37- 46 Al-Khwarizmi Engineering Journal,Vol. 11, No. Influences of the Twisted Plate Jafar M. Hassan* Mohammed F. Mohammed*** *,**,*** Department of Mechanical Engineering / University of Technology *** (Received Abstract In order to enhance the efficiency and with low additional cost, twisted used for test. Family of twisted strips are inserted inside each collector risers with different twisted ratios (TR=3,4,5). The collectors are connected in parallel conditions (solar radiation and ambient transfer rate occurs at twisted ratio (3) . solar collector at different flow rate Keywords: Twisted strip, solar collectors 1. Introduction Extensive researches, both numerically and experimentally had been conducted on the operating and performance study of thermosyphon and forced circulation on the solar water heating systems. These studies, however, were mainly focused on the design and optimization of the overall system with little attention given to study the thermofluid behavior inside the collector. In recent years, many techniques have been proposed for enhancement of the heat transfer rate. These can be classified into two main groups: Passive technique not requiring additional power sources and active technique requiring additional external power inputs. In the case of the passive technique, convection heat transfer from surfaces with attachments of different solid shapes geometries, such as baffles, fins, ribs, twist strips, have been exploited, especially; twisted strip Khwarizmi Engineering Journal,Vol. 11, No. 3, P.P. 37- 46(2015) wisted Strips Insertion on the Performance of late Water Solar Collector Jafar M. Hassan* Qussai J. Abdul-Ghafour Mohammed F. Mohammed*** Department of Mechanical Engineering / University of Technology *Email: Jafarmehdi1951@yahoo.com **Email: kaisygj@yahoo.com *** Email: mohammed2007msc@yahoo.com (Received 19 November 2014; accepted 31 March 2015) efficiency of flat plate solar water collectors without changing additional cost, twisted strips are inserted inside its riser pipes. Three flat plate collectors are twisted strips are inserted inside each collector risers with different twisted ratios The collectors are connected in parallel mode (Z-Configuration) and are exposed to the same conditions (solar radiation and ambient temperature) .The experimental results show occurs at twisted ratio (3) .Consequently, for the same twisted ratio the flow rate used (60,100 and 150) ℓ /hr. were 49 %, 57% and 63% solar collectors. Extensive researches, both numerically and experimentally had been conducted on the operating and performance study of thermosyphon and forced circulation on the solar water heating systems. These studies, however, were mainly focused on the design and ptimization of the overall system with little attention given to study the thermofluid behavior In recent years, many techniques have been proposed for enhancement of the heat transfer rate. These can be classified ps: Passive technique not requiring additional power sources and active technique requiring additional external power inputs. In the case of the passive technique, convection heat transfer from surfaces with attachments of different solid shapes at different geometries, such as baffles, fins, ribs, twist strips, have been exploited, especially; twisted strip which is widely used in many industries experimental investigations of twist coil for enhancing heat transfer and efficiency have been being appeared experimentation both strip and wire coil that’s carried out in the range of Reynolds number from (5000 – 45,000) and Prandtl number from (0.7 30). The maximum heat enhancement for twisted strip and wire coil insert is 3.5 and 2.0 times higher than the plain one. twisted strip insertion on heat transfer and flow friction characteristics in a concentric double pipe heat exchanger have been studied exp by Watcharin et al. [2] introduced by using twisted strip placed inside the inner test tube of the heat exchanger with different twist ratios (TR=5,7). The experimental results revealed that the increase in heat transfer the twisted-strip inserts is found to be strongly influenced by strip-induced swirl generation or vortex motion. Over the range investigated, the Al-Khwarizmi Engineering Journal (2015) erformance of Flat Ghafour** Department of Mechanical Engineering / University of Technology changing in its original shape Three flat plate collectors are twisted strips are inserted inside each collector risers with different twisted ratios