Heat Transfer Calculation Method Research Articles

Suggested Method for Heat Transfer Calculation During Film Condensation Inside Pipes with Movable Frontiers

Suggested Method for Heat Transfer Calculation During Film Condensation Inside Pipes with Movable Frontiers

Thermal performance calculation with heat transfer correlations and numerical simulation analysis for typical LNG open rack vaporizer

Open rack vaporizer (ORV) is a type of commercial heat exchanger widely used in large gasification plants for base load Liquefied Natural Gas (LNG) receiving terminals. The heat source is seawater which is abundant and easily obtained. The aim of this study is to build a relatively accurate model of quantitative calculation for heat transfer in ORV. The heat transfer correlations and calculation method are described and discussed for inside and outside of the tube in ORV, then the calculation results are compared with the data of a practical case. Meanwhile, numerical simulation is established by FLUENT to verify the heat transfer of the LNG and seawater. The deviation between the correlation calculation model and the numerical simulation is within 10%. In addition, the effects of different operating parameters on heat transfer are investigated separately. Both the inlet pressure and the mass flow of methane have significant effects on the thermal performance of the tube, and the effects of the inlet temperature of water is rather slighter. The determination for the optimal correlation and calculation model may provide guidance for the design of ORV.

Numerical prediction of heat loss from a test ribbed rectangular channel using the conjugate calculations

Conjugate heat transfer of air and steam in a rectangular channel with 90° ribs along two opposite walls was investigated experimentally and numerically. The stainless steel test section was 80 mm × 40 mm × 2.5 mm and the ribs were 80 mm × 2.5 mm × 2.5 mm with 25 mm between ribs. The tests investigated the effects of coolant mass flow rate (the corresponding Reynolds numbers in the range of 10,000-50,000) on the conjugate heat transfer enhancement with the ribs. Two conjugate heat transfer calculation methods with different models were developed. For the first model (CHT-Q model) solid domain was viewed as a uniform internal heat source with the adiabatic exterior surfaces, while for the second model (CHT-T model) the outwall temperature was specified by the fitting polynomials of measured data with the zero internal heat. Comparisons between the experimental and numerical results showed that the SST k–ω turbulence model was more suitable for the conjugate heat transfer in such channels. Regardless of numerical error, an approximation of heat loss was specified by the successive trial calculations of the CHT-Q model, while a relatively accurate heat loss was evaluated by the post-processing of the CHT-T calculation. Local heat transfer coefficient can be determined accurately by the quantified heat loss of test system. The critical impact of conjugate heat transfer was demonstrated. Furthermore, the steam coolant compared to air exhibited a higher heat transfer performance by 12–25% for both the ribbed and smooth walls at the same Reynolds number.

Numerical study of using different Organic Rankine cycle working fluids for engine coolant energy recovery

Engine waste heat recovery technology especially Organic Rankine cycle (ORC) has been widely studied in order to achieve higher overall thermal efficiency, reduce the engine emissions and improve the fuel economy. The coolant energy occupies around 30% of the fuel energy can be used as the heat source for ORC system. This paper studies thermal status of the engine heated components when using different ORC working fluids as engine coolant to avoid the heat loos using heat exchanger to transfer coolant to the ORC fluid. A Solid-Liquid Conjugated Heat Transfer (SLCHT) calculation method is developed to calculate the heat transfer inside the engine, which can solve the temperature field of both solid zone and fluid zone. The simulation results have been validated by the experimental data from a 6-cylinder medium duty diesel engine, when water is the coolant in the system. The simulation model is then used to predict the temperature profile using different ORC working fluids and investigate the influence of different ORC working fluids on the cooling effects of the engine heated parts. The maximum temperature of the heated components has been selected as the evaluation parameters. The results reveals that applying selected ORC working fluids in engine as coolant is not practical under the designed conditions, which will make the engine overheated. Further investigation showed that increasing mass flow rate of the coolant can decrease the thermal status of the heated components but still cannot meet the cooling demands even under 200% of the original mass flow rate. The variations of the coolant outlet temperature and exergy were also analysed.

