Article

Thermal conductivity of vegetable oils in a of wide range of temperatures, pressures and concentration solvents

High temperature high pressure
(2008)
Abstract

ABSTRACT Results of experimental research on the thermal conductivity of vegetable oils (corn, olive, sunflower seed, cotton seed, sesame, soy–bean, almond, nut, peanut, grapes and others) in the temperature range 293.6–553.2 K and pressure range 0.101–49.1 MPa are given the chosen oils were produced at the plants of Dushan -be. Thermal conductivity was investigated by means of a cylindrical bicalorimeter of the first kind of regular heat regime. The common relative errors of measu-rement of heat conductivity for a confidence coefficient, a, of 0.95 were respectively 4.5%. An empirical equation was developed with the help of which heat conductivity, specific heat capacity, and diffusivity of the chosen oils can be calculated. The practical application of scientific achievements requires knowledge of the properties of different materials and products which are subjected to storage, technological treatment, and use. Among them thermo physical properties and their quantitative characteristic are of great importance, as thermal treatment is widely used in the national economy, specifically in the food industry. Development, improvement, and intensification of the thermal treatment processes are based on the main principles of modern technology. These are: knowledge and analysis of the thermal conductivity of products as objects of the treatment; choice of methods and optimal regimes of the process; and development on this basis of construction of suitable apparatus. At the same time modern science solves an inverse problem: development of ways to predict in order to produce final products with predetermined thermo physical characteristics. Therefore, the characteristics of the structure of food products as multicomponent systems (especially in the case of interpenetration of the components which takes place in moist colloidal porous materials) and the development of methods of preliminary calculation of their thermo physical characteristics are of great importance. Raw materials, materials and products of the food industry represent complex object for treatment. The behavior of thermal properties in various thermo-dynamic coordinates was analyzed. The received material has allowed to make the equation of a condition in viral form and thus are allocated second and third viral coefficients. The viral coefficients was obtained by two independent methods, namely, graphically and analytically. The latter method allowed a step by step extension of me interval of densities on the isotherm with the inclusion of additional experimental points. 1. INTRODUCTION The problems of the use of the energy of small currents in the context of them severe deterioration of ecological conditions today have become urgent and topical, and their solution demands the consideration of an entire series of problems connected with production and personnel, and econo-mic and technical issues. In such a general arrangement the problem in hard is very hard. It is not enough to produce a solution in an analytical form; moreover, the nume-rical method of solution calls for great computer tine and memory. In ad-dition, an experimental definition of the physico-chemical properties of the oils is needed. In [1,2] it was shown the temperature and pressure dependence of thermal conductivity &#; for oil and solvents, also for some oil and solutions in wide temperature and pressure rang. The heat transfer mechanism can’t be explained on the basis of classical heat transfer mechanisms for constant material structure. The experimenter has to consider these effects in solution model of the dynamic method using appropriate parameters. As a result, additional unknown parameters have to be estimated during the experiment. Many of them are not independent, i.e. there is high correlation between the parameters. The analysis of the sensitivity coefficients gives the picture of the parameter