Forced Convection Heat Transfer From a Cylinder in Carbon Dioxide Near the Thermodynamic Critical Point

1971 ◽  
Vol 93 (3) ◽  
pp. 290-296 ◽  
Author(s):  
J. R. Green ◽  
E. G. Hauptmann
Keyword(s):  
Heat Transfer ◽  
Critical Temperature ◽  
Forced Convection ◽  
Temperature Difference ◽  
Forced Flow ◽  
Fluid Temperature ◽  
Bulk Fluid ◽  
Transfer Rates ◽  
Heated Cylinder ◽  
Increasing Temperature

In an attempt to determine the heat transfer rates in forced flow normal to a heated cylinder and to provide some insight into the mechanisms in heat transfer in the critical region, heat transfer rates have been measured for both free and forced flow of supercritical carbon dioxide normal to a horizontal heated cylinder. The 0.006-in-dia cylinder was held at various constant temperatures by a feedback circuit. The effects of bulk fluid temperature, bulk fluid pressure, and surface temperature were studied for a range of bulk fluid temperatures and pressures from 0.8 to 1.4 times the critical temperature and pressure, and free-stream velocities from 0 to 3 fps. The temperature difference between the heated cylinder and the bulk fluid was varied from 1 to 300 deg F. Several photographs of the flow field are presented. In a supercritical fluid the heat transfer rate increases smoothly and monotonically with increasing temperature difference, increasing velocity, and increasing pressure. In fluid with the bulk temperature below the pseudo-critical temperature the heat transfer coefficient shows large peaks when the cylinder temperature is near the pseudo-critical temperature. The heat transfer coefficient decreases with increasing temperature difference when the bulk fluid temperature is above the pseudo-critical temperature. Supercritical forced convection does not exhibit the characteristic maximum in heat transfer rate shown in forced-flow nucleate boiling. Heat transfer rates at larger temperature differences are very similar in forced-flow film boiling and supercritical forced-flow heat transfer. With this horizontal constant-temperature cylinder, no “bubble-like” or “boiling-like” mechanisms of heat transfer were observed in supercritical free or forced convection.

Pseudoboiling Heat Transfer to Supercritical Pressure Water in Smooth and Ribbed Tubes

1970 ◽  
Vol 92 (3) ◽  
pp. 490-497 ◽  
Author(s):  
J. W. Ackerman
Keyword(s):  
Heat Transfer ◽  
Forced Convection ◽  
Heated Surface ◽  
Supercritical Pressure ◽  
Heat Fluxes ◽  
Film Boiling ◽  
Fluid Temperature ◽  
Bulk Fluid ◽  
Pressure Water ◽  
Supercritical Pressure Water

Investigations of heat transfer to supercritical pressure fluids have been going on for some time, and correlations have been developed for both free and forced-convection conditions. In these investigations, unpredictable heat transfer performance has sometimes been observed when the pseudocritical temperature of the fluid is between the temperature of the bulk fluid and that of the heated surface. The unusual performance has been attributed to many causes, but one for which more evidence is being collected is that of a pseudofilm-boiling process similar to film boiling which occurs at subcritical pressures. This paper, which is an extension of work reported earlier on forced-convection heat transfer to supercritical pressure water, presents experimental evidence which suggests that a pseudofilm-boiling phenomenon can occur in smooth-bore tubes. During the period from 1963–1966, tubes with ID’s from 0.37 to 0.96 in. were tested at pressures from 3300–6000 psia and at heat fluxes and mass velocities in the range of interest in steam-generator design. The effects of heat flux, mass velocity, tube diameter, pressure, and bulk fluid temperature on both the occurrence and characteristics of pseudofilm boiling are discussed. Results of a second series of tests conducted in 1967, which show that ribbed tubes suppress pseudofilm boiling at supercritical pressure much like they do film boiling at subcritical pressures, are also discussed.

Natural Convection in an Inclined Rectangular Cavity With Different Thermal Boundary Conditions at the Top Plate

1988 ◽  
Vol 110 (2) ◽  
pp. 350-357 ◽  
Author(s):  
T. G. Karayiannis ◽  
J. D. Tarasuk
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Boundary Conditions ◽  
Forced Convection ◽  
Rectangular Cavity ◽  
Forced Flow ◽  
Cold Plate ◽  
Transfer Rates ◽  
Average Heat ◽  
Thermal Boundary Conditions

