Ministry of Education and Science of the Russian Federation
Federal Agency for Education
Saratov State Technical University
Determination of wet air parameters
Methodical instructions
for students specialties 280201
day and absentee forms of training
Saratov 2009.
purpose of work: deepening knowledge in the section of technical thermodynamics "Wet air", study of the method of calculating parameters wet air and receiving skills in working with measuring instruments.
As a result of work, it must be assimilated:
1) the basic concepts of wet air;
2) Methods for determining wet air parameters
settlement dependencies;
3) Methods for determining wet air parameters
I-D-diagram.
1) determine the value of the parameters of wet air
settlement dependencies;
2) determine the parameters of wet air with
I-D diagrams;
3) make a report on the executed laboratory work.
Basic concepts
Air that does not contain water vapor is called dry air. In nature, dry air does not occur, since the atmospheric air always contains some amount of water vapor.
A mixture of dry air with water vapor is called wet air. Wet air is widely used in drying and ventilating installations, air conditioning devices, etc.
A characteristic feature of the processes occurring in wet air is that the amount of water vapor contained in the air changes. Couples can partially condense and, on the contrary, water evaporates into the air.
A mixture consisting of dry air and superheated water vapor is called unsaturated wet air. Partial pressure of a pair of RP in the mixture is less than the pressure of the pH saturation corresponding to the temperature of the humid air (RP<рн). Температура пара выше температуры его насыщения при данном парциальном давлении.
The mixture consisting of dry air and a dry saturated water vapor is called saturated wet air. The partial pressure of water vapor in the mixture is equal to the pressure of saturation corresponding to the temperature of wet air. The pair temperature is equal to condensation temperature at a particular steam pressure.
A mixture consisting of dry air and a wet saturated water vapor (that is, in the air there are particles of condensed steam, which are in suspension and falling in the form of dew), is called oversaturated wet air. The partial pressure of the water vapor is equal to the pressure of the saturation corresponding to the temperature of the humid air, which is equal in this case the temperature of the condensation in it in it. In this case, the temperature of the wet air is called the dew point temperature t.r. If the partial pressure of the water vapor is for some reason more than the saturation pressure, the part of the steam is condensed as a dew.
The main indicators characterizing the state of wet air are moisture content d., relative humidity j., Entalpy I. and density r..
The calculation of the parameters of wet air is performed using the Mendeleev-Klapairone equation for the perfect gas, which with a sufficient approximation obeys the wet air. We consider wet air as a gas mixture consisting of dry air and water vapor.
According to the Dalton law, the pressure of wet air r equally:
where rV. - partial pressure of dry air, PA;
rP - partial pressure of water vapor, PA.
The maximum value of the partial pressure of the water vapor is equal to the pressure of saturated water vapor pH, appropriate humid air temperature.
The amount of water vapor in the mixture in kg, incident on 1 kg of dry air, is called moisture content d., kg / kg:
https://pandia.ru/text/78/602/images/image003_38.gif "width \u003d" 96 "height \u003d" 53 "\u003e, since, then; (3)
Since, then, (4)
where V. - volume of gas mixture, m3;
R.in, R.p - Gas permanent air and water vapor equal
R.in\u003d 287 J / (kg × k) R.p\u003d 461 J / (kg × k);
T. - Waste air temperature, K.
Considering that 
, and substituting the expressions (3) and (4) in formula (2), we finally get:
Div_adblock64 "\u003e
Relative humidity j. called the ratio of the density of steam (i.e. absolute humidity r.p) to the maximum possible absolute humidity (density r.pmax) at a given temperature and pressure of wet air:
As r.p and r.pmax are determined at the same temperature of wet air, then
https://pandia.ru/text/78/602/images/image013_6.gif "width \u003d" 107 "height \u003d" 31 "\u003e. (8)
The density of dry air and the water vapor is determined from the Mendeleev-Klapairone equation recorded for the data of the two components of the gas mixture of software (3) and (4).
R. Located by the formula:
https://pandia.ru/text/78/602/images/image015_6.gif "width \u003d" 175 "height \u003d" 64 src \u003d "\u003e.
Wet air enthalpy I. represents the sum of the enthalpy 1 kg of dry air and d. kg of water vapor:
I.= i.in+ d.× i.p . (11)
Enthalpy of dry air and couple:
https://pandia.ru/text/78/602/images/image017_4.gif "width \u003d" 181 "height \u003d" 39 "\u003e, (13)
where t.m.- indications of the wet thermometer, ° C;
(tC.- t.m.) - psychrometric difference, ° C;
h. - correction to the temperature of the wet thermometer,% is determined
according to the schedule located on the stand, depending on t.m. and speed
To determine the pressure of wet air, a barometer is used.
