The physical behavior of the new refrigerant R723, an azeotropic mixture of 60% Ammonia and 40% Dimethyl Ether, was investigated for use in adsorption heat pumps and refrigeration systems. The potential use of this refrigerant blend in adsorption systems with components made of copper instead of stainless steel provides with a motive for experimental investigation. In this work the experimental results of an activated carbon – R723 pair generator are presented when operating with driving temperatures ranging from 100oC up to 170oC and condensing temperatures of 20oC and 35oC. By comparing the measured temperature of the refrigerant liquid in the receiver and the saturated temperature calculated from the measured pressure it is shown that the refrigerant R723 remains stable throughout the adsorption – desorption process even when operating at pressures as high as 16 bar

Lychnos, George

Tamainot-Telto, Zacharie

English

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http://wrap.warwick.ac.uk/          Original citation: Lychnos, George and Tamainot-Telto, Zacharie (2014) Experimental investigation of activated carbon – R723 pair for use in adsorption heat pump and refrigeration systems. In: 2014 International Sorption Heat Pump Conference, Maryland, USA, 31 Mar -3 Apr 2014. Published in: Proceedings of 2014 International Sorption Heat Pump Conference (Number 28). pp. 1-6.  Permanent WRAP url: http://wrap.warwick.ac.uk/63870   Copyright and reuse: The Warwick Research Archive Portal (WRAP) makes this work of researchers of the University of Warwick available open access under the following conditions.  Copyright © and all moral rights to the version of the paper presented here belong to the individual author(s) and/or other copyright owners.  To the extent reasonable and practicable the material made available in WRAP has been checked for eligibility before being made available.  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For more information, please contact the WRAP Team at: publications@warwick.ac.uk  28, Page 1International Soprtion Heat Pump Conference, March 31-April 3, 2014Experimental investigation of activated carbon – R723 pair for use in adsorption heatpump and refrigeration systemsGeorge LYCHNOS*, Zacharie TAMAINOT-TELTOUniversity of Warwick, School of Engineering,Coventry, CV4 7AL, UK* Corresponding Author(Tel. +44 2476573364, Fax +44 24 76418922, E-mail: G.Lychnos@warwick.ac.uk)ABSTRACTThe physical behavior of the new refrigerant R723, an azeotropic mixture of 60% Ammonia and 40% DimethylEther, was investigated for use in adsorption heat pumps and refrigeration systems. The potential use of thisrefrigerant blend in adsorption systems with components made of copper instead of stainless steel provides witha motive for experimental investigation. In this work the experimental results of an activated carbon – R723 pairgenerator are presented when operating with driving temperatures ranging from 100oC up to 170oC andcondensing temperatures of 20oC and 35oC. By comparing the measured temperature of the refrigerant liquid inthe receiver and the saturated temperature calculated from the measured pressure it is shown that the refrigerantR723 remains stable throughout the adsorption – desorption process even when operating at pressures as high as16 bar.1. INTRODUCTIONThe key objective of this paper is the investigation of the use of refrigerant R723 in adsorption heat pumps andrefrigeration systems. Activated carbon – Ammonia pairs have been investigated extensively by researchers(Tamainot-Telto et al. 2009c; Wang et al. 2006) for use in sorption cooling systems. Although significantadvances have been made that improve the performance (Metcalf 2009; Tamainot-Telto et al. 2009b) thesesystems are entirely manufactured with stainless steel (due to the presence of ammonia) which is moreexpensive and heavier than copper or copper alloys (widely preferred and used in the conventional refrigerationand heat pump systems). The compatibility of R723 with refrigeration copper tube or its alloy CuNi10 when themoisture content within the sorption system does not exceed 400ppm is well established (OSCAR Final Report2005; Palm 2008). As a blend refrigerant, the key concern remains the separation of his two components incourse of adsorption or desorption process. Although the initial work (Tamainot-Telto et al. 2009a) has alreadydemonstrated the potential of this refrigerant at restricted operated conditions in both pressure (0.9 to 8.5 bar)and temperatures (20oC to 70oC), the current work has widen the operating conditions within the full range ofadsorption heat pump and refrigeration systems: 1 to 16 bar for the pressures and 20oC to 170oC fortemperatures. The sketch of the experimental set-up used to cycle the reactor containing activated carbon-R723pair is shown in Figure 1. This work consists of looking into both the adsorption and desorption process in orderto identify possible changes in the refrigerant’s physical behaviour.2. EXPERIMENTAL SETUPThe experimental set-up is illustrated in Figure 1. It consists primarily of