The Influence Of Thermal Contact Resistance On Protective Performance Of Firefighter-clothing

This article discuss the thermal performance test of different thermal protective fabrics, comparative study on three layers of domestic and foreign firefighter-clothing insulation structure,According to two kinds of thermal protection test:TPP/RPP methods and Stored energy method explore the factors affecting the performance of thermal protective fabric and thermal stored energy. According to the heat transfer mechanism of the protection system, the thermal resistance of fabric composition provide a certain protection to heat transfer, meanwhile the surface properties are influenced by fabric material properties, surface structure and the volume of air caused by inadequate contact between fabric and human body skin, make different degree of contact between fabric and human skin and affect the heat transfer greatly.So this paper introduces the concept the contact thermal resistance, especially when simulating human body movement with compression, the existence of the contact thermal resistance can significantly reduce heat flow. Based on three layer firefighter protection system, modify the thermal insulation layer with a variety of surface properties. Three groups with different surface morphology fabric combination of two controlled trials were made. Explore factors of decrease of thermal energy storage release that affect the thermal protective performance, to explore the effect of contact thermal resistance to the thermal protective performance, provide a theoretical support for the development of new materials and the application of new structure.The experiment chose outer fabric layer with better performance used in domestic and overseas. PBI / Kevlar as the fire protective layer, the Nomex with PTFE membrane laminated fabric as the Waterproof and moisture permeable layer. Nomex felt as the thermal Insulating layer(non-woven method). Particularly adding a morphology layer change the degree of contact between the thermal insulating layer and sensor. In the experiment chose four different morphology layer depending on the characteristics of each: Smooth thin layer of polyester, Mesh gauze full of holes,Corduroy with different bump intervals and homemade morphology layer withdifferent interval. Firstly, measure physical properties of the layers of fabric. In today’s firefighter-clothing practical three-layer structure as the base type.Morphology layer was added to get different combinations, Select high performance fire protection layer and waterproof breathable layer of stable protective effect.Exclude inconsistent stored heat absorbing impact because of different combinations.Measure the physical properties of layers with different morphologies and their impact on thermal resistance.By comparing the Second-degree burn time of different combinations used TPP/RPP approach or Stored energy approach. Analysis showed: In the TPP/RPP approach experiments, the TPP value is larger, the better the thermal protective performance we get. The influence factors of thermal protection mainly combined thickness, density, air content(before and after the extrusion), degree of contact. For the fabric with same fiber, The TPP value and the fabric thickness, surface density has a positive correlation. In thermal stored energy experiments, mainly is the energy storage release methods affect the minimum exposure time cause second-degree burn time: the release by Natural or release by compress, compress time, the addition of interval and the physical properties of the interval. In the stored energy experiments to join easily deformed interval is beneficial to improve the thermal protective performance of fabric combination.In-depth analysis of the heat flow curve. Heat flow trends in the different test methods indicate,Second-degree burn time is actually control by the total heat flux received by the sensor. The total heat flow is greater, the minimum exposure time causing second-degree burn is shorter. On the contrary, the total heat flow is smaller,minimum exposure time causing second-degree burn is longer.In this experiment, using thermal protective performance tester(TPP) standard heating process, Data collection and analysis of the second-degree burn time is mainly supported by NI virtual instruments, use Labview : a virtual temperature tester by graphical language programming Collect temperature and heat flow. Finally using Henriques skin burn integral model for the analysis of the time causing the second-degree burn, to get the minimum exposure time for second-degree burn.