Radiation cooling of buildings at night

The cooling of small buildings at night by radiation loss to the sky has been investigated by monitoring the thermal performance of two huts: one roofed with galvanised steel decking painted white, which acts as a ‘black body’ for wavelengths greater than 3 μm; the other with aluminium decking to which aluminised ‘Tedlar’ sheet had been glued, the ‘Tedlar’ acting as a selective surface absorbing and radiating mainly in the 8–13 μm band.

The hut with the painted roof was cooled marginally better than that with the ‘Tedlar’ covered roof. Useful cooling powers of 22 Wm⁻² were achieved at a roof temperature of 5°C, ambient 10°C, and the gross cooling power probably exceeded 29 Wm⁻². Calculations based on a simple simulation of the sky radiation yield an upper limit of 40 Wm⁻² for the cooling power of the surfaces and suggest that an ideally selective surface operating under the best possible clear-sky conditions has little advantage over a black body radiator unless the temperature of the surfaces is significantly lower than the ambient air temperature.     

Four-equation turbulence model for prediction of the turbulent boundary layer affected by buoyancy force over a flat plate

Turbulent convective heat transfer with appreciable buoyancy effect over a heated or cooled horizontal flat plate is numerically analyzed by solving four equations for mean square temperature variance , its rate of destruction _θ, turbulent kinetic energy κ and the rate of kinetic energy dissipation . Turbulent time-scale ratio R of temperature fluctuations relative to velocity fluctuations defined by is found to vary widely across the boundary layer. For both highly stable and highly unstable conditions, the ‘four-equation’ model yields better results for mean temperature profile and surface heat flux than the two-equation model. It is also found that the magnitude of thermal von Karman constant κ_θ is not a universal constant but it depends on the thermal stratification of the boundary layer.     

Thermal shock fracture experiments on large size plates of A533-B steel

The paper gives a complete report on a five-year research program concerning the fracture behaviour of the pressure vessel steel A533-B under thermal shock conditions. Five tests on 140-mm thick plates carrying a surface through-thickness crack were performed with different material conditions and thermal histories. The results confirmed the applicability of the Linear Elastic Fracture Mechanics approach and of the arrest toughness criterion. Moreover, the confidence limits achievable by a material characterization procedure based on Charpy-V tests were assessed. The prevention of crack initiation under a decreasing stress intensity factor and crack-tip temperature (‘simple’ warm pre-stressing effect) was largely confirmed, while reinitiation prevention after thermal-mechanical histories including complete unloading could not be demonstrated.     

Energy allocations for cooking in UP households (India): A fuzzy multi-objective analysis

Planning for proper deployment of energy resources for different end uses is important. The choice of energy resources involves an effort to synthesise suggestions coming from various areas as well as the subjectivity of the decision maker. The fuzzy approach is becoming important in such decision scenarios. In this paper, the multi-objective energy resource allocation problem is studied in a fuzzy manner, with the linear fuzzification of objectives, which include economic, environmental, technical and other concerns. The concept of operational adequacy measure, as a measure of the degree of satisfaction, is introduced. The cooking energy sources for the household sector of Uttar Pradesh (India) are considered as an illustration of the approach. Scenario development has also been implemented. LPG, biogas and fuelwood should be readily promoted under all circumstances. Solar thermal energy can be promoted except in the ‘economic-oriented’ scenario, where charcoal gets preference. Grid electricity finds favour in the ‘energy conservation and rationalisation’ scenario. The overall operational adequacy measure is 0.454, which decreases under different scenarios. The minimum satisfaction is achieved in the ‘environment-oriented scenario’. A ranking of the objective functions and the optimal and non-optimal sources has also been determined.     

