CHAPTER 4 EXPERIMENTAL STUDIES

Transcription

1 113 CHAPTER 4 EXPERIMENTAL STUDIES 41 INTRODUCTION Based on the results of the theoretical studies on the air-cooled GAX based vapour absorption refrigeration syste that were carried out, the design and fabrication of the syste have been done The results of the pinch point analysis helps to identify the streas responsible for heat recovery and thereby heat load capacity for exchange between the streas This helps to design the internal heat recovery coponents such as high pressure GAX, low pressure GAX, solution cooler, solution heat exchanger 2, condensate precooler The heat load obtained for these coponents are used in the experiental test-rig design An experiental investigation of the perforance of the air-cooled GAX based vapour absorption refrigeration syste designed for 105 kw cooling capacity is presented The experiental plan and procedure, easureent of paraeters and data reduction are discussed in detail in this chapter 42 COMPONENTS OF THE SYSTEM The coponents of the air-cooled GAX based vapour absorption refrigeration syste, are the absorber, condenser, evaporator, generator, high pressure GAX, low pressure GAX, solution heat exchanger 1, solution heat exchanger 2, solution cooler and condensate pre-cooler The coponents of the air-cooled GAX based vapour absorption refrigeration syste are designed for the heat loads obtained fro the therodynaic analysis,

2 114 corresponding to a cooling capacity of 105 kw At the designed conditions of the generator, sink and evaporator teperatures of 150 C, 45 C and -10 C, respectively and at a split factor of 08, based on the pinch point analysis, the aount of heat recovered in the various internal heat exchanging coponents are given in Table 41 Table 41 Heat load of the internal heat exchanging coponents Coponent Heat Load (kw) High Pressure GAX 36 Low Pressure GAX 46 Solution Heat Exchanger Solution Heat Exchanger 2 36 Solution Cooler 53 Condensate Pre-Cooler 13 The coponents are designed using standard procedure with relevant heat and ass transfer equations / coefficients The specifications of the designed coponents are given in Table 41 The coponent drawings are shown fro Figures 41 to EXPERIMENTAL SET UP All the coponents are fabricated as per design specifications, and then assebled after testing for leaks The scheatic of the experiental setup of the air-cooled GAX based vapour absorption refrigeration syste is shown in Figure 412

3 115 Table 42 Specifications of the ajor coponents of the syste Coponent Design Conditions Specifications Absorber (Figure 41) Weak solution teperature: 45 C Strong solution teperature: 67 C Inlet air teperature: 28 C Outlet air teperature: 38 C Mass flow rate of weak solution: 0058 kg/s Mass flow rate of strong solution: 0050 kg/s Mass flow rate of refrigerant: 0008 kg/s Type: Finned Material: Mild steel Tube Diaeter (ID): 15 Thickness: 4 Tube Length: 750 Nuber of Tubes: 20 Heat Transfer Duty: 2185 kw Heat Transfer Area: Coponent Design Conditions Specifications Condensor (Figure 41) Refrigerant vapour teperature: 48 C Refrigerant liquid teperature: 46 C Inlet air teperature: 28 C Outlet air teperature: 38 C Mass flow rate of refrigerant: 001 kg/s Type: Finned Material: Mild steel Tube Diaeter (ID): 15 Thickness: 4 Tube Length: 750 Nuber of Tubes: 16 Heat Transfer Duty: 1196 kw Heat Transfer Area: :072 2

4 116 Table 42 (Contd ) Coponent Design Conditions Specifications Evaporator (Figure 42) Refrigerant liquid teperature: -12 C Refrigerant vapour teperature: -10 C Mass flow rate of refrigerant: 001 kg/s Type: Shell and Coil Material: Mild steel Shell Diaeter (OD): 600 Shell Length: 1150 Coil Diaeter (OD): 254 Thickness: 74 Length: 1360 Nuber of Coils: 28 Heat Transfer Duty: 105 kw Heat Transfer Area: Coponent Design Conditions Specifications Generator (Figure 43) Weak solution teperature: 119 C Strong solution teperature: 150 C Mass flow rate of weak solution: 0058 kg/s Mass flow rate of strong solution: 0048 kg/s Type: Direct Fired Material: Mild steel Diaeter (ID): 4886 Diaeter (OD): 514 Length: 1552 Heat Transfer Duty: 2327 kw Heat Transfer Area: 1 2

