Saturated Humid Air Research Articles

High potency of application on an open direct-contact thermal storage using humid air

To reuse low-temperature wasted heat as a thermal resource for high temperature, a direct-contact adsorption thermal storage was focused using humid air and zeolite 13X particles as the working fluid and adsorbent, respectively. Only a few previous studies have chosen the working fluid in gaseous form because it is unavailable for latent heat in generating heat sources. Recovering waste heat in humid air to generate hotter steam is unique and becomes an originality of our present work. The time required to regenerate zeolite particles and the maximum temperature of the generated steam were investigated assuming a warm-up device for a vehicle. The time required to regenerate zeolite was investigated by changing the dew point, temperature, and superficial velocity of the inlet humid air. It was mainly affected by the temperature of the inlet air. The absorbent was regenerated within 30 min when the humid air preheated to 200 °C was supplied. On the other hand, the maximum steam temperature was investigated by changing the superficial velocity and temperature of saturated inlet humid air. As one of the significant and novel finding in this work, the steam of >200 °C was obtained as a high-temperature heat source even with saturated humid air unavailable latent heat. Moreover, as theoretical knowledge, it was revealed that the maximum temperature of the heat source can be estimated by the relationship between the heat balance on the packed bed and adsorption equilibrium.

Defining relative humidity in terms of water activity: III. Relations to dew-point and frost-point temperatures

Relative humidity (RH) is a fundamental quantity used in many fields of engineering and science, and in particular in meteorology and climate research. Relative fugacity (RF) and, equivalently, relative activity of water vapour in humid air have recently been proposed as a physically well-founded, unambiguous common metrological reference quantity for several conventional but mutually inconsistent definitions of RH. The RF definition is valid is valid under real-gas conditions and above boiling and sublimation temperatures. While differences between RH and RF mostly remain within uncertainties of typical present-day RH measurements, such systematic discrepancies are expected to be of substantial climatological relevance. Consequently, interdisciplinary harmonisation of RH definitions is overdue within the SI framework. Dew-point and frost-point temperatures are preferred measurands in humidity metrology using, for example, chilled-mirror hygrometers. Here, relations are presented for estimating RF from those temperatures, based on equations of state of the 2011 IUGG 5IUGG: International Union of Geodesy and Geophysics, https://iugg.org/. standard TEOS-10, the ‘international thermodynamic equation of seawater—2010’. Recommendations are given for numerically computing RF using the open-source TEOS-10 SIA library 6 6SIA Library: Sea-Ice-Air Library of TEOS-10, http://teos-10.org.. The asymptotic limiting laws of RF for nearly saturated humid air exhibit the familiar form of Clausius–Clapeyron-like equations, despite departing from ideal-gas assumptions. Under various practical conditions, these simple equations may cover the full humidity range with only minor residuals compared to the full numerical TEOS-10 solution for RF.

From speed of sound to vapour pressure: an undergraduate school experiment as an example of systematic error research

This article presents an undergraduate project for measuring the speed of sound in the air as a function of air temperature. The measurement is implemented in two versions. The simplicity of the basic experiment in dry air is used for a detailed analysis of systematic errors: the measured values are corrected with an additive constant and optimized to match the expected parabolic dependence of the speed of sound on temperature. Such a time correction is correlated with the physical content, that is, by changing the phase of oscillation of the pressure difference at the reflection of the sound at the open end of the tube. The second part of the experiment involves measuring the speed of sound in saturated humid air as a function of air temperature and allows for a substantive connection of two areas of physics (waves and thermodynamics). The measured water vapour pressure, within the range of statistical errors, follows the theoretical course up to the upper limit of the measured temperature range (60 °C) surprisingly well.

