Cooling Tower Performance

Transcription

1 Cling Twer Perfrmance Purpse: Thery 1. Student has deep understanding n principles f cling twer 2. Student can use the psychrmetric chart fr determining the specific humidity, specific enthalpy, relative humidity 3. Student can calculate effectiveness f the cling twer, t range, t apprach 4. Student can plt the relevant data fr seeking the cnclusin What a cling twer is A special kind f heat exchanger which allws air and water t cme in cntact t lwer the temperature f ht water. During the cntact, sme part f the water evaprates and decreases the temperature f left water. The cmpnents f cling twer Typical cmpnents f cling twer will be described in the fllwing picture

2 Type f cling twer Type f cling twer is defined primarily by the directin f the air flw when it cntacts with the water and way f creating air flw. If the air cntacts the water in crssing directin, the cling twer will be called as crssflw. If the water cntacts the air flw in ppsite directin, the cling twer is classified as cunterflw cling twer. If the air flw is a natural flw (buyancy flw), the cling twer is natural draft type. And when air flw is a frce flw, it will be called as mechanical draft. Psychrmetric chart A psychmetric chart is a methd t represent psychrmetric prcess that is a thermdynamic prcess in mixture f air and vapr. In a psychrmetric chart, relatins amng thermdynamic prperties can easily t determine. A typical psychrmetric chart f 1 atm pressure is fllwing. Figure 1. A typical psychrmetric chart where ellipses shw the parameters f psychrmetric prcess axes.

3 An example f determining parameters n a psychrmetric prcess with t_dry = 20 C and t_wet = 13 C can be referred in the fllwing picture. The crssing pint f the t_dry (temperature f dry bulb) and t_wet (temperature f wet bulb) was used fr determining the ther parameters. They are specific vlume, specific enthalpy, abslute humidity (the vapr cntent f air), and percentage humidity. accessed March 16 th 2017 Sme links that students can access fr free: Drift Eliminatr 2. Fill 3. Damper 4. Air Pump 5. Switches 6. Temperature display 7. Make-up water tank 8. Manmeter 9. Water flw-rate level

4 Manual f labratry activities 1. T start perating the cling twer Make sure that the heaters are switched-ff. Open the air damper and water flw valve Turn n the main switch and check the air and water flws. Check the temperature displays. Add water fr wet bulbs Add make-up water When everything is running well, start the experiment thrugh adding heat lad. 2. T stp peratin f cling twer Turn-ff all the heaters. Keep the air and water flws until the water utlet and inlet temperature are equal and cnstant. Turn-ff the main switch fr shutting dwn the pump. Clse the damper and plug the pwer ut. 3. Sme basic safety principles D nt let the temperature f lad t exceed 70 C. If the temperature f the lad > 70 C degree, the ht water pump may get int truble. ( Shut dwn the system and check the pump ) Check the lad water. The water shuld be in range. Lack f water will break the heaters. Add the make-up water befre the water surface reach minimum level. D nt let the temperature f lad t exceed 70 C. If the temperature f the lad > 70 C degree, the ht water pump may get int truble. ( Shut dwn the system and check the pump ) Check the lad water. The water shuld be in range. Lack f water will break the heaters. Add the make-up water befre the water surface reach minimum level. 4. Cllecting data Cllect the data (t1, t2, t3, t4, t5, t6, manmeter, water make up) fr the next variatin cnditin Run Lad 1.5 kw 1.5 kw 1 kw 1 kw 1 kw 1 kw 1.5 kw 1.5 kw Water g/s g/s g/s g/s g/s g/s g/s g/s flw Damper Fully pen Half pen Fully pen Half pen Fully pen Half pen Fully pen Half pen Fr every run, calculate air flw, specific humidity inlet, specific humidity utlet, specific enthalpy inlet, specific enthalpy utlet

5 Prcedures fr cllecting data 1. Befre starting the first run, take the psitin f manmeter 2. Set the make-up water t be zer psitin 3. D starting prcedure 4. Set cnditins t be 1 st run, take nte n manmeter 5. Wait arund 10 minutes until the cling twer steady 6. Take data f water make-up, t1, t2, t3, t4, t5, t6, 7. Add the water make-up and take nte its level psitin 8. Set the cnditin fr the next run and repeat activities frm the step 5 th. 9. During waiting the cling twer reaching steady, determine specific humidity inlet, specific humidity utlet, specific enthalpy inlet, specific enthalpy utlet by pltting the data f the preceding run. 10. Calculate effectiveness, t apprach and t range f the preceding run. 11. D stpping prcedure after all data are cllected.

