Optimal number and location of heaters in 2-D radiant enclosures composed of specular and diffuse surfaces using micro-genetic algorithm

In this study, a combinatorial optimization methodology has been presented for determining the optimal number and location of equally powered heaters over some parts of the boundary, called the heater surface, to satisfy the desired heat flux and temperature profiles over the design surface while keeping the total heaters power constant but floating the number of heaters. In a typical enclosure, candidate locations were numerous for placing the heaters. The optimal number and location could be found by checking among all the possible combinations of heater power ranges and locations on the heater surface. The possibility of checking only a small portion of the total search space was increasingly desirable for finding an overall optimal solution. Micro-genetic algorithm was a candidate method which displayed a significant potential in achieving that task. Micro-genetic algorithm was used to minimize an objective function which was expressed by the sum of square errors between estimated and desired heat fluxes on the design surface. Radiation element method by ray emission model (REM²) was used to calculate the radiative heat flux on the design surface. It enabled us to handle the effects of specular surfaces and blockage radiation due to enclosure geometry. The capabilities of this methodology were demonstrated by finding the optimal number and position of heaters in two irregular enclosures. The effects of refractory surface characteristics (i.e., diffuse and/or specular) on the optimal solution have been studied in detail. The results show that the refractory surface characteristics have profound effects on the optimal number and location of heaters.     

Inverse boundary design of square enclosures with natural convection

An optimization technique is applied to design of heat transfer systems in which the natural convection is important. The inverse methodology is employed to estimate the unknown strengths of heaters on the heater surface of a square cavity with free convection from the knowledge of the desired temperature and heat flux distributions over a given design surface. The direct and the sensitivity problems are solved by finite volume method. The conjugate gradient method is used for minimization of an objective function, which is expressed by the sum of square residuals between estimated and desired heat fluxes over the design surface. The performance and accuracy of the present method for solving inverse convection heat transfer problems is evaluated by comparing the results with a benchmark problem and a numerical experiment.     

Generating application design data for solar air heating systems

This paper consists of two parts. The first part provides a graphical method of determining, under different operating conditions, the design data for a system using air heaters of known characteristics, i.e. of known η vs (Δt_m/I) curves for different flow rates. The interdependent operating parameters are the inlet and outlet fluid temperatures and the fluid flow rate. The unknown third parameter, when two others are fixed, is determined by the application of a design procedure outlined in the first part of the paper. The fluid rate per unit area is usually specified when presenting an air heater performance curve. However, while maintaining the same fluid flow rate per unit area, different curves are obtained for air heaters of different dimensions. Explicit importance to this fact does not seem to have been given in the literature so far. A methodology, by which performance curves obtained from a certain air heater of specific dimensions can be suitably modified so as to predict the performance of similar heaters having different dimensions, constitutes the second part of the paper.     

Analytical approach of thermosyphon solar domestic hot water system performance

An efficient and simple simulation approach for thermosyphon solar water heaters has been developed and compared with experimental data. This approach, valid for solar-only systems, gives the ability to link the system main design and constructional parameters with the expected energy output through an analytical determination of the coefficients of the characteristic input–output equation of the system. The proposed methodology can be used not only for energy optimization of the system in the design phase but also for evaluation of test results of an existing system in order to improve it further.     

Performance of artificially roughened solar air heaters—A review

The conversion, utilization and recovery of energy invariably involve a heat exchange process, which makes it imperative to design more efficient heat exchanger. The use of artificial roughness in different forms, shapes and sizes is the most common and effective way to improve the performance of a solar air heater. Several studies have been carried out to determine the effect of different roughness element geometries on heat transfer and friction in solar air heaters. This study reviews various roughness element geometries employed in solar air heaters for performance enhancement. Based on the correlations of heat transfer and friction factor developed by various investigators, an attempt has been made to compare the thermohydraulic performance of roughened solar air heaters.     

