Numerical and experimental investigation on the performance of the capillary tube using R-134a and R-600a

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1 Number 1 Volume 18 December 01 Journal o Engineering Numerical and experimental investigation on the perormance o the capillary tube using R-134a and R-600a Pro.Dr.Qasim Saleh Mehdi Mech. Eng. Dept. College o Engineering AL-Mustansiriya University qasim60@yahoo.com Mech. Eng. Dept College o Engineering AL-Mustansiriya University Baydaa1971@yahoo.com Abstract In this paper, isobutane (R-600a) is used as a suitable substitute or (R-134a) when changing the length o capillary tube. And the experimental data on capillary tube are obtained under dierent conditions such as (subcooling and ambient temperatures) on domestic rerigerator (9t3 size), this data shows that (R-600a) a suitable substitute or (R134a).The test presented a model or a steady state, two-phase low in capillary tube or vapour compression system.the numerical model depends on conservation equations (mass, energy and momentum) as wall as the equation o state or rerigerant. The solution methodology was implemented by using inite dierence techniques. The system results indicate that it is possible to change the rerigeration system using (R-134a) by shorter capillary tube length about (8.6%) when using (R-600a).The theoretical results or dierent variables such as(subcooling and ambient temperatures) showed a good agreement with the "ASHRAE" tables and experimental results. K Ey Word: Rerigeration; Capillary Tube; Domestic rerigerator; R-134a; R-600a. التحليل العملي والعددي على الجريان الاديباتي لمواي ع التثليج البديلة في الانبوب الشعري الخلاصة بيداء جابر نبهان د.قاسم صالح مهدي جامعة المستنصريه / كلية الهندسة / قسم الميكانيك تم في هذا البحث استخدام ماي ع التثليج R-600a كبديل لماي ع التثليج R-134a من خلال تغير طول الا نبوب الشعري حيث تم الحصول على بيانات عملية لا نبوب شعري تحت مختلف الظروف مثل (درجة التبريد الا ضافي ودرجة حرارة المحيط ( لثلاجة منزلية سعة (9 قدم 3 ) والتي ا وضحت بان R-600a هو ماي ع التثليج المناسب ل( R-134a ). قدم هذا الاختبار الحالة المستقرة للجريان الثناي ي للماي ع داخل الا نبوب الشعري في منظومة التثليج الانضغاطية. اعتمدت النمذجة العددية على معادلات حفظ (الكتلة الطاقة الزخم ( بالا ضافة ا لى معادلة الحالة للماي ع. منهجية الحل نفذت باستخدام تقنية الفروق المحددة في حل المعادلات. ونتاي ج المنظومة تشير ا لى ا مكانية تغير منظومة التثليج 1403

2 Pro.Dr.Qasim Saleh Mehdi Numerical and experimental investigation on The perormance o the capillary tube using R-134a and R-600a المستخدمة R-134a بواسطة تقصير طول الا نبوب الشعري بحوالي (% 8.6 )عندما نستخدم. R-600a النتاي ج النظرية لمتغيرات مختلفة مثل (درجة التبريد الا ضافي ودرجة حرارة المحيط ( تشير ا لى تطابق جيد مع جداول "ASHRAE" وكذلك مع النتاي ج العملية لهذا البحث. الكلمات الري يسية: التبريد الانبوب الشعري الثلاجة المنزلية R-600a R-134. Introduction The capillary tube is one type o expansion device used in small vapour compression rerigerating and air conditioning systems. The capillary tube is made rom an extremely small-bore hollow copper tube (in the order o mm diameter) o about - 5m length [Bansal and Rupasinghe, 1998]. Liquid rerigerant enters the capillary tube, and as it low through the tube, the pressure drops because o riction and acceleration o the rerigerant. Its simplicity, low initial cost and low starting torque o compressors are the main reasons or its use. The low enters the capillary tube in a subcooled condition, while in a subcooled the pressure drop is linear and the temperature is constant. Once the pressure drops down to saturation condition, a superheated liquid low is realized or a short distance (metastable region). In this region vapour bubbles appear and pressure suddenly drops. However, this is a metastable region because o the existence o superheat liquid together with saturated liquid and vapour luid. Ater this region the local thermodynamic equilibrium state, liquid-vapour two phases is reached as shown in Fig. (1).Choked low usually is encountered at the tube exit. Especially in the past 0 years or so, the low characteristics o rerigerant passing through capillary tubes have been widely studied experimentally or analytically with alternative and common traditional rerigerants. Koizumi and Yokoyama (1980), measured pressure and temperature distributions or rerigerant R- low in adiabatic capillary tubes, veriying the occurrence o the delay o vaporization. The authors proposed a simple calculation method to ind the length o the liquid region. Such method was developed or adiabatic low, based on integration o the momentum equation and assuming two-phase homogeneous low. The experimental results showed a delay o vaporization ranging rom o C to 4 o C and the average length o the metastable low was 0.39m. The maximum length was 0.6m, and calculations agree with experimental data within ±3%. Li et al. (1990), investigated the eects o the diameter, back pressure, subcooling degree and mass low rate on metastability or R-1. It was ound that a decrease in the length o 1404