Procedure and methods of processing
Experiment results
Measure the temperature of dry and wet thermometers. Determine the true magnitude of the temperature of the wet thermometer by formula (13). Find a difference D.t. = tC. - t.m East And in a psychrometric table to determine the relative humidity of the air.
Knowing the size of relative humidity, from the expression (7) to find partial pressure of water vapor.
pO (12), (13).
The specific volume of wet air is in the formula:
Mass of wet air M., kg, in the laboratory room is determined by the formula:
where V. - the size of the room, m3;
r - Pressure of wet air, Pa.
The results of calculations and the readings of the instruments are in the table according to the following form.
Protocol for recording tests of measuring instruments
and results of calculations
Name of determined value | Designation | Dimension | Numerical value |
|
Pressure of wet air | ||||
Temperature dry thermometer | ||||
The temperature of the wet thermometer | t.m. | |||
Saturated Para Pressure | ||||
Partial pressure of water vapor | ||||
Dry Air Partial Pressure | ||||
Waste air density | ||||
Absolute humidity | r.p | |||
Gas constant wet air | ||||
Wet air enthalpy | ||||
Mass of wet air |
Next, determine the basic parameters of wet air over measured tC. and t.m. With the I-D diagram. The intersection point on the I-D diagram isotherms corresponding to the temperatures of wet and dry thermometers, characterizes the condition of wet air.
Match the data obtained according to the i-D diagram, with the values \u200b\u200bdefined using mathematical dependencies.
The maximum possible relative error of determining the partial pressure of water vapor and dry air is determined by the formulas:
https://pandia.ru/text/78/602/images/image022_2.gif "width \u003d" 137 "height \u003d" 51 "\u003e; 
,
where through D is indicated by the limit of the absolute measurement error
The limit of the absolute error of the hygrometer in this laboratory work is ± 6%. The absolute permitted error of thermometer thermometers is ± 0.2%. The paper has a barometer with a 1.0 accuracy class.
Report on work
The report on the laboratory work must contain
following:
1) short description work;
2) protocol for recording measuring instruments and
results of computing;
3) Figure with an I-D diagram, where the state of the wet
air in this experiment.
CONTROL QUESTIONS
1. What is called wet air?
2. What is called saturated and unsaturated wet air?
3. The Act of Dalton is applied to the wet air.
4. What is called dew point temperature?
5. What is called absolute moisture?
6. What is called moisture air content?
7. What limits may change moisture content?
8. What is called relative humidity?
9. In the i-D diagram, show the line J \u003d const, i \u003d const; d \u003d const, tc \u003d const, TM \u003d const.
10. What is the maximum possible pair density at this humid air temperature?
11. What is determined by the maximum possible partial pressure of water vapor in wet air and what is it equal?
12. From what parameters of wet air depends the temperature of the wet thermometer and how does it change when they change?
13. How can the partial pressure of the water vapor be determined in the mixture, if the relative humidity and the temperature of the mixture are known?
14. Write the Mendeleev-Klapairone equation for dry air, water vapor, wet air and explain all the magnitude included in the equation.
15. How to determine the density of dry air?
16. How to determine the gas constant and enthalpy of wet air?
LITERATURE
1. Lyaskov base of heat engineering. M.: Higher School, 20c.
2. Zubarev on technical thermodynamics / ,. M.: Energy, 19c.
Determination of wet air parameters
Methodical instructions for laboratory work
according to the courses "Heat Engineering", "Technical thermodynamics and heat engineering"
Among: Sedelkin Valentin Mikhailovich
Kuleshov Oleg Yuryevich
Kazantseva Irina Leonidovna
Reviewer
Editor
License ID number 000 dated 11/14/01
Signed in print format 60x84 1/16
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Saratov State Technical University
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Fig. 1. Displaying air processing processes on the D-H diagram
Fig. 2. Image on the D-H diagram of air parameters during air conditioning
Basic Terms and Definitions
The atmospheric air is a non-aggravated mixture of gases (N2, O2, AR, CO2, etc.), which is called dry air, and water vapor. Air condition is characterized by: temperature T [° C] or T [K], pressure of barometric RB [Pa], absolute slack \u003d RB + 1 [bar] or partial rapar, density ρ [kg / m3], specific enthalpy (heat generation) H [KJ / kg]. The state of moisture in atmospheric air is characterized by the moisture content of absolute D [kg], relative φ [%] or moisture content D [g / kg]. The pressure of the atmospheric air of the Republic of Belarus is the sum of partial pressures of dry air of PC and water vapor RP (Dalton law):
rB \u003d PC + RP. (one)
If gases can be mixed in any amounts, then the air may accommodate only a certain amount of water vapor, because the partial pressure of the water vapor of RPV in the mixture cannot be more partial pressure of the saturation of the pH of these vapors at a given temperature. The existence of the limit partial saturation pressure is manifested in the fact that all overpressure of water over this amount is condensed.
