This invention relates to a refrigeration apparatus for transcritical operation with screw compressors featuring geometrically controlled inlet and outlet ports operating at least on three pressure levels. The pressure levels comprise the suction pressure prevailing on the compressor suction side and being close to the pressure in the evaporator, the intermediate pressure prevailing at the economizer port, and the discharge pressure acting on the compressor discharge side and being close to the pressure in a gas cooler. The pertinent sides of the compressor are also designated as low-pressure side, intake side or suction side, and as high-pressure side or discharge side respectively. The pressure on the high-pressure side is higher than the pressure at the critical point of the refrigerant. Therefore, this process is designated as transcritical or overcritical refrigeration process. The economizer port is arranged between suction- and discharge side of the compressor. At the economizer port, the inlet process to the working cavity starts when there is no more flow connection of this working cavity to the compressor suction side. In this phase, the geometric volume of the working cavity considered has reached its maximum. Depending on the wrap angle of the rotor profile of the male rotor, number of lobes of both rotors, the geometric volume of the working cavity considered can be constant (transfer phase) or can decrease due to rotation of rotors.
The invention relates to a refrigeration apparatus featuring a heat exchanger, a so-called aftercooler, arranged in or at the low-pressure liquid separator and communicating with the liquid separator, and in this aftercooler the refrigerant—the working fluid—being under discharge pressure is subcooled prior to its expansion nearly to evaporation temperature, thus changing from the vaporous phase to the liquid phase, before it is expanded into the evaporators at the throttling device of the refrigeration apparatus.
The pressure upstream of this throttling device is kept constant by opening or closing it more or less respectively enabling the compressor to operate at constant discharge pressure. The refrigerating capacity of the refrigeration apparatus changes depending on the temperature to which the refrigerant was cooled down in the gas cooler. It will be reduced as a result of higher outlet temperatures at the gas cooler, because at higher gas cooler outlet temperatures more working fluid will evaporate in the low-pressure liquid separator for cooling-down the working fluid in the aftercooler prior to expansion than at lower gas cooler outlet temperatures. Therefore, the efficiency of the refrigeration apparatus will decrease with increasing temperature at the gas cooler.
The object of the invention is to improve the process and to increase the efficiency of the refrigeration apparatus.
According to the invention the refrigeration apparatus for transcritical operation comprises in addition to the components gas cooler, aftercooler, evaporator with low-pressure liquid separator, compressor, first controllable throttling device and interconnecting piping between the mentioned components a second controllable throttling device and an intercooler that comprises two flow paths separated by heat-exchanging surfaces, wherein a first flow path inlet of the intercooler is connected to the gas cooler outlet, a first flow path outlet of the intercooler is connected to the aftercooler inlet, a second flow pass inlet of the intercooler is connected to the outlet of the second throttling device and a second flow pass outlet of the intercooler is connected to the economizer port of the compressor, and the second throttling device inlet is connected to the piping either upstream or downstream of the aftercooler and the second throttling device outlet is connected to the second flow pass inlet of the intercooler.
According to the invention, a part of the refrigerant is taken from the main flow either upstream or downstream of the aftercooler and led via the second controllable throttling device, where the refrigerant pressure decreases from discharge pressure to intermediate pressure and the temperature drops, to the second flow path of the intercooler to cool down the working fluid in the first flow path of the intercooler. In this way, the refrigerant being under discharge pressure is cooled down on one side of the heat-exchanging surfaces of the intercooler, while the refrigerant on the other side of the heat-exchanging surfaces of the intercooler evaporates being under intermediate pressure. The refrigerant evaporated is led to the economizer port of the compressor.
Due to this operation of the intercooler, the aftercooler is unloaded. As a result of the unloading, less amount of vapor is created in the aftercooler on the side of the low-pressure liquid separator. Thus, with the same compressor size, more vapor can be taken from the evaporator. Therefore, the refrigerating capacity of the refrigeration apparatus and its efficiency will increase.
In the following, the invention is explained in detail by an example of embodiment.
The accompanying drawings show in:
The refrigeration apparatus for transcritical operation according to
In the Pressure-Enthalpy diagram according to
Due to cooling the refrigerant vapor in intercooler 24, there will be created less vapor in aftercooler 27 on the side of low-pressure liquid separator 25. Thus, with the same compressor size, more vapor can be taken from the evaporator. Therefore, the refrigerating capacity of the refrigeration apparatus and its efficiency will increase.
The refrigeration apparatus for transcritical operation according to
In the Pressure-Enthalpy diagram according to
Number | Date | Country | Kind |
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DE102006035784.1 | Aug 2006 | DE | national |