Inlet Of Heat Exchanger Research Articles

Six years of high-resolution monitoring data of 40 borehole heat exchangers

Ground-source heat pumps (GSHPs) coupled with borehole heat exchangers (BHEs) are energy-efficient technologies for heating and cooling buildings. However, these systems often fail to operate at their full potential due to discrepancies between the assumptions made during the design phase and the actual conditions during operation. To enhance overall GSHP performance, it is crucial to collect and analyze long-term monitoring data from operating BHE fields. To our knowledge, no long-term, high-resolution dataset of double U-tube BHEs is currently publicly available. Additionally, most studies typically monitor only the inlet and outlet of the entire ground heat exchanger rather than individual BHEs, hindering detailed performance analysis. With this data descriptor, we present a 6-year dataset from a BHE field comprising 40 BHEs, each with sensors for volume flow and inlet/outlet temperatures, recorded every 30 seconds. We believe this dataset will enhance understanding of individual BHE performance, provide validation for BHE models, and thus support better GSHP design and operation.

The preliminary design of emergency core cooling scheme and loss-of-coolant accident analysis for Tsinghua high flux reactor

This paper proposes the preliminary emergency core cooling scheme for Tsinghua High Flux Reactor. According to the thermohydraulic characteristics of high flux reactors, forced circulation needs to be maintained by emergency pumps in the early stage. When the decay power is low enough, natural circulation between core and the reactor pool is initiated to remove the residual core heat. The sources of safety injection are accumulators and reactor pool. Accumulator injection can ensure core safety in the early stage and reactor pool injection can maintain long time stable forced circulation. To avoid emptying the reactor pool, the waterproof zone needs to be built. The waterproof zone consists of reactor pool and several finite volume dry pools. All pipelines and equipment in the reactor coolant system are placed in the dry pools. Once break accident occurs, the dry pool where the break is located can collect the leaked coolant. With the increase of break back pressure, the break flow is restricted. The current scheme is modeled by Relap5 and different size breaks at four locations (namely core inlet, core outlet, primary heat exchanger inlet and main pump inlet) are assumed. According to the response characteristics of the scheme, the accident process can be divided into five stages: non-shutdown stage, high-injection stage, low-injection stage, stable forced circulation stage and natural circulation stage. Critical heat flux predicted by Sudo CHF correlations is adopted as the primary safety criterion. Through analysis, a success path is found to maintain core safety for a wide range of loss-of-coolant accident scenarios.

Simulation of heat and pressure transfer in concentric heat exchangers for small industrial scale

Abstract A Heat exchanger is a tool in industry which aims to transfer energy from hot fluid to cold fluid. The amount of heat transferred is an important parameter of the design and performance of heat exchangers. Concentric tube is a type of heat exchanger that is widely used in industries such as material processing and food preparation. One way to get the value of heat transfered before manufacturing a heat exchanger is to carry out computational fluid dynamic simulations. This simulation will make it easier for us to understand the heat transfer phenomenon that occurs from hot fluid to cold fluid. The aim of this study is to calculate how much heat transfer and pressure drop there is in a laboratory scale cocentric tube type heat exchanger. We also get a picture of the pressure drop that occurs due to fluid friction with the inner pipe walls. Experiments and simulations carried out in this study will then be validated. Variations in flow rate on the tube and shell sides are applied. the greater the flow rate, the greater the transfer of heat. The same trend is shown by variations in pressure. The greater the pressure, the greater the pressure drop that occurs. In this study, the pressure drop from the heat exchanger inlet to the heat exchanger outlet was 0.015%.

Examining the potential of sigma-thermic heat transfer fluid and its nanofluid in a natural circulation loop through CFD studies

