Single Heat Exchanger Research Articles

A generalized superstructure-based framework for process synthesis

We propose a general framework for the formulation of superstructure-based optimization models for holistic process synthesis. First, we redefine the fundamental problems of reactor, separation, and heat exchanger network synthesis, by presenting generalized problem statements, to make them amenable to seamless integration with each other. Second, we describe the general forms of models that can be developed to address these generalized problems and identify some key characteristics. Notably, for each system, we identify internal variables used only within the system, cost variables used in the objective function, and, importantly, coupling variables for the coupling between systems. Third, we outline some literature models that can be used to address the generalized problems and present new models to couple the three systems. Finally, we show how the individual components (systems and coupling models) can be integrated to formulate a single simultaneous reactor, separation, and heat exchanger network synthesis.

Methanation of coke oven gas over Ni-Ce/γ-Al2O3 catalyst using a tubular heat exchange reactor: Pilot-scale test and process optimization

Traditional industrial methanation of coke oven gas (COG) to produce natural gas generally requires three or more adiabatic reactors, thus resulting in a longprocess flow, rapid deactivation of catalyst and high investment cost. Herein, a new methanation process of COG (denoted as NCtSNG) over the Ni-Ce/γ-Al2O3 catalyst was proposed, wherein a tubular heat exchange reactor and an adiabatic reactor were connected in series. The pilot-scale methanation test using a single tubular heat exchange reactor was performed, and the result demonstrated that heat exchange reactor would insure a low temperature of catalyst layer (below 500 °C), which can not only improve the efficiency of the exothermic methanation but also prolong the catalyst lifetime. A reliable simulation of the NCtSNG process was then established and validated by using the commercial software Aspen Plus based on the pilot test, and the key operation parameters and conditions were optimized so as to provide significant basic data for future industrial production. It was estimated that the new NCtSNG process presents high energy efficiency of 80%, low production cost of 2.15 CNY/m3-SNG, and low CO2 emission of 0.61 kg/m3-SNG, thus showing a great superiority in market competition.

Effect of depth and fluid flow rate on estimate for borehole thermal resistance of single U-pipe borehole heat exchanger

Accurate estimates for ground thermal parameters and borehole thermal resistance are important to improve the design of borehole heat exchangers (BHEs) in ground-coupled heat pump systems(GCHPs). In order to improve the estimating accuracy of borehole thermal resistance, this paper presents a simple analytical method for evaluating the actual averaged –over-the –depth mean fluid temperature (MFT) in the U-pipe of BHE to calculate borehole thermal resistance Rb. Furthermore, the effects of borehole depth and volumetric flow rate on the calculating RMSE distribution between borehole thermal resistance Rb and effective borehole thermal resistance Rb∗ are investigated. The conclusion shows that the relative deviation between the two borehole thermal resistances corresponding to the volumetric flow rate 1.5e-4m3/s increases from 4.2% to 29.7% when borehole depth changes from 50 m to 200 m. Finally, the borehole depths corresponding to different volumetric flow rate are optimized to find the boundary line where Rb are nearly equal to Rb∗ in the operating time, and the impacts of grout thermal conductivity and heat rate per unit depth of BHE on the boundary line are quantitatively analyzed. Volumetric flow rate has more effect on Rb with the higher grout thermal conductivity, the relative error between the two Rb corresponding to V = 1.5e-4m3/s and V = 3e-4 m3/s is 10.8% for kg = 2.3 W/(m.°C). The effect of heat rate per unit depth of BHE on Rb is very limited, the relative error between the two Rb corresponding to q1=50 W/m and q1=80 W/m is 5.4% under V = 1.5e-4m3/s, and it is only 3.7% under V = 3e-4 m3/s.

What dominates heat transfer performance of hybrid nanofluid in single pass shell and tube heat exchanger?