Mechanism of Increasing the Permeability of Water-Bearing Coal Rock by Microwave Steam Explosion

Microwave heating of water-bearing coal can promote pore water evaporation. The pores are broken under the action of steam pressure, increasing the permeability of the coal. This study is aimed at investigating the mechanism of permeability improvement of water-bearing coal rock by microwave steam explosion. First, a microwave oven was used to irradiate and heat five groups of coal rock with different water contents; the NMR test was then conducted on the heated sample. Second, the internal vapor pressure and temperature changes during the heating process were obtained through the T-connector for samples with different water contents. Finally, a numerical experiment was used to explore the deformation characteristics of pores under three filling conditions. The experimental results showed that the total porosity increased significantly when the water content of coal increased from 0% to 8%, while the permeability increased by nearly 4.78 times. The extreme value of gas pressure inside the sample showed an increasing trend. The gas pressure and temperature were in line with the equation of state for an ideal gas during the rising phase. Numerical experiments showed that the pore boundary shrunk inward under vacuum conditions, and compressive stress appeared at the tip. The saturated humid air and liquid water conditions expanded the pore boundaries outward and caused tensile stress at the tip, with the latter being nearly 2.3 times larger than the former, making it more conducive to the development of pores. The findings of this study can be used as a reference value for the expansion of coalbed methane extraction technology.

Thermal Performance of Heat Exchanger Using Zeolite/vapour Adsorption

About 60% of the energy input in the chemical industry is discarded from the plant. Energy saving can be achieved in the entire plant by recovering these waste heats and reusing them as power and heat sources in the power plant. An adsorption heat pump has been developed for the purpose of regeneration of such unused energy. In this study, saturated humid air was supplied to a device packed with 13X zeolite particles of 4 mm in diameter. The time variation of temperature in the apparatus was measured experimentally. Then, the maximum temperature was estimated from the relationship between heat balance and adsorption equilibrium. The trend of the maximum temperature calculated from the heat balance is consistent with experiment. Further, it was found from the result of the heat balance equation that the sensible heat of the humid air supplied and the heat of adsorption of the zeolite are mainly distributed to the sensible heat of the zeolite. In the future, it is important to make effective use of the sensible heat of this zeolite. In order to extract more thermal energy from the device, it is necessary to improve the heat transfer between the packed bed and medium. A double pipe heat exchanger having a zeolite packed bed on the annular side was proposed as an apparatus. Flow direction of the humid air supplied to device was changed in two different ways. The one of them is supplying humid air radial flowly to the device and another is supplying the air in parallel flow. The influence of flow direction on heat transfer between packed bed and medium is studied with numerical simulation.

РАСЧЕТ ПРОЦЕССОВ ТЕПЛОМАССООБМЕНА В КАНАЛАХ ОРОСИТЕЛЕЙ ВЕНТИЛЯТОРНЫХ ГРАДИРЕН ПРИ НАЛИЧИИ УЧАСТКА ВЛАЖНОГО НАСЫЩЕННОГО ВОЗДУХА

The flow of air in the fan cooling tower sprinkler channels in certain initial conditions may be characterized by the presence of a section of saturated humid air. In this case, the calculation of mass transfer according to the criterion equation of mass transfer, obtained from the analogy of the processes of heat and mass transfer, gives an overestimated result of the mass flow value. For the section of saturated air, the intensity of the mass transfer process is calculated using the function of changing the density of saturated steam from the air temperature. The works studying water cooling processes in the fan cooling tower sprinkler channels contain no assessment of the influence the saturated air presence has on the intensity of water cooling. The paper proposes a method for calculating the processes of heat and mass transfer in the cooling tower channels in the presence of a section of saturated air flow, taking into account the peculiarities of calculating mass transfer between water and saturated air. The values of the discrepancy between the final water temperature in calculations according to the proposed method and the method for unsaturated air are given. It is shown that the presence of a saturated air zone leads to an increase in the final temperature of the water compared to the calculations using formulas for unsaturated air. It is revealed that the discrepancy of water temperature calculated by different methods increases with the length of the channel, the value of the initial relative humidity of the air decreases with the growth in the initial air temperature. The offered methodology and obtained results can be used in the deve¬lopment of regime maps and at the design stage of fan cooling towers.

