Research On New Semiconductor Refrigeration System Using Metal Foam

With the rapid development of electronic integration technology, electronic devices are also moving towards miniaturization, light weight and intelligence. However, the miniaturization of integrated electronic devices increases the power density while the heat dissipation is also increasing. Traditional cooling technologies have been difficult to meet the cooling requirements. Therefore, it is particularly important to study the heat dissipation of electronic components with high heat flux density. In this paper, an air-cooled heat dissipation method is proposed, that is, on the basis of semiconductor refrigeration technology, combined with a foam metal radiator, a refrigeration system is designed and its refrigeration effect is tested through an experimental model.

1. Theoretical basis and experimental device

The semiconductor cooler is a heat transfer tool. When a current passes through a thermocouple pair formed by a piece of N-type semiconductor material and a piece of P-type semiconductor material, heat transfer occurs between the two ends, resulting in a temperature difference to form the hot and cold ends. However, the semiconductor itself has resistance, which generates heat when the current passes through it, which affects the heat transfer. The heat between the two plates also undergoes reverse heat transfer through the air and the semiconductor material itself. When the hot and cold ends reach a certain temperature difference and the two heat transfer amounts are equal, the forward and reverse heat transfer cancel each other out, and the temperature of the cold and hot ends will not continue to change. Therefore, in order to achieve a lower temperature, methods such as heat dissipation can be used to reduce the temperature of the hot end.

Metal foam is a porous metal material with a porosity of more than 90% and a certain strength and stiffness. This type of metal material has high air permeability, large pore surface area, and small material bulk density. When the airflow passes through, it has a large contact area, which is conducive to heat exchange.

Refrigeration is realized by semiconductor refrigeration sheet. Considering that the cold surface of the semiconductor refrigeration sheet cannot be in direct contact with the heat dissipation object, and the natural convection heat transfer effect of the cold surface of the cold surface to the air is not significant, it is attached to the foam metal surface to increase heat exchange. area, to achieve the effect of strengthening the exchange of cold energy. The cooling semiconductor and the foam metal are bonded by silicone grease to reduce the contact thermal resistance. Part of the airflow takes away the cooling energy, forming cold air and dissipating heat to the target, and the hot surface is also taken away by the airflow and discharged into the environment.

The experiment uses cross-connected double air ducts, one of which is used to export cold air and the other is used to export hot air. Connect the fans at the entrance of the cold and hot air ducts to provide airflow, and leave the necessary measuring holes and installation holes when processing the air ducts.

When the refrigeration semiconductor is energized, a temperature difference is generated, the air flow through the cold surface is cooled to become cold air, and the air flow through the hot surface cools it down and is discharged from the hot air duct. The lower the temperature of the hot side and the lower the temperature of the cold side, the better the cooling effect. There are 4 symmetrical temperature measuring points (denoted as T5, T6, T7, T8 in the experiment, unit ℃) at the outlet of the cold air duct, and 4 anemometers are arranged symmetrically to measure the outlet air temperature, while the inlet air temperature is determined by the ambient temperature. Install an anemometer to measure the wind speed at the exit. In addition, the surface of the foam metal in contact with the semiconductor cold surface is arranged with 4 measuring points symmetrical in the center, and 4 thermocouples are spot welded on the copper plate to measure the temperature of the copper plate welded on the bottom surface of the foam metal, which is collected by the Keishley data acquisition system. , collected 100 times, and averaged respectively (recorded as T1, T2, T3, T4 in the experiment, unit ℃), used to calculate the relative heat transfer coefficient of refrigeration.

The numerical simulation results of the cold air duct temperature field of this model: the ambient temperature is 298K (25°C), and in the simulated cold air duct of 400mm*100mm*40mm, the semiconductor refrigeration chip works under the rated conditions of 12V and 6A, and the foam metal material is copper. , the size is 100mm*100mm*40mm, and it is 5 ppi. The theoretical effect of refrigeration can be confirmed from the results.

2. The experimental process

2.1 Experimental equipment

1 plexiglass cross air duct, 2 all-copper core 80W speed-regulated centrifugal fans, refrigerating semiconductor (rated working condition 12V, 6A) 50mm*50mm, 2 electronic anemometers, 4 electronic anemometers, 1 glass thermometer Supports, several copper foam metal, PC, copper constantan thermocouple, ice bottle, Keishiley 2700 data acquisition system, data acquisition card, linear stabilized power supply, etc.

2.3 Experimental steps

Build a test bench according to the design, and read the room temperature Ts (°C), which is 26.5°C.

