Water Heating Process Research Articles

Theoretical study of a high-temperature heat pump system composed of a CO2 transcritical heat pump cycle and a R152a subcritical heat pump cycle

A high-temperature heat pump system composed of a CO2 transcritical cycle and a R152a subcritical cycle is proposed for heat and cooling cogeneration. Emphasis is placed on analyzing and comparing thermodynamic performance of the combined system to the single heat pump and singe CO2 refrigeration systems working alone. Entransy dissipation rate and T-Q diagram are also applied to illustrate temperature match behavior of heating process of supply water. Besides, performance comparisons were also conducted between the systems with and without intermediate heat exchanger and between the systems with different working fluids. The studies indicate that there exist appropriate ranges of CO2 discharging pressure for CO2 transcritical cycle to meet the requirements of pinch point temperatures for heat transfer processes. Increasing CO2 discharging pressure, both the system heating and cooling capacities are increased. However, total system power consumption first slightly decreases and then increases exponentially. As for the overall system COP and exergy efficiency, both are increased with increasing CO2 discharging pressure. Under the same operating conditions, the system COP and exergy efficiency of this combined system are increased by about 54.7% and 175%, respectively, as compared to the single R152a heat pump and single CO2 transcritical cycle working alone.

CFD Simulation of Heating Process of Greenhouse Irrigation Water in Wintering Period

Abstract. In order to solve the problem of low greenhouse irrigation water temperature during the wintering period, the heating process of irrigation water in heating reservoir was investigated under the combined effect of air heat and soil heat with solar greenhouse in Xinyi Town, Lishi District, Shanxi Province as the carrier using three-dimensional non-steady-state methods in computational fluid dynamics (CFD). A dynamic computational model was established to predict the heating process of irrigation water. The measured data were used to reveal the dynamic hexahedron boundary conditions of the heating reservoir in the greenhouse. The simulation results of computation model were validated, and the errors and causes were analyzed. It was shown that the simulated heating process of irrigation water was consistent with the measured data under the influence of changes in boundary conditions, with an average relative error <5.46% and the maximum absolute error of <1.64°C; the correlation coefficient between the simulation values and measured values was greater than 0.96, indicating that CFD simulation of heating process of irrigation water is feasible. Keywords: Agricultural engineering, CFD simulation, Greenhouse, Irrigation water temperature, Solar greenhouse heating reservoir, Three-dimensional non-steady-state, Wintering period.

Exergy applied to the heat conduction analysis in glass covers of a solar cooker box-type with internal and external reflectors

In this work, an exergy evaluation to determine the energy availability across to glass covers, place where the solar radiation enters toward a solar cooker box-type is done. Considering the heating process of water, the energy not used is quantified by means of exergy. The results allow identifying the glasses in the cover as the zone where the solar cooker could be improved. The conduction heat transfer losses for the glasses is most big than 75%. Because the values for the conduction heat losses are around 90%, which are very important, this allows to identify the cover glass as the area where improvements could be made in this type of solar cookers.

The Effects of Laser Wavelength and Particle Size on Heating and Melting of Gold Nanoparticles Dispersed in Liquid

In this research the heating process and melting of water surrounded homogenous gold nanospheres irradiated by nanosecond laser pulses at the wavelengths of 355, 532, 633, and 900 nm are studied. The estimation of absorbed energy by gold nanoparticles with radius range 1-40 nm and their maximum temperature is calculated using the absorption efficiency of the nanoparticles at corresponding laser wavelength. The dependency of the melting temperature of nanoparticles upon their size is also considered. It is seen that the progress in the melting process strongly depend on the laser wavelength and particle size. The laser wavelength of 532 nm has been found appropriate for effective photothermal heating of a large gold nanoparticle. Controlling the laser irradiation wavelength is crucial to achieve the best conditions for the desired applications such as localized heating and nanowelding.

