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• The behavior of the linear compress with transient acoustic load is analyzed. • The temperature distribution along the regenerator is theoretically calculated. • The variation of the efficiency and displacement of the compressor is analyzed. The working condition of the linear compressor greatly affects the performance of the cryocooler. When the cryocooler operates during a transient working state like the cool down process, the linear compressor is also in a transient working state and could lead to deviation from designed steady state condition. In order to study the transient behavior of a linear compressor during the cool down process, a theoretical model based on the finite difference method is proposed. The temperature distribution of the regenerator during the cool down process is calculated. The variation of the impedance of the cold finger is then calculated. The transient behavior of the linear compressor are studied according to the impedance match between the compressor and the cold finger. The theoretical model shows that the transient behavior of the linear compressor is determined by the variation of the cold finger impedance during the cool down process and the increase of the input power could be larger than 40% with constant input voltage through the whole cool down process. A Sage simulation model of the cryocooler is built and the cool down experiments are carried out. The simulation and the experiment results are consistent with the theoretical model. It's also shown that the theoretical model could provide better prediction of the transient behavior of the linear compressor. The study of the transient behavior of the linear compressor could help improve the design and control of the linear compressor especially for the transient process. [ABSTRACT FROM AUTHOR]

Copyright of ERA Forum is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper presents a linked model to simulate the transient performance of heating-up of a heat pump water heater (HPWH) with a water tank. This linked model consists of a quasi-steady model to simulate the behavior of the vapor compression system and a CFD model that describes the transient flow and temperature fields in the water tank. The interaction between these two models is implemented by the data exchange through the interface between the tank wall and nearby water in the tank. Heat flux profiles of the condenser coils are obtained from the system model and delivered to the water tank CFD model as boundary conditions; CFD model outputs water-side flow and temperature information to the system model for heat transfer calculations. An iterative algorithm is designed to achieve matched solutions of these two models. This linked model is experimentally validated. The results show this model is capable of capturing the dynamic progression of the vapor compression system, as well as the transient fluid dynamics and thermal behavior in the water tank. [ABSTRACT FROM AUTHOR]

Copyright of Irrigation & Drainage is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Long wave radiation heat transfer is the dominant cooling mode of the Ceiling Radiant Cooling Panels (CRCP). This unique cooling mode makes the calculation of indoor long wave radiation heat transfer extremely important. Actually, indoor radiation heat transfer is usually under non-steady state conditions. General calculation methodology (simplifying radiation heat transfer or using the equivalent network method of steady state) is complex and less accurate when solving this kind of problem. In addition, general methodology fails to solve the situation that the temperatures of some interior surfaces are lacking but the heat flows are known. This paper provides a calculation methodology improving the Gebhart method for modeling the non-steady state radiation heat transfer between indoor surfaces. Given parameter variations (temperature and net radiant heat flow) of the surfaces are transformed into discrete column vectors of unit time, and then matrix equations are established, which can greatly reduce the work. This methodology has been verified experimentally, which can be regarded as a theoretical basis for solving indoor non-steady state radiation heat transfer of CRCP systems. [ABSTRACT FROM AUTHOR]

A new high temperature heat pump using water as refrigerant has been designed and built for testing on a laboratory test bench that reproduces the operating conditions of real-case industrial applications. Experimental investigations of this heat pump were carried out in the condensing temperature range of 130–140 °C. A new dynamic model has also been developed using Modelica to take into account the presence of non-condensable gases and the purging mechanism. In addition, a new combined finite-volume and moving boundary method (FV-MB) approach is applied for the plate heat-exchanger models and a moving boundary (MB) approach between phases is implemented for the models of the purging and the flash evaporation systems. The start-up phase of this high-temperature heat recovery and heat enhancement of the heat pump are simulated experimentally and numerically. A comparison between both results is presented and analyzed. Global energy savings and the environmental benefits have been illustrated. [ABSTRACT FROM AUTHOR]

Dans cette étude, les distributions de température sont développées à travers les conditions transitoires pour atteindre l’état stationnaire dans un échangeur à deux tubes coaxiaux. Un schéma unidimensionnel de différences finies a été utilisé pour analyser la distribution de température et de pression dans cet échangeur de chaleur. Les propriétés thermophysiques des fluides utilisées varient avec la température le long de l’échangeur. La conduction thermique axiale dans les parois et le transfert convectif à travers les interfaces sont pris en compte. Les fluides transitant dans l’échangeur sont monophasiques. Le programme développé analyse la circulation des fluides à co-courant (anti-méthodique) et à contre-courant (méthodique).

