Or consider the above indicators of the two options. The project has good social and economic benefits.

2 experimental research and theoretical analysis 2.1 design parameters and structural dimensions of the insulated container box cover ~ 30T, relative humidity 50 ~ 6T, and the semiconductor refrigeration box is mainly used to preserve fresh blood, so the design requires the box temperature U = 4 box The design diagram is shown on the left: the tank wall is mainly composed of three parts: the inner wall, the outer wall and the intermediate insulation layer. In order to reduce the heat conduction heat resistance inside the box and fix the intermediate heat conduction copper block, the inner wall of the box uses 2mm thick aluminum plate; in order to make the outer wall stronger and has good thermal insulation performance, the outer wall is made of 5mm thick PVC plastic plate. The intermediate insulation layer adopts polyurethane one-shot foaming technology in order to obtain good insulation performance.

2.2 Determination of operating parameters Fan forced heat transfer, due to volume limitation, the cold end uses natural heat transfer. The heat transfer temperature difference Aih, At, both take 15T. The design condition can be = -11, and the temperature difference between the hot and cold ends is obtained by the generation to determine the single-stage semiconductor refrigeration chip.

2.3 Determination of the cooling capacity The cooling capacity is determined by the heat load. Since the semiconductor refrigeration and heat preservation container adopts good insulation measures, the heat load is small.

Some researchers conducted a reverse load test (InverseHealLeakTest) to determine the heat load of the container, put a heater and thermocouple temperature probe inside the box, another heater and temperature probe on the back of the box, by adjusting the power of the heater The heat load of the container was measured. However, by using this method to measure the heat load, the temperature on the back side of the box often reaches 100T or more, and the position of the semiconductor cooling fin of the container is close to the back of the case, which may cause unnecessary damage to the semiconductor refrigeration sheet.

In this test, two methods are used to determine the heat load: 1. Theoretical calculation method (iterative method); 2. Test method.

The theoretical calculation method (iterative method) is to obtain the thermal conductivity of three materials (PVC plastic, aluminum, polyurethane foam layer), assuming the external wall temperature of a box, the known ambient temperature and the temperature inside the tank wall, and the calculation environment for the box. Whether the radiant heat and convective heat of the body is equal to the conduction heat of the inner wall of the tank to the internal environment of the tank. If they are equal, the temperature of the outer wall of the box is assumed to be correct, and the heat load of the box can be easily calculated. If they are not equal, the temperature of the outer wall of the box is re-assumed according to the calculation result until it is equal to.

After theoretical calculation, the heat load of the box is 8.61w. The test method is to put the test box into a 25-inch incubator, put 380ml of water into the test box, put a calibrated thermocouple in the water, observe the water temperature. The time it takes to rise from 2 to 6 inches. After testing, the time is 12 minutes and 11 seconds.

Therefore, the heat load, = 2" Although the test method is relatively coarse, it can basically reflect the heat load of the container, and will not cause any possible damage to the semiconductor refrigeration sheet.

2.4 Selection of semiconductor refrigeration components At present, there are not many semiconductor materials suitable for low-temperature refrigeration. Domestically produced thermoelectric materials are better. P-type has a 27V3-young 27V3 solid solution alloy, and N-type is a 27V3-23 solid solution alloy. Two kinds of semiconductor materials of different polarities (P type, N type) are connected into a galvanic pair, and energy transfer occurs when a direct current is passed; when the current flows from the N type element to the P type element, heat is absorbed, and this end face is a cold surface. On the contrary, when the current flows from the P-type to the >1 type, the end surface is called the hot surface. A pair of basic thermocouples have a small amount of cooling. In actual use, many thermocouples are required to form a semiconductor refrigerating sheet (assembly), as shown in the following figure.

There are two refrigerating sheets in the figure: the left side is a two-stage semiconductor refrigerating sheet (sealing, ceramic surface), and the right side is a single-stage semiconductor refrigerating sheet (no sealing, ceramic surface).

The main parameters reflecting the thermoelectric performance of the semiconductor refrigeration chip are the maximum current value Imax, the maximum heat absorption Qmax, the maximum rated voltage Vmax and the maximum temperature difference DTmax. Since the fixing method of the semiconductor refrigeration sheet adopts a mechanical fixing method instead of a welding fixing method, it is selected. Ceramic surface. Since the thermal conductive silica gel exists in the working environment of the semiconductor refrigerating sheet, and the thermal conductive silica gel is a viscous liquid before it is completely dried, the selected semiconductor refrigerating sheet must be sealed.

