Transient Heat Loss Research Articles

A transient heat losses model for two-tank storage systems with molten salts

Concentrating Solar Power (CSP) is a proven and mature technology for energy supply. In recent years, electricity generation based on this technology has increased worldwide, to a large degree due to its high dispatchability when coupled with an energy storage system. Commercially, most plants store the energy in molten salts in a two-tank configuration. This study focuses on this storage configuration and proposes a mathematical model for the thermal losses in these tanks, both at nominal conditions and during transients. With this model at its core, a computational tool for thermal performance analysis in OpenModelica is developed. This dynamic thermal model includes the estimation of local heat loss due to assembly defects, which are heat flows that cannot be determined by theoretical modelling. The development of a semi-empirical correlation for estimating local heat loss is also presented. Simulation results showed that this local heat loss may represent a share about 40% of the total heat loss in a small-scale tank. A comparison of the characteristics of the model proposed in a previous work is also presented to establish the innovation of the model. Two thermal storage systems with different tank designs and sizes were simulated to compare the results using the present model with data available in the literature. Results show good agreement in transient thermal behaviour of heat flows, temperatures, and cooling rates when compared with data from other authors for the same tank.

Heat Loss Analysis of a 2D Pump’s Transmission

Highly enhanced pump power density inevitably results in a profound rise in pump temperature, which seriously influences both power loss and service performance. Heat loss analysis is an important part of analyzing the mechanical and cooling efficiency of a 2D piston pump. This paper focuses on heat loss analysis of this pump’s transmission. Firstly, theoretical and experimental studies are carried out on the thermal–hydraulic model to investigate the heat loss of the pump’s transmission. A pump test rig is developed and thermal experiments are conducted, from 1000 rpm to 6000 rpm. Furthermore, its transient thermal simulation model is implemented with Ansys software to capture the pump’s thermal status. The test convective heat transfer coefficients and temperature data are set in the model, and the simulation results are mutually validated with the experimental ones. Finally, the transmission’s heat loss is compared with its reference churning loss formula. The distribution of the transient heat loss is 49.66% into the end cap, 27.74% into the cylinder head, 13.30% into the inner cylinder, and 9.30% into the oil. The heat loss simulation results agree with the churning loss below 4000 rpm; therefore, the transmission thermal model is accurate and efficient.

Precise surface temperature measurements at kHz-rates using phosphor thermometry to study flame-wall interactions in narrow passages

The thermographic phosphor ScVO4:Bi3+ is used to obtain time-resolved surface temperature measurements with sub- °C precision at 5 kHz. Measurements are used to study transient heat loss and flame-wall interactions (FWI) within a dedicated narrow two-wall passage (crevice) in an optically accessible fixed volume chamber. This passage emulates a crevice relevant in many technical environments, where FWI is less understood due to lack of detailed measurements. Chemiluminescence (CH*) imaging is performed simultaneously with phosphor thermometry to resolve how the flame's spatiotemporal features influence the local surface temperature. ScVO4:Bi3+ is benchmarked against Gd3Ga5O12:Cr,Ce, a common phosphor used at low-kHz rates in FWI environments. ScVO4:Bi3+ is shown to offer higher luminescence signal levels and temperature sensitivity as well as negligible cross dependence on the excitation laser fluence, improving the precision and repeatability of the wall temperature measurement. ScVO4:Bi3+ is further used to resolve transient heat loss for variations in crevice spacing and uniquely capture temperature transients associated with flame dynamics. Taking advantage of these precise surface temperature measurements the wall heat flux is calculated with crevice spacing of 1.2 mm, where flame extinction is prevalent. Wall heat flux and estimated quenching distance are reported for flames that actively burn or extinguish at the measurement location.

Evaluating the dynamics of occupancy heat gains in a mid-sized airport terminal through agent-based modelling

The occupancy heat gains of airport terminal buildings are driven by the dynamics of passenger flow. In this paper, we evaluate the heat losses from the human body in a transient state to estimate the sensible and latent loads on the HVAC system. The study pertains to a mid-sized airport terminal building in a tropical wet and dry climate of India. The pattern of passenger movement, service time and discretionary activity choices are evaluated through field measurement and subjective surveys. The sequence of passenger movement, dwell time and occupancy profile at different zones for departure and arrival sequences are estimated through validated agent-based simulations. Transient heat losses from the human body are established through thermo-physiology simulations based on the occupancy dynamics. Hourly sensible and latent heat load profiles of different zones are deduced for different terminal operation periods. The evaporative heat losses from human body varies considerably during passenger transit resulting in significant latent heat gain differences among the zones. Despite lower activity levels in certain zones, latent heat loads from occupancy are higher because of preceding activity sequences. The sensible to latent heat load ratio varies from 0.7:0.3 to 0.52:0.48 across the zones during different operational periods.