are exposed to the same ental results show that, the highest heat daily efficiencies for the 57% and 63% respectively. which is widely used in many industries. The experimental investigations of twist strip and wire for enhancing heat transfer and efficiency have been being appeared by Rose and Briggs [1] xperimentation both strip and wire coil that’s carried out in the range of Reynolds number from 45,000) and Prandtl number from (0.7– enhancement for twisted strip and wire coil insert is 3.5 and 2.0 times higher than the plain one. Influences of the twisted strip insertion on heat transfer and flow friction characteristics in a concentric double pipe heat exchanger have been studied experimentally ] the swirling flow was introduced by using twisted strip placed inside the inner test tube of the heat exchanger with different . The experimental results increase in heat transfer rate of strip inserts is found to be strongly induced swirl generation or vortex motion. Over the range investigated, the Jafar M. Hassan maximum Nusselt numbers for using the enhancement devices are (188%) and (159%) respectively, higher than that for the plain tube. Alireza and Kamran [3] study experimental impact of heat enhancement devices on the thermal performance of Single-tube flat solar collector. Different passive heat enhancement devices that include twisted strip, coil-spring wire and conical ridges were studied. The flow rate is close to the typical flow rates in thermosyphon (natural). The comparison showed that the heat enhancement devices are ineffective in enhancing heat transfer rate in the studied range and geometry. Nagarajan et al. [ experimentally the heat transfer and friction factor characteristics of solar parabolic through collector fitted with full length twisted strips inserts of twist ratio (6, 8 and 10) have been presented. The transitional flow regime is selected for this study with the Reynolds number range (1192 to 2534). The experimental data obtained were compared with those obtained from plain tube published data. The effects of full length twisted strip inserts on heat transfer and friction factor were presented. The heat transfer coefficient enhancement for twisted inserts is higher than that for plain tube for a given Reynolds number. Herrero M. et present an enhancement techniques applied to flat-plate liquid solar collectors towards more compact and efficient designs. Tu enhancement passive techniques can consist of adding additional devices which are incorporated into a smooth round tube (twisted strips, wire coils), modifying the surface of a smooth tube (corrugated and dimpled tubes) or making special tube geometries (internally finned tubes). For the typical operating flow rates in flat collectors, the most suitable technique is inserted devices. This type of inserted device provides better results in laminar, transitional and low turbulence fluid flow regimes. Akeel [6] Study the heat transfer in a horizontal tube by means of six types of twisted tape inserts for the range of Reynolds number extends from 4500 to 23500 as follows : normal twisted tape regularly spaced twisted tape, triangular-cut twisted tape, rectangular-cut twisted tape, semicircular twisted tape, and drilled twisted tape. The experiential results show that the enhancement of heat transfer increases as the type of twisted tape changes from one to six, respectively. and Amnart [7] present a numerical analysis of laminar fully developed periodic flow and heat transfer in a constant temperature circular tube with single twisted tape inserted. The twisted tape is introduced and inserted in the Al-Khwarizmi Engineering Journal, Vol. 11, No. 3, P.P. 38 maximum Nusselt numbers for using the enhancement devices are (188%) and (159%) han that for the plain tube. xperimentally the impact of heat enhancement devices on the tube flat-plate Different passive heat enhancement devices that include twisted strip, spring wire and conical ridges were studied. The flow rate is close to the typical flow rates in comparison showed the heat enhancement devices are ineffective in enhancing heat transfer rate in the studied range [4] investigate heat transfer and friction factor characteristics of solar parabolic through collector fitted with full length twisted strips inserts of twist ratio (6, 8 and 10) have been presented. The transitional flow regime is selected for this study s number range (1192 to 2534). The experimental data obtained were compared with those obtained from plain