In this case, the moisture can fall out in the form of water droplets, ice crystals, fog or frost. The smallest moisture content in the air can be adjusted to zero (at low temperatures), and the greatest - about 3% by weight or 4% by volume. The absolute humidity D is the amount of pair of [kg] contained in one cubic meter of wet air:
where MP is a pair mass, kg; L is the volume of wet air, M3. In practical calculations per unit of measurement, which characterizes the steam content in wet air, is taken by moisture content. The moisture content of wet air D is the amount of steam contained in the volume of wet air consisting of 1 kg of dry air and MV [g] steam:
d \u003d 1000 (MP / MC), (3)
where MC is a mass of dry part of wet air, kg. The relative humidity φ or the degree of humidity, or a hygrometric indicator, is called the ratio of partial pressure of water vapor to partial pressure of saturated vapor, expressed as a percentage:
φ \u003d (RP / PN) 100% ≈ (D / DP) 100%. (four)
Relative humidity can be determined by measuring the intensity of water evaporation. Naturally, the lower humidity, the more active the evaporation of moisture will go. If the thermometer is wrapped with a damp cloth, then the thermometer readings will decrease relative to the dry thermometer. The difference in the temperatures of dry and wet thermometers give a certain value of the degree of humidity of atmospheric air.
The specific heat capacity of air C is the amount of heat required for heating 1 kg of air per 1 K. The specific heat capacity of dry air at constant pressure depends on the temperature, however, for practical calculations of SD systems, the specific heat capacity of both dry and wet air:
sS.V \u003d 1 kJ / (kg⋅k) \u003d 0.24 kcal / (kg⋅k) \u003d 0.28 W / (kg⋅k), (5)
The specific heat capacity of water vapor SP is taken equal to:
sP \u003d 1.86 kJ / (kg⋅k) \u003d 0.44 kcal / (kg⋅k) \u003d 0.52 W / (kg⋅k), (6)
Dry or explicit heat is warm, which is added or removed from the air without changing the aggregate state of the steam (temperature changes). Hidden heat - Heat, going to change the aggregate state of steam without changing the temperature (for example, drying). Nalthapia (heat generation) of wet air HB.V. is the amount of heat that is contained in the volume of wet air, the dry part of which weighs 1 kg.
Otherwise, this is the amount of heat that is necessary for heating from zero to this temperature of this amount of air, the dry part of which is 1 kg. Usually take specific enthalpy of air H \u003d 0 at air temperature T \u003d 0 and moisture content d \u003d 0. Enthalpy of dry air HC.V is equal to:
hC.B \u003d CT \u003d 1,006T [kJ / kg], (7)
where C is the specific air heat capacity, KJ / (kg⋅k). Nalthapia 1 kg of water vapor is equal to:
hB \u003d 2500 + 1,86T [kJ / kg], (8)
where 2500 is a hidden heat of evaporation of 1 kg of water at a temperature zero degrees, KJ / kg; 1.86 - heat capacity of water vapor, KJ / (KG⋅K). In the temperature of the wet air T and moisture content D enthalpy of humid air is equal to:
hB \u003d 1.006T + (2500 + 1,86t) × (D / 1000) [kJ / kg], where d \u003d (φ / 1000) DN [g / kg], (9)
The heat and cooling capacity of the Q system of air conditioning can be determined by the formula:
Q \u003d M (H2 - H1) [KJ / H], (10)
where m is air flow, kg; H1, H2 - initial and finite air enthalpy. If the wet air is cooled with unchanged moisture content, the enthalpy will decrease, and the relative humidity will increase. The moment will come when the air becomes saturated and its relative humidity will be 100%. At the same time, evaporation from the air of moisture in the form of dew - steam condensation.
This temperature is called a dew point. The temperature of the dew point for various dry air temperatures and relative humidity is given in Table. 1.The point of dew is the limit of possible cooling of wet air with constant moisture content. To determine the dew point, it is necessary to find such a temperature at which the air-containing air D will be equal to its moisture capacity of the DN.
Graphic construction of air treatment processes
To facilitate the calculations, the high-air heat generation equation represents in the form of a graph that called the D-Infamum (technical literature is sometimes used by the term I-DDiagram). In 1918, Professor of St. Petersburg University L.K. Ramsin offered a D-ingram, which clearly reflects the relationship between the parameters of the wet air T, D, H, φ at a certain atmospheric pressure of PB.
With the help of D-ingram, the graphic method is simply solved tasks, the solution of which analytically requires although simple, but painstaking computing. In technical literature, there are various interpretations of this diagram, which have minor differences from the D-Infamum of Ramzin.
