SU1253263A1 - Method of determining the convective heat exchange coefficient in film boiling - Google Patents

Description

1.1

The invention relates to heat engineering and can be used in experimental installations designed to determine heat transfer coefficients during film boiling.

The aim of the invention is to simplify the process by lowering the maximum temperature of the tube wall and reducing the velocity of the cooling gas gas.

Figure 1 shows a device that implements the proposed method; Fig. 2 shows a liquid boiling curve.

The tubular sample 1 is heated by an electrical current supplied through the tires 2. The cooling gas is supplied through the inner tube 3 which has openings in the lower part through which the gas enters the annular space between the inner surface of the sample 1 and the outer surface of the gas supply tube 3 and cools sample. A gas deflector 4 is attached to the gas supply tube in its lower part. The coolant supply pipe is rigidly connected by the rocker arm 5 with the float 6. The test tube sample is placed in the tank 7, in the lower part of which there is a pipe 8 of the fluid supply. The portion of the curve corresponds to the bubble boiling regime on the sample surface, II-III to the transient regime, III-IV to the film boiling regime.

The temperature T „„ „and the heat load q ,, |, determine the limit of the existence of the film boiling point. Point Y with temperature T and heat load qj corresponds to the initial state of the sample heated in air and cooled from the inside with gas. Point U1 corresponds to the film boiling regime on the sample surface in a liquid.

For specific conditions (boiling in a large volume of water at atmospheric pressure with an underheating of 20 ° C on a vertical tube with an internal diameter of 0.01 m), the temperature at point III is 400 ° C. The value of the minimum heat flux at point 111

is approximately q, x5x x10 W / m. They take with reserve the necessary values that must be ensured with an increase in electrical power - q 10 W / m, Tu 500 ° C. Then, using the well-known heat transfer dependencies, the necessary cooling air velocity at atmospheric pressure m / s can be determined.

Before applying the electric load, the cooling gas is passed through the tube 3 at a speed of m / s.

Then, electric heating of the tubular sample 1, which is in the air, begins. The electrical load is still as long as the temperature measured during film boiling

jwHH minimum value5

0

specific heat flux q 5 10 W / m. After that, the tank 7 through the pipe 8 serves the liquid. As the level of the liquid in the tank rises, the float 6 and the associated tube 3 float up. At the same time, the cooling zone of the inner surface moves upwards, and a whip of night liquid boiling occurs on the non-gas-cooled submerged part of the tube. As the sample is immersed, the film boil. Spreads over the entire surface, and tube 3 is removed from the sink. If the state of the sample is determined by the point Y (see Fig. 2) before immersion, then it will correspond to the immersion of the sample. point U1, i.e. will be on the plot

0 film boiling III-IV boiling curve. The desired value of the heat transfer coefficient d is determined by the measured values of thermal power and temperature of the tube wall and liquid

45

ON known addiction

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- electrical power;

- the area of the outer surface of the heated tube; - temperature of the tube wall; - fluid temperature.

45 fi.

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Editor M.Payfylovska

Compiled by A. Kostanovsky

Tehred V.Kadar i / Corrector S.Shekmar

Order 398S / 1 Circulation 776 Subscription

VNIIPI USSR State Committee

for inventions and discoveries 113035, Moscow, Zh-35, Raushsk nab., 4/5

Production and printing company, Uzhgorod, st. Project, 4

2

Claims (1)

METHOD FOR DETERMINING HEAT TRANSFER COEFFICIENT FOR FILM BOILING, including electric heating of the tube with an increase in its power, simultaneous cooling of its internal surface with gas, measurement of heat dissipation, surface temperature of the tube and liquid and determination of the heat transfer coefficient from the measured values, which differs in that simplification of the method by reducing the maximum temperature of the tube wall and reducing the speed of the cooling gas, upon reaching the power level of electric heating, providing exceeding the specific heat flow and temperature of the wall of the tube to a predetermined minimum value in film boiling, a gradual start liquid immersion tube with a simultaneous decrease in gas cooled inner surface of the tube. SU <..> 1253263. 1253263