correlations. Therefore, the realization of the intercomparison measurement should carefully consider the measurement methods and measured parameters. It is assumed that data obtained in scope of given method are not correlated. Then, such a data, obtained by different methods can be compared. Various techniques are used for measuring thermo physical parameters of materials. The techniques can be divided into two classes, namely into steady state and dynamic ones [3-4]. While the former use a steady state temperature field inside the sample, the latter use a dynamic temperature field. As the basis characteristics of the dynamic temperature field are the specific heat and the thermal diffusivity or thermal conductivity; the measurement techniques based on the dynamic methods may give all three parameters. The measurement procedure of the dynamic methods consists of two steps: 1. Study of the underlying model of the method. The solution of the partial deferential equation for the heat transport with appropriate initial and boundary conditions for the sample must be known. These conditions should correspond to the technical arrangement of the experiment. Usually, a set of solutions has to be pro-vided to obtain the detailed picture of measuring process. 2. Realizations of the experiment. The experiment must stipulate the theo-retical assumptions made in the previous step; Discrepancies between the theore-tical model and the experimental results are the largest source of the data uncertainty. The measuring process consists of a generation of the field by the heat source and mapping of the temperature field. Using the model of the method and the experimental data, the thermo physical parameters are calculated. This paper is devoted to the dynamic techniques where measuring probes e.g. heat source and the thermometer are placed inside the sample, This experimental arrangement might suppress the sample surface influence on the measuring process. Methods using different symmetries of the temperature field (cylindrical and plane symmetry), various arrangements of the measuring probes: two-probe system, which consists of a heat source and a thermometer and one-probe system in which the heat source and thermometer are unified and different ways of the temperature field generation (pulse and step-wise) are discussed. These techniques are based on a class of method denoted as Transient Methods. We investigated the thermal conductivity and density systems oils + solvents in the temperature rang 293-473 K and pressure range (0.101-49.l) MPa. 2.EXPERIMENT APPARATURS 2.1 Heat conductivity For measuring the thermal conductivity of water solutions we designed and constructed an experimental device revering on the method of a cylindrical bicalorimeter of the first land of regular heat regime (see Fig. l) [3].The device consists of the cylindrical bicalorimeter (2), a loaded-piston manometer of type MP-2500, a pressure vessel, an automated thermo physical complex (АТС), and electric indicators. It was found that during increasing of temperature to 393K, the heat conductivity of the water + transformer oil system increase and then decrease [3]. Fig.l Experimental apparatus 2.2 The methods of monotonous regime for investigations heat conductivity solutions. For measurements heat conductivity and thermal conductivity make mono-tonous regime [9]. Heat resistively between bar and contaction plate define by formula: (1) где Ро – heat resistivity objects , m2ּК/W; РК – recovery, account heat resistivity contact, and heat resistivity thermocouple , m2ּК/W. Figure 2. Chem of methods. 