Document byJdjQ7bJDwjwXZ7XJY5jwa21

260 CHAPTER 16 1965 Guide And Data Book ** G. L. Larson, D. W. Nelson, and R. W. Kubasta ASHVE Rss&asch Repoet No. 936--Investigation of air outlets in class room ventilation (ASHVE Transactions, VoL 38, 1932, p. 463). ** D. W. Nelson and D. J. Stewart: ASHVE Research Re port No. 1076--Air distribution from side wall outlets (ASHVE Transactions, Vol. 44, 1938, p. 77). m G. L. Tuve: Measuring air Sow {Healing, Piping and Air Conditioning, December 1941). National Advisory Committee for Aeronautic* Technical Notes No. 546 (November 1935). F. R. Ingram, E. Diez-Caoseco, and L. Silverman: The characteristics of double Pitot tubes (ASHVE Journal Section, Heating, Piping and Air Conditioning, November 1942, p. 708). ** flow measurement, instruments and apparatus {ASMS Paver Test Codes, 1959, Fart 5 of Chapter 4). M D. D. Wile: Air flow measurement in the laboratory (Re frigerating Engineering, June 1947, p. 515). ** J. B. Dick: Measurement of ventilation mring tracer gas technique (ASHVE Journal Section, Heating, Piping and Air Conditioning, May 1950, p. 131). * C. W. Coblcntz ana P. R. Achenbach: ASHAE Research Report No. 1616--Design and performance of & portable infil tration meter (ASHAE Transactions, Vol. 63, 1957, p. 477). " W. H. Carrier: The temperature of evaporation (ASHVE Transactions, Vol. 24, 1918, p. 25). ** H. B. Nottage: ASHVE-Reseabcb Report No. 1401--A proposed psychrometric chart (ASHVE Transactions, Vol. 56, 1950,p. 411). ** " H. Carrier and C. O. Mackey: A review of iitlng psychrometric data in relation to practical engineering prob lems {ASMS Transactions, January 1937, p. 33). Discussion {ASME Transactions, August 1937, p. 528). ** Arnold Wexlcr: Divided Flow Low Temperature Humidity Test Apparatus (National Bureau of Standards Research Paver No. 1894). ** H. A. Daynes: Gas Analysis by Measurement of Thermal Conductivity (Cambridge Press, New York, 1933). a H. M. Vernon: The measurement, in relation to human comfort, of the radiation produced by various heating systems {Institution .Heating Ventilating Engineering Proceedings, Vol. 31, p. 160). **T. Bedford and C. G. Warner: The globe thermometer in studies of heating and ventilating (Institution Heating Venti lating Engineers Journal, Vol. 2, 1935, p. 544). ** D. J. Sutton and P. E. McNall, Jr.: A two-sphere radiom-1 eter (ASHVE Transactions, Vol. 60, 1954, p. 297). * A. C. Willard, A. P. Krats, and M. K. Fahnestock: The application of the eupatheoscope for measuring the perform ance of direct radiation and convection in terms of equivalent temperature (ASHVE Transactions, VoL 39, 1933, p. 303). * C. P. Yagiou: Physical procedures in air analysis--Instru ments and methods for recording thermal factors affecting hu man comfort (American Journal Public Health Supplement, Vol. 26, March 1936, p. 76). C. P. Yagiou, A. P. Krats, and C.-E. A. Winslow: Instruments and methods for recording thermal factors affecting human comfort, I1--Report of subcommittee on physical procedures in air analysis (American Journal Pub lic Health Supplement, Vol. 27, March 1937, p. 84). C.-E. A. Winslow and Leonard Greenberg: The thermointegrator--a new instrument for .the observation of thermal, interchanges (ASHVE Transactions, Vol. 41, 1935, p. 149). . u Standard Method of Testfor Thermal Conductivity of Materials by Means ofthe Guarded Hot Plate (adopted July 1942 by ASHVE, ASTM Designation C 177-45). Tentative Method of Test for Thermal Conductivity of Pipe Insulation (ASTM Designation C 335-54T). M D. D'Eustachio and R: E. Schreiner: A study of transient heat method for measuring thermal conductivity (ASHVE Transactions, VoL 58, 1952, p. 331). {* F. C. Hooper and F. R. Lepper: Transient heat flow ap paratus for the determination of thermal conductivity (ASHVE Transactions, Vol. 56, 1950, p. 309). " F. C.' Hooper and S. C. Chang: Development of thermal conductivity probe (ASHVE Transactions, VoL 59, 1953. n 463). " C. P. Lents: A transient beat flow method of determining thermal conductivity: Application to insulating {Ca nadian Journal of Technology, Vol. 30, June 1952, p. 153). " Tentative Method of Test for Thermal Conductance and Transmittance of Built-up Sections by Means of Guarded Hot Box (American Society for Testing Materials, ASTM-C-236- " P. Nicholls: ASHVE Research Report No. 685--Measur ing heat transmission in building structures and a heat trans mission meter (ASHVE Transactions, Vol. 30, 1924, p. 65). " R. G. Huebscher, L. F. Schutrum, and G. V. Pannelee: A low-inertia low-resistance heat flow meter (ASHVE Transac tions, VoL 58, 1952, p. 275). 