Improving the energy efficiency of a control cabinet air conditioner through the use of variable refrigerant flow capacity control

Paper presented at the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malta, 16-18 July, 2012.Control cabinet air conditioners are used to regulate the temperature of an enclosure containing electrical equipment. Normally, these air conditioners are selected for worst-case conditions, and work on an on/off control. This paper describes the work carried out to analyse the performance of an air conditioner (AC) with variable refrigerant flow (VRF) for a masters degree dissertation [1]. The performance of a standard on/off air conditioner was first measured. The implementation of VRF in a control cabinet was carried out successfully by installing a variable-speed compressor within a standard AC unit. Experiments performed showed that the energy savings are 14% at full load and between 8 and 32% at part load. For most conditions, the enclosure temperature could be controlled to a stable value with a flat enclosure temperature profile. Maintaining a stable enclosure temperature reduces electronic component failure. A computer model was created using Microsoft Visual Basic for Applications, which could be used within Microsoft EXCEL. For a given set of ambient temperatures and enclosure loads, the model estimates the power consumption of a standard AC and a VRF AC and calculates the potential savings. When applied to various scenarios, savings of 18-25% were achieved. The system efficiency can be improved further by other changes to the AC design. A mathematical software model of the AC was built using Visual Basic Express 2005, to evaluate these potential improvements. It was shown that the COP could be improved by increasing the air-flows and by controlling evaporator superheat. By using an electronic expansion valve, the degree of superheat could be accurately controlled. Changes in refrigerant charge were found to have more effect at high ambient temperatures, with the cooling capacity being maximised with only small changes in power consumption.dc201

Experimental investigation of the effects of hydrogen enhanced combustion in Si and Ci engines on performance and emissions

Paper presented at the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malta, 16-18 July, 2012.Hydrogen enhanced combustion (HEC) is promoted as an end-user add-on that has the capability of reducing both engine tailpipe emissions and fuel consumption. An experimental investigation was carried out to measure the effects of HEC in typical engines through laboratory dynamometer testing. Three engines – (1) a carburetted petrol engine, (2) a fuel injected petrol engine and (3) a diesel engine – were tested to investigate the effects of adding hydrogen to the air intake of the engines and measure the effects on performance and emissions (HC, CO and CO2). The engines were tested at different engine speeds and loads to simulate a wide range of operating conditions. The hydrogen was produced from the electrolysis of a solution of distilled water and sodium hydroxide using two different electrolyser designs. The electrolyser constructions were suitable for automotive applications, that is, small in size and consuming current within the capability of a typical car alternator. Both the hydrogen and oxygen that were produced by electrolysis were added to the engine‘s intake during the tests. Results showed that the addition of HHO is most effective in stabilizing and enhancing the combustion of lean air-fuel mixtures inside the petrol injected engine, allowing for lower HC, CO and CO2 emissions. Thus hydrogen enhanced combustion could play a role in stabilizing lean burn petrol engines.dc201

Computer modelling of high temperature air combustion

Paper presented at the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malta, 16-18 July, 2012.High Temperature Air Combustion, HiTAC, is an innovative combustion technology which offers improved heat transfer and a reduction in fuel consumption and NOx emissions. This paper describes a project in which a computational fluid dynamic model of a furnace working on high temperature air combustion technology was developed using FLUENT® CFD software. The model was validated against experimental data obtained from KTH in Sweden. The predicted results compared very well with this experimental data, and were also closer than the predictions from the model built by KTH. The model was applied to a steam boiler of Malta’s Delimara Power Station. Two scenarios were considered: the boiler with conventional combustion and the boiler converted to HITAC. To reduce computational time, a 400:1 scaled down version of the boiler was modelled based on NOx scaling. Further reductions were made by taking advantage of the symmetry of the boiler and by obtaining the solution for a single burner, and then prescribing the parameter profiles for the single burner to the full boiler model as boundary conditions. The computer model results showed much lower NOx emission levels when firing the boiler with methane compared to heavy fuel oil. Further reductions in NOx emissions were obtained with HITAC technology and using methane as a fuel.dc201

Challenges in developing a solar powered stirling engine for domestic electricity generation

Paper presented at the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malta, 16-18 July, 2012.This paper investigates the challenges in developing a solar powered Stirling engine for domestic electricity generation. All the system components, the parabolic troughs, heat transfer fluid and the Stirling engine are individually analysed. The analysis includes a market survey and performance assessments of such components. A mathematical analysis for the Stirling engine is carried out in order to understand the affect of varies parameters with the work output per cycle and the engine efficiency. Such parameters are the phase angle between pistons, the diameter ratio of the power and displacer piston, and change in temperature.dc201

Challenges in developing a solar powered stirling engine for domestic electricity generation

This paper investigates the challenges in developing a solar powered Stirling engine for domestic electricity generation. All the system components, the parabolic troughs, heat transfer fluid and the Stirling engine are individually analysed. The analysis includes a market survey and performance assessments of such components. A mathematical analysis for the Stirling engine is carried out in order to understand the affect of varies parameters with the work output per cycle and the engine efficiency. Such parameters are the phase angle between pistons, the diameter ratio of the power and displacer piston, and change in temperature.peer-reviewe

Stabilisation of the Fc Fragment of Human IgG1 by Engineered Intradomain Disulfide Bonds