Thermal impacts on pressure transient tests using a coupled wellbore/reservoir analytical model

This work investigates the impact of temperature effect on pressure-transient measurements made at any gauge location along a slanted wellbore completed with a production tubing. The analysis is based on a coupled transient-wellbore/reservoir thermal analytical model, which considers flow of a slightly compressible, single-phase fluid in a homogeneous infinite-acting reservoir system. The analytical model provides temperature- and pressure-transient data for drawdown and buildup tests, accounting for Joule-Thomson, adiabatic fluid-expansion, conduction and convection effects. Regarding pressure transient analysis (PTA), thermal distorted pressure data might lead to the interpretation of false geological heterogeneities, because the transient heat loss during the buildup period provides an increase in the pressure exerted by the wellbore-fluid column and a change in the gauge location due to pipe contraction. Though some of the derived expressions are lengthy, they encompass an intrinsic simplicity in that one can compute pressure- and temperature-transient data on a spreadsheet. Analytical results are compared with those of a commercial thermal wellbore/reservoir simulator showing a good agreement. Thermal impacts on PTA interpretations are demonstrated by showing that a homogenous reservoir can be wrongly interpreted as a double-porosity system. A field case is presented, consisting of a drill stem test conducted in a multi-layered heterogeneous reservoir.

A correlation-based model for building ground-coupled heat loss calculation using Artificial Neural Network techniques

Heat loss from a building through the ground becomes relatively important as the above-grade components of the building fabric are built more energy efficient. For annual space heating and cooling load calculations that require short computation time, with reasonable accuracy, for modelling heat losses to ground through the foundations, this study presents a new correlation-based model. The correlation algorithms were derived from the results of a commercial 3D transient heat transfer program using Artificial Neural Network. We demonstrate that for steady-state heat loss through slab-on-ground, the proposed correlation model agrees with the CSIRO analytical solution within 6.8%, and for transient heat loss through slab-on-ground and basement the new model agrees with a well validated commercial 3D heat transfer program. The new simplified approach presented covers most foundation configurations of interest, with low processing requirements, and is ideal for use in building energy performance simulations due to the short computation time.

Transient heat loss analysis of fabrics using a dynamic sweating guarded hot plate protocol

Moisture management is important for the human comfort of clothing, especially while perspiring. Ideally, the fabric chosen for a garment enables moisture to migrate away from the skin surface, facilitating the liquid to be evaporated into the surrounding environment, which causes a cooling sensation for the wearer. This process is influenced by factors such as fiber type, fabric construction, and fabric treatments, all of which impact the resulting wicking and moisture management properties of the fabric. This research explored the heat loss associated with combined water absorption, wicking, and evaporative cooling during wetting of fabrics. A dynamic sweating guarded hot plate was used to measure transitional heat loss as water was introduced at a steady rate over a 65-minute testing period. The results on a cotton and polyester blend fabric as well as a wool fabric indicated that the liquid water absorption and transport processes significantly influence heat loss properties during this transition. However, the results also show novel aspects in the efficiency of cooling associated with the wicking of sweat and different stages of wetting of fabrics leading to different cooling power. Furthermore, this method raises questions as to whether current sweating guarded hot plate technologies are an appropriate representation of human sweat production or that the scalability of sweat production per unit area is limited. This developed testing method can be successful in quantifying the differences in transitional heat loss and will enable testing of fabrics for comfort in changing conditions.

Flame/flow dynamics at the piston surface of an IC engine measured by high-speed PLIF and PTV

Resolving fluid transport at engine surfaces is required to predict transient heat loss, which is becoming increasingly important for the development of high-efficiency internal combustion engines (ICE). The limited number of available investigations have focused on non-reacting flows near engine surfaces, while this work focuses on the near-wall flow-field dynamics in response to a propagating flame front. Flow-field and flame distributions were measured simultaneously at kHz repetition rates using particle tracking velocimetry (PTV) and planar laser induced fluorescence (PLIF) of sulfur dioxide (SO2). Measurements were performed near the piston surface of an optically accessible engine operating at 800 rpm with homogeneous, stoichiometric isooctane-air mixtures. High-speed measurements reveal a strong interdependency between near-wall flow and flame development which also influences subsequent combustion. A conditional analysis is performed to analyze flame/flow dynamics at the piston surface for cycles with ‘weak’ and ‘strong’ flow velocities parallel to the surface. Faster flame propagation associated with higher velocities before ignition demonstrates a stronger flow acceleration ahead of the flame. Flow acceleration associated with an advancing flame front is a transient feature that strongly influences boundary layer development. The distance from the wall to 75% maximum velocity (δ75) is analyzed to compare boundary layer development between fired and motored datasets. Decreases in δ75 are strongly related to flow acceleration produced by an approaching flame front. Measurements reveal strong deviations of the boundary layer flow between fired and motored datasets, emphasizing the need to consider transient flow behavior when modeling boundary layer physics for reacting flows.

