-\u003e 13.03.2012 - supercooling in refrigerators

Superchilding of the liquid refrigerant after the condenser - essential way Increase the cooling capacity of the refrigeration unit. The decrease in the temperature of the hyposhed refrigerant per degree corresponds to an increase in the performance of a normally functioning refrigeration unit by about 1% at the same level of power consumption. The effect is achieved due to a decrease in the percientation of the fraction of steam in the vapor-like mixture, which is a condensed refrigerant, which comes to the TRV of the evaporator even from the receiver.

In low-temperature refrigeration installations, the use of supercooling is particularly efficient. In them the hypothermia of the condensed refrigerant to significant negative temperatures Allows you to increase the cooling capacity of the installation by more than 1.5 times.

Depending on the size and design of refrigeration units, this factor can be implemented in an additional heat exchanger, installed on a liquid line between the receiver and TRV of the evaporator, in various ways.

Precooling of refrigerant due to external sources of cold

• in a water heat exchanger due to the use of available sources is very cold water
• in air heat exchangers in the cold season
• in an additional heat exchanger with cold pairs from an external / auxiliary refrigeration unit

Supercooling due to the internal resources of the refrigeration unit

• in the heat exchanger - the monochloride due to the expansion of the freon part circulating in the main refrigeration circuit - is implemented in installations with two-stage compression and in satellite systems, as well as in installations with screw, piston and spiral compressors that have intermediate suction ports
• in regenerative heat exchangers with cold pairs, absorbed into the compressor from the main evaporator - is implemented in installations operating on refrigerants with a low value of the adiabatic indicator, mainly HFC (HFCs) and HFO (GFD)

exchange of supercooling, using external sources of cold, still quite rarely applied in practice. Supplements from cold water sources is used, as a rule, in heat pumps - water heating installations, as well as in medium and high-temperature installations, where there is a source of cool water in the immediate vicinity of them - used artesian wells, natural reservoirs for ship installations, etc. . Supercooling from external additional refrigerators It is extremely rarely implemented and only in very large industrial cold installations.

The supercooling in air heat exchangers is also used very infrequently, since this option of refrigeration plants is still unattended and unusual for Russian refrigerators. In addition, the designers are confused by seasonal fluctuations in the values \u200b\u200bof increasing the cooling capacity of installations from the use of air overcohelteries in them.

Supplement systems using domestic resources Widely used in modern refrigeration plants, and with compressors of almost all types. In installations with screw and two-stage piston compressors The use of supercooling confidently dominates, since the ability to ensure the absorption of vapors with intermediate pressure is implemented directly in the design of these types of compressors.

The main task currently in front of manufacturers of refrigeration and climatic installations various destinationis improving the performance and effectiveness of compressors included in them and heat exchange equipment. This idea has not lost its relevance since the development time refrigeration equipment Since the origin of this industry, industry to this day. Today, when the cost of energy resources, as well as the size of the park of the operated and commissioned refrigeration equipment has reached such impressive heights, improving the efficiency of systems producing and consuming cold has become an urgent world problem. Taking into account the fact that this problem is integrated, the current legislation of the majority of European states stimulate developers refrigeration systems to increase their efficiency and performance.

In the condenser, the gaseous refrigerant, compressed by the compressor, goes into a liquid state (condensed). Depending on the working conditions of the refrigeration circuit, the refrigerant pair can be condensed completely or partially. For the proper functioning of the refrigeration circuit, complete condensation of the refrigerant vapor in the condenser is necessary. The condensation process takes place at a constant temperature called condensation temperature.

The hyposhee of the refrigerant is the difference between the temperature of the condensation and the refrigerant temperature at the outlet of the condenser. While there is at least one gas molecule in a mixture of gaseous and liquid refrigerant, the mixture temperature will be equal to the condensation temperature. Therefore, if the temperature of the mixture at the outlet of the capacitor is equal to the condensation temperature, it means that there are pairs in the refrigerant mixture, and if the refrigerant temperature at the output of the capacitor is below the condensation temperature, this clearly indicates that the refrigerant has completely passed into a liquid state.

Overheating of refrigerant - This is the difference between the refrigerant temperature at the exit of the evaporator and the boiling point of the refrigerant in the evaporator.

