ESDU 79034 gives a method derived from ESDU 74040 that greatly simplifies the prediction of pressure loss for tube lay-outs typical of shell-and-tube heat exchanger design@ that is with tubes in-line or staggered in either square or equilateral triangular lay-out. The method applies to tube pitch/diameter ratios of 1.2 to 3 and superficial Reynolds numbers (that is based on a flow velocity calculated on a flow area that neglects the area occupied by the tube) of one to a million based on tube diameter. Equations are given for a loss coefficient as a function of the pitch/diameter ratio and superficial Reynolds number for each of the four cases@ and graphs of the curves are included. Correction factors are also given to correct values of the loss coefficient for the effects of viscosity variation due to temperature@ flow inclination to the tube@ and surface roughness of the tube. A comprehensive worked example illustrates the use of the data.