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• Identified possible design options of CHERs. • Performed mathematical modeling of CHERs incorporating mixing effect for complex reaction schemes. • Exhibited capabilities of CHERs to carry out rapid and highly exo- or endo-thermic reactions. • Demonstrated that a single flexible CHER can be used to carry out multiple reaction schemes with minor modifications. Objective of this paper is to contribute towards overcoming the barriers limiting industry scale applications of the Compact Heat Exchanger Reactor (CHER). This objective could be achieved by exhibiting capabilities of the CHERs to carry out rapid and highly exo- or endo-thermic chemical reactions. Also, classification of CHERs and preparation of guidelines for the selection of CHERs for the given application (without the needs of extensive experimentation requirements) could prove to be helpful. In order to achieve these, several possible design options of CHERs have been identified and mathematical modelling of these design options has been carried out. The main purpose of the modelling work is to understand the impact of different designs on the rate and product distribution of single liquid phase multiple chemical reactions. The results achieved exhibit capabilities of the CHER to carry out rapid and highly exo- or endo-thermic multiple chemical reactions. The results also serve as a tool to check suitability of different designs of the CHER to carry out more than one type of reaction schemes. The development and results of the mathematical modelling for the CHER are discussed in this paper. The conclusions suggest that a single flexible CHER can be used to carry out multiple reaction schemes with minor modifications. [ABSTRACT FROM AUTHOR]

Highlights • H 2 is autothermally generated from ethanol in a parallel-plates reactor. • Adequate thermal coupling between combustion and reforming of ethanol is predicted. • Feasible integration between the reactor and heat exchangers is proved. • Splitting the fuel feed reduces hot spots while enables extra H 2 yields. • Importance of proper heat loss quantification is evidenced. Abstract This paper deals with the study of the integration of ethanol steam reforming and ethanol combustion in a parallel plates reactor aiming a hydrogen production of 1 kW th equivalent. The study was performed by means of a mathematical model of a non-adiabatic reactor and the associated heat exchangers used for preheating purposes. Focus is given here to the influence of the insulation of the reactor and heat exchangers, the fuel concentration, fuel distribution policy to the reactor, and reforming flowrate. Thermal coupling between combustion and reforming of ethanol in terms of energetic integration is feasible and an adequate behavior of the reactor and the heat exchangers is predicted. The importance of heat losses to the environment is evidenced since they represent about 35–50% of the heat released by the combustion. Ranges of ethanol fuel concentration (0.6–2.0% of ethanol fuel) and distribution (1 or 2 feed ports), and ethanol reforming load (0.37–0.63 kg/h) were studied to find windows for these variables where a satisfactory operation is possible. [ABSTRACT FROM AUTHOR]

With bore fields for energy extraction and injection, it is often necessary to predict the temperature response to heat loads for many years ahead. Mathematical methods, both analytical and numerical, with different degrees of sophistication, are employed. Often the g-function concept is used, in which the borehole wall is assumed to have a uniform temperature and the heat injected is constant over time. Due to the unavoidable thermal resistance between the borehole wall and the circulating fluid and with varying heat flux along the boreholes, the concept of uniform borehole wall temperature is violated, which distorts heat flow distribution between boreholes. This aspect has often been disregarded. This paper describes improvements applied to a previous numerical model approach. Improvements aim at taking into account the effect of thermal resistance between the fluid and the borehole wall. The model employs a highly conductive material (HCM) embedded in the boreholes and connected to an HCM bar above the ground surface. The small temperature difference occurring within the HCM allows the ground to naturally control the conditions at the wall of all boreholes and the heat flow distribution to the boreholes. The thermal resistance between the fluid and the borehole wall is taken into account in the model by inserting a thermally resistive layer at the borehole wall. Also, the borehole ends are given a hemispherical shape to reduce the fluctuations in the temperature gradients there. The improvements to the HCM model are reflected in a changed distribution of the heat flow to the different boreholes. Changes increase with the number of boreholes. The improvements to the HCM model are further illustrated by predicting fluid temperatures for measured variable daily loads of two monitored GCHP installations. Predictions deviate from measured values with a mean absolute error within 1.1 and 1.6 K. [ABSTRACT FROM AUTHOR]

The transient response of heat exchangers plays a significant role in the time-dependent performance of thermal management systems, particularly in resource-limited situations with high power density and fast-acting heat sources. A scaled thermal management testbed with a plate-frame heat exchanger was built to emulate a thermal subsystem. This paper describes a methodology for dynamically characterizing the behavior of a commercial, off-the-shelf plate-frame heat exchanger both experimentally and computationally. Statistical design of experiments principles was used to develop a test plan composed of 20 test cases for dynamic model validation. The dynamic performance of the heat exchanger was evaluated with a physics-based model, and statistical surrogate models were derived from the experimental results. Additionally, a lumped mass model was employed to determine the dynamic parameters of the heat exchanger using the experimental data. The model efficiently and accurately predicts the experimental results across the entire experimental exploration space. The lumped mass model predicts the transient response without using computationally expensive resources such as a full numerical, thermo-fluid dynamic solvers. This approach has significant implications for developing practical models of thermal components particularly for the field of thermal controls. [ABSTRACT FROM AUTHOR]

This paper presents a fundamental study of ultra-lean flames stabilized behind a thin, highly conducting metallic rectangular bluff body acting as a flame holder. Using high fidelity numerical simulations, we reproduce a phenomenon observed experimentally, showing that in this configuration steady hydrogen–methane flames can exist at equivalence ratios below the flammability limit associated with planar unstrained flames with the same hydrogen–methane proportion. These ultra–lean hydrogen–enriched mixtures exhibit a distinct stabilization mechanism compared to pure methane flames: they stabilize in the form of inverted closed V or U flames farther away from the flame holder as the inflow reactants velocity is reduced, leading eventually to blow-off for sufficiently small velocities. Conversely, as the reactants flow rate is increased, the flames anchor closer to the flame holder, and surprisingly no blow-off is observed at high velocities. This response is shown to be linked to the presence of hydrogen in the fuel mixture and its large diffusivity, which results in locally richer mixtures in the strained, curved flame base. [ABSTRACT FROM AUTHOR]

