Convective heat transfer in the channel entrance with a square leading edge under forced flow pulsations

2019 ◽  
Vol 129 ◽  
pp. 74-85 ◽  
Author(s):  
I.A. Davletshin ◽  
N.I. Mikheev ◽  
A.A. Paereliy ◽  
I.M. Gazizov
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Leading Edge ◽  
Forced Flow ◽  
Channel Entrance ◽  
Flow Pulsations ◽  
Forced Flow Pulsations

scholarly journals An Experimental Investigation of the Convective Heat Transfer on a Small Helicopter Rotor with Anti-Icing and De-Icing Test Setups

Aerospace ◽  
2021 ◽  
Vol 8 (4) ◽  
pp. 96
Author(s):  
Abdallah Samad ◽  
Eric Villeneuve ◽  
Caroline Blackburn ◽  
François Morency ◽  
Christophe Volat
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Leading Edge ◽  
Liquid Water Content ◽  
Rotor Blades ◽  
Direct Result ◽  
Average Error ◽  
Good Prediction ◽  
Series Of Experiments

Successful icing/de-icing simulations for rotorcraft require a good prediction of the convective heat transfer on the blade’s surface. Rotorcraft icing is an unwanted phenomenon that is known to cause flight cancelations, loss of rotor performance and severe vibrations that may have disastrous and deadly consequences. Following a series of experiments carried out at the Anti-icing Materials International Laboratory (AMIL), this paper provides heat transfer measurements on heated rotor blades, under both the anti-icing and de-icing modes in terms of the Nusselt Number (Nu). The objective is to develop correlations for the Nu in the presence of (1) an ice layer on the blades (NuIce) and (2) liquid water content (LWC) in the freestream with no ice (NuWet). For the sake of comparison, the NuWet and the NuIce are compared to heat transfer values in dry runs (NuDry). Measurements are reported on the nose of the blade-leading edge, for three rotor speeds (Ω) = 500, 900 and 1000 RPM; a pitch angle (θ) = 6°; and three different radial positions (r/R), r/R = 0.6, 0.75 and 0.95. The de-icing tests are performed twice, once for a glaze ice accretion and another time for rime ice. Results indicate that the NuDry and the NuWet directly increased with V∝, r/R or Ω, mainly due to an increase in the Reynolds number (Re). Measurements indicate that the NuWet to NuDry ratio was always larger than 1 as a direct result of the water spray addition. NuIce behavior was different and was largely affected by the ice thickness (tice) on the blade. However, the ice acted as insulation on the blade surface and the NuIce to NuDry ratio was always less than 1, thus minimizing the effect of convection. Four correlations are then proposed for the NuDry, the NuWet and the NuIce, with an average error between 3.61% and 12.41%. The NuDry correlation satisfies what is expected from heat transfer near the leading edge of an airfoil, where the NuDry correlates well with Re0.52.

A Study of Three-Dimensional Mixed Convective Heat Transfer From Short Vertical Cylinders in a Horizontal Forced Flow

2000 ◽  
Author(s):  
David A. Scott ◽  
P. H. Oosthuizen
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Three Dimensional ◽  
Forced Flow ◽  
Low Velocity ◽  
Buoyancy Forces ◽  
The Mean ◽  
Mixed Convective Flow ◽  
Comparison Of The Results

Abstract Heat transfer from relatively short vertical isothermal cylinders in a horizontal forced fluid flow has been considered. The flow conditions are such that the buoyancy forces resulting from the temperature differences in the flow are in general significant despite of the presence of a horizontal forced flow of air, that is, mixed convective flow exists. Because the cylinders are short and the buoyancy forces act normal to the forced flow, three-dimensional flow exists. The experiments were performed in a low velocity, open jet wind tunnel. The study involved the experimental determination of the mean heat transfer coefficient and a comparison of the results with a previous numerical analysis. Mean heat transfer rates were determined using the ‘lumped capacity’ method. The mean Nusselt number has the Reynolds number, Grashof number and the height to diameter ratio of the cylinders as parameters. The results have been used to determine the conditions under which the flow departs from purely forced convection and enters the mixed convection regime, i.e., determining the conditions for which the buoyancy effects should be included in convective heat transfer calculations for short cylinders.

