First, the principle of vapor compression type refrigeration
Vapor refrigeration is the use of certain low-boiling-point liquid refrigerants at different pressures when the vaporization of the nature of the absorption of heat to achieve artificial refrigeration.
In refrigeration technology, vaporization is the process by which a liquid refrigerant becomes gaseous when it reaches boiling. Liquid into a gaseous state must be absorbed from the outside world in order to achieve heat, so it is the heat absorption process, the temperature of the liquid refrigerant evaporation vaporization is called the evaporation temperature, condensation refers to the steam cooled to equal to or lower than the saturation temperature, so that the steam is converted into a liquid state. In our daily life, we can observe many evaporation and heat absorption phenomenon. For example, we rub some alcohol on the hand, alcohol quickly evaporate, then we feel rubbing alcohol part of the reaction is very cool. Another example is the commonly used refrigerant Freon F-12 liquid sprayed on the object, we will see the surface of the object will soon form a layer of white frost, this is because the F-12 liquid sprayed on the surface of the object immediately absorbs heat, so that the surface temperature of the object falls rapidly (of course, this is not practical refrigeration methods, refrigerant F-12 can not be recovered and recycled). F-12 cannot be recovered and recycled). At present, some medical institutions using cryotherapy that is the use of this principle.
Vapor compression refrigeration is the use of liquid refrigerant vaporization heat absorption, steam condensation exothermic principle of refrigeration.
Two, the refrigeration cycle
The compressor is to ensure that the power of refrigeration, the use of the compressor to increase the pressure of the refrigerant in the system, so that the refrigerant in the refrigeration system cycle, to achieve the purpose of refrigeration. Beginning of the compressor to inhale the evaporation of low-temperature and low-pressure refrigerant gas, and then compressed into high-temperature and high-pressure gas sent to the condenser; high-pressure and high-temperature gas by the condenser after the condenser cooled to condense the gas into a room temperature and high pressure liquid; when the room temperature and high pressure liquid flow into the thermal expansion valve, throttled into a low-temperature and low-pressure wet vapor, flowing into the evaporator, from the surrounding objects to absorb the heat, the temperature of the room through the air conditioning duct system cooled down after evaporation of refrigerants back to the compressor, and repeat the evaporation. After evaporation, the refrigerant returns to the compressor and repeats the next refrigeration cycle, thus realizing the purpose of refrigeration.
Three, refrigerant in the refrigeration system in the state
From the compressor outlet through the condenser to the expansion valve in front of the section known as the high pressure side of the refrigeration system; this section of the pressure is equal to the condensing temperature of the refrigerant saturation pressure. High-pressure side is characterized by: refrigerant exothermic to the surrounding environment is condensed to liquid, refrigerant flow out of the condenser, the temperature is reduced to supercooled liquid.
From the outlet of the expansion valve to the return gas into the compressor this section is known as the low-pressure side of the refrigeration system, the pressure of the evaporator, such as the saturation pressure of the evaporation temperature. The low-pressure side of the refrigerant was first wet vapor state, in the evaporator after absorbing heat from the wet refrigerant vapor gradually into a vapor refrigerant. At the outlet of the evaporator, the temperature of the refrigerant rises to a superheated gas state. Subcooled liquid refrigerant through the expansion valve, due to throttling, from high pressure down to low pressure (but not consume power, there is no heat exchange); at the same time, a small portion of the liquid refrigerant vaporization, the temperature is reduced, this low-pressure low-temperature refrigerant into the evaporator after evaporation (vaporization) heat absorption. Low-temperature, low-pressure gaseous refrigerant is sucked into the compressor, and through the compressor into the next refrigeration cycle.
