Heat Extraction Capability Research Articles

Prediction and optimization of heat extraction in ground source heat pump system using surrogate model

Ground source heat pump (GSHP) system, which extracts underground heat for building heating and cooling, uses renewable energy to decrease CO2 emissions for the goals of carbon peaking and carbon neutrality. Hence, the prediction and optimization work is significate especially for existing GSHP system. This study focuses on the prediction of heat extraction and optimization of operational strategy based on a three-story house installed with GSHP system located in Cleveland, Ohio, USA. Firstly, the numerical model is built to simulate operation of ground heat exchanger (GHE). Then, Latin hypercube sampling (LHS) is employed to generate different parameter combinations that are calculated to get the heat extraction results for training XGBoost-based surrogate model. Finally, the particle swarm optimization (PSO) is used to realize the optimization of operational strategy. The results indicate that the numerical model can simulate the GHE well, and the accuracy of surrogate model can reach 0.990. The COP of GSHP system is maximized to protect the soil heat balance and reduce the electrical energy consumption. The optimization method also makes it possible to evaluate the heat extraction capability, and prepare for the extra heat demand in advance.

Modeling of Wellbore Heat Transfer in Geothermal Production Well

Electricity supply in Nigeria has been insufficient to aid development. It has also been observed that fossil fuels that supply energy has not been friendly to the environment, as a result an alternative energy source is needed. Geothermal energy has come to fill this gap. This work modelled wellbore heat transfer in geothermal wells and investigated the best heat mining fluid that will conserve heat during heat transfer at the wellbore during heat production. This work employed the mechanisms that greenhouse gases use to absorb heat from the sun and retain it to warm the earth. Simulation of heat extraction capability of steam and CO2 were studied. It was observed at reservoir conditions (248 °F) that steam Mass heat capacity (2.433 KJ/kg °F) is higher than that of CO2 (1.088 KJ/kg °F). At 204. 8 °F mass heat capacity of CO2 is 1.1915KJ/kg OF and that of steam is 2.4058 KJ/kg °F. This implies that steam retains more heat than CO2. From the study at wellbore fluid temperature of 276.8 °F, and at a flow rate of 1300 lb/hr, the wellbore heat transfer from steam (0.158 mmbtu/day) is slightly higher than that of CO2 (0.105 mmbtu/day). CO2 conserves more heat than steam when used as a heat transfer fluid. The heat transfer capabilities of the mining fluids determine the production capability of the heat resources and the quantity of electricity generation. The study recommended CO2 deployment as heat mining fluid in the exploitation of heat in geothermal resources in Nigeria. This will reduce the greenhouse effect of CO2 in our environment while also encouraging rapid development and economic growth, more especially with the rising cost of energy from fossil. Availability of geothermal energy will increase the supply of electricity in Nigeria.

Experimental and parametric analysis of a novel hybrid thermal management strategy for cylindrical lithium‐ion cells

AbstractThis paper reports on a novel hybrid thermal management strategy. It uses secondary coolants (air and liquid) to withdraw heat simultaneously from the composite phase change material, resulting in increased heat extraction capability of the composite phase change material and improved thermal environment of the battery module. The significance of this strategy is that the fluid used in the liquid cooling stays stationary. Comprehensive experimental and numerical studies are performed, and parametric studies are conducted to reduce the volume of the phase change material, size of the air duct, and airflow Reynolds number. The numerical results showed that the maximum temperature was limited to 27.8°C, and a high‐temperature uniformity of 0.4°C was obtained. Furthermore, the required volume of the composite phase change material is reduced by ~50%. Additionally, beyond a 6 mm height of the air duct, the reduction in maximum pressure drop is not significant enough, and it is considered the optimal height, and a Reynolds number of 1950 is considered the optimal airflow Reynolds number. Therefore, the proposed thermal management concept for the battery module can sustain the thermal environment needed for the effective operation of Lithium‐ion batteries.

