Ministry of Education and Science of the Russian Federation
Novosibirsk State Technical University
_____________________________________________________________
for FEN students all forms of learning
Novosibirsk
2010
UDC 621.565 (07)
Compiled: Cand. tehn Sciences, Doc. ,
Reviewer: Dr. tech. Sciences, prof.
The work was prepared at the Department of Heat Electrical Stations
© Novosibirsk State
technical University, 2010
1. Practical consolidation of knowledge according to the second law of thermodynamics, cycles, refrigeration units.
2. Familiarization with the IF-56 refrigeration unit and its technical characteristics.
3. Study and construction of refrigeration cycles.
4. Determining the main characteristics, refrigeration Installation.
1. Theoretical Fundamentals of Work
Refrigeration Installation
1.1. Reverse cycle Carno
The refrigeration unit is designed to transfer heat from a cold source to hot. According to the wording of Clausius, the thermodynamics of heat cannot go from a cold body to hot. In the refrigeration unit, such heat transfer occurs not by itself, but due to the mechanical energy of the compressor spent on the compression of the vapor of the refrigerant.
The main characteristic of the refrigeration unit is a refrigeration coefficient, the expression of which is obtained from the equation of the first law of thermodynamics recorded for the reverse cycle of the refrigeration unit, taking into account that for any cycle, the change in the internal energy of the working fluid D u.\u003d 0, namely:
q.= q.1 – q.2 = l., (1.1)
where q.1 - Heat, given to the hot source; q.2 - heat taken from a cold source; l. – mechanical work compressor.
From (1.1) it follows that heat is transmitted to the hot source
q.1 = q.2 + l., (1.2)
a Refrigerator Coefficient is a fraction of heat q.2, transmitted from a cold source to hot, per unit of the expended compressor
(1.3)
Maximum refrigeration factor value for a given temperature range between T.mountain Hot I. T.cold heat sources has a carno reverse cycle (Fig. 1.1),
Fig. 1.1. Reverse cycle Carno
for which the heat supplied with t.2 = const. From a cold source to the working fluid:
q.2 = T.2 · ( s.1 – s.4) = T.2 · DS (1.4)
and heat given at t.1 = const. From the working body to a cold source:
q.1 = T.one · ( s.2 – s.3) = T.1 · DS, (1.5)
In the reverse cycle of carno: 1-2 - adiabatic compression of the working fluid, as a result of which the temperature of the working fluid T.2 becomes higher temperatures T.hot-source mountains; 2-3 - isothermal heat dissipation q.1 from the working fluid to the hot source; 3-4 - adiabatic expansion of the working body; 4-1 - isothermal heat q.2 from a cold source to the working fluid. Taking into account relations (1.4) and (1.5), equation (1.3) for the refrigeration coefficient of the back cycle of carno can be represented as:
The higher the value E, the more effective is the refrigeration cycle and the smaller work. l. will need for heat transfer q.2 from a cold source to hot.
1.2. Cycle of parokompression refrigeration unit
Isothermal supply and removal of heat in the refrigeration unit can be carried out if the refrigerant is the low-boiling liquid, the boiling point of which at atmospheric pressure t.0 £ 0 OC, and with negative temperatures boiling pressure boil p.0 should be more atmospheric to eliminate air seats into the evaporator. Low compression pressure allow you to make a lightweight compressor and other elements of the refrigeration unit. With a significant hidden heat of vaporization r. Low specific volumes are desirable. v., which reduces compressor dimensions.
A good refrigerant is ammonia NH3 (at boiling point t.k \u003d 20 OS, saturation pressure p.k \u003d 8.57 bar and when t.0 \u003d -34 OS, p.0 \u003d 0.98 bar). The hidden heat of the vaporization is higher than in other refrigerators, but its disadvantages - toxicity and corrosion activity in relation to non-ferrous metals, therefore, in household refrigeration units, ammonia does not apply. Not bad refrigerants are methyl chloride (CH3CL) and ethane (C2H6); Sulfurian anhydride (SO2) due to high toxicity does not apply.