Abstract: The experimental validation of a transient geothermal heat pump model is presented. A commercial heat pump unit is fully instrumented to measure capacity and power usage by the compressor and the fan. On the refrigerant side, flow rates, pressures and temperatures are measured at various key points to capture the transient behavior under cycling conditions. Flow rates and inlet and outlet temperatures of the secondary fluids are also measured to check the energy exchanges at the evaporator and condenser. An uncertainty analysis shows that it is difficult to maintain a small uncertainty in such elaborate experiments. Eight cases corresponding to a combination of operating conditions are studied. In the four cases in which the unit was running in heating mode, it is seen that, contrary to expectations, the pressures equalize in the whole refrigeration circuit before the end of the off-cycle. Overall, there is a relatively good agreement between the model and the experiments. [Copyright &y& Elsevier]

Abstract: A transient model of a water-to-air geothermal heat pump subjected to cycling operation is proposed in this paper. A distributed approach is used where each component is modeled individually and then linked into a so-called global model. The model can predict the state of the refrigerant throughout the circuit during normal operation and at compressor shut down where there may still be some small refrigerant flow. The governing equations of refrigerant and secondary fluid flows, along with tube wall temperatures evolutions, are solved using the finite volume method. The originality of the proposed model lies in its distributed approach which allows to capture both the on-cycle and the off-cycle, with fan on or off at compressor shut-down. Results presented in a companion paper show that the model is able to predict with relatively good agreement the measured transient behavior of a geothermal heat pump. [Copyright &y& Elsevier]

Abstract: A mathematical model for heat transfer from surrounding environment to a single food package is developed. A simplified analytical solution for three-dimensional (3D) unsteady temperature distribution in the food package with rectangular geometry taking into account the ambient temperature is obtained. The model is developed to be used as an efficient tool for estimating the effects of temperature abuse on the food product inside a single packaging unit. The food product is considered to be a homogenous solid body. The packaging material and air inside the package are modeled using an effective heat transfer coefficient. The developed model is validated by a comparison with experimental results obtained for fresh haddock fillets in expanded polystyrene (EPS) boxes exposed to temperature abuse and by comparison with numerical results obtained by the commercial software FLUENT. A satisfactory agreement was obtained between the experimental and numerical results. [Copyright &y& Elsevier]

Abstract: In order to improve industrial energy efficiency, the development of a high temperature heat pump using water vapor as refrigerant is investigated. Technical problems restraining the feasibility of this industrial heat pump are surmounted by a specifically designed heat pump and the development of a new twin screw compressor. This article presents the development of a new dynamic model of this twin screw compressor and of the heat pump using flash evaporation. This model takes into account the presence and the purging mechanism (purging reservoir) of the non-condensable gases especially during the start-up procedure. A finite volume (FV) approach is used for the plate heat-exchangers models while a moving boundary (MB) approach between phases is implemented for the purging and the flash evaporation systems models. The models are developed using Modelica as a modeling language without any library involvement and taking into account as many details as possible to closely represent the real system. [Copyright &y& Elsevier]

Abstract: This paper presents a generalized intrinsically mass conservative evaporator model based on the moving-boundary approach. The heat exchanger model is based on a numerical scheme which can switch between the two-zone (two-phase and superheated) and one-zone (two-phase) representations. The switching algorithms adopt pseudo-state equations in order to track the un-active variables and ensure reasonable initial conditions when rezoning, keeping the robustness whenever superheated region appears or disappears. State variables are chosen to have an intrinsically mass conservative model. This choice is well suited when the evaporator operates at low mean void fraction conditions. Numerical results show that the simulation is consistent with integral forms of energy and continuity equations. The numerical stability to changing flow regimes is demonstrated through simulation test cases. A validation case is presented showing that the model transient behaviour can well predict the performance of an experimentally validated finned coil finite-volume evaporator model. [Copyright &y& Elsevier]