Investigation of Heat Transfer Enhancement Techniques on a Scalable Novel Hybrid Thermal Management Strategy for Lithium-Ion Battery Packs

This paper introduces a novel hybrid thermal management strategy, which uses secondary coolants (air and fluid) to extract heat from a phase change material (paraffin), resulting in an increase in the phase change material’s heat extraction capability and the battery module’s overall thermal performance. A novel cold plate design is developed and placed between the rows and columns of the cells. The cold plate contains a single fluid body to improve the thermal performance of the battery module. Experimental studies were conducted to obtain the temperature and heat flux profiles of the battery module. Moreover, a numerical model is developed and validated using the experimental data obtained. The numerical data stayed within ±2% of the experimental data. In addition, the ability of nanoparticles to increase the thermal conductivity of water is examined and it is found that the cooling from the liquid cooling component is not sensitive enough to capture the 0.32 W/m K increase in the thermal conductivity of the fluid. Furthermore, in order to enhance the air cooling, fins were added within the air duct to the cold plate. However, this is not feasible, as the pressure drop through the addition of the fins increased by ~245%, whereas the maximum temperature of the battery module reduced by only 0.6 K. Finally, when scaled up to an entire battery pack at a high discharge rate of 7 C, the numerical results showed that the overall temperature uniformity across the pack was 1.14 K, with a maximum temperature of 302.6 K, which was within the optimal operating temperature and uniformity ranges. Therefore, the developed thermal management strategy eliminates the requirement of a pump and reservoir and can be scaled up or down according to the energy and power requirements.

A comparative analysis of the performance of backfill heat exchangers in deep mine geological environments

With the increase of mineral mining depth, the technologies of constructing heat exchanger in stopes to exploit geothermal resources from deep mines have received great attention. The heat extraction capacities of heat exchangers are closely related to the geological environments of deep mines, especially backfill mines. Therefore, a three-dimensional unsteady heat transfer and seepage coupling model of backfill heat exchangers (BFHEs) is created and verified in this work using COMSOL simulation software. Then, the influences of geological environments, involving groundwater seepage, initial temperature and thermal conductivity of surrounding rock etc., on the ability of five BFHEs with the equal buried tube length to extract heat in different configurations are investigated by this model. The findings indicate that groundwater flow can significantly improve the performance of BFHEs. Double-layer tube BFHEs have the best overall performance in the studied seepage velocity range. Only when there is no or little seepage is the performance of single-layer tube BFHEs equivalent to that of double-layer tube BFHEs. The heat extraction capacity of BFHEs is greatly improved under seepage conditions with the increase in the initial temperature of surrounding rock, although the impact is low in the absence of groundwater seepage. The benefit of backfill body's thermal conductivity on BFHEs' ability to transport heat is significantly greater than that of surrounding rock, but the effect becomes smaller as the value increases. Further increasing the thermal conductivity of the backfill body will not considerably increase the heat extraction capability of BFHEs after it reaches 2.5 (W·m−1·K−1). Therefore, if the cost is too high, continued enhancement is not recommended. The findings offer theoretical recommendations for optimizing BFHEs’ setup to better adapt to deep mine geological environments and increase geothermal extraction capability.

Machinability analysis for drilling Ti6Al4V ELI under sustainable techniques: EMQL vs LCO2

As a result of the widespread use of Ti6Al4V ELI in the medical industry for implants that are subjected to high loads, these biomedical implants must be accurately machined to prevent unfavourable joint or muscular inflammatory conditions. This oftentimes involve drilling holes into the implants for joint assembly during surgery. It is well known that titanium is a very difficult to machine material and therefore, requires appropriate cooling and lubrication during machining. With the help of SEM and line-scan EDS analysis, the current study focuses on analysing various sustainable machining techniques, such as electrostatic minimum quantity lubrication (EMQL) and liquid carbon dioxide (LCO2 cryogenic coolant), while drilling Ti6Al4V ELI (Grade 23) holes in terms of hole surface quality, wear mechanisms, and chip morphology. Poor surface quality of the hole was produced under EMQL cutting, with around 42–71% larger surface roughness values (Rz) compared to cryogenic LCO2 conditions. The hole surface consisted of different defects such as adhesion, microfractures, smearing etc., as a residue of the drilling operation under both EMQL and cryogenic LCO2 conditions. Tool life was significantly improved under LCO2 cutting environment (approximately by 416%) in comparison with EMQL technique. Adhesion and abrasion were found to be the main tool wear modes. Likewise, the machined chips exhibited cracks and adhered particles further demonstrating that EMQL coolant did not provide sufficient lubrication and heat extraction capability. Cryogenic LCO2 coolant outperformed EMQL lubrication for all machinability indicators, according to the study, making it a superior cutting environment for machining Ti6Al4V. Moreover, cryogenic LCO2 coolant dissipates into air during the machining process rendering it a sustainable and environmentally friendly machining coolant fluid.

