Thermal behavior of a porous electric heater

The performance of a proposed porous electric heater is investigated. The porous heater exchanges heat with the working fluid through its large volumetric surface area. As a result, it produces lower surface temperature as compared with the conventional heater for the same imposed heating power. Two mathematical models are presented to describe the thermal behavior of both heaters. Axial diffusion is included in the governing equation of the solid conventional heater. The predictions of both models are compared at different operating conditions where it is found that porous heaters have much better thermal performance than the conventional heaters.     

On enthalpy management in small buildings

Enthalpy management requirements of residential and small commercial buildings are analyzed and integrated approaches to energy-efficient and cost-effective heating and cooling schemes are proposed. Improved design and operating strategies are suggested to make more efficient use of off-the-self (or other readily accessible) technology for space conditioning. The use of Comfort Range Thermal Storage (temperatures in the approximate range of 65–75 °F) and special operational strategies are central to these approaches. Fossil-fuel heaters, heat pumps, solar collectors, electric driven air coolers, all can be used more efficiently when they are effectively interfaced with selected thermal storage systems. A central heated (fossil fuel) and cooled (electric air-conditioner) residence located in Long Island, New York, is considered as an example. With Comfort Range Thermal Storage, it is found that the revised operating approach leads to 50% savings in space conditioning costs, with the basic functional features of the building unchanged from those of a typical well-insulated frame residence. Additional insulation results in further savings.

Devices, methods and strategies employed to achieve these results include the use of Comfort Range Thermal Storage as well as one or more of the following:

1. (1) Variable firing rate fossil fuel heater.

2. (2) Thermally purgeable fossil fuel heater.

3. (3) Outside air for all fossil fuel heater requirements.

4. (4) Separation of the combustion and heat transfer function from the thermal storage function of a conventional boiler.

5. (5) Use of off-peak electrical energy.

6. (6) User-oriented controls for space conditioning applications to allow conscious reprogramming of temperature to suit variations in life-style of the occupants.

7. (7) Control of energy flow at windows during the heating and cooling seasons.

8. (8) Comfort Range Thermal Storage in the temperature range of 65–75 °F.

9. (9) Functionally composite building materials.

Not all the above options are suitable for inclusion in new structures. Not all can be retrofitted to existing structures. Nevertheless, substantial energy and cost savings are selectively possible in all cases of fossil-fuel heating systems. Retrofitting of existing masonry buildings promises particularly significant economies. Such structures are typically uninsulated. Retrofit strategies which include insulation, permit economies substantially greater than those which result solely from the insulation-prescribed reduced heat losses. Such retrofitting, as well as the retrofitting of substantial thermal storage capacity to existing insulated frame buildings can result in substantial cost reductions for space heating and cooling.     

地热暖风机优化与实验研究

确定了描述地热低温暖风机技术经济性能的９个运行变量和８个结构变量以及它们之间的关系。以供暖成本最低为目标，研究低温暖风机的经济结构条件并求得最优解，得出有关结论     

Energy efficiency and indoor thermal perception: a comparative study between radiant panel and portable convective heaters

This study investigates experimentally the thermal perception of indoor environment for evaluating the ability of radiant panel heaters to produce thermal comfort for space occupants as well as the energy consumption in comparison with conventional portable natural convective heaters. The thermal perception results show that, compared with conventional convection heater, a radiantly heated office room maintains a lower ambient air temperature while providing equal levels of thermal perception on the thermal dummy head as the convective heater and saves up to 39.1% of the energy consumption per day. However, for human subjects’ vote experiments, the results show that for an environmentally controlled test room at outdoor environment temperatures of 0°C and 5°C, using two radiant panel heaters with a total capacity of 580 W leads to a better comfort sensation than the conventional portable natural convective heater with a 670 W capacity, with an energy saving of about 13.4%. In addition, for an outdoor environment temperature of 10°C, using one radiant panel heater with a capacity of 290 W leads to a better comfort sensation than the conventional convection heater with a 670 W capacity, with an energy saving of about 56.7%. From the analytical results, it is found that distributing the radiant panel heater inside the office room, one on the wall facing the window and the other on the wall close to the window, provides the best operative temperature distribution within the room.     

热网加热器设计研究

热网加热器是热力系统供热机组的重要组成部分,它是利用汽轮机的抽汽、减温减压的锅炉蒸汽或其它热源来加热热力系统中的网路回水和工业生产等用热水网路回水的加热设备。文中介绍热网加热器的主要结构选型设计、性能及参数、设计计算方法及设计要点,同时还介绍了热网加热器所配备的附件。     

The Performance of Porous Electric Heaters

The performance of a proposed porous electric heater is investigated. The porous heater exchanges heat with the working fluid through its large volumetric surface area. As a result, it produces lower surface temperature as compared with the conventional heater for the same imposed heating power. Two mathematical models are presented to describe the thermal behavior of both heaters and the predictions of both models are compared at different operating conditions.     

