Specific Heat Source Research Articles

Simulation of continuous thermally regenerative electrochemical flow cycle and coupled with photovoltaic/thermal system

Thermally regenerative electrochemical cycle (TREC) is an efficient, clean and feasible low-temperature thermoelectric conversion technology. Coupling it with flow battery (FB) can not only achieve continuous operation, but also can be used to realize the heat energy recovery of the photovoltaic/thermal (PV/T) system. In this paper, a continuous TREC-FB system including two charging-free cells is proposed for outputting power at both high and low temperatures. An electrochemical-thermodynamic coupling algebraic model is established to explore the effects of electrolyte flow rate, temperature difference and design parameters of heat exchanger on the power density (PTREC) and thermoelectric efficiency (ηele,TREC) of the TREC-FB. Experimental study on TREC-FB is carried out for model validation. The results show that PTREC is determined by the temperature difference and the electrolyte flow rate, which contribute to enhanced voltage and mass transfer, respectively. For specific heat source scenarios, the ηele,TREC is mainly affected by the flow rate, followed by the heat transfer area AH, and finally is the flow channel height and the thermal conductivity of the heat exchanger. Moreover, for the continuous TREC-FB-PV/T coupled system, the energy conversion efficiency reaches an average of 11 % within one day by optimizing the designed temperature difference.

Optimization and exergy analysis of a cascade organic Rankine cycle integrated with liquefied natural gas regasification process

One of the most efficient methods of exergy recovery during the regasification process is integrating the LNG stream with an Organic Rankine Cycle (ORC) to generate electricity. This study employs a cascade structure of ORC consisting of two double-stage condensations operating at 6 bar regasification pressure. To obtain an optimal ORC system integrated with an LNG, three optimization levels for a specific heat source are addressed, including process variables, working fluids, and structure. Ten process variables and two working fluid variables for the top and bottom cycle among 13 candidates of refrigerants were optimized to provide the maximum power output. The results determined that refrigerants of R41 and R1150 have the best performance in the optimized process conditions for the top and bottom cycles, respectively. For the regasification of 36 tonnes per hour of an LNG stream, the produced net power and the exergy efficiency are achieved by 2116.76 kW and 0.29, respectively. The exergy analysis revealed that employing the double-stage condenser ORC is not a good choice. Accordingly, a cascade-parallel structure is proposed for further studies.

Response spatiotemporal correlation and transient temperature field direct reconstruction for heat conduction system

In this paper, according to a spatiotemporal correlation characteristic of the temperature response of a transient heat conduction system, a response spatiotemporal correlation (RSTC) model of the temperatures between measurement space and estimation space of the system is proposed. Furthermore, a RSTC based direct reconstruction (RSTC-DR) method is developed for a transient temperature field reconstruction problem of a heat conduction system with unknown heat sources. In the offline stage, firstly, mapping eigenvectors of a heat conduction system are determined by the transfer equations without specific heat source information. Then, according to the correlation degree between the mapping eigenvectors, a finite number of representative spatial points (RPs) are extracted. Meanwhile, a fuzzy membership relationship between the mapping characteristics of the RPs and that of the temperature field is determined. Namely, effective mapping characteristic coverage of the RPs to the whole temperature field is realized. Moreover, a RSTC model between the measurement spatial points (MPs) and the RPs is obtained by the step response model of the temperature field. In the online stage, based on the RSTC model, the temperature responses of the RPs are estimated by employing the time series vector of the temperature measurements of the MPs. Next, according to the fuzzy membership relationship, the temperature field can be reconstructed in real time by synthesizing the temperature estimations of the RPs. The RSTC-DR method is employed to achieve the non-destructive reconstruction of the transient temperature field of a two-dimensional heat conduction system. The temperature field is reconstructed by the numerical experiment to verify the effectiveness of the proposed method and to discuss its adaptability. Furthermore, the practical effectiveness of the method is demonstrated by applying the existing experimental data.

Optimizing printed thermoelectric generators with geometry and processibility limitations

Fully printed thermoelectric generators (TEGs) are a promising solution for large scale energy harvesting and waste heat recovery in a broad range of applications. Due to large variations in heat transfer coefficients and temperatures, it is necessary to include these properties of the specific heat source in the design process of the TEGs. Oftentimes, this leads to additional, geometric requirements for the devices. The limited layer thickness of the printing process imposes further limitations on the device geometry. Here, we present an analytical method to design and optimize fully printed TEGs manufactured by a screen-printing technique and considering its geometric design limitations. The design process includes choosing between a planarly printed device architecture and a folded device architecture. Furthermore, the limited device thickness and the presence of a filler material in printed TEGs result in device designs optimized for output power, which vary from conventional thermal impedance matching. The fill factor is hereby an important degree of freedom for the optimization. Furthermore, we demonstrate, that two materials with the same figure of merit zT will yield different output powers for the same device, if their thermal conductivities differ. This implies that considering the geometric limitations of the intended application already in the development of the printable thermoelectric materials can yield a larger power output for the device.