Combined Heat & Power: CHP Present & Future

Combined Heat and Power (CHP) is an efficient way to generate electricity and heat by utilizing the waste heat from the electric generator in place of heat from a separate boiler. Currently, most electricity is purchased from a central utility company that generates power at 35% efficiency; the balance of fuel input energy is lost as heat. With CHP some of the electricity is generated onsite and the waste heat from the generator (water jacket and exhaust) is used for space and water heating and other industrial processes that require heat. This reduces the fuel requirements to the boiler which also reduces emissions of Green House Gases (GHG) and other pollutants. Overall CHP efficiencies can make upwards to 85%. CHP is also known as Buildings Cooling, Heating & Power (BCHP), CHP for buildings (CHPB), Integrated Energy Systems (IES), Total Energy System (TES), Tri-generation (Trigen) and Cogeneration. CHP is best fit where there is demand for heat (or cooling load) and electricity is simultaneous e.g. hospitals, the hotel industry, educational institutes. Exhaust heat can be applied to support cooling loads with absorption chillers.

Experimental Analysis of Modified Stepped Solar Still

Fresh water is the basic requirement of human life. Water for drinking purpose, industrial and agricultural purposes demands ample quantity of fresh water. The solar desalination systems have the advantage of low maintenance and operational cost. In spite of high investment cost of solar stills, they are friendly to the nature. In the present article, a modified stepped solar still has been designed, fabricated and tested. The modification includes fabricating steps on which small earthen lamps are placed. The maximum temperature on the steps was found to be 67oC. In case of conventional solar still the maximum temperature recorded was 53oC. The maximum temperature of water at the steps was 26.41% higher than the basin temperature of conventional solar still. The maximum productivity of the modified solar still was 326.66% higher than conventional solar still. The optimum water input flow was found to be 250 ml/hr. I. Introduction Fresh water is primary requirement of human race. Water for drinking purpose and other industrial and agricultural purposes demands large quantity of fresh water (1). The solar desalination systems have the advantage of low maintenance and operational cost. Although solar stills have high investment cost, they are compatible with the environment (2). About 6.3 billion people are living on earth in which 400 million people are at living in water scarce areas which would rise to four billion by mid-century (3). The fabrication of solar still is simple and can be constructed by locally available materials and unskilled people. Solar stills are widely used for desalination in small scale. (4). According to an estimation, about 97% of available water sources are saline and/or consist of harmful bacteria and 2% are in the form of frozen glaciers and polar ice. Hence, only 1% of the earth's water can be used for drinking and domestic purposes (5).The arising requirement for water is primarily due to the increase of population and fast growth of industries (7). The heat energy of sun can be used in solar collectors, solar cooking, desalination and cooling systems (8). Generally, for steam generation, water heating processes and CPCs are used, as they are capable of producing higher temperatures in comparison of flat plate collectors, they can also be used for desalination purpose (9).Most of the arid, remote and semi-arid regions are lack natural fresh water in the southern part of the country and are dependent heavily on underground water for drinking purpose (10). Higher productivity is obtained in multiple-effect diffusion solar still (MEDS) (11). Solar stills are largely used for water purification in rural and remote areas with limited demand and low population when the potential of brine water sources and solar energy are available (12). II. Literature review There has been a lot of work in the field of solar stills to enhance its performance. Researchers have improved the performance by various means such as change in geometry, employment of mirrors in various orientation, use of waste heat etc. Park et al. (2016) designed a multiple-effect diffusion (MED) hybrid solar still with dual heat sources of solar thermal energy and waste heat. Performance tests with waste heat were performed with three operational parameters: (1) the seawater level in the basin (2) the seawater flow rate to the wick and (3) the amount of heat input into the hybrid still. It was observed that the productivity of the hybrid still increases with the increasing heat input, which recorded productivity of 18.02 kg/m 2 at waste heat amount of 22.37 MJ/d. The maximum productivity of distillate was obtained at the lowest seawater level with the experiment including waste heat source. The maximum performance of the MED solar still was achieved at the operation condition obtaining maximum productivity at the second effect plate (13). El-Agouz modified a stepped solar still using a storage tank for salt and sea water with continuous water circulation. Investigation was made on effect of installing a storage tank and cotton black absorber for modified stepped solar still on the distillate productivity. The indication was given by the results that, the productivity of the modified stepped still was higher than conventional solar still by 43% and 48% for sea and salt water with black absorber respectively, while 53% and 47% of sea and salt water, respectively with cotton absorber. The daily efficiency for conventional solar still was 20% lower than the modified stepped still. At a feed water flow rate of 3 LPM for salt water and 1 LPM for sea water, maximum efficiency of modified stepped still was obtained (8).

