制冷空调系统热气旁通方式对比.ppt

* With discharge valve temperature of 310 to 325 F oil vaporizes or thins causing rings and cylinder walls to wear . At 350 F mineral oil will breakdown (carbonize). * * * * * * * * * * * The Venturi-Flo consists of a converging and diverging section. The diverging section following the throat is used to reduce the high throat velocity of the refrigerant, converting the velocity energy of the refrigerant back to pressure energy. The outlet pressure is less than the inlet pressure by an amount equal to the wall frictional losses. Rule of Thumb for Static Regain Increase velocity decrease static pressure Decrease velocity increase static pressure The Orifice type consists of a straight approach to an orifice plate which is a concentric hole in a metal plate. This distributor depends on the high pressure drop across the orifice and resulting turbulence to provide distribution. The approaching refrigerant streamline nearest the pipe wall turns in rather abruptly at the plate toward the orifice. This parallel flow continues past the edge of the orifice and is swept along through the orifice by the center mass of the refrigerant flow. The refrigerant flow continues through the orifice with the minimum jet area forming downstream of the orifice plate. The uncontrolled expansion in the large downstream section causes a turbulent pattern to be set up between the minimum jet area, orifice plate and the walls. Thus with the orifice plate the velocity energy is not reconverted to pressure energy, but rather is dissipated in violent turbulence in the downstream section. * From the pervious analysis, it can be seen that the Venturi-Flo distributor has two basic advantages over the orifice plate or pressure drop type. - First there is the pressure recovery feature. -Secondly, the contour flow pattern channels the flow to the tubes which means even distribution; whereas, the orifice plate type depends upon p