Performance And Optimization Of Capillary Tube Length In A Split Type Air Conditioning System

Performance And Optimization Of Capillary Tube Length In A Split Type Air Conditioning System

Performance and Optimization of Capillary Tube Length In a Split Type Air Conditioning System

D.V.Raghunatha Reddy1 Dr P.Bhramara2 Dr K.Govindarajulu3

1 Assit.Prof, Dept of ME, A.T.R.I.Uppal, Hyderabad-500039, A.P, India.

1 Research Scholar, Dept of ME Dept., J N T U.A, Anantapur, A. P., India

2Assoc. Prof, Dept. Of ME, JNTUH College of Engineering Hyderabad A.P India

Professors, Dept of ME, JNTUA College of Engineering Ananthapur A.P, India

3

ABSTRACT

The objectives of this research were to evaluate the optimization of a capillary tube in a split- type air conditioning system and to determine the coefficient of performance (COP) of the system. The optimization was determined by mathematical calculation to evaluate COP of a split-type air conditioning system within 5 different sizes of capillary tube. Following this, the experimental equipment was designed and constructed to verify the COP data obtained from the calculation. The results found that from the theoretical analysis and experiment, the COP was changing in a direction contrary to the diameter of the capillary tube. When the capillary tube diameter is smaller, COP values tend to be higher.

KEYWORDS: Air-conditioning system, Optimization of Capillary tube, BAC Lab, Mathematical and Experimental Calculations, COP

I INTRODUCTION

Air conditioning and refrigeration systems play an important role in industry, infrastructure and households. The industrial sector includes the food industry, textiles, chemicals, printing, transport and others. Infrastructure includes banks, restaurants, schools, hotels and recreational facilities. Therefore, installation, repair and maintenance of equipment to function properly are important for the operations associated with those activities. At present reducing pressure valves used in air conditioning and refrigeration systems can be classified into two types: expansion valves and capillary tubes. The capillary tube is made from copper pipe, with a diameter around 0.5 mm to 5 mm and length around 0.5 m to 5 m. Its use depends on power and load capacity of the system. The capillary tube is often used with small cooling load or small changing load systems, such as refrigerators, water coolers and small air conditioners.

Problems from the blockage in the capillary tube results in lower injection of refrigerant into the evaporator, so there will be less cooling. Typically this problem c a n be solved b y changing a new capillary tube. However, this also results in refrigerant being released from the system, which makes for higher cost and time wastage. Furthermore, the size of the replacement capillary tube must be the same and some sizes are difficult to source, which makes the maintenance cost even higher.

Taking into consideration these problems, the objective of this research is to determine the appropriate size of a new capillary tube that can replace the old blocked one and to construct an experimental equipment system with different capillary tubes to measure the real values. The resulting values will show which size of capillary tube can be used instead of the old one. This will be more convenient for maintenance and will save costs when fixing air conditioning and refrigeration systems.

1. Objective:

   1. To evaluate the performance of an air conditioner system for different capillary lengths, mathematically and experimentally.

   2. To compare experimental and mathematical model and select best capillary length for the system

II Mathematical Solution for Capillary Tube:

Theoretically, the appropriate size of capillary tube can be calculated from the refrigerant effect, Coeficiento f performance (COP) and others. The system is assumed to work as an isentropic process and there are five different sizes of capillary tubes in this calculation.

To undertake simulation with any value it is necessary to use the results from the previous test in t h e r e a l w o r k e n v i r o n m e n t . The c o m p r e s s o r i n f o r m a t i o n , RNB5522EXC, i s f r o m t h e compressor manufacturer and has been adjusted into the theoretical calculation to determine the value of the variables depending on the different size of capillary tubes by evaluating COP at the various states of capillary tubes in the isentropic process. Theoretically, the appropriate size of capillary tube can be decided by evaluating coefficient of performance (COP) of the system for the different capillary lengths. Five different sizes of capillary tubes are considered for analysis.

To undertake simulation with any value it is necessary to use the results from the previous test in the real work environment. The compressor information, RNB5522exc, is from the compressor manufacturer and has been adjusted into the theoretical calculation to determine the value of the variables depending on the different size of capillary tubes by evaluating COP at the various states of capillary tubes in the isentropic process.

