1、 In tern a tiona 1 Jo urna 1 of Hea ting, Ven tila ting, Air-conditioning and Refrigerating Research Editor Reinhard Radermacher, Ph.D., Professor and Director, Center for Environmental Energy Engineering, Department of Mechanical Engineering, University of Maryland, College Park, USA Associate Edit
2、ors James E. Braun, Ph.D., P.E., Professor, Ray W. Herrick Laboratories, Alberto Cavallini, Ph.D., Professor, Dipartmento di Fisicia Tecnica, University of Padova, Italy Qingyan wan) Chen, Ph.D., Professor of Mechanical Engineering, School of Mechanical Engineering, Purdue University, West Lafayette
3、, Indiana, USA Srinivas Garimella, Ph.D., Associate Professor and Director, Advanced Thermal Systems Laboratory, Department of Mechanical Engineering, Iowa State University, Ames, Iowa, USA Leon R. Gicksman, Ph.D., Professor, Departments of Architecture and Mechanical Engineering, Massachusetts Inst
4、itute of Technology, Cambridge, USA Pega Hrnjak, Ph.D., Res. Professor and Co-Director ACRC, Department of Mechanical and Industrial Engineering, University of Illinois, Urbana-Champaign, USA Bjarne W. Olesen, Ph.D., Professor, International Centre for Indoor Environment and Energy Technical Univers
5、ity of Denmark Nils Koppels All, Lyngby, Denmark Roger R. Schmidt, Ph.D., Distinguished Engineer, iBM Systems and Technology Group, IBM Covoration, Poughkeepsie, New York, New York, USA Jeffrey D. Spitler, Ph.D., P.E., Professor, School of Mechanical and Aerospace Engineering, Oklahoma State Univers
6、ity, Stillwater, Oklahoma, USA Shengwei Wang, Ph.D., Professor and Associate Head, HVAC nor may any part of this book be reproduced, stored in a remeval system, or transmitted in any form or by any means-electronic, photocopying, recording, or other-without permission in wTiting from ASHRAE. Abstrac
7、ts-Abstracted and indexed by ASHRAE Abstract Center; Ei (Engineering Information, Inc.) Ei Compendex and Engineering Index; IS1 (Institute for Scientific Information) Web Science and Research Alert; and BSRIA (Building Services Research IS0 EN 7730, EN 13779; ASHRAE Standard 55). It would not be rea
8、sonable to require the criteria for the indoor environment to be fulfilled 100% of the operation time. Often in national building codes or standards deviation from the comfort range is allowed for a limited time (100 hours in the Danish standard DS-474). A mea- sure of the yearly quality of the indo
9、or environment could be how much of the time of occu- pancy the indoor environment is within the specified criteria (70%, go%, or 95%). FUTURE The coming years will show how this directive will impact the HVAC industry. From the beginning of a building project, considerations of which HVAC system to
10、 use must be evalu- ated. This should give the HVAC designer and consulting engineer a chance to get involved at an earlier stage of the building process. More focus will be put on differences in energy perfor- mance of systems, where a lot of data is still needed for many systems to be able to calc
11、ulate yearly energy performance. This will require some new research. REFERENCES ASHRAE. 2004. Standard 55-2004, Thermal environment conditions for human occupancy. Atlanta: CEN CR 1752. 1998. Ventilation for buildings: Design criteria for the indoor environment. Brussels. Directive 2002/91/EC of th
12、e European Parliament and of the council of 16 December 2002 on the energy DS 474. 1993. Standard for specification of the indoor thermal environment. Copenhagen, Danish Stan- ISO/DIS prEN13790. 2005. Thermal performance of buildings-Calculation of energy use for space heat- EN 13779. 2004. Ventilat
13、ion for non-residential buildings-Performance requirements for ventilation and American Society of Heating, Refrigerating and Air-conditioning Engineers, Inc. performance of buildings. European Commission. dards Association. ing and cooling. CEN, Brussels. room-conditioning systems. Brussels. VOLUME
14、 11, NUMBER 4, OCTOBER 2005 509 IS0 EN 7730. 2005. Moderate thermal environments-Determination of the PMV and PPD indices and specification of the conditions for thermal comfort. Geneva, International Standards Organization. M 343-EN-2004. Mandate to CEN, CENELEC and ETSI for the elaboration and ado
15、ption of standards for a methodology calculating the integrated energy performance of buildings and estimating the environ- mental impact, in accordance with the terms set forth in Directive 2002/91EC. prEN1525 1. 2005. Criteria for the indoor environment including thermal, indoor air quality, light
16、 and noise. CEN, Brussels. VOLUME 1 1, NUMBER 4 HVAC accepted September 1 0, 2004 Part I of this article was published in Volume 1 I, Issue 3, July 2005 This paper intends to present a comprehensive summary ofthe various studies that were con- ducted with respect to the lubricant influence on refrig
17、eradoi1 mixture properties, condensa- tion, and pressure drop, and tries to identifr some general relationships. In addition, the research methods and correlations presented on each of these subjects are summarized. Finally, technical recommendations regarding the lubricant influence in each of thes
