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The present study investigates two models—two limiting cases—for the internal heat and mass transfer in a multicylinder dryer: the first model assumes that complete redistribution of heat and moisture in the thickness direction occurs instantaneously. The second model assumes that moisture transfer occurs only by vapor diffusion and that heat transfer takes place by conduction and condensation. The two models are written in dimensionless form, and applied for the same set of standard paper machine data. For basis weights below approximately 0.05 kg d.s./m2 the results are so close that the first, simple model is sufficient. A higher limiting basis weight—approximately 0.16 kg d.s./m2—was previously indicated by comparison of model predictions, assuming the simple model, to extensive sets of machine data from four different paper machines. [Copyright &y& Elsevier]

A mathematical model describing the heat and mass transfer in the dryer section of a paper machine has been applied to the production data from four paper machines. Model predictions for the machine speed are compared to actual machine speeds for a total of 163 data sets. The mathematical model assumes that the temperature and moisture content remain homogeneous in the thickness direction of the sheet. For three paper machines producing paper with basis weights ranging from 0.056 to 0.159 kg d.s./m2 the model predictions are adequate. For the paper machine producing the heaviest grades with basis weights ranging from 0.189 to 0.390 kg d.s./m2 the model predictions are flawed by a systematic error. For low machine velocities/high basis weights the machine velocity is over-predicted and for high machine velocities/low basis weights the machine velocity is under-predicted. This systematic error is caused by the assumption of homogeneous moisture content and temperature within the sheet being severely in error for thick sheets. [Copyright &y& Elsevier]

Superheaters are high-temperature cross-flow heat exchangers. Steam flows inside the tubes, and the flue gas outside in a direction perpendicular to the axes of the tubes. However, they differ very substantially from the other heat exchangers operating at low temperatures because of the high dependence of steam heat capacity on temperature and radiation heat transfer on the flue gas side. Also, the flow tube arrangement is usually complicated. Due to the work of superheaters in a harsh environment, they are prone to damage. About 40% of the emergency shutdowns of boilers are caused by overheating of the tube material which in turn causes them to break. The paper presents the mathematical model of the superheater. The finite difference model with distributed parameters is based on the solution of energy conservation equations for steam, tube wall, and flue gas. The CFD superheater model was also developed to verify the finite-difference model. The model developed in the paper can be used to assess the fouling degree of the superheater tubes by ash. [ABSTRACT FROM AUTHOR]

Mini-groove flat heat pipe, due to high thermal conductivity, good temperature uniformity, simple structure and so on, is very suitable to be used to cool electronic devices with high heat flux and required temperature uniformity. In this paper, the axial flow and heat transfer mathematical model of mini grooves flat heat pipe in steady state is built to study the distributions of pressure, velocity of working fluid, wall temperature, etc. along the axial direction. As the wick structure plays an important role in the mini-groove flat heat pipe heat transfer enhancement, this paper utilizes the above model to investigate the influence of the size of the mini-grooves and wall with grooves along the axial direction on the heat transfer coefficient of mini grooves flat heat pipe. The best solution of the size of the mini grooves and wall with grooves along the axial direction is put forward. [ABSTRACT FROM AUTHOR]

This paper numerically investigates the performance and heat and mass transfer processes that occur in counter-flow indirect evaporative air coolers. Different types of counter-flow air coolers were compared: a typical counter-flow unit, the same unit operating as a heat recovery exchanger, a regenerative unit and a novel modified exchanger, proposed by authors. Additionally the paper investigated impact of location of the perforated holes in the channel plate of regenerative air cooler. The numerical model is based on a one-dimensional heat and mass transfer analysis that was validated against existing experimental data. The results obtained from the simulation reveal the high effectiveness of the presented units. It was established that selected arrangements of the presented exchangers are characterized by the different efficiency in different air-conditioning applications. [ABSTRACT FROM AUTHOR]