This, for example, Mollier diagram (Mollier), Caryer Chart (Carrier), published by the American Society for Heating, Cooling and Air Conditioning (ASHRAE), Diagram of the French Association of Artificial Climate, Ventilation and Cold (AICVF). The last diagram is very accurate, performed by a tricolor print.
However, in our country was distributed and used at present, as a rule, the chart of Ramzin. It is available in many textbooks, it uses design organizations. Therefore, we are taken as a basis (Fig. 1). The price of the Ramzina D-Infamum is built in the Koomgol coordinate system. At the axis, the ordinates are postponed the values \u200b\u200bof the enthalpy H, and along the abscissa axis, located at an angle of 135 ° to the ordinate axis, the moisture content d is postponed. The beginning of the coordinates (point 0) corresponds to the values \u200b\u200bH \u003d d \u003d 0.
Below the point 0 are postponed negative values Entalpy, above - positive. At the thus thus obtained, the line isotherm t \u003d const, the lines of constant relative humidity φ \u003d const, the partial pressure of water vapor and moisture content are constructed. The lower curve φ \u003d 100% characterizes the saturated state of the air and is called a border curve. With increasing barometric pressure, the saturation line is shifted upwards, and when the pressure drops down.
Thus, when calculating the calculations for the SC, located in the region of Kiev, it is necessary to use a barometric pressure diagram \u003d 745 mm RT. Art. \u003d 99 kPa. On the D-likegram, the region located above the border curve (φ \u003d 100%) is an area of \u200b\u200bunsaturated steam, and the area is lower than the border curve - oversaturated wet air.
In this area, the saturated air contains moisture in the liquid or solid phase. As a rule, this condition of air is unstable, therefore, the processes in it are not considered on the D-likegram. On the D-likegram, each point above the border curve reflects a certain condition of air (temperature, moisture content, relative humidity, enthalpy, partial pressure of water vapor).
If the air is subjected to a thermodynamic process, the transition from one state (point A) to another (point B) corresponds to the D-opprase line A-B. In general, this is a curve line. However, we are only interested in the initial and final states of the air, and the intermediates do not matter, therefore, the line can be represented by a straight line connecting the initial and final state of the air.
To determine the point on the D-thought of a point corresponding to a certain state of air, it is enough to know two parameters independent of each other. The desired point is at the intersection of lines corresponding to these parameters. After carrying out perpendicular to the lines on which other parameters are postponed, determine their values. Also determined on the D-chaigram temperature of the dew point.
Since the temperature of the dew point is the lowest temperature, which can be cooled with air at constant moisture content, then to find the point of the dew, it is sufficient to hold the line d \u003d const until the intersection with the curve φ \u003d 100%. The intersection point of these lines is the dew point, and the temperature corresponding to it is the temperature of the dew point. Using the D-ingram, you can determine the air temperature over the wet thermometer.
To do this, from a point with a given air parameters, we carry out isoenthalt (H \u003d const) to the intersection with the line φ \u003d 100%. The temperature corresponding to the intersection point of these lines is the temperature of the wet thermometer. The technical documentation for air conditioners stipulates the conditions under which the nominal cooling capacity was measured. As a rule, this temperature of dry and wet thermometers corresponding to the relative humidity of 50%.
The process of air heating
When air heated, the line of the thermodynamic process passes by straight a-in With constant moisture content (d \u003d const). Air temperature and enthalpy increase, and relative humidity decreases. Heat consumption for air heating is equal to the difference in enthalpy of finite and initial air condition.
Air cooling process
The process of cooling air on the D-likegram is reflected in the straight directed vertically down, (direct a-s). The calculation is made similar to the heating process. However, if the cooling line goes below the saturation line, the cooling process will go on straight a-s And then on the line φ \u003d 100% of the C1 point to the C2 point. Parameters of the C2: D \u003d 4.0 g / kg, T \u003d 0.5 ° C.
Drainage process of wet air
Drain of wet air absorbents without changing the heat generation (without removal and heat supply) occurs in a straight line H \u003d const, that is, by straight a-ddirected up and left (straight a-d1). In this case, moisture content and relative humidity decrease, and the air temperature increases, because In the process of absorption, the steam condensation occurs on the surface of the absorbent, and the exempted hidden heat of the pair goes into the heat is explicit. The limit of this process is the intersection point of direct H \u003d const with the ordinate d \u003d 0 (point d1). The air at this point is completely freed from moisture.
Adiabatic humidification and air cooling
Adiabatic moisturizing and cooling (without heat exchange C external environment) On the D-inappramm from the original state (point N) is reflected in a straight directed downward H \u003d const (point K). The process occurs when air is in contact with water constantly circulating in a circuit cycle. The temperature of the air drops, moisture content and relative humidity increase.
