Kĩ thuật lạnh - Chapter 10: Refrigeration accessories

Common uses of shutoff valves include: - Isolating the liquid-line filter drier and suction filter to allow easier core (or unit) replacement - Isolating the compressor from the rest of the system to allow for repair or replacement - Isolating the charge within the condenser or a receiver to allow access to the rest of the system 12/2015 Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ 9

pdf96 trang | Chia sẻ: nguyenlam99 | Ngày: 21/01/2019 | Lượt xem: 66 | Lượt tải: 0download
Bạn đang xem trước 20 trang tài liệu Kĩ thuật lạnh - Chapter 10: Refrigeration accessories, để xem tài liệu hoàn chỉnh bạn click vào nút DOWNLOAD ở trên
CHAPTER 10: REFRIGERATION ACCESSORIES Lecturer: ME.Nguyễn Duy Tuệ 12/2015 Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ 1 OBJECTIVES I thi h t t d tn s c ap er, s u en can : - How to calculatate and know installation it i f f i t i icr er on or re r geran p p ng - Understand the function of some vessels and th i h i ht l l ido er accessor es suc as : s g g ass, so eno valve. 12/2015 2Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ REFERENCES [1] R f i t I d t i l H db k Th. e r geran n us r a an oo - e McGraw-Hill Companies. [2] T D f t h i l d t. rane, an oss ec n ca ocumen 12/2015 3Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ CONTENT REFRIGERANT PIPING VESSELS OTHER EQUIPMENTS 12/2015 4Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ REFRIGERANT PIPING 1. Design principles: M t l ffi i t li id fl t t- us supp y su c en qu owra e o evaporator - Pressure drop must be low - Have enough velocity to draw oil back to compressor - Don’t let refrigerant come back to compressor - Piping must be dry and clean 12/2015 5Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ REFRIGERANT PIPING 12/2015 6Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ REFRIGERANT PIPING 2. Suction pipe: - Undersizing the suction line reduces compressor capacity by forcing it to operate at a lower suction pressure to maintain the desired evaporator temperature. - Oversizing the suction line increases initial project costs and may result in insufficient refrigerant gas velocity to move oil from the evaporator to the compressor 12/2015 7Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ REFRIGERANT PIPING Pressure drop arcording to saturate temperature reduction by ASHRAE standard: Refrigerant velocity in suction pipe should be 7~12m/s. Refrigerant velocity should higher 3m/s for horizontal pipe and higher than 7m/s in vertical pipe 12/2015 8Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ REFRIGERANT PIPING - While operating, the suction line is filled with superheated refrigerant vapor and oil. The oil flows on the bottom of the pipe and is moved along by the refrigerant gas flowing above it. - When the system stops, the refrigerant may condense in the pipe depending on the ambient conditions. This may result in slugging if the liquid refrigerant is drawn into the compressor when the system restarts. 12/2015 9Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ REFRIGERANT PIPING - To promote good oil return, suction lines should be pitched 1/8 inch per foot (10.4 mm/m) in the direction of refrigerant flow. - Evaporator connections require special care because the evaporator has the potential to contain a large volume of condensed refrigerant during off cycles. - To minimize slugging of condensed refrigerant, the evaporators should be isolated from the suction line with an inverted trap as shown 12/2015 10Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ REFRIGERANT PIPING The trap should extend above the top of the evaporator before leading to the compressor. - With multiple evaporators, the suction piping should be designed so that the pressure drops are equal and the refrigerant and oil from one coil cannot flow into another coil. - Traps may be used at the bottom of risers to catch condensed refrigerant before it flows to the compressor. Intermediate traps are unnecessary in a properly sized riser as they contribute to pressure drop. 12/2015 11Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ REFRIGERANT PIPING - Usually with commercially produced air conditioning equipment, the compressors are “prepiped” to a common connection on the side of the unit. - Suction line filter driers are available to help clean the refrigerant before it enters the compressor. Because they represent a significant pressure drop -> be added in some circumstances such as after compressor burnout. 