3 Number 1 Volume 18 December 01 Journal o Engineering metastable low region as the capillary tube diameter increases. The mass low rate increased as consequence o a larger underpressure o vaporization P vap, and an increase in T sub caused a decrease in P vap. It was also veriied that the position o the lashing inception was not aected by backpressure variations. Chen et al. (1990), developed a correlation or the delay o vaporization or R- 1 low through capillary tube based on the nucleation theory initially developed by Alamgir and Lienhard (1981) and with experimental data o Li et al. (1990). For instance, Dirik et al. (1994) veriied that Chen s correlation was suitable or R-134a low through capillary tubes, and Bittle and Pate (1996) used such correlation or R-, R-134a, R-15a and R-410A. Valladares et al. (00), showed that the importance o considering the metastable region in the mathematical model gives more accurate mass low rate predictions. Results presented included both metastable low modeling and non-metastable low modeling.also homogeneous and separated low model or metastable low was presented using dierent empirical correlation which was essential in the numerical model. Li Yang and Wen Wang (007), studied a generalized correlation or predicting the rerigerant mass low rate through the adiabatic capillary tube with approximate 1405 analytic solutions based on the extensive data or R-1, R-, R-134a, R-90, R-600a, R- 410A, R-407C, and R404A, in which a homogeneous equilibrium model or two-phase low was employed. The predicted values rom the correlation agree well with the experimental data or those seven rerigerants. The aim o this paper is to evaluate the overall perormance o the rerigeration system, in the steady state condition through experimental and theoretical modeling using R- 134a and R-600a. The work will also include the ollowing points: 1. Investigating the perormance o alternative rerigerant R-600a to be used in the same system.. Analyzing the experimental data or various conditions or low in an adiabatic capillary tube using Bourdon gauge to measure pressure, and using thermocouple type (T) to monitor temperature, along the capillary tube. 3. Comparing the calculation results with experimental results. Mathematical Model The pressure distribution pattern along a tube depends on a many actors such as the tube geometry (i.e. tube length, inner diameter, roughness) and rerigerant entrance conditions (i.e. condensing pressure, degree o sub-cooling and/or quality). The mass low rate has

