Small refrigerators. Determination of the characteristics of the refrigeration unit Compressors are repairable products and require periodic maintenance

All small refrigerating machines produced in our country are freon. They are not mass-produced for operation on other refrigerants.

Fig.99. Scheme of the IF-49M refrigerating machine:

1 - compressor, 2 - condenser, 3 - expansion valves, 4 - evaporators, 5 - heat exchanger, 6 - sensitive cartridges, 7 - pressure switch, 8 - water control valve, 9 - dryer, 10 - filter, 11 - electric motor, 12 - magnetic switch.

Small refrigeration machines are based on the freon compressor-condensing units of the corresponding capacity discussed above. The industry produces small refrigerators mainly with units with a capacity of 3.5 to 11 kW. These include machines IF-49 (Fig. 99), IF-56 (Fig. 100), KhM1-6 (Fig. 101); XMV1-6, XM1-9 (Fig. 102); HMV1-9 (Fig. 103); machines without special brands with AKFV-4M units (Fig. 104); AKFV-6 (Fig. 105).

Fig.104. Scheme of a refrigeration machine with an AKFV-4M unit;

1 - KTR-4M condenser, 2 - TF-20M heat exchanger; 3 - water control valve VR-15, 4 - pressure switch RD-1, 5 - compressor FV-6, 6 - electric motor, 7 - filter-drier OFF-10a, 8 - evaporators IRSN-12.5M, 9 - expansion valves TRV -2M, 10 - sensitive cartridges.

Machines with VS-2.8, FAK-0.7E, FAK-1.1E and FAK-1.5M units are also produced in significant numbers.

All these machines are intended for direct cooling of stationary cold rooms and various commercial refrigeration equipment of enterprises. Catering and grocery stores.

Wall-mounted ribbed coil batteries IRSN-10 or IRSN-12.5 are used as evaporators.

All machines are fully automated and equipped with thermostatic valves, pressure switches and water control valves (if the machine is equipped with a water-cooled condenser). The relatively large of these machines - XM1-6, XMB1-6, XM1-9 and XMB1-9 - are also equipped with solenoid valves and a chamber temperature switch, one common solenoid valve is installed on the reinforcement board in front of the liquid collector, with which you can turn off the supply of freon to all evaporators at once, and chamber solenoid valves - on pipelines supplying liquid freon to the cooling devices of the chambers. If the chambers are equipped with several cooling devices and freon is supplied to them through two pipelines (see diagrams), then a solenoid valve is placed on one of them so that not all cooling devices of the chamber are turned off through this valve, but only those that it feeds.

Compressor type:

refrigeration piston non-straight-through, single-stage, stuffing box, vertical.

Purpose for works in stationary and transport refrigerating installations.

Technical specifications , ,

Parameter	Meaning
Cooling capacity, kW (kcal/h)	12,5 (10750)
freon	R12-22
Piston stroke, mm	50
Cylinder diameter, mm	67,5
Number of cylinders, pcs	2
Crankshaft speed, s -1	24
The volume described by the pistons, m 3 / h	31
Inner diameter of connected suction pipelines, not less than, mm	25
Internal diameter of connected injection pipelines, not less than, mm	25
Overall dimensions, mm	368*324*390
Net weight, kg	47

Characteristics and description of the compressor ...

Cylinder diameter - 67.5 mm
Piston stroke - 50 mm.
Number of cylinders - 2.
Rated shaft speed - 24s-1 (1440 rpm).
It is allowed to operate the compressor at a shaft speed of s-1 (1650 rpm).
Described piston volume, m3/h - 32.8 (at n=24 s-1). 37.5 (at n=27.5 s-1).
Type of drive - through V-belt transmission or clutch.

Refrigerants:

R12 - GOST 19212-87

R22- GOST 8502-88

R142- TU 6-02-588-80

Compressors are repairable products and require periodic maintenance:

Maintenance after 500 hours; 2000 h, with oil change and gas filter cleaning;
- Maintenance after 3750 h:
- current repair after 7600 hours;
- medium, repair after 22500 hours;
- overhaul after 45000 hours

In the process of manufacturing compressors, the design of their components and parts is constantly being improved. Therefore, in the supplied compressor, individual parts and assemblies may differ slightly from those described in the passport.

The principle of operation of the compressor is as follows:

