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Abstract The influence of pressure and rod to rod spacing on the nucleate pool boiling heat transfer in water from vertical electrically heated tube-bundle was investigated experimentally through this work. The tuba bundle consists of three stainless steel tubes, each is 500 mm long and12 mm in outside diameter. According to the results obtained from experimental analysis adopted in this study, the following points may be concluded :- i) The outer surface temperature of the heating tube decreases in the direction of bubble flow, i.e. its valus at upper end of the heating tube is lower than that at lower end. ii) Increasing the system pressure causes en increses in the outer surface temperature at the same level and for the same hest flux. iii) The outer surface temperature of the heating tube decreases with increasing rod to rod spacing (S/d ratio). iv) The coefficient of heat transfer at the upper and of the test section is heigher than its value at lower end. This is true for all pressures and ell S/d ratios. v) For all pitch to diameter ratios, the coefficient of heat transfer increases as the system pressure increases at the same level and for the same heat flux. |