As the demand for energy around the world increases, there is a need to produce efficient, sustainable and clean energy with the resources available. Energy production involves the process of heat exchange at multiple levels and hence needs to be highly efficient. This paved the way towards adopting heat transfer enhancement techniques which enable an easier flow of heat between two fluids by reducing the overall convective thermal resistance. This is made possible through the increase of surface area or/and heat transfer coefficient. Extended surfaces are one such technique that has been in use for decades and studied extensively (Manglik (2003), Webb and Kim (2005)). In Chapter 1, a review of few extended surfaces such as plain fin and tube, wavy fin and tube, louvered fin and tube, plain plate fins, wavy fins, offset strip fins, louvered fins and their correlations have been discussed. Using these correlations, in Chapter 2, two heat exchangers, a plain fin and tube heat exchanger and a compact plate fin heat exchanger have been designed for a specific air cooled condenser application. The heat exchangers will pre-cool the ambient air that is used to condense the steam in ACC units in power plants. In Chapter 3, a novel heat exchanger, which is a hybrid of the offset and wavy fin heat exchanger, has been developed. This novel heat exchanger aims to combine the best attributes of the offset and wavy fins and produce a relatively superior heat transfer performance for concomitant pressure drop penalty. Two types of offset corrugated surfaces, S-shaped and C-shaped have been discussed. These surfaces have been characterized by two non-dimensional parameters, γ (corrugation aspect ratio) and ε (fin spacing). A two dimensional study (h >> s) on periodically fully developed, laminar flow with air (Pr = 0.7) as working fluid for 10 ≤ Re ≤ 1000, 0.1 ≤ γ ≤ 0.5, 0.5 ≤ ε ≤ 2 was numerically simulated. Results have been given in terms of fanning friction factor (f) and colburn factor (j) against Reynolds number (Re). It was found that the offset-wavy fin performed much better than the plain wavy fin, yielding an average of 1.4 times heat transfer enhancement for γ = 0.25, 0.375, 0.5 and a peak enhancement of 1.9 times for γ = 0.1 at constant pressure drop.