The process limit is the point on the curve φ \u003d 100%, which is the temperature of the wet thermometer. At the same time, the same temperature should acquire recycling water. However, in real SLE with adiabatic cooling processes and air humidification, the point φ \u003d 100% is not achieved somewhat.
Air mixing with various parameters
On the D-ingram, the mixed air parameters (with parameters corresponding to the points (x and y) can be obtained as follows. Connect points x and y direct. Mixed air parameters lie on this straight, and the point Z divides it to segments, back proportional air mass Each is component parts. If you designate the proportion of the mixture n \u003d gx / gy, then straight x-y Find a point z, it is necessary to directly x-yolve on the number of parts N + 1 and to postpone the segment equal to one part.
The mixture point will always be closer to the parameters of that air, the dry part of which has a large mass. When mixing two volumes of unsaturated air with states corresponding to points x1 and y1, it may happen that the straight X1-y1 cross the saturation curve φ \u003d 100% and the point Z1 will be in the field of fogging. This position of the point of the mixture Z2 shows that, as a result of the mixing, moisture drops from the air.
The point of the mixture Z1 will switch to a more stable state on the saturation curve φ \u003d 100% to the point Z2 in Isaenthalpe. At the same time, DZ1 - DZ2 gram of moisture drops on each kilogram of the mixture.
Corner coefficient on D-inagram
Attitude:
ε \u003d (H2 - H1) / (D2 - D1) \u003d ΔH / ΔD (11)
uniquely determines the nature of the process of changing wet air. Moreover, the values \u200b\u200bof ΔH and ΔD may have a "+" or "-" sign, or they can be zero. The value of ε is called a heat-woof ratio of the process of changing wet air, and when the process is displayed on a D-inagram - an angular coefficient:
ε \u003d 1000 (ΔH / Δd) \u003d ± (Qizb / MV), KJ / kg,(12)
In this way, corner coefficient It is equal to the ratio of excess heat to the mass of the moisture separated. The angular coefficient is depicted by segments of the rays on the frame of the D-ingram field (the scale of angular coefficients). So, to determine the angular coefficient x-Z process It is necessary from point 0 (on the temperature scale) to carry out a direct parallel line of the X-Z process to the scale of angular coefficients. In this case o-N line Spends an angular coefficient equal to 9000 kJ / kg.
Thermodynamic model SKV
The process of preparation of air before serving it in the air-conditioned room is a set of technological operations and is called air conditioning technology. The heat-woofer processing technology of air-conditioned air is determined by the initial parameters of air supplied to the air conditioner, and the required air parameters in the room are determined.
To select air treatment methods, a D-ingram is built, which allows you to find such technology under certain source data, which will ensure the predetermined air parameters in the serviced room with minimal energy, water, air, etc. The graphic display of air treatment processes on the D-likegram is called the thermodynamic model of the air conditioning system (TDM).
The parameters of the outer air supplied to the air conditioner for subsequent processing are changed during the year and day in the large range. Therefore, we can talk about outer air as a multidimensional function XH \u003d XN (T). Accordingly, the combination of supply air parameters has a multidimensional function XPR \u003d CPR (T), and in the maintenance room XP \u003d XP (T) (parameters in the working area).
The technological process is an analytical or graphic description of the process of movement of the multidimensional function XN to XPR and further to XP. Note that under the variable state of the X (φ) system, the generalized indicators of the system at various points of space are understood and at various points in time. The thermodynamic model of the movement of the XH function to XP is built on the D-opprase, and then determined the air processing algorithm, the necessary equipment and the method of automatic control of air parameters.
The construction of TDM is beginning with applying the state of the outdoor air of this geographical point to the D-shaped. The estimated area of \u200b\u200bpossible states of outer air is accepted by SNiP 2.04.05-91 (parameters b). The upper limit is the isotherm Tl and Isorentalpa HL (limit parameters of the warm period of the year). The lower boundary is the isotherm TZM and Isaenthalpa Hsz (the limit parameters of the cold and transition periods of the year).
The limit values \u200b\u200bof the relative humidity of the outer air are taken according to the results of meteorological observations. In the absence of data, the range from 20 to 100% is taken. The multidimensional function of the possible parameters of the outer air is enclosed in the ABCDEFG polygon (Fig. 2). Then it is applied to the D-ingram required (calculated) the value of the condition of air indoors or in the working area.
It may be a point (precision air conditioning) or a working area of \u200b\u200bP1R2R3R4 (comfortable air conditioning). Next, determine the angular coefficient of change of air parameters in the room ε and conduct the process of the process through the boundary points of the working area. In the absence of data on the heat-humid process in the room, it is estimated to be taken in KJ / kg: enterprises of trade and catering - 8500-10000; visual halls - 8500-10000; Apartments - 15000-17000; Office rooms - 17000-20000.
