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Analysis of transport properties for hydro fluorocarbon (hfcs)
 

Analysis of transport properties for hydro fluorocarbon (hfcs)

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    Analysis of transport properties for hydro fluorocarbon (hfcs) Analysis of transport properties for hydro fluorocarbon (hfcs) Document Transcript

    • International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 3, April (2013), © IAEME163ANALYSIS OF TRANSPORT PROPERTIES FOR HYDROFLUOROCARBON (HFCS) REFRIGERANT FOR AIR –CONDITIONING SYSTEMB.HADYA1, Dr. P. USHA SRI21Assistant Professor, Mechanical engineering department, U.C.E., Osmania University2Associate Professor, .Mechanical engineering department, U.C.E., Osmania UniversityABSTRACTThis paper presents the simulated results of an Air-Conditioning Condenser with hydrofluorocarbon(HFCs) group refrigerant of 1 ‘TR’ capacity with available experimental data ofcondensing temperature (Condensing Temperature 54.45°C pressure 14.72 bar) with differentambient conditions (Ambient air Temperatures) as per Indian scenario. The critical factors whichinfluences design consideration for optimum performance of Air-Conditioning are, ambienttemperature, Compressor selection, Condenser design, air flow through condenser, selection ofrefrigerant and refrigerant properties. The overall heat transfer coefficient (U) W/m2K and Condensersurface area (A) m2influences the size of a condenser, i.e the sizing of condenser is described byUA-value evaluation. The evaluation should include, Gross heat rejection, ambient temperature,temperature difference and air flow rate. The ambient temperatures of air (cooling medium) from25°C to 40°C were chosen and results obtained were shown and compared with different ambienttemperature. For the ambient temperature 25°C the simulated UA-value is 0.149 kW/ K and 40 °C theUA-Value is 0.487 kW/ K. The refrigerant properties play an important role in refrigeration and airconditioning, if the condenser with constant air flow rate, the density of the selected refrigerant varieswith ambient temperature, for the ambient Temperature 25 oC and 40 oC, the simulated densityobtained were 961 kg/m3and 893 kg/m3. From the simulated results for higher ambient temperatureswith constant air flow rate 960 (m3/h), for selected condensing temperature the condensereffectiveness reduces due to decrease in the log mean temperature difference (LMTD) value. Thevariation of UA-value is depends on the type of condenser, compressor capacity, type of refrigerantused and other transport properties.For Air –Conditioning installation the important consideration on condenser design is type ofload i.e latent heat load and sensible heat load in this present analysis only latent heat load isconsidered at constant condensing temperature for evaluation.Keywords: Hydro fluorocarbon (HFCs) Alternate refrigerant, Condensing Temperature, UA-valueand LMTD.INTERNATIONAL JOURNAL OF ADVANCED RESEARCH INENGINEERING AND TECHNOLOGY (IJARET)ISSN 0976 - 6480 (Print)ISSN 0976 - 6499 (Online)Volume 4, Issue 3, April 2013, pp. 163-169© IAEME: www.iaeme.com/ijaret.aspJournal Impact Factor (2013): 5.8376 (Calculated by GISI)www.jifactor.comIJARET© I A E M E
    • International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 3, April (2013), © IAEME1641.0 INTRODUCTIONThe significance of refrigeration and air conditioning is increasing every day, the refrigerantused in refrigeration system plays very important role in refrigeration system. Refrigerant likeChloro- fluorocarbon (CFC), Hydro Chloro fluorocarbon (HCFC) has been used for many decadesas a working medium because of their better performance, but due to some environmental impactthere is a need to search for alternate refrigerant like hydro fluorocarbon(HFCs), Hydrocarbon(HCs)have emerged as zero ozone potential depletion and low global warming potential with favorableperformance[1-3].In refrigeration Cycle heat is received at low temperature and rejected at hightemperature, while a net work is done on the fluid (refrigerant).The practical refrigeration cycle iscomposed of flow processes, each process being carried out in a separate component. Figure 1 showsthe simple vapour compression refrigeration cycle, the main components of refrigerating system areCompressor, condenser expanding Device and evaporator the function of the compressor is tocompresses the vapour refrigerant to condenser, condenser is located at high pressure side and itsfunction is to remove heat from hot vapour refrigerant discharged from the compressor, the functionof the expansion valve is to reduce the pressure. Evaporator