Biofouling Monitors for Noncylindrical OTEC Heat Exchanger Tubes

1982 ◽  
Vol 104 (3) ◽  
pp. 257-261
Author(s):  
T. M. Kuzay ◽  
C. B. Panchal ◽  
A. P. Gavin
Keyword(s):  
Heat Transfer ◽  
Heat Exchangers ◽  
Steel Tube ◽  
Stainless Steel Tube ◽  
Thermal Energy Conversion ◽  
Shell And Tube ◽  
Ocean Thermal Energy ◽  
Analytical Approaches

Heat-transfer monitors (HTMs) have been used since 1976 to measure the reduction in the seawater heat-transfer coefficient due to buildup of biofouling and corrosion products inside circular tubes of shell-and-tube heat exchangers being developed for ocean thermal energy conversion (OTEC) plants. For OTEC heat exchangers (HXs) with other tube geometries, special, modified HTMs, which we call STMs, are being sought. The analytical approaches and calibration results to date are summarized for STMs of two types: (i) an STM simulating a rectangular seawater passage in a compact, aluminum, plate-fin HX, and (ii) an STM for a helical stainless-steel tube. The development of type 1 has been successful. A software change is needed for type 2.

Performance of Parallel-Flow Gas-to-Gas Micro-Double-Tubes-Heat Exchangers

2009 ◽  
Author(s):  
Chungpyo Hong ◽  
Yutaka Asako ◽  
Koichi Suzuki
Keyword(s):  
Heat Transfer ◽  
Heat Exchangers ◽  
Circular Tube ◽  
Steel Tube ◽  
Parallel Flow ◽  
Bulk Temperature ◽  
Stainless Steel Tube ◽  
Cross Sectional ◽  
Partition Wall ◽  
Annular Tube

Heat transfer performance of two-stream parallel-flow gas-to-gas micro-double-tubes-heat exchangers was investigated numerically. The flow passages of the micro- double-tubes-heat exchanger are a circular tube for hot passage and a concentric annular tube for cold passage. A circular tube of r = 50 μm and a concentric annular tube of ri = 51 μm and ro = 71 μm with an identical cross-sectional area were chosen and the selected length was 20mm, respectively. Then, the partition wall is assumed to be a stainless steel tube with 1 μm in thickness. Numerical methodology is based on the arbitrary-Langrangian-Eulerian method. Computations were performed for wide flow range to find the effects of capacity ratio on the heat transfer characteristics of gas-to-gas micro-double-tubes-heat exchangers. The results are presented in form of temperature contours, bulk temperature, total temperatures and heat flux variation along the length. Also, the effectiveness and the number of transfer units approach and the estimation of the heat exchange rate were discussed.

Shell-and-Plate-Type Heat Exchangers for OTEC Plants

1984 ◽  
Vol 106 (3) ◽  
pp. 286-290 ◽  
Author(s):  
H. Uehara ◽  
H. Kusuda ◽  
M. Monde ◽  
T. Nakaoka ◽  
H. Sumitomo
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Heat Exchangers ◽  
Porous Plate ◽  
Working Fluid ◽  
Performance Tests ◽  
Overall Heat Transfer Coefficient ◽  
Thermal Energy Conversion ◽  
Ocean Thermal Energy ◽  
Plate Type

New titanium, shell-and-plate type heat exchangers for ocean-thermal-energy-conversion (OTEC) plants have been developed which include three different plate types (fluted, impinging, and porous-surface) for the evaporator and two kinds of plates (No. 1 and No. 2) for the condenser. Performance tests with fresh water show that the overall heat transfer coefficient U of the evaporator using the porous plate is the highest among the three plates; it can reach 4000–4500 W/m2K using ammonia as the working fluid and 3500–4000 W/m2K for a Freon, R-22. The U of the condenser using the No. 2 plate is higher than that using the No. 1 plate; it can reach 3800–4500 W/m2K for ammonia and 2000–3500 W/m2K for R-22.

Optimization of a Closed-Cycle OTEC System

1990 ◽  
Vol 112 (4) ◽  
pp. 247-256 ◽  
Author(s):  
Haruo Uehara ◽  
Yasuyuki Ikegami
Keyword(s):  
Heat Exchangers ◽  
Sea Water ◽  
Working Fluid ◽  
Turbine Efficiency ◽  
Thermal Energy Conversion ◽  
Calculation Results ◽  
Change Temperature ◽  
Ocean Thermal Energy ◽  
Powell Method ◽  
Method Of Steepest Descent

Optimization of an Ocean Thermal Energy Conversion (OTEC) system is carried out by the Powell Method (the method of steepest descent). The parameters in the objective function consist of the velocities of cold sea water and warm sea water passing through the heat exchangers, the phase change temperature, and turbine configuration (specific speed, specific diameter, ratio of blade to diameter). Numerical results are shown for a 100-MW OTEC plant with plate-type heat exchangers using ammonia as working fluid, and are compared with calculation results for the case when the turbine efficiency is fixed.

The Effect of Baffles in Shell and Tube Heat Exchangers

2009 ◽  
Vol 62-64 ◽  
pp. 694-699 ◽  
Author(s):  
E. Akpabio ◽  
I.O. Oboh ◽  
E.O. Aluyor
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Exchangers ◽  
Proper Position ◽  
Process Industries ◽  
Overall Heat Transfer Coefficient ◽  
Shell And Tube ◽  
Optimal Values ◽  
Side Flow

Shell and tube heat exchangers in their various construction modifications are probably the most widespread and commonly used basic heat exchanger configuration in the process industries. There are many modifications of the basic configuration which can be used to solve special problems. Baffles serve two functions: Most importantly, they support the tubes in the proper position during assembly and operation and prevent vibration of the tubes caused by flow-induced eddies, and secondly, they guide the shell-side flow back and forth across the tube field, increasing the velocity and the heat transfer coefficient. The objective of this paper is to find the baffle spacing at fixed baffle cut that will give us the optimal values for the overall heat transfer coefficient. To do this Microsoft Excel 2003 package was employed. The results obtained from previous studies showed that to obtain optimal values for the overall heat transfer coefficient for the shell and tube heat exchangers a baffle cut of 20 to 25 percent of the diameter is common and the maximum spacing depends on how much support the tubes need. This was used to validate the results obtained from this study.

Thermal Effectiveness of Multiple Shell and Tube Pass TEMA E Heat Exchangers

1988 ◽  
Vol 110 (1) ◽  
pp. 54-59 ◽  
Author(s):  
A. Pignotti ◽  
P. I. Tamborenea
Keyword(s):  
Heat Transfer ◽  
Heat Capacity ◽  
Heat Transfer Coefficient ◽  
Heat Exchangers ◽  
Rate Ratio ◽  
Algebraic Solution ◽  
Tube Heat Exchanger ◽  
Transverse Mixing ◽  
Shell And Tube ◽  
The Heat Transfer Coefficient

The thermal effectiveness of a TEMA E shell-and-tube heat exchanger, with one shell pass and an arbitrary number of tube passes, is determined under the usual symplifying assumptions of perfect transverse mixing of the shell fluid, no phase change, and temperature independence of the heat capacity rates and the heat transfer coefficient. A purely algebraic solution is obtained for the effectiveness as a function of the heat capacity rate ratio and the number of heat transfer units. The case with M shell passes and N tube passes is easily expressed in terms of the single-shell-pass case.

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