Electrical transformer insulation systems are evaluated based on economic, safety, and environmental standpoints using total life cycle analysis. Because of the inherent high efficiency of liquid-cooled transformer designs, new developments focus on improving the environmental and safety properties of fire resistant (less-flammable, high fire point) fluids. This article reports the latest findings on dielectric systems using natural ester (vegetable oil) fluids. Because esters naturally have lower oxidation resistance than mineral oils, a novel blend of base oils and additives were developed to overcome this potential handicap. Single- and three-phase prototype field installations using these new dielectric coolants are discussed.

Vegetable-oil-based dielectric coolants

Heat capacity of liquids : critical review and recommended values

A study was carried out in which new experimental data on heat capacities of pure liquid organic and some inorganic compounds were compiled, critically evaluated, and recommended values provided. Compounds included in the compilation have a melting point below 573 K. The bulk of the compiled data covers data published in the primary literature between 1993 and 1999 and some data of 2000. However, some data from older sources were also included. The data were taken from almost 1030 literature references. Parameters of correlating equations for temperature dependence of heat capacities of liquids were developed. This paper is an update of a two volume monograph entitled Heat Capacity of Liquids: Critical Review and Recommended Values (96ZAB/RUZ) that was published in 1996 in the Journal of Physical and Chemical Reference Data as Monograph No. 6 and was the product of the IUPAC Project No. 121/11/87.

Heat Capacity of Liquids: Critical Review and Recommended Values. Supplement II

Prediction of heat capacities and heats of vaporization of organic liquids by group contribution methods

The liquid specific heat capacity of fatty acids can be accurately estimated using the Rowlinson-Bondi method. This method requires the specific heat capacity of ideal gases, the critical temperature, and the acentric factor for each acid. The liquid specific heat capacity of triacylglycerols and vegetable oils can be estimated using mixture properties corre- sponding to the fatty acid composition and a correction factor, which accounts for the triacylglycerol form. The experimental data of triacylglycerols were used to produce the generalized correction factor. The estimated values were compared to ex- perimental values and the error was found to be within ± 5%. Paper no. J9307 in JAOCS 77, 1001-1005 (September 2000). A critical review of the existing estimation methods and their reliability in the estimation of physical properties of triacyl- glycerols and palm oil has been given by Noor Azian et al. (1). It can be deduced from this review that the method pro- posed by Phillips and Mattamal (2) for estimating liquid spe- cific heat capacity is rather specific and no generalization can be drawn from this method. On the other hand, the method proposed by Halvorsen et al. (3) for the estimation of liquid density of triacylglycerols and oil mixtures is rather attractive and may be extended to other properties. The fact that the properties of different types of oil can be estimated using the method makes it doubly at- tractive. This paper proposes an estimation method for specific heat capacity of fatty acids, triacylglycerols, and vegetable oils uti- lizing experimental data obtained in this work based on the approach proposed by Halvorsen et al. (3) for liquid density EXPERIMENTAL PROCEDURES The specific heat capacity of simple triacylglycerols (trilaurin, trimyristin, tripalmitin, and tristearin); mixed triacylglycerols (1,2-dimyristoyl-3-oleoyl (MMO), 1,2-dimyristoyl-3-palmi- toyl (MMP), 1,2-dipalmitoyl-3-oleoyl (PPO), and 1,2-dioleoyl- 3-palmitoyl (OOP)); 1,3-dipalmitoyl-2-oleoyl (POP); 1-palmi- toyl-2-oleoyl-3-stearoyl (POS); 1,3-distearoyl-2-oleoyl (SOS); 1-palmitoyl-2,3-dioleoyl (POO); 1,2-dioleoyl-3-stearoyl (OOS); triolein (OOO); refined, bleached, deodorized palm oil (RBDPO), and cocoa butter were determined using a Seiko (Seiko Instrument Inc., Tokyo, Japan) heat-flux differential

Liquid Specific Heat Capacity Estimation for Fatty Acids, Triacylglycerols, and Vegetable Oils Based on Their Fatty Acid Composition

The specific heat capacities of some triglycerides commonly found in palm oil were determined with a heat-flux differential scanning calorimeter. The specific heat capacity measurements were made under the optimum operating conditions determined earlier: scan rate 17 deg·min−1, sample mass 21 mg and purge gas (nitrogen) flow rate 50 ml/min. Pure triglycerides (four simple and four mixed) were used in the experiments. The four simple triglycerides were trilaurin, trimyristin, tripalmitin and tristearin, and the mixed triglycerides were 1,2-dimyristoyl-3-oleoyl, 1,2-dimyristoyl-3-palmitoyl, 1,2-dipalmitoyl-3-oleoyl and 1,2-dioleoyl-3-palmitoyl. The results of this study are compared with literature values and also with values obtained by using estimation methods. The experimental specific heat capacities are within ±1% precision with a 95% confidence level.

Specific heat capacities of pure triglycerides by heat-flux differential scanning calorimetry

Reproducible specific heat capacities (Cp) of triglyeerides can be obtained by using heat-flux DSC under improved operating conditions. The improved operating parameters, such as the scanning rate, the sample mass and the atmosphere within the DSC chamber, were established via statistical analysis of the experimental data with trilaurin as a sample. The specific heat capacity results on trilaurin were compared with the values calculated by using estimation methods. The precision of the specific heat capacity measured for trilaurin under these conditions was within +1%.

A. A. Hasan

Papers

Specific heat capacities of pure triglycerides by heat-flux differential scanning calorimetry

Improved conditions for measurement of the specific heat capacities of pure triglycerides by differential scanning calorimetry