scholarly journals Testing of Heat Transfer Coefficients and Frictional Losses in Internally Ribbed Tubes and Verification of Results through CFD Modelling

Energies ◽  
2021 ◽  
Vol 15 (1) ◽  
pp. 207
Author(s):  
Sławomir Grądziel ◽  
Karol Majewski ◽  
Marek Majdak ◽  
Łukasz Mika ◽  
Karol Sztekler ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Friction Factor ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Department Of Energy ◽  
Transfer Coefficients ◽  
Cfd Modelling ◽  
Heat Transfer Coefficients

This paper presents experimental determination of the heat transfer coefficient and the friction factor in an internally rifled tube. The experiment was carried out on a laboratory stand constructed in the Department of Energy of the Cracow University of Technology. The tested tube is used in a Polish power plant in a supercritical circulating fluidized bed (CFB) boiler with the power capacity of 460 MW. Local heat transfer coefficients were determined for Reynolds numbers included in the range from ~6000 to ~50,000, and for three levels of the heating element power. Using the obtained experimental data, a relation was developed that makes it possible to determine the dimensionless Chilton–Colburn factor. The friction factor was also determined as a function of the Reynolds number ranging from 20,000 to 90,000, and a new correlation was developed that represents the friction factor in internally ribbed tubes. The local heat transfer coefficient and the friction factor obtained during the testing were compared with the CFD modelling results. The modelling was performed using the Ansys Workbench application. The k-ω, the k-ε and the transition SST (Share Stress Transport) turbulence models were applied.

Heat Transfer Enhancement by Turbulent Impinging Jets

2000 ◽  
Author(s):  
M. Kumagai ◽  
R. S. Amano ◽  
M. K. Jensen
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Stokes Equations ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Impinging Jets ◽  
Transfer Model ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

Abstract A numerical and experimental investigation on cooling of a solid surface was performed by studying the behavior of an impinging jet onto a fixed flat target. The local heat transfer coefficient distributions on a plate with a constant heat flux were computationally investigated with a normally impinging axisymmetric jet for nozzle diameter of 4.6mm at H/d = 4 and 10, with the Reynolds numbers of 10,000 and 40,000. The two-dimensional cylindrical Navier-Stokes equations were solved using a two-equation k-ε turbulence model. The finite-volume differencing scheme was used to solve the thermal and flow fields. The predicted heat transfer coefficients were compared with experimental measurements. A universal function based on the wave equation was developed and applied to the heat transfer model to improve calculated local heat transfer coefficients for short nozzle-to-plate distance (H/d = 4). The differences between H/d = 4 and 10 due to the correlation among heat transfer coefficient, kinetic energy and pressure were investigated for the impingement region. Predictions by the present model show good agreement with the experimental data.

Using Gradient Heat Flux Measurement to Experimentally Determine Local Heat Transfer Coefficient on Combustion Chamber Surface in a Diesel Engine

2019 ◽  
pp. 87-96
Author(s):  
V.B. Sapozhnikov ◽  
V.Yu. Mityakov ◽  
A.V. Mityakov ◽  
A.V. Vintsarevich ◽  
D.V. Gerasimov
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Combustion Chamber ◽  
Local Heat Transfer ◽  
Flux Measurement ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Engine Operation ◽  
Heat Transfer Coefficients

We used gradient thermometry to determine local heat transfer coefficients on the fire deck surface. We studied two modes of engine operation, that is, motored and fired. We show that the heat transfer coefficient distribution over the fire deck surface is inhomogeneous. Our investigation results may be used to validate existing models of heat transfer in a combustion chamber.

Distribution of local heat transfer coefficient values in the wall region of an agitated vessel

2008 ◽  
Vol 62 (1) ◽  
Author(s):  
Magdalena Cudak ◽  
Joanna Karcz
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Turbulent Regime ◽  
Transfer Coefficients ◽  
Measuring Point ◽  
Agitated Vessel ◽  
Heat Transfer Coefficients

AbstractExperimentally found local heat transfer coefficients are analyzed as a function of the measuring point on the heat transfer surface area of the agitated vessel wall and of the impeller eccentricity. Eccentric Rushton turbine and A 315 impeller are considered. Local heat transfer coefficients were measured by means of the computer-aided electrochemical method. The measurements were performed in an agitated vessel with inner diameter 0.3 m, filled with liquid up to the height equal to the vessel diameter. The experiments were carried out within the turbulent regime of the Newtonian liquid flow in the agitated vessel. The results were compared with the data obtained for the agitated vessel equipped with an eccentrically located axial flow propeller or an HE 3 impeller. Experimental studies show that the distributions of the heat transfer coefficient values depend on the impeller eccentricity, impeller type and the direction of the liquid circulation in the agitated vessel.