17 J. T. Gier and R. V. Dunkle: Using the heat flow meter to study heat transfer (Refrigerating Engineering, VoL 62. October 1954, p. 63). u I m B = R Testing and Rating Codes for Low Pressure Heating Boilers (Institute of Boiler and Radiator Manufac turers, 1947). ** Commercial Standard for Warm Air Furnaces Equipped with Vaporising Pol-type OH Burners (National Bureau of Standards, C.S. 104-26). " Martin Shepherd: Rapid determination of m1l amounts of carbon monoxide {Industrial and Engineering Chemistry,' Analytical Edition, 19, 77, 1947). 41 Martin Shepherd: Determination, of email amounts of carbon monoxide in air by various reference methods {Notional Bureau of Standards Journal of Research, 38, 351, 1947, R. P. 1777). Commercial Standard for Mechanical Draft Oil Burners Designed for Domestic Installations (National Bureau of Stand ards, C.S. 75-42). Clyde Orr and J. M. Dalla Valle: Pine Particle Measurement (Macmillan Company, New York, 1959). -MA.-E. Reif: Aerosols: Physical Properties, Instrumentation' and Techniques, Aviation Medicine (Pergamon Press, New York, - ** R. S. Dill: A test method for air filters (ASHVE Trans actions, VoL 44, 1938, p. 379). - * M. B. Jacobs: Analytical Chemistry of Industrial Poisons,' Hazards and Solvents (Interscience Publishers Inc., New York. 1941). 47 J. J. Bloomfield and J. M. Dalla Valle: The Determination and Control of Industrial Dust {U. S. Public Health Bulletin No. 217, 1935). u F. A. Patty; Sampling and Analysis of Atmospheric Con taminants {Industrial Hygiene and Toxicology, Vol. 1, Inter- science Publishers Inc., New York, 1948). " E. E. Gross, Jr;: Noise measuring and-sound-control (Re frigerating Engineering, Vol. 66, May. 1957, p. 49). " A. P. Peterson and L. L. Beranek:. Harxdbook of Noise Control (General Radio Co., Cambridge, 195*) 71 L. L. Beranek: Acoustics (McGraw-Hill Book Co., New York). . ' 77 H. F. Olson: Elements of Acoustical Engineering (D. Van Nostrand Co., New York). 71 American Tentative Standards for Sound Level Meters for Measurement of Noise and Other Sounds (American Standards Association, Z24.3-1944). CHAPTER 17 DEHUMIDIFICATION BY SORBENT MATERIALS Moisture Content of Air, Sorbents, liquid Absorbents, Liquid Absorption Systems, Solid Adsorbents, Solid Adsorption Systems, Sorption Dehumidifiers for Berated Pressures DEHUMIDIFICATION as used herein is the reduction can be defined as that temperature at which condensation of 0f. the water-vapor content of air or other gases. The moisture begins when moist air is cooled. This temperature term thus describes a special case of dehydration which covers can be determined by observing, either visually or by means the removal of moisture in any form from a gas. The degree of of a photoelectric cell, the condensation of water vapor on a dehumidification required varies greatly with different ap polished metal surface that is being slowly chilled. Indirect plications, and is one of the prime considerations influencing methods for measuring moisture include wet- and dry-bulb the choice of a method. psychrometry, adiabatic expansion, electrical resistivity, Dehumidification may be accomplished by chilling, as and methods which depend on the hygroscopic properties of described in Chapter 33 and 34, by the use of sorbents, or various materials. For a discussion of these methods, refer to by compression in combination with chilling, sorbents, or National Bureau of Standards Circular 512.1 both chilling and sorbents. When an air-water vapor mixture is compressed, (I) its Within the past decade, drying of gases has become an in ability to hold water is decreased, (2) water vapor will start to creasingly important operation. Some of the more important condense at a higher temperature, and (3) the dew point of commercial applications include the following: the mixture at elevated pressure will be higher than that of 1. Lowering the relative humidity to facilitate handling of hygroscopic materials. . 