STEMMUS-UEB v1.0.0: integrated modeling of snowpack and soil water and energy transfer with three complexity levels of soil physical processes

A snowpack has a profound effect on the hydrology and surface energy conditions of an area through its effects on surface albedo and roughness and its insulating properties. The modeling of a snowpack, soil water dynamics, and the coupling of the snowpack and underlying soil layer has been widely reported. However, the coupled liquid–vapor–air flow mechanisms considering the snowpack effect have not been investigated in detail. In this study, we incorporated the snowpack effect (Utah energy balance snowpack model, UEB) into a common modeling framework (Simultaneous Transfer of Energy, Mass, and Momentum in Unsaturated Soils with Freeze-Thaw, STEMMUS-FT), i.e., STEMMUS-UEB. It considers soil water and energy transfer physics with three complexity levels (basic coupled, advanced coupled water and heat transfer, and finally explicit consideration of airflow, termed BCD, ACD, and ACD-air, respectively). We then utilized in situ observations and numerical experiments to investigate the effect of snowpack on soil moisture and heat transfer with the abovementioned model complexities. Results indicated that the proposed model with snowpack can reproduce the abrupt increase of surface albedo after precipitation events while this was not the case for the model without snowpack. The BCD model tended to overestimate the land surface latent heat flux (LE). Such overestimations were largely reduced by ACD and ACD-air models. Compared with the simulations considering snowpack, there is less LE from no-snow simulations due to the neglect of snow sublimation. The enhancement of LE was found after winter precipitation events, which is sourced from the surface ice sublimation, snow sublimation, and increased surface soil moisture. The relative role of the mentioned three sources depends on the timing and magnitude of precipitation and the pre-precipitation soil hydrothermal regimes. The simple BCD model cannot provide a realistic partition of mass transfer flux. The ACD model, with its physical consideration of vapor flow, thermal effect on water flow, and snowpack, can identify the relative contributions of different components (e.g., thermal or isothermal liquid and vapor flow) to the total mass transfer fluxes. With the ACD-air model, the relative contribution of each component (mainly the isothermal liquid and vapor flows) to the mass transfer was significantly altered during the soil thawing period. It was found that the snowpack affects not only the soil surface moisture conditions (surface ice and soil water content in the liquid phase) and energy-related states (albedo, LE) but also the transfer patterns of subsurface soil liquid and vapor flow.

Thermal efficiency of metal foams on pool boiling

This paper presents an experimental work on pool boiling using HFE-7100 at saturated conditions, under atmospheric pressure, and copper and nickel foams as the heating surface with four different thicknesses varying between 0.5 mm and 3 mm, followed by an analysis of the effect of foam fin-efficiency based on Ghosh model. All foams showed a better heat transfer coefficient (HTC) than the plain surface; however, as the heat flux increased, the HTC from the thicker nickel foams decreased due to the bubble vapor flow inside the foam. On the other hand, the thinner nickel foam showed better HTC at high heat fluxes with a maximum enhancement of 120%. The foam efficiency presented a similar tendency with the HTC, i.e., as the thickness decreases the efficiency increases; however, as compared with copper foams with a similar area but different porous diameter, the copper foams are 40% more efficient than the nickel ones due to the foam material, which has a thermal conductivity 4.5 times higher.

Investigation of the characteristics of ion saturation current in plasma over the keyhole in the process of electron beam welding

The energy spectra of the ion saturation current of the Langmuir probe in the plasma formed over the keyhole directly during the process of electron-beam welding of steel 09G2S with the varied parameters (e.g., the welding speed and focus coil current) has been investigated. The presence of typical zones with the energy spectrum peaks in the low-frequency and high- frequency bands has been shown. It has been established that the peak location in the high- frequency range of the energy spectrum does not depend on the welding modes and the position of the probes relative to the keyhole. The low-frequency range of the energy spectrum depends on the vapor flow density of the keyhole and is rather sensitive to the welding modes. The use of electron beam oscillation makes it possible to control plasma flows and hydrodynamic processes in the penetration channel.

An evaporation flux of pure vapor in the method of lattice Boltzmann equations

The regularities of the evaporation flux of pure vapor in the method of lattice Boltzmann equations (LBE) are investigated. The simulations show that the mass flux during the evaporation of a flat surface is proportional to the difference in the densities of the saturated vapor at the surface temperature and surrounding vapor, which is in good agreement with the Hertz–Knudsen law. A simple method is proposed for setting the vapor flow at the flat boundary of the computational domain for the LBE method.