Experimental investigation on CNC turning of SS304 using nano particle based minimum quantity lubrication

Stainless steel 304 has excellent mechanical qualities, good fatigue resistance, and resistance to oxidation. Additionally, the turning of SS304 under MQL needs to be addressed. This work aims to evaluate the machinability study using carbide cutting inserts and nanoparticle-assisted MQL on CNC turning. As a methodology, Response Surface Methodology, Box Behnken Design, and response surface optimization were used. Based on the fitted regression model, a 3D plot was used to analyse the collected machining data. Researchers have been attracted to nano fluids over the last decade due to their improved thermal conductivity and heat extraction capability. The current study creates a new nanofluid by adding HBN nano particles in cutting fluid. Likewise, its machining performance is assessed while turning an SS304 workpiece utilising the minimum quantity lubrication (MQL) technique based on nanoparticles. Additionally, the outcomes are examined with MQL with conventional cutting fluid and dry machining. The experimental study clearly shows that HBN nano fluid performs better than conventional cutting fluid with MQL and Dry machining in terms of surface roughness, tool wear, Flank Wear.

Machinability Investigation of Nitronic 60 Steel Turning Using SiAlON Ceramic Tools under Different Cooling/Lubrication Conditions.

The machining of nickel-based super alloys is challenging, owing to the generation of high cutting temperatures, as well as difficulty in maintaining dimensional accuracy and minimizing surface roughness, which compels the use of cutting fluids for reducing these issues due to efficient cooling/lubrication strategies. The present work investigates the comparative performance of four cooling/lubrication techniques: dry cutting, wet, minimum quantity lubricant (MQL) and compressed-air modes in turning Nitronic 60 steel using a new-generation SiAlON ceramic inserts. Several machinability parameters were analyzed for performance evaluation. For this purpose, 16 cycles of turning trials were performed based on Taguchi’s L16 orthogonal array experimental design by varying cutting conditions and lubrication modes. MQL exhibits beneficial effects as compared to the other lubrication conditions concerning low cutting force, improved surface finish, decreased cutting temperature, longer tool life, and lower white layer thickness on machined surface. Burr formation on the saw-tooth chip surface, as well as friction, greatly influenced the tool flank wear due to improper cooling and poor lubrication approach in dry, wet, and compressed-air-cooled machining environments in comparison to MQL-machining. From an economical perspective, the tool life in MQL machining improved by 11%, 72%, and 138% in the comparison with flooded, compressed-air, and dry conditions, respectively. The results of the study demonstrate that using the MQL system can help with heat extraction capability, and provide some promising outcomes.

Optimization of energy tunnel heat extraction section design based on simulated annealing algorithm

Energy tunnel is an alternative energy-saving technology of ground source heat pump （GSHP）， which has been applied in China in recent years. However， the current engineering practice still lacks the mature design method， and the heat extraction section design of the energy tunnel usually depends on engineering analogy. It is necessary to develop a convenient and reliable method to assist energy tunnel design. To address this problem，an optimization framework is developed to guide the heat extraction section design of energy tunnel in the severe cold region based on numerical simulation and simulated annealing algorithm. With this framework， the location of the heat extraction section can be automatically selected based on the in-site geological and meteorological conditions. Then， sensitivity analysis in terms of different design parameters of the heat extraction section is conducted to investigate their influence on heat transfer efficiency and heat extraction section design. The results show that smaller pipe spacing， lower inlet water temperature， and higher flow rate of circulating medium in pipes will benefit the higher heat exchange efficiency， shorter design length of heat extraction section， and the resultant lower cost. In addition， the deviation of the starting position within several meters will not affect the total heat extraction capability for a certain length of the heat extraction section. The proposed methodology will provide important support for the energy tunnel design in engineering practice.

A Generative Human-in-the-Loop Approach for Conceptual Design Exploration Using Flow Failure Frequency in Functional Models1

A challenge systems engineers and designers face when applying system failure risk assessment methods such as probabilistic risk assessment (PRA) during conceptual design is their reliance on historical data and behavioral models. This paper presents a framework for exploring a space of functional models using graph rewriting rules and a qualitative failure simulation framework that presents information in an intuitive manner for human-in-the-loop decision-making and human-guided design. An example is presented wherein a functional model of an electrical power system testbed is iteratively perturbed to generate alternatives. The alternative functional models suggest different approaches to mitigating an emergent system failure vulnerability in the electrical power system's heat extraction capability. A preferred functional model configuration that has a desirable failure flow distribution can then be identified. The method presented here helps systems designers to better understand where failures propagate through systems and guides modification of systems functional models to adjust the way in which systems fail to have more desirable characteristics.

