Determination of air-to-air heat wheel sensible effectiveness using temperature step change data

Fathieh, Farhad; Besant, Robert W.; Evitts, Richard W.; Simonson, Carey J.

doi:10.1016/j.ijheatmasstransfer.2015.04.028

Cited by 33 publications

(37 citation statements)

References 17 publications

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“…On the basis of the presented charts (Figs. 5,6,7,8,9,10,11,12,13,14), one can notice that the function of the temperature effectiveness is shaped in a similar way for all presented variants of the rotor's depth, i.e., its value rises due to moisture accumulation (in the form of water film or frost layer). Another similarity is an increase in "dry" area with increasing outdoor air temperature.…”

Section: Results Of Simulationsmentioning

confidence: 69%

“…The researchers also presented a variety of methods that allow determining the sensible and latent effectiveness of the rotary heat/energy exchanges. Fathieh et al [14] analyzed the possibility to predict sensible effectiveness of air-to-air heat wheel on the basis of cyclic and single-step change transient experiments performed on the parallel-plate heat exchanger made of the same material. Their results indicated that this method may be successfully used to determine the sensible effectiveness of the parallel-flow rotors.…”

Section: Introductionmentioning

confidence: 99%

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The influence of geometrical parameters on heat and mass transfer processes in rotary heat exchangers

2019

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This paper focuses on the influence of geometrical parameters of the rotary heat exchanger on its operation under highspeed rotor conditions. Proposed mathematical model of heat recovery wheel is based on a structure of the counter-flow heat exchanger model. After implementation of a numerical method on the modified α-model, the computer simulations were conducted. They allowed considering the distribution of the active heat and mass transfer zones ("dry," "wet" and "frost") on the matrix channel surface depending on the outdoor air conditions for different variants of rotor size. The obtained results indicate that the increase in the wheel's depth leads to the increase in temperature effectiveness of heat recovery (from 0.667 to 0.814). Moreover, it was also established that the threshold temperature under which the frost is accumulated on the core surface also rises with the rotor depth (from − 10.7 to −9.6 °C). It was concluded that under certain outdoor air temperature conditions (t 1i > -10.7 °C, for rotor depth equal to 0.40 m), the mass transfer rate of the condensed water vapor in the channels of the return air side is equal to the evaporation mass transfer rate in the channels of the supply air side, and hence, the temperature efficiency reaches the same value level as under "dry" operating conditions. It was established that only under frost accumulation conditions, the increased temperature effectiveness is observed. Keywords Thermal wheel · Waste heat recovery · Mathematical model · Energy saving List of symbols cSpecific heat capacity (J/(kg K)) D Diameter of the plate channel (m) Δ̄e vap 1

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Section: Results Of Simulationsmentioning

confidence: 69%

Section: Introductionmentioning

confidence: 99%

The influence of geometrical parameters on heat and mass transfer processes in rotary heat exchangers

2019

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“…Recently, this formulation was used by Graf et al [16] in their simulation of a silica gel adsorber. Furthermore, the models of air-to-air heat wheels with silica gel of Fathieh et al [30,31] are based on the assumptions of the LDF approach. This results in an LDF formulation for the temperature response of the heat wheel [30] or a double exponential model for the humidity response of the heat wheel [31].…”

Section: Mass Transfer Model For the Loose Grains Configurationmentioning

confidence: 99%

“…Furthermore, the models of air-to-air heat wheels with silica gel of Fathieh et al [30,31] are based on the assumptions of the LDF approach. This results in an LDF formulation for the temperature response of the heat wheel [30] or a double exponential model for the humidity response of the heat wheel [31]. Due to its simplicity, we use this approach in the following paper, although the assumption of the diffusion in the adsorbed phase might not be correct.…”