5 117 Table 42 (Contd ) Coponent Design Conditions Specifications High Pressure GAX (Figure 44) Weak solution inlet teperature: 45 C Weak solution outlet teperature: 59 C Refrigerant inlet teperature: 112 C Refrigerant outlet teperature: 48 C Mass flow rate of weak solution: 0058 kg/s Mass flow rate of refrigerant: 001 kg/s Type: Shell and Tube Material: Mild steel Shell Diaeter (ID): 1035 Thickness: 108 Shell Length: 1194 Tube Diaeter (ID): 36 Thickness: 24 Tube Length: 1200 Nuber of Tubes: 132 Heat Transfer Duty: 365 kw Heat Transfer Area: Coponent Design Conditions Specifications Low Pressure GAX (Figure 45) Weak solution inlet teperature: 59 C Weak solution outlet teperature: 68 C Strong solution inlet teperature: 76 C Strong solution outlet teperature: 67 C Refrigerant teperature: 38 C Mass flow rate of weak solution: 0058 kg/s Mass flow rate of strong solution: 0048 kg/s Mass flow rate of refrigerant: 0002 kg/s Type: Shell and Tube Material: Mild steel Shell Diaeter (ID): 3032 Thickness: 206 Shell Length: 331 Tube Diaeter (ID): 36 Thickness: 24 Tube Length: 375 Nuber of Tubes: 76 Heat Transfer Duty: 457 kw Heat Transfer Area: 054 2

6 118 Table 42 (Contd ) Coponent Design Conditions Condensate Refrigerant liquid inlet teperature: 46 C Pre-Cooler Refrigerant liquid outlet teperature: 20 C Refrigerant vapour inlet teperature: -10 C (Figure 46) Refrigerant vapour outlet teperature: 38 C Mass flow rate of refrigerant: 001 kg/s Coponent Design Conditions Solution Weak solution inlet teperature: 68 C Heat Weak solution outlet teperature: 102 C Exchanger 1 Strong solution inlet teperature: 120 C (Figure 47) Strong solution outlet teperature: 76 C Mass flow rate of weak solution: 0058 kg/s Mass flow rate of strong solution: 0048 kg/s Specifications Type: Shell and Tube Material: Mild steel Shell Diaeter (ID): 1541 Thickness: 142 Shell Length: 1456 Tube Diaeter (ID): 94 Thickness: 33 Tube Length: 1500 Nuber of Tubes: 76 Heat Transfer Duty: 133 kw Heat Transfer Area: Specifications Type: Tube-in-Tube Material: Mild steel Outer Tube Diaeter (OD): 409 Thickness: 74 Length: 1456 Inner Tube Diaeter (ID): 36 Thickness: 24 Length: 1456 Nuber of Tubes: 24 Heat Transfer Duty: 1223 kw Heat Transfer Area: 068 2

7 119 Table 42 (Contd ) Coponent Design Conditions Specifications Solution Heat Exchanger 2 (Figure 48) Weak solution inlet teperature: 102 C Weak solution outlet teperature: 112 C Strong solution inlet teperature: 130 C Strong solution outlet teperature: 120 C Mass flow rate of weak solution: 0058 kg/s Mass flow rate of strong solution: 0048 kg/s Type: Tube-in-Tube Material: Mild steel Inner Tube diaeter (ID): 627 Thickness: 103 Tube Length: 1210 Outer Tube diaeter (ID): 203 Thickness: 16 Tube Length: 1210 Heat Transfer Duty: 357 kw Heat Transfer Area: Coponent Design Conditions Specifications Solution Cooler (Figure 49) Weak solution inlet teperature: 112 C Weak solution outlet teperature: 119 C Strong solution inlet teperature: 150 C Strong solution outlet teperature: 130 C Mass flow rate of weak solution: 0058 kg/s Mass flow rate of strong solution: 0048 kg/s Type: Shell and Tube Material: Mild steel (Shell) Mild Steel (Tube) Shell Diaeter (ID): 1541 Thickness: 142 Shell Length: 1456 Tube Diaeter (ID): 102 Thickness: 152 Tube Length: 750 Nuber of Tubes: 4 Heat Transfer Duty: 526 kw Heat Transfer Area: 024 2

8 120 Table 42 (Concluded) Coponent Weak Solution Reservoir (Figure 410) Coponent Refrigerant Reservoir (Figure 411) Specifications Type: Vertical Cylinder Material: Mild steel Diaeter (ID): 3071 ; Thickness: 168 Length: 385 Specifications Type: Vertical Cylinder Material: Mild steel Diaeter (ID): 1282 ; Thickness: 131 Length: 385

9 AIR OUT LOW PRESSURE REFRIGERANT VAPOUR IN HIGH PRESSURE REFRIGERANT VAPOUR IN STRONG SOLUTION IN HIGH PRESSURE REFRIGERANT LIQUID OUT WEAK SOLUTION OUT AIR IN Figure 41 Scheatic of the absorber and the condensor 121

10 CHILLED WATER OUT REFRIGERANT IN REFRIGERANT OUT CHILLED WATER IN Figure 42 Scheatic of the evaporator 122

11 WEAK SOLUTION IN REFRIGERANT VAPOUR OUT STRONG SOLUTION OUT Figure 43 Scheatic of the generator 123

12 REFRIGERANT VAPOUR IN WEAK SOLUTION OUT WEAK SOLUTION IN REFRIGERANT VAPOUR OUT Figure 44 Scheatic of the high pressure GAX 124

