Research On Heat Transfer Performance Of Heat-dissipation Module For Construction Machinery

China’s economy has leapt forward and a large number of infrastructure has startedsince we followed the policy of reform and opening. In order to adapt to socialdevelopment and technical progress, construction machinery is also facing a series of newchallenges as the main construction equipment. Importance of efficiency, energyconservation and environmental protection gradually becomes prominent and thegovernment is more and more strict in energy conservation and emission reduction. Ourcountry is trying to formulate and implement National Ⅲ emission standard forconstruction machinery at present, which means there would be more stringentrequirements for product design.Double-drum vibratory roller is widely used in the construction of airports and roadsas a representative of construction machinery. There are many heating parts inside theengine cabin of double-drum vibratory roller, and ambient temperature is high duringworking. If the heat generated by system could not be removed in time, it would makeworking performance unstable. Construction machinery uses “cooling fan&radiatorgroup” as the heat-dissipation module, which uses the differential pressure generated bythe cooling fan to make cold air flow through the radiator for heat exchange between coldair and thermal fluid. The performance of the heat-dissipation module includes heattransfer capacity and power consumption, the former is related to the performance ofradiator and the latter is related to the performance of cooling fan. If the heat-dissipationmodule has better performance, there would be more heat transferred with same powerconsumption, and the energy conservation effect would be more obvious. Therefore, doingresearch on the performance of the heat-dissipation module should start respectively fromcooling fan, radiator and their matching etc.Based on the project in the National Science&Technology Pillar Program during theTwelfth Five-year Plan Period,"Intelligent Construction Machinery Design for EnergyConservation and Safety"(NO.2013BAF07B04), aiming to improve performance of theheat-dissipation module, CFD numerical simulation was used in this paper to makeimprovement in performance of cooling fan, radiator and flow field of engine cabin. (1) Research on cooling fan for improving inlet air status of radiatorBased on a cooling fan that is widely used in domestic construction machinery, itsperformance is simulated with CFD numerical method in a virtual wind tunnel. Thesimulation result was compared with the experimental data to verify the correctness ofmodel. The cooling fan is redesigned with single aerofoil method. The results show that theinlet and outlet air status of new fan is improved, which would benefit enhancing radiatorperformance.(2) Analysis of interaction between cooling fan and radiatorThe performance of cooling fan in the shroud with radiator resistance was analyzed,actual air flow generated by the fan was taken as the evaluation criterion, the performanceof cooling fan was analyzed under different conditions, which include distance betweenradiator and cooling fan, thickness of radiator and combination of radiators. The resultsshow that the air flow increases at first and decreases then as distance increases. Impact ofrotation speed of fan on the air flow decreases as the thickness increases. With the lowpressure zone near center of rotation offset, air flow decreases rapidly when the height ofradiator is equal to half of shroud height.(3) Heat transfer performance enhancement of radiator based on airfoil tubeCFD was used to simulate performance of element unit of tube-fin radiator that isused by a domestic double-drum vibratory roller. In order to enhance heat transferperformance and reduce flow resistance, NACA0018airfoil was taken as tube geometricalprofile. JF comprehensive evaluation factor was taken to assess fin performance. Theresults show that JF comprehensive evaluation factor of new fin increases about15.97%compared with the original fin.(4) Analysis and experimental verification of airflow field of engine cabin undermulti-working conditionCFD method was used to analyze the airflow field of engine cabin of the domesticdouble-drum vibratory roller under multi-working condition, and the prototype machinewas tested. The results show that the error between the simulation results and experimentdata is small. With the influence of hot-air backflow, The radiator performance underbackward working condition is better than that under forward working condition, vehiclespeed is related to the discrepancy. With the influence of cooling fan excursion, the outlettemperature of thermal fluid of inter-cooler decreases and outlet temperature of thermalfluid of oil radiator changes slightly.(5) Building a fan rotation speed model that changes with ambient temperature Considering ε, physical parameters, volume flow rate of air and inlet temperature ofcold and thermal fluid, the calculation model that takes cooling fan rotation speed andambient temperature as independent variables was built based on the formula for heatdissipating capacity in ε—NTU. Based on the domestic double-drum vibratory roller, a fanrotation speed model that changes with the ambient temperature was built on the premiseof keeping heat dissipating capacity constant. The results show that within the range from-30℃to45℃, rotation speed and shaft power are higher under forward condition withhigh vehicle speed and they are lower under backward working condition with high vehiclespeed. When ambient temperature is low, there is little discrepancy between shaft powerunder each condition. When the ambient temperature is45℃, the discrepancy becomesobvious. It is an effective research way to combine CFD simulation and one-dimensionaltheoretical calculation.(6) System improvement for decreasing flow resistance and increasing air flowIn order to decrease flow resistance and increase air flow, the improvement ofperformance of heat-dissipation module for the domestic double-drum vibratory roller wasmade in several ways, such as adjusting distance between cooling fan and radiator,changing shape characteristics of the engine cabin, reducing resistance characteristics ofradiator and enhancing performance characteristics of cooling fan. The results show thatradiator performance can be enhanced by the ways mentioned above.