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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: A single-blow transient test technique based on axial dispersion model is proposed for the determination of both heat transfer coefficient and axial dispersion coefficient in plate heat exchangers, characterized by NTU and dispersive Peclet number respectively. The present experimental analysis deals with the effect of flow maldistribution on the transient temperature response for U-type plate heat exchangers. The experiments are carried out with uniform and non-uniform flow distributions for various flow rates and two different numbers of plates. Special effort has been made to differentiate the deviation from plug flow due to flow maldistribution and fluid backmixing. The fluid axial dispersion is used to characterize the backmixing and other deviations from plug flow. Due to unequal distribution of the fluid, the velocity of the fluid varies from channel to channel and hence the heat transfer coefficient variations are also taken into consideration. The computed outlet fluid temperatures are compared with experimental outlet temperatures, and the values of dispersive Peclet numbers are estimated. The results indicate that in order to get parameters independent of the number of plate used in single-blow experiment, it is essential to isolate flow maldistribution from backmixing. This paper has brought out a practical way in which this isolation can be done in the process of data reduction through suitable computational model. [Copyright &y& Elsevier]

Abstract: This paper presents a heat and mass transfer simulation of an adsorber, taking into consideration the geometry of the heat exchanger and the diffusion in the adsorbent medium. In this model, an increment in the direction of heating/cooling fluid containing one (or more) fin pitch was considered. In the domain of this increment, the distribution of the adsorbent temperature was evaluated in the radial and axial directions. The model is validated by experimental data of different adsorbents, volume flows and temperatures. All data were collected in an adsorber test-bench at Fraunhofer ISE. As a result it was found a coefficient of multiple determination of around 0.94 and an error of 20% during the transient. Finally, the model was run on typical operation for cooling application and compared with data from literature. A numerical energy balance was also evaluated. In summary, the results obtained by a independent group shows the same range of confidence of the model developed here, in terms of the tendency of the curves and even the absolute values. [Copyright &y& Elsevier]

Abstract: In the present study, a 3D numerical simulation of a whole heat exchanger with middle-overlapped helical baffles is carried out by using commercial codes of GAMBIT 2.3 and FLEUNT 6.3. At first, the computational model and numerical method of the whole heat exchanger with middle-overlapped helical baffles is presented in detail, and parallel computation mode is adopted for the simulation of a whole heat exchanger with six cycles of the middle-overlapped helical baffles of 40° helical angle on a grid system of 13.5-million cells; second, the validation of the computational model is performed by comparing the total pressure drop and average Nusselt number of the whole heat exchanger with experimental data. Reasonably good agreement is obtained, and the reasons causing to the discrepancy are analyzed. The shell-side fluid pressure and temperature fields of the whole area are then presented. Finally the cycle average Nusselt number of different cycle in the heat exchanger are compared and it is found that within the accuracy allowed in engineering computation, periodic model for one cycle can be used to investigate the heat transfer and pressure drop characteristics for different heat exchanger to save computational source. The companion paper will provide details of simulation results using the periodic model for different helical angles and different structures of helical baffles. [Copyright &y& Elsevier]