Craig R. Bradshaw

Bio: Craig R. Bradshaw is an academic researcher from Oklahoma State University–Stillwater. The author has contributed to research in topics: Gas compressor & Heat exchanger. The author has an hindex of 10, co-authored 44 publications receiving 377 citations. Previous affiliations of Craig R. Bradshaw include Purdue University.

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

Abstract: A comprehensive model of a miniature-scale linear compressor for electronics cooling is presented. Linear compressors are appealing for refrigeration applications in electronics cooling. A small number of moving components translate to less theoretical frictional losses and the possibility that this technology could scale to smaller physical sizes better than conventional compressors. The model developed here incorporates all of the major components of the linear compressor including dynamics associated with the piston motion. The results of the compressor model were validated using experimental data from a prototype linear compressor. The prototype compressor has an overall displacement of approximately 3 cm 3 , an average stroke of 0.6 cm. The prototype compressor was custom built for this work and utilizes custom parts with the exception of the mechanical springs and the linear motor. The model results showed good agreement when validated against the experimental results. The piston stroke is predicted within 1.3% MAE. The volumetric and overall isentropic efficiencies are predicted within 24% and 31%, MAE respectively.

Linear compressors for electronics cooling: energy recovery and its benefits.

Abstract: A comprehensive model of a linear compressor for electronics cooling was previously presented by Bradshaw et al. (2011) then enhanced and used for a sensitivity analysis of the leakage gap, eccentricity, and piston geometry by Bradshaw et al. (2013). The current work utilizes the previously developed model to explore the energy recovery characteristics of a linear compressor as compared to those of a reciprocating compressor. The impact of dead (clearance) volume on both a linear and reciprocating compressor is analyzed. In contrast to a reciprocating compressor the overall isentropic efficiency of the linear compressor remains relatively unaffected by an increase in dead volume up to a certain point. This behavior is attributed to the ability of the linear compressor to recapture the energy of the compressed gas during the expansion process. This characteristic behavior allows a linear compressor to be used for efficient capacity control from roughly 35–100%.

Modeling of a semi-hermetic CO2 reciprocating compressor including lubrication submodels for piston rings and bearings.

Abstract: A comprehensive model for a semi-hermetic CO2 reciprocating compressor is presented. This comprehensive model is composed of three main sub-models simulating the geometry and kinematics, the compression process, and frictional power loss. Valve and leakage sub-models are included in the compression process model. The frictional power loss model includes the friction at the bearings and between the piston ring and cylinder wall. The predicted results of the comprehensive model are validated using external compressor performance measurements of compressor input power and mass flow rate. The mass flow rate and compressor input power are predicted to within 4.03% and 6.43% mean absolute error, respectively, compared to the experimental datum. Additionally, a parametric study is presented which investigates compressor performance as a function of the stroke-to-bore ratio.

A Comprehensive Model of a Novel Rotating Spool Compressor

Abstract: A comprehensive simulation model of a novel rotating spool compressor is presented. The spool compressor provides a new rotary compression mechanism with easily manufactured components. A detailed analytical geometry model of the spool compressor is presented, which includes the geometry of the vane. This geometry model is included in an overall comprehensive compressor model that includes sub-models for friction, leakage, and heat transfer. The results of the comprehensive model were validated using experimental data from a prototype compressor. The prototype compressor has an overall displacement of 23.9 cm3, and was operated using R410A as the working fluid. The model predicts the volumetric efficiency, discharge temperature, and shaft power of the prototype compressor to within 3.13% MAE, 16.5 K and −13.2 W average deviation, respectively. The trends and spread in the data indicate that additional effort should be focused on the operation of the active sealing elements within the compressor.

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

Abstract: 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.

Review of the current technologies and performances of hydrogen compression for stationary and automotive applications

Abstract: Hydrogen could play an important role as an energy vector in the coming decades in the framework of Sustainable Development. It is the universe's most abundant element and thus a never-ending source of energy. Hydrogen can be directly converted into electric energy by using fuel cells without producing toxic gases. It can also be produced by renewable sources such as biomass, solar and wind energies with no impact for the environment. However, although hydrogen represents a promising eco-friendly solution for energy transition, several issues related to its storage and delivery remain to be solved if it is to be widely used in both stationary and automotive applications. Hydrogen has the lowest volumetric energy density among the commonly used fuels, i.e., 0.01079 MJ/L at atmospheric pressure. Compression is the direct solution to overcome this obstacle. High pressure levels can give satisfying energy densities. The present review summarises the state of the art of the most classical hydrogen compression technologies. We shall present the technical and design features of mechanical compressors, i.e., reciprocating, diaphragm, linear and ionic liquid compressors, as well as of innovative non-mechanical technologies specifically conceived for hydrogen applications, such as cryogenic, metal hydride, electrochemical and adsorption compressors. The basic operating principles and the potential performance levels for each compression technology are analysed. Specifically, their current uses in hydrogen applications and their technological limits are described along with proposals of possible ways of improving their performance levels.

A review of linear compressors for refrigeration

Abstract: Linear compressor has no crank mechanism compared with conventional reciprocating compressor. This allows higher efficiency, oil-free operation, lower cost and smaller size when linear compressors are used for vapour compression refrigeration (VCR) system. Typically, a linear compressor consists of a linear motor (connected to a piston) and suspension springs, operated at resonant frequency. This paper presents a review of linear compressors for refrigeration system. Different designs and modelling of linear compressors for both domestic refrigeration and electronics cooling (miniature VCR system) are discussed. Key characteristics of linear compressor are also described, including motor type, compressor loss, piston sensing and control, piston drift and resonance. The challenges associated with the linear compressors are also discussed to provide a comprehensive review of the technology for research and development in future.

A State-of-the-Art Review of Compact Vapor Compression Refrigeration Systems and Their Applications

Abstract: We present a critical review of the literature on the fundamentals, design, and application aspects of compact and miniature mechanical vapor compression refrigeration systems. Examples of such systems are those envisaged for electronics and personal cooling. In comparison to other refrigeration technologies (e.g., solid-state), vapor compression enables the attainment of low evaporating temperatures while maintaining a large cooling capacity per unit power input to the system. Over the past decade, there have been a significant number of studies devoted to the miniaturization of system components, with the most critical being the compressor. When compared with competing cooling technologies, such as flow boiling in microchannels, jet impingement, and spray cooling, refrigeration is the only one capable of lowering the junction temperature to values below the ambient temperature. The combination of vapor compression refrigeration with the aforementioned technologies is also possible, necessary, and benefi...