Measurement of the isobar heat capacity of fluids in the critical area by the method of flowing adiabatic calorimeter

With regard to the problem of refining the fundamental equations of state of hydrocarbons, the methodological and design features of the experimental measurement of the isobaric heat capacity in the critical region by the method of a flow adiabatic calorimeter are considered. The pressure measurement system has been improved by introducing a differential manometer into the measuring circuit, which made it possible not only to increase the accuracy of pressure determination, but also to implement a universal scheme of calorimetric experiment. The use of a universal scheme of the calorimetric experiment allows one to determine two values of the isobaric heat capacity at pressures that differ by the value of the pressure loss in the calorimeter. Such an approach in the critical region is relevant, since it makes it possible to quite simply and reliably determine the value of the derivative of the heat capacity with respect to pressure, which is used to estimate not only the error in assigning the value of heat capacity to pressure, but also the equilibrium conditions of the experiment in a flow-through calorimeter. The technique of determining and making a correction for the inhomogeneity of the supply wires of the differential thermocouple, for the throttling of the flow of matter in the calorimeter is considered. Correct relations are obtained for determining the average temperature of the measurement experiment for various methods of measuring the temperature and temperature difference in a flow-through calorimeter. The results of experimental measurements of the isobaric heat capacity of n-pentane in the critical region, obtained using the universal scheme of the calorimetric experiment, for n-pentane were measured on an isobar of 3.400 MPa (critical pressure 3.355 MPa), which is the closest to the critical point at practice of flow calorimetry

ВПЛИВ РОЗЧИННИХ РЕЧОВИН НА СТАН ВОДИ В РОСЛИННИХ ТКАНИНАХ ТА КІНЕТИКУ ЇХ СУШІННЯ

В роботі наведено літературні дані щодо впливу розчинних речовин різного типу на процес та механізм зв’язування води. Порівняно результати визначення стану води у вихідній рослинній сировині, які були отримані з розрахунку за межею гігроскопічності, з результатами прямого експерименту за методом диференціальної сканувальної калориметрії. Встановлено, що додаткове зв’язування води, вище ніж отримане з розрахунку, обумовлено наявністю розчинних речовин в рослинному соку. Сумісним аналізом експериментальних кривих зміни стану води, енергограм сушіння, кривих сушіння та кривих швидкості сушіння показано, що критичні точки процесу сушіння знаходяться у відповідності з динамікою зміни стану води в рослинних тканинах та кінетикою зміни питомої теплоти її випаровування. Встановлено значне зростання енерговитрат на випаровування води вже в другому періоді сушіння. Отримані результати дозволяють стверджувати, що воно відбувається через початок видалення води з гідратних оболонок розчинених речовин. На підґрунті проведеного дослідження уточнено механізм і послідовність видалення води зі зрізів рослинних тканин при сушінні. The paper presents literary data on the influence of soluble substances of different types on the process and mechanism of water binding in aqueous solutions. Using the method of differential scanning calorimetry, the state of water in the parenchyma tissues of apples and potatoes, in the root crops carrots and beet, and the woody tissues of annual willow shoots was determined. A change in the state of water in these plant tissues during dehydration has been studied. The results of the determination of the state of water in the initial plant raw material obtained from the calorimetric experiment were compared with the results obtained from the calculation according to the hygroscopicity limit according to the assumptions of the sorption isotherms method. It has been established that the amount of bound water in the tissues of plants obtained from the calorimetric experiment is higher than the amount of bound water obtained on the calculation from the limit hygroscopicity of plant tissues. The additional binding of water is due to the presence of soluble substances in plant juice. Using the method of synchronous measurement of mass loss of tissues during drying and the amount of heat consumed for dehydration, an experimental determination of the specific heat of evaporation of water from plant tissues during drying was performed (the drying energy curves have obtained). Using joint analysis curves of change of the state of water in plant tissues, curves of drying energy, drying curves and drying rate curves, it was established that the critical points of the drying process are in accordance with the dynamics of changes in the state of water in plant tissues and the kinetics of the change in the specific heat of evaporation of water. A significant increase in energy consumption for the evaporation of water was detected already in the second drying period of plant tissues. The results obtained allow us to state that this increase in energy costs is due to the beginning of the removal of water from the hydrated shells of substances dissolved in plant juice. On the basis of the research, the mechanism and sequence of water removal from the cut of plant tissues during drying has been made more accurate.