Adaptive simulation of 3D thermometry maps for interventional MR-guided tumor ablation using Pennes’ bioheat equation and isotherms

Minimally-invasive thermal ablation procedures have become clinically accepted treatment options for tumors and metastases. Continuous and reliable monitoring of volumetric heat distribution promises to be an important condition for successful outcomes. In this work, an adaptive bioheat transfer simulation of 3D thermometry maps is presented. Pennes’ equation model is updated according to temperature maps generated by uniformly distributed 2D MR phase images rotated around the main axis of the applicator. The volumetric heat diffusion and the resulting shape of the ablation zone can be modelled accurately without introducing a specific heat source term. Filtering the temperature maps by extracting isotherms reduces artefacts and noise, compresses information of the measured data and adds physical a priori knowledge. The inverse heat transfer for estimating values of the simulated tissue and heating parameters is done by reducing the sum squared error between these isotherms and the 3D simulation. The approach is evaluated on data sets consisting of 13 ex vivo bio protein phantoms, including six perfusion phantoms with simulated heat sink effects. Results show an overall average Dice score of 0.89 ± 0.04 (SEM < 0.01). The optimization of the parameters takes 1.05 ± 0.26 s for each acquired image. Future steps should consider the local optimization of the simulation parameters instead of a global one to better detect heat sinks without a priori knowledge. In addition, the use of a proper Kalman filter might increase robustness and accuracy if combined with our method.

Temperature field modelling in the form grinding of involute gear based on high-order function moving heat source

Grinding is one of the primary methods to enhance the tooth surface quality. For gear form grinding, due to the complexity of grinding movement and nonuniform grinding conditions of the tool and workpiece geometry, the accurate prediction for gear grinding temperature is difficult to achieve by using a single specific heat source shape. Therefore, a new temperature model based on high-order function curve moving heat source distribution in the grinding zone was established. Compared with the traditional models, using the new model can avoid assuming the heat source distribution shape in advance and greatly reduce the disadvantages caused by improper heat source shape assumptions under the nonuniform grinding conditions along the tooth profile. In this model, the analysis of geometry model of gear form grinding, characteristic parameters of abrasive grains and moving point heat source theory were comprehensively considered. Additionally, the finite element numerical simulation and gear grinding experiments were outperformed to analyze the gear grinding temperature. Comparison results show the highest temperature based on high-order function curve heat source appears earlier and closer to the front of the grinding contact arc compared with triangular and rectangular heat source distribution shapes. Furthermore, the tooth surface temperature in the grinding zone obtained by new model has better consistency with the experimental measurement results. The relative errors of the analytical and numerical simulation results of the maximum temperature are within 5.2 % and 6.4 %, respectively. These findings prove the accuracy and superiority of the temperature prediction model based on high-order function moving heat source distribution for gear form grinding, and it has a guiding role in the optimization of the workpieces with complex profiles in form grinding.

Photothermal mediated rolling circle amplification toward specific and direct in situ mRNA detection

Rolling circle amplification (RCA) had the prospect of assisting clinic diagnosis with advantage in in situ mRNA detection at single cell level. However, for direct mRNA detection, RCA had relatively low detection specificity and efficiency. Here, we introduced 4-(10, 15, 20-Triphenylporphyrin-5-yl)phenylamine (TPP) modified Au nanoparticle (Au-TPP) to improve the specificity of in-situ RCA. Through photothermal effect, Au-TPP acted as the specific heat source upon irradiation of 635 nm laser. The photothermal mediated RCA would be initiated only when the Au-TPP as well as the padlock anchored adjacently on the same target mRNA. Furthermore, we introduced ‘C’ form target-specific oligonucleotide linker probes to make generic padlock and Au-TPP for different mRNA targets, so that for a new mRNA target one does not have to redesign the padlock and the Au-TPP probe. By these strategies, we successfully developed a specific and photothermal mediated hyperbranched rolling circle amplification for direct in situ mRNA detection, suitable for both formalin-fixed paraffin-embedded (FFPE) tissue section and frozen tissue section.

