Numerical Simulation of Borehole Heat Transfer with Phase Change Material as Grout

2014 ◽  
Vol 577 ◽  
pp. 44-47 ◽  
Author(s):  
Jin Long Wang ◽  
Jing De Zhao ◽  
Ni Liu
Keyword(s):  
Heat Transfer ◽  
Heat Capacity ◽  
Phase Change ◽  
Phase Change Materials ◽  
Transfer Characteristic ◽  
Heat Pumps ◽  
Ground Source Heat Pumps ◽  
Numerical Heat Transfer ◽  
Ground Source ◽  
Key Factor

Ground source heat pumps (GSHP) have been widely used in recent years. The heat transfer between borehole heat exchanger (BHE) and earth is the key factor impacting on the performance of GSHP. However, in order to setup BHE, a large amount of area of land is necessary, since the heat capacity of earth is limited. In this paper, phase change materials (PCMs) are used as grout instead of common materials. Thus, the heat capacity of soil has been improved, but the heat transfer characteristic of BHE has also changed. To prove its feasibility, the 3-dimensional numerical heat transfer simulation has been carried for three models which grout are respectively soil, PCMs, and PCMs with heat transfer enhancement measures. The characteristics of heat transfer and the land areas used of the three models are compared. The results show that the land area can be reduced effectively with PCMs as backfilling, while heat transfer enhancements must be adopted because the conductivity of PCM is small.

scholarly journals Field Test and Numerical Simulation on Heat Transfer Performance of Coaxial Borehole Heat Exchanger

Energies ◽  
2020 ◽  
Vol 13 (20) ◽  
pp. 5471
Author(s):  
Peng Li ◽  
Peng Guan ◽  
Jun Zheng ◽  
Bin Dou ◽  
Hong Tian ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Thermal Properties ◽  
Heat Exchanger ◽  
Flow Rate ◽  
Thermal Response ◽  
Heat Pumps ◽  
Inlet Temperature ◽  
Borehole Heat Exchanger ◽  
Ground Source Heat Pumps ◽  
Ground Source

Ground thermal properties are the design basis of ground source heat pumps (GSHP). However, effective ground thermal properties cannot be obtained through the traditional thermal response test (TRT) method when it is used in the coaxial borehole heat exchanger (CBHE). In this paper, an improved TRT (ITRT) method for CBHE is proposed, and the field ITRT, based on the actual project, is carried out. The high accuracy of the new method is verified by laboratory experiments. Based on the results of the ITRT and laboratory experiment, the 3D numerical model for CBHE is established, in which the flow directions, sensitivity analysis of heat transfer characteristics, and optimization of circulation flow rate are studied, respectively. The results show that CBHE should adopt the anulus-in direction under the cooling condition, and the center-in direction under the heating condition. The influence of inlet temperature and flow rate on heat transfer rate is more significant than that of the backfill grout material, thermal conductivity of the inner pipe, and borehole depth. The circulating flow rate of CBHE between 0.3 m/s and 0.4 m/s can lead to better performance for the system.

Application of Artificial Neural Networks to Predict Heat Transfer From Buried Pipe for Ground Source Heat Pump Applications

2013 ◽  
Author(s):  
Hakan Demir ◽  
Ş. Özgür Atayılmaz ◽  
Özden Agra ◽  
Ahmet Selim Dalkılıç
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Numerical Study ◽  
Energy Resource ◽  
Heat Pumps ◽  
Burial Depth ◽  
Buried Pipe ◽  
Ground Source Heat Pumps ◽  
Ground Source ◽  
Artificial Neural

The earth is an energy resource which has more suitable and stable temperatures than air. Ground Source Heat Pumps (GSHPs) were developed to use ground energy for residential heating. The most important part of a GSHP is the Ground Heat Exchanger (GHE) that consists of pipes buried in the soil and is used for transferring heat between the soil and the heat exchanger of the GSHP. Soil composition, density, moisture and burial depth of pipes affect the size of a GHE. Design of GSHP systems in different regions of US and Europe is performed using data from an experimental model. However, there are many more techniques including some complex calculations for sizing GHEs. An experimental study was carried out to investigate heat transfer in soil. A three-layer network is used for predicting heat transfer from a buried pipe. Measured fluid inlet temperatures were used in the artificial neural network model and the fluid outlet temperatures were obtained. The number of the neurons in the hidden layer was determined by a trial and error process together with cross-validation of the experimental data taken from literature evaluating the performance of the network and standard sensitivity analysis. Also, the results of the trained network were compared with the numerical study.

On Fluid Flow and Heat Transfer in a Pipe With a U-Bend

2013 ◽  
Author(s):  
Christopher G. Cvetkovski ◽  
Hoda S. Mozaffari ◽  
Stanley Reitsma ◽  
Tirupati Bolisetti ◽  
David S.-K. Ting
Keyword(s):  
Heat Transfer ◽  
Flow Characteristics ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Heat Pumps ◽  
Heat Transfer Fluid ◽  
Heated Wall ◽  
Dean Number ◽  
Ground Source Heat Pumps ◽  
Ground Source

