Abstract
Authors in this work want to demonstrate the possibility to increase the heat transfer efficiency by using simple wire coil inserts to create turbulent flow in the boundary layer as well as air blowing into the annulus of the pipe. In the study, Wilson plot approach was applied in order to estimate heat transfer coefficients for all heat exchanger (HX) configurations. The study focuses on experimental values of heat transfer coefficient (HTC) and pressure drops. The primary objectives of the work are to: I. Provide an experimental comprehensive database for HTC and pressure drops; II. Analysis effect of different flow conditions e.g. water mass flow rate, the void fraction on heat transfer and hydraulic performance of tested elements. III. Compare influences of both passive and active methods at the efficiency of simple heat exchangers constructions; IV. Validation experimental results with selected experimental models from the open literature.
Highlights
In recent years, investigations aimed at increasing heat transfer efficiency are of primary importance [1,2]
It should be noted that experimental results for straight double tube heat exchanger (HX) (SDTHX) have a good fit with that correlation
It should be emphasized that HXs working at two-phase flow-regime are characterized larger thermal power as well as larger pumping power consumptions Despite the fact that, ε-NTU analysis (Fig.6) shows that all of the designs presented are of similar efficiency
Summary
Investigations aimed at increasing heat transfer efficiency are of primary importance [1,2]. The growing, negative industry impact on environment strongly accelerates the search for new solutions in the field of heat transfer engineering [6] They are many papers in open literature focuses on heat transfer enhancement techniques in plain heat exchangers constructions. Sheikholeslami et al [7] presented comprehensive literature review of passive techniques, such as various turbulators (coiled tubes, extended surfaces (fin, winglet),rough surfaces(corrugated tube, rib) and swirl flow devices such as twisted tape, conical ring, snail entry turbulator, vortex rings, coiled wire). They noted that wire coils turbulator provide the best performance increase while maintaining reasonable increase of pressure drop. They concluded that passive techniques are more popular as heat transfer techniques because of the simple manufacturing process and a possibility to employed to existing heat exchanger
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