Experimental study of the flow and heat transfer of a gas–water mixture through a packed channel

Waste heat recovery from the flue gas of gas-fired boilers was studied experimentally by measuring the flow and heat transfer of air and water through six kinds of packing with saturated humid air as the simulated flue gas. The experiments measured the effects of inlet air temperature, inlet air velocity and circulating water flow rate on the flow and heat transfer. The results show that higher inlet air temperatures and lower inlet air velocities lower the flow resistance and increase the heat transfer coefficient. The stainless steel packing had better surface wettability and larger thermal conductivity than the plastic packing, which enhanced the heat transfer between the water and the saturated moist air. When both the flow resistance reduction and the heat transfer enhancement were considered, the experimental results gave an optimal packing-specific surface area. A packed heat exchanger tower was designed for waste heat recovery from the flue gas of gas-fired boilers based on the experimental results which had better flow and heat transfer characteristics with lower pump and fan power consumption, more stable system operation and less thermal fluctuations compared with a non-packed heat transfer system with atomized water.

Effect of morphology of nanoscale hydrated channels on proton conductivity in block copolymer electrolyte membranes.

Hydrated membranes with cocontinuous hydrophilic and hydrophobic phases are needed to transport protons in hydrogen fuel cells. Herein we study the water uptake and proton conductivity of a model fuel cell membrane comprising a triblock copolymer, polystyrenesulfonate-block-polyethylene-block-polystyrenesulfonate (S-SES), as a function of water activity in both humid air and liquid water. We demonstrate that the water uptake and proton conductivity of S-SES membranes equilibrated in liquid water are fundamentally different from values obtained when they were equilibrated in humid air. The morphological underpinnings of our observations were determined by synchrotron small-angle X-ray scattering and cryogenic scanning transmission electron microscopy. A discontinuous increase in conductivity when nearly saturated humid air is replaced with liquid water coincides with the emergence of heterogeneity in the hydrated channels: a water-rich layer is sandwiched between two polymer-rich brushes. While the possibility of obtaining heterogeneous hydrated channels in polymer electrolyte membranes has been discussed extensively, to our knowledge, this is the first time that direct evidence for the formation of water-rich subdomains is presented.

Adsorption Study of Silica Gel Particle for Improvement in Design of Adsorption Beds Used in Solar Driven Cooling Units

Simulations using Ansys Fluent 6.3.26 have been performed to look into the adsorption characteristics of a single silica gel particle exposed to saturated humid air streams at Re=108 & 216 and temperature of 300K. The adsorption of the particle has been modeled as a source term in the species and the energy equations using a Linear Driving Force (LDF) equation. The interdependence of the thermal and the water vapor concentration field has been analysed. This work is intended to aid in understanding the adsorption effects in silica gel beds and in their efficient design.

“Partial pressures” of humid air in wide pressure and temperature ranges

“Partial pressure” in humid air is a question very much concerned by scientists and no satisfactory answer has been found to date. This paper proposes a novel method to obtain the “partial pressures” of the water vapor and dry air in humid air. The results obtained by the proposed method are quite different from that obtained by Dalton’s partial pressure law. The fundamental behaviors of water vapor and dry air are studied in depth in wide pressure and temperature ranges. Semi-permeable membrane models are proposed and applied for both saturated and unsaturated humid air. “Improvement factors” are developed to quantitatively describe the magnitude of the interaction between dissimilar molecules. One discovery is that the “partial pressure” of the water vapor in saturated humid air equals Ps, rather than (f·Ps) which was formerly believed. The other is that the interaction between dissimilar molecules may be omitted when temperature is above “cutting-off temperature” for unsaturated humid air. This paper satisfactorily answers the quest of “partial pressures” in humid air from a new perspective.