HyperVapotrons are highly robust and efficient heat exchangers able to transfer high heat fluxes of the order of 10–20 MW/m 2 . They employ the Vapotron effect, a complex two phase heat transfer mechanism, which is strongly linked to the hydrodynamic structures present in the coolant flow inside the devices. HyperVapotrons are currently tested in the Joined European Torus (JET) and the Mega Amp Spherical Tokamak (MAST) fusion experiments and are considered a strong candidate for the International Thermonuclear Experimental Reactor (ITER). The efficiency of heat transfer and the reliability of the components of a fusion power plant are important factors to ensure its longevity and economical sustainability. Optimisation of the heat transfer performance of these devices by the use of nanofluids is investigated in this paper. Nanofluids are advanced two phase coolants that exhibit heat transfer augmentation phenomena. A cold isothermal nanofluid flow is established inside two HyperVapotron models representing the geometries used at JET and MAST. A hybrid particle image velocimetry (PIV) method is employed to measure the flow and create a dense velocity vector map of a region of interest. The vector spatial resolution is 30 μm. The instantaneous and mean flow structures of a nanofluid are compared to those present during the use of a traditional coolant (water) in order to detect any departure from the hydrodynamic design operational regime of the device. It was discovered that the flow field of the JET model is considerably affected when using nanofluids, while the flow in the MAST geometry does not change significantly by the introduction of nanofluids. Evidence of a shear thinning mechanism is found inside the momentum boundary layer of the nanofluid flows and it might be important to calculating the pumping power losses of a functional nuclear fusion power plant cooling system ran with nanofluids instead of water. [ABSTRACT FROM AUTHOR]

This paper presents a mathematical model to determine the minimum energy targets for a batch process with flexible schedule. Techniques developed for flexible-schedule batch processes typically result in nonlinear formulations. The proposed model was formulated as a mixed integer linear programming model (MILP). The model is developed based on the source-demand classification of process streams instead of the typical classification of hot and cold streams. In such classification, each stream is simultaneously treated as a source at its shifted supply temperature, and as a demand at its shifted target temperature. Such classification eliminates the model's non-linearity and reduces its complexity as well as the solution time. The mathematical model can be used to calculate the utility targets for a flexible-schedule batch process. Application of the proposed mathematical formulation demonstrates significant energy saving potential. The first illustrative example predicted a potential reduction of 11% cold utility and 14% hot utility. In the second illustrative example, up to 35% hot utility reduction and 62% cold utility reduction could be achieved. [ABSTRACT FROM AUTHOR]

The paper focuses on the analysis of steady-state properties of autothermal structures with a fluidized bed. The concept of autothermicity is discussed, and typical autothermal structures are presented. A method for the determination of the steady-states of such systems is described. Quantitative analysis of steady-states multiplicity is presented for two autothermal structures, that is a fluidized-bed reactor with an external heat exchanger, and with a partial recirculation of hot gases. A two-phase bubbling bed model is employed to describe quantitatively the behavior of the catalytic fluidized bed. The influence of selected design and operating parameters on steady-state characteristics is analyzed for two simple kinetic models. The effect of these parameter on the desired product yield is evaluated for the multiple-reaction process. The results obtained have both scientific and practical importance. [ABSTRACT FROM AUTHOR]

Abstract: This paper proposes a new frequency domain method to model the heat transfer between the injected/extracted heat and the temperature of the fluid exiting a borehole heat exchanger. The method is based on in situ measurements and focuses particularly on the short-term borehole heat transfer. It uses a rational function of the Warburg variable in the Laplace domain to model the borehole heat transfer. The rational model is transformed to a time domain model using inverse Laplace transformation. This time domain model makes it possible to calculate the temperature response on a random heat variation signal. The paper also demonstrates a new way to perform the classical thermal response test. Instead of injecting a constant amount of heat, the experiments have been performed using multiple short-duration heat injections. In this way, the obtained rational heat transfer model contains information about both the short- and the long-term heat transfer. The results obtained using the proposed modeling method are compared with those obtained from a state-of-the-art analytical method. The time domain model can be used to design a controller to optimize the performance of a Ground Source Heat Pump system, the efficiency of which depends strongly on the temperature of the fluid exiting the borehole. [Copyright &y& Elsevier]

Abstract: In this paper, a transient numerical model for a liquid-to-air membrane energy exchanger (LAMEE) is developed and the results are compared to the experimental data. The data for the sensible, latent and total effectiveness are compared with transient and steady-state simulations for various values of NTU and operating parameters (Cr∗, inlet temperature and humidity) while the exchanger undergoes a step change in inlet conditions and reaches a new steady-state. The transient and steady-state performances are shown to be a function of the design and operating parameters. The paper also shows that buoyancy forces become important and affect the LAMEE performance under certain operating conditions. The verified numerical model is used to investigate the impact of outdoor air conditions on the LAMEE performance. [Copyright &y& Elsevier]

Abstract: For multi-stream plate-fin heat exchangers (MPFHEs), a crucial factor affecting performance is the layer pattern used to distribute hot and cold streams. However, for the design of MPFHE layer pattern, so far it still remains at semi-qualitative, empirical or trial-and-error stage, lacking efficient approaches to obtain the optimum. In this paper, an effective layer pattern optimization model using genetic algorithm (GA) is developed in detail. It includes the chromosome of binary string that represents hot and cold layers alternatively arranged, the dual fitness functions that act on chromosome individuals alternatively, the constraint that requires the spacing layers between hot and cold streams to be no less than 1 and no greater than 2, the selection of optimization tool and the corresponding setting of GA parameters. When used to optimize the layer pattern of actual MPFHE, this model exhibits well. The average thermal efficiency of exchanger reaches up to 98% of that obtained under the ideal common wall temperature assumption. Furthermore, the study of this paper make it clear the association of previous classical deviation from ideal of layer pattern zigzag curve with MPFHE thermal performance, which is not a strict monotonic decreasing relation as people thought to be, but a multiple vs. multiple relation. [Copyright &y& Elsevier]

In this paper we consider control-oriented modeling of a sensible thermal energy storage (TES) tank with a helical immersed heat exchanger (IHX) coil. A key focus of the modeling approach is to minimize the number of dynamic states required to adequately describe the system dynamics. The resulting model is well-suited for model-based control design, real-time simulation, and hardware-in-the-loop testing aimed at intelligent operation of TES systems. We use a discretized approach to model the temperature dynamics of the water within the storage tank. We use a quasi-steady approach to model the IHX coil dynamics, thereby limiting computational complexity. In simulation, the model runs up to 1200× faster than real-time. A simulated case study of model-based feedback control demonstrates the utility of the modeling approach. The model contains four tuning parameters that are empirically determined using experimental data collected from a commercially available domestic hot water storage tank. The model is then validated, both temporally and spatially, against data collected during the simultaneous charge/discharge mode. Finally, we quantify the trade-off between model fidelity and increased control volume discretization, showing that a 60 node model yields a RMSE value under 4.5%. [ABSTRACT FROM AUTHOR]

