Current Heat Exchanger Research Articles

Composites with Synergistically Enhanced Thermodynamic and Mechanical Properties for Geothermal Heat Exchangers

Geothermal energy, derived from the radioactive decay of elements within the Earth's core, is a renewable and clean energy source. The extraction of geothermal energy primarily depends on ground heat exchangers. To address the issue of incompatibility between corrosion resistance, high thermal conductivity, and mechanical performance in current ground heat exchangers, this study develops composites (PEPOE/SCA@SiC) composed of high‐density polyethylene (HDPE) modified with toughener polyethylene‐octene copolymer elastomer (POE) and silicon carbide (SiC) crystals modified with γ‐aminopropyltriethoxysilane (SCA). HDPE offers excellent corrosion resistance, SiC crystals provide efficient phonon transport, and SCA improves the interface compatibility of the composite. The thermal conductivity of PEPOE/SCA@SiC reaches 3.83 W m−1K−1, with a maximum tensile strength of 20.3 MPa, a tensile elastic modulus of up to 498 MPa, and a maximum bending stress of 22.2 MPa with a bending elastic modulus of 561 MPa. Corrosion resistance tests indicate no signs of corrosion in PEPOE/SCA@SiC when exposed to geothermal simulation fluids at 90 °C for 30 days. This study demonstrates that PEPOE/SCA@SiC composites have substantial potential for application in ground heat exchangers, offering promising prospects for advancing sustainable use of geothermal energy and environmental protection.

Investigation on heat transfer performance of energy diaphragm walls under groundwater flow condition

The flow of groundwater affects the transport of heat, subsequently impacting the heat transfer performance of energy diaphragm walls. To investigate the effect of groundwater flow on the thermal performance of energy diaphragm walls in the actual project, a three-dimensional finite element model of the thermo-hydro coupling was established. This model's accuracy was confirmed using in-situ experimental data. Subsequent analyses explored the influence of groundwater flow velocity on the long-term heat transfer efficiency of energy diaphragm walls and the temperature field distribution in both the wall and adjacent soil during winter/summer cyclical operations. Studies have shown that the increase of groundwater flow velocity can promote the migration of heat accumulated in the wall and in the soil around the wall to a position farther away from the wall along the flow direction, thereby promoting the long-term heat exchange efficiency of the thermo-active diaphragm walls. Moreover, as winter and summer operating conditions transition, the previously accumulated heat in the wall and surrounding soil aids in boosting the current mode's heat exchange efficiency. In addition, groundwater flow also facilitates the movement of heat accumulated at the bottom of the excavation face, allowing the ground's temperature field to stabilize faster. This indirectly bolsters the heat exchange efficiency of the energy diaphragm walls. The research results may enrich the understanding of the heat transfer behavior of energy diaphragm walls under actual working conditions.

Heat Transfer Enhancement in Heat Exchanger using Double Sinusoidal Shape Fins

Heat Transfer Enhancement in Heat Exchanger using Double Sinusoidal Shape Fins

History of the iron furnace using the physical-chemical blast furnace model

The physical–chemical blast furnace model first built by Michard and Rist has proven to be a very efficient tool to predict and drive the present blast furnaces. It mostly describes the iron blast furnace as a counter current gas-solids dual heat and oxygen exchanger. The onset of coke gasification (orelse of iron oxide direct reduction), leads to a two-zones exchange model. This theory is used to look back at the operation of the earlier and smaller iron furnaces such as the early XIXth century charcoal blast furnace or the much older low shaft furnaces. It shows the interest of using physical-chemical models to better understand the operation of past production tools.