two vessels, the receiver whichcontains the refrigerant (marked with number 1 in Fig 1) and the generator which contains the activated carbon(marked with number 2 in Fig 1). They are connected with ½” OD stainless tube (0.71 mm thickness) and threeball valves. The receiver is immersed in a constant temperature water bath. Two pressure transducers are placedin line to monitor the pressure changes of the system. Each pressure transducer’s rating range is 0 to 17 bar.Three type-K thermocouples shielded with stainless steel are used to monitor the temperature of the constanttemperature water bath, the saturated temperature of the refrigerant inside the receiver (with its measuring28, Page 2International Soprtion Heat Pump Conference, March 31-April 3, 2014junction close to the bottom of the vessel to ensure that it stays always wet) and the temperature of the generatorat the centre. A silicone rubber heating tape is wrapped around the generator with time percentage dial controlfor regulating the heat input and therefore keeping the driving temperature constant during desorption. All thesystem components exposed to the refrigerant were made of stainless steel. A data acquisition system is used foracquiring the signals from the thermocouples and pressure transducers connected to a PC which runs a datalogging software.Figure 1: Sketch of the experimental rig.3. EXPERIMENTAL PROCEDURE AND RESULTSThe generator is a cylindrical vessel (0.35 l capacity) filled up with dried activated granular carbon 208C(Chemviron) weighed approximately 162 g (Mc). The generator is under vacuum; it was heated up to 110oC andvacuumed with a vacuum pump connected through valve C in order to remove moisture and air. The receiver isa cylindrical vessel (0.13 l capacity) that was loaded with R723 refrigerant (about 4/5 of the total volume)through valve A. Valve B remained closed throughout the charging process. When both the receiver and thegenerator are in thermal equilibrium (ambient temperature) valve B is opened slowly, the refrigerant gas flowsin the generator (bed) and adsorption takes place. This is the initial loading of the generator. In Figure 2 thetemperature of the bed Tbed and saturation temperature Tsat,rec as measured in the receiver are illustrated againsttime during the initial loading and cooling of the generator. The maximum concentration of R723 adsorbed bythe carbon was calculated from the mass difference of the saturated carbon (after the initial loading) divided bythe mass of the dried carbon (kg of R723 / kg of carbon):(1)The experiments carried out after the initial adsorption take place in two stages:Stage 1. Desorption takes place when the generator is heated up at desired driving temperature (regulated withthe tape heater control); valve B is open therefore the refrigerant condenses in the receiver which is kept coolwith the aid of the constant temperature bath. The process ends after heating up for approximately 30-40 min atthe desired driving temperature when the system reaches steady state. Then we close valve B and the pressure ofthe generator drops as the system is left to cool down to ambient temperature.Stage 2. Valve B is opened slowly and then R723 gas flows from the receiver to the generator where is adsorbedby the activated carbon. This is the adsorption stage, in the beginning the generator’s temperature is risingbecause of the adsorption, reaches a maximum and then is left to cool down to the ambient temperature (end).28, Page 3International Soprtion Heat Pump Conference, March 31-April 3, 2014Table 1 summarises the experimental conditions. The experimental results of experiment 1a (see Table 1) areillustrated in figures 3 and 4. Figure 3 shows the measured pressures of the generator (Pgen) and the receiver(Psat,rec) compared to the predicted saturation pressure Psat(Trec) as predicted based on the temperaturemeasurements of the receiver and saturation pressure Psat(Tbed) as predicted based on the temperaturemeasurements of the bed during stages 1 and 2. Figure 4 shows the measured temperatures of the generator(Tbed) and the receiver (Tsat,rec) during stages 1 and 2.Similar temperature and pressure profiles were obtained from the other experiments when carried out at highertemperatures and pressures. By comparing the measured temperature (T1) of the refrigerant liquid in thereceiver (C) and the saturated temperature calculated from the measured pressure (PT1) (BOC Gases 2012), weare able to conclude whether there is component separation or change in component ratio; in fact thetemperature differences in all the experiments carried out were between 1 – 2.5 oC. Even when operating underthe experimental conditions of 4b (see Table 1) the pressure difference between the saturation measuredpressure Psat,rec and predicted pressure Psat,pred after cooling was less than 0.5 bar (see Figure 5). Similarly thepressure differences Psat,rec - Psat,pred observed in the rest of the experiments ranged between 0.4 and 0.5 bar.Table 1: The experimental conditionsExperiments 1a 1b 2a 2b 3a 3b 4a 4bTdriv (oC) 100 100 125 125 150 150 170 