On the optimal heat source location of partially heated energy storage process using the newly developed simplified enthalpy based lattice Boltzmann method

The present study aims to fill the knowledge gap in the partially heated energy storage process by finding the optimal heat source location. A new simplified enthalpy based lattice Boltzmann method is proposed for the present work. The new model follows the predictor–corrector step, while the traditional model follows the collision-streaming step. Compared to the traditional model, this new model has the same accuracy, but it has advantages on virtual memory saving and physical boundary treatment due to its unique structure. Besides, in the partially heated energy storage process, the heat source location can pose significant impact on the charging efficiency and the energy storage rate. The optimal heat source location is where the maximum charging efficiency and energy storage rate are achieved. Results indicate that, a small region with the length of 0.1 l can be deemed as the optimal region for the heat source location, for that the charging time and the energy storage rate at various locations inside that region are almost the same. The optimal region decreases with the increase of Rayleigh and Prandtl numbers. In addition, the optimal regions for some specific heat source lengths and Rayleigh numbers are obtained. Based on these results, a map is provided to indicate the variations of the optimal region. According to this map, the optimal heat source locations for more varied conditions can be estimated through the heat source length and the Rayleigh number, which would be quite useful and significant for the thermal design in various engineering applications.

Effect of fluid dryness and critical temperature on trans-critical organic Rankine cycle

Abstract In this paper, the effect of fluid dryness (represented by ξ = ds/dT, where T is temperature, s is entropy) and critical temperature on the trans-critical ORC performance is investigated. The thermal efficiency of fifty-two working fluids is examined at four typical heat source temperatures. The results show that the critical temperature and fluid dryness have a significant impact on the system thermal efficiency. At a specific heat source temperature, the thermal efficiency increases with increasing of fluid critical temperature, and decreases with increasing of fluid dryness. The exergy destructions contributed by evaporator and condenser dominate the total exergy loss of the system. The exergy loss induced by condenser is more sensitive to the variation of fluid dryness than that induced by evaporator. Suitable working fluids are proposed based on the comprehensive criteria of cycle performance, toxicity, flammability and environment friendliness.

Energy and Exergy Analysis of the S-CO2 Brayton Cycle Coupled with Bottoming Cycles

Supercritical carbon dioxide (S-CO2) Brayton cycles (BC) are soon to be a competitive and environment friendly power generation technology. Progressive technological developments in turbo-machineries and heat exchangers have boosted the idea of using S-CO2 in a closed-loop BC. This paper describes and discusses energy and exergy analysis of S-CO2 BC in cascade arrangement with a secondary cycle using CO2, R134a, ammonia, or argon as working fluids. Pressure drop in the cycle is considered, and its effect on the overall performance is investigated. No specific heat source is considered, thus any heat source capable of providing temperature in the range from 500 °C to 850 °C can be utilized, such as solar energy, gas turbine exhaust, nuclear waste heat, etc. The commercial software ‘Aspen HYSYS version 9’ (Aspen Technology, Inc., Bedford, MA, USA) is used for simulations. Comparisons with the literature and simulation results are discussed first for the standalone S-CO2 BC. Energy analysis is done for the combined cycle to inspect the parameters affecting the cycle performance. The second law efficiency is calculated, and exergy losses incurred in different components of the cycle are discussed.

Zeotropic mixture active design method for organic Rankine cycle

Using mixture working fluids has been proven to be an effective way to improve the performance of organic Rankine cycles (ORC). Instead of recommending mixtures or compositions for a specific heat source, this work is focused on providing preliminary design guidelines of zeotropic mixture working fluids for ORC. The zeotropic mixture active design method is provided for mixture selection without massive calculation or blind trial. The designed mixtures have better performance than the optimal pure working fluid. The designed zeotropic mixtures should have the same key properties as the optimal pure working fluids and also have temperature glide matching with the cooling source. Firstly, the authors’ previous study on the optimal pure working fluid screen criteria is simply reviewed. Then, how the mixture’s temperature glide influencing on the cycle performance is analyzed. Finally, the zeotropic mixture active design method is provided and verified. Some debatable questions regarding to the mixtures are also answered.