Abstract: Recent research on vapor injection technique has been mostly focused on performance improvement using different system configurations. The flash tank cycle typically shows better performance than the internal heat exchanger cycle. However, the flash tank cycle control strategy is not yet clearly defined. In this study, a novel cycle control strategy is proposed for an R-410A vapor injection flash tank heat pump system and its feasibility was experimentally investigated. The proposed novel cycle control strategy utilized an electronic expansion valve (EEV) for the upper-stage expansion and a thermostatic expansion valve for the lower-stage expansion, and applied an electric heater in the vapor injection line to introduce superheat to the injected vapor by providing a control signal to the upper-stage EEV. Both transient and steady-state system behaviors were studied. The proposed cycle control strategy was found to be able to provide reliable control to the system. [Copyright &y& Elsevier]

Abstract: Several phenomena that affect energy consumption, noise level and reliability of compressors are associated with transient effects that occur during the compressor startup and shutdown. This paper presents a simulation methodology, experimentally validated, developed to analyze the compressor in such transients. Because the time scale associated with the compressor thermal behavior is much larger than that related to the mechanical physics, a thermal equilibrium condition has been considered herein for convenience. Results for valve displacement, piston motion, pressure in the compression chamber and resistive torques are provided to illustrate the application of the methodology and to assist an understanding of the physical aspects that affect the compressor performance throughout the startup and shutdown. It is observed that the dynamics of suction and discharge valves are greatly affected. Moreover, the model is employed to estimate the minimum voltage required for the compressor startup as a function of the equalized pressure and the auxiliary coil actuation time. [Copyright &y& Elsevier]

Abstract: The development of control algorithms for refrigeration systems requires models capable of simulating transient behavior with sensible computational time and effort. The most pronounced dynamics in these systems are found in the condenser and the evaporator, especially the transient behavior of the evaporator is of great importance when designing and tuning controllers for refrigeration systems. Various so called moving boundary models were developed for capturing these dynamics and showed to cover the important characteristics. A factor that has significant influence on the time constant and nonlinear behavior of a system is the amount of refrigerant charge in the evaporator which is considerably reduced when microchannel heat exchangers are utilized. Here a moving boundary model is used and adapted to simulate and compare the transient behavior of a microchannel evaporator with a fin-and-tube evaporator for a residential air-conditioning system. The results are validated experimentally at a test rig. [Copyright &y& Elsevier]

Abstract: In this paper, the results of a research project aimed at deriving simple, high-performance, auto-tuning, robust control algorithms for evaporators controlled by means of EEVs (Electronic Expansion Valves) are reported. Control design is performed by resorting to a detailed virtual prototyping environment described in . The proposed control scheme consists of two nested loops. In the inner loop, the plant is connected in feedback to a PID controller. It is assumed that the structure of the process model is given but its parameters are unknown. The outer loop is composed of a parameter estimator and an adaptation algorithm that updates the parameters of the PID controller on the basis of the result of a system identification procedure. Performance of the proposed controller is evaluated in the virtual prototyping environment by means of simulations. [Copyright &y& Elsevier]

Abstract: Numerical methods are provided to analyze dynamic characteristics as well as steady-state performance of a multi-type heat pump system. Lumped parameter method was applied to simulate the compressor and expansion device. Additionally, fully distributed method was used for analyzing the condenser and evaporators. The transient terms in the governing equations for heat exchangers were solved adopting the wave equation solutions. The simulation results predict the steady-state performance of a heat pump system with the deviation of ±10%. The transient simulation showed satisfactory responses of temperatures and pressures for various compressor speeds or expansion valve openings. From the results, it was shown that the operating conditions of secondary fluid of one indoor unit had minor influence on the performance of the other unit, while opening of expansion valve affected the transient responses of both evaporators significantly. [Copyright &y& Elsevier]

