No abstract

No abstract

Composite graphite plates (CGPs) have attracted interest due to competitive benefits such as cheaper cost, lower density, and excellent corrosion resistance. Their mechanical and electrical qualities, on the other hand, are insufficient to meet the PEMFC's standards. In this study, a structural design of CGPs with different functional layers is proposed. In order to attain higher electrical conductivity and air tightness, the surface layer was molded graphite plate with resin infiltration treatment, and the middle layer was a carbon fiber fabric (CFF) as a reinforcing functional layer. The results show that the surface layer prepared from flake graphite (FGL) have a density of 2.1 g/cm3, while the surface layer made by expanded graphite (EGL) have a density of about 1.7 g/cm3 with higher porosity. As a result, the CGPs prepared by using FGL as the surface layer has higher airtightness and structural strength. The CFFs must be oxidized to promote the effective bonding with resin, and the addition of carbon nanotubes (CNTs) can effectively improve the interfacial bonding and reduce the area specific resistance (ASR). At a resin content of 20 wt.% with 2 wt.% CNTs in resin, a CGPs with multilayer construction possess a thickness of 0.4 mm, an in-plane conductivity of 446 S/cm, an ASR of 6.4 mΩ·cm2, a flexural strength of 72 MPa, and a Helium permeability of around 4.4*10-6 std cm3/cm2·s. In addition, the graphite particle size has a significant effect on the electrical conductivity, and the analysis on the cross-sectional morphology of the surface layer indicated that this is primarily due to the anisotropic properties of graphite, with larger particle tends to be more orderly distributed after compression resulting in higher in-plane conductivity.

The present study proposes a rapid cooling method based on vacuum spray cooling, and establishes an experimental system to study the cooling performance of this method by taking tofu as an example. In this study, the effects of vacuum spray cooling, vacuum cooling and immersion vacuum cooling on the cooling rate, water holding rate, PH, TPA and other properties of tofu were compared. The total cooling time of vacuum spray cooling (13.86 min) was shorter than that of immersion vacuum cooling (33.39 min) but longer than that of vacuum cooling (10.64 min) for a temperature decrease from 70°C to 4°C. For weight loss from 70°C to 4°C, vacuum spray cooling (2.96%) was significantly less than that of vacuum cooling (10.21%). The PH value after cooling has no significant difference, but the color difference and water holding capacity of the sample after vacuum spray cooling are obviously better. However, the textural properties of the sample cooled by vacuum spray cooling were close to (for elasticity and viscosity) and better (for hardness and chewiness) than those of immersion vacuum cooling. In addition, compared with the two cooling methods in terms of storage, vacuum spray cooling can effectively maintain the moisture content, water holding rate, PH, chromatism and TPA of tofu, thus extending the fresh-keeping period of tofu. The conclusions of this paper provide theoretical support for prolonging the preservation period of food and optimizing the cooling process.