1、PDF外文：http:/ The effect of oil in refrigeration: Current research issuesand critical review of thermodynamic aspects Mohammed Youbi-Idrissia,1, Jocelyn Bonjourb, aCemagref, Refrigerating Processes Research Unit, Parc de Tourvoie, BP 44, 92163 Antony Cedex, France bCETHIL UMR5008 C
2、NRS INSA-Lyon Univ. Lyon1, Ba t. Sadi Carnot, 9 rue de la Physique, INSA-Lyon, F-69621 Villeurbanne Cedex, Franc A lubrication agent is necessary in almost all the refrigeration vapour compression systems,particularly for the correct operation of the compressor. However, a certain portion of t
3、he oilalways circulates with the refrigerant through the cycle. This circulation is at the origin ofa deviation from the theoretical behaviour (i.e. based on pure refrigerant) of the components.This article aims at reviewing the oil-related researches in the field of refrigeration. Previousreviews i
4、n the literature focused on the thermo-hydraulic consequences of the presence of oil； we will analyse here its thermodynamical consequences. In a first part, a brief literature review will give an overview of current scientific and technological issues concerning the impact of oil on components or o
5、n whole refrigeration systems. The typical approaches and methods employed to address this problem will be described. These researches require sound tools for the evaluation of thermodynamic properties of refrigerantoil mixtures.The second part of this article is hence a critical review of these too
6、ls, and focuses particularly on liquidvapour equilibrium, absorptiondiffusion, and mixture enthalpy calculation. a 2007 Elsevier Ltd and IIR. All rights reserved. 1. Introduction In the refrigeration and air-conditioning vapour compression systems, oil is necessary for a correct working of the compr
7、essor.Its main role is indeed to ensure the existence of a thin oil film allowing the lubrication of the mechanical movingelements (pistons, connecting rod/crank, valves, .), i.e. toprotect them against wear. The lubricant simultaneously ensures several secondary roles among which serving as a tight
8、ness element, limiting the noise, or helping the evacuationof chemical impurities or deposits that may be present in the system. Lastly, in many situations, the oil is also used as a heat transfer medium for cooling the compressor. All these favourable actions of oil show that oil is definitely usef
9、ul in refrigeration units. However, the presence of a lubricant is also accompanied by several drawbacks, among which the most often cited is a reduction in heat transfer coefficients in the two-phase heat exchangers (condenser and evaporator).The presence of oil also induces changes in the flow con
10、figurations,increases pressure drops, modifies the thermodynamic equilibrium and thermodynamic properties of the refrigerant (liquidvapour equilibrium, enthalpy, viscosity,surface tension, etc.). The question of the impact of oil in refrigeration is hence still of uttermost importance. It was alsora
11、ised in the context of the development of new environment friendly refrigerants (or rediscovery of old refrigerants) over the last two decades.For all these reasons, many oil-related researches in the field of refrigeration have been conducted over the last years；we propose to analyse them in this a
12、rticle through a critical review. In these works, several themes can be distinguished and are classified here: 1. Technology-oriented researches: these works often deal with oil injection methods, lubrication efficiency or quality in compressors, sensors and principles for measurement of the mixing
13、ratio of oil to refrigerant in the mixture, . 2. Measurement/modelling of thermophysical properties of oil or refrigerantoil mixtures (viscosity, density, specific heat, .). 3. Heat transfer and pressure drops of refrigerantoil mixtures during boiling and condensation. 4. Measurement/modelling of th
14、ermodynamical properties of oil or refrigerantoil mixtures (including solubility, miscibility and enthalpy). 5. Thermodynamical analysis of the impact of oil on a whole system, or on a component. 6. Miscellaneous other studies motivated by the presence of oil in refrigeration (e.g. ice slurry with o
15、il as carrier fluid,cleansing of oil in refrigerating equipment, etc.). Most of the Energy and Thermal Science published materials deal with classes 2, 3, 4 and 5. Indeed, researches belonging to the technology class (class 1) are usually rather linked to Mechanical Engineering (e.g. tribology), to
16、Industrial Engineering,or to Automation Engineering. These works are hence published in journals specialized in these fields, rather than in journals linked to Energy and Thermal Science. They could obviously be the subject of a review, but it would be more relevant to publish it in the leading jour