Analysis of human thermoregulatory mechanisms using 2-D computational model

A numerical investigation is reported comparing various human thermoregulation mechanisms under hot and cold stress. The passive system of the developed model consists of 12 spherical/cylindrical segments and is modeled using the Pennes bioheat equation and finite difference method. The active system accounts for all regulatory responses, including the counter current heat exchange between veins and arteries; the respiratory heat loss; and threshold, gain, and maximum intensity of response mechanisms. The developed code analyzes various thermoregulatory defense mechanisms under hot and cold environments. Results indicate that shivering and sweating are more effective than other defense mechanisms under cold and hot conditions, respectively. Suppressing shivering will be more effective than the stoppage of vasoconstriction for inducing therapeutic hypothermia. The normal basal metabolic heat generation is essential to maintain a constant body temperature. It is seen that the changes in threshold temperatures of thermoregulatory mechanisms significantly affect the core more than the peripheral regions. The result may be helpful for better management of therapeutic hypothermia, hot/cold stress management, and design of drug protocols.

Optimal distribution of heat exchanger area for maximum efficient power of thermoelectric generators

Based on the multi-element thermoelectric generator model established in the previous literature, finite-time thermodynamic theory is used to deduce the efficient power expression of the thermoelectric generator. For a fixed number of thermoelectric elements and total heat exchanger area, the maximum efficient power is obtained by optimizing heat exchangers area distribution and output current. The effects of the number of thermoelectric elements and the total heat exchanger area on the maximum efficient power are analyzed. The results show that there is an optimal heat exchangers area distribution and an optimal output current to maximize the efficient power of the thermoelectric generator. Thermal efficiency at maximum efficient power is always better than at maximum power output. The total heat exchanger area is increased from 0.03 m2 to 0.09 m2, the maximum efficient power is increased from 0.02 W to 0.26 W, and the corresponding optimal output current and optimal heat exchangers area distribution are increased by 138% and 6.7%, respectively. In the actual designing process of the thermoelectric generator, the influences of the number of thermoelectric elements, the total heat exchanger area, the output current and the heat exchangers area distribution on its performance should be considered.

Experimental Investigation of the Heat Transfer between Finned Tubes and a Bubbling Fluidized Bed with Horizontal Sand Mass Flow

The sandTES technology utilizes a fluidized bed counter current heat exchanger for thermal energy storage applications. Its main feature is an imposed horizontal flow of sand (SiO2) particles fluidized by a vertical air flow across a heat exchanger consisting of several horizontal rows of tubes. Past international research on heat transfer in dense fluidized beds has focused on stationary (stirred tank) systems, and there is little to no information available on the impact of longitudinal or helical fins. Previous pilot plant scale experiments at TU Wien led to the conclusion that the currently available correlations for predicting the heat transfer coefficient between the tube surface and the surrounding fluidized bed are insufficient for the horizontal sand flow imposed by the sandTES technology. Therefore, several smaller test rigs were designed in this study to investigate the influence of different tube arrangements and flow conditions on the external convective heat transfer coefficient and possible improvements by using finned tubes. It could be shown that helically finned tubes in a transversal arrangement, where the horizontal sand flow is perpendicular to the tube axes, allows an increase in the heat transfer coefficient per tube length (i.e., the virtual heat transfer coefficient) by a factor of 3.5 to about 1250 W/m2K at ambient temperature. Based on the literature, this heat transfer coefficient is expected to increase at higher temperatures. The new design criteria allow the design of compact, low-cost heat exchangers for thermal energy storage applications, in particular electro-thermal energy storage.

Effect of Chemical Reaction towards MHD Marginal Layer Movement of Casson Nanofluid through Porous Media above a Moving Plate with an Adaptable Thickness

In the current workflow and heat exchange of a Casson nanoliquid across a penetrable media above a moving plate with variable thermal conductivity, adaptive thickness and chemical reaction are analyzed. First, the governing nonlinear equations of partial derivative terms with proper extreme conditions are changed into equations of ordinary derivative terms with suitable similarity conversions. Then the resulting equations are worked out using the Keller box method. The effects of various appropriate parameters are analyzed by constructing the visual representations of velocity, thermal, and fluid concentration. The velocity profile increased for shape parameter, and the opposite trend is observed for magnetic, Casson, porosity parameters. Temperature profile increases for magnetic, Casson, Brownian motion parameter, and thermophoresis parameters. Concentration profiles show a decreasing trend for wall thickness, Brownian movement, chemical reaction parameters. Also, skin friction values and calculated and matched with previous literature found in accordance. Also, local parameters Nusselt and Sherwood numbers are calculated and analyzed in detail.