Improved thermodynamic design of organic radial-inflow turbine and ORC system thermal performance analysis

The Organic Rankine Cycle (ORC) has obvious advantages in the utilization of low-temperature heat source (80–300°C). Based on specific heat source, this paper determines design conditions of radial-inflow turbine with six kinds of dry working fluids. This paper presents a new method for modeling of ORC based on radial-inflow turbine with the novel selection of initial design parameters. In the selection procedure of the initial design parameters, the properties of organic working fluids should be taken into consideration to control the increase of υ2/υ1, which can lead to the large relative velocity ratio and the poor performance of the radial–inflow turbine. The study shows that the applicable selection area of initial design parameters differentiates from that recommended in the literature for organic working fluids. The lowest cycle ideal efficiency with R123 results in the minimums of the cycle thermal efficiency and the cycle net power, which reaches 8.33% and 67.24kW, respectively. Although the relative internal efficiency of the radial-inflow turbine with R600a is in the middle level, the highest cycle thermal efficiency and cycle net power reach 9.17% and 74.59kW, respectively. The results show that the ORC systems with R600 and R600a both have better cycle performance with smaller geometric dimensions and more excellent thermal matching with specific heat source.

The definition of non-dimensional integration temperature difference and its effect on organic Rankine cycle

The integration temperature difference ΔTi considers the heat transfer routes, linking the heat transfer process with the thermodynamic behavior of heat exchangers. The first and second non-dimensional integration temperature differences are defined as ΔTi,h∗=ΔTi/Th,i and ΔTi,s∗=ΔTi/(Th,i-T0) respectively, where Th,i is the heat source temperature and T0 is the environment temperature. This paper is the first to experimentally verify the significance of the non-dimensional integration temperature differences on organic Rankine cycle (ORC) systems. The first non-dimensional temperature difference is shown to have linear relationship with the revised entropy generation numbers (Ns). With increases of the second non-dimensional integration temperature difference, the expander powers, system thermal and exergy efficiencies had parabola distributions. They simultaneously reached maximum at ΔTi,s∗=0.282, under which the vapor cavitation in the expander disappears and the exergy losses of heat exchangers are acceptable to elevate the expander efficiency. Beyond the optimal point, the ORC performance is worsened either due to the vapor cavitation in the expander, or due to the poor thermal matches in the evaporator and condenser. The second non-dimensional integration temperature difference comprehensively reflects the effects of heat source temperatures, heating powers and organic fluid flow rates and pressures, etc. It balances exergy destructions of various components to optimize the system. Thus, it can be an important parameter index to maximize the power or electricity output for a specific heat source. The usefulness of the integration temperature difference and the future work are discussed in the end of this paper.

Modelling the performance of a scroll expander for small organic Rankine cycles when changing the working fluid

A scroll expander modelling procedure is proposed in this work. Based on an original semi-empirical model present in literature for an open-drive scroll expander operating with HCFC-123, re-calculating some specific parameters allows to improve the simulation procedure that is now generalized to be used with fluids other than HCFC-123.Mass flow rates and shaft power outputs are calculated and compared for some working fluids, highlighting the differences in expander performance. Considering the scroll expander is not an adiabatic machine, heat transfer effects are discussed as well. The scroll expander model is later used to calculate the efficiency of a simple organic Rankine cycle, with the power output of the expander fixed at 1, 1.5 and 2 kW. Although the proper working fluid should be selected according to the specific heat source, the assessment of the expander potential with substituting fluids suggests that better cycle efficiency seems to be possible with HCFC-141b, as reported in other literature works. However, considering HCFC phase-out regulations, the results of calculations with third- and fourth-generation refrigerants are detailed as well. In particular, using HCFO-1233zd(E) as a working fluid brings about a limited efficiency penalty.

Selection of working fluids for micro-CHP systems with ORC

With depleting fossil fuel reservoirs and the corresponding emissions of air pollutants, we urgently need to look for alternative, renewable and sustainable energy options to counteract our strong dependence on fossil fuels for energy supplies. Solar thermal, geothermal, biomass combustion heat energy and waste heat recovery may be applied to drive combined heat and power (CHP) systems with organic Rankine cycle (ORC). Working fluid is a critical factor to affect the efficiency of the ORC, therefore optimal selection of the working fluid for an ORC-based system needs to be studied. This paper presents the comparison and optimization of 8 mostly-applied working fluids nowadays and gives a preferable ranking by means of spinal point method. The organic working fluids (organic refrigerants) for the medium-to-low temperature ORC have thermodynamic, environmental and economic criteria, such as preferable boiling temperature, high enthalpy drop (i.e., high thermal efficiency), favourable heat transfer characteristics, highly thermal and chemical stability, non-flammability, low toxicity, no ozone depletion and low cost. According to these criteria and spinal point method, the 8 mostly-applied organic working fluids are characterized and listed in order of preferable selection: HFE7000, HFE7100, PF5050, R123, n-pentane, R245fa, R134a and isobutene. An adequate organic fluid should be selected considering these selection criteria and the specific heat source. ► Fluid selection for the low-temperature ORC is critical to improve its performance. ► Isentropic or “dry” fluids are more adequate due to the non-superheating ORC. ► Selection criteria of working fluids for ORC are illustrated and described. ► Optimal working fluid ranking is presented by spinal point method. ► Optimal fluids rank: HFE7000, HFE7100, PF5050, R123, n-pentane, R245fa, R134a and isobutene.

