Heat Output Power Research Articles

Thermodynamic Performance of Heat Exchangers in a Free Piston Stirling Engine

There is an increasing request in energy recovery systems that are more efficient, environmentally friendly and economical. The free piston Stirling engine has been investigated due to its structural simplicity and high efficiency, coupled with its cogeneration ability. This study presents the numerical investigation of quasi-steady model of a gamma type free piston Stirling engine (FPSE), including the thermodynamic analysis of the heat exchangers. Advanced thermodynamic models are employed to derive the initial set of operational parameters of the FPSE due to the coupling of the piston’s (displacer and piston) dynamics and the working process. The proximity effect of the heater and cooler on the regenerator effectiveness in relation to the heat losses, output power, net work and thermal efficiency of the FPSE are also observed and presented in this study. It can be observed that at temperatures of 541.3 °C and 49.8 °C of the heater and cooler, respectively, with heater volume of 0.004 m3, regenerator volume of 0.003 m3 and cooler volume of 0.005 m3, the FPSE produced an output performance of 996.7 W with a thermal efficiency of 23% at a frequency of 30 Hz. This approach can be employed to design effective high performance FPSE due to their complexity and also predict a satisfactory performance.

ИССЛЕДОВАНИЕ ТЕМПЕРАТУРНОГО ПОЛЯ ПРИ ТОЧЕНИИ С НАЛОЖЕНИЕМ ВИБРАЦИЙ

The temperature of a cutting process influences significantly the quality of the treated surface and the performance of a tool. The rational use of vibrations, including the ultrasonic frequency vibrations is one of the means to improve the efficiency of a cutting process. However, there are no analytical studies of the temperature of turning with vibration superposition. It was accepted that the total heat output power when turning was equal to the sum of heat output powers of sources aroused as the result of the transition to the heat of work of deformation and work of friction forces on the leading and flank surfaces of a tool. The paper presents the mathematical dependences for calculation of the components of the total power of heat release. The authors took into account that the yield stress, which determines the cutting and frictional forces on the contact surfaces of a cutter, workpiece, and chip, depends on the temperature in the plastic deformation area. The law of distribution of thermal power density on the shear plane was taken as uniform; the combined law was adopted on the surface of the contact of a chip with the front surface of a cutter; the asymmetric normal law was adopted on the surface of the contact of a cutter with a workpiece. The authors gave the dependence for the calculation of the cutting depth when applying vibrations in the direction perpendicular to the treated surface. Heat exchange at the boundaries of the objects contacting with the process liquid or air is given in the form of the Newton-Richman law. The thermal conductivity equations of the contacting objects were solved in combination with the general boundary conditions in the contact zone using the finite element method. The method of calculation based on the discrete analogs of the heat conduction equations is implemented in the original programs. The authors compared the results of calculation of temperatures when turning without the vibrations superposition with the experimentally obtained results, in this case, the discrepancy between the calculated and experimental values does not exceed 10 %. The simulation of the turning process with the superposition of ultrasonic vibrations showed that the main component of the cutting force Pz reduced by a mean of 11 %, the maximum temperature in the zone of contact of the back surface of a cutter with a workpiece reduced by 20 %, and the maximum temperature in the zone of contact of the front surface of a cutter with a chip reduced by 26 %.

Experimental study of water cooling effect on heat transfer to increase output power of 180 watt peak photovoltaic module

Photovoltaic (PV) modules require solar radiation to generate electricity. This study aims to determine the effect of water cooling PV modules on heat transfer, output power, and electrical efficiency of PV modules. The experiments carried out in this study were to vary the heights of flooded water (with and without cooling water replacement control) and cooling water flow. Variations in the height of flooded water are 0,5 cm, 1 cm, 2 cm, and 4 cm. While the flow rate variations are 2 L/min, 4 L/min, and 8 L/min. The flooded water replacement control will be active when the PV surface temperature reached 45°C. When the temperature dropped to 35°C, the cooler is disabled to let more photon to reach PV surface. The results showed that the lowest heat transfer occurred in the variation of 4 cm flooded water height without water replacement control, i.e. 28.53 Watt, with an average PV surface temperature of 32.92°C. The highest average electric efficiency occurred in the variation of 0,5 cm flooded water height with water replacement control, i.e. 13.12%. The use of cooling water replacement control is better due to being able to skip more photons reach PV surface with low PV temperature.

