制冷技术(英文版)Ch13-090604.doc

Chapter 13. Refrigerant Flow Control13-1) Hand Expansion Valves 手动膨胀阀 Fig.13-1, Hand expansion valve13-2) Capillary tube 毛细管EvaporatorSuction to compressorGasStrainerCapillary tube Inlet from a condenser or a receiver of condenserFig.13-2, Capillary tubeTable 13-1a, Table for refrigerant R134a to select the size of the capillary tube (LBP)用于低温-30 0CQMCapillary tube internal diameter (mm) & Evaporating temperature (C)0.6 mm11.21.5-30C-23.3-30-23.3-30-23.3-30-23.3-30-23.3-30-23.3-30-23.3Capillary tube length (m)931.802.47m2.601052.031.952.061162.251.581.671282.481.301.383.003.171402.7022.661512.932.142.261743.381.611.703.323.511983.831.251.322.582.722214.282.062.173.904.122444.721.681.773.183.362675.181.391.472.652.792915.663.944.193496.761.541.632.722.894077.881.191.982.104659.011.604.114.3452310.141.263.223.4058211.261.012.592.7364012.392.132.2469813.511.781.8781415.771.364.384.6193018.021.033.303.49104720.272.302.42116322.522.062.18Here, the cooling capacity tested under ASHRAE (LBP：Low Back Pressure, freezer application;) condition corresponding to the indicated mass flow rate M (liquid sub-cooled down to 32, return gas superheated up to 32,).Table 13-1b, Table for refrigerant R134a to select the size of the capillary tube (HMBP)用于空调QMCapillary tube internal diameter (mm) & Evaporating temperature (C)2-5.0(C)7.2-5.07.2-5.07.2-5.07.2-5.07.2-5.07.2-5.07.2-5.07.2Capillary tube length (m)1162.324.113.861402.792.882.711604.304.041863.721.621.533.323.122214.421.141.082.362.234.434.162334.652.132.003.993.762795.581.471.402.782.634.884.593266.511.061.022.041.933.603.403727.441.551.472.752.604198.372.064659.301.741.664.674.4258211.621.091.052.992.8369813.952.051.9581416.271.471.425.004.7393018.601.111.083.843.64104720.923.002.86127925.571.981.903.943.74151230.221.371.332.792.66174534.872.051.985.014.76197739.521.551.513.903.72221083.082.95290858.111.661.63348969.741.091.10Fig.13-3, Balance points with a reciprocating compressor and capillary tube 4当毛细管选定后，系统的工况（平衡点）就确定了Fig.13-4, Unbalanced conditions because of starving or flooding of the evaporator 4当毛细管装上后，系统的非平衡工况13-3) Thermostatic expansion Valves- Superheat Control 1) Internally thermostatic expansion valves5, 3.5bar5,3.5bar5,3.5bar15,3.5bar15,5bar (1.5 bar)Adjusting screwSpringStrainerNeedle and seatBellows or diaphragm Inlet from receiverSuction to compressor Refrigerant 134a Fig.13-5, The principle of internal equalizer thermostatic expansion valve2) Externally thermostatic expansion valves 5,3.5bar 0,3bar 10,3bar 10,4.2bar 1.2barAdjusting screwSpringStrainerNeedle and seatBellows or diaphragm2,3.2bar Inlet from receiverSuction to compressorRefrigerant 134aFig.13-6, The principle of external equalizer thermostatic expansion valve13-4) Automatic Expansion Valves - Evaporator pressure ControlBellows or diaphragmNeedle and seatStrainerInlet from receiverSpringOutSpring pressureEvaporator pressure Adjusting screw Fig.13-7, Automatic Expansion Valve13-5) Electronic Expansion ValvesThe electronic expansion valve is used for frequency conversion air condition to automatically control refrigerant flow rate , thus to enable air conditioning system to work in the optimized conditions and realize fast freezing , precision temperature controlling and power saving. Three types of electronic expansion valves are presently available, namely, step motor valves, pulse-width-modulated valves, and analog valves.1) Step Motor valvesFig.13-9, Step motor valve2) Pulse-width-modulated ValvesThe control of flow rate is achieved from changing the time ratio of on to off.Fig.13-10, Pulse-width-modulated Valve3) Analog valvesKeep the valve pin (or plunger) at various intermediate positions by varying the strength of the coils magnetic field Fig.13-11, Analog valve4) Control of the electronic expansion valveFig.13-12, The Principle of the Electronic Expansion ValvesFig 13-13, A refrigeration system for a cool storeFig 13-14, The control of temperature and pressure in a cool store refrigeration systemREFERENCES1, Roy J. Dossat, Principles of Refrigeration, 2nd Edition, John Wiley & Sons, New York, USA, 19782, Capillary tube of copper and copper alloys, GB/T 15313, Appliances Components Companies，/java/X?cgi=tecnica.InformacionTecnicaArticulo2.pattern&seccion=informaciontecnica#TablasGraficos4, Stoecker W.F., Jones J.W., Refrigeration and air conditioning, 2nd Edition, McGraw-Hill Book Company, New York, USA.,19825, HE F.M.，Comparison between Electronic Expansion Valve and Thermostatic Expansion Valve，World Shipping，2004, 27(5)44-456, Lazzarin R., Noro M., Experimental comparison of electronic and thermostatic expansion valves performances in an air conditioning plant, International journal of refrigeration,2008, 31(113-118)7, He X.D., Liu S., Asada H.H., Modeling of vapor compression cycles for multivariable feedback control of HVAC systems, ASME J. Dynamic systems, measurement, and control ,1997,119 (2) 183-1918, Aprea C., Mastrullo R., Experimental evaluation of electronic and thermostatic expansion valves performances using R22 and R407C, Appl. Therm. Eng. 2002, 22 (2) 205-2189, Li X.Q., Chen J.P., Chen Z.J., et al., A new method for controlling refrigerant flow in automobile air conditioning, Appl. Therm. Eng. 2004,24 (7) 1073-108510, Chen W., Zhou X.X., Deng S.M., Development of control method and dynamic model for multi-evaporator air conditioners, Energy Conversion and Management, 2005, 46 (3) 451-46511, Choi J.M.,