6 Prperties Water flw rate (g/s) Damper psitin Half Opened Fully Half Fully Opened Opened Opened Cling lad (kw) Dry bulb temperature f inlet; t1 ( C) Wet bulb temperature f inlet; t2 ( C) Dry bulb temperature f utlet; t3 ( C) Wet bulb temperature f utlet; t4 ( C) Input water temperature; t5 ( C) Output water temperature; t6 ( C) Make-up water cnsumptin (cm) Specific enthalpy f air inlet, h in (kj/kg) Specific humidity f air inlet, ωin (g/kg dry air) Specific enthalpy f air utlet, h ut (kj/kg) Specific humidity f air utlet, ω ut (g/kg dry air) Cling range = t5 t6 ( C) Temperature apprach, t apprach = t6-t2 ( C) Effectiveness f cling twer; η=(t5-t6)/(t5- t2) air flw rate; m = pressure γ B

7 Grup assignment: Every grup shuld prepare pwer pint presentatin (in English). The presentatin shuld include 1. Prcedures f cllecting data and devices set-up 2. 2 graphs; they are the effect f water flw rate t effectiveness and cling range, and the effect f air flw rate t effectiveness and cling range 3. 2 psychrmetric chart wrks as samples 4. Answers f questins (will be delivered at the end f the labratry class) 5. Cnclusins. Persnal assignment: Every student must submit a small reprt n Tuesday in the cming week f the labratry class (specific time and place will be infrmed at class). The reprt shuld cntain 1. 2 graphs; they are the effect f water flw rate t effectiveness and cling range, and the effect f air flw rate t effectiveness and cling range 2. 1 psychrmetric chart wrk as sample 3. Answers f questins (will be delivered during the class).

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10 Appendix : Thery Cling Twer Terms Cling Range Cling Lad Make-up Drift Or Carry Over Packing r Fill Apprach t Wet Bulb Drain Dwn The difference between the water temperature at entry t and exit frm the twer. The rate at which heat is remved frm the water. This may be expressed in kw, Btu/h r k Cal/h. The quantity f fresh water which must be supplied t the water circuit t make gd the lsses due t evapratin and ther causes. Drplets f water which are entrained by the air stream leaving the twer. The materials ver which the water flws at it fall thrugh the twer, that a large surface area is presented t the air stream. The difference between the temperature f water leaving the twer and the wet bulb temperature f the air entering. Water deliberately remved frm the water system t prevent the excessive cncentratin f disslved slids due t evapratin and sludge due t impurities frm the atmsphere. Basic Principles Cnsider the surface f a warm water drplet r film in cntract with an air stream Assuming that the water is htter than the air, it will be cled. (i) (ii) (iii) By radiatin This effect is likely t be very small at nrmal cnditins and may be neglected. By cnductin and cnventin This will depend n the temperature difference, the surface area, air velcity, etc. By evapratin This is by far the mst imprtant effect. Cling takes place as mlecules f H 2O diffuse frm the surface int the surrunding air. These mlecules are then replaced by thers frm the liquid (evapratin) and the energy required fr this is frm the remaining liquid. Evapratin frm a Wet Surface The rate f evapratin frm a wet surface int the surrunding air is determined by the difference between the vapur pressure at the liquid surface, i.e. the saturatin pressure crrespnding with the surface temperature, and the