Abstract: Snow cover is a common and relatively stable land cover condition in winter for cold north regions in China. Snow cover has significant effects on water and heat transfers in frozen soil; it needs to be considered in the study of frozen soil water–heat coupled movements. On the basis of previous research results and physical process analysis of water and heat movements in snow cover and soil, a snow cover–soil union water–heat coupled movements model is established in this paper. The numerical simulation was conducted by using a finite difference method. The results indicate that the simulated values have a similar trend to the measured values and the numerical simulation had big relative errors. However, the average absolute errors of the total and liquid moisture content in frozen soil were all less than 4%, and that of the frozen soil temperature was 1.37 °C. The errors of the numerical simulation were still within the acceptable range. Thus, the snow cover–soil union water–heat coupled movement model constructed in this paper is rational. [Copyright &y& Elsevier]

Highlights • A novel graded-grooves wick design was put forward for flat heat pipe. • An accurate mathematical model is established for mini-grooves flat heat pipe. • Effective thermal conductivity of proposed heat pipe is increased by 12.4%. • Local wick size & vapor chamber volume have great effects on thermal performance. • Grooves wick in slope type is suggested for practical application. Abstract Thermal management of micro electronic devices is one of the major issues for electronics application. Mini-grooves flat heat pipe is suitable to be used for small space electronics rapid cooling due to its high thermal conductivity, simple structure and good temperature uniformity. In this paper, an axial fluid flow and heat transfer mathematical model of mini-grooves flat heat pipe in steady state is built to study the axial distributions of key parameters such as pressure, velocity and wall temperature. As the wick structure plays an important role in the mini-grooves flat heat pipe heat transfer enhancement, the influence of mini-grooves size and wall with grooves along the axial direction on the heat transfer coefficient of mini-grooves flat heat pipe is studied. It is found that aiming at designing the optimum mini-grooves flat heat pipe, the local wick needs to be close to in saturated state, and the vapor chamber needs to be large. In this way, a novel graded-grooves wick design is put forward for flat heat pipe, which can increase the effective thermal conductivity coefficient by 12.4% with heat transfer rate 5.0 W. And the grooves wick in slope type with simple fabrication accords with practical application. [ABSTRACT FROM AUTHOR]

In the sugar juice evaporation process, the temperature of incoming juice is raised to the boiling point, and the water content of the juice is reduced by evaporation. The main process outputs are raw sugar and molasses. Heat transfer coefficients are important parameters in the simulation of this process. Due to scaling, the values of heat transfer coefficients decrease over time, and cleaning must be carried after a certain period of operation. Although correlations of heat transfer coefficients and recommended values of scaling rates are available in the literature, there are uncertainties in their values. Therefore, reliance on these correlations to predict when an evaporator station requires cleaning may be in error. In this paper, a method of online determination of heat transfer coefficients and scaling rates using measured values of process parameters is presented. Testing of this method indicates that it can produce accurate values of heat transfer coefficients and scaling rates despite possible errors in input data. [ABSTRACT FROM AUTHOR]

This paper presents numerical study on the use of nanofluids to replace conventional ethylene glycol/water mixture as heat carrier in a BoreHole Heat Exchanger. Nanofluids contain suspended metallic nanoparticles: increasing their concentration, in comparison to the base fluid, the thermal conductivity increases and the volumetric heat capacity decreases. The first effect is positive for the reduction of borehole thermal resistance, since it causes the grow of fluid convective heat transfer coefficient, while the second one is detrimental, due that it decreases the heat transfer between fluid and borehole wall. A numerical model based on energy and momentum balances is used to evaluate which is the best nanofluid with low nanoparticles volumetric concentration (0.1%–1%) that ensures the highest decreases of borehole thermal resistance and minimum increases of pressure drop among silver, copper, aluminium, alumina, copper oxide, graphite and silicon oxide. Moreover, a simple economic analysis was done. Results show that copper is characterized by highest borehole thermal resistance reduction, that reaches the value of about 3.8%, in comparison to that of base fluid, when nanoparticles volumetric concentration is 1%, but also the second one highest pressure drop. In this case, the cost of copper-based nanofluid is about 10 € m −1 , i.e. about 12% of total cost of BoreHole Heat Exchange – Ground Source Heat Pump system. [ABSTRACT FROM AUTHOR]