Comparative study of the behaviour of conventional gasketed and compact non-gasketed flanged pipe joints under bolt up and operating conditions

Bolted flanged joints comprise an assembly of a number of important individual components, which are required to perform well together in service. The ideal requirement for a bolted flange joint is a ‘zero-leak’ condition. However, whilst recommended design procedures for bolted flange joints are available in international codes and standards, leakage problems are still faced by industry. These are common in both normal operating (internal pressure loading) and critical event conditions. The drive is, therefore, to find a flange joint assembly, which provides ‘zero-leak condition’ and requires little or no maintenance and handling. Considerable investigation in the area of optimised bolted joints has been in progress for the past 10 years comparing traditional gasketed joints and ‘compact non-gasketed’ joints, using both analytical and experimental approaches. In this present study, two-dimensional non-linear finite element studies have been performed for both gasketed and non-gasketed bolted flange pipe joints. Based on the stress results for the flange and the bolt and the flange rotation/displacement, compact non-gasketed flange joints are shown to be a viable and preferable alternative to the conventional gasketed flange joints. Recommendations are made for a best-fit flange model for static load conditions with ‘zero-leak’ sealing in a flange joint.     

Dynamic behaviour of a boundary layer with condensation along a flat plate: comparison with suction

The dynamical behaviour of laminar and turbulent boundary layers inside which a condensation phenomena exists, has been experimentally and numerically studied. The temperature difference between the exchange cold wall and the saturated air-steam flow at atmospheric pressure and moderate temperature ( 0–90°C) does not exceed 20°C. Evaluation of the mass flux at the wall in such a case, allows the prediction of the ‘equivalent suction rate’ in a sucked boundary layer for the same external conditions but without any temperature difference. The comparison between the two phenomena reveals interesting similarities and some differences.     

Performance of evaporator-collector and air collector in solar assisted heat pump dryer

A solar assisted heat pump dryer has been designed, fabricated and tested. This paper presents the performance of the evaporator-collector and the air collector when operated under the same meteorological conditions. ASHRAE standard procedure for collector testing has been followed. The evaporator-collector of the heat pump is acting directly as the solar collector, and the temperature of the refrigerant at the inlet to the evaporator-collector always remained below the ambient temperature. Because of the rejection of sensible and latent heats of air at the dehumidifier, the temperature at the inlet to the air collector is lower than that of the ambient air. Hence, the thermal efficiency of the air collector also increases due to a reduction of losses from the collector. The efficiencies of the evaporator-collector and the air collector were found to vary between 0.8–0.86 and 0.7–0.75, respectively, when operated under the meteorological conditions of Singapore.     

Energy productivity improvements and the rebound effect: An overview of the state of knowledge

The ‘rebound effect’ from more efficient use of energy has been well investigated, with plenty of evidence suggesting that the ‘direct’ rebound effect is relatively small for most energy services—typically less than 30%. However, the same conclusion may not apply to ‘indirect’ and ‘economy-wide’ rebound effects. Here, several authors suggest that improved energy efficiency may increase energy consumption in the medium to long term, a view that undermines the rationale for energy efficiency as an instrument of climate-related energy policy and has been ardently debated. One of the main reasons behind the debate is the lack of a rigorous theoretical framework that can describe the mechanisms and consequences of the rebound effect at the macro-economic level. Proponents of the rebound effect point to ‘suggestive’ evidence from a variety of areas including economic history, econometric measurements of productivity and macro-economic modelling. This evidence base is relatively small, highly technical, lacks transparency, rests upon contested theoretical assumptions and is inconclusive. This paper provides an accessible summary of the state of knowledge on this issue and shows how separate areas of research can provide relevant insights: namely neoclassical models of economic growth, computable general equilibrium (CGE) modelling and alternative models for policy evaluation. The paper provides a synopsis of how each approach may be used to explain, model and estimate the macro-economic rebound effect, criticisms that have been suggested against each, and explanations for diversity in quantitative estimates. Conclusions suggest that the importance of the macro-economic rebound effect should not be underestimated.     

Effective metal temperature in creep life assessment

In assessing remaining creep life of high temperature components, the thermal history, as expressed by the ‘effective metal temperature’ is an important input. This temperature can be derived from quantifiable thermally induced changes such as growth of internal scale or coarsening of carbide particles in the microstructure. Conventional practice is to use this temperature to predict the consequences of a different thermally activated process, i.e. creep. Under isothermal steady-state conditions, this approach is valid. Under the variable loading conditions typical of operating plants, however, effective temperatures for different processes may not be identical. The paper addresses this issue, comparing effective metal temperatures for creep, oxidation and carbide coarsening under several forms of variable loading.     

