  With the elementary energy release events introduced in a previous paper (Liu
& Fletcher 2009) we model the chromospheric evaporation in flaring loops. The
thick-target hard X-ray (HXR) emission produced by electrons escaping from the
acceleration region dominates the impulsive phase and the thin-target emission
from the acceleration region dominates the low-energy thermal component in the
gradual phase, as observed in early impulsive flares. Quantitative details
depend on properties of the thermal background, which leads to variations in
the correlation between HXR flux and spectral index. For lower temperature
and/or higher density of the background electrons, the HXRs both rise and decay
more quickly with a plateau near the peak. The plateau is less prominent at
higher energies. Given the complexity of transport of mass, momentum, and
energy along loops in the impulsive phase, we propose a strategy to apply this
single-zone energy release and electron acceleration model to observations of
flares associated with single loops so that the energy release, electron
acceleration, and evaporation processes may be studied quantitatively.
