PERFORMANCE IMPROVEMENT OF DOUBLE PIPE HEAT EXCHANGER BY USING TURBULATOR
The various techniques for achieving improved heat transfer are usually referred to as “heat transfer augmentation” or “heat transfer enhancement” and the heat exchanger provided with heat transfer enhancement techniques as “Augmented Heat Exchanger”. The objective is to reduce as many of the factors as possible: Capital Cost, Power Cost, Maintenance Cost, Space and Weight, Consistent with safety and reliability. Present work describes the principal techniques of industrial importance for the augmentation of single phase heat transfer on the inside of tubes namely twisted tapes. So twisted tape should be used in heat exchanger when high heat transfer rate is required and pressure drop is of no significance.
Experimental Investigation of Heat Transfer Enhancement Methods on the Thermal Performance of Double Pipe Heat Exchanger
The aim of this study is to improve the heat transfer in a double tube heat exchanger by using four samples of the inner tube (smooth tube, half circular finned tube, circular finned tube and circular helical finned tube). The experiments were carried out by using the four kinds of fluids flow, namely, (a parallel flow of cold water inside the inner tube, a parallel flow of hot water inside the inner tube, the counter flow of cold water inside the inner tube and the counter flow of hot water inside the inner tube). The comparative results of the finned tubes with respect to the smooth tube showed the highest values of heat transfer coefficient obtained at the circular helical finned tube instate of hot water flow inside the tube. The convection heat transfer coefficient increased by (250 and 165)% for both flows (parallel and counter), respectively in case of turbulent flow, while in state of the hot water flow on the outer surface of the inner tube, the heat transfer coefficient increased by 230 % for parallel flow and in the case of the counter flow increased by 260 %. The fanning friction factor was affected by a condition of the working fluids where in the case of hot fluid flows outside surface of the inner tubes, the min. values of fanning friction factors was obtained from smooth tube sample which is ranged from 0.01 to 0.05 and other samples are ranged from 0.008 to 0.05.
Pressure drop and heat transfer comparison for both microfin tube and twisted-tape inserts in laminar flow
Abstract Experiments were carried out to compare pressure drop and heat transfer coefficients for a plain, microfin, and twisted-tape insert-tubes. The twisted-tape experiments include three different twist ratios each with two different widths. The data were taken at Reynolds numbers well in the laminar region. The heat transfer data were obtained in a single shell-and-tube heat exchanger where steam is used as a heat source to obtain a uniform wall temperature and the working fluid in the tube is oil. The twist ratio and the width of the tape seem to have a large effect on the performance of the twisted-tape insert. The results demonstrate that as the twist ratio decreases, the twisted-tape will give better heat transfer enhancement. The loose-fit (W=10.8 mm) is recommended to be used in the design of heat exchanger where low twist ratios (Y=5.4, and Y=3.6) and high pressure drop situations are expected since it is easier to install and remove for cleaning purposes. Other than these situations, the tight-fit tape gives a better performance over the loose-fit tape. For the microfin tube tested in this paper, the data shows a small increase in both heat transfer and pressure drop. This type of microfin tube is not recommended to be used in laminar flow conditions.