Thermal variations of water in the Nam Song stream/Mekong river: I. A mathematical model

River water temperature affects nearly every physical property related to water quality management. Therefore, anthropogenic change of water temperature is often undesirable. The objectives of this study were to develop an analytical model describing the thermal regime of a river–dam system. The model will be tested in a second manuscript using data from the Nam Song Basin in East Asia. The model incorporates three stages: (a) short time water heating process, (b) longer time water heating and (c) water cooling. Unified and continuous presentation of the above three solutions describes the complete thermal cycle. It showed that the longer the travel time from a dam (the Nam Song dam in this study) to the measuring point (slow flow rate), the larger the amount of energy absorbed and the higher its associated water temperature. According to the model the temperature of a water volume increases at a rate of ~1.2 °C/km downstream when water flow rate is 1 km/h. When water flows at a rate of 4 km/h, temperature increases at a rate of ~0.25 °C/km downstream. The model turns out to be a simple case of the kinematic wave theory, which is much easier to solve than large-scale computer simulation. For successful test of the model the specific parameters of the Nam Song River were used. Naturally, these parameters are changed from one river to another. Thus, to use the model for prediction of thermal regime in other rivers, their local specific parameters should be taken.

Thermodynamic analysis of solar assisted multi-functional trigeneration system

In this study, modelling and thermodynamic analysis of solar assisted trigeneration system was carried out. The required thermal energy for gas and vapor cycles were supplied from solar tower which is a new concept for gas cycle applications. Additionally, an absorption refrigeration cycle, vapor production process, drying process and water heating process were integrated to the system. Energy and exergy efficiencies of the trigeneration system were determined by the application of first and second law analyses. The results showed that the gas cycle efficiency was found to be 31%, vapor cycle efficiency was found to be 28% and coefficient of performance (COP) values of the refrigeration system was found to be 0.77. Also the highest exergy destruction rate was found to be 4154 kW in solar tower. Keywords: Solar tower, Trigeneration, Gas cycle, Vapor cycle, Energy, Exergy

Urban Stormwater Temperature Surges: A Central US Watershed Study

Impacts of urban land use can include increased stormwater runoff temperature (Tw) leading to receiving water quality impairment. There is therefore a need to target and mitigate sources of thermal pollution in urban areas. However, complex relationships between urban development, stormwater runoff and stream water heating processes are poorly understood. A nested-scale experimental watershed study design was used to investigate stormwater runoff temperature impacts to receiving waters in a representative mixed-use urbanizing watershed of the central US. Daily maximum Tw exceeded 35.0 °C (threshold for potential mortality of warm-water biota) at an urban monitoring site for a total of five days during the study period (2011–2013). Sudden increases of more than 1.0 °C within a 15 min time interval of Tw following summer thunderstorms were significantly correlated (CI = 95%; p < 0.01) to cumulative percent urban land use (r2 = 0.98; n = 29). Differences in mean Tw between monitoring sites were significantly correlated (CI = 95%; p = 0.02) to urban land use practices, stream distance and increasing discharge. The effects of the 2012 Midwest USA drought and land use on Tw were also observed with maximum Tw 4.0 °C higher at an urban monitoring site relative to a rural site for 10.5 h. The current work provides quantitative evidence of acute increases in Tw related to urban land use. Results better inform land managers wishing to create management strategies designed to preserve suitable thermal stream habitats in urbanizing watersheds.