1- The base; 2- Plate; 3- Contact plate; 4- Copper cell in the investigetions materials; 5- The bar. Heat resistivity objects calculated in the formula: (2) thus: h – height objects (height cell), m; λ – heat conductivity objects, W/(mּК). The basis formulas (1)-(2) resaved formula for heat conductivity objects. (3) Thus : σс – recovery, account specific heat capacity copper cell to the investi-gations objects (4) thus Со – common capacity objects , J/К; Сс - common capacity bar, J/К . (5) thus Со(t) – value specific heat capacity cell and investigation objects, J/(kg К); mo – mass investigation objects, kg. (6) thus СМ(t) – specific heat capacity copper , J/(kgּК); mс –mass bar , kg. Common heat conduction plate define in the next formula: (7) From equation (3) received : . (8) Calculation common heat conductivity objects to the proper to the middle tempera-ture objects , which calculations to the next formula : (9) thus - middle temperature objects ,˚С; tc - temperature , from which measurements heat conductivity ,˚С; At – sensitivity thermocouple chromel-alumel , К/mV; no –difference temperature in the objects , mV. 3.MODEL AND THEORY The account is carried out on model as the cylinder having porous structure, and in pores is astringent. Processes of carry of heat through such structure we shall consi-der stage by stage. At the first stage we shall estimate heat conductivity of a porous grain consisting from sand, assuming, that in pores there is a water. We use known model mutual penetrating of a material (model G. N. Dulnev etc.), which compo-nents form mutual penetrate run through a lattice. At the first stage we shall esti-mate heat conductivity of a material of the cylinder, i. e. mutual penetrating of a porous material filling buy road-metal [5]: , (9) here, m -parameter, characterise crack materials. This cylinder considers, that it is second components a material, one road-metal, second components a material lime etc. , (10) mr- volume concentration road-metal. At a finishing third stage carried out account heat conductivity “&#;&#; ” of granular system, which grains have heat conductivity, “&#;&#;”, and between them there is a gas-fill. (11) It is possible to make of comparison a conclusion, that on the offered technique it is possible to calculate heat conductivity of the described. 3.RESULTS AND DISCUSIONS In the present investigation, seven transformer oil and water system have been studies and these are presented in Table 1-4.These transformer oil and water are marked in the phase diagram in order to facilitate a discussion of the experimental results. The standard deviation of the experimental data from the average value was generally fount to be about 5-6% and the highest standard deviation was recorded to be 6%. Table 1. Physical-chemical characteristic n-hexane СН3(СН2)4СН3 Molecular mass. . . . . . . . . . . . . . . . . . . . . . . . . . . 86.172 Density . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.65937 g/сm3 Viscosity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.3243 SPS Surface (15 ºС). . . . . . . . . . . . . . . . 18.94 dn/sm Dielectric constants (20 ºС) . . . . . . . . . . . . . 1.89 Temperature boiling. . . . . . . . . . . . . . . . . . . . . . . . . . 68.747 ºС Specific heat capacity (26,84 ºС). . . . . . . . . . . . . . . . . . . . . . . . 195 J/mol Heat conductivity (60 ºС) . . . . . . . . . . . . . . . . . . . . . . 0.136 W/mּК Table 2. Experimental data heat conductivity (λּ103, W/(mּК)) systems cartamus oil and n-hexane in dependence temperature in the air atmospheric pressures n, % mass. . T, K 0 25 50 75 100 291.4 111 233 355 477 599 303.2 110 237 364 501 618 313.9 109 240 372 503 634 332.5 107 245 393 520 659 358.7 106 249 392 534 677 373.4 104 248 394 538 683 393.8 102 247 395 540 686 Table 4. Experimental data density (ρ, kg/m3) systems cartamus oil in depen-dence temperature and pressures Pressures Р, МPа Т, К 4.91 9.81 19.62 29.43 39.24 49.10 293.5 932.5 947.8 960.1 970.5 988 1003 321.5 901.4 918.5 935.3 950.0 966.7 988 332.5 878.5 895.2 912.5 930.0 948.5 970.0 351.6 846.7 868.7 888.9 908.5 926.7 950.0 372.6 832.6 854.1 874.7 893.6 918.7 941.2 391.5 802.3 815.2 850.1 823.4 847.8 923.5 413.6 770.0 794.5 812.3 848.1 862.3 900.4 435.4 742.4 768.7 796.7 812.6 850.6 882.0 Table 5. - Experimental data density (ρ, kg/m3) systems (75% cartamus oil +25% n-hexane) mass. in dependence temperature and pressures Pressures Р, МPа Т, К 4.91 9.81 19.62 29.43 39.24 49.10 293.4 1002.4 1020.6 1054.6 1094.6 1146.7 1192.6 333.2 975.3 994.3 1028.2 1069.2 1118.4 1162.7 358.5 955.2 979.2 1014.3 1053.4 1100.7 1144.3 383.6 938.4 962.5 998.7 1036.6 1080.3 1124.5 413.2 915.1 942.3 980.3 1018.1 1060.2 1101.6 443.8 895.2 922.6 961.8 1000.3 1032.7 1076.4 473.0 872.9 904.5 943.1 980.5 1012.3 1055.3 Table 6.