New calculation method for thermodynamic properties of humid air in humid air turbine cycle – The general model and solutions for saturated humid air

The article proposes a new calculation method for thermodynamic properties (i.e. specific enthalpy, specific entropy and specific volume) of humid air in humid air turbine cycle. The research pressure range is from 0.1 MPa to 5 MPa. The fundamental behaviors of dry air and water vapor in saturated humid air are explored in depth. The new model proposes and verifies the relationship between total gas mixture pressure and gas component pressures. This provides a good explanation of the fundamental behaviors of gas components in gas mixture from a new perspective. Another discovery is that the water vapor component pressure of saturated humid air equals PS, always smaller than its partial pressure (f·PS) which was believed in the past researches. In the new model, “Local Gas Constant” describes the interaction between similar molecules. “Improvement Factor” is proposed for the first time by this article, and it quantitatively describes the magnitude of interaction between dissimilar molecules. They are combined to fully describe the real thermodynamic properties of humid air. The average error of Revised Dalton's Method is within 0.1% compared to experimentally-based data.

Decomposition of volatile organic compounds in a plasma-catalytic reactor

A combined plasma-catalytic reactor was used for purification of air. The air was circulated through a grained catalyst, in which a pulsed-discharge plasma was excited at one time at atmospheric pressure. Acetone, ethyl lactate, and propylene glycol monomethylethyl acetate were used as impurities. The dry air and saturated humid air were purified. Results on the decomposition of the impurities with the use of a heated catalyst and a plasma in an inert filling material were also obtained. The combined reactor showed points in its favor for the purification conditions realized at a relatively small specific power consumption of ~100 J/liter.

Thermodynamic properties for humid gases from 298 to 573 K and up to 200 bar

For the needs of process design, the model proposed in our previous papers was extended to calculate the thermodynamic properties of humidity, heat capacity, molar volume, partial pressure of water vapour, enthalpy and entropy for humid gases (nitrogen, oxygen, air or a nitrogen–oxygen mixture). The comparison with other models from 300 to 473 K and 1 to 100 bar shows that the results calculated with different models are consistent within 50 bar and 400 K; out of this range, there is some difference. Meanwhile, mole ratios of nitrogen to oxygen in the saturated humid air were calculated from 323 to 523 K and 50 to 250 bar. It is found that the mole ratio of nitrogen to oxygen keeps almost constant, and the effect of the slight changes in the ratio of nitrogen to oxygen on the humidity, enthalpy and entropy of humid air is small enough to be neglected. Moreover, the enthalpy of dry air was predicted, and the comparison with other models again proved the reasonable assumptions and prediction capability of the new model.

Spin-on nanoparticle tin oxide for microhotplate gas sensors

A colloidal suspension of tin oxide nanoparticles is used to prepare a highly sensitive gas sensing film on a microhotplate. Fabrication consists of spin-coating the solution over an array of micromachined hotplates and annealing. A thermolithographic process using a nitrocellulose coating is demonstrated. Scanning electron microscopy images show the films to be smooth and consisting of 10 nm particles. Response to methanol shows a resistance change of a factor of two between zero-grade dry air and a concentration of 10 nmole/mole (10 ppB) at an operating temperature of 350°C. Sensitivity is observed at operating temperatures as low as 150°C, with generally lower recovery times. Tests comparing the response in saturated humid air and dessicated dry air show that recovery to wet air exposures is greatly accelerated at temperatures above 300°C. Stable response with no evident poisoning of the sensor was observed in a run lasting 120 h consisting of methanol and ethanol exposures. Temperature-programmed sensing was used to create different response patterns in air, methanol, and toluene, useful for identification of a detected gas. The results suggest colloidal suspensions may be used in combination with the microhotplate platform to produce a low-power, highly sensitive, device that is fabricated using planar technology.