13 STRONG SOLUTION IN WEAK SOLUTION IN REFRIGERANT VAPOUR IN STRONG SOLUTION OUT WEAK SOLUTION OUT Figure 45 Scheatic of the low pressure GAX 125

14 REFRIGERANT VAPOUR OUT REFRIGERANT LIQUID OUT REFRIGERANT LIQUID IN REFRIGERANT VAPOUR IN Figure 46 Scheatic of the condensate pre-cooler 126

15 STRONG SOLUTION IN WEAK SOLUTION OUT WEAK SOLUTION IN STRONG SOLUTION OUT Figure 47 Scheatic of the solution heat exchanger 1 127

16 128 STRONG SOLUTION IN FLUE GAS OUT WEAK SOLUTION OUT WEAK SOLUTION IN FLUE GAS IN STRONG SOLUTION OUT Figure 48 Scheatic of the solution heat exchanger 2

17 129 STRONG SOLUTION IN STRONG SOLUTION OUT WEAK SOLUTION IN WEAK SOLUTION OUT Figure 49 Scheatic of the solution cooler

18 130 WEAK SOLUTION OUT Figure 410 Scheatic of the weak solution reservoir REFRIGERANT OUT Figure 411 Scheatic of the refrigerant reservoir

19 WEAK SOLUTION STRONG SOLUTION REFRIGERANT LPGAX SC SX2 6 7 FGO FGI B 10 G HPGAX 8 EV SX SR 1 PT PT 23 A C F RR 18 E PRV 19 SFM RFM CPC SP LEGEND A Absorber FGO Flue Gas Outlet SC- Solution Cooler E Evaporator B Burner G - Generator SFM Solution Flow Meter EV Expansion Valve C Condensor HPGAX High Pressure GAX SP Solution Pup F Fan CPC Condensate Pre-Cooler LPGAX Low Pressure GAX SR Solution Receiver FGI Flue Gas Inlet PRV Pressure Reducing Valve SX1 Solution Heat Exchanger 1 RFM Refrigerant Flow Meter PT Pressure Transducer SX2 Solution Heat Exchanger 2 RR Refrigerant Reservoir Figure 412 Scheatic of the experiental set up 131

20 Figure 413 Pictorial view of the coponents of the experiental set up before insulation 132

21 Figure 414 Pictorial view of the experiental set up before insulation 133

22 Figure 415 Pictorial view of the coponents of the experiental set up after insulation 134

23 1 Absorber 2 Burner Condenser 4 Condensate Pre-Cooler 5 Evaporator 6 Generator 7 High Pressure GAX 8 Low pressure GAX 9 Pressure Transducer 10 Refrigerant Flow Meter 11 Solution Cooler Solution Heat Exchanger 1 13 Solution Heat Exchanger 2 14 Solution Pup 15 Weak Solution Reservoir Figure 416 Pictorial front view of the experiental set up after insulation 135

24 Figure 417 Pictorial rear view of the experiental set up after insulation 136

25 Power Analyzer Data Logger Figure 418 Pictorial view of the experiental set up with easuring instruents 137

26 138 The pictorial views of the coponents, and the experiental set up before and after insulation are shown in Figures 413 to 418 The syste has two pressure levels The absorber is at evaporator pressure and the generator at condenser pressure Weak solution (ws) is puped by a 15 kw solution pup (SP) of diaphrag type, fro the absorber (A) to the high pressure GAX (HPGAX) The HPGAX is an indirect counter current gas liquid heat exchanger, which cools the refrigerant vapor (state point 16) coing fro the generator through the solution cooler (SC), by the incoing weak solution entering the HPGAX at state point 2 The heat of rectification is thus transferred to preheat the incoing weak solution The weak solution enters the low pressure GAX (LPGAX) The LPGAX absorbs a partial aount of the refrigerant vapor (state point 24) fro the condensate pre-cooler (CPC) The siultaneous absorption of the refrigerant vapour takes place in both the LPGAX and the absorber, due to the splitting of the refrigerant vapour at a split factor of 08 to the absorber and the LPGAX The pipe diaeter fro the outlet of the condensate pre-cooler to the low pressure GAX, is reduced in such a way that the refrigerant flow rate is at a split factor of 08 for a diaeter ratio of 1:2 Thus the split factor is aintained constant during experients and it is not easured The heat of absorption, and the cooling of strong solution fro state point 12 to 13 are utilized to heat the weak solution fro state point 3 to 4, thus reducing the heat input Then, the weak solution enters the solution heat exchanger 1 (SX1) SX1 is the heat exchanger siilar to the one used in the conventional single effect syste, where it exchanges heat with the strong solution returning fro the generator through the solution heat exchanger 2 (SX2) It does not differ fro SHX The weak solution then enters the solution heat exchanger 2 (SX2) In the SX2, the weak solution (state point 5) is heated by both the strong solution (state point 9) and the waste flue gases fro the burner leaving the SX2 After extracting the energy fro the flue gas and the strong solution in the SX2, the weak solution finally enters the generator through the Solution Cooler (SC), where it is further