11 vapur pressure in the surrunding air. The latter is determined by the ttal pressure f the air and its abslute humidity, In an enclsed space, evapratin can cntinue until the tw vapur pressure are equal, i.e. until the air is saturated and at the same temperature as the surface. Hwever, if unsaturated air is cnstantly circulated, the wet surface will reach an equilibrium temperature at which the cling effect due t the evapratin is equal t the heat transfer t the liquid by cnductin and cnvectin frm the air, which under these cnditins, will be at the higher temperature. The equilibrium temperature reached by the surface under adiabatic cnditins, i.e. in the absence f external heat gains r lsses, is the wet bulb temperature, well knwn in cnnectin with hygrmetry. In a cling twer f infinite size and with an adequate air flw, the water leaving will be at the wet bulb temperature f the incming air. Fr the reasn, the difference between the temperature f water leaving a cling twer and the lcal wet bulb temperature is an indicatin f the effectiveness f the cling twer. The Apprach t Wet Bulb is ne f the imprtant parameters in the testing, specificatin, design and selectin f cling twers. Cnditining within a cling twer packing are cmplex due t the changing air temperature, humidity and water temperature as the tw fluids pass thrugh the twer usually in a cntra flw fashin. Cling Twer Perfrmance The fllwing factrs affect the perfrmance f a cling twer: (i) The air flw rate (ii) The water flw rate (iii) The water temperature (iv) The air temperature and humidity at inlet (particularly the wet bulb temperature) (v) The type f packing used (vi) The area and vlume f the packing The Bench Tp Cing Twer enables these factrs t be varied s that an verall appreciatin f cling twer characteristics can be btained. Thermdynamics Prperties Water

12 The specific enthalpy f saturated water is assumed t be zer at the triple pint (0.01 C and bar (611Nm 2 ), which is taken as datum. Thermdynamic table give the specific enthalpy f saturated water (h f) at a range f temperatures abve the datum cnditins, e.g. frm the tables (Ref.7, Page 54) at 20 C, the value f (h f) is 83.9 kj Kg -1,the saturated pressure is bar (2.337kN m -2 ) and the specific vlume is m 3 kg -1. Water is the Bench Tp Cling Twer is at atmsphere pressure, usually abut bar (101.3 kn m -2 ), and if the water is at say 20 C it must be cmpressed liquid, as its pressure is abve the saturatin pressure. h h v p p The specific enthalpy f cmpressed liquid is given by S that water at 20 C and kn m -2 has a specific enthalpy f h = 83.9 x ( ) J kg -1 h = 83.9 x J kg -1 h = 84 kj kg -1 It will be seen that at the cnditins likely t be encuntered in a cling twer, h = h f at the given temperature, i.e. the crrectin f pressure is insignificant. Specific Heat Capacity (Cp) If water is cled frm say 50 C t 20 C at atmspheric pressure, its specific enthalpy will fall frm t 83.9 kj kg -1, i.e. a decrease f kj kg -1 h This is an average change f = 4.18 kj kg -1 t 30 dt The rate f change f enthalpy with respect t temperature, ( i.e. ) is given symbl Cp (ften called the specific dh heat at cnstant pressure). Over the range f temperatures likely t be used in Bench Tp Cling Twer, we may therefre use fr water, h = Cp t) where Cp = 4.18 kj kg -1 and h Cpt Daltn s and Gibbs Laws Air is a mixture f dry air (xygen, nitrgen and ther gases) and water vapur. The behavir f such a mixture is set ut in the laws f Daltn and Gibbs frm which the fllwing may be deduced: (i) The ttal pressure f the air is equal t the sum f the pressures which the dry air and the water vapur each and alne wuld exert if they were ccupy the vlume f the mixture at the temperature f the mixture. (ii) The dry air and the water vapur respectively bey their nrmal prperty relatinships at their partial pressures. (iii) The enthalpy f the mixture may be fund by adding tgether the enthalpies which the dry air and water vapur each wuld have as the sle ccupant f the space ccupied by the mixture and at the same temperature. The water water vapur steam r misture cntent f the air is dented by its HUMIDTY. Mass f Water Vapur Abslute r Specific Humidity (ω) is the rati (i) Mass f Dry Air Relative humidity ( ) is the rati f f sat Partial Pressure f Water Vapur in the Air Saturatin Pressure f Water Vapur at the same Temperature (ii) Percentage Saturatin is the rati Mass f Water Vapur in a given vlume f Air Mass f same vlume f Saturated Water Vapur at the same Temperature (iii)

