IJCRR - 4(9), May, 2012
Date of Publication: 17-May-2012
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A REVIEW OF FLOW CHARACTERISTICS OF REFRIGERANT FLOWING THROUGH NON ADIABATIC CAPILLARY TUBE
Author: Deepak Raj Tiwari, R. C. Gupta
Abstract:This paper gives summary of research on the characteristics of different refrigerant considering Non Adiabatic flow inside the capillary tube expansion device for various applications. This paper gives the summary of range of geometric and operating parameters like capillary tube length, diameter, suction line diameter, suction line length, heat exchanger length, surface roughness of capillary tube, suction line inlet temperature, coil pitch, inlet sub cooling, condenser pressure, and evaporator pressure etc. The outcome of different research is summarized in tabular form. This paper also gives type of approach, correlation proposed and some special information about investigation. It is found that the literature in Non Adiabatic capillary tube is scare so more investigation is required.
Keywords: Expansion device, straight & coiled capillary tube, correlations, parameter
A capillary tube is a constant restriction type expansion device used in small vapor compression refrigeration system (below 10KW) like domestic refrigerator, window air conditioning system. Since friction resistance inside capillary tube is directly proportional to length and inversely proportional to inside diameter so that length of capillary tube is kept large (2 to 5m) and diameter is kept small (0.00033m to 0.0015m). The pressure drop through the capillary tube is due to friction and acceleration. Capillary tube maintains flow rate of fluid (refrigerant) flowing through it at desired level so capillary tube works as an automatic flow rate controller for the refrigerant when load is varying. Capillary tube is most commonly used as expansion device because of this compressor can start at low torque. Also capillary tube is simple, less costly and there is no moving part in this. In most of the literature capillary tube is Adiabatic means no heat transfer from the capillary tube to the surrounding. A few researches are found in non Adiabatic capillary tube which works as counter flow heat exchanger in simple vapor compression refrigeration system. So this paper gives the information about refrigerant used, correlation proposed, and range of parameters, and other important information related to Non Adiabatic capillary tube. Mainly two types of capillary tube are used in simple vapor Compression refrigeration system:
Adiabatic capillary tube:
The Adiabatic capillary tube arrangement is shown in fig1. In vapor compression refrigeration system the sub cooled liquid refrigerant from condenser enters
in the capillary tube and flows without transferring heat to surrounding. When sub cooled liquid flows through Adiabatic capillary tube the pressure is reduces linearly and a point is reached where the liquid flashes into vapor this point is known as flash point at which first particle of vapor is formed. The temperature of refrigerant remains constant until flash point and reducing after flash point.
Non Adiabatic capillary tube :
In non Adiabatic type of arrangement the capillary tube is bonded with suction line by soldering or brazing as shown in fig2 So that arrangement is works as counter flow heat exchanger. By making this arrangement there are two advantages first there is delay in vaporization and second superheated vapor is going to compressor so compressor damage can be avoided.
In vapor compression refrigeration system Non Adiabatic capillary tube is used in two configuration first in lateral type and second in concentric type. In lateral type of configurations as shown in fig3(b) the capillary tube is directly brazed or soldered with the suction line going to the compressor so that forming a counter flow heat exchanger in which the heat is transferred from
capillary tube to suction line which is going to compressor. Some initial length of capillary tube is kept Adiabatic and some last length of capillary tube is also kept Adiabatic and remaining is bonded with suction line. In concentric type of configuration as shown in fig3 (a) capillary tube is kept inside the suction line and heat is transferred from tube to suction line. The hot refrigerant is flowing through the capillary tube and the cold refrigerant in the annulus between the capillary tube outer surface and suction line inner surface.
In both lateral and concentric type of arrangement capillary tube can be straight, spiral, or helical. The helically coiled Non Adiabatic capillary tube is most widely used in domestic refrigerator. if the capillary tube is used in straight manner it requires more space as compare to helical or spiral but if capillary tube is used in vertical position the space requirement is reduced because there is sufficient space in back side of the refrigerator.