Quality Determination for Drinking Water by Using Image Quality Assessment

Without human involvement, the need for an automatic algorithms for quality assessment takes place especially for the case of distinguishing the quality of drinking water when the latter has the same color. Image quality assessment is closely related to image similarity assessment in which quality is based on the differences between a degraded image and the unmodified image. Based on a design of a full reference image quality measure with the help of an assumption that one of the captured images can be modeled to be the original one. The similarity measure can serve then as a quantitative measurement of the quality of the second image. A comparison between images has been tested and then analyzed by using laboratory investigations first and then by image quality metrics. Images have been captured by adopting a designing system prepared for this purpose. Results show that difference in water turbidity, heating process, and magnetization affect strongly upon images band histogram during the comparison that has been made here between drinking water samples. Among the various metrics that have been used here, the results show that Normalized Cross-Correlation (NK) and Structural Content (SC) are the best used measures in the presented assumption.

EXPERIMENTAL VALIDATION OF A DYNAMIC MODEL FOR A RESIDENTIAL HEAT PUMP WITH IMMERSED CONDENSER

This work describes the validation of a dynamic model for a vapor compression residential heat pump with an immersed condenser. A detailed description of the modelling methodology for each component (compressor, capillary tube, evaporator, and immersed condenser) and the solution methodology employed in the complete heat pump system are presented. The main contribution of this work is in the dynamic modeling of the thermal processes occurring within the heat exchangers. Instabilities of the solutions for the heat exchangers are minimized by considering spatially and temporal varying errors. Another contribution of the model is the investigation of the temperature distribution inside the water storage tank, which highlights the possibility of using immersed condensers for this purpose without significant thermal stratification in the tank. Simulation results and experimental results are compared for transient operations using multivariate profiles of temperature, pressure and mass flow rates in heat exchangers during the water heating process.

Electrical and Thermal Performance Analysis for a Highly Concentrating Photovoltaic/Thermal System

A 30 kW highly concentrating photovoltaic/thermal (HCPV/T) system has been constructed and tested outdoors. The HCPV/T system consists of 32 modules, each of which consists of point-focus Fresnel lens and triple-junction solar cells with a geometric concentrating ratio of 1090x. The modules are connected to produce both electrical and thermal energy. Performance analysis has been conducted from the viewpoint of thermodynamics. The experimental results show that highest photovoltaic efficiency of 30% and instantaneous thermal efficiency of 30% can be achieved at the same time, which means the total solar energy conversion efficiency of the HCPV/T system is higher than 60%. The photovoltaic efficiency increases with direct irradiance when the direct irradiance is below 580 W/m2, but it remains nearly unchanged when the direct irradiation is higher than 580 W/m2. The instantaneous thermal efficiency decreases during water heating process. However, the electrical performance of the system is not affected obviously by water temperature. Highest exergetic efficiency of 35.4% can be produced by the HCPV/T system. The exergetic efficiency is mainly affected by irradiation level, which is similar to the characteristics of photovoltaic performance.

The investigation of the impact of basic operational parameters on the dynamics of water jacket in a biomass boiler using numerical and experimental methods

Biomass boiler application, despite its many advantages, is dependent upon many technical aspects, which require tests and optimization. Because of practical constraints, one of the most problematic areas of research is the analysis of phenomena occurring inside the water jacket of the boiler during the combustion process. The issue referred to above is significant due to its direct impact on the heating up of the operating medium for current power of the device and the total efficiency. The paper presents the analytical possibilities of the operating medium in a biomass boiler water jacket. The experimental works conducted as a part of the study were performed using an actual device – EKOPAL RM 40 straw boiler. They were aimed at defining the values of significant boundary conditions. Resistance thermometers and K-type thermocouples connected to a data acquisition system were placed in selected points of the water jacket and the combustion chambers to allow the monitoring of the conditions of the water heating process during biomass combustion. A measurement of inlet water mass flow rate was performed. To develop a numerical model of heat transfer into the water jacket, ANSYS CFX software was applied. The results of the experiments and simulations were compared and discussed. The paper describes the methodology and instruments used to perform the experimental studies, as well as some optimization solutions developed based on the results of the numeric alanalysis.

