Krister Ström

EVALUATION OF THE ORIGINAL AND THE MODIFIED LEE-KESLER EQUATION OF STATE

In this work, the Lee-Kesler equation of state has been used together with the extended corresponding states principle. In order to improve the predictability of the equation in a more narrow acentric factor range, two new reference fluids have been chosen. The parameters in the Lee-Kesler equation have been estimated for the two reference fluids, CFC12 (dichlorodifluoromethane) and HFC134a (1,1,1,2-tetrafluoroethane), with the Error-in-Variables Model. This model allows both dependent and independent variables to be subject to errors. Calculations have been made for the two reference fluids as well as for other compounds, and the predicted thermodynamic properties have been compared with experimental values. Comparative calculations have also been carried out for some of the previously suggested modifications of the Lee-Kesler correlation.

A MODIFIED LEE-KESLER EQUATION OF STATE FOR REFRIGERANTS

For calculation of the thermodynamic properties of refrigerants it is proposed that the extended corresponding states principle (ECSP) should be used using two specific reference fluids, CFC12 (CCI2F2) and HFC134a (CF3CH2F), in order to cover the field of interest for most refrigerants. The specific parameters of these refrigerants have been determined for the Lee-Kesler modification of the Benedict-Webb-Rubin equation of state. In the parameter estimation, it has been taken into accounl that all variables are subject to errors by using the so-called Error-in-Variables-Model (EVM). The parameters have been estimated from experimental pressure-volume-temperature data, vapour pressure and saturated liquid and vapour volume data for CFC12 and HFC134a. The extended corresponding states principle proposed in this work with CFC12 and HFC134a as reference fluids has been used in calculations of the thermodynamic properties of a number of refrigerants. In comparison with the original Lee-Kesler equation this conc...

Excess Enthalpy and Vapor-Liquid Equilibria with the MHV2 and Soave Mixing Rules

Calculations and predictions of excess enthalpy (HE) and vapor-liquid equilibrium (VLE) were performed using the Gibbs energy mixing rules MHV2 and a modification of it by Soave. The Soave-Redlich-Kwong equation of state was combined with the UNIQUAC equation. Four sets of parameters estimated in the UNIQUAC model were used for each of seven binary systems: the first estimated from VLE data, the second and the third estimated from HE data for two versions of the UNIQUAC equation, and the fourth estimated from both HE and VLE data simultaneously. It was found that HE calculations can be performed with the mixing rules; the average relative errors fell from around 200% for the conventional mixing rule to around 60% for MHV2 combined with DECHEMA UNIQUAC parameters and was as little as 20% when the UNIQUAC parameters had been estimated from HE and VLE data simultaneously. However, the approach suffers from the same shortcomings as far as cross-prediction between HE and VLE data is concerned, as does the UNIQUAC equation used alone. There is a discrepancy between values obtained with the mixing rule and those obtained with the UNIQUAC equation directly. This discrepancy is smaller for the Soave modification of the mixing rule.

CALCULATION OF VAPOR LIQUID EQUILIBRIUM AND EXCESS ENTHALPY WITH THE UNIQUAC EQUATION

The UNIQUAC equation was used for calculation of vapor liquid equilibrium (VLE)as well as excess enthalpy (hE). Four sets of binary interaction parameters were applied: first, parameters estimated only from VLE data, then parameters from hE data for both the original UNIQUAC equation and the Anderson modification, and finally parameters estimated from hE and VLE data simultaneously. Calculations were performed for seven binary systems with polar components, representing different hE behavior. The cross-prediction of hE from VLE data works better than the reversed prediction. The model with parameters estimated simultaneously to both kinds of data can be applied successfully to both kinds of calculations, but it is a compromise between the models estimated from one kind of data.

EVALUATION OF THE ORIGINAL AND THE EXTENDED CORRESPONDING STATES PRINCIPLE FOR REFRIGERANTS

Abstract The corresponding states and extended corresponding states principles have been evaluated for refrigerants. In the two corresponding states techniques the Riedel and Wagner vapour pressure correlations have been used to express the vapour pressure for the reference fluids. As reference fluids CFC12 and HFC134a have been used. These two fluids cover the acentric factor interval wherein refrigerants are found. Parameters have been estimated for CFC12 and HFC134a according to the Reidel and Wagner vapour pressure correlations used in the extended corresponding states principle. Experimental vapour pressure data for CFC12 and HFC134a have been used to estimate parameters according to Riedel and Wagner used in the hypothetical fluid and deviation function used in the corresponding states principle. The Riedel and Wagner correlations are of equal accuracy in vapour pressure calculations. The results from the corresponding states and extended corresponding states principle are comparable due to the conf...

Washing of pulp using evaporator condensate

One way to effectively reduce the water consumption and obtain a wash liquid with low concentration of metal ions at the pulp mill IS to use recycled condensate as wash liquid. The condensate originates froth the evaporator system where. recycled liquor is evaporated before it is burnt ill the recovery boiler The main problem with recycling of condensate is the fact that these always contain Impurities of varying concentration These Impurities plainly cause odour problems in the process or in the final product To investigate the field of application, one unbleached pulp and ogle blenched pulp were washed with four different condensates with different COD concentrations the washing results were consistently good for condensates with low concentration of COD, but sonic Unexpected results were obtained for the case where the condensate with the highest concentration of COD was used To investigate the characteristics of the pulp, an adsorption study including manganese, calcium and magnesium was performed. The adsorbed amounts of ions were all fouled to be within the normal range.

A proposal for two new parameters based on shape/size and polarity, to be used in a four-parameter corresponding states expression

A four-parameter corresponding states expression has been used, together with two new parameters proposed in this work. The corresponding states expression is general and relaxes the frequent restriction that one or more of the reference fluids should have parameter values equal to zero. The new third parameter, a shape-size parameter, is based on fundamental molecular properties such as bond lengths and bond angles. The fourth parameter is a polarity parameter that takes both dipole and quadrupole moments into account. Since the parameter estimation is based only on a small number of substances, the results should be regarded as preliminary. Calculations of vapor pressure show that the corresponding states expression proposed in this work, together with the two new parameters, give deviations of the same order as a three-parameter expression with Pitzers acentric factor. The effects due to geometry and polarity, which are both included in the acentric factor, are thus separated into two parts.