Experimental and Mathematical Research of Convection Heat Transfer for a High Integral Finned Tube Heat Exchanger

This research exhibits an experimental and numerical investigation for the characteristics of heat transfer by utilizing an integral and smooth high finned tube and shows how the integral high fins affect in improving the transfer of heat. In the experimental work, the experimental rig consists of a cold water loop, a hot air loop and the trial part which is a concentric parallel flow double pipe heat exchanger. The first test smooth tube made of brass has external and internal diameter (32 mm) and (22 mm), respectively, the second test section made of the same material has external fins, the third test section possesses internal fins, and the fourth test section has internal and external fins. The dimensions of the fin are (2 mm) in thickness, (2 mm) in height and pitch (2.5 mm) center to center. And, the water flow rates are (6, 8, 10, 12 and 14 L/min). The inlet water to the trial tube was at temperatures (15, 25, 35, and 45oC). The investigational results manifested that the air side heat transfer coefficient of the smooth tube was lesser than the integral high finned tube. The ratio of improvement when using the integral high finned tube was (47.5%, 60.5% and 67.5 %). Numerical simulation was applied on the current heat exchanger to study both the transfer of heat and the field of flow by using ANSYS, FLUENT15 package. Steady state, Newtonian flow, incompressible and three dimensional analyses were assumed. The comparison between experimental work and numerical results elucidated a good agreement.

Fluid Flow and Heat Transfer Characteristics Investigation in the Shell Side of the Branch Baffle Heat Exchanger

The branch baffle heat exchanger, being an improved shell-and-tube heat exchanger, for which the flow manner of the shell-side fluid is a mixed flow of oblique flow and local jet. The computational fluid dynamics (CFD) method has been implemented to investigate the fluid pattern and heat transfer performance. The accuracy of the modeling approach has been confirmed by an experimental approach using a Laser Doppler Velocimeter system. Flow field, temperature field, and pressure field are displayed to study the physics behavior of fluid flow and thermal transport. Heat transfer coefficient, pressure drop, and efficiency evaluation criteria are analyzed. In contrast with the shell-and-tube heat exchanger with segmental baffles and shutter baffles, the pressure loss in the proposed heat exchanger with branch baffles has been dramatically improved, accompanied by a slight decrease in heat transfer coefficient under the same volume flow rate. The efficiency evaluation criteria of the heat exchanger with branch baffles are 28%-31%,13.2%-14.1% higher than those with segmental baffles and shutter baffles, respectively. Further analysis in accordance with the field synergy principle illustrates that the velocity and pressure gradients of the heat exchanger with branch baffle have finer field coordination. The current heat exchanger structure provides a reference for the future optimization design to reach energy saving and emission reduction.

Multi-plant direct heat integration based on the risk-based Shapley value and Alopex-based evolutionary algorithm

Current heat exchanger network (HEN) synthesis is mainly focused on minimizing the total annual cost (TAC), and then allocating the minimized TAC among plants. However, the obtained HENs usually have complex inter-plant heat matches, and if unplanned shutdowns occur, connected plants will suffer huge economic losses. Consequently, some plants may be unsatisfied with their allocated costs and prefer not to join this multi-plant coalition. In this study, a natural risk-based Shapley value curve is used to represent the variation of cost allocation under shutdown risks between 0% and 100%. Alopex-based optimization strategies are proposed to optimize the modified HEN model with core constraints that can restrict the Shapley value curve to the core range as feasible cost allocation solutions. Therefore, HEN configurations and acceptable cost allocation plans under any shutdown risks are determined simultaneously. Two cases demonstrate that the proposed methodology can reduce shutdown-induced economic losses and facilitate multi-plant cooperation.

