Xiangli Li

Study of a U-tube heat exchanger using a shape-stabilized phase change backfill material

This article describes the use of FLUENT software to simulate the heat transfer performance of U-tube heat exchangers in the ground source heap pump using the backfill materials of shape-stabilized phase change materials and crushed stone concrete. In this study, the shape-stabilized phase change material is a mixture of decanoic acid and lauric acid with the following mass concentration compositions: decanoic acid = 60%, silica = 10%, and expanded graphite = 6%. The mixture of shape-stabilized phase change material has a coefficient of thermal conductivity of 1.528 W/(m·K) and a latent heat of 109.2 kJ/kg. From the results of a 12-h simulation of the heat transfer dynamics, the heat exchange for a unit borehole depth of backfilling with shape-stabilized phase change material is 1.223 times the heat exchange for a unit borehole depth of backfilling with crushed stone concrete. In addition, the thermal influence radius of the backfill materials of shape-stabilized phase change material is 0.9 times of that of crushed stone concrete. As a result, under the same area of the buried pipes region, the shape-stabilized phase change material backfill can achieve a heat exchange 1.359 times that of crushed stone concrete backfill. Meanwhile, using shape-stabilized phase change material could contain the sustaining decline in coefficient of performance of heat pump at refrigerate condition to a certain extent and the appropriate physical parameters of phase change materials are also crucial.

Factor Analysis for Evaluating Energy-Saving Potential of Electric-Driven Seawater Source Heat Pump District Heating System Over Boiler House District Heating System

Although the seawater source heat pump district heating system is often regarded as a renewable energy utilization system, it cannot be guaranteed to obtain the energy-saving effect. The authors provided an energy-saving judgement method for the electric-driven seawater source heat pump district heating system over the conventional boiler house district heating system in former research. However, many factors will influence the energy efficiency of the system. In order to enhance its energy efficiency and make the best use of the system, detail analysis of those factors is conducted in the paper. First, an energy-saving potential evaluation model is derived for the system with part-time operation mode. Then all the factors influencing the energy efficiency of the system are ascertained and analyzed. These factors include the electricity generation efficiency, energy performance of seawater source heat pump units, the seawater temperature, the energy consumption of the seawater pump, the local outdoor air temperature, and the heating district radius. The research results are expected to provide clear directions for the seawater source heat pump system to raise its energy efficiency.