Abstract: This paper describes the application of exergy analysis to human heat and mass exchange with the indoor environment. The basis for this paper is the existence of a formal similarity between the parameters defining human heat and mass transfer governed by physiological processes and the parameters defining exergy destruction. Basic heat and mass transfer is calculated using a standard two-node human physiological model. To enable an exergy analysis the model was divided according to heat and mass transfer over appropriate boundaries. The exergy analysis was performed for each process with regard to the type of exergy that participates in heat and mass exchange with respect to the indoor environment. The results provide insight into the complex interactions between the human body and environment as characterized by exergy destruction. Furthermore, the analysis indicates that at given physiological parameters only a certain combination of environmental conditions ensures minimal exergy destruction. These environmental and human conditions coincide with expected level of thermal comfort. [ABSTRACT FROM AUTHOR]

Abstract: Enthalpy exchangers have been used as an efficient means to recover both sensible heat and moisture from exhaust ventilation air. A cross-flow plate-fin structure is the most popular arrangement for the exchanger core due to its compactness and high mechanical strength even with very small channel wall thickness. Traditionally, hygroscopic paper is selected as the plate and fin materials. Though the sensible effectiveness with this material is satisfactorily high, the latent effectiveness is disappointingly low due to the low moisture diffusivity in paper. To solve this problem, in this study, a novel concept is proposed to augment moisture transfer in the exchanger. Plates and fins are made with different materials. A novel membrane – the composite supported liquid membrane (CSLM) is used as the plate material. Paper is still used as the fin material for its cheapness and high support strength. To make comparisons, two cores, one is paper-fin and paper-plate, and another one is paper-fin and membrane-plate, are constructed and tested for heat and moisture recovery. Simultaneous heat and moisture transfer in the plate-fin core is studied. Mathematical model governing the heat and moisture transfer in the cores is set up and numerically solved. Both the experimental data and numerical results indicate that the latent effectiveness of the paper-fin and membrane-plate core is 60% higher than the traditional paper-fin and paper-plate core, due to the high moisture diffusivity in the CSLM. [Copyright &y& Elsevier]

• The desirable operating conditions to achieve high operational efficiency are obtained. • The performance of the IEC under different operating conditions is investigated. • The mathematical model is validated against published data. • The optimal dimensions that give good efficiency in climates with moderate humidity are highlighted. [Display omitted] This paper presents a study investigating and analyzing the effect of heat and mass exchanger (HMX) dimensions and the flow parameters on the indirect evaporative cooler (IEC) system's performance. For this purpose, a mathematical model based on heat and mass transfer concepts was developed, and the model was verified using experimental and simulation results from published papers. Simulations were performed based on different operating and structural conditions affecting the outlet air temperature, cooling capacity, coefficient of performance, and wet-bulb efficiency. Results showed that the optimal dimensions that give good efficiency in climates with moderate humidity, the length of the duct should be between 0.6 to 1.0 m , the width of the channel between 0.3 to 0.5 m , and the channel gap between 0.004 to 0.008 m. It has also been observed that the increasing working air velocity has a positive effect on cooling performance, and its velocity should not be less than 1 m / s. As for increasing the product air velocity, it reduces the heat exchange period, which is undesirable, so it should not exceed 1 m / s. The prescribed flow rate ratio between product and working air should be 0.3 to 0.5. This analysis provides desirable operating conditions to achieve high operational efficiency as well as optimal dimensions for designing such a cooler. [ABSTRACT FROM AUTHOR]

This paper presents a general mathematical optimization model and the related deterministic algorithm for synthesizing heat-exchanger networks (HEN). The methodologies commonly used to solve a HEN problem are based on heuristic methods. These algorithms reach a presumed best solution with respect to the investigated set of process streams, whereas our approach determines the optimal configuration. In this paper the proposed method is applied to the solution of a few simple HEN synthesis problems and the results are compared with those obtained utilizing heuristic or meta-heuristic methods. HEN''s problem is represented by a general mathematical model that can be applied to small and medium sized problems and is solved by using a deterministic method with a reasonably brief computation time. Notably, this approach can represent a unique general model of a wide class of heat-exchanger networks, independently of their specific physical configuration. [Copyright &y& Elsevier]

• The mathematical model is useful for analyzing the heat exchanger performance. • The most probable variant of heat exchanger operation is established. • There is a risk of frost accumulation within the fixed-bed regenerator. The paper describes an original mathematical model of heat and mass transfer for a fixed bed regenerator used to determine the effect of internal airflow leakage on heat exchanger efficiency. First, the build and operating principles of a fixed-bed heat exchanger were discussed. The presence of internal leakage was shown along with a proposed solution for its elimination. Then, a mathematical model based on a modified ε-NTU method for numerical simulation and analysis of coupled heat and mass transfer in a fixed-bed heat exchanger was presented. The model was supplemented with an additional detailed submodel designed to determine frost surface temperature and frost growth analysis. Initial numerical simulations of the operation of the model were performed for low outdoor air temperature conditions. Different zones of heat and mass transfer within the regenerator matrix were distinguished. The presence of accumulated frost area and its influence on the course of heat and mass transfer processes was revealed. In addition, the presence of a relative humidity limit curve associated with a mass balance deficiency conditioning the occurrence of frost accumulation was established. [ABSTRACT FROM AUTHOR]

This paper presents a new step-wise sequential solution strategy for the synthesis of heat integrated water networks (HIWNs) comprising of two mathematical models. The first model minimizes water and energy costs. The optimal freshwater and water flow rates within the HIWN are determined from this model. Using these optimal flow rates, different configurations of HIWN are evaluated for the purpose of heat integration. The second model is the stage-wise heat exchanger network (Yee and Grossmann, 1990), which is solved for each of the evaluated network configuration in a sequential manner. Using this proposed strategy, a set of locally optimal HIWNs are produced and the best one is chosen based on the minimum total annual cost (TAC). The proposed sequential strategy is applied to small and medium sized examples in the literature. The results show that the proposed new sequential solution strategy can be successfully applied to small and medium sized HIWN problems. [ABSTRACT FROM AUTHOR]