Experimental investigation on thermochemical heat storage using manganese chloride/ammonia

Thermal energy storage plays a key role in the application of renewable energy and low-grade thermal energy. A laboratory test unit of thermochemical heat storage with manganese chloride (MnCl2) as the reactive salt and ammonia (NH3) as the working gas was constructed, in which expanded graphite was used to improve the heat and mass transfer performance of composite materials. The experimental campaigns show some promising conclusions on the heat storage performances of such a storage unit. With 3.78 kg of composite materials, the highest thermochemical heat storage density is about 1391 kJ/kg when the charging and discharging temperature is 174 °C and 50 °C, respectively. The corresponding volume density of thermochemical heat storage is 179 kWh/m3. The maximum of thermochemical heat storage efficiency obtained is 48%. The maximum of instantaneous thermochemical heat output power is more than 50 kW. The maximum for the average thermochemical heat output power reaches to 9.9 kW under the experimental conditions. The application prospects of such a thermochemical heat storage system are presented. The promising results have been gained, but some problems must be envisaged. The improvement measures to overcome these problems are also brought forward in order to make the thermochemical heat storage technology realize a successful application in practical systems.

Dispatch Model of Combined Heat and Power Plant Considering Heat Transfer Process

Due to the coupling of its heat and power output, combined heat and power (CHP) has limited flexibility, which is one of the main reasons for variable renewable energy source (RES) curtailment problem in Northern China. Almost all the existing studies have modelled the CHP's output characteristics as a feasible operation region of electric power and heat power. However, only the extraction steam of a CHP unit that used for district heating can be controlled directly, without considering the extraction steam's heat transfer process, the actual heat power output cannot be precisely decided. Thus this paper proposes a detailed CHP dispatch model based on the principles of heat transfer. A three-stage heat transfer model of the extraction steam is used to describe the heating process. Then, a joint dispatch model concerning CHP units, conventional thermal power units, and RESs is given. Finally, the impacts of different factors on the extraction steam's heat transfer process and its influence for RES accommodation are analyzed. Results show that considering heat transfer process is essential in modelling the CHP plant that used for district heating, especially when the CHP plant is working at a status that deviates from the rated one significantly.

Helical configuration for thermoelectric generation

Performance of thermoelectric (TE) generator (TEG) depends on its physical structure in addition to the properties of TE materials. This study numerically simulated the characteristic performances of a three-dimensional (3-D) helical TE module using finite-volume method, and compared them with those of a conventional straight module. The effect of geometric parameters of helical TE module on the characteristic performances was analyzed, and an optimal helical design was proposed to obtain higher performance. The simulation results show that the helical module can harvest more heat than the straight module, and thus generate higher output power because the conversion efficiencies of two modules are approximately equal. The increase in pitch of the helical module has a positive influence on the characteristic performances, including more heat harvesting and output power, as well as higher conversion efficiency. However, the radial expansion of helical module brings an opposite effect on the unit performances, which is defined by dividing the characteristic performances by the number of p–n pairs, and unit input heat, unit output power, and unit heating area of helical module are decreased with module diameter. Higher performance can be generated by the use of helical module with longer pitch and shorter diameter.