After that, they build a zone of supply air parameters. To do this, on the lines ε, conducted from the boundary points of the R1R2R3R4 zone, lay the segments corresponding to the calculated temperature difference:
Δt \u003d tp - TPR, (13)
where TPR - calculated temperature Supply air. The problem solving is reduced to the transfer of air parameters from the multidimensional function of the XN to the XP function. The value Δt is taken by norms or calculated, based on the parameters of the cooling system. For example, when using water as a coolant, the final water temperature in the TW irrigation chamber will be:
tw \u003d t2 + Δt1 + Δt2 + Δt3, (14)
where T1 is the water temperature at the chiller outlet (5-7 ° C); ΔT1 is an increase in the water temperature in the pipeline from the chiller to the air conditioner water heat exchanger (1 ° C); Δt2 - water heating in irrigation chamber (2-3 ° C); Δt3 - water heating due to the coefficient of bypassing (1 ° C). In the way, the temperature of the water in contact with air will be tw \u003d 9-12 ° C. Practically air humidity reaches the values \u200b\u200bof no more than φ \u003d 95%, which increases TW to 10-13 ° C. The temperature of the supply air will be:
tw \u003d t2 + Δt2 + Δt3 + Δt4, (15)
where Δt4 is air heating in the fan (1-2 ° C); ΔT5 - air heating in the supply air duct (1-2 ° C). In the way, the temperature of the supply air will be 12-17 ° C. The permissible drop of temperatures of the removed and supply air Δt for industrial premises is 6-9 ° C, trading rooms - 4-10 ° C, and with an height of the room more than 3 m - 12-14 ° C.
In general, the parameters of the air removed from the room differ from air parameters in the working area. The difference between them depends on the way of supplying air to the room, the height of the room, the multiplicity of air exchange and other factors. Zones U, P and P on the D-H diagram have the same shape and are located along the line ε at distances corresponding to the differences of temperature: Δt1 \u003d tp - TPR and ΔT2 \u003d TD - TP. The ratio between TPR, TPOM and T is estimated by the coefficient:
m1 \u003d (TPO - TPR) / (TD - TPR) \u003d (HP - HPR) / (Hud - HPR),(16)
Thus, the air conditioning process is reduced to bringing a plurality of outdoor air parameters (ABCDEF polygon) to a permissible set of supply air parameters (polygon P1P2P3P4). In design, tend to use electronic D-H diagrams various options which can be found on the Internet.
One of the common diagrams is a diagram developed by Daichi (Moscow), www.daichi.ru. Using this diagram, you can find the parameters of wet air with different barometric pressure, construct the processes lines, determine the parameters of a mixture of two air flows and other implementations of this transformation can be represented by various structural schemes of the SC: direct flow, with air recirculation or heat recovery that will be Considered in subsequent numbers of our magazine.
Wet airit is a mixture of dry air with water vapor. In fact, the atmospheric air always contains some water vapor, i.e. It is wet.
The water vapor contained in the air is usually in a cleaned state and is subject to the laws for the perfect gas, which allows these laws to apply these laws for wet air.
Couple in the air (overheated or saturated) It is determined by its partial pressure p.which depends on the general pressure of wet air p. and partial pressure of dry air p.:
Saturated air– air with the maximum content of water vapor at a given temperature.
Absolute humidity - weight of water vapor contained
in 1 m.wet air (steam density) during its partial pressure and humid air temperature:
Relative humidity - the ratio of the actual absolute humidity of the air to the absolute humidity of saturated air at the same temperature:
At a constant temperature, air pressure changes in proportion to its density (the law of the boil - Mariotta), therefore the relative humidity of the air can also be determined by the equation:
where p.- air saturation pressure at a given temperature;
p.- partial pressure steam at a temperature:
For dry air \u003d 0, for saturated - \u003d 100%.
Dew point - temperature t.at which steam pressure p.becomes equal to saturation pressure p.. When air cooled below the dew point, water vapors are condensed.
air (11.5)
Using the equation of the ideal gas state for wet air components (steam and dry air), dependences (11.2), (11.3) and (11.5), as well as molecular weights of air (\u003d 28.97) and steam (\u003d 18,016), receive a calculated formula :
air (11.6)
For the case when the wet air is at atmospheric pressure: p \u003d B..
Waste air heat capacity At constant pressure, it is defined as the sum of heat dissipation 1 kg dry air I. d., kg Water vapor:
(11.7)
In calculations, you can accept: 
Wet air enthalpy at a temperature t. Determined as the sum of enthalpy 1 kg dry air I. d., kg Water vapor:
Here r. - hidden heat of vaporization, equal to ~ 2500 kJ / kg.. Thus, the estimated dependence to determine the value of the enthalpy of wet air takes the form:
(11.9)
Note: Value I. refers to 1. kg Dry air or K (1+ d.) kgwet air.
