Abstract: An experimental investigation of pool boiling heat transfer is carried out in a horizontal tube bundle with 8 rows and 3 columns of tubes, and a pitch - to - diameter ratio of 1. 667. The working fluid is R-113. Heat transfer coefficients are measured for each row of tube, and it is found that the heat transfer coefficient increases for higher heat flux and higher position in the tube bundle. The measurements show that there exists a large bundle effect. In addition, boiling curve hysteresis in tube bundle is found. The correlations of boiling heat transfer coefficients are obtained.