Four, refrigeration
In the refrigeration cycle, circulating flow of refrigerant from the cooled object absorbed heat is called unit weight refrigeration, with the symbol q, the unit is kcal/kg, unit weight refrigeration is expressed in the effect of refrigeration cycle of a special parameter, which is determined by the nature of the refrigerant, the cycle of temperature and other conditions, the lower the evaporation temperature, the higher the condensing temperature, the smaller its value, the higher the evaporation temperature, the higher the condensing temperature, the lower its value, the lower its value, the lower its value, the higher its value. The lower the evaporation temperature, the higher the condensation temperature, the smaller the value, and vice versa, the larger. Refrigeration unit cooling capacity is absorbed from the cooled object in a unit of time and the heat released in the condenser, expressed by the symbol Q, the unit is kcal/kg. the size of Q value is equal to the cold weight flow G and the unit weight of refrigeration capacity q product, that is: Q = G?q . In practice, sometimes in order to facilitate access to the rough calculation of the cooling capacity can also be calculated by the following formula
Q = L?(t2 -t1 )
The L circulating air volume, (t2 -t1 ) for the temperature difference between the inlet and outlet air.
In Japan, Europe and the United States and other countries refrigeration commonly used to express the cold tons, but the Japanese cold tons and the United States cold tons in the numerical value of a slight difference in Japan, the unit of cold production with the Japanese cold tons, 1 day cold tons of water that 1,000 grams of 0oC in 24 hours to make the 0oC ice consumed by the amount of cold:
1 day cold tons = 3320kcal / h
1 U.S. cold tons = 3024Lcal / h
Commonly used unit conversion of refrigeration capacity:
1KW = 860kcal / h (large calories / hour)
1kcal / h = 3.968BTU / h (British thermal units / hour)
V. Refrigerant
Refrigerant is a working substance that carries out the refrigeration cycle.
(a) the requirements of the refrigerant
Ideal refrigerant chemical properties are non-toxic, non-irritating odor, corrosion of metals, and lubricants do not have a chemical reaction, not easy to burn, not easy to explode, and requires the refrigerant to have good thermodynamic properties, that is, at atmospheric pressure it is in the evaporator evaporator evaporation temperature should be low, evaporative pressure is best with the atmospheric pressure is similar; Refrigerant in the condenser, condensing temperature corresponding to the pressure should be moderate, unit refrigeration capacity should be large, the heat of vaporization should be large, and the specific heat of liquid should be small, the specific heat of gas should be large. Requirements for the physical properties of the refrigerant: solidification temperature should be low, the critical temperature should be high (preferably higher than the ambient temperature), thermal conductivity and exothermic coefficient should be large, the specific gravity and viscosity should be small, the leakage should be small.
(ii) types of refrigerants
There are many types of refrigerants, the actual application can be based on the type of refrigerant, evaporation temperature, condensing temperature and pressure and other thermodynamic conditions, as well as refrigeration equipment to consider the use of the location. Refrigerants can be divided into four categories: namely, inorganic compounds, hydrocarbons, Freon and *** boiling solution.
1, inorganic compounds refrigerants are ammonia, water and carbon dioxide, etc.;
2, hydrocarbon refrigerants are ethane, propylene, etc.;
3, Freon (FREON) is the 1830s began to use a refrigerant, than ammonia later than the last 60 years or so, it is the halogenated saturated hydrocarbons (fluorine, chlorine, bromine) derivatives of the general term, or It is composed of fluorine, chlorine and hydrocarbons. Currently used as a refrigerant is mainly methane (CH4) and ethane (C2H6) in the hydrogen atom, all or part of the fluorine chlorine bromine atoms replaced by the formation of compounds, in addition to the name, the chemical molecular formula specifies the abbreviation code of the various categories of Freon.
1) Freon abbreviation code of Freon molecular compounds that do not contain hydrogen atoms of the first number coded as 1, ethane coded as 11, propane (C3H8) coded as 21, and then write the number of fluorine atoms. For example, F-12, known as dichlorodifluoromethane, molecular formula CF2CL2 in a carbon atom, does not contain hydrogen for methane. Therefore, the first number is coded as 1, and there are two fluorine atoms, it is written as F-12.
