Forced Convection Heat Transfer in Spray Formed Copper and Nickel Foam Heat Exchanger Tubes

2012 ◽  
Vol 134 (6) ◽  
Author(s):  
Nicholas Tsolas ◽  
Sanjeev Chandra
Keyword(s):  
Heat Transfer ◽  
Nickel Foam ◽  
Convection Heat Transfer ◽  
Spray Coating ◽  
Thermal Spray Coating ◽  
Heat Fluxes ◽  
Fluid Temperature ◽  
Transfer Coefficients ◽  
Surface Heat Fluxes ◽  
Inertial Coefficient

A thermal spray coating process was used to deposit dense 2 mm thick metal skins on the surfaces of square cross-section channels (300 mm × 20 mm × 20 mm) of nickel and copper foams with 10 and 40 PPI (pores per inch) pore densities. A heater was wrapped around the channels to apply surface heat-fluxes varying from 427 to 6846 W/m2. Compressed air was blown through the channels at flow rates of 5–80 l/min. Foam and fluid temperature distributions along the length of the channel and the pressure drop across it were measured. The foam was modeled as a porous medium and properties such as permeability K and inertial coefficient CF were determined from the experimental data. Local and average convective heat transfer coefficients were calculated from air and foam temperature measurements. Nusselt numbers were calculated and correlated in terms of the Reynolds, Prandtl, and Darcy numbers. Heat transfer to air flowing through a 10 PPI foam channel was shown to have increased nearly seven times compared to that of hollow tube with the same dimensions.

Radiation and Convection Heat Transfer in a Porous Bed

1968 ◽  
Vol 90 (1) ◽  
pp. 51-54 ◽  
Author(s):  
W. A. Beckman
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Collection Efficiency ◽  
Convection Heat Transfer ◽  
Heat Fluxes ◽  
Fluid Temperature ◽  
Radiation Heat ◽  
Radiation Heat Flux ◽  
Flowing Fluid ◽  
Porous Bed

The one-dimensional steady-state temperature distribution within an isotropic porous bed subjected to a collimated and/or diffuse radiation heat flux and a transparent flowing fluid has been determined by numerical methods. The porous bed was assumed to be nonscattering and to have a constant absorption coefficient. Part of the radiation absorbed by the porous bed is reradiated and the remainder is transferred to the fluid by convection. Due to the assumed finite volumetric heat transfer coefficient, the bed and fluid have different temperatures. A bed with an optical depth of six and with a normal incident collimated radiation heat flux was investigated in detail. The radiation incident on the bed at the fluid exit was assumed to originate from a black surface at the fluid exit temperature. The investigation covered the range of incident diffuse and collimated radiation heat fluxes expected in a nonconcentrating solar energy collector. The results are presented in terms of a bed collection efficiency from which the fluid temperature rise can be calculated.

Experimental and Numerical Investigation of Convection Heat Transfer of CO2 at Supercritical Pressures in a Vertical Mini Tube

2004 ◽  
Author(s):  
Pei-Xue Jiang ◽  
Yi-Jun Xu ◽  
Run-Fu Shi ◽  
S. He
Keyword(s):  
Heat Transfer ◽  
Wall Thickness ◽  
Fluid Pressure ◽  
Convection Heat Transfer ◽  
Local Heat Transfer ◽  
Fluid Temperature ◽  
Convection Heat ◽  
Transfer Coefficients ◽  
Bulk Fluid ◽  
Heat Transfer Coefficients

Convection heat transfer of CO2 at supercritical pressures in a vertical mini tube with a diameter of 0.948 mm was investigated experimentally and numerically. The local heat transfer coefficients, bulk fluid temperatures and wall temperatures were measured and presented. The effects of inlet fluid temperature, fluid pressure, mass flow rate, heat flux and wall thickness on the convection heat transfer in the mini tube were investigated. The experimental results were compared with calculated results using well-known correlations and numerical simulations. The results showed that the variable thermophysical properties of supercritical CO2 significantly influenced the convection heat transfer in the vertical mini tube and that for the studied conditions the influence of the wall thickness on the convection heat transfer in the mini tube was not great. For bulk fluid temperatures higher than the pseudo-critical temperature, the simulation results and the correlation results for the convection heat transfer coefficients in the mini tube corresponded well to the experimentally measured results.