Freons are widely used as refrigerators - fluorochloro derivatives of the simplest hydrocarbons (mainly methane). The distinctive properties of freon are their chemical resistance, non-toxicity, lack of interaction with structural materials for t. < 200 оС. В прошлом веке наиболее wide use Received R12, or freon - 12 (CF2Cl2 - Dyftorudichloromethane), which has the following thermal characteristics: molecular weight M \u003d 120.92; Boiling point at atmospheric pressure p.0 \u003d 1 bar; t.0 \u003d -30.3 OC; Critical parameters R12: p.kr \u003d 41.32 bar; t.kr \u003d 111.8 OS; v.kr \u003d 1.78 × 10-3 m3 / kg; Adiabstract index k. = 1,14.
Freon production - 12, as the substance destroying the ozone layer, was prohibited in Russia in 2000, only the use of the already produced R12 or extracted from the equipment was allowed.
2. operation of the refrigeration installation IF-56
2.1. refrigerator aggregate
The IF-56 unit is designed to cool the air in the refrigeration chamber 9 (Fig. 2.1).
Fan "HREF \u003d" / TEXT / CATEGORY / VENTILYTOR / "REL \u003d" BOOKMARK "\u003e fan; 4 - receiver; 5 -Conacitor;
6 - filter-desiccant; 7 - choke; 8 - evaporator; 9 - Refrigerated Camera
Fig. 2.2. Cycle refrigeration
In the process of throttling of liquid freon in choke 7 (process 4-5 V pH-Diagram) It partially evaporates, the main evaporation of freon occurs in the evaporator 8 due to the heat taken from the air in the refrigeration chamber (the isobaro-isothermal process 5-6 p.0 = const. and t.0 = const.). Preheated steam with temperature enters the compressor 1, where it is compressed from pressure p.0 to pressure p.K (polytrophic, valid compression 1-2d). In fig. 2.2 also depicted theoretical, adiabatic compression 1-2A s.1 = const...gif "width \u003d" 16 "height \u003d" 25 "\u003e (process 4 * -4). Liquid freon flows into receiver 5, from where through the filter-desiccant 6 goes to the choke 7.
Technical data
Evaporator 8 consists of finned batteries - convectors. Batteries are equipped with choke 7 with thermostatic valve. Condenser 4 with forced air cooled, fan performance V.B \u003d 0.61 m3 / s.
In fig. 2.3 shows a valid cycle of a parocompression refrigeration unit, built according to its test results: 1-2A - adiabatic (theoretical) compression of the steam of the refrigerant; 1-2D - action-visible compression in the compressor; 2D-3 - the isobaric cooling of the vapor to
condensation temperature t.TO; 3-4 * - the isobaro-isothermal condensation of the steam of the refrigerant in the condenser; 4 * -4 - condensate undercooling;
4-5 - throttling ( h.5 = h.4) as a result of which the liquid refrigeration agent partially evaporates; 5-6 - isobaro-isothermal evaporation in the evaporator refrigeration chamber; 6-1 - isobaric overheating of a dry saturated pair (point 6, h.\u003d 1) to temperature t.1.
Fig. 2.3. Refrigeration cycle in pH-Diagram
2.2. performance features
Basic operational characteristics Refrigeration installation are cooling capacity Q.Power consumption N., Refrigeratory consumption G. and specific cooling capacity q.. Cooling capacity is determined by the formula, kW:
Q. = GQ. = G.(h.1 – h.4), (2.1)
where G. - consumption of the refrigerant, kg / s; h.1 - enthalpy couple at the exit from the evaporator, KJ / kg; h.4 - enthalpy of a liquid refrigerant before choke, KJ / kg; q. = h.1 – h.4 - specific cooling capacity, kJ / kg.