tube published data. The effects of full length twisted strip inserts on heat transfer and friction factor were presented. ent enhancement for twisted inserts is higher than that for plain tube for Herrero M. et al. [5] nhancement techniques that be plate liquid solar collectors towards more compact and efficient designs. Tube-side enhancement passive techniques can consist of adding additional devices which are incorporated into a smooth round tube (twisted strips, wire coils), modifying the surface of a smooth tube (corrugated and dimpled tubes) or making special tries (internally finned tubes). For the typical operating flow rates in flat-plate solar collectors, the most suitable technique is inserted This type of inserted device provides better results in laminar, transitional and low Akeel and Ameer in a horizontal tube by tape inserts for the range of Reynolds number extends from 4500 to twisted tape regularly cut twisted tape, cut twisted tape, semicircular-cut twisted tape, and drilled twisted tape. The experiential results show that the enhancement of heat transfer increases as the type of twisted tape changes from one to six, respectively. Withada a numerical analysis of laminar fully developed periodic flow and heat transfer in a constant temperature-surfaced circular tube with single twisted tape inserted. The twisted tape is introduced and inserted in the middle of the tested tube. The effects of twisted ratios (1, 2, 3, 4, 5and 6) are presented for Reynolds number values ranging from Re = 100 to 2000. They found that the heat transfer in the circular tube with the twisted tape is more effective than that with no twis The increase in the twist ratio leads to decrease in the Nusselt number and friction factor. objective of the present work is to enhanced the performance of the flat plate solar collector by inserting twisted strips with r The task was accomplished by connecting three collectors in (Z-Configuration) different flow rates. 2. Experimental Work 2.1. Experimental Test Rig The experimental test rigs consist of three identical flat plate solar collectors, each one with absorbing area (80cm * 120cm) with one glass cover as shown in Fig. 1. Also equally spaced (10cm) parallel copper riser pipes of (10.5mm inner and 11mm outer (1200mm) length. These pipes are connected with two headers, one on each end. The joints between headers and copper pipes ends are made by adapter screws as shown in purpose of these adapter screws is f separating of riser pipes from the headers to inserting twisted strips inside them. A copper sheet with (0.5mm) thickness is used as the solar radiation absorber as shown in fig. 3 pipes are fixed on the absorbing plate by welding lead along the riser's pipes. was manufactured in fabricated work as curve surrounds riser pipes to increase the surface area of contacts between Fig. 4. Fig. 1 Experimental test rig. Khwarizmi Engineering Journal, Vol. 11, No. 3, P.P. 37- 46 (2015) middle of the tested tube. The effects of twisted ratios (1, 2, 3, 4, 5and 6) are presented for Reynolds number values ranging from Re = 100 found that the heat transfer in the circular tube with the twisted tape is more ith no twisted tape inserted. ratio leads to decrease in the Nusselt number and friction factor. The objective of the present work is to enhanced the performance of the flat plate solar collector by inserting twisted strips with ratios (TR=3, 4 and 5). The task was accomplished by connecting three Configuration) parallel mode at Experimental Work Experimental Test Rig The experimental test rigs consist of three identical flat plate solar collectors, each one with absorbing area (80cm * 120cm) with one glass 1. Also, it consists of eight equally spaced (10cm) parallel copper riser pipes inner and 11mm outer) diameters, and (1200mm) length. These pipes are connected with two headers, one on each end. The joints between headers and copper pipes ends are made by adapter screws as shown in Fig. 2. The main purpose of these adapter screws is for easy separating of riser pipes from the headers to inserting twisted strips inside them. A copper thickness is used as the solar as shown in fig. 3. The riser pipes are fixed on the absorbing plate by welding pipes. The absorbing plate fabricated way through the work as curve surrounds riser pipes to increase the contacts between them as shown in Experimental test rig. Jafar M. Hassan Fig. 2. Joins header and riser piped end by adapter screw. Fig. 3. copper sheet welding to the