2. Air conditioning for comfort (in combination with cooling under certain design conditions, such as high moisture load in comparison to sensible heat load). 3. Drying air for wind tunnels. 4. Dehydrating natural gas. 5. Providing protective atmospheres for the heat treatment of Tnpt*U 6. Maintaining controlled humidity conditions in warehouses for storage. 7. Preserving ships of the "Mothball Fleet." 8. Drying of gases which are to be liquefied. 9. Numerous static applications in which a dry atmosphere must be maintained in a closed space or container, such as the cargo hold of a ship. the same mixture at atmospheric pressure. The effect on the dew point of compressing or expanding an air-water vapor mixture can be determined from Fig. 2. The relationship of dew-point temperature to grains of moisture per actual cubic foot of air does not change much with pressure in the range of 0 to 300 peig. Consequently, grains of water per cubic foot for elevated pressures can be read directly from Fig. 1, re membering that actual cubic feet of air are used. SORBB4TS Sorbents are solid or liquid materials which have the property of extracting and holding other substances (usually gases or vapors, e.g., water vapor) brought into contact with The use of sorbents for drying of refrigerants is discussed in Chapter 49, Moisture in Refrigerant Systems. them. The sorption process always generates heat, the major part of which is the result of the condensation of water vapor. The weight of water held by a substance will increase or de MOISTURE CONTENT OF AIR crease, depending upon whether the vapor pressure of the A knowledge of air-water vapor mixtures and their thermo dynamic properties is necessary for proper understanding of this chapter. The reader is, therefore, referred to Chapter 3, Psychrometrics, for definitions of terms and for thermo dynamic properties of moist air (Table 1) or properties of water at saturation (Table 2). The moisture content of air is indicated by ite absolute ' humidity, vapor pressure, dew-point temperature or relative humidity. Moisture contents of air at one atmosphere pres sure in tiie terms normally used in the Hphnmiftifiratinn field ere presented in the conversion chart. Fig. 1. To-use this chart, merely read horizontally across to convert a given type of measurement to the one desired. Dew-point temperature is a convenient m*g*ns for measuring moisture content and is frequently used in HfthnrnidficAtinn work. Dew-point temperature, or saturation temperature, Tbe eeMrtl re*possibility for this chApter it --to TC Llll Sorption. water held by the substance is less or greater, respectively, than tiie partial pressure of water vapor in the surrounding atmosphere. All materials are sorbents to a greater or lesser degree. As generally used, however, the term sorbents refers to those materials having a large capacity for moisture as compared to their volume and weight. Such materials.are divided into two genera) classifications: 1. Absorbent--A sorbent which changes either physically, chemically, or both, during the sorption process. Calcium chloride . is an example of a solid absorbent. When water is absorbed on tliia material, analysis shows that chloride is coo- - verted into a hydrate and reaches a saturation point at . CaCU-2HiO, after which additional moisture tends to cause the . material to lose its crystalline shape and dissolve in the water that was absorbed. With additional water there is a chase'change" from the solid to the liquid. liquid absorbents include sulfuric acid, solutions of the halogen group such as lithium chloride, lithium bromide, and the ethylene glycols. 2. Adsorbent--A sorbent which does not change physically or chemically during tlw sorption process. At no tune is there a phase change or solution of an adsorbent. Certain solid materials, such