27 139 heated by the strong solution leaving the generator In the generator, the external heat input fro a diesel fired burner is supplied to generate the refrigerant vapour The purified vapor leaves the HPGAX and enters the condenser at state point 17 Both the absorber and the condenser are aircooled The air circulation is accoplished by a 075 kw fan The liquid refrigerant fro the condenser enters the condensate precooler (CPC) The CPC is the econoizer that is used in the syste, which heats the refrigerant vapour fro the evaporator by sub-cooling the liquid refrigerant fro the condenser, before being throttled The refrigerant vapour fro the CPC enters the absorber and the LPGAX Table 42 shows the type, heat transfer area and the designed heat duty of the various coponents of the air-cooled vapour absorption refrigeration syste Table 43 Coponent details SNo Coponent Type Heat ( 2 ) Transfer Heat Duty Area (kw) 1 Absorber Finned Condenser Finned Evaporator Shell and Coil Generator Direct Fired High Pressure GAX Shell and Tube Low Pressure GAX Shell and Tube Condensate Pre-Cooler Shell and Tube Solution Heat Exchanger 1 Tube-in-Tube Solution Heat Exchanger 2 Tube-in-Tube Solution Cooler Shell and Tube

28 CHARGING PROCEDURE The individual coponents of the syste are fabricated as per the design specifications and subjected to hydraulic pressure testing upto 20 bar to check for any leakage Due to liited facility in the laboratory, the pressure testing of the individual coponents was restricted upto 20 bar only The pressure is aintained for a period of 2 to 3 days The coponents are then assebled and instruented with pressure, teperature, and flow rate easureents at the required location, as shown in Figure 412 The entire syste was again tested for leakage following the above procedure The syste is then evacuated to an extent of 30 of Hg and the vacuu is aintained for 3 days To reove the non-condensable gases that ay be present, the syste after evacuation is first charged with the refrigerant vapour The syste is charged with calculated quantities of the refrigerant and absorbent The calculation procedure to deterine the required quantity of refrigerant and absorbent are given in Appendix 2 and the specifications of the equipents such as the solution pup, absorber and condenser fan, burner and power analyzer are given in Appendix 3 45 MEASUREMENT OF PARAMETERS The details of the instruentation are presented in this section The paraeters that are to be easured are the pressure, teperature, density and ass flow rate of the solution, the air velocity, density and ass flow rate of the refrigerant, and ass flow rate of the fuel The uncertainty analysis of the easured / calculated paraeters is presented in Appendix Pressure Pressure easureents are ade by calibrated Pressure Transducers The low and high pressures in the syste are easured with the instruent ranging fro 0 to 10 bar and 0 to 25 bar respectively, with an uncertainty of ± 020%

29 Teperature Teperatures are easured with T type copper-constantan therocouples The ends of all the therocouples are connected to a data acquisition syste (Make: Agilent 34970A) The therocouples were calibrated at ice point of water and abient teperature Good agreeent is observed between the theroeter readings and easured readings of the teperature using T-type therocouples The therocouples are fixed at various locations on the experiental set up The easureents are ade with an uncertainty of ± 05 o C These data are stored in a data acquisition syste 453 Flow Rate The ass flow rate of the weak solution and the refrigerant are easured by coriolis ass flow eters with an uncertainty of ± 02% and ± 015% respectively 454 Concentration The density and the teperature of both the weak solution and the refrigerant are easured by coriolis ass flow eters Using the correlation which gives the relation between the specific volue, the teperature and the concentration of the saturated aonia-water solution, the concentration of the weak solution and the refrigerant are deterined as given below v( T, X) 3 3 j i aij X T (41) i 0 j 0 The coefficient of Equation (41) is taken fro the ASHRAE Handbook Fundaental (1993)

30 Fuel Consuption The fuel flow rate to the generator is easured by a digital weighing achine with an uncertainty of ± 005% 456 Heat Loss The heat loss fro the surface of the generator to the surrounding is calculated, based on the easureent of the teperatures at the generator surface, insulation surface and the theral conductivity of the insulation aterial The aount of heat loss fro the generator to the surroundings is estiated to be 0175 kw, which is about 15% of the actual generator heat input The calculation procedure is entioned in Appendix 5 46 EXPERIMENTAL PLAN AND PROCEDURE The following ranges of operating conditions are fixed for testing the perforance of the fabricated experiental setup (a) (b) The ass flow rate of the weak solution is varied between kg/s and kg/s The fuel flow rate to the generator is varied between 1kg/h and 15 kg/h, by using different nozzles in the burner First, the absorber condenser fan is switched on, followed by the diesel fired burner to supply heat input to the generator The weak solution is then circulated between the absorber and the generator, by switching on the solution pup for the generation of the refrigerant vapour in the generator The condensing and evaporating teperatures varies with the cooling ediu and water teperatures respectively The evaporating and condensing teperatures were aintained by regulating the flow of strong solution and