Analysis of Passive Tube Condensation With Non-Condensable Gas Using Heat and Mass Analogy Model

In this study, we used the heat and mass analogy model to be able to predict the heat transfer properties of a condenser tube operating in passive mode. The most important advantage of analogy model comparing boundary layer model is simplicity and fast computation, that’s why it can be applied to various engineering problems for many cases. The heat and mass analogy model is based on the heat transfer balance between liquid film and gas mixture area. The main problem for the liquid film region is the heat transfer coefficient (HTC) which is affected negatively in the presence of non-condensable gas. Therefore, our main goal is to increase the HTC and condensation heat transfer rate by updating the analogy code. In the gas-vapor mixture region, heat transfer mainly occurred as latent condensation and sensible heat transfer. In order to maintain this balance between the mixture and liquid film, the interface temperature is iterated. After defining a specified tolerance value of the heat and mass analogy model codes, this iteration process was started to be used at the entrance of a condenser tube. The gas and vapor mixture is considered to be saturated at the liquid/gas interface in the heat and mass transfer analogy model. Via boundary layer study of species concentration and energy balance, the non-condensable gas effect on condensation is added into the equation. For the condensation heat transfer coefficient of turbulent vapor flow associated with laminar condensate, numerical predictions were made and they were satisfactory. The predictions were compared with the experimental data from the literature to be able to test the model. Non-condensable gas mass fraction and vapor-non-condensable mixture temperature were presented in the form of radial and axial profiles.

Experimental Study of a Loop Heat Pipe with Direct Pouring Porous Wick for Cooling Electronics

A pouring silicate wick was manufactured to explore the influence of process and physical properties on the production and performance of loop heat pipes (LHP). This paper theoretically analyzed the advantages of pouring porous wick and introduced the technology of pouring silicate directly on evaporator. Based on this, the heat transfer performance of copper-methanol LHP system with pouring porous wick was tested under different positions. The results showed that with the input of multiple heat sources, the LHP could start up and maintain a stable temperature from 40 W to 160 W. When the vapor grooves were located above the compensation chamber, it was difficult to start up positively. By adding gravity assistance, the system could obtain more stable liquid supply and vapor flow, so as to realize start up. In the variable heat load test, the LHP showed good adaptability to the change of heat load. The thermal resistance of the system decreased with the increase of heat load. The thermal resistance of the evaporator almost unchanged and was always lower than 0.05 °C/W, which indicated that the pouring porous wick in the evaporator had good heat load matching.

Evaporation front and its motion

The evaporation demands upon a rock or soil surface can exceed the ability of the profile to bring sufficient amount of liquid water. A dry surface layer arises in the porous medium that enables just water vapor flow to the surface. The interface between the dry and wet parts of the profile is known as the evaporation front. The paper gives the exact definition of the evaporation front and studies its motion. A set of differential equations governing the front motion in space is formulated. Making use of a set of measured and chosen values, a problem is formulated that illustrates the obtained theory. The problem is solved numerically and the results are presented and discussed.

Thrust Augmentation of Micro-Resistojets by Steady Micro-Jet Blowing into Planar Micro-Nozzle

The present work investigates the impact of steady micro-jet blowing on the performance of a planar micro-nozzle designed for both liquid micro-thrusters and nitrogen cold-gas micro-resistojets. Two micro-injectors have been placed into the divergent region along the sidewalls, injecting a secondary flow of propellant perpendicularly to the wall where they have been located. The micro-jet actuator configuration is characterized by the dimensionless momentum coefficient cμ. The best performance improvement is retrieved at the maximum cμ for both water vapor (Δ%T,jet = +22.6% and Δ%Isp,Tjet = +2.9% at cμ = 0.168) and nitrogen gaseous flows (Δ%T,jet = +36.1% and Δ%Isp,Tjet = +9.1% at cμ = 0.297). The fields of the Mach number and the Schlieren computations, in combination with the streamline visualization, reveal the formation of two vortical structures in the proximity of secondary jets, which energize the core flow and enhance the expansion process downstream secondary jets. The compressible momentum thickness along the width-wise direction θxy in presence of secondary injection reduces as a function of cμ. In particular, it becomes smaller than the one computed for the baseline configuration at cμ > 0.1, decreasing up to about and -57% for the water vapor flow at cμ = 0.168, and -64% for the nitrogen gaseous flow at cμ = 0.297.