الفهرس 
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Abstract
ABSTRACT In the present work, the heat transfer process of the closed two-phase offset thermosyphon is experimentally and theoretically studied. The experimental model is designed and constructed such that the effect of various parameters controlling the thermosyphon behavior can be studied. Inclination angles, filling ratio, the ratio between condenser to evaporator length and offset length are the operating parameters of the offset thermosyphon. The experiments are carried out for the value of heat flux of 7.35, 13.8, 22 and 28.3 kW/m2 for each experiment. Water as working fluid is charged with a ratio of 25, 50, 75, 100 and 125% with respect to the evaporator volume for each thermosyphon configuration. The effect of offset length of 100, 130 and 180 mm is examined for each operating condition. The effect of inclination angles of –15 (ccw), 0 (vertical), 15, 30 and 45o are examined. Three different values of the ratio between condenser to evaporator length of 3, 1.5 and 1 are used. According to the measured values of the problem variables, the value of mean heat transfer coefficient is calculated. A correlation is proposed to estimate the Nusselt number as a function of Rayleigh number and problem parameters. Moreover, the thermal performance of elbow shape thermosyphon is experimentally and theoretically studied. The effect of problem parameters on heat transfer process is discussed. Filling ratio and the ratio between condenser to evaporator length, at vertical position, are the operating parameters of the elbow thermosyphon. In the theoretical model the governing equations describing the problem of heat transfer in linear thermosyphon are approximated to a set of linear algebraic equations using finite difference technique. Computer program is developed to solve these approximated governing equations. from the model, liquid film velocity, vapor velocity, liquid film thickness and wall temperature can be obtained. The agreement between the results of previous experimental works and theoretical results is fairly good in most investigated conditions. The theoretical model is used to predict the performance of offset and elbow thermosyphon by determining the equivalent linear thermosyphon for each type.