Compressor performance analysis compares compressor type effects

In 1986, the CO content in the atmosphere reached 525 mg/kg, and increased by 0.4% per year. Under certain conditions, increasing the CO concentration can enhance plant photosynthesis, but its effect on the greenhouse effect is also obvious if the CO concentration in the atmosphere continues. The continuous increase, the resulting greenhouse effect will warm the global climate, thus disturbing the natural development and dynamic balance of the Earth's ecosystem, causing a series of catastrophic effects on humans. If CO is used as a refrigerant, it not only reduces the greenhouse effect, but also makes full use of natural materials, greatly reducing costs, saving energy, and fundamentally solving the problem of environmental pollution of compounds. NH has excellent thermal performance, low cost and easy to detect leaks, and high operating efficiency. HO has no harm to the ecological environment and the human body. It is the most friendly refrigerant with the environment. It has high safety and reliability. Its theoretical COP value is higher than R22 and R134a. This topic is aimed at the special properties of natural working fluid NH. Research on environmental protection and energy conservation in every aspect of the refrigeration system.

As a comparison of the performance of the refrigerant, the energy-saving design of the compressor is to increase the pressure to the supercritical pressure in the compressor of the transcritical cycle, and then enter the gas cooler and be cooled by the cooling medium (water or air). In order to improve the economic performance of the system, an internal heat exchanger may be provided to exchange the high pressure gas of the cooler in the internal heat exchanger with the low temperature and low pressure steam in the compressor return pipe, so that the high pressure gas of the cooler is discharged. Further cooling, while the low temperature and low pressure steam in the compressor return line is further superheated.

The performance of the refrigerant as a comparison of the characteristics of the working fluid characteristics of the compressor improvement measures strong irritating odor, lighter than air, can be smelled when the concentration reaches 0.0005%, a small leak can be found in time, and this concentration is much lower than NH The optimal speed of the combustion concentration compressor is inversely proportional to the square root of the molar mass. The compressor with the same cooling capacity has a small working volume, the size of the parts is small, and the cost is reduced. The air-cooled closed type for the small refrigeration system of the air conditioner and the refrigerator is developed. The compressor utilizes good ventilation performance and detection performance, and uses a safe and reliable shaft sealing device to improve the safety of the open compressor refrigeration system, develop a suitable lubricating oil, and solve the problem of insolubility with ordinary lubricating oil. Strictly control the amount of filling without color and taste, without any damage to the environment, excellent physical and chemical properties, no adverse effects on humans, low operating pressure, small volume per unit volume, large compressor displacement required The compression is relatively large, the volumetric efficiency of the compressor is reduced, the throttling loss is increased, and the exhaust gas temperature is too high, the heat loss is increased, the lubrication effect is deteriorated, and a suitable centrifugal compressor refrigeration system or a multi-stage compression refrigeration cycle is developed. In order to reduce the exhaust gas temperature and increase the greenhouse gas, in the case where the flammability and toxicity are severely restricted, there is a strong competitiveness. The critical temperature for subcritical circulation operation is low, and when the ambient temperature is slightly higher, the refrigeration capacity drops sharply. The power consumption is increased, and the economic performance is affected by the use of a transcritical refrigeration cycle. After the gas is liquefied, the characteristic of evaporation (vaporization) latent heat can be absorbed to achieve the purpose of refrigeration.

(a) System flow (b) Thermal cycle Ph diagram Transcritical cycle It can be clearly seen from the figure that under ideal conditions, the cooling capacity of the refrigeration system increases, and at the same time, the irreversible loss can be reduced, and the environment can be avoided. The direct effect of temperature on system performance. Therefore, it has good economy. Since the molecular weight of CO is small, according to Truun's law, the refrigeration capacity is large, and the unit volume cooling capacity at 0 ° C is 5 to 8 times higher than that of a general refrigerant. Therefore, for a compressor of the same size, the refrigeration system The efficiency can be greatly increased; for refrigeration systems of the same cooling load, the size of the compressor and system can be significantly reduced. The viscosity of CO is small, and the moving viscosity of CO-saturated liquid is only 23.8% at 0 °C; the flow resistance of the fluid is small, the heat transfer can be improved by increasing the flow rate, and the size of the flow channel can be reduced, and the weight of the whole machine can be reduced; The heat transfer performance is better than that of CFC, which can greatly improve the heat dissipation of the hermetic compressor.

