Pipe Heat Exchanger Research Articles

A Finite Element Model for Investigating Unsteady-State Temperature Distribution and Thermomechanical Behavior of Underground Energy Piles

The underground energy geostructure represented by the energy pile is one of the key paths for the cooperative development of underground space and geothermal energy. Because of its advantages of low cost, high efficiency and no extra occupation of underground space, it has become a feasible alternative to the borehole heat exchanger. The change in the temperature field of the energy pile and its surrounding ground not only affects the geological environment but also influences the thermomechanical performance and the durability of the structure. However, the temporal and spatial unsteady-state temperature distribution of piles and surrounding rock under typical intermittent and unbalanced thermal load conditions is still unclear. In this paper, a finite element model was applied to analyze the unsteady-state temperature distribution, and the thermomechanical behavior of the energy pile group was developed and verified. The temperature field distribution of pile and surrounding rock under typical intermittent working and unbalanced thermal load conditions were determined. Moreover, the thermomechanical behavior characteristics of the energy pile group were investigated. Finally, the influences of pile layout on the thermomechanical behavior of the energy pile group were identified by designing six different scenarios. The results indicate that under typical intermittent operation conditions, the temperature of the energy pile and surrounding ground near the heat exchange pipe varies periodically. For areas with unbalanced cooling and heating loads, long-term operation of energy piles leads to thermal accumulation, and the maximum temperature of energy piles occurs in the first daily cycle. In summer/winter working conditions, the increase/decrease in pile temperature induces axial compression/tensile stress. When the pile group is partially used as the energy pile, the non-energy pile acts as the “anchor pile”, and it generates the added tensile stress.

Numerical investigation of geothermal pavements: Design optimisation & boundary conditions

Geothermal pavements comprise a newfound type of thermal geo-structures, an innovation in pavement construction contributing to ground source heat pump (GSHP) systems, resulting in a better cost-efficiency compared to conventional GSHP systems. Ground heat exchangers are formed by embedding pipe into the pavement structure (e.g., base, sub-base or subgrades). Developing accurate models with appropriate boundary conditions is crucial to obtaining a deep understanding of the performance and function of geothermal pavement systems. This paper introduces an experimentally validated 3D finite element model (FEM) and compares the effect of surface boundary condition choices on the results of the simulation. The model uses two different approaches for boundary conditions: i) using ambient temperature and ii) implementing energy balance equations on the surface, as surface boundary conditions. The model is further utilised to perform a parametric study and the results are employed by a statistical tool (Minitab) to determine the optimum heat exchanger design for a geothermal pavement project in Adelaide, an Australian city subjected to temperate climate conditions and good solar irradiation throughout the year. Results show that the choice of both boundary conditions leads to similar fluid temperature trends, but with differences in values, particularly during the heating season, resulting in a reduced embedded pipe length of up to 30 % and up to a 10 % better annual average coefficient of performance (COP(when using the energy balance equations on the surface. The parametric study shows that the system annual COP increases with the length of the pipe and spacing between the pipes, whilst the pipe depth placement is inversely proportional to the annual average COP given the advantages obtained during the heating season over the cooling season. Finally, considering the interaction effect between various parameters, a pipe heat exchanger with 400 m length, 0.76 m pipe spacing and 0.45 burial depth is evaluated as the best design to maximise COP for the case study at hand.

Effects of internal airflows on the heat exchange potential and mechanics of energy walls

Energy walls are earth retaining structures equipped with pipe heat exchangers that harvest thermal energy sources from underground. Unlike fully embedded energy geostructures such as energy piles, energy walls interact not only with the ground but also with internal airflows under a wide range of conditions. Yet little is known as to how the internal airflows affect the heat exchange potential and mechanics of energy walls. In this paper, we conduct a systematic investigation into the effects of internal airflows on various aspects of energy wall performance, from the harvestable thermal power to the structural behavior. We construct and validate a numerical model of a full-scale energy wall. We then utilize the model to develop a comprehensive understanding of how internal airflows affect the energy, geotechnical, and structural performance of energy walls under a wide range of site and operational conditions. Results show that an internal airflow not only increases the heat exchange potential of energy walls but also leads to marked variations in the thermally induced axial forces, shear forces, and bending moments in the walls. Our findings consistently indicate that even minimal airflows should be considered in the analysis and design of energy walls.