riser pipes Fig. 4. Absorbing plate geometry Al-Khwarizmi Engineering Journal, Vol. 11, No. 3, P.P. 39 Joins header and riser piped end by adapter copper sheet welding to the riser pipes. Absorbing plate geometry. The collector frame is made of aluminum bars of (1.5mm) thick. A glass sheet is used as a transparent cover (4mm) thick glass wool insulation of (50 mm) thickness was used as insulator to decrease the collector back and side heat losses. A cylindrical galvanized steel tank with (0.58 m) outside diameter and (1 m) height is used for storing h insulated by a (50mm) thickness glass wool. In order to circulate the water in the system, a small circulation water pump (CRS25/4 closed loop to make the forced circulation. The water flow rate in the closed loop is using valves and measured with flow meter 15-Range (60-600LPH) with accuracy 4% flow rates used, are (60,100 and 150) spray paint (RUSTOLEUM high heat) as the absorber surface paint is used high absorptance (0.92-0.96 used to substrates with low emittance (0.24) [ 2.2. Measuring Devices Analyzing In order to measure the temperature at various points of the absorbing plate collectors, T-type thermocouple constantan) with the accuracy of [9]. The thermocouples were calibrated before beginning of the experiments. The measurement of the temperature distribution of the absorbing plate is done using three thermo located at the centerline of the absorbing plate and the others at top and bottom with space distance of (50cm) from the centerline as shown in All thermocouples are connected to the data logger, that’s connected to thermometer (UT325-0.1C resolution). The data is interfaced to the computer and then displayed as a table. The ambient temperature is measured using a digital electronic thermometer. The solar power radiation on the collector is record by solar meter with rang varied from 2000 W ̸m2). This device measures the total solar radiation (beam and diffuse) per unit area of the collector surface. The solar power meter was oriented due to the south at the collector tilt angle (30). This device can read the in (SD Ram). Khwarizmi Engineering Journal, Vol. 11, No. 3, P.P. 37- 46 (2015) The collector frame is made of aluminum bars of (1.5mm) thick. A glass sheet is used as a thick of the collector. A glass wool insulation of (50 mm) thickness was decrease the collector back A cylindrical galvanized steel tank with (0.58 m) outside diameter and (1 m) height is used for storing hot water. The tank is insulated by a (50mm) thickness glass wool. In order to circulate the water in the system, a small (CRS25/4-180) is used in closed loop to make the forced circulation. The water flow rate in the closed loop is controlled by using valves and measured with flow meter (lzs- 600LPH) with accuracy 4%. The flow rates used, are (60,100 and 150) ℓ /hr. The spray paint (RUSTOLEUM high heat) as the is used. This Coating has 0.96) for solar radiation is to substrates with low emittance (0.24) [8]. Devices and Data In order to measure the temperature at various points of the absorbing plate, inlet and outlet of thermocouple (copper- with the accuracy of (±0.5 ͦC) is used ]. The thermocouples were calibrated before beginning of the experiments. The measurement of the temperature distribution of the absorbing plate is done using three thermocouples, one located at the centerline of the absorbing plate and the others at top and bottom with space distance of (50cm) from the centerline as shown in Fig. 5. All thermocouples are connected to the data logger, that’s connected to a digital electronic 0.1C resolution). The data is interfaced to the computer and then . The ambient temperature is measured using a digital electronic thermometer. The solar power radiation on the collector is th rang varied from (0 to . This device measures the total solar radiation (beam and diffuse) per unit area of the collector surface. The solar power meter was oriented due to the south at the collector tilt angle (30). This device can read the data and save them Jafar M. Hassan Fig. 5. Position of thermocouples of absorber plate The governing equations used in the present work are: 1. Water mass flow rate (�� �) �� � � �� . �� The water density varies with its temperature according to the equation [10] �� � 1000 ∗ �1 � �� � 288.9414� �T � 68.12963�� ∗ �� � 3.9863�� 2. Useful energy (��) ���� !" � �� � . �#$��� !" . ��%&� � 3. The collector efficiency for individual solar collector ' �� !" � ()*+,-. /0 .12 4. The mean fluid