Heat Loss Coefficient Research Articles

Low temperature heating system for greenhouses based on enclosed water curtain and liquid foam insulation

A greenhouse water curtain heating system allows heating of the greenhouse by low-temperature water, which can be obtained from residual waste heat sources. The water curtain can be applied on the outside of the greenhouse roof or enclosed between two foils. But also enclosed water curtains suffer from high heat losses, which limits the integration of low temperature waste heat sources. An effective way of reducing the heat losses is to combine the water curtain system with retractable liquid foam enclosed between two foils. But until now, a systematic evaluation of the thermal performance of such system combination is still lacking. Thus, this study aims to fill in this research gap by evaluating the heat transfer characteristics of a double-foil greenhouse roof section installed with a combined water curtain and liquid foam system. Experimental tests have been conducted under a wide range of temperature scenarios in a climate chamber where the heat loss and heat gains from the water curtain is measured. The results have been compared with the data in the existing studies. This study revealed that combining the water curtain system with liquid foam, reduces the heat losses by half compared to using just the water curtain: the heat loss coefficient was reduced from 4.4 W·m−2·K−1 down to 2.0 W·m−2·K−1. The heat losses through the roof using the combined system are also lower than the heat losses from a double foil greenhouse with other heating systems. An average water curtain temperature of 5.1 °C above the inside greenhouse temperature can compensate for the heat losses through the roof at an outdoor temperature of −19 °C. Based on the study results, recommendations for market implantation of this technology are provided. This study confirms energetic benefit of combining water curtains and the liquid foam technology.

Investigation of the effect of solar water heating of vacuum tube on heat loss coefficient

In the solar thermal utilization system, it is necessary to study the factors that affect the heat loss of the hot water storage tank. Therefore, the heat loss coefficient of the hot water storage tank in the all-glass vacuum tubular solar water heater is calculated using experiments and measured data in the present study. Then the problem is analyzed in forced circulation and non-forced circulation conditions. According to the results of the investigation, the heat loss coefficient of the thermal storage tank in the forced circulation state is 12.6 times that of the non-forced circulation condition. The heat loss coefficient is impacted by the tank temperature, intake, and exit water temperatures, circulating water flow rate, wind speed, and ambient temperature, as determined by a linear regression analysis of the experimental data. It is found that in the non-forced circulation, wind speed significantly affects the heat loss coefficient, specifically, the heat loss coefficient increases by 0.49 W/(m2·℃) for every 1 m/s increase of wind speed when all other factors are constant. But wind speed can be neglected in the forced circulation condition. Moreover, it is observed that as the inlet water temperature increases, the corresponding heat loss coefficient increases.

Structure and extinction of reverse smolder waves in the presence of heat losses: A premixed-flame perspective

A reverse smolder wave is structurally analogous to a premixed flame in the sense that the solid fuel and the gaseous oxidizer enter the reaction zone in a co-current manner. Such structural similarity is explored in this work to analytically examine the structural characteristics and extinction properties of planar reverse smolder waves that are driven by a forced oxidizer flow, based on the activation-energy asymptotic method. The analysis covers both the adiabatic condition and the non-adiabatic condition resulting from an external heat loss. Within the framework of the adopted diffusive-thermal model, two distinct reaction regimes are identified, namely the fuel-rich regime and the fuel-lean regime, separated in between by a stoichiometric state, which corresponds to a critical gas mass flux (for the adiabatic condition) or a critical heat loss coefficient (for the non-adiabatic condition). It is found that, under both adiabatic and non-adiabatic conditions, extinction occurs exclusively in the near-stoichiometric fuel-lean regime, in the sense that the values of characteristic quantities at the extinction limit are at most O(ε) away from those at the corresponding stoichiometric state, where ε is a small parameter inversely proportional to the activation energy. It is then demonstrated how this near-stoichiometric character can be exploited to seek a series-form representation of all the quantities characterizing the extinction limit, where the normalized initial oxygen mass fraction and the oxygen Lewis number are identified as two primary control parameters. A close examination of the differences between reverse smolder waves and premixed flames identifies a mechanism that may account for why reverse smolder waves are generally more robust than premixed flames when subjected to heat losses. Further, it is justified that limiting kinetics as a unified bottom-level mechanism can provide a uniform characterization of the extinction conditions of non-adiabatic reverse smolder waves.

