Central air conditioning refrigeration consultation

First, the principle of vapor compression refrigeration

Steam refrigeration is to realize artificial refrigeration by using the endothermic characteristics of some liquid refrigerants with low boiling point when they vaporize at different pressures.

In refrigeration technology, evaporation refers to the process that liquid refrigerant becomes gaseous when it reaches boiling. The transformation from liquid to gas can only be realized by absorbing heat energy from the outside, so it is an endothermic process. The evaporation temperature of liquid refrigerant is called evaporation temperature, and condensation means that the steam is cooled to equal to or lower than the saturation temperature, so that the steam is converted into liquid. In daily life, we can observe many phenomena of evaporation and heat absorption. For example, if we rub some alcohol on our hands, the alcohol will evaporate quickly, and then we feel that the reaction of rubbing alcohol is very cold. For another example, if the commonly used refrigerant Freon F- 12 liquid is sprayed on the object, we will see that the surface of the object will quickly form a layer of frost. This is because when F- 12 liquid is sprayed on the surface of an object, it will absorb heat immediately, so that the surface temperature of the object will drop rapidly (of course, this is an unrealistic refrigeration method, and the refrigerant F- 12 cannot be recycled). At present, the cryotherapy adopted by some medical institutions makes use of this principle.

The principle of vapor compression refrigeration is that liquid refrigerant absorbs heat when it vaporizes and releases heat when it condenses.

Second, the refrigeration cycle

The compressor is the power to ensure refrigeration. The compressor is used to increase the pressure of the refrigerant in the system, so that the refrigerant can circulate in the refrigeration system to achieve the purpose of refrigeration. Start the compressor to suck the low-temperature and low-pressure refrigerant gas after evaporation and refrigeration, and then compress it into high-temperature and high-pressure gas and send it to the condenser; The high-pressure and high-temperature gas is cooled by a condenser and condensed into a normal-temperature and high-pressure liquid; When the high-pressure liquid at room temperature flows into the thermal expansion valve, it is throttled into low-temperature and low-pressure wet steam, which flows into the evaporator to absorb the heat of the surrounding objects, so that the temperature of the air-conditioned room is cooled through the air duct system, and the evaporated refrigerant returns to the compressor to repeat the next refrigeration cycle, thus achieving the refrigeration purpose.

3. State of refrigerant in refrigeration system

The part from the compressor outlet through the condenser to the expansion valve is called the high pressure side of the refrigeration system; The pressure of this part is equal to the saturation pressure of the refrigerant at the condensation temperature. The characteristic of high pressure side is that the refrigerant releases heat to the surrounding environment and condenses into liquid. When the refrigerant flows out of the condenser, the temperature drops and becomes supercooled liquid.

The section from the outlet of the expansion valve to the return air entering the compressor is called the low pressure side of the refrigeration system, and its pressure is equal to the saturation pressure of evaporation temperature in the evaporator. The low-pressure side part of the refrigerant is in the state of wet steam at first, and after absorbing heat in the evaporator, the refrigerant gradually changes from wet steam to vapor refrigerant. At the outlet of the evaporator, the temperature of the refrigerant rises to the superheated gas state. When the supercooled liquid refrigerant passes through the expansion valve, it drops from high pressure to low pressure due to throttling (but it does not consume work and there is no external heat exchange); At the same time, a small amount of liquid refrigerant evaporates and the temperature decreases accordingly. This low-pressure and low-temperature refrigerant evaporates (vaporizes) to absorb heat after entering the evaporator. The gaseous refrigerant with low temperature and low pressure is sucked into the compressor and enters the next refrigeration cycle through the compressor.

Fourth, cooling capacity.

In the refrigeration cycle, the heat absorbed by each kilogram of circulating refrigerant from the cooled object is called the refrigerating capacity per unit weight, which is expressed by the symbol Q and the unit is kcal/kg. The refrigerating capacity per unit weight is a special parameter indicating the effect of refrigeration cycle, which is determined by the properties of refrigerant, cycle temperature and other conditions. The lower the evaporation temperature, the higher the condensation temperature, and the smaller its value, and vice versa. The refrigerating capacity of the refrigeration device is the heat absorbed from the cooled object and released in the condenser per unit time, which is represented by the symbol Q and the unit is kcal/kg. The value of q is equal to the product of cold weight flow g and refrigerating capacity per unit weight q, that is, q = g? Q: In practical work, sometimes in order to get a rough calculation of refrigeration capacity conveniently, the following formula can also be used for calculation.

