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蒸发器设计计算已知条件:工质为R22,制冷量kW3,蒸发温度Ct70,进口空气的干球温度为Cta211,湿球温度为Ctb5.151,相对湿度为34.56%;出口空气的干球温度为Cta132,湿球温度为Ctb1.112,相对湿度为80%;当地大气压力PaPb101325。(1)蒸发器结构参数选择选用mmmm7.010紫铜管,翅片厚度mmf2.0的铝套片,肋片间距mmsf5.2,管排方式采用正三角排列,垂直于气流方向管间距mms251,沿气流方向的管排数4Ln,迎面风速取smwf/3。(2)计算几何参数翅片为平直套片,考虑套片后的管外径为mmddfob4.102.02102沿气流方向的管间距为mmss65.21866.02530cos12沿气流方向套片的长度为mmsL6.8665.21442设计结果为mmsL95.892565.2132532每米管长翅片表面积:fbfsdssa1000422215.210004.10414.365.212522mm23651.0每米管长翅片间管子表面积:fffbbssda)(5.210002.05.24.1014.3mm203.0每米管长总外表面积:mmaaabfof23951.003.03651.0每米管长管内面积:mmdaii2027.0)20007.001.0(14.3每米管长的外表面积:mmdabb2003267.00104.014.3肋化系数:63.14027.03951.0iofaa每米管长平均直径的表面积:mmdamm202983.020086.00104.014.3(3)计算空气侧的干表面传热系数①空气的物性空气的平均温度为Ctttaaf1721321221空气在下C17的物性参数3215.1mkgfKkgkJcpf1005704.0rfPsmvf61048.14②最窄截面处空气流速smsssswwfffdfb58.52.05.25.24.102525311max③干表面传热系数干表面传热系数用小型制冷装置设计指导式(4-8)计算15.04.00max42618.00014.0booffaavdw15.04.0603267.03951.01048.140104.058.52168.00014.000792.0kmWPcwrpff23232max402.68704.0100558.5215.100792.0(4)确定空气在蒸发器内的变化过程根据给定的进出口温度由湿空气的焓湿图可得kggdkggdkgkJhkgkJh443.7,723.8,924.31,364.432121。在空气的焓湿图上连接空气的进出口状态点1和点2,并延长与饱和气线0.1相交于点w,该点的参数是CtkggdkgkJh8,6.6,25。在蒸发器中空气的平均比焓值kgkJnhhhhnhhhh由焓湿图查得kggdCtmm8,2.16析湿系数42.182.166.6846.2146.21wmwmttdd(5)循环空气量的计算hkghhQqdam06.944924.31364.4336003210,进口状态下干空气的比体积baPdTRv1110016.01101325723.80016.012115.2734.287kgm3846.0循环空气的体积流量hmvqqdamav/67.798846.006.94431,,(6)空气侧当量表面传热系数的计算bfbffjaaaa0对于正三角形排列的平直套片管束,翅片效率f小型制冷装置设计指导式(4-13)计算,叉排时翅片可视为六角形,且此时翅片的长对边距离和短对边距离之比4.24.1025dB,1bm且BA3.027.1BAm3.014.227.155.2肋折合高度为mmdhb7.1055.2ln35.01155.224.10ln35.0112mmff106.643102.023642.12.68220凝露工况下翅片效率为8683.0107.1006.64107.1006.64)(33thhmhmthf当量表面传热系数bfbffjaaaa03951.003.0365.08683.02.6842.1)/(06.852KmW(7)管内R22蒸发时的表面传热系数R22在Ct70时的物性参数为:饱和液体密度33.1257mkgl饱和蒸气密度343.26mkgg液体粘度sPal6102.202气体粘度sPag610815.11汽化热kgkJ56.1990液体热导率KmWl/102.133蒸气热导率KmWg/1093.93液体普朗特数62.2rlP蒸气普朗特数92.0rgPR22在管内蒸发的表面传热系数由小型制冷装置设计与指导式(4-5)计算。计算查的R22进入蒸发器时的干度25.01x,出口干度0.12x。则R22的总质量流量为hkgxxQqm16.7225.0156.1993600336001200作为迭代计算的初值,取27200mWqi,R22在管内的质量流速smkggi2'160。