Non-linear assessment of critical failure modes in the first wall of the European TBM

The assessment of the different components of the Helium Cooled Pebble Bed (HCPB) and Helium Cooled Lithium Lead (HCLL) Test Blanket Modules (TBMs) based on elastic FE analyses has been performed considering main failure modes and respective structural design criteria. This study has been carried out for the operation at full power and for the so-called Approach 2 cooling that is set up at reduced heat extraction capability for compliance with temperature targets to be relevant to DEMOnstration power plant blanket system. Consequently this situation is the worst condition in terms of cooling performance as a result it reveals that many locations in the First Wall (FW) become critical in the sense that certain criteria are not fulfilled, particularly those for immediate plastic flow localization, progressive deformation (ratcheting) and creep-fatigue interaction. Of course one can better reach code compliance by improving the cooling performance (so called Approach 1) but it will degrade the DEMO relevancy.The critical failure modes are re-assessed performing non-linear analysis using an elasto-viscoplatic model, particularly developed for RAFM steels such as the structural material EUROFER97 by Aktaa & Schmitt, and considering the appropriate design criteria of the inelastic route of RCC-MRx and SDC-IC. Despite the conservatism in these criteria, the results show all-clear signal with respect to immediate plastic flow localization and at least much smaller breaches of the limits with respect to the other failure modes. Reporting details and results of the non-linear failure assessments demonstrates their potential and capability in supporting specific and efficient improvements to the design of highly loaded components. The conservatism in the considered design criteria and ways for its reduction are discussed in addition.

High Power, Thermally Efficient, X-band 3D T/R Module With Calibration Capability for Space Radar

Earth observation from space radar is based on the active electronically steerable antenna (AESA) whose performances count on reliable and powerful transmit/receive modules (TRM). To this aim, as a follow-up of the successful demonstration of a low-footprint transmit/receive hybrid module concept based on 3-D packaging and interconnect technologies (3DTRM), the interest for carrying out additional development work took a further step aiming at achieving a three-fold module performance improvement as well as at consolidating the novel proposed 3-D technology for space applications. First, the possibility of performing an AESA highly accurate calibration was implemented by embedding a wide band, high directivity directional coupler in the module circuitry without any total module footprint increase. Second, the heat extraction capability of the metal-ceramic hermetic package was enhanced through a re-design of the monolithic microwave integrated circuit (MMIC)-to-sink interface. And finally, the gallium arsenide (GaAs) MMIC high power amplifier (HPA) of the first 3DTRM version was replaced by a gallium nitride (GaN) HPA MMIC, obtaining both a higher transmit output power at 5 dB of compressed gain and an improved power added efficiency (PAE) at module level.

A Non-Gas-Based Cryotherapy System for the Treatment of Cervical Intraepithelial Neoplasia: A Mixed-Methods Approach for Initial Development and Testing.

Gas-based cryotherapy is the most widely used treatment strategy for cervical intraepithelial neoplasia (CIN) in low-resource settings, but reliance on gas presents challenges in low- and middle-income countries (LMICs). Our team adapted the original CryoPen Cryosurgical System, a cryotherapy device that does not require compressed gas and is powered by electricity, for use in LMICs. A mixed-methods approach was used involving both qualitative and quantitative methods. First, we used a user-centered design approach to identify priority features of the adapted device. U.S.-based and global potential users of the adapted CryoPen participated in discussion groups and a card sorting activity to rank 7 features of the adapted CryoPen: cost, durability, efficacy and safety, maintenance, no need for electricity, patient throughput, and portability. Mean and median rankings, overall rankings, and summary rankings by discussion group were generated. In addition, results of several quantitative tests were analyzed including bench testing to determine tip temperature and heat extraction capabilities; a pathology review of CIN grade 3 cases (N=107) to determine target depth of necrosis needed to achieve high efficacy; and a pilot study (N=5) investigating depth of necrosis achieved with the adapted device to assess efficacy. Discussion groups revealed 4 priority themes for device development in addition to the need to ensure high efficacy and safety and low cost: improved portability, durability, ease of use, and potential for cure. Adaptions to the original CryoPen system included a single-core, single-tip model; rugged carrying case; custom circuit to allow car battery charging; and sterilization by high-level disinfection. In bench testing, there were no significant differences in tip temperature or heat extraction capability between the adapted CryoPen and the standard cryotherapy device. In 80% of the cases in the pilot study, the adapted CryoPen achieved the target depth of necrosis 3.5 mm established in the pathology review. The LMIC-adapted CryoPen overcomes barriers to standard gas-based cryotherapy by eliminating dependency on gas, increasing portability, and ensuring consistent freeze temperatures. Further testing and evaluation of the adapted CryoPen will be pursued to assess scalability and potential impact of this device in decreasing the cervical cancer burden in LMICs.