Experimental Investigation on Heat Transfer and Pressure Drop of Nanodiamond-Engine Oil Nanofluid in a Microfin Tube

2010 ◽  
Author(s):  
M. A. Akhavan-Behabadi ◽  
M. Ghazvini ◽  
E. Rasouli
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Heat Transfer Enhancement ◽  
Convection Heat Transfer ◽  
Heat Fluxes ◽  
Engine Oil ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Nusselt Numbers

In this study, the effect of adding nanodiamond powder as an additive to engine oil on laminar flow heat transfer enhancement and pressure drop increasing is experimentally investigated. The plain and microfin tubes were used as the test sections and were heated by an electrical coil heater to produce constant heat fluxes. Thermal conductivity and heat capacity of nanofluids were measured for different volume fractions and temperatures. Convection heat transfer coefficients and Nusselt numbers of nanofluids were obtained for different nanoparticle concentrations as well as various Peclet and Reynolds numbers. Experimental results show the enhancement of heat transfer due to the nanoparticles presence. Furthermore, the effect of particle concentration on pressure drop was studied for different heat fluxes. Finally, the performance evaluation of both nanofluid and microfin tube from the point view of heat transfer enhancement and pressure drop increasing is done.

Free Jet Impingement Heat Transfer of a High Prandtl Number Fluid Under Conditions of Highly Varying Properties

1999 ◽  
Vol 121 (3) ◽  
pp. 592-597 ◽  
Author(s):  
J. E. Leland ◽  
M. R. Pais
Keyword(s):  
Heat Transfer ◽  
Heated Surface ◽  
Jet Impingement ◽  
Turbulent Jets ◽  
Heat Fluxes ◽  
Lubricating Oil ◽  
Fluid Temperature ◽  
Transfer Coefficients ◽  
Constant Property ◽  
Wide Range

An experimental investigation was performed to determine the heat transfer rates for an impinging free-surface axisymmetric jet of lubricating oil for a wide range of Prandtl numbers (48 to 445) and for conditions of highly varying properties (viscosity ratios up to 14) in the flowing film. Heat transfer coefficients were obtained for jet Reynolds numbers from 109 to 8592, nozzle orifice diameters of 0.51, 0.84 and 1.70 mm and a heated surface diameter of 12.95 mm. The effect of nozzle to surface spacing (1 to 8.5 mm), was also investigated. Viscous dissipation was found to have an effect at low heat fluxes. Distinct heat transfer regimes were identified for initially laminar and turbulent jets. The data show that existing constant property correlations underestimate the heat transfer coefficient by more than 100 percent as the wall to fluid temperature difference increases. Over 700 data points were used to generate Nusselt number correlations which satisfactorily account for the highly varying properties with a mean absolute error of less than ten percent.

Local Heat Transfer Coefficients Measurement Under Micro Jet Impinging Using Nitrogen Gas (N2)

2016 ◽  
Author(s):  
Jeong-Heon Shin ◽  
Tomer Rozenfeld ◽  
Ashwin Vutha ◽  
Yingying Wang ◽  
Gennady Ziskind ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Temperature Distribution ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Heat Fluxes ◽  
Fluid Temperature ◽  
Transfer Coefficients ◽  
Nitrogen Gas ◽  
Heat Transfer Coefficients ◽  
Temperature Detector

Experimental and simulation studies were performed to reveal local heat transfer coefficients under jet impinging in micro domain with Nitrogen gas. The experimental device was made of a 500 μm thick Pyrex and 400 μm thick silicon wafers. On the Pyrex wafer, four 100 nm thick resistance temperature detector (RTD) thermistors and a heater were fabricated from titanium. Jet orifices were etched by deep reactive ion etching (DRIE) on a silicon wafer, which was attached to the Pyrex wafer through a vinyl sticker (250 μm thick). A 1.9 mm × 14.8 mm × 250 μm micro channel was formed by laser drilling into the sticker. Varying flow rates of Nitrogen gas and heat fluxes of the heater, temperatures of the four thermistors were collected and local heat transfer coefficients were inferred enabling to divulge the jet impinging cooling characteristics. Initial simulations were used to complement experiments and to obtain detailed flow patterns of the jet, temperature distribution on the heater area, and fluid temperature distribution.