13 It can be shwn that at the cnditins within a cling twer, i.e. at high humidities, there is very little difference between the Relative Humidity and the Percentage Saturatin and fr cnvenience, they will be regarded as equal in the fllwing. Hygrmeter are instruments fr measuring the H 2O cntent f the atmsphere. Many different types f the hygrmeter are available but the Bench Tp Cling Twer uses the well knwn wet and dry bulb type fr which a large amunt f data is available. In this hygrmeter, the wet bulb thermmeter bulb is enclsed by a water wetted fabric sleeve. Evapratin frm this sleeve causes the temperature indicated by the wet bulb thermmeter t be lwer than that indicated by the dry bulb temperature. ( see page 15) Observatin f these temperatures in cnjunctin with published tables r charts enables the humidity and ther prperties f the air t be determined. Alternatively, the pressure f the water vapur in the atmsphere may be btained by substitutin in the equatin (due riginally t Regnault, August and Apjhn). p s p satw x10 pt ( t0 t w ) Where p s satw p t t 0 is the pressure f the water vapur in the air/(mbar) p is the saturatin pressure f water vapur at the temperature f wet bulb/(mbar) is the ttal air pressure (nrmally atmspheric pressure)/(mbar) is the temperature f dry bulb/ C t w is the (sling) temperature f wet bulb/ C Effect f Air Velcity n the Indicated Wet Bulb Temperature The sling wet bulb temperature used by the psychmetric charts and tables is that indicated by a wet bulb sensr placed in an air stream having a velcity f 3.5 m s -1 r mre At high relative humidities, there is little errr if the sensr is placed in a stream having a lwer velcity, but at lw relative humidities an appreciable errr may ccur. At utlet frm the Bench Tp Cling Twer the sensrs are placed in air with a very high relative humidity and where the air velcity is high. The wet bulb temperature indicated will therefre be accurate. The wet bulb sensr in the air chamber is in a regin-where the velcity is lwer and where the relative humidity is much lwer. It is therefre advisable t cnfirm the wet bulb reading as fllws: (i) (ii) (iii) Ease the bung securing the wet bulb sensr frm the tp f the air chamber. Draw the sensr upward until the air escapes between the scket and the sleeve. The air velcity ver the sleeve will nw be abut 10 m/s and the sling temperature will quickly be indicated by the sensr. Cmpare the sling reading with that previusly indicated any discrepancy can be allwed fr in subsequent bservatins at the same cnditins. The applicatin f the freging Laws and relatinships and the evaluatin f prperties is best illustrated by a wrked example as fllws.

14 Cling Twer เร ยบเร ยงโดย อ.ดร.ว รศ กด เล ศส ร โยธ น ว ตถ ประสงค 1. เพ อศ กษาระบบแลกเปล ยนความร อนแบบ cling twer 2. เพ อศ กษาถ งป จจ ยท ม อ ทธ พลจ อประส ทธ ภาพในการเปล ยนแปลงความร อนของระบบน น 3. เพ อประย กต ทฤษฎ สมด ลพล งงานและมวล ก บระบบจร ง เคร องม อทดลอง Bench Tp Cling Twer