Oscillating nanofluid droplet for micro-cooling

AC electrowetting is used to induce oscillation in a nanofluid droplet with significant changes in the shape dependent parameters at an optimized frequency. The presence of the synthesized silver nanoparticles not only enhances the wetting characteristics of the resulting nanofluid droplets, but leads to the augmentation of their heat extraction capability from a hot spot. The low frequency AC electrowetting induced droplet shape deformation generates surface waves and associated internal flow inside the droplet. This augments the convective heat transfer process resulting in additional evaporative cooling. The imposed internal flow and mixing also contribute to the reuse of the residual (after evaporation) nanoparticles to recreate the nanofluid droplet on the substrate. The generated surface waves are characterized using image analysis of the oscillating droplets in terms of their amplitude, frequency and damping. A model based on Stoke's drift phenomenon is used to analyze the results indicating augmented heat transfer in the low frequency regime.

Numerical investigation of the phase change process of low melting point metal

Low melting point metals (LMPMs) are a new kind of phase change materials (PCMs) which exhibit excellent heat extraction capability due to their high thermal conductivity. Such a characteristic renders it distinctive melting mode which hardly exists in conventional paraffin PCMs. In this paper, comprehensive numerical investigation is carried out to reveal the melting process of LMPMs. First, comparative simulations of typical paraffin eicosane and typical LMPM gallium is conducted. Then, dimensionless analysis is performed based on a series of parametric studies and corresponding dimensionless correlations are given under both constant wall temperature condition and constant heat flux condition. Further, the critical dimensionless values within which the correlations are applicable are suggested. Finally, a preliminary exploration is performed to illustrate the influence of natural convection under relatively high Ra number condition. This study can serve as a valuable reference for future practical thermal design of LMPMs based thermal management systems and thermal energy storage systems.

Characterization and experimental investigation of Al2O3 nanoparticle based cutting fluid in turning of AISI 1040 steel under minimum quantity lubrication (MQL)

During metal cutting operation, cutting fluid plays a vital role by cooling and lubricating the tool-work piece interface and removing chips from the cutting zone. As a result, a cutting fluid may significantly affect the tribological conditions at these interfaces. However, human health and environment both are affected negatively by the excessive use of conventional cutting fluid. This has led to the development of a new class of cutting fluid with superior thermal and tribological properties to restrict its extravagant use during machining. A colloidal mixture of metallic or non-metallic nano meter sized particles in a base fluid is called nanofluid. For the last one decade, nanofluids have attracted the attention of researchers due to its improved thermal conductivity and heat extraction capability. In the present work, a new nanofluid is prepared by mixing Al2O3 nanoparticles in conventional cutting fluid at different concentrations. The prepared nanofluid is characterized for its thermal conductivity and viscosity at all nanoparticle concentrations. Furthermore, its machining performance is examined in turning workpiece of AISI 1040 steel using minimum quantity lubrication (MQL) technique. The results are also compared with that of dry machining and wet/MQL machining using conventional cutting fluid. The experimental study clearly reveals that performance of Al2O3nanofluid in terms of surface roughness, tool wear, cutting force and chip morphology is found to be better compared to dry machining, wet machining with conventional cutting fluid and MQL using conventional cutting fluid.