We report the stabilization of the human IgG1 Fc fragment by engineered intradomain disulfide bonds. One of these bonds, which connects the N-terminus of the CH3 domain with the F-strand, led to an increase of the melting temperature of this domain by 10°C as compared to the CH3 domain in the context of the wild-type Fc region. Another engineered disulfide bond, which connects the BC loop of the CH3 domain with the D-strand, resulted in an increase of Tm of 5°C. Combined in one molecule, both intradomain disulfide bonds led to an increase of the Tm of about 15°C. All of these mutations had no impact on the thermal stability of the CH2 domain. Importantly, the binding of neonatal Fc receptor was also not influenced by the mutations. Overall, the stabilized CH3 domains described in this report provide an excellent basic scaffold for the engineering of Fc fragments for antigen-binding or other desired additional or improved properties. Additionally, we have introduced the intradomain disulfide bonds into an IgG Fc fragment engineered in C-terminal loops of the CH3 domain for binding to Her2/neu, and observed an increase of the Tm of the CH3 domain for 7.5°C for CysP4, 15.5°C for CysP2 and 19°C for the CysP2 and CysP4 disulfide bonds combined in one molecule

Structure-Function Studies of DNA Binding Domain of Response Regulator KdpE Reveals Equal Affinity Interactions at DNA Half-Sites

Expression of KdpFABC, a K+ pump that restores osmotic balance, is controlled by binding of the response regulator KdpE to a specific DNA sequence (kdpFABCBS) via the winged helix-turn-helix type DNA binding domain (KdpEDBD). Exploration of E. coli KdpEDBD and kdpFABCBS interaction resulted in the identification of two conserved, AT-rich 6 bp direct repeats that form half-sites. Despite binding to these half-sites, KdpEDBD was incapable of promoting gene expression in vivo. Structure-function studies guided by our 2.5 Å X-ray structure of KdpEDBD revealed the importance of residues R193 and R200 in the α-8 DNA recognition helix and T215 in the wing region for DNA binding. Mutation of these residues renders KdpE incapable of inducing expression of the kdpFABC operon. Detailed biophysical analysis of interactions using analytical ultracentrifugation revealed a 2∶1 stoichiometry of protein to DNA with dissociation constants of 200±100 and 350±100 nM at half-sites. Inactivation of one half-site does not influence binding at the other, indicating that KdpEDBD binds independently to the half-sites with approximately equal affinity and no discernable cooperativity. To our knowledge, these data are the first to describe in quantitative terms the binding at half-sites under equilibrium conditions for a member of the ubiquitous OmpR/PhoB family of proteins

RNA Is an Integral Component of Chromatin that Contributes to Its Structural Organization

Chromatin structure is influenced by multiples factors, such as pH, temperature, nature and concentration of counterions, post-translational modifications of histones and binding of structural non-histone proteins. RNA is also known to contribute to the regulation of chromatin structure as chromatin-induced gene silencing was shown to depend on the RNAi machinery in S. pombe, plants and Drosophila. Moreover, both in Drosophila and mammals, dosage compensation requires the contribution of specific non-coding RNAs. However, whether RNA itself plays a direct structural role in chromatin is not known. Here, we report results that indicate a general structural role for RNA in eukaryotic chromatin. RNA is found associated to purified chromatin prepared from chicken liver, or cultured Drosophila S2 cells, and treatment with RNase A alters the structural properties of chromatin. Our results indicate that chromatin-associated RNAs, which account for 2%–5% of total chromatin-associated nucleic acids, are polyA− and show a size similar to that of the DNA contained in the corresponding chromatin fragments. Chromatin-associated RNA(s) are not likely to correspond to nascent transcripts as they are also found bound to chromatin when cells are treated with α-amanitin. After treatment with RNase A, chromatin fragments of molecular weight >3.000 bp of DNA showed reduced sedimentation through sucrose gradients and increased sensitivity to micrococcal nuclease digestion. This structural transition, which is observed both at euchromatic and heterochromatic regions, proceeds without loss of histone H1 or any significant change in core-histone composition and integrity

Crystal Structure of the Minimalist Max-E47 Protein Chimera

Max-E47 is a protein chimera generated from the fusion of the DNA-binding basic region of Max and the dimerization region of E47, both members of the basic region/helix-loop-helix (bHLH) superfamily of transcription factors. Like native Max, Max-E47 binds with high affinity and specificity to the E-box site, 5′-CACGTG, both in vivo and in vitro. We have determined the crystal structure of Max-E47 at 1.7 Å resolution, and found that it associates to form a well-structured dimer even in the absence of its cognate DNA. Analytical ultracentrifugation confirms that Max-E47 is dimeric even at low micromolar concentrations, indicating that the Max-E47 dimer is stable in the absence of DNA. Circular dichroism analysis demonstrates that both non-specific DNA and the E-box site induce similar levels of helical secondary structure in Max-E47. These results suggest that Max-E47 may bind to the E-box following the two-step mechanism proposed for other bHLH proteins. In this mechanism, a rapid step where protein binds to DNA without sequence specificity is followed by a slow step where specific protein:DNA interactions are fine-tuned, leading to sequence-specific recognition. Collectively, these results show that the designed Max-E47 protein chimera behaves both structurally and functionally like its native counterparts