In this paper, a numerical study of heat and mass transfer in counter-flow indirect evaporative air coolers is presented using an approach proposed by previous work. The mathematical model equations of continuity, momentum, energy and concentration are solved by the finite volume method to obtain the value of primary outlet dimensionless temperature. This mathematical model developed is validated against published data acquired from literature. The key target of presented analysis is to develop a performance correlation based on five dimensionless factors: ratio of channel length to half width of secondary air channel, ratio of water to secondary air mass flow rate, primary air inlet Reynolds number, secondary air inlet dimensionless temperature and water film inlet dimensionless temperature. Numerical simulations are performed by changing the value of each dimensionless factor under a constant value for other parameters. The simulation results are regressed to obtain the empirical constants of the correlation. The value of outlet dimensionless temperature is varied from 0.47 to 0.92. The developed correlation can predict the performance of the counter-flow indirect evaporative air coolers within a discrepancy of 12.6%. The correlation would be helpful to provide a simpler equation to improve the calculation speed within the engineering allowable accuracy range. [ABSTRACT FROM AUTHOR]

With increasing social and economic developmental activities, high grade energy sources are depleting at faster rate and also inviting menace of environmental problems. Therefore, to reduce dependency on high grade energy sources for cooling applications and to protect environment, adsorption cooling systems are promising alternatives that are powered by low grade heat sources like solar heat, industrial/automobile waste heat etc. and also use environment friendly refrigerants. But, these systems have still low performances, large size and high cost. Therefore, in order to overcome these difficulties, many researchers are focussing on different ways to improve heat and mass transfers in the heat exchangers of the system to enhance its performance. These strategies include the use of advanced adsorbent material and advanced adsorption cycles, design improvement in heat exchangers and development of mathematical models for optimization of design/operating parameters of the cooling systems. In this paper, various mathematical models for adsorption systems are presented that include thermodynamic models, lumped parameters models; and heat and mass transfer models. These models include equations governing the heat and mass transfer in the main components of the cooling systems. The advantages of this method are that it can produce large volumes of results at no more cost and it is very cheap to perform parametric studies, for instance, to optimize equipment performance. The various numerical methods and experimental validations have been also presented and discussed. [ABSTRACT FROM AUTHOR]

Several mathematical models of human thermoregulation have been developed, contributing to a deep understanding of thermal responses in different thermal conditions and applications. In these models, the human body is represented by two interacting systems of thermoregulation: the controlling active system and the controlled passive system. This paper reviews the recent research of human thermoregulation models. The accuracy and scope of the thermal models are improved, for the consideration of individual differences, integration to clothing models, exposure to cold and hot conditions, and the changes of physiological responses for the elders. The experimental validated methods for human subjects and manikin are compared. The coupled method is provided for the manikin, controlled by the thermal model as an active system. Computational Fluid Dynamics (CFD) is also used along with the manikin or/and the thermal model, to evaluate the thermal responses of human body in various applications, such as evaluation of thermal comfort to increase the energy efficiency, prediction of tolerance limits and thermal acceptability exposed to hostile environments, indoor air quality assessment in the car and aerospace industry, and design protective equipment to improve function of the human activities. [ABSTRACT FROM AUTHOR]

