SU1341505A1 - Method of determining heat transfer coefficient - Google Patents

Abstract

The invention relates to methods for thermophysical measurements. The aim of the invention is to improve the accuracy of determining the heat transfer coefficient. The method involves melting the metal, overheating the molten metal by 25-35 ° C, immersing the molded metal of the test object and the control part, increasing them in the metal melt until the system reaches the crystallization temperature of the metal, blowing the test objects with air for 15-25 s, removing them from the metal melt, removing the metal crusts hardened on the surface of the test objects, determining the heat transfer coefficients of the test object and control-. Noah details according to the experience, the calculation of the heat transfer coefficient control de-. by criterion dependences, calculation of the heat transfer coefficient of the investigated part. The control part is selected so that its carrying capacity would be equal to the carrying capacity of the test object. 1 hp f-ly, 1 ill. se (L 00 4 SP

Description

one

The invention relates to thermal measurements and can be used in industries related to the development and manufacture of heat exchangers and heat engines for various purposes, in particular for determining heat transfer to air in gas turbine blades.

The aim of the invention is to improve the accuracy of determining the heat transfer coefficient.

The drawing shows the objects to be examined before conducting the experiment, the initial state.

The test piece, for example, the gas turbine bed 1, and the control piece 2, for example, a straight pipe that has the same throughput capacity as the test piece, is connected to the collector 3, the medium to which it is cooled comes through pipe 4. The collector 3 ensures equal cost of the cooler through the convectively cooled part and through the control part 2. Evacuation of the part cooler through the exhaust manifolds 5 and 6. Metal 7, such as zinc, is in a solid state and placed in crucible 8.. The method is carried out as follows.

The metal is melted and overheated by 25-35 °. The diagnosed part 1 and the control part 2 are immersed in the melt. After j .. 200-300 s the melt system - the cooled parts equilibrate, the temperature of the molten metal and the cooled parts becomes the same. At the moment when the temperature of the melt – cooling system becomes equal to the crystallization temperature of the metal (for zinc T 419.4 ° C), the medium to be cooled is blown through the test and control parts. Through- Orr 15-20 with parts removed from the melt. According to the thickness of the metal crust formed on the parts to be cooled and the temperature difference between the wall of the parts and the medium to be cooled, the heat transfer coefficients are determined: for the convectively cooled part K, d "and for the control part K.

After completion of the experiment, the heat transfer coefficient from the inner surface of the control is determined.

15052

details of the pipe to the air according to the criterion dependencies of straight linear pipes.

Then the heat transfer coefficient K is determined. Through the wall to the air, taking into account its thermal resistance and the value of the heat transfer coefficient obtained (taking into account the lime criterion dependences). For this, classical dependencies are used.

The ratio of the value of the heat transfer coefficient K, obtained by t5 calculation by known criteria

dependencies, to the value .K

obtained from the experiment on the thickness of the metal crust formed and the temperature difference between the pipe and the cooling medium,

0 specifies the amendment due to the error of experience.

Multiplying this ratio by the value of the heat transfer coefficient K, we obtain the value of the heat transfer coefficient 5 of the transfer Cd, which already takes into account the error of experience.

Example. A gas turbine blade with a size of 0.1 m (chord 0.03 m) was placed in the molten

0 Zinc brand Zinc, simultaneously with a steel tube with a length of 0.18 m, outer diameter O, 066 m, inner one — 0.04 m. After reaching the crystallization temperature of zinc 419.4 ° C, the blade and tube were simultaneously blown with air with flow through each object 3i10 kg / s The air temperature at the inlet to the blade and tube. amounted to 60 C. Purging was carried out

Q for 15 s. The thickness of the crust in the area of the entrance edge of the middle section of the blade was 0.002 m, at the end of the pipe - 0.0025 m.

5 The heat transfer coefficient, calculated according to literary dependencies, was 390, according to experimental data - 410. Heat transfer coefficient directly from experience

g was for blade 450.

Heat transfer coefficient in the region of (area of the input edge of the middle section of the blade:

. to; .l "2.p 430BT / M K.

The use of the proposed method in comparison with the known method provides a reduction in the error in determining the heat transfer coefficient by 8-10%.

Claims (2)

1. A method for determining the heat transfer coefficient through a wall of a convectively cooled part, for example, turbine blades, which means that the part is placed in the molten metal and at a temperature of crystallization of the latter blows it with a cooling medium, and the heat transfer coefficient is judged by the thickness of the formed metal crust and temperature differences between the test piece and the cooling medium, characterized in that, in order to improve the accuracy of the data obtained, at the same time with the test piece the control usknoy capacity equal to the capacity of the investigated parts, while providing equality OX costs 1341505 and the desired coefficient is determined by the formula TO. TO, Ct TO, where K d, (, n is the value of the coefficient of heat transfer through the wall of the investigated. convectively cooled part, obtained in experiment K Q - the value of the coefficient heat transfer through the wall of the control part, obtained in the experiment; K t- - the value of the coefficient heat transfer through the walls of the control part, calculated by criterion dependencies. 2. Method 1, characterized in that a straight smooth tube is selected as the control part. room Editor L.Povkhan Compiled by V. Filatov Tehred A. Kravchuk Order 4428/46 Circulation 776 Subscription VNIIPI USSR State Committee Inventions and discoveries 113035, Moscow, Zh-35, Raushsk-nab. 4/5 Production and printing company, -y. Uzhgorod, st. Project, 4 Proofreader A.Zimokosov