MEASUREMENTS OF EXCESS-ENTHALPIES AT HIGH-TEMPERATURE AND PRESSURE USING A NEW-TYPE OF MIXING UNIT

A flow mixing unit (calorimetric cell and auxiliary devices) has been designed for measuring the enthalpy of mixing or reaction of two fluid s (gas + liquid or liquid + liquid). The indicator of the heat effect is a differential heat flux calorimeter, SETARAM C-80, allowing measur ements at temperatures up to 300 degrees C. The mixing cell is made of a stainless-steel capillary (o.d. 1.6 mm, length 2.4m) which is coile d in a cylindrical form and tightly fitted in the thermopile well of t he calorimeter. The fluids are delivered from the high pressure piston pumps and circulated through the system at controlled flow rates rang ing from 100 to 1500 mu L-min(-1). The tests were carried out at press ures up to 20 MPa. Special care was taken to allow good thermostatting of fluids entering the mixing cell. Check measurements were made with one liquid-liquid system (C2H5OH + H2O) and one gas-liquid system (CO 2 + C6H5CH3); our enthalpies of mixing agreed with the literature valu es in most cases to 2%. For the system ethanol + water the experiments have been also performed at temperature of 250 degrees C and pressure s of 15 and 20 MPa. The endothermal mixing effect was higher than expe cted indicating an increase in the excess heat capacity.