The rapid introduction of a fluid from a high pressure source into a lower pressure receiver can result in rapid heating of the mixed fluid in the receiver. The extent of temperature rise will depend on the initial conditions of the source and receiver fluids including temperature, pressure, composition, phase, and the rate of mass inflow.
For the special case of ideal gas inflow from a high pressure source into a low pressure receiver that also contains an ideal gas, we can demonstrate from first principles that the final temperature will asymptote to γTo, where To is the high pressure source fluid temperature. This condition is encountered for example when compressed natural gas vehicles are filled, or when a high pressure gas is introduced into a downstream receiver due to the failure of a heat exchanger tube or control valve.
When introduction of mass and energy into the receiver vessel occurs rapidly, heat exchange between the fluid, vessel walls, and the surroundings becomes negligible. This can lead to high fluid temperatures that may cause material of construction problems, and/or cause the decomposition of chemicals or mixtures containing ethylene or other reactive components. Slower introduction of mass and energy into the receiver allows for more heat exchange with the vessel walls and surroundings resulting in lower peak fluid temperatures. We also discuss the potential for compression ignition and the increase in temperature that can be caused by spontaneous bubble compression.
We first develop the overall fundamental mass and energy balances for a non-ideal, multi-phase constant volume system to illustrate how mass and energy can be added or depleted from a constant volume system. We then simplify these general balances to represent a single gas phase with nonideal behavior. We further simplify the single phase balances using ideal gas behavior to derive the fluid temperature asymptote of To. This asymptote provides a simple screening criteria.
Process Safety Office® SuperChems™ is a very useful and reliable dynamic simulation software that can provide insight into compression heating for simple and complex systems with chemical reactions and/or non-ideal behavior.
Consider a vessel containing a reacting two-phase multicomponent mixture of total volume V, temperature T, and pressure P. It is assumed that both the vapor and liquid phases are always in thermal, mechanical, and diffusional equilibrium. The vapor and liquid phases are considered to be homogeneous in composition and state. When a change of phase is exhibited, mass may be transferred from one phase to the other. Thus, the state of either phase may be altered by a change in composition, temperature, or pressure.
The value of any thermodynamic property, M, in either phase may be expressed as a function of temperature, pressure, and number of moles of the individual mixture components...
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