Development of a novel indirect-expansion solar-assisted multifunctional heat pump with four heat exchangers

A novel indirect-expansion solar-assisted multifunctional heat pump with four heat exchangers was proposed in this paper, which integrates a heat pump air conditioner, a solar water heater and a heat pump water heater. In addition to these three basic operation modes, it also provided five energy-saving operation modes, which resulted in a higher utilization ratio of the solar energy and lower operational cost. Experiments of the solar-assisted space heating mode, air source heat pump water heating mode and solar-assisted heat pump water heating mode have been investigated in detail at different outdoor temperatures and different water temperatures. The novel indirect-expansion solar-assisted multifunctional heat pump is especially suitable for the regions abundant in solar radiation where the space heating, space cooling and water heating are required all the year round. Practical applications: The novel IX-SAMHP can provide space cooling, space heating, hot water by one system. The space used for those appliances can be reduced effectively. Solar energy was used to assist the space heating and water heating and defrost process and it can save the energy consumption efficiently.

Investigations on single-phase natural circulation loop dynamics part 1: Model for simulating start-up from rest

Single-phase natural circulation loops are used in many industrial systems like nuclear reactors, geothermal systems, solar water heating systems and process industry. The present paper presents a 1-D model for simulating the startup from rest of water cooled single-phase natural circulation loops. A pseudo-conductivity model was developed previously by the authors to account for heat diffusion caused by local convection currents and the results of numerical simulation for loops having horizontal heater and horizontal cooler were presented. In the present study, the model has been used to simulate the start-up of loops having different heater and cooler orientations and the applicability of the model as a general tool for simulating start-up of rectangular natural circulation loops is assessed. The paper presents more insight into the behavior of pseudo-conductivity models developed to simulate start-up of these loops from state of zero flow.

Novel method of stabilizing water pretreatment for reverse osmosis desalination

The preparation of functionalized filter media (FFM), its ability to release active antiscalant substances and its application for water treatment in water heating processes and as a pretreatment in reverse osmosis (RO) desalination were investigated in this study. FFM is a novel method of stabilizing water pretreatment designed to be free of the disadvantages of conventional methods of water scaling potential reduction which require expensive equipment, produce significant amounts of waste, have high reagent consumption or are strongly dependent on water composition. FFM was derived from anion exchange resin modified with phosphonate and polymer scale inhibitors. In order to choose the most suitable anion exchange resin for preparation of FFM, different types of resins were tested for sorption of phosphonate compounds. The effect of the anionic composition of water and the effect of the polymer inhibitor on the rate of phosphonate release were investigated. Finally, FFM was tested as a scaling reduction water treatment for a water heating process with heating coils and as a pretreatment before reaching the RO unit. In both cases the results obtained show great promise for the functionalized material in antiscaling water pretreatment.

Modeling of fluid flow and heat transfer in a trough solar collector

This paper analyzed the flow and heat transfer processes in a trough solar collector of the direct steam generation (DSG) system. A flow and heat transfer model of the working fluid in the absorber was established and solved using the finite difference method. Experimental results of liquid water and dry air heating processes validated the model. The experimental results, got under the condition that the vacuum in the tube was destroyed, were used to test the developed model. The calculation results of the model agreed with the experimental data. The dynamic characteristics of the collector outlet parameters under variations of solar radiation intensity were analyzed in this paper. The impulse response of the DSG system was complex as a short-time fluctuation of the solar radiation notably affected the water region length, the two-phase region length and the steam region length, which led to large fluctuations in the outlet temperature. Therefore, the outlet temperature of the once-through DSG system was difficult to control. Extra heat was required to maintain the normal operation of the system.

