AMOL A. GAWALI et al ISSN: 2348-4098 DATE OF PUBLICATION: JUNE 28, 2014 VOLUME 02 ISSUE 05 JUNE 2014

EXPERIMENT ANALYSIS AND PERFORMANCE TESTING OF CAPILLARY TUBE AND THERMOSTATIC EXPANSION VALVE

1AMOL A. GAWALI, 2MADHAV S. JOSHI, 3RUPESH L. RAUT, 4RAHUL A. BHOGARE

1, 3, 4Student, Heat Power Engineering, Walchand College of Engineering, Sangli, Maharashtra, INDIA

2Associate Professor, , Walchand College of Engineering, Sangli, Maharashtra, INDIA

Email: [email protected], [email protected], [email protected], [email protected]

ABSTRACT

This paper provide an overview of the project, the fundamental physics underlying the operation of fixed and variable expansion devices, and summarizes results of the analyses performed to compare them. This paper analyzes a broad spectrum of strategies for actively or passively controlling the inlet state of fixed‐geometry expansion devices such as capillary tube and Thermostatic expansion device, to match mass flow rates with minimal performance degradation in an efficient R12 system. A TXV (Thermal Expansion Valve) system was selected as per load requirement and type of . Results yielded insights that can be generalized to other and systems. TXV were found to produce and control degree of superheat of refrigerant, higher efficiency than capillary tubes across the entire range of operating conditions, although the difference can be mitigated by proper choice of the latter’s length and diameter.

INDEX TERMS: capillary tube; thermostatic expansion valve; fixed and variable restriction; cop;

1. INTRODUCTION because it regulates refrigerant flow into the . An expansion The selection of the expansion device is device which is misapplied or of particular importance to the incorrectly sized will ordinarily result in operation of the refrigeration system operational difficulties and poor system

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performance. For example, an at the evaporator outlet. Fig 2 shows undersized expansion device will thermostatic expansion valve. As prevent sufficient refrigerant from superheat at the evaporator outlet rises flowing into the evaporator causing a due to increased heat load on the reduction in the design cooling evaporator, the TEV increases capability of the system. An oversized refrigerant flow until superheat returns expansion device may allow too much to the valve’s setting. Conversely, the refrigerant into the evaporator causing TEV will decrease refrigerant flow when liquid refrigerant to flow back to the superheat lowers as a result of a compressor. Capillary tubes are used to decreased heat load on the evaporator. expand the refrigerant from the The effect of this type of regulation is it condenser pressure to the evaporator allows the evaporator to remain as pressure in low capacity refrigerating nearly fully active as possible under all machines such as domestic refrigerators load conditions. and window type room air conditioners. 2. EXPANSION DEVICE FUCTION It also balances the system pressure in the refrigeration cycle however; it has The basic function of expansion device no provision to adjust the mass flow used in refrigeration system (1) Reduce rate when load conditions changes. In pressure from condenser pressure to spite of this fact, capillary tubes are evaporator pressure, and (2) regulate preferred in small capacity refrigerating the refrigerant flow from the high‐ machines, where the load is fairly pressure liquid line into the evaporator constant due to its several advantages at a rate equal to the evaporation rate in such as simplicity, low cost, zero the evaporator. Under ideal conditions, maintenance, and requirement of a low the mass flow rate of refrigerant in the starting torque motor to run the system should be proportional to the compressor.Fig1 shows simple capillary cooling load sometimes; the product to tube. The thermostatic expansion valves be cooled is such that a constant provide an excellent solution to evaporator temperature has to be regulating refrigerant flow into a direct maintained. In other cases, it is expansion type evaporator. The TEV desirable that liquid refrigerant should regulates refrigerant flow by not enter the compressor. In such a case, maintaining a nearly constant superheat the mass flow rate has to be controlled

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in such a manner that only superheated (1) the refrigerant has to overcome the vapor leaves the evaporator. Again, an frictional resistance offered by tube ideal refrigeration system should have walls this leads to some pressure drop. the facility to control it in such a way (2) The liquid refrigerant flashes that the energy requirement is (evaporates) into mixture of liquid and minimum and the required criterion of vapor as its pressure reduces. The temperature and cooling load are density of vapor is less than that of the satisfied. Some additional controls to liquid. Hence, the average density of control the capacity of compressor and refrigerant decreases as it flows in the the space temperature may be required tube. (3) The mass flow rate and tube in addition, so as to minimize the energy diameter (hence area) being constant, consumption. the velocity of refrigerant increases since = ρVA. The increase in velocity or The expansion devices used in acceleration of the refrigerant also refrigeration systems can be divided requires pressure drop into fixed opening type or variable opening type. As the name implies, in fixed opening type the flow area remains fixed, while in variable opening type the flow area changes with changing mass flow rates. Capillary tube

belongs to the fixed opening type, while the thermostatic expansion valve Figure 1: Capillary Tube belongs to the variable opening type. 2.2 THERMOSTATIC EXPANSION 2.1 CAPILLARY TUBE VALVE A capillary tube is a long, narrow tube of Thermostatic expansion valve is the constant diameter. Typical tube most versatile expansion valve and is diameters of refrigerant capillary tubes most commonly used in refrigeration range from 0.5 mm to 3 mm and the systems. It is variable opening type length ranges from 1.0 m to 6 m. The expansion device. A thermostatic pressure reduction in a capillary tube expansion valve maintains a constant occurs due to the following two factors degree of superheat at the exit of

