Standard Heat Exchanger Research Articles

Experimental investigation on the use of PCM heat exchangers in Geo-energy piles and walls

The current paper aims to experimentally investigate the thermal performance of geo-energy piles and walls fabricated with Phase Change heat exchangers. Four prototype concrete geo-energy structures (i.e., piles and walls) were tested using two distinct types of heat exchangers, including standard heat exchangers and PCM heat exchangers. The PCM heat exchangers utilized in the current study were filled up with two different types of Phase Change Materials (PCM) with melting points of 26 °C and 42 °C for geo-energy piles and walls, respectively. The thermal efficiency of the geo-energy piles/walls was experimentally assessed over 100 h of continuous operation under cycles of cooling and heating. The findings illustrated that using PCM heat exchangers led to enhancing the heat transfer efficiency of geo-energy piles by 75 % and 43 % in heating and cooling operations, respectively, compared to those achieved using a standard heat exchanger. Furthermore, the heat transfer performance of geo-energy walls with a PCM heat exchanger was enhanced by 43 % and 32 % in heating and cooling tests, respectively, compared to those achieved using a standard heat exchanger. Moreover, the findings indicated that the inclusion of PCM heat exchangers in geo-energy structures contributed to reducing: the impact on soil temperature and thermal interference radius as well as the potential structural damage due to thermal stress.

Hybrid Solid Oxide Fuel Cell/Gas Turbine Model Development for Electric Aviation

A thermodynamic model was developed and validated to analyze a high-performance solid oxide fuel cell and gas turbine (SOFC-GT) hybrid power system for electric aviation. This study used a process simulation software package (ProMax) to study the role of SOFC design and operation on the feasibility and performance of the hybrid system. Standard modules, including compressor, turbine, heat exchanger, reforming reactor, and combustor were used from the ProMax tool suite while a custom module was created to simulate the SOFC stack. The model used an SOFC test data set as an input. Additional SOFC stack performance effects, such as pressure, temperature, and utilization of air and fuel, were added from open source data. System performance predictors were SOFC specific power, fuel-to-electricity conversion efficiency, and hybrid system efficiency. Using these input data and predictors, a static thermodynamic performance model was created that can be modified for different system configurations and operating conditions. Prior to creating the final aircraft performance model, initial demonstration models were developed to validate output results. We used the NASA SOFC model as a benchmark, which was created with their Numerical Propulsion System Simulator (NPSS) software framework. Our output results matched within 1% of both the NASA model and open source SOFC performance data. With confidence gained in the accuracy of this model, a 1-MW SOFC-GT hybrid power system was constructed for an aircraft propulsion concept. Overall hybrid system efficiencies of > 75% FTE were observed during standard 36,000 feet cruise flight conditions.

Evaluation of the internal combustion engine pre-heating methods and their influence on the cold engine start performance at an ambient temperature of –40°C

Introduction (statement of the problem and relevance). Starting an internal combustion engine (ICE) at negative ambient temperatures is difficult for a number of reasons. A decrease in the volatility of gasoline leads to the liquid fuel deposition on the cylinder walls, as a result of which the fuel-air mixture ignition is difficult or impossible. Another reason is the geometric dimensions reduction of the gaps in the plain bearings, which is a consequence of the use of materials with different thermal expansion coefficients in the engine design. The high kinematic viscosity of the oil creates a higher hydraulic resistance in the system. These factors complicate the engine oil flow to friction pairs, which can lead to an oil starvation and bearing shell life reduction.The purpose of the research was to determine the optimal pre-heating mode from the point of view of the process energy efficiency and the preservation of the engine resource.Methodology and research methods. To control the thermal state, the internal combustion engine and the cooling circuit were equipped with measuring equipment. The values of temperature, pressure and volume flow sensors were recorded. To implement the pre-heating modes proposed in the article, an engineering engine control unit was used, which allowed making changes in the basic software configuration.Scientific novelty and results. An alternative method of pre-heating has been proposed, including preheating of the engine oil-water heat exchanger to reduce the time for reaching the minimum oil pressure at the main gallery inlet during a cold start. The article provides descriptions of the regular and proposed pre-heating cycles, their assessment in accordance with the represented criteria. Experimental data on pre-heating cycles and cold starts at an ambient temperature of –40°C are presented. The necessity of warming up the engine standard water-oil heat exchanger before a cold start has been experimentally proved, the curves of pressure changes at the main gallery inlet, depending on the pre-heating mode, are given.Practical significance. Reducing the negative influence of cold start on the ICE resource.

