Strategies to raise the off-design efficiency of chiller machines

Most HVAC systems in large buildings are equipped with centrifugal chillers which are typically designed for maximum efficiency at 70% at 80% of their full-load. But, below about 30% full-load, their part-load efficiency starts to deteriorate rapidly (increasing kilowatts per ton). For older centrifugal chillers, this rapid drop may start at even higher part-load, rendering their operation at low part-load undesirable. In many cases chillers are over-sized, forcing operation below 50% of the full-load most of the time. Furthermore, the field performance of most chiller machines is genearlly not documented, and there is no tradition of recording chiller performance history. There is growing incentive-driven interest in chiller monitoring. But, field visits, discussions with HVAC engineers and opinions from manufacturers have proven that virtually no chiller systems are currently monitored for kilowatts per ton. Only recently has field data gathering been initiated, and part-load performance of chillers in the field started drawing serious attention. The problem, however, still remains poorly disclosed to the end-user. As a result, chiller machines actually operate at much lower efficiency than the design values. There are opportunities for profoundly improving their field performance. Part-load operation is particularly poor for sites with single centrifugal chillers. This research is an appraisal of strategies for improving the part-load performance of chiller systems. A review of simulation results and field data indicate that chiller machines operate at higher kilowatts per ton than allowed for by current technology. Energy consumption of various chiller types and configurations for a generic building indicate that there are possibilities for lowering chiller energy consumption, and these opportunities can be harvested with simple measures.     

Heat recovery from automotive engine

Heat recovery from automotive engines has been predominantly for turbo-charging or for cabin heating. Studies relative to application of the recovered heat to run absorption chillers is scarce. In this project, a 10.55 kW (three ton) absorption chiller was modified for hot gas intake and matched to a 2.8 L V6 internal combustion engine. Mathematical model and experimental test results suggest that the concept is thermodynamically feasible and could significantly enhance system performance depending on part-load of the engine. However, possible challenges during transient operations as well as issues related to scalability and reliability require further investigation.     

Alcohol Determination in Distilled Alcoholic Beverages by Liquid Phase Fourier Transform Mid-Infrared and Near-Infrared Spectrophotometries

Fourier transform mid-infrared spectrophotometry (FT-MIR), 1180–950 cm^?1, and near-infrared spectrophotometry (NIR), 1720–1660 nm, have been used complementarily for the direct determination of ethanol and methanol in distilled alcoholic beverages. In mid-infrared ethanol and methanol identified separately, hence, it has been used to confirm the absence or presence of methanol. In the absence of methanol, both were used to determine the alcoholic strength independently; however, near-infrared was used without diluting the samples. Ethanol and methanol contents were evaluated using the calibration curves established by a plot of peak height or peak area versus concentration % (w/w). The linearity range for ethanol was up to 15 and 50 % (w/w) for mid- and near-infrared, respectively. The developed methods are simple, fast, precise, and accurate. Moreover, the results obtained were in excellent agreement with the results obtained from gas chromatographic measurements. No sample preparation was required at all, and in all samples, methanol was not detected.     

Aero-elastic behavior of a flexible blade for wind turbine application: A 2D computational study

This paper presents a computational study into the static aeroelastic response of a 2D wind turbine airfoil under varying wind conditions. An efficient and accurate code that couples the X-Foil software for computation of airfoil aerodynamics and the MATLAB PDE toolbox for computation of the airfoil deformation is developed for the aero-elastic computations. The code is validated qualitatively against computational results in literature. The impact of a flexibility of the airfoil is studied for a range of design parameters including the free stream velocity, pitch angle, airfoil thickness, and airfoil camber. Static aero-elastic effects have the potential to improve lift and the lift over drag ratio at off-design wind speed conditions. Flexibility delays stall to a large pitch angle, increasing the operating range of a flexible blade airfoil. With increased thickness the airfoil deformation decrease only linearly.     