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evaporator; hence it is most effective for for refrigerant R‐12.Experiment setup dry in preventing the consist of four major part of slugging of the since it refrigeration system such as does not allow the liquid refrigerant to compressor, which compress enter the compressor. The schematic refrigerant, condenser which rejects the diagram of the valve is given in Figure 2. heat from refrigerant at constant This consists of a feeler bulb that is pressure .expansion device which drop attached to the evaporator exit tube so down the temperature and pressure of that it senses the temperature at the exit the refrigerant. And finally evaporator of evaporator. The feeler bulb is which is absorbs heat from refrigerated connected to the top of the bellows by a space. All the component of the capillary tube. The feeler bulb and the refrigeration system is displayed on narrow tube contain some fluid that is portable the metallic panel. The unit called power fluid. The power fluid may consist 0.3 TR capacity compressor, be the same as the refrigerant in the condenser thermostatic Expansion refrigeration system, or it may be Valve and capillary tube and evaporator. different. In case it is different from the Here for the experiment purpose two refrigerant, then the TEV is called TEV expansion devices capillary and with cross charge. thermostatic expansion valve are used in system.fig 3, shows line diagram of simple vapor compression system. Evaporator coil is deep in water calorimeter to so that the water temperature lowers down due to loss of heat energy due to evaporation process. Heater is providing at the bottom of the

calorimeter which offers the heat load Figure 2: Thermostatic Expansion Valve which is balanced by the refrigeration 3. EXPERIMENT SET‐UP effect produce by the system.

Calorimeter contain sufficient of water A setup manufactured to experimentally that the evaporative coils totally investigate the performance of capillary immersed. Temperature of water tube and Thermostatic Expansion valve

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present in calorimeter is measured with the help of digital temperature indicator. Pressure gauges are attached at inlet and outlet of condenser as well as Evaporator. For safety of compressor purpose high temperature and low temperature cut off switch is provide

Table ‐1: Specification of Experiment Set‐up Figure 4: p‐h Diagram for R‐12 Sr. Parameters Description No

1 Type Refrigeration Tutor

2 Refrigerant R12

3 Capacity 0.33 TR

4 Compressor Hermetically Sealed, single cylinder reciprocating

5 Condenser Finned coils, Air cooled Figure 5: Actual Setup Line Diagram 6 Expansion Capillary tube and TXV device

7 Evaporator Bare tube type 4. EXPERIMENT READINGS FOR

CAPILLARY

The readings for capillary tube is taken by allowing flow of refrigerant R‐12 through capillary tube while refrigerant flow to TXV is restricted with the help of manual valve. This reading is use to calculate system actual, theoretical and Carnot COP.

Figure 3: Vapor Compression cycle

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Table ‐2: Capillary Tube Readings

S. No. Parameter Unit Readings

1 Condenser pressure in bar 11.5

2 Condenser pressure out bar 11.2

3 Evaporator pressure in bar 3.2

4 Evaporator pressure out bar 3.0

5 Refrigerant flow rate lph 28

6 Condenser inlet temperature 0C 53

7 Condenser outlet temperature 0C 30

8 Evaporator inlet temperature 0C 3

9 Evaporator outlet temperature 0C 12

Time for 10 revolution of compressor 10 sec 62 meter

Time for 10 revolution of Heater 11 sec 32 (energy)meter

4.1 CALCULATION FOR CAPILLARY h2= 230 kJ/kg, TUBE h3 = h4= 90 kJ/kg, From P‐h chart of R‐12 shown in Figure Carnot cop=4.15 4. Theoretical cop =2.5 h1 = 190 kJ/kg, Actual cop=1.67

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Table ‐3: Thermostatic Expansion Valve Readings

S. No. Parameter Unit Readings

1 Condenser pressure in bar 10.7

2 Condenser pressure out bar 10.5

3 Evaporator pressure in bar 2.4

4 Evaporator pressure out bar 2.2

5 Refrigerant flow rate lph 16

6 Condenser inlet temperature 0C 58

7 Condenser outlet temperature 0C 34

8 Evaporator inlet temperature 0C ‐3

9 Evaporator outlet temperature 0C 16

Time for 10 revolution of 10 sec 70 compressor meter

Time for 10 revolution of Heater 11 sec 36 (energy)meter

4.2 CALCULATION FOR Theoretical cop =3.6 THERMOSTATIC EXPANSION VALVE Actual cop= 1.944 From P‐h chart of R‐12, shown in figure 4.3 FORMULAE USED FOR 4. CALCULATION h1 = 190 kJ/kg, Input given by compressor h2= 220kJ/kg, Wcomp, ip = (Nc ×3600) / (tc×3200) h3 = h4=80 kJ/kg, Input given by heater Carnot cop= 5.2

