| The sequential cooling refrigeration system uses a set of refrigeration system to cool the10 refrigerators at different ambient temperatures and different cold storage temperatures by adjusting the frequency of the air cooler and the compressor.The whole system consists of a set of air-cooled condensing units,a finned tube evaporator,an axial fan,10 refrigerators of same size,air supply pipelines and electric control devices.The experiment is based on the sequential cooling system,and the minimum cooling capacity configuration of the cold storage is studied.In the experiment,10 refrigerators are cooled successively at different ambient temperatures,changing the temperature range of the cold storage,adjusting the frequency of the air cooler and the compressor.Change the cooling time and heating time of the cold storage by changing the air volume and refrigeration capacity of the cold storage.The cooling capacity configured in the refrigeration system not only satisfies the sequential cooling under different conditions of the cold storage,but also avoids the state of low-load operation of the compressor.The mathematical model of temperature preservation and cooling of cold storage is established.In the experiment,the ambient temperature control group was 15?and 30?,and the cold storage temperature control group was-12?~-10?,-6?~-4?,and 0?~2?.Under this condition,regulate compressor frequency and cooling fan frequency.The cooling time and heating time under different working conditions were measured,and analyse the effects of the frequency of the air cooler and the compressor on the cooling and heating of the cold storage under different working conditions.The following conclusions are drawn:(1)When the frequency of the air cooler is 35Hz?40Hz?45Hz?50Hzthe average air supply volume of the cold storage is 59.21m~3/h?64.38m~3/h?74.65m~3/h?83.96m~3/h?respectively.The air supply volume of the 10 cold storages fluctuated on the average air supply level.Since the length of the air supply duct is short and the resistance loss is small,it can be considered that the air supply volume of the cold storage is independent of the position of the cold storage and is proportional to the frequency of the cold air blower.(2)When the temperature of the cold storage is different,the influence of fan frequency on the cooling and heating of the cold storage is different.As the temperature of the cold storage decreases,the influence of the frequency of the air cooler on the cooling time decreases.When the temperature of cold storage is-12?~-10?,-6?~-4?,and 0?~2?,the frequency of fan increases from 30Hz to 50Hz,the cooling time of a single cold room decreases by 32s?29s and 26s,and the heating time increases by 47s,59.7s and 92.5s,respectively.When the working condition keep unchanged and the fan frequency is smallar,the influence of frequency on cooling time is greater.When the fan frequency is larger,the influence of frequency on cooling time of cold storage is smaller.When the temperature of cold storage is-12~-10?,the fan frequency increases from 30Hz to 40Hz,the cooling time decreases by 24.4%,the fan frequency increases from 40Hz to 45Hz,and the cooling time decreases by only 12.25%.(3)Under different refrigeration conditions,the lower the storage temperature,the greater the variation of the operating time coefficient.When the ambient temperature is 15C,the storage temperature is-12?~-10?and 0?~2?,the frequency of the fan increases from 30 Hz to 50 Hz,and the operating time coefficient decreases by 0.23 and 0.15,respectively.With the increase of fan frequency,the influence of fan frequency on the operating time coefficient of compressor is smaller.When the temperature of cold storage is0?~2?and the frequency of fan is 50 Hz,the operating time coefficient of compressor is0.24,the cooling capacity is large.The frequency of fan can be adjusted to 30 Hz to reduce the operating power of fan,and the operating coefficient can be increased to 0.38.(4)When the compressor frequency is 50 Hz and the ambient temperature is 15?,the operating time coefficient of the compressor is less than 0.5,and the cooling capacity meets the cooling requirements of the cold storage;when the ambient temperature is 30?,the operating time coefficient is more than 0.5,but when the operating coefficient is more than 0.4,it can not meet the requirements of use.When the operating time coefficient of compressor varies with fan frequency at different ambient temperatures,the maximum error and minimum error are 16%and 2.6%respectively,compared with the theoretical value.(5)With the increase of compressor frequency,the cooling time decreases by 39 s,29s and 27 s,and the heating time increases by 29.5 s,38.6 s and 72.4 s,respectively.When the working condition is unchanged,the operating time coefficient of the compressor decreases with the increase of the compressor frequency.The lower the storage temperature,the greater the influence of compressor frequency on the operating time coefficient.When the cold storage temperature is-12~-10?and 0~2?,the compressor frequency increases from30Hz to 50Hz,and the running time coefficient decreases by 0.11 and 0.09,respectively.When the temperature of the cold storage is higher than-6 C,the running time coefficient is less than 0.45,and the cooling capacity meets the cooling requirements of the cold storage.When the temperature of the cold storage is lower than-10 C,the running time is more than0.45.Compared with the theory,the maximum error is 21%,and the minimum error is 3%.(6)At different ambient temperatures,the operating time coefficient of the compressor decreases with the increase of compressor frequency.When the ambient temperature is 30?,the compressor frequency is 30 Hz,the maximum operating time coefficient of the compressor is 0.79,the cooling capacity can not meet the cooling of the cold storage,the frequency is increased to 50 Hz,and the operating time coefficient is reduced to 0.47.The maximum and minimum errors of the theoretical and experimental runtime coefficients are16%and0.8%.(7)Under the same cooling condition,when the thickness of the enclosure structure is small,the change of the thickness of the enclosure structure has a great influence on the running time coefficient of the compressor.When the thickness of the enclosure structure is large,the change of the thickness of the enclosure structure has a little influence on the running time coefficient of the compressor.When the enclosure thickness is 100 mm and the compressor frequency is 36 Hz,the running time coefficient is equal to 1.The refrigeration system can maintain the storage temperature and the compressor can not stop.In the design of cold storage,the reasonable thickness of maintenance structure can be selected according to the running time coefficient.The maximum and minimum errors of the theoretical and experimental runtime coefficients are 7%and 2%. |
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