Numerical investigation of a vertical triplex‐tube latent heat storage/exchanger to achieve flexible operation of nuclear power plants

The current numerical investigation is carried out to assess the possibility of integrating a latent heat thermal energy storage (TES) in a nuclear power plant (NPP) system. This would allow improving the capability of such plants to operate in a load-following mode by eliminating the gap between energy supply and energy demand by the grid. In contrary to previously published TES designs, the phase change material (PCM) triplex-tube containers are vertically oriented in the present study to take advantage of melting/solidification enhancements induced by the buoyancy forces. In addition, two different fluids simultaneously co-circulating within the storage, hence, allowing for this component to operate as a storage system (under extreme charging/discharging conditions) or as simple heat exchanger (under normal steady-state conditions). The computational domain, in this study, is reduced from the full TES geometry to a single triplex-tube container owing to the homogeneous triangular positioning of the annular tubes within the storage vessel. The results show that the time required to fully melt the solid PCM is around 27 hours during charging mode, thus, allowing for a relatively long-time margin even under an extreme postulated accident scenario consisting in the inability of the secondary loop to remove heat from the system. In the opposite discharging mode, the time needed to fully solidify the 100% liquid PCM is 17 hours. During the simultaneous charging and discharging (SCD) mode, with constant load, the fraction of liquid PCM is nearly fixed with time. Hence, TES in this mode is said to take the role of a standard heat exchanger. Finally, simulations conducted for the SCD mode, with variable load, demonstrate that the coupled system can follow the daily variations in the grid demand without having any significant impact on the constant operation of the reactor. In this operating mode, the PCM is changing phases from solid to liquid and vice versa to adapt to the energy demand variations as anticipated.

On the Effectiveness of Heat-Exchanger Bypass Control

In heat exchangers with bypassing, a fraction of the flowrate of one fluid (typically the one whose temperature needs to be controlled tightly) bypasses the exchanger and mixes right after the exchanger outlet with the fraction flowing through the exchanger. The advantages of this configuration are long known. Among them, the most significant is that it can improve heat-transfer control because the temperature dynamics is significantly faster than in a standard heat-exchanger configuration. Additionally, it can increase the rangeability of the process wherein the heat exchanger operates. Existing rules of thumb do not provide univocal indications for assigning the design bypass flowrate. In this study, using a simple graphical representation of steady-state heat and mass balances originally proposed for conventional heat-exchanger design, we clarify why and under which design conditions bypass control can be effective. Increased rangeability results from the fact that the heat-exchanger steady-state gain can be assigned by design when a bypass configuration is used, whereas it typically cannot in a conventional heat exchanger. The design bypass flowrate should therefore be assigned so as to make the heat exchanger operate in a region where the steady-state gain is relatively high (and constant).

Optimal Plate Heat Exchangers of Power Generation Systems

Plate heat exchangers are an effective type of heat exchange equipment and can be used in many power plants. The article analyzes the use of corrugated plate heat exchangers in a number of installations. Their optimization was done according to the economic criterion of optimality, taking into account capital investments and operating costs. The analysis of the plate heat exchangers uses as oil coolers (a number of loads with oil mass flow rates 10….250 kg/s) and water heaters (heat power 100…2000 kW) of steam turbine plants. It has been established that plate oil coolers are more economical than shell-and-tube ones. Also, the anti-icing system plate air heaters of gas turbine plants with a power of 1 to 20 MW considered. The air for the anti-icing system was taken after the compressor and was additionally heated by exhaust gases. It has been established that it is necessary to install an additional flue gas smoke exhauster for using plate heat exchangers. Air must be extracted after the compressor, otherwise, low air density leads to high hydraulic losses, which makes it impossible to use plate heaters. Optimum air velocities are in the range of 0.4…0.6 m/s, flue gas velocities are 4…6 m/s. The use of standard plate heat exchangers with corrugated plates is impractical for GTU powers above 5 MW. Optimization of plate regenerators of supercritical CO2 cycles with recompression for powers from 1 to 15 MW has been done. Optimum velocities of hot CO2 are about 0.8 m/s, cold ones 0.3…0.5 m/s. The optimal sizes of plate heat exchangers are recommended for all of the above applications.

Influence of circulating pump efficiency on the heat exchange process in a plate heat exchanger used in a solar heating installation

In solar heating systems with an absorber area of more than 20 m2, a plate heat exchanger is used as a separator between the primary glycol-based refrigerant and secondary water. The use of a plate heat exchanger enables an increase in the heat exchange area compared to the standard coil heat exchangers located inside the domestic hot water tank. An important problem is to determine the volume flow rate on both the primary and secondary side of the exchanger. The paper presents an analysis of the influence of the circulation pump efficiency on the primary and secondary side of the heat exchanger installed in a solar heating installation on the intensity of the heat exchange process.