This paper presented a novel mathematical programming model for the simultaneous optimization of heat integrated water allocation networks featuring parallel heat exchanger network (HEN) structure. In the HEN structure, both freshwater and wastewater can be split freely. This model was suitable for both uniform wastewater treatment and separate wastewater treatment cases. The proposed model was formulated as a MINLP (mixed-integer non-linear programming) problem, making it applicable to large scale problems. The main objective was to minimize the total annual cost. Three literature examples, including a large scale example, were illustrated to demonstrate the applicability of the model. It was shown that the proposed method was as accurate as the literature methods for small scale problems, but performed better for large scale problem applications. [ABSTRACT FROM AUTHOR]

This study makes use of a novel methodology for the synthesis of heat exchanger networks, which is aimed at overcoming the shortcomings associated with the use of shortcut models to represent individual exchangers in the synthesis network. The new approach entails the use of a number of correction factors to get networks which are based on the use of shortcut models, such as the mixed integer non-linear programming (MINLP) stage-wise superstructure (SWS) of Yee and Grossmann (1990) to more closely represent physically achievable heat exchangers and ensure that the MINLP network topology optimisation step of these models converge on a real design, rather than an approximated one. In this paper, the SWS formulation is used for the generation of an initial network after which its objective function is modified to include the correction factors that force its objective function towards the cost of a network whose individual exchangers are designed using methods such as Bell–Delaware and heuristics. The modified objective function includes parameters that modify the areas obtained by the shortcut based MINLP model so as to more closely represent the areas obtained by the detailed models and also includes a novel method for including the number of shells required for each exchanger duty. The correction factors account for pressure drops, F t correction factors, number of shells, TEMA considerations, and changes to the overall heat transfer co-efficient of each stream match. The methodology is applied to two examples and the solutions are comparable with other solutions obtained in literature and were shown to produce good solutions. The reason that the method is effective is because many potential networks are evaluated during the iterative procedure and the best network, based on the detailed exchanger designs, is chosen. In this way it is possible to use the detailed exchanger designs to “guide” the MINLP optimisation towards more realistic networks and also to generate many different potential networks. [ABSTRACT FROM AUTHOR]

This paper presents a numerical study of heat and mass transfer in indirect evaporative air coolers with four air flow patterns: parallel-flow, counter-flow, cross-flow and regenerative. The numerical simulation was performed on the basis of original two-dimensional heat and mass transfer models (in the case of cross-flow heat exchanger the model was 3D). The mathematical models developed were validated against published experimental data presented in Appendix A . It was established, that heat and mass transfer processes in the wet channels of counter-flow, cross-flow and regenerative indirect evaporative coolers are characterized by creation of two particular heat and mass transfer zones. Detail analysis of the temperature and humidity ratio distributions and boundary conditions, characterizing the coupled heat and mass transfer process in each of these determined zones, revels the violation of the Lewis relation unity under a certain inlet and operation conditions. A theoretical method for estimating the Lewis factor was proposed. Using the developed models the thermal performances of the conventional designs of indirect evaporative air coolers were analyzed numerically and preferable climatic zones for considered heat exchanger were established. Four novel heat exchangers utilizing the advantages of the basic cycles heat exchangers were presented. [ABSTRACT FROM AUTHOR]

This paper concerns heat exchange devices with a zigzag configuration containing multi-phase change materials (m-PCMs). A two dimensional mathematical model was established to model the charging behaviour. An experimental system was built to validate the model. The modelling results agree reasonably well with the experimental data for a single PCM, establishing confidence in the model. Extensive modelling was then carried out under different conditions. The results show that the use of m-PCMs intensifies the charging process in comparison with the use of a single PCM. Given other conditions, a larger phase change temperature difference between the m-PCMs gives a more remarkable enhancement of the charging process, and the use of m-PCMs with an unequal mass ratio gives further intensification. The modelling results also show that, for a given input power, an optimal fluid velocity exists for obtaining a high rate of the melting process. [ABSTRACT FROM AUTHOR]

This paper investigates a mathematical simulation of the heat and mass transfer in the two different Maisotsenko Cycle (M-Cycle) heat and mass exchangers used for the indirect evaporative cooling in different air-conditioning systems. A two-dimensional heat and mass transfer model is developed to perform the thermal calculations of the indirect evaporative cooling process, thus quantifying the overall heat exchangers’ performance. The mathematical model was validated against the experimental data. Numerical simulations reveal many unique features of the considered units, enabling an accurate prediction of their performance. Results of the model allow for comparison of the two types of heat exchangers in different applications for air conditioning systems in order to obtain optimal efficiency. [ABSTRACT FROM AUTHOR]

Abstract: The formation of particulate deposits on flue gas heat exchanger surfaces will reduce heat transfer efficiency, increase the instability of equipment operation and introduce a major uncertainty into the heat exchanger design. In this paper, a numerical model was developed to predict the flue-ash particle deposition rate by considering particles transport, sticking and rebound behaviors based on the software FLUENT, extended by user-defined functions (UDFs). The numerical model was applied to cross-flow tube bundle heat exchangers with a 6-row tube arrangement. The effects of six parameters (particle diameter, flow velocity, spanwise tube pitch, longitudinal tube pitch, tube geometry shape, and arrangement) on fouling rate, as well as on the heat transfer and hydrodynamics performance, were examined. It was found that particle deposits accumulated primarily in the flow stagnation region, recirculation region, the vortex separation and reattachment regions. Increasing particle diameter moved the deposition zones towards the windward side of tubes. Using both oval tubes and staggered arrangements can reduce the fouling rate. With the increase in longitudinal tube pitch, both the particulate deposit rate and the heat transfer performance increased. To account for fouling and heat transfer performance, a tube spacing value of 2 was recommended. [Copyright &y& Elsevier]

