Small Heat Exchanger Research Articles

The Development of a Next-Generation Latticed Resistojet Thruster for CubeSats

CubeSat and small satellite resistojet heat exchanger designs are based on conventional concepts that have been used since the 1960s, being primarily limited to helical or twisted tape heat exchangers. The design flexibility enabled by new additive manufacturing technologies is yet to be properly harnessed. This study introduces a novel resistojet concept that incorporates a highly miniaturized lattice structure as the heat exchanger. A conjugate heat transfer analysis determined that the lattice with a diamond unit cell had superior thermal performance compared to the same lattice with a gyroid unit cell and increased the heat transfer rate by up to 11% compared to a helical heat exchanger of the same volume. Performance testing of the prototype thruster with integral diamond lattice indicated that specific impulses of up to 94 s were possible with a 30-Watt heater using nitrous oxide as the propellant. The prototype thruster weighed only 22 g and demonstrated a 67% reduction in the power required to achieve the same specific impulse as previous nitrous oxide resistojets designed for the small satellite platform. The development of highly miniaturized latticed resistojets is shown to be feasible and highly attractive for CubeSats, where mass and power are of the utmost importance.

Simulation study on optimization design of small gas water heat exchangers

Simulation study on optimization design of small gas water heat exchangers

Enhancing Closed System Efficiency through CuO Nanofluids: Investigating Thermophysical Properties and Heat Transfer Performance

Working fluids play a crucial role in closed systems to ensure efficient performance, particularly in systems for heating, cooling, or power generation, where the heat transfer coefficient is pivotal. This study delves into the thermodynamic properties and stability of copper oxide (CuO) nanofluids as alternative working fluids in closed systems. Investigating colloidal suspensions of CuO nanoparticles, the research aims to enhance heat transfer efficiency. CuO nanoparticles, sized at 40nm and 80nm, were dispersed in base fluids like water, ethylene glycol, and oil sans surfactants. The study, divided into static and dynamic phases, examines key nanofluid properties including viscosity, thermal conductivity, specific heat, and heat transfer rate. Through methodologies such as KD2 Pro for thermal conductivity, rheometer for viscosity, and small heat exchanger for heat transfer rate analysis, the effects of volume concentration, temperature, and nanoparticle size on nanofluid performance were evaluated. Sedimentation analysis employed both quantitative (standard deviation calculations) and qualitative (sediment capture methods) approaches. The findings highlight the superior heat transfer rate of 40nm CuO nanofluid at 0.467% volume concentration which is 9.08 kJ/s, suggesting its potential to optimize system efficiency, particularly in heating, cooling, and power generation applications.

Investigating the coupling effect of ventilation and GHEs on temperature distribution and heat transfer characteristics

Tunnel lining geothermal heat exchangers (GHEs) offer numerous advantages, including small area, cost-effectiveness and high heat exchange efficiency. It is a good equipment to utilize geothermal energy in tunnels. However, few research has been conducted on the combined impact of tunnel lining GHEs and ventilation on the temperature field of the surrounding rock. In this study, laboratory test model of combined impact of heat transfer between ventilation and GHEs was established, the effects of different flow rates and wind speeds on temperature field and heat exchange characteristics of the rock were investigated, and the changes in heat transfer under different operational conditions were analyzed. The findings reveal that tunnel ventilation initially enhances the heat transfer efficiency of GHEs, but subsequently decreases the overall heat transfer. Moreover, higher wind speeds exacerbate this negative impact. The radius of the heating ring decreases with increased heat transfer, and the temperature of the surrounding rock rises with heightened heat exchange at same locations within the heating ring. There are reasonable ranges of wind speed and GHEs flow rate, which are 1.5 m/s–2 m/s for wind speed and 0.4 m/s–0.6 m/s for flow rate, respectively. These results are important for the evaluation of thermal effect of tunnel lining GHEs and ventilation design.

