Research On Heat Transfer Optimization And Energy Saving Of Server Cabinet With Combined Cold Sources Based On Thermodynamic Exergy Analysis

The rapid development of Internet technology has promoted the process of the era big data and the surging demand for data,which also drives the rapid rise and growth of the data center industry.As a pivot for the computation,storage and interaction of large amounts of data,data centers are required to operate continuously for 8760 hours a year.However,with the continuous expansion of the scale of data centers around the world,the huge energy consumption and heat dissipation issues brought by the operation stage become increasingly prominent.Therefore,the research on heat dissipation and energy saving in data center is a hot topic at present.Data center is composed of IT equipment,cooling system,lighting system,power supply and distribution system.However,the energy consumption of the cooling system accounts for 40%to 50%of the total energy consumption,which has a great potential for energy efficiency improvement.So the optimization of heat exchange process is of great significance to the energy conservation of data center In terms of the composite cold source cabinet with a wide range of application in the data centers,it combines air-cooled and water-cooled technologies to achieve low-temperature air supply within the range of single-stage cabinet to ensure the heat dissipation of the server.Compared with the traditional cooling mode of CRAC unit combine with raised floor,the combined cold source cabinet has the advantage of less mixed loss of hot and cold air,uniform cooling capacity,strong cold source regulation,high cooling water temperature and large energy saving potential.However,the traditional single-stage heat exchanger has a phenomenon that the heat transfer parameters do not match the characteristics of the heat source of the cabinet.The area of the cabinet heat exchanger cannot be effectively used,and the advantages of high cold source temperature and strong extremity regulation cannot be fully utilized,resulting in local overheating or waste of cooling capacity.Sometimes,in order to eliminate hot spots,turn off the free cooling mode or reduce the temperature of chiller,so the energy consumption of the entire cooling system is maintained at a high level.This paper starts with the analysis of the thermodynamic characteristics of the cabinet flow and heat transfer process,thermodynamic exergy analysis models of server and heat exchanger are established.Taking the minimum exergy loss as the optimization goal,a two-stage heat exchange process based on the least exergy loss is proposed.The heat transfer performance of the cabinet and the server load rate can be synchronized by optimizing the heat transfer process and parameters.The temperature of the cold source and the energy efficiency of the chiller can be effectively improved.Hot spots are eliminated,the uniformity and stability of data center can be ensured.This research is carried out from the following aspects:First,the development level and scale of data centers are investigated and summarized,and the construction growth rate in recent years is compared and the development trend is summarized.The problems of energy conservation and heat dissipation caused by this are increasingly prominent.The technical principles of air cooling,liquid cooling and phase change cooling are introduced,and the advantages and disadvantages are compared.Finally,a composite cold source cabinet is determined as the research object.The exergy theory based on the second law of thermodynamic is adopted to combine the“quantity”and“quality”of energy,providing a theoretical basis for proposing efficient energy-saving methods.Then,the flow and heat exchange processes at cabinet-level is constructed by taking the server and heat exchangers as the heat exchange nodes,the air and cold water as the heat exchange media.On this basis,the heat exchanger process on the server-side is simplified to a one-dimensional flat forced convection heat exchange,and the heat exchange process on the heat exchanger side is simplified to air-water countercurrent heat transfer.A mathematical model of exergy loss is established to complete the analysis of energy flow,and provide guidance and direction for optimization.Then,perform exergy loss and exergy efficiency analysis to determine the key parameters affecting the thermodynamic performance:air velocity and total transfer area?NTU?,and the influence trend of parameters on exergy loss is analyzed.Next,the single-stage heat exchange process is optimized and improved,and the method of two-stage heat exchange process at the front and back of the cabinet with different heat exchanger area ratios is put forward.Under the premise that the total heat exchange area?NTU?is unchanged,a high degree matching between the cold and heat sources is realized by adjusting every stage heat exchanger area NTU₁?NTU₂ and air flow rate.Four optimization design schemes including single-stage heat exchange and two-stage heat exchange with different area ratios are proposed.It's obtained that the two-stage heat exchange with the front-to-back area ratio is 20%:80%has the least exergy loss by using MATLAB simulation calculation,and the server motherboard temperature is logical and safe.Finally,in the experiment,the cabinet arrangement form of scheme with minimum exergy loss is adopted,and the measured values of fluid and energy efficiency parameters under different rack load rates are tested and compared with the theoretically optimal calculation value of the minimum exergy loss scheme.At the same time,error analysis is completed.The test results show that within the allowable error range,the measured value is close to the calculated value,the EER can reach 8.3 in summer and11.5 in winter.The temperature difference in the cabinet can be controlled within±2?.