② The hydrogen-containing methane derivatives of the number of the first as l, plus the number of hydrogen atoms for the first number. Then write the fluorine atom for example F-22 (CHF2CL) also known as monochlorodifluoromethane, because methane is 1, the number of hydrogen atoms is 1, add up to 2, and the number of fluorine atoms is 2, so it is abbreviated as F-22.
4, *** boiling solution is a mixture of more than two refrigerants. The evaporation and condensation processes are also not separated. Just like a refrigerant. Currently practical R500, R502 and so on. Compared with R22, the pressure is slightly more, and the refrigeration capacity is increased by about 13% at lower temperatures. In addition, under the same evaporation temperature and condensation temperature. Compressor exhaust temperature is lower. Can expand the use of a single compressor temperature range, so the development prospects are good.
On the issue of refrigerant pollution of the atmosphere, which is related to human health and survival of the major events, but also all of us **** with the issue of concern. Over the years, many experts have carried out in-depth research on this, a new CFC alternatives, not only to the atmosphere ozone layer depletion potential (ODP) is zero, more importantly, refrigerant emissions into the atmosphere on the greenhouse effect caused by the direct impact of the global warming potential (GwP) must also meet the requirements. The destruction of the ozone layer has become a 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, and China acceded to the International Convention on the Montreal Protocol in 1991, and committed itself to the control schedule of ozone-depleting substances, i.e., the complete phase-out of R 12 and R 22 will take place in 2010 respectively. China joined the International Organization of the Montreal Protocol in 1991 and committed to the control schedule of ODS, i.e., the complete phase-out of R 12 and R 22 by 2010 and 2030 respectively. At present, many alternative products to R 12 and R 22 are being introduced one after another, such as: R134a, R600aKLB, R407c and so on. Their use of the effect and the comparison of various performance indicators, is through the laboratory and the actual use of feedback, we believe that with the passage of time and the continuous progress of science and technology, more excellent performance, more environmentally friendly requirements, more cost-effective competitiveness of refrigerants will be more used in the refrigeration and air conditioning industry.
(C) the use of refrigerants and storage
A variety of refrigerants, physical and chemical properties are different, at different temperatures, with different saturation pressures, at room temperature, some pressure is high, some pressure is low, but no matter how the pressure is, a variety of refrigerant cylinders are pressure vessels, the use of more careful. Due to the different nature of various refrigerants, most of them are explosive. In the cylinder corrosion has not been tested, or meet the outside world of the sudden exposure to sunlight or ignition sources, there is a possibility of explosion, and some refrigerants are still toxic. Therefore, the storage, handling and use of refrigerants must be careful.
No matter what kind of refrigerant is used up, the cylinder valve should be closed immediately, in the maintenance system, if the refrigerant from the system will be pumped into the cylinder, it should be sufficiently cooled, and strictly control the weight of the injected cylinder, never full, generally not more than 60% of the cylinder volume, so that there is a certain margin for its expansion at room temperature. In addition, in the use of halogen lamps to the refrigeration system leak detection, meet the color change, to determine the leak, should be immediately removed from the suction port, so as to avoid phosgene poisoning.
Six, the structure and composition of the refrigeration system
Constitutes the basic refrigeration system has four main components: compressor, evaporator, condenser, expansion valve. In order to improve the performance of the refrigeration system to achieve better performance, there are usually a number of auxiliary devices: liquid line solenoid valve, liquid sight glass, liquid pipeline filter drier, high and low pressure controller.
(a) compressor
Compressor according to its structure is divided into three categories: open, semi-closed, fully closed. At present, most of the air-conditioning equipment room specializing in the use of hermetic compressor, only a part of the air-conditioning force Bot air-conditioning models with semi-hermetic compressor.
The hermetic refrigeration compressor is a compressor and motor together, the device in a closed iron shell to form a whole. From the outside only the compressor suction and discharge pipe joints and motor wires; compressor shell is divided into two parts, compressor and motor mounted, the upper and lower iron shell with electric welding into one. Normally can not be disassembled, so the machine is reliable.