汽车采暖系统浅述

简述了国内外汽车采暖装置的发展概况,介绍了采暖装置的分类、各种加热器的特点及汽车采暖系统的构成和供暖原理.着重讲述了独立式汽车燃油加热器的结构与工作原理,并提出了我国加热器行业存在的不足和今后发展建议.     

Energy conservation and payback periods of natural circulation type solar water heaters

Energy savings in relation to different fuels, namely firewood, coal, kerosene, LPG and electricity have been calculated for a pressurized natural circulation type solar water heater with blackboard paint and a selective surface on the absorber. The payback periods have been computed by considering 10% compound annual interest, 5% annual maintenance cost and 5% inflation per year in maintenance cost and fuel prices. The cash flow has also been worked out for both solar water heaters. The cash flow is more for a solar water heater with a selective surface. The payback periods are 2.08–8.67 years for a solar water heater with a selective surface and 2.13–8.96 years for a solar water heater with blackboard paint. The estimated life of a heater is about 15 years. This shows that use of a solar water heater for heating water is very economical.     

提高热电厂效率的几项措施

从热经济性角度提出提高热电厂效率的几项技术和措施:通过凝汽器补充软化水,将外供蒸汽过热度降低;使用喷射式混合加热器回收热力除氧器排汽,作为生水加热器;利用压力匹配器代替减压减温器;用两相流加热器代替面式高压加热器等。     

大型火电机组加热器动态学模型的研究

以在大型火电机组中广泛使用的三段式加热器为研究对象，充分考虑了加热器结构参数的工质物性参数对传热过程的影响以及静态计算与动态教学模型间的差别，建立了加热器动态数学模型。仿真实验与工程应用证明该模型具有较高的静态计算精度和良好的动态响应特性，具有较广泛适用性和一定的工程应用价值。     

Effect of geometrical parameters on thermal efficiency and fuel consumption of heaters of a natural gas pressure reduction station using Sobol statistical sensitivity analysis

The main objective of natural gas pressure reduction station or city gate stations (CGSs) is to adjust gas pressure within a standard range for home usage. CGSs usually utilize heaters for pressure tuning, which generally consume a considerable amount of energy. In this paper, the effect of six influential parameters, namely, the length of gas-coil, the diameter of gas-coil, the radius of heater shell, length of heater shell, fire tube diameter, and length, on the amount of fuel consumption and thermal efficiency is investigated using Sobol statistical sensitivity analysis. The results show that gas-coil length and diameter are not effective in fuel consumption and thermal efficiency. In contrast, increasing the heater shell radius, heater shell length, and fire tube radius has the same effect as they cause a linear increase in fuel consumption. According to results taken from Sobol analysis, they similarly have an influence of 19%–23% on fuel consumption and 21%–22% on thermal efficiency. Finally, it was revealed that the effect of fire tube length on fuel consumption and thermal efficiency of the heater was 37% and 35%, respectively.     

Energy consumption in greenhouses and selection of an optimized heating system with minimum energy consumption

In this paper, heat loss is precisely computed by a proposed code considering different climates. Estimating the costs of different central heating system, unit heaters were selected as the most feasible system. Finally, considering the heating capacity and unit heater's dimensions a computational fluid dynamics model was developed to find the optimized configuration of unit heaters in a typical greenhouse. Using this model, the required thermal load for a greenhouse based on the daily temperature of Arak city in 2017 was computed with a smart control system. It was found that savings in energy consumption were approximately 5447 m³ of natural gas each year.     

Analysis of thermal response of a food self-heating system

This paper presents a distributed model of heat transfer in a self-heating unit for group meals and its numerical simulation. A magnesium alloy and water exothermic reaction provides the necessary energy. The resulting governing equations of chemical reaction and heat conduction that depicts the heater performance were solved to develop an approximate analytical solution, to which experimental data found from literature were compared and curve fitted. Then, a model of a complete food-heating unit for group meals, which include a stack of four sets of food tray, heating tray, and heater sandwiched between them, as well as the cardboard container, was developed. The governing equations for heat conduction in the complete model were solved. The response in thermal performance of the heating system to the parameters that influence heating profiles of the heater such as decay constant and heat generation capacity were studied. The results show that the system thermal performance is most significantly affected by heat generation and a proper combination of heaters with different heat generation capacity can improve temperature uniformity between food trays. The results are useful for designing and optimizing self-heating multi-food tray units.     

Influence of Thermophysical Wall Properties During Pool Boiling on Large Diamond and SiC Heaters

The results of pool boiling experiments with synthetic diamond and silicon carbide (SiC) heaters are presented for water as the boiling liquid. The diamond and SiC heaters varied considerably in thermal conductivity, but they had smooth, nearly identical surfaces, which was also the case in regard to their contact angles for water. Temperature sensors and electric heating wires were directly vapor-deposited underneath the surfaces. The experiments were carried out with comparable large heaters (15 mm × 15 mm) for pure water under atmospheric pressure (1 bar) in a pool boiling cell. The heat transfer characteristics including the corresponding boiling curves were obtained. In prior work, it was found that the influence of the thermophysical wall properties might be substantial in the case of special heater geometries, leading to trapped bubbles, but no significant differences between both materials were observed in the case of conventional heater configurations.     

