ESDU 74040 gives curves that enable the pressure loss to be calculated taking into account by-passing, tube inclination and external roughness, upstream turbulence, number of tube rows, and fluid property variations due to temperature variations. The data relate to regular arrays of in-line or staggered tubes. The ranges of experimental data (from 50 sources) used to build the correlation are tabulated together with estimates of accuracy at each stage of the calculation procedure (detailed in a convenient flowchart). For tube arrangements in square or equilateral triangular lay-out, ESDU 79034 can be used to find the pressure loss. ESDU 73031 allows the heat transfer to be estimated.