scholarly journals Variations of thermophysical properties and heat transfer performance of nanoparticle-enhanced ionic liquids

2019 ◽  
Vol 6 (4) ◽  
pp. 182040 ◽  
Author(s):  
Fang-Fang Zhang ◽  
Fei-Fei Zheng ◽  
Xue-Hong Wu ◽  
Ya-Ling Yin ◽  
Geng Chen
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Mass Fraction ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Measurement Range ◽  
Maximum Enhancement ◽  
Wide Range ◽  
Mass Fractions ◽  
Classical Models

The ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate ([EMIm]Ac) was investigated as a promising absorbent for absorption refrigeration. To improve the thermal conductivity of pure [EMIm]Ac, IL-based nanofluids (ionanofluids, INFs) were prepared by adding graphene nanoplatelets (GNPs). The thermal stability of the IL and INFs was analysed. The variations of the thermal conductivity, viscosity and specific heat capacity resulting from the addition of the GNPs were then measured over a wide range of temperatures and mass fractions. The measured data were fitted with appropriate equations and compared with the corresponding classical models. The results revealed that the IL and INFs were thermally stable over the measurement range. The thermal conductivity greatly increased with increasing mass fraction, while only slightly changed with increasing temperature. A maximum enhancement in thermal conductivity of 43.2% was observed at a temperature of 373.15 K for the INF with a mass fraction of 5%. The numerical results revealed that the dispersion of the GNPs in the pure IL effectively improved the local heat transfer coefficient by up to 28.6%.

scholarly journals High-Resolution Measurements of Local Heat Transfer Coefficients From Discrete Hole Film Cooling

1999 ◽  
Vol 123 (4) ◽  
pp. 749-757 ◽  
Author(s):  
S. Baldauf ◽  
A. Schulz ◽  
S. Wittig
Keyword(s):  
Heat Transfer ◽  
High Resolution ◽  
Film Cooling ◽  
Density Ratio ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Wide Range ◽  
Surface Patterns

Local heat transfer coefficients on a flat plate surface downstream a row of cylindrical ejection holes were investigated. The parameters blowing angle, hole pitch, blowing rate, and density ratio were varied over a wide range, emphasizing engine relevant conditions. A high-resolution IR-thermography technique was used for measuring surface temperature fields. Local heat transfer coefficients were obtained from a Finite Element analysis. IR-determined surface temperatures and backside temperatures of the cooled test plate measured with thermocouples were applied as boundary conditions in this heat flux computation. The superposition approach was employed to obtain the heat transfer coefficient hf based on the difference between actual wall temperatures and adiabatic wall temperatures in the presence of film cooling. The hf data are given for an engine relevant density ratio of 1.8. Therefore, heat transfer results with different wall temperature conditions and adiabatic film cooling effectiveness results for identical flow situations (i.e., constant density ratios) were combined. Characteristic surface patterns of the locally resolved heat transfer coefficients hf are recognized and quantified as the different ejection parameters are changed. The detailed results are used to discuss the specific local heat transfer behavior in the presence of film cooling. They also provide a base of surface data essential for the validation of the heat transfer capabilities of CFD codes in discrete hole film cooling.

Influence of Wall Sub-Cooling on Local Heat Transfer for Forced Convection Condensation of Steam/Air in a Horizontal Tube

2016 ◽  
Author(s):  
Huiqiang Xu ◽  
Qiunan Sun ◽  
Haifeng Gu ◽  
Xiaofan Hou ◽  
Zhongning Sun
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Mass Fraction ◽  
Local Heat Transfer ◽  
Horizontal Tube ◽  
Local Heat ◽  
Condensation Heat Transfer ◽  
Fraction Mixture ◽  
Condensation Heat Transfer Coefficient

For the purpose of analyzing the influence of wall sub-cooling on condensation heat transfer characteristic in the presence of noncondensable gases inside a horizontal tube, experiments for air-cooling and water-cooling at the secondary side outside the condenser tube have been conducted. By comparing the experimental data of different inlet air mass fraction, mixture gases velocity and coolant volume flow rate, the variation of local heat transfer coefficient with wall sub-cooling was obtained. The results show that for annular and wavy flow, the condensation heat transfer coefficient increases with increasing wall sub-cooling but decreases for stratified flow. For annular and wavy flow, the positive influence of wall sub-cooling on condensation heat transfer coefficient is enhanced by the rise of inlet noncondensable gas mass fraction, mixture gases velocity and pressure.