Local thermal non-equilibrium effects on phase transition of fiber reinforced thermoplastic composites with temperature-dependent heat generation

Under the excitation of external fields, fiber reinforced thermoplastic (FRTP) composites can be thermally processed due to the internal heat generation, in which the local thermal non-equilibrium (LTNE) can be significant during the phase transition. In this study, a representative elementary volume scale Lattice Boltzmann model was developed to simulate the phase transition process of FRTP composites with the temperature-dependent internal heat source. The results from LTNE model and local thermal equilibrium (LTE) model were compared in terms of the phase interface evolution and the local temperature difference between fibers and matrix, so that the LTNE effects on phase transition behaviors were examined with different material properties and internal heat sources. It is found that the LTNE effects cannot be ignored in FRTP composites, and the main mechanisms include the dynamic local heat generation, endothermic phase transition of matrix, and relatively high thermal conductivity of fiber. A small heat exchange between the fibers and matrix results in a large local temperature difference and a slow phase transition. A high internal heat generation enhances the phase transition and LTNE effects, but an increase in the temperature range for heat generation leads to a slow phase transition with slight change in LTNE effects. With the increase of matrix fraction, LTNE effects first increase and then decrease due to the combined results of the more internal heat generation and the increase of endothermic mass of matrix and the less heat loss through fibers. This study is significant for guiding the reliable thermal processing of FRTP composites in emerging industrial applications.

A numerical study on convective condensation of flue gas in tubular heat exchangers

The accurate calculation of heat transfer process in the condensing heat exchanger plays a crucial role in the waste heat recovery. In this study, the convective-condensation heat transfer process in a condensing heat exchanger with five small heat exchangers is analyzed through utilizing a new numerical simulation model. The method that loads the latent heat of condensation as the heat generation rate is adopted. Under the two working conditions in this study, the deviations of outlet temperature between numerical and experimental results are 1.3 and 2.2 K, respectively, while the deviations of total condensate water flow are 8.5 % and 5.5 %, respectively. Under the drier working condition, the average temperature reduction (5.8 K) per row of tubes in the first small heat exchanger where no condensation occurs is higher than that (2.6 K) in the third small heat exchanger where the water vapor starts to condense. It indicates that the release of latent heat of condensation slows down the cooling rate of the flue gas. In the small heat exchanger where the water vapor starts to condense, the amount of condensate water on the wall of each row of tubes increases first and then decreases slowly along the flow direction of the flue gas.

Numerical simulation of flow and heat transfer characteristics of small compact heat pipe heat exchangers for communication cabinets

In response to the current high demand for communication, additional communication base stations are being constructed, leading to more stringent heat dissipation requirements. In the past, the use of air conditioning or direct ventilation using fans to solve the heat dissipation was very effective. However, the former incurred higher input and operating costs. The latter was cost-effective but posed risks such as moisture and dust intrusion, short circuits, and thermal control issues inside the cabinet. This paper presents a scheme of small compact heat pipe heat exchanger (SCHPHE) for cabinet heat dissipation. The heat transfer and flow characteristics of annular fin and plate fin SCHPHEs under the same conditions are numerically simulated. The numerical simulation results are summarized and analyzed after making modifications to the design parameters. The advantages and disadvantages of the SCHPHE with annular fin and the SCHPHE with plate fin are analyzed under various parameters (fin height, fin thickness, and fin spacing) changes. Furthermore, the paper provides a prediction equation for the heat transfer capacity of the SCHPHE with variations in its specifications.

INVESTIGATION OF ENERGY, EXERGY, AND EMISSION PERFORMANCE OF TURBULATORS INSERTS HEAT EXCHANGER WITH TERNARY HYBRID NANOFLUID COOLANT

