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Performance investigation on an integrated multi-stage cylindrical-tank solar water heater

Performance investigation on an integrated multi-stage cylindrical-tank solar water heater
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  Performance investigation on an integrated multi-stage cylindrical-tank solar water heater  Tadahmun  A. Yassen, Mousa M. Waes, Omer K. Ahmed, Tahseen Ahmad Tahseen, and M. B. Baharom Citation:  AIP Conference Proceedings  2035 , 040003 (2018); doi: 10.1063/1.5075567View online: Table of Contents: by the  American Institute of Physics  Performance Investigation on an Integrated Multi-StageCylindrical-Tank Solar Water Heater Tadahmun A. Yassen 1, b) , Mousa M. Waes 2 , Omer K. Ahmed 3 , Tahseen Ahmad Tahseen 1 , M.B. Baharom 4,5, a) 1  Department of Mechanical Engineering, College of Engineering, Tikrit University, Tikrit, Iraq 2  Kirkuk Technical College, Northern Technical University, Iraq 3 Technical institute of Hawija, Northern Technical University, Hawija, Kirkuk, Iraq 4 Centre for Automotive Research and Electric Mobility (CAREM), Research and Innovation, Universiti Teknologi  Petronas, 32610 Seri Iskandar,Perak, Malaysia .5  Department of Mechanical Engineering, Faculty of Engineering, Universiti Teknologi Petronas, 32610 Seri  Iskandar,Perak, Malaysia. a) Correspondingauthor:  b) Abstract. This research is about performance investigation of a multiple-tank integrated-solar collector storage heater. A  prototype of the heater having a capacity of 300 Liter was constructed and experimentally tested outdoors to observe the variation of water temperature in the storage tanks. A Fluent program is used to predict the storage water temperature. The experimental data was verified with the results from the simulation model. In vice versa, the simulation model was validated using the experimental data. Two cases have been studied, namely with and without flow rate. The results show that the maximum water temperature exited from the storage tanks during February month of 2010 was 48℃. The results illustrated that the present integrated solar water heater was a success in providing hot water suitable for day time use by households during the winter in Iraq.Keywords: Integrated system; performance; solar; water heater. INTRODUCTION The usages of solar energy and their conversion into thermal, electric or chemical energy are common nowadays. Its applications include heating, cooling, water heating, desalination, power generation, cooking, drying of agricultural crops and others. Solar water heaters are one of the simplest and most widespread applications of solar energy in the world today. The Arab countries are among the world's richest areas of solar energy. The sun is available for long  periods of time throughout the year. Solar water heaters contain three main parts namely solar collector, storage tank and water distribution pipes. The cost of solar water heaters is the mainstay of its spread and use, hence it needs a lot of attention from researchers to develop and make it less expensive and more efficient to use especially in war-torn country like Iraq. Many researchers tried to reduce this cost using an integrated solar water heater, which incorporates the solar collector and the storage tank in a single unit(1).A numerical code which was capable of prognosticating the thermal behavior of a double tank integrated collector storage system (ICS) with a compound parabolic concentrator (CPC) had been developed by Kessentini and Bouden(2).A concept design of an ICS device was built and tested in both open and closed area to inspect the variation of water temperature in the storage tanks. The experimental results indicated a significant water temperature increase in the storage tanks during the day and a satisfactory temperature preservation during the night. The bottom tank received more heat as it was better exposed to the sun while the change in the demonstrated temperature in the upper  placed tank were smaller due to its better thermal insulation providing a good storage of hot water temperature to the ICS system. Garnier et al.(3)in an Integrated Collector Storage Solar Water Heater (ICS-SWH). Their model design 6th International Conference on Production, Energy and Reliability 2018 AIP Conf. Proc. 2035, 040003-1–040003-8; by AIP Publishing. 978-0-7354-1761-8/$30.00 040003-1  was adopted in the form of a rectangular-shaped box combining the solar collector and storage tank and it was optimized for simulation in the Scottish climate. During the three-month period, tests and experiments had been conducted on the ICS-SWH in order to produce empirical data to compare with the computed outputs. Computed longitudinal temperature stratification results were observed to be in good agreement with the experimental data. Dharuman et al.(4)experimentally studied an integrated solar water heater. The absorber area of the test device surface was 1.3 m and 2m and the volume was 170 liters, of which extractable volume per day was 100 liters. Its outletwas examined under various standard working environment. 100 liters of hot water was withdrawn from the sump at 7:00 am every morning, and the tank was then refilled with cold water comes from the mains. The records showed that the collected water mostly had a temperature in a range of 50 to 60  ̊ C, in the first morning and range of 45  –  50  ̊ C in the next morning. Daytime collection efficiencies of about 60% and overall efficiencies of about 40% were obtained.Al-Jubori(5)experimentally and numerically examined a novel design of storage solar collectors to investigate its  practicality for domestic use. These storage collectors can be installed as storage water tanks to replace the ordinary cubical or cylindrical tanks used in Iraqi houses.The study involved two different principal engineering forms. One of the ideas, using the form of rectangular and triangular collectors was suggested by Al-Jubori(5). The system was derived from cutting a cube at different cutting planes. The second form is a cylindrical storage collector which was derived from cutting a cylinder at an inclined cutting plane. The researcher found that the triangular tank configurationwas more efficient than the other two tanks configuration. The daytime data collection efficiency of the triangular collector at no load condition in winter was found to be 48.7% for a maximum mean storage temperature of 40.5  ̊ Cand a maximum hot water temperature at the tip of the collector of 65  ̊ C. Khalifa and Abdul Jabbar(6)experimentally studied the performance of a solar hot-water storage system consisting of 8-cm diameter tubing connected in series to serve as the absorption and storage tank. Theauthors presented the results of the overall heat loss coefficient, efficiency factor, useful heat gain and distribution temperature at the tube surface which were in good agreement  between the theoretical and experimental data of the storage collector. Ahmed et al.