In the hermetic refrigeration compressor, there are piston compressor and scroll compressor. In the recent production of air-conditioning system for the machine room, the compressor are used for the hermetic scroll type refrigeration compressor. Its structure is mainly composed of the following items: rotary inlet and outlet valves; pressure gauge interface; built-in overload protection; elastic seat; crankcase heater; built-in lubricating oil pump.
Scroll refrigeration compressor's biggest advantages are:
1, simple structure: the compressor body only needs 2 parts (moving disk, fixed disk) can replace the piston compressor in the 15 components.
2, high efficiency: suction gas and transforming processing gas is separated to reduce the heat transfer between suction and processing, can improve the efficiency of the compressor. The scroll compression process and transformation process are very quiet.
(B) evaporator
1, evaporator classification:
Evaporator according to the type of medium to be cooled can be divided into the evaporator to cool the liquid (dry evaporator) and cool the air with the evaporator (table cooled evaporator) of the two categories.
The evaporator used in the air conditioning system is generally the evaporator for cooling air. When the refrigeration system of Freon liquid into the expansion valve throttled into the evaporator, belonging to the vaporization process, this time need to absorb a lot of heat, so that the room temperature is gradually reduced to achieve the effect of refrigeration and dehumidification.
2, A-type evaporator
"A" structure of the evaporator has the advantage that the structure has a larger wind area and lower wind speed to prevent the wind with water. The evaporator is equipped with 1/2" copper tube aluminum fins and stainless steel condensate tray for better heat transfer.
The evaporator coil is divided into multiple entry and staggered arrangement, whereby each refrigeration system can be spread across the windward side of the coil, when a single refrigeration system is running, the sensible heat cooling capacity up to the total refrigeration capacity of 55% -60%.
3, the evaporator dehumidification
In the normal refrigeration cycle, the indoor fan runs at normal speed, supply design airflow and the most economical energy to meet the requirements of the cooling capacity.
(1) Simple dehumidification
When dehumidification is required, the compressor operates, but the motor speed of the indoor unit is reduced, usually 2/3 of the original speed, so the air volume is also reduced by 1/3, and the temperature of the air through the cooling coil becomes supercooled, resulting in a good condensing effect, which increases the dehumidification capacity. To this method to increase the amount of dehumidification brought about by the drawbacks are: when the air volume decreased by 1 / 3, usually within a few seconds of the temperature of the air out of the 2oC-3oC, when the sudden reduction in the speed of the temperature to reach the maximum permissible value of 1 ℃ per 10 minutes, resulting in a reduction in the reliability of the control; when the air volume is reduced by 1 / 3, the filtration efficiency is reduced, the number of air exchanges and the amount of ventilation have a great impact on the amount of ventilation. Cause the indoor control accuracy is reduced and uneven temperature distribution; due to the lower temperature of the air outlet, the need to turn on the electric heater to improve the room temperature, resulting in imprecise temperature control and increase operating costs.
(2) Specialized dehumidification cycle
Cooling winding is divided into the upper and lower two parts, respectively, for the total cooling winding l / 3 and 2 / 3. In the normal cooling mode, the refrigeration mass flows through the two parts of the cooling winding. In the dehumidification mode, the normally open solenoid valve is closed, which cuts off the Freon refrigerant 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 temperature of the air passing through the lower winding is very low, usually at least 3oC lower than that of the air in the cooling cycle, so the dehumidification effect is increased, but the disadvantage is that the total refrigeration capacity is reduced and the suction pressure is lowered.
(3) Bypass gas regulator
A bypass gas regulator is installed on the top of the "A" type evaporator, which is closed in the normal cooling mode, and all the returned gases pass through the two cooling windings evenly. When it is necessary to carry out dehumidification operation, the bypass gas regulator is completely open, so that 1/3 of the return gas bypassed through the top of the A frame winding without cooling, and the other 2/3 of the return gas uniformly through the A frame winding, the temperature of the discharged gas is rapidly reduced to increase the effect of dehumidification.
The effect of this dehumidification method is the same as the specialized dehumidification cycle, but the advantage is that the total cooling capacity will remain unchanged.
