scholarly journals Effect of Substrate Conductivity on the Transient Thermal Transport of Hygroscopic Droplets during Vapor Absorption

Micromachines ◽  
2020 ◽  
Vol 11 (2) ◽  
pp. 193 ◽  
Author(s):  
Zhenying Wang ◽  
Daniel Orejon ◽  
Khellil Sefiane ◽  
Yasuyuki Takata
Keyword(s):  
Vapor Pressure ◽  
Thermal Effect ◽  
Pure Water ◽  
Heat Removal ◽  
Mass Transfer Process ◽  
Relative Strength ◽  
Droplet Surface ◽  
Liquid Desiccant ◽  
Isothermal Model ◽  
Vapor Absorption

In all kinds of liquid desiccant dehumidification systems, the temperature increase of the desiccant solution due to the effect of absorptive heating is one of the main reasons of performance deterioration. In this study, we look into the thermal effects during vapor absorption into single hygroscopic liquid desiccant droplets. Specifically, the effect of substrate conductivity on the transient heat and mass transfer process is analyzed in detail. The relative strength of the thermal effect and the solutal effect on the rate of vapor absorption is investigated and compared to the thermal effect by evaporative cooling taking place in pure water droplets. In the case of liquid desiccants, results indicate that the high thermal conductivity of copper substrates ensures more efficient heat removal, and the temperature at the droplet surface decreases more rapidly than that on Polytetrafluoroethylene (PTFE) substrates. As a result, the initial rate of vapor absorption on copper substrates slightly outweighs that on PTFE substrates. Further analysis by decomposing the vapor pressure difference indicates that the variation of vapor pressure caused by the temperature change during vapor absorption is much weaker than that induced by the concentration change. The conclusions demonstrate that a simplified isothermal model can be applied to capture the main mechanisms during vapor absorption into hygroscopic droplets even though it is evidenced to be unreliable for droplet evaporation.

Porous Hydroxyapatite with Tailored Crystal Surface Prepared by Hydrothermal Method

2005 ◽  
Vol 284-286 ◽  
pp. 353-356 ◽  
Author(s):  
Koji Ioku ◽  
Giichiro Kawachi ◽  
Nakamichi Yamasaki ◽  
Hirotaka Fujimori ◽  
Seishi Goto
Keyword(s):  
Aspect Ratio ◽  
Vapor Pressure ◽  
Hydrothermal Method ◽  
Saturated Vapor Pressure ◽  
Crystal Surface ◽  
Saturated Vapor ◽  
Pure Water ◽  
Porous Hydroxyapatite ◽  
Exposure Method ◽  
The Mean

Porous plates of hydroxyapatite (Ca10(PO4)6(OH)2; HA) with about 0.5 to 5 mm in thickness and porous HA granules of about 40 µm to 1 mm in size with tailored crystal surface were prepared by the hydrothermal vapor exposure method at the temperatures above 105 °C under saturated vapor pressure of pure water. Porous HA plates with about 75 % porosity prepared at 120 °C were composed of rod-shaped crystals of about 20 µm in length. Porous HA granules prepared at 160 °C were also composed of rod-shaped crystals of about 20 µm in length with the mean aspect ratio of 30. These crystals were elongated along the c-axis. Rod-shaped HA crystals were locked together to make micro-pores of about 0.1 to 0.5 µm in size. Both of materials were nonstoichiometric HA with calcium deficient composition. These materials must have the advantage of adsorptive activity, because they had large specific crystal surface and much micro-pores.