12/2015 12Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ REFRIGERANT PIPING Observe some diagrams: 12/2015 13Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ REFRIGERANT PIPING 12/2015 14Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ REFRIGERANT PIPING + Double suction riser: - In a double suction riser at full capacity, the refrigerant flow passes through both risers with enough velocity to move the oil. - At minimum capacity, oil in the riser flows backward and fills the trap at the bottom. Once the trap is full of oil, refrigerant flow through the large diameter riser is cut off and only refrigerant gas flows through the smaller diameter riser. - The sum of the two risers is sized for full capacity. The smaller diameter riser is sized for 12/2015 15 minimum capacity. Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ REFRIGERANT PIPING 12/2015 16Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ 12/2015 17Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ REFRIGERANT PIPING 3. Discharge pipe: - Undersizing discharge lines will reduce compressor capacity and increase compressor work. Over sizing discharge lines increases the initial cost of the project and may result in insufficient refrigerant gas velocity to carry oil back to the compressor. - Discharge lines should be sized for no more than 2 to 3°F (1.1 to 1.7°C) pressure loss. The actual pressure drop in PSI will depend upon the refrigerant. 12/2015 18Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ REFRIGERANT PIPING 12/2015 19Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ REFRIGERANT PIPING 12/2015 20Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ REFRIGERANT PIPING - Discharge lines carry both refrigerant vapor and oil. Since refrigerant may condense during the off cycle, the piping should be designed to avoid liquid refrigerant and oil from flowing back into the compressor. - Traps can be added to the bottom of risers to catch oil and condensed refrigerant during off cycles, before it flows backward into the compressor. 12/2015 21Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ REFRIGERANT PIPING - Discharge lines should be pitched 1/8 inch per foot (10.4 mm/m) in the direction of refrigerant flow towards the condenser - Whenever a condenser is located above the compressor, an inverted trap or check valve should be installed at the condenser inlet to prevent liquid refrigerant from flowing backwards into the compressor during off cycles. - With reciprocating compressors, a discharge muffler is installed in the discharge line to minimize pulsations (that cause vibration). Oil is easily 12/2015 22 trapped in a discharge muffler, so it should be placed in the horizontal or downflow portion of theChapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ REFRIGERANT PIPING - With some reciprocating compressors, a discharge muffler is installed in the discharge line to minimize pulsations (that cause vibration). Oil is easily trapped in a discharge muffler, so it should be placed in the horizontal or downflow portion of the piping, as close to the compressor as possible. 12/2015 23Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ REFRIGERANT PIPING Discharge Line Piping Details 12/2015 24Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ REFRIGERANT PIPING We could design double pipe same as suction pipe, if some problem occure in oil carrying 12/2015 25Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ REFRIGERANT PIPING 12/2015 26Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ REFRIGERANT PIPING 4. Liquid pipe: - Liquid lines connect the condenser to the evaporator and carry liquid refrigerant to the TX valve. - If the refrigerant in the liquid line flashes to a gas because the pressure drops too low or because of an increase in elevation, then the refrigeration system will operate poorly. Liquid sub-cooling is the only method that prevents refrigerant flashing to gas due to pressure drops in the line. - The actual line size should provide no more 12/2015 27 than a 2 to 3°F (1.1 to 1.7°C) pressure drop. Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ REFRIGERANT PIPING - The actual pressure drop in PSI (kPa) will depend on the refrigerant. - Oversizing liquid lines is discouraged because it will significantly increase the system refrigerantcharge. This, in turn, affects the oil charge. 12/2015 28Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ REFRIGERANT PIPING This figure shows the condenser below the evaporator. 12/2015 29Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ REFRIGERANT PIPING - As the liquid refrigerant is lifted from the condenser to the evaporator, the refrigerant pressure is lowered. Different refrigerants will have different pressure changes based on elevation. - Pressure drop in the liquid line is the sum of the friction loss, plus the weight of the liquid refrigerant column in the riser. 