Abstract: The transient heat transfer during nucleate boiling of refrigerant HFE-7100 is investigated numerically and the results are compared to experimental data. The Volume-of-Fluid solver of the OpenFOAM CFD package was modified and extended for the numerical simulation of single bubble boiling. The model tracks the bubble shape during growth, departure and vertical rise and incorporates evaporation at the liquid–vapor interface as well as microscale heat transfer at the 3-phase contact line. The simulation results give insight into the transient heat transfer between the solid wall, the superheated liquid layer and the growing vapor bubble. The boundary conditions have been chosen according to temporally and spatially highly resolved experimental investigations. Global parameters such as bubble size and mean wall superheat as well as local phenomena such as the cooling of the heater at the contact line are in good agreement to the experimental data. [Copyright &y& Elsevier]

Abstract: This paper presents an advanced switched modeling approach for vapor compression cycle (VCC) systems used in Air Conditioning and Refrigeration. Building upon recent work (), a complete dynamic VCC model is presented that is able to describe the severe transient behaviors in heat exchangers (condenser/evaporator), while maintaining the moving-boundary framework, under compressor shut-down and start-up operations. The heat exchanger models retain a constant structure, but accommodate different model representations. Novel switching schemes between different representations and pseudo-state variables are introduced to accommodate the transitions of dynamic states in heat exchangers while keeping track of the vapor and liquid refrigerant zones during the stop–start transients. Two model validation studies on an experimental system show that the complete dynamic model developed in Matlab/Simulink can well predict the system dynamics in shut-down and start-up transients. [Copyright &y& Elsevier]

Abstract: A new dynamic simulation program for predicting the transient behavior of absorption chillers with arbitrary cycle configurations has been developed. This program combines an object-oriented formulation and a parallel processing program architecture. A new algorithm for calculating the flow rate in a solution circulation line has been also developed. The simulated results of transient behavior of a double-effect absorption chiller cycle agree with the measured behavior of a machine from startup to shutdown. For example, predicted values of the cooling capacity of the chiller, the pressure and temperature of the high temperature generator agree with experimental values almost within 10%. This program has been applied in the development stage of a new machine: a high-performance triple-effect absorption chiller. As a result, this machine operates smoothly without any significant problems, and achieves COP of over 1.6 on the basis of high heat value. [Copyright &y& Elsevier]

Abstract: Firstly, a brief review of the MPCL system design and work principle is presented and a proposed experimental system is described. Special attention was paid to the system start-up and dynamic working characteristics under different conditions such as heat load variation, mass flow rate or sinusoidal temperature variation of boundary condition. According to the experimental findings, the transient liquid transfer between the main loop and accumulator was analyzed to explain the transient phenomena during the experiments. From the experiments, it was demonstrated that the system presents a good performance and has more stable characteristics for start-up processes and normal operation than the heat pipe, CPL or LHP system. The paper presents MPCL system has self-adjusting ability. Because the accumulator, which is just like the “brain” of the system, determines stable capability, and each action of the vapor–liquid interface in it could cause the temperature or pressure change of the evaporator. [Copyright &y& Elsevier]

Abstract: In this paper some results of a research project aimed at deriving high-performance, adaptive control algorithms for electronic expansion valves (EEVs) to be used in finned-coiled, dry-expansion evaporators for refrigeration systems are reported. With the aim of developing a software environment that can be used for controller design, rapid prototyping, optimization of data collection and test design, virtual prototyping approach to design was adopted. The development of a distributed dynamic simulation model of the evaporator coupled with an electronic expansion valve, and its use for deriving autotuning PID control algorithms is described. Experimental results confirm the effectiveness of this kind of approach. [Copyright &y& Elsevier]

Copyright of Annals of Forest Science (EDP Sciences) is the property of EDP Sciences and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract: The transient model of thermal components usually consists of three basic governing equations: continuity equation, energy equation, and momentum equation. For different reasons, the momentum equation is used in three different forms: transient, steady-state, and zero pressure drop. In this paper, the three forms of momentum equation are numerically studied and compared at both component level and system level, particularly in the residential applications. It is found that the results with transient and steady-state momentum equation are pretty close at both levels. Therefore, the steady-state momentum equation is recommended in refrigeration system and component transient modeling because of the robustness and the computation speed. To consider only the system-level cases, it is also found that the transient results without pressure drop give very close estimation of control parameters in comparison with the results taking account into the transient or steady-state pressure drop. [Copyright &y& Elsevier]