In this paper, a 3D mathematical model is proposed to investigate the physical transport phenomena in weld pool and vapour plume during the stationary vacuum electron beam welding on 2219 aluminium alloy plate. Three beam current cases are employed to investigate the heat transfer, fluid flow, keyholing, keyhole backfilling and collapsing processes, and the resulting spiking defect and residual crater. In the model, a keyhole-tracing heat source is adopted to simulate the energy interactions between electron beam and material with the help of VOF technique. Results indicate that the beam profile and heat flux distribution decreases the growing speed of keyhole dimensions. The increase of beam current raises the evaporation intensity, keyhole wall temperature, keyholing depth and keyhole instability. On the premise of same heating time, a larger beam current produces a spiking defect in partially-penetrated weld. Finally, all the simulation results are validated against experiments. [ABSTRACT FROM AUTHOR]

This paper designs a new structure of solar air collector, and establishes the mathematical model of heat transfer process. In order to obtain the excess energy during the day to night use, the air collector will be with the phase change energy storage device coupled operation so that phase change energy storage equipment store heat during the day, night to continue to provide heat by phase changing. Its change thermal process mathematical model is established and the joint operation, to study various different factors on the outlet temperature and heat collecting efficiency effect or other necessary parameters to improve the equipment size. [ABSTRACT FROM AUTHOR]

The paper is focuses on the numerical simulation and analysis of coupled heat and mass transfer under ice formation conditions in the cross-flow plate heat exchanger. The simulation is performed using the original mathematical model. The presented model was validated against experimental data. The obtained results showed satisfactory agreement with the data obtained from the experimental measurements. Numerical simulation reveals many unique features of considered heat exchanger connected with the heat and mass transfer occurring in the return air channel under ice formation conditions. The results of computer simulation showed that the efficiency gains are sensitive to various inlet conditions, and allow for estimation of the safe operating conditions for different inlet return airflow parameters, based not only on the exhaust air temperature but also on its relative humidity and different thermal efficiency of the exchanger. Several goals were achieved, including: establishing the most unfavorable operating conditions (from the standpoint of ice formation on the plate surface of the return air channels) for cross-flow plate heat exchanger, which correspond to the inlet value of the return airflow dew point temperature equaled to 0 °C, impact of the ice formation on temperature effectiveness, impact of inlet relative humidity on temperature effectiveness and safe operating conditions and safe operating conditions for variety of inlet exhaust air parameters. [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 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]

This paper investigates a mathematical simulation and optimization of the heat and mass transfer processes in the indirect evaporative air cooler. The heat exchanger uses a novel combined parallel and regenerative counter-flow arrangement. A two-dimensional heat and mass transfer model is developed to perform the thermal calculations of the indirect evaporative cooling process. Mathematical model was validated against existing experimental data. The results obtained from the simulation reveal the high effectiveness of the presented unit. The exchanger was compared with the conventional regenerative unit. The results of comparison show, that the presented unit is characterized by higher effectiveness. The impact of the selected unitless operating factors on the performance of the investigated heat exchanger was established. The conducted multi-criteria optimization allowed to establish Pareto-optimal operating conditions and preferable climatic zones for the presented heat exchanger. [ABSTRACT FROM AUTHOR]

This paper investigates a mathematical simulation of heat and mass transfer in eight different types of the Maisotsenko Cycle (M-Cycle) heat and mass exchangers (HMXs) used for indirect evaporative air cooling. A two-dimensional heat and mass transfer model is developed to perform the thermal calculations of the indirect evaporative cooling process and quantifying the overall performance. The mathematical model was validated against experimental data. A numerical simulation reveals many unique features of the considered HMXs, enabling an accurate prediction of their performance. Results of the model allow for comparison of the analyzed devices in order to improve the performance of the original HMX. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we investigate the time-dependent heat and mass transfer in a molten carbonate fuel cell at start-up. Thus, a three-dimensional, transient mathematical model is presented through a comprehensive inclusion of various physical, chemical and electrochemical processes that occur within the different components of molten carbonate fuel cells. The model is proposed as a predictive tool to provide a three-dimensional demonstration of variable variations at system start-up. The local distribution of field variables and quantities are showcased. It reveals that the electrochemical reaction rate is dominated by the over-potential, not by the reactants' molar fraction. Reversible heat generation and consumption mechanisms of the cathode and anode are dominant in the first 10 s while the heat conduction from the solid materials to the gas phase is negligible. Meanwhile, activation and ohmic heating have nearly the same impact within the anode and cathode. Based on these findings, the importance of heat conduction and its main features are finally assessed. [Copyright &y& Elsevier]