Simulation‐based assessment of electric load management programs

The paper describes a methodology for assessing the contribution of storage type loads to an electric energy system's load curve and for evaluating the impact of load shedding actions, as part of load management programs, on the system's load curve. The methodology uses physically based individual load models and an aggregation procedure that accounts for both statistical reference patterns of the energy service demand and for the random nature of load use. A simulation case study of electric water heaters fed by a single transformer station is presented, to illustrate the effects of load control. The proposed methodology presents the possibility of evaluating—both at individual consumer level and at system level—the impacts of load management (LM) on the quality of service provided, besides anticipating the impact on the system's load curve. It allows an effective design of LM programs through variables such as the number of different load shedding schedules and their frequency of use by the utility. Copyright © 1999 John Wiley & Sons, Ltd.     

Thermal performance assessment of recyclic double-pass flat and V-corrugated plate solar air heaters

Double-pass solar air heaters occupy an important place among solar air heating systems, because of minimal heat loss and maximum thermal efficiency with marginal heater size and cost. In the present work, investigations related to the thermal performance predictions have been carried out for double-pass flat and V-corrugated absorber plate solar air heaters under recycle operation. The mathematical models proposed herein are solved using an analytical approach that uses an iterative solution procedure. Furthermore, based on simulation results obtained from the analytical study, the optimum value of the recycle ratio, the mass flow rate, the absorptivity and the emissivity at which the heaters yield the maximum value of the thermal efficiency have been identified and presented using response surface methodology (RSM). The results of RSM revealed that the mathematical models are significant. In addition, results of the present study are validated and compared with previous studies. A reasonable agreement and significant improvement have been achieved.     

Design and implementation of LQR/LQG strategies for oxygen stoichiometry control in PEM fuel cells based systems

This paper presents the oxygen stoichiometry control problem of proton exchange membrane (PEM) fuel cells and introduces a solution through an optimal control methodology. Based on the study of a non-linear dynamical model of a laboratory PEM fuel cell system and its associated components (air compressor, humidifiers, line heaters, valves, etc.), a control strategy for the oxygen stoichiometry regulation in the cathode line is designed and tested. From a linearised model of the system, an LQR/LQG controller is designed to give a solution to the stated control problem. Experimental results show the effectiveness of the proposed controllers design.     

Utilizing demand-side management as tool for promoting solar water heaters in countries where electricity is highly subsidized

In many countries, especially those that produce petrol, electricity consumption is often subsidized. This policy leads to very low electricity costs and precludes the widespread use of solar water heaters, which have proven to be economically viable and are extensively utilized in other countries. Herein, we propose a new demand-side planning methodology to deal with such cases and perform an experimental finding–based economic assessment to study the feasibility of reducing subsidies in return for providing brand new solar water heaters to consumers. Specifically, solar water heaters are proposed to be supplied and installed free of charge as part of a demand-side management program in the Erbil province (Kurdistan region, Iraq). Assuming a duration of ten years, we show that the proposed project has a net present value of approximately US$776.6 million and requires an investment of US$90 million, further demonstrating that the successful launch of this project should dramatically reduce the winter peak load of 54 MW.     

Inverse design involving combined radiative and turbulent convective heat transfer

This work considers an inverse boundary design problem which involves radiation and convection heat transfer. The objective is finding the heat flux distribution required on heaters located on the top and side walls of a two-dimensional enclosure that satisfies both the temperature and heat flux distributions prescribed on the design surface of the enclosure. A turbulent air flow is generated by a fan located inside the chamber. The problem is described by a system of non-linear, ill-conditioned equations, which is solved by an iterative procedure. The solution are obtained by regularizing the system of equations by means of the TSVD method.     