12/2015 30Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ REFRIGERANT PIPING 5. Refrigerant piping calculation : Step 1: Diameter calculation: 4.Vd Where: .vπ= - V=G:δ refrigerant volume flowrate(m3/s) - G : mass flowrate of refrigerant (kg/s) - v : refrigerant velocity (m/s) - d : diameter , (m) 12/2015 31Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ REFRIGERANT PIPING Step 2 : Pressure drop calculation : + Method 1 : Use Darcy – Weisbach fomular : 2 2L v v. . . . . ( ) 2 2 P Pa d λ δ ζ δΔ = + L : piping length, ( m ) λ : friction factor, (dimensionless) v : refrigerant velocity, (m/s) ρ : refrigerant density ,(kg/m3) ζ: pressure-drop coefficient for fitting 12/2015 32Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ REFRIGERANT PIPING The friction factor f is a function of the Reynolds number and the roughness of the pipe, and can be read from a Moody chart .The Reynolds number, Re, is a dimensionless group Th fl i l i if R 2100 d t b l t ife ow s am nar e< an ur u en Re>3000 12/2015 33Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ REFRIGERANT PIPING The other quantity needed to determine the friction factor from Moody chart is the relative roughness, ε/D. The roughness ε of the surfaces of two different materials used for refrigerant pipe and tubes are: 12/2015 34Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ REFRIGERANT PIPING Viscosities of several refrigerants in their saturated liquid and saturated vapor states. 12/2015 35Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ 12/2015 36Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ 12/2015 37Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ 12/2015 38Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ REFRIGERANT PIPING Example 1 : What is the pressure drop per m of tube length when 1.51 kg/s of R-22 vapor at -6.7°C flows through copper tubing that is 74.8 mm ID? 12/2015 39Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ REFRIGERANT PIPING + Solution : From the Moody chart, at the above values of Re and ε/D, the friction factor f is found to be 0.0108. 12/2015 40Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ REFRIGERANT PIPING Finally substitute applicable terms into the pressure drop equation 12/2015 41Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ REFRIGERANT PIPING Example 2 : Calcualte friction factor of steel pipe when carrying amonia liquid at 35oC and velocity at 0,51 m/s in 51mm ID ? 12/2015 42Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ REFRIGERANT PIPING + Solution : 12/2015 43Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ REFRIGERANT PIPING + Pressure drop coefficient for fitting, TL[1]: We have to add weight of refrigerant column: ΔPcđ =h.g.ρ ,(Pa) h : refrigerant column of riser (m), g : acceleration, (m/s2) : refrigerant density (kg/m3) 12/2015 44 ρ , Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ REFRIGERANT PIPING We could use this weight of column riser: + Note : we have to add pressure for downward pipe 12/2015 45Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ REFRIGERANT PIPING + Method 2 : Using equivalant length: Many designers find it convenient to express the pressure drop of fittings and open valves as equivalent length of straight pipe. This equivalent length, Ltđ, can then simply be added to the actual length of straight pipe to determine the total pressure drop. Set : Ltđ = (ζ.d)/λ ,(m) λ )(... 2 .).( 2 Paghv d llP td ρρ ++=Δ 12/2015 46Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ REFRIGERANT PIPING A typical value of the friction factor λ (or f) for refrigeration applications is approximately 0.02. 12/2015 47Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ VESSELS 1. Oil seperator : - Oil separators remove oil from the compressor's discharge gas, temporarily store the oil, and then return it to the compressor's crankcase. Oil separators are located close to the compressor in the discharge line - Oil separators are essential on low or ultra-low temperature refrigeration systems and on large air conditioning systems up to 150 tons. - Oil separators can also act as discharge mufflers to quiet compressor pulsation and vibration 12/2015 48 noises. Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ VESSELS + Oil separator principles: - Reduce mixture of oil-vapour immediately - Change mixture’s direction by internal baffle - Use the fine mesh to filt oil -> Oil droplets to form and drop to the bottom of the separator. When the level of oil gets high enough to raise a float, an oil return needle is opened and the oil is returned to the compressor crankcase through a small return line connected to the compressor crankcase. 12/2015 49Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ VESSELS The pressure difference between the high and low sides of the refrigeration or air conditioning system is the driving force for the oil to travel from the oil separator to the crankcase. 