Engineering design and analysis of Indian LLCB TBM set

India is developing Lead Lithium cooled Ceramic Breeder (LLCB) Test Blanket Module (TBM) for testing in ITER for the validation of fusion blanket design tools, tritium breeding performance and high grade heat extraction capability relevant to Indian DEMO. LLCB TBM is designed to withstand various ITER loads and its combinations, like thermal, mechanical including the high pressure coolant loads, electromagnetic loads during plasma disruption and seismic loading conditions. LLCB TBM system is designed in compliance with ITER Safety requirements and guidelines. A few challenging part in the design includes the design of helium cooled First Wall (FW) and back plates, the attachment system between TBM and the shield block to withstand loads for all the ITER operational modes, routing of high temperature process pipes between TBM and the shield block, interfaces between process pipes and the connecting flange, design of manifolds of different process fluids etc. Analysis has been performed on the LLCB TBM set using a Finite Element code, ANSYS. Relevant codes and standards, namely the French code RCC-MR, has been followed for the design analysis. The details of the analysis and further plans and proposals for improvement in design will be discussed in this paper.

Heat evolution and dissipation in organic light-emitting diodes on flexible polymer substrates

We investigated the effect of the heat generated in organic light-emitting diodes (OLEDs) on their performance with a focus on the thermo-physical properties of the substrates. OLEDs were fabricated on polyethylene terephthalate (PET), polyimide (PI), and glass substrates, and the instantaneous and time-resolved performances of the OLEDs were compared. The device operation temperature (T) was predicted via heat transfer analysis using the finite element method (FEM). The value of T during operation was experimentally measured using an infrared (IR) camera, and the results were compared with the numerically calculated values. The effects of T on the time-resolved electroluminescence (EL) spectra of the OLEDs on the different substrates were also investigated. The experimental results of this study agreed well with the numerical predictions that the T of the OLEDs on the polymers are higher than the T of the OLEDs on glass during operation due to the relatively low thermal diffusivity (α) of the polymer substrates used in this study. The results also showed that the performance and reliability of the flexible OLEDs (f-OLED) are highly dependent on the heat extraction capabilities of the substrates; thus, the current density (J), luminescence (L), voltage (V) characteristics, and efficiencies (η) over time of the OLEDs on PET and PI are inferior to the OLEDs on the glass substrate.

Mechanical design and thermo-hydraulic simulation of the infrared thermography diagnostic of the WEST tokamak

The WEST (Tungsten (W) Environment in Steady state Tokamak) project is a partial rebuild of the Tore Supra tokamak to make it an X-point metallic environment machine aimed at testing ITER technologies in relevant plasma environment. For the safe operation of the WEST tokamak, infra-red (IR) thermography is a crucial diagnostic as it is a sound and reliable way to detect hotspots or abnormal heating patterns on the plasma facing components (PFCs). Thus WEST will be fitted with middle/short-IR (1.5–2μm or 3–5μm) cameras in the upper port plugs to get a full view of the critical PFCs (in particular the new lower divertor) and radio-frequency (RF) heating antennas and one camera at the equatorial level to monitor the new upper divertor and the first wall.This paper describes the design of the up-to-date optical system along with the hydraulic analysis and the thermal and mechanical finite element analysis conducted to ensure adequate heat extraction capabilities. Boundary conditions and simulation results will be presented and discussed as well as technological solutions retained.

Comparative performance of ‘U-tube’ and ‘coaxial’ loop designs for use with a ground source heat pump

Abstract The installation cost and coefficient of performance (COP) of a ground source heat pump (GSHP) system can be greatly affected by the design of its ground loop. An experimental investigation was conducted to compare the performance of two loop designs for use with the ground source heat pump of an ‘energy pile’ installation or a conventional borehole system. A coaxial loop (a 40 mm OD coaxial tube with a 20 mm OD interior pipe) and a U-tube (20 mm OD pipes) of a length of 72 m were constructed, tested and analysed in terms of ground heat extraction capability and hydraulic flow characteristics. The use of the coaxial loop design could potentially reduce the cost of drilling boreholes and make the installation easier on site, as the effective diameter would be smaller than a comparable U-tube with the same mass flow rate, considering that the U-tube requires a minimum 10 mm spacer between the legs. Hydraulic performance tests have shown that the U-tube achieved the transitional-turbulent flow at a glycol flow rate of approximately 0.14L/s, whereas the flow in the coaxial remained laminar across the glycol flow rate range of 0.05–0.25L/s. Heat pump performance tests have shown that the U-tube achieved a COP of at least 0.08 greater than the coaxial loop across the range of glycol flow rates investigated, while the heat output was at least 12% greater when using the U-tube. Therefore, it can be concluded that the coaxial loop in its current form is seen not to add any performance benefit against the U-tube.