Why do you need to overheat a couple of already swollen refrigerant? The meaning of this is to be confident that the entire refrigerant is guaranteed to go into a gaseous state. The presence of a liquid phase in the refrigerant entering the compressor can lead to a hydraulic impact and output compressor. And since the boiling of the refrigerant occurs at a constant temperature, we cannot argue that the entire refrigerant has flown up until its temperature exceeds its boiling point.

In the internal combustion engines have to face phenomenon cutyl oscillations shafts. If these oscillations threaten the strength of the crankshaft in the operating range of the rotational frequency of the shaft, anti-vibrators and dampers are used. They are placed on the free end of the crankshaft, i.e., where the greatest twears arise

oscillations.

external forces make the crankshaft of a diesel engine to perform twist fluctuations

These forces are the pressure of gases and the inertia forces of the rocker-crank mechanism, under the variables of which a continuously changing torque is created. Under the influence of uneven torque, the segment of the crankshaft is deformed: twisted and spinned. In other words, in the crankshaft of the shaft there are twisting oscillations. The complex dependence of the torque from the corner of the rotation of the crankshaft can be represented as the sum of sinusoidal (harmonic) curves with different amplitudes and frequencies. At a certain rotational speed of the crankshaft, the frequency of the perturbation force, in this case of any component of the torque, may coincide with the frequency of the shaft's own oscillations, i.e. the phenomenon of the resonance will come, in which the amplitudes of the rolling oscillations of the shaft can become so great that the shaft may collapse.

To eliminate The phenomenon of resonance in modern diesel engines, special devices are applied. Wide distribution received one of the types of such a device - the pendulum anti-vibrator. At that moment, when the movement of the flywheel during each of his oscillations will accelerate, the cargo of the anti-vibrator according to the law of inertia will strive to preserve its movement at the same speed, i.e. it will begin to lag at some angle from the section of the shaft, to which the anti-virus is attached (position II) . The load (or rather, its inertial force) will be as it were to "slow down" the shaft. When the angular velocity of the flywheel (shaft) during the same oscillation will begin to decrease, the cargo, obeying the law of inertia, will strive to "pull" the shaft (position III),
Thus, the inertial forces of the suspended cargo during each oscillation will periodically affect the shaft in the direction opposite to the acceleration or deceleration of the shaft, and thereby change the frequency of its own oscillations.

Silicone dampers. The damper consists of a hermetic case, inside which the flywheel (mass) is located. The flywheel can freely rotate relative to the hull reinforced at the end of the crankshaft. The space between the case and the flywheel is filled with silicone fluid having a greater viscosity. When the crankshaft rotates uniformly, the flywheel at the expense of friction forces in the fluid acquires the same with the shaft the frequency (speed) of rotation. And if there are twisted oscillations of the crankshaft? Then their energy is transferred to the body and will be absorbed by viscous friction by the body and inertial weight of the flywheel.

Modes of small revolutions and loads. The transition of the main engines to the modes of small revolutions, as well as the transition of auxiliary on the modes of small loads, is associated with a significant reduction in fuel supply to cylinders and an increase in excess air. At the same time, air parameters are reduced at the end of the compression. It is especially noticeable to change the RS and TC in the engines with gas turbine supervision, since the gas turbocompressor on small loads practically does not work and the engine automatically goes to the mode of operation without chance. Small portions of burning fuel and high air excess reduce the temperature in the combustion chamber.

Due to the low temperature of the cycle, the combustion process of fuel flows sluggishly, slowly, part of the fuel does not have time to burn and flows through the cylinder walls in the crankcase or carrying out the exhaust gases into the exhaust system.

The worsening of the combustion of the fuel also contributes to the poor mixing of fuel with air, due to a decrease in the fuel injection pressure when the load is dropped and reduce the speed of rotation. The uneven and unstable fuel injection, as well as low temperatures in the cylinders, cause unstable operation of the engine, often accompanied by flash passes and increased smoking.

Nagara formation proceeds especially intensively when used in heavy fuel engines. When working on low loads due to poor spraying and relatively low temperatures in a heavy fuel drop cylinder, do not completely fade away. When the droplets are heated, the light fractions gradually evaporate and burned, and in its kernel there are extremely heavy high-boiling fractions, the basis of which is aromatic hydrocarbons with the most durable bonding between atoms. Therefore, the oxidation of them leads to the formation of intermediate products - asphaltenes and a resin with high stickiness and capable of firmly kept on metal surfaces.

