

Influence of Inlet Mass Flow Rate on Heat Transfer of Supercritical Liquefied Natural Gas in Horizontal Tubes

2014 ◽  
Vol 960-961 ◽  
pp. 433-437 ◽  
Author(s):  
Hai Yu Meng ◽  
Shu Zhong Wang ◽  
Lu Zhou ◽  
Zhi Qiang Wu ◽  
Jun Zhao ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Surface Heat ◽  
Bulk Temperature ◽  
Transfer Coefficients ◽  
Surface Heat Transfer ◽  
Heat Transfer Coefficients ◽  
Horizontal Tubes

The submerged combustion vaporizer (SCV) is a new kind of vaporizer for liquefied natural gas (LNG). In this paper, a numerical study has been carried out to investigate the heat transfer characteristics of supercritical LNG in horizontal tubes. The thermo-physical properties of supercritical LNG were used for this study, and the influence of inlet LNG mass flow rate on heat transfer was investigated. Numerical results showed that the LNG flow in horizontal tubes included two stages. In the first stage, the surface heat transfer coefficients increased significantly with the increase of the fluid bulk temperature and reached a maximum value when the fluid bulk temperature equaled the pseudo-critical point . After the maximum, the surface heat transfer coefficients fell rapidly with the increase of the fluid bulk temperature. With increasing the inlet LNG mass flow rate, the surface heat transfer coefficients increased due to the increased fluid velocity in horizontal tubes.

Forced Convection Condensation of Steam on a Small Bank of Horizontal Tubes

1992 ◽  
Vol 114 (3) ◽  
pp. 708-713 ◽  
Author(s):  
A. G. Michael ◽  
W. C. Lee ◽  
J. W. Rose
Keyword(s):  
Heat Transfer ◽  
Water Flow Rate ◽  
Cooling Water ◽  
Transfer Coefficients ◽  
Cross Sectional ◽  
Small Bank ◽  
Heat Transfer Coefficients ◽  
Horizontal Tubes ◽  
Cooling Water Flow Rate ◽  
In Series

Heat transfer measurements are reported for condensation of steam flowing vertically downward over a small bank of staggered horizontal tubes having 10 rows with 4 and 3 tubes per row. The tubes in each row were connected in series and separately supplied with cooling water. The cooling water flow rate and temperature rise were measured individually for each row and tube-wall temperatures were measured on selected tubes. Data were obtained at slightly above atmospheric pressure and the range of steam approach velocity (based on the cross-sectional area of the duct) was 6 to 23 m/s. A general trend of decreasing heat transfer coefficient with depth in the bank was found. However, superimposed on this was a “saw-tooth” effect with the three-tube rows having higher coefficients than the rows with four tubes. The amplitude of the coefficient variation decreased down the bank and was also less pronounced at lower vapor velocities. When compared with other experimental data for condensation of steam on small staggered banks, the present data exhibit somewhat higher vapor-side, heat transfer coefficients.

Detailed Flow Analyses Through Crossover Holes Between Two Adjacent Rib-Roughened Cooling Channels and the Resulting Impingement Heat Transfer

2018 ◽  
Author(s):  
Fei Xue ◽  
Mohammad E. Taslim
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Mass Flow ◽  
Flow Rate ◽  
Reynolds Numbers ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Impingement Heat Transfer

Impingement cooling in airfoils cooling cavities, solely or combined with film and convective cooling, is a common practice in gas turbines. Depending on the cooling cavity design, the mass flow rate through individual crossover holes could vary significantly in the flow direction thus creating jets of different strengths in the target cavity. This jet flow variation, in turn, creates an impingement heat transfer coefficient variation along the channel. A test section, simulating two adjacent cooling cavities on the trailing side of an airfoil, is made up of two channels with trapezoidal cross-sectional areas. On the partition wall between the two channels, eleven crossover holes create the jets. Two distinct exit flow arrangements are investigated — a) jets, after interaction with the target surface, are turned towards the target channel exit axially and b) jets are exited from a row of racetrack-shaped slots along the target channel. Flow measurements are reported for individual holes and heat transfer coefficients on the eleven target walls downstream the jets are measured using the steady-state liquid crystal thermography technique. Smooth as well as rib-roughened target surfaces with four rib geometries (0°,45°, 90° and 135° rib angles) are tested. Correlations are developed for mass flow rate through each crossover hole for cases with different number of crossover holes, based on the pressure drop across the holes. Heat transfer coefficient variations along the target channel for all rib geometries and flow conditions are reported for a range of 5000 to 50000 local jet Reynolds numbers. Major conclusions of this study are: 1) A correlation is developed to successfully predict the mass flow rates through individual crossover holes for geometries with six to eleven crossover holes, based on the pressure drop across the holes, 2) impingement heat transfer coefficient correlates well with the local jet Reynolds number for both exit flow arrangements, and 3) the case of axial flow in the target channel exiting from the channel end, at higher jet Reynolds numbers, produced higher heat transfer coefficients than those in the case of flow exiting through a row of slots along the target channel opposite to the crossover holes.