Abstract: The paper aims to overview various mathematical models for modeling the simultaneous heat and mass transfer process in the liquid desiccant dehumidifier. Firstly, the dehumidification principle is introduced briefly. Then the models are interpreted in terms of two classes of dehumidifiers. For the adiabatic dehumidifier, the models are mainly classified into three types: finite difference model, effectiveness NTU (ε–NTU) model, and simplified models. For the internally cooled dehumidifier, there are also three kinds of models: models without considering liquid film thickness, models considering uniform liquid film thickness, and models considering variable liquid film thickness. This review is meaningful for comprehending the development process and research status of the models and choosing suitable models for prediction. In addition, some suggestions are proposed for the model improvement. [Copyright &y& Elsevier]

• Characteristics of catalyst particles floating in OFR were studied. • Mechanism of heat transfer was revealed by decomposing it into sub-processes. • Floating velocity U f and heat transfer coefficient h OFR were well predicted. In order to study the floating and heat transfer characteristics of catalyst particles in oscillating flow reactor (OFR), a self-made OFR device was employed to measure the floating velocity and heat transfer coefficient under different operating conditions and solid volume fractions (Re n : 203–1008, Re o : 269–3307, α s : 5%–20%), and the corresponding mathematical models were proposed. The results shown that oscillatory force had a high correlation with the solid phase volume fraction in OFR, and the floating velocities in OFR were obtained by experiments and models respectively. Compared with other drag force models, the Gidaspow and Arastoopour model can better describe the force between catalyst particles and liquid in OFR. The heat transfer coefficient increased first and then decreased with increasing oscillatory intensity, and it decreased with increasing solid volume fraction. The predicted values of floating velocity U f and heat transfer coefficient h OFR were compared with the experimental data, and the results shown that most of relative errors of U f and h OFR are within the range of 20% and 30% respectively in this paper. The research results provide basic data and theoretical base for the industrial application of OFR. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we developed a mathematical model to numerically analyze the coal pyrolysis and heat transfer inside a heated coal particle. The distributed activation energy model (DAEM) was used to depict the coal pyrolysis. The heat transfer and temperature variation of a coal particle were modeled with a transient energy conservation equation. The endothermic effect of decomposition and the transpirational convective heat transfer were taken into account in the model. We firstly validated the coupled comprehensive model with published experimental data of both pulverized coal and large particles. Then, the temperature history and coal pyrolysis of coal particle heated were numerically analyzed. To physically understand the transient temperature and volatile evolution of coal particle, we clarified the effects of endothermic of pyrolysis, transpirational convection and particle size. [Copyright &y& Elsevier]

Abstract: This article is about heat transport limitation standard-used construction wick heat pipes with various working fluids operating at temperatures from −30 °C to 140 °C. In this paper is the proposal and verification of a mathematical model for calculating heat transport limitations of heat pipe. The calculations of the various variants of the wick structure of heat pipe and working fluid are presented in diagrams as a dependency of the heat transport limitations on the working temperature. In the conclusion, the effect of these limits on the cooling power of the heat pipe is evaluated. [Copyright &y& Elsevier]

