Journal of Physics: Conference Series PAPER OPEN ACCESS Capillary Tube and Thermostatic Expansion Valve Comparative Analysis in Water Chiller Air Conditioning To cite this article: Putu Wijaya Sunu et al 2018 J. Phys.: Conf. Ser. 953 012063 View the article online for updates and enhancements. This content was downloaded from IP address 46.232.99.193 on 13/03/2018 at 04:22
Capillary Tube and Thermostatic Expansion Valve Comparative Analysis in Water Chiller Air Conditioning Putu Wijaya Sunu 1,*, I Made Rasta 2, Daud Simon Anakottapary 3, I Made Suarta 4 I D M Cipta Santosa 5 1, 2, 3, 4, 5 Mechanical Engineering Department, Bali State Polytechnic, Badung-Bali, 80364 Indonesia. *e-mail: wijayasunu@pnb.ac.id Abstract. The aims of this study to compares the performance characteristics of a water chiller air conditioning simulation equipped with thermostatic expansion valve (TEV) with those of a capillary tube. Water chiller system filled with the same charge of refrigerant. Comparative analyses were performed based on coefficient of performance (COP) and performance parameter of the refrigeration system, carried out at medium cooling load level with the ambient temperature of 29-31 o C, constant compressor speed and fixed chilled water volume flowrate at 15 lpm. It was shown that the TEV system showed better energy consumption compared to that of capillary tube. From the coefficient of performance perspective, the thermostatic expansion valve system showed higher COP (± 21.4%) compared to that of capillary tube system. 1. Introduction In the last few years, heat exchanger optimization [1, 2], energy consumption in building [3, 4], thermal power plant, air conditioning system (HVAC) [5, 6] and others application are always became the main concern many researcher. It is challenging to optimize the energy used of all the equipment facilities. Especially for optimization the HVAC for building energy consumption, due to the complexity of the facilities experimental modeling is great choice to do this investigation. Air cooled and water cooled chiller are the most common equipment HVAC system for building. Figure 1 shows the schematic diagram for chiller system. There are four components in vapor refrigeration cycle for air/ water cooled chiller which are compressor, condenser, metering device and the heat exchanger/evaporator. One of them that plays important role in refrigeration system is metering device. A metering device provides a pressure drop point. This device has function to hold refrigerant back in condensed state and feed refrigerant into evaporator. A capillary tube allows the pressure of the system to equalize during the off cycle thus reducing the compressor starting torque, no moving part hence it does not need maintenance and the capillary tube is inexpensive. This device operate under relatively no change in load and easily clogged by small particles or moisture inside the refrigeration system [7]. The thermostatic expansion valve (TEV) circulates refrigerant by preserve a nearly constant superheat of the evaporator. The TEV control refrigerant flow depend on the load by increasing/decreasing the flow until the superheat return to the valve s setting. Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Published under licence by Ltd 1
Condenser Expansion device Compressor Evaporator FCU Pump Figure 1. Schematic diagram of water chiller Many investigation were done to explore the phenomena behind the capilary tube and TEV. [8] compared the effect of installed with a capillary tube and TEV toward the performance of an air conditioner system. The investigation showed that the coefficient of performance (COP) of refrigeration system with the TEV was higher than that of with the capillary tube. [9] investigated the effect of R407C refrigerant with different expansion devices on vapour compression refrigeration system. The TEV give more refrigeration effect as compare to capilary tube and its performance increase as load increase. [10] has performed the experiment on 0.33 TR vapour compression system using refrigerant R12. The thermostatic expansion valve (TEV) and Capillary tube used for analysis with R12. The analysis focuses on Coefficient of Performance (COP). The results of Coefficient of Performance shows that the TEV gave more benefit on COP of the refrigeration system about 25%. The expansion device regulate refrigerant flow to match operating condition of the system. Based on previous research, this investigation present the main role of capilary tube and thermostatic expansion valve. The objective of this investigation is to compare the performance of refrigeration system through the performance parameters from air cooled chiller. 