Heat Exchange in “Human body - Thermal protection - Environment” System

This article is devoted to the issues of simulation and calculation of thermal processes in the system called “Human body – Thermal protection - Environment” under low temperature conditions. It considers internal heat sources and convective heat transfer between calculated elements. Overall this is important for the Heat Transfer Theory. The article introduces complex heat transfer calculation method and local thermophysical parameters calculation method in the system called «Human body – Thermal protection – Environment», considering passive and active thermal protections, thermophysical and geometric properties of calculated elements in a wide range of environmental parameters (water, air). It also includes research on the influence that thermal resistance of modern materials, used in special protective clothes development, has on heat transfer in the system “Human body – Thermal protection – Environment”. Analysis of the obtained results allows adding of the computer research data to experiments and optimizing of individual life-support system elements, which are intended to protect human body from exposure to external factors.

Study on a design method for hybrid ground heat exchangers of ground-coupled heat pump system

The hybrid ground heat exchangers (GHEs) of ground-coupled heat pump (GCHP) systems refer to a GCHP system using both vertical and horizontal GHEs. With the proposed optimal load ratio of horizontal to vertical GHEs, three-dimensional numerical heat transfer GHE models were established using independent heat transfer calculation method, and a design method for hybrid GHEs of GCHP system was put forward and then applied in one project. A combined heat transfer calculation method considering the mixing outlet water temperature was proposed and validated by a built experimental platform, which shows an improvement in accuracy prediction compared to the independent heat transfer calculation. It indicates the mixing outlet water temperature plays an important role in calculation accuracy and should serve as the boundary condition in modelling. The heat transfer performance of GHEs can be characterized by the independent heat transfer results in a certain range of load ratio.

Semianalytic method for heat transfer calculation in the liquid film under conditions of a constant heat flux on the wall

For calculating the heat transfer in the free-falling liquid film, a semianalytic method is offered in which the temperature field in the liquid is presented as a series of basis functions which satisfies boundary conditions. The proposed method is demonstrated by the example of the problem regarding the film heating under conditions of the constant heat flux on the wall taking into account the heat transfer on the interfacial surface. The analytical solution is derived for the thermal initial section, on which the liquid heating occurs in a thin layer near the wall. Calculations using the proposed method are well agreed with the numerical solution obtained by the finite-difference method and with experimental data.

Three-dimensional accuracy with two-dimensional computation speed: using the Kiva™ numerical framework to improve foundation heat transfer calculations

Calculation of heat transfer from building foundations is a computationally intensive three-dimensional problem that can require several weeks to solve using current computing hardware. The Kiva numerical framework was developed to compare foundation heat transfer calculation methods and determine approaches that reduce computation time without sacrificing a balance of capability, ease-of-use, and accuracy. This paper demonstrates the application of the Kiva framework to determine an accurate method of approximating three-dimensional heat transfer effects using two-dimensional coordinate systems. In two-dimensions, problems that would otherwise take days or weeks to solve can be solved in less than a minute. Three existing two-dimensional approximation methods along with a new boundary layer adjustment method are tested across a range of foundation types, shapes, and insulation configurations. The boundary layer adjustment method is shown to provide results within 3% mean absolute deviation from the three-dimensional solution.

Improvement of starting characteristics of a diesel engine with low compression ratio by using of inlet electric air heaters

The paper deals with the improvement of starting characteristics of diesel engine with low compression ratio. The processes in inlet manifold and cylinder of diesel engine during pre-start preparation and start-up are submitted as the subject of study. The purpose is to improve the starting characteristics of diesel engine with low compression ratio by using of inlet electrical air heaters instead of electric torch device. The object of study is a modification of tractor constant power engine of 4ChN 15/20.5 type with low compression ratio equal to 12.5. During the experiment one electric torch device and three tubular electric heaters with heat power of 0.8 kW each were sequentially installed in the inlet manifold of diesel engine. A calculation method for heat transfer from the surface of inlet manifold to the ambient air is proposed. Conditions of fuel self-ignition in the combustion chamber of diesel engine with electric torch device are theoretically substantiated, as well as its critical shortcomings, namely: raise of temperature of fuel self-ignition due to the decrease in oxygen concentration of air charge in cylinders, as a result of its consumption in the flame of electric torch device; ability to work only during engine cranking by electric starter with a limited timespan of 20 seconds. It is proved that a valid method providing the cold starting of 4ChN 15/20.5 diesel engine with low compression ratio equal to 12.5 is air preheating by tubular electric heaters placed throughout the length of inlet manifold, with total heat power of 1.6-2.4 kW. Rational design parameters of a cold start aid system with tubular electric heaters and its operation modes are determined. The results of the study were used for modernization of production models of ChTZ-Uraltrac tractor diesel engines and for development of new ones, so they can be recommended for introduction in engine building companies.