Natural convection inside a rectangular cavity with different temperature boundary conditions on the cold top plate was studied using a Mach-Zehnder interferometer for θ = 15, 45, and 60 deg to the horizontal. At θ = 60 deg coupling with external forced convection and non-coupled heat transfer from a cavity with an isothermal top plate was studied. In all experiments the bottom hot plate was isothermal. The Rayleigh number Ra was varied from subcritical to 6×105 and the cavity aspect ratio ARx, from 6.68 to 33.4. The Reynolds number of the external forced flow Redh was constant and approximately equal to 5.8×104. It was found that for Ra ≲ 3×104 the differing thermal boundary conditions at the top plate did not affect the local or average heat transfer rates from the cavity. For Ra ≳ 3×104 coupling at the top plate compared to the non-coupled case resulted not only in a reduction in the variation of the local heat transfer rates at the cold plate, but also in a significant reduction in the variation of the average transfer rates from hot and cold plates of the cavity. Forced convection at the top plate as compared to natural convection resulted only in a small reduction in the heat transfer coefficient at the cold plate. Correlation equations for coupled and noncoupled average heat transfer rates are presented.

Combined Free and Forced Convection in a Horizontal Circular Tube

1966 ◽  
Vol 88 (2) ◽  
pp. 147-152 ◽  
Author(s):  
S. T. McComas ◽  
E. R. G. Eckert
Keyword(s):  
Free Convection ◽  
Forced Convection ◽  
Reynolds Numbers ◽  
Forced Flow ◽  
Appreciable Effect ◽  
Fluid Temperature ◽  
Bulk Fluid ◽  
Grashof Number ◽  
Free And Forced Convection ◽  
Flow Heat

The effect of free convection on laminar forced flow heat transfer in a horizontal uniformly heated tube was investigated. The Grashof number was varied from 1000 down to the order of one, the low Grashof number runs agreeing with the prediction for pure forced convection within ±8 percent. The effect of the secondary flow created by free convection was observed as a decrease in the wall to bulk fluid temperature difference required to transfer heat as compared to the pure forced flow case in the region far from the tube inlet. This effect was found to increase as the ratio of Grashof number to Reynolds numbers increased. No appreciable effect of free convection was found in the thermal development region.

Supercritical Water Choking Flow Experiments Through a Convergent-Divergent Test Section

2020 ◽  
Author(s):  
Alberto Teyssedou ◽  
Altan Muftuoglu ◽  
Akila Hidouche
Keyword(s):  
Critical Temperature ◽  
Temperature Difference ◽  
Supercritical Water ◽  
Test Section ◽  
Critical Mass ◽  
Fluid Temperature ◽  
Flow Data ◽  
Bulk Fluid ◽  
Choked Flow ◽  
Discharge Pressure

Abstract The heat transport system of GEN-IV Supercritical Water-Cooled Nuclear Reactors (SCWRs) will operate at pressures close to 25 MPa and outlet temperatures of up to 898 K (625°C). The design and safety analyses of this type of reactors still necessitate amongst others, experimental information and validation of critical (choked) flows models of water above the thermodynamic critical state. Up to now, choked flow data were collected at atmospheric discharge pressure conditions, without changing the discharge pressure to verify the occurrence of choking flow; in most of the cases, using fluids different from water. This paper presents experimental supercritical water choking flow data collected by using a convergent-divergent test section by changing the discharge pressure to verify the occurrence of choked flow. The critical mass flux is presented as a function of the temperature difference between a pseudo-critical temperature and the bulk fluid temperature. This representation allows us to assess similar experiments performed by using different test sections. Hence, a comparison of actual data with those previously obtained using 1.0 mm and 1.4 mm diameter sharp-edged orifices, shows peculiar differences. The actual experiments were limited by very low values of choking mass flow rates. Furthermore, in some cases, it was observed the presence of an increase in the discharge pressure that seems to indicate the existence of shock-wave structures. We are also able to estimate a pseudo-critical temperature difference below which choking flow systematically occurs.

An Experimental Investigation of Heat Transfer and Buoyancy Induced Transition from Laminar Forced Convection to Turbulent Free Convection over a Horizontal Isothermally Heated Plate

1978 ◽  
Vol 100 (3) ◽  
pp. 429-434 ◽  
Author(s):  
H. Imura ◽  
R. R. Gilpin ◽  
K. C. Cheng
Keyword(s):  
Heat Transfer ◽  
Free Convection ◽  
Forced Convection ◽  
Leading Edge ◽  
Finite Amplitude ◽  
Heated Plate ◽  
Transfer Rates ◽  
Longitudinal Vortices ◽  
Turbulent Flow Regime ◽  
Laminar Forced Convection