31 143 the refrigerant using the pressure reducing valve and refrigerant expansion valve The flow rates of the refrigerant, the pressure and teperature of the coponents, air velocity, and fuel flow rate are noted periodically After the refrigerant reservoir is filled about 50%, the pressure reducing valve between the condensate pre-cooler and the evaporator is adjusted in such a way that a constant flow of liquid refrigerant is established The level of the weak solution in the weak solution reservoir in aintained constant for the steady state operation, regulating the flow of the strong solution fro the generator to the absorber through the expansion valve The refrigerant is also aintained at a constant level in the refrigerant reservoir When two to three successive readings are alost the sae, it can be concluded that the syste has attained the steady state As a safety precaution, since water has good affinity towards aonia, sufficient quantity of water has been kept as it can easily dilute the concentration of the refrigerant Safety face asks and gloves were also used while operating the syste Any traces of aonia leaked into the atosphere, can be easily detected before it reaches the toxic level due to its pungent odour 47 DATA PROCESSING The circulation ratio (CR) is deterined by the easured flow rate of the weak solution and the refrigerant CR ws/r (42)

32 144 The heat recovered by the internal heat recovery coponents is estiated fro the ass flow rate of the weak solution and the fluid enthalpies The heat recovered by the high pressure GAX is Q (h h) (43) HPGAX ws 3 2 The heat recovered by the low pressure GAX is Q (h h) (44) LPGAX ws 4 3 The heat recovered by the solution heat exchanger 1 is Q (h h) (45) SX1 ws 5 4 The heat recovered by the solution heat exchanger 2 is Q (h h) (46) SX2 ws 6 5 The heat recovered by the solution cooler is Q (h h) (47) SC The heat recovered by the condensate pre cooler is Q (h h ) (48) CPC In Equations (43) (48), the teperatures were easured, using calibrated copper-constantan therocouples (T-type) To calculate the enthalpy, the easured teperature and the solution concentration were used in the correlation proposed by Sun (1997) The heat rejected by the absorber and condensor is Q Cp (t t ) (49) AC a a ao ai The easured teperatures were recorded in a data acquisition syste The air velocity was easured by an aneoeter at the inlet to the

33 145 absorber and condenser The air flow rate is then calculated using the following relation a = (density of air) x (area) x (air velocity) (410) The heat supplied to the generator is Q (CV) (411) fuel fuel fuel CV fuel = 44,000 kj/kg Air-Fuel ratio = 14:1 (Ganesan 2002) The cooling capacity is estiated by calculating the rate of heat reoval fro a constant quantity of water Q E wcpw dt/d (412) The volue of the evaporator shell is calculated and the required quantity of water is filled in The water teperature in the evaporator shell was easured at three different locations (top, iddle and botto) using copper-constantan therocouples The easureents were recorded and stored periodically every 15 inutes A graph between tie and teperature is plotted and the slope is taken for the calculation The variation of abient air teperature during the course of experient varies in the range of ± 3 C only This variation does not contribute significantly on the perforance of the syste The fuel COP is then deterined using the relation COPfuel Q E Q (413) fuel The total COP is calculated considering the auxiliary power required to operate the solution pup, fan and the burner COPtotal Q E (Q fuel WSP Wf W b ) (414)

34 146 power analyzer The auxiliary powers were easured by using a calibrated digital 48 RESULTS AND DISCUSSION The perforance of the syste was evaluated by varying the ass flow rate of the weak solution and the fuel flow rate to the generator 481 Variation of the syste pressures Figure 419 shows the variation of the syste pressures with tie for a constant weak solution and fuel flow rate and split factor The split factor is defined as the ratio of the ass flow rate of the refrigerant to the absorber, to the total ass flow rate of the refrigerant in the cycle The low ws kg / s fuel 105 kg / h Z = 08 Pressure (bar) Condensor Evaporator Tie (h) Figure 419 Variation of the syste pressures with tie