The improvement of technologies necessitates using a meticulous heat dissipation method to enhance the exergy efficiency of small air heat exchangers. To improve thermal performance, plain tube (PT) heat exchangers (HX) use passive inserts, such as dimpled twisted turbulator inserts (DTTI) and twisted turbulator inserts (TTI) filled with a ternary hybrid nanofluid (THNF) based on water. Energy, exergy use, and environmental impacts in the future are the primary foci of the inquiry on THNF replacement inserts. Using water as the operating fluid, copper oxide (CuO), aluminum oxide (Al<sub>2</sub>O<sub>3</sub>), and titanium oxide (TiO<sub>2</sub>) nanoparticles are dissolved. The resultant THNF is injected at 0.06%, 0.09%, and 0.12%. Energy, exergy, and emissions are used to study certain features of control fluid flow. The results of the experiments show that using TTI and DTTI along with THNF makes a small air heat exchanger much more efficient at heating and cooling. When DTTI and TTI turbulator plugs are used in regular tubes with THNF of 0.12% (v/v) concentration, friction factor, heat transfer, reversibility, and exergy change all get much better. When DTTI or TTI turbulator plugs are put into the core of the tube, the carbon dioxide (CO<sub>2</sub>) release goes up by 2.6 to 2.1. People who use DTTI with THNF of 0.12% (v/v) concentration as the operating fluid and a tube plug will get performance evaluation criterion (PEC) numbers between 1.076 and 1.04. A careful study of friction factor, heat transfer, exergy efficiency increase, and environmental effect shows that DTTI is a superior passive device for enhancing heat transfer efficiency, particularly when combined with THNF of 0.12% (v/v) concentration.

Thermodynamic Modelling, Technical and Operational Issues of Supercritical Carbon Dioxide Power Generation Cycles for Industrial Applications: A Literature Review

Future electricity production systems will be able to harness the power of supercritical carbon dioxide (S-CO<sub>2</sub>) as it moves through thermal cycles. It serves the same goal as sources of energy such as fossil fuels, nuclear power, solar power, and the recovery of waste heat (or surplus heat from industrial processes). When the heat source temperature is between 350°C and 800°C, CO<sub>2</sub> as a working fluid exhibits excellent thermal efficiency. Its novel technological benefits over conventional steam Rankine cycles, such as the use of small turbo gear and compact heat exchangers, have captured the attention of scientists. It has excellent operational flexibility and may induce significantly cheaper energy costs. Aligned with these goals, this paper presents a panoramic work, exploring the current state of the art of S-CO<sub>2</sub> power generation, with a particular emphasis on the technical and operational perplexities. After providing a comprehensive overview of the thermodynamic principles that underpin this study, the foundation is established for an engaging discourse on the continuous research and development of supercritical carbon dioxide (S-CO<sub>2</sub>) cycles in power generation. Upon delving into the thermodynamic facets of CO<sub>2</sub> that propel this investigation, the spotlight is cast upon dissecting the existing state of research and development of S-CO<sub>2</sub> cycles in power generation before transitioning into encapsulating the principal domains of application and noteworthy thermodynamic modelling inquiries of S-CO<sub>2</sub> cycles. The present advancements and hurdles within the primary application areas are succinctly summarized, while future research trends are identified.

Impact of Stack Temperature on Solid Oxide Electrolysis System Operation for Lunar Production of Hydrogen and Oxygen Propellants

Solid oxide electrolysis (SOEC) systems have the potential to produce hydrogen and oxygen propellant from lunar ice found in the permanently shadowed cream on the moon. Because SOEC systems electrolyze steam instead of liquid water as in more conventional alkaline and proton-exchange membrane electrolysis systems, they require lower stack voltages for thermal-neutral operation (about 1.29 V/cell vs. 1.48 V/cell for liquid-fed cells) and thus can have lower stack specific energy as defined by stack power requirements per kg of hydrogen produced. However, at a system level, power requirements in a remote lunar setting for vaporizing the steam and flowing it through the stack increase system-level power demands such that the advantages of the SOEC system are reduced due to the balance of plant loads contributing as much as 20 to 25% of the system energy at 800 deg. C. Our team at Mines collaborated with our partners at OxEon Energy to demonstrate an SOEC system with a stack operating temperature of 800 deg. C that demonstrated an overall system-level specific energy just below 50 kWh electric per kg of hydrogen. That study and a supporting model validation study provided a basis for showing the viability for high-temperature SOEC to be scaled-up for lunar production of hydrogen and oxygen propellant for propulsion. The current study builds on that previous work by exploring the impact of SOEC stack temperature on both the stack and balance of plant power requirements. This study explores the trade-offs between reduced balance of plant parasitics and increased stack mass with lower SOEC operating temperatures and explores the advantages of higher conducting mixed-ionic-electronic conducting electrolytes with electron blocking layers to increase current densities at lower temperatures.This study was performed using stack and balance of plant models that have been calibrated in the lab-scale demonstration of an SOEC system with an electrically driven steam generator, a scroll-compressor for driving the steam flow, and cathode and anode exhaust recuperators for heat recovery to the stack inlet steam flow. The system also includes H2 drying from the SOEC cathode exhaust by heat exchange with the incoming water stream. The current study looks updates the previous model by replacing the compressor with a higher pressure steam generator and an expansion valve that allows the operation of the system without the parasitic loads of a compressor. In the current study, three different electrolytes traditional yttrium-stabilized zirconia (YSZ), higher conductivity scandium-stabilized zirconia (ScSZ), and mixed ionic-electronic conducting gadolinium-doped ceria (GDC) with a YSZ blocking layer. The GDC bilayer electrolyte cells have the highest conductivity and allow for reasonable hydrogen production at operating temperatures below 700 deg. C. The results show that the lower operating temperatures enabled by the GDC bilayer electrolyte and by the ScSZ electrolytes not only reduce the system mass with smaller heat exchangers and thermal insulation, but also lower requirements for steam generation by enabling more heat recovery in the steam generator. The impact of stack operating temperatures on the feasibility of scaling up a lunar-deployed SOEC system to produce more than 1 kg/h are presented to further emphasize the feasibility of SOEC systems as part of a lunar propellant production facility.