In addition, the CO thermal performance is stable, the lubrication conditions are easily satisfied, and the material of the refrigeration system is not chemically corroded, which can improve the sealing performance of the open type compressor in the automobile air conditioning system and reduce leakage.

However, the adiabatic index of CO is higher, so the working pressure of CO's transcritical refrigeration cycle is much higher than that of the conventional subcritical two-phase refrigeration cycle, and the compression sealing of high-pressure ratio refrigeration system is higher. An effective sealing structure must be used. For reciprocating piston compressors, multiple piston rings can be used or high-precision automatic centering labyrinth seals can be used to reduce leakage.

For the design of the suction and exhaust valves of the reciprocating piston compressor, attention should be paid to the optimal matching of the gas pressure difference between the two sides of the valve and the spring force of the valve. The mathematical model of the movement of the valve plate is established, and the best is calculated by computer aided design. Valve spring force, select the size of the spring.

At the same time, the high pressure ratio increases the exhaust temperature of the compressor, and the compressor needs to be well cooled, but the high heat insulation index reduces the expansion loss caused by the clearance volume of the compressor, especially the reciprocating piston compressor. The amount of gas inhaled increases, the output gas volume increases, and the economic performance is improved.

Compressor performance analysis compares compressor type influences volumetric efficiency factors Power consumption improvement measures Reciprocating piston and cylinder wall clearance leakage and valve gas return, piston top clearance volume suction and exhaust valve resistance loss makes power consumption Increase the use of appropriate mixing ratio, select a well-functioning piston ring, use the characteristics of high adiabatic exponential expansion curve to reduce the clearance, leakage between the rotor-type sliding vane and the rotor, between the end caps, and between the chutes, the rotor and the end The unbalanced rotary moment of inertia of the leakage eccentric shaft between the cover and the cylinder, the resistance loss of the exhaust valve increases the strength of the eccentric shaft and the sliding piece, and the double-rotor technology is used to select the appropriate sealing material for the scroll-type scroll and static The friction loss between the axial and radial leakage bearings between the scrolls improves the machining accuracy and the quality of the machined surface, selects a reasonable fit clearance, and improves the assembly quality. By comparison, the CO refrigeration compressor is more than the CFC12 system compressor of the same specification. The weight can be reduced by 30% to 40%.

The CO has large refrigeration capacity, small viscosity and high design flow rate, which makes the volume flow of the system small, the overall size is small, and the weight is light. With the development of science and technology, the continuous optimization of compressor design, and the continuous improvement of processing and manufacturing processes, the development of energy-saving CO refrigeration system compressors will have broad prospects.

The energy-saving design of the heat exchanger is to improve the thermal efficiency of the refrigeration system and reduce the energy consumption, and the heat exchanger should have a sufficiently high heat transfer efficiency. The energy-saving approach should be considered from the aspects of enhancing heat transfer of heat exchange equipment, reducing power consumption of equipment, improving economy, reducing process complexity, and improving equipment reliability. Heat transfer enhancement has the following aspects: (1) reducing the heat exchange area, reducing the volume and weight of the equipment; (2) increasing the heat exchange capacity to improve the heat transfer capacity of the existing heat exchanger; (3) reducing the heat transfer agent transport Power consumption. Firstly, the heat transfer process of the heat exchange equipment is analyzed; then the heat resistance of the heat exchanger is analyzed to determine which part of the heat resistance is the largest; and the heat resistance of the heat resistance of the link is taken to make the heat transfer resistance of the side The smallest to achieve the effect of enhanced heat transfer. Firstly, we try to strengthen the heat transfer on the smaller side of the surface heat transfer, so that the side thermal resistance is reduced to be roughly equivalent to the other side, and at the same time, the heat exchange between the two sides can be enhanced to obtain a significant effect.