Estimation of power of heaters in a radiant furnace for uniform thermal conditions on 3-D irregular shaped objects

For uniform thermal conditions on 3-D irregular shaped design objects, this paper reports estimation of optimal power of the panel heaters placed along the walls of a 3-D radiant furnace. Hemispherical, cylindrical, conical, and a combination of cylindrical and conical, and finally a case study of a car body model are considered as the design objects (DOs). The entire surface areas of the furnace walls and that of the DO are divided into surface elements. The surface elements of the furnace walls are made of the panel heaters. In this boundary design problem, the objective function is developed as an error function of estimated and the desired heat fluxes on the surfaces of DO. The radiative exchange among the surface elements is computed using the radiation element method by ray emission model (REM²), and the objective function is minimized using the micro-genetic algorithm (MGA). Power of the panel heaters are estimated for different sizes of the DOs. Although the panel heaters have been placed along the furnace walls, for uniform thermal conditions, for a given DO, not all are required. Having known that not all are required, to ease the control, estimations have also been shown by grouping the heaters along the furnace walls. This study provides a guideline for a priori knowing the heater setting and their corresponding power requirement in heating of 3-D irregular shaped objects.     

Performance and Service Life Considerations—Closed Feedwater Heaters

Because of the potential restriction of plant capacity and increases in fuel consumption cost that result from the removal of closed feedwater heaters from service, there is a need for the application of new design and operation concepts that enhance both the thermal performance and the availability of heaters and their associated systems. Practical operating practices, which take into consideration the highly localized environments in closed feedwater heaters and the individual susceptibilities to failure of the various tube materials in common use, have evolved from direct experience with closed feedwater heater problems. Many electric utilities have adapted these operating concepts in their standard operating procedure. Life extension programs for feedwater heaters that are repaired or to be replaced must include the provision for new operating concepts. Heaters that are subjected to the same operation conditions that led to the original failures may be expected to fail for the same reasons, often in a much shorter time. The acquisition of accurate data on operating performance, the location of tube distress, combined with the application of new, successful practices in feedwater heater design, operation, and maintenance, have provided the best assurance of a satisfactory service life of closed feedwater heaters.     

Design and Analysis of Infrared Heating with Overlapping Heater Array Scheme for Industrial Application

A recently developed infrared (IR) local heating method is fairly effective to reduce springback of advanced high strength steel in manufacturing processes of car chassis. Although parabolic heaters, consisting of an IR lamp located on the focus of a parabolic reflector, can reduce springback in stamping processes, non-negligible temperature changes are generated in the heated area. For this reason, an improved heater has been required for the IR heating method. In this work, an overlapping heater array is designed to solve the problem of the parabolic heater for the IR local heating method. The overlapping heater array can reduce the temperature change in the heated area. In the overlapping heater array, the parabolic heaters are connected in series. The connected parabolic heaters are then placed on both sides of a thin sheet metal and intersected to reduce the temperature change. In order to design a more efficient overlapping heater array, a simple design parameter was employed. The numerical and experimental verifications have shown that the overlapping heater array drastically reduces the temperature change in the heated area.     

Effect of surface particle interactions during pool boiling of nanofluids

The pool boiling characteristics of nanofluids is affected by the relative magnitudes of the average surface roughness and the average particle diameter. In the present work, an attempt has been made to study the interactions between the nanoparticles and the heater surface. The experimental methodology accounts for the transient nature of the boiling phenomena. The boiling curves of electro-stabilized Al₂O₃ water-based nanofluids at different concentrations on smooth and rough heaters and the burn-out heat flux have been obtained experimentally. Extensive surface profile characterization has been done using non-intrusive optical measurements and atomic force microscopy. A measure of the surface wettability has been obtained by determining the advancing contact angle. These results give an insight into the relative magnitudes of dominance of the prevalent mechanisms under different experimental conditions. Boiling on nanoparticle coated heaters has been investigated and presented as an effective solution to counter the disadvantageous transient boiling behavior of nanofluids.     

Energy and monetary benefits of portable heaters

A methodology is outlined that has been used to study the sensitivity of the performance of portable electric and kerosene space heaters to several parameters, including: the price of fuel for the conventional central heating system, the price of portable heater fuel, the thermal integrity of the structure, the size of the room that the portable heater is used to heat, the setback temperature for the central heating system, the duration of use, rates of air exchange with other spaces, and geographic location. Results are used to identify the conditions for which portable heaters are most beneficial and to which parameters the savings are most sensitive. The results show that savings are most sensitive to the thermal integrity of the structure, the price of fuel for the conventional heater, the thermostat setting during setback, and the duration of use of the portable heater. Payback periods for portable heaters are found to range from several months to more than six years.     

