Experimental investigation of a flat plate heat pipe performance using IR thermal imaging camera

This paper presents results and analysis of an experimental investigation into determining the thermal performance of a flat plate heat pipe using infra red (IR) thermal imaging camera. Steady state and transient temperature distribution of the evaporator surface of the flat plate heat pipe were measured using a single heat source with varied heat flux inputs. For performance comparison, the experimental measurements were also carried out on an identical flat plate heat pipe with a defect and on a solid copper block of similar dimensions. It was shown that temperature excursion on the surface of the fully functioning flat plate heat pipe is less than 3 °C for operating temperatures up to 90 °C and heat flux inputs ranging from 4 to 40 W/cm². Furthermore, the thermal spreading resistance of the flat plate heat pipe was found to be about 40 times smaller than that of the solid copper block and flat plate heat pipe with a defect.     

Monitoring of methanogen density using near-infrared spectroscopy

In order to improve anaerobic digester productivity, raising the microbial mass in the reactor and the prediction of changes in the biomass is required. In this study the possibilities for using near-infrared spectroscopy (NIR) to monitor methanogen density in a biogas process was examined. Methane production from H₂ and CO₂ was carried out with acclimated-methanogens with fed-batch substrate gas (H₂/CO₂, 80:20 v/v) at pH 7 and 37°C. The cells of the methanogens were washed and dried, and then original NIR spectra for predicting methanogen density were recorded. The specified absorption spectra were collected and examined. As a result, absorption spectrum peaks were found to be predominantly based on alpha proteins and lipids mainly from the cytoplasm and cell membranes of the methanogens. Furthermore, NIR was used to monitor the methane fermentation system using acetic acid as substrate. The responses from NIR analysis were correlated to methanogen density of fermentation broth by partial least-squares regressions. The correlation coefficient (R), model standard error of calibration (SEC) and standard error of prediction (SEP) of the test calibration for methanogen density were 0.99, 0.14 gl⁻¹ and 0.55 gl⁻¹, respectively. For volatile fatty acids (acetic acid) R, SEC and SEP were 0.99, 0.36 gl⁻¹ and 0.63 gl⁻¹, respectively. The results indicated that within the range of the density of methanogens and the concentration of acetic acid used in this study, it was possible to monitor the important variables of methanogen density and acetate concentration simultaneously in pure substrate-fed anaerobic digesters.     

Quantification of liquid water accumulation and distribution in a polymer electrolyte fuel cell using neutron imaging

Operating parameters, material properties and flow field geometry have a deterministic role on the water storage and distribution within the flow channels and porous media in a fuel cell. However, their effects are not yet precisely understood. In this study, extensive neutron imaging experiments were conducted to visualize and quantify the amount of liquid water in the fuel cell channels and diffusion media as a function of inlet gas flow rate, cell pressure and inlet relative humidity. A seven-channel parallel flow configuration PEFC was used to isolate these parameters from flow field switchback interaction effects.

The neutron imaging experiments were performed at different inlet gas flow rates, operating cell pressures and inlet relative humidities. At each operating condition, the distribution of liquid water in the diffusion media under the lands, and in or under the channels was obtained. Furthermore, at three different cell pressures (0.2 MPa, 0.15 MPa and 0.1 MPa), liquid water distribution and quantification was obtained. The liquid water mass in the cell decreased with increasing pressure for over-humidified anode inlet conditions. Comparison of the fuel cell performance with the total liquid water mass in the cell indicates a non-monotonic relationship between liquid water content and performance. Furthermore, cell performance was highly sensitive to incremental changes in the membrane liquid water content.     

Lifetime-based phosphor thermometry of an optical engine using a high-speed CMOS camera

The surface temperature inside an optical engine was measured both with and without heating the intake gas. The temperature distribution was measured by lifetime-based phosphor thermometry using 10 time-sequential images during a single decay recorded by a non-intensified high-speed complementary metal oxide semiconductor camera and by accounting for the pixel-to-pixel variation in the nonlinearity of the sensor. Consequently, the system was simple and compact. One goal of this research is to use a single camera to measure the temperature field because it is easy to use such a system in practical experiments. The shot-to-shot standard deviation of the decay constant for uniform temperature conditions was 0.17–0.33% at 80–160 °C and it varied ±0.15% with position, indicating that the pixel nonlinearity is highly nonuniform. The present measurement method had a measurement error of ?2.25 to 1.15 °C and it exhibited a similar level of shot-to-shot fluctuations (±0.42–2.34 °C). This technique was used to measure the temperature in an optical engine and it gave reasonable temperature maps.     