temperature is calculate by �3 � 45678459), � 2.3. Test Model In this model, using twisted investigate the influence of heat enhancement devices on the thermal performance of the flat plate solar collector arrays. In this study, t twisted strips elements are made from thin, flat strips of thickness (0.7 mm) and (10.5mm) wide of aluminum material and are twisted through (180 degree) to form helices shapes. twisted in different ratios (TR=3,4,5) fig. 6 .Helices rotations of this ratios are formed for a full length of riser pipes of (1100 mm ) as shown in Fig. 7. In this model, three flat plate solar collectors connection in parallel (Z configuration)as shown in fig.8 (Collector one with twist ratio 3, Collector two with twist ratio 4 and Collector three with twist ratio 5) for different flow rates .The twist ratio is defined as: Al-Khwarizmi Engineering Journal, Vol. 11, No. 3, P.P. 40 sition of thermocouples of absorber plate. The governing equations used in the present …(1) The water density varies with its temperature �/�508929.2 ∗ …(2) � �%<=� …(3) collector efficiency for individual solar …(4) uid temperature is calculate by ...(5) strip was to investigate the influence of heat enhancement devices on the thermal performance of the flat plate solar collector arrays. In this study, the strips elements are made from thin, flat strips of thickness (0.7 mm) and (10.5mm) wide material and are twisted through shapes. The strips are =3,4,5) as shown in .Helices rotations of this ratios are formed for a full length of riser pipes of (1100 mm ) as three flat plate nnection in parallel (Z (Collector one with twist ratio 3, Collector two with twist ratio 4 Collector three with twist ratio 5) for different flow rates .The twist ratio is defined as: �> � ? @ The twist strip geometry as shown in 2.4. Test Procedure The forced circulation of solar flat plate collectors were connected as a closed loop. The experiment was carried out in Baghdad from (15th April to 10th May 2014) and these experiments were carried out during sunny days only .The slope angle of three clos (30 deg. due to south). The collectors was tested under steady-state conditions in which the solar intensity, ambient temperature, inlet and outlet temperature difference were considered constant for period of time. The period was an hour for a clear day. The type of test was to estimate the instantaneous performance of the system. The system was tested with three different flow rates of water through the collector loop . These flow rates were (60,100 and 150) each case, experiments usually started at 8 am and continued until 5 pm .In each test and each time period all the measurements of temperatures, solar radiation intensity were recorded for each collector. Each test was repeated twice at different periods of time to ensure the experimental repeatability. Fig. 6. A twist strips with different twist ratio Fig. 7. A twisted strip inside riser pipe. Khwarizmi Engineering Journal, Vol. 11, No. 3, P.P. 37- 46 (2015) ... (6) The twist strip geometry as shown in Fig. 9. The forced circulation of solar flat plate collectors were connected as a closed loop. The experiment was carried out in Baghdad from (15th April to 10th May 2014) and these experiments were carried out during sunny days only .The slope angle of three closed looped collectors in The collectors was tested state conditions in which the solar intensity, ambient temperature, inlet and outlet temperature difference were considered constant for period of time. The period was taken as half an hour for a clear day. The type of test was to estimate the instantaneous performance of the The system was tested with three different flow rates of water through the collector loop . (60,100 and 150)ℓ /hr. In each case, experiments usually started at 8 am and continued until 5 pm .In each test and each time period all the measurements of temperatures, solar radiation intensity were recorded for each Each test was repeated twice at different of time to ensure the experimental with different twist ratios. twisted strip inside riser pipe. Jafar M. Hassan Fig. 8. Schematic diagram of test rig . Fig. 9. Twisted strip geometry 3. Results and Discussion 3.1. Relationship between Solar Energy and Useful Energy Fig 10. Shows the useful energy have the same trends of the solar radiation. The results show that, when the water flow rate inlet to the collector increases, the useful energy gain increases. This affects due to, as the flow rate temperature rise through