• Energy Research

This paper evaluates the discharging mechanism in a PCM (phase change material) to air heat exchanger for the purpose of space heating using a composite of copper foam and PCM. The composite system is modelled with both 2-D and 3-D computational fluid dynamics approach for different inlet air temperatures to consider the effect of room temperature using the thermal non-equilibrium model for the porous medium compared with the thermal equilibrium one. The results show the significant advantages of composite heat exchanger compared with a PCM only case. For the inlet air temperature of 22 °C, the composite unit is solidified in 43% shorter time with 73% higher heat retrieval rate compared with that for the PCM only. After 10 h, the temperature variation between the inlet and outlet of the air channels for latent heat storage heat exchanger system with the composite system is 41 °C and 34 °C for the inlet air temperatures of 0 °C and 22 °C, respectively, while it is 33 °C and 29 °C for the system with PCM only. This study show the possible usage of PCMs in the energy storage heaters by introducing metal foams which is not possible using PCM only alternatives.

This paper evaluates the discharging mechanism in a PCM (phase change material) to air heat exchanger for the purpose of space heating using a composite of copper foam and PCM. The composite system is modelled with both 2-D and 3-D computational fluid dynamics approach for different inlet air temperatures to consider the effect of room temperature using the thermal non-equilibrium model for the porous medium compared with the thermal equilibrium one. The results show the significant advantages of composite heat exchanger compared with a PCM only case. For the inlet air temperature of 22 °C, the composite unit is solidified in 43% shorter time with 73% higher heat retrieval rate compared with that for the PCM only. After 10 h, the temperature variation between the inlet and outlet of the air channels for latent heat storage heat exchanger system with the composite system is 41 °C and 34 °C for the inlet air temperatures of 0 °C and 22 °C, respectively, while it is 33 °C and 29 °C for the system with PCM only. This study show the possible usage of PCMs in the energy storage heaters by introducing metal foams which is not possible using PCM only alternatives.

Abstract This study numerically investigates the performance of the melting process for a PCM based heat storage system under the effect of different variables in a vertical container with a copper metal foam. Different cases were studied and compared including the effects of variable porosities and pore densities, non-equilibrium porous medium model, a multiple-segment metal foam case and different heater locations in the system on the liquid fraction and temperature as presented by contour plots and diagrams. The results show high performance for the copper foam-PCM unit compared with on its own PCM, for reducing the melting time by almost 85%. By changing the location of constant temperature heater from the bottom to the side and top surface, the melting time decreases by 70.5% and 4.7%, respectively. By using a multiple-segment porous system, the melting time reduces by 3.5% compared with the case of uniform porosity. Furthermore, the more accurate non-equilibrium numerical model shows a 7.4% difference in the melting time compared with the equilibrium model. This study optimises the design to improve practical application performance and to reduce waste energy.

Abstract This study numerically investigates the performance of the melting process for a PCM based heat storage system under the effect of different variables in a vertical container with a copper metal foam. Different cases were studied and compared including the effects of variable porosities and pore densities, non-equilibrium porous medium model, a multiple-segment metal foam case and different heater locations in the system on the liquid fraction and temperature as presented by contour plots and diagrams. The results show high performance for the copper foam-PCM unit compared with on its own PCM, for reducing the melting time by almost 85%. By changing the location of constant temperature heater from the bottom to the side and top surface, the melting time decreases by 70.5% and 4.7%, respectively. By using a multiple-segment porous system, the melting time reduces by 3.5% compared with the case of uniform porosity. Furthermore, the more accurate non-equilibrium numerical model shows a 7.4% difference in the melting time compared with the equilibrium model. This study optimises the design to improve practical application performance and to reduce waste energy.

Abstract The objective of this numerical study is to develop a latent heat storage (LHS) air heater in both charging and discharging processes to find the geometrical and operating conditions for dwelling space heating. The aim of the storage heater is to provide a uniform output temperature according to the required heating load of a typical room in the required heating hours. The phase change material (PCM) is embedded in a copper porous structure to enhance the rate of heat transfer and overcome the low thermal conductivity of PCMs. The geometrical parameters is first obtained from analysing the discharging process including the height, air channel and PCM shell widths and air mass flow rate according to the discharging time as well as the output temperature of the air. Then, the charging mechanism is assessed to find the required area for the employed rectangular heating element. The results show the significant advantages of composite metal foam/PCM-air heat exchanger in comparison with the PCM-only unit on both the discharging time (56.5% reduction) and the uniformity of output temperature. The system with the height of 30 cm, PCM and air channel thickness of 15 cm and 2 cm, respectively, and a depth of 1 m, is capable to provide the desired output temperature of 47 °C for almost 17.4 h with the air mass flow rate of 0.01 kg/s. The charging analyses shows that the dimensions of the required rectangular heating element with constant temperature of 100 °C is 15 × 60 cm located at both sides of the unit.