Abstract: Conventional network structure modifications for retrofitting heat exchanger networks (HENs) usually require a large network superstructure, which might lead to very large scale retrofit models, and thus increases the computational difficulties of optimization, especially for industrial applications. This paper presents a novel optimization approach of retrofitting HENs for both small scale and industrial scale problems. To overcome the drawback of the existing retrofit research, a simple but efficient method is proposed to determine the network retrofit superstructure based on the concept of pinching match. Then two optimization stages (network structure optimization and investment optimization) are solved with the MILP-based iteration method that has been developed. The proposed approach has many benefits for solving HEN retrofit problems. First, smaller size of retrofit superstructure is provided based on the pinching match analysis. Second, the MILP-based iteration method developed converts conventional a mixed integer non-linear programming (MINLP) to a mixed integer linear programming (MILP), and significantly reduce the computational difficulties of nonlinear programming associated with configurational changes or structural modifications for existing heat exchanging arrangements, which is upgraded based on the MILP-based iterative method proposed by Pan et al. (2012a) for retrofitting HENs with heat transfer intensifications, as the earlier work was only applicable to the cases without network topology modification. In case studies, the new proposed approach is compared with the existing methods in two literature examples and one industrial problem, demonstrating that the new proposed approach is able to obtain better and more realistic solutions for HEN retrofitting considering the economic trade-offs between energy savings and investments. [Copyright &y& Elsevier]

Abstract: Heat transfer by natural convection occurs in many physical problems and engineering applications such as geothermal systems, heat exchangers, petroleum reservoirs and nuclear waste repositories. These problems and phenomena are modeled by ordinary or partial differential equations. In most cases, experimental solutions cannot be applied to these problems, so these equations should be solved using special techniques. Recently, much attention has been devoted to these methods to construct analytic solutions; such as the perturbation method. Perturbation techniques are dependent upon small parameter. Thus, it is worthwhile developing a new technique independent of small parameter. The Reconstruction of Variational Iteration Method technique is a powerful and convenient algorithm in finding the solutions for the equations. While this method is capable of reducing the size of calculation, it overcomes the difficulty of the perturbation technique or Adomian polynomials by applying Laplace Transform. In this paper an analysis has been performed to study the natural convection of a non-Newtonian fluid between two infinite parallel vertical flat plates and the effects of the non-Newtonian nature of fluid on the heat transfer are studied. In order to compare with exact solution, velocity and temperature profiles are shown graphically. The obtained results are valid with significant accuracy. [Copyright &y& Elsevier]

Abstract: Adequately representing the dynamic performance of a water-to-air heat exchanger under transient conditions would help design optimized control strategies for a high-energy-efficiency HVAC system. In this paper, the water-to-air heat exchanger is considered as a multi-input-and-multi-output system (MIMO), and the corresponding dynamic model is developed with the mass and energy balance equations based on which the state-space model for transient behavior of the heat exchanger is derived. The model has been validated by a series of dynamic response experiments including the transient responses of exit air temperature and humidity as well as exit water temperature subjected to the disturbances of inlet water temperatures (Case I: Start up the chiller; and Case III: Stop the chiller) and a sudden change in the water flow rate (Case II: The water flow rate increases by 0.058kg/s). The time of experimental validation on the transient response simulation is set as 1200s in all the cases. The simulated results obtained by the state-space model have been compared with the experimental data, which shows that the state-space model developed in this study is capable of predicting the transient performance of the water-to-air heat exchangers satisfactorily (the average error is less than 15.0%). Meanwhile, the influence of input disturbances and initial conditions on the transient behaviors of the heat exchanger is discussed through the model simulation. The results show that the input disturbances and the initial conditions will produce significant influence on the proportionality coefficient of the response variables, but little influence on the time constant of the response ones. [Copyright &y& Elsevier]

Abstract: This paper deals with the derivation of a low-dimensional mathematical model of a compact plate heat exchanger capturing the significant nonlinearities and the essential dynamic behavior in an accurate way. Thereby, the model is based on the basic laws of thermodynamics and the similitude theory of Nußelt. It is shown that reasonable simplifications according to the specific design and the typical operating conditions of compact plate heat exchangers together with a semi-discretization of the spatial domain by means of the finite volume method provides a compact finite-dimensional approximation of the underlying partial differential equations (pdes). In this context, two different interpolation schemes of the finite volume method are compared, i.e. a classical upwind scheme and a new concept based on an approximate stationary solution of the underlying pdes. The latter ensures high accuracy even for very low-order discretizations, which is shown by means of simulation and measurement results. [Copyright &y& Elsevier]

Abstract: Waste heat recovery by means of a Rankine Cycle is a promising approach for achieving significant reductions in fuel consumption and, as a result, exhaust emissions of passenger car engines. This approach is already well established in industrial applications such as gas and steam power plants or ship propulsion systems. While these systems are mainly designed for stationary operation, the behaviour in highly dynamic operating conditions becomes more important when the principle is transferred to a passenger car engine. Knowledge of the dynamic response of the employed heat exchangers plays an important role in performance prediction and control system design of the steam cycle. Hence, a dynamic model of the exhaust gas heat exchanger employing the moving-boundary principle was developed and is presented in this paper. The model describes both design operation and the heat-up procedure of the component. For achieving high model accuracy in the resulting broad range of operating conditions, new approaches for modelling wall temperature distribution and zone switching were developed. Simulations of stationary operating points as well as the response to typical disturbances of the system’s input variables are in good agreement with test bench measurements. The model is used to develop a control system for dynamic operation on the test bench. Further studies of the operating characteristics reveal varying dynamic behaviour depending on the heat flow rate from exhaust gas to working fluid as well as coupling of evaporation pressure and outlet steam temperature. [Copyright &y& Elsevier]

Abstract: This paper presents results obtained from a numerical simulation for the horizontal slinky-loop heat exchanger of a ground-source heat pump system. A three-dimensional numerical model was developed and the results of the thermal performance of various heat exchanger configurations are presented. The investigation was carried out on five types of loop pitch (loop spacing), three types of loop diameter, three values of soil thermal properties, and allowing continuous and intermittent operation. Comparison was made for the heat transfer rate, the amount of pipe material needed, as well as excavation work required for the horizontal slinky-loop heat exchanger. The results indicate that system parameters have a significant effect on the thermal performance of the system. [Copyright &y& Elsevier]

Abstract: In this paper a numerical model to analyze the thermal behaviour of vertical ground heat exchangers with a helical shaped pipe is presented. This type of configuration can be a suitable alternative to conventional ground heat exchangers, especially when the heating and cooling loads of the building are very low. The model describes the heat transfer problem by means of a network of interconnected thermal resistances and capacitances. Moreover, as the investigated ground heat exchanger is usually installed in shallow depth, the model takes into account the interaction between the ground and the ambient environment which affects the fluid heat carrier temperature into the heat exchanger and, as a consequence, the energy efficiency of the heat pump. After a sensitivity analysis on the mesh parameters, the presented model is compared with experimental data and the simulation results show good agreement with the measurements. Finally, analyses to investigate the influence of the weather conditions, of the axial heat transfer and of the pitch between the turns of the helical pipe for two types of ground are carried out. [Copyright &y& Elsevier]