Section: Mass Transfer Model For the Loose Grains Configurationmentioning

confidence: 99%

“…This kind of experiment can be compared to flash analysis as first presented by Parker et al [34] or other methods that are suited to determine heat transfer parameters. It is worth noting that also in the field of air-to-air energy wheels that are used for air dehumidification, kinetic measurements (temperature jumps or humidity jumps) are performed in order to determine model parameters [30,31]. Here, it could also be an option to perform inert temperature jumps in order to study only the heat transfer characteristics without the influence of the adsorption material.…”

Section: Experimental Setup and Measurement Proceduresmentioning

confidence: 99%

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Advanced Measurement and Simulation Procedure for the Identification of Heat and Mass Transfer Parameters in Dynamic Adsorption Experiments

et al. 2017

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Thermally-driven heat pumps can help to mitigate CO 2 emissions by enhancing the efficiency of heating systems or by driving cooling systems with waste or solar heat. In order to make the thermally-driven systems more attractive for the end consumer, these systems need a higher power density. A higher power density can be achieved by intensifying the heat and mass transfer processes within the adsorption heat exchanger. For the optimization of this key component, a numerical model of the non-isothermal adsorption dynamics can be applied. The calibration of such a model can be difficult, since heat and mass transfer processes are strongly coupled. We present a measurement and simulation procedure that makes it possible to calibrate the heat transfer part of the numerical model separately from the mass transfer part. Furthermore, it is possible to identify the parts of the model that need to be improved. For this purpose, a modification of the well-known large temperature jump method is developed. The newly-introduced measurements are conducted under an inert N 2 atmosphere, and the surface temperature of the sample is measured with an infrared sensor. We show that the procedure is applicable for two completely different types of samples: a loose grains configuration and a fibrous structure that is directly crystallized.

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Determination of the sensible heat effectiveness and pressure loss of a rotary regenerative heat exchanger using CFD

Zmrhal

Zelensky²,

Boháč³

et al. 2023

Build. Simul.

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The paper presents a new method to determine the sensible effectiveness and pressure loss of rotary regenerative heat exchangers using computational fluid dynamics (CFD). It is based on CFD simulations of a single thermal wheel microchannel with a small cross-sectional area and thin walls, with cyclic inlet and outlet boundary conditions. Two unique measurement set-ups were designed and built for the experimental measurement of the heat exchanger characteristics. Five different types of thermal wheels were manufactured, measured, and simulated in ANSYS Fluent. All wheels achieve an effectiveness greater than 73% under certain (air flow) conditions, which is the minimum effectiveness required by Ecodesign (in the EU). For the examined exchangers, the effectiveness ranges from 66.5% to 83.3%, depending on the boundary conditions and geometric parameters of the rotors. The highest sensible effectiveness is achieved by heat exchangers with the largest heat exchange surface Ac; on the other hand, these wheels have the largest pressure loss. The paper discusses the use of a simplified ε-NTU correlation model for the HVAC systems (typically C* = 1). The correlation model and CFD results were compared and found to be different from each other. The results of the CFD simulation were compared with measurements to prove that the proposed simulation method can predict the behaviour of the real heat exchanger as a whole. It was demonstrated that the sensible effectiveness and pressure loss of the rotary heat exchanger predicted by the CFD simulations correspond well to the measured values within the measurement uncertainty ±1.3%. The proposed method can be used for the comparison of different rotary regenerative heat exchangers before their manufacturing and for verification that they meet the EU Ecodesign requirements set by the current legislation. It reduces the cost of the initial optimisation and testing of new designs.

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Determination of air-to-air heat wheel sensible effectiveness using temperature step change data

Cited by 33 publications

References 17 publications

The influence of geometrical parameters on heat and mass transfer processes in rotary heat exchangers

The influence of geometrical parameters on heat and mass transfer processes in rotary heat exchangers

Advanced Measurement and Simulation Procedure for the Identification of Heat and Mass Transfer Parameters in Dynamic Adsorption Experiments

Determination of the sensible heat effectiveness and pressure loss of a rotary regenerative heat exchanger using CFD

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