Enhancing near-infrared solar cell response using upconverting transparentceramics

In order to demonstrate efficiency improvement of solar cells through utilization of frequency-shifted sub-band-gap photons, we prepared Y₃Al₅O₁₂ transparent ceramics co-doped with 3.0 at% Yb³⁺ and 0.5 at% Er³⁺ (YAG:3.0Yb/0.5Er) by solid state reaction. The material’s upconversion luminescence was investigated and it was found that near-infrared light could be effectively converted to green light centered at 563 nm, where a dye-sensitized solar cell normally possessed high spectral response. Using a thin disk of YAG:3.0Yb/0.5Er transparent ceramics attached to the rear of the dye-sensitized solar cell, the near-infrared response of the dye-sensitized solar cell was enhanced, due to the frequency upconversion.     

Validation of a three dimensional PEM fuel cell CFD model using local liquid water distributions measured with neutron imaging

This work presents the validation carried out for a three dimensional CFD 50 cm² PEM fuel cell model, particularly focus on the prediction of liquid water distributions within the cell. The CFD model was previously validated against a set of experimental polarization curves, where model results adequately matched the experimental curves. An extension of the validation is presented in this work, by performing a comparison of the local liquid water distributions predicted by the model with the liquid water distributions of the real cell. The experimental measurements were obtained by means of Neutron Imaging, where a set of different cell operating conditions was tested. Although the exact quantitative results are not directly comparable due to differences in the cell setup, qualitative results show a very good agreement between the model results and the water distributions observed in the neutron radiographs. A model validation approach using local variable distributions (such as liquid water in this case) in addition to the integral quantities (i.e. polarization curves) is necessary to ensure the validity of models.     

Experimental studies of a new solar water heater system using a solar water pump

The research goal was to develop a new solar water heater system (SWHS) that used a solar water pump instead of an electric pump. The pump was powered by the steam produced from a flat plate collector. Therefore, heat could be transferred downward from the collector to a hot water storage tank. The designed system consisted of four panels of flat plate solar collectors, an overhead tank installed at an upper level and a large water storage tank with a heat exchanger at a lower level. Discharge heads of 1, 1.5 and 2 m were tested. The pump could operate at the collector temperature of about 70–90 °C and vapor gage pressure of 7–14 kPa. It was found that water circulation within the SWHS ranged between 12 and 59 l/d depending on the incident solar intensity and system discharge head. The average daily pump efficiency was about 0.0014–0.0019%. Moreover, the SWHS could have a daily thermal efficiency of about 7–13%, whereas a conventional system had 30–60% efficiency. The present system was economically comparable to a conventional one.     

X-ray imaging of water distribution in a polymer electrolyte fuel cell

At present, water management in a polymer electrolyte fuel cell (PEFC) is a major subject of research. In fact, proper water management is vital to achieve maximum performance and durability from a PEFC. Consequently, this study is conducted to visualize quantitatively the water distribution in a PEFC by means of an X-ray imaging technique. The X-ray images of the PEFC components with and without water are clearly distinguished. Reference to the visualized X-ray images, enables quantitative evaluation of the water distribution in the region between the separator and the gas-diffusion layer (GDL). Likewise, the meniscus of water in the channels of the PEFC is clearly observed.     

Feasibility of lowering the condenser's inlet water temperature of a chiller using thermal water storage

A novel approach is proposed for applying cool thermal storage to reduce the on-peak demand of a water-cooled chiller. By charging the store at night via a cooling tower, and using this water to supply the condenser of a chiller during on-peak hours, cooler than normal water is supplied to the chiller. A feasibility study of this system was conducted using TRNSYS — a transient simulation modeling program examining varying capacities of cooling tower and thermal store volumes. These systems were tested using geographic weather data that demonstrated conducive diurnal changes in wet-bulb temperature (T_wet). Results suggest that the use of cool water thermal storage in this way can reduce both on-peak energy demand and on-peak power use by as much as 35%. System optimization is dependent on the thermal storage efficiency, the capacity of the cooling tower, and the diurnal change in T_wet.     