- Experimental data density (ρ, kg/m3) systems (50% cotton oils + 50% n-hexane) mass. in dependence temperature and pressures Pressures Р, МPа Т, К 4.91 9.81 19.62 29.43 39.24 49.10 293.4 931.3 958.6 990.4 1021.6 1060.4 1098,9 323.8 912.4 938.7 968.1 1001.4 1038.1 1074.1 353.6 884.5 910.3 941.6 976.3 1012.4 1048.7 382.7 872.3 898.0 932.4 968.2 1003.8 1038.3 403.6 855.3 883.2 916.7 951.3 988.2 1020.8 433.2 834.6 861.3 894.2 930.2 968.4 1000.2 468.9 810.2 838.5 870.3 908.5 945.3 976.7 , m2 /s (12) that λ, Ср and ρ –heat conductivity (W/(mּК)), specific heat capacity (J/(kgּК)) and density (kg/m3) investigation systems in the temperature. For generalized experimental data heat–and temperature conductivity sys-tems in dependence the temperature from air pressures we make flowing functions [3,4]: (13) (14) that λ – accordingly heat conductivity investigations objects from the temperature Т; λ1– heat conductivity from the temperature Т1; Т1=293 К. Dependence equations (13) we are make for обработки experimental data heat – and temperature conductivity ethers organics materials [3]. Check-up expression (13) and (14) for investigations systems demonstration ,which they quality and quantity describe temperatures dependence heat conductivity and temperature conductivity this solutions. They lines described this equations: (15) . (16) Helps equations (15) and (16) me bee calculations heat conductivity and tempe-rature conductivity investigations systems (vegetable oils) in dependence temperature, if it is known λ1 and ρ1. Very intercedes which λ1 and ρ1 in the equations (15) and (16) bind to the concentrations water. This equations lines and curve: , W/(m K) (17) kg/m3 (18) From equations (15), (16) and (17) are resaved: (19) kg/m3 (20) Table 7.- Coefficients А, В and С equations (20) Solvents Coefficients n-hexane Diethil ethers Benzene А, kg/m3 -3.34ּ10-2 -2.44ּ10-2 -2.69ּ10-2 В, kg/m3 -0.76 -1.06 -1.26 С, kg/m3 1025.9 1029.3 1042.5 ACKNOWLEDGMENTS The authors gratefully acknowledges the assistance of the Development ”Automatizeition systems” Mr.Naimov A.A.,for the material presented in the figures and for helpful comments based on their analysis of considerable thermo physical data. REFERENCE 1. Dulnev, G. N., Zarichniyak, U. P. Heat conductivity of solutions and composition materials. L.1974.216p. 2. Safarov, M. M. Thermophysical properties simple ethers and water solutions hydrazine in the dependence tem- peratures end pressures. Dissertation d. t. s. Dushanbe .1993. 450p. 3. Safarov M.M. Guseinov K.D. Thermophysical properties simple ethers in the dependence temperatures and pressures.(Monograf), Dushanbe, 1996 ,196p. 4. Shakhverdiev A N, Naziev Ya. M, Safarov J. T. Zh.Fiz.K.hi.m, Russian Journal of Physical Chem- istry, Moscow, Russia, 1992, 66, p 454-458. 5. Kuroki, T., Kagawa, N., Endo, H., Tsuruno, S., and Magee, J., W. Paper in XIV International Sympo- sium of Thermophysical Properties. Colorado, USA, 2000, 19 p. 6. Rivkin, S.L., Aleksandrov, A.A. Tertnodinamicheskie svoistva vody i vodyanogo para (The thermodynamic properties of water and water vapor), Energiya: Moscow, USSR. 1975, 80 pp. (in Russian). 7. Rabinovich S.G. Pogreshnosti izmerenii (Measuring Errors), Energiya: Leningrad,USSR. 1978, 261 pp. (In Russian). 9. Platunov E.S. Teplophisicheckie izmereniya v monotonom pejime M.1973.136 p.
Keywords

- vegetable oils,
- heat conductivity,
- density,
- solvents,
- temperatures,
- pressures.

Disciplines

Publication Date

Winter December, 2008
Citation Information

Mahmadali Mahmadievich Safarov. "Thermal conductivity of vegetable oils in a of wide range of temperatures, pressures and concentration solvents" *High temperature high pressure*(2008)

Available at: http://works.bepress.com/mahmadali_mahmadievich_safarov/1/