Due to the stated circumstances long work The engines on the modes of small revolutions and loads occurs intensive contamination of the cylinders and especially the exhaust path of the products of incomplete combustion of fuel and oil. The outlet channels of the operating cylinder covers and the outlet nozzles are covered with a dense layer of asphalt-resinous substances and coke, often by 50-70% of the flowing section that reduce their passage section. In the outlet pipe, the thickness of the Nagar layer reaches 10-20 mm. These deposits when improving the load on the engine are periodically flammorated, causing fire in the exhaust system. All oily deposits burn out, and dry carbon dioxide generated during combustion blows into the atmosphere.

The wording of the Second Law of Thermodynamics.
For the existence of a thermal engine, 2 sources are needed - a hot source and a cold source (environment). If the thermal motor works only from one source, it is called the 2nd birth eternal engine.
1 Formulation (OSVALDA):
"The Eternal Engine of the 2nd kind is impossible."
The perpetual engine of the 1st genus is a thermal motor, in which L\u003e Q1, where Q1 is the suspended heat. The first law of thermodynamics "allows" the ability to create a heat engine fully turning the expended heat of the Q1V operation L, i.e. L \u003d Q1. The second law imposes more stringent restrictions and argues that the work should be less than the heated heat (L The perpetual engine of the 2nd genus can be carried out if the heat of Q2 is transmitted from a cold source to hot. But for this, the heat spontaneously should move from the cold body to hot, which is impossible. Hence the 2nd formulation (Clausius):
"The heat cannot spontaneously moves from a colder body to the more heated."
For the operation of the thermal engine, 2 sources are needed - hot and cold. 3rd wording (carno):
"Where there is a difference in temperatures, perhaps doing work."
All these formulations are interrelated, from one formulation you can get another.

Indicator efficiency It depends on: compression degree, excess air coefficient, combustion chamber design, advance angle, speed, fuel injection duration, spraying and mixing quality.

Increase indicator efficiency (by improving the combustion process and reduce fuel heat losses in compression and expansion processes)

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For modern engines, a high level of thermal tension of CPGs is characterized due to the forcing of their workflow. This requires technically competent care of the cooling system. The necessary heat sink from the heated surfaces of the engine can be achieved either by an increase in the difference in the temperature of the water T \u003d T.V.V. - T.VX, or an increase in its consumption. Most of the diesel firms are recommended for modes T \u003d 5 - 7 gr.c, for soda and water T \u003d 10 - 20 gr. The limitation of the temperature difference is caused by the desire to preserve the minimum temperature stresses of cylinders and the sleeves at their height. The intensification of heat transfer is carried out due to the high speed of water movement.

When cooled by intricate water, the maximum temperature-ra 50 gr. Only closed cooling systems allow you to use the advantages of high-temperature cooling. With increasing the temperature of ox. Waters reduce friction losses in the piston group and slightly increases eff. The power and efficiency of the engine, with an increase in TV, the temperature gradient in the thickness of the sleeve is reduced, thermal stresses are reduced. With a decrease in the temperature ox. Water increases chemical corrosion due to condensation on a sulfuric acid cylinder, especially when burning sulfur fuels. However, there is a restriction of water temperature due to limitations of the in-cylinder mirror (180 gr. C) and its further increase can lead to a violation of the strength of the oil film, its disappearance and the appearance of dry friction. Therefore, most firms are limited to the volume of 50 -60 gr. C and only when burning high-continuous fuels is allowed 70-75 gr. FROM.

Heat transfer coefficient - a unit that denotes the passage of heat flux with a capacity of 1 W through an element of a construction structure with an area of \u200b\u200b1 m2 when the outer air temperature difference and the internal temperature in 1 Kelvin W / (M2K).

The definition of the heat transfer coefficient sounds as follows: energy loss by a square meter of the surface with the difference in temperature of the outer and internal. This definition entails the relationship of Watt, square meters and Kelvin W / (m2 · k).

To calculate heat exchangers, a kinetic equation is widely used, which expresses the relationship between the heat flux Q and the surface F of heat transfer, called the main equation of heat transfer: Q \u003d KFΔTCRτ, where K is a kinetic coefficient (heat transfer coefficient characterizing the heat transfer rate; Δtcs - the average driving force or the average temperature difference between the coolants (average temperature pressure) on the heat transfer surface; τ - time.

