【摘要】：作為一個人口大國,農(nóng)業(yè)發(fā)展始終是社會經(jīng)濟增長的關(guān)鍵點。當前能源危機的加劇,自然災害頻發(fā),環(huán)境污染加劇,使節(jié)能可靠的日光溫室熱濕調(diào)控系統(tǒng)引起了廣泛關(guān)注。在此背景下,本文開展了土壤——空氣換熱器的研究。土壤作為該換熱系統(tǒng)蓄放熱的最主要載體,其土壤內(nèi)部的熱濕分布將直接影響換熱器運行效果。為此,本文探究了日光溫室土壤——空氣換熱系統(tǒng)在運行中,非飽和土壤蓄放熱過程的熱濕耦合遷移規(guī)律。土壤中的溫度和濕度場之間相互影響,溫度梯度將促使土壤空隙中濕分的移運,濕分的遷移又將帶走熱量引起溫度的變化。針對這一復雜問題,運用Fluent軟件建立了,水平換熱管周圍非飽和土壤中熱濕耦合傳遞的雙場驅(qū)動模型,將溫度梯度、土水勢作為濕分遷移的驅(qū)動力,模擬非飽和土壤蓄放熱過程中溫濕度的動態(tài)分布。為直觀探究土壤蓄熱過程中三維的熱濕耦合作用,模擬了各向同性的非飽和土壤溫濕度動態(tài)分布,對溫濕度之間相互耦合作用進行了分析;之后建立了日光溫室中農(nóng)耕土壤濕度分層模型,打破了前人對土壤各向同性的認識,并分析了濕度分層對換熱運行的影響。最后,將熱濕耦合模型與純導熱模型進行對比,指出濕分遷移引起的能量變化。結(jié)果表明,溫濕度場的分布密切相關(guān)。在土壤中溫度梯度作用下,土壤中的濕分沿溫度梯度反方向遷移,并依次堆積形成濕峰。各向同性土壤中,距管中心距離相同的各點,同時出現(xiàn)濕峰。管內(nèi)空氣溫度越高,濕度峰值越明顯。在各向異性的分層土壤中,其土壤水平方向的溫濕度分布與豎直方向明顯不同。土壤含水率的差別導致土壤熱物性的改變。在豎直方向上土壤含濕量差別較大,土壤中水分的分布更容易受到初始水分分層的影響,在濕度梯度和溫度梯度共同作用下產(chǎn)生明顯移運。在自然狀態(tài)下運行土壤空氣換熱器,土壤空氣換熱器溫度和濕度影響半徑均小于0.5米范圍,且在換熱過程中,土壤溫度的變化有明顯的延時效應。隨著與換熱管距離的增加,溫度變化的延時效應越明顯。同樣也表明,在換熱器正常運行中,為避免管間相互影響,則需保證管間距大于1米。與純導熱模型對比,非飽和土壤中濕分遷移引起的熱量的轉(zhuǎn)移,使土壤獲得更大的蓄放熱能力。
[Abstract]:As a populous country, agricultural development has always been the key point of social and economic growth. With the aggravation of energy crisis, frequent natural disasters and environmental pollution, the energy saving and reliable heat and humidity control system in solar greenhouse has attracted wide attention. In this context, the soil-air heat exchanger is studied in this paper. As the main carrier of the heat transfer system, the heat and moisture distribution in the soil will directly affect the operation effect of the heat exchanger. Therefore, in this paper, the heat and moisture coupling migration of unsaturated soil during the operation of soil-air heat transfer system in solar greenhouse is studied. The temperature gradient will promote the movement of moisture fraction in the soil void, and the migration of moisture fraction will take away heat to cause the change of temperature. Aiming at this complex problem, a two-field driving model of thermal-moisture coupling transfer in unsaturated soil around horizontal heat exchanger pipe is established by using Fluent software. The temperature gradient and soil water potential are taken as the driving force of moisture transport. The dynamic distribution of temperature and humidity in unsaturated soil during heat storage and exothermic process was simulated. In order to investigate the three-dimensional thermo-moisture coupling in the process of soil heat storage, the dynamic distribution of the isotropic unsaturated soil temperature and humidity was simulated, and the interaction between temperature and humidity was analyzed. The model of soil moisture stratification in solar greenhouse was established, which broke the previous understanding of soil isotropy, and analyzed the influence of moisture stratification on heat transfer. Finally, the heat and moisture coupling model is compared with the pure heat conduction model, and the energy changes caused by wet fraction migration are pointed out. The results show that the distribution of temperature and humidity field is closely related. Under the action of the temperature gradient in soil, the wet fraction in the soil migrated in the opposite direction of the temperature gradient, and the wet peak was formed in turn. In isotropic soil, there is a wet peak at the same distance from the center of the tube. The higher the air temperature in the pipe, the more obvious the peak humidity. In anisotropic layered soils, the distribution of temperature and humidity in the horizontal direction is obviously different from that in the vertical direction. The difference of soil moisture content leads to the change of soil thermal properties. In the vertical direction, the moisture content of the soil varies greatly, and the distribution of soil moisture is more easily affected by the initial moisture stratification, resulting in obvious migration under the combined action of the moisture gradient and the temperature gradient. The influence radius of temperature and humidity of soil air heat exchanger is less than 0.5 m, and the variation of soil temperature has obvious delay effect in the process of heat transfer. With the increase of the distance from the heat exchanger tube, the delay effect of temperature change becomes more obvious. It is also shown that in order to avoid the interaction between tubes in the normal operation of the heat exchanger, the distance between the tubes should be more than 1 meter. Compared with the pure heat conduction model, the heat transfer caused by wet fraction migration in unsaturated soil makes the soil obtain greater heat storage and exothermic capacity.
【學位授予單位】：太原理工大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TU83

【參考文獻】

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1 黃奕l，

本文編號：2250013