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换热器的优化选型W. Lub 和 S.A. Tassoub英国米德尔塞克斯，布鲁内尔大学机械设计工程部【摘要】板式换热器的优化选型是根据换热器的用途和工艺过程中的参数和NTUKAMCttm，即传热单元数NTU和温差比（对数平均温差换热的动力）选择板片形状、板式换热器的类型和结构。 【关键词】平均温差 NTU 板式蒸发器 冷凝器 1 平均温差tm从公式QKtmA，tm1AA（t1t2）dA中可知，平均温差tm是传热的驱动力，对于各种流动形式，如能求出平均温差，即板面两侧流体间温差对面积的平均值，就能出换热器的传热量。平均温差是一个较为直观的概念，也是评价板式换热器性能的一项重要指标。1.1 对数平均温差的计算当换热器传热量为dQ，温度上升为dt时，则CdQdt，将C定义为热容量，它表示单位时间通过单位面积交换的热量，即dQK（thtc）dAKtdA，两种流体产生的温度变化分别为dthdQCh，dtcdQCc，dtd（thtc）dQ（1Cc1Ch）,则dA1k（1Cc1Ch）（dtt），当从A0积分至AA0时，A01k（1Cc1Ch）（thotci）（thitco），由于两种流体间交换的热量相等，即QCh（thitho）Cc（tcotci），经简化后可知，QKA0（thotci）（thitco）（thotci）（thitco），若t1thitco，t2thotci，则QKA0（t1t2）（t1t2）KA0tm，式中的tm（t1t2）（t1t2）。顺流 tm（thitci）（thotco） （thitci）（thotci）逆流 tm（thitco）（thotci） （thitco）（thotci）对于各种流动型式，在相同的进口、出口温度条件下，逆流的平均温差最大。当板式换热器入口和出口两流体的温差t1和t2之间的差不大时，可采用算术平均温差（t1t2）2，一般t1t2小于1.5时，可采用，若tt2为3时，则误差约为10%。1.2 传热单元数法在传热单元数法中引入一个无量纲参数NTU，称为传热单元数，它表示板式换热器的总热导（即换热器传热热阻的倒数）与流体热容量的比值NTUKAMC，它表示相对于流体热容流量，该换热器传热能力的大小，即换热器的无量纲“传热能力”。对于板式换热器来说，KAMCttm，式中ttm称为温差比，上式中的右边的工艺过程用NTUp表示，左边的换热设备的条件用NTUE表示。NTUp是流体温度的变化与平均温差的比值，表示的是用1tm的变化引起几度流体温度变化的值，当tm大时，NTUp则小；当tm小时，它有变大的倾向。相反，在NTUp变大的过程中，tm的温度变化较大，NTUp较小时，其tm的温度变化较小（见表1）。表1 tm，NTUp的关系 tm大tm小NTUp小NTUp大NTUp大NTUp小tm的温度变化大tm的温度变化小板式换热器的优化设计计算，就是在已知温差比NTUE的条件下，合理地确定其型号、流程和传热面积，使NTUp等于NTUE。1.3 换热过程和NTU与供热空调相关的换热过程如下如示： 用蒸汽加热水 水水换热a. 蒸汽133133c. 一次水6560水565（生活热水） 二次水4540（采暖）b. 蒸汽133133d. 一次水149水5565（采暖）二次水137（制冷）e. 一次水2924二次水2621（制冷机的冷却）以上5例工艺过程的NTUp（见表2）表2 供热空调工艺过程的NTUp 过程tmNTUpa13313356594.86（655）94.860.632b133133556572.88（6555）72.880.13c6560454020.00（4540）200.25d1491371.44（137）1.444.17e292426213.00（2621）31.671.4 板式换热器和NTUENTUE表示板式换热器的能力，换热器的面积是具有一定传热长度的单位传热体的组合，总传热长度是单位长度和流程数的乘积。当NTUE是总数时，若每1流程数为NTUe时，则NTUEnNTUe（其中n是流程数）。当NTUeNTUENTUp时，换热器为单程。若NTUeNTUp时，则换热器应为多流程，故设计时应先预定n。由于每种板片单程的NTUe值基本上是定值，如适合表2中e的流量为25m3h的单程板式换热器的NTUe为17。从NTUeAKMC可知，当NTUe为定值时，AK成反比，仍以e为例，当K500kcalh时，A1.672500050083.5，流程数n83.5175。当K2500kcalh时，A16.7，流程数n1。每一流程的NTUe如下所示：K500，NTUeNTUEn0.33，K2500时，NTUe1.67。由此可知，根据NTUe即可求出换热器的流程数，传热系数和传热面积。从以上可知，若板式换热器设计不合理，可能使换热面积过大，也可能使板间流速太高，阻力过大。1.5 板式换热器制造技术的进步，板片种类的增加，提高了板式换热器对各种工艺过程的适应性。 大NTU（8），小tm（12）的板式换热器满足了区域供冷和热泵机组蒸发器、冷凝器的要求。从以上分析可知，tm是换热的驱动力，若tm小，即意味着驱动力小，要实现两种流体之间的换热，必须增大传热系数，增大传热面积，为了使传热面积不至过大，唯一的是增大传热系数K。 浅密波纹板片是北京市京海换热设备制造有限责任公司开发的新型板片，它的传热系数约为7000WK，是水平平直波纹板的2倍，是人字形波纹板的1.5倍，在区域供冷中时，检测的tm约为1.2。在作为冰蓄冷的乙二醇和冷冻水的换热器使用中，tm约为1.5。 板式蒸发器、板式冷凝器也是北京市京海换热设备制造有限责任公司开发的适应于热泵机组的新型换热器。与管壳式蒸发器、冷凝器相比，它具有如下优点：单位体积内板式蒸发器、板式冷凝器的传热面积约是管壳式换热器的3倍；板式蒸发器的传热系数约为10001200 WK，板式冷凝器的传热系数约为15002000 WK均为管壳式换热器的23倍；在板式蒸发器上采用了使制冷剂液体分布均匀的分配器装置，当蒸发器板片数较多时，可能会出现制冷剂液体分配不均的，不能充分利用所有蒸发传热面积，使蒸发温度低于设计计算温度。采用分配器后即能克服上述问题。有关单位检测数据说明，板式蒸发器、板式冷凝器的传热系数在tm约为2.53时，在15002000 WK之间，且阻力小，满足了热泵机组的要求。 小NTU（0.32），大tm（4090）的板式换热器满足了热回收工艺和工艺加热、冷却的要求。当工艺过程在大tm的条件下进行换热时，说明驱动力大，所需的传热面积较小，对传热系数要求也不高，但，这种工艺过程或者工作压力高，或者工作温度高，或者工艺加热、冷却过程的液体中含有纤维或直径较大的颗粒，对板式换热器的承压、耐温能力提出了要求，对换热器的板间距提出了要求。 排（烟）气水板壳式换热器（省能器），排（烟）气空气板壳式换热器（空气预热器）是北京市京海换热设备制造有限责任公司和兰石化共同开发出来的新型板式换热器，全焊接板式换热器中介质的换热是通过板管束来实现的，组成板管束的板片由专用模具压制成型，全焊接式板束装在压力壳内。波纹板片具有静搅拌作用，能在很低的雷诺数下形成湍流，且污垢系数低，传热系数是管壳式换热器的23倍。为了适应换热量大，流体压降小的要求，板间距大，当量直径约为28。为了满足工艺的要求板束工作压力（反压）P4.5Mpa，板束工作压力（正压）同壳体工作压力，不受限制；工作温度t550。乌鲁木齐石化分公司40万吨年连续重整采用了进料（冷介质）和出料（热介质）的板壳式换热器，进料流量50th，进、出口温渡88，470。出料流量50th，进、出口温度100，500，对数平均温差约38，总传热系数约为380kcalh，热负荷达23106kcalh，进料压降20Kpa，出料压降50Kpa。 多效蒸发板式加热器（换热器），这种换热器既是工艺加热装置，又是重要的热回收装置。以前由于板式换热器的流道小（板间距1.55.0），不适宜于气气换热和蒸气冷凝；且易堵塞，故不宜用于含悬浮物的流体。为了尽量地发挥板式换热器的长处，克服存在问题，适应工艺的要求，北京市京海换热设备制造有限责任公司开发出了新型的多效蒸发板式换热器，这种板式换热器属宽流道型，其板间距为8.0，适合于蒸气冷凝，适合于含悬浮物的流体，且不易堵塞，最大处理量达1200m3h。