SummaryBattery chargers are an important component in electric and plug‐in hybrid vehicles and various other clean energy systems. The thermal management in battery charger is a crucial aspect that influences its overall performance and cyclic stability. Passive cooling technology using heat sinks is preferred in developing battery chargers due to its reliability, quietness, and efficiency (no parasitic power). In the present work, new hybrid passive heat sinks (HPHS) with various fin geometries, namely inclined interrupted fins, pin fins, and straight interrupted fins, have been developed by adding a phase change material (PCM) layer to passively cooled bare fin heat sinks (BFHS). The developed heat sinks have the same geometric footprint as that of the battery charger, IC650 built by the industrial partner of the project Delta‐Q Technologies. Experimental investigations were carried out to analyze the effects of PCM quantities and continuous (80‐120 W) and intermittent (duty cycle operation) thermal loads on the heating‐cooling performance of the HPHS. Temperature contours obtained using infrared images show that the proposed HPHS provides a more uniform temperature with reduced hot spots compared to BFHS. The heating and cooling performances of straight interrupted fins‐based HPHS were found better for all thermal loads and PCM quantities tested due to their smaller thermal resistance. Increasing the PCM volume fraction from 0.2 to 0.6 improves the load shedding capacity. However, the added thermal resistance requires optimal consideration. While conducting different cyclic operations for inclined interrupted fins‐based HPHS, a maximum overall thermal management ratio of 0.45 was achieved. The proposed HPHS minimizes the temperature fluctuations more effectively while operating at high loads and shorter duty periods. This new passively cooled hybrid heat sink can notably improve the overall performance and reliability of battery chargers during both continuous and intermittent operations.

The thermal masses of components influence the performance of many adsorption heat pump systems. However, typically when experimental adsorption systems are reported, data on thermal mass are missing or incomplete. This work provides original measurements of the thermal masses for experimental sorption heat exchanger hardware. Much of this hardware was previously reported in the literature, but without detailed thermal mass data. The data reported in this work are the first values reported in the literature to thoroughly account for all thermal masses, including heat transfer fluid. The impact of thermal mass on system performance is also discussed, with detailed calculation left for future work. The degree to which heat transfer fluid contributes to overall effective thermal mass is also discussed, with detailed calculation left for future work. This work provides a framework for future reporting of experimental thermal masses. The utilization of this framework will enrich the data available for model validation and provide a more thorough accounting of adsorption heat pumps.

In this study, a new comprehensive model is developed that can predict the effective thermal conductivity and thermal contact resistance of the packed bed adsorbers, as a function of water uptake, number of adsorbent layers, particle size, bed porosity, temperature, contact pressure, and gas pressure. The proposed model is successfully validated against experimental data for AQSOA FAM-ZO2, measured by a heat flow meter. The relative differences of the experimental data and predicted values for the packed bed effective thermal conductivity are 2% and 3% at 25 and 80 degrees C, respectively. By increasing the water uptake from 0 to 0.3 kg kg(ads)(-1), effective thermal conductivity of a 2 mm FAM-ZO2 randomly packed bed is predicted to increase by 17% for temperature of 25 degrees C and 18% for temperature of 80 degrees C. (C) 2018 Elsevier Ltd. All rights reserved.

Adsorption thermal energy storage has received considerable attention as it can overcome the mismatch between supply and demand of renewables, providing high energy storage per volume. In the packed bed adsorption thermal energy storage, pressure drop is of key concern since higher pressure drop leads into lower energy storage efficiency. In this paper, an experimental and modeling investigation on the pressure drop inside the adsorption packed beds is performed. An accurate semi-analytical closed-form relationship is proposed to calculate the pressure drop inside a column of adsorbent materials, taking into account the Laplacian friction, as well as the inertial effects. The model covers a wide range of porosity, between low-permeability medium, a dense packed bed of spherical particles, and high-permeability media, a pure viscous fluid. A modified permeability is defined to consider the inertial effect for a moderate range of the particle Reynolds number (0 < Re-p < 300). An experimental apparatus is designed for measuring the pressure drop for different bed sizes and inlet air velocities. The proposed model shows good agreement with the experimental data with the relative difference of 7.6% at 0.73 m/s for silica gel and 15.3% at 0.84 m/s for zeolite 4A packed beds. The experiment reveals that the effect of water uptake on the pressure drop of packed bed with wet adsorbent is negligible in the tested particle Reynolds number range, with a relative difference of less than 1.0% compared to dry adsorbent for 18-30 cm long columns. The proposed formula for pressure drop, consequently, can be applicable for wet adsorbents regardless of the water uptake amount, with a good level of accuracy. Moreover, the analytical model shows up to +/- 2% change in pressure drop due to heat of adsorption of the tested adsorber columns.