Solar water heaters with phase change material thermal energy storage medium: A review

Latent heat thermal energy storage is one of the most efficient ways to store thermal energy for heating water by energy received from sun. This paper summarizes the investigation and analysis of thermal energy storage incorporating with and without PCM for use in solar water heaters. The relative studies are classified on the basis of type of collector and the type of storage used i.e. sensible or latent. A thorough literature investigation into the use of phase change material (PCM) in solar water heating has been considered. It has been demonstrated that for a better thermal performance of solar water heater a phase change material with high latent heat and with large surface area for heat transfer is required.     

Exergy based analysis of solar air heater having discrete V-down rib roughness on absorber plate

The artificially rib roughened solar air heaters perform thermally better than the conventional flat-plate solar air heater under same operating conditions. However, the artificial rib roughness leads to higher friction factor thereby increasing pumping power. The second law based exergy analysis is suitable for design of rib roughened solar air heaters as it incorporates quality of useful energy output and pumping power. The exergetic efficiency of a solar air heater having discrete V-down rib roughness is studied analytically and the results obtained are compared with that of a conventional flat-plate solar air heater. Flow Reynolds number and rib-roughness parameters, viz., relative roughness pitch, relative gap position, relative gap width, angle of attack and relative roughness height have combined effect on heat transfer as well as fluid friction. The exergy based criterion suggests use of the discrete V-down rib roughened solar air heater for the Reynolds number range normally used in solar air heaters. It was found that there exist optimum roughness parameters of the discrete V-down rib for a given Reynolds number (or temperature rise parameter) at which the exergetic efficiency is highest. Curves of optimum rib-roughness parameters are also plotted.     

Potential application of solar thermal systems for hot water production in Hong Kong

This paper presents the evaluation results of conventional solar water heater (SWH) systems and solar assisted heat pump (SAHP) systems for hot water production in Hong Kong. An economic comparison and global warming impact analysis are conducted among the two kinds of solar thermal systems and traditional water heating systems (i.e. electric water heaters and towngas water heaters). The economic comparison results show that solar thermal systems have greater economic benefits than traditional water heating systems. In addition, conventional SWH systems are comparable with the SAHP systems when solar fractions are above 50%. Besides, analysis on the sensitivity of the total equivalent warming impact (TEWI) indicates that the towngas boosted SWH system has the greatest potential in greenhouse gas emission reduction with various solar collector areas and the electricity boosted SWH system has the comparative TEWI with the SAHP systems if its solar fraction is above 50%. As for SAHP systems, the solar assisted air source heat pump (SA-ASHP) system has the least global warming impact. Based on all investigation results, suggestions are given on the selection of solar thermal systems for applications in Hong Kong.     

Selecting a heating system for FRP and plastic tanks and vessels

Tank heating system design considerations such as temperature differentials and limits, thermal resistance components, and power requirements are reviewed, and the merits of two heater styles are analyzed in terms of efficiency, safety, and economy of operation. The two heater styles considered are self-limiting and low-watt-density constant wattage. Both styles are available as panel or strip heaters. The benefits and drawbacks of each design are noted with respect to a particular design example, while neither style is preferred overall, it is noted that for safe operation the self-limiting heater should be used with a thermostatic control     

Economic evaluation and optimization of solar heating systems

A procedure is developed for assessing the economic viability of a solar heating system in terms of the life cycle savings of a solar heating system over a conventional heating system. The life cycle savings is expressed in a generalized formby introducing two economic parameters, P₁ and P₂, which relate all life cycle cost considerations to the first year fuel cost or the initial solar system investment cost. Using the generalized life cycle savings equation, a method is developed for calculating the solar heating system design which maximizes the life cycle savings. A similar method is developed for determining the set of economic conditions at which the optimal solar heating system design is just competitive with the conventional heating system. The results of these optimization methods can be presented in tabular or graphical form. The sensitivity of the economic evaluation and optimization calculations to uncertainties in constituent thermal and economic variables is also investigated.     

Comparative study of various optimization criteria for SDHWS and a suggestion for a new global evaluation

This study compares various optimization criteria for a solar domestic hot water system (SDHWS). First of all, we present the various parameters used to evaluate a SDHWS. We consider the energetic, exergetic, environmental (CO₂ emissions) and financial (life cycle cost) analysis. Various optimization criteria of a standard solar hot water system are then proposed. The optimized solutions are compared with a standard hot water system. The most suitable criteria take into account both energetic (therefore environmental) and financial evaluations. The most powerful solutions tend to increase the collector area - increasing the solar fraction during the mid-season - and reduce the tank volume, thereby decreasing the thermal losses and financial cost.Some of the usual evaluation criteria for SDHWs cannot be used as optimization criteria because they do not consider the auxiliary heater, resulting in inaccurate indications of the system’s performance. Therefore, it seemed important to propose a new evaluation method which integrates the life cycle savings, primary energy savings and CO₂ emission savings with regard to a referenced solution based on a radar diagram of these three fractions. This mode of representation is particularly useful when various auxiliary heaters are compared.