Performance of a PEM water electrolyser using a TaC-supported iridium oxide electrocatalyst

Polymer electrolyte membrane (PEM) water electrolysis is an attractive way of producing carbon-free hydrogen. One of the drawbacks of this method is the need for precious metal-based electrocatalysts. This calls for a highly efficient utilization of the precious metal, which can be obtained by dispersing the precious metal compound onto a catalyst support. Electrocatalysts with 50, 70 and 90 wt.% of IrO₂ on a TaC support were tested in a laboratory PEM water electrolyser and compared with pure IrO₂. The temperature was set at 90, 110, 120 and 130 °C respectively and the cell voltage was varied between 1.4 and 1.8 V. The load characteristics and electrochemical impedance spectra were obtained and compared for a range of electrocatalysts. The highest current densities and the lowest charge transfer and cell resistances were found for the 70 wt.% IrO₂ electrocatalyst. By contrast, the pure IrO₂ electrocatalyst showed the lowest current densities and the highest charge transfer and cell resistance. For example, the relative difference in current densities between the 70 wt.% IrO₂ and the pure IrO₂ electrocatalyst attained 36% at 130 °C and 1.7 V. All of the supported electrocatalysts showed a higher efficiency of utilization of the precious metal than the pure IrO₂.     

Study of a solar water heater using stationary V-trough collector

There are various types of solar water heater system available in the commercial market to fulfill different customers’ demand, such as flat plate collector, concentrating collector, evacuated tube collector and integrated collector storage. A cost effective cum easy fabricated V-trough solar water heater system using forced circulation system is proposed. Integrating the solar absorber with the easily fabricated V-trough reflector can improve the performance of solar water heater system. In this paper, optical analysis, experimental study and cost analysis of the stationary V-trough solar water heater system are presented in details. The experimental result has shown very promising results in both optical efficiency of V-trough reflector and the overall thermal performance of the solar water heater.     

Uncertainty and method limitations in a short-time measurement of the effective thermal transmittance on a building envelope using an infrared camera

Buildings' thermal insulation has received a lot of attention these past years, in an effort to reduce the sector's high energy consumptions. A number of non-destructive methods have been used in order to evaluate in situ the building envelope's effective thermal transmittance, characterised, however, by long-lasting measurement periods. This paper examines the uncertainty and method limitations to use short-time measurements using an infrared camera for this purpose, but also within real environmental conditions that are inevitably unsteady during the measurement series. Experimental measurements were realised with three different infrared cameras, and the results show that a value of effective thermal transmittance could be estimated in situ by a relative uncertainty that does not exceed 20% (coverage factor?=?2), a reliable estimation as long as all systematic errors are identified and diminished through calculations.     

Simulation of a solar domestic water heating system using a time marching model

This paper presents the modelling and simulation of a solar water heating system using a time marching model. The results of simulations performed on an annual basis for a solar system, constructed and operated in Yugoslavia, which provides domestic hot water for a four-person family are presented. The solar water heater consists of a flat-plate solar collector, a water-storage tank, an electric heater, and a water-mixing device. The mathematical model is used to evaluate the annual variation of the solar fraction with respect to the volume of the storage tank, demand hot water temperature required, difference of this temperature and preset storage tank water temperature, and consumption profile of the domestic hot water demand. The results of this investigation may be used to design a solar collector system, and to operate already designed systems, effectively. The results for a number of designs with different storage tank volumes indicate that the systems with greater volume yield higher solar fraction values. The results additionally indicate that the solar fraction of the system increases with lower hot water demand temperature and higher differences between the mean storage water and the demand temperatures. However, when a larger storage tank volume is used, the solar fraction is less sensitive to a variation of these operation parameters.     

Effect of Surface Temperature on Fouling of Cooling-Tower water

We will not, however, be too flattered by our victories over nature. Each such victory takes revenge on us. Each of these victories has, true, at the first turn, those consequences which were considered, but, at the second and third turn, quite different unexpected consequences that often destroy the importance of the first consequences.     