The fan is driven by a 220V power supply, and the cooling semiconductor is powered by a linear voltage stabilized power supply.

Keep the wind speed V2 of the hot air duct fan unchanged, adjust the working voltage U or current I of the refrigeration semiconductor, adjust the wind speed V1 of the cold air duct fan, and read T1~T8 in turn; then change V2, adjust the working voltage or current of the refrigeration semiconductor, and adjust the cold air duct. Fan wind speed V1, read T1~T8 in sequence; repeat as above, where V2 is 0.5m/s, 1.0m/s, 2.0m/s, 3.0m/s, 4.0m/s, V1 is 0.5m/s respectively , 1.0m/s, 1.5m/s, 2.0m/s, 2.5m/s, 3.0m/s, 3.5m/s, 4.0m/s, (U, I) are respectively (1.4V, 1.0A) , (3.1V, 2.0A), (46V, 3.0A), (6.3V, 4.0A), (8.2V, 5.0A)..

The average temperature at the outlet of the cold air duct Tb=(T5+T6+T7+T8)/4, the average temperature of the metal foam bottom copper plate in contact with the semiconductor cold surface Ta=(T1+T2+T3+T4)/4; by the formula h*ΔTa* S=Q=Cp*(m/t)*ΔTb, calculate the cooling power Q and the relative heat transfer coefficient h, where the left side of the equation is the cold surface heat transfer power, and the right side is the cooling power calculated by air cooling. S – the area of the bottom surface of the metal foam, ΔTa=Ts-Ta, h is the actual heat transfer coefficient with S as the heat transfer area, Cp is the specific heat of air at room temperature, take 1.004KJ/

From Figure 2 to Figure 4, as the wind speed of the cold air duct is lower, the outlet air temperature is lower, and the cooling effect is better. The higher the power of the cooling sheet, the lower the air temperature at the outlet of the cold air duct, but when the power reaches the maximum in the experiment, the air temperature at the outlet of the cold air duct will increase again, because the heat dissipation conditions of the hot surface are limited, the temperature rises, and the temperature of the cold surface is corresponding. pick up.

Since the experiment is affected by instruments and environment, although the curve fluctuates to a certain extent, the overall conclusion is that with the increase of the wind speed V2 of the hot air duct, the air temperature Tb at the outlet of the cold air duct decreases, and the cooling effect is good.

Through the calculation of the experimental data, the actual heat transfer coefficient h of the cold surface with S as the heat exchange area, the cooling power Q, and the cooling semiconductor power W can be obtained. The data analysis shows that when only changing the wind speed and flow at the outlet of the cold air duct, i.e., q increases, the outlet air temperature increases and the cooling power Q increases; when only the cooling semiconductor power is changed, that is, W increases, the outlet air temperature decreases, and the cooling power decreases. The power Q increases; when only the wind speed of the hot air duct is changed, that is, the V2 increases, the outlet air temperature decreases and the cooling power Q increases. The actual heat transfer coefficient h of the cold surface with S as the heat exchange area, h increases with the increase of V1, and increases with the increase of V2; but when the cooling semiconductor power W increases, h gradually decreases.

In the experiment, the highest value of cooling power Q is measured in the state of V2=3m/s, U=6.3V, I=4A, V1=4m/s, which proves that the cooling power needs to comprehensively consider whether the heat dissipation conditions meet the corresponding power and airflow quality. Flow size, cooling wind speed and other factors.

3. Conclusion

In this paper, an experimental prototype using a foam metal semiconductor refrigeration system is designed. According to the experimental results and statistical analysis of the data, the following conclusions are drawn:

(1) Under the same conditions, the lower the cold air wind speed, the lower the outlet air temperature; the higher the electric power of the refrigeration semiconductor, the lower the outlet air temperature; the hot air duct wind speed increases, and the cold air duct outlet air temperature decreases.

(2) Under the same conditions, the outlet wind speed of the cold air duct increases, the outlet air temperature increases, and the cooling power Q increases; the cold semiconductor power W increases, the outlet air temperature decreases, and the cooling power increases; the hot air duct wind speed increases, the outlet air temperature decreases , the cooling power increases.

(3) The actual heat transfer coefficient h of the cold surface with S as the heat exchange area increases with the increase of V1, and increases with the increase of V2; the power of the refrigeration semiconductor increases, and h gradually decreases.

(4) For lower cooling power, choose lower cold air speed, higher hot air speed and electric power; for higher cooling power, choose higher cold air speed and hot air speed, and higher electric power.