Q=L？ (t2 -t 1)

Where l circulating air volume, (T2-T 1) is the temperature difference between inlet and outlet.

In Japan, Europe, America and other countries, the refrigeration capacity is usually expressed in cold tons, but there is a slight difference in numerical value between Japanese cold tons and American cold tons. In Japan, the unit of refrigerating capacity is Japanese cold tons, and 1 daily cold tons represents the refrigerating capacity consumed by1000g of 0oC water to make 0oC ice within 24 hours:

1 day cold ton = 3320kcal/h

1 American cold tons = 3024 lcal/h

Unit conversion of common refrigeration capacity:

1KW = 860 kcal/hour (kcal/hour)

1 kcal/hour = 3.968 British thermal units/hour

Verb (short for verb) cooled

Refrigerant is the working substance of refrigeration cycle.

(1) Requirements for Refrigerant

The ideal refrigerant requires non-toxicity, no irritating smell, low corrosiveness to metals, no chemical reaction with lubricating oil, and good thermodynamic performance, that is, its evaporation temperature in the evaporator is low at atmospheric pressure, and its evaporation pressure is preferably close to atmospheric pressure; In the condenser, the pressure corresponding to the condensation temperature of refrigerant should be moderate, the unit refrigeration capacity should be large, and the vaporization heat should be large, while the specific heat of liquid should be small and the specific heat of gas should be large. Physical properties of refrigerants are required: low solidification temperature, high critical temperature (preferably higher than ambient temperature), high thermal conductivity and heat release coefficient, low specific gravity and viscosity, and low leakage.

(2) Type of refrigerant

There are many kinds of refrigerants, which can be considered according to the thermodynamic conditions such as refrigerant type, evaporation temperature, condensation temperature and pressure, and the place where refrigeration equipment is used. Refrigerant can be divided into four categories: inorganic compounds, hydrocarbons, freon and boiling solutions.

1, and the inorganic composite refrigerant includes ammonia, water and carbon dioxide;

2. Hydrocarbon refrigerants include ethane and propylene;

Freon is a kind of refrigerant that was used in 1930s. It is about 60 years later than ammonia. It is the general name of halogen derivatives (fluorine, chlorine and bromine) of saturated hydrocarbons, or it is composed of fluorine, chlorine and hydrocarbons. At present, the main refrigerants used are compounds in which all or part of the hydrogen atoms in methane (CH4) and ethane (C2H6) are replaced by those in Fuwan. In addition to the name, the chemical formula also stipulates the abbreviation codes of various freons.

(1) Short code for Freon. The initial number of freon molecular compounds without hydrogen atoms is 1, ethane is 1 1, and propane (C3H8) is 2 1. Then write down the number of fluorine atoms. For example, F- 12 is called dichlorodifluoromethane, and the molecular formula CF2CL2 has a carbon atom, which is methane without hydrogen. So the initial number is 1, and there are two fluorine atoms, so it is written as F- 12.

② Let the first digit of the methane derivative containing hydrogen be L, plus the number of hydrogen atoms as the first digit. Then write down fluorine atoms such as F-22 (chf2cl), also called monochlorodifluoromethane. Because methane is 1, the number of hydrogen atoms is 1, which adds up to 2 and the number of fluorine atoms is 2, it is abbreviated as F-22.

4.* * * Boiling solution is a mixture of two or more refrigerants. Evaporation and condensation processes are not separated. Just like refrigerant. At present, R500 and R502 are more practical. Compared with R22, its pressure is slightly higher, and the refrigeration capacity is increased by about 13% at lower temperature. In addition, at the same evaporation temperature and condensation temperature. The exhaust temperature of the compressor is low. It can expand the service temperature range of a single compressor and has a good development prospect.

