scholarly journals Heat Transfer Performance Potential with a High-Temperature Phase Change Dispersion

Energies ◽  
2021 ◽  
Vol 14 (16) ◽  
pp. 4899
Author(s):  
Ludger Fischer ◽  
Ernesto Mura ◽  
Poppy O’Neill ◽  
Silvan von Arx ◽  
Jörg Worlitschek ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Local Heat Transfer ◽  
High Temperature Phase ◽  
Operating Conditions ◽  
Phase Changes ◽  
Temperature Phase ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Nusselt Numbers

Phase change dispersions are useful for isothermal cooling applications. As a result of the phase changes that occur in PCDs, they are expected to have greater storage capacities than those of single-phase heat transfer fluids. However, for appropriate heat exchanger dimensions and geometries for use in phase change dispersions, knowledge about the convective heat transfer coefficients of phase change dispersions is necessary. A test unit for measuring the local heat transfer coefficients and Nusselt numbers of PCDs was created. The boundary condition of constant heat flux was chosen for testing, and the experimental heat transfer coefficients and Nusselt numbers for the investigated phase change dispersion were established. Different experimental parameters, such as the electrical wall heat input, Reynolds number, and mass flow rate, were varied during testing, and the results were compared to those of water tests. It was found that, due to the tendency of low-temperature increases in phase change dispersions, the driving temperature difference is greater than that of water. In addition, larger heat storage capacities were obtained for phase change dispersions than for water. Through this experimentation, it was acknowledged that future investigation into the optimised operating conditions must be performed.

An experimental investigation of natural convection in the melted region around a heated horizontal cylinder

1979 ◽  
Vol 90 (2) ◽  
pp. 227-239 ◽  
Author(s):  
A. G. Bathelt ◽  
R. Viskanta ◽  
W. Leidenfrost
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Phase Change ◽  
Local Heat Transfer ◽  
Horizontal Cylinder ◽  
Conclusive Evidence ◽  
Transfer Coefficients ◽  
Quantitative Evidence ◽  
Analysis And Design ◽  
Heat Transfer Coefficients

Melting from an electrically heated horizontal cylinder embedded in a paraffin (n-octadecane, fusion temperature 301·3 °K) has been studied experimentally. The shape of the solid-liquid interface has been determined photographically, and the local heat transfer coefficients have been measured using a shadowgraph technique. The experiments provide conclusive evidence of the important role played by natural convection in melting a solid due to an embedded cylindrical heat source. The four distinct pieces of quantitative evidence which contribute to this conclusion are the melt shape, surface temperature, local and average heat transfer coefficients and their variation with time.The experimental findings prove the importance of natural convection in phase change problems involving melting and indicate that continued practice of neglecting the effects in the analysis of such problems does not appear reasonable. Natural convection should be considered in analysis and design of systems involving phase change.

Influence of a Honeycomb Facing on the Heat Transfer in a Stepped Labyrinth Seal

2000 ◽  
Vol 124 (1) ◽  
pp. 133-139 ◽  
Author(s):  
K. Willenborg ◽  
V. Schramm ◽  
S. Kim ◽  
S. Wittig
Keyword(s):  
Heat Transfer ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Labyrinth Seal ◽  
Honeycomb Structure ◽  
Operating Conditions ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Wide Range ◽  
Geometrical Effects

The influence of a honeycomb facing on the heat transfer of a stepped labyrinth seal with geometry typical for modern jet engines was investigated. Heat transfer measurements were obtained for both a smooth stator and a stator lined with a honeycomb structure. In addition, an LDV system was used with the scaled up geometry to obtain a high local resolution of the velocity distribution in the seal. The experiments covered a wide range of pressure ratios and gap widths, typical for engine operating conditions. Local heat transfer coefficients were calculated from the measured wall and gas temperatures using a finite element code. By averaging the local values, mean heat transfer coefficients were determined and correlations for the global Nusselt numbers were derived for the stator and the rotor. The LDV results showed strong geometrical effects of the honeycomb structure on the development of the flow fields for the honeycomb seal. The distribution of the local heat transfer coefficients are compatible with the flow features identified by the LDV results and reveal a significantly reduced heat transfer with the honeycomb facing compared to the smooth facing.