18、e aspects are pro- vided in this paper. INTRODUCTION Cavallini et al. (2000) suggested that users of literature correlations to predict the lubricant influence on condensation note the reference temperature as well as two other points. The first point is to veri the vapor quality range for the given
19、 correlation, since the lubricant influence on condensation heat transfer is sensitive to the vapor quality. The other point is that in some cases the local oil concentration could vary from the oil concentrations that were reported within a given study due to measurement uncertainties and the diffi
20、culty to control the local oil concen- tration. Since the correlations are based on the reported oil concentrations, some inaccuracies could exist. Thome (1998) and Gidwani et al. (1998) presented literature review studies on the lubricant influences on refrigerant condensation and pressure drop. Th
21、e current work is intended to include more recent research studies and identie some general relationships. REFRIGERANT/OIL MIXTURE PROPERTIES Miscibility When immiscibility occurs, two liquid phases coexist: one is an oil-rich phase, and the other is a refiigerant-rich phase. In totally immiscible r
22、efrigerant/oil mixtures, the lubricant and the refrigerant can be treated separately. The immiscibility is likely to occur in the evaporator, which leads to the fact that more oil is trapped in the evaporator than in the condenser. Appar- ently, totally immiscible and partially miscible refrigerant/
23、oil pairs can lead to compressor oil starvation. Bo Shen and Eckhard A. Groll are at Purdue University, Ray W. Herrick Laboratories, West Lafayette, Ind. 511 512 HVAC the other is to use an equation of state to describe the vapor phase behavior and to use the activity coefficient model to describe t
24、he liquid phase behavior. Yokozeki et al. (2002), Hesse and Kruse (1988), and Bertucco et al. (1999) adopted the former method. Martz et al. (1996) implied that the method of using an equation of state and a mixing rule appeared to need too many uncertain oil properties. Thus, they recommended the u
25、se of the activity coefficient method. This recommendation was adopted by most investigators. The key of this method is to get the activity coefficient of the liquid phase. The activity coefficient is used to correct the Lewis-Randall rule for a non-ideal mixture. Martz et al. (1 996) compared six t
26、heoretical models for calculating the activity coefficient. As a result, the authors recommended the Heil and Prausnitz (1 966) model to correlate the thermodynamic behavior of refrigeradoi1 mixtures. Wahlstrm and Vamling (2000) studied five activity coefficient models using the sol- ubility data of
27、 twenty mixtures of five different HFC refrigerants mixed with four different pen- taeryhritol ester oils. In the comparison, the Flory-Huggins and WIQUAC models appeared better than the others. The authors also modified these two models by describing the influence of the chemical structure on the s
28、olubility. Marvillet et al. (2003) introduced the relationship proposed by Cavestri et al. (1994) to estab- lish the semi-empirical solubility relationship of a refrigerant/oil mixture, which is an extension of Raoults law. Conde (1 996) suggested his semi-empirical relationship by revising the Wagn
29、er equation. Both of these relationships were proposed for their general use. However, several semi-empirical constants in them need to be determined by experiments. There were several investigators who provided semi-empirical solubility correlations for particular refrigeradoi1 514 HVAC McMullan et
30、 al. (1991) for R-22 with one paraffinic oil; Yeau-Ren et al. (2001) for R-410A with ISO-32 and ISO-100; Yeau-Ren et al. (2001) for R-407C with ISO-32 and ISO-100; Greb- ner and Crawford (1993b) for R-12 with two mineral oils; Eckels et al. (1993) for R-134a with 169-SUS and 369-SUS; Grebner and Cra
31、wford (1993b) for R-134a with two synthetic oils; Kang and Pate (1994) for R-134a with one propylene glycol, one mixed acid ester, and one branched acid ester oil; Kang and Pate (1994) for R-32 with one propylene glycol, one mixed acid ester, and one branched acid ester oil; and Kang and Pate (1994)
32、 for R-125 with one propy- lene glycol, one mixed acid ester, and one branched acid ester oil. Mixture Property Calculation Methods 1. All of the oil exists in the liquid phase, and the gas phase consists of only refrigerant vapor. 2. The mixture saturation temperature is not the saturated refrigera
33、nt temperature. It changes with oil concentration and vapor quality. Hence, this mixture saturation temperature is the reference temperature to decide the properties of the separated components. 3. The oil concentration changes with the vapor quality; thus, the mixture properties are deter- mined by