A field portable membrane introduction mass spectrometer with in-line standard infusion and sample heat exchanger for real-time monitoring of volatile organic compounds in aqueous samples

Abstract Maintaining a steady sample temperature when analyzing real-time samples in the field is crucial for Membrane Introduction Mass Spectrometry (MIMS). Diffusion through the membrane interface is temperature dependent, and sample temperature might vary depending on the sample source. In order to reduce this source of inaccuracy, an in-field and online continuous monitoring system based on (MIMS) coupled with a heat exchanger and in-line standard addition was developed for monitoring volatile organic compounds (VOC) in actual field samples. Parametric studies of the heat exchanger have been conducted in the laboratory. In order to maintain control on instrumental signal drift during continuous, long-term analysis periods, the system used continuous infusion of internal standard (tuloene-d8) into the sample stream and also provided the possibility to infuse, in the same way, an analyte for standard addition calibration. This set-up has been utilized in the field for analyzing both natural water sources and heavily polluted process water. The system was demonstrated to offer a rapid method for quantifying volatile hazardous pollutants in aqueous matrices with good time-resolution.

EVALUATING THE WORKING EFFICIENCY OF A STATIC COOLING SYSTEM UNDER MODERNIZATION OF A POWER INSTALLATION BY DYNEL REPLACEMENT

Problem. Every year the transport engineering industry creates new and improves old transport means, the volume of which exceeds millions of units annually, this includes cars, boats, tanks, etc. In most cases, modernization is not cost-effective due to the introduction of a large number of changes in the design. A separate unit is a ground transportation vehicle, which was produced in large quantities more than 40 years ago, it is obsolete technically and requires modernization. One of the possible options for modernization is the replacement of the obsolete diesel by a more modern, more powerful one. In the case of this machine, a variant with a diesel engine upgrade of the 5TDF type is proposed. Goal. Determine the methodology for assessing the working capacity of the regular cooling system of a ground-based transport vehicle with a V-46-6 diesel engine during modernization by replacing the internal combustion engine with domestic-produced diesel. Methodology. The analysis of design features of the cooling systems for the regular and new diesel, the speed of the heat carriers, their types, etc., was used to estimate the amount of heat by the standard cooling system with a standard diesel engine and simulate the operation of the standard heat exchangers together with a new diesel engine of the type 5TDF with the subsequent estimation of an opportunity of maintenance of working capacity of the given diesel engine by comparison of the brought up heat by a diesel engine and the greatest possible quantity of heat taken away exchangers. Result. The performance of the power plant was evaluated during the modernization of the ground transport vehicle with the V-46-6 diesel engine by replacing the diesel with a new one, type 5TDF with the preservation of the regular elements of the cooling system. It is determined that the regular cooling system allows to ensure the operation of a power plant of a ground transport vehicle with a diesel engine of the type 5TDF at the operating mode of operation. Origina­lity. Due to the fact that earlier similar studies were carried out in the stand conditions this technique will allow us to simulate the operation of the cooling system before installing a new diesel engine on the upgraded facility. Practical value. The method allows to evaluate the efficiency of the regular cooling system of the modernized transport vehicle with the new engine of the power plant.

An appropriate use of the thermal response test for the design of energy foundation piles with U-tube circuits

Energy foundation piles can be an efficient cost-effective solution for ground source heat pump applications. As they are very different from standard ground heat exchangers, numerical or analytical models usually used to investigate their thermal performance must be carefully analysed before they can be applied.The total length of ground heat exchangers is a critically important factor in the overall design of a ground source heat pump. Ground thermal properties are the primary parameters affecting the size of ground heat exchangers. The thermal response test is the most commonly used procedure to determine the ground’s thermal conductivity.The current study investigated a thermal response test on a 20m long energy foundation pile equipped with a double U-tube circuit. The test measurements were interpreted using both the infinite line source model and inverse numerical analysis by means of a detailed model that was able to consider both the actual geometry of the pile and the axial heat transfer. The results indicated an approximately 50% difference between the two values of ground thermal conductivity. The effect of this evaluation on the calculation of the energy piles’ total length was first investigated utilizing a method outlined in the literature. The consequences on the long term energy performance of a ground source heat pump system were then investigated using numerical simulations and taking into consideration the effect of the spacing between the foundation piles. It was found that the total length calculated using the result based on the infinite line source model was about 20% lower than that obtained using the inverse numerical approach. An approximately 10% difference in the heat pump’s seasonal energy efficiency was also found.