Pin-Fin Heat Transfer: Contribution of the Wall and the Pin to the Overall Heat Transfer

1992 ◽  
Author(s):  
A. M. Ai Dabagh ◽  
G. E. Andrews
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Diameter Ratio ◽  
Duct Flow ◽  
Transfer Coefficients ◽  
Pin Fin ◽  
Heat Transfer Coefficients

The differences in the heat transfer coefficient between the pin and the wall in pin-fin heat transfer was determined for three pin length to diameter ratios. A staggered pin-fin array was used with a 50% duct flow blockage by the pins. The axial pitch-to-pin diameter ratio, X/D, was 1.5 and the transverse pitch-to-diameter ratio, S/D, was 2.0. Three pin length-to-diameter ratios, T/D, of 0.7. 1.0 and 2.2 were investigated. The mean heat transfer coefficient results were very similar to previous work for similar geometries. The axial variation of heat transfer coefficient showed this to be fairly uniform with a small peak at the fourth row. Around each pin four measurements of the heat transfer coefficients were made with four on the fin surface at each end. Thus 12 local heat transfer coefficients were made per pin-fin. These showed that for all three geometries the wall or fin heat transfer was always greater by 15–35% than the pin for the same velocity and Re.

Convective Heat Transfer of Alumina Nanofluids in a Microchannel

2010 ◽  
Author(s):  
Saeid Vafaei ◽  
Dongsheng Wen
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Axial Distance ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

This work reports an experimental study of convective heat transfer of aqueous alumina nanofluids in a horizontal microchannel under laminar flow condition. The variation of local heat transfer coefficients, in both entrance and developed flow regime, is obtained as a function of axial distance. The heat transfer coefficient of nanofluids is found to be dependent upon not only nanoparticle concentration but also mass flow rate. Different to the behavior in conventional-sized channels, the major heat transfer coefficient enhancement is observed in fully developed region in microchannels. Discussions of the results suggest that the heterogeneous nature of nanoparticle flow should be considered.

Heat Transfer Coefficient Distributions for the Convective Cooling of Non-Cylindrical Geometries in Crossflow Using Extended Surfaces

1997 ◽  
Author(s):  
Andrew J. Neely ◽  
Peter T. Ireland ◽  
Les R. Harper
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Gas Turbines ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Convective Cooling ◽  
Heat Transfer Coefficients ◽  
Cylindrical Geometries

An experimental investigation of the performance of extended fin surfaces for the forced convective cooling of a range of engine component geometries in crossflow is reported. The experiments were undertaken to measure the surface heat transfer coefficient distributions of external finning around non-cylindrical geometries for use in aviation gas turbines in which the cooling performance/mass ratio must be maximised. The geometries examined were a box (square with rounded corners), a flute (rectangle with circular ends) and a 30° wedge. These models were sized to have equivalent cross sectional area to allow a direct comparison of performance. Perspex models coated with thermochromic liquid crystal were tested at a range of Reynolds numbers in a heat transfer wind tunnel in which a step change in flow temperature was used to measure the transient thermal behaviour of the fins. This technique enables the full surface mapping of local heat transfer coefficients on the surface of the fins. These measurements are compared with those for the equivalent smooth geometries and also with empirical calculations from the literature where available. A comparison with previous cylindrical measurements is also made. Knowledge of the distributions of local heat transfer coefficients enables the optimisation of the geometry through strategies such as baffling of the fins. Some examples of these strategies have been implemented and the results are reported. The finned geometries are seen to outperform the unfinned geometries (by factors greater than 3) though by factors less than simply the increase in area. The enhancement in h results because the increased surface area of the fins more than outweighs the decrease in local h on the fin surface as compared to the smooth geometries.

A Numerical Evaluation of a Simple Procedure for Using Transient Surface Temperature Measurements to Determine Local Convective Heat Transfer Rates

1999 ◽  
Author(s):  
Patrick H. Oosthuizen ◽  
David Naylor
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Heat Conduction ◽  
Transfer Coefficient ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Inverse Heat Conduction ◽  
Transfer Coefficients ◽  
Transfer Rates ◽  
Heat Transfer Coefficients