when the crankshaft rotates, the pistons get back
progressive movement. When the piston moves down in the space formed by the cylinder and valve plate, a vacuum is created, the suction valve plates bend, opening holes in the valve plate through which refrigerant vapor passes into the cylinder. Filling with refrigerant vapor will continue until the piston reaches its bottom position. When the piston moves upwards, the suction valves close. The pressure in the cylinders will increase. As soon as the pressure in the cylinder is greater than the pressure in the discharge line, the discharge valves will open the holes in the ‘Valve plate’ for the passage of refrigerant vapor into the discharge cavity. Having reached the upper position, the piston will begin to descend, the discharge valves will close and there will be a vacuum in the cylinder again. Then the cycle repeats. The compressor crankcase (Fig. 1) is a cast iron casting with supports for the crankshaft bearings at the ends. On one side of the crankcase cover there is a graphite gland, on the other hand the crankcase is closed with a cover in which a cracker is located, which serves as a stop for the crankshaft. The crankcase has two plugs, one of which serves to fill the compressor with oil, and the other to drain the oil. On the side wall of the crankcase there is a sight glass designed to control the oil level in the compressor. The flange at the top of the crankcase is designed to attach the cylinder block to it. The cylinder block combines two cylinders into one cast iron casting, which has two flanges: the upper one for attaching the valve plate to the block cover and the lower one for attaching to the crankcase. In order to protect the compressor and the system from clogging, a filter is installed in the suction cavity of the unit. To ensure the return of oil accumulating in the suction cavity, a plug with a hole is provided connecting the suction cavity of the block with the crankcase. The connecting rod and piston group consists of a piston, connecting rod, finger. sealing and oil scraper rings. The valve board is installed in the upper part of the compressor between the cylinder blocks and the cylinder cover, it consists of a valve plate, suction and discharge valve plates, suction valve seats, springs, bushings, discharge valve guides. The valve plate has removable saddles of suction valves in the form of hardened steel plates with two oblong slots in each. The slots are closed with steel spring plates, which are located in the grooves of the valve plate. Saddles and plate are fixed with pins. Discharge valve plates are steel, round, located in the annular grooves of the plate, which are the valve seats. To prevent lateral displacement, during operation, the plates are centered by stamped guides, the legs of which rest against the bottom of the annular groove of the valve plate. From above, the plates are pressed against the valve plate by springs, using a common bar, which is attached to the plate with bolts on bushings. 4 pins are fixed in the bar, on which bushings are placed, limiting the rise of the discharge valves. The bushings are pressed against the valve guides by buffer springs. Under normal conditions buffer springs do not work; They serve to protect valves from breakage during hydraulic shocks in case of liquid refrigerant or excess oil entering the cylinders. The valve board is divided by an internal partition of the cylinder head into suction and discharge cavities. In the upper, extreme position of the piston between the valve plate and the bottom of the piston there is a gap of 0.2 ... 0.17 mm, called linear dead space. The stuffing box seals the drive end of the crankshaft that goes out. Type of stuffing box - graphite self-aligning. Shut-off valves - suction and discharge, are used to connect the compressor to the refrigerant system. An angle or straight fitting, as well as a fitting or tee for connecting devices, is attached to the body of the shut-off valve on the thread. When the spindle is rotated clockwise, in the extreme position, the spool blocks the main passage through the valve into the system and opens the passage to the fitting. When the spindle is rotated counterclockwise, in the extreme position it closes with a cone the passage to the fitting and completely opens the main passage through the valve into the system and blocks the passage to the tee. In intermediate positions, the passage is open both to the system and to the tee. Lubrication of the moving parts of the compressor is carried out by splashing. Lubrication of the connecting rod journals of the crankshaft occurs through drilled inclined channels in the upper part of the lower connecting rod smut. The upper head of the connecting rod is lubricated with oil flowing from the inside of the bottom, piston and falling into the drilled hole of the upper head of the connecting rod. To reduce oil carryover from the crankcase, an oil is used by a removable ring on the piston, which dumps some of the oil from the cylinder walls back into the crankcase.

The amount of oil to be filled: 1.7 + - 0.1 kg.

Refrigeration performance and effective power, see the table:

Options	R12		R22	R142
	n=24 s-¹	n=24 s-¹	n=27.5 s-¹	n=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. The data are given on the mode: boiling point - minus 15°С; condensation temperature - 30°С; suction temperature - 20°C; fluid temperature in front of the throttle device 30 ° C - for freons R12, R22; boiling point - 5°C; condensation temperature - 60 C; suction temperature - 20°C; liquid temperature in front of the throttle device - 60°C - for freon 142;

Deviation from the nominal values ​​of cooling capacity and effective power within ± 7% is allowed.

The difference between discharge and suction pressures should not exceed 1.7 MPa (17 kgf/s*1), and the ratio of discharge pressure to suction pressure should not exceed 1.2.

The discharge temperature must not exceed 160°C for R22 and 140°C for R12 and R142.

Design pressure 1.80 MPa (1.8 kgf.cm2)

Compressors must maintain tightness when tested with an overpressure of 1.80 MPa (1.8 kgf.cm2).

When operating on R22, R12 and R142 the suction temperature must be:

tvs=t0+(15…20°С) at t0 ≥ 0°С;

tvs=20°С at -20°С< t0 < 0°С;

tair= t0 + (35…40°С) at t0< -20°С;

Refrigeration unit

The IF-56 unit is designed to cool the air in the refrigerating chamber 9 (Fig. 2.1).