Influence of a Honeycomb Facing on the Heat Transfer in a Stepped Labyrinth Seal

2000 ◽  
Author(s):  
K. Willenborg ◽  
V. Schramm ◽  
S. Kim ◽  
S. Wittig
Keyword(s):  
Heat Transfer ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Labyrinth Seal ◽  
Honeycomb Structure ◽  
Operating Conditions ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Wide Range ◽  
Geometrical Effects

The influence of a honeycomb facing on the heat transfer of a stepped labyrinth seal with geometry typical for modern jet engines was investigated. Heat transfer measurements were obtained for both a smooth stator and a stator lined with a honeycomb structure. In addition, an LDV system was used with the scaled up geometry to obtain a high local resolution of the velocity distribution in the seal. The experiments covered a wide range of pressure ratios and gap widths, typical for engine operating conditions. Local heat transfer coefficients were calculated from the measured wall and gas temperatures using a finite element code. By averaging the local values, mean heat transfer coefficients were determined and correlations for the global Nusselt numbers were derived for the stator and the rotor. The LDV results showed strong geometrical effects of the honeycomb structure on the development of the flow fields for the honeycomb seal. The distribution of the local heat transfer coefficients are compatible with to the flow features identified by the LDV results and reveal a significantly reduced heat transfer with the honeycomb facing compared to the smooth facing.

Heat Transfer to an Airfoil in Oscillating Flow

1971 ◽  
Vol 93 (4) ◽  
pp. 461-468 ◽  
Author(s):  
J. A. Miller ◽  
P. F. Pucci
Keyword(s):  
Heat Transfer ◽  
Oscillation Frequency ◽  
Leading Edge ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Oscillating Flow ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Nusselt Numbers ◽  
Consequent Increase

Local heat transfer coefficients to an airfoil in an oscillating stream have been measured for a range of frequencies and oscillation amplitudes. Results at moderate angles of attack are in agreement with previously reported findings. However, at large angles of attack, including those associated with stall in steady flow, a strong periodic starting vortex shed from the leading edge leads to a dramatic reattachment of the flow and consequent increase in local Nusselt Numbers of as much as five-fold. These effects are shown to be amplified by increasing oscillation frequency and amplitude.

Average Nusselt Number for Pressure and Suction Sides of Squealer Turbine Blade Tip

2011 ◽  
Author(s):  
Chaouki Ghenai
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Turbine Blade ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Cavity Depth ◽  
Heat Transfer Coefficients ◽  
Nusselt Numbers ◽  
Blade Tip

Numerical simulations of the flow field and heat transfer of squealer blade tip are performed in this study. The effect of Reynolds number (Re = 10000–40000), the clearance gap to width ratios (C/W = 5%–15%) and the cavity depth to width ratios (D/W = 10%, 20% and 50%) on fluid flow and heat transfer characteristics are obtained. The temperature and velocity distributions inside the cavity, the local heat transfer coefficients, and the average Nusselt numbers for the pressure and suction sides of the turbine blade tip are determined. This paper presents the results of the effects of Reynolds number, clearance gap and width ratios on the Nusslet number for the pressure and suction sides of squealer turbine blade tip. The results show a good agreement with the experimental data obtained by Metzger and Bunker. New correlations for the average Nusselt numbers for turbine blade tip pressure and suction sides are presented.