Evaluasi pengeringan kunyit menggunakan pengering rak vertikal sumber energi sekam padi metode konveksi paksa

The drying process carried out in the open is prone to exposure to dust and animal waste. In addition, it takes a long time and is very dependent on the weather. The purpose of this research is to thermally evaluate a forced convection type vertical shelf dryer using rice husk energy using a single furnace model. This is done through the conversion of rice husks into thermal using a heat exchanger. Rice husks are burned directly in a furnace equipped with heat exchange pipes. This pipe functions to circulate heated environmental air into the drying chamber with the help of an exhaust fan. The test was carried out to dry a sample of white turmeric with a mass of 3191 grams for 600 minutes. The sample mass is evenly distributed on 4 vertical shelves in the drying chamber. The test results show that the ambient temperature increased by an average of 73.57%, namely from 28.57 o C to 49.58 o C. This temperature is the average temperature that occurs in the drying chamber in the turmeric drying process. The average drying temperature on each shelf differs depending on the distance from the heat source. On shelves 1, 2, 3, and 4, respectively, they are 54.21 o C, 50.93 o C, 47.62 o C, and 45.57 o C. Overall, the water content of white turmeric after drying reached 6.335% from the initial water content of 79.6%. The average efficiency of the dryer is 32.97%. During the drying process, there is a decrease in efficiency. This is because the energy absorbed by white turmeric decreases due to reduced water content. This dryer model can be used as an alternative in post-harvest handling for small farmers that is energy efficient and sustainable.

Investigation of an innovative Canadian well system combined with a frozen water/PCM heat exchanger for air-cooling in hot climate

In recent years, due to many reasons, such as environmental and economic problems, the use of shallow geothermal as a clean energy source has been of great interest inside the scientific community. However, the main targeted application is air cooling and heating in buildings by using a buried pipe in the ground known as Earth to Air Heat Exchanger (EAHE). This system (EAHE) alone cannot fulfill the comfort conditions in countries characterized by hot and cold climates, and an auxiliary system is required. The present work proposes a new hybrid system consisting of coupling the EAHE (primary system) with a concentric two pipes heat exchanger (secondary system). The inner pipe has multiple longitudinal fins filled with frozen water or a mixture of ethylene glycol and water as a phase change material (PCM). The air is cooled when exchanging heat with a frozen PCM in the secondary heat exchanger (Water/PCM HEX). A theoretical investigation of the proposed hybrid system has been carried out. However, transient models have been developed for both heat exchangers, and the nonlinear equations obtained have been solved using numerical methods. The simulation of the behavior of this hybrid system located in Madinah city (Kingdom of Saudi Arabia), presenting a hot climate, has been carried out. The effect of geometrical parameters and operation conditions on the outlet air temperature and the operation period has been investigated. The study results show that the convective heat transfer coefficient is significant in the Water/PCM HEX. As long as its value is low, the cooling is not significant; as shown by decreasing the freezing temperature from 0 °C to −10.71 °C, the gain in the outlet air temperature dropping is <1 °C. When the external pipe diameter has been reduced from 8 to 6 in., the air is cooled down by almost 5 °C. The proposed system presents an attractive cooling solution during peak periods, especially for hot climates less severe than Madinah.

