3###, Page 1 A New Model for the Performance Analysis of Evacuated Tube Solar Collectors Ahmed Aboulmagd 1 , Andrea Padovan 2 , Rejane De Césaro Oliveski 3 , Davide Del Col 2* 1 Cairo University, Faculty of Engineering, Mechanical Power Dept.,Cairo, Egypt a.aboulmagd@eng.cu.edu.eg 2 Università di Padova, Dipartimento di Ingegneria Industriale, Via Venezia 1, Padova, Italy davide.delcol@unipd.it 3 University of Vale do Rio dos Sinos, Department of Mechanical Engineering, São Leopoldo, Brazil decesaro@unisinos.br *Corresponding Author ABSTRACT This paper describes a new model for the performance analysis of the evacuated tube solar collectors. The analyzed collector is equipped with truncated compound parabolic reflectors, but the analysis is also extended to the case of collectors without reflectors. An original software is developed under MATLAB environment for the simulation purposes. A novel numerical procedure is implemented to obtain the solution for the nonlinear set of equations representing the mathematical model. In the model the variation of parameters is considered in the circumferential, longitudinal and radial directions. The length of the tube, where the heat transfer fluid flows, can be divided into a specified number of segments and the energy analysis is performed for each segment along the tube length in order to obtain the variation of different parameters in the longitudinal direction. The model analyzes separately the optics and the heat transfer in the evacuated tubes and this approach allows to extend the analysis to new configurations. The model can simulate the efficiency curve under steady state conditions, according to the standard EN 12975-2 (EN 12975-2. Thermal solar systems and components - solar collectors - part 2: test methods. Brussels: CEN; 2006). A comparison with experimental data shows the accuracy of the model. 1. INTRODUCTION Solar collectors can provide a useful response to the heat demand in buildings, such as heating of domestic water and spaces. Among the different types of solar collectors, the evacuated tube ones can work more efficiently when the temperature difference between operating fluid and ambient air is high and the solar radiation is low, which are the typical operating conditions during space heating of buildings. Beside the heating application, there is also need for addressing the increasing energy consumption due to the summer air conditioning. In the latter application, solar collectors can supply absorption machines, where the temperature levels required for the input heat are higher than 80 °C (Kalogirou, 2004). In the work of Zambolin and Del Col (2012), an experimental comparison of thermal performance of flat plate and evacuated tube solar collectors was performed. The efficiency of the evacuated tube collector is higher when the reduced temperature difference is higher than 0.035 (m 2 K)/W. Assuming global solar irradiance of 1000 W/m 2 this would mean that the performance of the evacuated tube collector is higher when the temperature difference between ambient air and heat transfer fluid is higher than 35 K. If ambient air temperature is 5 °C (winter case), such value of reduced temperature difference occurs when the solar collector produces heat at 40 °C. If ambient air temperature is 25 °C (summer case), such value of reduced temperature difference occurs when the solar collector produces heat at 60 °C. The evacuated tube collectors may be subdivided in two main types. In the direct flow through collector the heat transfer liquid is pumped in the tubes. The second type consists of heat pipes inside vacuum sealed glass tubes. In most of cases, both types of collector are equipped with a CPC (Compound Parabolic Concentrator) to optimize the collection of solar radiation. Among the direct through flow type, the U-tube evacuated tube solar collector appears to be a well-developed type of collector. It has the advantages of high-pressure-bearing ability compared with the all-glass evacuated tube [2]. Theoretical and 3 rd International High Performance Buildings Conference at Purdue, July 14-17, 2014