For the refrigeration system with NH as the working fluid, the heat exchange area of ​​the evaporator and the condenser can be appropriately reduced due to its excellent heat transfer performance, thereby reducing the cost and reducing the energy consumption. The heat exchanger of the refrigeration system with CO as the refrigerant, even if the working pressure of the CO cross-critical cycle is high, the thickness of the heat transfer tube wall is determined by the strength safety factor of 7 times the working pressure, and the tube is small due to the small volume flow of the system. The path is still small. The characteristic of the CO transcritical refrigeration cycle is that the high-pressure high-temperature refrigerant superheated steam discharged from the compressor only undergoes single-phase heat dissipation and cooling. For the heat exchanger, the heat transfer temperature difference of the heat exchanger is reduced by careful design, thereby reducing the heat exchange loss. The heat transferred by the heat exchanger Q=KFΔT is determined by three factors: the average temperature difference ΔT of the hot and cold fluid, the heat transfer coefficient K and the heat transfer area F. Under certain conditions, trying to increase any of these factors can increase the amount of heat transfer. Discussed separately below.

Increasing the average temperature difference between the hot and cold fluids should be as countercurrent or close to the reverse flow as possible when the inlet and outlet temperatures of the hot and cold fluids are the same. However, in the case of countercurrent arrangement, it should be considered that the maximum temperature of the cold and hot fluids is at the same end of the equipment, so that the wall temperature of the heat transfer surface of the end is higher, thus improving the material requirements, and should be based on safety and economy. After the economic and technical comparison, it was decided. A reasonable measure is to connect the heat transfer surfaces in series, such as the reverse flow in the low temperature section and the downstream flow in the high temperature section.

For multi-tube baffling, care should be taken to avoid the occurrence of temperature crossover or post-heat transfer. For example, when a single-shell double-tube heat exchanger adopts a first-flow backward flow arrangement, the final temperature of the cold fluid water in the pipe is close to the initial temperature t1 of the CO hot fluid outside the pipe, and may be higher than the final temperature t1 of the hot fluid. The heat utilization rate is high and temperature crossover does not occur. If the downstream flow is reversed and the temperature of the cold fluid outlet exceeds the CO hot fluid outlet temperature, the temperature crossover will occur in the subsequent sections, so that the effective average temperature is lowered and the heat utilization rate is lowered. It is also possible to increase the difference between the inlet and outlet temperatures of the cold side water and the hot side to increase the average temperature difference, that is, to minimize the inlet temperature of the cold side fluid water. However, the temperature of the cold fluid (water) is limited by the natural and economic conditions of the process. Similarly, the temperature of the hot fluid (CO) is also affected by factors such as the operating conditions of the refrigeration system, the reliability of the equipment, and the economics of operation.

Enlarging the heat exchange area by increasing the heat transfer area to enhance heat transfer is an effective way to increase the heat transfer capacity of the heat exchanger, but it may bring huge equipment, increase the metal consumption, or bring manufacturing, installation, operation, etc. Difficult problem. Therefore, a small diameter pipe can be used to increase the heat transfer area under a certain metal consumption. The smaller the pipe diameter, the larger the total surface area under a certain metal weight, and the smaller the pipe diameter, which is advantageous for increasing the velocity of the fluid and increasing the surface heat transfer coefficient, thereby increasing the heat exchange strength. However, the small pipe diameter increases the flow resistance of the fluid, and the power consumption of the system increases. Therefore, it should be considered comprehensively when selecting the pipe diameter. Expandable surfaces, such as ribbed tubes, bellows, plate-fin heat transfer surfaces, etc., increase the heat transfer area per unit volume due to the addition of ribs, and at the same time promote turbulent flow of fluid through the surface, thereby enabling heat transfer The intensity is further increased.