HAZARDS OF STANDARD HEAT-EXCHANGE EQUIPMENT IMPLEMENTATION IN CHEMICAL TECHNOLOGY WITHOUT CONSIDERING THE PROCESS SPECIFIC CHARACTER

Standard equipment is a considerable part of modern equipment of chemical plants. In particular, standard heat exchangers are widespread. Possible deviations in the operation of heat exchangers at plants from the preset parameters of their operation can lead to deterioration of the operation of the whole technological system. For this reason an attempt is made in the article to suggest a hypothesis explaining what can lead to disfunction in the operation of heat exchangers. The authors use a method of calculating technological reliability to study the operability of a vertical shell-and-tube heat exchanger. First, the size of the heat transfer surface of the vertical heat exchanger is calculated for specific conditions of work, and a standard device is chosen. Then a method of calculating the technological reliability of the calculated and standard heat exchangers is applied. An operating problem is solved on the assumption that external impacts on the heat transfer process are not fixed, but varied and are within their acceptable intervals. After comparing the probability of the workability of the calculated heat exchanger and of the chosen standard apparatus, a conclusion is made about the expediency of using the standard heat exchanger.

A thermal hydraulic calculation method of an intermediate heat exchanger of a loop type FBR

This paper describes a thermal-hydraulic calculation of an intermediate heat exchanger (IHX) with the computational fluid dynamics (CFD) code CFX. The motivation of this paper is to clarify a heat transfer degradation phenomenon in the IHX through three-dimensional calculation. The whole IHX of the “Monju” reactor is modeled with three parts, i.e., the primary side, the secondary side and the heat transfer region. Through a partial calculation using these models, the flows on the primary side and the secondary side are shown to be axisymmetric. Therefore, a sector model is adopted for the calculation model in the heat transfer region. The calculated temperatures in the IHX are compared with the measured results using the IHX in the “Monju” reactor. Good agreement is obtained for the predicted outlet temperatures and temperatures on the shell surface. As a result of the CFD calculation, it is evaluated that a heat transfer in the lower plenum on the secondary side is dominant under the low flow rate conditions. This fact contributes to lower the heat transfer coefficient in the IHX when the standard heat exchanger theory is applied to calculate the overall heat transfer coefficient between the primary and the secondary sides.

Performance study of solar power plants with CO2 as working fluid. A promising design window

In this paper a systematic analysis is reported on the use of CO2 as heat carrier fluid in solar thermal receivers and as thermodynamic working fluid. It includes the performance of close-to-critical regenerative Brayton cycles, which opens a broad field of cycle possibilities with low pressure ratios (very simple turbines) complemented with large but standard heat exchangers as regenerators. Radiation intensities needed to reach relevant efficiencies are in the range above 25kW/m2, but receiver efficiencies do not increase significantly beyond that value, featured as a threshold. Receivers are made of multi-tube bundles enclosed in glass-windowed collectors with compensated pressure and dilatation, which eliminates the problem of gas leakage through rotating joints and other non-hermetic fits. This leads to needing concentrators compatible with those collectors, which can be either finely optimized Linear Fresnel Reflectors or central minitowers. CO2 was chosen for this study because its critical temperature (31°C) is very close to environmental temperature, which conveys very positive features for the efficiency of the cycle. The overall result of the theoretical study is the identification of a set of different types of efficient, flexible and robust CSP plants with CO2 as the only fluid which deserves further research at experimental level and in the design and construction of new plant components.

Sızma Testleri İçin Bir Model Ağ Üzerinde Siber Saldırı Senaryolarının Değerlendirilmesi

The scope of this work is to investigate the effects of baffle cut and baffle spacing on the heat transfer coefficient and pressure drop in a shell and tube heat exchanger. For this aim, analyses are made for a standard dimensioned heat exchanger with variable baffle cut and spacing. It is observed that both heat transfer coefficient and pressure drops values decrease with the increase of baffle cut and baffle spacing. This paper demonstrates successful application of Genetic Algorithm for the optimal design of shell-and-tube heat exchangers. Approximate design methods for shell-and-tube have been investigated and a generalized procedure has been developed to run the GA algorithm and to find the global minimum heat exchanger area

Heat exchanger simulations involving phase changes

Heat exchangers in which phase changes occur are widely applied in industry. Condensing vapor streams and boiling liquid streams are important components in almost all flowsheets of chemical processes. The accurate modeling of these systems is important at the design stage so that heat exchangers with adequate heat-transfer area are purchased and installed.The purpose of this paper is to illustrate that some caution must be exercised in developing simulation models for heat exchangers when liquid is vaporized or vapor is condensed. Use of simple standard heat exchanger models can lead to incorrect differential temperature driving forces and gross under-estimation of heat-transfer area.

