Dew point meter

Use dew-point meter to determine moisture content from critical supply point Requirements... 

Determine the moisture content at critical points. Use dew-point meter. Requirements... 

In a modern dew-point instrument, a sample is equilibrated within the headspace of a sealed chamber containing a mirror, an optical sensor, an internal fan, and an infrared thermometer (Figure A2.2.2). At equilibrium, the relative humidity of the air in the chamber is the same as the water activity of the sample. A thermoelectric (Peltier) cooler precisely controls the mirror temperature. An optical reflectance sensor detects the exact point at which condensation first appears a beam of infrared light is directed onto the mirror and reflected back to a photodetector, which detects the change in reflectance when condensation occurs on the mirror. A thermocouple attached to the mirror accurately measures the dew-point temperature. The internal fan is for air circulation to reduce vapor equilibrium time and to control the boundary layer conductance of the mirror surface (Campbell and Lewis, 1998). Additionally, an infrared thermometer measures the sample surface temperature. Both the dew-point and sample temperatures are then used to determine the water activity. The range of a commercially available dew-point meter is 0.030 to 1.000 aw, with a resolution of 0.001 aw and accuracy of 0.003 aw. Measurement time is typically less than 5 min. The performance of the instrument should be routinely verified as described in the Support Protocol. 

A hydrocarbon dew point meter uses a chilled-mirror instrument by which almost invisible films, having sensitivities on the order of 1 ppm, become detectable. Optical fibers are used to detect the reduction of light intensity, and miniature thermocouples measure the surface temperature of the mirror. For total hydrocarbon measurement, the flame ionization analyzer is reliable and accurate, but it requires the attention of operators and also consumes compressed gases. 

The ceramic pellet with the porous Ni/SiO2 electrodes was placed in a 316 stainless-steel holder. A glass gasket was used in order to eliminate gas leak through interfaces between the anode and cathode. The anode was supplied with a gas mixture of H2 + H2O or CH4 + H2O. The H2 concentration was 20%. The ( I I, concentration was 10%. Results for other H2 or CH4 concentrations were reported elsewhere [4,5]. H2O was added to the CH4 or H2 gas flow by a bubbler immersed in a constant temperature bath. The cathode was supplied with a mixture of O2 and H2O. The H2O concentration in the cathode was 20%. The concentrations of H2, O. CH4, CO, CO2 and other hydrocarbons at the outlets of the anode and cathode were detected by gas chromatography. The H2O concentration was measured by a dew-point meter. The gas flow rate was controlled to a constant flow rate by mass-flow regulators. The fuel-cell holder was placed in an electric furnace controlled to a constant temperature. Temperature was measured by C-A thermocouples. I-V curves were determined by a two-terminal direct-current method. 

An early example of a dew point meter was developed by the British Coal Research Association (BCURA) reported by Flint [1948]. The dew point meter consists of a glass thimble located at the end of the probe inserted into the flue gas. The thimble is progressively cooled by an air stream and the surface temperature measured by means of a suitable thermocouple. The junction of the thermocouple is fused into the glass and forms one electrode of an electrical conductivity cell. When condensation occurs the aqueous acid film produced on the surface of the... 

A convenient method of continuously monitoring the gas for H2O content is to measure the dew point using a commercially available dew-point meter. Certain meters, working on a conductance or capacitance principle, can be set to control the input, or drying, parameters, or to trigger alarms if a certain limiting value is exceeded. 

Moist room air leaking into dry-process air Dew point meter incorrect... 

Two light bulbs for heating the chamber are installed below the fans and circular holes in the platform. The chambers used in the 50 °C tests were insulated all around with 38 mm thick boards of Styrofoam. The joints were sealed with75 mm wide transparent packing tape. A thermometer and probes for the dew-point meter and Chromalox were inserted through conical one-hole rubber stoppers that fitted into matching reinforced holes in the top plate of the chamber (Fig. 5). 

The Basic Protocol describes the determination of water activity of a product using a chilled mirror dew-point water activity meter. Dew point is a primary measurement of vapor pressure that has been in use for decades (Harris, 1995). Dew-point instruments are accurate, fast, simple to use, and precise (Richard and Labuza, 1990 Snavely et al., 1990 Roa and Tapia de Daza, 1991). In a dew-point instrument, water activity is measured by equilibrating the liquid-phase water in the food sample with the vapor-phase water in the headspace, and then measuring the vapor pressure of the headspace. The basic principle involved in dew-point determinations of vapor pressure in air is that air may be cooled without change in water content until it saturates. The dew-point temperature is the temperature at which the air reaches saturation. It is determined in practice by measuring... 

Roa, V. and Tapia de Daza, M.S. 1991. Evaluation of water activity measurements with a dew point electronic humidity meter. Lehensmittel-Wissen-schaft Technol. 24 208-213. 

The cooler part of the combustion air preheater - the tail end of the flue-gas-heat-recovery train - is more likely to corrode due to sulfur dioxide (S02) condensing from the flue gas. In this area, cast iron or glass will resist the acid attack. Carbon steel preheater tubes, joined with 1.5 to 2 meters of SS 304 tubes at the cold end of the tube sheet, can ensure reasonable service life. Typically, the flue gas temperature to the stack is maintained above the dew point of S02 to prevent condensation. During startup and shutdown, condensation of S02 will occur88. 

