Search

Abstract: This paper presents a literature review of thermal comfort. Both rational and adaptive thermal comfort approaches are presented. An overview of the human body thermoregulatory system as well as the mathematical modelling of heat exchanged between human body and its environment in the situations of both awaked and sleeping people is presented. [Copyright &y& Elsevier]

• 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]

This paper presents a coal mill model that considers the effect of coal moisture on its accuracy. This mathematical model is derived through the analysis of mass flow, heat exchange, and energy transferring balances in which all heat input into or output from the coal mill are calculated quantitatively to reduce the number of unknown parameters that need to be identified. The work presented in this paper focuses on modeling Mill Parter Ship-type coal mills that are widely used in the coal-fired power plants in China. The unknown model parameters are identified using a real-coded genetic algorithm. Simulation results indicate that the model effectively represents the mid-high process of coal mill dynamics and can be used to estimate the key parameters in coal mills, which are difficult to measure or cannot be measured. On this basis, the model can be used for the state monitoring, control optimization, and fault diagnosis of coal mills. [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]

In this paper, a water-heated humidification dehumidification (HDH) desalination system, which is powered by the waste exhaust gas from a furnace, is applied to produce water. In order to overcome the corrosion from the seawater on the dehumidifier with a general heat exchanger, the packed bed is used to achieve the dehumidification process. Based on the mathematical models for the HDH desalination system, the relevant thermodynamic and economic performance are acquired. Furthermore, the influences from the effectiveness, top and ambient temperatures on the aforementioned performance are also investigated. The simulation results show that peak values of the water production and gained-output-ratio (GOR) are obtained as 84.60 kg h −1 and 1.44 at the balance condition of the dehumidifier. The total cost for all the heat and mass transfer areas rises from 470.81$ to 701.46$ when the mass flow rate of the dry air increases from 0.1 kg s −1 at to 0.5 kg s −1 , while the unit cost of water production (UCWP) ascends from 6.20$ kg −1  h to 13.41$ kg −1  h. Furthermore, raising the effectiveness, reducing the spraying temperature into the humidifier is always effective to cut the unit cost of water production, while it is only useful within a limited range of air mass flow rate for a higher ambient temperature. [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 paper presents numerical analysis of heat recovery exchanger, which operates as an indirect evaporative air cooler in summer conditions and as a typical heat recovery unit during winter season. The numerical simulation is performed with the original mathematical model which is able to simulate the operation during summer and winter season. The model was validated against existing experimental data (operation as indirect evaporative air cooler) and against experimental data collected by authors at Wroclaw University of Technology (operation as heat recovery exchanger). Obtained results allowed for analysis of heat and mass transfer process occurring in considered exchanger during round-year operation. The characteristic heat and mass transfer zones for evaporative air cooler and heat recovery exchanger were established. Results also allowed for analysis of most important problems connected with achieving highest efficiency of the exchanger and achieving safe operating conditions during winter season (preventing the exchanger from freezing). Safe operating conditions (parameters of the ambient air in winter which would guarantee that no frost would be formed on the plates) were established. The analysis of the effectiveness of the novel exchanger with selected factors (i.e. obtained cooling capacity, thermal efficiency and relative effectiveness) was also presented in the paper. [ABSTRACT FROM AUTHOR]

The aim of the study is to develop a new method for numerical modeling of tubular cross-flow heat exchangers. Using the method proposed in the paper, a numerical model of a car radiator was developed and implemented in a digital control system of the radiator. To evaluate the accuracy of the numerical method proposed in the paper, the numerical model of the car radiator was compared with an analytic model. The proposed method based on a finite volume method and integral averaging of gas temperature across a tube row is appropriate for modeling of plate fin and tube heat exchangers, especially for exchangers in which substantial gas temperature differences in one tube row occur. The target of control is to regulate the number of fan revolutions per minute so that the water temperature at the heat exchanger outlet is equal to a set value. Two control techniques were developed. The first is based on the numerical model of the heat exchanger developed in the paper while the second is a digital proportional–integral–derivative control. The first control method is very stable. The digital proportional–integral–derivative controller becomes unstable when the water volume flow rate varies considerably. The developed techniques were implemented in digital control system of the water exit temperature in a plate fin and tube heat exchanger. The measured exit temperature of the water was very close to the set value of the temperature if the first method was used. The experiments show that the proportional–integral–derivative controller works also well but becomes frequently unstable if the water flow rate varies. [ABSTRACT FROM AUTHOR]