Testing on the Transient Heat Loss Coefficient of All-Glass Evacuated Tube Collectors in Severe Cold Areas

Testing on the Transient Heat Loss Coefficient of All-Glass Evacuated Tube Collectors in Severe Cold Areas

Transient molten salt two-tank thermal storage modeling for CSP performance simulations

Solar thermal power plants are a promising way of providing renewable electricity. Unlike other renewable energy technologies, solar thermal power plants have the ability to store thermal energy, which decouples the electric power generation from hours of available solar irradiation. Today, the only applied commercial thermal storage system is a two-tank sensible heat thermal storage based on molten salts. This work focuses on the transient heat loss modeling of such molten salt thermal energy storage tanks. More precisely, this paper proposes a degree of physical modeling which describes the governing heat transfer mechanisms sufficiently accurate, obtaining a suitable tool for concentrating solar power (CSP) performance simulations, applicable for parabolic trough collector, as well as for central receiver plants. A fully transient storage tank model has been developed and simulated over 3 sets of 6 reference days, providing typical weather conditions of a solar thermal power plant location as model input. The model has been successfully compared to heat loss data that was observed at real application molten salt storage tanks. Several modeling assumptions, used heat transfer correlations and simplifications are outlined. Modelica has been used as modeling language.

Static and dynamic characteristics of antiparallel diode as part of switching power module

A numerical simulation of the operation of a fast antiparallel diode in the switching power module of an autonomous voltage inverter is carried out. The time of turning off the transient and the static and transient heat losses in the diode are calculated as a function of the electrophysical parameters of the semiconductor diode structure.

An examination of procedures for predicting heat losses from underground structures

Numerical predictions for heat losses from two-dimensional underground structures of variable geometry are presented. The calculations include the effects of wind velocity, surface radiation, and deep soil temperature, none of which have been previously explored. Results are compared with calculations made using ASHRAE procedures for predicting such losses. It is demonstrated that the present study results differ from the ASHRAE procedures by 20% depending upon geometry, wind conditions, and deep soil temperature. A limited number of results for the transient heat losses are presented to guide the designer with regard to peak losses and time lags. A new calculation procedure is developed and presented based upon the numerical result. This procedure is simple yet more flexible and allows for the inclusion of variations in wind velocity, surface radiation, soil thermal conductivity, soil temperature at depth in addition to structure geometry.

Lack of integrative control of body temperature after capsaicin administration.

BackgroundBody temperature is usually regulated by opposing controls of heat production and heat loss. However, systemic administration of capsaicin, the pungent ingredient of hot peppers, facilitated heat production and heat loss simultaneously in rats. We recently found that the capsaicin-induced heat loss and heat production occur simultaneously and that the biphasic change in body temperature is a sum of transient heat loss and long-lasting heat production. Moreover, suppression of the heat loss response did not affect capsaicin-induced heat production and suppression of heat production did not affect capsaicin-induced heat loss. These observations suggest the independent peripheral mechanisms of capsaicin-induced thermal responses. Thus, the capsaicin-induced thermal responses apparently lack an integrated control.MethodsMale Wistar rats were maintained at an ambient temperature of 24 ± 1°C on a 12 h on-off lighting schedule at least for two weeks before the experiments. They were anesthetized with urethane (1.5 g/kg, i.p.) and placed on a heating pad, which was kept between 29 and 30 °C. Skin temperature(Ts) was measured with a small thermistor, which was taped to the dorsal surface of the rat’s tail, to assess vasoactive changes indirectly. Colonic temperature(Tc) was measured with another thermistor inserted about 60 mm into the anus. O2 consumption was measured by the open-circuit method, and values were corrected for metabolic body size (kg0.75). Capsaicin (Sigma) was dissolved in a solution comprising 80% saline, 10% Tween 80, and 10% ethanol, and injected subcutaneously at a dose of 5 mg/kg. Each rat received a single injection of capsaicin because repeated administration of capsaicin renders an animal insensitive to the subsequent administration of capsaicin. Laminectomy was performed at the level of the first and second cervical vertebrae to expose the cervical spinal cord for sectioning. The brain was transected at 4-mm rostral from the interaural line with an L-shaped knife.ResultsAfter administration of capsaicin, O2 consumption increased from 13.5 ± 0.4 mL/min/kg0.75 at 0 min to a peak of 15.9 ± 0.4 mL/min/kg0.75 at 71 min and gradually declined but remained higher than the basal value until the end of the 4-h observation period. Ts also immediately increased from 27.7 ± 0.2 °C to 31.9 ± 0.3 °C at 39 min, and it returned to the baseline level within 90 min after the capsaicin administration. Tc initially decreased from 37.1±0.1 °C to 36.8 ± 0.2 °C at 43 min and then gradually increased over the baseline level and remained at 37.6 ± 0.2 °C until the end of the experiment, in spinalized rats, the capsaicin-induced increase in O2 consumption was largely attenuated, while the basal O2 consumption was similar to that of control rats. The basal Ts of spinalized rats was 32.4 ± 0.3 °C, which was higher than that of control rats. Capsaicin increased Ts by less than 1 °C, and Tc did not change after the capsaicin administration. O2 consumption of decerebrated rats was statistically higher than that of control rats after the injection of capsaicin. However, capsaicin did not increase Ts, showing a lack of a vasodilatory response. Decerebration between the hypothalamus and midbrain prevented the capsaicin-induced heat loss but not the heat production response.ConclusionThese results show that the capsaicin-induced heat production and heat loss are controlled separately by the brainstem and by the forebrain, respectively, and suggest that the body temperature regulation is performed without an integrative center.