The pollution of refrigerants to the atmospheric environment is a major event related to human health and survival, and it is also a concern of all of us. Many experts have conducted in-depth research on this issue for many years. A new CFC substitute not only has zero ozone depletion potential (ODP) in the atmosphere, but more importantly, it must also meet the requirements of global warming potential (GwP) caused by the direct impact of refrigerants discharged into the atmosphere on the greenhouse effect. The destruction of ozone layer has become the focus of global environmental concern. The international community formulated the Vienna Convention for the Protection of the Ozone Layer and the Montreal Protocol on Substances that Deplete the Ozone Layer in 1985 and 1987 respectively. China joined the international convention organization of the Montreal Protocol on 199 1, promising to control ozone-depleting substances. At present, many substitute products of R 12 and R 22 are coming out one after another, such as R 134a, R600aKLB, R407c, etc. Their use effect and comparison of various performance indexes are constantly fed back through laboratory and practical application. We believe that with the passage of time and the continuous progress of science and technology, refrigerants with better performance, more environmental protection requirements and more cost-effective competitiveness will be more used in refrigeration and air conditioning industry.

(3) Use and storage of refrigerants

Various refrigerants have different physical and chemical properties and have different saturation pressures at different temperatures. At room temperature, some pressures are high and some are low. But regardless of the pressure, all kinds of refrigerant cylinders are pressure vessels, so be careful when using them. Most refrigerants are explosive because of their different properties. When the corrosion of the cylinder is not checked, or when it is exposed suddenly or the fire source is encountered from the outside, it may explode, and some refrigerants are still toxic. Therefore, the storage, handling and use of refrigerants must be careful.

No matter which refrigerant is used up, the cylinder valve should be closed immediately. When overhauling the system, if the refrigerant is pumped out of the system and pressed into the cylinder, it should be fully cooled and the weight injected into the cylinder should be strictly controlled. Shall not be filled, generally not more than 60% of the cylinder volume, so that it can expand at room temperature. In addition, when detecting the leakage of refrigeration system with halogen lamp, if the color changes and the leakage point is determined, the suction port should be removed immediately to avoid phosgene poisoning.

Six, the structure and composition of refrigeration system

The basic refrigeration system consists of four parts: compressor, evaporator, condenser and expansion valve. In order to improve the performance of refrigeration system and achieve better performance, there are usually many auxiliary devices: liquid pipeline electromagnetic valve, liquid observation mirror, liquid pipeline drying filter, high and low pressure controller and so on.

(1) compressor

According to its structure, compressors can be divided into three types: open, semi-closed and fully closed. At present, most of the special air conditioners for computer rooms use fully enclosed compressors, and only some models of Libert air conditioners use semi-enclosed compressors.

The fully enclosed refrigeration compressor is a whole consisting of a compressor and a motor installed in a closed iron shell. From the outside, there are only the suction and exhaust pipe joints of the compressor and the wires of the motor; The compressor shell is divided into upper and lower parts. After the compressor and motor are installed, the upper and lower iron shells are welded into a whole by electric welding. Usually it can't be disassembled, so the machine is more reliable.

Among the totally enclosed refrigeration compressors, there are piston compressors and scroll compressor. In the recently produced special air conditioning system for computer room, the compressors used are all fully enclosed scroll refrigeration compressors. Its structure is mainly composed of the following items: rotary intake and exhaust valves; Pressure gauge interface; Built-in overload protection; Elastic frame; Crankcase heater; Built-in lubricating oil pump.

The biggest advantages of scroll refrigeration compressor are:

1, simple structure: compressor body only needs two parts (moving plate and fixed plate) to replace 15 parts in piston compressor.

2. High efficiency: The suction gas is separated from the shift treatment gas to reduce the heat transfer between suction and treatment, which can improve the efficiency of the compressor. The compression process and transformation process of vortex are very quiet.

(2) Evaporator

1, classification of evaporator:

According to the type of the cooled medium, evaporators can be divided into two categories: evaporators for cooling liquid (dry evaporator) and evaporators for cooling air (surface cooling evaporator).

Evaporators used in air conditioning systems are usually evaporators for cooling air. The liquid freon in the refrigeration system enters the expansion valve for throttling and is sent to the evaporator, which belongs to the vaporization process. At this time, it is necessary to absorb a lot of heat, so that the room temperature is gradually reduced to achieve the effect of refrigeration and dehumidification.

2. Type A evaporator

The advantages of "A" evaporator are large windward area, low head-on wind speed and preventing water from being carried against the wind. The evaporator is equipped with 1/2 "copper tube aluminum fin and stainless steel condensing plate to promote better heat transfer.

The evaporator coil is divided into multiple paths and staggered, so that each refrigeration system can be distributed on the windward side of the coil. When a single refrigeration system is running, the sensible heat refrigeration capacity can reach 55%-60% of the total refrigeration capacity.

