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Abstract
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.
Nomenclature
| t | = | time(s) |
| T | = | temperature (k) |
| href | = | reference enthalpy (kJ/kg) |
| Tref | = | reference temperature(k) |
| Cpcmp | = | specific heat capacity at constant pressure of PCM (J/(kg•k)) |
| Cpw | = | specific heat capacity at constant pressure of water (J/(kg•k)) |
| Ts | = | solidus temperature(°) |
| Tl | = | liquidus temperature(°) |
| Nu | = | Nusselt-number |
| Gra | = | Guerra Akio number |
| Pr | = | Planck number. |
| Re | = | Reynolds number |
| Amush | = | constant |
| vp | = | traction speed(m/s) |
| vi | = | velocity component of i direction(m/s) |
| vw | = | flow velocity of the water in U tube (m/s) |
| Ef | = | the total energy of fluid in porous medium (J) |
| Es | = | the total energy of the solid region in porous medium (J) |
| keff | = | effective thermal conductivity of porous medium (W/m.s) |
| kf | = | liquid thermal conductivity of porous medium (W/m.s) |
| ks | = | solid thermal conductivity of porous medium (W/m.s) |
| kpcm | = | thermal conductivity of PCM (W/m.s) |
| αcsc | = | thermal diffusivity of the crushed stone concrete (m2/s) |
Greeks
| β | = | liquid fraction |
| ϵ | = | constant which less than 0.001 |
| γ | = | porosity in porous medium |
| λf | = | heat conductivity coefficient of fluid |
| λa | = | heat conductivity coefficient of air |
Subscripts
| ref | = | reference |
| eff | = | effective |
| csc | = | crushed stone concrete |
| w | = | water |
| L | = | liquid |
| s | = | solid |
| f | = | fluid |
| a | = | air |
Superscripts
| pcm | = | Phase change material |
Funding
The authors sincerely appreciate the Project supported by the National Natural Science Foundation of China (Grant No. 51278076).
Additional information
Notes on contributors
Xiangli Li
Xiangli Li, PhD, is an Associate Professor. Cang Tong is Doctoral Candidate. Lin Duanmu, PhD, is a Professor. Liangkan Liu is a Master's Degree Student.
Cang Tong
Xiangli Li, PhD, is an Associate Professor. Cang Tong is Doctoral Candidate. Lin Duanmu, PhD, is a Professor. Liangkan Liu is a Master's Degree Student.
Lin Duanmu
Xiangli Li, PhD, is an Associate Professor. Cang Tong is Doctoral Candidate. Lin Duanmu, PhD, is a Professor. Liangkan Liu is a Master's Degree Student.
Liangkan Liu
Xiangli Li, PhD, is an Associate Professor. Cang Tong is Doctoral Candidate. Lin Duanmu, PhD, is a Professor. Liangkan Liu is a Master's Degree Student.