Lubrication Model for Vapor Absorption/Desorption of Hygroscopic Liquid Desiccant Droplets

2021 ◽  
pp. 67-70
Author(s):  
Zhenying Wang ◽  
George Karapetsas ◽  
Prashant Valluri ◽  
Khellil Sefiane ◽  
Yasuyuki Takata
Keyword(s):  
Liquid Desiccant ◽  
Vapor Absorption

Hydrothermal Preparation of Porous Hydroxyapatite with Tailored Crystal Surface

2005 ◽  
Vol 288-289 ◽  
pp. 521-524 ◽  
Author(s):  
Alin Iuga ◽  
Giichiro Kawachi ◽  
Nakamichi Yamasaki ◽  
M. Toda ◽  
Hirotaka Fujimori ◽  
...  
Keyword(s):  
Aspect Ratio ◽  
Vapor Pressure ◽  
Saturated Vapor Pressure ◽  
Crystal Surface ◽  
Saturated Vapor ◽  
Pure Water ◽  
Hydrothermal Preparation ◽  
Porous Hydroxyapatite ◽  
Exposure Method ◽  
The Mean

Porous sheets of hydroxyapatite (Ca10(PO)4(OH)2; HA) with about 50 µm to 1 mm in thickness and porous HA granules of about 50 µm to 1 mm in size with tailored crystal surface were prepared by the hydrothermal vapor exposure method at the temperatures above 105 °C under saturated vapor pressure of pure water. Porous HA sheets with about 75 % porosity prepared at 120 °C were composed of rod-shaped crystals of about 30 µm in length. Porous HA granules prepared at 160 °C were also composed of rod-shaped crystals of about 20 µm in length with the mean aspect ratio of 30. These crystals were elongated along the c-axis. Rod-shaped HA crystals were locked together to make micro-pores of about 0.1 µm in size. Both of materials were nonstoichiometric HA with calcium deficient composition. These materials must have the advantage of adsorptive activity, because they had large specific crystal surface and much micro-pores.

Diffusion Cells for Integrating Temperature and Humidity Over Long Periods of Time

1988 ◽  
Vol 125 ◽  
Author(s):  
Fred Trembour ◽  
Franklin L. Smith ◽  
Irving Friedman
Keyword(s):  
Vapor Pressure ◽  
Pressure Gradient ◽  
Pure Water ◽  
Volcanic Glass ◽  
Saturated Solution ◽  
Rubber Stopper ◽  
Centrifuge Tube ◽  
Final Design ◽  
One Year ◽  
Vapor Pressure Gradient

ABSTRACTThe rate of many processes, including the diffusion of water into rhyolitic volcanic glass (obsidian), as well as the racemization of amino acids is temperature dependent, and a knowledge of temperatures integrated over time periods of at least a year is necessary to quantify these processes. The construction and properties of simple devices consisting of small plastic containers that change weight at a rate that is a function of temperature and the activity of water will be described. The cells function because water diffuses through the plastic across a constant vapor-pressure gradient. This vapor-pressure gradient is maintained constant between the substances within the cell and the materials outside the cell. The plastic cells are usually filled with water and surrounded by a dehydrating agent, such as silica gel. A better arrangement is to fill the cell with a mixture of solid sodium chloride (NaCl) and a saturated solution of NaCl, and to surround the cell with pure water. A number of plastics have been investigated, including polycarbonate, polystyrene, tefzel, polyallomer, and methacrylate. The cells have been sealed by various methods including screw caps, room-temperature vulcanizing silicone rubber sealant, and rubber stoppers. The final design consists of a small cell made of a polycarbonate plastic centrifuge tube containing solid NaCl plus NaCl-saturated solution sealed with a rubber stopper and placed in a polypropylene tube containing pure water. Our aim has been to develop cells that are sufficiently sensitive to yield a precision of ±0.2°C when exposed for one year at temperatures that range from 0° to 40°, and that will fit into metal fittings that can be screwed into standard 3/4-inch plastic water pipe (approximately 1 inch outside diameter).

Absorption of Water Vapor Using Superabsorbent Polymer Composite Material

2020 ◽  
Vol 858 ◽  
pp. 129-139
Author(s):  
Ariel Verzosa Melendres ◽  
Rolan Pepito Vera Cruz
Keyword(s):  
Composite Material ◽  
Water Vapor ◽  
Relative Humidity ◽  
Pure Water ◽  
Polymer Composite Material ◽  
Air Transport ◽  
Water Vapor Absorption ◽  
Vapor Absorption ◽  
Digital Microscope ◽  
Pass Through