4 Pro.Dr.Qasim Saleh Mehdi Numerical and experimental investigation on The perormance o the capillary tube using R-134a and R-600a Signiicant inluence on the luid low, especially in the two-phase region and aects the pressure drop and quality o the rerigerant. The exit condition, either choked or unchoked, also depends considerably on the mass low rate. For a given condensing pressure and tube length, the mass low rate through the capillary tube remains constant or evaporating pressure lower than the choke value. Fig. () shows the schematics o typical capillary tube. The ollowing assumptions are made in this model: Straight horizontal and constant inner diameter and roughness capillary tube, One-dimensional low, Adiabatic and homogeneous two-phase low, The low in the single-phase metastable region is considered, Thermodynamic equilibrium through the capillary tube. According to the assumption above, the governing equations used in describing the low are presented as ollows: I. Entrance Region In this region losses due to sudden contraction and dynamic pressure head losses, magnitude o this drop is calculated rom equation: [Fatouh, 007] P G 1 ρ 1 C c = ( ) ( )( SL con 1) (1) The contraction coeicient (C con ) is correlated as a unction o area ratios (A /A 1 ) in the ollow ing or m: 3 A A A C con = + () A1 A1 A1 Where A 1 and A are the cross section area o the condenser outlet tube and the capillary tube, respectively. II. Single -Phase (Sub-Cooled Liquid) Region In this region, the luid is assumed to be incompressible and steady. Also pressure drop is linear, and the rerigerant is entirely in the liquid state. The capillary tube length in the single-phase (subcoold) region can be given by: [Bansal and Wang, 004] ρ ( Pcond Psat ) d c ( k i + 1) ) (3) sp L s = p sub G /, Where (k i ) is the entrance loss coeicient (or square edged, k i =0.5) and (ƒ sp ) i s t h e s in g le - p h a s e r ic ti o n a ct o r. (k i ) can be determined rom: [Bansal and Wang, 004] 1406

5 Number 1 Volume 18 December 01 Journal o Engineering d = c k i (4) Dcond. or (d c /D cond. ) < 0.76 ( sp ) can be determined rom: [Churchill, 1977] sp = + (5) 3 Re ( ) sp Asp + Bsp Where: 1963], [Koizumi and Yokoyama, 1980] and [Li et al., 1990], which means that vaporization does not occur at P s but at some point (P v ) below it, which is also known as the nonthermodynamic equilibrium. The capillary length in this region is known as the metastable length. [Chen et al., 1990] studied the low through capillary tubes and presented a correlation to predict (5) the underpressure (P s -P v ). It is as ollows: ( Ps Pv ) kat sat νg T sub dc (10) σ Where = Re 1.5 νg 1 ν 1 Tc \ D : is the reerence length. \ D 1 A.457ln sp = (6) e Re sp d c B sp = (7) Re sp ρud c Gdc Re = = µ µ m& G = = ρ. U = constant A III. Single-Phasem Etastable Region 16 (8) (9) The delay o vaporization has been observed rom some experiments [Mikol, = k 4 (11) T a sat σ 10 The metastable length can then be given by: L meta = ( Ps Pv ).d cρ sp / spg (1) The metastable length generally decreases with the degree o sub-cooling and increases with increasing condenser temperature, increasing tube inner diameter. [Bansal and Wang, 004] IV. Region Equilibrium Two-Phase Region [Stoecker & Jones, 198] and [Bansal and Rupasinghi, 1998] presented a low model through the two-phase region based on conservation o mass, energy and momentum. 1407

6 Pro.Dr.Qasim Saleh Mehdi Their models will be regarded in this study. Consider a control volume in the two-phase region as shown in Fig. ().The conservation o mass can be expressed as ollows: m& = ρau = constant (13) m& = ρ U (14) A G U = = Gν (15) ρ For steady-state adiabatic with no external work and neglecting the elevation dierence, the conservation o energy can be expressed as ollows: h + U = constant (16) The luid enthalpy and speciic volume are determined by the ollowing equations: h = ( 1 χ ) h + χ. hg (17) ν = ( 1 χ) αν + χ. νg (18) Considering the energy balance between point (1) and any point along the capillary tube in two-phase low region, substituting equations (17) and (18) into equation (16) gives: U G h = h + χ( hg h ) + ( ν (1 χ) ν g χ) + (19) Numerical and experimental investigation on The perormance o the capillary tube using R-134a and R-600a Expanding the right-hand side and rearranging gives: G Gν U1 [( ν g ν ) ] χ + [ Gν ( νg ν ) + ( hg h )] χ+ [ h 1 + h ] = 0 (0) This is in the orm o a quadratic equation in which the quality (χ) can be expressed as: 1 U1 h g Gνν g+ ( Gνν g+ hg) ( Gν g)[ Gν h 1 + h ] χ= (1) Gν g Where h g =h g -h, and υ g =υ g -υ The conservation (15) o momentum can be expressed by again considering the element o luid as shown in Fig. (3). The sum o the pressure orces acting on the let and the right (16) ends and the shear orce acting on the inner pipe wall is equal to the time rate o change o linear momentum o the system. Thereore, πd c πd c ( P ) ( P + dp) τ wπd cdl = mdu & () 4 4 Where τ w is the wall shear stress and deined as: ρu τ w = (3) 8 On rearranging, we get: dc dp mdu & dl = [ + ] (4) ρu AρU For a constant mass low rate such that d m & = 0, we have: du dρ = (5) U ρ 1408