Also used specific volume Cooling capacity, kj / m3:
q.v \u003d. q./ v.1 = (h.1 – h.4)/v.1. (2.2)
Here v.1 - the specific volume of steam at the exit from the evaporator, M3 / kg.
The consumption of the refrigerant is located according to the formula, kg / s:
G. = Q.TO/( H.2D - h.4), (2.3)
Q. = c.’pM.V.IN( t.AT 2 - t.IN 1). (2.4)
Here V.B \u003d 0.61 m3 / s - the performance of the fan, cooling capacitor; t.IN 1, t.B2 - air temperature at the inlet and outlet of the condenser, ºС; c.’pM. - medium bulk isobar air heat capacity, KJ / (m3 · k):
c.’pM. = (μ cPM.)/(μ v.0), (2.5)
where (μ. v.0) \u003d 22.4 m3 / kmol - the volume of kilo praying air under normal physical conditions; (μ. cPM.) - The average isobaric molar heat capacity, which is determined by the empirical formula, KJ / (Kolol · K):
(μ cPM.) \u003d 29,1 + 5,6 · 10-4 ( t.B1 +. t.AT 2). (2.6)
Theoretical power of adiabatic compression of the steam of the refrigerant in process 1-2a, kW:
N.A \u003d. G./( H.2a - h.1), (2.7)
Relative adiabatic and actual cooling capacity:
k.A \u003d. Q./N.BUT; (2.8)
k. = Q./N., (2.9)
presenting heat transmitted from a cold source to hot, per unit theoretical power (adiabatic) and valid (electrical power of the compressor drive). The refrigeration coefficient has the same physical meaning and is determined by the formula:
ε = ( h.1 – h.4)/(h.2D - h.1). (2.10)
3. Refrigeration tests
After starting the refrigeration unit, it is necessary to wait for the stationary mode ( t.1 \u003d const t.2D \u003d const), then measure all the instrument readings and put in the measurement table 3.1, based on the results of which to build a refrigeration cycle in pH- I. tS.--Ordates using a steam chart for freon-12 shown in Fig. 2.2. The calculation of the main characteristics of the refrigeration unit is performed in Table. 3.2. Evaporation temperatures t.0 and condensation t.K find depending on pressures p.0 I. p.To Table. 3.3. Absolute pressure p.0 I. p.K are determined by formulas, bar:
p.0 = B./750 + 0,981p.0m, (3.1)
p.K \u003d. B./750 + 0,981p.Km, (3.2)
where IN – atmosphere pressure Barometer, mm. RT. st.; p.0m - excess pressure of evaporation by pressure gauge, ATI; p.Km - excessive condensation pressure on pressure gauge, ATI.
Table 3.1.
Value | Dimension | Value | Note |
|
Evaporation pressure p.0m | by manometra |
|||
Condensation pressure p.KM | by manometra |
|||
Temperature in the refrigeration chamber, t.HC | by thermocouple 1. |
|||
The temperature of the chest of refrigerant in front of the compressor, t.1 | by thermocouple 3. |
|||
The temperature of the chest of refrigerant after the compressor, t.2D | by thermocouple 4. |
|||
Condensate temperature after a condenser, t.4 | in terms of thermocouple 5. |
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Air temperature after a condenser, t.AT 2 | by thermocouple 6. |
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Air temperature in front of the condenser, t.IN 1 | by thermocouple 7. |
|||
Compressor drive power, N. | vattmetter |
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Evaporation pressure p.0 | by formula (3.1) |
|||
Evaporation temperature t.0 | table. (3.3) |
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Condensation pressure p.TO | by formula (3.2) |
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Condensation temperature, t.TO | table. 3.3. |
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Enthalpy of the chest of refrigerant in front of the compressor, h.1 = f.(p.0, t.1) | by pH-Diagram |
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Enthalpy vapor of refrigerant after compressor, h.2D \u003d f.(p.TO, t.2D) | by pH-Diagram |
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Enthalpy vapor of refrigerant after adiabatic compression, h.2A. | by pH-diagram |
|||
Enthalpy condensate after a condenser, h.4 = f.(t.4) | by pH-diagram |
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The specific volume of steam in front of the compressor, v.1=f.(p.0, t.1) | by pH-Diagram |
|||
Air flow through condenser V.IN | By passport fan |
Table 3.2.