3. Dehumidification function of evaporator

In the normal refrigeration cycle, the indoor fan runs at normal speed, providing the design air volume and the most economical energy to meet the requirements of refrigeration capacity.

(1) Simple dehumidification function

When dehumidification is needed, the compressor runs, but the motor speed of the indoor unit is reduced, which is usually 2/3 of the original speed, so the air volume is also reduced by 1/3, and the temperature of the outlet air passing through cooling coils becomes too cold, and the condensation effect is good, that is, the dehumidification capacity is increased. The disadvantages of this method are: when the air volume decreases by 1/3, the air temperature usually drops by 2 oc-3 oc in a few seconds, and when the speed of sudden cooling reaches the maximum allowable value, it drops by 1℃ every 10 minute, which leads to the reduction of control reliability; When the air supply volume decreases by 1/3, the filtration efficiency decreases, which has a great influence on the air exchange times and ventilation volume, resulting in the decrease of indoor control accuracy and uneven temperature distribution; With the decrease of air outlet temperature, it is necessary to turn on the electric heater to improve the room temperature, which leads to inaccurate temperature control and increased operating cost.

(2) Special dehumidification cycle

The cooling winding is divided into upper and lower parts, accounting for 1/3 and 2/3 of the total cooling winding respectively. In the normal cooling mode, the refrigerant flows through two parts of the cooling winding. In the dehumidification mode, the normally open solenoid valve is closed, thus cutting off the Freon refrigerant leading to the upper winding (1/3 part) of the cooling winding, and all the Freon refrigerant flows to the lower winding (2/3 part) of the cooling winding. The air temperature passing through the lower winding is very low, which is usually at least 3oC lower than that in the refrigeration cycle, so the dehumidification effect is increased, but its disadvantage is that the total refrigeration capacity will be reduced and the suction pressure will be reduced.

(3) Bypass gas regulator

The bypass gas regulator is installed at the top of the "A" evaporator. In the normal cooling mode, the regulator is closed, and all the returned gas passes through the two cooling windings evenly. When dehumidification operation is needed, the bypass gas regulator is fully opened, so that 1/3 of the return air bypasses the top of the A-frame winding without cooling, and the other 2/3 of the return air uniformly passes through the A-frame winding, so that the exhaust gas temperature is rapidly reduced and the dehumidification effect is increased.

The effect of this dehumidification method is the same as that of the special dehumidification cycle, but its advantage is that the total refrigeration capacity remains unchanged.

(3) Condenser

Condensers can be divided into three types according to their cooling forms: water-cooled, air-cooled, evaporative and shower.

(1) water cooling:

In a water-cooled condenser, the heat released by the refrigerant is taken away by the cooling water. Cooling water can flow once or be recycled. When using circulating water, a cooling tower or cold water pool is needed. Water-cooled condenser has shell-and-tube structure, sleeve structure and submerged structure.

② Air-cooled

In an air-cooled condenser, the heat released by the refrigerant is taken away by the air. Its structure is mainly composed of several groups of copper pipes. Because of the poor heat transfer performance of air, fins are usually installed outside the copper tube to increase the heat transfer area on the air side, and a ventilator is used to accelerate the air flow, so that the air is forced to convection to increase the heat dissipation effect.

(3) Evaporation type and water spraying type:

In this kind of condenser, the refrigerant is condensed in the tube and cooled by water and air at the same time outside the tube.

At present, air-cooled air conditioning is the main type of imported air conditioning for computer rooms. The air-cooled condenser will be described in detail below.

Air cooled condenser? 10 copper tube, aluminum fin structure and speed regulating motor for fan ensure that the condenser can be used evenly in winter and summer, and the condensation pressure will not change too much in extremely cold and hot environment.

The air-cooled condenser is suitable for the ambient temperature range of -30oC-+40oC. When the ambient temperature is high, the pressure of the condenser will increase, which will be sensed by the pressure sensing mechanism of the governor, and this change will be transformed into the change of output voltage, thus changing the speed of the motor and achieving the purpose of adjusting the forced convection effect.