7 Number 1 Volume 18 December 01 Journal o Engineering Substituting equation (5) into equation (4) gives: dc ρdp dρ dl = [ + ] (6) G ρ The capillary tube between points (1) and (4) can be divided into numerous sections as shown in Fig. (4). The two-phase riction actor ( ) can be calculated rom [Lin et al., 1990] correlation as given: ν sp = φ i sp (7) ν Where sp is calculated rom equation (5). φ : Friction multiplayer is given by: Re ( A + ) B ν g φ = + 1 χ 1 (8) ν 3 Re ( Asp + Bsp ) 1 Where: The two-phase Reynolds number is deined by: Ud c Re = (9) µ ν Where: U = Gν = G( χν + (1 χ) ν ) (30). g Dynamic viscosity (µ ) can be determined rom: [Beattie and Whalley, 1981] µ = α µ + µ 1 α )(1 +.5α ) (31) Where: α g ( χν g = (3) ν + χν g Thus rom equation (6), the two-phase length can be expressed as: [Wongwises and Pirompak, 001]. L P 4 P4 ρ dρ = d c dp + (33) G P1 ρ P1 Thus, total capillary tube length is the summation o the above three lengths in the three dierent regions as: L L + L + L Tot =, (34) sp sub meta The pressure drop in two-phase region can be calculated rom the equation: [Ahmed, 001] G L χi + χi+ 1 i Pi + 1 = ν ν g + G ν g ( χi 1 i d + c + P χ ) (35) Experimental Apparatus and Measurements The experimental test rig includes the actual rerigeration system (domestic rerigerator in size 9t 3 ) which was originally manuactured to work with R-134a. A schematic diagram o a single door domestic rerigerator with the instruments and their locations has been shown in Fig. (5). The apparatus was designed to allow simultaneous control o the pressure and temperature o the liquid entering the capillary tube and also the evaporator pressure.the pressure distribution along capillary tube was measured by precision Borden type gauges. And temperature measurement o the lowing 1409

