In this thesis, heat transfer and pressure drop during condensation of R-404A inside horizontal twisted tape inserted tubes has been investigated experimentally. The experimental set-up which was used in this study was a well instrumented vapor compression refrigeration cycle which utilized R-404A as refrigerant. This set up consist of a test condenser which all the experiments were carried out on it. In addition there is a primary condenser and secondary condenser to achieve the required vapor qualities in order to investigate the effect off vapor quality on heat transfer and pressure drop. All these condensers are double pipe counter flow water cooled heat exchangers which refrigerant flows inside the internal cooper tube, while water flows in the annulus. The experimental investigation was carried out in the plain tube and four twisted tape inserted tube. At each experiment several parameters were measured, such as refrigerant mass velocity, inlet and outlet water temperatures, inlet and outlet refrigerant temperatures, etc. Heat transfer coefficients were calculated by use of the collected data. Also, pressure drop between the inlet and outlet of test condenser is measured by differential pressure transmitter. In order to verify integrity of the experimental set up, Comparison between plain tube results and exiting correlation was done. Investigation of the results for twisted tape inserted tube shows that for the same mass velocity twisted tape ratio reduction increases both heat transfer coefficient and pressure drop. Also for the same twisted ratio increase of mass velocity and vapor quality increase heat transfer and pressure drop. A new correlation for the prediction of heat transfer coefficient and pressure drop were developed by utilizing the gained results for the twisted tape inserted tubes. Finally performance evaluation was done and it is observed that at all conditions using twisted tape inserts are unfavorable. However, twisted tape inserts can be employed in specific application such as when because of limited space, compact heat exchangers are needed and higher pumping power is reasonable. An experimental investigation was conducted to find the influence of twisted tape inserts on the pressure drop and heat transfer coefficient during force convective condensation of R-404A vapor in a horizontal tube. The test section was a double pipe counter flow heat exchanger. The refrigerant flowed in the inner tube and cooling water flowed in the annulus. Experimental tests were carried out for plain tube and four tubes with twisted tapes inserts of 4, 7, 10 and 14 twisted ratio with mass velocities from 71.2 to 142.4 kg/m 2 s and vapor qualities from 0.24 to 0.87. Investigation clearly showed that using twisted tapes inside the tubes increases pressure drop and heat transfer coefficient in the range of 89 to 239% and 29 to 72% respectively higher than that for the plain tube on the nominal area basis. An empirical correlation was developed to predict the increased pressure drop and heat transfer during condensation inside a horizontal tube in the presence of twisted tape inserts. By comparing the predicted and experimental data, it was found that the majority of the present data falls within ±20% of the proposed correlations. In addition, the performance evaluation for the twisted tape inserted tubes was accomplished. Key words : Heat Transfer Increase, Condensation, Twisted Tape, Pressure Drop, R-404A.