则总流通面积为24'1025.1360016016.723600mqqAim每根管子的有效流通截面积2522108.540086.014.34mdAii蒸发器的分路数16.2108.51025.154iAAZ结合分液器的实际产品现状,取分路数为Z=2每一分路中R22的质量流量为hkgZqgmm08.36216.72每一分路中R22在管内的实际质量流速为smkgAggimi258.172108.5360008.363600于是40101.256.1998.1722.7rgqBii09634.03.125743.26625.0625.0115.08.05.08.00lgxxC224.00086.08.93.12578.1722222ilirlgdgF08.2756102.2020086.0625.018.1721Re6lildxigilrllldP4.08.0Re023.00086.00932.062.208.2756023.04.08.011.207flccrlcliFBCFCC4520301252.2101.22.667224.02509634.0136.111.2077.043.09.0KmW235.4050(8)传热温差的初步计算Cttttttaaaam44.9713721ln1321ln020121(9)传热系数的计算管内污垢热阻ir可以忽略,接触热阻以及导热热阻之和取为KmWr200048.0KmWraakjiiof2006.4906.8510048.0027.035.40503951.0111(10)核算假设的iq值202.46844.96.49mWkqmo268512.468027.03951.0mWqaaqoiofi计算表明,假设的27200mWqi初值与核算的值26851mW较接近,故假设有效,可用。(11)蒸发器结构尺寸的确定蒸发器所需的表面传热面积20'417.072003000mqQAii20'0408.62.4683000mqQAo蒸发器所需传热管总长maAloft21.163951.0408.6'0'迎风面积2,074.03600367.798mwqAfavf取蒸发器的宽度mmB350,高mmH300。实际迎风面积为2105.03.035.0mAf。已选定垂直于气流方向的管间距为mms251,故垂直于气流方向的每排管子数为122530011sHn深度方向为4排,共布置48根传热管,故传热管的实际总长为mlt8.164835.0传热管的实际内表面传热面积为2454.042.00086.014.34835.048mdAii09.1417.0454.0'iiAA04.121.168.16'ttll下面计算蒸发器的实际外表面积48根m35.0长的管其翅片间管子表面积2505.00002.05.235035.00104.014.348m管子左右两边都要伸出一定距离,分别取为mm10,mm3;U型管需要用弯头相接,取弯头半径为mmR5.12。由于管径很小,伸出部分换热可以忽略不计。每一翅片(宽mm5.312,深约为mm90)总的外表面积220487.0401.014.34809.03125.02m总翅片数为1405.2350再加1为141片翅片的总外表面积2867.60487.0141m套片管的总外表面积2372.7505.0867.6m根据“计算单元”计算的总外表面积只有2638.68.163951.0mlftt二者有一定差距,但是在误差范围之内。综上分析设计,可以定出翅片结构参数如下:高度为mm5.312,深度为mm95.8925365.21,宽度为mm390220350。(12)空气侧阻力计算空气侧阻力计算根据小型制冷装置设计与指导式(4-10和4-12)进行。首先计算tp1.21000102510001014.31000102510000,dAAtcttf由小型制冷装置设计与指导图(4-21)确定,6.38531048.1401.058.5Re60maxfdvdw155.165.2125210201ssdsdsPPLT1x5.2102501dsPT由TP及dRe查得4.0tzf,于是762.01.2144.0,ttctztAANff318.101521.0Re508.0dsfdf318.1521.01025)6.3853(508.0023.0PawAAfpftcttf5.20215.1258.51.2762.022max2,fcfftwAAfp2max2258.5215.1101682.05.24.10253651.0023.026Pa07.19所以Pappptf57.3907.195.20由7.042.111可以查表得修正系数18.1Pappw7.4618.157.39
本文标题:蒸发器计算说明
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