Condensation of Different Refrigerants on the Outside Surface of Smooth Cylindrical Tubes

2017 ◽  
Author(s):  
Tailian Chen
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Saturation Temperature ◽  
Cylindrical Tube ◽  
Condensation Heat Transfer ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Cylindrical Tubes ◽  
Condensation Heat Transfer Coefficient

The Nusselt model of condensation provides the fundamental theory in predicting the heat transfer during the condensation process. Widely verified, its significance lies in the fact that it has been used as the baseline in evaluating the heat transfer enhancement of the condensation and often used as the basis of validating the test rig for multiphase heat transfer. The aim of this work is to re-examine the correlation for condensation on smooth cylindrical tubes. The heat transfer coefficients during condensation of four different refrigerants R123, R245fa, R134a, and R22 on the outside surface of a smooth cylindrical tube were individually measured at large degrees of subcooling, up to 25 K. The experiments were conducted at a fixed saturation temperature of 36.1 °C. Measurements showed that, for each refrigerant, the condensation heat transfer coefficient decreases with increasing degree of subcooling. At a given degree of subcooling, a higher-pressure refrigerant corresponds to a higher condensation heat transfer coefficient, with the exception that the condensation heat transfer coefficients of R134a and R245fa are nearly the same in spite of much higher pressure of the former. The predictions from the Nusselt theory for condensation heat transfer over cylinder tubes match very well with the measurements, where the predictions are 3–9% lower than the measurements for all refrigerants within the range of degree of subcooling considered in this work. A modified constant in the Nusselt number provides more accurate prediction of condensation on smooth cylindrical tubes.

Spatial Variation of Heat Transfer to Pistons and Liners of Some Medium Speed Diesel Engines

1970 ◽  
Vol 185 (1) ◽  
pp. 203-218 ◽  
Author(s):  
W. J. Seale ◽  
D. H. C. Taylor
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Cooling Water ◽  
Radial Variation ◽  
Transfer Coefficients ◽  
Air Concentration ◽  
Maximum Heat ◽  
Heat Transfer Coefficients ◽  
Maximum Heat Transfer

Heat transfer coefficients have been measured on the gas side of pistons and liners, the water side of liners, and the oil side of pistons. A significant radial variation in heat transfer across the piston crown has been found. The position of the maximum heat transfer coefficient appears to be coincident with the maximum air concentration, or the position the tips of the fuel sprays have reached at the time of ignition, and the radial variation of heat transfer is possibly related to the amount of fuel burnt at each radius. For four-stroke engines, equations are presented to describe this variation. Heat transfer coefficients at the exposed section of the liner have been found to be similar to the values at the outer edge of the piston. Heat transfer between piston undercrown and cooling oil has been measured for various types of cooling arrangement and, for jet cooling, an expression has been suggested for the heat transfer coefficient. Equations have also been derived to enable coefficients to be predicted for heat transfer from liner to cooling water.

Analysis of Annular and Stratified Flows for Vapor Condensation Heat Transfer in Horizontal Tubes

2013 ◽  
Vol 753-755 ◽  
pp. 2717-2721
Author(s):  
Jun Xia Zhang ◽  
Li Wang ◽  
Jian Wen Wang
Keyword(s):  
Heat Transfer ◽  
Liquid Film ◽  
Annular Flow ◽  
Stratified Flow ◽  
Condensation Heat Transfer ◽  
Condenser Tube ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Horizontal Tubes ◽  
Annular Flows

The greater part of the horizontal condenser tube is occupied by the stratified and annular flows, which play important roles in condensation heat transfer coefficients. Both a volume of fluid (VOF) interface tracking method and k-ε two equations model was applied to analyze the characteristics of the stratified and annular flows for horizontal tubes, obtaining distribution of velocity, contours of both temperature and local condensation heat transfer coefficients. The computation shows that an annular flow having thinner liquid film attached on the inner surface of tubes appears at the inlet of the horizontal condenser tube because vapor exerts a higher interfacial shear stress on the gas-liquid interface, therefore, there are a higher local condensation heat transfer coefficients there. Next, as vapor quality decreases and condensate gravity increases along the condenser tube length, the condensation flow pattern transforms from the annular flow into the stratified flow in which local condensation heat transfer coefficients decreases and distributes unevenly along the circumference as liquid film at the bottom of the condenser tube become thicker. In addition, in the stratified flow, a wave structure is formed in the middle of the condensate pool at the bottom of the condenser tube because condensate on the top of the condenser tube slides into the bottom of the condenser tube and collapse each other. The heat transfer rate calculated by the present method is compared to those predicted from a Shah correlation, the agreement is found to be good, and both errors is within 7%.

Detailed Flow and Heat Transfer Analyses in a Rib-Roughened Trailing-Edge Cooling Cavity With Impingement

2019 ◽  
Vol 141 (5) ◽  
Author(s):  
Fei Xue ◽  
Mohammad E. Taslim
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Channel Flow ◽  
Flow Rate ◽  
Target Surface ◽  
Reynolds Numbers ◽  
Transfer Coefficients ◽  
Flow Measurements ◽  
Heat Transfer Coefficients

A rig, simulating two adjacent cooling cavities on the trailing side of an airfoil, made up of two trapezoidal channels is tested. Eleven crossover holes on the partition wall between the two channels create the jets. Two exit flow arrangements are investigated—(a) jets, after interaction with the target surface, are turned toward the target channel exit axially and (b) jets exit from a row of racetrack-shaped slots along the target channel. Flow measurements are reported for individual holes and heat transfer coefficients on the eleven target walls downstream the jets are measured using liquid crystals under steady-state conditions. Smooth as well as ribbed target surfaces with four rib angles are tested. Correlations are developed for mass flow rate through each crossover hole, varying the number of crossover holes. Heat transfer coefficient variations along the target channel are reported for a range of 5000–50,000 local jet Reynolds numbers. Major conclusions are: (1) Correlations are developed to successfully predict the air flow rate through each crossover hole for partition walls with six to eleven crossover holes, based on the pressure drop across the holes, (2) impingement heat transfer coefficient correlates well with local jet Reynolds number for both exit flow arrangements, and (3) case of target channel flow exiting from the channel end, at higher jet Reynolds numbers, produce higher heat transfer coefficients than those in the case of flow exiting through a row of slots along the target channel opposite to the crossover holes.

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.

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