17、nals of these domains. On the contrary, the articles belonging to class 6 (miscellaneous) are too dispersed to allow a critical literature review. The questions of thermophysical properties (class 2) andheat transfer/pressure drops in two-phase flows (class 3) are the subject of a very large number
18、of publications. A two-part review article was published in Shen and Groll (2005a,b). These themes will hence not be studied here, and we will focus on classes 4 and 5, which are believed to form a consistent group in that sense that they directly rely on thermodynamics.Mermond et al. (1999) perform
19、ed a review of several correlations allowing the calculation of oil properties and compared a fewmethods used to determine the properties of refrigerantoil mixtures. Conde (1996) focused on some methods aiming at evaluating the thermophysical properties of oils and their solutions in refrigerants. A
20、 part of the present article can be viewed as an updated extension of their works. This article is divided into two main parts. Section 2 is dedicated to the thermodynamical impact of oil on the behaviour of components or whole refrigeration systems. Its goal is to give an overview of current techno
21、logical or scientific issues through a brief analysis of a choice of some typical recent publications. This will show that these research works require sound tools for the evaluation of thermodynamic properties of refrigerantoilmixtures. Section 3 consists in a critical reviewof these tools,and focu
22、ses particularly on liquidvapour equilibrium, dynamic effects (absorptiondiffusion), andmixture enthalpy calculation. 2. Thermodynamical analysis of the impact of oil in refrigeration As exposed in Section 1, we will not discuss here the effect of oil on heat transfer in the heat exchangers or on th
23、e pressure drops, but only the thermodynamic effects. The presence of oil influences the behaviour of almost each component of refrigeration units. It is, however, usually admitted that the condenser is the least sensitive component to the presence of a lubricant, and the literature is consequently
24、scarce on that subject, while the compressor, the evaporator and the pipes or capillary are the subject of a larger number of publications, some of which are analysed in the next sections. 2.1. Impact on components 2.1.1. Compressor A major effect of the presence of a lubricant in the compressor is
25、the foaming phenomenon: the foam is due to the oil refrigerant interaction because of the blade rotation and/or the vapour blow. For instance, Yanagisawa et al. (1991) experimentally investigated the foaming occurring in a hermetic casing that simulates a hermetic rotary compressor. They noticed tha
26、t the foaming becomes violent at high compressor blade speed and at high flow rate of the blowing vapour, but that these both effects are not necessarily cumulative. The foaming is relatively violent when the pressure is close to the saturation pressure corresponding to the temperature in the casing
27、. Some other information such as the foam lifetime, effects of the oil mixing ratio, of the viscosity, etc., were also investigated. Another concern with oil is the question of its circulationrate (OCR, Oil Circulation Ratio), or conversely its return to the compressor. The OCR seems to be relativel
28、y independent of the operating conditions, at least for R-290/POE oil or R-407C/POE oil, but the OCR seems to be slightly higher with POE oils than with mineral oils (Navarro et al., 1998, 2004,2005). The oil return can be analysed in terms of presumed benefits of a high miscibility vs. actual lubri
29、cation properties of the refrigerantoil mixtures (which are poorer than those of pure oil properties, since a portion of liquid refrigerant can be dissolved in the oil) and overall energy efficiency.Reyes-Gavilan et al. (1996a,b) showed that a well-chosen non-miscible oil can perform as well as a PO
30、E miscible oil in a R-134a household refrigerator, i.e. both yield about the same energy efficiency with about the same amount of oil trapped along the circuit. In some other works, the question of oil return is linked to specific configurations, such as a pair of compressors working in parallel: Wi
31、nandy and Cuevas (2003) monitored and analysed the oil level of two compressors linked with line allowing for the pressure and oil-level equalization, with various ON/OFF conditions for each compressor cycle. The oil management must be given a specific care, particularly when the compressors work under part load. Lastly,