An Experimental Investigation of Convective Heat Transfer From Wire-On-Tube Heat Exchangers

1997 ◽  
Vol 119 (2) ◽  
pp. 348-356 ◽  
Author(s):  
J. L. Hoke ◽  
A. M. Clausing ◽  
T. D. Swofford
Keyword(s):  
Heat Transfer ◽  
Experimental Investigation ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Heat Exchangers ◽  
Steel Wire ◽  
Convective Heat Transfer Coefficient ◽  
Wire Diameter ◽  
Forced Flow ◽  
Geometrical Parameters

An experimental investigation of the air-side convective heat transfer from wire-on-tube heat exchangers is described. The study is motivated by the desire to predict the performance, in a forced flow, of the steel wire-on-tube condensers used in most refrigerators. Previous investigations of wire-on-tube heat exchangers in a forced flow have not been reported in the literature. The many geometrical parameters (wire diameter, tube diameter, wire pitch, tube pitch, etc.), the complex conductive paths in the heat exchanger, and the importance of buoyant forces in a portion of the velocity regime of interest make the study a formidable one. A key to the successful correlation of the experimental results is a definition of the convective heat transfer coefficient, hw, that accounts for the temperature gradients in the wires as well as the vast difference in the two key characteristic lengths—the tube and wire diameters. Although this definition results in the need to solve a transcendental equation in order to obtain hw from the experimental data, the use of the resulting empirical correlation is straightforward. The complex influence of the mixed convection regime on the heat transfer from wire-on-tube heat exchangers is shown, as well as the effects of air velocity and the angle of attack. The study covers a velocity range of 0 to 2 m/s (the Reynolds number based on wire diameter extends to 200) and angles of attack varying from 0 deg (horizontal coils) to ±90 deg. Heat transfer data from seven different wire-on-tube heat exchangers are correlated so that 95 percent of the data below a Richardson number of 0.004, based on the wire diameter, lie within ±16.7 percent of the proposed correlation.

Enclosure Phenomenon in Varying Forced Flow Convection

2019 ◽  
Author(s):  
Ribhu Bhatia ◽  
Sambit Supriya Dash ◽  
Vinayak Malhotra
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Flow Field ◽  
Transfer Coefficient ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Relative Effectiveness ◽  
Convection Heat Transfer ◽  
Forced Flow ◽  
Forced Convective Heat Transfer

Abstract Systematic experimentation was carried out on forced convection heat transfer apparatus under varying non-linear flow conditions to understand the energy transfer as heat, with the purpose of enhancing performance of numerous engineering applications. Plate orientations, types of enclosures (solid, meshed, perforated), flow velocity variations etc. are taken as governing parameters to effect convective heat transfer phenomenon which is perceived as deviations in value of heat transfer coefficient. RV zonal system is utilized to simplify the fundamental understanding of heat transfer coefficient variation with surface orientation under varying flow field. The objectives of this work are as follows: 1) To establish relative effectiveness of forced convective heat transfer under varying flow field. 2) To investigate the implications of varying shapes and sizes of perforations on confined forced convective heat transfer. To understand the controlling mechanism and role of key controlling parameters.

A Numerical Study of Assisting and Opposing Mixed Convective Heat Transfer From a Horizontal Isothermal High Aspect Ratio Rectangular Cylinder

2012 ◽  
Author(s):  
Patrick H. Oosthuizen
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Numerical Study ◽  
Rectangular Cross Section ◽  
Boussinesq Approximation ◽  
Forced Flow ◽  
Width Ratio ◽  
Flow Conditions ◽  
Rectangular Cylinder

Mixed convective heat transfer from an isothermal cylinder with a rectangular cross-section and a relatively large height-to-width ratio has been numerically studied. The axis of the cylinder is horizontal with the longer sides of the rectangular cylinder being vertical. There is a vertical forced flow over the cylinder. The flow conditions considered are such that in general mixed forced and natural convective flow exists. Both the case where the buoyancy forces act in the same direction as the forced flow (assisting flow) and the case where they act in the opposite direction to the forced flow (opposing flow) have been considered. The flow has been assumed to be two-dimensional and the Boussinesq approximation has been adopted. Attention has been restricted to the flow of air and results have therefore been obtained for a Prandtl number of 0.74. The flow conditions considered are such that laminar or turbulent flow can exist. The main attention is this work has been directed at determining the effect of the flow parameters on the mean heat transfer rate from the cylinder and on determining the conditions under which the flow can be assumed to be forced convective and under which it can be assumed to be natural convective.

Convective Heat Transfer From a Free Rotating Disk Subjected to a Forced Crossflow

2014 ◽  
Author(s):  
Christian Helcig ◽  
Stefan aus der Wiesche
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Rotating Disk ◽  
Reynolds Numbers ◽  
Forced Flow ◽  
High Angular Resolution ◽  
Angle Of Incidence ◽  
Transfer Coefficients

The understanding of the heat transfer and flow field behavior of rotating systems is essential from a fundamental point of view and for turbo machinery design. The majority of the publications considers enclosed rotating disk systems and only little is known about the convective heat transfer of free rotating disk systems in a forced flow. In this paper, a free rotating disk system, with particular look on the angle of incidence was investigated. The convective heat transfer from a rotating disk depends at least on three characteristic variables, namely the crossflow, rotational Reynolds numbers and the angle of incidence which are determining the mean Nusselt number. A clear study of the symmetry behavior of the flow field was conducted based on the measurement of the convective heat transfer coefficients. The angle of incidence was scanned with high angular resolution over the entire range between the both extreme cases of a perpendicular disk and a disk in a parallel forced flow. A large number of crossflow and rotational Reynolds numbers were covered by the experiments, too. Based on the experimental and theoretical results, a discussion of the different phenomena and heat transfer regimes is given in this paper.