Flow Boiling of R134a and R134a/Propane Mixtures at Low Saturation Temperatures Inside a Plain Horizontal Tube

2008 ◽  
Vol 130 (6) ◽  
Author(s):  
A. Rabah ◽  
S. Kabelac
Keyword(s):  
Heat Transfer ◽  
Flow Boiling ◽  
Local Heat Transfer ◽  
Horizontal Tube ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Azeotropic Point ◽  
Heat Transfer Coefficients ◽  
Wide Range ◽  
Maximum Decrease

Local heat transfer coefficients for flow boiling of pure 1,1,1,2-tetrafluoroethane (R134a) and binary mixtures of propane (R290) and R134a were measured. The experimental setup employed a vapor heated plain horizontal tube (di=10mm, do=12mm, L=500mm). The measurements covered a wide range of saturation temperatures (233≤Ts≤278K), mass fluxes (100≤ṁ≤300kg∕m2s), qualities (0≤ẋ≤1), and concentrations (0≤z̃≤0.65). In the zeotropic region of R134a/R290 mixtures, the measured local heat transfer coefficient was found to show a maximum decrease by a factor of 2 relative to that for pure R134a. At the azeotropic point (65% R290), it was found to increase by a factor of 1.2. The measured local heat transfer coefficients for both R134a and R134a/R290 were compared with a number of correlations.

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.

scholarly journals Local Heat Transfer in Turbine Disk-Cavities: Part I — Rotor and Stator Cooling With Hub Injection of Coolant

1990 ◽  
Author(s):  
R. S. Bunker ◽  
D. E. Metzger ◽  
S. Wittig
Keyword(s):  
Heat Transfer ◽  
Liquid Crystal ◽  
Mass Flow ◽  
Flow Rate ◽  
Gas Turbines ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Computer Assisted ◽  
Disk Radius ◽  
Wide Range

Results are presented from an experimental study designed to obtain detailed radial heat transfer coefficient distributions applicable to the cooling of disk-cavity regions of gas turbines. An experimental apparatus has been designed to obtain local heat transfer data on both the rotating and stationary surfaces of a parallel geometry disk-cavity system. The method employed utilizes thin thermochromic liquid crystal coatings together with video system data acquisition and computer-assisted image analysis to extract heat transfer information. The color display of the liquid crystal coatings is detected through the analysis of standard video chromanance signals. The experimental technique used is an aerodynamically steady but thermally transient one which provides consistent disk-cavity thermal boundary conditions while yet being inexpensive and highly versatile. A single circular jet is used to introduce fluid from the stator into the disk-cavity by impingement normal to the rotor surface. The present study investigates hub injection of coolant over a wide range of parameters including disk rotational Reynolds numbers of 2 to 5 · 105, rotor/stator spacing-to-disk radius ratios of .025 to .15, and jet mass flow rates between .10 and .40 times the turbulent pumped flow rate of a free disk. The results are presented as radial distributions of local Nusselt numbers. Rotor heat transfer exhibits regions of impingement and rotational domination with a transition region between, while stator heat transfer shows flow reattachment and convection regions with evidence of an inner recirculation zone. The local effects of rotation, spacing, and mass flow rate are all displayed. The significant magnitude of stator heat transfer in many cases indicates the importance of proper stator modeling to rotor and disk-cavity heat transfer results.

scholarly journals High Resolution Measurements of Local Heat Transfer Coefficients by Discrete Hole Film Cooling

1999 ◽  
Author(s):  
S. Baldauf ◽  
A. Schulz ◽  
S. Wittig
Keyword(s):  
Heat Transfer ◽  
High Resolution ◽  
Film Cooling ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Constant Density ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Wide Range ◽  
Surface Patterns

Local heat transfer coefficients on a flat plate surface downstream a row of cylindrical ejection holes were investigated. The parameters blowing angle, hole pitch, blowing rate, and density ratio were varied in a wide range emphasizing on engine relevant conditions. A high resolution IR-thermography technique was used for measuring surface temperature fields. Local heat transfer coefficients were obtained by a Finite Element analysis. IR-determined surface temperatures and backside temperatures of the cooled testplate measured with thermocouples were applied as boundary conditions in a heat flux computation. The superposition approach was employed to obtain the heat transfer coefficient hr referring to adiabatic wall temperatures in the presence of film cooling. Therefore, heat transfer results with different wall temperature conditions and adiabatic film cooling effectiveness results of identical flow situations (constant density ratios) were combined. Characteristic surface patterns of the locally resolved heat transfer coefficients hf depending on the various parameters were recognized and quantified. The detailed results are used to discuss the specific local heat transfer behavior in the presence of film cooling. They also provide a base of surface data essential for the validation of the heat transfer capabilities of CFD-codes in discrete hole film cooling.