This study investigates the impact of hot heat exchanger (HHX) inlet temperature on Sigma-thermic heat transfer fluid (STHF or STF) performance in a natural circulation loop. Various fluids, including STHF and STHF-based nanofluids, with volumetric concentrations ranging from 0.5% to 3%, are employed in the loop. The primary objective is to analyze the thermal performance of the loop under different conditions, focusing on temperature distribution, Nusselt number, friction factor, effectiveness, and mass flow rate. 3D numerical simulations are conducted, and the numerical model is validated against existing literature. The developed model incorporates considerations for viscous dissipation and axial conduction to predict the heat transfer potential of the loop. As the HHX inlet temperature increases, the mass flow rate rises. Notably, STHF/CuO nanofluids exhibit a more substantial enhancement than other nanofluids. At a 1 vol% concentration, the mass flow rate increases by 9.5%, 4%, and 2.7% for STHF/CuO, STHF/Al2O3, and hybrid nanofluids, respectively, compared to pure STHF. The study reveals significant improvements in mass flow rates and heat transfer efficiency with increasing HHX inlet temperatures, especially with STHF/CuO nanofluids. The total entropy generation reduction is notable, with percentages ranging from 2% to 18.5% for various nanofluids compared to pure STHF.

Multiparameter optimization of the acid gas removal process using self-heat recuperation technology in IGCC system based on genetic algorithm

The acid gas removal (AGR) process in the integrated gasification combined cycle (IGCC) system consumes a large amount of heat and reduces the generation efficiency. Process modification of self-heat recuperation (SHR) technology based on vapor compression heat pumps is expected to reduce the energy consumption of the AGR process. On this basis, this paper conducted a comprehensive and parametric analysis of the AGR process integrated with a vapor compression heat pump. Wherein, two key parameters, the stripper pressure (P1) and the heat pump heat exchanger inlet pressure (P2), were analyzed in detail to understand the energy consumption characteristics of each module of the system. By establishing the optimization objective functions of minimizing system operating cost and exergy loss respectively, the system multi-parameter optimization was conducted based on the genetic algorithm by coding and solving in HYSYS and MATLAB. The corresponding parameter variables for the optimal cases of the two optimization objectives are also comparatively derived. The results showed that P1 mainly changes the SHR capacity of the system by changing the allowable flow rate of the SHR mass under different working conditions, while P2 mainly affects the SHR capacity of the system by changing the heat of the fraction at the top of the stripper. The minimum operating cost of the system decreased to 0.0655 $/kgH2S, which is 1.50 % lower compared to the original case. The minimum exergy loss of the system is reduced from 7788.89 kW to 7398.59 MW, which is about 5.01 % lower than that of the original case.

UTOP accident analysis and mitigation measures of lead-cooled fast reactor considering coupling effect with SCO2 Brayton cycle

The lead-cooled fast reactor (LFR) coupled with SCO2 Brayton cycle is an advanced nuclear power generation system which has high efficiency and high compactness. The purpose of this study is to investigate the impact of coupling effect between LFR and SCO2 cycle on the safety analysis of unprotected transient overpower (UTOP) accident, and to propose mitigation measures to UTOP accident with the aid of SCO2 cycle. Firstly, the dynamic simulation model of a 100 MW small modular natural circulation LFR coupled with SCO2 Brayton cycle was developed using APROS software, and was verified through the steady-state and transient simulations. Secondly, the UTOP accident of the LFR coupled with SCO2 Brayton cycle was analyzed, including a comparative case which simplified SCO2 cycle as a fixed boundary in the analysis. Finally, two measures to mitigate the UTOP accident by charging more SCO2 to the circulation loop from the storage tank and by maintaining constant SCO2 temperature at the inlet of in-reactor heat exchangers (IRHXs) were proposed. The results indicate that the conventional method of simplifying power generation system as the fixed boundary underestimated the severity of accident. Specifically, the maximum fuel cladding temperature was about 40 °C higher when considering the coupling effect of reactor and SCO2 cycle than that of assuming SCO2 cycle as the fixed boundary, which greatly exceeded the safety limit. Moreover, within the scope of present UTOP accident conditions, the measures proposed in this study could mitigate the severity of accident. The maximum cladding temperature was reduced by 15–23 °C in the condition of maintaining constant SCO2 temperature at IRHX inlet, and was reduced by 5–7 °C in the condition of charging more SCO2 to the circulation loop, compared with the condition not applying any measures.