Abstract: A first-principles model for simulating the transient behavior of household refrigerators is presented in this study. The model was employed to simulate a typical frost-free 440-l top-mount refrigerator, in which the compressor is on–off controlled by the freezer temperature, while a thermo-mechanical damper is used to set the fresh-food compartment temperature. Innovative modeling approaches were introduced for each of the refrigerator components: heat exchangers (condenser and evaporator), non-adiabatic capillary tube, reciprocating compressor, and refrigerated compartments. Numerical predictions were compared to experimental data showing a reasonable level of agreement for the whole range of operating conditions, including the start-up and cycling regimes. The system energy consumption was found to be within ±10% agreement with the experimental data, while the air temperatures of the compartments were predicted with a maximum deviation of ±1°C. [Copyright &y& Elsevier]

Abstract: Dynamic models of vapor compression systems are useful tools in developing feedback controllers and are gaining increasing attention in recent years. The dominant dynamics are typically those of the evaporator and condenser, which are difficult to model. Accuracy and execution speed of system models therefore are highly dependent on the modeling approach of the heat exchangers. The two common approaches are the finite-volume (FV) and the moving-boundary (MB) methods. Both have been used successfully and reported in the literature, but there is little discussion presented for either choice. This paper presents the development and comparative study of shell-and-tube heat exchanger dynamic models using both the FV and the MB approaches. Detailed model formulations are provided and stability is demonstrated as components and within a complete centrifugal chiller system model. The system models are validated using data from a 300kW R134a centrifugal chiller test stand. The FV formulation is found to be more robust through start-up and all load-change transients, but executes slower. The moving-boundary method can handle all load-change transients but start-up stability is more sensitive to compressor and expansion valve formulations. The moving-boundary formulation also executes about three times faster than the finite-volume while maintaining nearly identical accuracy. With the homogenous two-phase assumption, charge prediction is seen to be less accurate in the moving-boundary approach. [Copyright &y& Elsevier]

Abstract: Simulation is commonly used to develop control and diagnostic algorithms. Because vapor compression cycles are essentially heat management devices, transient and steady-state heat exchanger performance must be predicted accurately. However, for hardware- and software-in-the-loop purposes, the simulation must run in real-time. To reconcile these competing needs, a new lumped parameter or moving-boundary heat exchanger model was created. Accuracy concerns are addressed by including finned surfaces, nonlinear air temperature distributions, and non-circular passages. In its current form, the model is applicable to single pass, cross-flow heat exchangers. The mathematical basis of the model is given and shown to be consistent with integral forms of the energy and continuity equations. Although known to be more computationally efficient than finite volume models, moving-boundary models become singular and fail under certain conditions. To address this shortcoming, particular attention was focused on algorithms for switching between different representations and rezoning wall temperatures. Robustness to changing flow regimes is demonstrated through simulation test cases, and model application to a chiller system is shown. As such, the model provides improved accuracy, robustness, and operating range while maintaining real-time capability. [Copyright &y& Elsevier]

Abstract: This paper is the second paper out of two which present the development of a dynamic model for single-effect LiBr/water absorption chillers. The first part describes the model in detail with respect to the heat and mass balances as well as the dynamic terms. This second part presents a more detailed investigation of the model performance, including performance analysis, sensitivity checks and a comparison to experimental data. General model functionality is demonstrated. A sensitivity analysis gives results which agree very well to fundamental expectations: it shows that an increase in both external and internal thermal mass results in a slower response to the step change but also in smaller heat flow oscillations during the transient period. Also, the thermal mass has been found to influence the heat flow transients more significantly if allocated internally. The time shift in the solution cycle has been found to influence both the time to reach steady-state and the transients and oscillations of the heat flow. A smaller time shift leads to significantly faster response. A comparison with experimental data shows that the dynamic agreement between experiment and simulation is very good with dynamic temperature deviations between 10 and 25s. The total time to achieve a new steady-state in hot water temperature after a 10K input temperature step amounts to approximately 15min. Compared to this, the present dynamic deviations are in the magnitude of approximately 1–3%. [Copyright &y& Elsevier]