Advanced energy recovery systems design of stenter processes: Energy, exergy and Techno-economic analyses

Stenters used for drying during the dyeing process, waste considerable thermal energy through exhaust gas. This energy waste is one of the major bottlenecks to improving the sustainability of the textile dyeing field. To find the most efficient recovery of the waste heat from the stenters for supplying various energy sources and reducing energy consumption within overall textile system, this study compares three heat recovery systems: (Case- 1) air preheating, (Case-2) hot-water generation, and (Case-3) power generation. Energy, exergy, and economic analyses indicated that all cases demonstrated superior results those obtained using the base case. In terms of energy consumption, Case-1 demonstrated a 60.8 % reduction achieved through decreased fuel consumption. In particular, the economic analysis indicated that Case-1 was the most favorable option because it possesses the lowest operating costs by significantly reducing fuel consumption for air preheating. Additionally, the simple configuration of the process and the use of a small heat exchanger contribute to a lower capital cost. Thus, Case-1 could the most efficiently recover and utilize the heat wasted from the stenter at a relatively low investment cost among proposed systems. This demonstrated the potential for energy and cost savings within the textile industry.

Heat Transfer Enhancement in Heat Exchanger using Double Sinusoidal Shape Fins

Heat Transfer Enhancement in Heat Exchanger using Double Sinusoidal Shape Fins

Innovative concept of splitting water flow rate of cross flow heat exchangers as a solution for reduction of non-uniformity effect – Thermal modelling and feasibility analysis

The water flow rate of water-air cross-flow Heat Exchangers (HXs) is split into various smaller flow rates in this research work, which circulates into several smaller HXs that are put together. In fact, as the non-uniformities in the airflow velocity distributions increase, the thermal performance declines. These non-uniformities, especially in automotive applications, are represented by velocity magnitudes on a part of the HX front area and zero velocities on the remaining part. The innovative idea and the originality of the present study consists on dividing the water flow rates into various passageways as they reach a water-flow HX, where each passage is associated with several smaller HXs. In relation to the air flow, the smaller HXs are sequentially combined. The advantage of such splitting leads to keeping parts of the area of the initial HX from being subjected to low convection heat transfer with zero or negligible velocities and subsequently allows for an increase in the thermal performance globally. Moreover, the dividing idea enables faster but hotter airflow to be applied to each of the individual HXs. Computations for double-split HX utilizing a developed computational code are used to demonstrate the viability of this design. A traditional cross-flow water-air HX's thermal performance can be improved by up to 26.2 % using the novel idea, it has been demonstrated.