A data-driven framework for characterising building archetypes: A mixed effects modelling approach

Building archetypes are a common solution to study the energy demand of cities and districts. These are generally based on building information such as construction year and function. However, there can be large differences in the energy demand of buildings of the same archetype due to factors such as the preferences of occupants, quality of the building construction, and unrecorded renovations. This work uses a non-linear mixed effects model to capture these random differences. The model uses weather measurements to generate the daily heating load of buildings for the whole year. The model is generated and tested using data from 56 Norwegian apartments. Results show that 91% of measurements from an out-of-sample test set fall inside the 95% prediction interval. Additionally, the model allows us to compute a proxy of the heat loss coefficient, which characterises the heating performance of the population of apartments. Finally, two sub-categories of apartments are identified by clustering the model estimates for the studied population. The model is general, computationally light and uses existing data that are commonly collected in many buildings. The suggested method offers a more robust and reliable method to segment building archetypes using only weather data and energy demand.

Design and performance characteristics of a solar box cooker with phase change material: A feasibility study for Uttarakhand region, India

• A low-cost ($55.01) box cooker is especially designed for the people of Uttarakhand region of India. • Thermal performance enhancement is achieved by using aluminum made hollow capsules and encapsulated PCM over the cooking plate. • Encapsulated PCM enhanced the heat transfer rate about 301 W/m°C between cooking plate and cooking stuff. • Cooking power and thermal efficiency are obtained about 53.21 W and 52.10%, respectively. • Feasibility analysis shows the possibility of fair adoption of the tested box cooker in India. In the present work, the thermal performance of a low-cost solar box cooker (SBC) has been improved through the concept of extended fins and heat storage medium. To achieve the goal, about 144 aluminium made small capsule shaped containers have been filled with PCM and placed horizontally over the absorber. Experiments have been conducted on the three different configurations such as, SBC without any modification, SBC with hollow capsules and SBC with an encapsulated PCM. Experimental study mainly emphasizes on a high heat transfer rate and reduced cooking times through the applied modifications. Thermal performance has been found improved by using encapsulated PCM during the cooking trials. Results showed that the last configuration is the best among the three different configurations developed for cooking experiments. Thermal efficiency has been found improved by 52.2%, heat transfer coefficient improved by 301 W/m o C, cooking power enhanced about 53.21 W, and the overall heat loss coefficient reduced about 4.11 W/m o C on the third configuration. The modified SBC purposely designed for the people from hilly regions who are unable to access the clean cooking fuels. Present design is economic ($55.01) and feasible for cooking of common edibles available in Uttarakhand and nearby regions in India. The payback period ranges from 0.80 years to 4.01 years for different fuels. Notified that the modified cooker also meets the Bureau of Indian standards (BIS) developed for solar cookers.

Calculating the heat loss coefficients for performance modelling of seasonal ice thermal storage

This paper details the use of piece-wise linear regression and non-linear optimisation to determine the heat transfer properties of two ice thermal stores of different volumes (85 m3 and 11 m3). The available energy of each ice storage was determined by the fraction of ice stored in the vessel. The heat loss coefficient was determined using an optimisation algorithm. Using this approach it was possible to determine the heat loss coefficients occurring at different layers of the storage. Validation of the approach yielded a relative mean error of 5.4% and 3.8% for the 85 m3 and 11 m3 storage respectively. This approach is dependent on the measurement of temperature at different segments and the quantity of ice in the storage. It is believed that this approach is scalable and could contribute to a performance database that could provide inputs to energy modelling studies.

