Supercritical pressure heat transfer

Technical Appendices, which provides readers with additional information and data on current nuclear power reactors and NPPs thermophysical properties of reactor coolants, thermophysical properties of fluids at suhcritical and critical/supercritical pressures, heat transfer and pressure drop in forced convection to fluids at supercritical pressures, world experience in nuclear steam reheat, etc. 

Mayer, W., Telaar, J., Branam, R., Schneider, G., Hussong, J. (2003). Raman measurements of cryogenic injection at supercritical pressure. Heat Mass Transfer, 39, 709-719. 

The derived correlation can be used for supercritical fluid heat transfer calculations, in circular and other flow geometries, for heat exchangers, steam generators, nuclear reactors and other heat transfer equipment, for future comparison with other datasets, and for verification of computer codes and scaling parameters between water and modeling fluids. This correlation can be also used for supercritical carbon dioxide and other fluids. However, its accuracy might be less in these cases. Some specifics of pressure-drop calculations were also listed in the paper. 

Designs include the once-through boiler, which can operate at sub-critical, critical, or supercritical pressures and at all commercial temperatures, and the radiant boiler, where heat absorption is largely by radiant energy transfer. 

The solvent elimination appro2K h is quite straightforward for supercritical fluids lAich are often gases at atmospheric pressure. Each chromatographic peedc is deposited fron the end of a restrictor, connected to the end of the column by a heated transfer line, onto a small area of infrared-transparent support [110,128,129,134]. The support can be moved manually to collect each peak at a n osition or stetq>ed continuously to record the... 

The interest in heat-transfer for high-pressure systems is related to the extraction of a valuable solute with a compressed gas. The compressed fluid is usually a high-pressure gas-often a supercritical fluid, that is, a gas above its critical state. In this scenario, the prevalent heat-transfer mechanism is convection. 

A power plant operating on heat recovered from the exhaust gases of internal-combustion < uses isobutane as the working medium in a modified Rankine cycle in which the upper pressure I is above the critical pressure of isobutane. Thus the isobutane does not undergo a change of p" as it absorbs heat prior to its entry into the turbine. Isobutane vapor is heated at 4,800 kPa to 2 and enters the turbine as a supercritical fluid at these conditions. Isentropic expansion in the turh produces superheated vapor at 450 kPa, which is cooled and condensed at constant pressure, resulting saturated liquid enters the pump for return to the heater. If the power output of the modi Rankine cycle is 1,000 kW, what is the isobutane flow rate, the heat-transfer rates in the heater condenser, and the thermal efficiency of the cycle ... 

In this paper, we now report measurements of heat transfer coefficients for three systems at a variety of compositions near their lower consolute points. The first two, n-pentane--CO2 and n-decane--C02 are supercritical. The third is a liquid--liquid mixture, triethylamine (TEA)--H20, at atmospheric pressure. It seems to be quite analogous and exhibits similar behavior. All measurements were made using an electrically heated, horizontal copper cylinder in free convection. An attempt to interpret the results is given based on a scale analysis. This leads us to the conclusion that no attempt at modeling the observed condensation behavior will be possible without taking into account the possibility of interfacial tension-driven flows. However, other factors, which have so far eluded definition, appear to be involved. 

The results for the TEA--water mixtures at atmospheric pressure are shown in Figure 6. These are for TEA mole fractions of x 0.05 and 0.59. The LOST is 18.2 at x - 0.09. We also obtained a very similar data set at the latter mole fraction, but we omitted it for clarity. For contrast and comparison, a data set for pure water is shown. These mixture results again show a sharp rise in heat transfer coefficient as condensate first appeared. In fact, the appearance was remarkably similar to the n-decane--C02 results for x - 0.973 discussed above, but the visibility of the phase separation was enhanced by the presence of a fine emulsion at the phase interface and the absence of strong refractive index gradients characteristic of the supercritical systems. This permitted the structure of the interface to be seen more clearly. In Figure 7 we show photographs that typify the appearance of the two phases. In all cases observed here, both in supercritical vapor--liquid and in liquid--liquid systems, the dense phase appears to wet the cylinder surface regardless of composition. 

J. W. Ackerman, Pseudoboiling Heat Transfer to Supercritical Pressure Water in Smooth and Ribbed Tubes, J. Heat Transfer (92) 490-498,1970. 

B. Shiralker and P. Griffith, The Effect of Swirl, Inlet Conditions, Flow Direction, and Tube Diameter on the Heat Transfer to Fluids at Supercritical Pressure, J. Heat Transfer (42) 465-474,1970,... 

Shen YB, Poulikakos D., Impinging jet atomization at elevated and supercritical ambient temperature and pressure conditions. Experimental Heat Transfer, JAN-MAR, Vol. 11, Issue 1, pp. 23-40, 1998. 

When a fluid is compressed and heated above the critical conditions (or to supercritical conditions, sc), the differences between gas and liquid disappear. For carbon dioxide, this occurs for temperatures above 31 °C and pressures above 7.3 MPa. For reactions (such as alkylations, aminations, hydroformylations, hydrogenations and Fischer Tropsch synthesis) occurring in supercritical fluids, the reaction rate is often increased dramatically because of improved desorption of heavy molecules minimizing the oxygen and hydrogen solubility limitations, improved heat transfer, and improved selectivity by a catalyst by minimizing pore diffusion limitations. 

In this Chapter we have made an attempt to describe mixing and heat and mass transfer in supercritical fluids. Using Laser Doppler Anemometry, Computational Fluid Dynamics and High-Pressure Calorimetry, some basic guidelines have been derived. When compared to the behavior of ordinary liquids, the behavior of SCCO2 is quite different, especially near the critical point. However, when the thermodynamic behavior of CO2 is taken into account (in terms of constant-pressure heat capacity, viscosity, and thermal conductivity), its behavior is consistent with that of other liquids. 

Instrumentation depends on the information needed from the investigation. For a minimum outfit it is necessary to install measuring equipment for pressure and temperature in the extractor, precipitator, before and after the pump or compressor and in the gas supply. Furthermore, gas flow, concentration of extract and modifier in the supercritical gas, downstream of the extractor and the precipitator must be determined. It is useful to install temperature measurement devices at different locations in the extractor and precipitator and downstream to any heat transfer equipment. 

To evaluate liquid hydrogen properly as a coolant, more experimental information is required concerning the heat-transport mechanism through the thermal film for both subcritical and supercritical conditions. For this report, subcritical pressures 30-70 psi and a narrow range of bulk temperatures are included in the experimental conditions. The heat-transfer characteristics of hydrogen were measured in an electrically heated vertical tube. The tube was instrumented for surface temperature and pressure-drop measurements. The temperature difference between the wall and bulk fluid was varied from approximately 40° to 1000°R. The maximum heat flux was 0.8 Btu/in. -sec. 

Pioro, I.L., H.F. Khartabil, and R.B. Duffey. 2002. Literature survey devoted to the heat transfer and hydraulic resistance of fluids at supercritical and near-critical pressures, AECL-12137, FFC-FCT-409, February, Ontario, Canada. 

Jackson, J.D. and Hall, W.B. (1979) Forced convection heat transfer to fluids at supercritical pressure, in Turbulent Forced Convection in Channels and Bundles, vol. 2 (eds S. Kakac and D.B. Spaldin). Hemisphere, Washington. 

Pioro, I.L., Duffey, R.B., 2007. Heat Transfer and Hydraulic Resistance at Supercritical Pressures in Power Engineering Applications. ASME Press, New York, NY, USA, 334 p. 

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