Design Of Air-cooled Heat Exchangers Research Articles

Аerodynamic drag at small Reynolds numbers and the method of calculation of the air velocity in one- and many-row finned beams with an exhaust shaft

The periodic switching of fans at certain ambient air temperatures and a constant power is a promising method to enhance the energy operating efficiency of air-cooled heat exchangers. Equipping these heat exchangers with devices increasing the propulsion (for example, an exhaust shaft) facilitates the intensification of heat transfer due to strengthening the free movement of air by lifting forces. Meanwhile, the heat exchanger is used at the mixed convection regime. To make the thermal design of air-cooled heat exchangers with an exhaust shaft, we must have data on the aerodynamic drag of tube beams at small Reynolds numbers (Re < 1000) that permit to calculate the air flow velocity. However, at present, studies on the aerodynamic drag at mixed convection are virtually missing. Moreover, it is necessary to take into account the influence of external air flows on the gravitational pull created by the shaft since air-cooled heat exchangers are designed for outdoor use. Using the results of the experimental investigation, we obtained information about the mass-exchange processes in the finned beam and the exhaust shaft, developed a method for calculating the air velocity in one- and many-row finned beams with the exhaust shaft and determined their aerodynamic drag at small Reynolds numbers. We also established the influence of external air flows on the gravitational pull created by the shaft.

Experimental Study for Counter to Cross Flow Air-cooled Heat Exchangerof Annular Tube having Internal Circular grooving at Different pitches - A Review

The objective of this study is to provide modern analytical and empirical tools for evaluation of the thermal-flow performance or design of air-cooled heat exchangers (ACHE) and cooling towers. This review consist various factors which effect the performance of ACHE. We introduced systematically to the literature, theory, and practice relevant to the performance evaluation and design of industrial cooling. Its provide better understanding of the performance characteristics of a heat exchanger, effectiveness can be improved in different operating conditions .The total cost of cycle can be reduced by increasing the effectiveness of heat exchanger.

Impacts of geometric structures on thermo-flow performances of plate fin-tube bundles

Continuous plate fin-tube heat exchangers are commonly applied to natural draft dry cooling system in power plants due to their excellent thermo-flow performances, but the effects of geometrical structures on the air-side flow and heat transfer characteristics have not been thoroughly clarified yet. In this study, the air-side flow and heat transfer models of plate fin-tube bundles are developed, and the numerical modeling and methods are validated by the experimental test. The thermo-flow characteristics of the plate fin-tube bundles at various parameters of air face velocity, fin oblique angle, fin spacing, fin thickness and tube external diameter are numerically simulated. The buoyancy effect due to natural convection is also investigated. The results show that the performance evaluation criterion (PEC) varies little with the fin oblique angle. As the fin spacing increases, the average PEC will increase despite of a considerable heat transfer reduction. The increased fin thickness and tube external diameter are both beneficial to the thermo-flow characteristics, but the buoyancy effect on the flow and heat transfer performances can be neglected. The fin oblique angle of 30°, fin spacing of 10 mm, fin thickness of 0.3 mm and tube external diameter of 18 mm are recommended within the scope of investigation. The correlations between the Nusselt number, friction factor and the Reynolds number and geometrical parameters are recommended using the orthogonal experimental design method, which can be used to the optimal design of air-cooled heat exchanger in power plants.

Dimensional characteristics of wind effects on the performance of indirect dry cooling system with vertically arranged heat exchanger bundles

Ambient winds play a crucial role in the operation of indirect dry cooling system in power plants, so it is of use to study the wind effects on the thermo-hydraulic performances of various cooling deltas and sectors in the air-cooled heat exchanger and overall indirect dry cooling system. On the basis of a typical indirect dry cooling system with heat exchanger bundles outside, the computational models of air-side fluid and heat flows coupled with the performances of the circulating water and exhaust steam are developed. The velocity, pressure and temperature fields of cooling air at various wind speeds are presented and the air mass flow rate, inlet air temperature as well as the heat rejection for each cooling delta, each sector are calculated, by which the outlet water temperature of the air-cooled heat exchanger and the back pressure of turbine are obtained. The results show that the cooling deltas suffer from different actions of ambient winds and the conspicuous dimensional characteristics of wind effects on the thermo-hydraulic performances of indirect dry cooling system are presented. The performances of upwind cooling deltas are superior to those at the rear, and they are all better than the side ones. At high wind speeds, the side cooling deltas and sectors get improved in thermo-hydraulic performances to an extent as the wind speed increases, but the performances of the backward ones are deteriorated seriously due to the obstacle of high pressure converting from the strong ambient winds. There exists a critical wind speed, at which the air flow rate is lowest and the outlet water temperature of air-cooled heat exchanger reaches its maximum, the indirect dry cooling system performance is most deteriorated, resulting in an unfavorable turbine back pressure. The study of wind effects on the indirect dry cooling system performances is helpful to the design of air-cooled heat exchangers and dry-cooling towers.

Air-Cooled Heat Exchanger Design Using Successive Quadratic Programming (SQP)

A nonlinear optimization algorithm is applied to the design of air-cooled heat exchangers. In such equipment, the cold fluid (air) is impelled across banks of finned tubes by means of fans in forced or induced draft. The hot stream flows inside the tubes in one or more passes, and the process that takes place may be cooling of either a gas or a liquid, or condensation of either a pure vapor or a mixture. The objective function is the minimum cost of the unit (investment and operation), subject to certain geometric and thermohydraulic constraints. The optimization algorithm used is that developed by Biegler and Cuthrell [1], and programmed by them in the OPT package. The problem posed in this case is made of 10 optimization variables, subject to five constraints related to geometric and operational parameters of the heat exchanger.

Air-Cooled Heat Exchanger Design Using Successive Quadratic Programming (SQP)

Air-Cooled Heat Exchanger Design Using Successive Quadratic Programming (SQP)