Fundamental design of a continuous biomass gasification process using a supercritical water fluidized bed

A novel biomass gasification (first stage of hydrogen production from biomass) process using a supercritical water fluidized bed was proposed and the fundamental design of the process was conducted. The flow rate was determined by evaluating the minimum fluidization velocity and terminal velocity of alumina particles enabling fluidization with the thermodynamic properties of supercritical water. Three cases were examined: a bubbling fluidized bed in which water was used mainly as the fluidized medium and biomass were added for gasification, a bubbling fluidized bed fluidized by biomass slurry feed alone, and a fast fluidized bed fluidized by biomass slurry feed alone. According to calculations of the residence time and thermal efficiency assuming heat recovery with a heat exchanger efficiency of 0.75, the bubbling fluidized bed fluidized by biomass slurry alone was appropriate for continuous biomass gasification using a fluidized bed.     

Solar distillation of water using a V-trough solar concentrator with a wick-type solar still

A V-trough solar concentrator has been combined with an inclined flat-plate wick-type solar still. Outdoor testing was carried out with and without the solar concentrator on clear days in summer and winter. The equipment was used to investigate the enhancement of the outdoor performance of the wick-type solar still by the solar concentrator.It has been concluded that use of the solar concentrator with the inclined wick-type solar still can lead to a greater fractional increase in still efficiency and productivity on clear days in winter than on clear days in summer.     

Temperature measurements of the bluff body surface of a Swirl Burner using phosphor thermometry

Flames are often stabilised on bluff-bodies, yet their surface temperatures are rarely measured. This paper presents temperature measurements for the bluff body surface of the Cambridge/Sandia Stratified Swirl Burner. The flame is stabilized by a bluff body, designed to provide a series of turbulent premixed and stratified methane/air flames with a variable degree of swirl and stratification. Recently, modellers have raised concerns about the role of surface temperature on the resulting gas temperatures and the overall heat loss of the burner. Laser-induced phosphorescence is used to measure surface temperatures, with Mg₄GeO₆F:Mn as the excitation phosphor, creating a spatially resolved temperature map. Results show that the temperature of the bluff body is in the range 550–900 K for different operating conditions. The temperature distribution is strongly correlated with the degree of swirl and local equivalence ratio, reflecting the temperature distribution obtained in the gas phase. The overall heat loss represents only a small fraction (<0.5%) of the total heat load, yet the local surface temperature may affect the local heat transfer and gas temperatures.     

Energetic approach of waste water processing using dry kernel as a fuel

The aim of this paper is to identify a suitable usage of the enormous amount of dry kernel, a biomass derived from olive-oil processing, as a combustible fuel in the disposal process of waste water. The method recommended besides the disposal of waste water, allows the recovery of the diluted substances with a remarkable reduction of functional costs. The method is supported by a two-year long experimental campaign during which more than 13,000 tons of waste water were processed.     

Multivariate optimization of a solar water heating system using the Simplex method

Two Simplex computer library packages for multivariate optimization have been tested on an hour-by-hour simulation of a solar water heating system. The two packages are: MINUITS written at CERN (Geneva), and the E04CCF routine which is part of the U.K. Numerical Algorithms Group Library. Technical and economic optima have been derived for three of the following variables simultaneously: collector area, tilt, azimuth, and store volume. The two packages give the same results. The meteorological data used were one (composite) year for Hamburg (Germany) and 1964 for Kew (U.K.). The Hamburg data were also condensed to form a year consisting of 60 averaged days. The optima derived with the 60-day year were very close to those obtained with the 365-day year.The Simplex method, which is a direct search method, is known to be very robust. It is particularly suited to hour-by-hour simulations of solar heating systems since the function being minimized is not monotonically decreasing towards the minimum in sufficient significant figures. For this reason, optimization methods which use derivatives are not appropriate unless the system performance is first expressed as a differentiable function. Because the Simplex method can be used directly on hour-by-hour simulations, it is extremely flexible and can be applied to a simulation of any system.     

过热蒸汽喷水混合装置的节能效益分析

依据热力学的基本原理,分析了实现蒸汽喃水混合装置节能的原理,提出了该装置的应用条件,应用喷水混合装置节省用汽的实质是利用蒸汽的潜热,对于示很好利用蒸汽潜热的用热系统,在对生产工艺无影响的情况下,该技术具有一定的应用价值,由于该装置本身并不能提供能源,相反在喷水混合过程中不可逆损失较大,所以即使在未完全利用蒸汽潜热的场合,它也不一定是节能的最佳手段。