With the improvement of building level in our country, the improvement of people's living environment, makes present household decoration become extremely hot. According to the statistics of China Building Decoration Association, the rate of China's newly built residential decoration reached more than 95. In order to achieve a unified and beautiful appearance of the radiator and the interior, most residents try to hide or decorate the radiator, and it is a typical method to install a decorative cover for the radiator. But in fact, the installation of decorative cover has a great impact on the indoor heat dissipation of the radiator, especially whether the structure and details of the decorative cover are properly handled or not, is the key factor affecting the indoor air flow distribution.

At present, the application of high-performance CFD software technology in the field of HVAC is still a weak link. 1. In the research field of heating radiator, it is rare to use high-performance CFD software to analyze the indoor flow field of radiator. The following paper will use the computational fluid dynamics CFD method, through the commercial Pheonics3.3 software to simulate and analyze the heating radiator installed with decorative cover, the influence of indoor air flow field distribution, preliminary exploration of its reasonable structure.

2CFD Model

Under the condition that the room is well sealed (), the heat release process of the heating radiator is a typical natural convection heat transfer process in large space. The air close to the outer surface of the radiator is heated by contact, which makes its density become smaller and generates buoyancy. The hot air rises, and the cold air in the lower part of the radiator and the room flows into supplement and is also heated and rose. And so it goes until it reaches thermal equilibrium. According to the characteristics of natural convection, LVEL turbulence model will be used in CFD analysis and simulation.

LVEL turbulence model was proposed in 1993 by Spalding et al., CHAM Research Institute, Imperial University of London, and was one of the turbulence models unique to commercial Pheonics software. The main idea is to imagine a similar velocity distribution for a flow similar to a channel, and to relate the dimensionless distance y from the wall to the dimensionless velocity u parallel to the wall. Then, by differentiating u/y, the mathematical relationship between the dimensionless effective viscosity v and the Reynolds number Re is obtained.

The LVEL turbulence model gets its name LVEL mainly because of the several parameters needed to calculate the effective viscosity v. Of these, L represents the distance from the nearest wall (Thedistancefromthenearestwall), VEL on behalf of the local velocity (localvelocity) and laminar viscosity (laminarviscosity).

For u/y, a difference scheme can be used to cover the whole range of laminar and turbulent flow, and linked by the following equation (Spalding wall law), y=u1EeKu-1-Ku- (Ku) 2- (Ku) 36- (Ku) 424 (1), where K is vonKarman constant, = 0.417; Logarithmic constant, E is equal to 8.6; The expression in square brackets is the first five terms of the Talyor expansion of the power function.

The dimensionless effective viscosity v can be obtained by the following formula: v=1KEeKu-1-Ku- (Ku) 2- (Ku) 36 (2)

This means that v=1 near the wall when u is very small, and v=Ky when u is very large. Since Re is defined as the product of u and v, the Re of each point in the flow can be obtained by the following formula: Re=uu1EeKu-1-Ku- (Ku) 2- (Ku) 36 (Ku) 424 (3)

The experimental comparison results show that the LVEL model is a low Reynolds number turbulence model suitable for engineering, and it has a better solving accuracy for the flow problem in the transition zone at Reynolds number. Especially when there are many walls or obstacles in the calculation domain, the LVEL model has high feasibility, reliability, economy and accuracy for the solution under the rough grid.

3 Simulation junction and analysis

In this paper, the air flow in a 4 (4 (3m) closed room is simulated by using Pheonics3.3 commercial software for two typical wooden mesh decorative cover structures (and). The radiator dimension is 1000mm long, 530mm wide, 45mm thick; The radiator is connected on the same side, and the connecting pipe diameter is 25mm. The hot water is supplied from the top to the bottom, and the inlet water is 95) and the return water is 70). The computational grid was divided into rectangular grids, and the number of grid nodes was 25 (20=500). The simulation results were shown in 3 and 4 respectively.

In fact, the above two kinds of decorative cover structure have some unreasonable. Experiments show that its heat loss is between 1530. It can be seen from the indoor air flow field distribution of the decorative cover structure that the decorative cover is not conducive to the natural convection heat transfer of indoor air. On the one hand, the air has a short journey along the surface of the radiator, and the air has not developed to the turbulent stage, that is, it flows out of the wooden mesh above the decorative cover of the radiator, which greatly weakens the heat transfer effect. On the other hand, because the top of the decorative cover is closed, the hot air forms a static layer that occupies a certain space here, and impedes the floating of hot air, reducing the air flow rate (0.10.2m/s) and the overall heat transfer effect. The structure of the renovated decorative cover and its indoor air flow field are respectively shown as and. The original whole wooden grid is divided into two parts, the middle is connected by a closed board, the radiation area basically remains the same. After the modification, the length of air floating along the length is lengthened, the air flow rate is also increased (0.20.5m/s), the hot air flows out from the upper part of the radiator, the original static hot air layer is reduced, the hot air flow rate is increased, and the natural convection degree of the radiator is greatly enhanced.

As can be seen from the indoor air flow field distribution of 4 decorative cover structure, the decorative cover emphasizes the coordination between the radiator and the decorative edge line of the indoor wall skirt, which greatly reduces the amount of air entering the radiator from the bottom of the decorative cover. In this way, although there are wooden mesh holes in the upper part of the decorative cover, the radiator still cannot reach the normal natural convection heat dissipation, which is also an unreasonable design. The structure of the renovated decorative cover and its indoor air flow field are respectively shown as and. The air inlet area at the bottom of the renovated decorative cover has increased compared with the original, which can also reflect that the indoor air flow field after the renovation is more uniform than before, the flow rate is about 0.10.15m/s higher, and the natural convection heat transfer effect also increases.

4 Conclusion

(1) After the heating radiator is equipped with a decorative cover, the proportion of radiation and heat transfer will change, and sometimes there may even be a complete isolation of radiation heat or convection heat transfer, and its adverse effects are certain. And for those who design and make the wrong decorative cover, the loss of heat will be greater, but also make the building energy consumption increase, is not conducive to building energy saving. Therefore, in the design of decorative cover, it is necessary to avoid as far as possible the decorative cover opening is too small, the louver ventilation rate is very low, the opening position is set at will, regardless of the smooth air convection, only open a vent and other factors that are not conducive to heat dissipation.

(2) According to the tenth Five-Year plan of the Ministry of Construction, China will soon implement heating charging by heat. In order to enable the user to adjust the room temperature according to their needs, the radiator will be installed with heat meter and temperature control valve and other necessary equipment, if the temperature control valve and the radiator are installed together in the closed decorative cover, not only the user can not operate the temperature control valve, but also because of the change of the temperature control valve temperature environment, easy to make its regulation control failure, resulting in long-term heat consumption loss.

(3) Whether from the Angle of heat transfer, or from the point of view of economics, heating radiator decoration cover is more harm than good, especially contrary to the Ministry of Construction is to advocate the building energy saving 50 long-term planning goal. From the experience of foreign production of heating radiator, foreign radiator on the product appearance quality and beautification of the degree of attention, no less than the pursuit of thermal performance of radiator. Therefore, for the domestic radiator, in order to ultimately solve the problem of decorative cover, manufacturers must be in line with the international standards, pay attention to the safety and economy of the radiator at the same time, emphasize the decorative radiator, from light, thin, beautiful, new 6 up and down.