1. MATHEMATICAL CALCULATIONS:

   Mass Flow Rate Equation:

   Substituting the mass flow rate data in the above equation we have: From above equation the constants we will get as:

   C1= 117.7158,

   C2= 2.7149,

   C3= -0.2007,

   C4= -0.8751,

   C5= 8.5×10-3,

   C6= 0,

   C7= 0.0197,

   C8= 3.3866×10-4,

   C9= 3.1417×10-4

   Substituting the constants in the equation (A) the mass flow rate equation can be written as follows:

   m = 117.7158 + 2.714966 – 0.20077 – 0.875139 + 8.5913 10-3 + 0.019749

   + 3.38664 10-4 – 3.14175 10-4

   substituting the various condenser and evaporator temperatures in the above equation well get the mass flow rate (kg/h) as below

   Mass flow rate data of compressor RNB5522EXC

2. Mass Flow Rate (g/s)At Various Condenser And Evaporatortemperature:

   Condenser Temperature(°C)	Mass flow rate(g/s)
   	Evaporator Temperature (°C)
   	0	5	10
   40	26.793	31.917	38.243
   45	26.542	31.286	37.475
   50	26.510	31.455	36.438
   55	26.547	31.278	34.735
   60	26.704	31.148	33.553

   Dimensions of five different capillary tubes used for calulations and experiment are D = 1.524mm (0.06). diameter is constant for all the lengths of the tube.

   L1 = 0.889m (35) L2 = 0.8382m (33) L3 = 0.762m (30)

   L4 = 0.635m (25), L5 = 0.508m (20).

3. Mass flow rate through the capillary tube can be evaluated from the equation below:

   Where

   m = Flow rate R-22 (g/s). D= Diameter ( mm)

   L= Length (m) T=Condenser Temperature.(oC)

   DSC=Degree of Sub cooling (oC) C1= constant = 0.249029

   C2= constant = 2.543633 C3= constant = -0.42753 C4= constant = 0.746108 C5= constant = 0.013922

   Mass flow rate equation can be rearranged to get sub-cooled temperature:

   The above equation is valid for the single capillary system but the equation is modified for twin capillary system as follows:

   Substituting the values of mass flow rate and dimensions of the tube in the abve equation sub-cooled temperatures can be shown follows

4. Model calculation for degree of sub-cooling(DSC) :

5. Degree of Sub-Cooling (°C) At Various Condenser And Evaporator Temperatures

The values of degree of sub-cooling from the above table is used to calculate C.O.Ps by assuming 10°C of superheat at the inlet of the compressor

The C.O.Ps found out through the above mentioned procedure are tabulated as follows

C.O.PS at various condenser and evaporator temperatures

III EXPERMIENTAL PROCEDURE:

Experiments are conducted at Tecumseh products India pvt.ltd in the balance ambient calorimeter lab.

1. BAC test lab

   BAC lab was established to test the room air conditioning appliances (window and split type) as per different standards under balanced temperature conditions. The lab is divided into two test rooms namely indoor test room and outdoor test room. Each test room is enclosed by another chamber isolating the test rooms from the atmospheric influence by creating a space known as controlled air space. A constant dry bulb temperature equal to that of the dry bulb temperature inside the test room is maintained within the controlled air space shows the view of the balance ambient calorimeter (BAC) lab

   BAC lab view

   Each test room consists of the following equipment

   • Chillers: Used to maintain the ambient temperatures.

   • Blowers: Used to distribute the air inside the test room in order to maintain equilibrium.

   • Steamers: Used to maintain the relative humidity.

   • Heaters : Used to maintain the dry bulb temperature

   • Temperature sensors: Used to measure temperature inside the room

   • Energy meter: Used to calculate power consumption of appliance and lab equipment.

   • Temperature controllers : Used to maintain dry bulb and wet bulb temperatures

   • Computer: The lab is pre-programmed, controlled and monitored by software called as Lab view. The software automates the lab avoiding manual intervention reducing error levels.

     1

     8

     2

     7

     5

     3

     4

     6

     dry bulb temperature / outdoor wet bulb temperature

     Monitored outdoor dry bulb temperature / outdoor wet bulb temperature

     Monitored indoor dry bulb temperature / indoor wet bulb temperature

     Indoor and outdoor controlled air space dry bulb temperature

   • Total OD cooling capacity indicator

   • Stabilization indicator

   • Outdoor and indoor unit test rooms dry bulb and wet bulb temperatures

   • Once the standard is defined in the program the temperatures defined in the standard are maintained inside the test rooms with the aid of steamers, blowers, heaters and chillers through an automated process.