Empirical formulas for borehole thermal resistance of parallel U-type cast-in-place energy pile

The borehole thermal resistance (mK/W) is an essential design factor of a ground source heat pump system, which allows to predict changes in the circulating fluid temperature. However, there are no proven and/or practical solutions to the borehole thermal resistance of ground heat exchangers with large borehole diameters and multiple U-type pipes, such as a large-diameter cast-in-place energy pile. In this study, empirical formulas were provided to estimate the borehole thermal resistances of large-diameter cast-in-place energy piles equipped with multiple pairs of U-type heat exchange pipes. First, the borehole thermal resistances of parallel U-type energy piles were evaluated through a series of in-situ thermal performance tests. Then, a numerical model for parallel U-type energy piles was developed and verified using the field test results. With the developed numerical model, the effects of various influencing factors on the borehole thermal resistances of parallel U-type energy piles were identified. Finally, empirical formulas were developed and verified by comparing with the field tests and numerical simulations. Consequently, the empirical formulas could predict the borehole thermal resistance of parallel U-type energy piles with a difference of less than 0.23% compared to the numerical model and 6.4% compared to the field test results.

Design and Thermal Environment Analysis of a Decentralized Cooling System with Surface-Mount Heat Pipe Exchangers on Servers in Data Centers

This paper proposes a decentralized cooling system combined with a traditional computer room air conditioning unit and server-level heat pipe exchangers for thermal environment optimization in a data center. Two cooling strategies, with heat exchangers installed above and below the servers respectively, are proposed and compared with the original CRACs system in terms of thermal environment. The simulation results of the original data center model are in good agreement with the on-site measurement results, and thus its reliability can be validated. The results show that a decentralized cooling system can effectively improve the thermal environment in data centers. To obtain the highest cooling efficiency, altogether 18 cases, where heat pipe exchangers were installed at different locations and heights, are analyzed and compared. The results show that the thermal environment is optimal when heat pipe exchangers are installed 0.01 m below each server. The local hotspot temperature is reduced by 6.8 °C, and the temperature distribution of the rack is the most uniform, which can effectively reduce the heat accumulation in data centers.

Performance Analysis of Methanol in Heat Pipe Heat Exchanger – An Experimentation and Numerical study using ANFIS

In electronic cooling systems and utilization of waste heat to safeguard the electronic components from overheating the heat pipe are used. This study focus with the experimentation and numerical comparison of an Heat Pipe Heat Exchanger (HPHE) using methanol. The investigation focuses on various orientation angles (0° and 90°) and extended with (10° to 80°) angles. The maximum Reynolds number obtained as 1.33% for 0° than 90°, similarly 8.56% for 60° comparing with 10°. The minimum thermal resistance obtained as 2.65% for 0° than 90°, similarly 3.81% for 60° while related with 10°. The observed average minimum thermal resistance for experimental value as 3.29% and predicted value as 3.46%. From the investigation it’s evident that experimental results are closes to the numerical values using ANFIS - Neuro fuzzy system. In the utilization of waste heat recovery system the HPHE shows better performance and this can scaled and utilized for electronic component cooling applications.

ВЛИЯНИЕ КОНСТРУКЦИОННОГО МАТЕРИАЛА ТЕПЛООБМЕННЫХ ТРУБ И ТЕРМИЧЕСКОГО СОПРОТИВЛЕНИЯ ЗАГРЯЗНЕНИЙ ПОВЕРХНОСТИ ТЕПЛОПЕРЕДАЧИ НА ИНТЕНСИВНОСТЬ ТЕПЛООБМЕНА

The influence of the structural material of heat exchange pipes and the thermal resistance of contamination of the heat transfer surface on the intensity of heat exchange is considered. The necessity of taking these factors into account when designing heat exchangers is shown

On the thermal performance enhancement of spiral-coil energy piles with a thermal recovery system