Abstract: Seawater-source heat pump systems (SWHP) are recognized to be outstanding heating, cooling and water heating systems. A large number of SWHP systems have been used in residential and commercial buildings in coastal areas due to the attractive advantages of high efficiency and environmental friendliness. In this paper, two mathematical models that described heat transfer process of casted heat exchanger (CHE) adopted by SWHP systems in the icing and non-icing conditions in winter have been developed and validated by an experimental study. The CHE is consisted of pipes immersed in the seawater and used for transferring heat between the seawater and the heat exchanger pipes of the SWHP. In addition, a computer code has been implemented to simulate the effects of flow rate of the secondary refrigerant, length of the CHE and the temperature of the seawater on the heat transfer performance. The effect of the ice outside the pipe due to the low seawater temperature on heat transfer has been discussed and the comparison of the heat transfer rate in two conditions demonstrates that the effect of icing on heat transfer performance is great. As a result, application of SWHP systems with CHE in coastal areas in China is feasible due to the favorable geographical conditions and environment. [Copyright &y& Elsevier]

Abstract: The total insulation value of a bedding system is a significant factor affecting the neutral temperature in a sleeping thermal environment. This paper reports on a study of developing a mathematical model for predicting the total insulation values of various bedding systems. The factors influencing the total insulation value of a bedding system such as the percentage coverage over a human body, types of bed with mattress and bedding, etc., were included in the model. The predicted total insulation values using the model developed were compared with the experimental results previously obtained in a related study. It was shown that the predicted total insulation values of different bedding systems agreed well with the experimental values. A statistics analysis further suggested that the mathematical model developed was able to predict the total insulation values of different bedding systems with an acceptable accuracy. Finally, using the model developed the impacts of key influencing factors on the total insulation value of a bedding system were assessed. [Copyright &y& Elsevier]

Abstract: This paper aims to prolong the heat pump frost time and reduce its growth with heat recovery facility, which should mix the exhausted indoor and outdoor air before entering the evaporator. An ideal mathematic model is developed for heat transfer, frost generation and airside pressure drop. The properties of the mixture would be obtained by solving the mass and energy conservation equations. A parametric analysis is performed to investigate the effects of air inlet temperature, relative humidity and air mass flow rate on total heat transfer coefficient, frost thickness and airside pressure drop, respectively. The results show that rationalizing the ratio of indoor and outdoor air could prolong frosting time and reduce the frost thickness greatly. The total heat transfer coefficient, frost thickness and airside pressure drop increase monotonically with time going, but are not proportional. Decreasing the mixture inlet air temperature and relative humidity could essentially reduce frost growth on the tube surfaces. This can also be observed when increasing the air mass flow rate. [Copyright &y& Elsevier]

Abstract: This paper presents a steady state simulation model to predict the performance of a small split type air conditioner with integrated water heater. The mathematical model consists of submodels of system components such as evaporator, condenser, compressor, capillary tube, receiver and water heater. These submodels were built based on fundamental principles of heat transfer, thermodynamics, fluid mechanics, empirical relationships and manufacturer’s data as necessary. The model was coded into a simulation program and used to predict system parameters of interest such as hot water temperature, condenser exit air temperature, evaporator exit air temperature, mass flow rate of refrigerant, heat rejection in the condenser and cooling capacity of the system. The simulation results were compared with experimental data obtained from an experimental rig built for validating the mathematical model. It was found that the experimental and simulation results are in good agreement. [Copyright &y& Elsevier]

This paper presents a mathematical model based on a three-phase theory, which is used to describe the mass and heat transfer between the gas and solids phases in a batch fluidised bed dryer. In the model, it is assumed that the dilute phase (i.e., bubble) is plug flow while the interstitial gas and the solid particles are considered as being perfectly mixed. The thermal conductivity of wet particles is modelled using a serial and parallel circuit. The moisture diffusion in wet particles was simulated using a numerical finite volume method. Applying a simplified lumped model to a single solid particle, the heat and mass transfer between the interstitial gas and solid phase is taken into account during the whole drying process as three drying rate periods: warming-up, constant rate and falling-rate. The effects of the process parameters, such as particle size, gas velocity, inlet gas temperature and relative humidity, on the moisture content of solids in the bed have been studied by numerical computation using this model. The results are in good agreement with experimental data of heat and mass transfer in fluidised bed dryers. The model will be employed for online simulation of a fluidised bed dryer and for online control. [Copyright &y& Elsevier]

