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  • Obviously the wor http www apexbt

    2018-11-13

    Obviously, the work done in this process has nothing to do with propellant force. In other words, the work A used to define the propellant force in the second statement should not be the work done by the free expansion of the propellant gas. Furthermore, it Chloroquine is not clear whether the expansion “at atmospheric pressure” in this statement means the expansion at constant exterior pressure (pext = pa = 1 atm) or at constant system pressure (p = pext = pa = 1 atm). If it refers the former case, thenas pext = pa = 1 atm is independent of system pressure (propellant gas products), and only one state variable is specified both in the initial and final states of the system (i.e., Tv of the initial state and p = pa = 1 atm in the final state), V1 and V2 could not be given specified values. This means that the value of the work A seems having no direct relationship with the propellant force fv. If it refers the latter, i.e., the system pressure keeps p = pext = pa = 1 atm from the initial state to the final one, the propellant should burn in an adiabatic cylinder such designed in advance that its initial volume just makes the pressure of the burned gas at temperature Tv reach 1 atm. Then the expansion work should be In order to give the work A a positive value, it is necessary to let T2 > TV. This means that an additional heat should be introduced to the system. The work A in this case could never be the equivalent of propellant force. The definitions given in the third statement seems to be ambiguous. The physical process described by the definition is not clear. And it could not give the mathematical expression, , directly from the definition. In some other literature, the physical definition of propellant force is ignored [8,9].
    In order to give a more perfect physical definition, it is regarded that two requirements should to be met: Suggested definition 1: The work done by a kilogram of burned propellant gas products (supposed as ideal gas) at initial temperature of Tv K expanding to a final state at temperature of 0 K during an adiabatic reversible expansion process would be mainly dependent on the quantity of , and thus the product is defined as propellant force fv, expressed as fv = . This definition could mathematically be presented aswhere φ is a coefficient. It could be proved that φ = 1/θ in the above equation, and here θ = k−1. According to the first law of thermodynamicswhere Q represents heat and U is energy of a unit mass of burned propellant gas. The sign of Q here is specified as positive when heat is released from the system, and vice versa. As the process is adiabatic,then, Eq. (2) giveswhere is heat capacity at constant volume for a unit mass of burned propellant gas. As where is heat capacity at constant pressure for a unit mass of burned propellant gas; k is adiabatic exponent/ratio of heat capacity, Eq. (3) could then be rewrote as The suggested definition 1 shows that the ability of a propellant to do work in the ideal conditions is mainly dependent on the quantity of force constant, because the varying range of k for propellant gas products would be much smaller than that of . For two propellants that have similar magnitude of fv, the ability to do work in the ideal case would depend on the value of k (or θ), the less the k value is, the bigger the ability of a propellant to do work would be. Suggested definition 2: The difference between the enthalpy and energy of the gas products at temperature of Tv K produced by the burning of one kilogram of propellant is called the propellant force. And the following mathematical expression could then be givenwhere H is enthalpy of a unit mass of burned propellant gas. In fact, Eq. (5) shows that the difference between the enthalpy and the energy of the gas products at temperature of Tv K produced by the burning of one kilogram of propellant equals to the product of the pressure multiplied by the volume of the gas system. It represents the pressure potential energy, or the ability to do work, of the burned propellant gas.