The pile foundation designed to ensure building stability when equipped with heat exchanger pipes to harvest geothermal energy is called an energy pile. Ground Source Heat Pump (GSHP) systems combined with energy piles have been used and developed as sustainable and efficient HVAC systems. Energy piles suffer from cold or heat accumulation in and around the pile, degrading their long-term performance. The current study seeks to alleviate this problem by proposing a thermal recovery system. The proposed system circulates ambient air in the pile foundation to extract the accumulated heat. A three-dimensional transient computational fluid dynamics model of the GSHP system coupled with the energy pile and the suggested recovery system is developed. This model is then used to investigate the effect of the various design parameters on the performance of the system and to determine the optimum system parameters. It is demonstrated that the maximum provided cooling load of the system with the proposed recovery system is 50% higher than the conventional system without the recovery. Moreover, the fifteen-year average COPannual of the system with double Ground-Air Heat Exchanger (GAHE) pipes and the system with one GAHE pipe is 30% and 16% more than the system without recovery.

Experimental study on thermo-mechanical responses of pre-bored grouted planted piles with different restraint conditions

Geothermal energy piles (GEPs) are an innovation technology of vertical ground heat exchangers (GHXs) which can be used for the heating and cooling of building combined with ground source heat pumps. The main barriers to adoption are the inconvenient installation and a lack of the knowledge regarding the potential effect of temperature changes on pile foundations compared to traditional GHXs. The installation process can be facilitated by using pre-bored grouted planted (PGP) GEPs, which simplify the installation of heat exchange pipes and hence reduce the installation time. It is desirable to investigate the thermo-mechanical responses of this GEP for understanding the potential effects of the temperature changes.A PGP GEP was installed in a building during construction that incorporated two heating tests with different conditions (a short-term Test 1 without building load, and a long-term Test 2 with strong structural restraints and building load) to investigate the behavior of the PGP GEP. A fiber Bragg grating (FBG) sensor system was used to evaluate temperature and strain behaviors of the test pile and two adjacent boreholes. The results show that the nonuniform spatio-temporal response of temperature induced the nonuniform thermal-induced stress along the pile depth. The end-restraints had significant effects on the thermo-mechanical response over the full pile. A comparison between the PGP GEP and other types of GEPs were conducted, and the similarities and differences between them were discussed.

Performance analysis of a parabolic trough collector using a heat pipe exchanger

AbstractIn this article, a detailed performance analysis of a capillary heat pipe coupled with a parabolic trough collector is performed. The influence of different parameters on the overall system's performance was studied namely; beam radiation and the inclination of the PTC. Results showed that using a heat pipe as an absorber improves the performance of the PTC. At Tmax, the coupling of the heat pipe with PTC leads to a 33% increase in the system's global efficiency and a significant reduction in the heat losses by 46.55%. The inclined arrangement configuration improved the global efficiency of the system by 13%. The obtained results were compared with the experimental data provided by the literature and reasonable agreement was observed, thus confirming the model's validity.

СПОСОБ ПОВЫШЕНИЯ ЭФФЕКТИВНОСТИ ВОЗДУШНОГО КОНДЕНСАТОРА ПРОПАНА

A method for evaluating the efficiency of heat transfer from the outer surface of finned heat exchange pipes to atmospheric air in air cooling apparatus is considered

A Novel Approach for Performance Analysis of Air–Air Wickless Heat Pipe Heat Exchanger

Abstract Wickless heat pipe heat exchangers (HPHE) consistently showed instabilities and omits many experimental tests. The performance of a heat pipe is governed by many parameters, and the effects of which may influence each other. The objective of this paper is to develop a new approach for an air–air heat pipe heat exchanger that takes into consideration the effect of heat transfer coefficients, saturation temperature, and thermal resistances inside the heat pipes as well as maximum heat transfer limit. The approach is based on analyzing inner heat pipe parameters with HPHE external working conditions. Results are also assessed for higher heat capacities ratio and found that the thermal resistances inside a heat pipe are a limiting factor, leading the HPHE system to perform poorly in particular for Cr ≤ 1. Overall heat transfer coefficients at HPHE sides as well as HPHE effectiveness as a function of Cr are assessed. Trying to follow the Chaudourne (1992, “The Heat Pipe Heat Exchangers: Design, Technology and Applications,” Design and Operation of Heat Exchangers, Springer, Berlin, Heidelberg, pp. 386–396) profile for conventional heat exchangers, HPHE effectiveness is determined and limited to 0.5 number of transferred units. The established model is verified by the existing literature and demonstrates numerical results that agree with the experimental data within a 2.86% error.

