Molecular Origin of Fast Evaporation at the Solid–water–vapor Line in a Sessile Droplet

By analyzing the behaviors of water molecules at the solid–water–vapor contact line, we explore the molecular origins of large evaporation rates at the contact line and find new ways to...

Assessment of global total column water vapor sounding using a spaceborne differential absorption radar

The feasibility of using a differential absorption radar (DAR) to retrieve total column water vapor from space is investigated. DAR combines at least two radar tones near an absorption line, in this case a water vapor line, to measure humidity information from the differential absorption on and off the line. From a spaceborne platform, DAR can be used to retrieve total column water vapor by measuring the differential reflection from the Earth's Surface. We assess the expected precision, yield, and potential biases of retrieved total column water vapor values by applying an end-to-end radar instrument simulator to near-global weather analysis fields collocated with CloudSat measurements. The approach allows us to characterize the DAR performance across a globally representative dataset of atmospheric conditions including clouds and precipitation as well as different surface types. We assume a hypothetical spaceborne G-band radar with pulse compression orbiting the earth at 405 km with a 1 m antenna, equivalent to a footprint diameter of 850 m, and 500 m horizontal integration. The simulations include the scattering effects of rain, snow, as well as liquid and ice clouds, spectroscopic uncertainties, and uncertainties due to the initial assumed water vapor profile. Results indicate that, using two radar tones at 167 and 174.8 GHz with a transmit power of 20 W ensures that both pulses will reach the surface at least 70 % of the time in the tropics and more than 90 % of the time outside the tropics, and that total column water vapor can be retrieved with a precision better than 1.3 mm.

Experimental and Numerical Analysis of Start-Up of a Capillary Pumped Loop for Terrestrial Applications

A study on the start-up phases of a capillary pumped loop for terrestrial application (CPLTA) is proposed in this paper. Experimental analysis and numerical modeling, using a one-dimensional spatial discretization model, based on thermohydraulic equations and solved by nodal network/electrical analogy, are presented to study the thermal and hydraulic behavior of the loop for methanol and n-pentane as working fluids, during start-up transient phases. The experimental observations are backed up by the numerical model to help the transient and steady analysis of this kind of loop. The precise numerical study allows to have a better understanding of the complicated phenomena happening during the start-up and to have a global view of the behavior of the capillary pumped loop for integrated power (CPLIP) during these phases. In this study, it will be also shown the influence of vapor line solid walls thermal inertia and its impact on the dynamic behavior and on the success of the start-up of the loop.

Experimental Investigation of the Operation Modes of a Flat Loop Heat Pipe

The paper presents the experimentally investigated operation modes of a flat loop heat pipe (LHP). The LHP is an efficient heat transfer device operating on the principle of evaporation-condensation cycle and successfully applied in space technology, including cooling heat-stressed components of electronic devices and computer equipment.We have experimentally studied how design parameters of the vapor line and its coolant flow influence on the LHP operation mode and also have determined the causes for emerging oscillatory mode of the LHP operation at low heat load. The paper depicts the experimentally measured temperatures in the LHP characteristic points and the photographs of the coolant flow in the vapor line.Based on the experimental data, we have drawn the following conclusions:A vapor-liquid coolant flow in the vapor line in the range of the heat loads under consideration has been detected. There is no superheating vapour observed.The flow regime of the vapor-liquid mixture depends on both the heat load and the vapor pipe diameter. The decrease in the internal diameter of the investigated vapor line section from 7 mm to 4 mm led to the increase of its vapor content and to the decrease of the heating surface temperature when the heat loads were above 80 W. For example, the temperature of the heating surface T1 decreased from 109.5 °С to 100 °С at a heat load of 110 W. Reducing the heat load from 80 W to 60 W leads to a change in the flow regime of the vapor-water mixture from the annular to the slug regime. Found that at low heat loads (up to 40 W), there is no LHP loop operation observed. Periodic fluctuations in the water level in the vapor line are detected. The LHP operates in thermo-syphon mode. For these heat loads, the influence of the vapor line diameter on the thermal state of the LHP is not observed.Found that at low heat loads the LHP operation mode depends only on the flow regime of the coolant in the vapor line. With the annular regime of the coolant flow in the vapor line, a stationary mode of operation of the LHP is observed. When changing the flow regime of the coolant from the annular to the slug, the LHP operation mode is changed from stationary to oscillatory.