Tilt Angle Optimization and Investigation of the Behavior of a Flat Plate Solar Collector Using MATLAB for Kurdistan Climate Conditions-Iraq

The goal of this study is to investigate the heat transfer as well as optimizing the tilt angle of an active flat plate solar collector. In addition, MATLAB software is used for study the flat plate solar performance of the collector. The entire test rig, with a complete control system, has been set up to collect practical data in September and October 2021. The results showed that the collector efficiency rises with the usable heat rate, peaking at 77% in the autumn (14 October) at the optimal heat rate of 975 W and an outlet water temperature of 64℃. However, the system efficiency for the sunny environment is 53% with an outlet temperature of 36℃ in winter (6 Jan). According to this investigation, the monthly average value and yearly value of optimum tilt angle were found to be 30° to 40° and 30°, respectively, for Erbil climate conditions. Also, this study reveals that the average heat loss coefficient between theoretical models and experimental work was 4.352 W/m2.℃. Furthermore, the temperature difference, corresponding to the same amount of heat loss coefficient, was 14.4℃ for the practical model but 15.25℃ for the theoretical part. This study proposes that using the entire experimental data from a Flat Plate Solar Collector instead of using average values and comparing it to the mathematical equations implemented in the MATLAB software, the thermal efficiency of the system was increased by 5%.

Comparative performance analysis of flat plate solar collector having circular &trapezoidal corrugated absorber plate designs

Flat plate Solar collectors are in use for a long time and have well-established technologies for low-temperature thermal applications. Use of newglazing materials, absorber plate designs, selective coatings, and advanced working fluids, thermal conversion efficiencies of these devices can be further improved. Design modification always comes under top priority because it brings auxiliary changes that further modify the system's overall efficiency. Increasing energy demand puts extra attention on the researchers to develop solar thermal energy-based systems. The presented experimental analysis is based on the design modification of the collector absorber plate to modify the contact area between the absorber plate and collector tubes. We performed a comparative performance of the circular absorber surface and the trapezoidal surface of contact with absorber tubes. The following results indicate that the trapezoidal absorber surface serves better over circular and plate absorber surfaces.Thermal efficiency increases by 8.74% and 12.85% for absorber plate's circular and trapezoidal corrugated surfaces. Exergy efficiency is improved by 16.88, 23.31%, and the overall heat loss coefficient decreases by 7.49 and 8.72% for circular and trapezoidal corrugated surfaces, respectively. The collector's heat removal factor is also significantly higher for trapezoidal corrugated absorber plate than the normal collector absorber surface.

QARABAĞ “YAŞIL” ENERJİ ZONASI ÜÇÜN GÜNƏŞ PANELLƏRİ İSTİLİK ENERJİSİ İSTEHSALININ QİYMƏTLƏNDİRİLMƏSİ

The analysis of the prospects for the efficient use of renewable energy sources is relevant from the point of view of the implementation of the order on the transformation of the Karabakh region of Azerbaijan into a "green" energy zone. The article is devoted to the application of solar panels for climatic parameters of the Gubadli region of Karabakh and the assessment of thermal energy production capacity through a calculation program. The number of Hevelius SCM-12-180-58 (made in Poland) tubular panels located in an area of 50 m2 in the Gubadli region is 12, performance coefficient is 70%, the heat loss coefficient of vacuum pipes is 0.5 W/m2 , the average amount of thermal energy obtained by solar radiation is 1625 kW/m2 and the total heat production is 14837 kW/h per year. The methodology can be applied to any region.