15 Thery Cling Twer Terms Cling Range Cling Lad Make-up Drift Or Carry Over Packing r Fill Apprach t Wet Bulb Drain Dwn The difference between the water temperature at entry t and exit frm the twer. The rate at which heat is remved frm the water. This may be expressed in kw, Btu/h r k Cal/h. The quantity f fresh water which must be supplied t the water circuit t make gd the lsses due t evapratin and ther causes. Drplets f water which are entrained by the air stream leaving the twer. The materials ver which the water flws at it fall thrugh the twer, that a large surface area is presented t the air stream. The difference between the temperature f water leaving the twer and the wet bulb temperature f the air entering. Water deliberately remved frm the water system t prevent the excessive cncentratin f disslved slids due t evapratin and sludge due t impurities frm the atmsphere. Basic Principles Cnsider the surface f a warm water drplet r film in cntract with an air stream Assuming that the water is htter than the air, it will be cled. (i) (ii) (iii) By radiatin This effect is likely t be very small at nrmal cnditins and may be neglected. By cnductin and cnventin This will depend n the temperature difference, the surface area, air velcity, etc. By evapratin This is by far the mst imprtant effect. Cling takes place as mlecules f H 2O diffuse frm the surface int the surrunding air. These mlecules are then replaced by thers frm the liquid (evapratin) and the energy required fr this is frm the remaining liquid. Evapratin frm a Wet Surface The rate f evapratin frm a wet surface int the surrunding air is determined by the difference between the vapur pressure at the liquid surface, i.e. the saturatin pressure crrespnding with the surface temperature, and the vapur pressure in the surrunding air. The latter is determined by the ttal pressure f the air and its abslute humidity,

16 In an enclsed space, evapratin can cntinue until the tw vapur pressure are equal, i.e. until the air is saturated and at the same temperature as the surface. Hwever, if unsaturated air is cnstantly circulated, the wet surface will reach an equilibrium temperature at which the cling effect due t the evapratin is equal t the heat transfer t the liquid by cnductin and cnvectin frm the air, which under these cnditins, will be at the higher temperature. The equilibrium temperature reached by the surface under adiabatic cnditins, i.e. in the absence f external heat gains r lsses, is the wet bulb temperature, well knwn in cnnectin with hygrmetry. In a cling twer f infinite size and with an adequate air flw, the water leaving will be at the wet bulb temperature f the incming air. Fr the reasn, the difference between the temperature f water leaving a cling twer and the lcal wet bulb temperature is an indicatin f the effectiveness f the cling twer. The Apprach t Wet Bulb is ne f the imprtant parameters in the testing, specificatin, design and selectin f cling twers. Cnditining within a cling twer packing are cmplex due t the changing air temperature, humidity and water temperature as the tw fluids pass thrugh the twer usually in a cntra flw fashin. Cling Twer Perfrmance The fllwing factrs affect the perfrmance f a cling twer: (i) (ii) (iii) (iv) (v) (vi) The air flw rate The water flw rate The water temperature The air temperature and humidity at inlet (particularly the wet bulb temperature) The type f packing used The area and vlume f the packing The Bench Tp Cing Twer enables these factrs t be varied s that an verall appreciatin f cling twer characteristics can be btained.

17 Thermdynamics Prperties Water The specific enthalpy f saturated water is assumed t be zer at the triple pint (0.01 C and bar ( 611 N m 2 ), which is taken as datum. Thermdynamic table give the specific enthalpy f saturated water (h f) at a range f temperatures abve the datum cnditins, e.g. frm the tables (Ref.7, Page 54) at 20 C, the value f (h f) is 83.9 kj Kg -1,the saturated pressure is bar (2.337kN m -2 ) and the specific vlume is m 3 kg -1. Water is the Bench Tp Cling Twer is at atmsphere pressure, usually abut bar (101.3 kn m -2 ), and if the water is at say 20 C it must be cmpressed liquid, as its pressure is abve the saturatin pressure. The specific enthalpy f cmpressed liquid is given by h h f v f ( p psat) S that water at 20 C and kn m -2 has a specific enthalpy f h = 83.9 x ( ) J kg -1 h = 83.9 x J kg -1 h = 84 kj kg -1 It will be seen that at the cnditins likely t be encuntered in a cling twer, h = h f at the given temperature, i.e. the crrectin f pressure is insignificant. Specific Heat Capacity (Cp) If water is cled frm say 50 C t 20 C at atmspheric pressure, its specific enthalpy will fall frm t 83.9 kj kg -1, i.e. a decrease f kj kg -1 This is an average change h t f = 4.18 kj kg -1 dt The rate f change f enthalpy with respect t temperature, ( i.e. dh ) is given symbl Cp (ften called the specific heat at cnstant pressure). Over the range f temperatures likely t be used in Bench Tp Cling Twer, we may therefre use fr water, Daltn s and Gibbs Laws h = Cp t ) where Cp = 4.18 kj kg -1 And h Cpt ) Air is a mixture f dry air (xygen, nitrgen and ther gases) and water vapur. The behavir f such a mixture is set ut in the laws f Daltn and Gibbs frm which the fllwing may be deduced: (i) (ii) The ttal pressure f the air is equal t the sum f the pressures which the dry air and the water vapur each and alne wuld exert if they were ccupy the vlume f the mixture at the temperature f the mixture. The dry air and the water vapur respectively bey their nrmal prperty relatinships at their partial pressures.

