Small refrigeration machines. Determination of the characteristics of the refrigeration system Compressors are repairable products and require periodic maintenance

All small refrigeration machines produced in our country are freon. They are not mass-produced to operate on other refrigerants.

Fig. 99. Refrigerating machine IF-49M:

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

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

Fig. 104. Refrigeration machine diagram with AKFV-4M unit;

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

All these machines are intended for direct cooling of stationary refrigerating chambers and various commercial refrigeration equipment of catering establishments 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 regulating valves (if the machine is equipped with a water-cooled condenser). Relatively large of these machines - XM1-6, XMV1-6, XM1-9 and XMV1-9 - are equipped, in addition, with solenoid valves and chamber temperature switches, one common solenoid valve is installed on the armature shield in front of the liquid manifold, with which you can turn off the supply of freon to all evaporators at once, and the chamber solenoid valves - on the 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 installed on one of them so that not all the cooling devices of the chamber are turned off by means of this valve, but only those that it supplies.

Compressor type:

refrigeration piston non-direct-flow, single-stage, stuffing box, vertical.

Designed for work in stationary and transport refrigeration units.

Technical specifications , ,

Parameter	Value
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 rotation frequency, s -1	24
The volume described by the pistons, m 3 / h	31
Internal diameter of the connected suction pipelines, not less, mm	25
Internal diameter of the connected discharge pipelines, not less, mm	25
Overall dimensions, mm	368*324*390
Net weight, kg	47

Compressor characteristics and description ...

Cylinder diameter - 67.5 mm
The piston stroke is 50 mm.
The number of cylinders is 2.
The nominal shaft speed is 24s-1 (1440 rpm).
The compressor can operate at a shaft rotation speed s-1 (1650 rpm).
The described piston volume, m3 / h - 32.8 (at n \u003d 24 s-1). 37.5 (at n \u003d 27.5 s-1).
The type of drive is through a V-belt transmission or a clutch.

Refrigerating agents:

R12 - GOST 19212-87

R22- GOST 8502-88

R142- TU 6-02-588-80

Compressors are repairable items and require periodic maintenance:

Maintenance after 500 hours; 2000 h, with oil change and gas filter cleaning;
- maintenance after 3750 h:
- current repairs after 7600 hours;
- average, repair after 22500 hours;
- overhaul after 45,000 hours

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

The principle of operation of the compressor is as follows:

when the crankshaft rotates, the pistons are reciprocated
translational motion. When the piston moves down in the space formed by the cylinder and the valve plate, a vacuum is created, the suction valve plates bend, opening the holes in the valve plate through which refrigerant vapors pass into the cylinder. The filling with refrigerant vapor will continue until the piston reaches its bottom position. When the piston moves up, the suction valves are closed. The pressure in the cylinders will increase. As soon as the pressure in the cylinder exceeds the pressure in the discharge line, the discharge valves will open the holes in the 'Valve plate' for the refrigerant vapor to flow into the discharge chamber. Having reached the upper position, the piston will begin to lower, the discharge valves will close and there will be a vacuum in the cylinder again. Then the cycle repeats. Compressor crankcase (Fig. 1) is a cast iron with support for crankshaft bearings at the ends. On one side of the crankcase cover there is a graphite oil seal, on the other side 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 is used to fill the compressor with oil and the other to drain the oil. A sight glass is located on the side wall of the crankcase for monitoring the oil level in the compressor. The flange in the upper part of the crankcase is intended for attaching 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 with the block cover and the lower one for attaching to the crankcase. In order to protect the compressor and system from clogging, a filter is installed in the suction cavity of the unit. To ensure the return of the oil accumulating in the suction cavity, a plug with an opening is provided that connects the suction cavity of the block with the crankcase. The connecting rod-piston group consists of a piston, a connecting rod, finger. sealing and oil scraper rings. The valve plate is installed in the upper part of the compressor between the cylinder blocks and the cylinder head and consists of a valve plate, suction and discharge valve plates, suction valve seats, springs, bushings, and discharge valve guides. The valve plate has removable suction valve seats in the form of hardened steel plates with two elongated 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 secured with pins. The plates of the discharge valves 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 to the valve plate by springs using a common bar, which is bolted to the plate with bushings. 4 fingers are fixed in the bar, on which bushings are placed that limit the lifting of the discharge valves. The bushes are pressed against the directional valves by buffer springs. The buffer springs do not work under normal conditions; They serve to protect the valves from breakage during hydraulic shocks in the event of liquid coolant or excess oil entering the cylinders. The valve plate is divided by the inner baffle of the cylinder head into a suction and a discharge chamber. 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 the linear dead space, the oil seal seals the outward drive end of the crankshaft. Gland type - graphite self-aligning. Shut-off valves - suction and discharge, are used to connect the compressor to the refrigerant system. An angle or straight union, as well as a union or tee for connecting devices, is attached to the body of the shut-off valve. When the spindle rotates clockwise, it closes the main passage through the valve to the system with a spool in the extreme position and opens the passage to the fitting. When the spindle rotates 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, closes the passage to the tee. In intermediate positions, the passage is open both to the system and to the tee. The moving parts of the compressor are lubricated by spraying. The crankshaft connecting rod journals are lubricated through the drilled sloped channels in the upper part of the lower connecting rod head. The upper connecting rod head is lubricated with oil flowing down from the inner side of the bottom, piston and entering the drilled hole of the upper connecting rod head. To reduce oil carryover from the crankcase, the oil is a removable ring on the piston, which dumps part of the oil from the cylinder walls back into the crankcase.