Abstract: Ground source heat pump systems are often coupled to the ground by circulating a fluid through vertical Borehole Heat Exchangers (BHEs). The design of a system requires estimates of the ground thermal conductivity and the borehole thermal resistance, which are usually determined by an in situ thermal response test on a completed borehole. The usual test interpretation methods average the inlet and outlet fluid temperatures and use this mean temperature as the average temperature along the borehole length. This assumption is convenient but does not strictly apply. For a coaxial heat exchanger this paper develops an analytical model for the vertical temperature profiles, which can be used instead of the mean temperature approximation to estimate borehole resistance. The model is verified with measured temperatures on a BHE, where an optical technique allows continuous measurements along a coaxial borehole during a distributed thermal response test. A sensitivity study shows that the proposed method corrects errors in the mean temperature approximation, which overestimates the borehole resistance in a coaxial borehole. [Copyright &y& Elsevier]

Abstract: A dynamic evaporator model of air source heat pump (ASHP), considering the ratio of the latent heat to sensible heat of wet air, is presented to analyze the performance of ASHP under frosting. The performance parameters, such as the heating capacity, COP and the outlet temperature of compressor, are simulated with CYCLEPAD. Then a semi-empirical correlation that predicts frost accumulation on the air-side of fin-tube heat exchanger is developed with dimensionless analysis and also modified by a test conducted under cold-moist conditions in winter. In addition, eight influence factors are considered involving the ambient conditions and structures of heat exchanger, whose effects are analyzed as well. Among them, the equivalent diameter of air flow cross-section in fin-tube deq is especially proposed. Lastly, the relationships between the ratio, the performance parameters and the frost accumulation are discussed in this paper, followed by an evaluation of an optimal defrosting time interval to improve the ASHP’s energy efficiency and operational reliability at cold-moist conditions in central-south China. [Copyright &y& Elsevier]

Abstract: Many energy conversion and other thermal-fluid systems exhibit unsteady convective heat exchange. In such systems, generic spatiotemporal variations in the flow give rise to variations in the heat flux for a given fluid–solid temperature difference, which can be interpreted as spatiotemporal fluctuations of the instantaneous heat transfer coefficient. These variations can lead to unsteady conjugate heat transfer, in which the exchanged heat flux arises from an interaction between the bulk fluid temperature and the temperature in the solid. Further, the nonlinear coupling between the fluctuating temperature differences and the heat transfer coefficient can lead to an effect we refer to as augmentation, which quantitatively describes the ability of a particular arrangement to have a different time-mean heat flux from the product between the mean heat transfer coefficient and the mean temperature difference across the fluid. It is important to be able to understand and to model in a simple framework the effects of the material properties, the geometry and the character of the heat transfer coefficient on the thermal response of the fluid–solid system, and consequently to predict the overall heat transfer performance of these systems. This paper, which follows on from its predecessor [1], is concerned with the phenomenon of augmentation in simple, one-dimensional, unsteady and conjugate fluid–solid systems. A simple semi-analytical one-dimensional model of heat transfer with a time-varying heat transfer coefficient, which was presented in Mathie and Markides [1], is applied herein to two different paradigm problems. Such a model can be an important tool in the design of improved heat exchangers and thermal insulation, through for example, the novel selection of materials to exploit these augmentation effects. The first flow considered is a thin, wavy fluid film flowing over a heated plate. This film flow exhibits a periodic fluctuation in the heat transfer coefficient, that is linked to the wavy interfacial deformations of free surface of the liquid film. The second flow considered concerns the heat transfer behind a backwards-facing step, which exhibits broadband fluctuations in the heat transfer coefficient due to the flow separation and turbulence behind the step. The model predictions of the augmentation ratio for these problems are also compared to direct measurements from each case. Good agreement is observed with the experimental results for the global heat transfer trends. In both cases the augmentation ratio was negative, reflecting a reduction in time-averaged heat transfer. For the backwards-facing step flow a low magnitude of augmentation ratio was observed, however, the thin film flows exhibited augmentation ratios of as high as 10%. [Copyright &y& Elsevier]

Abstract: This paper proposes a new method for fouling detection in a heat exchanger. It is based on the modeling of the system in a fuzzy Takagi–Sugeno representation derived from a physical model. With this representation, the design of a fuzzy observer with unknown inputs of polynomial types is obtained via a LMI formulation. Main advantages of the proposed method are that neither specific sensor, excepted standard ones, nor special operating conditions such as steady state regime are required. Some realistic simulations show the efficiency of the proposed technique. [Copyright &y& Elsevier]

Abstract: This paper presents an experimental and numerical case study of the heat transfer around the helical ground heat exchanger. With varying helical pitch, indoor thermal response tests were conducted in a dry sand. The tests were analyzed based on axisymmetric finite element analyses and recently published heat source models for spiral coil heat exchanger including our modifications of them by adding finite-length line source solution to consider vertical return pipe at center of helical heat exchanger. In addition to reasonable agreements in soil temperature rises at exteriors the helical heat exchanger, existence of return pipe was found to be important for estimation of heat transfer inside helical exchanger. Besides, the heat source models were found to be applicable to approximate mean fluid temperature during TRTs. The numerical and analytical models were applied to field thermal response test for an energy pile reported in literature. Compared with numerically estimations, the analytical solutions considerably overestimated temperature rise at the exterior of the energy pile. The results reveal that reasonable considerations in estimation of effective thermal properties may be needed when applying the heat source models for energy pile, even though they would evaluate reliable heat transfer behavior of helical heat exchanger embedded in a homogeneous ground. [Copyright &y& Elsevier]

