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高低溫試驗箱（機(jī)）的傳熱原理——熱對流
高低溫試驗箱（機(jī)）的傳熱原理——熱對流
在高低溫試驗箱進(jìn)行試驗時，對流通散熱在散熱試驗樣品熱交換中占有極重要的部分，熱量從試驗樣品表面?zhèn)鬟f到周圍空氣中去的傳熱系數(shù)，受周圍空氣速度的影響，空氣速度越高則熱交換的效率也越高，這就是行業(yè)內(nèi)常說的換熱（現(xiàn)高低溫試驗箱的標(biāo)準(zhǔn)空氣流速均為3.7M/S），如果試驗樣品的熱量過大則應(yīng)相應(yīng)增加風(fēng)機(jī)功率，以達(dá)箱內(nèi)精度平衡，同樣，在環(huán)境溫度相同時，空氣速率越高，試驗樣品表面溫度就越低。
During tests at high and low temperature test chamber, the circulation cooling in cooling heat transfer
plays an important part of the test samples, from the test sample surface heat transfer coefficient of heat
transfer to the surrounding air, the influence of the surrounding air velocity, air speed, the higher the
heat exchange efficiency is higher, this is often said that the heat transfer in industry （now the standard
of the high and low temperature test chamber of air velocity of 3.7 M/S）, if the sample test of excessive
heat should be appropriate to increase the fan power, so as to achieve the accuracy of balance in the oven,
likewise, in the environment temperature phase at the same time, the higher the air velocity, temperature,
the lower the test sample surface.
氣流除影響任一位置上試驗樣品的表面溫度外，還影響試驗樣品表面上的溫度公布，對不同的氣流速度和氣流方向來說，在試驗樣品表面溫度及溫度分布之間不存在任何簡單關(guān)系，同樣明顯的是如果要使試驗符合實際條件，試驗時就要對試驗箱規(guī)定的某一特定的氣流速度和氣流方向，這將涉及到高低溫試驗箱設(shè)計方面的許多問題，為了便于把試驗結(jié)果果與實際的環(huán)境條件比較，有必要規(guī)定一個清晰的、能重現(xiàn)的試驗條件，這就導(dǎo)致“自由空氣條件”的使用（注：“自由空氣條件”使用無限空間內(nèi)的空氣條件，此時，在該空間內(nèi)空氣運動僅受散熱試驗樣品本身的影響，由試驗樣品輻射的能量在該空間內(nèi)吸收，因此，試圖在試驗箱中重現(xiàn)自由空氣條件的試驗是不切實際的，北京鴻達(dá)天矩試驗設(shè)備有限公司提醒廣大用戶不要采用此類試驗方法）。
Airflow in addition to the influence on the surface temperature of the test samples at any place, also affect
the temperature of the test sample surface, for different air velocity and flow direction in the test sample
surface temperature and there is no simple relation between temperature distribution, it is also clear if you want
to make the test in line with the actual conditions, will be to test chamber when the test rules of a particular
air velocity and airflow direction, this will involve many problems in the design of high and low temperature test
chamber, in order to facilitate the test results compared with the actual environmental conditions, it is necessary
to rule a clear, can repeat test conditions, this leads to the use of "free air condition" （note: "free air condition"
to use the air in the infinite space conditions, at this point, in the ?
采用自由空氣條件，通常并不導(dǎo)致使用價格高昂或者不切實際的大型試驗室，既然自由空氣條件有某些技術(shù)上的優(yōu)點，而且比規(guī)定的強(qiáng)迫空氣條件易于做到，所以用作散熱試驗樣品進(jìn)行低溫和高溫試驗時的優(yōu)選方法，在有些情況下，采用無強(qiáng)迫空氣循環(huán)方法進(jìn)行試驗可能產(chǎn)生一些困難，因而在允許采用低速空氣進(jìn)行強(qiáng)迫空氣循環(huán)的場合給出了兩種供選用的方法：
1、適用于高低溫試驗箱的尺寸大得足以滿足試驗要求，但試驗箱的升溫或降溫需要采用強(qiáng)迫空氣循環(huán)的試驗。
2、適用于試驗箱較小不能滿足試驗要求，或由于別的原因不能使用*種方法的試驗。
USES the free air condition, usually does not lead to use expensive or unrealistic large laboratory, now that the
free air condition has some technical advantages, and than forced air condition is easy to do, so when used as a heat
test samples in low temperature and high temperature test of optimization methods, in some cases, using the method of
forced air circulation experiment may produce some difficulties, thus the allowed the use of low speed air to forced
air circulation situation shows the two alternative methods:
1, suitable for high and low temperature test chamber size is big enough to meet the test requirements, but the test
chamber heating or cooling needs of the forced air circulation test.
2, suitable for small test chamber can't meet the test requirements, or by ?