Rice. 2.1. Refrigeration unit IF-56

1 - compressor; 2 - electric motor; 3 – fan; 4 - receiver; 5 -capacitor;

6 - filter-drier; 7 - throttle; 8 - evaporator; 9 - refrigerator

Rice. 2.2. Cycle refrigeration unit

In the process of throttling liquid freon in throttle 7 (process 4-5 in ph-diagram), it partially evaporates, while the main evaporation of freon occurs in the evaporator 8 due to the heat taken from the air in the refrigerator chamber (isobaric-isothermal process 5-6 at p 0 = const And t 0 = const). Superheated steam with a temperature enters compressor 1, where it is compressed from pressure p 0 to pressure p K (polytropic, real compression 1-2d). On fig. 2.2 also shows a theoretical, adiabatic compression of 1-2 A at s 1 = const. In the condenser 4, freon vapors are cooled to the condensation temperature (process 2e-3), then condense (isobaric-isothermal process 3-4 * at p K = const And t K = const. In this case, liquid freon is supercooled to a temperature (process 4*-4). Liquid freon flows into the receiver 5, from where it flows through the filter-drier 6 to the throttle 7.

Technical data

Evaporator 8 consists of finned batteries - convectors. The batteries are equipped with a choke 7 with a thermostatic valve. Forced air-cooled condenser 4, fan performance V B \u003d 0.61 m 3 / s.

On fig. 2.3 shows the actual cycle of a vapor-compression refrigeration plant built according to the results of its tests: 1-2a - adiabatic (theoretical) compression of the refrigerant vapor; 1-2d - actual compression in the compressor; 2e-3 - isobaric cooling of vapors up to
condensing temperature t TO; 3-4 * - isobaric-isothermal condensation of refrigerant vapor in the condenser; 4 * -4 - condensate subcooling;
4-5 - throttling ( h 5 = h 4), as a result of which the liquid refrigerant partially evaporates; 5-6 - isobaric-isothermal evaporation in the evaporator refrigerator compartment; 6-1 - isobaric superheating of dry saturated steam (point 6, X= 1) up to temperature t 1 .

Rice. 2.3. Refrigeration cycle in ph-diagram

Performance characteristics

The main operational characteristics of the refrigeration unit are the cooling capacity Q, power consumption N, refrigerant 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– refrigerant consumption, kg/s; h 1 – steam enthalpy at the evaporator outlet, kJ/kg; h 4 - enthalpy of the liquid refrigerant in front of the throttle, kJ/kg; q = h 1 – h 4 – specific cooling capacity, kJ/kg.

The specific volumetric cooling capacity, kJ / m 3:

q v= q/v 1 = (h 1 – h 4)/v 1 . (2.2)

Here v 1 is the specific volume of steam at the outlet of the evaporator, m 3 /kg.

The flow rate of the refrigerant is found by 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 m 3 / s - the performance of the fan that cools the condenser; t IN 1 , t B2 - air temperature at the inlet and outlet of the condenser, ºС; c’pm- average volumetric isobaric heat capacity of air, kJ / (m 3 K):

c’pm = (μ from pm)/(μ v 0), (2.5)

where (μ v 0) \u003d 22.4 m 3 / kmol - the volume of a kilo mole of air under normal physical conditions; (μ from pm) is the average isobaric molar heat capacity of air, which is determined by the empirical formula, kJ/(kmol K):

(μ from pm) = 29.1 + 5.6 10 -4 ( t B1+ t AT 2). (2.6)

Theoretical power of adiabatic compression of refrigerant vapors in the process 1-2 A, kW:

N A = G/(h 2A - h 1), (2.7)

Relative adiabatic and actual cooling capacities:

k A = Q/N A; (2.8)

k = Q/N, (2.9)

representing the heat transferred from a cold source to a hot one, per unit of theoretical power (adiabatic) and actual (electrical power of the compressor drive). The coefficient of performance has the same physical meaning and is determined by the formula.

The IF-56 unit is designed to cool the air in the refrigerating chamber 9 (Fig. 2.1). the main elements are: a freon piston compressor 1, an air-cooled condenser 4, a throttle 7, evaporative batteries 8, a filter-drier 6 filled with a desiccant - silica gel, a receiver 5 for collecting condensate, a fan 3 and an electric motor 2.

Rice. 2.1. Scheme of the IF-56 refrigeration unit:

Technical data

Compressor brand
Number of cylinders
Volume described by pistons, m3/h
refrigerant
Cooling capacity, kW
at t0 = -15 °С: tк = 30 °С
at t0 = +5 °С tк = 35 °С
Electric motor power, kW
External surface of the condenser, m2
External surface of the evaporator, m2

Evaporator 8 consists of two finned batteries - convectors. batteries are equipped with a throttle 7 with a thermostatic valve. Forced air-cooled condenser 4, fan performance

VB = 0.61 m3/s.

On fig. Figures 2.2 and 2.3 show the actual cycle of a vapor-compression refrigeration plant built according to the results of its tests: 1 - 2a - adiabatic (theoretical) compression of the refrigerant vapor; 1 - 2d - actual compression in the compressor; 2d - 3 - isobaric cooling of vapors up to

condensation temperature tk; 3 - 4* - isobaric-isothermal condensation of refrigerant vapor in the condenser; 4* - 4 - condensate subcooling;

4 - 5 - throttling (h5 = h4), as a result of which the liquid refrigerant partially evaporates; 5 - 6 - isobaric-isothermal evaporation in the evaporator of the refrigeration chamber; 6 – 1 – isobaric superheating of dry saturated steam (point 6, х = 1) up to temperature t1.