Abstract: This paper is the first of two which presents the development of a dynamic model for single-effect LiBr/water absorption chillers. The model is based on external and internal steady-state enthalpy balances for each main component. Dynamic behaviour is implemented via mass storage terms in the absorber and generator, thermal heat storage terms in all vessels and a delay time in the solution cycle. A special feature is that the thermal capacity is partly connected to external and partly to internal process temperatures. In this paper, the model is presented in detail. For verification, the model has been compared to experimental data. The dynamic agreement between experiment and simulation is very good with dynamic deviations around 10s. General functionality of the model and a more detailed comparison with experimental data are presented in Part II of this paper. [Copyright &y& Elsevier]

Abstract: A novel CO2 heat pump system was provided for use in fuel cell vehicles, when considering the heat exchanger arrangements. This cycle which had an inverter-controlled, electricity-driven compressor was applied to the automotive heat pump system for both cooling and heating. The cooling and heating loops consisted of a semi-hermetic compressor, supercritical pressure microchannel heat exchangers (a gas cooler and a cabin heater), a microchannel evaporator, an internal heat exchanger, an expansion valve and an accumulator. The performance characteristics of the CO2 heat pump system for fuel cell vehicles were analyzed by experiments. Results for steady and transient state performance were provided for various operating conditions. Furthermore, experiments to examine the arrangements of a radiator and an outdoor heat exchanger were carried out by changing their positions for both cooling and heating conditions. The arrangements of the radiator and the outdoor heat exchanger were tested to quantify cooling/heating effectiveness and mutual interference. The improvement of heating capacity and coefficient of performance (COP) of the CO2 heat pump system was up to 54% and 22%, respectively, when using preheated air through the radiator instead of cold ambient air. However, the cooling capacity quite decreased by 40–60% and the COP fairly decreased by 43–65%, for the new radiator-front arrangement. [Copyright &y& Elsevier]

Abstract: The thermal behaviour of a new two-phase secondary refrigerant has been analysed. The “stabilised ice slurry” is a suspension in a low viscosity oil of ultraporous polymeric particles filled with water. In order to determine the convective heat transfer coefficient of this secondary refrigerant with water–ice phase change, an experimental set-up was built. It allows determining the local heat transfer coefficients inside two heat exchangers, having rectangular sections (80×8mm2) of 1m length, by mean of fluxmeters located along the working section. The slurry is first cooled and frozen in one of the exchangers, then heated and melted in the other exchanger. The results obtained for laminar or transitional flows shows that the heat transfer coefficients of the ice slurry are obviously higher than the heat transfer coefficients obtained with the single-phase fluid (oil). Correlations giving the local and global Nusselt numbers, depending on the Graetz or Reynolds numbers and on the particle mass fraction, have been established. [Copyright &y& Elsevier]

Abstract: A detailed one-dimensional steady and transient numerical simulation of the thermal and fluid-dynamic behavior of capillary tube–suction line heat exchangers considering metastable region and separated flow has been developed in Part I of this paper. The developed numerical model allows analysis of aspects such as geometry, type of fluid, critical or non-critical flow conditions and metastable region. The accuracy of the detailed simulation model is demonstrated in this part (Part II) of the paper by comparing simulation results with a wide range of steady state experimental data from the technical literature, which include the refrigerant mass flow rate, outlet suction line temperature, and temperature profile along concentric and lateral capillary tube–suction line heat exchangers. Of the 196 data points evaluated for mass flow rate 96.4% are within an error of ±15%, 81.1% are within ±10% with a mean deviation of ±6.3%. Of the 143 data points evaluated for outlet suction line temperature 89.5% are within an error of ±2°C, with a mean deviation of ±0.98°C. The numerical results obtained are used to understand the refrigerant flow behavior inside non-adiabatic capillary tubes. Some divergence problems in the numerical solution process is found to be the discontinuity in non-adiabatic capillary tube flow characteristics caused by re-condensation of the refrigerant within the heat exchanger zone; this aspect needs special attention while modeling the non-adiabatic capillary tube flow. Other important parameter to be evaluated experimentally with special care is the capillary tube internal diameter due to its strong influence on the refrigerant flow results (results of any study based on the nominal diameter are to be used with caution). [Copyright &y& Elsevier]