Chemical Heat Storage of Thermal Energy from a Nuclear Reactor by Using a Magnesium Hydroxide/Expanded Graphite Composite Material

Abstract In this work, chemical heat storage is proposed for the accumulation of the surplus thermal energy generated by a nuclear reactor during low demand of electricity and its re-utilization for the peak demands. Thermal energy is converted into chemical energy or vice versa by operating a reversible chemical reaction, consisting in the dehydration of magnesium hydroxide (Mg(OH)2) and the hydration of magnesium oxide (MgO). It is required that thermal energy has to be released promptly in order to follow the demand of electricity. To satisfy these features, the thermal conductivity of Mg(OH)2 and MgO has been enhanced by using expanded graphite (EG). A composite material, named EM, was obtained by mixing Mg(OH)2 and EG in a water suspension. After drying of the mixture, EM was compressed in figure of tablets (diameter of 10 mm, thickness of around 6 mm). The reactivity of the packed bed of EM tablets was and studied experimentally in order to determine its heat storage and heat output performances and compared to a packed bed made of pure Mg(OH)2 pellets. From the experimental results of stored heat and heat power output, it was possible to estimate the amounts of Mg(OH)2 and EM required for the peak shaving of electricity in a nuclear power station. A Rankine cycle in the power station has been modified to include a chemical heat storage reactor. The range of admissible variation of electrical power output from the steam turbine was estimated from the enthalpy and mass balances under the heat storage and heat output operation modes, respectively. The volume of EM tablets required to store the same amount of thermal energy of Mg(OH)2 pellets resulted 13.6% smaller.

Microcalorimetry coupled with statistical analysis techniques for bio-activity evaluation of medicinal animal horns and shells

Microcalorimetry is an important analytical tool continuously measuring the heat output generated in the physical, chemical or biological processes. Here, the microcalorimetric method was used to evaluate the bio-activity differences of seven medicinal animal horns and shells on splenic lymphocytes. The cells were placed in the 20-mL glass ampoules containing RPMI-1640 and the test drugs (10 mg mL−1), and the heat output and motility of the cells were examined with an isothermal microcalorimeter. From the measured power–time curves, some quantitative thermokinetic parameters were obtained. By analyzing these parameters using principal component analysis, two main parameters, the maximum heat-output power P m and total heat output Q, were optimized, through which the effects of the seven drugs on splenic lymphocytes were quickly evaluated: 10 mg mL−1 of Cornu Cervi Pantotrichum showed stronger promotion effect than Cornu Cervi on the growth and proliferation of splenic lymphocytes, whereas the other five horns and shells animal drugs including Cornu Saigae Tataricae, Cornu Caprae Hircus, Cornu Bubali, Squama Manis and Carapax Trionycis at 10 mg mL−1 all inhibited the growth of splenic lymphocytes, and Cornu Saigae Tataricae expressed the strongest inhibitory effect. The result of hierarchical clustering analysis on the quantitative parameters indicated that the drugs with promotion effect on splenic lymphocytes clustered into one group and the other drugs with inhibitory effect consisted of another group. The results have highlighted the bio-activity differences of the seven horns and shells animal drugs referring to immune functions from the cell level, providing meaningful references for the clinical use of the valuable drugs.

N-type thermoelectric material Mg2Sn0.75Ge0.25 for high power generation

Thermoelectric power generation is one of the most promising techniques to use the huge amount of waste heat and solar energy. Traditionally, high thermoelectric figure-of-merit, ZT, has been the only parameter pursued for high conversion efficiency. Here, we emphasize that a high power factor (PF) is equivalently important for high power generation, in addition to high efficiency. A new n-type Mg2Sn-based material, Mg2Sn0.75Ge0.25, is a good example to meet the dual requirements in efficiency and output power. It was found that Mg2Sn0.75Ge0.25 has an average ZT of 0.9 and PF of 52 μW⋅cm(-1)⋅K(-2) over the temperature range of 25-450 °C, a peak ZT of 1.4 at 450 °C, and peak PF of 55 μW⋅cm(-1)⋅K(-2) at 350 °C. By using the energy balance of one-dimensional heat flow equation, leg efficiency and output power were calculated with Th = 400 °C and Tc = 50 °C to be of 10.5% and 6.6 W⋅cm(-2) under a temperature gradient of 150 °C⋅mm(-1), respectively.