Influence of nanoparticle volume concentration and proportion on heat transfer performance (HTP) of Al2O3 – Cu/water hybrid nanofluid in a single pass shell and tube heat exchanger is analyzed. Multiphase mixture model is adopted to model the flow. Three-dimensional governing equations and associated boundary conditions are solved using finite volume method. The numerical results are validated with the experimental results. Results indicate that optimized nanoparticle volume concentration and proportion dominate HTP of hybrid nanofluid. Heat transfer coefficient and Nusselt number are monotonic increase functions of nanoparticle volume concentration and proportion. The percentage increase in heat transfer coefficient of hybrid nanofluid is 139% than water and 25% than Cu/water nanofluid. At higher Reynolds number, the increment in Number of Transfer Units (NTU) between water and hybrid nanofluid is close to 75%. Maximum enhancement in Nusselt number for hybrid nanofluid exceeds 90% when compared to nanofluid (Al2O3/Water nanofluid). Consequently, highest heat transfer performance is attained for hybrid nanofluid systems. Effectiveness of heat exchanger increases almost to 124% when hybrid nanofluid is employed. We show that it is higher than water as well (conventional coolant). Results are expected to be helpful in further industrial-scale deployment of nanofluids, which is an area that is currently relevant for ongoing academia-industry partnership efforts worldwide.

Shell Side Single-Phase Experimental Heat Transfer Analysis of a Vertically Oriented Single Segmental Baffle Bundle With Dimpled Tubes

Abstract This paper presents single-phase shell side heat transfer performance of a vertically oriented shell and tube bundle. Steady-state single-phase experiments were conducted to determine the shell side Nusselt number with water and water/glycol solution as working fluids for both counter and parallel flow configurations. Experiments were carried out for Reynolds number varying from 3000 to 15,000 with Prandtl number ranging from 10 to 20. Counter flow configuration showed slightly better performance. Nusselt number correlations are presented for both configurations using a modified Wilson plot method. Comparison of results with previous studies and commercial software are presented. Thermal performance for all flow rate conditions showed close comparison to the results from a reputable commercial software. The correlation was further validated by comparing results for 30 different cases to calculations from 2 widely used commercial softwares. Comparison showed that the correlation can be used for the design of single-phase single segmental shell and tube heat exchangers.

Spectroscopic analysis of Jet A-1 heteroatomic components

This article presents the chemical analysis of jet fuel (Jet A-1) heteroatomic components generated as a result of thermal stressing. Jet A-1 was thermally stressed by flow and static tests in a single tube heat exchanger in the autoxidation regime (150–300 °C). Jet A-1 samples were analyzed by electrospray ion mass spectrometry (ESI-MS), Fourier transform infrared (FTIR) and 13C nuclear magnetic resonance (NMR) spectroscopy. Mass spectra of Jet A-1 recorded higher molecular weight components in the mass range 300–1000 Da. FTIR spectra revealed absorption bands for oxygen-containing species such as alcohol, phenol, and ether. Jet A-1 NMR spectra recorded heteroatomic alkoxy species. A lichen substance, gyrophoric acid was identified as Jet A-1 component. ESI-MS, FTIR and NMR spectra of unstressed jet fuel recorded peaks corresponding with gyrophoric acid. Natural products polyphenols and lichen derived compounds are excellent antioxidants, and their advantages as potential fuel additives are discussed.

Heat transfer simulation, analysis and performance study of single U-tube borehole heat exchanger

This paper presents the analysis, simulation and performance study of heat transfer in a single U-tube borehole heat exchanger (BHE). Unsteady heat transfer method was used to analyze the heat transfer process of both inside and outside the borehole. Implicit numerical method applied on heat transfer equations obtained from energy balance (accompanied with thermal resistance model) was used to obtain the solution. The variation of mean fluid temperature, average borehole wall, grout and nearby ground temperature as well as borehole loading with borehole depth and time were investigated. Dynamic simulation was also performed to assess the influence of important parameters. The effect of two parameters, fluid mass flowrate and thermal conductivity of grout, on mean fluid temperature, borehole wall, grout and ground temperature as well as on borehole loading and borehole thermal effectiveness were investigated. The outcome of this study can substantially reduce the time devoted for research and to quickly determine the impact of various parameters on performance of vertical single U-tube borehole heat exchanger. Furthermore, the obtained result can be utilized as a reference for the design and optimization of heating and cooling system integrated with ground coupled heat pump system.

Theoretical thermal analysis of heat recovery by two phase closed Thermosyphon from engine exhaust

Due to the increase in energy requirements for various process industries and depletion of fossil fuel reservoirs, it is necessary to recover the heat energy which is exhausted to the environment from different sources. Effective utilization and recovery of waste heat is of great importance for the preservation of energy sources and protection of an environment and health hazards. For many industrial practices because of high effectiveness the application of Thermosyphon is increasing for the recovery of waste heat. The focus of the present study is to investigate theoretically the performance parameters (thermal and geometrical) of the Single tube wickless heat pipe heat exchanger (Thermosyphon) for heat recovery at simulated diesel engine exhaust conditions (Air temperature of ~150, 250 and 350 °C and under forced convective heating and cooling at different Reynolds number). From the theoretical analysis it was observed that effectiveness of Thermosyphon was over 50% for each of the conditions and it was increased up to 88% with decreasing inlet hot air velocity down to 1 m/s at temperature of 350 °C. It was also observed that at equal heat capacity rate of hot and cold fluids the effectiveness is minimum.

