Parallel Operation Characteristics Analysis of Sewage Source Heat Pump Units in Winter

Sewage source heat pump unit operates under partial load most of the time, and study on the law of coefficient of performance (COP) of the unit varying with load ratio can provide basis for the heat pump units running in high efficiency. A mathematical model determining COP, evaporation temperature and condensation temperature of a single unit was proposed. Under the condition of uniform load distribution, the model was established according to different ways of bearing partial load with the same type multi...

Comparative study on heat transfer enhancement of metal foam and fins in a shell-and-tube latent heat thermal energy storage unit

Metal foam and fins are two popular structures that are employed to enhance the heat transfer of phase change materials in shell-and-tube heat storage units.However,it remains unclear which structure is better in terms of energy storage performance.In this study,the heat transfer enhancement performances of metal foam and fins are compared to provide guidance on the optimal structure to be chosen for practical applications.Three fin structures(four fins,two vertical fins,and two horizontal fins)are considered.Under the full configuration(volume fraction of metal=3%),the unit with four fins was found to have a faster melting rate than those with vertical or horizontal fins.In other words,increasing the number of fins helps to accelerate the melting process.Nevertheless,the unit with metal foam enhancement has the highest melting rate.Under the half configuration(volume fraction of metal=1.5%),the melting rate of the unit enhanced by metal foam is significantly decreased,whereas there is no remarkable changes in the units enhanced by fins.However,metal foam is still shown to be the best thermal enhancer.The energy storage rate of the unit enhanced by metal foam can be up to 10 times higher than that of the unit enhanced by fins.

Heat units-based potential yield assessment for cotton production in Uzbekistan

Cotton yields in Uzbekistan are significantly lower than those in similar agro-climatic regions,requiring the estimation of crop potential and baseline yield to track progress of production enhancement efforts.The current study estimated potential cotton development and baseline yield(maximum given no production constraints)using total heat units(THU)and potential cotton yield(PCY),respectively.Calculations were based on heat units(HU)for a 30-year(1984-2013)period.Long-term average THU and PCY,as well as PCY at three different exceedance probabilities(p=0.99,p=0.80,and p=0.75),were calculated for 21 selected weather stations across cotton-growing areas of Uzbekistan.After confirmation that the current planting date(April 15)is optimal,a comparison of THU with the accepted cotton production cutoff threshold(1444°C)suggested that areas with lower elevations and latitudes are more appropriate for cotton production.Yield gap analysis(relative difference between long-term average PCY and actual yields)confirmed that Uzbekistan cotton production is below potential,while the spatial distribution of yield gaps outlined where efforts should be targeted.Areas near the stations of Nukus,Kungrad,Chimbay,and Syrdarya should be further investigated as benefit/cost ratio is highest in these areas.A comparison between state-set yield targets and PCY values,taking into account climatic variability,suggested that all areas except Jaslyk,Nurata,and Samarkand have safe,appropriate targets.These results present a starting-point to aid in strategic actions for Uzbekistan cotton production improvement.

Decentralized Demand Management Based on Alternating Direction Method of Multipliers Algorithm for Industrial Park with CHP Units and Thermal Storage

This paper proposes a decentralized demand management approach to reduce the energy bill of industrial park and improve its economic gains.A demand management model for industrial park considering the integrated demand response of combined heat and power(CHP)units and thermal storage is firstly proposed.Specifically,by increasing the electricity outputs of CHP units during peak-load periods,not only the peak demand charge but also the energy charge can be reduced.The thermal storage can efficiently utilize the waste heat provided by CHP units and further increase the flexibility of CHP units.The heat dissipation of thermal storage,thermal delay effect,and heat losses of heat pipelines are considered for ensuring reliable solutions to the industrial park.The proposed model is formulated as a multi-period alternating current(AC)optimal power flow problem via the second-order conic programming formulation.The alternating direction method of multipliers(ADMM)algorithm is used to compute the proposed demand management model in a distributed manner,which can protect private data of all participants while achieving solutions with high quality.Numerical case studies validate the effectiveness of the proposed demand management approach in reducing peak demand charge,and the performance of the ADMM-based decentralized computation algorithm in deriving the same optimal results of demand management as the centralized approach is also validated.

Simulation of the flow and thermal breakthrough of a forced external circulation standing column well

The flow and thermal breakthrough phenomenon in a forced external circulation standing column well(FECSCW)directly affects heat transfer efficiency and load-carrying capacity.A numerical model for FECSCW is developed to analyze the migration of the temperature and velocity front under the flow and thermal breakthrough.The results indicated that thermal breakthrough began after simulation running 2.5 min and was completely formed after 12 min.The inlet water,which directly entered the production well without heat exchange with the aquifer,accounted for 12.8%.When the porosity of the backfill material decreased from 0.35 to 0,the coefficient of per-formance(COP)of the heat pump unit increased by 1.6%on average,and the thermal breakthrough strength decreased by an average of 45.3%within 25 min.Where seepage velocity near the well wall was greater than 1×10^(−3) m·s^(−1),faster velocity front migration was observed,while the migration advantage of the temperature front was more prominent outside of this region.Through quantitative analysis of flow and thermal breakthrough,temperature and velocity front migration,and COP change of heat pump unit,theoretical suggestions were pro-vided for the thermal transfer mechanism near the thermal well wall.The extended research in this study can be applied to the design and optimization of forced external circulation standing column well system.