Of course, because of the stepless speed regulation device, the change of motor speed can be smooth. The outdoor condenser of the special air conditioner in the machine room has been adjusted and calibrated before leaving the factory, but the setting drift of the governor occurs from time to time due to the vibration during long-distance transportation or long-term use. If this happens, please refer to the instruction manual of the corresponding model to make appropriate adjustments. Usually, the process of outdoor machine speed regulation is: when the high pressure of outdoor machine is about 14kgf/cm2, the fan starts to rotate, and reaches full load speed at 20-24kgf/cm2, and the speed regulation performance is the best at 14- 18kgf/cm2.

(4) Thermal expansion valve

1, structure of thermal expansion valve:

At the top of the expansion valve, a sealed container is composed of a corrugated film temperature sensor with a sealed box cover and a capillary tube, and Freon is filled into the container to form an induction mechanism. The refrigerant filled in the suction mechanism may be the same as or different from the refrigerant in the refrigeration system. For example, F-22 is used in the refrigeration system, and F- 1.2mm or F-22 can be installed in the temperature sensing package. The temperature sensing bulb is used to sense the superheated steam temperature at the outlet of the evaporator, and the capillary tube is used as the connecting tube between the sealed box and the temperature sensing bulb to transmit pressure. The elastic deformation performance after stress is very good. The adjusting lever is used to adjust the opening superheat of the expansion valve and the elasticity of the elastic spring during debugging. When the adjusting lever rotates inward, the spring is compressed, and when the adjusting lever rotates outward, the spring is released. The transmission rod transmits pressure against the valve needle seat and the transmission disk. The valve needle seat is provided with a valve needle for opening or closing the valve hole.

2. Working principle of thermal expansion valve

The expansion valve senses the change of superheat at the outlet end of the evaporator through the temperature sensing ball, which causes the pressure change of the filling material in the temperature sensing system (the temperature sensing system is a closed system composed of the temperature sensing ball, capillary tube, transmission diaphragm and transmission bellows), which acts on the transmission diaphragm to make it move up and down, and then transmits the force to the transmission rod through the transmission diaphragm to push the valve needle to move up and down, thus closing or opening the valve. It plays the role of reducing pressure and throttling, automatically adjusts the refrigerant supply of the evaporator, so that the outlet end of the evaporator keeps a certain degree of superheat, thus ensuring the full utilization of the heat transfer area of the evaporator and reducing the phenomenon of liquid colliding with the cylinder.

3. Type of expansion valve: (internal balance, external balance)

The pressure acting on the lower part of the transmission diaphragm in the valve body of the thermal expansion valve is the evaporation pressure after throttling (this pressure enters the space below the diaphragm through the gap between the transmission rod and the transmission plate). This structure is called internal balanced expansion valve. The pressure acting on the lower part of the transmission diaphragm in the valve body of the thermal expansion valve is not the evaporation pressure after throttling, but the pressure at the outlet end of the evaporator is introduced into the valve of the lower space structure of the transmission diaphragm through the external balance pipe, which is called the external balance thermal expansion valve. Compared with the internal balance expansion valve, the superheat of the external balance thermal expansion valve is much smaller, so the external balance thermal expansion valve can give full play to the role of the heat transfer area of the evaporator and improve the efficiency of the refrigeration device. When the resistance and pressure loss of the evaporator are small, the internal balance thermal expansion valve can be selected. When the evaporation resistance is high, the pressure loss is high or there is a liquid distributor, the external balance thermal expansion valve should be selected. External balanced expansion valves are generally used in distributors. External balanced thermal expansion valve is usually used in special air conditioners. Although the thermal expansion valve is only a small component, it plays an indispensable role in the refrigeration system, so it is called the four major components of the refrigeration system together with the refrigeration compressor, evaporator and condenser.

(5) Other accessories of the refrigeration system.

1. Solenoid valve for liquid pipeline

The pulse signals from the pressure relay and temperature relay in the refrigeration system can automatically control the solenoid valve in the liquid pipeline. When the compressor stops, a large amount of freon enters the evaporator due to inertia and thermodynamic properties of freon. When the compressor starts again, the wet steam enters the suction port of the compressor and causes wet stroke, which makes it difficult to start, and even causes the valve plate to rupture in serious cases. The arrangement of the solenoid valve in the liquid pipeline can avoid this situation. In an ideal air conditioning system, the start of the compressor also depends on the solenoid valve. At rest, the solenoid valve divides the high and low pressure into two parts, and the lower pressure of the low pressure part is lower than the opening value of the low pressure controller. Therefore, the compressor is in a stopped state. When the compressor needs to be started, the electromagnetic valve is opened by the computer output signal. When the valve is opened, the high pressure is quickly released to the low pressure. Only when the low pressure reaches the opening value of the low pressure controller can the compressor be started.

