1、 英文文献 翻译 原文 New plate heat exchanger optimization Selection W. 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 exchang
2、ers 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 temperatur
3、e difference between NTU plate evaporator condenser 1 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, t
4、wo 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,
5、 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-tc
6、o) - (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
7、 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 units In the heat transfer unit of the introduction of a few dimensionless paramete
8、rs 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
9、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
10、 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 temperatu
11、re changes, NTUp smaller, its tm small changes in temperature (see table 1). Table 1 tm, NTUp relations tm large tm small NTUp small NTUp large NTUp large NTUp small tm large changes in temperature tm small changes in temperature Plate heat exchanger, the optimal design, is known NTUE temperature di
12、fference than the conditions, to determine a reasonable model, processes and heat transfer area, equivalent to NTUp NTUE. 1.3 heat transfer process and the NTU Heating and air-conditioning related to the heat transfer process if the show are as follows: steam heating water water - water heat exchang
13、er 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)
14、 Table 2 heating air-conditioning process of NTUp process tm NTUp a 133133 565 94.86 （ 65 5） 94.86 0.632 b 133133 5565 72.88 （ 65 55） 72.88 0.13 c 6560 4540 20.00 （ 45 40） 20 0.25 d 149 137 1.44 （ 13 7） 1.44 4.17 e 2924 2621 3.00 （ 26 21） 3 1.67 1.4 plate heat exchanger and NTUE NTUE plate heat exch
15、anger 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,
16、 then NTUE = n NTUe (where n is the number of processes). When NTUe = NTUE = NTUp, the heat exchanger for one-way. If NTUeNTUp, 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
17、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 =
18、 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
19、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
20、. 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
21、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
22、 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.