   • The unit starts running the varying dry bulb and wet bulb temperatures can be monitored on the calorimetric screen

   • The dry bulb and wet bulb temperatures are stabilized over the defined values the in-condition light turns and a report is generated.

   • The report generated narrates the complete test summary. Therefore the judgment can be made basing in the cooling capacity and EER obtained from the report.

3.1Results from Experiment:

IV RESULTS AND DISCUSSIONS:

The performance of 1.5tonn split type air conditioning system is evaluated mathematically and experimentally. The results from mathematical model and experiments are discussed in the following sections: Mathematical model:

Mathematically C.O.PS are evaluated at various condenser and evaporator temperatures by considering the sub- cooled temperature and assuming the 5°C of superheat at the inlet of compressor.

1. The Results Are Tabulated in Table C.O.PS evaluated at Various Evaporator and Condenser Temperatures:

   Condensor Temperature (°C)	Evaporator Temperature (°C)	C.O.P
   		Tube1 (L1=35)	Tube2 (L2=33)	Tube3 (L3=30)	Tube4 (L4=25)	Tube5 (L5=20)
   40	5	7.326	7.286	7.220	7.095	6.780
   	10	9.095	9.047	8.970	8.821	8.639
   45	5	6.099	6.063	6.005	5.894	5.758
   	10	6.633	6.596	6.536	6.421	6.28
   50	5	5.164	5.132	5.080	4.980	4.858
   	10	6.231	6.194	6.134	6.019	5.878
   55	5	3.417	3.394	3.358	3.287	3.201
   	10	4.150	4.123	4.080	3.999	3.897
   60	5	3.326	3.302	3.264	3.191	3.101
   	10	4.042	4.014	3.969	3.882	3.776

2. Mathematical results by changing Condenser temperature and Evaporator temperature:

   Capillary tubes	Mathematical results
   	Condenser Temperature (0c)	Evaporator Temperature (0c)	COP
   Tube 1	53.46	8.2	6.212
   Tube 2	53.67	8.9	6.296
   Tube 3	54.29	9.3	6.274
   Tube 4	55.08	9.5	6.197
   Tube 5	55.28	9.9	6.234

   Length Of The Capillary Vs C.O.P (Mathematical Model):

   6.32

   6.3

   6.28

   6.26

   6.24

   6.22

   6.2

   6.18

   6.16

   6.14

   889 838 762 635 508

   cop

3. Comparison between the Mathematical Results And Experimental Results

From the mathematical and experimental models it is found that Tube 2(largest length) has the maximum C.O.PS

1. and 2.254 respectively. The experimental results correspond with the results from calculation (mathematical model) or at least they show the same trend. From the above graphs it is apparent that when the capillary tube length is increased C.O.P is higher.

   Length of the Capillary Vs C.O.P (From Experiments)

   2.28

   2.26

   2.24

   2.22

   2.2

   2.18

   2.16

   2.14

   2.12

   2.1

   2.08

   889 838 762 635 508

   cop

   Capillary tube length in mm

   Comparison between Experimental and Mathematical Results

   5

   4.5

   4

   3.5

   3

   2.5

   2

   1.5

   1

   0.5

   0

   Category 1

   Category 2

   Category 3

   Category 4

   Series 1

   Series 2

   Graph shows the comparison between experimental and mathematical values. Around 30-35% of deviation was noticed between mathematical and experimental values. This deviation in the mathematical and experimental values might be due to the following reasons:

   • Frictional losses in the compressor were not considered in analysis.

   • Electrical losses are also not considered.

   • Fan motor efficiency is also not considered

V Relative COP:

The ratio of the actual COP to theoretical COP is known as Relative COP

36

35.5

35

34.5

34

33.5

889 838 762 635 508

Relativ

1. NOMENCLATURE:

   A cross-sectional area (m2)

   D diameter (m)

   H specific enthalpy (kJ/ kg-1)

   1. Boltzmanns constant

   2. length (m)

   3. mass flow rate (kg /s)

   P pressure (kPa)

   s entropy (kJ/ kg K)

   T temperature ()

   V velocity (m/s)

   v specific volume (m3/ kg)

   x vapor quality (dimensionless)

   Cp specific heat (kJ/ kg K)

   Dc capillary tube diameter (m)

   Ds suction line diameter (m)

   1. gravitational acceleration (m/ s2)

   2. specific enthalpy (J/ kg)

   Q heat transfer rate (W)

   s specific entropy (J/kg K)