is an important device used in lowpressure side of refrigeration system the function of evaporator is to absorb heat from the mediumwhich is to be cooled by means of refrigerant [3-7].2.0 LITERATURE STUDYCondensers are heat exchangers designed to remove the heat absorbed by the refrigerant inthe evaporator and heat of compression added by the compressor. This is achieved by transferringheat from the refrigerant vapour discharged by the compressor to some external cooling medium,usually water or air. As result of vapour refrigerant condenses back to the liquid at constant pressure.Thus the function of a condenser is to get rid of the heat absorbed previously and reliquify therefrigerant [8-9].In the condenser the pressure is maintains constant, but the temperature is constantonly during the removal of latent heat from the refrigerant i.e. only in the condensing portion.2.1Classification of CondensersCondensers are classified as Air cooled condenser, Water cooled condenser and Evaporativecondenser.2.1.1 Air Cooled condenserAir cooled condensers were initially used for small refrigerating systems, but now they aredesigned in large sizes with capacity of above 100kW.Air cooled refrigerators are widely used fordomestic refrigerators, freezers, water coolers and room air- conditioners.Air cooled condenser is one in which the removal of heat is done by air which passes throughthe finned tubes (copper or steel) with the size of 6 mm 18 mm outside diameter, depending upon thesize of condenser. Generally copper tubes are used because of its excellent thermal conductivity andheat transfer rate. Condenser absorbs heat from the vapour refrigerant and condenses it in to liquid.This liquid refrigerant flows out at the bottom of the condenser to expansion device. The main
    • International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 3, April (2013), © IAEME165advantages of air cooled condensers are simplicity in design, high flexibility, low installation andmaintenance cost and negligible corrosion effect [10-12]However, their use is restricted to small capacities because of low heat transfer and unevendistribution of air on condenser surface. For the increase in ambient temperature causes reduction inthe capacity of the condenser. The air cooled condensers requires a large quantity of air. They arefurther classified as: Natural draught type and Forced draught type the force draught type further subdivided as Chassis mounted type and Remote type.Natural draught condensers are used in small capacity plants such as domestic refrigerators.Refrigerant vapour enters at the cooling air rises vertically over the condenser surface. Thesufficiently large enough to ensure that the condensation is complete, and liquid refrigerant is subcooled before it enters the expansion valve.In forced draught condenser, a fan or blower provides a steady flow of air for removal of heatfrom the refrigerant that flows through the copper tubes. The surface area of the tubes is extended byproviding aluminum fins fan is directly driven by motor or belt driven. Force draught condensers areused for large refrigerators, food freezers, water coolers and air conditioners. Force draughtcondensers are sub-divided into chassis mounted and remote type. In chassis mounted typecompressor and condenser s are mounted on the common chassis as a single unit (Condensing Unit).Its size is small and, and the capacity is limited up to 3 tons. . In remote type, the condenser is locatedaway from the compressor. It is usually located on the roof or windows. This type of condensers isused for fairly large capacity refrigerant system.3.0 THEORETICAL ANALYSIS:Figure 2. Temperature Distribution in a CondenserFigure 2 shows the temperature distribution in condenser with liquid sub cooling anddesuperheating, the refrigeration effect and the heat rejection rate of the system will vary dependingon the actual balance of evaporator, compressor and condenser. Once the compressor and evaporatorselected to perform the required cooling, it is essential that condenser be selected on the basis of thecapability of these components. Thus the selection is made on the heat gain, but rather on the actualload on the condenser.Since the heat transfer through the condenser is by conduction, condenser capacity is functionof fundamental heat transfer equation.3.1 Theoretical calculations for Condenser and ambient air heat transfer rateQc = U .A. (LMTD) (1)Where, Qc = Condenser capacity in kWU = Overall Heat Transfer Coefficient W/m2KA = Effective Surface area m2LMTD = the log mean temperature difference between the condensing refrigerantand condensing medium i.e ambient air Temperature °C