Analysis of an enhanced closed-loop geothermal system

Closed-loop geothermal systems are a novel heat extraction technique not requiring continuous fluid supply. Heat extraction efficiency of closed-loop systems is often limited due to the small heat exchange area between the circulating fluid in the wellbore and surrounding rock. An enhanced closed-loop geothermal system (ECLGS) is considered here to improve the heat extraction efficiency of closed-loop systems. The objective of ECLGS is to increase heat transfer from surrounding hot rocks to the wellbore by artificial fractures propped with high-thermal-conductivity proppants. To explore the mechanism controlling heat extraction through ECLGS, a systematic study was conducted. First, a three-dimensional hydrothermal coupled model was developed and validated, and the effects of several parameters were analyzed. It was found that highly-conductive fractures could enhance heat extraction through closed-loop systems considerably. As the flow velocity of the circulating fluid increases, the net power starts to decrease after reaching a peak value. An increase in fluid heat capacity would enhance heat extraction but without requiring more pumping power. The four-wing fracture configuration causes higher heat extraction improvement than the branched fracture. A dimensionless analysis was performed for ECLGS, and three dimensionless numbers integrating different involved parameters were proposed. The proposed dimensionless numbers have been verified numerically. The effect that each dimensionless number has on production temperature has been investigated. Via dimensionless numbers, it becomes feasible to comprehensively assess the impacts of involved parameters, thus making designing closed-loop systems more convenient. The possible ways to apply proposed dimensionless numbers to building a closed-loop system have been illustrated.

Two-phase analysis of heat transfer of nanofluid flow in a cavity in the presence of a magnetic field, heating element, and a porous medium: A numerical approach

By increasing the efficiency of heating systems, more heat flux can be transferred in a certain dimension, thus lowering the operating temperature, or a specific heat flux can be transferred using a smaller heat exchanger. In this study, the flow of a Newtonian nanofluid in a square cavity containing a heating element filled with a porous medium is simulated under the effect of a uniform magnetic field in different rotation angles. The finite volume method (FVM) and two-phase mixture model were used. Water is used as the base fluid and Al2O3 nanoparticles are used as the solid nanoparticles. The heating element inside the cavity, which is filled with porous medium with porosity percentage ε moves up or down to the width of the element. The fields of velocity, streamlines, and temperature are physically plotted, and Nusselt number and entropy generations diagrams are plotted. The results show that the change in the angle of the cavity and the change in position of the heating element on the hot wall have significant effects on the physical patterns. Other results indicate that with increasing volume fraction of nanoparticles and Rayleigh number (Ra), Nusselt number increases. Also, increasing the volume fraction of nanoparticles and Hartmann number (Ha) decreases the entropy generation due to heat transfer and increases the entropy generation due to friction. Also, it was found that in the cavity without a heating element, with increasing θ, the amount of local velocity increases in more places; so that, in case A and θ=90°, it reaches its maximum value in the cavity without a heating element. As can be seen, by placing the heating element at θ=0°, the maximum local velocity occurs above the heating element. Gradually, this value decreases with increasing the angle of the cavity filled with the porous medium relative to the x-axis to reach its minimum value in the cavity with θ=90°.

Simultaneous working fluid and expander selection method for reaching low‐threshold technology organic Rankine cycle (ORC) design

AbstractMaximizing the utilization of an available source serves as the ideal approach, provided that only technical factors are considered. For sources with low heat flux, however, cost‐effective solutions are more suitable due to the minimal net power generated, regardless of the effectiveness of the energy conversion. In such cases, utilizing low‐threshold technology may be the most fitting solution, the layout of these cycles should be simple and inexpensive. In the case of organic Rankine cycles (ORCs)‐based power cycles, this means the omission of superheaters or recuperative heat exchangers and the use of simple expanders and small heat exchangers. Simplifying the design, however, requires additional considerations about the elementary steps of the cycle. This work presents a procedure to select favorable working fluids for ORC while considering the expander's internal efficiency. The criteria for favourability is to have a nonideal expansion process starting and ending in (or very near) saturated vapor states to avoid problems related to wetness/dryness between the given maximal and minimal expansion temperatures. It is demonstrated that the design can be simplified under the simultaneous working fluid and expander selection method presented in this study, regardless of the type and isentropic efficiency of the expander. The resulting methodology applies the novel classification of working fluids using the sequences of their characteristic points on temperature‐entropy space. The proposed approach is illustrated with a case study finding optimal working fluid for an ORC system fitted to industrial waste heat, a low‐temperature geothermal, and a cryogenic heat source.