With the attractive advantages of high efficiency and environmental friendliness, the ground-coupled heat pump system (GCHPs) has been widely applied in various buildings around the world in recent years, and the knowledge of underground thermal properties is a prerequisite for correct design of GCHPs. As an effective way to obtain thermal properties, thermal response test (TRT) has become a routine tool for the design of larger plants with ground heat exchangers (GHEs). This paper summarizes the specifications for in situ TRT, including test setup, minimum duration, heat input rate etc., analyzes the mathematical models currently available for GHE in TRT, and compares the parameter identification methods which are necessary to obtain reasonable properties according to in situ TRT data. In addition, this paper discusses and summarizes the shortages and imperfects of the current research on TRT and gives some recommendations for future work. [ABSTRACT FROM AUTHOR]

This paper deals with transient modelling of a large-scale salt gradient solar pond (SGSP – 50000 m 2 ) located in a semi-arid climate region. Precisely, the pond was exposed to meteorological data of the Agafay site (located 30 km south of Marrakesh-Morocco) covering the period from January 2015 to May 2017. We considered three different heat extraction technics (HET) including the reference one (R-HET) that limits the heat draw to the heat storage zone using horizontal tubes. The other two methods consider an additional heat draw from the intermediate non-convective zone using horizontal (HT-HET) and vertical (VT-HET) tubes. We elaborated a transient mathematical model based on energy balance equations for the pond (including the ground) and the extraction’s tubes. This model was solved using a MATLAB code based on the fully implicit finite-difference scheme that has been developed for this purpose . The study focuses on the examination of the thermal performances of the considered SGSP for each of the three heat extraction methods based on energetic and exergetic analysis. The obtained results reveal that the third method of heat extraction (VT-HET) provides higher energy and exergy efficiencies by reducing the total heat losses towards the pond’s surroundings and saving exergy from destruction. The amount of energy/exergy extraction improvement recorded is around 22.5%/30% compared to the reference heat extraction technic (R-HET) against an improvement of only 1.7%/0.6% for the HT-HET. [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 the mathematical modeling of a liquid-to-water heat pump with scroll compressor, brazed plate heat exchangers, additionally built-in liquid-vapor heat exchanger (LVHX) and a desuperheater for domestic hot water (DHW) production. The refrigerant is the zeotropic mixture R407C and the liquid used in the outdoor loop is a propylene-glycol water mixture. Developed mathematical model is validated on experimental data and used as a tool for the heat pump analysis. Simulation results are obtained for the effect of the degree of superheat at the evaporator outlet, the subcooling degree at the condenser outlet, the effect of using or not the LVHX and the effect of using or not the desuperheater for DHW for typical operating conditions of liquid-to-water heat pumps (EN-14,511-2, 2011) in the cooling and heating modes (low and medium temperature applications). Results show that the effect of the degree of superheat or the decision on the suitability of using or not a LVHX may be different for heat pumps that include or not a desuperheater for DHW. In particular, if DHW is a priority, the use of a LVHX is recommended because it leads to higher COP (or EER) values as well as to higher DHW heating powers. [ABSTRACT FROM AUTHOR]

