本文選題：地埋管換熱器　切入點：蓄冷相變　出處：《長安大學(xué)》2017年碩士論文

【摘要】：隨著社會經(jīng)濟的迅速發(fā)展,能源危機和環(huán)境污染問題已對人類的需求和健康構(gòu)成了嚴(yán)重威脅。為響應(yīng)節(jié)能環(huán)保政策,開發(fā)節(jié)能技術(shù)和尋求新能源已經(jīng)迫在眉睫。土壤源熱泵技術(shù)作為一種可再生能源技術(shù),對降低建筑能耗和能源污染起著高效作用。為了推進(jìn)土壤源熱泵技術(shù)的發(fā)展,地埋管換熱器與淺層巖土的換熱問題成為研究的焦點。本文基于有限元的思想,結(jié)合多孔介質(zhì)理論和流體動力學(xué)理論,采用Fortran語言工具,針對土壤源熱泵地埋管換熱問題,在等效直方管的基礎(chǔ)上,將U型地埋管等效成真正意義上的U型方管,建立了考慮固液相變過程的土壤蓄冷模型和地埋管換熱器管內(nèi)外耦合換熱模型,編制了三維動態(tài)數(shù)值計算程序。在應(yīng)用地埋管換熱器進(jìn)行土壤蓄冷和為嚴(yán)寒地區(qū)冬天取熱的過程中,地埋管換熱器周圍土壤中的地下水可能發(fā)生凍結(jié)的現(xiàn)象。為了描述地埋管換熱性能,本文引出了線性熱通量評價指標(biāo),對比分析了地下水固液相變過程對換熱性能的影響。在管內(nèi)紊流計算的基礎(chǔ)上,分析了不同地下水滲流速度、不同地埋管的入口流速、不同地埋管的入口溫度、不同回填材料及不同埋管管材對換熱性能的影響。利用程序計算得出如下結(jié)論:(1)土壤地下水的滲流有利于地埋管的換熱,滲流速度越大地埋管換熱器換熱性能越強,滲流速度每增加10m/a,線性熱通量平均增加0.06%;(2)隨著入口流速的提高,出口溫度隨之增加,線性熱通量顯著增大,但存在最佳入口流速;(3)在流量一定的條件下,隨著入口水溫的增加,埋管進(jìn)出口溫差會增大,線性熱通量也隨之增加;(4)導(dǎo)熱系數(shù)越高的回填材料,換熱效果越好,回填材料的導(dǎo)熱系數(shù)應(yīng)當(dāng)接近土壤的導(dǎo)熱系數(shù)。在低于土壤導(dǎo)熱系數(shù)時,單位回填材料導(dǎo)熱系數(shù)的增加對應(yīng)線性熱通量平均增加18.74W/m,增幅為15.3%;(5)采用導(dǎo)熱性能較好的HDPE管和PE管管有助于地埋管換熱器換熱性能的提高;(6)土壤蓄冷時的固液相變過程有助于地埋管換熱器的換熱,出口溫度在相變現(xiàn)象出現(xiàn)后會有一定的波動,有無相變過程的土壤蓄冷的線性熱通量相對差值為5.4%。
[Abstract]:With the rapid development of social economy, energy crisis and environmental pollution have posed a serious threat to human needs and health.In order to respond to the policy of energy conservation and environmental protection, it is urgent to develop energy saving technology and seek new energy.As a kind of renewable energy technology, ground source heat pump technology plays an efficient role in reducing building energy consumption and energy pollution.In order to promote the development of ground source heat pump (GSHP) technology, the heat transfer between ground heat exchanger and shallow rock has become the focus of research.Based on the idea of finite element, combined with the theory of porous media and hydrodynamics, this paper adopts Fortran language tool, aiming at the heat transfer problem of ground buried pipe of ground source heat pump, on the basis of equivalent straight square tube.The U-type buried pipe is equivalent to the U-shaped square tube in real sense. The soil cold storage model considering the solid-liquid phase transition process and the coupled heat transfer model inside and outside the tube of the buried tube heat exchanger are established, and a three-dimensional dynamic numerical calculation program is developed.In the process of soil cold storage and winter heat recovery in cold regions with ground buried tube heat exchanger, the groundwater in the soil around the ground buried tube heat exchanger may be frozen.In order to describe the heat transfer performance of buried pipes, the evaluation index of linear heat flux is introduced, and the effect of the solid-liquid phase transition process of groundwater on the heat transfer performance is analyzed.On the basis of turbulent calculation in pipe, the effects of different groundwater seepage velocity, inlet velocity of different buried pipe, inlet temperature of different buried pipe, different backfill material and different buried pipe material on heat transfer performance are analyzed.The results obtained by the program are as follows: (1) the seepage of soil groundwater is beneficial to the heat transfer of buried pipes, and the greater the seepage velocity, the stronger the heat transfer performance of the heat exchangers.For every 10 m / a increase in the flow velocity, the average linear heat flux increases by 0.06 / a) with the increase of the inlet velocity, the outlet temperature increases and the linear heat flux increases significantly, but there is an optimal inlet flow rate of 3) when the flow rate is constant, with the increase of the inlet water temperature,The temperature difference between the inlet and outlet of the buried pipe will increase, and the linear heat flux will increase. The higher the thermal conductivity of the backfill material is, the better the heat transfer effect will be, and the thermal conductivity of the backfill material should be close to that of the soil.When the thermal conductivity of the soil is lower than that of the soil,The increase of heat conductivity per unit backfill material corresponds to an average increase in linear heat flux of 18.74 W / m, an increase of 15.3W / m) the adoption of HDPE tubes and PE tubes with better thermal conductivity will contribute to the improvement of heat transfer performance of buried tube heat exchangers, such as the heat transfer performance of buried tube heat exchangers, and the solid liquid phase of soil during cold storage.The change process is helpful to the heat transfer of the ground buried tube heat exchanger.The exit temperature will fluctuate after the phase change, and the relative difference of the linear heat flux of the soil with or without phase transition is 5.4.
【學(xué)位授予單位】：長安大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TU83

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