According to the above design conditions and design requirements, a single-stage semiconductor refrigeration chip produced by Hangzhou Dahe Thermomagnetic Electronic Cable Co., Ltd. is selected. The cooling type is: 9500/127/085AS. According to its characteristic diagram, it can be achieved at around 12V. Both cooling capacity and cooling efficiency are good. The small insulated container should be used in the car. The DC voltage on the car is also the most common 12V. In addition, in other occasions, 12V is also the voltage value of the DC regulated power supply. If the voltage of the designed small insulated container is 12V. It will undoubtedly be extremely convenient to use. Therefore, the design working voltage is 12V. The maximum heat absorption Qmax refers to the maximum current value of the cold plate 3502/27/085AS selected by the heat sink 3 when the current is the maximum current Imax and the temperature difference DTzOt is 8.5A, the maximum heat absorption. 80W, the maximum rated voltage is 17.5V, the maximum temperature difference is 72T, which is composed of 127 pairs of thermocouples, sealant and ceramic surface. The semiconductor refrigeration chip has a volume of only 39.7x39.7x. 3 Several key factors affecting the cooling effect of the semiconductor refrigeration and insulation container. We have repeatedly designed, manufactured, processed, tested, re-engineered the semiconductor refrigeration box, and then carried out a series of experimental studies. A few points of experience and precautions are available.

3.1 About the hot end heat sink The hot end heat sink uses an aluminum finned heat sink (as shown) and a DC fan (shown) outside the heat sink.

The aluminum finned radiator is mainly because the aluminum finned heat sink has better heat dissipation effect and lighter weight.

3.1.1 Determination of fin parameters Due to the limitation of volume and quality, the aluminum finned radiator is not suitable for water cooling. It is only suitable for natural ventilation or forced ventilation cooling. The surface heat transfer coefficient is relatively low. If the fin thickness is too thin, This will result in the fin top not being able to participate in heat exchange resulting in a reduction in fin efficiency.

Considering comprehensively, the fin thickness is 2mm and the fin height is 25mm. 3.1.2 The heat dissipation mode selection test is carried out under the condition that the DC fan power supply is turned on or off. The purpose of the test is to determine the cooling effect of a semiconductor refrigeration insulated container under natural and forced air conditions. Since the DC fan is a fragile component, it is desirable to use natural ventilation. However, the test confirmed that when the external ambient temperature is 25T, the forced cooling and heat dissipation is adopted. The container has good cooling and heat preservation effect, and it is easy to drop to 4T. With natural ventilation and heat dissipation, the refrigeration and heat preservation effect of the container is not ideal, and the temperature inside the container is only better. The ambient temperature outside the box is 2 feet lower, and even if the temperature difference between the hot and cold ends is too large, there will be no cooling.

3.2 Selection of the heat dissipation method of the cold-end heat sink The inner wall of the test box is an aluminum plate, and the cold end of the semiconductor refrigeration chip is directly attached to the aluminum plate. There are three ways to choose the cold end "cold": 1, no additional radiator, directly with the aluminum plate for "cold"; 2, plus aluminum radiator; 3, plus aluminum fin radiator and DC fan . The three heat dissipation methods have their own advantages and disadvantages: the third method has good heat dissipation effect, but the structure is complicated and the volume is too large; the first method has relatively poor heat dissipation effect, but the structure is simple, and the test chamber volume is small. Analysis, it can be seen that the required cooling capacity of this test chamber is very small, only 56W, so it does not need too good heat dissipation equipment to meet the requirements; after testing, it is proved that the first heat dissipation method is adopted, so it is easy to reduce the internal temperature of the test chamber to 4T. Therefore, the first method is recommended for the cooling method of the cold end.

3.3 Design issues concerning the core components of the refrigeration and insulation box The core components are mainly designed in three aspects: 1. The selection of semiconductor refrigeration chips; 2. The selection of intermediate thermal conductive metal blocks; 3. Intermediate thermal conductive metal blocks and semiconductors The problem of the size of the area on which the cooling sheet contacts; 4, the relative position of the semiconductor refrigerating sheet and the intermediate thermally conductive metal block; 5, the connection problem of the hot end heat sink, the semiconductor refrigerating sheet, the heat conducting metal block, and the cold end aluminum plate. These five issues are not only the design of the core components, but also the most critical issue in the design of the entire refrigeration incubator. The suitability of these five questions will be directly related to the success of the refrigeration incubator design.

The selection of semiconductor refrigerating sheets has been introduced earlier.