35 147 and high pressures stabilize at about 4 bar and 18 bar respectively, and the syste reaches the steady state in about 120 inutes of operation 482 Variation of the coponent s teperatures Figure 420 shows the variation of the coponent s teperature and the abient teperature with tie The abient teperature was initially at 28 C, but reached upto 35 C during the operation of the syste It is observed fro Figure 420, that the generator teperature increases steadily and after nearly three hours, it stabilizes at a teperature of about 125 C The variation of the absorber and condenser teperatures with respect to tie also follows a pattern siilar to that of the generator The absorber teperature is higher than the condensor teperature due to the large aount of heat of ixing during the absorption process The evaporator teperature decreases with tie, initially The decrease in the evaporator teperature during the initial three hours of operation, is due to the heat capacities of the different coponents of the syste After 2 to 3 hours, it becae stable, thus providing the cooling capacity at a constant rate 145 ws kg / s fuel 105 kg / h Z = Teperature ( C) Absorber Evaporator Air inlet Condensor Generator Air outlet Tie (h) Figure 420 Variation of the coponent s teperature with tie

36 Teperature history of the internal heat recovery coponents The teperature history of the internal heat recovery coponents are shown fro Figures 421 to 423 The teperatures were easured at all the inlets and outlets of the coponents with respect to the solution / refrigerant streas The ass flow rate of the weak solution and the fuel flow rate are kg/s and 105 kg/h respectively The internal heat recovery coponents coprise of the CPC, HPGAX, LPGAX, SX1, SX2 and SC ws kg / s Teperature ( C) fuel 105 kg / h Z = 08 0 rli CPC rlo CPC rvi CPC rvo CPC wsi SX1 wso SX1 ssi SX1 sso SX Tie (h) Figure 421 Variation of the teperatures of the CPC and SX1 with tie

37 Teperature ( C) wsi LPGAX wso LPGAX ssi LPGAX sso LPGAX rvi LPGAX -25 wsi SX2 wso SX2 ssi SX2 sso SX Tie (h) Figure 422 Variation of the teperatures of the LPGAX and SX2 with tie 125 ws kg / s 100 Teperature ( C) fuel 105 kg / h Z = wsi HPGAX wso HPGAX rvi HPGAX rvo HPGAX wsi SC wso SC 0 ssi SC sso SC Tie (h) Figure 423 Variation of the teperatures of the HPGAX and SC with tie

38 150 The rise in the teperature of the weak solution is about 5 to 10 C in the GAX coponent, naely, the HPGAX and LPGAX, and also in the SC, whereas it is about 5 C in the SX2 The SX1 accounts for nearly 25 to 30 C rise in the aount of heat gained by the weak solution The effectiveness of the SX1 is deterined to be 80 to 85% 484 Circulation ratio and weight fraction The variation of the circulation ratio and the weight fraction, with respect to tie for a typical operating condition is shown in Figure 424 The circulation ratio has a greater ipact on the syste perforance The circulation ratio was initially high, because of the less aount of refrigerant circulation, and it becae steady after 2 hours fro the starting tie of the syste operation The weight fraction of the weak solution is high initially, ainly due to the refrigerant that was eptied out of the refrigerant circuit and stored in the solution after the previous run The weight fraction of the pure refrigerant reains alost constant fro the starting tie of the refrigerant circulation The refrigerant vapour leaving the HPGAX is condensed in the condensor and is stored in the refrigerant reservoir CR Z = 08 X r CR ws fuel kg / s 105 kg / h Weight Fraction (%) 3 X ws X ss Tie (h) Figure 424 Variation of the circulation ratio and weight fraction with tie

39 151 The concentration of the liquid refrigerant before it enters the evaporator through the condensate pre-cooler, is estiated by using the correlation which gives the relation between the specific volue, the teperature and the concentration The density and the teperature of the refrigerant is easured by a coriolis ass flow eter The HPGAX is very effective as the estiated concentration of the refrigerant, was found to be 099, as inferred fro Figure 424 The weight fraction of the strong solution also follows a trend siilar to that of the weak solution 485 Pinch point diagra for a typical operating condition The pinch point diagra for a typical operating condition is shown in Figure 425 The heating process is represented by state points 2 to G It represents the aount of heat recovered by the weak solution in the various internal heat recovery coponents Processes 8 to A represent the cooling process The difference in the heat load between state points 2 and A, is the absorber heat load The difference in the heat load between state points 2 and 8 represents the total aount of heat recovered by the heat recovery coponents The aount of the external heat input that is supplied to the generator is represented by the region between the state points 8 and G The pinch point is the closest approach teperature between the heating and cooling curves It can be inferred fro the above figure that the pinch point occurs between state points 4 and 11 on the heating and cooling curves respectively A pinch point of 7 C is obtained and a axiu cooling capacity of 95 kw is attained About 16 kw of internal heat has been recoveredthe experiental pinch point diagra which shows a pinch point of 7 C, has been plotted for a particular operating condition of generator, absorber, condenser and

