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A Method for Determining Transient Temperature of Concrete Aggregate in Air Precooling and Preheating

A technology of concrete aggregate and transient temperature, which is applied in the field of engineering heat transfer and heat transfer, can solve the problems of not reflecting the real situation of air temperature changes, not having a clear applicable engineering scope, and low calculation accuracy.

Active Publication Date: 2018-04-06
POWERCHINA XIBEI ENG
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

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Problems solved by technology

However, on the one hand, setting the virtual layer does not match the actual situation, which further brings calculation errors. On the other hand, the virtual layer is calculated according to the heat conduction law of the plate, which is quite different from the nearly spherical shape of the aggregate. Therefore, the calculation of the thickness of the virtual layer There are obvious errors
[0031] (3) The temperature of the air in this calculation method is always constant, which does not reflect the real situation that the air temperature changes with the heat exchange time
[0032] (4) There are many factors affecting the air precooling and preheating process of aggregates, such as the structural size of the silo, the accumulation void ratio, and the wind speed. Calculation accuracy is not high

Method used

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  • A Method for Determining Transient Temperature of Concrete Aggregate in Air Precooling and Preheating

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Embodiment 1

[0084] In order to overcome the low calculation accuracy and waste of energy in the existing determination methods, the present invention provides a method for determining the transient temperature of air precooled and preheated concrete aggregates. The present invention considers the effective thermal conductivity of aggregates + void porous media The influence of air convection must be taken into account. During the process of air precooling and preheating aggregates, the aggregates are naturally piled up in the silo, forming a co-existing combination with the void, so it can be considered that the aggregates in the silo and The voids form a porous medium. The convective heat transfer process between the aggregate in the silo and the air in the gap can be regarded as an unsteady heat conduction process produced by the convective heat transfer of the aggregate + void porous medium at the air inlet section, so that the error is reduced, and the calculated The temperature is mo...

Embodiment 2

[0095] On the basis of embodiment 1, in the present embodiment, fitting coefficient A, B, C, Fo in step 3) * , the specific calculation is as follows:

[0096] A=A'·Bi+A"

[0097] B=B'·Bi+B"

[0098] C=C'·Bi+C"

[0099]

[0100]

[0101]

[0102]

[0103]

[0104]

[0105]

[0106] In the formula, Z is the aggregate section height, δ is the height difference between inlet and outlet air, Bi is the Biot number, and the equivalent diameter of the silo is De.

[0107] The Calculation method of Biot number Bi and Fourier number Fo in step 2) is:

[0108] Effective thermal conductivity of porous media:

[0109] Equivalent diameter of silo:

[0110] Virtual Reynolds number:

[0111] Virtual convective heat transfer coefficient:

[0112] Fourier number:

[0113] Biot number:

[0114] In the formula, λ e is the thermal conductivity of porous media, ρ e is the density of the porous medium, c e is the specific heat of the porous medium, F is th...

Embodiment 3

[0129] Based on the basis of embodiment 1, the calculation process of each step in the present embodiment is as follows:

[0130] (1) Calculation module of thermal and physical properties of porous media

[0131] It is known that the void ratio ε of the stockpiled material in the silo, the cross-sectional wind speed u of the empty silo, the diameter d of the aggregate, and the thermal conductivity λ of the aggregate s , the aggregate density ρ s , the specific heat of the aggregate c s , the density of air ρ a , the specific heat of air c a , the thermal conductivity of air λ a , the Prandtl number Pr of air a , the dynamic viscosity of air μ a .

[0132] Wind speed at aggregate voids:

[0133] Equivalent diameter of void:

[0134] The Reynolds number of the air in the void:

[0135] The convective heat transfer coefficient of the air in the void is:

[0136]

[0137] Inside the complex formed by aggregates and voids, air convection is a crucial heat transf...

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Abstract

The invention provides a method for determining the transient temperature of air pre-cooled and pre-heated concrete aggregates. In the process of pre-cooling and pre-heating the aggregates through air, the aggregates are naturally stacked in a storage bin and form a mutual coexistence combination with gaps; therefore, the aggregates in the storage bin and the gaps form a kind of porous medium; a convective heat transfer process of air at the positions of the aggregates in the storage bin and the gaps can be regarded as an unstable-state heat conduction process generated under the action of convective heat transfer at the position of an air inlet section of the porous medium of the aggregates and the gaps; and the unstable-state heat conduction process of the porous medium of the aggregates in the storage bin and the gaps is equivalent to the unstable-state heat conduction process of a three-dimensional cube under the third boundary condition. Because four sides of the storage bin are insulated and only the air inlet section is in the heat transfer process under the third boundary condition, the transient temperature solution of the storage bin, namely the three-dimensional cylinder, can be simplified to the transient heat transfer problem of a one-dimensional infinite plate.

Description

technical field [0001] The invention belongs to the field of engineering heat transfer and heat transfer science, in particular to a method for determining the transient temperature of air precooling and preheating concrete aggregates. Background technique [0002] The purpose of pre-cooling and pre-heating of concrete aggregate is to control the pouring temperature of concrete and prevent cracks in the pouring body. Concrete aggregate precooling and preheating technology has the characteristics of strict temperature control, high strength, and complex system layout. It is a key factor related to the safety, economy and construction progress of water conservancy and hydropower projects, especially large-scale water conservancy and hydropower projects. [0003] Air precooling and preheating the concrete aggregate in the silo before concrete pouring is a temperature control method commonly used in engineering at present. Air pre-cooling and pre-heating of aggregates are carri...

Claims

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Application Information

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Patent Type & Authority Patents(China)
IPC IPC(8): G06F19/00
Inventor 卢飞关薇康智明郭朝红黄天润文宁李莉付廷伍曾秒唐大伟
Owner POWERCHINA XIBEI ENG
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