8 Pro.Dr.Qasim Saleh Mehdi rerigerant was made by (copper/constantan) thermocouples type s (T). Rerigerant temperatures were measured by mounting thermocouple's probe directly into a groove through the capillary tube wall. The selected capillary tube speciications are (0.8mm) and (.8mm) inside and outside diameters respectively, with long (.8m) or R-134a. This length o capillary tube was calculated theoretically, based on a constant inner diameter o the capillary tube. With respect to R-600a, the capillary tube length has been changed several times until the desired evaporator pressure was reached. As a result to the delay o vaporization phenomenon, and to ind the underpressure o vaporization, pressure and temperature sensors must be installed along the capillary tube. In order to measure the pressure drop along the capillary tube, pressure taps were made in the wall o capillary tube using (T) joint. Fig. (6) shows a photo o the (T) joint. The capillary tube cuts into parts, each two parts connected by (T) joint. A (T) joint (Brass covered with chromium) consist o two parts, the irst one is a tube with (3.4mm), (4mm) inside and outside diameters, respectively. This part is connected two parts o capillary tube by solder. The second one is also a tube with (3.4mm), (4mm) inside and outside diameters respectively. This part is constructed with a broad ends contains lair, Numerical and experimental investigation on The perormance o the capillary tube using R-134a and R-600a which was connected to pressure gauge in order to have a closed chamber. Results and Discussion 1. Computation Results The mathematical sample or simulation o capillary tube in adiabatic low depends on dividing the tube into three regions [liquid (single-phase), delay o vaporization (metastable) and two-phase low] regions. Figs (7), (8), (9) and (10) show the distribution o pressure and temperature along capillary tube or R-134a and R-600a, respectively. Pressure and temperature distribution or these igures were plotted at variable degree o subcooling. It can be noticed that as subcooling degree increases, then liquid region length increases, while in metastable and two-phase regions are decreases. Also, the liquid region length or R-134a is less than that or R-600a, while metastable region length and two-phase region length or R-134a are higher than that or R-600a. Figs (11), (1), (13) and (14) show the eect o dierent ambient temperatures on (ph) diagram at constant subcooling temperature dierence o (3 o C) and (8 o C) or R-134a and R-600a, respectively.. Experimental Results Fig. (15) shows increase o COP with superheat (suction temperature) where 1410

9 Number 1 Volume 18 December 01 Journal o Engineering subcooling degree is constant. It was observed that COP value or R-134a is lower than that or R-600a. Fig.(16) shows the underpressure o vaporization (p s -p v ) as a unction o the mass low rate. It was observed that at a ixed subcooling condition, the underpressure o vaporization increases with an increase o the mass low rate. This is because o the speciic volume or rerigerant vapour. Also, it can be shown that underpressure o vaporization or R-600a is less than that or R-134a in the same system, where R-600a has speciic volume or vapour higher than that or R-134a. Fig. (17) shows that the underpressure o vaporization is a unction o the subcooling degree or rerigerant. It can be seen that the underpressure o vaporization decreases with an increase in the subcooling o the rerigerant, T sub. ranges (3-13 o C).This is because o the pressure drop in a single-phase region. Figs (18) and (19) show the pull down time or R-134a and R-600a in the rerigerator reezer and rerigerator cabin, respectively. Pull down time is deined as the time required or changing the reezer air temperature rom ambient condition 303K (30 o C) to the desired inal temperature 61K (-1 o C) and the temperature o the air in the cabin should be maintained at 79K (6 o C) according to ISO standard or the considered rerigerator class [Mohanraj et al, 00] The time required to reach the required reezer air temperature o nearly (-1 o C) or R- 134a and R-600a are approximately (110 and 90 min) respectively. Moreover, the time required to reach the required cabin air temperature o nearly (6 o C) or R-134a and R- 600a are approximately (95 and 83 min) respectively. And as a result, it can be noticed that the pull down time (to reach steady state) or R-600a less than that o R-134a. Figs. (0) and (1) show the dierence in COP or rerigerants with ambient temperature and subcooling degree. It can be observed that COP o the system decreases with increasing ambient temperature. However, the COP o the system increases with increasing subcooling degree (and constant superheating degree T sup. ). And as a result, it can be concluded that COP o the system using by R- 600a is higher than that o R-134a. This is because o the R-600a operating with condensing pressures less than that o R- 134a at dierent ambient temperatures leading to less power consumption or R-600a when compared with R-134a. Conclusions (1) Through the theoretical results, it was noticed the ollowing: a. R-600a has operating pressures lower than that or R-134a at dierent working temperatures.