Thermodynamic Optimization of the Ethylene Oligomerization Chemical Process

The use of olefin oligomerization in the synthesis of liquid fuel has broad application prospects in military and civil fields. Here, based on finite time thermodynamics (FTT), an ethylene oligomerization chemical process (EOCP) model with a constant temperature heat source outside the heat exchanger and reactor pipes was established. The process was first optimized with the minimum specific entropy generation rate (SEGR) as the optimization objective, then multi-objective optimization was further performed by utilizing the algorithm with the minimization of the entropy generation rate (EGR) and the maximization of the C10H20 yield as the optimization objectives. The results showed that the point of the minimum EGR was the same as that of SEGR in the Pareto optimal frontier. The solution obtained using the Shannon entropy decision method had the lowest deviation index, the C10H20 yield was reduced by 49.46% compared with the point of reference and the EGR and SEGR were reduced by 59.01% and 18.88%, respectively.

Study of Gas-to-Liquid Heat Pipe Heat Exchanger

This study is focused on the study and development of a gas-to-liquid heat pipe heat exchanger (HPHE) based on numerical and experimental analysis. Stainless steel heat pipes were installed inside the heat exchanger in the form of three equilateral triangles, staggered into a hexagonal configuration to simulate the waste heat recovery from hot exhaust gas to a water flow. The first main aim of this study was focused on 3D design and numerical analysis, which were used to create and calculate the effect of similar input conditions on the overall system. The system was tested for the overall heat transfer by measuring the temperature change in both fluids. The heat transfer and overall average temperature were used to calculate the effectiveness of the system. In the second part of this study, a test of the waste heat recovery was undertaken with this setup, using water as the cooling fluid. The study was conducted with different input velocities and temperatures of waste hot air, controlled simultaneously by the input fan and air heater, whereas the cooling water was kept at a steady state of 30 °C and 0.0156 kg/s at the input. The hot air velocity was controlled by fans with different inlet air velocities of 0.3 m/s, 0.5 m/s, and 0.7 m/s. Moreover, the temperature of the air was changed from 150 °C to 250 °C with a step of 25 °C. The increase in temperature and the velocity of air was directly proportional to the amount of heat transferred from the air to the cooling water, and the effectiveness was also found to be inversely proportional to both of the varying input parameters. The numerical study showed a maximum increase of 12% in the heat transfer. The output temperatures of hot and cold fluids showed maximum increases of 7 K and 3 K, respectively. The numerical system with such input parameters can be evaluated further to predict the behavior of changes in the design and parameters.

Intensification of Heat and Mass Transfer in a Diabatic Column with Vortex Trays

We used vortex contact devices that we developed and investigated to make a new design of an alcohol diabatic distillation column with heat exchange pipes (as the reflux condenser) passing through concentrating section trays. In the column, ascending vapors partially condensed on the surface of vertically installed heat exchange tubes, forming a reflux. The reflux was then mixed with the draining liquid flow in the vortex contact devices placed on the trays. Heat was removed from the column through the boiling of the draining water film along the inner surface of the heat exchange pipes. We compared both diabatic and adiabatic columns fitted with the developed vortex contact devices on the trays. The proposed innovative contact system allows increasing productivity, reducing column dimensions and steam- and heat-transfer medium consumption, and increasing separation efficiency. Dependences for calculating the gas content, hydraulic resistance, and interphase surface required for designing the vortex contact devices of the proposed unit trays are presented.

