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 Wysłany: Czw 1:09, 25 Lis 2010 Temat postu: ghd stijltang Objective function on the heat trans |
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On the heat transfer system of objective function
The conditions required by the objective function, you can get optimal parameters. Case Study 3 to set up a countercurrent shell and tube heat exchanger, heat transfer to 604kW. Shell condensate heating medium is saturated, inlet temperature,[link widoczny dla zalogowanych], th1 = 158.8oC, outlet temperature tll2 = 70oC; tube side refrigerant is too cold water inlet temperature t: 60 ℃, the outlet temperature tc2 = 85oC. Assumed that the heat exchanger shell side 5l2 ・ ELECTRICAL ENGINEERING constant conditions day laborers in 2004, the heat transfer coefficient h0 = 4000W / (m2 ・ K), △ ph = 5kPa; tubes for the 25 × 20 stainless steel pipe,: 50.242W / (m ・ K); bilateral fouling resistance R. = 0.00034m2 ・ ~ C / W. Under these conditions, the heat exchanger tube side flow rate is optimized, so that the total cost of heat transfer system the minimum loss function value. In this case, due to hot and cold medium temperature constant, so the temperature does not vary with the available energy cost for tube side flow rate changes. However, with the tube side flow rate increases,[link widoczny dla zalogowanych], on the one hand can lead to loss of pressure can be increased costs, on the other hand will lead to reduced costs of heat exchanger material consumption. Therefore, there must be an optimum flow rate control process, making the heat transfer system, the value of the total cost of the minimum loss function. According to fluid mechanics, heat transfer and heat exchanger principle of the theory, after the deduction and finishing, the total cost function can be expressed as a function of tube side flow rate: P = P + () + PA (.) = 2T × To × lm. c. In (r2 / T. 1) + CphIn (Th2/Th1)] +. × 71o × {C7 × [(Cl'8 + C2) × C3 × C4 × 32 + Cl plus: 2 + c6J + H} + A × (Clw2 '+ C2) × C3 (16) where: C11 = 0 .000159; c2 = ln (post) + R1 (di) _0.0005844; ... 198; c3___ b __ = _498; c:. c: 650.7; 4 - ') dC5 = 2p ・ df = 2343.4; C6 = △ pN: 732.3 (at heat exchanger inlet flow rate of 1.0m / s calculation); C7:: 0.00001645 ; ・; = gm Korea hAPh = 0.2l2; A = 0.24 × 10 A (Y / (m2 ・ s)); p = 2.64 × 10 ~ (Y / (W ・ s));: 0 .44 × 10I7 (Y / (W.s)) by (16), the total cost of the function P can be obtained with the tube side flow rate curve (see Figure 1). It can be seen from Figure 1,[link widoczny dla zalogowanych], P minimum of about 0.002556Y / s, corresponding to the tube side flow rate of about 1.15m / s, the flow rate is the optimal heat exchanger tube side flow rate. O. 0026lO. 0l】 26O. 0o259i0.00258O. 00257O. 0o256O. 0o2554 Conclusion ◆ | A \ 1_. . . OO. 511.52wc / m. B-i Figure 1P-w curve (1) affect the heat transfer system through the loss of available energy cost analysis of various factors, considering the heat exchanger material consumption costs,[link widoczny dla zalogowanych], is proposed based on the second law of thermodynamics for thermal system optimization objective function. (2) the use of engineering thermodynamics, fluid mechanics and heat of the knowledge economy the objective function was derived, has been the objective function formula. References: [1] History of the United States, Wang Zhongzheng. Principle and design of heat exchanger [M]. Nanjing: Southeast University Press,[link widoczny dla zalogowanych], 1995. [2] BKIANA. Generalcriterionforratingheat ・ exchangerperformance [Jj. IntJheatMass B ,1978,21:655-658. [3] Ni Zhenwei. Heat exchanger thermal performance evaluation of the three indicators [J]. Engineering Thermophysics, 1984,5 (4) :387-389. [4] Ping-Jing Yao, Rong Zheng Xuan. System Simulation and Optimization of heat transfer and synthesis of [M]. Beijing: Chemical Industry Press, 1991. [5] Shen Victoria Road, Zheng Peizhi. Engineering Thermodynamics [M]. Beijing: Higher Education Press, 1983. [6] Xu Wenzhong. Tube side heat transfer system flow optimization problem [D]. Jinan: Shandong University. 2004.
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