New plate heat exchanger optimization SelectionW. Lub and S.A. Tassoub Department of Mechanical Engineering, School of Engineering and Design, Brunel University, Uxbridge, Middlesex, UK .Abstract: The plate heat exchanger Selection is based on the optimization of the use of heat exchangers and in the process of the parameters and NTU = KA / MC = t / tm, that is, transfer units of NTU and the temperature difference than (the average temperature difference - Heat transfer in power) choose plate shapes, plate heat exchanger and the type of structure. Key words: the average temperature difference between NTU plate evaporator condenser1 average temperature difference tm When the heat exchanger to heat-dQ, when the temperature rose to dt, C = dQ / dt, C will be defined as heat capacity, it said units of time through the exchange of heat per unit area, dQ = K (th-tc) dA = K tdA, two of the fluid temperature changes were dth =- dQ / Ch, dtc =- dQ / Cc, d t = d (th-tc) = dQ (1/Cc-1/Ch), while dA = 1 / k (1/Cc-1/Ch) (d t / t), when the A = 0 points to A = A0 when, A0 = 1 / k (1/Cc-1 / Ch) (tho-tci) / (thi-tco), because of two fluid exchange between the heat equivalent, that is, Q = Ch (thi-tho) = Cc (tco-tci), the simplified Know, Q = KA0 (tho-tci) - (thi-tco) / (tho-tci) / (thi-tco), if t1 = thi-tco, t2 = tho-tci , Q = KA0 ( t1- t2) / ( t1 / t2) = KA0 tm, in- tm = ( t1- t2) / ( t1 / t2) .Down tm = (thi-tci) - (tho-tco) / (thi-tci) / (tho-tci)Countercurrent tm = (thi-tco) - (tho-tci) / (thi-tco) / (tho-tci)For various flow patterns in the same import, export under the conditions of temperature, the average temperature difference between the largest counter-current.When the plate heat exchanger import and export of the fluid temperature difference between the two t1 and the difference between t2 not available when arithmetic average temperature ( t1 + t2) / 2, General t1 / t2 less than 1.5, May be, if t / t2 for 3:00, the error is about 10 percent.1.2 the number of transfer unitsIn the heat transfer unit of the introduction of a few dimensionless parameters NTU, known as the number of transfer units, it said plate heat exchanger of the total thermal conductivity (heat exchanger heat resistance of the countdown) and the ratio of fluid heat capacity NTU = KA / MC, it said in relation to heat fluid flow, heat transfer capacity of the heat exchanger of the size of the heat exchanger that is, non-dimensional heat transfer capability. The plate heat exchanger for, KA / MC = t / tm, where t / tm known as the temperature difference than, on the right side of the process used NTUp that left the conditions of heat transfer equipment used NTUE said. NTUp is fluid temperature changes in temperature and the average ratio that is used 1 tm of several changes in the value of fluid temperature changes, when tm large, NTUp is small when tm hours, it has become bigger The tendency. On the contrary, in NTUp larger in the process, tm of the larger temperature changes, NTUp smaller, its tm small changes in temperature (see table 1).Table 1 tm, NTUp relations tm largetm smallNTUp smallNTUp largeNTUp largeNTUp smalltm large changes in temperaturetm small changes in temperaturePlate heat exchanger, the optimal design, is known NTUE temperature difference than the conditions, to determine a reasonable model, processes and heat transfer area, equivalent to NTUp NTUE.1.3 heat transfer process and the NTUHeating and air-conditioning related to the heat transfer process if the show are as follows: steam heating water water - water heat exchangera. steam 133 133 c. a water 65 60 Water 5 65 (hot water) Secondary