(C) condenser
Condenser can be divided into three major types according to its cooling form: water-cooled, air-cooled, evaporative and shower.
①Water-cooled:
In the water-cooled condenser, the refrigerant releases heat to be taken away by the cooling water. The cooling water can flow once or be recycled. When circulating water is used, a cooling water tower or cold water pool is required. Water-cooled condensers are available in shell and tube, casing, immersion and other structural forms.
② air-cooled
In the air-cooled condenser, the heat released by the refrigerant is taken away by the air. Its structural form is mainly composed of a number of groups of copper tubes, due to the poor heat transfer performance of the air, it is usually in the copper tube outside the increase in ribs to increase the air side of the heat transfer area, while the use of ventilators to accelerate the air flow, so that the air forced convection in order to increase the effect of heat dissipation.
3 evaporative and water:
In this type of condenser, the refrigerant is condensed in the tube, the outside of the tube at the same time by the cooling of water and air.
At present, the type of imported air-conditioning equipment room is mainly air-cooled type. The following air-cooled condenser for a detailed description.
Air-cooled condenser using ?10 copper tubes, aluminum fins structure, the fan using adjustable-speed motor to ensure that the condenser in winter, summer can be balanced use, but also so that the condensing pressure in the very cold, very hot environment does not change too much.
Air-cooled condenser is suitable for ambient temperature -30oC - +40oC range, when the ambient temperature is high, it will cause the condenser pressure rises, which will be sensed by the governor of the pressure sensing mechanism of the pressure change, and this change into the change of the output voltage, which will cause changes in the motor speed in order to regulate the forced convection effect of the purpose. The purpose is to adjust the effect of forced convection.
Of course, due to the use of infinitely variable speed control device, then the motor speed change is very smooth transition. The outdoor condenser of the air conditioner for the server room has been adjusted and calibrated at the factory, but due to the vibration of long-distance transportation or long-term use, the setup of the governor may occasionally drift. If this occurs, you can refer to the appropriate model instructions for appropriate adjustment. Usually the outdoor unit to adjust the speed of the process: outdoor high-pressure pressure in the 14kgf/cm2 or so when the fan start, in 20-24kgf/cm2 to reach full load speed, and in the 14-18kgf/cm2 when the speed control performance for the best state.
(D) Thermal Expansion Valve
1, the structure of the thermal expansion valve:
Expansion valve by the top of the sealing box cover corrugated film temperature sensing package and capillary tube composed of an airtight container, which is filled with Freon to become the sensing mechanism, the sensing agency can be filled with the same refrigerant and refrigeration system, or different, for example, refrigeration system is F-22, the sensing package can be filled with Freon, the sensing agency can be different, such as refrigeration system is F-22, the sensing package can be filled with F-22, the sensing package can be filled with Freon. The sensing mechanism can be filled with the same refrigerant as the refrigeration system or different refrigerant, for example, the refrigeration system is F-22, the sensing package can be filled with F-12 or F-22, the sensing package is used to feel the temperature of superheated vapor at the outlet of the evaporator, and the capillary tube is used as the connecting tube between the sealing box and the sensing package to transfer the pressure on the diaphragm. It is wave-shaped. After the force of elastic deformation performance is very good, adjusting rod is used to adjust the opening of the expansion valve superheat, in the commissioning process with it to adjust the spring force, adjusting rod to the spin, spring compression, adjusting rod to the outside of the spin, the spring relaxation, the transmission lever top in the valve needle seat and transmission between the disk to transfer the pressure, the valve needle seat is equipped with a needle, used to open or close the small valve holes.