Value | Dimension | Value |
||
The average mole heat capacity of air, (M frompM.) | kJ / (Kombol × K) | 29.1 + 5.6 × 10-4 ( t.B1 +. t.AT 2) | ||
Bulk heat capacity of air, from¢ p.m. | kJ / (m3 × k) | (M. cP.m) / 22.4 | c.¢ p.m. V.IN( t.AT 2 - t.IN 1) | |
Refrigerant consumption, G. | Q.To / ( h.2D - h.4) | |||
Specific cooling capacity q. | h.1 – h.4 | |||
Cooling capacity Q. | GQ. | |||
Specific volumetric capacity, qV. | Q. / v.1 | |||
Adiabatic power, N.a. | G.(h.2a - h.1) | |||
Relative adiabatic cooling capacity TOBUT | Q. / N.BUT | |||
Relative real cooling capacity TO | Q. / N. | |||
Refrigerator coefficient e | q. / (h.2D - h.1) |
Table 3.3.
Freon-12 saturation pressure (CF.2 Cl.2 - Diftorudichloromethane)
1. Scheme and Description of the refrigeration unit.
2. Tables of measurements and calculations.
3. Completed task.
1. Build a refrigeration cycle in pH-Diagram (Fig. 1).
2. Make Table. 3.4, Using pH-Diagram.
Table 3.4.
2. Build a refrigeration cycle in tS.-Diagram (Fig. 2).
3. Determine the value of the refrigeration coefficient of the Carno reverse cycle according to formula (1.6) for T.1 = T.To I. T.2 = T.0 and compare it with the refrigeration coefficient of the real installation.
1. Sharov, Yu. I.Comparing the cycles of refrigeration installations on alternative refrigerants / // Energy and thermal power engineering. - Novosibirsk: NSTU. - 2003. - Vol. 7, - p. 194-198.
2. Kirillin, V. A.Technical thermodynamics / ,. - M.: Energia, 1974. - 447 p.
3. Vargaftik, N. B. Directory by thermophysical properties gases and liquids. - M.: Science, 1972. - 720 p.
4. Andryzchenko, A. I. Basics of technical thermodynamics of real processes. - M.: Higher School, 1975.
refrigerated piston is not direct-flow, single-stage, glad, vertical.
Purpose for work in stationary and transport refrigerators.
| Parameter | Value |
| Cooling capacity, kW (kcal / h) | 12,5 (10750) |
| Cladon | R12-22 |
| Piston stroke, mm | 50 |
| Cylinder diameter, mm | 67,5 |
| Number of cylinders, pcs | 2 |
| Crankshaft rotation frequency, s -1 | 24 |
| Volume described by pistons, m 3 / h | 31 |
| Internal diameter of connected suction pipelines no less, mm | 25 |
| Internal diameter of connected injection pipelines no less, mm | 25 |
| Overall dimensions, mm | 368*324*390 |
| Net weight, kg | 47 |
Cylinder diameter - 67.5 mm
Piston move - 50 mm.
The number of cylinders - 2.
Rated rates of rotation of the shaft - 24c-1 (1440 rpm).
The compressor is allowed at the rotational speed of the C-1 shaft (1650 rpm).
Described piston volume, m3 / h - 32.8 (at n \u003d 24 s - 1). 37.5 (at n \u003d 27.5 s - 1).
Type of actuator - through the clinorem transmission or coupling.