40 152 evaporator teperatures of 120 C, 52 C, 46 C and 2 C respectively, whereas the pinch point at the other operating conditions is greater than10 C Teperature ( C) Z = 08 ws kg / s fuel 105 kg / h A Q G Pinch point G 25 0 Q A Q IHR weak solution strong solution Heat Load (kw) Figure 425 Pinch point diagra for a typical operating condition 486 Heat load Figure 426 shows the variation of the heat supplied, the heat recovered and the heat rejected by the syste with respect to tie for the generator, absorber, condenser and evaporator teperatures of 120 C, 52 C, 46 C and 2 C respectively The heat supplied is estiated by adding the heat load of the evaporator and that of the generator Due to the increase in the refrigerant circulation the evaporator heat load increases, and this results in an increase in the aount of heat supplied to the syste, until the steady state is reached The heat recovered is estiated, by adding the heat loads of all the internal heat recovery coponents such as the CPC, HPGAX, LPGAX, SX1, SX2 and SC The aount of heat recovered by the heat recovery coponents increases gradually with tie, due to the rise in the teperature of the weak solution at the outlet of the corresponding coponent The SX1 contributes to about 60 to 70% of the total

41 153 aount of heat recovered internally The internal heat recovered in the GAX coponent and the SC is approxiately 15 kw each 25 ws fuel kg / s 105 kg / h t G = 120 C, t A = 52 C, t C = 46 C, t E = 2 C, Z = 08 Heat Load (kw) Heat Supplied Heat Recovered Heat Rejected Tie (h) Figure 426 Variation of the heat load with tie Overall, the heat recovery coponents provide nearly 16 kw of heat recovered to the generator The aount of heat rejected by the syste is the total aount of the heat rejected by both the absorber and the condenser The variation in the heat rejection load is not unifor, due to the variation in the absorber and condenser load in different abient conditions 487 Cooling capacity and COP The perforance of the syste in ters of the cooling capacity, fuel and total COP, with respect to tie is shown in Figure 427 The fuel COP, calculated based on the fuel consuption rate and the rate of heat reoval fro a fixed quantity of water, reached a axiu of 061 for the generator, absorber, condenser and evaporator teperatures of 120 C, 52 C, 46 C and 2 C respectively

42 ws kg / s fuel 105 kg / h t G = 120 C, t A = 52 C, t C = 46 C 15 COP t E = 2 C t E = -2 C Z = 08 COP fuel COP total Cooling Capacity Cooling Capacity (kw) Tie (h) Figure 427 Variation of the cooling capacity and the COP with tie The total COP, calculated by considering the parasitic power consuption, reached a axiu of 058 for the sae operating conditions, which is about 8 % less than the fuel COP The cooling capacity of the syste is about 74 kw and it reains alost constant When the evaporator teperature decreases fro 2 C to -2 C while the other operating paraeters reain constant, the cooling capacity and the perforance of the syste are reduced This is because, when the evaporator teperature decreases, the aount of the refrigerant ass flow rate decreases, and hence, the cooling capacity and the COP of the syste also decrease The decrease in the actual perforance of the syste, when the evaporator teperature varies fro 2 C to -2 C, is nearly 10 to 15%

43 Experiental runs Figure 428 depicts the perforance of the syste with respect to the experiental runs The ass flow rate of the weak solution is kept constant at kg/s, and the fuel flow rate to the generator at 105 kg/h The syste reached the axiu COP after 3 hours of operation during each ws fuel kg / 105 kg / h s t G = 120 C, t A = 52 C, t C = 46 C, t E = 2 C, Z = 08 COP Fuel Total Therodynaic Experient Runs Figure 428 Variation of the COP with experiental runs experiental run The fuel and the total COP of the syste vary between 060 and 063 and 056 and 059 respectively, for different experiental runs, for the sae operating conditions The deviation between the therodynaic and fuel COP is estiated to be 20 to 25% due to heat losses and the internal irreversibility in the syste For a particular set of experiental observations, the perforance paraeters are given in Appendix 5 The efficiency of the diesel fired burner is 95 to 98% For calculation purposes, the efficiency is taken as 100%

44 Effect of fuel consuption Figure 429 depicts the effect of the fuel flow rate in kg/h on the cooling capacity and the fuel COP of the syste, for an evaporator teperature of 2 C The ass flow rate of the weak solution is kept constant at kg/s and the split factor at 08 It is inferred fro the Figure that the cooling capacity increases with an increase in the fuel flow rate The increase COP t E = 2 C Z = 08 ws kg / s Fuel COP 6 Cooling Capacity Cooling Capacity (kw) Fuel Consuption (kg/h) Figure 429 Variation of the cooling capacity and COP with the fuel consuption in the fuel flow rate increases the heat input to the generator, which leads to the generation of ore aount of refrigerant vapour, for a constant weak solution flow rate As a result of the increased refrigerant vapour generation, the cooling capacity increases However, the fuel COP of the syste does not increase because, firstly, the heat of generation increases as the generator teperature increases Secondly, the generator efficiency decreases with an increasing fuel consuption rate It is found that the fuel COP of 061 is attained under the conditions analyzed for the fabricated syste