The greatest difficulty causes the calculation coefficient of heat transfer K.characterizing the speed of heat transfer process with the participation of all three types of heat transfer. The physical meaning of the heat transfer coefficient flows from the equation (); Its dimension:

In fig. 244 OB \u003d R - radius of crank and AB \u003d L - the length of the connecting rod. Denote by the ratio L0 \u003d L / R- is called the relative length of the connecting rod, for ship diesel engines is within 3.5-4.5.

however, in the theory of KSM, the inverse value λ \u003d r / l is used

The distance between the piston finger axis and the shaft axis when it turns it to the angle

AO \u003d AD + DO \u003d LCOSB + RCOSA

When the piston is in c. m. t., This distance is equal to L + R.

Therefore, the path passed by the piston when the crank is rotated at the angle A, will be equal \u003d L + R-AO.

By mathematical calculations we get the formula of the piston path

X \u003d R (1- Cosa + 1 / λ (1-Cosb)) (1)

The average speed of the VM piston along with the speed of the rotation is the indicator of the speed mode of the engine. It is determined by the formula Vm \u003d Sn / 30, where S is the stroke of the piston, m; P - rotational speed, min-1. It is believed that for modes Vm \u003d 4-6 m / s, for software Vm \u003d 6S-9 m / s and for waters Vm\u003e 9 m / s. The higher the VM, the greater the dynamic stresses in the parts of the engine and the greater the likelihood of their wear - primarily the cylindrophone group (CPG). Currently, the VM parameter has reached a certain limit (15-18.5 m / s), due to the strength of materials used in the engine, especially since the dynamic tension of the CPG is proportional to the square VM value. Thus, with an increase in VM, 3 times voltage in details will increase by 9 times, which will require an appropriate enhancement of the strength characteristics of materials used for the manufacture of parts of the CPG.

The average piston rate is always indicated in the factory passport (certificate) of the engine.

True piston rate, i.e. the speed of it at the moment (in m / s) is defined as the first derivative of the time in time. We substitute in formula (2) a \u003d ω T, where ω is the rotation frequency of the shaft in rad / s, T- time in sec. After mathematical transformations, we get a piston speed formula:

C \u003d RΩ (SINA + 0.5λSIN2A) (3)

where r - radius crank VM \\

ω - the angular frequency of rotation of the crankshaft in rad / s;

a - the angle of rotation of the crankshaft vigrarad;

λ \u003d r / L-ratio of the radius of the crank to the length of the connecting rod;

CO - the district speed of the center, the crank cervical cerial / s;

L is the length of the ride rod.

With the infinite length of the connecting rod (L \u003d ∞ and λ \u003d 0) the speed of the piston is equal

Differentizing the formula (1) in the same way

C \u003d Rω SIN (A + B) / COSB (4)

The values \u200b\u200bof the SIN function (A + B) are taken from tables of reference books and benefits depending on the directories.

Obviously, the maximum value of the piston velocity at L \u003d ∞ will be \u003d 90 ° and a \u003d 270 °:

Camax \u003d RΩ sin a .. Since CO \u003d πRN / 30 ICM \u003d SN / 30 \u003d 2RN / 30 \u003d RN / 15

CO / CM \u003d πRN15 / RN30 \u003d π / 2 \u003d 1.57 from where co \u003d 1.57 cm

Consequently, the maximum piston rate will be equal. Smaks \u003d 1.57 tbsp.

Imagine the speed equation in the form

C \u003d RωSIN A + 1 / 2λ RωSIN2A.

Graphically both members of the right part of this equation will be depicted with sinusoids. The first term of RωSIN A, representing the piston rate with an infinite length of the connecting rod, is depicted by a first-order sinusoid, and the second member1 / 2λ RωSIN2A-correction on the effect of the final length of the rod-sinusoid of the second order.

by building the specified sinusoids and folding them algebraically, we obtain a speed chart with regard to the indirect influence of the connecting rod.

In fig. 247 depicted: 1 - curveRωSIN A,

2 - curve1 / 2λ RΩSin2a

3 - Crowd.

Under the operational properties understand the objective features of fuel, which are manifested in the process of using it in the engine or unit. The combustion process is the most important and determining its operational properties. The process of combustion of fuel is definitely preceded by the processes of its evaporation, ignition and many others. The nature of the behavior of fuel in each of these processes is the essence of the main operational properties of fuels. Currently, the following operational properties of fuels are evaluated.