Microcalorimetry coupled with principal component analysis for investigating the anti-Staphylococcus aureus effects of different extracted fractions from Dracontomelon dao

With the prevalence resistance of Staphylococcus aureus to antibacterial agents, developing novel antibacterial agents is urgent. Recently, plant extracts have got more focus. In this study, the power-time curves produced by S. aureus under the action of the four extracted fractions (PE, CHCl3, EtOAc, and n-BuOH fractions) from the leaves of Dracontomelon dao were determined by microcalorimetry, and then some quantitative parameters, such as growth rate constant k, total heat output Qt, maximum heat-output power Pm, and the appearance time tm were obtained. By analyzing the parameters using principal component analysis, the anti-S. aureus effects of the four fractions were systematically evaluated and compared. Meanwhile, the total flavonoid contents in these fractions were analyzed. The results have evidenced that different fractions using various extraction solvents expressed various anti-S. aureus effects, and the inhibitory effects were presented in a flavonoid content-dependent manner. The EtOAc fraction with the highest total flavonoid content (41.86 %) expressed the strongest anti-S. aureus effect with half-inhibitory concentration (IC50) of 83.93 μg mL−1, which might be applied as a novel antibacterial agent in practice for some infectious diseases. In addition, the microcalorimetric method should be strongly suggested in screening for novel antibacterial agents for fighting against pathogenic bacteria.

A computational fluid dynamics study on the heat transfer characteristics of the working cycle of a β-type Stirling engine

A compressible CFD code has been developed to study the heat transfer characteristics of a β-type Stirling engine with a very simple design and geometry. The results include temperature contours, velocity vectors, and distributions of local heat flux along solid boundaries at several important time steps as well as variations of average temperatures, integrated rates of heat input, heat output, and engine power. It is found that impingement is the major heat transfer mechanism in the expansion and compression chamber, and the temperature distribution is highly non-uniform across the engine at any given moment. The results, especially the rates of heat transfer, are quite different from those obtained by a second-order model. The variations of heat transfer rates are much more complicated than the simple variations returned by the second-order model. This study sheds light into the complex heat transfer mechanism inside the Stirling engine and is very helpful to the understanding of the fundamental process of the engine cycle.

Synthesis, thermochemical and thermokinetic studies on the mononuclear copper Valen Schiff base complex

A mononuclear salen-type complex [Cu( vanen )(H 2 O)] was synthesized from the ligand [H 2 vanen = N , N - ethylene-bis(3-methoxysalicylideneimine)] and Cu(OAc) 2 ·H 2 O. Based on Hess law, a reasonable thermochemical cycle was designed. According to the cycle, the standard molar enthalpies of dissolution of samples in the calorimetric solvent of DMF ( N , N -dimethylformamide) were determined, respectively. The standard molar enthalpy change of the coordination reaction (Δ r H m θ ) was calculated to be -(16.61 ± 0.54) kJ/mol. Combined with some relevant literature data, the standard molar enthalpy of formation (Δ f H m θ ) of the complex was obtained to be -(756.5 ± 2.4) kJ/mol. At the temperature of 32 ℃, the metabolic thermogenetic curves of S. pombe under the influence of the complex with different concentration were determined by using a TAM air isothermal calorimeter. The relationships of the concentration of the complex with the microbial growth rate constant ( k ) of S. pombe , inhibition ratio (I), the half inhibition concentration (IC 50 ), the maximum heat output power ( P max ) and the time it took ( t max ) were analyzed. The results indicated that the complex possessed the Hormesis effect, which promoted the growth of S. pombe at lower concentration, but inhibited the growth at higher concentration.

A computational fluid dynamics study on the heat transfer characteristics of the working cycle of a low-temperature-differential γ-type Stirling engine

A three-dimensional compressible CFD code has been developed to study the heat transfer characteristics of a twin-power piston γ-type Stirling engine. The results include temperature contours, velocity vectors, and distributions of local heat flux along solid boundaries at several important time steps as well as variation of average temperatures, integrated rates of heat input, heat output, and engine power. It is found that Impingement is the major heat transfer mechanism in the expansion and compression chambers, and the temperature distribution is highly non-uniform across the engine volume at any given moment. This study sheds light into the complex heat transfer mechanism inside the Stirling engine and is very helpful to the understanding of the fundamental process of the engine cycle.