the collector decreases. This causes lower losses and therefore a corresponding increase in the gain Al-Khwarizmi Engineering Journal, Vol. 11, No. 3, P.P. 41 Schematic diagram of test rig . Twisted strip geometry. between Solar Energy Fig 10. Shows the useful energy have the same trends of the solar radiation. The results show inlet to the collector increases, the useful energy gain increases. This increases, the temperature rise through the collector decreases. This causes lower losses and therefore a the gain of the useful energy. The value of useful with inserted strip of twist ratio 3 is the others for the same solar intensity. This effect results the intensity of swirl generation. As the twist ratio decrease, swirl generation which would maximize the particle mixing and hence the heat transfer coefficient. 3.2. The Absorber Plate Temperature Variation Fig.11 shows, the temperature distribution of the absorber plate and ambient temperatures with time with different twist ratios. Among the various twist ratios, the minimum twist ratio (3) is found to have the lowest absorber plate temperature for all flow rate effective of heat transfer by swirl and fin effects. As the twist ratio increase, the swirl generation and fin effect decreases and minimizes the heat transfer and increase the absorber plate temperature. Table (1,2 and 3) shows the variatio of absorber plate temperature with time for the flow rate inlet at 150ℓ/hr. 3.3. Effect of Twist Ratio on Thermal Performance Analysis According to the flow rates range in the present work The instantaneous collector efficiencies curves are shown in 14) been observed clearly that as the flow rate increases, the efficiency of the solar collector also increases. The increase in the flow rate, leads to temperature difference decreases. The decreasing of the temperature difference lead to maximum energy transfer from the riser fluid, then the collector efficiency will increase. For the same values of the solar radiation maximum efficiency is obtained in minimum twist ratio (3), because the swirl generation is maximum in this twist ratio, which would increase the heat transfer of fluid travel. experimental daily efficiencies for the solar collector used strips with twist ratio (3) and flow rate of order 60,100 and 150 and 63% respectively. Tables (4, the instantaneous collector efficiencies for different flow rates. Khwarizmi Engineering Journal, Vol. 11, No. 3, P.P. 37- 46 (2015) of useful energy of the collector with inserted strip of twist ratio 3 is higher than others for the same solar intensity. This effect results the intensity of swirl generation. As the , swirl generation increase, the particle mixing and hence the heat transfer coefficient. Absorber Plate Temperature shows, the temperature distribution of the absorber plate and ambient temperatures with time with different twist ratios. Among the various twist ratios, the minimum twist ratio (3) is found to have the lowest absorber plate for all flow rate ranges due to effective of heat transfer by swirl and fin effects. As the twist ratio increase, the swirl generation and fin effect decreases and minimizes the heat transfer and increase the absorber plate Table (1,2 and 3) shows the variation of absorber plate temperature with time for the Effect of Twist Ratio on Thermal Performance Analysis According to the flow rates range in the present work The instantaneous collector efficiencies curves are shown in Fig’s (12,13 and ) been observed clearly that as the flow rate increases, the efficiency of the solar collector also increases. The increase in the flow rate, leads to temperature difference decreases. The decreasing of the temperature difference lead to the maximum energy transfer from the riser tube to then the collector efficiency will increase. of the solar radiation the maximum efficiency is obtained in minimum twist ratio (3), because the swirl generation is s twist ratio, which would increase the heat transfer of fluid travel. The experimental daily efficiencies for the solar collector used strips with twist ratio (3) and flow rate of order 60,100 and 150 l /hr. are 49 %, 57% Tables (4, 5 and 6) show instantaneous collector efficiencies with time Jafar M. Hassan Al-Khwarizmi Engineering Journal, Vol. 11, No. 3, P.P. 37- 46 (2015) 42 Table 1, Absorber plate temperature at twist ratio (3). Time Tp1 Tp2 Tp3 8.00 am 30.8 32.9 37 8.30am 32.3 34 39.5 9.00am 36.6 39.5 43.5 9.30am 41.2 43.2 46 10.00am 44.6 48.3 52 10.30am 47.4 50.2 53.2 11.0am 