Evaporation characterizes fuel ability to move from liquid state in vapor-shaped. This property is formed from such fuel quality indicators, as a fractional composition, pressure saturated vapor At different temperatures, surface tension and others. Evaporability is essential in the selection of fuel and largely determines technical and economic and performance features engines.

The flammability characterizes the characteristics of the process of ignition of mixtures of fuel vapor with air. The assessment of this property is based on such quality indicators as temperature and concentration limits ignitions, flare and self-ignition temperatures, etc. The fuel flammability indicator is the same value as its flammability; In the future, these two properties are considered jointly.

The combustibility determines the effectiveness of the process of burning fuel-air mixtures in the combustion chambers of the engines and the furnace devices.

Pouring characterizes the behavior of fuel when pumping it through pipelines and fuel systems, as well as when filtering it. This property determines the smoothness of the supply of fuel into the engine at different temperatures operation. Pulmonary fuels is evaluated by viscous-temperature properties, turbidity and frozen temperatures, limiting filtral temperature, water content, mechanical impurities, etc.

The addiction to the formation of deposits is the ability of fuel to form deposits of various kinds in combustion chambers, in fuel systems, in inlet and exhaust valves. Evaluation of this property is based on such indicators as ash content, coking, the content of resinous substances, unsaturated hydrocarbons, etc.

Corrosion activity and compatibility with non-metallic materials characterizes the ability of the fuel to cause corrosion lesions of metals, swelling, destruction, or changing the properties of rubber seals, sealants and other materials. This operating property provides for a quantitative assessment of the content of corrosion-active substances in fuel, the test of the resistance of various metals, rubber and sealants during contact with the fuel.

Protective ability is the ability of fuel to protect against corrosion materials of engines and aggregates when they contact them with an aggressive medium in the presence of fuel and primarily the ability of fuel to protect metals from electrochemical corrosion when water enters. This property is assessed by special methods involving the impact of ordinary, marine and rainwater on metals in the presence of fuel.

Anti-wear properties characterize the decrease in the wear of rubbing surfaces in the presence of fuel. These properties are important for engines in which fuel pumps and fuel-adjusting equipment are lubricated only by the fuel itself without using lubricant (for example, in the plunger fuel pump high pressure). The property is estimated by viscosity and lubricity.

Cooling capacity determines the possibility of fuel to penetrate and remove heat from heated surfaces when using fuel as a coolant. Evaluation of properties is based on such quality indicators as heat capacity and thermal conductivity.

Stability characterizes the retainability of fuel quality indicators during storage and transportation. This property evaluates the physical and chemical stability of fuel and its tendency to biological accuracy with bacteria, fungi and mold. The level of this property allows you to establish a warranty life of fuel in various climatic conditions.

Environmental properties characterize the effects of fuel and products of its combustion per person and environment. The assessment of this property is based on the fuel toxicity indicators and its combustion and fire and explosion products.

Beavenly maritime expanses furrowed obedient hands and the will of man big vessels given in motion using powerful engines that use ship fuel of various types. Transport ships can use different engines, but most of these floating structures are equipped with diesel engines. Fuel for ship enginesused in ship diesels, divide into two classes - distillate and heavy. Diesel summer fuel refers to distillate fuel, as well as foreign fuels "Marin Diesel Oil", "Gas Oil" and others. It has a slight viscosity, so not
Requires at the start of the preheating engine. It is used in high-speed and medium-round diesel engines, and in some cases, and in low-state diesel engines in start-up mode. Sometimes it is used as an additive to severe fuel in cases where it is necessary to lower its viscosity. Heavy varieties Fuels differ from distillate high viscosity, more high temperatures Throy, the presence of a larger number of severe fractions, a large content of ash, sulfur, mechanical impurities and water. Prices for ship fuel of this species are significantly lower..

Most of the ships use the cheapest heavy diesel fuel for ship engines, or, fuel oil. The use of fuel oil is dictated, first of all, for economic considerations, because prices for ship fuel, as well as, the total costs of transportation of goods by marine transport when using fuel oil are significantly reduced. As an example, it can be noted that the difference in the cost of fuel oil and other types of fuel used for ship engines is about two hundred euros per ton.