Increasing the heat transfer coefficient increases the total heat transfer coefficient of the heat exchanger to increase the heat transfer amount, which is also the main way to enhance heat transfer. A heat transfer process consists of several heat exchangers connected in series. The total thermal resistance of the heat transfer process is a superposition of the thermal resistance of each link. To effectively reduce the total thermal resistance and increase the total heat transfer coefficient, the main thermal resistance should be seized, and the thermal resistance of the link should be reduced to strengthen the surface heat transfer coefficient on the side of the maximum thermal resistance. Obvious effect. Generally, the metal wall has a large thermal conductivity and a small thermal resistance, and the wall thickness is also limited by the strength requirement, and cannot be arbitrarily reduced, and thus is not the main way to enhance heat transfer. The thermal resistance of convective heat transfer is the main part of the total thermal resistance of the heat transfer process, so it should be started from the enhanced convection heat transfer. The convective heat transfer intensity is related to many factors such as the physical properties of the fluid, the flow state, the geometry of the flow channel, the phase change of the fluid, and the surface condition of the heat transfer wall.

(1) The condenser does not undergo phase change in the condenser, only the gas is cooled. For the horizontal shell-and-tube water-cooled condenser, CO flows between the shell and the tube, and the steam is cooled outside the horizontal tube. The flow plate increases the number of shells to increase the disturbance of the CO flow process to enhance heat transfer; the CO cooling water flows in the tube, and the heat transfer tube is a copper light pipe. At this time, the surface heat transfer coefficient of CO vapor cooling and the heat transfer coefficient of the forced convection surface of the cooling water in the tube are compared, and the main thermal resistance of the heat exchange section is analyzed. If it is on the outside, low-ribbed tubes or various types of serrated high-efficiency heat exchange tubes can be used. The heat transfer coefficient of the heat exchange surface on the outer side is increased, and the heat transfer resistance is reduced. For example, the heat efficiency of the condenser is further increased, and the heat transfer area is reduced. The double-sided reinforcing tube can be used, and the outer surface of the tube is reinforced and cooled, and the inner side of the tube is used. The baffle structure for enhancing the heat exchange of the cooling water is such that the cooling water in the pipe is thinned or the boundary layer is destroyed, and the mixing of various parts of the water fluid is promoted to enhance the heat exchange.

In order to enhance the effect of heat transfer, to achieve the intended purpose. For air-cooled condensers, the gas-side thermal resistance outside the tube is the main thermal resistance of the total heat transfer process, and an extended surface, such as a winged surface, is used to enhance heat transfer. In the tube-plate heat exchanger, due to the influence of the tube, the flow of the fluid outside the tube along the surface of the plate fin has both progressive laminar and turbulent flow, and vortex flow and acceleration flow. Therefore, the heat exchange intensity of each part of the plate fin has a great difference. To strengthen the heat exchange strength of the plate fin, the fin can be perforated, and the fin is made into a bubbling type, a corrugated type, and a segmented cross. The zigzag type is used to disturb the airflow and destroy the development of the boundary layer, and at the same time, the airflow flowing through it can generate a vortex to enhance the heat exchange on the surface of the fin. When scaling, ashing or crystallization on the heat transfer surface, since the thermal conductivity of the dirt is small and the thermal resistance is large, it is often a major obstacle to heat transfer, so measures should be taken to reduce scaling and improve heat transfer during design operation. . Therefore, to improve the heat transfer coefficient mainly from the surface heat transfer coefficient on both sides and start, especially to obtain the surface heat transfer coefficient on the side of the heat exchanger on both sides of the tube to obtain a better heat transfer enhancement effect.

(2) In the evaporator O refrigeration system, the flasher can be used to replace the evaporator of the conventional refrigeration system. The water vapor generated in the flasher is compressed in multiple stages and then condensed into the condenser, and the condensed water is throttled into the flasher. The water/ice crystal mixture produced by the evaporation process is stored in the ice storage tank, and the cold amount required for the air conditioning system is taken out from the ice storage tank, and the cold water is also obtained to obtain the organic combination of refrigeration and ice storage.

