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

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Abstract

Measurements of the 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) were carried out by the calorimeter with the thermal relaxation method, which we have developed, at T = (280, 300, 320, and 360) K over the pressure range from (0.1 to 15) MPa. The comparison of the present cp values with the literature data as well as the calculated cp values by the equations of state (EoS) is presented. The behaviour of the present cp values are correlated as a function of temperature, and mole fraction, at p = 5 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.

References (12)

  • K. Tanaka et al.

    J. Chem. Thermodyn.

    (2007)
  • K. Tanaka et al.

    Rev. Sci. Instrum.

    (2006)
  • N.S. Osborne et al.

    J. Am. Chem. Soc.

    (1918)
  • R. Overstreet et al.

    J. Am. Chem. Soc.

    (1937)
  • M. Wrewsky et al.

    Z. Phys. Chem.

    (1924)
  • D.L. Hildenbrand et al.

    J. Am. Chem. Soc.

    (1953)
There are more references available in the full text version of this article.

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