Heat Transfer in the Oscillating Turbulent Boundary Layer

1969 ◽  
Vol 91 (4) ◽  
pp. 239-244 ◽  
Author(s):  
James A. Miller
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Mean Velocity ◽  
Heat Transfer Coefficients ◽  
Nusselt Numbers ◽  
Local Coefficients

Measurements of local heat-transfer coefficients in the fully established oscillating turbulent boundary layer over a flat plate are reported. In the range of frequencies from 0.1 to 200 cps and amplitudes from 8 to 92 percent of the freestream mean velocity, increases in local Nusselt numbers of 3 to 5 percent were found. It is concluded that substantial increases in local coefficients, sometimes reported in oscillating flows of low standing wave ratio, may be traced to reduced transition Reynolds numbers.

scholarly journals Heat Transfer in the Oscillating Turbulent Boundary Layer

1969 ◽  
Author(s):  
J. A. Miller
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Mean Velocity ◽  
Heat Transfer Coefficients ◽  
Nusselt Numbers ◽  
Local Coefficients

Measurements of local heat transfer coefficients in the fully established oscillating turbulent boundary layer over a flat plate are reported. In the range of frequencies from 0.1 to 200 cps and amplitudes from 8 to 92 percent of the freestream mean velocity increases in local Nusselt numbers of 3 to 5 percent were found. It is concluded that substantial increases in local coefficients sometimes reported in oscillating flows of low standing wave ratio may be traced to reduced transition Reynolds numbers.

The Multi-Phase Flow Test Facility “EMMA” to Investigate Local Heat Transfer Coefficients and Liquid Water Films at Wet Steam Conditions

2020 ◽  
Author(s):  
Florian Felix Lapp ◽  
Simon Hecker ◽  
Sebastian Schuster ◽  
Dieter Brillert
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Measurement Methods ◽  
Wet Steam ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Phase Change Phenomena ◽  
Multi Phase

Abstract Conventional power plants are obliged to compensate for the fluctuations in power generation, due to the rising amount of renewable energies, to ensure grid stability. Consequently, steam turbines are more frequently facing load variation and startup/shut-down cycles leading to an increase of thermal stress induced by phase change phenomena. The review of existing test facilities providing measurement data of heat transfer coefficients influenced by multiphase phenomena, such as surface wettability and dry-out, revealed the necessity for a new measurement application. This paper presents the design of the Experimental Multi-phase Measurement Application “EMMA” to generate the required conditions in combination with an academic turbine housing geometry. The performed investigations are focused on the local distribution of heat transfer coefficients (HTC) and the surface wettability affected by phase change phenomena. Two main film formation mechanisms can be observed, depending on the thermal gradient between the fluid and the wall. These are a) saturated/superheated steam in contact with a sub-cooled wall leading to film-wise/drop-wise condensation and b) primary condensed wet steam droplets depositing on a superheated wall, leading to evaporation. Both, the liquid film and the local heat transfer are measured simultaneously. An overview of applicable thickness measurement methods for transparent liquid films is given and the applied optical measurement system is further described. Moreover the HTC measurement methods are presented considering the occurring case of phase change.

Analysis of Turbulent Flow and Heat Transfer in Internally Finned Tubes and Annuli

1979 ◽  
Vol 101 (1) ◽  
pp. 29-37 ◽  
Author(s):  
S. V. Patankar ◽  
M. Ivanovic´ ◽  
E. M. Sparrow
Keyword(s):  
Heat Transfer ◽  
Turbulent Flow ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Finned Tubes ◽  
Heat Transfer Coefficients ◽  
Nusselt Numbers ◽  
Flow And Heat Transfer ◽  
Fully Developed Turbulent Flow

The fully developed turbulent flow and heat transfer characteristics for tubes and annuli with longitudinal internal fins were analyzed via a mixing length model. The model takes account of the proximity of both the fin surfaces and the tube wall as well as of the gradients in the radial and circumferential directions. Application was made to air flows, and a single adjustable constant in the model was fixed by comparisons with experimental data for the friction factor and the circumferential-average Nusselt number for internally finned tubes. The local heat transfer coefficients exhibited a substantial variation along the fin height, with the smallest value (essentially zero) at the base and the largest value at the tip. Lesser and more gradual variations were exhibited by the local heat transfer coefficients on the wall of the tube or annulus. In general, the fins were found to be as effective a heat transfer surface as the wall (per unit area). Average Nusselt numbers and friction factors are presented for both the tube and the annulus.

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