Discussed are energy conversion and energy flux accompanied to oscillations of viscous fluid. The energy conversion per unit volume is shown to be ρ
m(∂
T/∂
p)
S«
p⋅
dS/
dt»+«
u⋅
∇p» for a small cycle, for which variations of pressure
p and entropy
S are small. ρ
m is time average of the density,
u is the velocity and
∇p is the pressure gradient. « » indicates double operations of spatial average over crosssectional area of flow-channel and time average. «
u⋅
∇p» is a negative quantity corresponding to dissipation due to viscosity of fluid. The average of energy flux is shown to be enthalpy flux ρ
m«
H⋅
u» approximately, in the case that the velocity
u and the mass flux «ρ⋅
u» are small and the wave length is long. ρ and
H are variations of the density and the enthalpy respectively. The enthalpy flux for small cycle is shown to be summation of heat flux and work flux: ρ
m«
H⋅
u»=ρ
mTm«
S⋅
u»+«
p⋅
u» where «
p⋅
u» is the work flux and ρ
mTm«
S⋅
u» is the heat flux. Final discussions are on the energy conversion, the work flux and the heat flux of adiabatic reversible small-cycle, isothermal small-cycle, polytropic small-cycle, isobaric small-cycle and isochoric small-cycle.
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