However, maritime shipping rules are prescribed in certain modes of operation, for example, when maneuvering, use more expensive low-viscous ship fuel, or, solarium. In some marine waters, for example, the La Mans Strait, due to the complexity in the favings and the need to comply with the requirements of the ecology, the use of fuel oil, as the main fuel, is generally prohibited.

Fuel selection largely depends on the temperature at which it will be used. Normal launch and planned operation of a diesel engine is provided in summer period with a cetane number of 40-45, in winter It is necessary to increase it to 50-55. In motor fuels and fuel oil, the cetane number is within 30-35, in diesel - 40-52.

TS-diagrams are used primarily for the purposes of illustration, since in the PV diagram area under the curve expresses the work produced by a pure substance in the reversible process, and in the TS diagram area under the curve is depicted for the same conditions obtained heat.

Toxic components are: carbon oxide CO, CH hydrocarbons, nitrogen oxides NOX, solid particles, benzene, toluene, polycyclic aromatic hydrocarbons PAU, benzapine, soot and solid particles, lead and sulfur.

Currently, the norms for emissions harmful substances Ship diesel engines IMO, an international maritime organization. These standards should satisfy all current ship diesel engines.

The main components dangerous for a person in exhaust gases are: NOX, CO, CNHM.

A number of ways, for example, a direct injection of water can only be implemented at the design and manufacture of engine and its systems. For already existing model Row Engines These ways are unacceptable or require substantial costs of engine upgrading, replacing its aggregates and systems. In a situation where a significant reduction in nitrogen oxides without re-equipment of serial diesel engines - but here is the case, the most effective way It is the use of a three-component catalytic neutralizer. The use of the neutralizer is justified in those areas where there are high requirements for NOX emissions, for example in large cities.

Thus, the main directions to reduce harmful emissions of diesel engines can be divided into two groups:

1)-improving the design and engine systems;

2) Promotions that do not require engine modernization: the use of catalytic neutralizers and other means of cleaning OG, improving the composition of the fuel, the use of alternative fuels.

Air conditioner

Freed air conditioning can be carried out in several ways, each of them has its advantages, disadvantages and accuracy.

The choice of air conditioning refueling method depends on the level of professionalism of the wizard, the necessary accuracy and tools used.

It is also necessary to remember that not all refrigerants can be refueling, but only one-component (R22) or conditionally isotropic (R410A).

Multicomponent freons consist of a mixture of gases with different physical propertieswhich, when leucing, volatile unevenly, and even with a small leak, their composition changes, so the systems on such refrigerants must be fully reworked.

Refueling air conditioner by freon by weight

Each air conditioner is charged at a factory with a certain amount of refrigerant, the mass of which is specified in the documentation for air conditioning (also indicated on the nameplate), there is also information about the number of freon that needs to be added additionally for each meter of the freon route (usually 5-15 gr.)

When refilling this method, it is necessary to completely free the refrigeration contour from the remaining freon (into the balloon or to boil into the atmosphere, the ecology does not at all harm it in the article on the effect of freon on the climate) and dismiss. After pouring the specified amount of refrigerant by weight or using a refueling cylinder into the system.

The advantages of this method in high accuracy and sufficient simplicity of the air conditioning refueling process. The disadvantages include the need to evacuate freon and evacuation of the contour, and the refueling cylinder, besides, has a limited volume of 2 or 4 kilograms and large dimensions, which allows it to be used mainly in stationary conditions.

Refueling air conditioner freon over supercooling

The supercooling temperature is the difference between the temperature of the freon condensation defined on the table or the scale of the pressure gauge (is determined by the pressure read from the pressure gauge connected to the high pressure line directly on the scale or on the table) and the temperature at the outlet of the condenser. The supercooling temperature should usually be in the range of 10-12 0 C (manufacturers indicate the exact value)

The value of overcooling is below these values \u200b\u200bindicates the lack of freon, it does not have time to cool enough. In this case, it should be disposed of

If the supercooling is higher than the specified range, then in the system, the excess of freon and it must be merged until the optimal hypothermia values.

You can refuel with special devices that immediately determine the magnitude of the hypothermia and the condensation pressure, and it is possible with the help of separate instrument and thermometer collector and the thermometer.

The advantages of this method include sufficient accuracy of refueling. But the accuracy of this method affects the contamination of the heat exchanger, therefore, before refueling this method, it is necessary to clean (rinse) an outdoor condenser.