water 45 40 (heating)b. Steam 133 133 d. a water 14 9 Water 55 65 (heating) secondary water 13 7 (refrigeration)e. a water 29 24 Secondary water 26 21 (refrigerator cooling)More than five cases of the process NTUp (see table 2)Table 2 heating air-conditioning process of NTUp processtm NTUpa13313356594.86（655）94.860.632b133133556572.88（6555）72.880.13c6560454020.00（4540）200.25d1491371.44（137）1.444.17e292426213.00（2621）31.671.4 plate heat exchanger and NTUENTUE plate heat exchanger that the capacity of heat exchanger is the size of a certain length of the heat and the combination of heat transfer units, the total length of heat transfer process is the length and number of units of the product. When the total number of NTUE is, if the number of processes for every 1 NTUe, then NTUE = n NTUe (where n is the number of processes).When NTUe = NTUE = NTUp, the heat exchanger for one-way. If NTUe NTUp, the heat exchanger for many processes, it should be designed to target n. As each plate of one-way NTUe value is essentially fixed value, such as in e Table 2 for the flow of 25 m3 / h of the one-way NTUe plate heat exchanger for 17 square meters. From NTUe = A K / MC tells us that when NTUe to be on duty, A K is inversely proportional, still e example, when K = 500kcal / h time, A = 1.67 25000/500 = 83.5 , the process of n = 83.5/17 5. When K = 2500kcal / h time, A = 16.7 square meters, the flow of n = 1. Each process NTUe as follows: K = 500, NTUe = NTUE / n = 0.33, K = 2500 when, NTUe = 1.67. So, can be obtained under NTUe the flow of heat exchangers, heat transfer coefficient and heat transfer area. From the above we can see that if the plate heat exchanger design unreasonable and likely to heat transfer area is too large, may also be partitioned so that flow is too high, too much resistance.1.5 plate heat exchanger manufacturing and technological progress, plate type of increase, raising the plate heat exchanger of the various processes of adaptation. the NTU ( 8), small tm ( 1 2) the plate heat exchanger to meet the district cooling and heat pump units evaporator, condenser requirements. From the above analysis know, tm is the driving force of heat transfer, if tm small, means that the driver of small, to achieve the heat transfer between the two fluid, we must increase heat transfer coefficient, increasing heat transfer area, in order to Heat to make up too large, is the only increase heat transfer coefficient K. shallow plate of corrugated Beijing, Beijing is the heat transfer equipment manufacturers limited liability company developed a new type of plate, the heat transfer coefficient of about 7000 W / K, is the level of the flat corrugated board two times, is chevron Corrugated sheets of 1.5 times, in the regional cooling, the detection of tm is about 1.2. As in ice storage of ethylene glycol and chilled water use in the heat exchanger, tm is about 1.5. plate evaporator, condenser plate Beijing, Beijing is also the heat transfer equipment manufacturers limited liability companies adapt to the development of a new type of heat pump units in the heat exchanger. And the shell-and-evaporator, compared to the condenser, which has the following advantages: unit volume in the evaporator plate, the plate condenser is a heat transfer area of shell and tube heat exchanger of three times the plate evaporator heat transfer coefficient About 1000 1200 W / K, the condenser plate heat transfer coefficient of about 1500 2000 W / K are shell heat exchanger two to three times the plate on the evaporator used to Refrigerant