In this study, the effective thermal conductivity (ETC) of uniformly-sized packed bed adsorber is modeled as a function of water uptake, number of adsorbent layers, particle size, bed porosity, temperature, contact pressure, and interstitial gas pressure. The model is validated against experimental data for 2 mm AQSOA FAM-Z02, measured by heat flow meter method (ASTM standard C518), and the maximum relative differences between the predicted values and the experimental data are 2% for ETC and 8% for total thermal conductivity. For 0.32 kg kg(ads)(-1) water uptake, at 30 degrees C, ETC of an open-system 2 mm FAM-Z02 SC-arranged packed bed adsorber is 2.2 times higher than the ETC of a closed-system (0.1031 W m(-1) K-1 compared to 0.0474 W m(-1) K-1). ETC charts are presented based on the equilibrium water uptake isotherms for 0.5 and 2 mm FAM-Z02 packed beds, which provides a detailed and clear picture of ETC of packed bed adsorbers for both open and closed thermal energy storage applications. For each packed bed storage volume, an optimum particle size can be predicted by the presented model, which ensures the highest packed bed total thermal conductivity. (C) 2018 Elsevier Ltd and IIR. All rights reserved.

Low thermal conductivity in packed bed adsorbers is a crucial challenge facing widespread adoption of low-grade heat adsorption thermal energy storage systems. In this work, thermal conductivities of 2-mm diameter AQSOA FAM-Z02 packed bed adsorbers with different numbers of adsorbent layers are measured, using a NETZSCH HFM 436/3/1E Lambda, in the temperature range of 10-80 degrees C and under atmospheric pressure. Effects of thermal contact resistance (TCR) between the adsorbent particles and the bed metal surfaces are deconvoluted from the total thermal resistance. Effective thermal conductivities of the adsorber packed bed are 0.188 and 0.204 W m(-1) K(-1)at temperatures of 10 and 80 degrees C, respectively. It is observed that the relative importance of TCR compared to the total thermal resistance of a monolayer FAM-Z02 packed bed, is 67% at 25 degrees C and under contact pressure of 0.7 kPa, which i significant and should be considered in the design of adsorption systems. (C) 2018 Elsevier Ltd. All rights reserved

In an adsorption chiller, the refrigerant (water) operating pressure is low (0.5–5 kPa) and the cooling power generation of a flooded evaporator is affected by the height of water column. To resolve this issue, we experimentally investigate the performance of a flooded evaporator as a function of water height. The results show an optimum water height equal to 80% of the tube diameter leading to achieve the highest cooling power. Under this condition, the internal and external thermal resistances on the inside and outside of the evaporator tubes account for up to 73% of the overall thermal resistance. To reduce the internal thermal resistance, twisted and Z-type turbulent flow generators are incorporated into the evaporator tubes. The evaporator cooling power shows an increase by 12% and 58% when twisted tape and Z-type turbulators are used at a cost of an increase in the internal pressure drop by 2.5 and 14.5 times, respectively. The twisted tape and Z-type turbulators improve the average specific cooling power of the adsorption chiller by 9% and 47%, respectively. To reduce the external thermal resistance, the outside surface of the evaporator tubes is coated with porous copper. The coated evaporator increases the overall heat transfer coefficient by 1.4 times and improves the specific cooling power of the adsorption chiller by 48% compared to the uncoated tubes.

A modified lumped parameter model has been used to study transient conduction in phase change materials (PCM) in cylindrical coordinates. The two-point Hermite approximation is used to compute the average temperatures and the temperature gradient in each phase. The performance of PCM has been analyzed during the charging processin terms of energy storage and density. The effect of Stefan number on melting front dynamics is comprehensively studied. The results are verified with exact solutions as well as steady-state asymptotes and also show good agreement with existing experimental data.

Sorption processes in packed beds are inherently transient and the maximum vapor removal occurs at the beginning of the adsorption cycle. Consequently, temperature swing adsorption (TSA), consisting of charging (adsorption) and regeneration (desorption), is required in order to frequently refresh the packed bed and provide sustainable dehumidification. In this study, the effectiveness of thin desiccant columns in controlling air humidity under periodic charge and regeneration cycles is analyzed. An experimental apparatus was designed to measure the rate of adsorption and desorption under different operating conditions. The TSA strategy is imposed by low and high temperature heat sources. Moreover, a numerical one-dimensional transient model is provided and validated by the experiments under different ambient conditions. Using this model, the effect of design factors such as cycle time, airflow, and regeneration temperature are investigated in order to optimize the performance of the desiccant dehumidifier.