【正文】 36。 （2）小NTU（∽～2），大△tm（∽40～90℃）的板式換熱器滿足了熱回收工藝和工藝加熱、冷卻的要求。 （1）大NTU（∽8），小△tm（∽1～2）的板式換熱器滿足了區(qū)域供冷和熱泵機組蒸發(fā)器、冷凝器的要求。從以上可知，若板式換熱器設計不合理，可能使換熱面積過大，也可能使板間流速太高，阻力過大。每一流程的NTUe如下所示：K＝500，NTUe＝NTUE／n＝，K＝2500時，NTUe＝。h℃時，A＝25000／500＝㎡，流程數(shù)n＝／17≈5。K成反比，仍以e為例，當K＝500kcal／㎡從NTUe＝A若NTUe﹤NTUp時，則換熱器應為多流程，故設計時應先預定n。NTUe（其中n是流程數(shù)）。 表1 △tm，NTUp的關系 △tm大 △tm小 NTUp小NTUp大NTUp大NTUp小△tm的溫度變化大△tm的溫度變化小 換熱過程和NTU 與供熱空調相關的換熱過程如下如示： ⑴用蒸汽加熱水 ⑵水—水換熱 a. 蒸汽 133→133℃ c. 一次水 65→60℃ 水 5→65℃（生活熱水） 二次水 45←40℃（采暖） b. 蒸汽 133→133℃ d. 一次水 14→9℃ 水 55→65℃（采暖） 二次水 13←7℃（制冷） e. 一次水 29→24℃ 二次水 26←21℃（制冷機的冷卻） 以上5例工藝過程的NTUp（見表2） 表2 供熱空調工藝過程的NTUp 過程△tmNTUp a 133→133℃ 5→65℃（65－5）／＝b133→133℃ 55→65℃ （65－55）／＝ c 65→60℃ 45←40℃ （45－40）／20＝d14←9℃ 13←7℃ （13－7）／=e29→24℃ 26←21℃ （26－21）／3＝ 板式換熱器和NTUE NTUE表示板式換熱器的能力，換熱器的面積是具有一定傳熱長度的單位傳熱體的組合，總傳熱長度是單位長度和流程數(shù)的乘積。相反，在NTUp變大的過程中，△tm的溫度變化較大，NTUp較小時，其△tm的溫度變化較?。ㄒ姳?）。對于板式換熱器來說，KA／MC＝△t／△tm，式中△t／△tm稱為溫差比，上式中的右邊的工藝過程用NTUp表示，左邊的換熱設備的條件用NTUE表示。平均溫差是一個較為直觀的概念，也是評價板式換熱器性能的一項重要指標。 主要參考文獻[1]賈紹義,[M]..[2]王志魁,劉麗英，[M]..[3][M]..[4]國家醫(yī)藥管理局上海醫(yī)藥設計院編[M]..[5][M]..[6]中華人民共和國國家標準GB 1511999《鋼制管殼式換熱器》.[7]中華人民共和國國家標準GB 1502011《壓力容器》.[8]JB/T47362002《補強圈標準》.[9]HG/T 2059220635 2009《鋼制管法蘭、墊片和緊固件》.[10]根據(jù)GB 7132008《鍋爐和壓力容器用鋼板》和GB 3531《低溫壓力容器用低合金鋼板》. New plate heat exchanger optimization Selection W. Lub and . 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 mean temperature difference △tm From the formula Q = K△tmA, △TM = 1 / A ∫ A (T1 T2) dA knowable, mean temperature difference △ TM is the driving force for heat transfer, flow form, such as to calculate the average temperature, the surface temperature difference between the fluid on both sides of the average area value, can heat exchange heat exchanger. The average temperature is a more intuitive concept, but also an important index to evaluate the performance of plate heat exchanger the number of transfer units In 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, nondimensional 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 bee 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). Plate 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.Table 1 △tm, NTUp relations △tm大 △tm小 NTUp小NTUp大NTUp大NTUp小△tm的溫度變化大△tm的溫度變化小 heat transfer process and the NTU Heating and airconditioning related to the heat transfer process if the show are as follows: ⑴steam heating water ⑵ water water heat exchanger a. 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 airconditioning process of NTUp 過程△tmNTUp a 133→133℃ 5→65℃（65－5）／＝b133→133℃ 55→65℃ （65－55）／＝ c 65→60℃ 45←40℃ （45－40）／20＝d14←9℃ 13←7℃ （13－7）／=e29→24℃ 26←21℃ （26－21）／3＝ plate heat exchanger and NTUE NTUE plate heat exchanger that the capacity of heat exchanger is the size of a certain length of the heat and the bination 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 th