The influence of geometrical and operational parameters on thermofluid performance of discontinuous colonial self‐swirl‐inducing baffle plate in a tubular heat exchanger

AbstractAn exploratory investigation was conducted to analyze a tubular heat exchanger's turbulent heat transfer characteristics using an innovative baffle plate design. The design incorporated a perforated conical baffle plate and an adjustable rectangular deflector. The strategic placement of this baffle plate at the heat exchanger inlet facilitated a swirling flow downstream. To assess the impact of this design, three baffle plates with varying pitch ratios (l/D) were positioned in the direction of the flow. The study examined the effects of pitch ratio (ranging from 0.6 to 1.2), deflector inclination angle (ranging from 30° to 50°), and Reynolds numbers (ranging from 16,500 to 29,500). Moreover, the size of the conical baffle plate (H/D) was altered (from 0.25 to 0.15). The findings highlighted the substantial influence of pitch ratio, inclination angle, and height ratio on the heat exchanger's performance. Notably, the configuration featuring an inclination angle of 50° and height ratio of 0.15 exhibited an average performance improvement of 22% compared to other height ratios, inclination angles, and pitch ratios.

Operational characteristics of a free-piston Stirling generator with resonant self-circulating heat exchangers

Heat transfer is one of the most critical issues faced by free-piston Stirling generators (FPSGs) during power amplification, and the emergence of resonant self-circulating heat exchangers offers an alternative solution. In this study, a high-power FPSG with resonant self-circulating heat exchangers has been numerically studied using commercial software SAGE and thermoacoustic post-processing. The principle feasibility and operational characteristics of the proposed system with different loop lengths are verified based on comparative analysis with the Component Test Power Convertor. Results show that introducing a self-circulating heat exchanger can achieve high-power heat transfer through a steady flow. However, it results in a significant degradation in the performance of the FPSG, where the acoustic power loss in the loop is the most critical cause. The pump used to generate the steady flow also requires additional power consumption. Furthermore, systems with shorter loops of non-integer multiples of wavelength have higher system efficiency and lower pump power consumption. For example, the output electric power can achieve 9.9 kW (corresponding to a thermal-to-electric efficiency of 18.8%) when the loop length is 2 m, where the power consumption of the pump is only 0.19 kW. Meanwhile, the pipe diameter of the loop and the temperature difference between the inlet and outlet of the high-temperature heat exchanger should be determined by considering both the performance of the FPSG and the power consumption of the pump.

Effect of saline-fog temperature and collection-duct height on fog-desalination effectiveness

Fresh water is vital for the continuation of human life, but unfortunately, the world is currently suffering from a severe shortage of fresh water sources. Recently, the use of fogging technique in desalination was introduced, and promising preliminary results have been reported. In this study, the effect of three operating and design parameters: the vertical height of the horizontal duct (vapor extraction point), heat-exchanger inlet water temperature, and feed water salinity, on the product-water salinity is experimentally investigated. The following experimental conditions are applied: feed water salinities, 30,000 ppm and 10,000 ppm; vertical heights, 150 cm, and 235 cm; and heat-exchanger inlet water temperatures: 50 °C, 70 °C, and 90 °C besides no heating condition. The product-water salinity values reach 2874 ppm and 1028 ppm when the fog is generated without supplementary heating for the feed water salinity values of 30,000 ppm and 10,000 ppm, respectively. The process effectiveness is also explored, and the results show that the effectiveness is highly dependent on the operation mode and feed water salinity. The effectiveness values reach 91.33% and 92.49% when the fog is generated without supplementary heating for the feed water salinity values of 30,000 ppm and 10,000 ppm, respectively. It is worth mentioning that the salinity of the product water increases with the heat exchanger temperature. Additionally, the higher the horizontal collection duct, the lower the salinity of the product water. A mathematical model was developed and validated to describe the evaporation process of the droplet. The model showed good agreement with the experimental results.

Optimal designs for flow uniformity at inlet of microchannel flat tube heat exchanger

Microchannel flat tube heat exchangers and circular tubes commonly used in thermal engineering applications vary in size and shape. Uniform flow distribution is an essential factor affecting the performance of heat exchangers. This paper proposes three types of inlet distributors to achieve connection and reduce the non-uniformity of the working fluid flow: Column-type, Diffuser-type, and Drainage-type. The flow uniformity, pressure drop, and heat transfer efficiency of R410A refrigerant two-phase flow in a microchannel flat tube heat exchanger with various mass fluxes are investigated by numerical simulation. Verification is done by experiment and empirical correlation. The concept of heat transfer offset rate is proposed to characterize the impact of flow uniformity on heat transfer. The eddy current at the distributors is a significant factor in the uneven distribution of the flow field. Different distributors will affect the distribution of gas and liquid phases. The standard deviation of the mass flow rate in Column-type is less than 9.10%, and uniformity is best when the mass flux is low. The heat transfer coefficient is 5800 W/m2K, and the heat transfer offset rate is less than 5.77%. When the mass flux exceeds 300 kg/(m2s), the flow distribution performance of the diversion flow is the best, and the flow standard deviation can be reduced by up to 36.56% at high flow.