Abstract: A detailed one-dimensional steady and transient numerical simulation of the thermal and fluid-dynamic behavior of capillary tube–suction line heat exchangers has been carried out. The governing equations (continuity, momentum, energy and entropy) for fluid flows, together with the energy equation in solids, are solved iteratively in a segregated manner. The discretized governing equations in the zones with fluid flow are coupled using a fully implicit step-by-step method. An implicit central difference numerical scheme and a line-by-line solver were used in solids. A special treatment has been implemented in order to consider transitions (subcooled liquid region, metastable liquid region, metastable two-phase region and equilibrium two-phase region). All the flow variables (enthalpies, temperatures, pressures, mass fractions, heat fluxes, etc.) together with the thermophysical and transport properties are evaluated at each point of the grid in which the domain is discretized. The numerical model allows analysis of aspects such as geometry, type of fluid, critical or non-critical flow conditions, metastable regions and transient cases. Comparison of the numerical simulation with experimental data presented in the technical literature will be shown in Part II of the present paper. [Copyright &y& Elsevier]

Abstract: In this paper, a transient model of a silica gel–water adsorption chiller, which is developed in Shanghai Jiao Tong University (SJTU), is developed in order to simulate the evaporating, condensing, and adsorption temperature. Furthermore, this model is verified by a series of experiments. The theoretical studies and experimental data show that the coefficient of performance (COP) is influenced significantly by the variation rates of the heat source temperatures. The results also show that when this chiller is driven by solar energy, a buffer tank should be adopted in the system in order to get better performance when solar insolation is low, and should not be utilized when solar insolation is high, otherwise low COP will be gotten for the reason of the consumption of high electric energy. [Copyright &y& Elsevier]

Abstract: A series of experiments were conducted on a heat pump equipped with a distillation column. The system was operated with R32 and with a 30/70% by mass mixture of R32/134a to examine the difference between the transient performance trends with a pure fluid (R32), and those with a zeotropic mixture (R32/134a). Additionally, the effects of varying heat transfer fluid mass flow, compressor speed, and accumulator sump heat input were examined. Each test was 1h in duration. The heat pump capacities did not generally achieve steady state during the R32/134a tests. Steady state was generally achieved during the R32 tests. As a percentage of the final (end-of-test) capacity, the rate of capacity increase was greater during the R32/134a tests than during those conducted with the pure fluid. The R32/134a tests exhibited capacity oscillations early in each transient that were not present during the R32 tests. The results show that circulating refrigerant mass and composition are the primary controlling factors with regard to transient capacity. [Copyright &y& Elsevier]

Abstract: A generalized model based on the moving-boundary approach is developed to describe the transient behavior of dry-expansion evaporators in the vapor-compression refrigeration system. To improve the robustness of the traditional moving-boundary model under larger disturbances, the time-variant mean void fraction is employed instead of the constant. Numerical integration is applied to get the mean properties in the two-phase region and the superheated region. The interface wall temperature between the two-phase and the superheated regions is also evaluated by a new weighted mean. Qualitative case study shows that the present model can well predict the transient behaviors of evaporators under larger disturbances and keep the robustness whenever superheated region appears or disappears. [Copyright &y& Elsevier]

This paper investigates the effects of mix design factors on the thermal properties of Superpave asphalt concrete. The thermal properties were measured using a guarded testing device (k-alpha device) developed recently at the University of New Brunswick. Two aggregate types, three gradations (determined by the material retained on a 4.75 mm sieve), and four compaction levels (at 35, 70, 100, and 160 gyrations) were investigated. The aggregate was 12.5 mm maximum nominal size with PG58-34 asphalt binder used for all mixes. The findings show that the thermal conductivity of the asphalt concrete ranged from 1.7 to 2.1 W/m·K. The specific heat capacity varied with the aggregate source and ranged from 940 to 2000 J/kg·K. The thermal diffusivity was found to vary with aggregate source. The aggregate type was found to have the most significant effect on the thermal properties. The compaction level had an effect but not a statistically significant one. The range of thermal properties determined in this paper is comparable to that found in the literature. [ABSTRACT FROM AUTHOR]