Use of Non Adiabatic capillary tube is started in 1948 by Staeblar. Staeblar determined the length of capillary tube by using the capacity balance method. 1.22 m length is bonded with suction line. Bolstad and Jordan  have find that evaporator pressure has a minor effect on mass flow rate of R-12. Temperature falls rapidly in heat exchanger region. Pate and Tree  considering counter flow heat exchanger in which air flows in suction line and refrigerant in capillary tube. They found that due to increase in sub cooling, delay in flash point and thus shorter two phase region. Again Pate and Tree  shows the effect of capillary tube length on pressure, quality and temperature. Escanes developed a numerical simulation model by control volume formulation. Both critical and non critical flow has been considered. Bansal et al. proposed a empirical model for refrigerant R-134a. Model is found to agree with earlier studies within ±8% for both the Adiabatic and Non Adiabatic capillary tubes. Bansal has proposed a correlation for length of capillary tube. Dekang chen et al.; experimentally investigate the flow of R-134a and found that under pressure of vaporization decreases with an increase of the heat transfer between the capillary tube and suction line. O. GarcValladares made a numerical simulation using R-134a and found Good degree of Correlation between numerical and experimental results for the case of a Concentric Non Adiabatic capillary. B. Xu, et al. also proposed a numerical model for R-134a. The model predictions agreed with available experimental and analytical data to within ±20%. Jiraporn Sinpiboon et al gives a mathematical model for R-12, R-134a and R152a and measured mass flow rate of R134a has discrepancy of 14.3% and 9.50% for different model. Claudio Melo et al.  make Experimental investigation for R-600a.He found that absolute mean deviation error for the refrigerant mass flow rate and suction line outlet temperature was 0.07 kg/h (5.1%) and 0.6°c , respectively. P.K. Bansal et al gives numerical model for R-134a. It is found that the Non Adiabatic capillary tube flow characteristic is discontinuous in some situations. Yasar Islamoglu et al uses artificial neural network (ANN) approach. The results showed that the ANN approach could be considered as an alternative and practical technique to evaluate the refrigerant suction line outlet temperature and mass flow rate. Y. Chen, et al.  gives numerical model for Co2. The increase of inner diameter, cooling pressure and outside heat transfer coefficient will lead to longer capillary length also increasing evaporating temperature and cooling capacity lead to a shorter length. C. Yang et al. gives numerical model. It was found that R-134a performs better in terms of heat transfer rate and evaporator capacity than R-600a. O. Garc?´a-Valladares et al. make Numerical simulation for R-12 R-134a, R22, R152a and R410A. A detailed numerical model of concentric and lateral capillary tube suction line heat exchangers have been developed. O. Garc?´a-Valladares et al gives Numerical simulation for R410A R-134a R-600a and R152a. Of the 196 data points evaluated for mass flow rate 96.4% are within an error of ±15%, 81.1% are within ± 10% with a mean deviation of ±6.3%. Neeraj Agrawal et al  give Homogeneous flow model for CO2. The increased mass flow through larger tubes causes increase in heat transfer rate by about 68%, for a tube diameter increase of 50%. Again Neeraj Agrawal et al. gives Homogeneous flow model for CO2 . As the capillary becomes larger, decrease in throttling effect increases the mass flow rate, hence heat transfer rate increases. Christian J.L. Hermes et al. uses Computational model for HFC-134a HC- 600a. It was found that the model predicts 91.5% of the measured refrigerant mass flow rate for Adiabatic and 79.3% for Non Adiabatic flows within an error band of ±10%. A.L. Seixlack et al. investigate R-134a. Mass flow rate can be predicted within error band of 3.6% and 5% for two fluid model and homogenous model respectively. Mohd. Kaleem Khana et al  experimentally investigate R-134a. It has been found the proposed correlation predicts the refrigerant mass flow rate in the error band of ±7% of the measured experimental mass flow rate. Christian J.L. Hermes et al., Analytically investigate flow of R-134a and HC 600a. Comparisons between the model predictions and the experimental data revealed that more than 90% and nearly 100% of all data can be predicted within ±10% and ±15% error bands, respectively.
This paper presents the summary of literature on Non Adiabatic capillary tube with various refrigerants, range of parameter selected, and type of approach. In most of the literature the effect of various geometric and operating parameters on mass flow rate has given. In spiral type of Non Adiabatic capillary rube the mass flow rate is less as compare to straight Non Adiabatic capillary tube. It is found in literature that the length for Non Adiabatic capillary tube is more as compare to adiabatic capillary tube. The literature available for Non Adiabatic capillary tube is scare so more investigation is required.
ACKNOWLEDGEMENT We are acknowledging the immense help received from the scholars whose articles are cited and included in references of this manuscript. We are also grateful to authors/editors/publishers of all those articles, journals, and books from where the literature for this article has been reviewed and discussed.