10 Pro.Dr.Qasim Saleh Mehdi b. Pressure ratio or R-134a close to pressure ratio o R-600a. c. The rerigeration system using R-600a has COP (5%) higher in comparison with R-134a. d. The rerigeration system using R-600a has volumetric capacity lower than that or R-134a. e. The rerigeration system using R-600a has a discharge temperature lower than that or R-134a and the increase in rerigerant subcooling allows or lowering the discharge temperature which may increase the compressor lie. () Through the experimental results, it was noticed the ollowing: a. COP or the system working by R-600a is higher than that or R-134a at dierent ambient temperatures and subcooling degrees. b. Power consumption or the system working by R-134a is higher than that or R-600a. c. Capillary tube used or R-600a must be shorter than that used or R-134a about (8.6%) or the same system. d. The underpressure o vaporization decreases with an increase subcooling degree. Numerical and experimental investigation on The perormance o the capillary tube using R-134a and R-600a e. The underpressure o vaporization or R-600a during its passage through capillary tube is less in comparison with R-134a.. Pull down time or R-600a is less than that or R-134a. Reerences Ahmed Abdul-Nabi Omran, 001, "Comparative Perormance o Rerigerants R- & R-90 in Vapour Compression System and Steady the eects on the Capillary tube". M.Sc. Thesis, University o Technology. Bansal, P.K., Rupasinghi, A.S., 1998, "A homogeneous model or adiabatic capillary tubes". Applied thermal engineering, vol. 18, pp. (07-19). Bansal, P.K., Wang, G., 004, "Numerical analysis o choked rerigerant low in adiabatic capillary tubes". Applied thermal engineering, vol. 4, pp. ( ). Beattie,D.R.H. and Whalley,P.B.,1981,"A simple two phase Frictional Pressure Drop Calculation Method". International Journal o Multiphase Flow, vol.8, pp Chen, Z.H., Li, R.Y., Chen, Z.Y., 1990, "A correlation or metastable low o rerigerant R-1 through capillary tubes". ASHRAE Trans., vol. 96, pp. ( ). 141

11 Number 1 Volume 18 December 01 Journal o Engineering Churchill, S.W., 1977, "Frictional equation spans all luid low regions". Chemical Engineering, vol. 84, pp. (91-9). Fatouh, M., 007, "Theoretical investigation o adiabatic capillary tubes working with propane/ n-butane/ isobutene blends". Energy Conversion and Management, vol. 48, pp. ( ). Koizumi, H., Yokoyama, K., 1980, "Characteristics o rerigerant low in a capillary tube". ASHRAE Trans., vol. 86, pt., pp. (19-7). Li, R.Y., Chen,Z.H.,Lin,S.,Chen,Z,Y., 1990, "Metastable low o R-1 through capillary tubes". International Journal o Rerigeration, vol. 13, pt. 3, pp. ( ). Li Yang and Wen Wang, 007, "A generalized correlation or the characteristics o adiabatic capillary tubes". International Journal o Rerigeration, pp. (1-7). Lin, S., Li,R.Y.andChen,Z.H., 1990, "Nnmerical modelling o thermodynamic non-equilibrium low o rerigerant through capillary tubes". ASHRAE Transaction, vol.96, pt. 1, pp. (54-549). Mikol, E.P., 1963, "Adiabatic Single and Two-Phase Flow in Small Bore Tubes". ASHRAE Trans., vol. 5, pp. (75-86). Mohanraj, M.,Jayaraj,S.and Muraleedharan,C., 00, "Improved Energy Eiciency or HFC-134a Domestic Rerigerator Retroitted with Hydrocarbon Mixture HC-90/HC-600a) as Drop in Substitute". National Institute o Technology, Calicut. Stoecker, W.F., and Jones, J.W., 198, "Rerigeration and Air Conditioning". Mc Graw Hill, New York. Valladares, O.G., Segarra,C.D.and OlivaA., 00, "Numerical simulation o capillary tube expansion devices behavior with pure and mixed rerigerants considering metastable region". Applied Thermal Engineering, vol., pp. ( ). Wongwises, S., and Pirompak, W., 001, "Flow Characteristics o pure Rerigerants and Rerigerant Mixtures in Adiabatic Capillary Tubes". Applied Thermal Engineering, vol. 1, pp. ( ). Nomenclature A : Area (m ) α : Void raction C con : Contraction coeicient (-) \ D : Reerence length (m) D cond : Condenser inner diameter (m) e : Inner surace roughness (mm) ƒ : Friction actor (-) G : Mass lux ( kg/m.s ) h : Speciic enthalpy (kj/kg) jd c : Capillary tube inner diameter (m) k a : Boltzmann s constant (J/k) 1413