Vertical ground source heat pumps operate by pumping a heat transfer fluid through a pipe buried in the ground. There is a U-Bend at its deepest point to return the fluid to the surface. Incidentally, the U-Bend does more than packing the extensive length of the heat transferring conduit within a single compact borehole. Large flow structures called Dean’s vortices are generated in the bend and these, along with the resulting turbulence produced, are known to significantly enhance the heat transfer processes, and hence, shorten the required length. This study examines the specific roles of Reynolds and Dean numbers on the flow structure and the resulting heat transfer in a pipe with a U-Bend. Water flowing in a pipe without and with heated wall was simulated using FLUENT. The model was verified based on available data in the literature. The efficacy of the local heat transfer rate along the pipe was cast with respect to the subtle changes in the flow characteristics under varying Reynolds number and Dean number.

scholarly journals A numerical study on heat transfer performances of horizontal ground heat exchangers in ground-source heat pumps

PLoS ONE ◽  
2021 ◽  
Vol 16 (5) ◽  
pp. e0250583
Author(s):  
Hang Zou ◽  
Peng Pei ◽  
Chen Wang ◽  
Dingyi Hao
Keyword(s):  
Heat Transfer ◽  
Heat Exchangers ◽  
Heat Pumps ◽  
Working Fluid ◽  
Total Heat Transfer ◽  
Ground Source Heat Pumps ◽  
Spiral Coil ◽  
Ground Heat Exchangers ◽  
Ground Source ◽  
Heat Transfer Capacity

Horizontal ground heat exchangers (HGHEs) have advantages such as convenient construction and low cost; however, their application and popularization are restricted owing to traditional linear HGHEs occupying large space and presenting low total heat transfer capacity. Spiral-coil and slinky-coil HGHEs have been proposed, but currently a comprehensive comparison and evaluation for these types of HGHEs are still needed. In this study, a three-dimensional heat transfer model of the three types of HGHEs for ground source heat pumps (GSHPs) was established. Based on the simulation results, the long-term heat transfer performances were investigated, including the temperature field of surrounding energy-storage soils, outlet working fluid temperature, coefficient of performance (COP) of units, and surplus temperature of the energy-storage soils. A new concept named heat transfer capacity per heat-affected area was proposed in this paper. It is found that the spiral-coil HGHEs have the best performances in terms of working-fluid outlet temperature, unit COP, total heat transfer capacity, heat transfer rate heat-affected area. The linear HGHEs shows the best performances in terms of mitigating heat imbalance risk and heat transfer rate per length. The results provide a reliable basis for selection of HGHE types in engineering practice and improvement guide in the future.

Phase-Change Nanofluids With Enhanced Thermophysical Properties

2009 ◽  
Author(s):  
Zenghu Han ◽  
Bao Yang ◽  
Yung Y. Liu
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Capacity ◽  
Phase Change ◽  
Thermophysical Properties ◽  
Phase Change Materials ◽  
Effective Heat Capacity ◽  
Heat Transfer Fluids ◽  
Effective Heat ◽  
Indium Nanoparticles

The colloidal dispersion of solid nanoparticles (1–100nm) has been shown experimentally to be an effective way to enhance the thermal conductivity of heat transfer fluids. Moreover, large particles (micrometers to tens of micrometers) of phase-change materials have long been used to make slurries with improved thermal storage capacity. Here, a hybrid concept that uses nanoparticles made of phase-change materials is proposed to simultaneously enhance the effective thermal conductivity and the effective heat capacity of fluids. Water-in-perfluorohexane nanoemulsion fluids and indium-in-polyalphaolefin nanofluids are examples of fluids that have been successfully synthesized for experimental studies of their thermophysical properties (i.e., thermal conductivity, viscosity, and heat capacity) as functions of particle loading and temperature. The thermal conductivity of perfluorohexane was found to increase by up to 52% for nanoemulsion fluids containing 12 vol. % water nanodroplets with a hydrodynamic radius of ∼10 nm. Also observed in water-in-perfluorohexane nanoemulsion fluids was a remarkable improvement in effective heat capacity, about 126% for 12 vol. % water loading, due to the melting-freezing transitions of water nanodroplets to ice nanoparticles and vice versa. The increases in the thermal conductivity and dynamic viscosity of these nanoemulsion fluids were found to be highly nonlinear against water loading, indicating the important roles of the hydrodynamic interaction and the aggregation of nanodroplets. For indium-in-polyalphaolefin nanofluids, the thermal conductivity enhancement increases slightly with increasing temperature (i.e., about 10.7% at 30°C to 12.9% at 90°C) with a nanoparticle loading of 8 vol. %. The effective volumetric heat capacity can be increased by about 20% for the nanofluids containing 8 vol. % indium nanoparticles with an average diameter of 20 nm. Such types of phase-change nanoemulsions and nanofluids possess long-term stability and can be mass produced without using as-prepared nanoparticles. The observed melting-freezing phase transitions of nanoparticles of phase-change materials (i.e., water nanodroplets and indium nanoparticles) considerably augmented the effective heat capacity of the base fluids. The use of phase-change nanoparticles would thus provide a way to substantially enhance the thermal transport properties of conventional heat transfer fluids. Future development of these phase-change nanofluids is expected to open new opportunities for studies of thermal fluids.

Enhancing Heat Capacity of Colloidal Suspension Using Nanoscale Encapsulated Phase-Change Materials for Heat Transfer

2010 ◽  
Vol 2 (6) ◽  
pp. 1685-1691 ◽  
Author(s):  
Yan Hong ◽  
Shujiang Ding ◽  
Wei Wu ◽  
Jianjun Hu ◽  
Andrey A. Voevodin ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Capacity ◽  
Phase Change ◽  
Phase Change Materials ◽  
Colloidal Suspension
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