34、 the local oil concentration in the liquid phase. Jensen and Jackman (1984), Baustian et al. (1986a, 1986b), and Conde (1996) conducted in-depth summaries about the refrigerant/oil mixture properties. Conde (1 996) also introduced multiple methods for predicting pure lubricant properties based on a
35、given lubricant density. Table 1 in the appendix provides an overview of the prediction methods. The correlations presented in Table 1 are recommended, since other investigators have vali- dated their applicability. Thome and Phil (1995) recommended the correlation of Takaishi and Oguchi (1987) as a
36、 general method to predict the refrigeranuoil bubble temperature, and Bayani et al. (1995) also recommended Equation 4 for predicting the mixture density. Equation 5 is pro- posed by Yokozeki (1992). Yokozeki et al. (2002) used this correlation to predict the mixture viscosities of HFC-alkylbenzene
37、mixtures. Choi et al. (1999) also adopted this correlation for their generalized pressure drop equation. Jensen and Jackman (1 984) validated the correlations from Equation 6 to Equation 8 with the experimental data of R-113-naphthenic oil. There are other mixture properties needed for calculating h
38、eat transfer and pressure drop, such as the mix- ture molecular mass, critical pressure, and latent heat of vaporization. But Thome and Phil (1995) indicated that these properties are not considered main influence factors and, therefore, the pure refrigerant properties can be used instead. In order
39、to predict the needed mixture properties, three assumptions are indispensable: LUBRICANT INFLUENCE ON REFRIGERANT CONVECTIVE CONDENSATION ences on convective condensation. Table 2 in the appendix presents the details of the experimental studies on the lubricant influ- Factors Affecting Refrigerant/O
40、il Convective Condensation The lubricant influences on convective condensation are consistent since nearly all investiga- tors found that lubricants decrease the convective condensation heat transfer. When a lubricant impacts both evaporation and condensation adversely, the lubricant tends to have l
41、ess influence on convective condensation. This conclusion is supported by the observations of Eckels et al. (1994b), Schlager et al. (1988), Cawte (1992), and Fukushima and Kudou (1990). The high mix- ture viscosity and the concept of the oil-rich layer can be used to explain the difference in oil i
42、nfluence between the evaporation and condensation heat transfer in a horizontal tube. During evaporation, the oil-rich layer exists at both the solid-liquid interface and the liquid-vapor inter- VOLUME 11, NUMBER 4, OCTOBER 2005 515 face. However, during condensation, the oil-rich layer can only exi
43、st at the solid-liquid interface since the lubricant is continuously dissolved by the condensing refrigerant. Therefore, the oil-rich layer is continuously removed by the liquid refrigerant at the top of a horizontal tube, and the top of the tube maintains a high heat transfer performance. On the ot
44、her hand, lubricants tend to lead to higher condensation temperatures of the refrigeranuoil mixture, which would compensate the degradation of the heat transfer coefficient due to the increased viscosity. There is one exception reported in the literature by Shao and Granryd (1994, 1995). These autho
45、rs measured the heat transfer and pressure drop performance of R- 134doil mixtures. They found that the refrigeranuoil mixture had a higher condensation coefficient at the beginning of the condenser and a lower heat transfer coefficient toward the latter part of the condenser. A possible reason for
46、this phenomenon is that the refrigeranuoil mixture has a higher condensation temperature compared to the pure refrigerant and, thus, it begins to condense earlier in the con- denser compared to the pure refrigerant. In addition, Shao and Granryd indicated that the defini- tion of the condensation re
47、ference temperature is important and that the heat transfer coefficient calculated using the pure refrigerant saturation temperature is larger than the one calculated using the mixture dew temperature. Effect of Oil Concentration. The adverse influence of the lubricant on the condensing heat transfe
48、r increases with oil concentration. However, this relationship is nonlinear. At small oil concentrations of less than 3%, the lubricant influence is negligible. Schlager et al. (1988) and Eckels et al. (1994b) pointed out that the heat transfer curves of refrigeranuoil mixtures with dif- ferent low
49、oil mass fractions are all very close to each other and that the heat transfer decreases slightly with an increase in oil concentration. Cho and Tae (2001) conducted experiments with mixtures of R-22-mineral oil and R-407C-POE oil. The heat transfer characteristics of both refrigerant/oil mixtures decreased with increasing oil concentration. Sur and Azer (199 1) observed reductions in heat transfer coefficients of 7%, 12%, and 16%, with oil concentrations of 1.2%, 2.8%, and 4.0% in R-113, respectively. Tichy et al. (1985) found 10% and 23% reduc- t