The transcritical cycle is different from the traditional subcritical two-phase refrigeration cycle. The high-pressure refrigerant before the fluid flows through the pressure-reducing element is not a condensed liquid, and the influence of the ambient temperature on the performance of the system is not sensitive to the latter. After flowing through the pressure reducing element, the CO gas is cooled and partially liquefied, and the wet steam enters the evaporator to vaporize, and absorbs a large amount of heat of the surrounding medium, that is, outputs a cooling amount. The liquid in the evaporator is not completely vaporized, but is designed to have a small amount of liquid surplus, so that its outlet state is in the two-phase region, which can improve the heat transfer efficiency of the evaporator, and a reservoir is provided at the outlet of the evaporator, and It is integrated with it to prevent compressor blowdown, and the dedicated return line on the reservoir facilitates compressor return. The low-pressure saturated steam coming out of the reservoir enters the low-pressure side passage of the internal heat exchanger and becomes superheated steam entering the compressor. Due to the small viscosity of CO, it is easy to form turbulent flow. In the turbulent flow, since the velocity field and the temperature field of the fluid core region are relatively uniform, the flow resistance and convective heat transfer resistance mainly exist in the adherent laminar bottom layer. It can be seen that the measure taken for the turbulent heat transfer is to destroy the boundary layer, that is, to increase the disturbance in the boundary layer to reduce the thickness of the bottom layer of the laminar flow boundary layer. The strengthening method can increase the speed of the fluid, reduce the diameter of the pipe, shorten the length of the pipe and use the spiral pipe, or use a wall spoiler, such as triangular, giant, trapezoidal and other continuous rough ribs or grooves. Rough surface. They can be perpendicular to the direction of fluid flow, or spiraled, causing the boundary layer to detach when the fluid flows through the rough surface, and the fluid can be rotated in the case of a large helix angle, thereby enhancing the heat exchange intensity.

In addition, a spring wire ring can be inserted into the tube, and a transverse groove or a spiral groove of a certain pitch and depth can be crushed outside the round tube according to design requirements. At this time, convex transverse ribs or spiral ribs are formed on the inner wall of the tube. The groove of the outer wall of the pipe and the protrusion of the inner wall can simultaneously enhance the heat transfer effect on the fluid on both the inner and outer sides of the pipe. Although the shape of the above spoiler is very different, the heat transfer mechanism is similar. When the fluid flows through the spoiler, the flow breakaway zone is generated to form vortices of different strengths. These vortices change the flow of the fluid. The structure increases the turbulence of the fluid in the near wall region, thereby increasing the surface heat transfer coefficient between the fluid and the wall surface.

In the cooling liquid type dry evaporator and the cooling air type fin tube type or smooth tube type evaporator, the refrigerant flows in the tube, forced convection boiling occurs in the tube, and the enhanced heat transfer can also increase the vaporization core and increase the bubble. Out of frequency. New high-efficiency heat transfer tubes can be developed, artificially processing a large number of tiny pits on the surface, and these micropores become effective vaporization cores to enhance boiling heat transfer.

There are two main types of efficient heat transfer tubes. One type is a machined surface, that is, a large number of special-shaped micropores are machined on the heat exchange surface by mechanical processing, and there are fine grooves between the micropores to allow the micropores to communicate with each other. Studies have shown that these specially shaped micropores maintain a stable vaporization core with little superheat. Because in the boiling process, these micropores always maintain a certain amount of residual steam, and the fine grooves communicating with each other between the micropores play a mutual activation role. The other type is a liquid-filled evaporator with a cooling liquid type. The refrigerant is filled outside the tube, and the refrigerant is filled into a certain liquid level in the casing, and the heat of the refrigerant in the tube is absorbed between the tubes to be vaporized, so that the refrigerant is cooled. The agent is cooled. A layer of porous metal layer may be covered by physical and chemical methods, such as sintering, brazing, flame spraying, ionization deposition, etc. on the outer surface of the tube. The micropores of the sintered and sprayed surfaces have the shape of the machined surface recesses and serve the same function as the recesses. Experiments show that the heat transfer performance of the sintered tube is better than that of the surface machined tube, but the processing process is complicated.

For a cooling air finned tube evaporator or a smooth tube evaporator, when the outside air comes into contact with a wall below the saturation temperature, condensation or even frosting of the water vapor in the air may form a thermal resistance, which should be considered. Enhance heat transfer. For the air conditioner evaporator, the water vapor in the air outside the tube will condense and appear in the form of beads or membranes. The thickness of the water film stuck on the outer surface of the evaporator should be reduced as much as possible to allow the condensed liquid to be drained from the evaporator as soon as possible. , reducing the thermal resistance of the liquid film layer. It can increase the flow rate of air, disturb the condensate film, and select the appropriate tube bundle arrangement to enhance heat transfer.