2, the working principle of the thermal expansion valve
Expansion valve through the temperature sensing package to feel the changes in the degree of superheat at the outlet end of the evaporator, resulting in temperature sensing system (temperature sensing system is composed of temperature sensing packages, capillary tubes, drive diaphragm and drive the bellows of this interconnected parts of the composition of the closed system) filled with substances to produce pressure changes, and act on the drive diaphragm. Prompting the diaphragm to form the up and down displacement, and then through the transmission piece will be transmitted to the transmission rod and drive the valve needle up and down to move, so that the valve off or open, play the role of pressure reduction and throttling and automatic adjustment of the evaporator refrigerant supply and keep the evaporator outlet end has a certain degree of superheat to ensure that the full use of the evaporator area of heat transfer, as well as to reduce the phenomenon of liquid shock cylinder.
3, the types of expansion valves: (internal balance, external balance)
The pressure acting on the lower part of the transmission diaphragm in the thermal expansion valve body for the evaporative pressure after throttling (this pressure through the gap between the drive rod and the drive sheet into the diaphragm of the lower part of the space) this structure is known as the balance of the expansion valve. Acting on the thermal expansion valve body drive diaphragm lower pressure is not throttled evaporative pressure, but through the external balance tube will be the pressure of the outlet end of the evaporator into the drive diaphragm lower space structure of the valve, known as the external balance type thermal expansion valve. Compared with the internal balanced expansion valve, external balanced thermal expansion valve superheat is much smaller, so the external balanced thermal expansion valve, can give full play to the role of the heat transfer area of the evaporator and improve the effect of refrigeration devices, in the evaporator resistance is small, pressure loss is not big, can choose the internal balanced thermal expansion valve; when the evaporation resistance is large, pressure loss is relatively large or with liquid distributor, should choose the external balanced thermal expansion valve. Should choose the external balance type thermal expansion valve. If the distributor is used, the external balanced expansion valve is generally used. In the special air conditioner is usually used in the external balanced thermal expansion valve. Thermal expansion valve is only a very small part, but it is essential in the role of the refrigeration system, so it is with the refrigeration compressor, evaporator, condenser, and known as the refrigeration system of the four major components.
(E) other refrigeration system accessories
1. Liquid line solenoid valve
Liquid line solenoid valve in the refrigeration system can be subjected to pressure relays, temperature relays issued by the pulse signal to form an automatic control. In the compressor shutdown, due to inertia and the thermal properties of Freon, so that a large number of Freon into the evaporator, in the compressor to start again, the wet vapor into the compressor suction port caused by the wet stroke, it is not easy to start, and in severe cases, even the valve piece broken. The installation of a solenoid valve in the liquid line prevents this situation. The startup of the compressor in the GALLERTO air conditioning system also depends on the solenoid valve. When the solenoid valve is at standstill, it divides the high and low pressures into two parts, and the lower pressure in the low-pressure part is lower than the opening value of the low-pressure pressure controller. The compressor is therefore at a standstill. When the compressor needs to start, through the computer output signal to turn on the solenoid valve, when the valve opens, the high pressure is quickly released to the low pressure, when the low pressure reaches the low-pressure controller to open the value, the compressor can start.
2. Liquid mirror
Liquid mirror in the refrigeration system in the refrigeration solenoid valve and filter drier between, as the name implies, it is used to observe the liquid flow state, according to the number of bubbles can be used as a refrigerant injection amount of reference, according to the color of the liquid mirror can be seen in the system of the content of water.
3. Liquid pipeline filter drier:
Usually, the liquid pipeline filter drier is non-removable. The internal molecular sieve structure, can remove a small amount of impurities in the pipeline water, etc., to purify the system. Due to the fact that oxides will appear in the pipeline during welding and the purity of Freon refrigerant varies, the Freon refrigerant we use is required to be imported. When the filter drier of the liquid pipeline is clogged, it will cause the suction pressure to decrease, and there will be a temperature difference between the two ends of the filter, if this happens, the filter needs to be replaced.