12/2015 50Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ VESSELS + Oil separator structure : 12/2015 51Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ VESSELS 2. High pressure receiver : Sized to accept the full pumpdown volume of refrigerant in the entire system at 80% full. On large systems, it is sized to supply ½ hour of liquid supply buffer to the low side. There are two kinds of high pressure receiver : vertical or horizontal vessel 12/2015 52Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ VESSELS 3. Low pressure receiver : This vessel is one that performs both the role of liquid/vapor separation and liquid storage at low pressure. It contain low temperature liquid after coming out expansion valve to supply to evaporator equally 12/2015 53Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ VESSELS Liquid level in low pressure receiver : 12/2015 54Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ VESSELS - The surge volume serves the purpose of accommodating liquid that might be forced out of evaporators during defrost. - The reason for needing this ballast volume is that during startup or resumption of operation of one or more evaporators, the pump may withdraw refrigerant from the vessel at a greater rate than is supplied at that moment by the combination of the controlled liquid supply and from the return from the liquid/vapor line 12/2015 55Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ VESSELS + Computing the ballast volume: The ballast volume is provided to permit the pumps to draw liquid from the low-pressure receiver for a short interval to bring the liquid content of evaporators up to the steady-state amount following a shutdown. Typically, a five-minute time period is assumed adequate for this purpose, so the ballast volume is the design pump flow rate in volume flow per minute multiplied by 5. 12/2015 56Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ VESSELS + Computing the surge volume: Two major contributors to momentary excess flow into the low-pressure receiver are: - flooding of abnormal rates of liquid out of the evaporator due to defrost or to sudden increases of refrigeration load - the liquid in the liquid/vapor return line that rains back to the low-pressure receiver in the event of pump or power failures. 12/2015 57Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ VESSELS The fraction of liquid in the coil during operation depends on whether the coil is top or bottom fed. For a top-fed coil the percentage of liquid is often assumed to be about 30%. For bottom-fed coils the percentage is sometimes chosen as high as 80%. 12/2015 58Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ VESSELS 4. Suction line trap or Accumlator: - The purpose of the suction line accumulator is to protect the compressor against an accidental return of refrigerant in its liquid phase, by the suction pipes, which could cause a “liquid hammer” with a risk of mechanical destruction of the compressor. - By adding a heat exchanger in the suction accumulator, this improves the subcooling, reduces the risks of the remaining refrigerant in liquid and it improves substantially the efficiency of the 12/2015 59 installation. Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ VESSELS + Accumulator structure : performance priciple is same as oil separator 12/2015 60Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ VESSELS + Accumulator position : 12/2015 61Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ VESSELS 5. Interstage desuperheater ( flash tank or subcooler ): The purpose of the vessel is to desuperheat discharge vapor from the low-stage compressor by bubbling it through the liquid in the vessel or subcooling liquid with a heat exchanger 12/2015 62Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ VESSELS + Flash tank with and without subcooling : 12/2015 63Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ VESSELS +A flash-tank/desuperheater with (a) desuperheating by bubbling vapor through liquid and (b) desuperheating by spraying liquid into vapor. 12/2015 64Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ VESSELS 5. Thermosyphon receiver : - A small but important vessel is the thermosyphon receiver which is an integral part of that type of oil cooling concept for screw compressors. - The key requirement is that it provides a reserve for five minutes of flow to the oil cooler if the supply of liquid from the condenser is interrupted. 12/2015 65Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ VESSELS 5. Thermosyphon receiver : 12/2015 66Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ VESSELS - Some designers and contractors combine the thermosyphon receiver and the system receiver as shown in this figure. 