The energy-saving way of step-down components with NH as a refrigerant is the fundamental way to solve the CFC replacement and protect the environment. However, the irreversible loss of CO cross-critical cycle increases, and its COP value is at least 20% lower than that of conventional circulation. Therefore, the characteristics of the cycle should be improved to conduct research and development of energy-saving products. The conventional refrigeration cycle uses a thermal expansion valve, an electronic expansion valve, and a capillary to depressurize, cool, and control the flow rate of the refrigerant. When the load of the evaporator changes, the thermal expansion valve can automatically adjust the flow rate of the refrigerant to control the superheat of the refrigerant at the outlet of the evaporator.

Type structure characteristics of the expander Research on the performance of the reciprocating piston is simple. The processing technology and reliability are easy to ensure that the resistance loss of the intake and exhaust valves is large. The performance is adjusted with the differential pressure, intake air temperature and intake air volume. The position of the exhaust valve is adjusted by the number of cylinders and the rotational speed, and the valve and the tie rod are rationally designed to reduce leakage and prevent liquid leakage.

The screw type does not have an unbalanced mass force, and can operate smoothly and without vibration, achieving high rotation speed.

It can better handle the gas-liquid two-phase flow, and the liquid expansion can improve the sealing gap between the rotors and reduce the fluid flow loss. The slide valve can realize the energy adjustment of 10%~100% stepless low loss, and the new profile Design, improve the strength and toughness of rotors, cylinders and other components, pressure resistance, improve sealing performance. Rotor-type structure is simple, easy to process, high efficiency, low cost, high reliability, large leakage, only intake valve, resistance loss Small to overcome the dead point, improve the seal, improve the strength of the eccentric shaft and the sliding piece, less vortex moving parts, less friction, less vibration, less noise, higher efficiency, large leakage between the static scroll, no air valve, resistance Loss of small force, static scroll imbalance force and internal torque, increase strength The electronic expansion valve uses the action of the thermistor to adjust the liquid supply of the evaporator. The function of the capillary depends on the length of the tube, the diameter of the tube, the heat exchange, the roundness of the capillary and the mounting position. Although these kinds of pressure reducing elements have cooled and pressed the refrigerant, they are all irreversible processes, and the irreversible loss increases as the pressure difference and the cooling load increase. Therefore, an expander can be used as a step-down element. For a CO cross-critical cycle, an expander is more feasible than a conventional working medium, and the expansion ratio is 2 to 4, which is 1/10 of the conventional working medium, and the proportion of the expansion work is proportional. Also large, recycling this part of the energy will greatly improve the economic efficiency of the refrigeration system, and has practical significance for energy conservation.

The corrosion of the surface of the sheet is more serious. To determine the corrosion resistance of the laser surfacing layer, the anodic polarization curve of the surfacing material is measured by 0.1 equivalent H medium, as shown in Fig. 7.

The passivation layer material has a small passivation current and a critical passivation current density, and has a wide passivation region range and a small passivation region current density. It shows that the material is easy to passivate, the corrosion rate is small, and it has good corrosion resistance in acidic medium. 4 Application and conclusions (1) After laser surfacing on the LWD200 horizontal decanter blade, the accumulated running surface is 1000h. The gloss is bright, the wear is less, and there is no peeling and cracking in the surfacing.

(2) The microstructure of the laser surfacing layer is refined and the columnar crystal also meets the requirements for use. Therefore, the technique is applied to the surface of the horizontal screw centrifuge for the wear-resisting layer surfacing and is easy to implement and has high practical value.

(3) Laser surfacing forms a hardened layer with a thickness of 1 mm on the surface layer, the hardness is increased by 2 times, the wear resistance of the simulation test is improved by 5 times, and the corrosion resistance is better in an acidic medium.

Nickel Base Corrosion Resistant Alloy

Nickel-based corrosion-resistant alloys generally refer to nickel-based metal materials with strong corrosion resistance. The corrosion-resistant alloys produced by Seonjip are mainly used in the fields of petrochemical, energy, marine and so on.

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