Calorimetric analysis of ice onset temperature during cryoablation: a model approach to identify early predictors of effective applications

Aim of the present study is to analyze thermal events occurring during cryoablation. Different bovine liver samples underwent freezing cycles at different cooling rate (from 0.0075 to 25 K/min). Ice onset temperature and specific latent heat capacity of the ice formation process were measured according to differential scanning calorimetry signals. A computational model of the thermal events occurring during cryoablation was compiled using Neumann’s analytical solution. Latent heat (#1 = 139.8 ± 7.4 J/g, #2 = 147.8 ± 7.9 J/g, #3 = 159.0 ± 4.1 J/g) of all liver samples was independent of the ice onset temperature, but linearly dependent on the water content. Ice onset temperature was proportional to the logarithm of the cooling rate in the range 5 ÷ 25 K/min (#3a = − 12.2 °C, #3b = − 16.2 °C, #3c = − 6.6 °C at 5K/min; #3a = − 16.5 °C, #3b = − 19.3 °C, #3c = − 11.6 °C at 25 K/min). Ice onset temperature was associated with both the way in which the heat involved into the phase transition was delivered and with the thermal gradient inside the tissue. Ice onset temperature should be evaluated in the early phase of the ablation to tailor cryoenergy delivery. In order to obtain low ice trigger temperatures and consequent low ablation temperatures a high cooling rate is necessary.

Solar Photovoltaic Panels with Finned Phase Change Material Heat Sinks

Phase change material (PCM) based passive cooling of photovoltaics (PV) can be highly productive due to high latent heat capacity. However, the low rate of heat transfer limits its usefulness. Thus, the presented work aims at the improvement in PV cooling by using finned PCM (FPCM) heat sinks. In the present study, PCM heat sink and FPCM heat sinks were investigated numerically for PV cooling and the extracted heat is used for space heating. 4 kWp PV, PV-PCM and PV-FPCM systems were studied under the weather conditions of Southeast of England. It was observed that the PCM heat sinks can drop the peak PV temperature by 13 K, whereas FPCM heat sinks can enhance the PV cooling by 19 K. The PCM heat sinks can increase the PV electrical efficiency from 13% to 14%. Moreover, the daily electricity generation can be boosted by 7% using PCM and 8% by using FPCM heat sinks. In addition, 7 kWh of thermal output was achieved using the FPCM heat sink, and the overall efficiency of system increased from 13% to 19%.

Sustainable fiber reinforced cementitious panels containing PCM: Mechanical and thermal performance

An experimental study was planned and executed for the application of Phase Change Materials (PCM) containing fiber-reinforced cementitious panels on buildings. The objective of the research was to enhance the thermal performance of the panels. Panels with the dimensions of 60x120x2.5 cm were produced and experimental investigations about the thermal and the mechanical performance of the composites were carried out. PCM containing composites showed higher latent heat capacity and lower thermal conductivity. Reinforcement with chopped fibers compensated the strength loss due to PCM in cementitious panels. Specific fracture energy of the panels increased with increase of PCM ratio. PCM containing fiber reinforced cementitious panels showed great potential for energy efficient buildings with enhanced thermal and mechanical properties.

The effect of PCM layer on the natural air flow movement in the façade cavity of BiPV system

The incorporation of a phase change material (PCM) in building integrated photovoltaic (BiPV) façade can be applied to improve its thermal performance including more effective electrical conversion, however their real interaction needs to be investigated at adequate level. The aim of the presented paper is focused on the application of a material with high latent heat capacity based on PCM in the structure of double-skin BiPV façade. The key aspect concerns on an analysis of natural air flow movement affected by the storing/releasing heat energy from the PCM during daytime/night-time of days. The experimental campaign was performed using an experimental outdoor test cell where two full-scale façade samples (reference BiPV and experimental BiPV/PCM) were investigated. The strong effect of thermal inertia of the PCM identified by experimental measurements was observed on the façade air cavity temperature and air flow movement. Experimental results revealed that natural air flow regimes in façade cavities are nearly equal in the daytime, but in the night-time are totally different. The thermal emission from PCM increase the air temperature in the façade cavity and increase the velocity of air flow movement (PCM started solidified), mainly in the night-time.

Energy Performance of an Encapsulated Phase Change Material PV/T System

This study aimed to investigate the performance of a novel encapsulated phase change material (PCM) photovoltaic/thermal (PV/T) system. A PCM, which has a high latent heat capacity, can absorb energy from a PV cell and reduce the operating temperature, improving both the electrical and thermal efficiencies of the panel. In this study, a computer model based on a PCM PV/T panel is developed, and its accuracy is verified using experimental data. The effect of the phase change temperature on the performance of the panel was analyzed by numerical simulation. When the phase change temperature was 30.1 °C, the system exhibited a maximum electrical efficiency of 8.2% and a thermal efficiency of 71.8%. When the phase change temperature was 20.24 °C, the system had a maximum exergy efficiency of 33.7%. In general, the temperature of the PCM integrated into the PV/T system should not be too high.

The Effects of Nucleating Agents on Phase Transition of a Salt Hydrate Phase-Change Material for Thermal Energy Storage Heat Exchangers

Salt hydrate based Phase-Change Materials (PCM) typically store and discharge large quantities of heat during their phase transition process. However, the repeated use of these PCM, especially when they are completely dehydrated and superheated in a cyclic process, is impeded by certain irreversible behavior. These include (1) phase segregation: where the PCM degrades to forms a lower hydrate during phase transition while losing its storage capacity, and (2) subcooling: when crystallization and rehydration from the liquid PCM state occurs at a temperature lower than their phase transition point. Higher degrees of subcooling (ΔTs), which is how much the PCM has to be super cooled below its phase transition temperature for crystallization to begin, adversely affects its performance and in some cases renders it ineffective. Lithium Nitrate Trihydrate [(LNT) LiNO3.3H2O] is one of the more promising candidate among these inorganic salt hydrate PCMs because of its rather stable phase change behavior and relatively very high latent heat capacity (282kJ/kg). Nevertheless, when completely in superheated liquid phase, it requires a high degree of subcooling (ΔTs > 20°C), which limits its utility. This study reports a novel nucleating agent — Zinc Nitrate Hexahydrate (ZNH) that reduces the subcooling to below 5°C (1000 Cycles). However, the latent heat capacity reduced to half the initial value after the cycling.

Thermal Response of Mortar Panels with Different Forms of Macro-Encapsulated Phase Change Materials: A Finite Element Study

This paper presents a numerical investigation of thermal response of mortar panels, incorporating macro-encapsulated paraffin in different forms. Two types of macro capsules were fabricated and tested in this study using an instrumented hot plate device. The experimental results show that macro encapsulated paraffin reduced the temperature and increased time lag in the mortar panels due to the latent heat capacity of paraffin. Finite element models adopting the effective heat capacity method to model phase change effects were able to capture the overall thermal response of panels incorporated with paraffin well. Then, a parametric study was conducted using the validated finite element (FE) modelling technique to investigate the effects of different forms of macro capsules, the quantity of paraffin and the position of macro capsules. It was found that the tube and sphere macro capsules showed similar thermal responses, while the plate shaped capsules may cause a non-uniform temperature distribution in mortar panels. The quantity and position of paraffin have significant effects on the thermal response of the mortal panels. A higher paraffin content results in a significantly longer temperature lag and a lower temperature during the phase transition of paraffin. Furthermore, placing the paraffin away from the heating face can cause a longer temperature lag on the other face, which is desirable for building façade applications.