Nanotechnology Applications in Ground Heat Exchanger Pipes: A Review

The use of Ground Source Heat Pumps (GSHPs) has grown exponentially around the world over recent decades. The GSHP represents an alternative device to electric heating systems and oil boilers. Additionally, it requires a lower power consumption and less maintenance than combustion-based heating systems. Moreover, the CO2 emissions produced by a GSHP are lower than other systems based on burning oil, gas, or biomass. However, the main obstacle for the widespread use of GSHPs is the high cost of Ground Heat Exchanger (GHE) installation, a technology that exhibits low thermodynamic efficiencies. Over the past decade, some studies have been conducted to improve heat transfer in GHE pipes using traditional working fluids, creating new pipe materials or designing new heat exchanger configurations. The main contribution of this paper is a summarization of the outcomes of theoretical, numerical and experimental studies to improve heat transfer in GHEs using nanotechnology. Additionally, the development of new fluids (nanofluids) and new materials (nanoparticles and nanocomposites) applied to heat exchanger pipes and the designs and configurations of GHEs are highlighted. As a result, the present review provides a perspective for future research regarding the use of nanotechnology to reduce the costs involved in GHE for GSHP improvement.

Thermal resistance analysis of an energy pile and adjacent soil using radial temperature gradients

This paper examines the thermal resistances of energy piles and surrounding soils. A field-scale bored energy pile was installed through stiff sandy clay and dense sand and instrumented to measure temperatures on the external walls of the heat exchanger pipes, at the pile-soil interface, and in the soil. The radial temperature gradients between the pipes and the pile-soil interface, and the pile-soil interface and the soil, were used to evaluate the pile and soil thermal resistances, respectively. The thermal resistances were on the same order of magnitude with values of 0.053 mK/W, 0.072 mK/W, and 0.066 mK/W for the pile, stiff sandy clay, and dense sand due to similarities in their thermal properties. The analysis suggests that pile and soil thermal resistances are influenced by the pile dimensions, number of pipes, concrete cover, soil type and duration of heating. Hence, meticulous interpretation of thermal resistances considering these parameters should be conducted to understand heat transfer processes in energy piles accurately. Estimates of the pile thermal resistance from the equivalent diameter and thermal response test methods were found to be inconsistent with each other, highlighting the significance of considering steady state in-situ radial temperature gradients in designing energy pile systems.

Numerical investigation of heat exchanger pipe equipped with chamfered circular ring separated from wall to intensify thermo-hydraulic performance

Chamfered circular ring (CCR) innovated from conventional circular ring by introducing chamfered surface on its periphery at 30o attack angle is numerically investigated to study its effect on fluid flow characteristics, heat transfer enhancement, and friction factor in a heat exchanger pipe. In order to study flow blockage effect on overall performance of device, three diameter ratios (DR = Di/Do = 0.6, 0.7 and 0.8) with three spacing ratios (SR = s/D = 1, 2 and 3) are used. Turbulent model k – ε, RNG with enhanced wall treatment is used to solve governing equations. Results showed that CCR chamfered surface produced nozzle jet effect on pipe wall surface through clearance of 1 mm, which further induced turbulent and recirculating flow effect near pipe wall area. This resulted into higher heat transfer rate. All the diameter ratios with SR = 1 showed thermal performance factor value more than unity at most of the lower Reynolds number. The range of TPF shown by DR = 0.6, 0.7 and 0.8 with SR =1 is 1.21–0.93, 1.23–0.97, and 1.19–0.99, respectively. Compromised results of TPF are shown by DR = 0.7 and DR = 0.8 at SR = 1. Chamfered circular ring has shown better results over circular ring, perforated conical ring, short length twisted tape, twin co-twisted tape, wire rod bundles, and perforated twisted tape. Numerical results showed better agreement with predicted results within the range of 10%. Highest TPF of 1.23 is shown by DR = 0.7 and SR = 1 at Re 6000.