| The heat exchanger equipment holds important position in the industrial production, its heat-transfer performance's quality has the great significance to the energy conservation. At present, the finned tube type heat interchanger is widely applied in the energy and power, the chemical industry, the metallurgy, the air conditioning, and the food refrigeration processing and so on many industries, particularly in the field of refrigeration and air conditioning, the finned tube type heat interchanger's application is more extensive, so optimize and improve the air side heat transfer characteristic and flow resistance characteristic of the finned tube heat exchanger, also the corresponding field of refrigeration and air conditioning to become a very important research topic.The heat interchanger air side performance is influenced by its own structural parameters and external environmental factors, its own structural parameters includes the fin pitch, fin thickness, and number of tube rows and so on,and the external environmental factors including the heat exchanger temperature of inlet air dry bulb temperature,the wet bulb face temperature and the air velocity,the air flow as well as the air inlet conditions (free air intake, restricted into the wind) and so on.At present, working in the frost conditions is basically plain fin heat exchanger, but the highly effective wing piece's using has not been reported. Under the dry operating mode carries on the fundamental research and the experimental study indicated that opens a small round hole on the even wing piece is one kind of simple effective measure of strengthened heat transfer, its strengthening mechanism is enhanced boundary layer air holes can destroy the disturbance, thus causes the partial heat transfer coefficient increased. The symmetrical round hole wing piece and the three symmetrical large diameter round hole wing piece (also refered to as SK fin) to rest on this principle to develop for the improvement basis.The earlier period simulation and the related experiment confirmed that, raletive to the rectangular flate fin, the SK wing piece has the most superior strengthened heat transfer effect. Fang Zhaosong using the FLUENT software to the even wing piece, the symmetrical round hole wing piece and the SK wing piece air side's flowing and the heat transfer has carried on the numerical simulation, to under the different wind speed's velocity field, the temperature field and the Nuxieerte number distributed numerical simulation result has carried on the analysis,the simulation results indicated: Numerical simulation's result agree well with the early time experimental result tallies well, error control within 10%. At the same time, the simulation results also indicated: Under the same level condition, the SK wing piece's average heat transfer coefficient is higher than 25.7% compared to the even wing piece average. On the basis of the simulation results demonstrate that SK-type heat transfer fin is a superior film-type, Fang Zhaosong used the wind tunnel test platform under the rime operating mode to the even wing piece, the symmetrical round hole wing piece and the SK finned tube type heat interchanger has carried on the heat transfer and the refrigeration performance relative property experiment, the experimental result indicated: under frosting conditions, compared with plain fin and fin hole, the SK fin heat transfer effect is best.To further explain that the SK-type fin superior strengthening heat transfer effect, and transforms the scientific research achievement into the productive forces, enables the SK-type fin to be possible the quantification production. Zhang Jie et al. have manufactured a plain fin air conditioner forced draft fan and SK-type fin air conditioner forced draft fan each, and the construction of the existing standards by cold artificial climate chamber to transform, has carried on the relative property industry prototype experiment to the two air conditioner forced draft fan's energy conservation performance. The experimental result confirmed that: This project develops the SK-type refrigeration heat interchanger is one kind of heat-transfer property is a energy conservation product with outstanding heat transfer performance and high energy efficiency.The results of these studies can not fully reflect the SK-type fin's air-side characteristics, at present, the related air side heat exchanger performance study is divided into: experimental research and numerical simulation. As a result of the two heat transfer fluid in the flow inside the heat exchanger is extremely complex, making it difficult to obtain reliable simulation results. Therefore, the current characteristics of the air side heat exchanger research, mainly experimental study primarily.Based on the previous experimental research and theoretical study, using the existing wind tunnel test platform, in the frost conditions, using the experimental method to study the SK-type finned tube heat exchanger heat transfer characteristic and flow resistance characteristic, and return to the SK-type finned tube Nu and f correlation criteria. The experimental results show that:①When inlet air temperature constantly for 28℃, in the experimental period, SK fin surface frost layer growth is always in crystal growth stage, the cooling capacityΦ, the fin surface heat transfer coefficient h and the pressure dropΔP values of the SK-type finned tube heat exchanger along with inlet air velocity and relative humidity increases increases. While at the same inlet air velocity and relative humidity, the cooling capacity of heat exchangerΦ, fin surface heat transfer coefficient h and the pressure dropΔP values are constantly increasing with the frosting time increases.②When inlet air temperature constantly for 28℃, SK-type fin surface frost has gone through three stages:crystal growth period, frost layer full growth period and the frost layer growth period. At this point, the cooling capacityΦ, the fin surface heat transfer coefficient h, the pressure dropΔP values and the COP of the SK-type finned tube heat exchanger along with inlet air velocity and relative humidity increases increases. While at the same inlet air velocity and relative humidity, the cooling capacity of heat exchangerΦ, fin surface heat transfer coefficient h and the COP are carried out with the frosting time increases first and then gradually decreased.Under frosting conditions, carries on the thorough analysis to the different inlet air velocity and the relative humidity to the SK finned tube type heat interchanger heat transfer and the resistance characteristic influence, and further clarified SK fin tube heat exchanger internal flow of heat exchange and the internal mechanism of deepening of the SK-type finned tube heat exchanger working understanding of the process under frosting conditions, the SK-type finned tube heat exchanger thermal resistance and the basis for the optimal design based on its provide technical support for industrial applications. |