Local Heat Transfer Coefficient During Condensation in a 0.8 mm Diameter Pipe

2006 ◽  
Author(s):  
Alberto Cavallini ◽  
Davide Del Col ◽  
Marko Matkovic ◽  
Luisa Rossetto
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Operating Conditions ◽  
Local Heat Transfer Coefficient ◽  
Wide Range ◽  
The Heat Transfer Coefficient

The first preliminary tests carried on a new experimental rig for measurement of the local heat transfer coefficient inside a circular 0.8 mm diameter minichannel are presented in this paper. The heat transfer coefficient is measured during condensation of R134a and is obtained from the measurement of the heat flux and the direct gauge of the saturation and wall temperatures. The heat flux is derived from the water temperature profile along the channel, in order to get local values for the heat transfer coefficient. The test section has been designed so as to reduce thermal disturbances and experimental uncertainty. A brief insight into the design and the construction of the test rig is reported in the paper. The apparatus has been designed for experimental tests both in condensation and vaporization, in a wide range of operating conditions and for a wide selection of refrigerants.

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.

scholarly journals Heat Transfer Behaviour and Flow Field Characterisation of Impinging Synthetic Jets for a Wide Range of Parameters

2010 ◽  
Author(s):  
Rayhaan Farrelly ◽  
Alan McGuinn ◽  
Tim Persoons ◽  
Darina Murray
Keyword(s):  
Heat Transfer ◽  
Flow Field ◽  
High Speed ◽  
Local Heat Transfer ◽  
Field Measurements ◽  
Local Heat ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Flow Measurements ◽  
Wide Range

Impinging synthetic jets are considered as a potential solution for convective cooling, in applications that match their main characteristics (high local heat transfer rates, zero net mass flux, scalability, active control). Nevertheless the understanding of heat transfer to synthetic jets falls short of that available for steady jets. To address this, this paper uses detailed flow field measurements to help identify the main heat transfer mechanisms in impinging synthetic jets. Local heat transfer measurements have been performed for an impinging round synthetic jet at a range of Reynolds numbers between 1000 and 3000, nozzle to plate spacings between 4D and 16D and stroke lengths (L0) between 2D and 32D. The heat transfer results show evidence of distinct regimes in terms of L0/D and L0/H ratios. Based on appropriate scaling, four heat transfer regimes are identified which justifies a detailed study of the flow field characteristics. High speed particle image velocimetry (PIV) has been employed to measure the time-resolved velocity flow fields of the synthetic jet to identify the flow structures at selected L0/H values corresponding to the identified heat transfer regimes. The flow measurements support the same regimes as identified from the heat transfer measurements and provide physical insight for the heat transfer behaviour.

Local Heat Transfer in Turbine Disk Cavities: Part I—Rotor and Stator Cooling With Hub Injection of Coolant

1992 ◽  
Vol 114 (1) ◽  
pp. 211-220 ◽  
Author(s):  
R. S. Bunker ◽  
D. E. Metzger ◽  
S. Wittig
Keyword(s):  
Heat Transfer ◽  
Liquid Crystal ◽  
Mass Flow ◽  
Flow Rate ◽  
Gas Turbines ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Computer Assisted ◽  
Disk Radius ◽  
Wide Range

Results are presented from an experimental study designed to obtain detailed radial heat transfer coefficient distributions applicable to the cooling of disk-cavity regions of gas turbines. An experimental apparatus has been designed to obtain local heat transfer data on both the rotating and stationary surfaces of a parallel geometry disk-cavity system. The method employed utilizes thin thermochromic liquid crystal coatings together with video system data acquisition and computer-assisted image analysis to extract heat transfer information. The color display of the liquid crystal coatings is detected through the analysis of standard video chromanance signals. The experimental technique used is an aerodynamically steady but thermally transient one, which provides consistent disk-cavity thermal boundary conditions yet is inexpensive and highly versatile. A single circular jet is used to introduce fluid from the stator into the disk cavity by impingement normal to the rotor surface. The present study investigates hub injection of coolant over a wide range of parameters including disk rotational Reynolds numbers of 2 to 5 × 105, rotor/stator spacing-to-disk radius ratios of 0.025 to 0.15, and jet mass flow rates between 0.10 and 0.40 times the turbulent pumped flow rate of a free disk. The results are presented as radial distributions of local Nusselt numbers. Rotor heat transfer exhibits regions of impingement and rotational domination with a transition region between, while stator heat transfer shows flow reattachment and convection regions with evidence of an inner recirculation zone. The local effects of rotation, spacing, and mass flow rate are all displayed. The significant magnitude of stator heat transfer in many cases indicates the importance of proper stator modeling to rotor and disk-cavity heat transfer results.

Sign in / Sign up

Export Citation Format

Share Document