This paper presents a mathematical model for the numerical prediction of the performance of crossflow cooling towers. The mathematical model is based on the heat and mass transfer equations. The leading parameters are the Lewis number Le, the number of transfer units U, the percentage of water evaporation, the water losses and the tower efficiency. This model is used to predict the thermal behavior of six cooling towers located in the South of Tunisia. These towers are employed to decrease the temperature of geothermal water from 65°C to 34°C using a crossflow air. The total flow rate of water is 900 kg s−1 and that of dry air is 1840 kg s−1. Several experimental data have been collected on site, in order to adopt the mathematical model.The model has been used to predict the performance of cooling towers in terms of the meteorological conditions prevailing in the South of Tunisia. An optimal water loss quantity has been determined. On an annual basis, the actual water losses by evaporation represent 4% of the total water flow rate which correspond to 106 m3 year−1. This represents the annual consumption of 20 000 inhabitants. [Copyright &y& Elsevier]

• Inverse method used to improve original T-history method equations to determine PCMs latent heat. • The method shown to be suitable method to calculate latent heat of low thermal conductivity bulk PCMs. • New transient modelling is more suitable for calculating latent heat with cooling rates than using original equations. High temperature phase change materials (PCMs) are being proposed as thermal energy storage media in concentrated solar power plants. The thermophysical properties of PCMs, such as the latent heat of fusion/solidification need to be defined to enable system design and evaluate system performance and cost analysis. Several methods have been used to measure the latent heat of fusion/solidification of PCMs including the T-history method. The original assumption of the T-history method is the Biot number should be less than 0.1 where the lumped capacitance method is applicable. However, when the Biot number is more than 0.1 then the original equations are not applicable to estimate the latent heat of PCM. This paper demonstrates how a one-dimensional heat transfer mathematical model can be used by applying an inverse method to overcome the limitation of the lumped capacitance method in the original T-history method to determine the latent heat of PCMs. The mathematical model demonstrates that variation of the temperature distributions inside the samples for the discharge curves. Furthermore, this model shows the errors in the latent heat values if the T-history method is used. It is evident from the discharge curves of low thermal conductivity PCMs that the original simplified equations used for interpreting the T-history test results are not applicable for calculating the latent heat at different ambient temperature. [ABSTRACT FROM AUTHOR]

• The mathematical model of the multi-panel RHR was established. • Investigation of the refrigerant flow distribution of the multi-panel RHR. • The mathematical model was validated with the experimental data. • The ratio of radiation to convection of the multi-panel RHR is 10.2%. • Analysis on thermal potentials of the RHR with the limited and critical flow rates. The refrigerant-heated radiator (RHR) is an efficient and feasible heating terminal for space heating. In order to improve the efficiency of RHR, a multi-panel RHR was proposed in this paper. To investigate the thermal potentials of the multi-panel RHR, a heat transfer and pressure drop model of the multi-panel RHR was established. To predict the refrigerant flow distribution of the multi-panel RHR effectively, a hydraulic model was established. Combining the hydraulic model with the heat transfer and pressure drop model, a comprehensive mathematical model of the multi-panel RHR was set up. The feasibility and effectiveness of the mathematical model were validated with experimental data. The thermal potential of the multi-panel RHR was investigated with the mathematical model. The results indicated that the ratio of radiation to convection of the multi-panel RHR is 10.2%. Meanwhile, the refrigerant flow rate that makes the outlet refrigerants of all panels in the supercooled region is limited. Once the refrigerant flow rate reaches the limit value, the pressure drop of the RHR will increase rather than the heating capacity. Therefore, the predictions of the limited flow rate of RHR under different condensation temperatures are conducted, and relevant regressions can be extended to the RHR with more panels. [ABSTRACT FROM AUTHOR]