12/2015 67Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ VESSELS 6. Oil pot : - A small vessel frequently installed beneath the low-pressure receiver and other larger vessels is an oil pot whose purpose is to accumulate oil to facilitate periodic draining. - It’s used for Amonia which is immiscible with oil - Since the oil pot is usually classified as a vessel, it must be protected by relief valves. 12/2015 68Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ VESSELS + Oil pot structure: 1 45 3 2 6 1. Sight glass, 2. Pressure gauge, 3. Relief valve, 4. Connected to suction pipe, 5. From other vessels 12/2015 69Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ VESSELS 7 Liquid-vapour suction heat exchanger :. Objectives of that : - Increasing the system performance - Subcooling liquid refrigerant to prevent flash gas formation at inlets to expansion devices - Fully evaporating any residual liquid that may remain in the liquid-suction prior to reaching the compressor 12/2015 70Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ VESSELS 12/2015 71Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ VESSELS 12/2015 72Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ VESSELS 8. Purging system : Air in the condenser will raise head pressure, mainly due to its insulating properties. Air molecules in the gas from the compressor will be blown to the quiet end of the condenser. This air accumulates on the heat transfer surfaces. 12/2015 73Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ VESSELS + How can air come in ? - By leaking through condenser seals and valve packings when suction pressure is below atmospheric conditions - When the system is open for repairs, coil cleaning, equipment additions - When charging by refrigerant trucks; adding oil - By the breakdown of refrigerant or lubricating oil; or from impurities in the refrigerant. 12/2015 74Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ VESSELS To determine the amount of air in a refrigeration system, consider these symptoms: - High discharge temperatures; - High condensing (head) pressures; - High condensing subcooling; - Slightly vibration of high pressure gauge - High amp draws. + Principle of air purging equipment : - We condense refrigerant in mixture of air+refrigerant, because refrigerant have higher boiling temperature than air 12/2015 75Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ VESSELS + Air purging structure: 12/2015 76Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ OTHER EQUIPMENTS 1. Solenoid valve : A solenoid valve is used to stop the flow of refrigerant within the system. These valves are magnetically operated, and an electric winding controls the opening and closing of the valve. The valve is typically a normally-closed type of valve so that it is closed when it is deenergized. 12/2015 77Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ OTHER EQUIPMENTS Solenoid valve is used to control the flow of multi sections evaporator. In this application, a valve is installed in the liquid line, upstream of the expansion valve for each individually controlled section of the evaporator coil. 12/2015 78Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ OTHER EQUIPMENTS Another common use of a solenoid valve is to enable system pump-down and prevent the refrigerant from migrating through the system when the compressor is shut off. 12/2015 79Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ OTHER EQUIPMENTS 2. Liquid line filter drier : - It is installed upstream of the solenoid valve and the expansion valve. - It prevents moisture (water) and foreign matter, introduced during the installation process, from entering the expansion valve and the solenoid valve. - Realize, however, that there is no substitute for cleanliness during system installation. 12/2015 80Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ OTHER EQUIPMENTS - When water is mixed with refrigerant and oil, and heat is added by the compressor, acids are formed that can damage the valves or compressor. Additionally, certain foreign materials such as copper and brass particles can act as a catalyst in chemical reactions that result in the formation of acids. - These acids can corrode system components and cause the oil to sludge. - The filter drier should be installed close to the solenoid valve to provide the most protection for the 12/2015 81 solenoid and expansion valves. Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ OTHER EQUIPMENTS + Position of filter : 12/2015 82Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ OTHER EQUIPMENTS + Structure of filter: - A typical liquid-line filter drier includes a molded, porous core. The core has a high affinity for moisture and removes foreign matter from the refrigerant. - The two common types of filter driers are replaceable core and sealed. The replaceable core type allows the core to be easily replaced. The sealed type is completely closed, reducing the chances of refrigerant leaks. 