This chapter is designed to provide detailed and practical information on methods for measuring viscosity for the nonexpert. The chapter starts with a brief theoretical and mathematical overview of viscosity and presents correlations that can be used to account for the effects of pressure and temperature. Next we describe the theory of operation and advantages and disadvantages of the major measurement methods, including drag‐type, flow‐type, and vibrational viscometers. The chapter includes tables of information on commercially available viscometers, reviews the ASTM standards for measuring viscosity, and guides the reader through a set of questions/answers that can be used to select the appropriate viscometer for a given application.
The most significant mechanical difference between materials classified as “fluids” and those classified as solids is in their reaction to shear stresses. This chapter begins by discussing the units by which viscosity is measured. Then the distinction between the larger field of rheology and its subfield viscometry is made in the context of differentiating between the so‐called Newtonian and non‐Newtonian fluids. The chapter provides a brief theoretical and mathematical overview of viscosity. It provides detailed and practical information on methods for measuring viscosity. The chapter develops the mathematical formulations governing viscosity, and explains the roles and relations between “shear” viscosity and “bulk” viscosity. It focuses on the use of laboratory‐type viscometers; however, some information is included on the use of process viscometers. The ASTM viscosity standards come in two types: (a) standards focused on methods (method standards) and (b) standards based on materials (material standards).
Recent efforts have lead to the development of a silicon microfluidic cooling device known as the micro-Columnated Loop Heat Pipe (μCLHP) [1] [2] [3] . The μCLHP, like a traditional heat pipe, utilizes phase change of a liquid to rapidly draw heat away from a concentrated hot spot. Proper hermetic packaging of this device is critical for the reliable testing of the recirculating fluid. This work presents a novel approach to filling and hermetically sealing the μCLHP. A miniature valve (Beswick M3SV-N) is bonded to the silicon fill ports of the μCLHP. The use of a resealable valve, as opposed to a permanent sealing method, allows the device to be filled, sealed, and then evacuated for testing with different fluids and at multiple pressures. Building on work by Murphy [4], the fill ports on the μCLHP were metalized with a 10nm Cr - 200 nm Ni - 10 nm Au stack. Then a lead based solder was used to bond the stainless steel adapter to the metalized layers. Hermeticity testing of devices sealed using these miniature valves demonstrated average hourly percent weight losses between 0.170 % – 0.821 %. While this bonding method has been developed specifically for the μCLHP, it is broadly applicable to most ceramic microfluidic devices, especially those fabricated from silicon and glass. Due to the time intensive manufacturing process of microfluidic devices made from these hard materials, a novel, robust, resealing method that allows reuse of a single silicon microfluidic device for multiple test conditions is highly desirable.
Recent efforts have led to the development of a silicon microfluidic cooling device known as the microcolumnated loop heat pipe (μCLHP). The μCLHP, like a traditional heat pipe, utilizes phase change of a liquid to rapidly draw heat away from a concentrated hot spot. Proper gas-tight packaging of this device is critical for the reliable testing of the recirculating fluid. This work presents a novel approach to filling and sealing the μCLHP. A miniature valve (Beswick M3SV-N) is bonded to the silicon fill ports of the μCLHP. The use of a resealable valve, as opposed to a permanent sealing method, allows the device to be filled, sealed, and then evacuated for testing with different fluids and at multiple pressures. Building on earlier work, the fill ports on the μCLHP were metalized with a Cr (10 nm)/Ni (200 nm)/Au (10 nm) stack. Then a lead-based solder was used to bond the stainless steel adapter to the metalized layers. Leak testing of devices sealed using these miniature valves demonstrated average hourly percent weight losses between 0.17% and 0.82%. While this bonding method has been developed specifically for the μCLHP, it is broadly applicable to most ceramic microfluidic devices, especially those fabricated from silicon and glass. Due to the time-intensive manufacturing process of microfluidic devices made from these hard materials, a novel, robust, resealing method that allows reuse of a single silicon microfluidic device for multiple test conditions is highly desirable.
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