   1. temperature (K)

   2. overall heat transfer coefficient (W/m2 K)

   3. velocity (m/ s)

   Hc heat transfer coefficient in capillary tube (W/m2 K)

   Hs heat transfer coefficient in suction line (W/m2 K)

   Lf final length of capillary tube (m)

   Lhx heat exchange region length (m)

   Lin initial length of capillary tube (m)

   Lsp single-phase flow length (m)

   Ltp two-phase flow length (m)

   m mass flow rate (kg/sec)

   z position (m)

2. CONCLUSIONS:

   From the experimental work, the following conclusions are drawn for a capacity of 1.5 Tons Split type Air- Conditioning system, at Tecumseh at Hyderabad.

   All the parameters are at standard test conditions as per IS 10617 for R-22 Refrigerant. Condenser Temperature: 50-55°C

   Evaporator Temperature: 7- 10°C INDOOR UNIT CONTIONS:

   Dry Bulb Temperature (DBT) – 27°C Wet Bulb Temperature (WBT) – 19°C OUTDOOR UNIT CONTIONS:

   Dry Bulb Temperature (DBT) – 35°C Wet Bulb Temperature (WBT) – 24°C Capillary Tube size: 0.06"×33"×2 nos.

   1. When the diameter is held constant and lengths of the capillary tube is varied, the length 33"(838 mm) gives the maximum COP of the system.

   2. When the length of capillary tube decreases, as the refrigeration effect also decreases. When the capillary tube diameter is kept constant.

   3. The Degree of sub cooling increases as the length of the tube increases. Practically, maximum degree of sub-cooling that can be achieved is 15°C. Because, compressor work will also increases as the degree of sub cooling increases.

   4. Compressor work will be minimum in between the range of evaporator temperature 8 -10 °C for using Air-Conditioning system

   5. Normally the Actual COP to theoretical COP (i.e. Relative COP) is 32-35%. For Split type Air- Conditioning system.

Comparison between the standard size and recommended capillary tube size:

REFERENCES:

1. Akkarat Poolkrajang and Nopporn Preamjai Optimization of capillary tube in air conditioning system, Asian Journal on Energy and Environment.

2. C.P Arora, Refrigeration and Air conditioning. Tata McGraw-Hill Book Company.

3. Balance Ambient Test Facility Lab manual (BATAF) Tecumseh Products India Pvt. Ltd.

   1. Stocker, W.F. and Jones J.W. (1982), Refrigeration & Air Conditioning. McGraw- Hill Book Company, Singapore.

   2. Jung, D., Park, C. and Park B. (1999). Capillary tube selection for HCFC22 Alternatives, Department of Mechanical Engineering, Inha University, Inchon, Korea

   1. ASHRAE (2001). 2001 Ashrae Handbook Fundamentals SI Edition. Atlanta, USA.

   2. A Text book of Refrigeration and Air conditioning by R.S.Khurmi and J.K.Gupta.

Authors

D.V.Raghunatha Reddy B.Tech. (ME) from JNT University College of Engineering, Hyderabad M.Tech.(R&A.C) from JNTUAnantapur, working as a Assistant Professor i n M E Dept, A u r o r a s T e c h n o l o g i c a l R e s e a r c h a n d I n s t i t u t e U p p a l , Hyderabad, and pursuing Ph.D from JNTUniversity, Anantapur His current research interests are in the areas of simulation of refrigeration systems in different techniques.

P.Bhramara, B.Tech. (ME) from JNT University College of Engineering, Hyderabad M.Tech.(R&A.C) from Coimbatore Engineering College Coimbatore, and completed Ph.D.(Heat Transfer) from JNTU, Hyderabad in . She has one year of Industrial experience and 12 years of teaching experience. Presently she is working as Associate Professor, JNTU College of Engineering, JNTUH, Kukatpally, Hyderabad. Her research interests in Two Phase Heat Transfer, Instrumentation & Data acquisition Refrigeration & Air Conditioning, Computational Fluid Dynamics.

K.Govindarajulu B. Tech. (Mechanical) S.V.U. Tirupati, M. Tech. (Heat Power) JNTU, Hyderabad and Ph.D. (Boiling Heat Transfer), I.I.T., Rookee, Professor in Mechanical Engineering from JNTU Ananthapur He has 30 years of teaching experience. He has many research publications in various international and national journals and conferences, and he has received as a BEST TEACHER AWARD IN THE YEAR 2012