4. High and low pressure controllers
In the refrigeration system, high and low pressure controllers are protection devices. High pressure protection is the upper limit of protection, when the high pressure pressure reaches the set value, high pressure controller disconnect, so that the compressor contactor coil release, the compressor stops working, to avoid damage to parts in the ultra-high pressure operation. The high pressure protection is a manual reset, when the compressor is to be restarted, the reset button has to be pressed first. Of course, before restarting the compressor, the causes of high pressure should be checked and eliminated before the machine can operate normally. Low pressure protection is a protection device set to avoid the refrigeration system running under too low pressure. Its setting is divided into high limit and low limit. Its control principle is: low-pressure disconnection value is the upper limit and lower limit of the pressure difference value, reopen the machine is the upper limit value. Low-pressure controller is automatically reset, so operators are required to frequently observe the operation of the machine, the alarm should be dealt with in a timely manner, to avoid the compressor for a long time and frequently start and stop and affect the life.
The simplest refrigeration by the four major components: ① compressor; ② condenser; ③ throttle; ④ evaporator; our daily use of refrigerators, just by the four components plus the box composition, the box is like a cold storage. However, the refrigerator on the ③ throttle valve in technology by the same role of the capillary tube instead. First of all, what is meant by refrigeration. Refrigeration two words can only be said to be a technical term, strictly speaking is wrong, the world does not have that country's scientists can create a "cold" to. That in the end what is cold, first of all, for example: in the winter months, the temperature dropped to -5 ℃, we say: today's weather is really cold, but the Northeast people say not cold; in the big day, the temperature in +32 ℃, we will say that not too hot, but the temperature suddenly dropped to +25 ℃, we will say too cold; this cold is with the people's common sense to determine the definition of the physics of the definition of no cold. In the project cold is followed by the production needs. Such as the boss asked, cold storage to play cold? You said to play cold, this cold refers to -18 ℃; the boss asked, the fruit library temperature is stable? You say very stable, the meaning of this answer is that the fruit library temperature stabilized at ± 0 ℃, this is our industry on the definition of cold. But we still put this use of mechanical equipment to cool the object down to the required temperature method called refrigeration, this is the terminology. What is meant by refrigeration, for example, we will be equipped with a kilogram of 20 ℃ cold water kettle put on a piece of iron plate burned to 500 ℃, not long before the water boiled, if you do not take open the kettle, not long before the water is dry. People and say that the steel plate is heating the water, and the other way around, you can also say that the water is cooling the steel plate. And, how many degrees down, can be calculated, because a kilogram of water from 20 ° C to 100 ° C, it needs the outside world to provide it with 80 calories of heat, water from 100 ° C to burn dry, it needs the outside world to provide 539 calories of heat, that is to say, a kilogram of 20 ° C cold water burned to dry to the outside world to provide 619 calories of heat. If according to the refrigeration point of view it extracted from the outside world or steel plate 619 calories of heat and turned into water vapor, so that the steel plate cooled down, this is the refrigeration, is the use of water on the steel plate refrigeration. If the water is poured on the steel plate, it is more intuitive. In the refrigeration process mentioned above, if the size of the steel plate is certain, and exclude the cooling factor of the outside air, then how many degrees the steel plate has cooled down can be calculated precisely. The physical quantities of 'heat', 'temperature', 'calorie', '℃', etc. mentioned here are, I think, understandable to anyone who has studied physics. Anyone who has studied physics can understand. It is taught in junior high school physics that heat is always transferred from an object with a high temperature to an object with a low temperature by conduction, convection and radiation, and never the other way around. When an object loses some heat, its temperature is also lowered a bit. Our aim is to reduce the temperature of goods by transferring the heat in the goods and in the air to the refrigerant