Process oriented industrial classification based on energy intensity

The Standard Industrial Classification (SIC) code has been used in the United States to categorize manufactured products. This classification is useful for many commercial and business related applications. However, when checked against energy use data collected through the Industrial Assessment Center (IAC) of San Diego State University (SDSU), the energy use profile of the SIC groups showed objectionable deviations within each group, rendering the code less than useful for overall energy based grouping and analyses. In this paper, a Process Oriented Energy Intensity Classification (POEIC) is introduced. When examined with data from about 270 plants of the IAC, this new classification offered more coherent and consistent energy use profile with smaller standard deviation for the selected energy intensity parameters than that of the SIC code.     

Effect of crop residues on grain yield response of sorghum (t Sorghum bicolor) (L.) to application of N and P fertilizer

A field experiment was conducted on two soil types for seven years (1988–1994) to investigate the effect of the presence of crop residue on grain yield response of sorghum to NP fertilizer applied every year or once only at the start of the experiment. Grain yield was increased by the NP fertilizer alone, but was not further significantly increased by application of both residues and NP fertilizer. During the study period yields decreased abruptly with decreasing rainfall after the first year particularly on the Typic Pellustert. Thus there was a difference according to soil type. This revised version was published online in August 2006 with corrections to the Cover Date.     

Profitability and occupational injuries in U.S. underground coal mines

Background

Coal plays a crucial role in the U.S. economy yet underground coal mining continues to be one of the most dangerous occupations in the country. In addition, there are large variations in both profitability and the incidence of occupational injuries across mines.

Objective

The objective of this study was to examine the association between profitability and the incidence rate of occupational injuries in U.S. underground coal mines between 1992 and 2008.

Data and method

We used mine-specific data on annual hours worked, geographic location, and the number of occupational injuries suffered annually from the employment and accident/injury databases of the Mine Safety and Health Administration, and mine-specific data on annual revenue from coal sales, mine age, workforce union status, and mining method from the U.S. Energy Information Administration. A total of 5669 mine-year observations (number of mines × number of years) were included in our analysis. We used a negative binomial random effects model that was appropriate for analyzing panel (combined time-series and cross-sectional) injury data that were non-negative and discrete. The dependent variable, occupational injury, was measured in three different and non-mutually exclusive ways: all reported fatal and nonfatal injuries, reported nonfatal injuries with lost workdays, and the ‘most serious’ (i.e. sum of fatal and serious nonfatal) injuries reported. The total number of hours worked in each mine and year examined was used as an exposure variable. Profitability, the main explanatory variable, was approximated by revenue per hour worked. Our model included mine age, workforce union status, mining method, and geographic location as additional control variables.

Results

After controlling for other variables, a 10% increase in real total revenue per hour worked was associated with 0.9%, 1.1%, and 1.6% decrease, respectively, in the incidence rates of all reported injuries, reported injuries with lost workdays, and the most serious injuries reported.

Conclusion

We found an inverse relationship between profitability and each of the three indicators of occupational injuries we used. These results might be partially due to factors that affect both profitability and safety, such as management or engineering practices, and partially due to lower investments in safety by less profitable mines, which could imply that some financially stressed mines might be so focused on survival that they forgo investing in safety.     

Measurement of caffeine in coffee beans with UV/vis spectrometer

In this research work using UV/vis spectrophotometer the molar decadic absorption coefficients and transitional dipole moment of pure caffeine in water and dichloromethane were obtained at 272 and 274.7 nm. The molar decadic absorption coefficients of caffeine in water and dichloromethane at these wavelengths are 1115 and 1010 m² mol⁻¹, respectively. The calculated values for the transitional dipole moment of caffeine in water and in dichloromethane are 10.40 × 10⁻³⁰ and 10.80 × 10⁻³⁰ C m, respectively. After characterizing caffeine in water and dichloromethane, fast and simple methods were developed that enable to quantify the content of caffeine in coffee beans. The methods helped in extracting caffeine from coffee dissolved in water by dichloromethane, and Gaussian fit was applied to eliminate the possible interference with the caffeine spectra.