Acceptable temperatures for surfaces in brief contact with human skin

On process plants, thermal insulants are often used for personnel protection as well as for the reduction of the rate of energy wastage. This paper develops the pertinent theory with respect to acceptable ‘safe-touch’ surface temperatures and so challenges some of the recommendations appearing in British Standard Code of Practice 3005:1969.     

Renewable-Energy paradox in paradise: A case stuty of Hawaii

Hawaii is committed to replacing imported oil with indigenous, renewable energy resources to enhance the economic and environmental security of the state's citizens. A case study of Hawaii's fuel-energy balance by the end of the 21st century which features two scenarios, a ‘Business-as-Usual’ energy system, based on imported fossil fuels, and a ‘Renewable-Energy’ scenario, based on an alternative energy system consisting entirely of indigenous, renewable energy resources, is presented.

In the year 2100, a projected total energy consumption of approximately 335 million gigajoules would be provided from a hypothetical renewable-energy system of approximately 13 gigawatts-electric of installed capacity. This system would feature methanol-from-biomass to meet liquid fuel requirements for surface transportation, industrial, commercial, and residential sectors; hydrogen via electrolysis in liquid form for air transportation and as a gaseous fuel for industrial purposes; and electricity generated from geothermal, ocean thermal, wind, and photovoltaic sources for all power applications.

A comprehensive economic analysis, including capital costs, operating and maintenance costs, air pollution costs for the total fuel cycle of each energy system, and a local multiplier effect factor of 3·75 per dollar, indicates that between the years of 1987 and 2100 the ‘Business-as-Usual’ scenario will have expended approximately $600 billion (1986 US dollars), and the ‘Renewable-Energy’ scenario will have cost approximately $400 billion. By switching from imported fossil fuels to indigenous, renewable energy resources during this time period, Hawaii's citizens could save approximately $200 billion to help preserve paradise.     

Boiling heat transfer phenomena from microporous and porous surfaces in saturated FC-72

Particle size effects on boiling performances of micro-porous enhanced surfaces are studied using five different sizes of diamond particles. By comparing the coating thicknesses with the superheated liquid layer thickness, the coatings are classified into two groups: ‘micro-porous’ and ‘porous’ coatings. The superheated liquid layer thickness is calculated using one-dimensional transient thermal conduction. Micro-porous coating shows different characteristics of boiling performances compared to porous coating in incipient superheat, nucleate boiling and CHF.     

Evaluation of premature failure of a gas turbine component

A case study of certain gas turbine stator vanes which fail prematurely is presented, with a view to determining whether operational procedure might have caused the failures. The engines had been operated from a ‘hot-and-high’ environment, and this could have contributed to the failures.

Computational fluid dynamics (CFD) techniques were employed in order to obtain an accurate design point thermal history. The resulting convection boundary conditions were then interpolated over a finite element mesh. Transient thermal and stress analyses were performed. At the same time, microstructural analyses of the service-exposed material were carried out to estimate the maximum temperature seen by the component. These showed that higher than expected vane metal temperatures were experienced. Emphasis was placed on the procedures outlined in the USAF Engine Structural Integrity Program¹, since little detail was known about the actual engine operating histories.     

Effect of a booster mirror on the performance of a ‘built-in’ storage solar water heater

In this paper, the performance of a ‘built-in’ storage solar water heater-flat mirror system has been presented. Numerical calculations have been made for a typical cold day (viz. 28 Jan. 1980) at Delhi. The booster mirror causes a minimum temperature rise during the moring and a temperature difference of 7°C excess with respect to the reference panel occurred. The reflectance of the mirror is taken as 0·88.     

Thermal performance of a parallel earth air-pipes system

In the present analysis the thermal performance of a parallel earth air-pipe system has been evaluated in terms of annual heating and cooling potential. The influence of the pipes on each other's thermal performance has been considered. The effect of seasonal variation of environmental parameters (ambient temperature, solar radiation, relative humidity, earth temperature etc.) has been considered. The results are obtained for the hot-dry climate of Jodhpur and the composite climate of Delhi. From the various possible earth surface treatments to increase the effectiveness of earth storage systems for air conditioning purposes, the results are presented for wet-shaded earth surface conditions, the most effective earth surface treatment for the climate considered. Thermal performance of the parallel air-pipe system is evaluated for the two cases. In the first case, inlet air temperature to the pipes is taken to be the hourly mean of the ambient air temperature of the average day of each month, and, in the second case, the inlet air temperature is taken to be equal to that of a conditioned room whose set-point temperature varies from month to month.     