Design and thermal performance evaluation of a novel solar air heater

In the present scenario, numerous applications perform on solar energy for cooking, heating and cooling, and power generation, globally. Solar air heaters are one of these applications purposely used for, drying, timber seasoning and space heating. In the present work, a solar air heater (SAH) has been designed to produce a good exhaust temperature for long hours especially in the case of poor ambient conditions or during off sunshine hours. A mixture of desert and granular carbon in the ratio of 4:6 has been used as thermal heat storage inside the SAH. Two halogen lights of 300 W are used to increase the exhaust temperature of the SAH by placing them in the inlet and outlet ducts. All the experiments have conducted on natural and forced convection for performance evaluation on two similar design solar air heaters (with and without heat storage). The comparisons are made with two similar design solar air heaters carrying desert and granular carbon, as an individual heat storing media, to find out an optimum design of a SAH with long term heating. The thermal efficiencies of the novel SAH range from 18.04% to 20.78% of natural convection and 52.21%–80.05% with forced convection.     

高_低压加热器低水位运行的分析研究

阐述了高、低压加热器低水位运行的危害,应用等效焓降法对高、低压加热器低水位运行的125MW及200MW机组进行了热经济性研究,分析出其影响程度,从结构设计、现场运行等方面指出了引起加热器无水位、低水位运行的原因及改进办法,对电厂的运行具有很大实用价值。     

The cost-effectiveness of heat pumps in specific buildings in South Africa

Water heating heat pumps are extremely energy efficient and large savings can be realized when they are compared to direct electrical resistance heaters. In spite of the energy efficiency of heat pumps, a large number of residential buildings in South Africa still use electrical heaters to heat water. The reason for this is that heat pumps are considerably more expensive than electrical heaters. Building owners tend to choose the system with the smallest initial cost and do not compare the two systems on the basis of life-cycle cost. It is also difficult to calculate the life-cycle cost of a heat pump because it depends on many factors like climatological conditions and water temperature. In this paper a methodology is developed to calculate the life-cycle cost of a heat pump hot water installation. The model is used to investigate the effect of daily runtime, electricity tariff, hot water consumption and geographical location on the cost-effectiveness of heat pumps. The cost-effectiveness of heat pumps increases with daily run time, water consumption and electricity tariff. Heat pumps are more cost-effective near the coast than in the interior. If sized correctly, heat pumps are more cost-effective than electrical heaters for all major cities in South Africa. The cost-effectiveness of heat pumps for two specific buildings, one a university student hostel in Potchefstroom and the other a hotel in Durban, is also investigated. For both cases it was found that heat pumps are more cost-effective than direct electrical resistance heaters.     

烧结-热等静压炉结构优化与仿真

通过对烧结-热等静压炉石墨发热体的优化设计,改善石墨筒内温度场的均匀性,以解决实际生产中存在的石墨筒内温度分布不均匀、底部空间和靠近两个炉门侧空间温度偏低的问题,并对石墨发热体改进前后石墨筒内温度场分布情况进行了数值仿真。结果显示,改进后石墨筒内及整炉烧结制品表面温度场均匀性得到明显的改善,减少了由于炉门处未布置发热体所带来的影响。     

应用层次分析法综合评价家用太阳热水器

采用层次分析法对家用太阳热水器的热性能，经济性，可靠性以及使用寿命等多项因素进行综合评价。通过建立评价家用太阳热水器的层次结构及确定评价指标，借助计算机计算模型，可简捷，方便地排出各种不同型式家用太阳热水器的优劣，为用户选择产品和生产厂家优化设计提供依据，也可用来作为评比太阳热水器的一种方法。