Refueling air conditioner refrigerant overheating

Overheating is the difference between the refrigerant evaporation temperature defined by the saturation pressure in the refrigeration circuit and the temperature after the evaporator. It is practically determined by measuring the pressure on the suction valve of the air conditioner and the temperature of the suction tube at a distance of 15-20 cm from the compressor.

Overheating is usually located in the limit 5-7 0 C (the exact value indicates the manufacturer)

The decline in overheating speaks of the excess of freon - it must be merged.

The supercooling above the norm indicates the lack of refrigerant, the system must be refueling until the required overheating value is reached.

This method is sufficiently accurate and it can be significantly easier if you use special devices.

Other refrigeration refrigeration methods

If the system has an observation window, then the presence of bubbles can be judged by freon shortage. In this case, the refrigeration circuit is refrigerated until the bubble stream disappears, it is necessary to do this by portions, after each to wait for the stabilization of the pressure and the absence of bubbles.

You can also refuel by pressure, while achieving the temperatures of condensation and evaporation specified by the manufacturer. The accuracy of this method depends on the purity of the condenser and the evaporator.

The thermal balance of the surface capacitor has the following expression:

G. K ( h to -h to 1)=W.(t 2B -T 1B)with B., (17.1)

where h K. - Enthalpy couple entering the condenser, KJ / kg; h to 1 \u003d s in t to- Condensate enthalpy; with B.\u003d 4.19 kJ / (kg × 0 s) - water heat capacity; W.- cooling water consumption, kg / s; t 1B, T 2B- The temperature of the cooling water at the inlet and outlet of the condenser. Consumption of condensed pair G. K, kg / s and enthalpy h K. Known at the calculation steam turbine. The condensate temperature at the outlet of the capacitor is taken equal to the pair of saturation t P.appropriate r K.taking into account the hypothermia of condensate D t K.: t K \u003d T P -D. t K..

Condensate supercooling (The difference between the temperature of steam saturation at a pressure of the capacitor's neck and the condensate temperature in the suction pipe of the condensate pump) is a consequence of lowering the partial pressure and a saturated pair temperature due to the presence of air and steam resistance of the condenser (Fig. 17.3).

Fig.17.3. Changes in the parameters of the steam-air mixture in the condenser: a - a change in the partial pressure of steam P n and pressure in the P K condenser; b - change in temperature of steam t n and relative air content ε

Using the Dalton law to the steam-air conductor moving in the condenser, we have: p K \u003d P + P inwhere p P. and r B. - Partial pressure of steam and air in the mixture. The dependence of the partial pressure of steam from pressure in the condenser and relative air content e.=G. in / G. K has the form:

(17.2)

At the entrance to the capacitor, the relative air content is small and r P "R to. As a steam condensation, the value e. Growing and partial pressure steam falls. In the lower part, the partial pressure of the air is most significantly, because It increases due to the growth of air density and value e.. This leads to a decrease in the temperature of steam and condensate. In addition, there is a steam resistance of the condenser determined by the difference

D. p K \u003d P K - R K.(17.3)

Usually D. r K.\u003d 270-410 Pa (determined empirically).

The condenser, as a rule, enters the wet pairs, the condensation temperature of which is uniquely determined by the partial pressure of steam: a smaller partial pressure of the steam corresponds to a smaller saturation temperature. Figure 197.3, B shows the graphs of changes in the temperature of steam t n and the relative air content ε in the condenser. Thus, as the steam-air mixture is moved to the place of suction and condensation of the steam, the temperature of steam in the condenser decreases, as the partial pressure of the saturated steam is reduced. This is due to the presence of air and increase its relative content in the steam-air mixture, as well as the presence of steam resistance of the condenser and reduce the overall pressure of the steam-air mixture.

In such conditions, the condensation of DT K \u003d T n-c condensate is formed, which leads to the loss of heat with cooling water and the need for an additional heating of condensate in the regenerative turbine system. In addition, it is accompanied by an increase in the amount of oxygen dissolved in the condensate, which causes corrosion of the tubular system of regenerative heating nutrient water boiler.