Design and thermodynamic analysis of supercriticalCO2reheating recompression Brayton cycle coupled with lead‐based reactor

A reheating process is generally incorporated in a supercritical CO2 (S-CO2) Brayton cycle to enhance its efficiency. The heat transfer process from the reactor coolant to the working fluid of the power cycle is a key issue encountered when designing reheating power systems for the lead-based reactor. The traditional reheating system, called RH-1, utilizes an intermediate coolant circuit. In this paper, a novel reheating system, called RH-2, is proposed. It eliminates the intermediate coolant circuit and combines the processes of the primary heating and reheating in a single heat exchanger. A thermodynamic analysis of three different systems for the lead-based reactor integrated with the S-CO2 power cycle with or without reheating was conducted to evaluate the performance of the proposed system. The results confirmed that the performance of RH-2 was the best of all the three systems. Under the same reactor conditions, the system efficiency of RH-2 was greater than those of RH-1 and the recompression (no reheating) system by 1.2% and 1.7%, respectively. RH-2 could also maintain higher efficiency when the main operating parameters varied. The efficiency of RH-2 was higher at different core outlet temperatures and split ratios. The maximum efficiency at optimal maximum pressure of RH-2 was greater than those of the other two systems. RH-2 was less sensitive to the variations in the isentropic efficiencies of the components than the other two systems, while the turbine isentropic efficiency demonstrated a significantly higher impact on the system efficiency than the two compressors (approximately 3.8 times).

Thermal analysis, pressure drop and exergy loss of energy efficient shell, and triple meshed helical coil tube heat exchanger

ABSTRACTMajority of studies has been reported in literature in recent years on performance of shell and helical coil tube heat exchanger. The present work attempts to design and analyze experimentally hot water temperature difference, Nusselt number, Dean number, exergy loss, effectiveness and pressure drop in a shell, and triple meshed helical coil tube (TMHCT) heat exchanger. The effects of hot water flowing in TMHCT ranging from 1 to 3 L/min at different inlet temperatures (50°C, 60°C, 70°C, 80°C) and cold water flow in range of 1–3 L/min on shell side at constant inlet temperature 25°C were investigated throughout the experiment. The results show that the heat transfer characteristics increase with increasing hot water volume flow rate and inlet temperature. It was also found that the performance enhancement of shell and TMHCT heat exchanger with least penalty of pressure drop was noticed as compared to existing shell and single helical coil tube heat exchanger.

A new heat transfer model for single U-pipe ground heat exchanger

A new heat transfer model for single U-pipe ground heat exchanger is proposed, including two parts: firstly, the single U-pipe is simplified as an equivalent pipe, and a 1D numerical model is established to calculate the average fluid temperature and borehole wall temperature; then, considering the nonlinear distribution of the fluid temperature based on a quasi-3D model, the inlet and outlet fluid temperatures of the U-pipe are derived as functions of the average fluid temperature and borehole wall temperature, respectively. To verify the feasibility of the proposed model, it is applied to an uninterrupted sandbox test and an interrupted sandbox test, and the calculated inlet and outlet fluid temperatures are compared with experimental data and the results of other models. Compared with other models, the fluid temperatures calculated by the proposed model are in better agreement with the experimental data especially during the short time and the interruption time, and four kinds of errors of the proposed model are basically smaller. The absolute errors of the fluid temperatures calculated by the proposed model are within 0.23 °C except during the early 4 h and the interruption time. The results show that the proposed model has high precision with short calculation time.

