Studies on isothermal steady state frictional pressure drop for flow of petroleum base oil SN70, SN150, Diesel and water are carried out in spiral coils with diameter to length ratio, 0.00042, 0.00047, 0.00073, 0.00164, 0.00189, 0.003 and 0.0037. An attempt is made to correlate friction factors with a better and more appropriate dimensionless group for flow of Newtonian fluids through spiral coiled tubes. An innovative approach of correlating heat transfer data with the newly established dimensionless group is presented. Heat transfer experiments are performed for spiral coils with diameter to length ratio 0.000474, 0.00042, 0.001896, 0.00198, 0.000942, 0.00164 in laminar flow regime. Suitable correlations for friction factors and Nusselt numbers are proposed. Relationship between pressure drop and heat transfer is studied. The incapability of the conventional analogy equations to estimate the heat and momentum transfer coefficients for laminar flow through straight or curved tubes is explained based on the viscous and form drag existing in straight and curved pipe flow. The limitations of the existing analogy equations are examined critically. A new general analogy equation is derived for laminar flow through spiral and straight tubes considering the influencing geometrical parameters of the tube. Keywords: Forced Convection; Heat and Mass transfer; Heat Exchangers; Thermal Systems.

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