Analytical thermal modeling of a heat pipe solar water heater system integrated with phase change material Mohammad Sajad Naghavi, Mahyar Silaakhori, Mohammad Mehrali, Hendrik Simon Cornelis Metselaar, Irfan Anjum Badruddin Department of Mechanical Engineering Faculty of Engineering University of Malaya 50603 Kuala Lumpur Malaysia msnaghavi@gmail.com , h.metselaar@um.edu.my Abstract: The model introduced here is about the integration of heat pipe solar water heater system (HPSWH) with phase change material (PCM). Two goals were being pursued in this design; first, controlling the overheating of supplied water during the day and second, extending the operation time of the solar water heater system. To achieve these two goals, the energy entering to the heat pipe needs to be adjusted with respect to the amount of absorbed solar radiation energy. In presented configuration, PCM is placed at the bottom of the solar absorber plate and heat pipe to absorb and store extra gained thermal energy of the absorber plate which is not collected by the heat pipe. Based on actual weather data of a station in Malaysia, as a tropical climate country, thermal behavior and annual energy production estimation of the basic and improved systems will be evaluated. Approximate analytical solutions were been used to estimate the amount of absorbed solar energy and thermal behavior of supplying water. One-phase approximation solution is applied to estimate the thickness and stored energy of the PCM. Findings of this research indicate the feasibility of integration of PCM as amechanism for improvement of the overall performance of the HPSWH system. Key-words: Solar thermal system, thermal energy storage, approximate solution, Stefan problem 1Introduction The periodic feature of renewable energy such as solar has become a major barrier in the wide spreading use of this energy. The solution to this barrier is the usage of energy storage system, which store energy during the pick time and release energy at time with shortage of energy. Solar energy systems are widely divided in two purposes, first, electricity generation and second, solar heat absorption. Solar heat absorption systems mostly used for water heating. Various configurations of solar water heating systems have been introduced in commercial scales, which their difference mainly are in heat absorption method, heat exchanging mechanism, piping system and storage process. Currently, the models of the solar water heater systems that have been introduced to the market have an efficiency of 40% to 60% of absorbable solar energy. One of the higher performance models is heat pipe solar water heater (HPSWH) system. PCMs attract attention as one of the potential thermal energy storage system due their higher energy storage densities and isothermal phase transition [1-4]. The main advantages of PCMs are low cost, high storage density, high energy security for supplying of energy, isothermal operation, and easy construction to the system [5, 6]. PCM has been used for many applications, which included thermal comfort, electronic cooling, space craft, water heating, building, and etc. [7-10].The enormous potential of solar energy has made the PCMs very attractive for space heating/cooling, green house heating, cooking, hot water production, etc. Due to time gap between availability of solar energy and need, energy storage is emphasized to ensure continuous and efficient supply. Solar energy can be stored in either sensible or latent heat form. The latter is more preferred, as it offers high energy density and transfers energy under isothermal conditions. Thermal energy storage (TES) occurs in two forms of sensible heat and latent heat. The latent heat is more preferred in TES systems. Several configurations of solar thermal systems, which were integrated with PCMs, as a heat storage enhancer, have been developed and analyzed theoretically or experimentally, within the past few years [5, 11-20]. In most of the designs, PCM were placed in the storage tank or heat exchanger device [5, 19, 21-29]. For latent heat storage applications, many types of Computer Applications in Environmental Sciences and Renewable Energy ISBN: 978-960-474-370-4 197