Assisting and Opposing Combined Convective Heat Transfer and Nanofluids Flows Over a Vertical Forward Facing Step

2014 ◽  
Vol 5 (1) ◽  
Author(s):  
H. A. Mohammed ◽  
Omar A. Hussein
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Volume Fraction ◽  
Convection Heat Transfer ◽  
Vertical Channel ◽  
Heat Fluxes ◽  
Recirculation Region ◽  
Fluid Temperature ◽  
Laminar Mixed Convection ◽  
Forward Facing Step

Numerical simulations of two-dimensional (2D) laminar mixed convection heat transfer and nanofluids flows over forward facing step (FFS) in a vertical channel are numerically carried out. The continuity, momentum, and energy equations were solved by means of a finite volume method (FVM). The wall downstream of the step was maintained at a uniform wall heat flux, while the straight wall that forms the other side of the channel was maintained at constant temperature equivalent to the inlet fluid temperature. The upstream walls for the FFS were considered as adiabatic surfaces. The buoyancy assisting and buoyancy opposing flow conditions are investigated. Four different types of nanoparticles, Al2O3, CuO, SiO2, and ZnO with different volumes' fractions in the range of 1–4% and different nanoparticle diameters in the range of 25–80 nm, are dispersed in the base fluid (water) are used. In this study, several parameters, such as different Reynolds numbers in the range of 100 < Re < 900, and different heat fluxes in the range of 500 ≤ qw ≤ 4500 W/m2, and different step heights in the range of 3 ≤ S ≤ 5.8 mm, are investigated to identify their effects on the heat transfer and fluid flow characteristics. The numerical results indicate that the nanofluid with SiO2 has the highest Nusselt number compared with other nanofluids. The recirculation region and the Nusselt number increase as the step height, Reynolds number, and the volume fraction increase, and it decreases as the nanoparticle diameter increases. This study has revealed that the assisting flow has higher Nusselt number than opposing flow.

Effect of Aspect Ratio and Tube Orientation on Free Convection Heat Transfer to Water and Mercury in Enclosed Circular Tubes

1961 ◽  
Vol 83 (1) ◽  
pp. 87-93 ◽  
Author(s):  
Floyd W. Larsen ◽  
James P. Hartnett
Keyword(s):  
Heat Transfer ◽  
Free Convection ◽  
Convection Heat Transfer ◽  
Temperature Fluctuations ◽  
Heat Fluxes ◽  
Radius Ratio ◽  
Uniform Heat Flux ◽  
Fluid Temperature ◽  
Convection Heat ◽  
Free Convection Heat

Free convection heat transfer to water and to mercury in a circular tube closed at the bottom end, open to a cooled reservoir at the top, and heated through the wall with a uniform heat flux, has been investigated with emphasis on the effect of length-to-radius ratio and tube inclination. Dimensionless wall and fluid temperatures are presented for several tube inclinations over a range of imposed dimensionless heat fluxes to a tube of length-to-radius ratio 14.6; these results are compared to earlier measurements in a tube of length-to-radius ratio 21.0. Over the range of the investigation the flow was apparently in fully mixed turbulent motion, as evidenced by the large fluid temperature fluctuations recorded during the tests. Inclination of the tube was found to result in a considerable decrease in temperature fluctuations and a corresponding increase in heat transfer above that observed with the tube axis vertical.

The Analysis of Heat Transfer in Automotive Turbochargers

2009 ◽  
Author(s):  
Nick Baines ◽  
Karl D. Wygant ◽  
Antonis Dris
Keyword(s):  
Heat Transfer ◽  
Pressure Ratio ◽  
Internal Heat ◽  
Heat Fluxes ◽  
Lubricating Oil ◽  
Inlet Temperature ◽  
Fluid Temperature ◽  
Transfer Coefficients ◽  
Internal Surfaces ◽  
The Difference

Heat transfers in an automotive turbocharger comprise significant energy flows, but are rarely measured or accounted for in any turbocharger performance assessment. Existing measurements suggest that the difference in turbine efficiency calculated in the conventional way, by means of the fluid temperature change, under adiabatic conditions differs considerably from the usual diabatic test conditions, particularly at low turbine pressure ratio. In the work described in this paper, three commercial turbochargers were extensively instrumented with thermocouples on all accessible external and internal surfaces in order to make comprehensive temperature surveys. The turbochargers were run at ranges of turbine inlet temperature and external ventilation. Adiabatic tests were also carried out to serve as a reference condition. Based on the temperature measurements, the internal heat fluxes from the turbine gas to the turbocharger structure, and from there to the lubricating oil and the compressor, and the external heat fluxes to the environment, were calculated. A one-dimensional heat transfer network model of the turbocharger was demonstrated to be able to simulate the heat fluxes to good accuracy, and that the heat transfer coefficients required were ultimately found to be mostly independent of the turbochargers tested.

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