45 Influence of the sink teperatures on the circulation ratio Figure 430 shows the variation of the circulation ratio with respect to the sink teperature for the generator and evaporator teperatures of 120 C and 2 C respectively For a constant weak solution flow rate, as the 150 ws kg / s t G = 120 C, t E = 2 C t G = 120 C, t E = 2 C 120 Z = 08 CR Sink Teperature ( C) fuel fuel fuel 140 kg / h 125 kg / h 105 kg / h Figure 430 Variation of the circulation ratio with the sink teperatures sink teperature increases, the circulation ratio increases This is because, as the sink teperature increases the weak solution concentration decreases, which results in a lower degassing width The lower degassing width increases the circulation ratio For a constant sink teperature, the increase in the fuel flow rate lowers the circulation ratio This is due to the increase in the refrigerant flow rate, for a constant weak solution rate 4811 Influence of the sink teperatures on the heat load The variation of the heat supplied, heat recovered and heat rejected with the sink teperatures is shown in Figure 431 The heat supplied is the suation of the evaporator and generator load and the heat rejected is the

46 158 suation of the absorber and condenser heat load The heat recovered by the syste is the total heat load of all the internal heat recovery coponents, such as the high pressure GAX, the low pressure GAX, solution heat exchangers 1 and 2, solution cooler and the condensate pre-cooler As the sink teperature increases, the total heat supplied reduces, due to the decrease in the evaporator load at higher sink teperatures The heat rejected fro the syste also decreases with the sink teperature However, the heat recovered by the syste increases due to the increase in the teperature difference across the internal heat recovery coponents The reason for large difference between the heat supplied to the syste and the heat rejected by the syste as inferred fro the Figures 426 and 431 is because, the heat loss fro the other coponents and the connecting pipelines were not easured 25 ws kg / s fuel 105 kg / h t G = 120 C, t E = 2 C Heat Load (kw) Heat Supplied Heat Recovered Heat Rejected Sink Teperature ( C) Figure 431 Variation of the heat load with the sink teperatures

47 Influence of the sink teperatures on the cooling capacity and COP The variation of the cooling capacity and the COP of the syste with respect to the sink teperatures is shown in Figure 432, for a constant weak solution flow rate of kg/s and fuel flow rate of 105 kg/h When the sink teperature increases, the decrease in the degassing width increases the circulation ratio For a constant weak solution flow rate, the increase in the circulation ratio reduces the refrigerant ass flow rate Hence the cooling capacity decreases The decrease in the cooling capacity decreases the COP of the syste 08 ws kg / s fuel 105 kg / h t G = 120 C, t E = 2 C 10 COP Fuel COP Total COP Cooling Capacity Cooling Capacity (kw) Sink Teperature ( C) Figure 432 Variation of the cooling capacity and the COP with the sink teperatures

48 Second law efficiency Figure 433 shows the variation of the second law efficiency with respect to the sink teperatures, for a constant weak solution flow rate and constant generator and evaporator teperatures With increase in the sink teperature, the fuel and the carnot COP decreases Since the rate at which the carnot COP decreases is higher that that of fuel COP, the second law efficiency increases 045 ws kg / s fuel 105 kg / h t G = 120 C, t E = 2 C 040 Second law efficiency Sink Teperature ( C) Figure 433 Variation of the second law efficiency with the sink teperatures 49 ECONOMIC ANALYSIS The incorporation of high pressure GAX, low pressure GAX, solution cooler and the solution heat exchanger 2 increases the first cost of the proposed syste Hence, it ay not be econoically viable when copared to that of a siple syste with only a solution heat exchanger and condensate pre-cooler However, for sall and ediu capacities up to 35 kw, air-

49 161 cooled systes are ore econoically viable copared to water-cooled systes, due to large size of the cooling tower, installation probles etc Since the water cooled systes need a cooling tower, cooling water pup etc, the installation cost will be higher than that of an air-cooled one, by 20 to 25%, for the sae capacity For a conventional aonia-water syste, the COP is about 05 and in the GAX syste it is about 061, at a generator, absorber, condenser, evaporator teperatures of 120 C, 52 C, 46 C, 2 C respectively The aount of internal heat recovery is about 30 to 40 % ore than in the conventional one, which would reduce the operating costs by about 20% 410 CONCLUSION In this chapter, the design of the coponents of the air-cooled GAX based vapour absorption refrigeration syste, the working fluid charging procedure, the easureent of paraeters, and the experiental plan and procedure have been presented The results of the experiental investigations on the air-cooled GAX based vapour absorption refrigeration syste are discussed The influence of the various paraeters such as the sink teperature and the fuel flow rate on the perforance of the syste is also discussed The perforance paraeters studied are the circulation ratio, internal heat recovered and the coefficient of perforance The conclusions drawn fro the experiental investigations are presented in the next chapter