An experimental examination of a helically coiled conical cavity receiver with Scheffler dish concentrator in terms of energy and exergy performance

In this paper, the thermal performance of a helically coiled conical cavity receiver is investigated under actuation radiation conditions with a 16 m2 parabolic Scheffler dish concentrator. Under three different radiation scenarios, the receiver thermal energy efficiency, exergy efficiency, and overall heat transfer coefficient are investigated. Water is employed as a heat transfer fluid, and the receiver is tested at a flow rate of 2.5 L per minute in a temperature range of 30–100 °C. During the stagnation test, the receiver's maximum stagnation temperature was recorded as 395 °C for an incoming beam radiation of 654 W/m2, which demonstrates the receiver's ability to generate pressurised steam. The overall heat loss coefficient calculated from the stagnation test is 116 W/m2-K. The heat transfer fluid input and output temperature differences, as well as incoming beam radiation, are found to have a significant impact on the receiver's energy and energy efficiency. Under maximum beam radiation conditions during the second experiment (672 W/m2), the average thermal energy efficiency and exergy efficiency were determined to be 70.20% and 8.69%, respectively. Based on the findings, this receiver has the potential to be employed in temperature applications up to 100 °C and above for steam generation under pressurised conditions.

Research of efficiency of solar coating in the heat supply system

Abstract According to the energy development strategy of Ukraine, implementation of energy efficient buildings is needed, in which external protections are converters of solar energy into heat. The article presents studies of solar coating with direct coolant supply. Studies of the average value of the heat loss coefficient of the solar coating were also carried out. As a result, the efficiency of the solar coating under the mode of forced circulation of the coolant is 0.67, at natural circulation of the coolant – 0.57 and at its direct supply is 0.71. Experimental researches of thermal and physical parameters of a solar covering and system of heat supply on its basis showed in the corresponding dependences influence on its thermal characteristics of dynamic modes of the heat carrier, energy, kinetic characteristics of the environment.

A cost-effective water heating solution for the people of Chhattisgarh, India

In this paper, we offer a cost-effective water heating solution for the rural people of Chhattisgarh, India. A single glazed floating cover has been designed from locally available materials in the current effort to boost the effectiveness of open heating water outside in the sun. The cover's upper face is made of transparent polythene, while the lower face is made of black polythene. The floating cover must be kept over the water-filled thermocol insulated bucket/tub. The solar radiation transmits through glazing is absorbed by black polythene. The water in contact gets heated. The heated water can be utilized later in the day. A mathematical model of the proposed heater has been developed and validated by an experiment. The overall heat loss coefficient has been experimentally determined. A simple techno-economic analysis has been performed. The cost of heating water is Rs0.71/kWh (US$0.01/kWh) for the climate of Raipur, Chhattisgarh, India (21° 9′ 53.9748″ N and 81° 46′ 31.1052″ E). The proposed method's cost of heating water is about 85.8% less than the cost of water heating by electricity. The water temperature available in winters is between 29°C to 38°C, and the maximum degree of heating of water is about 17.1°C.

Energy and exergy based study on a box type solar cooker coupled with a Fresnel lens magnifier

ABSTRACT The variation of energy and exergy efficiency of a Box-type solar cooker (BTSC) incorporated with a Fresnel lens magnifier (FLMG) is evaluated in this study. The comparison in energy and exergy efficiency was investigated in the absence and presence of the FLMG to determine the efficiency variation of the BTSC by addition of the FLMG. With the implementation of FLMG, the average values of energy and exergy efficiencies had increased by 10% and 8.52%, respectively. The magnitude of energy efficiency with and without FLMG decreased with time, whereas the exergy efficiency enhanced with time for both cases. The manuscript discusses the effect of different thermodynamic parameters like temperature difference, energy and exergy output, absorber mean plate temperature, and heat losses in the modified cooker. The total heat loss coefficient ranged from 5.48 to 8.44 W/m2K and depended on the variation of wind velocity. The maximum heat loss and mean plate temperature were found to be 120 kJ and 128.3°C, respectively. The time for sensible heating was reduced by 16 mins by the implementation of the FLMG. The addition of the lens showed an increase in the Area concentration ratio (AR) of the BTSC by 48.7%. By comparing the cost and energy usage of LPG (Liquefied Petroleum Gas), the payback period and the quantity of carbon dioxide reduced per month were calculated as 3.19 years and 8.265 kg, respectively.