(7)researched about the consequence of some design parameters on the storage solar collector performance.The horizontal and inclined angle of the collector was investigated and the authors studied the effect of loading and non-loading conditions. In addition, three different water patterns such as continuous, intermittent and all water withdrawal at fixed time of day were studied. The results showed that the mean storage temperature in horizontal arrangement was higher compared to the inclinedcollector at no-load, but the inclined collector produced higher mean storage temperature when operating with load. In addition, several other studies on integrated solar water heaters were performed by several researchers such as Owolabi et al.(8), and Al-Kayiem et al.(9).The design of multi-stage cylindrical-tank solar-water heaters (IMCSH) used in this research have been implemented in Iraqi households but based on past literatures, the investigation on its performance has not been carried out. In this research, a prototype of IMCSH has been fabricated and experimentally tested to determine its  performance. The storage tanks were made from four 180-mm diameter pipes connected in series and integrated into a single unit. A numerical model was employed to prognosticate the performance of the system and verify the results with experimental data. METHODOLOGY This section presents the system design, operational principal, experimental setup, and measuring instrumentations. The system is an integrated solar water heater consisting of integrated storage-absorber tank, wooden  box, and a glass cover.A prototype model of a solar collector was constructed in the form of four cylinders as shownin Fig.1. Each cylinder is made of 180-mm diameter steelpipes having a length of 1220 mm and a volume of 0.075 m 3  per cylinder. The outer surface of the tank was painted with dark black color using locally made paint to increase absorption. A glass wool of thickness 75 mm was used to isolate the rear and lateral sides of the cylinder from solar radiation. The tank and insulation were installed in a wooden box to reduce heat loss to the surrounding. The glass cover has two layers of glass with a thickness of 6 mm on the opposite side of the sun to reduce thermal loss from the solar collector. It was also fixed with a special paste to prevent rain water and dust from entering into the collector. The solar collector tilt angle was 45  ̊ from horizontal facing to the south. 040003-2  (b) Figure 1. Photo and Schematic diagram of the integrated solar water heater. Experimental setup and Instrumentation Calibrated K-type thermocouples with an accuracy of 0.75% have been used to measure the temperature at various locations in the system. The first thermocouple was placed to display the temperature of the water entrance while the second was to measure the temperature of the water outlet. Three thermocouples were installed to measure the water exit from each tank to the next one starting from the first reservoir to the third one respectively. Two other thermocouples were placed to measure the temperature of the air inside the system, i.e. one below the glass, and one to show the temperature of the ambient air.The solar radiation has been calculated theoretically according to the theory of Lunde(10).Figure2shows experimental setup and the test rig of the integrated solar water heater.   (1)Water inlet to the storagetanks.(2)Glass cover. (3)Storage tanks. (4)Wood piece to support thestorage tanks.(5)Insulator.(6)Wood frame. 040003-3  (A, B, C, D) the storage tanks(1)Point of measurement of ambient air temperature(2)Point of measurement of the hot water exit temperature from the solar collector (3)Point of measurement of the air temperature inside the collector (4)Points of measurement of the hot water exittemperature from all storage tanks due to the arrangement(5)Connecting pipe between every two tanks,(6)Insulation under the storage tanks(7)Insulation on the sides(8)Wooden structure(9)Point of measurement of inlet cold water (10)Water control valve. Figure 2 . Integrated Solar Water Heater Test Rig Schematic Diagram with Temperature Measurement Points Measurement Procedure A series of regular experiments were conducted to study the performance of the integrated solar water heater system at the Tikrit University, Iraq at no-loading and different loading conditions. The experiments were conducted in steady-state conditions for a period of one hour during which the solar radiation, wind speed, and the fluctuation in water temperature were minimum. NUMERICAL SOLUTION ANSYS Fluent software was used to conduct computational fluid dynamics (CFD) modelling and simulation in this research. This program is based on finite volumes method to study the phenomenon of natural convection inside a storage tank. The differential transfer equations that govern natural convection phenomenon consist of equations of continuity (mass conservation), momentum and energyequations(9).The heat transfer equations are converted to differential equations as follows:          where  is any dependent variable,  is the exchange coefficient of  ,   is the source term of  Substituting the expression for the primary fluxes and the source term, thediscretization equation for  can be written as follows(11):                                              where                               And             The values of the above variables are tabulated in Table 1 and 2 below:Continuity, momentum and energy equations are integrated into each controlled volume after dividing the space within the tank into a number of these volumes. This method ensures that momentum and energy are maintained within each volume. An extension program called Gambit was used to construct the prototype and networking of the  problem as shown in Fig. 3(b)A tetrahedral element was selected in the grid generation model. 040003-4
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