Abstract: The application of ground heat exchangers (GHEs) has attracted much attention for its advantages in terms of energy-saving and emission-reduction. Therefore, it is significant to introduce heat transfer into investigation, the paper illustrated the existing heat transfer models in order to analyze the GHEs with buried coils. Line heat source, cylindrical heat source and ring-coil heat source are introduced step by step. For the present, the borehole GHEs are the mainstream, and in recent years pile foundation GHEs have been followed with interest on account of heat transfer superiority as well as lowering initial cost and saving land area. Concerning that groundwater flow exist in geological stratum sometimes, so that the thermal analysis about heat transfer should be composed of two cases, i.e. models under the condition of both pure conduction and combination that include conduction and advection. It is obvious that ring-coil model is on the verge of actual situation for pile foundation GHEs with buried coils from the academic research perspectives, nevertheless for some engineering computation problems which the result error can be permitted in the certain range, other heat transfer models can be chosen in order to simplify the calculation process. [Copyright &y& Elsevier]

Abstract: As we know, the mean temperature difference approach perfectly solves the problem of thermal design of a two-fluid heat exchanger. However, so far, the equivalent method has not been found for that of three-fluid heat exchanger. In this paper, a mean temperature difference method called IMTD (integral-mean temperature difference) is developed in detail for a parallel stream three-fluid heat exchanger with two communications. It includes the derivation of IMTD formulae, the illustration of design and simulation procedures of IMTD thermal model, the corresponding exemplary calculations and discussion, and the validation of IMTD thermal model. The research shows that the derived IMTD formulae and accelerated method proposed in the present IMTD model significantly improve the design process in the past analytical models. It realizes a fast convergence which is usually within 10 steps for all parallel stream flow arrangements. Moreover, the present model has the same accuracy as past exact analytical models and simultaneously can be comparable to past approximate analytical models in simplicity. [Copyright &y& Elsevier]

Abstract: Heat transfer intensification is an effective technique for improving energy recovery in heat exchanger networks (HEN) by enhancing heat transfer without any network topology modifications. In this paper, a novel optimization method has been developed for the synthesis of intensified heat exchanger networks with a simple mixed integer linear programming (MILP) model under retrofit scenario, and a robust solution strategy based on two iteration loops has been proposed. The new method has distinctive advantages over existing design methods, as the new MILP model can effectively and significantly reduce computational difficulties associated with nonlinear formulation in existing HEN retrofit formulations. Three cases have been tested to demonstrate the validity and efficiency of the proposed approach, which requires very short computational times to obtain optimal solutions when energy saving or profit is to be maximised through retrofit. [Copyright &y& Elsevier]

Abstract: In this paper the optimization of a heat-integrated catalytic exhaust purification system for specific use in monovalent CNG vehicles is presented. The respective simulation results are based on a multiphase 1D model of the counter current heat exchanger with catalytic coating. For validation, stationary measurements obtained with a laboratory scale prototype are shown. Furthermore, a novel cold start approach, based on a bypass system, is introduced. As inflow conditions for the transient simulations, raw emission data from a monovalent CNG vehicle, performing a full drive cycle on a dynamometer test bench, was used. Based on this simulation setup, an optimized operation strategy of the bypass during cold start has been developed. Subsequently, the geometric parameters of the heat exchanger reactor have been refined, following an optimal design strategy. [Copyright &y& Elsevier]

Abstract: Thermal energy storage (TES) has shown potential in improving the overall performance in energy systems, through shifting of thermal load demand, and through matching of uneven energy availability in time and in space. Latent heat TESs demonstrate advantages over sensible heat TESs for their high storage density and small temperature swing; however, lack of accurate knowledge in novel material properties and lack in a holistic design protocol often lead to difficulties in reaching technically viable storage design. With the aim of proposing a sound latent heat based TES design-to-validation protocol, this paper covers material property characterization through Temperature-history (T-history) method, heat exchanger design through heat transfer modeling, and model validation through experimental verification. A model for submerged cylindrically finned heat exchanger latent heat storage unit with phase change material was built. The results show that performance of gelled salt-hydrate based TES can be assessed with a pure conduction based model. This material property characterization-to-model verification approach may serve as a standard in providing accurate storage design for performance evaluation. [Copyright &y& Elsevier]

Abstract: Earth heat exchangers are essential parts of the ground-source heat pumps and the accurate prediction of their performance is of fundamental importance. This paper presents the development and validation of a numerical model for the simulation of energy flows and temperature changes in and around a borehole heat exchanger when a fluid circulates through a U-tube. Based on the time-dependent convection–diffusion equation, the FlexPDE software package is employed to solve the resulting boundary value problem that model a heat exchanger. First, the mathematical model is validated through a comparison with data obtained from experiments with real borehole set-ups in Cyprus. Then the validated model is used to study the heat flow and the temperature variation in the heat-exchanger. Finally conclusions are extracted on how various parameters like the U-tube diameter, the variation of the ground thermal conductivity and specific heat and the borehole filling material affect the temperature of the inlet and outlet fluid. [Copyright &y& Elsevier]

Abstract: The wave-finned flat tube heat exchangers are widely used in air-cooled condensers of a power plant. Due to the oblique arrangement of the wavy fins on the A-frame tube bundles of the air-cooled condenser, the finned tube is prone to fouling thus the thermo-flow performances of air-cooled condensers are likely to become deteriorated. A new configuration of wave-finned flat tube, in which the fin surface rotates to be perpendicular, is proposed in this paper to prevent the fouling from gathering on the finned tube. The physical and mathematical models for the fluid and heat flows of the cooling air through the present and proposed wave-finned flat tube bundles are setup, and the thermo-flow characteristics are compared. For the proposed finned tube, the influences of the fin pitch, height and the Reynolds number on the flow and heat transfer performances are investigated, and the correlations of the friction factor and Nusselt number are recommended. The results show that the buoyancy effect should be taken into account for the correlation of the friction factor at low Reynolds numbers, but this buoyancy force can be ignored for the Nusselt number. [Copyright &y& Elsevier]

Abstract: Phase change materials (PCMs) can store large amounts of heat or cooling in a small amount of material, they potentially have less weight and volume compared with other thermal energy storage materials. Thermal energy storage applications such as solar hot water systems and off peak refrigeration systems are able to use PCMs to store heat or cooling. However, research has shown that the effectiveness of these systems heavily depends on the arrangement of the PCM system, which affects both the storage density and the thermal resistance to heat transfer. However, specifying as well as determining an effective PCM system has been difficult in the past because it involves using numerical modelling which is time consuming. This paper presents the results of an experimental investigation carried out on a tube-in-tank design filled with PCM for cold storage applications. The PCMs used are salt hydrate with phase change temperature of −27°C and water. From the experimental measurements, the average heat exchange effectiveness of the storage tank was determined and a characteristic design curve has been developed as a function of the measured average NTU. [Copyright &y& Elsevier]