On transient heat losses from buried district heating pipes

The theory of steady-state heat loss determination from buried heating pipes has been reviewed as well as previous approaches to treat transient heat losses in the case of constant water temperatures. A new method has been developed to find an undisturbed ground temperature by which the transient heat loss can be calculated by the use of the steady-state heat loss equations. By numerical simulations, as well as by experiment, the position of this undisturbed ground temperature has been found. The position of this ground temperature is closer to the ground surface in the case of uninsulated pipes—or pipes with the insulation in poor condition—than in the case of insulated pipes. For pre-insulated pipes the position corresponds approximately to the top of the pipe casing. Copyright © 2000 John Wiley & Sons, Ltd.

Light masking of circadian rhythms of heat production, heat loss, and body temperature in squirrel monkeys.

Whole body heat production (HP) and heat loss (HL) were examined to determine their relative contributions to light masking of the circadian rhythm in body temperature (Tb). Squirrel monkey metabolism (n = 6) was monitored by both indirect and direct calorimetry, with telemetered measurement of body temperature and activity. Feeding was also measured. Responses to an entraining light-dark (LD) cycle (LD 12:12) and a masking LD cycle (LD 2:2) were compared. HP and HL contributed to both the daily rhythm and the masking changes in Tb. All variables showed phase-dependent masking responses. Masking transients at L or D transitions were generally greater during subjective day; however, L masking resulted in sustained elevation of Tb, HP, and HL during subjective night. Parallel, apparently compensatory, changes of HL and HP suggest action by both the circadian timing system and light masking on Tb set point. Furthermore, transient HL increases during subjective night suggest that gain change may supplement set point regulation of Tb.

Transient heat loss from thermal insulation pipe.

In transferring heat energy by fluid, it is well known that heat capacity of piping affects the heat loss at the transient state. Above all, heat loss from the piping of a solar collector system is one of the most important subjects from the viewpoint of increasing the performance of a system utilizing solar thermal energy. For reducing heat loss from the piping, we manufactured a piping made of only thermal insulation material, which we called a thermal insulation pipe; i.e., TIP. In order to demonstrate its effectiveness, we performed experiments of transient temperature response of the outlet of a piping system in comparison between a TIP and a piping which is composed of a metal pipe covered with thermal insulation material which we called ordinary insulation piping; i.e., OIP. Furthermore, numerical calculations and simple analysis of transient heat loss in both piping system were performed. This paper describes the effectiveness of the TIP from the comparison of the major results of experiments and calculations.

Short-Term Transient Temperature Calculations and Measurements for Underground Power Cables

A time-dependent heat transfer model based on the complete Fourier integral was developed for calculating cable temperatures during short-term transient conditions. A cyclic heat transfer calculation is used to obtain the initial temperature-time profile of the cable before the transient loading begins. The short-term transient model uses a lumped parameter formulation for the different cable regions and the Fourier integral to approximate the transient heat loss profile. Calculated conductor, jacket, and conduit temperatures show reasonable agreement with experimental results for a number of short-term transient tests with cables in a typical duct bank arrangement.