Transient detection of either maldistribution or flowrate change in a counter current plate-fin heat exchanger using an ARX model

Parametric models of ARX structure express the relationship between an input u(t) and one output yarx(t). The purpose of the study is first to identify such a transient model through temperature measurements in a calibration experiment. It relates the output, that is the temperature response at the outlet of each of the two fluids that flow inside the heat exchanger, to the temperature increase at the inlet of the hot fluid, considered as a transient thermal input. This model is validated in a different experiment and transient perturbation experiments are run with maldistribution or flowrate changes. They are processed in order to detect such structural changes with respect to the calibrated model and to get the steady state characteristics, transmittances and effectivenesses, of the exchanger. The advantages and drawbacks of this non-destructive technique, which does not rely on any heat transfer correlation, are detailed and discussed.

STUDY ON PARAMETERS IN COUNTER CURRENT DOUBLE PIPE HEAT EXCHANGER APPLYING CIRCULAR TURBULATOR

Many industries dealing with manufacturing and HVAC (heating, ventilation, and air cooling) are rely heavily on thermodynamics principles with respect to heat and mass transfer. The objective of this study is to do optimization to yield optimum heat transfer rate and minimized pressure drop with regard to number of circular turbulator (CT) and water debit on Nusselt number (Nu) in counter current double pipe heat exchanger. This work has applied the classical rule of thermal science dealing with Nusselt number in relation to convection and conduction of heat transfer rate due to temperature effect. The result shows the highest Nu found to be 835.3 at 5 CT and water debit of 9 L/min. The addition of CT number gives effect on fluid current due to vortex generation. This study also investigates the effect of CT number on friction coefficient that the friction coefficient of a heat exchanger in the absence of CT is lower than that in the presence of CT. For any CT number, the friction coefficient is reduced with increasing water debit. The study has also found that the thermal performance ratio has achieved higher values for heat exchanger in the absence of CT.

Experimental exergy analysis of a printed circuit heat exchanger for supercritical carbon dioxide Brayton cycles

Abstract Exergy analysis could improve the quality of energy in the printed circuit heat exchanger. However, most of the current researches were carried out based on the first law of thermodynamics, which only focus on heat transfer, pressure drop, and heat transfer rate of the heat exchanger. There are no reports about experimental analysis of the printed circuit heat exchanger using the exergy analysis. Therefore, in this study, experimental exergy analysis of a printed circuit heat exchanger used as a recuperator for the supercritical carbon dioxide Brayton cycle is introduced. In the tests, the zigzag channels are adopted for the current heat exchanger to achieve higher heat transfer capability. The maximum running temperature and pressure in the experiments are 715.2 K and 22.5 MPa, respectively. The Reynolds number varies from 3212 to 23888. Pressure drops and temperatures are measured at the inlet and outlet of both sides. The effects of the inlet temperatures and Reynolds numbers on the exergy loss and efficiency of the printed circuit heat exchanger are investigated. The results show that the low Reynolds number and high inlet temperature on the cold side have positive effects on the exergy efficiency. New Nusselt number and friction factor correlations are developed according to the test results.

Hybrid Electrothermal Model for Insulator-to- Metal Transition in VO2 Thin Films

Comprehensive model for the insulator to metal phase transition in vanadium dioxide thin film in the presence of external electrical stimulus is proposed. This model divides the film layer into several segments and solves the Joule heating equations due to current flow and heat exchange with the environment and Poole–Frankel equation to obtain carrier concentration in response to the applied voltage, and transition is checked for each cell separately. The model follows the experimental results and exhibits both switching and hysteresis effect in planar structures and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${S}$ </tex-math></inline-formula> -shaped current–voltage characteristics in sandwich metal–insulator–metal structure based on the vanadium dioxide thin film. This model shows that by reducing the vanadium dioxide layer thickness, the electric field-assisted transition plays the dominant role in the transition, and therefore, it is a promising tool for the design and analysis of vanadium dioxide structures with various electrode distances.