After theoretical analysis and trial and error, it is determined that the intermediate heat conducting metal block material is pure copper, and the area of ​​the surface of the intermediate heat conducting metal block contacting the semiconductor cooling sheet is recommended to be the same as the surface area of ​​the semiconductor cooling sheet. The semiconductor refrigerating sheet is close to the external heat sink, and the heat conducting metal block is close to the inner aluminum plate, and the heat conducting metal block undertakes the task of transmitting the cooling amount to the inside of the test box. The semiconductor refrigerating sheet is fixed by mechanical fixing method. This method is to coat all the contact surfaces with thermal adhesive to reduce the contact thermal resistance of the contact surface, and then fix it with screws to avoid leakage from the hot end heat sink through the screw to the cold end. Heat (sometimes this heat leak is very large, even a loss of more than ten degrees of temperature difference), the screw sleeve is made of plastic (nylon 66). Since the heat conducting metal block and the cold end slab are both cold ends, when the screws are fixed between them, the screws do not need to be covered with a plastic sleeve.

3.4 Determining the test plan Through the above theoretical analysis, test and result analysis, determine the final test plan: use DC cooling, working voltage 12V, external ambient temperature 25T or 30T, the temperature inside the box needs to reach tb=4. The internal size of the refrigerator, the length is 120mm, width 60mm, depth 200mm. Total refrigerating volume is 1.44L, external dimension is 180mm long, width is 120mm, height is 265mm. The outer wall of the test box is composed of three parts: the outermost PVC plastic plate, the middle polyurethane foam layer, the inner 2mm Aluminum plate. The semiconductor refrigeration chip selects a single-stage semiconductor refrigeration chip produced by Hangzhou Dahe Thermomagnetic Electronics Co., Ltd., the refrigeration film model is: 9500/27/085AS. The hot end uses aluminum finned heatsink, the size is 150mmx 125mmx30mm. The cold end is 2mm thick aluminum plate for heat dissipation. The middle heat-conducting metal block is made of copper block, the size is 40mmx 40mmx26mm, and the contact surface is coated with Lihua brand thermal silica gel.

When the external ambient temperature is 30 feet and the tank is empty, the test results are as follows: the horizontal axis is the time axis, and the vertical axis is the temperature of the middle air inside the heat preservation container. After 1 hour, 17 minutes and 35 seconds, the temperature was cooled from 30 feet to 5.41, and the inside of the box was kept at 5.41 in an external environment temperature of 300, and the container was filled with 3 bags of 250 ml and 1 bag of 100 ml infusion bag for 24 hours. The intermediate air temperature is finally maintained at 3.11 T. When the external ambient temperature is 250 and the tank is empty, the test results are as follows: the horizontal axis is the time axis, and the vertical axis is the temperature of the positive intermediate air inside the insulated container. After 1 hour, 18 minutes and 27 seconds, the temperature was cooled from 25T to 1.46, and kept at 1.46 in the external environment temperature of 25T, and the container was filled with 3 bags of 250ml and 1 bag of 100ml infusion bag for 24 hours, the inside of the box was in the middle. The air temperature is finally maintained at 1.970. It can be seen that the temperature control range of the temperature relay is set to 2~6T when the ambient temperature is 25 ~ 30, when the ambient temperature is 25 ~ 30, the test chamber The internal temperature can also be maintained at 2 ~ 6T. This proves that the design and manufacture of this semiconductor refrigeration and insulation container is successful.

4 Conclusion 4.1 It is feasible and advantageous to apply semiconductor refrigeration to insulated containers.

4.2 The cooling efficiency of the conventional compression chiller decreases with the decrease of the refrigerating capacity, while the cooling efficiency of the semiconductor refrigerating box is independent of the volume, and is only related to the temperature difference and voltage between the cold and hot ends of the semiconductor refrigerating sheet.

4.3 The ambient temperature of this test did not reach the maximum temperature in summer, but it is certain that after increasing the power or quantity of the cooling plate, even if the ambient temperature reaches the highest temperature in summer, the inside temperature of the insulated container can reach the required temperature.

4.4 Comprehensive efficiency and cost-effective factors, overcome the shortcomings of small cooling capacity and low COP, improve economical and rationally design the structure. Improving portability, and better insulation and temperature control measures are key to the design and use of thermoelectric coolers. Through the balance between manufacturing cost and operating cost, select the appropriate working point, determine the type and number of thermoelectric cooling fins that meet the cooling requirements, and rationally design the internal structure, external structure and good thermal insulation measures of the semiconductor refrigeration incubator. The main work of the refrigerator design.

The simple and convenient semiconductor refrigeration and heat preservation container has the advantages of small volume, light weight, no vibration, high stability and long service life. It will be more widely used in the transportation and storage of plasma, blood, animal semen or biological products, especially in future field health equipment.

(Finish)

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