2. Experimental Apparatus And Method The experimental apparatus is manufacture for analysis purpose. Table 1. Test rig specification. No Equipment Description 1 Compressor Hermetically sealed, Rotary 2 pk, R22 refrigerant 2 Condenser Air cooled, finned coil. 3 Expansion device Capillary tube 0.7 mm; thermostatic expansion valve. 4 Evaporator Shell and tube heat exchanger 5 Fan coil unit (FCU) Finned coil 6 Pump Centrifugal, 125 W Two expansion devices, capilary tube and thermostatic expansion valve are placed in the refrigeration system equipped with hand shut off valves for the individually analysis. The test rig specification are listed on table 1.The sketch of experimental apparatus of this study shown in figure 2. 2
Figure 2. The sketch of experimental apparatus 3. Instrumentation The refrigerant temperatures and air temperatures were measured by k-type thermocouples, attached to the copper pipe wall. The pressure of the refrigeration system were measured by pressure gauge which placed at four point of refrigeration cycle system. The temperatures data were digitalized using data logger and recorded in computer memory and the current of compressor was measured by digital ampere meter. 4. Result and Discussion Figure 3 shows the capilary tube and TEV cycle which plotted on p-h diagram. The cycle constitutes mainly four processes e.g. compression; heat rejection; expansion; and heat absorption. This investigation focus on the expansion device that devide the high pressure side and low pressure side of refrigeration system. First, the experiment were carried out for capillary tube and then thermostatic expansion valve (TEV) under same charging. All of the physical parameter observed from the system plotted to the p-h diagram using coolpack software from DTU. The coordinate point from p-h diagram then calculated to find the performance parameters. Figure 3 describe the pressure ratio of capillary tube was higher compare to that of TEV. This phenomena shows that the TEV controlled the expansion process better which was correlated to the pumping power of the compressor. 3
TEV Capilary Tube Figure 3. Expansion device cycle on p-h diagram Figure 4 shows the comparison of performance parameter between capillary tube (CT) and thermostatic expansion valve (TEV). Qe is heat absorbed in the evaporator; Qc is heat rejected in the condenser; W is compressor energy. Qe was correlated with the refrigerating effect of the system. The heat absorbed in the evaporator for TEV system were higher compared to that of CT system about 7.07%. The heat rejected from the condenser for the TEV were slightly higher than for CT system about 2.7%. The energy consumes by the compressor for TEV system were lower about 13.6% compared to that of CT system. 250 Performance Parameter 200 150 100 50 0 Qe (kj/kg) Qc (kj/kg) W (kj/kg) CT 151,1 196,13 45,03 TEV 161,79 201,42 39,63 Figure 4. The performance parameter Figure 5 describe the coefficient of performance (COP) in theoritical and actual for TEV and CT system. COP of TEV sytem were better than CT system. TEV provide more efficiency over wide range temperature operation. TEV improved the refrigerant return to the compressor by maintain the refrigerant superheat using sensing bulb. 4
Coefficient of Performance 6 5 4 3 2 1 0 Theoritical Actual CT 4,64 3,36 TEV 5,54 4,08 Figure 5. The sketch of experimental apparatus 5. Conclusions From the analysis of the system, it conclude that: 1. Coefficient of Performance (COP) of vapor compression refrigeration system for thermostatic expansion valve (TEV) is about 21.4 % more than capillary tube. 2. The overall performance parameter of the TEV system is reasonally good as compared to CT system 6. References [1] Sunu P W, Anakottapary D S, Santika W G 2016 Matec web of conference 58, 04006 [2] Sunu P W, and Rasta I M 2017 Acta Polytechnica 57(2):125 130 [3] Wang F, Lin H, Tu W, Wanga Y, Huang Y 2015 Procedia Engineering 121 1812 1818 [4] Anil K, Nitin G, Sachin P 2017 Energy Procedia 109 479 486 [5] Liu M S, Mark C C L, Wang C C 2011 Nanoscale Research Letters 6:297 [6] Naik B K, Muthukumar P 2017 Energy Procedia 109 ( 2017 ) 293 305 [7] Marcinichen J B, Melo C, Stähelin R 2004, 10th Brazilian Congress of Thermal Sciences and Engineering ENCIT paper CIT04-0748 [8] Stoecker W F, Smith L D III, Emde B N 1981 Influence of the expansion device on the seasonal energy requirements of a residential air conditioner ASHRAE Trans 87(1): 349 60. [9] Dhumal A H, Dange H M. 2014.. Int J Adv Engg Tech/Vol. V/Issue II/April-June, 96-99 [10] Amol A G, Madhav S J, Rupesh L, Raut, Rahul A, Bhogare 2014. International Journal Of Science, Engineering And Technology Volume 02 Issue 05 June. 5