Abstract: In this paper, a promising heat engine technology capable of utilizing low grade heat is examined. Based on a two-phase thermofluidic oscillator concept, the novelty and advantage of this particular system lie in its use of phase change and its lack of reliance on inertia to sustain oscillations, though it is recognized that inertia will always be present in any physical manifestation of the engine. The system is analysed using lumped linearized one-dimensional network models, both with and without inertia, based on thermoacoustic principles and extending these to account for phase change. The gain (temperature difference between source and sink heat exchangers) and frequency at which marginal stability (desirable continuous oscillations) can be achieved is calculated. The effects of the load resistance (fluid drag) and fluid inertia, as well as of the flow resistance due the feedback valve on the marginal stability gain, frequency and exergetic efficiency of the system are investigated. It is found that an increase in feedback resistance leads to a need for a higher gain for oscillatory behaviour to be achieved. In addition, even though an increase in either the resistance or inertia in the load, or the feedback resistance at low values of these variables has almost no effect on the required gain and the oscillation frequency of the system, an increase in these variables can lead at higher values to increased gains and reduced frequencies. A reduced feedback resistance and greater load inertia can also lead to considerably higher efficiencies, while increasing the load resistance allows for an increase in efficiency until a maximum is reached, after which the efficiency decreases again. The validity of certain approximations made previously is considered, and it is shown that these must be made with care. The results from this study can be used for the improved design and optimization of such oscillators, and similar systems. [Copyright &y& Elsevier]

Abstract: The objective of this paper is to study a method to achieve sub-wet bulb temperature by indirect evaporative cooling of air (without using a vapor compression machine). For this purpose, an analytical model is developed based on the effectiveness-NTU method (ε-NTU). The main idea for achieving a sub-wet bulb temperature by indirect evaporative cooling of air is by indirectly pre-cooling the working air before it enters the wet passage. It is shown that a modified analytical model for indirect evaporative coolers could be based on the ε-NTU method for sensible heat exchangers when proper adjustments are made by redefining the potential gradients, transfer coefficient, heat capacity rate parameters and assuming a linear saturation temperature-enthalpy relation of air. This modified model is used to find the performance of a regenerative indirect evaporative cooler. The model results show very good agreement with results from experimental measurements and a numerical model. [Copyright &y& Elsevier]

Abstract: A number of design methods have been proposed for the retrofit of heat exchanger networks (HEN) during the last three decades. Although considerable potential for energy savings can be identified from conventional retrofit approaches, the proposed solutions have rarely been adopted in practice, due to significant topology modifications required and resulting engineering complexities during implementation. The intensification of heat transfer for conventional shell-and-tube heat exchangers can eliminate the difficulties of implementing retrofit in HEN which are commonly restricted by topology, safety and maintenance constraints, and includes high capital costs for replacing equipment and pipelines. This paper presents a novel design approach to solve HEN retrofit problems based on heat transfer enhancement. A mathematical model has been developed to evaluate shell-and-tube heat exchanger performances, with which heat-transfer coefficients and pressure drops for both fluids in tube and shell sides are obtained. The developed models have been compared with the Bell-Delaware, simplified Tinker and Wills–Johnston methods and tested with the HTRI® and HEXTRAN® software packages. This demonstrates that the new model is much simpler but can give reliable results in most cases. For the debottlenecking of HEN, four heuristic rules are proposed to identify the most appropriate heat exchangers requiring heat transfer enhancements in the HEN. The application of this new design approach allows a significant improvement in energy recovery without fundamental structural modifications to the network. [Copyright &y& Elsevier]

Abstract: This paper investigates the transient heat conduction around the buried spiral coils which could be applied in the ground-coupled heat pump systems with the pile foundation as a geothermal heat exchanger. A transient ring-coil heat source model is developed, and the explicit analytical solutions for the temperature response are derived by means of the Green’s function theory and the image method. The influences of the coil pitch and locations are evaluated and discussed according to the solutions. In addition, comparisons between the ring-coil and cylindrical source models give that the improved finite ring-coil source model can accurately describe the heat transfer process of the pile geothermal heat exchanger (PGHE). The analytical solutions may provide a desirable and better tool for the PGHE simulation/design. [Copyright &y& Elsevier]

Abstract: The use of groundwater for cooling and heating purposes is of interest from both the economical and the ecological perspective. The groundwater heat pump (GWHP) system utilizes groundwater as alternative renewable and clean energy source for space heating and/or cooling, withdraws water from a production well, passes it through a heat exchanger and discharges the water into an injection well. By utilizing the relatively stable temperature of groundwater, GWHP system can achieve a higher coefficient of performance. Due to the utilization of groundwater stored in the aquifer, the assessment of the hydraulic capacity of the aquifer based on numerical groundwater models is always needed for the optimum design and the efficient performance of GWHP. In this paper, numerical methods of underground heat-water transfer, energy balance method and thermal storage method were presented to calculate the capacity of unit area of shallow groundwater aquifer. The model results indicate that the numerical method, which is based on performance efficiency of GWHP, represents the behaviour of groundwater pumping/recharging processes, and serves better than energy balance method and thermal storage method, in addition it has been proven itself that this method has the advantages of energy saving and environmental protection. The calculated capacity is positively related to aquifer thickness. It is found that it is easy for ground water recharge in alluvial and pluvial fan located at the piedmont, while the calculated capacity is relatively smaller compared with that of south-east plain where it is not easy for groundwater recharge. [Copyright &y& Elsevier]

Abstract: A new simplified scalable mathematical model, based on concepts of stream analysis, temperature paths and internal heat exchange, has been developed for synthesis of a multiple effect evaporator systems. In this model, fresh feed is assumed to be composed of product and number of condensate streams, which come out from different effects and these are treated as separate streams. For the present work a septuple effect flat falling film evaporator system, used for concentrating black liquor in an Indian Kraft Pulp and Paper mill, has been considered. This system is being operated under backward sequence with condensate-, feed- and product-flashing as well as steam splitting in first two effects. The set of linear algebraic equations for this model are self-generated through programming and is solved simultaneously using Gaussian Elimination Method with partial pivoting. Results of the present approach are validated with published model and industrial data. [Copyright &y& Elsevier]