Heat Transfer Characteristics Of Nitrogen Research Articles

Heat Transfer Characteristics of Nitrogen in Supercritical Region Using Redlich-Kwong Equation of State

Abstract The present paper studies through numerical methods, the thermodynamic heat transfer characteristics of free convection flow of supercritical nitrogen over a vertical cylinder. In the present analysis, the values of volumetric thermal expansion coefficient ($\beta$) are evaluated based on Redlich-Kwong equation of state (RK-EOS) and Van der Waals equation of state (VW-EOS). The calculated analytical thermal expansion coefficient values using RK-EOS are very close to NIST data values in comparison with VW-EOS. A set of coupled nonlinear partial differential equations (PDEs) governing the supercritical fluid (SCF) flow are derived, converted into non-dimensional form with the help of suitable dimensionless quantities and solved using Crank-Nicolson implicit finite difference method. The simulations are carried out for nitrogen in the supercritical region. The obtained numerical data is expressed in terms of graphs and tables for various values of physical parameters. The increasing value of reduced temperature decreases the average Nusselt number and skin-friction coefficient, whereas amplifying value of reduced pressure enhance the heat transfer rate and wall shear stress in the SCF region. Present results are compared with the previous results and the two are found to be in good agreement, i. e. the numerically generated results found to be in agreement with existing results.

Experiment and simulation on downward flow condensation of nitrogen in vertical tubes

The heat transfer characteristics of nitrogen downward flow condensation are measured in 2 mm and 1 mm vertical tubes. The saturation temperature of nitrogen ranges from 100.4 to 108.0 K. The mass flux varies from 32.7 to 78.6 kg/m2 s for 2 mm tube and from 52.4 to 314.4 kg/m2 s for 1 mm tube. Experimental results of the flow condensation heat transfer coefficient are proposed and analyzed for different vapor qualities, mass fluxes, tube diameters and saturation temperatures. An annular condensation model with the consideration of the interfacial shear stress and the gravity is proposed based on the assumption of uniform film thickness around the tube’s circumference, and the model is validated by the experimental data. Based on the model, the flow and heat transfer characteristics, including the thickness of the liquid film and the condensation heat transfer coefficient are analyzed. Finally, the model and several previous correlations of flow condensation heat transfer coefficient are evaluated by the comparison with the experimental data.

LNG FPSO 액화공정에 적용되는 플레이트 핀 열교환기의 열전달 특성

There are no domestic researches of plate fin heat exchanger in the field of cryogenic such as LNG FPSO liquefaction plant. In this study, condensing heat transfer characteristics of nitrogen according to three kinds of fin type in the plate fin heat exchanger were analyzed through simulation and experiment to secure independent technologies. In the simulation, nitrogen was condensed at 69bar and in serrated and wavy fin of plate-fin heat exchanger. The serrated fin shows the highest value of local heat transfer coefficient, followed by wavy and plain fin. The experimental results were shown errors less than 12% comparing with the simulation results.

Flow boiling heat transfer characteristics of nitrogen in plain and wire coil inserted tubes

Boiling heat transfer characteristics of nitrogen were experimentally investigated in a stainless steel plain tube and wire coil inserted tubes. Wire coils having different coil pitches and wire thicknesses were inserted into a horizontally positioned plain tube, which had an inner diameter of 10.6 mm and a length of 1.65 m. The coil pitches were 18.4, 27.6, and 36.8 mm, and the wire thicknesses were 1.5, 2.0, and 2.5 mm. Tests were conducted at a saturation temperature of −191 °C, mass fluxes from 58 to 105 kg/m 2 s, and heat fluxes from 22.5 to 32.7 kW/m 2. A direct heating method was used to apply heat to the test tube. The boiling heat transfer coefficients of nitrogen significantly decreased when the dryout occurred. Enhancement performance ratio (EPR), which is the ratio of heat transfer enhancement factor to pressure drop ratio, was used to evaluate the performance of the wire coil inserts. The maximum heat transfer enhancement of the wire coil inserted tubes over the plain tube was 174% with wire 3 having a twist ratio ( p/ D w) of 1.84 and a thickness ratio ( t/ D w) of 0.25. Wire 3-inserted tube showed the highest EPR among the tested tubes in this study.

Transient boiling heat transfer characteristics of nitrogen (bubble behavior and heat transfer rate at stepwise heat generation)

Transient boiling heat transfer characteristics of liquid nitrogen at stepwise heat generation is investigated. A series of heat transfer experiments are carried out using a 0.10 mm diameter horizontal platinum wire as the test heater. Bubble behavior is observed by taking high-speed movie photographs. The history of heat transfer rate corresponds well with the bubble behavior during the transition stage to film boiling. In the case of a low heat generation rate, boiling transition occurs due to the coalescence of nucleate boiling bubbles. In the case of a high heat generation rate, a vapor sheath grows along the heater wire. Boiling transition occurs due to the settling of the vapor sheath around the wire and the heat transfer rate just after the boiling transition becomes much lower than that of stationary film boiling. In the case of an extremely high heat generation rate, a lot of fine bubbles grow rapidly and simultaneously when the heater temperature reaches the homogeneous nucleation temperature. Boiling transition occurs due to the filling of fine bubbles on the heater.