Parametric performance of circumferentially grooved heat pipes with homogeneous and graded-porosity slab wicks at cryogenic temperatures

A recently developed, potentially high-performance nonarterial wick has been extensively tested. This slab wick has an axially varying porosity which can be tailored to match the local stress imposed on the wick. The purpose of the tests was to establish the usefulness of the graded-porosity slab wick at cryogenic temperatures between 110 K and 260 K, with methane and ethane as working fluids. For comparison, a homogeneous (i.e., uniform porosity) slab wick was also tested. The tests included: (1) maximum heat pipe performance as a function of fluid inventory, (2) maximum performance as a function of operating temperature, (3) maximum performance as a function of evaporator elevation, and (4) influence of slab wick orientation on performance. The experimental data was compared with theoretical predictions obtained with the computer program GRADE

Best of Both Worlds: Foreign Language Preparation for Purdue University’s Undergraduate Global Engineering Education Program

Over the years, Purdue University has drastically increased the number of engineering students studying and interning abroad from less than 3% in 2000 to more than 10% in 2010. In order to increase the capacity of global engineering education curriculum, there is a need to create different study abroad programs to suit different student interests. Yet, the need of foreign language preparation remains in question. At Purdue University, researchers and administrators observed that students often self-select into study abroad programs of varying intensity according to the varying foreign language and GPA requirements. Case studies of student participants from four different Purdue education abroad programs will be demonstrated in this paper in the following order: (1) Global Engineering Alliance for Research and Education (GEARE), (2) International Research and Education for Engineering (IREE), (3) Global Internship, and (4) China Maymester Abroad Program. These case studies will be used to illustrate the importance of foreign language preparation and the varying needs. These results will also demonstrate that the achieved level of foreign language competency impacts technical outcomes and engineering professionalism

Analytical prediction of stress and strain in adhesive tube-to-tube joints under thermal expansion/contraction

Adhesive joints are widely applied and studied for various industrial applications. The interest in adhesive joints has expanded to include heating, ventilation, air conditioning, and refrigeration (HVAC&R) systems having a significant number of joints employed for manufacturing. This study investigates an analytical modeling approach for predicting joint stress and strain distribution under static loading with thermal strain. A review of modeling techniques identified the need to develop a joint analytical model under loading conditions representative of HVAC&R applications. The details of the model, governing equations, assumptions, boundary conditions, and solution techniques are first reported. The model is validated via comparison to existing results before performing parametric studies to provide insights on the influences of thermal expansion and inner tube pressure on possible failure. It is found that the joint overlap length plays an important role in stress distribution, while the adhesive thickness has less impact. Overall, the results indicate that static loading failure is not likely a concern for joints in HVAC&R systems, but the thermal strain and stress induced by temperature fluctuations must be carefully considered. This modeling effort establishes a framework that can be used to generate criteria and instructions on designing adhesive joints across different HVAC&R</p

Optimization of Electrostatically Actuated Miniature Compressors for Electronics Cooling

This paper explores the feasibility of using electrostatically actuated diaphragm compressors in a miniature-scale refrigeration system for electronics cooling. A previously developed experimentally validated analytical model for the diaphragm compressor is used in conjunction with an optimization approach to determine the required dimensions for the compressor. The analysis reveals that the pressure rise and volume flow rate required for the electronics cooling application are not achieved using a single compressor because of material property limitations. A three-dimensional array of compressors is proposed instead with which the cooling requirements and the size restrictions for electronics cooling applications may be simultaneously satisfied

A Virtual EXV Mass Flow Sensor for Applications With Two-Phase Flow Inlet Conditions

In conventional vapor compression systems, electronic expansion valves (EXVs) are used for refrigerant flow control. Subcooled refrigerant enters the expansion device and is expanded to the evaporation pressure while the valve opening is modified to achieve the desired mass flowrate. The relationship between the inlet and outlet conditions, the opening, and the mass flowrate has been extensively studied, e.g. by Park et al. (2007) and appropriate empirical correlations have been developed. However, for certain operating conditions (e.g. low refrigerant charge) or applications that generally have two-phase inlet conditions (e.g. balancing valves used in a hybrid control scheme as proposed by Kim et al. (2008)), these correlations are not applicable, since even low inlet vapor fractions lead to a significant reduction of the valve mass flowrate at a given opening. This paper proposes a continuous correlation that can be used for both two-phase and subcooled valve inlet conditions. The benefit of the continuity is that there is a smooth transition between subcooled and two-phase inlet conditions, which is essential for control and simulation purposes. The new correlation employs the Buckingham-Pi theorem as proposed by Buckingham (1914). The selected dimensionless Pi-groups describe opening of the valve, subcooling, inlet and outlet pressures, driving pressure difference across the valve, inlet density, surface tension, and viscosity. The data that was used to determine the coefficients of the correlation was taken on a dedicated valve test stand, which was sized for the per-circuit capacity of a typical 5-ton R410A heat pump and a 3-ton R404A large room cooling system. The purpose of these tests was mainly to map the valves for the low pressure drops, high inlet qualities and large valve openings that occur when they are used as balancing valves in a hybrid control approach. Two commercially available valves of different rated capacity were tested. Due to the much higher valve capacity for subcooled inlet conditions, valve openings of less than 5% occurred in that case. This led to an accuracy of the correlation for these points that is less than what typically can be found for correlations with subcooled inlet conditions in the open literature. However, for two-phase flow inlet conditions, the resulting RMS of 1.0 g/s for the 8-PI correlation is sufficiently small to use the approach for estimating the refrigerant mass flow and using the EXV as a virtual flow sensor. The limitations of this approach in practical applications, as well as possible applications in fault detection and diagnostics are shown for application as balancing valves within a 5-ton R410A heat pump and a 3-ton R404A large room cooling system

Sensitivity Analysis of a Comprehensive Model for a Miniature-Scale Linear Compressor for Electronics Cooling

A comprehensive model of a linear compressor for electronics cooling was previously presented by Bradshaw et al. (2011). The current study expands upon this work by first developing methods for predicting the resonant frequency of a linear compressor and for controlling its piston stroke. Key parameters governing compressor performance – leakage gap, eccentricity, and piston geometry – are explored using a sensitivity analysis. It is demonstrated that for optimum performance, the leakage gap and frictional parameters should be minimized. In addition, the ratio of piston stroke to diameter should not exceed a value of one to minimize friction and leakage losses, but should be large enough to preclude the need for an oversized motor. An improved linear compressor design is proposed for an electronics cooling application, with a predicted cooling capacity of 200 W a cylindrical compressor package size of diameter 50.3 mm and length 102 mm