Saving energy with timers

In this study, it is aimed to save energy by placing timers in public offices and private workplaces for heating residential units with geothermal energy outside working hours and on holidays. For this, proportional valve control system design and application has been carried out. Proportional valve is connected to the heat exchanger return. The control form of the floating type proportional valve is on-off, the control of the proportional valve with analog input is applied in the form of PI control. It is realized by programming smart relays in both controls. PT100 was used to measure the heat exchanger inlet, return and temperature values entering the building.
 As a result of this study, the heat exchanger return temperature was adjusted to the temperature at which the buildings would not cool completely on holidays and after working hours, allowing more buildings to be heated with the energy saved.

Performance study of a free-piston Stirling heat pump with a circumferential temperature gradient in the heating heat exchanger

The free-piston Stirling heat pump (FPSHP) is efficient, environmentally friendly and has a wide available temperature range, making it a promising device for building heating. The temperature of the external heat-carrying fluid is different at the inlet and outlet of the heating heat exchanger, so there is a temperature gradient in the heating heat exchanger. The larger the scale of the FPSHP, the more pronounced the temperature gradient. However, the influence of such a temperature gradient on system performance has not been investigated so far. This paper therefore presents a detailed study of the FPSHP with a circumferential temperature gradient in the heating heat exchanger. The calculation results show that a cascade output of energy can be achieved when there is a circumferential temperature gradient in the heating heat exchanger. With the same outlet temperature, the larger the temperature difference between the inlet and outlet of the heating heat exchanger, the higher the COP. However, due to the mixing of internal working gases with different temperatures in the compression space, part of the high temperature heat is directly transferred to the low temperature module and output at a lower level, adversely affecting system efficiency. Fortunately, this adverse effect is found to be insignificant when compared with multiple independent small FPSHPs without circumferential temperature gradients. Considering the higher investment cost of multiple small FPSHPs, a single large FPSHP is also a good choice for large heating capacity demand.

Size reduction and enhanced power generation in ORC by vaporizing LNG at high supercritical pressure irrespective of delivery pressure

LNG regasification terminals generate power with Organic Rankine cycle (ORC) using LNG as the heat sink. A 3-stage ORC designed for regasification pressure of 70 bar(a) produces the highest net power with appropriate temperature approach in each heat exchanger and it is higher by 108 kW for LNG flow of 30 kg/s compared to the fixed temperature approach of 5 K. For 30 bar(a) delivery pressure, a regasification pressure of 70 bar(a) instead of 30 bar(a) produces about 17% higher net power and 1.9 times reduction of total heat exchanger area. The sizing parameter of the turbine becomes 12.3% lower. The analysis shows that total outlet volume flow rate through turbine, pump inlet and hot side of heat exchangers are 24.5%, 28.2% and 25.0% lower respectively for 70 bar(a) regasification pressure. The total capital investment for 30/30 bar(a) and 70/30 bar(a) systems are 18.8% and 21.8% respectively higher than that of 70/70 bar(a) system. For the delivery pressure of CNG at 30 bar(a), the net present value of 70 bar(a) regasification pressure is 1.7% higher than that for 30 bar(a) regasification pressure. This is over and above the flexibility of operation that the regasification terminal achieves with supercritical LNG.