2. Liquid mirror

The observation window is located between the solenoid valve and the drying filter in the refrigeration system. As the name implies, it is used to observe the state of liquid flow. According to the number of bubbles, it can be used as a reference for refrigerant injection. According to the color of the glass, we can see the water content in the system.

3. Liquid pipeline drying filter:

Usually, the liquid pipeline drying filter is not detachable. Molecular sieve structure is adopted inside, which can remove a small amount of impurities and moisture in the pipeline and purify the system. Because oxides will appear in the pipeline during welding, and the purity of Freon refrigerant is different, all the Freon refrigerants we use are required to be imported. When the liquid pipeline drying filter is blocked, the suction pressure will decrease and the temperature difference will appear at both ends of the filter. If this happens, the filter needs to be replaced.

4. High and low pressure controller

High and low pressure controller is a protective device in refrigeration system. High voltage protection is the upper limit protection. When the high pressure reaches the set value, the high pressure controller is disconnected, so that the compressor contactor coil is released, and the compressor stops working, so as to avoid damaging parts when running under ultra-high pressure. The high voltage protection was reset manually. When the compressor starts again, press the reset button first. Of course, before restarting the compressor, you should check the cause of high pressure first, and then the machine can run normally after being eliminated. Low pressure protection is a protective device to prevent the refrigeration system from running at too low pressure. Its setting is divided into upper limit and lower limit. The control principle is: the low-voltage disconnection value is the pressure difference between the upper limit and the lower limit, and the restart value is the upper limit. The low-pressure controller is automatically reset, which requires the operator to observe the operation of the machine frequently and deal with the alarm in time to prevent the compressor from starting and stopping frequently for a long time, which will affect the service life.

The simplest refrigeration consists of four components: ① compressor; ② condenser; ③ throttle valve; ④ Evaporator; The refrigerator we use every day is composed of these four elements and boxes, just like a cold storage. The throttle valve on the refrigerator is technically replaced by a capillary tube with the same function. First of all, what is refrigeration? The word refrigeration can only be said to be a technical term, strictly speaking, it is wrong. Scientists in no country in the world can create "cold". Then what is cold? Let's take an example first: in cold winter, the temperature drops to -5℃. We said: it's really cold today, but the northeast people say it's not cold; In dog days, when the temperature is +32℃, we will say it is not hot, but when the temperature suddenly drops to +25℃, we will say it is too cold. This cold is determined by human common sense, and there is no definition of cold in physics. The cooling in the project depends on the production needs. If the boss asks, is the cold storage cold? When you say cold, this cold is-18℃; The boss asked, is the temperature in the fruit warehouse stable? When you say stable, the answer is that the temperature of fruit warehouse is stable at 0℃, which is the definition of cold in our industry. But we still call this method of cooling objects to the required temperature by mechanical equipment refrigeration, a term. What is refrigeration? For example, if we put a kettle with one kilogram of cold water at 20℃ on an iron plate heated to 500℃, the water will soon boil. If we don't take the kettle away, the water will soon dry up. Everyone says that the steel plate is heating water, and conversely, it can be said that water is cooling the steel plate. And how many degrees it has dropped can be calculated, because one kilogram of water needs to absorb 80 calories from the outside when it rises from 20℃ to 100℃, and 539 calories when it boils from 100℃, which means that one kilogram of cold water at 20℃ needs to absorb 6 19 calories from the outside. From the point of view of refrigeration, it extracts 6 19 calories from the outside or steel plate and converts them into steam to cool the steel plate. This is refrigeration. Water is used to refrigerate steel plates. It will be more intuitive if you pour water on the steel plate. In the above refrigeration process, if the size of the steel plate is fixed and the refrigeration factor of the outside air is excluded, how many degrees the steel plate has dropped can be accurately calculated. I think anyone who has studied physics can understand the physical quantities such as heat, temperature, calorie and℃ mentioned here. Physics in junior high school says that heat is always transferred from a high-temperature object to a low-temperature object through conduction, convection and radiation, and it is never the other way around. When an object loses some heat, its temperature will drop a little. Our purpose is to transfer the heat in commodities and air to refrigeration through refrigeration system at a temperature lower than that of commodities.

