Effects Of Asymmetric Heating Research Articles

Experimental study on natural circulation flow instability in parallel boiling channels under low pressure

Two-phase flow instabilities in parallel boiling channels under natural circulation condition were experimentally studied at low pressure (0.2–0.6 MPa). The parallel boiling channels composed of two different form channels, namely a 3 × 3 rod bundle channel and a tube channel, were used as the testing section. In the present experiment, the flow oscillation behaviors can be classified into three typical modes based on their frequency spectrum characteristics: (1) small amplitude out-of-phase flow instability induced by the type-1 density wave oscillations in parallel boiling channels, (2) large amplitude out-of-phase flow instability with reversal flow induced by the occurrence of geysering in tube channel and (3) a kind of compound flow instability superposed by geysering and natural circulation instability. The influence of thermal hydraulic parameters on the evolution process of above three flow instabilities were analyzed. The marginal stability boundaries presented by the subcooling number (Nsub) and phase change number (Npch) at different system pressures are obtained and all unstable flow occurs in the negative region of the outlet equilibrium quality in the present experiment. Besides, the effects of asymmetric heating between two parallel channels on NC flow instability were also studied. The asymmetric heating can change the NC flow distribution in parallel boiling channels and reduce the system stability. The occurrence of out-phase oscillations in parallel channels can be suppressed with the increasing of heating power asymmetry.

SIMULATED PHOTOEVAPORATIVE MASS LOSS FROM HOT JUPITERS IN 3D

ABSTRACT Ionizing stellar photons heat the upper regions of planetary atmospheres, driving atmospheric mass loss. Gas escaping from several hot, hydrogen-rich planets has been detected using UV and X-ray transmission spectroscopy. Because these planets are tidally locked, and thus asymmetrically irradiated, escaping gas is unlikely to be spherically symmetric. In this paper, we focus on the effects of asymmetric heating on local outflow structure. We use the Athena code for hydrodynamics to produce 3D simulations of hot Jupiter mass loss that jointly model wind launching and stellar heating via photoionization. Our fiducial planet is an inflated, hot Jupiter with radius R p = 2.14 R Jup ?> and mass M p = 0.53 M Jup ?> . We irradiate the initially neutral, atomic hydrogen atmosphere with 13.6 eV photons and compute the outflow’s ionization structure. There are clear asymmetries in the atmospheric outflow, including a neutral shadow on the planet’s nightside. Given an incident ionizing UV flux comparable to that of the Sun, we find a steady-state mass loss rate of ∼ 2 × 10 10 ?> g s−1. The total mass loss rate and the outflow substructure along the substellar ray show good agreement with earlier 1D models, for two different fluxes. Our 3D data cube can be used to generate the outflow’s extinction spectrum during transit. As a proof of concept, we find absorption of stellar Lyα at Doppler-shifted velocities of up to ±50 km s−1. Our work provides a starting point for further 3D models that can be used to predict observable signatures of hot Jupiter mass loss.

Research on two-phase flow instability in parallel rectangular channels

In the present work, a theoretical model for Density Wave Oscillations flow instability in parallel rectangular channels is built with a lumped mathematical model based on homogenous hypothesis. The parallel channel comprises the entrance section, heating section and riser section and the model consists of the boiling channel model, pressure drop model, parallel channel model and constructive model, while subcooled boiling effect is neglected and the final nonlinear ordinary differential equations are solved by Gear method. The model is validated with experimental data of a single channel with constant pressure drop and that of a twin-channel flow instability experiment. Then the flow instability in twin rectangular channel system is studied under different conditions. The effects of pressure, P, inlet throttling coefficient, kin and exit throttling coefficient, kout are examined through the parameter plane of the subcooling number, Nsub and phase change number, Npch and the frequency of the oscillations, f. Finally, the effects of asymmetric heating and throttling on flow instability are also analyzed.

Balanced Contributions to the Intensification of Hurricane Opal as Diagnosed from a GFDL Model Forecast

Abstract Stationary and propagating asymmetric features of atmospheric or oceanic origin near a hurricane are known to have an impact on its evolution. Although theoretical and observational studies have investigated the influence of such features on hurricane intensification, the degree to which either environmental or near-core region asymmetries of heating, friction, or potential vorticity (PV), in contrast to symmetric processes, weaken or intensify a hurricane has not been established. The present study uses the symmetric balanced model formulation of Eliassen and its extension to asymmetric balance (AB) to evaluate the impact of heating and friction, as well as eddy fluxes, on the intensification of Hurricane Opal of 1995 in a Geophysical Fluid Dynamics Laboratory (GFDL) model forecast. The diagnostics are made in cylindrical coordinates, with the symmetric vortex as the basic state and asymmetries as the environment. The application of AB, which explicitly includes the effects of asymmetric heating...

The effect of asymmetric heating on the onset of thermal instability in the thermal entrance region of a parallel plate channel

This paper presents a time-dependent linear analysis on the onset of thermal instability of fully developed laminar flow in the thermal entrance region of a horizontal parallel plate channel heated asymmetrically; where the lower plate, upper plate and inlet are subjected to three different constant temperatures. The heating of the upper plate causes a thermal stratification, but the heating of the lower plate introduces a thermal destabilization. With the three different inlet, upper plate and lower plate temperatures, six heating configurations for the horizontal parallel plate channel are analysed and only three representative unstable heating configurations are shown. A criterion δ/ δt = 0 with δ/ δx ≠ 0 for the determination of the critical condition marking the onset of longitudinal vortex rolls yields results that agree well with the existing experimental data in comparison with the criterion δ/ δx = 0 used previously. The critical Rayleigh numbers and the corresponding critical wave numbers for the three unstable heating configurations with Pr = 0.7 and 7.0 are presented.