Convective Heat Transfer Through Film Cooling Holes of a Gas Turbine Blade Leading Edge

2005 ◽  
Author(s):  
Elon J. Terrell ◽  
Brian D. Mouzon ◽  
David G. Bogard
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Gas Turbine ◽  
Turbine Blade ◽  
Convective Heat ◽  
Film Cooling ◽  
Leading Edge ◽  
Gas Turbine Blade ◽  
Film Cooling Holes ◽  
Blade Leading Edge

Studies of film cooling performance for a turbine airfoil predominately focus on the reduction of heat transfer to the external surface of the airfoil. However, convective cooling of the airfoil due to coolant flow through the film cooling holes is potentially a major contributor to the overall cooling of the airfoil. This study used experimental and computational methods to examine the convective heat transfer to the coolant as it traveled through the film cooling holes of a gas turbine blade leading edge. Experimental measurements were conducted on a model gas turbine blade leading edge composed of alumina ceramic which approximately matched the Biot number of an engine airfoil leading edge. The temperature rise in the coolant from the entrance to the exit of the film cooling holes was measured using a series of internal thermocouples and an external traversing thermocouple probe. A CFD simulation of the model of the leading edge was also done in order to facilitate the processing of the experimental data and provide a comparison for the experimental coolant hole heat transfer. Without impingement cooling, the coolant hole heat transfer was found to account for 50 to 80 percent of the airfoil internal cooling, i.e. the dominating cooling mechanism.

A New Thermodynamic and Heat Transfer Model for Nanolubricants and Refrigerant Heat Transfer Processes in Smooth Copper Tubes

2020 ◽  
Vol 142 (8) ◽  
Author(s):  
Pratik S. Deokar ◽  
Lorenzo Cremaschi ◽  
Andrea A. M. Bigi
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Single Phase ◽  
Flow Boiling ◽  
Heat Transfer Model ◽  
Forced Flow ◽  
Transfer Model ◽  
Phase Flow ◽  
Two Phase

Abstract In air conditioning systems, lubricating oil leaves the compressor and circulates through the other system components. This lubricant acts as a contaminant affecting heat transfer in heat exchangers. The literature indicated that mixtures of refrigerants and nanolubricants, that is, nanoparticles dispersed in the lubricant oils, have potentials to augment heat transfer exchange effectiveness. However, the nanoparticle mechanisms leading to such heat transfer changes are still unclear and not well included in the models. In this work, an existing single-phase forced flow convective heat transfer model, originally developed for water-based nanofluids, was modified to include the effects of diffusion and mass balance of different shape nanoparticles within the laminar sublayer and turbulent layer of the flow. A new physics-based superposition heat transfer model for saturated two-phase flow boiling of refrigerant and nanolubricants was also developed by integrating the modified forced flow convective heat transfer model and a semi-empirical pool boiling model for nanolubricants. The new model included the several physical effects that influenced heat transfer, such as slip mechanisms at the nanoparticles and base fluid interface and its influence on the laminar sublayer thickness, momentum transfer from the nanoparticles to the growing bubbles, and formation of lubricant excess concentration at the tube surface and its influence on bubble growth and tube wetting. The new model was validated for single-phase convective heat transfer and two-phase flow boiling of refrigerant R410A with two nanolubricants, having nonspherical ZnO nanoparticles and spherical Al2O3 nanoparticles.

Effect of Flow Pulsations on the Cooling Effectiveness of an Impinging Jet

1994 ◽  
Vol 116 (4) ◽  
pp. 886-895 ◽  
Author(s):  
H. S. Sheriff ◽  
D. A. Zumbrunnen
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Dynamic Responses ◽  
Mean Flow ◽  
Velocity Change ◽  
Spatial Uniformity ◽  
The Mean ◽  
Flow Pulsations ◽  
Hot Film

An experimental investigation has been performed to study the effect of flow pulsations on local, time-averaged convective heat transfer to an impinging water jet. Sinusoidal and square-pulse waveforms were considered. For the square waveform, the flow was completely halted for a portion of the pulsation cycle. Hot-film anemometry was used to characterize both the steady and the pulsating flows with regard to turbulence level and the spatial uniformity in the velocity profile across the nozzle width in order to assess separately the influence of flow pulsation on convective heat transfer. Pulse magnitude, which was defined as the ratio of the mean-to-peak velocity change to the mean flow velocity, was varied from 0.5 to 100 percent. Pulse frequencies ranged from 5 to 280 Hz, which corresponded to Strouhal numbers based on jet width and velocity of 0.014 to 0.964. Observed effects on convective heat transfer are explained in terms of nonlinear dynamic responses of the hydrodynamic and thermal boundary layers, boundary layer renewal, and bulges in the jet free surface.

Sign in / Sign up

Export Citation Format

Share Document