    • International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 3, April (2013), © IAEME166From above equation UA-value and LMTD variation can be determined by changing ambient airflow rate and air inlet conditions (Temperature inlet)By Energy balance heat gained by cooling mediumQC = m* Cp* (TOUT, SEC- TIN, SEC) (2)Where,QC = Heat Transfer rate (3.5k W)m =Mass flow rate of air (0.32kg/sec.)Cp =Specific heat of air (1005 J/Kg K)TOUT, SEC= Air outlet temperature (K) which is to determineTIN, SEC = Air inlet temperature (298 K)4.0. SIMULATION ANALYSIS:For simulation, REFPROP version 6.01 (REFPROP is an acronym for RefrigerantProperties) used for finding out the properties of Refrigerant 32 which gives the most accurate purefluid property for simulation, developed by the National Institute of Standards and Technology(NIST) provides the thermodynamic and transport properties of refrigerants REFPROP also provideshigh accuracy data for pure refrigerants and refrigerant mixtures, for the simulation the density of therefrigerant 32 for the condenser were evaluated with ambient temperatures.Cool Pack (version 1.49) is a collection of simulation programs used for designing,dimensioning, analyzing and optimizing the refrigeration system, it consist of three main groupRefrigeration Utility ,EES Cool Tool, Dynamic analysis Tool. EES provides high accuracy propertydata for pure refrigerant and refrigerant mixtures and used to analyses Cycle performance, SystemDimensioning, Operation analysis, System Simulation and Comparison of Refrigerants.The Programsin cool pack covers following simulation purpose:Calculation of Refrigeration Properties (Property plots, thermodynamic and Thermo-physicaldata, Refrigerant Comparisons• Cycle Analysis –Compression of single Stage and Multi Stage.• System dimensioning-Calculation of component sizes from general configuration criteria• System Simulation-Calculation Operating conditions in a system with known components withtheir operating parameters.• Evaluation of Operation-Evaluation of the system Coefficient of Performance with less powerconsumption4.1. Simulation for R32 at condensing temperature of 54.45°C, inlet air temp 25°C and air flowrate is 960 m3/ h.Figure 3. Simulation of air ambient temperature at 25°C
    • International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 3, April (2013), © IAEME1674.2 Simulation for R32 at condensing temperature of 54.45°C, inlet air temp. 40°C and air flowrate is 960 m3/ h.Figure 4. Simulation of air ambient temperature at42°CFigure 3 &4 shows that the Simulation of Condensing Temperature of refrigerant 32 at 54.45°C for the model used for testing ambient conditions according to ASHRAE, ISO and other standarddata for higher ambient conditions. In this model, the testing situation is specified by setting the inputparameters like temperature Tc , TIN SEC , Ambient air flow rate VSEC(m3/h) and Capacity.5.0. RESULTS AND DISCUSSIONTable 1: Shows that variation of UA-value with LMTDTable 1 shows the variation of UA-value with log mean temperature difference and condenserdensity variation for the selected refrigerant for conditioning temperature 54.45°C of selectedrefrigerant R32 with different ambient temperaturs from 25°C to 40 °C. From the table 1, it isobserved that overall heat transfer coefficient is a function of ambient air flow rate and temperaturedifference.Air CooledCondenserTemp. ofcooling medium(Air)UA-Value(kW/K)LMTD(K)Density(kg/ m3)RefrigerantR32Condensertemp.(Tc)54.45°C25°C 0.149 23.52 96130°C0.191 18.28 939.635°C0.271 12.94 91740°C0.487 7.18 893
    • International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 3, April (2013), © IAEME168Figure.5. Variation UA-value (kW/K) with Ambient TemperatureFigure 6. The variation of density for the Refrigerant 32 with ambient air temperatureFigure 7. The variation of Condensing Temperature with LMTD.Figure 5 shows the simulated results of overall heat transfer coefficient with ambienttemperature UA-Value increases with ambient temperature for constant mass flow rate of air. Forfurther higher ambient temperature the UA-Value reduces. Figure 6 show that the density for theselected refrigerant varies with ambient temperature for the condenser of constant air flow rate .Figure7 shows the Log mean temperature difference (LMTD) variation with different ambient temperatures.Performance of selected condenser is depends on Overall heat transfer coefficient UA-valueincreases with ambient temperature , for higher ambient temperature with same mass flow rate UA-value reduces , if air circulation is increased effectiveness of condenser may be increased.