Influence of repair welding on cyclic thermal shock behaviour of a RPV nozzle corner

In piping as well as in RPV-nozzles and in surrounding parts of the cylindrical vessel shells, repeated cold water injections have been observed leading to crack initiation and subcritical crack growth.

In the framework of the German Reactor Safety Research Programme, cyclic thermal shock tests have been carried out at the RPV of the decommissioned HDR (Heissdampfreaktor) near Frankfurt applying extremely conservative temperature transients. The crack propagation under access of oxygenated pressurized water was evaluated by fracture mechanics methods. The validation by non-destructive examination, as well as by destructive testing at a trepan, proved the fracture mechanics results to be conservative.

The depression at the nozzle corner caused by the trepan removal has been repaired by ‘temper bead’ welding without stress relief heat treatment, similar to the ‘half bead’ technique of the ASME Boiler and Pressure Vessel Code.

The subsequent thermal shock stressing (1200 cycles) under similar parameters demonstrated, with respect to the weld repair:

1. (1) no material separation extending into the ferritic RPV-wall;

2. (2) the quality of repair welding is comparable to the quality of the as-delivered condition manufactured in the 1960s in a more conventional manner.

The positive experience derived from this work may be helpful in the future in dealing with any cases of cracking in thick-walled large diameter vessels which could require repair welding when a post-weld stress relief heat treatment is not possible.     

Field investigation of night radiation cooling under tropical climate

This paper discusses the feasibility of cooling by using night radiation under Thailand’s hot and humid climate. Four types of roof radiators were made by using common construction materials. They were examined under three sky conditions: clear, cloudy and rainy, respectively. Investigation was done, mainly, based on the temperature of different surfaces of a roof radiator. The experimental results showed that the depression of different surface temperatures is in the range of 1–6°C below ambient temperature under clear and cloudy skies. Under rainy skies, the temperature of different surfaces of roof radiators and ambient air was fairly close. Apart from sky conditions, the factors which affect the night radiation cooling are the thermal emissivity of materials and water condensation on the radiator surface area. Finally, this first study indicated that cooling by using night radiation is feasible mainly during tropical winter season.     

A demonstration site-built solar air collector using selective surface glazing, Boston, Massachusetts

A 450 ft ‘site-built’ air collector was completed in February 1981 in Boston, Massachusetss. The collector uses the Airco/Guardian ‘Passive Solar Glass’ with a selective surface coating on the inner lite of the collector's double glazing. This paper discusses the issues and theory that led to the building of the collector and estimates performance for the system. Preliminary data taken in late winter indicates that the system will perform seasonally as predicted.     

Electrical breakdown phenomena in (PEO)χLiF3CSO3 ion-conducting polymers

Electrical breakdown of (PEO)_χLiF₃CSO₃ polymers (with χ=4 to 14) has been studied using lithium electrode systems, in the temperature range 100–170 °C. The observed breakdown characteristics depend particularly on the temperature, the thickness of the polymer sample and the mechanical load applied to the cell stack. Breakdown is localized and it is likely that its source lies in poor contact between the electrodes and the polymer (and possibly inhomogeneities in the latter) leading to ‘hot spots’ where the current density is high enough to induce decomposition.     

Cooling-energy reduction in air-conditioned offices by using night ventilation

Night ventilation has been applied successfully to many passively-cooled or low-energy office buildings. This paper investigates the applicability of night ventilation in air-conditioned office buildings. A thermal and ventilation simulation model, together with suitable weather data were used to examine the potential for energy savings and/or improved internal comfort conditions by applying night ventilation cooling. It was found that natural ventilation strategies could save cooling energy in typical air-conditioned offices. However, the use of mechanical ventilation could lead to increased energy-consumption. If typical offices are modified to incorporate features assisting the application of night ventilation, then cooling energy could be saved when mechanical ventilation is used and further reduced in the case of natural ventilation. Such features would include exposed thermal mass or offices designed to ‘best practice’ guidelines, such as airtight construction and minimisation of internal and solar heat gains.