18 (iii) The enthalpy f the mixture may be fund by adding tgether the enthalpies which the dry air and water vapur each wuld have as the sle ccupant f the space ccupied by the mixture and at the same temperature. The water water vapur steam r misture cntent f the air is dented by its HUMIDTY. Mass f Water Vapur Abslute r Specific Humidity (ω) is the rati (i) Mass f Dry Air Relative humidity ( ) is the rati Partial Pressure f Water Vapur in the Air Saturatin Pressure f Water Vapur at the same Temperature (ii) Percentage Saturatin is the rati Mass f Water Vapur in a given vlume f Air Mass f same vlume f Saturated Water Vapur at the same Temperature (iii) It can be shwn that at the cnditins within a cling twer, i.e. at high humidities, there is very little difference between the Relative Humidity and the Percentage Saturatin and fr cnvenience, they will be regarded as equal in the fllwing. Hygrmeter are instruments fr measuring the H 2O cntent f the atmsphere. Many different types f the hygrmeter are available but the Bench Tp Cling Twer uses the well knwn wet and dry bulb type fr which a large amunt f data is available. In this hygrmeter, the wet bulb thermmeter bulb is enclsed by a water wetted fabric sleeve. Evapratin frm this sleeve causes the temperature indicated by the wet bulb thermmeter t be lwer than that indicated by the dry bulb temperature. ( see page 15) Observatin f these temperatures in cnjunctin with published tables r charts enables the humidity and ther prperties f the air t be determined. Alternatively, the pressure f the water vapur in the atmsphere may be btained by substitutin in the equatin (due riginally t Regnault, August and Apjhn). p s p satw x10 pt ( t0 t w ) Where p s is the pressure f the water vapur in the air/(mbar) p satw is the saturatin pressure f water vapur at the temperature f wet bulb/(mbar) p t t 0 is the ttal air pressure (nrmally atmspheric pressure)/(mbar) is the temperature f dry bulb/ C t w is the (sling) temperature f wet bulb/ C Effect f Air Velcity n the Indicated Wet Bulb Temperature The sling wet bulb temperature used by the psychmetric charts and tables is that indicated by a wet bulb sensr placed in an air stream having a velcity f 3.5 m s -1 r mre At high relative humidities, there is little errr if the sensr is placed in a stream having a lwer velcity, but at lw relative humidities an appreciable errr may ccur. At utlet frm the Bench Tp Cling Twer the sensrs are placed in air with a very high relative humidity and where the air velcity is high. The wet bulb temperature indicated will therefre be accurate.

19 The wet bulb sensr in the air chamber is in a regin-where the velcity is lwer and where the relative humidity is much lwer. It is therefre advisable t cnfirm the wet bulb reading as fllws: (i) (ii) (iii) Ease the bung securing the wet bulb sensr frm the tp f the air chamber. Draw the sensr upward until the air escapes between the scket and the sleeve. The air velcity ver the sleeve will nw be abut 10 m/s and the sling temperature will quickly be indicated by the sensr. Cmpare the sling reading with that previusly indicated any discrepancy can be allwed fr in subsequent bservatins at the same cnditins. The applicatin f the freging Laws and relatinships and the evaluatin f prperties is best illustrated by a wrked example as fllws.