distributor of liquid evenly distributed devices, when the evaporator plate a few more, may be uneven distribution of liquid refrigerant and can not take full advantage of all the heat and evaporation area, evaporation temperature lower than the calculated design temperature. After a distributor overcome these problems. Detection of data on the relevant units, evaporator plate, the plate condenser in the heat transfer coefficient tm about 2.5 3 , in 1500 2000 W / K between the resistance and small, satisfying the heat pump units Requirements. small NTU ( 0.3 2), the tm ( 40 90 ) of the plate heat exchanger to meet the heat recovery process and the process heating and cooling requirements. When the process in the tm conducted under conditions of heat transfer, that driving force, the heat and the smaller, the heat transfer coefficient demand is not high, but that this process or high-pressure work, or work High temperature, or process heating and cooling process in the liquid containing fiber diameter or larger particles, the plate heat exchanger, the pressure, temperature and ability to request, the heat exchanger to the plate spacing requirements. Pai (breathing) gas - water shell heat exchanger (Province can), Pai (breathing) gas - shell-air heat exchangers (air preheater) is a heat exchanger in Beijing Beijing-equipment manufacturers limited liability Portland petrochemical companies and co-developed a new type of plate heat exchanger, all welded plate heat exchanger in the heat transfer through the medium to achieve the control board, composed of board control by the plate for forming mold suppression, all-welded - Beam installed in the pressure shell. Corrugated plate with static mixing, in a very low Reynolds number formed under the turbulence, and low coefficient of dirt, the heat transfer coefficient is the shell and tube heat exchanger of the two or three times. In order to adapt to the heat transfer, fluid pressure on the request, board space, equivalent diameter of about 28 mm. In order to meet the demands of work pressure plate beam (Anti-pressure) P 4.5 Mpa, the pressure plate beam (pressure) with the pressure shell, unrestricted; temperature t 550 . Urumqi Petrochemical Company 400,000 tons / year for a restructuring of the feed (cold medium) and discharging (medium heat) of the plate heat exchanger, feed flow 50 t / h, import and export temperature crossing 88 , 470 . Expected to flow 50 t / h, import and export temperature 100 , 500 , the average temperature of about 38 , the heat transfer coefficient of about 380 kcal / h , thermal negative Heda 23 106kcal / h, feed Pressure Drop 20 Kpa, the expected pressure drop 50 Kpa. multi-effect evaporation plate heater (heat exchanger), which is a heat exchanger of heating device, it is important to heat recovery unit. As previously plate heat exchanger, the flow of small (1.5 to 5.0-mm pitch), not in the gas - gas and steam condensing heat exchanger, and easy to plug, it is not appropriate for the suspension of containing the fluid. In order to maximize plate heat exchanger to play the strengths to overcome the existing problems and adapt to the demands of Beijing-Beijing heat transfer equipment manufacturers limited liability company developed a new type of multi-effect evaporation plate heat exchanger, this plate heat exchanger A wide-flow, the board spacing of 8.0 mm, suitable for steam condensate, suitable for containing the suspension of fluid, and difficult to plug, the largest handling capacity of 1200 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