    • International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 3, April (2013), © IAEME1696.0 CONCLUSIONSSimulation results shows that for the condenser of capacity 1 “TR” Air-Conditioningsystem, the Overall Heat transfer coefficient is very effective up to ambient temperature 40oC with airflow rate of 960 m3/h. if the air flow rate is constant for ambient temperature 45 oC the condenserperformance is decreases because of the decrease in the LMTD, hence the system performance willdecrease. The density for the selected refrigerant varies with ambient temperature for the condenser ofconstant air flow rate at ambient Temperature 25 oC the simulated density obtained is 961 kg/m3, fortemperature 40 oC density 893 kg/m3. The effectiveness of the condenser can be increased byincreasing air flow rate. The variation of UA-value is depends on the type of condenser, compressorcapacity, type of refrigerant used and other transport properties. , From the simulation results it isobserved that overall heat transfer coefficient is a function of ambient air flow rate and temperaturedifference.For Air –Conditioning installation the important consideration on condenser design istype of load i.e latent heat load and sensible heat load in this present analysis only latent heat load isconsidered at constant condensing temperature for evaluation.AcknowledgementThis part of research work has been carried out under O.U/D.S.T-PURSE Programme,Scheme no A-38. Under the esteem Guide of Dr.P.Usha Sri, Associate Professor, Department ofMechanical Engineering, University College of Engineering (A), Osmania University- Hyderabad.REFERENCE[1] S.Devotta, A.S.Padalkar ansN.K.Sane, “Experimental Performance Analysis of a RetrofittedWindow Air Conditioner with R-407C”International Refrigeration and air conditioningconfrrence.Paper 533.[2] ASHRAE, Thermo physical Properties of Refrigerants Chapter 20, ASHRAE Fundamentals.[3] HVAC Handbook-2007 Indian Society of Heating Refrigerating and Air – ConditioningEngineers, Part I-Air Conditioning.[4] B.O.Bolaji, M.A. Akintundeand T.O.Falade, “Comparative Analysis of Performance of threeOzone- Friends HFC Refrigerants in a Vapour Compression Refrigerator”, Journal ofSustainable Energy &Environment 2 (2011) 61-64.[5] PhD. Theses of Dr. Azizuddin on Alternate Refrigerants for Air Conditioning[6] Bukola Olalekan Bolaji,”Effect of Sub-Cooling on the Performance of R12 Alternatives inDomestic Refrigeration system, Thammasat Int.J.Sc.Tech., Vol.15 Jan-March 2010.[7] D.B.Bivens and A.Yokozeki “ Heat transfer Coefficients and transport properties foralternative refrigerants ”,[8] Refrigeration and Air Conditioning Book by R.C. ARORA. International Refrigeration and Air–Conditioning[9] M.Mohanraj, S.Jayaraj. C.Muralidharan “Comparative Assessment of environmental –friendlyalternative to R134a in domestic refrigerants.” Energy Efficiency (2008), Vol.1:189-198[10] Refrigeration and Air Conditioning Book by C.P ARORA.and DOMKUNDWER.[11] REFPROP version 6.01 AND Cool Pack Version 1.49 Refrigeration and Air ConditioningSimul[12] Technical manual air -Conditioning application.[13] Dr. Ashok G. Matani And Mukesh K. Agrawal, “Performance Analysis Of VapourCompression Refrigeration System Using R134a, Hc Mixture And R401a As WorkingMedium”International Journal Of Mechanical Engineering & Technology (IJMET) Volume 4,Issue 2, 2013, pp. 112 - 126, ISSN PRINT : 0976 – 6340, ISSN ONLINE : 0976 – 6359