A key challenge in thermoelectric power conversion is to create a significant temperature difference ( Δ T ) across the thermoelectric generator (TEG). And one approach to create a larger temperature difference is to enhance heat transfer of the hot side of TEG. Thus, when a thermoelectric generator has been designed and manufactured, it is found that the heat exchangers of the thermoelectric device determines its performance. This paper investigated the differences as well as the advantages and disadvantages of three typical heat exchangers in a thermoelectric setup, and the power consumed by the auxiliary equipment to improve the thermoelectric performance were taken into account. For this purpose, a mathematical model has been developed. The accuracy of this model was verified via the experiments, by constructing and testing the prototypes. The results illustrate the net power output performance of thermoelectric devices with three different type of heat exchangers. The air cooling exchangers are shown a minimum auxiliary consumption whereas the heat pipe cooling exchanger are shown to be the most effective. At last, this article gets an economic analysis, and a new evaluation index associated with the power consumption of the auxiliary equipment is proposed. The results provided some practical guidelines for the design and application of practical thermoelectric power generations. [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: Coaxial Heat Exchangers (CHXs) are now used extensively in heat pump (HP) and refrigeration systems. The design of such systems requires estimation of CHX's thermal and hydraulic performance. This paper presents a generalized finite volume CHX model that is capable of simulating single-phase and two-phase flow with a smooth or fluted inner tube. The concepts of segment insertion and subdivision (moving boundary within the segment) are adopted in this model to track the phase change point along the flow channel. This allows for reliable model accuracy even with a lower number of discretized finite volumes, thereby reducing computation time. For the segment insertion and subdivision functions, four different approaches are provided in order to achieve the best accuracy and least computational effort under various flow configurations and fluid conditions. The simulation model can be applied to straight and helical tubes with choices of smooth, grooved and fluted tube surface. Empirical single-phase and two-phase correlations from the literature are adopted in the proposed model for the applicable surfaces. At present, there are no correlations for two-phase flow in fluted tube annuli, in the open literature. This paper proposes modifications to existing two-phase fluted surface heat transfer and pressure drop correlation formulations by applying empirical two-phase flow multipliers onto existing fluted tube single phase correlations. The solving methodology of this model requires the heat exchanger geometry, flow configuration, inlet states, as well as mass flow rates of the fluids to solve for the outlet conditions, heat load, pressure drop and charge of the CHX. Coupled with non-linear equation solver, the model can also provide the required mass flow rate for a specific superheat/subcooling on either side of the CHX. The model and modified correlations are validated against experimental data of brine-to-refrigerant fluted tube condenser and evaporator used in a heat pump application. [Copyright &y& Elsevier]

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: In this paper, a waste heat recovery system is proposed where a high speed turbocharged diesel engine acts as the topper of a combined cycle with exhaust gases used for a bottoming Rankine cycle. The paper describes a mathematical model to evaluate the performance of Rankine cycle system with a reciprocating piston expander. The paper focuses on the performance evaluation and parameter selection of the heat exchanger and reciprocating piston expander that are suitable to waste heat recovery of ICE (internal combustion engine). The paper also describes the experimental setup and the preliminary results. The simulation results show that a proper intake pressure should be 4–5 MPa at its given mass flow rate of 0.015–0.021 kg/s depending on the waste heat recovery of a turbocharged diesel engine (80 kW/2590 rpm). The net power and net power rise rate at various ICE rotation speeds are calculated. The result shows that introducing heat recovery system can increase the engine power output by 12%, when diesel engine operates at 80 kW/2590 rpm. The preliminary experimental results indirectly prove the simulation model by two negative work loops in the P–V curve, under a low intake pressure and steam flow rate condition. [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]

The management of coolant leakage in a Nuclear Reactor Containment is important to ensure the integrity of the second barrier and the safe operation of a nuclear power plant. In the nuclear plant, several reliable leak detection systems continuously monitored coolant leak. In this paper, we introduced a new unidentified leak detection method based on monitoring the condensate in the ventilation coolers. After built a heat exchanger model of the cooler and introduced the fan model in the commercial CFD code, we validated models and got a reasonable simulation of the leak steam condensate on the cooler. Then we built the detail three-dimensional (3D) PWR containment geometry model (including internal structures and ventilation systems). Based on the detailed flow field in this containment and the moisture condensation theory, we could get the condensate character on the coolers of the EVR ventilation system after unidentified leak. Analyses were carried out to quantify the condensate after the 1.0gpm (gal/min) and 1.5gpm leak at hot leg and cold leg located at the reactor pit and steam generator room. The result indicated that the start condensation time of 1.0gpm leak was about 75min and 45min of 1.5gpm, and the leak location had slight influence on the start condensation time. This work would contribute to a reasonable design of a leakage detection method for the unidentified leak in the containment. [ABSTRACT FROM AUTHOR]

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]

In the energy pile technology, pipes of the heat exchanger are installed in the concrete pile. When the pipes are configured in the form of spiral coils, they can usually be described by the solid cylindrical heat source model or the ring-coil heat source model. This paper investigates the temperature responses of these two heat source models in a double-layered ground, and the corresponding analytical solutions are established using the Green's function method. The Green's function, which delineates the temperature response induced by an instantaneous ring source in a double-layered ground, is obtained by the separation of variables technique, and in order to solve the nonlinear equations of the eigenvalues, a constrained Newton method is also developed. The analytical solutions are verified by two means. After that, computational examples are presented. The difference between the temperature response in a layered ground and that in a homogenous ground is discussed, and the computational error of using the homogeneous model to describe the temperature response of a layered ground is also studied. [ABSTRACT FROM AUTHOR]

