Isobaric specific heat capacity of {xH2O + (1 − x)NH3} with x = (0.0000, 0.1566, 0.1597, 0.3030, 0.3048, 0.4956, 0.7061, and 0.8489) at T = (280, 300, 320, and 360) K over the pressure range from (0.1 to 15) MPa
Introduction
The International Association for the Properties of Water and Steam (IAPWS) requested the measurement of the properties of the (ammonia + water) mixtures. Replying to the request of the IAPWS, we planned to measure the isobaric heat capacity of (ammonia + water) mixtures. We have developed the calorimeter [1] for measuring the isobaric specific heat capacity cp of fluids and fluid mixtures at high pressure by the thermal relaxation method. In this paper, the results of cp measurements for {xH2O + (1 − x)NH3} with x = (0.0000 to 0.8489) at T = (280.00 to 360.00) K, and p = (0.1 to 15) MPa are presented, and the behaviour of cp for the mixtures is discussed. Comparisons of the cp values for pure ammonia [2], [3] and the (ammonia + water) mixtures with the literature values [4], [5], [6] are reported. Moreover, we also discussed the systematic comparisons between the present results and calculated values from the Helmholts-type equations of state (EoS) for ammonia by Tillner-Roth et al. [7] and for (ammonia + water) mixture by Tillner-Roth and Friend [8], both of which are widely used in various applications including REFPROP (Version 8.0) [9].
Section snippets
Calorimeter, apparatus, and procedure
The calorimeter, apparatus, and procedure are described in detail elsewhere [1], [10]. A calorimeter was designed in order to measure the isobaric specific heat capacity of fluids and fluid mixtures in a wide range of temperatures and pressures by the thermal relaxation method. The calorimeter assembled in a pressure vessel is immersed in a thermostatted oil bath. The bath temperature which is considered as the sample temperature was kept constant within ±3 mK during the experiment. The
Results and discussion
We measured the isobaric specific heat capacity of {xH2O + (1 − x) NH3} with x = (0.0000 to 0.8489) at T = (280.00 to 360.00) K and p = (0.1 to 15) MPa. The results are given in table 1 with the expanded uncertainties. The coverage factor was chosen as k = 2.
Comparison with the literature values [2], [3] as well as the calculated cp values by the EoS [7] for pure ammonia (x = 0.0000) are shown in figure 1. Significant differences between the calculated cp values by the EoS and the present results are found,
Conclusion
We measured the isobaric specific heat capacities of {xH2O + (1 − x)NH3} with x = (0.0000 to 0.8489) at T = (280 to 360) K and p = (0.1 to 15) MPa. The total number of measurements are 55, and our data at p = 5 MPa are fitted to equation (13) as a function of temperature, and mole fraction.
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