Replacement of R404A with propane in a light commercial vertical freezer: A parametric study of performances for different system architectures

Among natural refrigerants, propane (R290) is one of the most interesting solution to guarantee energetic performance with a low direct environmental impact. Safety concerns related to its flammability are limiting its introduction in some fields of refrigeration, therefore the research is focused on new solutions to reduce refrigerant charge. In this work, two design options for a professional freezer working with R290 are considered: the first one with standard volumes heat exchangers available on the market and the second one with reduced volumes heat exchangers. After the optimization of the performances with respect to the refrigerant charge and the regenerative capillary tube length, a remarkable increase of the performance with respect to the baseline version, working with R404A, was observed, while containing the refrigerant charge amount in the limits allowed by actual standards.

Bifunctional thermoelectric tube made of tilted multilayer material as an alternative to standard heat exchangers

Enormously large amount of heat produced by human activities is now mostly wasted into the environment without use. To realize a sustainable society, it is important to develop practical solutions for waste heat recovery. Here, we demonstrate that a tubular thermoelectric device made of tilted multilayer of Bi0.5Sb1.5Te3/Ni provides a promising solution. The Bi0.5Sb1.5Te3/Ni tube allows tightly sealed fluid flow inside itself, and operates in analogy with the standard shell and tube heat exchanger. We show that it achieves perfect balance between efficient heat exchange and high-power generation with a heat transfer coefficient of 4.0 kW/m2K and a volume power density of 10 kW/m3 using low-grade heat sources below 100°C. The Bi0.5Sb1.5Te3/Ni tube thus serves as a power generator and a heat exchanger within a single unit, which is advantageous for developing new cogeneration systems in factories, vessels, and automobiles where cooling of excess heat is routinely carried out.

Üniversite Sanayi İşbirliği ve Fen Bilimleri Enstitüleri

The scope of this work is to investigate the effects of baffle cut and baffle spacing on the heat transfer coefficient and pressure drop in a shell and tube heat exchanger. For this aim, analyses are made for a standard dimensioned heat exchanger with variable baffle cut and spacing. It is observed that both heat transfer coefficient and pressure drops values decrease with the increase of baffle cut and baffle spacing. This paper demonstrates successful application of Genetic Algorithm for the optimal design of shell-and-tube heat exchangers. Approximate design methods for shell-and-tube have been investigated and a generalized procedure has been developed to run the GA algorithm and to find the global minimum heat exchanger area

Transfer of laboratory results on closed sorption thermo- chemical energy storage to a large-scale technical system

The studies reported here are focused on the development of an efficient, closed thermo-chemical heat storage system in an appropriate scale for the integration into industrial processes as well as heating systems. Such a storage method offers several advantages including the possibility of long-term storage with minimal thermal losses and a high- energy storage density compared to sensible and latent thermal storage principles. This makes it possible for medium- temperature solar collectors and other heat sources of high potential to be applied in industrial processes; which is rarely done nowadays due to the lack of suitable thermal storages. From the results of the tests on a laboratory scale unit with 1.5-liter storage volume, suitable storage materials as well as optimal process conditions such as the temperature and pressure ranges were identified. Applying these attained process conditions, different heat exchanger concepts were developed, tested and optimized in 15-liters storage units. The result was a new heat exchanger configuration that showed a more than 60% higher heat power rate than measured with standard heat exchangers in the bulk. The concept comprises a combination of several measures to increase the storage density by improving the mass and heat flow in the system with minimum loss of storage volume. As the last step, this improved concept was applied in an up-scaled heat storage system with 750-liters storage volume.

Numerical Performance Comparison of Different Tube Cross–Sections for Heat Recovery From Particle-Laden Exhaust Gas Streams

Abstract Heat recovery from exhaust gas streams is applicable to a wide variety of industries. However, high heat transfer resistance of gases and the presence of entrained particulate matter that readily fouls limits industry uptake of current heat recovery technology. Improvements to standard heat exchanger designs are needed. In this study Computational Fluid Dynamics (CFD) is used to investigate the effect of ten different tube cross-sections on heat transfer resistance, gas flow resistance and foulability. The average wall shear stress around the shape is used to predict foulability and an estimated asymptotic fouling resistance is used to calculate an equivalent fouled Coulburn j factor, jf. CFD results show the best tube for exhaust heat recovery is an elliptical tube closely followed by the flattened round tube. The ellipse shape produced fouled Coulburn j factor, jf values, expressed as a ratio of tube bank friction factor f, over 100% higher than that of standard round tube. A flattened round tube is also promising, given enough spacing between the tubes, and may be the practical economic optimum.