The supercooling can reach 2-3 0 S. The means of combating it is the installation of air coolers in the capacitor tube beam, from which the steam-air mixture is sued into ejector installations. In modern PTU, the supercooling is allowed not more than 1 0 C. Technical exploitation rules Strictly prescribe permissible air supplies to turbo systems that must be less than 1%. For example, for turbines capacity N E.\u003d 300 MW of air supplies must be no more than 30 kg / h, and N E.\u003d 800 MW - no more than 60 kg / hour. Modern capacitors with minimal steam resistance and rational layout of the pipe beam, in the nominal operation of the turbine installation practically do not have supercooling.

Under the hypathy of condensate, the condensate temperature is understood against the temperature of the saturated steam entering the condenser. It was noted above that the magnitude of the condensate hyposal is determined by the difference in temperature T n. -t. to .

The overcooling of condensate leads to a noticeable reduction in the cost-effectiveness of the installation, since the amount of heat transmitted in the coolant condenser increases with the condensation overcooling. An increase in condensate hyposal by 1 ° C causes fuel overruns in installations without regenerative heating of nutrient water by 0.5%. With regenerative heating of nutritious water, fuel reservoir in the installation is somewhat smaller. IN modern installations In the presence of condensers of the regenerative type, condensate undercooling under normal conditions of the condensation unit does not exceed 0.5-1 ° C. The condensate undercooling is caused by the following reasons:

a) violation of the air density of the vacuum system and elevated air suits;

b) high levels condensate in the condenser;

c) excessive cooling water consumption through a capacitor;

d) constructive disadvantages of the capacitor.

Increase the air content in the steady

the mixture leads to an increase in the partial pressure of air and, accordingly, to a decrease in the partial pressure of water vapor with respect to the total pressure of the mixture. As a result, the temperature of saturated water vapor, and therefore, the condensate temperature will be lower than it was before an increase in air content. Thus, one of the important activities aimed at reducing condensate hypothermia is to provide a good air density of the vacuum system of turbo system.

With a significant increase in the level of condensate in the condenser, such a phenomenon can be obtained that the lower rows of cooling tubes will be washed with condensate, as a result of which condensate will be transferred. Therefore, it is necessary to ensure that the condensate level is always below the lower row of cooling tubes. Best tool Preventing an invalid increase in condensate level is the automatic control device in the condenser.

Excess water consumption through the capacitor, especially at low temperatures, will lead to an increase in vacuum in the condenser due to a decrease in the partial pressure of water vapor. Therefore, cooling water consumption through the capacitor must be adjusted depending on steam load on the condenser and on the temperature of the cooling water. For proper adjustment cooling water consumption in the condenser will be supported by an economic vacuum and condensate supercooling will not go beyond minimum value For this condenser.

Controlling condensate may occur as a result of constructive disadvantages of the capacitor. In some contention condenser structures, as a result of the close location of the cooling tubes and the unsuccessful breakdown, they create a large steam resistance, which achieves 15-18 mm RT in some cases. Art. A large steam resistance of the capacitor leads to a significant reduction in pressure above the level of condensate. Reducing the pressure of the mixture above the level of condensate occurs due to a decrease in the partial pressure of water vapor. Thus, the temperature of the condensate is obtained significantly lower than the temperature of the saturated vapor entering the condenser. In such cases, to reduce condensate supercooling, it is necessary to go to the structural alterations, namely, to remove some parts of the cooling tubes for the purpose of the device in the pipe beam of corridors and reduce the steam resistance of the capacitor.

It should be borne in mind that the removal of a part of the cooling tubes and the decrease in the condenser cooling surface leads to an increase in the specific load of the condenser. However, an increase in the specific steam load is usually quite acceptable, since the condensers of old structures have a relatively low specific steam load.

We reviewed the main issues of operation of the equipment of the steam turbine condensation unit. It follows from the above that the main attention in the operation of the condensation installation should be drawn to maintaining an economic vacuum in the condenser and to ensure the minimum condensate hypothermation. These two parameters are largely influenced by the economy of turbine installation. To this end, it is necessary to maintain a good air density vacuum system Turbo installations, to ensure the normal operation of air outlery devices, circulating and condensate pumps, maintain a capacitor tube clean, monitor the water density of the capacitor, to prevent increased crude water suits, ensure normal cooling devices. Insulating control and measurement devices, automatic regulators, signaling and regulating devices allow the service personnel to monitor the condition of the equipment and behind the installation mode and maintain such operating modes under which highly economical and reliable installation operation is ensured.