Agent transfer, to achieve the purpose of reducing the temperature of goods. Our refrigeration system and the heating system of the boiler are identical in thermodynamics, and their heat conduction formulas are also identical. Let's compare boilers first, and then talk about the role of refrigerants in refrigeration. The kettle mentioned above can also be regarded as a boiler, but when the water boils, we will fill the thermos bottle. If we put a tube on the spout and lead it to the bathroom, we can take a sauna and the kettle becomes a small boiler. It should be noted that the water in the kettle is always 100℃, and the steam temperature at the kettle outlet is also 100℃. Why not 1 10℃ instead of 90℃? This is because the boiling temperature of water at atmospheric pressure is 100℃, which is determined by the physical properties of water. On the Qinghai-Tibet Plateau, the atmosphere is low, the water is boiled at about 70℃, and you can only eat raw rice without a pressure cooker. In the pressure cooker, the temperature can reach 1 10℃, because the weight of the exhaust valve of the pressure cooker just keeps the pressure in the cooker at 1Kg/CM2 gauge pressure (actually 2 atmospheres). Generally, a small boiler can burn 4Kg/CM2 gauge steam, the steam temperature is close to 140℃, and the water temperature in the boiler is 140℃ as well as the steam temperature. The temperature of the gas burner can reach about 1000℃. The burner transfers heat to water, so the temperature of water rises to the boiling point. From the boiling point to the boiling point (all become steam), the heat taken away by the gas stove is the same as that of the kettle cooling steel plate mentioned above. The flame near the bottom of the pot is a cooling process. The combustion temperature of coal in the boiler is about 1200℃. Without the cooling of water in the boiler, the exhaust pipe in the boiler will collapse. From our point of view, the water here is a refrigerant. On the other hand, after steam enters the bathroom, it immediately condenses into small water droplets (fog), releasing heat to raise the temperature of the bathroom. The same kilogram of water burns one kilogram of steam, which releases 539 calories in the bathroom and becomes water. When steam changes into water, the temperature of water droplets is 100℃, which is a condensation process. Of course, water droplets will continue to release heat and lower the temperature. When the water drops become water drops and fall to the ground or attach to the wall, it is only about 30℃. This is not a condensation process, but an ordinary cooling process. Similarly, the boiler steam is introduced into the indoor hot water heater (indoor heating exhaust pipe), and the hot water heater becomes the condenser of the steam. If the supplied steam pressure is 1Kg/CM2 gauge pressure (actually, it is 2 atmospheres), the surface temperature of the water heater is 1 10℃, and the water heater radiates heat to the indoor air, so that the indoor temperature rises and the steam condenses into water in the water heater. In refrigeration, the whole process is that the heat of coal combustion is absorbed by water and boiled into steam, and the steam comes to the hot water tank with the absorbed heat. The surface of the hot water tank radiates heat to the air, and the steam condenses into distilled water again after losing heat. This water can be returned to the boiler for further use through the equipment. Now back to the four elements of refrigeration:

(1) compressor with the same principle as air compressor;

(2) condenser, which can be understood as hot water heater or distiller (tin can) for wine industry;

③ Evaporator, which can be understood as the kettle or boiler mentioned above;

(4) Throttle valve can be understood as adding a valve from the high-level hot water tank upstairs to the boiler, turning it down a little, allowing distilled water to flow into the boiler to continue to use, preventing the water from running out of the hot water tank, and making the steam in the boiler recoil back to the hot water tank. This is different from our refrigeration, because the whole system is pressure balanced, the condensing part of the refrigeration system is high pressure, and the throttle valve controls the reasonable distribution of refrigerant to the evaporator, so that the evaporator is in a normal refrigeration working state.

The four main requirements of refrigerator refrigeration are:

(1) compressor, hidden behind the refrigerator, round head round brain guy;

(2) The condenser is the cooling fin behind the refrigerator;

③ Evaporator, the freezing rack in the early single-door refrigerator, can be clearly seen, and the finned tube similar to the air cooler can be seen by removing the inner container of the frost-free refrigerator;

(4) Throttle valve, there is a spiral thin copper tube, that is, capillary tube, behind the refrigerator. The shell of the refrigerator is equivalent to the outer body of the cold storage.