Dynamic model and experimental study of an air–water heat pump for residential use

This paper presents a study of the dynamic behavior of a vapor compression heat pump for residential water heating. The mathematical models for heat exchangers are formulated by using mass, momentum, and energy conservation equations, while capillary tube model is based on the equations of conservation of momentum. The model is formulated from the manufacturer experimental data and the energy conservation balance. The contribution of this study to the field of dynamic modeling appears on the convergence of models of heat exchangers, this being accomplished with a variable error in spatial and time minimizing the instabilities in the calculation. The coupling among the four components allows the determination of the spatial and temporal profiles of temperatures, pressures and mass flow rates, as well as the refrigerant distribution in the heat exchangers during the water heating process. The validation of the model is done by comparison with the experimental results.

青藏高原多年冻土区积雪对沼泽、草甸浅层土壤水热过程的影响

The average altitude of Tibetan Plateau is over 4000 m above sea level with vast areas of permafrost.The interaction between permafrost and the atmosphere is realized by the dynamic water-heat process within the active layer.The snowy condition on the earth surface directly impacts on the variations of the thickness of the active layer and the annual mean soil temperature in the permafrost area.Thus,the shallow soil water-heat process with or without snow cover is a very important uncertain factor in the water and energy circulation processes of the permafrost areas in Tibetan Plateau.In typical alpine meadow and swamp,the active soil moisture and temperature at different depth of layer were observed to reveal the influences of the snow cover changes on the soil water-heat processes.The results show that the thawing and freezing started-time of active soil were later and the duration of freezing were longer with snow cover than that without snow both in alpine meadow and swamp areas.With the snow cover,the active soil temperature variation rate decreased while the soil moisture variation rate increased.The snow cover plays important roles in restraining the soil temperature change and b accelerating the moisture change in active soil layer.The impacts of snow cover on soil temperature and moisture are greater in autumn and summer than that in winter and spring,and the influence is more dominant in melting process than in freezing process.Snow cover results in reducing the annual maximum soil temperature and rising the annual minimum soil temperature in alpine swamp.On the contrary,both the annual maximum and minimum soil temperature increase under snow cover in alpine meadow.By comparing the temperature differences between the annual maximum and minimum temperature of swamp and meadow soil with or without snow cover,it shows that the snow cover has greater influence on swamp soil temperature than on meadow soil.Some parameters,such as time of melting(Ts),duration of melting and increasing(Tr),the range of soil moisture content increasing(ΔWs),time of freezing(Td),duration of freezing(Tz) and the range of soil moisture content falling(ΔWd),were selected to objectively reflect the influence of snow cover on soil moisture during the freezing process.The results show that the snow cover has more influence on soil moisture in melting and rising process than that in freezing and falling process,and has a more influence on swamp soil moisture than on meadow soil.

A process model for simulating net primary productivity (NPP) based on the interaction of water-heat process and nitrogen: a case study in Lantsang valley

Terrestrial carbon cycle and the global atmospheric CO2 budget are important foci in global climate change research. Simulating net primary productivity (NPP) of terrestrial ecosystems is important for carbon cycle research. In this study, a plant-atmosphere-soil continuum nitrogen (N) cycling model was developed and incorporated into the Boreal Ecosystem Productivity Simulator (BEPS) model. With the established database (leaf area index, land cover, daily meteorology data, vegetation and soil) at a 1 km resolution, daily maps of NPP for Lantsang valley in 2007 were produced, and the spatial-temporal patterns of NPP and mechanisms of its responses to soil N level were further explored. The total NPP and mean NPP of Lantsang valley in 2007 were 66.5 Tg C and 416 g·m−2·a−1 C, respectively. In addition, statistical analysis of NPP of different land cover types was conducted and investigated. Compared with BEPS model (without considering nitrogen effect), it was inferred that the plant carbon fixing for the upstream of Lantsang valley was also limited by soil available nitrogen besides temperature and precipitation. However, nitrogen has no evident limitation to NPP accumulation of broadleaf forest, which mainly distributed in the downstream of Lantsang valley.