Refrigerators:
R12 - GOST 19212-87
R22 is GOST 8502-88
R142- TU 6-02-588-80
Maintenance after 500 hours; 2000 hours, with the replacement of oil and the cleaning of the gas filter;
- maintenance After 3750 h:
- current repair after 7600 hours;
- medium, repair after 22500 h;
- overhaul after 45000 hours
In the process of manufacturing compressors, the design of their nodes and parts is constantly being improved. Therefore, in the supplied compressor, individual parts and nodes may differ slightly from the data described in the passport.
when rotating the crankshaft, the pistons get reciprocated 
protective traffic. When the piston moves down in the space formed by the cylinder and the valve board, there is a vacuum, the plate of the suction valve begged, opening, the holes in the valve plate, through which the refrigerant pairs go into the cylinder. Filling of the refrigerant couples will occur until the piston comes to its lower position. When the piston moves, the suction valves are closed. The pressure in the cylinders will increase. As soon as the pressure in the cylinder becomes more pressure in the injection line, the discharge valves will open the holes in the 'valve plate' for the passage of the refrigerant vapor to the injection cavity. Having reached the top position, the piston will start to descend, the discharge valves will close and the cylinder will again be vacuum. Then the cycle is repeated. Compressor Carter (Fig. 1) is a cast iron casting, having a support from the crankshaft bearings. On the one hand, the crankcase lid is a graphite gland, on the other hand, the crankcase is closed with a lid, in which a tear serving an end for the crankshaft. Carter has two tubes, one of which serves to fill the oil compressor, and the other for draining the oil. On the side wall of the crankcase there is a viewing glass designed to control the oil level in the compressor. The flange at the top of the crankcase is designed to attach a block of cylinders to it. The cylinder block combines two cylinders into one cast-iron casting having two flanges: top for attaching a valve board with a block cover and lower for mounting to the Carter. In order to protect the compressor and the system from clogging in the absorption cavity of the unit, a filter is installed. To ensure the return of oil accumulating in the suction cavity, a plug with a hole connecting the suction cavity block with a crankcase is provided. The connecting rod-piston group consists of a piston, connecting rod, 
finger. Insoligative and oil-giving rings. The valve board is installed in the upper part of the compressor between the cylinder blocks and the cylinder lid, consists of a valve plate, suction and injection valve plates, seats of suction valves, springs, sleeves, guide injection valves. The valve plate has removable seats of suction valves in the form of steel coiled overlays with two oblong slits in each. The slots are closed with steel spring plates, which are located in the grooves of the valve plate. The saddle and the stove are fixed by pins. Plates of injection valves steel, round, are located in ring slabs, which are valve beds. To prevent lateral displacement, during operation, the plate is centered by stamped guides, the legs of which are resting in the bottom of the ring groove of the valve plate. From above, the plate is pressed to the valve plate springs, using a common plank that is attached to the stove bolts on the sleeves. 4 fingers are fixed in the bar, which placed sleeves that limit the rise of the injection valves. The bushings are pressed to the guide valves with buffer springs. Under normal conditions, buffer springs do not work; They serve for protected valves from damage in hydraulic blows in the case of a liquid refrigerant or excess oil in the cylinders. The valve board is divided internal partition Cylinder covers for suction and injection cavity. In the upper, extreme position of the piston between the valve board and the bottom of the piston there is a 0.2 ... 0,17 mm clearance, called a linear dead space, the gland seal seals the outgoing drive end of the crankshaft. Selinic type - graphite self-aligning. Shut-off valves - suction pressure of the injection, serve to connect the compressor to the refrigerant system. A corner or direct fitting, as well as a fitting or a tee for connecting devices, is fastened to the body of the shut-off valve. When the spindle rotates clockwise, in the extreme position, the spool overlaps the main passage through the valve into the system and opens the passage to the stacker. When the spindle rotates counterclockwise, it overlaps the cone in the extreme position, the passage to the stacker and opens the main passage through the valve and, blocks the passage to the tee. In intermediate positions, there is a passage of both the system and the tee. Lubrication of moving parts of the compressor is carried out by splashing. Lubrication of connecting rod crankshaft necks occurs through the drilled sloping canals at the top of the lower rod head. The top head of the connecting rod is lubricated with oil, flowing on the inside of the bottom, piston and falling into the drilled hole of the top head of the rod. To reduce the oil injury from the crankcase, the oil is the removable ring on the piston, which resets the side of the oil from the walls of the cylinder back to the crankcase.