20 ว ธ ทดลอง 1. ตรวจเช คความพร อมของระบบด งรายการต อไปน 1.1 เช ค water pump โดยเป ด pwer n และเป ด cntrl valve ของ flw rate ให ส ด ถ า pump ทางานปกต ควรอ านค าได 40g/s 1.2 เช ค air blwer โดยเป ด inlet shutter ให หมด ถ าเป นปกต ค าความแตกต างของความด นควรอ านได 23 mmh 2O 1.3 เต มน าท wet bulb thermmeter cells ท ง 2 ตาแหน ง 1.4 เช คระด บน าท flat valve ว าอย ส งกว าระด บท ต าส ด และเต มน าท make-up tank จนถ งรอยบาก 2. สาหร บการทดลองให ปฏ บ ต ตามข นตอนด งต อไปน 2.1 ต ง water flw rate และ air inlet pressure ท ค าส งส ดของ parameter sets ท กาหนดให ในช นเร ยน 2.2 เป ดสว ตข heater ให ม ค าเท าก บท ต องการ ถ า cling lad เป น 1.5 ให เป ดสว ตช ท ง 2 ต ว พร อมๆก น และ รอจนกระท งอ ณหภ ม น าร อนม ค าคงท ส งส ดในแต ละ cling lad at pint 2.3 เช คระด บน าใน make-up tank ให อย ท รอยบากและเร มทาการจ บเวลาระบบควรเข าส สมด ลภายในเวลา 10 นาท 2.4 ให ทาการบ นท กค าอ ณหภ ม ท ง 6 ค า โดยอ านจาก temperature indicatr ในนาท ท 8 (ใช เป นค าเปร ยบเท ยบ ว าระบบเข าส สมด ลหร อย งเม อนาท ท 10) และนาท ท ภายหล งจากการอ านค าอ ณหภ ม เสร จส นท นาท ท 10 ให บ นท กเวลา ป ดสว ตช pwer และหาปร มาตรน าท หายไปจาก make-up tank พร อมท งจดบ นท กไว 2.6 เปล ยน flw rate ของน าก บอากาศ และ cling lad จากน นปฏ บ ต ตามข อ จนครอบคล มท กค าท กาหนดให 3. ให คานวนหาค าต างๆ ด งต อไปน - Cling range - Apprach temperature - Efficiency - Water flw rate 4. จากค าอ ณหภ ม ท บ นท กไว ให หาค าด งต อไปน ของท งน าท งอากาศ - Specific enthalpy - Specific humidity Nte : ค าด งกล าวให หาจากแหล งข อม ล thermdynamics prperties f air and water และจาก psychrmetric chart ว เคราะห ผลการทดลอง 1. แสดงกราฟความส มพ นธ ระหว าง cling lad (kw) ก บค า apprach t wet bulb (K) 2. แสดงกราฟความส มพ นธ ระหว าง cling lad (kw) ก บค า อ ณหภ ม ของน าท งขาเข าและขาออกจาก cling twer 3. หาค า water flw rate และ air flw rate ท ให ประส ทธ ภาพส งส ด

21 4. เปร ยบเท ยบ %errr ของค าพล งงาน และอ ตราการระเหยไปของน าท ได จากการทดลองก บค าจร ง (พ จารณา จากสมด ลพล งงานและมวล) 5. อธ บายสร ปให สอดคล องก บว ตถ ประสงค

22 Cling Twer ตารางบ นท กข อม ล Parameter Test Number Air Inlet t 1 Dry Bulb C Air Inlet t 2 Wet Bulb C Air Outlet t 3 Dry Bulb C Air Outlet t 4 Wet Bulb C Water Inlet t 5 Temperature C Water Outlet t 6 Temperature C Water Make-up t 7 Temperature C (Assumed same as ambient Dry bulb temperature t1) Orifice x Differential Water Flw Rate Cling Lad Make-up Quantity mm H 2O m w gm s -1 Q kw m E kg Time Interval y s