Operation optimization of the coaxial deep borehole heat exchanger coupled with ground source heat pump for building heating

• The transient numerical model of the coaxial heat exchanger is established. • Operation optimization method for the heat pump system is developed. • The underground heat transfer model is validated using test data from literature. • The operation of the system before and after optimization is compared. Geothermal is considered to be one of the most promising renewable sources for district heating. Ground source heat pump systems coupled with the coaxial deep borehole heat exchanger have been widely applied because of their high efficiency. However, in order to reduce the total energy consumption of the system, there are few studies on the optimization of the water flow rates in the coaxial deep borehole heat exchanger by time to meet the load change during the heating season. In this paper, an optimization method for the two flow rates which are set at two time periods respectively every day in the coaxial deep borehole heat exchanger during the operation of the ground source heat pump system is proposed. The application of the method is to determine the applicable flow rates when the temperature of the next day is predicted. Space heating of a building (located in Tianjin, China) is taken as a scenario, comparisons were carried out on system operation before and after optimization, which shows that the method has a good effect on the energy-saving operation of the system. After optimization, the total power consumption of the system is reduced, the total performance coefficient of the equipment as well as the temperature difference between the inlet and outlet of the underground heat exchanger is increased, and the trend of flow rates changes with time is the same as the indoor and outdoor temperature difference.

Use of the Low-Potential Heat for Heating Helium in Rocket-Carrier Tank Pressurisation Systems

The energy efficiency of new technical developments is a critical issue. It should be noted that today the focus in this issue has seen a major shift to the maximum use of renewable energy sources. The purpose of this research is to reduce the weight of helium heat exchangers of the fuel tank pressurisation systems in modern rocket propulsion systems that use fuel components like liquid oxygen and kerosene-type fuel. This is the first time that the question has been raised about the possibility and advisability of increasing the temperature of helium at the heat exchanger inlet without the use of additional resources. The paper addresses the use of the waste (“low-potential”) heat and ”industrial wastes” present in propulsion systems. Basic laws of complex heat exchange and the retrospective review of applicable heat exchanger structures are applied as a research methodology. Two sources of low-potential heat are identified that have been previously used in the rocket engine building in an inconsistent and piecemeal manner to obtain and heat the pressurisation working fluid. These are the rammedair pressurisation during the motion of the rocket carrier in the atmosphere, and the tank pressurisation as a result of boiling of the top layer of oxidiser which is on the saturation line. This is the first time that the advisability has been substantiated of increasing the temperature of the working fluid at the heat exchanger inlet, first of all due to the use of the low-potential heat. This is also the first time that unemployed sources of low-potential heat and “industrial wastes” are found in modern deep throttling propulsion systems. These are the high-boiling-point fuel in the tank, behind the highpressure pump, at the exit of the combustion chamber cooling duct, and also the fuel tank structures, and the engine plume. A possibility is proved, and an advisability demonstrated of their implementation to increase the efficiency of pressurisation system heat exchangers. This is the first time that the methodology of combustion chamber cooling analysis has been proposed to be adopted for the heating of heat exchanger by the engine plume. This is the first time that a classification of waste heat sources has been developed which can be used to increase the pressurisation working fluid temperature. The identified reserves help to increase the efficiency of the helium heat exchangers of the tank pressurisation systems in the propulsion systems

Ne-liquefaction system development for the 940 nm infrared optical characteristics measurement

A Ne-liquefaction system cooled by a G-M cryocooler was developed. The heat load and liquefied rate of the system were analyzed theoretically. The neon gas was liquefied over 340 min while the condenser chamber was cooled down to 26.7 K. The gas pressures of the heat exchanger inlet and condenser are directly proportional to its absolute temperature, which decreased with the reduction of cryostat system temperature. The pressure of the heat exchanger inlet decreased from 105 kPa to 100.4 kPa with the pressure of the condenser decreased from 101 kPa to 100.1 kPa. Neon gas with a purity of 99.999% was used in liquefaction and the mass flow is set to 0.173 g/s. The production rate of liquid neon is determined to be 0.52 L/h. The liquid neon was collected in a glass vacuum dewar with a transparent window, which allows to observe the liquid level and conduct the optical tests. The refractive index and transmittance of the 940 nm infrared in liquid neon are 1.103 and 99.85%, respectively. The parameters will provide a valuable database on infrared equipment with liquid neon as a cryogen.