Performance of Thermo Hydraulic Designed Single Pass Earth Air Heat Exchanger

Performance of Thermo Hydraulic Designed Single Pass Earth Air Heat Exchanger

Investigation of Two-Phase Liquid-Droplet Flow With Particle Deposition in the Heat Exchanger

This article presents a numerical study of particle deposition in two fluids, i.e., liquid and droplet flow in a single row tube bundle heat exchanger. The tubes in the heat exchanger are modeled as heating sources. Two level-set functions are used to capture the liquid-droplet interface and the liquid-deposit front. The effects of different parameters, including Damköhler number, thermal conductivity of the deposit, viscosity of the liquid, and the heating power of the tube on the flow and heat transfer, are investigated. The deposit profiles on the tube surface are analyzed. Comparison is made for the averaged Nusselt number for the case without and with deposition. It is found that the tube surface has a thicker deposit at the upstream facing side compared with that of the downstream facing side. Generally, the heat transfer rate reduces with the growth of the deposit. Under certain conditions, heat transfer can be increased because of the increase in fluid velocity due to blockage of the flow area by the deposit. The averaged Nusselt number oscillated temporally in response to the droplet movement across the tube. Generally, the temperature at the liquid-deposit front decreases with thicker deposit formed. The averaged Nusselt number along the liquid-deposit front increases to a critical value initially, and it starts to decrease with the growth of the deposit.

Experimental investigation of multiple tube heat transfer enhancement in a vertical cylindrical latent heat thermal energy storage system

Thermal energy storage in phase change materials (PCMs) received considerable attention due to the capability of tackling the time mismatch between energy supply and demand, especially for renewable energy sources. Nevertheless, PCMs suffer from some drawbacks preventing their widespread commercialization. In this study, a geometrical heat transfer enhancement technique was investigated to increase the rate of heat transfer from the heat transfer fluid (HTF) to the PCM in a shell-and-tube heat exchanger. The performance of two designs of single and multiple (five) tube heat exchangers (i.e. STHX and MTHX, respectively) were experimentally investigated and compared in terms of average PCM temperature, liquid fraction and stored heat during a complete charging and discharging cycle. It was found that the MTHX out-performed the STHX in terms of phase change duration and stored heat. Furthermore, the validity of a common simplifying assumption in numerical investigation of MTHXs which is considering an artificial cylindrical boundary around each tube was experimentally investigated. This assumption was found to result in inaccuracy meaning that it should no longer be considered in future numerical studies.

Performance analysis of helical ground heat exchangers with different configurations

Recently, various configurations especially single U-tube ground heat exchangers have been studied to improve the thermal performance of ground heat exchangers. Although helical ground heat exchangers generally have better thermal performance than the others, only two simple types of them, a helix with an internal outlet pipe and helix with an external outlet pipe have been studied in past years. So, the novelty of this paper is comparing eight new types of helical ground heat exchangers to a single U-tube heat exchanger in terms of heat exchange rate, pressure drop, thermal resistance, effectiveness, and thermal performance capability, in order to find the best one. The considered models have the same heat transfer area, and all numerical simulations are performed by commercial CFD software. The validation of the numerical simulations is done based on experimental results. The results indicated that the triple helix heat exchanger has considerably the best thermal performance compared with other ground heat exchangers. It followed by double helix and helix (W-tube) ground heat exchangers those which approximately have the same thermal performance. In general, it can be concluded that a single U-tube heat exchanger has the worst thermal performance and the minimum pressure drop in comparison with all helical ground heat exchangers.

Investigation on the thermal and flow performances of a vertical spiral-tube ground heat exchanger in sand combined with kaolin additive

Based on a lab-scale setup, the thermal and flow performances of a single spiral-tube ground heat exchanger under certain operation mode (6 h on and 18 h off) were examined in terms of the influence of Reynolds number (3000–8000) and backfill materials (native sand, and sand/kaolin blend with 5% adding ratio of kaolin). The convective heat transfer coefficients for the tube buried in the blend were between 370 and 678 W/m2 K, which were higher than those in the sand. Also, the effectiveness of the heat exchanger in the blend was higher than that in the sand. The average values of the temperature restoration degree in the sand backfill and surrounding soil field after 18 h off increased by about 18–25%, compared to those after 6 h on, while that in the blend backfill and surrounding soil field increased by about 36–42%. It is an available option to add the kaolin into the sand for enhancing thermal performance of the ground heat exchanger. The intermittent operation mode should be also a feasible technique for prompting the thermal performance of the ground heat exchanger.

A multi-objective optimization strategy to reduce correlation and uncertainty for thermal response test analysis

The analysis of thermal response tests by optimization-based methods can lead to highly correlated parameters and to a relatively uncertain identification of the thermal parameters. The multi-objective optimization strategy examined here combines the common root mean square error to describe the misfit between the measured and simulated fluid temperature with the root mean square error between the temperature derivative of the same variables. The final objective function combines also the partial correlation coefficients of the temperature and derivative signals. The four objective functions are combined by scalarizing the multi-objective problem. The method proposed here was tested using three real data sets produced by the thermal response tests performed on a helical shaped pipe and on two single U-bent ground heat exchangers. The multi-objective strategy did not lead to different thermal parameters for the three tests, but it did generate a significant reduction in the correlation and uncertainty of the parameters. In addition, a more compact optimum shape can lead to a more rapid convergence time.