The urgency to look for promising sustainable alternatives to the conventional vapour compression technique for cooling applications has been strong. As the result, the gas-solid adsorption system has been considered as one of the alternatives to generate cooling effect. This paper reviews the development of this adsorption cooling technique in three different aspects: mathematical modelling, intrinsic, and extrinsic developments, in order to present an overview of this field from basic mathematical representations and designs to current research trends as well as innovative applications and configurations. Various adsorption equilibria, diffusion models, kinetics, and system modelling are reviewed. On the other hand, the roles of both the heat exchanger design parameters and the adsorbent materials are discussed followed by the different bed configurations and schemes. The impact of various operating parameters on the system performance is also covered. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a dynamic model of a counter flow water to oil heat exchanger when all inputs (inlet temperatures of the fluids and the mass flow rates) are simultaneously varying. Although interesting results about modeling of heat exchanger by linear parameter varying (LPV) can be found in , several problems remain to be solved such as the structure estimation or a proper initial MISO model for the optimization algorithms. This paper introduces a new model structure called quasi LPV model which simulates accurately the temperature and flow transients in a counter flow heat exchanger (COFHX). The quasi LPV model is compared to a realistic numerical model of a counter flow heat exchanger adjusted with the test rig heat exchanger of the University of Valenciennes in France. Comparisons indicate that the developed quasi LPV model is capable of predicting the transient performance of the heat exchangers satisfactorily. [Copyright &y& Elsevier]

Sodium cooled fast reactors (SFRs) have been developed in France for nearly 50 years with successively Rapsodie, Phenix and Superphenix plants. Nowadays, the so-called Astrid prototype is developed in France in the frame of Generation IV deployment. The Astrid project requires thermal hydraulic inputs to support the design and the safety analysis. This paper deals with some thermal hydraulic concerns in the primary circuit: the subassembly, the core, the hot plenum and the cold plenum. The so-called TRIO_U Computational Fluid Dynamic (CFD) code developed at CEA has been progressively adapted to these Astrid concerns. The paper presents the recent improvements, the present status and the remaining challenges for TRIO_U code on each topic. For the subassembly, refined modelling and sub-channel modelling have been developed in parallel. The validation process based on existing experimental data is in progress. A global core modelling including the inter-wrapper region and the connection to the hot plenum is depicted. The need of experimental validation is pointed out. The core outlet region requires refined Large Eddy Simulation computations to predict temperature fluctuations which can induce thermal fatigue. Validation based on sodium experimental data is briefly presented. Thermal stratification in the plenum is a key point for thermal stress analysis on the structures. Validation process includes the comparison to reactor data. Special developments using a Front Tracking method are carried out to deal with free surface and gas entrainment. A methodology including local and global modelling is developed and the validation process is in progress. For decay heat removal situations and especially in natural convection cases, the whole primary vessel – except at the moment the intermediate heat exchangers and the pumps – is modelled with TRIO_U code. Phenix ultimate tests performed in 2009 will be used for the qualification of these particular situations. [ABSTRACT FROM AUTHOR]

Abstract: Single borehole heat exchanger (BHE) and arrays of BHE are modeled by using the finite element method. The first part of the paper derives the fundamental equations for BHE systems and their finite element representations, where the thermal exchange between the borehole components is modeled via thermal transfer relations. For this purpose improved relationships for thermal resistances and capacities of BHE are introduced. Pipe-to-grout thermal transfer possesses multiple grout points for double U-shape and single U-shape BHE to attain a more accurate modeling. The numerical solution of the final 3D problems is performed via a widely non-sequential (essentially non-iterative) coupling strategy for the BHE and porous medium discretization. Four types of vertical BHE are supported: double U-shape (2U) pipe, single U-shape (1U) pipe, coaxial pipe with annular (CXA) and centred (CXC) inlet. Two computational strategies are used: (1) The analytical BHE method based on solution, (2) numerical BHE method based on solution. The second part of the paper focusses on BHE meshing aspects, the validation of BHE solutions and practical applications for borehole thermal energy store systems. [Copyright &y& Elsevier]

