Solid-State Laser Source of Tunable Narrow-Bandwidth Ultraviolet Radiation

A solid-state laser source of tunable and narrow-bandwidth UV light is disclosed. The system relies on light from a diode laser that preferably generates light at infrared frequencies. The light from the seed diode laser is pulse amplified in a light amplifier, and converted into the ultraviolet by frequency tripling, quadrupling, or quintupling the infrared light. The narrow bandwidth, or relatively pure light, of the seed laser is preserved, and the pulse amplifier generates high peak light powers to increase the efficiency of the nonlinear crystals in the frequency conversion stage. Higher output powers may be obtained by adding a fiber amplifier to power amplify the pulsed laser light prior to conversion

Method for Determining Air Side Convective Heat Transfer Coefficient Using Infrared Thermography

Air side convective heat transfer coefficients are among the most important parameters to know when modeling thermal systems due to their dominant impact on the overall heat transfer coefficient. Local air side convective heat transfer coefficients can often prove challenging to measure experimentally due to limitations with sensor accuracy, complexity of surface geometries, and changes to the heat transfer due to the sensor itself. Infrared thermography allows local heat transfer coefficients to be accurately determined for many different surface geometries in a manner which does not impact the results. Moreover, when determining convective heat transfer coefficients for a large number of samples, it is less costly in terms of both time and materials than other experimental methods. The method determines the heat transfer coefficient for an arbitrary region by determining the rate at which the surface temperature changes due to a step change in air temperature. To utilize the method a simple calibration is first done to determine the local thermal time constant under natural convection. Alternatively, if the thermal properties of the object are well known, a model may be used. In subsequent tests, the ratio of thermal time constant to that from the calibration test can be determined. As the material properties of the solid object are unchanged, the convective heat transfer coefficient scales inversely with the thermal time constant. A computer script has been created which automates the entire analysis process with the exception of determining the region of interest. The experimental method has been validated by comparison to other experimental methods, values from literature, and numerical simulations

Development of the Sandia Cooler.

This report describes an FY13 effort to develop the latest version of the Sandia Cooler, a breakthrough technology for air-cooled heat exchangers that was developed at Sandia National Laboratories. The project was focused on fabrication, assembly and demonstration of ten prototype systems for the cooling of high power density electronics, specifically high performance desktop computers (CPUs). In addition, computational simulation and experimentation was carried out to fully understand the performance characteristics of each of the key design aspects. This work culminated in a parameter and scaling study that now provides a design framework, including a number of design and analysis tools, for Sandia Cooler development for applications beyond CPU cooling

A fundamentally new approach to air-cooled heat exchangers.

We describe breakthrough results obtained in a feasibility study of a fundamentally new architecture for air-cooled heat exchangers. A longstanding but largely unrealized opportunity in energy efficiency concerns the performance of air-cooled heat exchangers used in air conditioners, heat pumps, and refrigeration equipment. In the case of residential air conditioners, for example, the typical performance of the air cooled heat exchangers used for condensers and evaporators is at best marginal from the standpoint the of achieving maximum the possible coefficient of performance (COP). If by some means it were possible to reduce the thermal resistance of these heat exchangers to a negligible level, a typical energy savings of order 30% could be immediately realized. It has long been known that a several-fold increase in heat exchanger size, in conjunction with the use of much higher volumetric flow rates, provides a straight-forward path to this goal but is not practical from the standpoint of real world applications. The tension in the market place between the need for energy efficiency and logistical considerations such as equipment size, cost and operating noise has resulted in a compromise that is far from ideal. This is the reason that a typical residential air conditioner exhibits significant sensitivity to reductions in fan speed and/or fouling of the heat exchanger surface. The prevailing wisdom is that little can be done to improve this situation; the 'fan-plus-finned-heat-sink' heat exchanger architecture used throughout the energy sector represents an extremely mature technology for which there is little opportunity for further optimization. But the fact remains that conventional fan-plus-finned-heat-sink technology simply doesn't work that well. Their primary physical limitation to performance (i.e. low thermal resistance) is the boundary layer of motionless air that adheres to and envelops all surfaces of the heat exchanger. Within this boundary layer region, diffusive transport is the dominant mechanism for heat transfer. The resulting thermal bottleneck largely determines the thermal resistance of the heat exchanger. No one has yet devised a practical solution to the boundary layer problem. Another longstanding problem is inevitable fouling of the heat exchanger surface over time by particulate matter and other airborne contaminants. This problem is especially important in residential air conditioner systems where often little or no preventative maintenance is practiced. The heat sink fouling problem also remains unsolved. The third major problem (alluded to earlier) concerns inadequate airflow to heat exchanger resulting from restrictions on fan noise. The air-cooled heat exchanger described here solves all of the above three problems simultaneously. The 'Air Bearing Heat Exchanger' provides a several-fold reduction in boundary layer thickness, intrinsic immunity to heat sink fouling, and drastic reductions in noise. It is also very practical from the standpoint of cost, complexity, ruggedness, etc. Successful development of this technology is also expected to have far reaching impact in the IT sector from the standpointpoint of solving the 'Thermal Brick Wall' problem (which currently limits CPU clocks speeds to {approx}3 GHz), and increasing concern about the the electrical power consumption of our nation's information technology infrastructure

Single-mode operation of a coiled multimode fiber amplifier

The authors report a new approach to obtain single-transverse-mode operation of a multimode fiber amplifier, in which the gain fiber is coiled to induce significant bend loss for all but the lowest-order mode. They have demonstrated this method by constructing a coiled amplifier using Yb-doped, double-clad fiber with a core diameter of 25 {micro}m and NA of {minus}0.1 (V {approx} 7.4). When operated as an ASE source, the output beam had an M{sup 2} value of 1.09 {+-} 0.09; when seeded at 1,064 nm, the slope efficiency was similar to that of an uncoiled amplifier. This technique does not require exotic fiber designs or increase system complexity and is inexpensive to implement. It will allow scaling of pulsed fiber lasers and amplifiers to significantly higher pulse energies and peak powers and cw fiber sources to higher average powers while maintaining excellent beam quality

Development of fiber-laser-based laser-induced fluorescence for detection of SO{sub 2}

Gaining a quantitative understanding of many aspects of the earth's climate system requires development of new detection methods for key atmospheric species and their incorporation into chemical sensors with high sensitivity, specificity, and time response. The authors have initiated a research program to develop these new chemical-sensing capabilities. The species they have targeted initially are oxides of nitrogen and sulfur, specifically NO and S0{sub 2} These molecules play a central role in the earth's climate, and anthropogenic activities (primarily fossil-fuel combustion) are the dominant source of both species. They are exploring the use of single-mode fiber lasers and amplifiers as compact, lightweight sources of tunable, narrow-bandwidth, deep-UV radiation. They have also begun spectroscopic studies to optimize UV laser-induced fluorescence for detection of S0{sub 2} with high sensitivity and specificity