Layer by Layer MLI Calculation Using a Separated Mode Equation

Abstract. Long endurance flight, on the order of days, is a leading flight performance characteristic for Unmanned Aerial Vehicles (UAVs). Liquid hydrogen (LH2) is well suited to providing multi-day flight times with a specific energy 2.8 times that of conventional kerosene based fuels. However, no such system of LH2 storage, delivery, and use is currently available for commercial UAVs. In this paper, we develop a light weight LH2 dewar for integration and testing in the proton exchange membrane (PEM) fuel cell powered, student designed and constructed, Genii UAV. The fuel tank design is general for scaling to suit various UAV platforms. A cylindrical vacuum-jacketed design with removable end caps was chosen to incorporate various fuel level gauging, pressurizing, and slosh mitigation systems. Heat and mechanical loadings were modeled to compare with experimental results. Mass performance of the fuel tank is characterized by the fraction of liquid hydrogen to full tank mass, and the insulation performance was characterized by effective thermal conductivity and boil-off rate.

Section: Numerical Analysis Of Heat Loadmentioning

confidence: 99%

Design of a reconfigurable liquid hydrogen fuel tank for use in the Genii unmanned aerial vehicle

Adam¹,

Leachman²

2014

“…Keller and Cunnington developed empirical relationships for several types of MLI based on a wide range of calorimetery data developed in the 1960s and 70s, and with the lack of any better alternatives, their relationships have become somewhat of an industry standard [14]. More recently, McIntosh developed a layer by layer calculation that attempts to move away from empirical relationships; however, multiple uncertainties, mostly with the netting spacer, that cannot be readily answered have led to this approach not being widely used [15]. With the use of discrete spacers, the new MLI developed by Quest and Ball appears to be an ideal candidate to apply such models with.…”

Section: Analytical Modelsmentioning

confidence: 99%

Thermal coupon testing of Load-Bearing Multilayer Insulation

Johnson¹,

Heckle²,

Hurd³

2014

Abstract. Advanced liquid hydrogen storage concepts being considered for long duration space travel incorporate refrigeration systems and cryocoolers to lower the heat load. Using a refrigeration loop to intercept the energy flowing through MLI to a liquid hydrogen tank at a temperature between the environment and the liquid hydrogen can lower the heat load on the propellant system by as much as 50%. However, the refrigeration loop requires structural integration into the MLI. Use of a more traditional concept of MLI underneath this refrigeration loop requires that a structural system be put in place to support the loop. Such structures, even when thermally optimized, present a relatively large parasitic heat load into the tank. Through NASA small business innovation research funding, Quest Thermal Group and Ball Aerospace have been developing a structural MLI based insulation system. These systems are designed with discrete polymeric spacers between reflective layers instead of either dacron or silk netting. The spacers (or posts) have an intrinsic structural capability that is beyond that of just supporting the internal insulation mechanical loads. This new MLI variant called Load Bearing MLI (LB-MLI) has been developed specifically for the application of supporting thermal shields within the insulation system. Test articles (coupons) of the new LB-MLI product were fabricated for thermal performance testing using liquid nitrogen at Kennedy Space Center (KSC) and using cryocooler based calorimetry at Florida State University. The test results and analysis are presented. Thermal models developed for correlation with the thermal testing results both at KSC and testing that was performed at Florida State University are also discussed.

“…aluminized mylar radiation shields with silk net spacers, Reference 6, equation (4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14).…”

Section: Heat Transfermentioning

confidence: 99%

“…Since the midaerospace cryogenic engineering has seen a sharp decline in the quantity of research. The subject of variable density multilayer insulation (VD-MLI) was pioneered and patented by McIntosh [7,8]. Many others studied the effects of layer density on MLI throughout the years preceding and innovation [9][10][11][12].…”

mentioning

confidence: 99%

Optimization of Layer Densities for Multilayered Insulation Systems

Johnson¹

2010

Numerous tests of various multilayer insulation systems have indicated that there are optimal densities for these systems. However, the only method of calculating this optimal density was by a complex physics based algorithm developed by McIntosh. In the much data were collected on the performance of these insulation systems with many different variables analyzed. All formulas generated included number of layers and layer density as geometric variables in solving for the heat flux, none of them was in a differentiable form for a single geometric variable. It was recently discovered that by equations became functions of layer density, temperatures, and material properties only. The thickness and number of layers of the blanket were merged into a layer density. These equations were then differentiated with respect to layer density. By setting the first derivative equal to zero, and solving for the layer density, the critical layer density was determined. This method was checked and validated using test data from the Multipurpose