Abstract A transient method, based on an inverse heat conduction solution, for experimentally determining the distribution of local heat transfer rates on the surface of a body has been numerically evaluated. The particular interest is in situations in which the heat transfer coefficients are relatively low and in which there are relatively large changes in the heat transfer coefficient over the surface of the body being considered. In the method, a solid body of the shape being investigated, constructed from a low conductivity material, is heated to a uniform temperature and then exposed to a test flow. Using a layer of temperature sensitive crystal placed over the surface of this model or by other means, the time taken for the temperature at a relatively small number of selected points on the surface to reach a selected value is determined. The surface heat flux rate distribution is then found from these measured times using a simple inverse heat conduction method. The feasibility of this method has been evaluated by considering relatively low Reynolds number flow over a square cylinder and natural convective flow over a circular cylinder. Known local heat transfer coefficient distributions for these situation have been applied as boundary conditions in the numerical solution of the transient cooling of a the “experimental” models. These solutions are used to generate “measured” data i.e. to generate simulated experimental data. The inverse heat transfer method has then been used to predict the local heat transfer coefficient distribution over the surface and the predicted and input distributions have been compared. The effect of uncertainties in the experimental measurements on this comparison has then been evaluated using various assumed uncertainty values. The results of the study indicate that the proposed method of measuring local heat transfer coefficients is capable of giving results of good accuracy.

Modeling Bubble Growth in Micro-Channel Cooling Systems

2007 ◽  
Author(s):  
Joshua L. Nickerson ◽  
Martin Cerza ◽  
Sonia M. F. Garcia
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Conduction Equation ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Local Heat Transfer Coefficient ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

The solution of the heat conduction equation in the liquid layer beneath a moving bubble’s base and the resulting local heat transfer coefficient are presented. An analytical model was constructed using separation of variables to solve the heat conduction equation for the thermal profile in the liquid film beneath the base of a bubble moving through a microchannel at a given velocity. Differentiating the resulting liquid thermal profile and applying the standard definition for the local heat transfer coefficient resulted in a solution for local heat transfer coefficient as a function of bubble length. Analysis included varying pertinent parameters such as film thickness beneath the bubble base, wall heat flux, and superheated temperature in the microchannel. Water and FC-72 were analyzed as prospective coolant fluids. Analytical data revealed that as the superheated temperature in the microchannel increases, local heat transfer coefficients increase and arrive at a higher steady-state value. Increasing wall heat flux achieved the same result, while increasing film thickness resulted in lower heat transfer coefficients. The model indicated that water had superior performance as a coolant, provided the dielectric fluid (FC-72) is not mandated.

Pressure Based Prediction of Spray Cooling Heat Transfer Coefficients

2007 ◽  
Author(s):  
Thierry Some ◽  
Eckhard Lehmann ◽  
Hitoshi Sakamoto ◽  
Jungho Kim ◽  
Jin Taek Chung ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Spray Cooling ◽  
Local Heat Transfer Coefficient ◽  
Transfer Coefficients ◽  
Local Pressure ◽  
Heat Transfer Coefficients

An important goal of spray cooling research is the ability to predict local heat transfer coefficient from the spray hydrodynamics. It is postulated in this work that the local pressure is the controlling parameter for local heat transfer coefficient. To test this hypothesis, local pressure and heat transfer data were obtained for a 1×1, 1×2, and 2×2 arrays of hollow cone sprays at two pressures and three standoff distances. A correlation between the pressure and heat transfer coefficient was determined, then used to “predict” the heat transfer coefficient from the pressure data. The local variations in heat transfer coefficient were captured well using this technique, and the area-averaged heat transfer coefficient could be predicted within 12.6%. The technique needs to be verified with different nozzles and fluids over a wider range of conditions.

Heat Transfer Coefficients Around Cylinders in Crossflow in Combustor Exhaust Gases

1977 ◽  
Vol 99 (4) ◽  
pp. 497-508 ◽  
Author(s):  
R. R. Dils ◽  
P. S. Follansbee
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Local Heat Transfer Coefficient ◽  
Exhaust Gas ◽  
Transfer Coefficients ◽  
Stagnation Line ◽  
Heat Transfer Coefficients

The local heat-transfer coefficient at the surface of a component placed in combustor exhaust gases can be determined from an analysis of surface temperature oscillations induced by fluctuations of the exhaust-gas temperature. Within a prescribed bandwidth, the relative amplitudes of the Fourier components of the gas and surface temperature waves are a simple function of the local heat-transfer coefficient and the thermal properties of the component. This method of measuring the local heat-transfer coefficient is described in this paper and heat transfer coefficients measured around small cylinders in crossflow (Re = 4000–20,000) are reported. Measurements of the transient response of cylinders abruptly placed in the exhaust-gas stream were conducted to determine the accuracy of the wide bandwidth method. Wide bandwidth gas temperatures and velocities and their cross correlations in the combustor exit were measured to characterize the large-scale exhaust-gas dynamics. It is shown that the stagnation line heat-transfer coefficients are uniformly higher than those obtained in low-turbulence cold gas streams; the magnitude of the stagnation line Nusselt number increases with the measured turbulent intensity. Away from the stagnation line in the unseparated region, the dependence of the local heat-transfer coefficients on the angle from the stagnation line is in agreement with earlier data measured in cold gas streams.

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