Importance of Three-Dimensional Vehicle Heat Exchanger Modeling

Abstract This article demonstrates, via a comprehensive study, the necessity of using a 3D computational fluid dynamics (CFD) approach for heat exchanger (HTX) modeling within underhood vehicle simulation. The results are presented as the difference between 1D and 3D CFD approaches with a focus on auxiliary fluid (e.g., coolant) temperature prediction as a function of primary fluid (e.g., air) inlet conditions. It has been shown that the 1D approach could significantly underpredict auxiliary fluid inlet temperature due to neglecting the spatial distribution of primary fluid velocity magnitude. The resultant difference in the auxiliary fluid flow HTX inlet temperature is presented and discussed as a function of the uniformity index (UI) of the primary fluid flow velocity magnitude. In addition, the 3D HTX model’s importance is demonstrated in an industrial example of full 3D underhood simulation.

Optimization of a heat pipe-radiator assembly coupled to a recuperated closed Brayton cycle for compact space power plants

• Analysis of recuperated closed Brayton cycle conditions is carried out. • Brayton cycle and heat pipe-radiator models are numerically coupled. • Heat source and cold heat exchanger inlet temperatures are optimized. • The specific mass minimization is used as the objective variable. • Optimization provides cycles with specific masses ranging from 40 to 50 kg/kW. Compact and efficient energy conversion systems for space applications enable the appearance of new mission opportunities and technological discoveries resulted from space exploration. Besides energy availability, another crucial factor of any energy conversion system for space purposes is its total mass and size. Focusing on a recuperated closed Brayton cycle (CBC), thermodynamic modeling of a CBC is proposed. Moreover, a thermal model is carried out to predict the overall properties of the cold side of the system (i.e., heat pipes and radiator) for different CBC conditions. Both models are coupled and their conjunct solution provides operational data for the design of the heat rejection system, such as the number of heat pipes (HP), total assembly mass, length, and second-law efficiency. Furthermore, by means of this coupling, the heat source temperature and the cold heat exchanger (CHE) inlet temperature are defined, using an optimization procedure where the specific mass (i.e., radiator mass to cycle power ratio) is minimized. Based on this objective variable, the optimized heat source temperature of 1200 K is achieved, while the CHE inlet temperature of 513.2 K is obtained. Such temperature conditions ensure the future design of a space energy conversion system that aligns good efficiency and compactness.

Comparison of Two Reverse-cycle Defrosting Methods for a R290 Split Room Air Conditioner

R290 has obvious advantages in aspects of environmental protection and thermal properties, and researches on R290 room air conditioners (RACs) are attracting more and more attention. As for R290 RAC, the suction temperature is continuously low and a large number of refrigerants are dissolved in the compressor oil sump during defrosting process, resulting in a longer time length of the start-up process after defrosting. Two reverse-cycle defrosting methods, the discharge-throttling method (DTM) and suction-discharge bypass method (SDBM) are proposed in order to solve these problems. This paper compares the two defrosting methods on an R290 RAC by experiment and the results show that the defrosting time of DTM is relatively short, but the temperature at the inlet and outlet of the indoor heat exchanger is relatively low after defrosting. The SDBM can alleviate the situation of low suction temperature in the defrosting process, but the viscosity of the oil sump is large in the early stage of defrosting and the time length of the start-up process after defrosting is longer. Both methods have their own advantages and disadvantages, and the paper will provide an experimental basis for the reliability study of R290 RACs.

Study on solar-ground source heat pump and combined heating system in severe cold area

This paper studies the operation strategy and economy of solar-ground source heat pump gas heating system in severe cold region. Two operation modes of the system are introduced: series operation and parallel operation, and the two operation modes are simulated. This paper compares and analyses the heat exchange of the ground pipe, the change of the water temperature at the inlet and outlet of the ground pipe heat exchanger, the heating efficiency coefficient cop and the refrigeration efficiency coefficient EER of the heat pump unit during the five-year operation of the combined heating system, and studies the change of the soil temperature, Finally, the economic analysis is made from the initial investment cost and operation cost of two different heating schemes. The results show that the maximum heat transfer efficiency of the parallel system is 2.5 times that of the serial system, and the total heat transfer between the parallel system and the heat network is 83.2 % higher than that of the serial system. The inlet and outlet water temperature of the buried pipe decreased under both operation modes. After five years of operation, although the operation cost of the parallel combined heating system is higher than that of the serial combined heating system, the parallel combined heating system has more advantages than the serial combined heating system in terms of the overall heating effect of the system and the influence degree of the system on soil temperature.