Electricity Generation from Abandoned Oil and Gas Wells

The objective of this study is to demonstrate the feasibility of acquiring geothermal energy using abandoned oil and gas wells. The equations of fluid flow and heat exchange were developed and solved by numerical methods. Computational results indicated that the two main factors of influencing heat exchange and output power were fluid flow rate and geothermal gradient. The net output power is 59.41 kW at a geothermal gradient of 45°C/km and flow rate of 0.04 m/s. The fluid outlet temperature after 10 years of operation is just 0.41°C lower than that of initial time.

Comparison of anti-bacterial activity of three types of di-O-caffeoylquinic acids in Lonicera japonica flowers based on microcalorimetry

The anti-bacterial activities of three types of di-O-caffeoylquinic acids (diCQAs) in Lonicera japonica flowers, a traditional Chinese medicine (TCM), on Bacillus shigae growth were investigated and compared by microcalorimetry. The three types of diCQAs were 3, 4-di-O-caffeoylquinic acid (3, 4-diCQA), 3, 5-di-O-caffeoylquinic acid (3, 5-diCQA), and 4, 5-di-O-caffeoylquinic acid (4, 5-diCQA). Some qualitative and quantitative information of the effects of the three diCQAs on metabolic power-time curves, growth rate constant k, maximum heat-output power Pm, and the generation time tG, total heat output Qt, and growth inhibitory ratio I of B. shigae were calculated. In accordance with a thermo-kinetic model, the corresponding quantitative relationships of k, Pm, Qt, I and c were established. Also, the half-inhibitory concentrations of the drugs (IC50) were obtained by quantitative analysis. Based on the quantity-activity relationships and the IC50 values, the sequence of inhibitory activity was 3, 5-diCQA > 4, 5-diCQA > 3, 4-diCQA. The results illustrate the possibility that the caffeoyl ester group at C-5 is the principal group that has a higher affinity for the bacterial cell, and that the intramolecular distance of the two caffeoyl ester groups also has an important influence on the anti-bacterial activities of the diCQAs.

The research on formation enthalpy of phenanthroline monohydrate and its influence on the growth metabolism of E. coli by microcalorimetry

A precision rotating-bomb combustion calorimeter (thermistor of which was constructed in the laboratory) was calibrated using benzoic acid with purity of 99.999 %. The combustion energy of phenanthroline monohydrate (phen·H2O) at 298.15 K was determined to be Δc U m = −(5,757.45 ± 2.53) kJ mol−1. Then, the standard enthalpy of combustion and the standard enthalpy of formation of phen·H2O were calculated to be Δc H m = −(5,759.93 ± 2.53) kJ mol−1 and Δf H m = −(391.34 ± 2.98) kJ mo1−1, respectively. Particularly, the effect of phen·H2O on growth and metabolism of Escherichia coli (E. coli) was also determined by a TAM air isothermal calorimeter at 37 °C. The thermokinetic parameters, including maximum heat output power (P max), growth rate constant (κ), generation times (t G), inhibitive rate (I), and half inhibition concentration (C I,50), were obtained. The results showed that phen·H2O possessed the bi-directional biological effect and Hormesis effect, which stimulated the growth of E. coli at lower concentration, but inhibited the growth at higher concentration. The half inhibition concentration C I,50 of phen·H2O was found to be 7.31 mg L−1.