51.2 52.9 56.3 11.30am 54.3 56.8 58.6 12 noon 57.4 60.9 63.4 12.30pm 61.8 64.3 67 1.00pm 64.7 68.4 70 1.30pm 66 68.8 70.5 2.00pm 67.7 70.5 72.4 2.30pm 68.3 70.4 71.5 3.00pm 66.3 68.5 70.7 3.30pm 64.2 66.5 68.7 4.00pm 62.1 65 67.3 4.30pm 60.2 64 65.2 5.00pm 58.5 61.5 63 Table 2, Absorber plate temperature at twist ratio (4). Time Tp1 Tp2 Tp3 8.00 am 31 33.5 38.4 8.30am 33 34.5 40.6 9.00am 37 40.6 43.5 9.30am 42.2 44.2 46.5 10.00am 45 49 52.6 10.30am 48.6 50.7 53.2 11.0am 52 54.3 57.1 11.30am 55.2 57.7 59.3 12 noon 58.5 61.5 64 12.30pm 62.8 65.2 67.7 1.00pm 65.5 69 70.5 1.30pm 67 69.1 70.4 2.00pm 68.1 71 72.4 2.30pm 69 71.4 72.2 3.00pm 67.4 69.3 71.2 3.30pm 65.3 67.5 69.5 4.00pm 62.1 65 67.3 4.30pm 60.2 64 65.2 5.00pm 58.5 61.5 63 Table 3, Absorber plate temperature at twist ratio (5). Time Tp1 Tp2 Tp3 8.00 am 31.7 34 39.9 8.30am 34 35.3 41 9.00am 38.2 41.2 44.5 9.30am 42.7 45.3 47.1 10.00am 45.5 49.7 53.2 10.30am 49.2 51.6 55.2 11.0am 52.9 55.1 58.6 11.30am 55.8 58.2 60 12 noon 59 61.8 64.5 12.30pm 63.5 65.8 68 1.00pm 66 69 70.7 1.30pm 67.4 69.3 71.7 2.00pm 68.5 71.5 72.9 2.30pm 69.6 71.9 72.7 3.00pm 68.3 69.5 71.5 3.30pm 66.8 68.5 70 4.00pm 65 66.5 68.5 4.30pm 63.7 65 67.3 5.00pm 61.5 63.5 65.7 Table 4, Instantaneous collector efficiencies with time at flow rate ( 60 ℓ/hr. ). Time Ƞi-TR3 Ƞi-TR4 Ƞi-TR5 8.00 am 0.533 0.5145 0.45 8.30am 0.544 0.47 0.44 9.00am 0.56 0.48 0.4333 9.30am 0.55 0.47 0.4287 10.00am 0.52 0.45 0.3792 10.30am 0.51 0.481 0.3712 11.0am 0.54 0.46 0.39 11.30am 0.58 0.47 0.38 12 noon 0.529 0.4658 0.38 12.30pm 0.471 0.4289 0.3788 1.00pm 0.453 0.4023 0.33 1.30pm 0.422 0.371 0.3116 2.00pm 0.445 0.3465 0.297 2.30pm 0.402 0.329 0.2747 3.00pm 0.37 0.284 0.2295 3.30pm 0.32 0.2633 0.2132 4.00pm 0.28 0.187 0.1408 4.30pm 0.221 0.089 0.044 5.00pm 0.08 0.054 0.02 Table 5, Instantaneous collector efficiencies with time at flow rate (100ℓ/hr.). Time Ƞi-TR3 Ƞi-TR4 Ƞi-TR5 8.00 am 0.7 0.6662 0.5921 8.30am 0.7017 0.6049 0.5565 9.00am 0.7234 0.6631 0.6028 9.30am 0.7177 0.6343 0.5508 10.00am 0.7287 0.6653 0.5703 10.30am 0.6715 0.6015 0.5316 11.0am 0.6419 0.5789 0.5034 11.30am 0.6291 0.5807 0.5202 12 noon 0.6352 0.5764 0.4705 12.30pm 0.5808 0.486 0.4386 1.00pm 0.5522 0.4673 0.4106 1.30pm 0.516 0.4354 0.3709 2.00pm 0.4981 0.395 0.3263 2.30pm 0.46 0.3745 0.32 3.00pm 0.42 0.3378 0.3378 3.30pm 0.3041 0.2211 0.1935 4.00pm 0.26 0.1659 0.1327 4.30pm 0.11 0.0787 0.0787 5.00pm 0.0921 0.0461 0.0461 Jafar M. Hassan Al-Khwarizmi Engineering Journal, Vol. 11, No. 3, P.P. 37- 46 (2015) 43 Table 6, Instantaneous collector efficiencies with time at flow rate (150 ℓ/hr.). Time Ƞi-TR3 Ƞi-TR4 Ƞi-TR5 8.00 am 0.7776 0.73 0.6957 8.30am 0.7983 0.79 0.69 9.00am 0.7569 0.7569 0.72 9.30am 0.77 0.77 0.7 10.00am 0.78 0.73 0.65 10.30am 0.7587 0.7 0.6225 11.0am 0.7461 0.7088 0.6342 11.30am 0.7112 0.67 0.57 12 noon 0.7256 0.6 0.55 12.30pm 0.6352 0.58 0.52 1.00pm 0.6134 0.55 0.5 1.30pm 0.5681 0.5289 0.45 2.00pm 0.53 0.48 0.4 2.30pm 0.5066 0.46 0.37 3.00pm 0.47 0.39 0.2909 3.30pm 0.43 0.36 0.3 4.00pm 0.3475 0.28 0.15 4.30pm 0.2143 0.1 0.0536 5.00pm 0.0781 0.07 0.6957 Fig. 10. Relationship between useful energy and solar radiation for different twist ratio and flow rates in Z-Configuration. Fig. 11 Relationship between absorber plate and ambient temperatures during day hours at 150 ℓ////hr. 0 100 200 300 400 500 600 700 800 900 1000 1100 W a tt Time Z-Configuration at 60 ℓ/hr. Solar radation 0 100 200 300 400 500 600 700 800 900 1000 1100 W a tt Time Z-configuration at 100 ℓ/hr. Solar radation 0 100 200 300 400 500 600 700 800 900 1000 1100 W a tt Time Z-Configuration at 150 ℓ/hr. Solar radation 20 26 32 38 44 50 56 62 68 74 80 T e m p e ra tu re ͦC Time Z-Configuration at twist 3 tp1 tp2 tp3 ta 20 26 32 38 44 50 56 62 68 74 80 T e m p e ra tu re ͦC Time Z-Configuration at twist ratio 4 tp1 tp2 tp3 ta 20 26 32 38 44 50 56 62 68 74 80 T e m p e ra tu re ͦC Time Z-Configuration at twist ratio 5 tp1 tp2 tp3 ta Jafar M. Hassan Al-Khwarizmi Engineering Journal, Vol. 11, No. 3, P.P. 37- 46 (2015) 44 Fig. 12. Performance test 60 ℓ/hr. at different twist ratios. Fig. 13. Performance test 100 ℓ/hr. at different twist ratios. Fig. 14. Performance test for 150 LLLL/hr. at different twist ratios. 