The dew point (T p) is the temperature to which a particular mixture of air and water vapor must be cooled to become saturated with respect to water vapor. If the mixture is cooled below the dew point, then the system becomes supersaturated and it will separate into a two-phase system of saturated air and liquid water. Many of the best humidity meters are actually dew point detectors. 

One thousand cubic meters of moist air at 101 kPa and 22°C and with a dew point of 11°C enters a process. The air leaves the process at 98 kPa with a dew point of 58°C. How many kilograms of water vapor are added to each kilogram of wet air entering the process ... 

Moist air at 38°C and 48% is heated in your furnace to 86°C. How much heat has to be added per cubic meter of initial moist air, and what is the final dew point of the air ... 

The Aqualab CX2 water activity meter (Decagon Devices Inc., Pullman, WA) detects water condensation on a chilled mirror (dew point temperature). The instrument is sensitive to water activity units of <0.001. Readings take 5 min or less and are accurate to 0.003 water activity units. 

The G.P. chamber is equipped with an air cooler of about 5500 BTU size (Item 3) is located about 1.8 meters off the floor. An evaporator control valve (Item 2) on the refrigerate line allows temperature control of the air cooler condenser coils. Temperature of the coils is maintained just above the dew point for 50% relative humidity. An electric baseboard heater (Item 6) is equipped with a hydrastatic thermostat control (Item 11). The base board heater is placed near the floor and opposite of the chamber door. A humidifier (Item 4) is located approximately 1.8 meters above the floor and just to the right of the air cooler. The nozzle of the humidifier is pointed slightly toward the back of the chamber. A humidistat (Item 10) is centered between the floor and end walls on the same side as the humidifier. A strategically located recording hygrothermograph is used to monitor both temperature and humidity. 

Focus attention on flow measurements of streams close to their bubble point or dew point. Flsishing of liquid or condensation of vapor can lead to major errors. Investigate any "noisy or heavily dampened flow meter signals. This may indicate unexpected fl ishing or condensation. 

We still had to determine the cause of the mechanical problems with the meter. A thorough analysis of the problem led to a simple solution that also eventually solved some of the other problems. A vaporizer was added to the enrichment LPG and the injection point was moved down stream of the meter. This addition solved not only the mechanical problems with the meters but also reduced the variation in gas composition seen by the meter. The Dew Point was now read before the addition of emichment, eliminating the question of hydrocarbon Dew Points. 

Dew point reading could be good but resin is still wet.) Blower rotation incorrect Air ducts blocked Air flow meter incorrect Desiccant bed contaminated Tightly packed material in hopper Check manufacturer s electrical instructions, and change blower rotation Remove obstruction Disengage line exiting dryer repair if needed Replace desiccant (see Note 3) Increase hopper size or drain hopper and refill... 

Figure 31.13 Experimental rotating jet spouted bed with central and peripheral air jets 1—air distributor, 2—screen, 3—distributor cover, 4—ball bearings, 5—v-belt, 6—pulley, 7—drive, 8—motor controller, 9—glass vessel, 10—bir blower, 11— electric heater, 12—PID controller, 13—Pitot tube, 14—gate valve, 15—pressure transducers, 16—pressure taps, 17—thermocouples, 18—multiplexer, 19—IR hygrometer, 20—dew-point sensor, 21—dew-point hygrometer, 22—humidity meter, 23—computer, 24—terminal panel, 25—filter. (From Jumah, 1995.)...

The accurate prediction of thermodynamic properties of natural gas systems is of interest for gas industry. Compressibility factors are used in energy and flow metering. It is also used in calculations of gas pressure gradient in tubing and pipelines. When large volumes of gas are traded between produeers, distributors, and consumers, error in the estimation of the amount of involved are of real economic significance. In gas condensate reservoirs, well-productivity often declines rapidly when pressure drops below the dew point pressure near-wellbore. Therefore, it is very important to accurately determine the dew point pressure. The pressure and temperature of most natural gas mixtures can be found up to 150 MPa and 500 K, respectively (Nasrifar and Boland, 2006). At these eonditions, methane, ethane, and nitrogen are almost always supercritical while other hydroearbons are subcritical. Thus, the equation of state of natural gas mixture must be aeeurate at supercritical and subcritical behavior of methane and heavy hydrocarbons, respectively. 

The REED SD-2010 Heat Stress Meter features a datalogger with 2GB SD memory card (optional) Air Temp. 0 to SOT WBGT 0 to 59°C Black Globe Temp. 0 to 80°C Wet Bulb Temp. -21.6 to 50.0°C Dew Point Temp. -25.3 to 48.9°C and Humidity Range 5 to 95% RH. Reed Instruments, www.reedin-struments.com/reedinst.html. Circle 263... 

Static methods. In which the system of interest is enclosed in a magnetically stirred variable volume cell [64, 76] which in some cases contains a window. The temperature and pressure within the cell are accurately metered. The cell volume may be changed either using a mercury piston or a mechanical piston and samples of the fluid phases present may be obtained, if required, under conditions of constant temperature and pressure by suitably reducing the cell volume. In the windowed cell version [76] sampling is unnecessary for binary systems since the cell may be charged with known amounts of the two components and conditions adjusted to obtain trace presence only of one of the phases. In this way the dew- and bubble-point curves for binary systems may be established and similarly the solubilities of solids in compressed fluids may be determined. 

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