Microcalorimetry coupled with chemometric techniques for toxicity evaluation of Radix Aconiti Lateralis Preparata (Fuzi) and its processed products on Escherichia coli

As a widely used traditional Chinese medicine (TCM), Radix Aconiti Lateralis Preparata (Fuzi) is not only efficacious but also poisonous. Its toxicity and processed products should be taken into account and effectively evaluated. In this study, a non-invasive and non-destructive microcalorimetric method was employed to evaluate and compare the toxicity of Fuzi and its three processed products including Yanfupian, Heifupian, and Danfupian on Escherichia coli (E. coli). Some important metabolic information, such as the power-time curves and some quantitative thermokinetic parameters including growth rate constant k, heat output power P, inhibitory ratio I, and half inhibitory concentration IC50, of E. coli growth affected by various concentrations of Fuzi and its processed products were obtained. Combined with chemometric techniques including multivariate analysis of variance and principal component analysis on this information, it could be seen that Fuzi and its processed products could be distinguished according to their toxic effects on E. coli. The IC50 values of 14.6 mg/mL for Fuzi, 59.2 mg/mL for Yanfupian, 118.3 mg/mL for Heifupian, and 182.7 mg/mL for Danfupian illustrated that the sequence of toxicity on E. coli was Fuzi > Yanfupian > Heifupian > Danfupian. This study provided a useful method and idea of the combination of microcalorimetry and chemometrics for studying the toxic effects of TCMs and other substances.

Isothermal microcalorimetric investigation of the toxic action of the effective constituents of Podophyllum emodi Wall on Tetrahymena thermophila BF5

The effects of podophyllotoxin (PPT), etoposide (VP16), and teniposide (VM26) on the growth of Tetrahymena thermophila BF5 (T.t.BF5) was investigated by the TAM AIR isothermal microcalorimetric system. The extent and duration of toxic effects on T.t.BF5 metabolism were evaluated by studying the growth rate constant (k), inhibitory ratio (I), maximum heat-output power (Pmax), peak time of maximum heat-output power (tp), and total heat production (Qt). Experimental results showed that the value of tp increased and the value of k and Pmax decreased with the increasing compound concentrations. Furthermore, the growth rate constant k was linear with compound concentration. The corresponding I was obtained from different k values. According to the IC10 (the concentration of inhibitor when the inhibitory ratio is 10 %), the relative toxicity of the three compounds was PPT (IC10 = 49.6 μg mL−1) > VP16 (IC10 = 117.5 μg mL−1) > VM26 (IC10 = 359.1 μg mL−1). The preliminary investigation of structure–activity relationships showed that the thienyl group was likely responsible for reducing the toxicity of the compounds.

Demethoxycurcumin: a potential antimicrobial agent

Demethoxycurcumin (DMC) is one of the major constituents in Curcuma longa L., and it is safe at a large dose range. In this study, the antimicrobial activity of DMC on Escherichia coli, Staphylococcus aureus, and Shigella dysenteriae was investigated by microcalorimetry and modified broth microdilution. Minimal inhibitory concentration and 50 % inhibiting concentration were determined by modified broth microdilution, which was fast and economical. Thermokinetic parameters were extracted from the heat-output power curves delineated by microcalorimetry, which was accurate and dynamic, and the multiple parameters were analyzed by similarity analysis and principle component analysis. The results demonstrated that DMC presented good antimicrobial activity, and the sequence of activity was as follows: E. coli > S. aureus > S. dysenteriae. This study provides a useful methodology for the determination of antimicrobial activity of natural products. In addition, it provides the foundation for the exploitation of DMC as a potential antimicrobial prodrug.

Microcalorimetry with correspondence analysis for studying the antibacterial effect of ephedrine on Escherichia coli

The power–time curves of Escherichia coli growth at 37°C affected by different concentrations of ephedrine were recorded by microcalorimetry. By analyzing some quantitative parameters from these curves using correspondence analysis, the effect of ephedrine on E. coli could be easily evaluated by analyzing the two main parameters, growth rate constant k2 and maximum heat-output power P2 of the second peak in the power–time curves. The results showed that the strong antibacterial effect of ephedrine on E. coli was concentration-depended: ephedrine at low concentration had poor inhibitory effect, and at high concentration notably inhibited the growth of E. coli. 376.8μg/ml of ephedrine could cause 50% inhibition on E. coli. Ephedrine presented strong antibacterial effect on E. coli, which might be used as a potential novel antibacterial agent in practice. Microcalorimetric investigation of the effect of antibacterial agent on bacterial pathogens was promising in comparison to other methods.