170Tcond (oC) 18.4 16.3 16.9 18.9 19.3 17.7 16.9 35Figure 2: Temperature profiles of the receiver Tsat,rec (saturation temperature) and generator Tbed during theinitial loading of the generator.28, Page 4International Soprtion Heat Pump Conference, March 31-April 3, 2014Figure 3: Pressure profiles of the generator (Pgen), the receiver (Psat,rec) compared to the saturation pressurePsat(Trec) as predicted based on the temperature measurements of the receiver and saturation pressure Psat(Tbed)as predicted based on the temperature measurements of the bed during desorption at 100oC (condensingtemperature 18.4oC) and adsorption.Figure 4: Temperature profiles of the generator (Tbed) and the receiver (Tsat,rec) during desorption at 100oC(condensing temperature 18.4oC) and adsorption.28, Page 5International Soprtion Heat Pump Conference, March 31-April 3, 2014Figure 5: Pressure profiles of the generator (Pgen), the receiver (Psat,rec) compared to the saturation pressure(Psat,pred) as predicted based on the temperature measurements of the receiver during desorption at 170oC(condensing temperature 35oC) and cooling.4. CONCLUSIONSThere was no unusual gas behavior observed throughout the whole series of experiments, i.e. there were not anyanomalies in pressure or temperature profiles that would justify gas separation and dissociation. With atemperature difference of less than 3K between the measured temperature of the refrigerant liquid in the receiverand the saturated temperature calculated from the measured pressure, the refrigerant is considered unchangedtherefore balanced. All test carried out were satisfactory within a large range of operating conditions. Even atdriving temperatures as high as 170oC and condensing temperature of 35oC (which results in pressures of 15 –16 bar during desorption) the saturation pressure measurements when compared to predicted ones showeddifferences within the measurement error. In fact the pressure differences were in the order of 0.5 bar when inthermal equilibrium. If there was gas separation (therefore altering significantly the ratio of ammonia - dimethylether initial mixture) the physical behavior of the refrigerant would have deviated significantly from the R723standard one reported in the literature.5. FUTURE WORKThe future work will be focused on porosity measurements of the activated granular carbon 208C – R723 pairunder a wide range of temperatures (20 – 200oC) and pressures (2 – 200 bar). This is mainly aimed to establishthe concentration of R723 within the carbon as function of both temperature and pressure.ACKNOWLEDGEMENTSThe project is supported by EPSRC (Grant EP/J000876/1) and Chemviron Carbons Ltd (Lockett Road,Lancashire WN4 8DE, UK).28, Page 6International Soprtion Heat Pump Conference, March 31-April 3, 2014REFERENCESBOC Gases (2012), Thermodynamic and physical properties of R723.Metcalf, S. J. (2009), Compact high efficiency carbon-ammonia adsorption heat pump, PhD, University ofWarwick.OSCAR Final Report (2005), Innovation in small capacity ammonia refrigeration plants, EU Contract No.ENK6-CT-2002-30020, Dresden, RTD. Institut fur Luft- und Kaltetechnik gGmbH (D)/DanishTechnological Institute (DK).Palm, B. (2008), Ammonia in low capacity refrigeration and heat pump systems, International Journal ofRefrigeration, 31(4): 709-715.Tamainot-Telto Z., Metcalf S. J. and Critoph R. E. (2009a), Investigation of activated carbon-R723 pair forsorption generator, International Heat Powered Cycles Conference, Berlin (Germany).Tamainot-Telto Z., Metcalf S. J. and Critoph R. E. (2009b), Novel compact sorption generators for car airconditioning, International Journal of Refrigeration, 32(4): 727-733.Tamainot-Telto Z., Metcalf S. J., Critoph R. E., Zhong Y. and Thorpe R. (2009c), Carbon–ammonia pairs foradsorption refrigeration applications: ice making, air conditioning and heat pumping, InternationalJournal of Refrigeration, 32(6): 1212-1229.Wang L. W., Wang R. Z., Lu Z. S., Chen C. J., Wang K. and Wu J. Y. (2006), The performance of twoadsorption ice making test units using activated carbon and a carbon composite as adsorbents, Carbon,44(13): 2671-2680.

Ammonia in low capacity refrigeration and heat pump systems,

Carbon–ammonia pairs for adsorption refrigeration applications: ice making, air conditioning and heat pumping,

Investigation of activated carbon-R723 pair for sorption generator, International Heat Powered Cycles Conference,

Novel compact sorption generators for car air conditioning,

Report (2005), Innovation in small capacity ammonia refrigeration plants,

The performance of two adsorption ice making test units using activated carbon and a carbon composite as adsorbents,

Thermodynamic and physical properties of R723.

Experimental investigation of activated carbon : R723 pair for use in adsorption heat pump and refrigeration systems

http://wrap.warwick.ac.uk/63870/1/WRAP_9472514-es-081114-ztt1_ishpc_us_orlando_2014.pdf

Experimental investigation of activated carbon : R723 pair for use in adsorption heat pump and refrigeration systems

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