^{1}1Institute of Physics of the Dagestan Scientific Center of the Russian Academy of Sciences, Makhachkala, Dagestan, Russia

^{2}National Institute of Standards and Technology, Boulder, Colorado, U.S.A.

**Keywords:** heat capacity, liquid-gas**property:** heat capacity, PVT**material:** ether

The recent ten years we can observe that, the alcohols and the ethers are widely used as the ecologically pure fuels and as the additives to traditional kinds of fuel. The application of this substances has an additive advantage because of they can be obtained from the plants – which are practically permanent resource. Here we observe the results of the thermophysical investigation of the diethyl ether (C_{2}H_{5}OC_{2}H_{5}). The urgence of additive investigations was caused by absence of considered experimental data in the fields of enginery importance. The measurement was held along the isochors on the adiabatic calorimeter-piezometer of the constant volume [1]. The experimental method was described in the several papers [2, 3 ]. The apparatus allowed the parallel measurement of some thermodynamical parameters: the pressure (P), the specific volume (V), the temperature (T), the isochoric heat capacity (C_{v}), and the derivative of the pressure to the temperature (∂P/∂T)_{v}. The investigation covered the region of the liquid-gas two-phase equilibrity, and the critical and supercritical regions. The new experimental data are obtained along 17 isochors (534÷212) kg/m^{3} in the temperature interval (340÷590)K and at the pressures up to 20 MPa. There are defined the parameters of the saturation curve P_{s}(T), of the coexistence curve ρ_{s}(T), and the values of the isochoric heat capacity C_{vs}(T) and of the derivative (∂P/∂T)_{vs} on the liquid-gas phase transition curve from the side of two-phase and of single-phase states; and the accuracy of the critical values of the parameters T_{c}, P_{c}, ρ_{c} is improved. The comparison with the published by another authors data is given. Basing on obtained experimental results, we have calculated the isobaric heat capacity C_{p}, the heat capacity C_{s}, the inner pressure Pint, the second derivatives of the pressure and of the chemical potential to the temperature d^{2}P/dT^{2} and d^{2}P/dμ^{2} on the liquid-gas phase transition curve.

- Kh.I.Amirkhanov, B.G.Alibekov, G.V. Stepanov, Isochoric Heat Capacity of Water and Steam (Amerind Publ. Co., New Delhi, 1974, p.216
- I.M. Abdulagatov, N.G. Polikhronidi, T.J. Bruno, R.G. Batyrova, G.V. Stepanov, Fluid Phase Equilib., 263, 71 (2008)
- N.G. Polikhronidi, R.G. Batyrova, I.M. Abdulagatov, J.W. Magee, G.V. Stepanov, J. of Supercritical Fluids, 33 (2005), 209-222

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