In technical calculations to determine wet air parameters is usually used I-D. Wet air diagram, proposed in 1918 by Professor L.K. Ramsin.
IN I-D. Chart (see Fig. 11.2) The main parameters that determine the heat-woolen air condition are graphically connected: temperature t., relaxed air humidity, moisture content d., Entalpy I., partial pair pressure P.contained in a steady mixture. Knowing two of any parameter, you can find the rest at the intersection of the relevant
lines I - D.-Diagram.
2. Laboratory installation scheme (device )
The relative humidity of the air in laboratory work is determined by a psychrometer type: "hygrometer psychrometric WIT-1".
Psychrometer (Fig. 11.1) consists of two identical thermometers:
"Dry" - 1 and "moored" - 2. The wetting of the thermometer 2 ball is carried out using a batted wick 3, lowered to a water vessel with water.
2 1
 |
3 t.
 |
4t.and air humidity φ for this instrument is established experimentally. According to the results of the experiments, a special psychrometric table (passport), placed on the front panel of a laboratory psychrometer.
On the intensity of the evaporation, the speed of the flow around the batted wick by air is significantly influenced, which makes the error in the testimony of a conventional psychrometer. This error is taken into account in the calculations by the introduction of amendments in accordance with the instrument's passport.
Note:from the discussed disadvantage, a psychrometer is free August, in which both thermometers (dry and moistened) are blown away with constant speed Air flow, created by a fan with a spring engine.
The atmospheric air is a mixture of gases (nitrogen, oxygen, noble gases, etc.) with some water vapor. The amount of water vapor contained in the air is essential for the processes occurring in the atmosphere.
Wet air - a mixture of dry air and water vapor. Knowledge of its properties is necessary for understanding and calculating such technical deviceslike dryers, heating and ventilation systems, etc.
Wet air containing the maximum amount of water vapor at a given temperature is called saturated. Air in which it does not contain the maximum possible amount of water vapor, called unsaturated. The unsaturated wet air consists of a mixture of dry air and superheated water vapor, and saturated wet air is made of dry air and saturated water vapor. Water steam is found in air usually in small quantities and in most cases in overheated state, therefore the laws of ideal gases are applicable to it.
Pressure of wet air INAccording to the Dalton law, equal to the amount of partial pressures of dry air and water vapor:
B \u003d P in + rp, (2.1)
where IN - barometric pressure, PA, r B., p P. - Partial pressure according to dry air and water vapor, PA.
In the process of the isobaric cooling of unsaturated wet air, saturation states can be achieved. The condensation of the water vapor contained in the air, the formation of fog testifies to achieving dew points or dew temperatures. The point of dew is the temperature to which the humid air must be cooled at a constant pressure so that it becomes saturated.
The dew point depends on the relative humidity. With a high relative humidity, the dew point is close to the actual air temperature.
Absolute humidity ρ n Determines the mass of water vapor contained in 1 m 3 wet air.
Relative humidity φ. Determines the degree of air saturation with water vapor:
those. The ratio of valid absolute humidity ρ P. to the maximum possible absolute humidity in saturated air ρ N. at the same temperature.
For saturated air φ \u003d 1 or 100%, and for unsaturated wet air φ < 1.
The magnitude of the moisture content expressed through partial pressures:
(2.4)
As can be seen from equation (2.4) with an increase in partial pressure p P. moisture content d.increases.
Enhalar air enthalpy is one of its main parameters and is widely used in the calculations of drying installations, ventilation and air conditioning systems. Enhalar air enthalpy refer to a unit of dry air (1 kg) and determine as an amount of dry air enthalpy i B. and water vapor i P., KJ / kg:
i \u003d i in + i p ∙ d(2.5)
iD - Wet air diagram
id - The wet air diagram was offered in 1918. prof. L.K. Ramsin. In the diagram (Fig. 2.1) on the abscissa axis postponed the values \u200b\u200bof moisture content d., g / kg, and on the axis ordinate - enthalpy i. Wet air, KJ / kg, assigned to 1 kg of dry air. For better use Square line chart i.\u003d const was held at an angle of 135 ° to lines d.\u003d const and values d. demolished on the horizontal line. Isotherm t.\u003d const) are applied in the form of straight lines.
By id - Wet air diagram for each state of wet air, you can determine the temperature of the dew point. To do this, from the point characterizing the condition of the air, you need to spend the vertical (line d.\u003d Const) before crossing the line φ \u003d 100%. Isotherm, passing through the resulting point, will determine the desired point of wet air dew.
Saturation curve φ \u003d 100% shares id - a diagram on the upper area of \u200b\u200bunsaturated wet air and the lower area of \u200b\u200bthe suspension, in which the moisture is dropped (the fog region).
id - The diagram can be used to solve problems associated with drying materials. The drying process consists of two processes: heating of wet air and its moisturizing, due to evaporation of moisture from the dried material.