Effect of humid air flow rate on the filmwise condensation inside a vertical cooled pipe: numerical and experimental study

This study consists of evaluating the effect of the saturated humid air flow rate on the heat and mass transfer in a vertical exchanger. One of the affected parameters is the shear stress along the liquid vapor interface. The second studied point is the effect of flow rate on the diffusion of the vapor in the mixture. A simple mathematical model is built from one-dimensional equations for the mass conservation, enthalpy and momentum. In order to validate the model, an experimental apparatus allows to have access to the local heat transfer passing through the wall. The experimental results are in good agreement with the theoretical predictions. They show that the cocurrent gas/liquid flow allows a better recovery of energy.

冷凍除湿器における主冷却器の負荷軽減化に関する検討

The refrigerated dryer mentioned in this paper is one of types of air purifiers, and is one of the popular types of compressed air dryers. The refrigerated dryer consists of a precool-reheater, main cooler, and refrigerator. In the precool-reheater, the cold humid air delivered from the main cooler is heated by the hot air delivered from the after-cooler, and changes into dry air, the relative humidity of which is fairly low. In the main cooler, the slightly hot humid air delivered from the cooling process in the precool-reheater is cooled further by the cooling medium in the refrigerator to the minimum temperature, which means a dew point of compressed air, and changes into cold and saturated humid air. The main cooler requires external energy to cool the compressed air, but the precool-reheater does not. For this reason, to miniaturize a refrigerated dryer, it is very important to reduce the thermal load in the main cooler. In this paper, the reduction in the thermal load in the main cooler is estimated with the power-saving factor that means the ratio of heating rate in the precool-reheater to one in the dryer, which is investigated theoretically and experimentally. As a result, the effect of the thermal conductance of the precool-reheater on the power-saving factor is clarified, considering compressed air temperatures at the main locations in the dryer. In addition, a proper guide for the design of a refrigerated dryer is derived, paying attention to the relationship not only between thermal conductances of an after-cooler and a refrigerated dryer but also between ones of a precool-reheater and main cooler.

Suction Characteristics of water-Ring Vacuum Pump. 3rd Report, Supercharging Effect of Chilled Seal Water.

A series of experiments was carried out on the suction characteristics of a water-ring vacuum pump pumping saturated humid air at 30°C, while the temperature of ring water was varied in the range of 10∼30°C. The steam flow induced by the temperature difference between the water in the suction air tank and the seal ring water drives air against an adverse pressure gradient. Thus, the partial pressure of air at the suction port of the pump was increased. The internal characteristics of the pump under such a condition is related to the standard pump characteristics pumping saturated humid air at an isothermal water-ring temperature. The combined performance is improved markedly by reducing the water-ring temperature, and it is predictable.

Heat and Mass Transfer With Dehumidification in Laminar Boundary Layer Flow Along a Cooled Flat Plate

The effects of dehumidification from humid air of laminar air flow over an isothermal cooled flat plate have been investigated using the similarity scheme. The results obtained for both saturated and unsaturated humid air are compared with those of dry air

Effects of temperature and composition on the viscosity of respiratory gases

The steady-state sensitivity of resistance pneumotachographs is proportional to viscosity. Dynamic characteristics of pneumotachographs, pressure transducers, and mass spectrometers are also viscosity dependent. We derive linear equations to approximate the viscosities of O2, N2, CO2, H2O, He, N2O, and Ar for temperatures between 20 and 40 degrees C by using published viscosity data and a nonlinear extrapolation equation. We verify the accuracy of the extrapolation equation by comparison with published data. Our linear equations for pure gas viscosities yield standard errors less than 0.35 microP. We also compare a nonlinear equation for calculating the viscosities of mixtures of gases with published measured viscosities of dry air, humid air, and He-O2 and N2-CO2 mixtures. The maximum difference between published and calculated values is 1.3% for 10% CO2 in N2. All other differences are less than 0.38%. For saturated humid air at 35 degrees C, a linear concentration-weighted combination of viscosities differs from our nonlinear equation by 4.9, 2.1, and 1.7% at barometric pressures of 32, 83, and 100 kPa, respectively. By use of our method, the viscosity of normal respiratory gases can be calculated to within 1% of measured values.