Abstract: This paper discusses the transient mixing and separation characteristics of isobutane with/from refrigeration oil. The mixing/separation processes are observed and investigated experimentally in a glass cylindrical vessel. Since liquid isobutane is less dense than refrigeration oil, the mixing process proceeds one dimensionally by diffusion from the interface between isobutane gas and refrigeration oil. The progress of mixing, therefore, is very slow compared with a combination of halocarbon refrigerant and refrigeration oil having convection flow during the mixing process. The diffusion process can be analyzed using a one-dimensional diffusion model with an appropriate diffusion coefficient, which increases linearly with temperature. The separation of isobutane from the oil–refrigerant mixture occurs at the interface and the denser oil from which isobutane is separated causes a convective flow. Bubble generation under the depressurized conditions is unstable, but in the most cases, it tends to start when a high super saturation degree is reached. The temperature change during the separation process is estimated using latent heat as the separation heat of refrigerant. [Copyright &y& Elsevier]

Abstract: In this study, experimental and theoretical studies on thermoelectric cooler (TEC) performance for cooling a refrigerated object (water in a tank) were performed. Microchannel heat sinks fabricated with etched silicon wafers were employed on the TEC hot side to dissipate heat. The measurements show that the temperature of the refrigerated object decreased with time. A theoretical model based on a lumped system was established to predict the transient behavior of the variation in temperature for the refrigerated object with time. The theoretical predicted temperature variation was in good agreement with the measured data. The relationship among the heat sink thermal resistances, TEC electric current input and minimum refrigerated objected temperature was examined based on the theoretical model. The calculated minimum temperatures were showed for the several cases of heat sink thermal resistance on the TEC hot side and electric current input. The minimum temperature can be obtained by increasing the electrical current input and decreasing the heat sink thermal resistance. [Copyright &y& Elsevier]

Abstract: A detailed mathematical model of a compressor driven metal hydride (CDMH) cooling system is presented. The model takes into account the transient characteristics of the coupled metal hydride reactors with external fins, reciprocating compressor and conditioned space. The model can be used for predicting the system performance during the initial pull-down as well as the stable cycling periods. Results are obtained for a 1kW capacity air conditioning system using optimized reactors packed with Zr0.9Ti0.1Cr0.55Fe1.45 hydride. The COP''s obtained are in the range of 1.7–2.2 depending on operating conditions while the specific cooling power obtained is about 600kJkgalloy−1 h−1. It is shown that in order to make these systems commercially viable it is important to select suitable materials with fast reaction kinetics. Since, system performance parameters can be predicted more effectively, the model can be used for design of optimized systems. [Copyright &y& Elsevier]

Abstract: In this paper, a controlled atmosphere storage model, developed earlier, is validated using an industrial CA cool storage facility with stepwise product loading strategy. The proposed combined continuous and discrete CA cool storage simulation model was able to represent the step response transients and continuous events, with accuracy less than the observed variability or at best with accuracy level as set by the measurement instrument. Moreover, the handling of discrete/continuous events enabled the implementation of practical operational procedures and to investigate their implication on plant performance/design and directly on the product quality. The model is a valid working model for design and optimization of CA cool storage facilities both with respect to plant performance and final quality of the stored product. [Copyright &y& Elsevier]

Simulation of dynamic processes in controlled atmosphere (CA) cool room storage systems has been developed. The model consists of three interacting sub-models for the prediction of the transient behavior of the processes in the three units, namely, the cool room, the refrigeration system and the gas-handling unit. Several modules representing each of the components in these units were developed based on energy and mass balances. The modules were then arranged to form the sub-models, which were interconnected, in turn, into the global CA cool storage system model. The modules were implemented in an object-oriented computational environment, (EcosimPro) which can handle both continuous and discrete events. The model was validated using experimental data from a pilot plant CA cool storage facility. Model predictions of the most important discrete and continuous processes were found to agree to the experimental data with a maximum difference less than the observed spatial variability or at best with the accuracy level as set by the measurement instruments. As product respiration and quality models are incorporated, it is possible to use the model for optimization of plant performance with respect to the final quality of the stored product. Moreover, the handling of discrete/continuous events enables the implementation of practical operational procedures and to investigate their implication directly on the product quality and plant performance/design. [Copyright &y& Elsevier]