Abduljalil A. Al-abidi

Heat Transfer Enhancement for PCM Thermal Energy Storage in Triplex Tube Heat Exchanger

Thermal energy storage is critical for reducing the discrepancy between energy supply and energy demand, as well as for improving the efficiency of solar thermal energy systems. Among the different types of thermal energy storage, phase-change materials (PCM) thermal energy storage has gained significant attention recently because of its high energy density per unit mass/volume at nearly constant temperature. This study experimentally investigates the using of a triplex tube heat exchanger (TTHX) with PCM in the middle tube as the thermal energy storage to power a liquid desiccant air-conditioning system. Four longitudinal fins were welded to each of the inner and middle tubes as a heat transfer enhancement in the TTHX to improve the thermal performance of the thermal energy storage. The average temperature of the PCM during the melting process in the TTHX with and without fins was compared. The PCM temperature gradients in the angular direction were analyzed to study the effect of the natural convection in the melting process of the thermal storage. The energy storage efficiency of the TTHX was determined. Results indicated that there was a considerable enhancement in the melting rate by using fins in the TTHX thermal storage. The PCM melting time is reduced to 86% by increasing of the inlet heat transfer fluid. The average heat storage efficiency calculated from experimental data for all the PCMs is 71.8%, meaning that 28.2% of the heat actually was lost.

Thermal Performance Enhancement of Triplex Tube Latent Thermal Storage Using Fins-Nano-Phase Change Material Technique

ABSTRACT Latent heat thermal energy storage (LHTES) systems using a phase change material (PCM) can reduce the heat-transfer rates during charging/discharging processes because of their inherently low thermal conductivity. In this study, heat-transfer enhancement using various configurations of longitudinal fins employing both a PCM and a nano-PCM in a large triplex-tube heat exchanger (TTHX) was numerically investigated via the Fluent 15 software. The results showed that the thermal conductivity of the pure PCM (0.2 W/m K) can be observably enhanced by dispersing 10% alumina (Al2O3) to 25%. Therefore, the melting time is reduced to 12%, 11%, and 17% for the internal, internal-external, and external fins, respectively, compared with the case of the PCM without nanoparticle. It is concluded that the model of external fins-nano-PCM embedded in a large TTHX is the most efficient model for achieving complete PCM melting in a short time (188 min), where improving the thermal performance to 14% and 11% compared with the TTHX with internal and internal-external fins-nano-PCM, respectively. The simulation results are validated and agree well with experimental results for the PCM and nano-PCM.

Experimental Study on Regenerator Performance of a Solar Hybrid Liquid Desiccant Air-Conditioning System

This chapter presents an experimental study on the performance of the liquid desiccant regenerator of a hybrid solar air-conditioning system. Lithium chloride (LiCl) solution is used as the working desiccant material. The effects of air temperature, air humidity ratio, and solution temperature on the performance of the regenerator are disused. The experimental results showed that the moisture removal rate (MRR) and effectiveness of the regenerator increase slowly as a function of the air inlet temperature. It was found that the MRR and effectiveness increased about 0.79 and 1.1 %, respectively. The moisture removal rate decreased with increasing air inlet humidity ratio and increased with desiccant inlet temperature.

Numerical Study of Solidification in Triplex Tube Heat Exchanger

Thermal energy storage is very important to eradicate the discrepancy between energy supply and energy demand and to improve the energy efficiency of solar-energy systems. The latent heat thermal energy storage systems have gained greater attention recently due to their reliability and high storage density at nearly constant thermal energy. The present work explores numerically the solidification process of a phase change material (PCM) in a triplex tube heat exchanger (TTHX) equipped with internal and external fins to enhance the heat transfer during the charging and discharging of the PCM. A two-dimension (2D) numerical model is developed using the Fluent 6.3.26 software program; the pure conduction and natural convection are considered for the simulation. Experimental and numerical data were adopted to validate the model from the literature; a good agreement has been found. Predicted results indicated that the solidification rate time of the TTHX with internal and external fins was about 50 % of the solidification time of the TTHX without fins.

Computer Simulation of Heat and Mass Transfer in a Cross Flow Parallel-Plate Liquid Desiccant-Air Dehumidifier

A MATLAB program using finite difference technique is investigated to predict the distribution of air stream parameters as well as desiccantsolution parameters inside the parallel plate absorber. The present absorber consists of 14 parallel plates with a surface area per unit volume ratio of 80 m2/m3. Calcium chloride as a liquid desiccant flows through the top of the plates to the bottom while the air flows through the gap between the plates making it a cross flow configuration. The model results show the effect of desiccant mass flow rate on the performance of the dehumidifier (moisture removal rateand the effectiveness). The results show that the maximum temperature and humidity ratio differences of the air are 2.56 °C and 11 g/Kg with a maximum solution mass flow rate of 160 g/s. The maximum temperature and minimum concentration differences of solution in the direction flow of solution are 3.185 °C and 0.34 % with a maximum solution mass flow rate of 160 g/s. The moisture removal rate increases rapidly with solution flow rate from 1.41 to 2.196 g s−1, but the moisture removal stagnates at high desiccant solution mass flow rates. The effectiveness achieves an increase of 0.39–0.66 when the solution mass flow rate increases from 30 to 160 g s−1.