| The quantity of data centers has been increasing with the continuing development and demand of information and communication technology(ICT).The increasing use of data center consumes annually 1.12%～1.5%(i.e.,203.4-271.8 billion kW·h/year)of all electricity consumption worldwide and the data processing demand will double every 2 years.Among the overall energy consumption in data centers,30%～50%is used for device and space cooling.Many efforts have been made to deal with reducing the energy consumption of the cooling system for data centers.The most widely used cooling technology in existing data center is a computer room air conditioner(CRAC),which poses several problems:high electricity consumption for getting the cooling source,great energy loss in the piping system,short circuiting and local hot spots.Heat pipe technology with high heat transfer ability make use of free cooling to ensure the cleanliness of data center and the information technology equipment(ITE)in the required temperature and humidity environmental conditions,thereby reduce the cooling system energy consumption.This dissertation presents the research on micro-channel separate heat pipe system(MCSHP)heat transfer characteristics and its application for cooling in data centers.The thermal characteristics of these under different design(geometrical parameters and filling ratios)and operational parameters(outdoor and indoor environmental parameters)were illustrated in this dissertation.To evaluate the performance of the water cooled multi-split heat pipe system(MSHPS)by using lake water source,we conducted a case study on a data center using Dongjiang lake water,in China,by comparing the cooling method against the conventional CRAC.Meanwhile,an optimized control strategy for this cooling system were developed to drive the system toward a high overall energy efficiency.Firstly,the thermal and operational performance tests of the air-cooled and water-cooled MCSHP were carried out in an enthalpy difference laboratory(EDL).For the air cooled MCSHP,the effect of different outdoor air conditions and air volume flow rates on the optimal filling ratio(FR)range was investigated.And the steady and transient state thermal characteristics of air cooled MCSHP were also studied.For the water cooled MCSHP,the superheating,two phase,and subcooling heat transfer rate,and thermal resistance of this system were analyzed.As a result of experiments,MCSHP have the same optimal FR range with different conditions.At the optimal FR,the MCSHP obtained a low temperature difference between the inlet and outlet of the evaporator section and condenser section(or cooling distribution unit(CDU)section),and also achieved the maximum heat transfer rate and the minimum thermal resistance.These experimental results can be used to analyze heat transfer mechanism of the MCSHP,optimize the system design and control,and develop theory model.In addition,a steady-state mathematical parameter model for an air cooled MCSHP wea constructed to determine the most suitable two phase heat transfer correlation according to the energy(enthalpy),momentum(pressure),and mass conservation.And the simulation results were compared to the experimental data collected under various conditions.The Gungor and Winterton correlation provides the lowest average relative error,and it is about 5%.The effects of design parameters and operational parameters on an air cooled MCSHP were analyzed by using the developed model.The refrigerant side heat transfer coefficient along the evaporator section and condenser section had the maximum value when the FR was 82%.As a design parameter,the height difference has a great impact on the refrigerant mass flow rate and cooling capacity.However,the impact is limited by the evaporator and condenser capacity when it reaches a certain value.Meanwhile,the sensitivity analysis of this system cooling capacity to the operational parameters was carried out by using the orthogonal array method.The result shows that inlet air temperature of the evaporator section and condenser section are the most sensitive variable,while the air volume flow rate of the evaporator section and condenser section are the secondary factor.Finally,a simple heat transfer model for the water cooled MCSHP was developed by using the e-NTU method,and the simulation results were validated using previous experimental results.Its relative error is in ±10%.Based on this model,an energy model for the MSHPS using lake water source was developed considering the effect of the variation of cooling load,thermal performance of the cooling plant,lake water temperature and weather conditions.Taken a typical data center as a case to study the enrgy consumption of this cooling plant to determine the optimal supply air temperature and supply chilled water temperature set points,which are 24℃ and 15℃,respectively.Meanwhile,the energy savings potential of this cooling plant compare to the conventional CRAC with or without water side free cooling.The results show that the cooling plant using lake water source achieved the maximum energy savings of 64.82%,and the cooling plant using water cooled SHP over the conventional CRAC obtained about 11.28%.In addition,the optimized control strategy of the MSHPS using lake water source was proposed to maximize the energy savings based on genetic algorithm(GA).By using this control strategy,the enegy consumption of this cooling plant reduced by 19.5%,and the operational hours of mode 1(free cooling mode)is high to 93%of the whole year. |