Fig. 2.1. id - Wet air diagram
Heating process proceeds with constant moisture content ( d.\u003d const) and depicted on id - diagram vertical line 1-2 (Fig. 2.1). The difference of enthalpy in the diagram determines the amount of heat consumed on heating 1 kg of dry air:
Q \u003d M in∙(i. 2 - i. 1), (2.6)
The perfect saturation process Air moisture B. drying chamber occurs at unchanged enthalpy ( i.\u003d const) and is depicted direct 2-3 '. The difference in moisture content gives the amount of moisture isolated in the drying chamber by each air kilogram:
M n \u003d m in∙(d. 3 - d. 2), (2.7)
The real drying process is accompanied by a decrease in enthalpy, i.e. i.≠ const and depicted direct 2-3 .
Real gases
1. Absolute humidity.
Mass number of steam in 1 m 3 air -
2. Relative humidity.
The ratio of the mass amount of steam in the steam-air mixture to the maximum possible amount at the same temperature
(143)
Mendeleev equation - Klapaireron:
For a para
Location: 
To determine the relative humidity of the air, the instrument "" Psychrometer "" is used, consisting of two thermometers: wet and dry. The difference in the thermometer readings is graded into values.
3. Moisture content.
The amount of steam in the mixture coming by 1 kg of dry air.
Let we have 1 m 3 of air. His mass -.
This cubic meter contains: - kg of steam, - kg of dry air.
Obviously: 
.
4. Enthalpy air.
It consists of two quantities: dry air and steam enthalpy.
5. Dew point.
The temperature at which the gas of this state, coolant, with constant moisture content (d \u003d const), becomes saturated (\u003d 1.0), is called a dew point.
6. The temperature of the wet thermometer.
The temperature at which the gas in the interaction with the liquid coolant is cooled at constant enthalpy (J \u003d const) becomes saturated (\u003d 1.0), is called the temperature of the wet thermometer T m.
Air condition diagram.
The diagram was drawn up by domestic scientist Ramsin (1918) and presented in Fig.169.
The diagram is presented for average atmospheric pressure P \u003d 745 mm Hg. Art. And in fact, the isobar of the equilibrium of the steam system is dry air.
The axis coordinates of the J-D chart deployed at an angle of 135 0. At the bottom there is an inclined line to determine the partial pressure of the water vapor P n. Dry Air Partial Pressure
Above on the diagram, saturation curve was carried out (\u003d 100%). The drying process on the diagram can be submitted only above this curve. For an arbitrary point "" A "" on the Ramsin diagram, you can define the following air parameters:
Fig.169.
Diagram J-D state Wet air.
Drying stories.
In the process of convective drying, for example, the air is interacting with air, in contact with the steam-air mixture, the partial pressure of the water vapor in which is. The moisture can leave the material in the form of a pair, if the partial pressure of steam in a thin boundary layer above the material surface or, as they say, it will be more in the material.
Driving force Drying process (Dalton, 1803)
(146)
In equilibrium state \u003d 0. The moisture content of the material corresponding to the equilibrium condition is called equilibrium moisture content (U p).
Let's experience experience. In the chamber of the drying cabinet at a certain temperature (T \u003d const), we will put absolutely dry substance for a long time. With a certain air in the cabinet, the moisture content of the material will reach u p. By changing, you can get a curve (isotherm) of moisture sorption with material. When decreasing, the desorption curve.
Figure 19 shows a curve of sorption - desorption of wet material (equilibrium isotherm).
Fig.170. Equilibrium isotherm with air with air.
1-region of hygroscopic material, 2-hygroscopic point, 3-region of wet material, 4-sorption area, 5-region desorption, 6-drying area.
The equilibrium curves distinguish:
1. Gigroscopic
2. nonhygroscopic material.
Isotherms are presented in Fig.171.
Fig.171. Equilibrium isotherms.
a) hygroscopic, b) nonhygroscopic material.
Relative humidity in the dryer and in the atmosphere.
After dryer when contacting with atmospheric air The hygroscopic material significantly increases moisture content on (Fig. 171 A) due to the adsorption of moisture from the air. Therefore, the hygroscopic material after drying should be stored under conditions that do not allow contact with atmospheric air (exicuation, wrapper, etc.).
Material balance.
As a student, a tunnel dryer is usually taken, because she has vehicles In the form of trolleys (drying bricks, wood, etc.). The installation scheme is presented in Fig. 172.
Fig.172. The diagram of the tunnel dryer.
1-fan, 2-calorifer, 3-dryer, 4-trolleys, 5-line recycle of exhaust air.
Designations:
Consumption and air parameters to the carrier, after it and after the dryer.
