Experimental Study On Heat Transfer Enhancement Of Reciprocating Pulsating Flow

In recent years, along with the promotion of ship energy efficiency design index, the energy saving in marine equipment have been got increasing concern and the heat transfer enhancement problem of marine heat exchangers have been attracted more attention. Based on this, the experimental method is applied to explore the pulsating heat transfer problem in this thesis. The pulsation source in experimental system using the reciprocating pump, the working fluid is water, the flow state is in laminar or transitional flow conditions and Reynolds number is in the range of 2000?Re?9000.Firstly, an experimental bench of the pulsating flow enhancing heat transfer is designed, which is to explore the relationship between the different surface structures, different pulse parameters(Reynolds number, the pulsating frequency, pulsating amplitude) and the effect of heat exchange. During the experiment, the data collection system can achieve precise control of the parameters and real-time collection and storage of data. Moreover, a self-designed reciprocating pump could meet the requirements of the pulsation frequency and amplitude. Meanwhile, three layer structure of heat sink chamber is designed including the heating copper, cover plate and chamber base. The pulsation heat transfer for both kinds of channels are discussed, which are the rectangular flat plate and periodic- variation grooved plate.The major findings of the study are as follows:(1) In the rectangular plate channel, under the condition of Re = 2406, A = 0.12 Mpa, f = 1.08 Hz, heat transfer performance is improved by 160% than the steady-state flow. In the the rectangular groove channel with periodical change, under the condition of Re = 2406, a = 0.12 Mpa, f = 1.08 Hz, heat transfer performance is increased by 200% than in steady-state flow;(2) Under different conditions of the Reynolds number and the pulsation amplitude, with the changing of pulse frequency, heat transfer efficiency presents the tendency of gradual increase first and then decrease, which means there is an optimum pulse frequency. In the experimental range of operating conditions, and the heat transfer enhancement is corrected positively with the pulsation amplitude;(3) Generally, the heat transfer efficiency for periodic-groove channel case is superior to the flat channel. These results show that: under the condition of laminar and pulsating flow, the pulsating flow can be effectively enhanced the efficiency of heat transfer.Then, target for plate heat exchangers, a comparison is carried out for the efficiency of heat transfer in the condition of pulsating flow and steady flow, which study the relationship among the pulsation amplitude, pulse frequency and the characteristics of heat transfer. The results show that with the increasing of the Reynolds number, regardless of the steady flow or pulsating flow, the total heat transfer coefficient of plate heat exchanger has increased, the heat transfer efficiency has a gradually decreasing trend, which are almost coexistent with the rule in the experiment in heat sink chamber. At the same time, under the condition of the Reynolds number, with the increase of pulse frequency, the heat exchange efficiency appeared first decreases and then increases, the lowest value appeared in the vicinity of the pulsation frequency f=0.66 Hz, the maximum value of the thermal efficiency is 1.598, appear in the vicinity of the Reynolds number Re=3774, pulsation frequency f=0.55 Hz.