The Surface Absorption Coefficient of S304L Stainless Steel by Nd:YAG Micro-Pulse Laser

The surface absorption coefficient of S304L stainless steel during Nd:YAG pulse laser welding process was derived by using the inverse engineering technique. The thermal-elastic-plastic finite element method is employed to calculate the temperature distribution, melting pool depth and shape with specific heat source. The derived melting pool depths and diameters with different values of absorption coefficient were compared with experimental results. In this study, the least square error method is used to obtain the equivalent absorption coefficient. The results show that the equivalent absorption coefficient of S304L stainless steel is in the range of 0.1~0.25 for low power intensity Nd:YAG impulse laser welding.

Effects of Nonuniform Tissue Properties on Temperature Prediction in Magnetic Nanohyperthermia

In tumor hyperthermia, effectively planning in advance and thus controlling in situ the heating dosage within the target region are rather critical for the success of a therapy. Many studies have simulated the temperature distribution during hyperthermia. However, most of them are based on fixed and known heat source distributions, which are generally very complex to compute. Besides, there is little information concerned the numerical analysis of temperature during magnetic hyperthermia loading with magnetic nanoparticles (MNPs), which has its specific heat source distribution features. Particularly, the parameters for different human tissues varied very much, which will cause a serious impact on the heat source and temperature distribution. This paper is aimed at investigating the effects of nonuniform tissue properties to the temperature prediction in magnetic nanohyperthermia and other possible effect factors including external EM field, MNP properties, tumor size and depth, surface cooling conditions, etc. It was found that the spatial heat source generated in the nonuniform model appears smaller than that in the uniform model. This is mainly resulted from the energy reflection when transmitting from fat to tumor and muscle under the same condition, while the temperature is higher on account of overall contribution of different parameters including tissue thermal conductivity, blood perfusion, density, heat capacity, and metabolic heat production rate, which also affect the temperature distribution apart from the heat source. Controlling the properties of the external EM field, MNPs and cooling water can acquire different temperature distributions. Tumors with different depths and sizes need specific plannings, which require as accurate as possible temperature prediction. The nonuniform model can be further improved to be applied in magnetic nanohyperthermia treatment planning and thus help optimize the surgical procedures.

6-3 焦電体を用いた非接触微小領域温度計測の研究(セッション6:マイクロ物理センサ)

In this paper, we propose a non-contact small area thermal measurement method by using a pyroelectric device. A PZT bulk material (5 x 5 x 0.5mm) is employed as a pyroelectric device. When the device moves at 10mm above from a heat source, a pyroelectric current caused by thermal radiation from the heat source is detected. When the device is scanned over the heat source at three constant speeds, 0.1mm/s, 1mm/s, and 11mm/s, change of the pyroelectric current is detected. Additionally at the 0.1mm/s and 1mm/s speeds, distribution maps of the detected pyroelectric current show specific heat source positions.

The Poisson equation for image texture modelling

The Poisson equation is a class of partial differential equations which describe a steady-state temperature distribution in a bounded object. This paper applies this equation to the modelling of image textures by constructing specific heat source functions and boundary conditions. The heat source function can be considered as an image transform function such that a set of texture features at different frequencies and orientations can be extracted from the transformed image, in conjunction with using a Gabor wavelet filer bank. Better performance of image texture retrieval by these features is achieved than using the features extracted directly from the original image texture.

Effects of thermal link in bolometric detectors

The effects of the thermal link on the dynamic behavior of bolometric detectors are discussed. A simple unidimensional model is used to describe the heat diffusion in the link between the sensor and the bath, and the exact general solution is given for the coupled system. Calculations of the dynamic behavior in the time and frequency domains are shown for specific heat sources. A useful approximated formula for the effective heat capacity of the detector is given.