Understanding and predicting the performance of passive heat and moisture exchangers using a numerical model.

To improve the understanding of the thermodynamics and performance of small passive hygroscopic Heat and Moisture Exchangers (HMEs), a computer model simulating HME function is required. We developed a numerical HME model to calculate the HME's water and heat exchange. The model was tuned and verified with experimental data and validated by applying it to HME design variations. Verification of the model's results to the experimental data shows that the tuned model yields reliable results. The mass of the core, which determines the HME's total heat capacity, is the most important parameter influencing the performance of passive HMEs. Increasing the HME's diameter is an effective way to improve an HME, as it yields higher performance and lowers breathing resistance. HMEs intended for use in warm or dry climates should contain more and those for use in cold humid climates should contain less hygroscopic salt.

Method of heat transfer magnification by utilization of perverted tape with working substance water

Heat exchanger is a fundamental component of intensity and refrigeration cycles. These cycles encourage the exchange of vitality from a specific way to other depending on the righteousness of temperature contrast. Within a heat exchanger, there is change in the temperature of the liquid that flows through the exchanger, which results in the fluctuation of the divider’s temperature owing to the flow of liquid through the exchanger. Heat exchanger is capable of shifting the heat from the hotter to the cooler fluid, thereby managing the heat present within the framework. Therefore, the proposal is to quickly change the ideal measure of warmth vitality. The inventers of heat exchanger quickly formulated a productive and smaller heat exchanger at a nominal expense. For enhancing warmth movement, two strategies have been designed; one is a functioning strategy that needs an outside power source; and the other is an aloof technique with no need for outer power source. The change of heat transfer has been observed for numurous kinds of perverted tape geometries with the twist ratios of 2.5, 3 and 3.5 by changing the Re in the span of 4000 to 15000.

Modeling and analysis for cleaner operation of a process to remove BTX from coke oven gas

Coke oven gas (COG) is a by-product of the coke production process which can be used as a fuel or in the production of chemicals such as methanol. In this research, a model of a BTX (Benzene, Toluene, Xylene) removal process for COG purification is developed, validated with commercial-scale plant data, and applied to improve performance and reduce energy consumption. The process includes a BTX scrubbing column and a distillation column for regeneration of the washing oil. Washing oil is represented as a mixture of BTX, naphthalene and pseudo-components.Three important phenomena with implications for energy conservation were identified using the model. First, the scrubbing efficiency is higher when the ASTM D20 distillation curve of the washing oil is lower. This phenomenon can be explained by the phase equilibrium and the difference in molar volume of the washing oil components. Second, it was found that if the setpoint of the distillation column top temperature exceeds 95 °C, the temperature in the upper portion of the column will increase significantly, which increases the amount of naphthalene in the light oil and decreases its quality. Third, the total energy consuption of the distillation column can be reduced without compromising the purification efficiency if feed temperature is decreased and the low-pressure steam flowrate is increased. Plant test result and model analysis showed that for an exisiting plant with a large vapor heat exchanger and small washing oil heat exchanger, the medium-pressure steam flowrate to the preheater can be reduced without modifying any equipment.

A fast approximate method for simulating thermal pile heat exchangers

Ground source heat pump systems, operating in conjunction with vertical ground heat exchangers, will play a key role in decarbonising heating and cooling of buildings. Design of traditional borehole heat exchangers relies on tools which implement routine analytical relationships between heat transferred and the temperature change in the ground and circulating thermal fluid. However, for novel piled foundations used as ground heat exchangers, there are few such analytical solutions available that are practical for routine implementation. This paper examines the use of a radial approximation to simulate the dynamic thermal behaviour of pile heat-exchangers. Originally developed for small diameter and high aspect ratio borehole heat exchangers, the approach is more challenging for piles since unsteady heat transfer within the pile material is more significant over typical timescales. Nonetheless, we demonstrate that for pile diameters between 300 mm and 1200 mm, generally the error is <1 °C with centrally placed heat transfer pipes or four or more pipes placed near the edge with circumferential spacing less than 550 mm. The radial model is therefore practical for most pile configurations. The strong performance of the model is demonstrated for a year of hypothetical heating and cooling cycles, and also against a field-scale thermal response test.