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.65 0 0.015 0.03 0.045 0.06 0.075 0.09 0.105 0.12 0.135 in st a n ta n e o u s e ff ic ie n cy ƞ i Tm-ta/GT Z-Configuration twist ratio 3 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.55 0 0.015 0.03 0.045 0.06 0.075 0.09 0.105 0.12 0.135in st a n ta n e o u s e ff ic ie n cy ƞ i Tm-ta/GT Z-Configuration twist ratio 4 0 0.1 0.2 0.3 0.4 0.5 0 0.015 0.03 0.045 0.06 0.075 0.09 0.105 0.12 0.135 in st a n ta n e o u s e ff ic ie n cy ƞ i Tm-ta/GT Z-configuration twist 5 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0 0.015 0.03 0.045 0.06 0.075 0.09 0.105 0.12 0.135 0.15 in st a n ta n e o u s e ff ic ie n cy ƞ i Tm-ta/GT Z-Configuration twist ratio 3 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0 0.015 0.03 0.045 0.06 0.075 0.09 0.105 0.12 0.135 0.15 in st a n ta n o u s e ff ic ie n cy ƞ i Tm-ta/GT Z-Configuration twist ratio 4 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.65 0 0.0150.030.0450.060.0750.090.1050.120.1350.15 in st a n ta n e o u s e ff ic ie n cy ƞ i Tm-ta/GT Z-Configuration twist ratio 5 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0 0.0150.030.0450.060.0750.090.1050.120.1350.150.1650.18in st a n ta n e o u s e ff ic ie n cy ƞ i Tm-ta/GT Z-Configuration twist ratio 3 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0 0.0150.030.0450.060.0750.090.1050.120.1350.150.1650.18 in st a n ta n e o u s e ff ic ie n cy ƞ i Tm-ta/GT Z-Configuration twist ratio 4 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.8 0 0.015 0.03 0.045 0.06 0.075 0.09 0.105 0.12 0.135 in st a n ta n e o u s e ff ic ie n cy ƞ i Tm-ta/GT Z-Configuration twist ratio 5 Jafar M. Hassan Al-Khwarizmi Engineering Journal, Vol. 11, No. 3, P.P. 37- 46 (2015) 45 4. Conclusions From the present work, we can conclude that: • The collector with minimum twist ratio (3) is found to have the lowest absorber plate temperature for the same test condition. • According to the flow rate ranges, the instantaneous collector efficiencies increase with increasing the flow rate for all twist ratios. • The maximum efficiency is obtained in minimum twist ratio (3), for all flow rates range presented in this work • The swirl generation and amount of heat transfer inside riser's pipes increase whenever twist ratio decreases. Nomenclature 5. References [1] Rose J.W., Briggs A., "Performance comparison of some tube inserts", Int., Commun, Heat Mass Transfer, vol. 29, p.45- 56, 2002. [2] Watcharin N., Smith E. and Pongjet P., "Effect of Twisted-strip Inserts on Heat Transfer in a Tube, the 2nd Joint International Conference on Sustainable Energy and Environment, A-030 ,P., 21-23 November 2006. [3] Alireza H. and Kamran S., "Experimental study on the effect of heat transfer enhancement devices in flat-plate solar collectors", International Journal of Heat and Mass Transfer, vol. 52, No. 19, pp. 4650- 4658, 2009. [4] Nagarajan p., Nitesh M. and Rohit C., "Experimental studies on heat transfer and friction factor characteristics of parabolic trough solar water heating system with and without twisted strips", Proceedings of the 37th National & 4th International Conference on Fluid Mechanics and Fluid Power, IIT Madras, Chennai, India, December 16-18, 2010. [5] Herrero Martín R., García Pinar A., Pérez García J.," Experimental heat transfer research in enhanced flat-plate solar collectors", world renewable energy congress, Sweden, 8-13 may, 2011. [6] Akeel A. and Ameer A., "Experimental Investigations in Circular Tube to Enhance Turbulent Heat Transfer Using Various Types of Twisted Tape Inserts", Eng. & Tech. Journal, vol.29, No.14, PP.2961-2973, 2011. [7] Withada, J. and Amnart B., "Effect of twisted ratio on flow structure heat transfer and thermal improvement in a circular tube with single twisted tape", Journal of Mathematics and Statistics 10 (1): 80-91, 2014. [8] Rhett N. , "The water wall-a passive solar collection and thermal storage device for Supplementary Radiant Heating", Master thesis, University of Nevada, Las Vegas, December 2013 . [9] www.thermocoupleinfo.com [10] Sinem E., "Assessment of impact of reservoirs contaminated bottom sediments on surface water quality by sediment water interaction model", Master thesis, the Graduate School of Engineering and Sciences, April 2011. AB Collector area ( m2) #$�� !" Specific heat capacity of water (kJ/kg.K) FR collector heat removal factor C4 Incident solar radiation (W/m2) �� � Water mass flow rate (kg/s) �� Water volume flow rate (m3/s) D Strip pitch (mm) ���� !" Useful energy(W) ta Ambient temperature ºC �%<= Fluid in temperature ºC �%&� Fluid out temperature ºC �3 Mean fluid temperature ºC TP Absorber plate temperature ºC �> Twist ratio E Strip width (mm) �� Water density kg / m3 ' �� !" 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