• M-Cycle cooling tower was numerically analyzed. • Critical heat and mass transfer process aspects were discussed. • Wet-bulb effectiveness for water cooling higher than 100% was achieved. • Critical factors with the highest impact on the performance were established. The following paper presents the first numerical comparison of heat and mass transfer processes in a traditional cooling tower and a solution based on the Maisotsenko cycle (M-Cycle). The results of the simulation allowed us to analyze the heat and mass transfer process occurring inside the M-Cycle and the traditional cooling tower and to observe its most important characteristics and features. The analysis was performed for two hypothetical situations: 1) both towers having the same external dimensions: the Number of heat Transfer Units (NTU) of M-Cycle cooling tower was two times smaller, due to its geometry; 2) two towers have the same mass transfer surface (i.e. identical NTU in wet channels). It was confirmed that M-Cycle Cooling Tower (MCT) can cool the water below the wet-bulb temperature (which is not achievable by conventional cooling towers), even in very hot and humid conditions (outdoor air temperature of 40 °C and humidity ratio of 20 g/kg). Also, the influence of the selected parameters (including inlet air temperature and humidity, inlet water temperature, NTU, and heat capacity ratio between water and air) on cooling tower performance are documented. Critical factors which have the highest impact on its effectiveness are established and discussed. The study confirmed high practical potential of using M-Cycle in water cooling applications. [ABSTRACT FROM AUTHOR]

• The original α-model is developed. • The most probable variants of year-round heat exchanger operation are established. • The different frost-free techniques are proposed. The paper presents an original mathematical model based on the modified ε-NTU method, developed for numerical simulations and analysis of coupled heat and mass transfer inside the rotary heat exchanger operating under frosting conditions. The proposed model was validated on the basis of experimental data. Positive validation results indicate that the developed model is capable to predict the behavior of the rotary heat exchanger at high rotor speed. Moreover, the nature of heat and mass transfer processes in the rotary heat exchanger under winter conditions is presented. Different variants of active heat and mass transfer zones in the regenerator channels are revealed. Schemes of safe (frost free operation – without a frost area accumulation) and unsafe operation (with a presence of frost area accumulation) of the device are discussed. Three methods of protecting the heat exchanger against frost are presented and analyzed. The influence of rotor speed on frost formation inside the matrix of rotary heat exchanger is discussed. For analyzed cases the increase in rotor speed by 65% results in an increase in heat exchanger effectiveness (from 0.70 to 0.87) with simultaneous decrease in the size of the frost area accumulation (Δ X ¯ 1) from 0.22 to 0.07. The 68% decrease in the rotor speed was accompanied by a decrease in the heat exchanger effectiveness (up to 0.58) with complete elimination of the frost area accumulation. A similar effect was also observed when the outdoor air temperature slightly increased (from –15 °C to –13.5 °C) while maintaining constant efficiency (0.70) of the heat exchanger. [ABSTRACT FROM AUTHOR]

• M-Cycle cooling tower was numerically analyzed. • Critical heat and mass transfer process aspects were discussed. • Wet-bulb effectiveness for water cooling higher than 100% was achieved. • Critical factors with highest impact on the performance were established. Following paper presents detail investigation of the Maisotsenko cycle (M-Cycle) cooling tower through numerical modeling. For the purpose of this study, ε-NTU model of the M-Cycle cooling tower (MCT) was developed and validated against experimental data. The results of the simulation allowed to analyze the heat and mass transfer process occurring inside the M-Cycle cooling tower and observe its most characteristic and important features. It was confirmed that MCT is able to cool the water below the wet-bulb temperature (which is not achievable by conventional cooling towers), even in very hot and humid conditions (outdoor air temperature of 40 °C and humidity ratio of. 20 g·kg−1). They also allowed to study the influence of the selected parameters (including inlet air temperature and humidity, inlet water temperature, NTU and heat capacity ratio between water and air) on the cooling tower performance. Critical factors which have highest impact on its effectiveness were established and discussed. The study confirmed high practical potential of using M-Cycle in water cooling applications. [ABSTRACT FROM AUTHOR]