Numerical Investigation of Heat Transfer Characteristics of scCO2 Flowing in a Vertically-Upward Tube with High Mass Flux

In this work, the heat transfer characteristics of supercritical pressure CO2 in vertical heating tube with 10 mm inner diameter under high mass flux were investigated by using an SST k-ω turbulent model. The influences of inlet temperature, heat flux, mass flux, buoyancy and flow acceleration on the heat transfer of supercritical pressure CO2 were discussed. Our results show that the buoyancy and flow acceleration effect based on single phase fluid assumption fail to explain the current simulation results. Here, supercritical pseudo-boiling theory is introduced to deal with heat transfer of scCO2. ScCO2 is treated to have a heterogeneous structure consisting of vapor-like fluid and liquid-like fluid. A physical model of scCO2 heat transfer in vertical heating tube was established containing a gas-like layer near the wall and a liquid-like fluid layer. Detailed distribution of thermophysical properties and turbulence in radial direction show that scCO2 heat transfer is greatly affected by the thickness of gas-like film, thermal properties of gas-like film and turbulent kinetic energy in the near-wall region. Buoyancy parameters Bu < 10-5, Bu* < 5.6 × 10−7 and flow acceleration parameter Kv < 3 × 10−6 in this paper, which indicate that buoyancy effect and flow acceleration effect has no influence on heat transfer of scCO2 under high mass fluxes. This work successfully explains the heat transfer mechanism of supercritical fluid under high mass flux.

Effects of chemical reaction, viscosity, thermal conductivity, heat source, radiation/absorption, on MHD mixed convection nano-fluids flow over an unsteady stretching sheet by HAM and numerical method

Investigations are performed for further observations of heat and mass transfer in magneto-hydrodynamic mixed-convectional nano-fluid flow with the assumption of variable viscosity and thermal-conductivity over an unsteady stretching sheet. Base fluid is Carboxy-methyl cellulose (CMC) water as a carrier fluid with different nano-particles such as [Formula: see text] (Titanium), Ag (Silver), [Formula: see text] (Aluminum), and Cu (Copper). Flow contains different physical parameters, such as heat source, chemical reaction effect, Schmidt number, and radiation absorptions effects are observed to be significant in the presences of magnetic field. Obtained equations are solved by numerically BVP4C-package (shooting method) and analytically by BVPh2.0-package (Homotopy Analysis Method “HAM”). Interested physical quantities are, viscosity-parameter ( A), Thermal-conductivity parameter ( N),Thermocapillary-number ( M), Hartmann-number (Ma), Prandtl-number (Pr), 4-nano-particles ([Formula: see text]), temperature Grashof number ([Formula: see text]), and mass Grashof number ([Formula: see text]) are the focus to the velocity, temperature, and solute concentration profiles. It is concluded that, Solute concentration of ([Formula: see text])-water has higher than the other 3-nano-fluids. Mass flux, heat flux, and Skin friction of fluids are direct functions of magnetic force, while inverse function of temperature. Magnetic force also decreased the speed of fluids and hence mass flux reduced which implies that, the temperature reduces. [Formula: see text] has also inverse relation with mass flux, heat flux, and skin friction, while direct relation with the speed of fluids. Similarly, [Formula: see text] has inverse relation with [Formula: see text], [Formula: see text], and [Formula: see text], but direct relation with [Formula: see text]. Different results are shown in graphical and tabular form.

Decadal variations of Hadley and Walker circulations in the tropics

Preliminary estimate of divergent Hadley and Walker circulation associated with inter-decadal variations in the tropics is made with 50-year reanalysis data and compared with their inter-annual counterparts. Interdecadal and inter-annual components are separated using harmonic analysis and meridional and zonal mass flux stream functions are used to calculate the strength of Hadley and Walker circulations. The magnitude of inter-decadal Hadley and Walker circulation anomalies are shown to be comparable to those associated with dominant inter-annual variations. How superposition of inter-decadal and inter-annual divergent circulations may influence regional climate is discussed.

Observational study on boundary-layer moist static energy budget over the tropical western Pacific and its variability associated with boreal summer intraseasonal oscillation

Moist static energy (MSE) in the atmospheric boundary layer (BL) is one of the essential parameters determining convective activity over tropical oceanic areas. It is thus important to quantitatively understand BL MSE budget processes and their variability. Among these processes, only few studies have evaluated contributions of entrainment across the BL top and convective downdraft. This study aims to estimate these contributions by analyzing upper-air and surface meteorological observations obtained using Research Vessel Mirai over the tropical western Pacific in June 2008. Daily-mean downward mass fluxes due to the two processes are calculated using BL dry static energy and moisture budget equations under the BL quasi-equilibrium approximation. Estimated mass fluxes are consistent with convective activity observed by a shipborne weather radar and a ceilometer. This study further examines how the mass fluxes and budget processes are modulated when a convectively active phase of boreal summer intraseasonal oscillation arrives at the observation area in the second half of the month. It is found that, while the contribution of the entrainment does not change significantly, the convective downdraft mass flux and the resultant BL MSE export increase 5 times and 3 times, respectively, in the convectively active period compared with those in the pre-active period. Furthermore, ~1/4 of the increase in the convective downdraft mass flux is attributable to the increase in MSE of convective downdraft air associated with mid-tropospheric moistening.