Abstract: The development of biofuels has gained much attention in recent years. Thermodynamic analyses to obtain energy from biofuels using fuel cells were addressed in previous works for a variety of processes. In those processes, the determination of the best conditions to achieve high efficiency values in the conversion of chemical energy into electrical power is a critical issue from the net global energy efficiency point of view. In this regard, a main aspect is to address the energy integration of the whole process. In a previous paper, the authors dealt with energy integration studies for glycerin- and ethanol-based processors coupled to PEM fuel cells resorting on the “multi-stream heat exchanger” feature provided by the simulation tool HYSYS. In that work, the aim was to maximize the energy recovery from the process streams that renders the maximum achievable net global efficiency. In this paper, the aim is to synthesize and design the optimal heat exchangers network (i.e. determination of the process configuration and units sizes) while maintaining the net global efficiency of the whole system at its achievable value. Three modifications to the original SYNHEAT model developed in 1990 by Yee and Grossmann for synthesizing heat exchanger networks are proposed in this work aiming at a better problem description, and consequently searching for best problem solutions. First, a modification in computing the minimum approach temperature difference is proposed. Second, the called “operation line method” is coupled to the SYNHEAT model to built-up the network superstructure to be optimized. Finally, the SYNHEAT model’s hypothesis of constant cp value for modeling heat exchange between process streams is improved by considering enthalpy variable instead of temperature variable, which is convenient when latent heat is transferred. The model variables number involved in the heat exchanger network synthesis problems solved has been reduced to less than a half by applying the operation line method. The proposed methodology and modifications made are of general application and not just for the specific cases addressed in this work. [Copyright &y& Elsevier]

Abstract: In this paper, a versatile TSPEP (two-step parameter estimation procedure) based on a three-dimensional numerical model of a geothermal system is presented. The procedure is applied to both simulated and experimental TRT (thermal response test) data in order to restore the grout and soil thermal conductivities and volumetric heat capacities. The TSPEP is essentially a two-step process. The first step uses the parameter estimation procedure, in the early transient regime to restore the grout thermal conductivity and volumetric heat capacity. The values from the first step are used as the input values in the second step, in which the parameter estimation procedure is applied to the late transient regime to restore the soil thermal conductivity and volumetric heat capacity. Further iterations of these two steps can be used to improve the accuracy of the procedure and are discussed in this paper. The time separation used between the estimation of the soil properties and the estimation of the grout properties partially uncouples the two problems and makes the estimation of these four parameters feasible. A criterion to select the time separation is discussed and validated in this paper. [Copyright &y& Elsevier]

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: In this paper, a computational study of the influence of the heat exchangers'' thermal resistances (in both the hot and cold side) on the efficiency of a thermoelectric generation device has been carried out. For this purpose, a computational model has been developed. This model uses the numerical method of finite differences to simulate the performance of the thermoelectric generation system, including the heat exchangers, the heat source and the heat sink. The accuracy of this computational model was experimentally verified, by constructing and testing a prototype. It was obtained that the maximum error between experimental and simulated values of electric power generated is lower than 5%. The generation of thermoelectric power, using as heat source the heat of the smoke from a paper mill''s combustion boiler, has been studied too. The results demonstrated that it is possible to generate about 1kW per meter of chimney height, that is, about 300W/m2. Therefore, it can be stated that this device has good prospects for the future. [Copyright &y& Elsevier]

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]

This paper considers the influence of heat exchangers to the efficiency of a household refrigerating system. A steady state mathematical model is used to compare three most commonly used heat exchanger designs. For each design, an optimal inner diameter of the heat exchanger, subject to the compressor''s capacity and the heat exchanger''s length is found. The influence of operating conditions, such as condensation and evaporation temperatures, superheat in the evaporator and sub-cooling in the condenser, to optimal dimensions of the heat exchanger is also analyzed in the paper. Presented guidelines and recommendations can be used for design and modernization of household refrigerators and freezers. [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]