Comparison of heat transfer coefficient on single tube and multi tube heat exchanger

Heat exchanger (HX) is a device that provides heat exchange between two fluids that have temperature difference. Heat exchanger is widely applied to industrial process, power plant, transportation, air conditioning and refrigeration. In this study, the heat transfer coefficient between single tube and multi tube with the same heat transfer surface area are compared. The dimension of single tube heat exchanger is 40 cm length with 9.5 cm diameters. On the other hand, the multi tubes heat exchanger consists of ten tubes with 0.95 diameters and 40 cm length. These heat exchangers are submerged in low temperature water and the ambient air is streamed by fan with 0.0032 kg/s, 0.0026 kg/s, and 0.002 kg/s of mass flow rate. The experiment is performed for two hours. The temperature of ambient, outlet air, and water are recorded using T-type thermocouple. The heat transfer coefficient are then analyzed. The result shows that heat transfer coefficient of multi-tubes heat exchanger are 26.6% higher than single tube heat exchanger.

An analytical model for transient heat transfer in ground-coupled heat exchangers of closed-loop geothermal systems

Vertical borehole heat exchangers are widely used as sustainable and reliable tools to effectively extract thermal energy from the ground. For an effectual design and implementation of these borehole heat exchangers, it is essential to have an in-depth understanding of heat transfer within the boreholes and the geothermal reservoir. While in situ tests and numerical heat transfer analyses are proven to provide reliable results, they usually need highly compatible hardware along with expensive software and expertise acquisition. The present study presents a ‘one-dimensional’ analytical heat transfer representation of borehole geothermal heat exchangers which can amenably predict the performance of these systems. For validation of the proposed model, several grid sizes are selected to represent a wide range of typical application scenarios. Selected scenarios are run to test the capability of the proposed analytical model versus its numerical counterpart. These scenarios are examined under two distinct test cases. In the first case, the proposed analytical solution is tested in estimating the borehole wall temperatures of single and multiple borehole arrangements in a time scale ranging from hours to years. The results obtained in this case are validated with two-dimensional numerical models with a constant flux boundary condition on the borehole wall. On the other hand, a second round of tests are focused on estimating the fluid outlet temperatures by introducing an actual fluid flow in the proposed three-dimensional, U-tube, ground-coupled heat exchanger scenarios within similar transient time-scale. In this sense, single borehole, double borehole, quadruple borehole and ‘N × N’ borehole scenarios; the latter representing very large grids, are numerically modeled and compared with the proposed analytical model. This comparison study shows the amenability of the proposed analytical model in predicting system performance with high precision. Numerical validations conducted with both two-dimensional and three-dimensional transient models have shown that the proposed unidimensional analytical solution is capable to estimate system performance in an effective manner. Overall, the proposed analytical solution is proven to provide robust results in prediction of transient heat transfer in single and multiple ground-coupled heat exchangers both in short and long term with high accuracy.

An integrated system-level and component-level optimization of heat transfer systems based on the heat current method

Heat transfer system (HTS) optimization is a key for energy conservation. However, optimization of the structural/operating parameters of HTSs and the geometrical structures of single heat exchangers are usually separate and independent. Based on the heat current method together with computational fluid dynamic simulation, this paper optimizes the fluid flow rates and the heat transfer areas in a HTS with prescribed plate spacing of heat exchangers to minimize the total pumping power consumption. Then, by applying the downhill simplex search algorithm, a multi-level nested strategy is developed to optimize the plate spacing of heat exchangers simultaneously. The optimized results show that when the heat transfer rate is 1300 W, the minimum total pumping power consumption is 18.42 W, the optimal heat transfer areas of each heat exchanger are 0.046, 0.076 and 0.058 m2, respectively, and the optimal plate spacing of the studied heat exchanger is 3.5 mm. Meanwhile, the multi-level collaborative optimization reduces the total power consumption by 27% comparing that regardless of plate spacing optimization. Besides, larger flow resistances of working fluids in pipeline need more compact heat exchangers with smaller plate spacing for energy conservation.