12/2015 83Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ OTHER EQUIPMENTS + Structure of filter: 12/2015 84Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ OTHER EQUIPMENTS 3. Moister – indicator sight glass: - It is installed in the liquid line, upstream of the expansion valve, and permits the operator to observe the condition of the refrigerant prior to entering the expansion valve. - The value of the sight glass is in its moisture indication ability - The sight glass should not be used to determine system refrigerant charge or subcooling. Actual temperature and pressure measurements are required to determine proper charge and 12/2015 85 subcooling. Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ OTHER EQUIPMENTS + Installation position : With the sight glass installed directly ahead of the expansion valve, it can also be used to detect the presence of bubbles in the liquid line. This would indicate that some of the liquid refrigerant has flashed into vapor upstream of the expansion valve. 12/2015 86Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ OTHER EQUIPMENTS 4. Suction line filter : Similar to the liquid-line filter drier, the suction line filter performs the task of removing foreign matter from the refrigeration system. It is installed in the suction line, just upstream of the compressor. 12/2015 87Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ OTHER EQUIPMENTS - The suction filter contains filter media to remove copper filings, flux, dirt, and other foreign matter that may have been introduced during the installation process or as the result of a compressor failure. - It protects the compressor parts from the abrasive action that could result if these materials enter the compressor. Dirt can obstruct oil passages, robbing the compressor bearings of lubrication. 12/2015 88Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ OTHER EQUIPMENTS The two common types of suction line filters are replaceable core and sealed. The replaceable core type allows the core to be easily replaced. The sealed type is completely closed, reducing the chances of refrigerant leaks. 12/2015 89Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ OTHER EQUIPMENTS - Replaceable core suction filters are commonly installed after a compressor failure has occurred. - The core is replaced after the foreign matter or acid has been removed from the system. Additionally, suction filters should be installed in all field-assembled systems. 12/2015 90Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ OTHER EQUIPMENTS 5. Hot gas muffler: - The purpose of the hot gas muffler is to smooth out the pulsations associated with the refrigerant vapor being discharged from a reciprocating compressor, reducing noise and vibration. - The pressure of the refrigerant vapor leaving a reciprocating compressor fluctuates rapidly because of the manner in which it is compressed by the reciprocating pistons 12/2015 91Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ OTHER EQUIPMENTS - The muffler contains a perforated tube inside a shell. - The pressure peaks cause some of the refrigerant vapor to pass from the perforated tube into the muffler shell. - This shell is divided into chambers that allow it to absorb these peaks. - In essence (in principle), the muffler shaves off the peaks of these pulsations and fills in the valleys, reducing the pulsating characteristic in the discharge line. 12/2015 92Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ OTHER EQUIPMENTS When used, the hot gas muffler should be located in the discharge line, as close to the reciprocating compressor discharge as possible. This minimizes the sound emission from the unmuffled section of discharge line. 12/2015 93Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ OTHER EQUIPMENTS 6. Shut off valve: Shutoff valves are used to isolate one part of the refrigeration system from the rest. Additionally, they can be used to trap the refrigerant charge in one component of the system, the condenser for example, to permit service or repair to another part of the system. 12/2015 94Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ OTHER EQUIPMENTS + Common uses of shutoff valves include: - Isolating the liquid-line filter drier and suction filter to allow easier core (or unit) replacement - Isolating the compressor from the rest of the system to allow for repair or replacement - Isolating the charge within the condenser or a receiver to allow access to the rest of the system 12/2015 95Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ OTHER EQUIPMENTS 12/2015 96Chapter 10: Refrigeration Accessories ThS.Nguyễn Duy Tuệ

Các file đính kèm theo tài liệu này:

  • pdfky_thuat_lanh_chuong_10_english_2727.pdf