12 Pro.Dr.Qasim Saleh Mehdi k i : Entrance loss coeicient (-) L : Length (m) m& : Mass low rate (kg/s) P : Pressure (N/m (pa)) P c : Pressure drop due to the area contraction (N/m ) Re : Reynolds number (-) T : Temperature ( o C ) U : Velocity (m/s ) υ : Speciic volume (m 3 /kg ) χ : Dryness raction (-) Greek Symbols ρ : Density (kg/m 3 ) µ : Dynamic viscosity (kg/m.s ) σ : Surace tension (N/m) τ : Shear stress at wall (N/m ) w Numerical and experimental investigation on The perormance o the capillary tube using R-134a and R-600a φ : Friction multiplayer (-) Subscripts c : Critical value cond :Condenser : Liquid phase g : Vapour phase i : Present reading according to element number i+1 : Next reading meta : Metastable sat,s : Saturated sp : Single-phase sub : Subcooling : Two-phase Tot : Total v : Vapour P P sat Figure (1): Typical pressure distribution along an adiabatic capillary tube. [Valladares, 004] 1414

13 Number 1 Volume 18 December 01 Journal o Engineering P v. L sp,sub L meta. L. 1 3 d c P cond. P evap. Figure (): Schematic diagram o a capillary tube [Valladares, 004] Pπd c /4 (P+dp)πd c /4 Figure (3): Flow model incremental volume, (two-phase). [Wongwises, Pirompak, 001] 1 P P 3 P i-1 P i P i+1 Figure (4): Schematic diagram o simulation approach, (two-phase). [Wongwises, Pirompak, 001] 1415

14 Pro.Dr.Qasim Saleh Mehdi investigation on capillary tube using Numerical and experimental The perormance o the R-134a and R-600a Figure (5): Schematic diagram o the experimental set-up. (Domestic rerigerator).where: P: Pressure gauge & T: Thermocouple. Figure (6): Photo o (T) joint. 1416

15 Number 1 Volume 18 December 01 Journal o Engineering Figure (7): Distribution the pressure and temperature or R- 134a along the capillary tube with T sub. =3 O C. Figure (8): Distribution the pressure and temperature or R-134a along the capillary tube with T sub. =8 O C. Figure (9): Distribution the pressure and temperature or R-600a along the capillary tube with T sub. =3 o C. Figure(10): Distribution the pressure and temperature or R-600a along the capillary tube with T sub. =8 o C 1417

16 Pro.Dr.Qasim Saleh Mehdi investigation on capillary tube using Numerical and experimental The perormance o the R-134a and R-600a Figure (6.11): Eect o dierent ambient temperatures on (p-h) diagram at T sub = 3 o C or R-134a. Figure (6.1): Eect o dierent ambient temperatures on (p-h) diagram at T sub. = 8 o C or R-134a. Figure (6.13): Eect o dierent ambient temperatures on (p-h) diagram at T sub.= 3 o C or R-600a. Figure (6.14): Eect o dierent ambient temperatures on (p-h) diagram at T sub. = 8 o C or R-600a. 1418

17 Number 1 Volume 18 December 01 Journal o Engineering Figure (15): Eect o suction temperature on the COP. Figure (16): Relationship between underpressure o vaporization and mass low rate, T sub. =8 o C. Figure (17): Relationship between underpressure o vaporization and subcooling. Figure (18): Change reezer air temperature with pull down time or R-134a and R-600a. 1419

18 Pro.Dr.Qasim Saleh Mehdi investigation on capillary tube using Numerical and experimental The perormance o the R-134a and R-600a Figure (19): Change cabin air temperature with pull down time or R-134a and R-600a. Figure (0): Eect o ambient temperature Figure (1): Eect o subcooling degree on the COP. 140