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

Cooling performance and effective power, see the table:

Options	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 are given for the following regime: boiling point - minus 15 ° С; condensation temperature - 30 ° С; suction temperature - 20 ° С; liquid temperature in front of the throttle device 30 ° С - for R12, R22 freons; boiling point - 5 ° С; condensation temperature - 60 С; suction temperature - 20 ° С: liquid temperature in front of the throttle device - 60 ° С - for freon 142;

A deviation from the nominal values \u200b\u200bof cooling capacity and effective power is allowed within ± 7%.

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

Discharge temperature should not exceed 160 ° С for R22 and 140 ° С 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 should be:

tvs \u003d t0 + (15 ... 20 ° С) at t0 ≥ 0 ° С;

tvs \u003d 20 ° С at -20 ° С< t0 < 0°С;

tvs \u003d t0 + (35 ... 40 ° С) at t0< -20°С;

Refrigeration unit

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

Figure: 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 - refrigerating chamber

Figure: 2.2. Cycle refrigeration unit

In the process of throttling liquid freon in throttle 7 (process 4-5 in phdiagram), it partially evaporates, while the main evaporation of freon occurs in the evaporator 8 due to the heat taken from the air in the refrigerating chamber (isobaric-isothermal process 5-6 at p 0 = const and t 0 = const). Superheated steam with temperature enters compressor 1, where it is compressed from pressure p 0 to pressure p K (polytropic, valid compression 1-2d). In fig. 2.2 also shows the theoretical, adiabatic compression of 1-2 A at s 1 = const... In the condenser, 4 pairs of freon are cooled to the condensation temperature (process 2d-3), then condense (isobaric-isothermal process 3-4 * at p K \u003d const and t K \u003d const... In this case, the liquid freon is supercooled to a temperature (process 4 * -4). The 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. 4 forced air cooled condenser, fan capacity V B \u003d 0.61 m 3 / s.

In fig. 2.3 shows the actual cycle of a vapor compression refrigeration unit, built according to the results of its tests: 1-2а - adiabatic (theoretical) compression of refrigerant vapors; 1-2d - actual compression in the compressor; 2d-3 - isobaric cooling of vapors to
condensing temperature t TO; 3-4 * - isobaric-isothermal condensation of refrigerant vapors in the condenser; 4 * -4 - condensate overcooling;
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 refrigerating chamber; 6-1 - isobaric superheat of dry saturated steam (point 6, x\u003d 1) to temperature t 1 .

Figure: 2.3. Refrigeration cycle in ph-chart

Performance characteristics

The main operational characteristics of the refrigeration unit are refrigeration capacity Q, power consumption N, refrigerant consumption G and specific refrigerating capacity q... Cooling capacity is determined by the formula, kW:

Q \u003d Gq \u003d G(h 1 – h 4), (2.1)

where G - refrigerant consumption, kg / s; h 1 - enthalpy of steam at the outlet from the evaporator, kJ / kg; h 4 - enthalpy of the liquid refrigerant before the choke, kJ / kg; q = h 1 – h 4 - specific refrigerating capacity, kJ / kg.

The specific volumetric cooling capacity, kJ / m 3:

q v \u003d q / v 1 = (h 1 – h 4)/v 1 . (2.2)

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

Refrigerant flow rate is found by the formula, kg / s:

G = Q K / ( h 2D - h 4), (2.3)

Q = c’ pm V IN ( t IN 2 - t IN 1). (2.4)

Here V В \u003d 0.61 m 3 / s - capacity of the fan cooling the condenser; t IN 1 , t В2 - 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 c 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 c pm) Is the average isobaric molar heat capacity of air, which is determined by the empirical formula, kJ / (kmol K):

(μ c pm) \u003d 29.1 + 5.6 · 10 -4 ( t B1 + t IN 2). (2.6)

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

N A \u003d G/( h 2A - h 1), (2.7)

Relative adiabatic and actual refrigerating capacities:

k A \u003d Q/N AND; (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 real (electric power of the compressor drive). The coefficient of performance has the same physical meaning and is determined by the formula.

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

Figure: 2.1. Refrigeration unit diagram IF-56:

Technical data

Compressor brand
Number of cylinders
The volume described by the pistons, m3 / h
Refrigerant
Cooling capacity, kW
at t0 \u003d -15 ° С: tк \u003d 30 ° С
at t0 \u003d +5 ° С tк \u003d 35 ° С
Electric motor power, kW
Condenser outer surface, m2
Evaporator outer surface, m2

Evaporator 8 consists of two ribbed batteries - convectors. the batteries are equipped with a 7 throttle with a thermostatic valve. 4 forced air cooled condenser, fan capacity

VB \u003d 0.61 m3 / s.

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

condensation temperature tк; 3 - 4 * - isobaric-isothermal condensation of refrigerant vapors in the condenser; 4 * - 4 - condensate overcooling;

4 - 5 - throttling (h5 \u003d h4), as a result of which the liquid refrigerant partially evaporates; 5 - 6 - isobaric-isothermal evaporation in the evaporator of the refrigerating chamber; 6 - 1 - isobaric superheat of dry saturated steam (point 6, x \u003d 1) to temperature t1.