本文選題：寬流道 + 板式換熱器　； 參考：《西安建筑科技大學》2015年碩士論文

【摘要】：隨著我國經(jīng)濟快速發(fā)展,對能源需求量逐年上升。傳統(tǒng)的燃煤鍋爐不僅不可避免的產(chǎn)生大量的煙塵,造成霧霾等空氣污染,并向大氣中排放大量溫室氣體,而且熱能級不匹配,煤是高品位能源,燃燒時溫度可達上千度,而建筑物供暖需求只需要維持18?C。二級出水屬于低品位能,環(huán)境友好,水量巨大,蘊含了巨大的能量,能夠滿足供暖需求。熱泵一般采用直接提取和間接提取二級出水熱量,而在直接提取過程中由于二級出水水質(zhì)復雜容易腐蝕熱泵機組,對機組長期運行不利;在間接提取中,目前運行的換熱器中普遍存在換熱系數(shù)不高、污垢生長過快或者運行費用偏高,沒有按照污垢生長的特點進行運行。污水廠出水雖然達到了二級出水排放標準,但是取水口水質(zhì)并非十分干凈,比如用水高峰期污水量超過污水廠處理能力,以及下雨天導致污水量猛增,污水廠將采取直接溢流排放的措施,在這些情況下排放水中大尺度雜物都會增加。為了使系統(tǒng)長期運行,保護熱泵機組,主要對間接式系統(tǒng)進行研究,對于二級出水這種污雜物水質(zhì)不穩(wěn)定的特點,對板式換熱器采用寬流道的結(jié)構(gòu)形式,可以有效防止阻塞情況的發(fā)生,并通過結(jié)構(gòu)優(yōu)化達到高傳熱的目的。首先,本課題對寬流道板式換熱器進行建模,使用計算流體軟件FLUENT進行模擬,采用平均努謝爾數(shù)的方法來衡量換熱效果,驗證了模擬結(jié)果的可靠性,采用雷諾數(shù)分離法擬合出相關傳熱準則方程和歐拉方程。其次,通過研究二級出水生物黏膜的組成和特性,對換熱器污垢生長影響因素進行分析,將生物膜污垢分為生長期和穩(wěn)定期。在生物膜增長期,由污垢積聚預測模型得出污垢熱阻生長的漸近型方程;在生物膜穩(wěn)定期,擬合了污垢厚度和流速的關系,以此可以求出相關流速下的污垢熱阻值。從板式換熱器的傳熱原理和熱力計算原理出發(fā),推導了換熱器面積計算、對數(shù)平均溫差、總傳熱系數(shù)以及流動阻力的計算公式,結(jié)合污垢熱阻漸近型方程,開發(fā)了二級出水換熱器設計軟件,該軟件能夠?qū)Q熱器污垢生長進行預測。最后,利用數(shù)值模擬對換熱器結(jié)構(gòu)進行優(yōu)化分析,綜合傳熱和流動特性27mm的流道間距比較好;運用三項指標對換熱器不同板間距受污垢的影響進行評價,結(jié)合污垢生長特點得出如下結(jié)論:二級出水側(cè)最佳運行流速為0.5~0.6m/s之間;通過變化蒸發(fā)器出水溫度,對比各項參數(shù)可知,當蒸發(fā)器出水溫度為8℃時,三項指標更好。
[Abstract]:With the rapid development of our economy, the energy demand is increasing year by year. Traditional coal-fired boilers not only inevitably produce a large amount of smoke and dust, resulting in air pollution such as haze, but also emit a large amount of greenhouse gases into the atmosphere, and the heat level is not matched. Coal is a high-grade energy source, and the temperature of combustion can reach thousands of degrees. Building heating needs only need to be maintained at 18 C. The secondary effluent belongs to low grade energy, environment friendly, huge water quantity, contains huge energy, can meet heating demand. Heat pump generally uses direct extraction and indirect extraction of secondary effluent heat, but in the process of direct extraction, because of the complex water quality of secondary effluent is easy to corrode the heat pump unit, it is unfavorable for the unit to run for a long time. At present, the heat transfer coefficient is not high, the fouling growth is too fast or the running cost is too high, so the heat exchanger does not run according to the characteristics of fouling growth. Although the effluent from the wastewater treatment plant has reached the secondary effluent discharge standard, the water quality at the water intake is not very clean. For example, the amount of sewage at the peak of water use exceeds the treatment capacity of the wastewater treatment plant, and the amount of sewage water increases sharply during rainy days. The plant will take direct overflow measures, in which large-scale debris will increase. In order to make the system run for a long time and protect the heat pump unit, the indirect system is mainly studied. It can effectively prevent congestion and achieve high heat transfer through structural optimization. First of all, the model of the plate heat exchanger with wide channel is modeled, and the simulation is carried out by using the computational fluid software FLUENT. The method of average Nuschel number is used to measure the heat transfer effect, and the reliability of the simulation results is verified. The related heat transfer criterion equation and Euler equation were fitted by Reynolds number separation method. Secondly, by studying the composition and characteristics of biological mucosa in secondary effluent, the factors affecting the fouling growth of heat exchanger were analyzed, and the biofilm fouling was divided into growth period and stable period. In the period of biofilm growth, the asymptotic equation of fouling thermal resistance growth is derived from the fouling accumulation prediction model, and the relationship between fouling thickness and flow velocity is fitted in the stable period of biofilm, and the fouling thermal resistance value under correlation velocity can be obtained. Based on the heat transfer principle and thermodynamic calculation principle of plate heat exchanger, the calculation formulas of heat exchanger area, logarithmic mean temperature difference, total heat transfer coefficient and flow resistance are derived, combined with the asymptotic equation of fouling thermal resistance. The design software of secondary effluent heat exchanger is developed, which can predict the fouling growth of heat exchanger. Finally, the structure of heat exchanger is optimized and analyzed by numerical simulation. The flow channel spacing of 27mm is better than that of heat transfer and flow characteristics, and the influence of fouling on different plate spacing of heat exchanger is evaluated by using three indexes. Combined with the characteristics of fouling growth, the following conclusions are drawn: the optimal operating velocity of the secondary effluent side is between 0.5~0.6m/s and the three indexes are better when the effluent temperature of the evaporator is 8 鈩，

本文編號：1891946