The amount of oil refilled: 1.7 + - 0.1 kg.
| Parameters | R12. | R22. | R142. | |
| n \u003d 24 s-¹ | n \u003d 24 s-¹ | n \u003d 27,5 s-¹ | n \u003d 24 s-¹ | |
| Cooling capacity, kw | 8,13 | 9,3 | 12,5 | 6,8 |
| Effective power, kW | 2,65 | 3,04 | 3,9 | 2,73 |
Notes: 1. Data is shown in the mode: Keeping Reader - minus 15 ° C; condensation temperature - 30 ° C; The suction temperature is 20 ° C; fluid temperature over a throttle device 30 ° C - for refrigeration R12, R22; Boiling point - 5 ° C; condensation temperature - 60 s; The absorption temperature is 20 ° C: the temperature of the fluid before the throttle device is 60 ° C - for chladone 142;
A deviation is allowed from the nominal values \u200b\u200bof cooling capacity and efficient. Memority within ± 7%.
The pressure difference and suction pressures should not exceed 1.7 MPa (17 kgf / s * 1), and the ratio of the pressure pressure to the suction pressure should not exceed 1.2.
The discharge temperature should not exceed 160 ° C for R22 and 140 ° C for R12 and R142.
Calculated pressure of 1.80 MPa (1.8 kgf. CM2)
Compressors must maintain tightness when checking excess pressure 1.80 MPa (1.8 kgf. CM2).
tVS \u003d T0 + (15 ... 20 ° C) at T0 ≥ 0 ° C;
tv \u003d 20 ° С at -20 ° С< t0 < 0°С;
tVS \u003d T0 + (35 ... 40 ° C) at T0< -20°С;
The IF-56 unit is designed to cool the air in the refrigeration chamber 9 (Fig. 2.1). The main elements are: Freonal piston compressor 1, air cooling capacitor 4, choke 7, evaporative batteries 8, filter-drier 6, filled with moisture absorber - silicogel, receiver 5 for condensate collection, fan 3 and electric motor 2.
Fig. 2.1. Scheme of the refrigeration unit IF-56:
Technical data
|
Compressor brand |
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Number of cylinders |
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Volume described by pistons, m3 / h |
|
|
Refrigerator |
|
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Cooling capacity, kw |
|
|
at T0 \u003d -15 ° C: TK \u003d 30 ° C |
|
|
at T0 \u003d +5 ° C TK \u003d 35 ° C |
|
|
Electric motor power, kW |
|
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The outer surface of the condenser, m2 |
|
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External surface of the evaporator, m2 |
The evaporator 8 consists of two ribbed batteries - convectors. Batteries are equipped with choke 7 with thermostatic valve. Condenser 4 with forced air cooled, fan performance
VB \u003d 0.61 m3 / s.
In fig. 2.2 and 2.3 shows a valid cycle of a parocompression refrigeration unit, built according to its test results: 1 - 2a - adiabatic (theoretical) compression of the steam of the refrigerant; 1 - 2D - action-visible compression in the compressor; 2D - 3 - the isobaric cooling of the vapor to
condensation temperature TK; 3 - 4 * - the isobaro-isothermal condensation of the steam of the refrigerant in the condenser; 4 * - 4 - condensate undercooling;
4 - 5 - throttling (H5 \u003d H4), as a result of which the liquid refrigeration agent is partially evaporated; 5 - 6 - isobaro-isothermal evaporation in the evaporator of the refrigeration chamber; 6 - 1 - isobaric overheating of a dry saturated pair (point 6, x \u003d 1) to T1 temperature.