The flow over a horizontal isothermally heated plate at Reynolds numbers below that at which hydrodynamic instabilities exist, is characterized by a region of laminar forced convection near the leading edge, followed by the onset of longitudinal vortices and their growth to a finite amplitude and finally a transition to a turbulent flow regime. Results are presented for the temperature profiles, the thermal boundary layer thickness, and the local Nusselt number. They are used to identify the various flow regimes. It was found that the transition from laminar forced convection to turbulent convection was characterized by the parameter Grx/Rex1.5 falling in the range 100 to 300. For values of this parameter greater than 300 the heat transfer rates were independent of Reynolds number and typical of those for turbulent free convection from a horizontal surface.

scholarly journals Heat transfer enhancement of car radiator using aqua based magnesium oxide nanofluids

2015 ◽  
Vol 19 (6) ◽  
pp. 2039-2048 ◽  
Author(s):  
Hafiz Ali ◽  
Muhammad Azhar ◽  
Musab Saleem ◽  
Qazi Saeed ◽  
Ahmed Saieed
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Thermal Management ◽  
Heat Transfer Performance ◽  
Inlet Temperature ◽  
Fluid Temperature ◽  
Transfer Enhancement ◽  
Volumetric Concentration ◽  
Flow Rates ◽  
Transfer Rates

The focus of this research paper is on the application of water based MgO nanofluids for thermal management of a car radiator. Nanofluids of different volumetric concentrations (i.e. 0.06%, 0.09% and 0.12%) were prepared and then experimentally tested for their heat transfer performance in a car radiator. All concentrations showed enhancement in heat transfer compared to the pure base fluid. A peak heat transfer enhancement of 31% was obtained at 0.12 % volumetric concentration of MgO in basefluid. The fluid flow rate was kept in a range of 8-16 liter per minute. Lower flow rates resulted in greater heat transfer rates as compared to heat transfer rates at higher flow rates for the same volumetric concentration. Heat transfer rates were found weakly dependent on the inlet fluid temperature. An increase of 8?C in inlet temperature showed only a 6% increase in heat transfer rate.

Conditions for Equivalency of Countercurrent Vessel Heat Transfer Formulations

1999 ◽  
Vol 121 (5) ◽  
pp. 514-520 ◽  
Author(s):  
R. B. Roemer
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Temperature Difference ◽  
Bulk Temperature ◽  
Transfer Coefficients ◽  
Bulk Fluid ◽  
Heat Transfer Coefficients ◽  
The Difference ◽  
Convective Heat Transfer Coefficients

Previous models of countercurrent blood vessel heat transfer have used one of two, different, equally valid but previously unreconciled formulations, based either on: (1) the difference between the arterial and venous vessels’ average wall temperatures, or (2) the difference between those vessels’ blood bulk fluid temperatures. This paper shows that these two formulations are only equivalent when the four, previously undefined, “convective heat transfer coefficients” that are used in the bulk temperature difference formulation (two coefficients each for the artery and vein) have very specific, problem-dependent relationships to the standard convective heat transfer coefficients. (The average wall temperature formulation uses those standard coefficients correctly.) The correct values of these bulk temperature difference formulation “convective heat transfer coefficients” are shown to be either: (1) specific functions of (a) the tissue conduction resistances, (b) the standard convective heat transfer coefficients, and (c) the independently specified bulk arterial, bulk venous and tissue temperatures, or (2) arbitrary, user defined values. Thus, they are generally not equivalent to the standard convective heat transfer coefficients that are regularly used, and must change values depending on the blood and tissue temperatures. This dependence can significantly limit the convenience and usefulness of the bulk temperature difference formulations.

A Study of Forced Convection Direct Air Cooling in the Downstream Vicinity of Heat Sinks

1990 ◽  
Vol 112 (3) ◽  
pp. 234-240 ◽  
Author(s):  
G. L. Lehmann ◽  
S. J. Kosteva
Keyword(s):  
Heat Transfer ◽  
Forced Convection ◽  
Heat Sink ◽  
Convection Heat Transfer ◽  
Heat Sinks ◽  
Air Cooling ◽  
Transfer Coefficients ◽  
Packaging System ◽  
Transfer Rates ◽  
Heat Transfer Coefficients

An experimental study of forced convection heat transfer is reported. Direct air cooling of an electronics packaging system is modeled by a channel flow, with an array of uniformly sized and spaced elements attached to one channel wall. The presence of a single or complete row of longitudinally finned heat sinks creates a modified flow pattern. Convective heat transfer rates at downstream positions are measured and compared to that of a plain array (no heat sinks). Heat transfer rates are described in terms of adiabatic heat transfer coefficients and thermal wake functions. Empirical correlations are presented for both variations in Reynolds number (5000 < Re < 20,000) and heat sink geometry. It is found that the presence of a heat sink can both enhance and degrade the heat transfer coefficient at downstream locations, depending on the relative position.

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