Study of laminar convection heat transfer in single-side-heating small-scale cooling channel with vibration cylinder

Traditional enhancing convective heat transfer methods are mainly based on the flow turbulence by vortex generators, however, with increasingly heat transfer needs, traditional stationary vortex generators have not met the cooling demand. Thus, active flow control technique is proposed to better enhance convective heat transfer performance. The vibration cylinder is set as a vortex generator to achieve fluid flow disturbance aiming to enhance heat transfer. This method did not change the structure of the channel wall but introduced the built-in vibration source to achieve flow perturbations. New cooling technique is achieved by adjusting vibration cylinder to achieve active flow control and thermal control management. Several test Cases are built to analyze influence of cylinder vibration on convective heat transfer. The investigation indicates that the heat transfer coefficient can be improved by a maximum 14.69%, and comprehensive heat transfer performance is improved by 16.13% than the traditional stationary cylinder channel. Finally, the cylinder vibration can better improve the cooling performance and maintain a smaller pressure drop change. The study aims to propose a new enhancing heat transfer technique of active flow control to improve current heat exchangers performance.

Critical Analysis of the Current State of Knowledge in the Field of Waste Heat Recovery in Sewage Systems

The need for efficient use of energy and sustainable energy management and the fact that large quantities of heat are deposited in the discharged sewage have contributed to the development of research on waste heat recovery. Gray water began to be seen not just as waste, but also as an alternative source of energy. Research related to the development, improvement, and finally, the popularization of waste energy recovery devices and systems has evolved rapidly over the last two decades. Initially, technologies for gray water reuse were not widely used, which was due to the low efficiency of the current heat exchangers and the significant investment outlays that would have to be covered by potential users. Research conducted by scientists from around the world has allowed us to eliminate construction flaws, improve efficiency, and also provide information on the selection of optimal waste heat recovery technology, depending on the installation conditions and operating parameters. The ability to correctly select the device allows for effective energy collection from gray water, which improves the investment profitability. This paper reviews the research regarding issues related to waste heat recovery from gray water in sewage installations and systems. A critical analysis of the current state of knowledge was carried out with a special consideration to the technologies intended for the residential buildings.

EFFECT OF NON-NEWTONIAN FLUIDS ON THE PERFORMANCE OF PLATE TYPE HEAT EXCHANGER

A plate heat exchanger constitutes a series of parallel plates, placed one on top of the other so as to permit the forming of a series of channels for fluids to flow between them.The objective of this analysis is to study the performance of the plate type heat exchanger (PHE) with the non-Newtonian fluid (sodium alginate). The experiment were conducted on Plate type Heat Exchanger for parallel and counter current flow patterns with different concentration (0.1%,0.5% and 1%) of cold fluid. A comparison among collateral flow and counter current flow heat exchanger was done. The obtained result shows that counter current flow heat exchanger proved to be more effective than parallel type heat exchanger.

Robust Control of a Class of Bilinear Systems by Forwarding: Application to Counter Current Heat Exchanger

In this paper we propose a robust control for the counter-current heat exchanger. By using energy balance equations, we propose a model in structured bilinear system that allows to capture the heat transfer and convection phenomena. We study the problem of regulating the output temperature of the cold (or hot) fluid by controlling the flow rate of the hot (or cold) fluid. Using an integral action and a forwarding based control method, we derive a non linear control which achieves output temperature regulation. Numerical simulations confirm the effectiveness of the proposed control.

A novel methodology for Rankine cycle analysis with generic heat exchanger models

This study presents a novel approach for Rankine cycle (RC) analysis, introducing a generic counter current heat exchanger (HX) model to enable basic fluid thermal and flow behaviour in HXs to be considered in a cycle optimisation process. The generic HX model does not represent a certain HX-type or even a manufacturable design, but applies fluid properties and a minimum amount of generic geometry parameters to estimate local heat transfer coefficients and pressure gradients. The proposed methodology thus permits simultaneous optimization of process state points and the trade-off between overall heat transfer coefficient and pressure drop without relying on a specific HX-geometry concept. The proposed methodology is demonstrated for evaluation of single-stage recuperated RC's of different HX size and working fluids, and compared with more conventional thermodynamic analyses. The comparison showed that the novel analysis resulted in lower net power output than the thermodynamic analyses due to working fluid-depending pressure drop in heat exchangers, and a quantitative HX size estimate in terms of total HX area based on working-fluid depended heat transfer coefficients. We therefore suggest the novel analysis as a low effort and more informative alternative to pure thermodynamic approaches for initial RC analyses.