Investigating Energy Use in a City District in Nordic Climate Using Energy Signature

This paper focuses on multi-family buildings in a Swedish city district, erected between 1965 and 1973, which are now in need of renovation. For the two types of multi-family buildings in the district, tower buildings and low-rise buildings, dynamic energy use is predicted by using an energy signature method. The energy signature is then used to calculate the primary energy use number of the building stock, according to calculations methods dictated by Swedish building regulations. These regulations are also used to assess which multi-family buildings are in need of renovation, based on the buildings’ primary energy use. For buildings that need energy renovations, it is simulated so that the energy use of each multi-family building complies with these same building regulations. The proposed methodology for simulating energy renovation also determines new energy signature parameters, related to building heat loss coefficient, balance temperature and domestic hot water usage. The effects of simulated renovation are displayed in a duration diagram, revealing how a large-scale renovation affects the district’s heat load in different annual periods, which affects the local district heating system. Sensitivity analysis is also performed before and after simulated energy renovation.

Theoretical analysis on the ignition of a combustible mixture by a hot particle

Mechanical spark is an important ignition source in various industrial processes involving combustible mixtures and it may cause serious safety issues. In this work, we analysed the ignition induced by hot particles in a combustible mixture. In Semenov's transient ignition criterion, we introduced a hypothetical heat loss coefficient accounting for the temperature inhomogeneity and obtained a revised ignition criterion which allows us to calculate the ignition delay time. Explicit expressions for the critical ignition temperature were derived and used to demonstrate the primary impacts of temperature inhomogeneity on the ignition process. Consistent with experimental and numerical results, the temperature inhomogeneity is intensified by either reducing the particle size or convective heat transfer at the particle surface, resulting in an increase of the critical ignition temperature. For flow separation on the particle surface, the boundary layer problem was solved based on a Blasius series. A temperature gradient for ignition was defined at the location of flow separation to reproduce the experimentally observed phenomenon that ignition prefers to occur first near the flow separation position. It is shown that the unsteadiness of particle cooling makes negligible contribution to the ignition process because of the exceedingly large density ratio between the particle and the ambient gas. In addition, the finite residence time of ignition for a fluid parcel due to its elevation from the particle surface leads to additional growth in the critical ignition temperature. However, such a correction appears to be inconsequential because the ignition of the fluid parcel restricted to the Frank–Kamenetskii region is close to the particle surface.

Optimisation of a recirculating domestic hot water system to minimise wait time and heat loss

Many houses suffer from a delay in hot water arrival, after opening the hot tap, due to the length of pipe work from the boiler or thermal store. Measurements in three properties showed delays of up to 46 s. A recirculation system could maintain the water in the pipe at a suitable temperature and for a 15 m pipe is expected to use 30 W less electrical power than a local thermal store at the delivery point. Time-steady eigenvector solutions to the linked temperature equations allow optimisation of the recirculation flow rate, pipe diameters and insulation thickness. The pumping power is <1 mW and a pumpless thermo-syphon system should be possible in some installations. Heat loss coefficients have been calculated for a pair of pipes in a common insulation sleeve to minimise the losses. A plug flow transient advection model for water and pipe temperature based on a sliding 1-D grid has been developed and validated for a single pipe, then extended to also model recirculating systems. Heat losses in a pumped system may be reduced using a timer so the system can cool overnight. The transient model predicts the relationship between flow and warm-up rate to optimise pump size and timing.

