- Tytuł:
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Analiza niestabilności przemian fazowych czynników energetycznych. Część II - Badania eksperymentalne własne
Analysis of instability in phase transitions of energy media. Part II- Own experiments - Autorzy:
- Bohdal, T.
- Powiązania:
- https://bibliotekanauki.pl/articles/1819659.pdf
- Data publikacji:
- 2010
- Wydawca:
- Politechnika Koszalińska. Wydawnictwo Uczelniane
- Tematy:
-
czynnik energetyczny
przemiana fazowa
nośniki energii
energy factor
phase transition
energy carriers - Opis:
-
W praktyce eksploatacyjnej mają często miejsce przypadki zaburzeń typu jednostkowego spowodowane wystąpieniem gwałtownej zmiany parametrów układu [3]. Jako przyczyny tego typu zaburzeń można wymienić, między innymi, wystąpienie niedrożności zaworu lub kanału przepływowego, powstanie awarii układu zasilania parownika lub skraplacza, zamknięcie lub otwarcie zaworu odcinającego, gwałtowna zmiana obciążenia cieplnego, uszkodzenie wentylatora chłodnicy lub skraplacza chłodzonego powietrzem itd. Oprócz zaburzeń jednostkowych mogą występować w obiegu chłodniczym zaburzenia generowane w sposób periodyczny, na przykład wskutek okresowego działania elementów automatyki chłodniczej, czy dynamicznej zmiany parametrów zasilania parownika, wynikających ze zjawiska migotania termostatycznego zaworu rozprężnego [4]. W części pierwszej [6] opracowania przedstawiono wyniki analizy danych literaturowych w zakresie niestabilności przemian fazowych czynników energetycznych. W niniejszej pracy przedstawiono wyniki własnych badań eksperymentalnych procesu wrzenia proekologicznego czynnika chłodniczego podczas przepływu w kanałach rurowych w warunkach zaburzeń generowanych jednostkowo. 2010
Experimental tests were conducted of bubble boiling under the conditions of impulse disturbances. The chief goal of the examinations was the recognition, registration and description of those phenomena which occur in the unstable states of the system inside a coil pipe during boiling in the flow of the refrigerant. The experimental tests were carried out on two stages. On the first stage, the development was produced of the refrigerant's boiling in a coil pipe by opening the cut-off valve on the refrigerant's inlet to the coil pipe. The opening of the valve enabled the flow of the refrigerant through a thermostatic expansion valve (which feeds the coil pipe) and the commencement of boiling in the coil pipe. The boiling process commenced at the start of the coil pipe and displaced along its length until the desired vapour overheating was achieved on the outflow. The flow of the refrigerant in the coil pipe was preceded by the transition of the signal of an increased pressure in the form of a wave which was displacing with vp velocity. Next, together with the transition of the front of the boiling refrigerant (the boiling front) the temperature of the wall along the coil pipe decreased. Therefore, a transition of the temperature wave occurred but with VT velocity. On the second stage, a decay was produced of the boiling of the refrigerant in the coil pipe by means of closing of the cut-off valve on the inlet of the refrigerant to the coil pipe. During this process, a transition of the signal of a reduced pressure occurred as first, in the form of a wave with vp velocity in the opposite direction to the flow of the agent. At the same time, a withdrawal was observed of the "boiling area" as a result of the compressor constantly sucking off the vapour of the refrigerant. Thus, the length of the "overheating area" increased. The wall temperature increased alongside with the decay of boiling, which was manifested in the transition of the wave temperature with VT velocity. The research results demonstrated that the processes of the development and decay of boiling in a coil pipe possess similar wave natures, while some of their physical quantities are different. The wave nature of the transfer of impulse disturbances in a diphase medium with a boiling refrigerant is to be considered as a joint feature. In each case when an impulse disturbance was produced (when the valve was being opened or closed), a transition of the pressure wave occurred with vp velocity, and then the refrigerant flew with mass flux density (wp), which was manifested in a change of the temperature of the refrigerant and the channel wall. Also, the transition of the temperature wave with VT velocity was registered each time, as well. It was established on the basis of the research conducted that the velocity values of the pressure wave vp were different in the case of the development and decay of boiling (opening and closing of the cut-off valve). Thus, higher values of vp corresponded to the values of the pressure change signal L1p during the development of boiling in relation to the case of a decay of boiling (Fig. 5). The fundamental reason for this is different values of the void fraction qJ of the refrigerant in the coil pipe. As concerns the development of boiling, the signal of pressure change L1p displaced inside the coil pipe which was filled practically with the dry saturated vapour of the refrigerant (possibly with a small admixture of liquid drops: fog qJ ~ 0); at the same time, when boiling decayed, the signal of pressure change L1p was transferred in a diphase system with a variable liquid content on the way from the expansion valve to the end of the coil pipe (quality x 0.15-7-1). Data from the literature confirm a strong dependence of velocity vp from the void fraction qJ. In the cases under exami!lation, the transition velocities of the pressure wave were over two times as high for the development of boiling in comparison with the decay of boiling for the same values of pressure change L1p. The process conditions mentioned above exert an influence on the value of the substitute Reynold's number Re and on the course of the experimental dependence which describes the development and decay of boiling (3). - Źródło:
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Rocznik Ochrona Środowiska; 2010, Tom 12; 95-107
1506-218X - Pojawia się w:
- Rocznik Ochrona Środowiska
- Dostawca treści:
- Biblioteka Nauki
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