which has a lower temperature than the goods, through a refrigeration system. Our refrigeration system and the boiler's heating system is thermodynamically speaking is exactly the same, their heat transfer formula is also exactly the same, we first boiler as an analogy, and further talk about the role of refrigerant in refrigeration. The above mentioned kettle can also be considered a boiler, but the water boiled, we fill the hot water bottle, if we set a tube on the spout, leading to the bathroom, it can be a sauna, the kettle will become a small boiler. It should be noted that the water in the kettle is always 100 ℃, the kettle outlet steam temperature is also 100 ℃, why not 110 ℃, not 90 ℃? This is because the boiling temperature of water at an atmospheric pressure is 100 ℃, which is determined by the physical properties of water. In the Tibetan Plateau, the atmospheric pressure is low, the water about 70 ℃ on the open, no pressure cooker can only eat the sandwich, and in the pressure cooker, the temperature can reach 110 ℃, because the weight of the pressure cooker exhaust valve, just so that the pressure inside the pot to maintain the pressure at 1Kg / CM2 table pressure (actually 2 atmospheric pressure). General small boilers can burn 4Kg / CM2 gauge pressure steam, steam temperature is also close to 140 ℃, the water temperature in the boiler is also the same as the steam temperature is also 140 ℃. Gas stove fire head temperature up to 1000 ℃ or so, the fire head will heat transfer to the water, so that the temperature of the water rises straight to the boiling point, a kilogram of water from the boiling point to dry (all into steam), will be taken away from the gas fire head of the heat and the kettle to the steel cooling is the same as mentioned above, close to the bottom of the pot of the flame is a cooling process. The coal in the boiler burns at about 1200 C. Without the cooling of the water in the boiler, the row of tubes in the boiler would be collapsed. From our point of view, the water in this case is the refrigerant. In turn, the water vapor into the bathroom immediately condensed into small water droplets (mist), put out heat to make the temperature rise in the bathroom, the same kilogram of water burned into a kilogram of steam, steam in the bathroom to put out 539 calories of heat after all into water, in the steam into water, the temperature of the small droplets of water is 100 ℃, which is a condensation process. Of course, the small water droplets will continue to release heat and reduce the temperature, and so the water droplets into water droplets fall to the ground or attached to the wall, only about 30 ℃, this is not a condensation process, but only the ordinary cooling process. The same will be the boiler steam to the indoor hot water Ting (indoor heating exhaust), hot water Ting for steam has become a condenser, if the supply of steam pressure 1Kg / CM2 gauge pressure (actually 2 atmospheric pressure), the surface temperature of the hot water Ting is 110 ° C, hot water Ting to the indoor air to emit heat, so that the indoor temperature rises, and steam in the hot water Ting condensation into water, if the indoor emitted 539 calorie If 539 calories of heat are distributed to the room, 1 kilogram of water will be condensed in the hot water. According to the refrigeration point of view, this whole process is the heat of coal combustion is absorbed by the water and boiled into steam, steam with the heat absorbed to the hot water, the surface of the hot water Ting to the air to emit heat, steam loss of heat from the new condensation into distilled water, which can be returned to the boiler through the device to continue to use the water. Now back to the four major elements of refrigeration:
①compressor, the same principle as the air compressor;
②condenser, can be understood as a hot water Ting or alcohol distillers (tin pots);
③evaporator, can be understood as a kettle or boiler, as mentioned above;
④throttling valve, can be understood as a hot water Ting from a high level of the upstairs between the boiler, plus a valve, open a little smaller, let the boiler back for further use. A valve, open a little smaller, so that the distillation of water flow into the boiler to continue to use, do not let the water in the hot water Ting water flow light so that the boiler in the steam backwash back to the hot water Ting, this point is different with our refrigeration, because the whole system is equal pressure, and refrigeration system condensing part of the high-pressure, the throttle valve is to control the refrigerant reasonably allocated to the evaporator, so the evaporator is in a normal refrigeration state of work.
The four main elements of refrigeration on the refrigerator are:
①compressor, hidden behind the refrigerator, the round head of the guy;
②condenser, that is, in the back of the refrigerator's radiator;
③evaporator, in the initial single-door refrigerator in the freezing frame, you can see very clearly, and dismantle the liner of the frost-free refrigerator can be seen as a chiller like the finned tubes;
3) evaporator, in the initial single-door refrigerator can be seen very clearly, and dismantle the liner of the frost-free refrigerator can be seen chiller-like fin tubes; < /p>
④Throttle, in the back of the refrigerator there is a section of thin copper tube wound into a spiral, that is the capillary tube. The shell of the refrigerator is comparable to the outer body of the cooler.