1. L.A. Staebler, theory and use of a capillary tube for liquid refrigerant control Refrigerating Engg. (1948) 55-59
2. M.M. Bolsted, R.C. Jordan theory and use of capillary tube expansion device: part2 – non Adiabatic, Refrigerating engg.57 (1949)519-523.
3. M.B. Pate, D.R. Tree, an analysis of pressure and temperature measurement along a capillary tube- suction line heat exchanger, ASHRAE Trans.90(1984)291- 301
4. M.B. Pate, D.R. Tree, a linear quality model for capillary tube suction line heat exchangers, ASHRAE Trans.90(1984) 3-17
5. F. Escanes, C.D. Perez, A olive, numerical simulation of capillary tube expansion device int. J. Refrigeration18(2)(1995)113- 122
6. P. K. Bansal and A.S. rupsinghe , An empirical model for sizing capillary tube International Journal of Refrigeration 19(1996)00044-8 .
7. Dekang chen, sui lin, et al., undepressure of vaporization of refrigerant R-134a through a Non Adiabatic capillary tube international journal of refrigeration 24(2001) 261-271
8. O. Garci_a-Valladares c.d. peraz-segarra, a. olivaet Numerical simulation of capillarytube expansion devices behavior with pure and mixed refrigerants considering metastable region. Part II: experimental validation and parametric studies Applied Thermal Engineering 22 (2002) 379–391.
9. B. Xu P.K. Bansal , Non Adiabatic capillary tube flow: a homogeneous model and process description Applied Thermal Engineering 22 (2002) 1801–1819
10. Jiraporn Sinpiboon Somchai Wongwises , Numerical investigation of refrigerant flow through non Adiabatic capillary tubes Applied Thermal Engineering 22 (2002) 2015–2032
11. claudio melo Luis Ant^onio Torquato Vieira , Roberto Horn Pereira non Adiabatic capillary tube flow with isobutene Applied Thermal Engineering 22 (2002) 1661–1672
12. P.K. Bansal B. Xu , A parametric study of refrigerant flow in non Adiabatic capillary tubes Applied Thermal Engineering 23 (2003) 397–408
13. Yasar Islamoglu Akif Kurt , Cem Parmaksizoglu Performance prediction for non Adiabatic capillary tube suction line heat exchanger: an artificial neural network approach Energy Conversion and Management 46 (2005) 223–232
14. Y. Chen J. Guet Non Adiabatic capillary tube flow of carbon dioxide in a novel refrigeration cycle Applied Thermal Engineering 25 (2005) 1670–1683
15. C. Yang P.K. Bansal ., numerical investigation of capillary tube suction line heat exchanger performance Applied Thermal Engineering 25 (2005) 2014–2028
16. O. Garc? a-Valladares Numerical simulation of non adiabatic capillary tubes considering metastable region. Part I: Mathematical formulation and numerical model International Journal of Refrigeration 30 (2007) 642-653
17. O. Garc? a-Valladares Numerical simulation of non adiabatic capillary tubes considering metastable region. Part II: Experimental validation International Journal of Refrigeration 30 (2007) 654-663
18. Neeraj Agrawal Souvik Bhattacharyya , Performance evaluation of a non Adiabatic capillary tube in a transcritical CO2 heat pump cycle International Journal of Thermal Sciences 47 (2008) 423–430
19. Neeraj Agrawal Souvik Bhattacharyya Parametric study of a capillary tube-suction line heat exchanger in a transcritical CO2 heat pump cycle Energy Conversion and Management 49 (2008) 2979–298
20. Christian J.L. Hermes Cla´udio Meloa, Joaquim M. Gonc¸alves modeling of non adiabatic capillary tube flows: a simplified approach and comprehensive experimental validation, International Journal of Refrigeration 31 (2008) 1358–1367.
21. A.L Seixlack , M.R. Barbazelli )Numerical analysis of refrigerant flow along non Adiabatic capillary tube using two fluid model Applied Thermal Engineering 29 (2009) 523-531
22. Mohd. Kaleem Khan Ravi Kumar , Pradeep K. Sahoo , Flow characteristics of refrigerants flowing through capillary tubes– A review Applied Thermal Engg. 29(2009) 1426-1439.
23. Christian J.L. Hermes Cláudio Melo, Fernando T. Knabben , Algebraic solution of capillary tube flows part2: capillary tube suction line heat exchanger, Applied Thermal Engg. 30 (2010) 770-775.