Abstract The objective of this numerical study is to develop a latent heat storage (LHS) air heater in both charging and discharging processes to find the geometrical and operating conditions for dwelling space heating. The aim of the storage heater is to provide a uniform output temperature according to the required heating load of a typical room in the required heating hours. The phase change material (PCM) is embedded in a copper porous structure to enhance the rate of heat transfer and overcome the low thermal conductivity of PCMs. The geometrical parameters is first obtained from analysing the discharging process including the height, air channel and PCM shell widths and air mass flow rate according to the discharging time as well as the output temperature of the air. Then, the charging mechanism is assessed to find the required area for the employed rectangular heating element. The results show the significant advantages of composite metal foam/PCM-air heat exchanger in comparison with the PCM-only unit on both the discharging time (56.5% reduction) and the uniformity of output temperature. The system with the height of 30 cm, PCM and air channel thickness of 15 cm and 2 cm, respectively, and a depth of 1 m, is capable to provide the desired output temperature of 47 °C for almost 17.4 h with the air mass flow rate of 0.01 kg/s. The charging analyses shows that the dimensions of the required rectangular heating element with constant temperature of 100 °C is 15 × 60 cm located at both sides of the unit.

The manufacture of 3D scaffolds with specific controlled porous architecture, defined microstructure and an adjustable degradation profile was achieved using two-photon polymerization (TPP) with a size of 2 × 4 × 2 mm(3). Scaffolds made from poly(D,L-lactide-co-ɛ-caprolactone) copolymer with varying lactic acid (LA) and ɛ -caprolactone (CL) ratios (LC16:4, 18:2 and 9:1) were generated via ring-opening-polymerization and photoactivation. The reactivity was quantified using photo-DSC, yielding a double bond conversion ranging from 70% to 90%. The pore sizes for all LC scaffolds were see 300 μm and throat sizes varied from 152 to 177 μm. In vitro degradation was conducted at different temperatures; 37, 50 and 65 °C. Change in compressive properties immersed at 37 °C over time was also measured. Variations in thermal, degradation and mechanical properties of the LC scaffolds were related to the LA/CL ratio. Scaffold LC16:4 showed significantly lower glass transition temperature (T g) (4.8 °C) in comparison with the LC 18:2 and 9:1 (see 32 °C). Rates of mass loss for the LC16:4 scaffolds at all temperatures were significantly lower than that for LC18:2 and 9:1. The degradation activation energies for scaffold materials ranged from 82.7 to 94.9 kJ mol(-1). A prediction for degradation time was applied through a correlation between long-term degradation studies at 37 °C and short-term studies at elevated temperatures (50 and 65 °C) using the half-life of mass loss (Time (M1/2)) parameter. However, the initial compressive moduli for LC18:2 and 9:1 scaffolds were 7 to 14 times higher than LC16:4 (see 0.27) which was suggested to be due to its higher CL content (20%). All scaffolds showed a gradual loss in their compressive strength and modulus over time as a result of progressive mass loss over time. The manufacturing process utilized and the scaffolds produced have potential for use in tissue engineering and regenerative medicine applications.

The manufacture of 3D scaffolds with specific controlled porous architecture, defined microstructure and an adjustable degradation profile was achieved using two-photon polymerization (TPP) with a size of 2 × 4 × 2 mm(3). Scaffolds made from poly(D,L-lactide-co-ɛ-caprolactone) copolymer with varying lactic acid (LA) and ɛ -caprolactone (CL) ratios (LC16:4, 18:2 and 9:1) were generated via ring-opening-polymerization and photoactivation. The reactivity was quantified using photo-DSC, yielding a double bond conversion ranging from 70% to 90%. The pore sizes for all LC scaffolds were see 300 μm and throat sizes varied from 152 to 177 μm. In vitro degradation was conducted at different temperatures; 37, 50 and 65 °C. Change in compressive properties immersed at 37 °C over time was also measured. Variations in thermal, degradation and mechanical properties of the LC scaffolds were related to the LA/CL ratio. Scaffold LC16:4 showed significantly lower glass transition temperature (T g) (4.8 °C) in comparison with the LC 18:2 and 9:1 (see 32 °C). Rates of mass loss for the LC16:4 scaffolds at all temperatures were significantly lower than that for LC18:2 and 9:1. The degradation activation energies for scaffold materials ranged from 82.7 to 94.9 kJ mol(-1). A prediction for degradation time was applied through a correlation between long-term degradation studies at 37 °C and short-term studies at elevated temperatures (50 and 65 °C) using the half-life of mass loss (Time (M1/2)) parameter. However, the initial compressive moduli for LC18:2 and 9:1 scaffolds were 7 to 14 times higher than LC16:4 (see 0.27) which was suggested to be due to its higher CL content (20%). All scaffolds showed a gradual loss in their compressive strength and modulus over time as a result of progressive mass loss over time. The manufacturing process utilized and the scaffolds produced have potential for use in tissue engineering and regenerative medicine applications.