  We present a new phenomenological model for the spectral energy distribution
of normal star-forming galaxies between 3 and 1100 microns. A sequence of
realistic galaxy spectra are constructed from a family of dust emission curves
assuming a power law distribution of dust mass over a wide range of
interstellar radiation fields. For each interstellar radiation field heating
intensity we combine emission curves for large and very small grains and
aromatic feature carriers. The model is constrained by IRAS and ISOCAM
broadband photometric and ISOPHOT spectrophotometric observations for our
sample of 69 normal galaxies; the model reproduces well the empirical spectra
and infrared color trends. These model spectra allow us to determine the
infrared energy budget for normal galaxies, and in particular to translate
far-infrared fluxes into total (bolometric) infrared fluxes. The 20 to 42
micron range appears to show the most significant growth in relative terms as
the activity level increases, suggesting that the 20-42 micron continuum may be
the best dust emission tracer of current star formation in galaxies. The
redshift dependence of infrared color-color diagrams and the far-infrared to
radio correlation for galaxies are also explored.