The hybrid ground-coupled heat pump (HGCHP) systems with supplemental heat rejecter/supplier can effectively solve heat imbalance problems in the subsurface, and consequently improve the operation performance of the geothermal systems. For example, solar energy and/or industrial waste heat may be used as stable heat sources for underground heat storage in northern China with higher heating load, and cooling towers are installed to release heat into the air in southern China, where more cooling demand is needed. This paper reviews and discusses different HGCHP systems, which have been applied in China. And based on the heat transfer model of vertical borehole heat exchangers (BHE) for HGCHP systems, physical and mathematical models of multistage series circuits are developed to illustrate the heat transfer process of the underground thermal storage. A set of parameters, such as borehole spacing, heat recharging rate fractions and thermal properties of soils, which affect the thermal performance of the ground heat exchangers are analyzed, and the optimal solutions are discussed for engineering application. [ABSTRACT FROM AUTHOR]

This paper sets out to make a dynamic analysis of a single-effect, lithium bromide–water (LiBr/H 2 O) absorption chiller. A mathematical model has been developed based on conserving mass, energy, and species, which considers the correlations of the convective coefficients of absorption refrigeration processes so as to determine the overall heat transfer coefficients of the heat exchangers of chillers. The implementation of this mathematical model was built on the Matlab platform, and resolved the system of non-linear equations by making explicit use of the finite difference method. The model has the ability to simulate and predict the behavior of internal and external parameters such as temperature, concentrations and pressures when these are subjected to disruptions in the power supply and thermal load. The largest absolute differences found when validating the model by means of the experimental numerical values in the water circuits were approximately 1.0 °C, 0.7 °C and 0.2 °C for hot, chilled and cold water, respectively. In terms of relative error, these divergences represent a maximum of 5% and a minimum of 0.3%. The model showed good results when subjected to disturbances in the load and power source, as it reproduced the behavior of the temperature parameters and the Coefficient of Performance (COP), in line with the comparisons made with the data provided by the manufacturer, the COP being approximately 0.7 for operating conditions. [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 presents a new mathematical programming model for the retrofit of heat exchanger networks (HENs), wherein the pressure recovery of process streams is conducted to enhance heat integration. Particularly applied to cryogenic processes, HENs retrofit with combined heat and work integration is mainly aimed at reducing the use of expensive cold services. The proposed multi-stage superstructure allows the increment of the existing heat transfer area, as well as the use of new equipment for both heat exchange and pressure manipulation. The pressure recovery of streams is carried out simultaneously with the HEN design, such that the process conditions (streams pressure and temperature) are variables of optimization. The mathematical model is formulated using generalized disjunctive programming (GDP) and is optimized via mixed-integer nonlinear programming (MINLP), through the minimization of the retrofit total annualized cost, considering the turbine and compressor coupling with a helper motor. Three case studies are performed to assess the accuracy of the developed approach, including a real industrial example related to liquefied natural gas (LNG) production. The results show that the pressure recovery of streams is efficient for energy savings and, consequently, for decreasing the HEN retrofit total cost especially in sub-ambient processes. [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]

The aim of this work is to develop a transient program for the simulation of a miniature Joule–Thomson (J–T) cryocooler to predict its cool-down characteristics. A one dimensional transient model is formulated for the fluid streams and the solid elements of the recuperative heat exchanger. Variation of physical properties due to pressure and temperature is considered. In addition to the J–T expansion at the end of the finned tube, the distributed J–T effect along its length is also considered. It is observed that the distributed J–T effect leads to additional cooling of the gas in the finned tube and that it cannot be neglected when the pressure drop along the length of the finned tube is large. The mathematical model, method of resolution and the global transient algorithm, within a modular object-oriented framework, are detailed in this paper. As a part of verification and validation of the developed model, cases available in the literature are simulated and the results are compared with the corresponding numerical and experimental data. [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: A generalized finite volume-based model to simulate Microchannel Heat Exchangers (MCHXs) with variable tube and fin geometries using a three-stream UA-AMTD method is presented in this paper. MCHXs with variable geometry can have different port dimensions, tube sizes and fin surfaces within the heat exchanger core and can have single or multiple tube banks. These novel MCHX design can further enhance the heat exchanger performance and improve its material utilization. A comprehensive literature review reveals that there is no experimental or numerical investigation of such innovative designs nor is there a modeling approach that can handle such flexible geometries. The model is validated against 227 experimental data points for eight different fluids, and eighteen MCHX geometries, including four different variable geometry microchannel condensers. This validation effort is the most comprehensive MCHX model validation presented in open literature. The average absolute capacity deviation between predicted and measured values was 2.7%. [Copyright &y& Elsevier]