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Wheater,ip =(Nh ×3600) / (th×3200) charge is lower than the manufactures specification. Carnot cop 2) Fixed expansion devices, such (COP) Carnot =TL / (TH‐TL) as capillary tubes, work at one preset Actual cop level and have no ability to compensate for load changes (COP) Actual=Wheater, ip / Wcomp, ip 3) Variations of capacity over the Theoretical cop ambient temperature range of 26 0C to

(COP) theoretical =Refrigerating effect / 55 0C can cause a performance loss of compressor work 85% with a cap tube system. A well tuned expansion valve system will lose = (h1‐h4) / (h2‐h1) less than one half this amounts, while 4.4 NOMENCLATURE AND maintaining better compressor SUBSCRIPTS temperature control.

W=work done 4) Thermostatic expansion valve Maximum efficiency over a wide h= temperature and load range, it gives Cop=coefficient of performance improved refrigerant return to the

Comp=compressor compressor assures better cooling at high temperatures and reduces the ip=input possibility of liquid slugging which can

L=lower destroy the compressor

H=higher 5) Carnot cop is higher than theoretical cop and actual cop in case of 1, 2, 3, 4=enthalpy point value. both thermostatic expansion valve and 5. CONCLUSION capillary tube.

6) Experimental results shows 1) A TXV equipped refrigeration thermostatic expansion valve has higher system provides energy saving.TXV Carnot,, theoretical and Actual cop than have shown that they maintain higher capillary tube. TXV has less compressor level of efficiency even when refrigerant work than capillary tube.

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7) It was found that the energy REFERENCES consumption of the thermostatic [1]. Jackson B. Marcinichen, Claudio expansion valve system was only lower Melo “Comparative analysis between a than that of the capillary tube system at capillary tube and an electronic higher cooling loads and at lower expansion valve in a household” Federal cooling capacities University of Santa 8) During experiment it is occurs CatarinaInternational Refrigeration and that thermostatic expansion valve able Conference. Paper 838, to drop down more pressure than the March 2006. capillary which is produce more [2]. Mutalubi Aremu Akintunde, refrigerant effect for the system. ”Effect of coiled capillary tube pitch on 9) During experiment it is occurs vapour compression refrigeration that thermostatic expansion valve able system performance” Federal University to control degree of superheat of of Technology, Department of refrigerant which causes reduction in Mechanical Engineering Akure, Ondo compressor work and energy saving of State, Nigeria pp 14‐22 ,July 2007 system. [3]. Nishant P. Tekade, Dr. U. S. ACKNOWLEDGEMENTS Wankhede, ”Selection of spiral capillary tube for refrigeration appliances” I with great pleasure take this International Journal of Modern opportunity to express my deep sense of Engineering Research, Vol.2, Issue.3, pp‐ gratitude towards Walchand College of 1430‐1434, May‐June 2012. Engineering, Sangli. . For allowing me to do the case study work on “Experiment [3]. Sporlan “Installing and servicing analysis and performance testing of thermostatic expansion valves” capillary tube and thermostatic bulletin10‐9, June 2001 expansion valve”. I also would like to [4]. Marco Noro,Renato Lazzarin, thank my guide Prof. M.S.Joshi, Daniele Nardotto, “Electronic expansion Department of Mechanical Engineering valve vs thermal expansion valve” for his valuable guidance and constant ASHRAE Journal, pp. 34‐39, February inspiration during the completion of this 2009 paper.

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[5]. Amit Kulkarni,Veerendra Mulay Rupesh L. Raut received the B.E. and Dereje Agonafer, ”Effect of the and M. Tech degrees in Mechanical Engineering from thermostatic expansion valve Pune University and Shivaji characteristics on the stability of a University in 2010 and 2014, refrigeration system” 2002 IEEE Inter respectively. Society Conference on Thermal Rahul A. Bhogare received the Phenomena, pp. 403‐412 B.E. and M. Tech degrees in Mechanical Engineering from Dr. [6]. Schmidt, Roger, “Low Babasaheb Ambedakar temperature electronic cooling”, University and MITCOE, Electronics Cooling Magazine, Kuthrud, Pune in 2010 and 2014, September 2000, Vol. 6, No. 3. respectively.

[7]. Pakawat Kritsadathikarn, Tirawat Songnetichaovalit, ”Pressure distribution of refrigerant flow in an adiabatic capillary tube” ScienceAsia 28 jan.2002, pp. 71‐76.

BIOGRAPHIES:

Amol A. Gawali received the B.E. and M. Tech degrees in Mechanical Engineering from Dr. Babasaheb Ambedakar University and Shivaji University

in 2010 and 2014, respectively.

Prof. Madhav S. Joshi received the B.E. and M. Tech degrees in Mechanical Engineering from Shivaji University 1976 and 1979, respectively. He is working as Associate professor in

Walchand college of Engineering since 1980 to till date.

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