The ability of superabsorbent polymers (SAP) to absorb water vapor was studied. A multilayer composite material was prepared where SAP particles were spread in the fluffy fibrous layer located in the middle of the composite structure. Distribution of SAP within the composite material permits air to pass through its porous structure effectively hence allowing efficient contact of air with SAP. SAP was able to decrease the relative humidity of air of a 3-L cabinet from 96% relative humidity (RH) to 52% and 49 % (RH) in 18 hours using 2 g and 4 g of SAP respectively. Study on the water vapor absorption ability of SAP placed together with pure water in a closed cabinet was conducted with and without convective air transport effect. Convective air transport was done by activating the 12 V fan allowing air recirculation speed at rates corresponding to constant voltage settings of 6 V and 12 V. Higher SAP water vapor absorption rate was obtained at higher air recirculation speed. SAP particles swelled after water vapor absorption with slight decrease in the porosity of composite material as observed through the digital microscope.

Experimental Investigation of Rewetting During Quenching of Hot Surface by Round Jet Impingement Using Al2O3–Water Nanofluids

2016 ◽  
Author(s):  
Avadhesh K. Sharma ◽  
Mayank Modak ◽  
Santosh K. Sahu
Keyword(s):  
Experimental Investigation ◽  
Cooling System ◽  
Removal Rate ◽  
Pure Water ◽  
Heat Removal ◽  
Jet Impingement ◽  
Dimensionless Number ◽  
Surface Cooling ◽  
Fuel Rods ◽  
Hot Surface

Impinging jet surface cooling is being used in many industrial and engineering applications due to their higher heat removal rate. Jet impingement is one of the methods to cool hot surfaces, especially in textile, metal and electronic industries. Due to high heat removal rate the jet impingement cooling of the hot surfaces is being used in nuclear industries. During the loss of coolant accidents (LOCA) in nuclear power plant, an emergency core cooling system (ECCS) cool the cluster of clad tubes using consisting of fuel rods. The usual water flow within a reactor core is bottom to top, parallel to the fuel rods. When a hot surface quenched at very high temperature using a jet of cold fluid, during the quenching the initial heat transfer is limited by film boiling. The effective cooling takes place only after the surface temperature is below the leidenfrost temperature. In the present work an experimental investigation has been carried out to analyze the rewetting phenomenon of a hot vertical stainless steel foil by circular impinging jets of pure water and Al2O3–water nanofluids. The rewetting time and rewetting velocity in the form of dimensionless number (Peclet number) obtained from the thermal images obtained from infrared thermal imaging camera (A655sc, FLIR System). Experiments are performed for different Reynolds number (Re = 5000, 8000), and Al2O3–water nanofluids concentration (Φ = 0.15%, 0.6%)

Ideal Solutions and Colligative Properties

2009 ◽  
Author(s):  
Christopher O. Oriakhi
Keyword(s):  
Vapor Pressure ◽  
Freezing Point ◽  
Pure Water ◽  
The Other ◽  
Dissolved Species ◽  
Pure Solvent ◽  
Ideal Solutions ◽  
Lower Vapor Pressure ◽  
Solution Changes ◽  
Colligative Properties

Colligative properties of solutions are those that depend only on the number of solute particles (molecules or ions) in the solution rather than on their chemical or physical properties. The colligative properties that can be measured experimentally include: • Vapor pressure depression • Boiling point elevation • Freezing point depression • Osmotic pressure Noncolligative properties, on the other hand, depend on the identity of the dissolved species and the solvent. Examples include solubility, surface tension, and viscosity. The addition of a solute to a solvent typically causes the vapor pressure of the solvent (above the resulting solution) to be lower than the vapor pressure above the pure solvent. As the concentration of the solute in the solution changes, so does the vapor pressure of the solvent above a solution. The vapor pressure of a solution of a nonvolatile solute is always lower than that of the pure solvent. For example, an aqueous solution of NaCl has a lower vapor pressure than pure water at the same temperature. The addition of solute to a pure solvent depresses the vapor pressure of the solvent. This observation, first made by Raoult, is now commonly known as Raoult’s law. The law states that the lowering of vapor pressure of a solution containing non-volatile solute is proportional to the mole fraction of the solute.

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