Analysis on efficiency of plate heat exchanger

1, test equipment and test pieces

The test loading system is MTS-2.5 tons of material performance tester. The specimen is cut out from the whole heat transfer plate, and a part of the rectangular plate is provided with a trapezoid gasket groove, and the plate material is shown by 316L. The gasket material is three yuan ethylene propylene rubber, hardness of Shaw's 80, the cross section of the gasket for the type of the main structure.

2, test content

The experiment consists of two parts:

(1) at room temperature, gasket simple compression rebound. The cross section is placed in a horizontal diamond seal gasket rigid plate, the steel cylinder is fixed on the testing machine, the fixture (7mm) applied compressive load, the displacement test pad under different loads. The actual assembly and operating conditions of the loading rate reference device, the control compression rate 0.018mm/s, and the rebound rate of 0.007mm/s.;

(2) gasket compression resilience under the constraint of ladder type seal groove.

A gasket with a cross section in the shape of a diamond is embedded in a trapezoidal groove of a rectangular plate. The other loading conditions are the same as those of the previous section. This test is called constrained compression rebound.

Test result analysis

1, simple compression

It is assumed that the rubber gasket is a super elastic material, the ratio of the thickness of the 3 main directions and the initial thickness of the compressed gasket is also called the compression ratio. Comprehensive type (1), (2): S=2WC=2[(WI1 I1WI2) I-WI2C I3WI3C-1] (4) by using the real relationship between stress and S, get the gasket after deformation of the actual stress expression: =-pI 2[WI1B-WI2B-1] (5) main stress components: i=-p 2[WI12i-WI2-2i] (i=1, 2, 3 (6) type) (5), B is a left Cauchy Green strain tensor (leftCauchy-Greenstraintensor), -pI represents the hydrostatic pressure tensor, I for the two order tensor unit. True stress tensor.

Simple compression, the gasket surface only 1 true stress in one direction, and because the rubber material has compressibility, 1=, are: 2=3=1, then the equation (6) can be simplified to: 1=2 (2-1) (WI1 WI21) (7) in the engineering practice, the removable plate heat exchanger gasket compression preload is generally 1535 of the initial thickness of the gasket, the compression deformation, the gasket stress area is greater than the instantaneous initial stress area. Respectively by the instantaneous stress area and initial stress area as the base of the real stress of 1 and the nominal stress e relationship: 1=e in Mooney-Rivlin model strain energy density function: W=C10 (I1-3) C01 (I2-3) (8) - (8) will be substituted for (7): 1=2 (2-1 (C10) C011) (9) in the Yeoh model in [10] strain energy density function: W=C10 (I1-3) C20 (I1-3) 2 C30 (I1-3) 3 (10) of the type (10) into the equation (7): 1=2 (2-1) [C10 2C20 (2 2-3) 3C30 (2 2-3) 2] (11) can be determined by using the least square method (9), (11) the material constants C10, C01, C20, C30, two model fitting the stress value as shown.

When the compression ratio is greater than 0.75, the Mooney-Rivlin model and the Yeoh model predict the SP error value is less than 5, showing the actual stress test value and the fitting curve. The fitting curve of Yeoh model is consistent with the experimental data.

2, constrained compression

In the trapezoidal groove constraint before and after, the relative change rate of real gasket stress, defined as constraints respectively in compression, simple compression under the condition of pressure ratio of the stress difference and simple compression stress, to reflect changes in the trapezoidal groove constraint before and after the gasket stress.

When is 0.9, the trapezoidal groove constraint, constrained compression of real stress was 1.25MPa, a simple compression increases when 9.65. is 0.75, the gasket stress increased from 3.11MPa to 5.58MPa, than the simple compression to improve 79.42.

The compression ratio is small and the constraint effect of ladder shaped groove heat transfer plate on the lateral deformation of the gasket is more obvious, can significantly improve the gasket preload, facilitates sealing (double sealing aluminum strip type insulating glass seal permeability).

3, rebound stage

Set out under the condition of the same compression ratio, simple compression gasket (referred to as simple rebound rebound) in the process of real stress measurement and the constraints in the compressed gasket (referred to as the rebound constraints rebound) the true stress.

R is the rebound stage, the relative rate of change of the compressive stress of the gasket before and after the trapezoidal groove constraint is defined as the ratio of the true compressive stress and the simple rebound pressure stress.

It can be seen that the compressive stress decreases with the increase of the springback of the simple rebound and compression rebound, and the reason is that the restraint effect of the trapezoidal groove on the gasket decreases with the increase of the springback.

It can be seen that the greater the amount of gasket compression, compression and constraint under simple compression stress is bigger, the reason is that the gasket and the greater the deformation of trapezoidal groove on the restriction role in growing and rebound the larger deformation of the two stress difference is smaller. In addition, the gasket curve 1, curve 2 reflects the compression and rebound deformation methods are not consistent, that gasket has time lag effect during deformation, but the common characteristic is the elasticity stage gasket surface of the true stress is smaller than the compression phase at the same compression ratio under compressive stress.

conclusion

(1) having a diamond shaped cross section of the test material is three Yuan rubber hardness 80 shore plate heat exchanger gasket 16CPVT plate heat exchanger gasket compression test and analysis of resilience compression resilience. The influence of trapezoidal groove on the compressive stress of gasket is revealed. Under the action of trapezoidal groove, the compressive stress of gasket is higher than that of simple compression in the compression and rebound stage. Vice versa。

(2) based on Mooney-Rivlin and Yeoh model respectively, when the compression ratio is larger than 0.75, was deduced and the compression ratio of stress in simple compression of the plate heat exchanger gaskets, provide a basis for the design of the gasket thickness, pre compression amount and the size and number of clamping bolt. The simulation results are less than 5

(3) simple compression and compression condition under the constraints of the actual gasket compression, rebound deformation is not consistent, with a significant time lag effect, but the common characteristic is the elasticity stage gasket surface of the true stress is smaller than the compression phase at the same compression ratio under real pressure stress value.