A control-oriented scalable model for demand side management in district heating aggregated communities

District heating networks have become widespread due to their ability to distribute thermal energy efficiently, which leads to reduced carbon emissions and improved air quality. Additional benefits can derive from novel demand side management strategies, which can efficiently balance demand and supply. However, their implementation requires detailed knowledge of heating network characteristics, which vary remarkably depending on urban layout and system amplitude. Moreover, extensive data about the energy distribution and thermal capacity of different areas are seldom available. For this purpose, the present work proposes a novel procedure to develop a fast scale-free model of large-scale district heating networks for system optimization and control. Each network community is represented and modeled as an aggregated region. Its physics-based model is identified starting from a limited amount of data available at the main substations and includes heat capacity and heat loss coefficients. The procedure is demonstrated and validated on the network of Västerås, Sweden, showing results that are in agreement with data from the literature. Thus, the model is well suited for real-time optimization and predictive control. In particular, the possibility to easily estimate the heat storage potential of network communities allows demand side management solutions to be applied in several conditions.

Energy, exergy performance and analysis of 50w solar photovoltaic module

With the speedy exhaustion of fossil fuels, chances for renewable energy including solar energy are limitless. The solar photovoltaic (PV) system produces both thermal energy and electrical energy by using solar radiation. In this article, an experimental study has been conducted for evaluating the electrical, thermal and exergy output of solar PV panel installed. Energy analysis was performed on the solar PV module by using first law of thermodynamics; exergy analysis was performed to determine the exergy efficiency and losses during the PV conversion by using the second law of thermodynamics. The various electrical and operating factors such as temperature, open-circuit voltage, short-circuit current, and overall heat loss coefficient for solar PV module.

Heat Exchange of the Cylindrical Liquid Body of a Limited Height with the Environment

The experimental investigations of the intensity of the heat exchange between the internal surface of the thin-wall metal cylinder and the studied liquid medium were carried out in conditions of its cooling (heating), i.e. under nonstationary heat exchange conditions. The existence of the regular thermal mode in the liquid medium surrounded by the thin-wall metal cylinder has been established. Local in time heat loss coefficients were derived using appropriate dimensionless equations for the stationary mode conditions of heat-exchange in a large volume. Heat loss coefficients were determined using regular thermal mode methods and computational-&amp;-experimental heat loss coefficients. The changes in the relative values of the heat loss coefficients were analyzed using the method of regular thermal mode and computational-&amp;-experimental heat loss coefficients. The deviations in the values of given coefficients in time are mainly within ± 10 %. Relative values of the heat loss coefficients deviate within ± 40 % using appropriate dimensionless equations for the conditions of the stationary mode of heat exchange in a large volume. This conclusion is natural because the cooling (heating) process is nonstationary.

Investigation of laminar forced convection heat transfer of nanofluids through flat plate solar collector

The paper analyzes laminar forced convection heat transfer for both single and mixture phase models utilizing Al2O3-water and CuO-water nanofluids as the working fluid and examines the effect of internal fins in the collector tubes in order to improve collector efficiency. A physical model with governing equations has been defined. Finite volume method has been utilized for discretizing governing equations and finite element method has been utilized for three-dimensional analysis of solar plate model with finned tubes. Convective heat transfer coefficient, Nusselt number and shear stress have been analyzed for Reynolds numbers from 200 to 700 with 0-5% volume fractions of nanofluid. Moreover, the efficiency of the collector has been investigated for constant flow rates from 0.02 to 0.04 mL/s and variable overall heat loss coefficient for the same range of volume fractions of nanofluid. It has been found that increment of shear stress and heat transfer coefficient occurred with the increment of concentration of nanoparticles and the Reynolds number. Investigation of particle size has not shown any notable variation with the mixture phase model. Mixture-phase model gives comparatively lower values due to the reduction of viscosity near the wall. Noticeable increment of efficiency has been observed by changing working fluid from Al2O3-water to CuO-water which has been further improved by utilizing variable overall heat loss coefficient. Efficiency increases up to 6.5% and 8.7% than the base fluid for utilizing Al2O3-water and CuO-water nanofluid respectively. Additionally, utilizing internal fins to the riser tubes, the efficiency increases up to 11%.