Study on Heat Transfer Calculation Method of Ground Heat Exchangers Based on Heat Pump Unit Operation Characteristics

For ground source heat pump (GSHP) system, the dynamic heat rejected to or extracted from the ground is an important parameter to analyze the heat transfer performance of ground heat exchanger (GHE). Coupled with dynamic indoor load and actual operation characteristics of heat pump unit, a method to calculate actual dynamic heat load input of GHEs was introduced and a calculation program was developed. In an actual GSHP system project, the dynamic heat load input of GHEs was calculated and used as a boundary condition, a three-dimensional heat transfer model of this GHE field was established, and then the water temperature variation of GHEs was obtained. The actual water temperature variation of GHEs was tested and it was similar to the theoretical calculation results, thus the method was validated and could be applied in the actual engineering projects.

Effect of Parapet Hole on Tundish Flow Field

According to the actual operating parameters of tundish in a steel mill, the flow pattern and temperature distribution of molten steel in tundish were studied by CFD and heat transfer calculation method. Changing the height of parapet hole, the effect of parapet hole on flow field and temperature field were simulated. The simulation results show that: the parapet hole height has large influence on flow recirculation position, which can impact surface temperature and outflow temperature of molten steel. When parapet hole height increases, the recirculation vortex moves towards the surface of molten steel in outflow zone, surface temperature rises, but outflow temperature decreases near the narrow wall. Comprehensive analysis show that, when the parapet hole height is 480mm, surface temperature is high, molten steel will not solidify at corner; the reduction of molten steel temperature is small at outflow hole.

Novel Multi-Stream Plate Exchanger under High Pressure-Structure and its Design Method

The general characteristic of current plate heat exchangers is first summarized in this paper. A new plate exchanger of multi-stream under high pressure is proposed, which is composed of the plates with opening the gyroidal flow-trough along the radius and the shell, it has some advantages, such as simple structure, high efficiency and available under high pressure. We introduce the structure of the plate, the shell and the slotting types. In addition, the process calculation method of heat-transfer is given and the strength calculation method for the key components of the novel exchanger is also presented. According to the stress analysis to the plate wall with ANSYS software, we have proved the reliability of the calculation method.

Theoretical and Computational Research of Heat Radiant Transfer in Cylinder

In order to obtain the radiation heat transfer theory and calculation methods, the movement of the gas particles, location, intensity, temperature, are researched in cylinder under different conditions with combustion system and the mode of heat transfer. Under high temperature conditions in the cylinder, the gas radiation heat transfer is researched in the complex heat transfer theory. A statistical correlation K narrow band model, a mean absorption coefficient, a gas line databases, by-line calculation method are found, through research and analysis emissivity, transmittance, absorption coefficient, typical models, mathematical equations, database, calculation methods. Examine the distribution performance of each database for different media concentration and temperature, a statistical narrow-band band parametric model accuracy is tested, using statistical narrow band model, the results of the use of by-line method. Research shows: selected spectral database, calculation method has a greater impact on the results. The research also shows the result coincides calculations based by-line HITEWP2010 database method, whether radiant heat or wall flux, statistical narrow band model. These are supplied to the internal combustion engine cylinder design.

Research on the Regionalism Air-Conditioning System Design of Car and Saving Energy

The air-conditioning load is directly related to energy consumption of the car. Based on the characteristics and sources of the air-conditioning load of the car driven in four typical cities, this paper gives an analysis on the air-conditioning load using the steady-state heat transfer calculation method. The result indicates the regionalism design on the air-conditioning system for car is feasible and beneficial to save energy.

Unsteady Heat Transfer Analysis: Saving-Energy and the Regionalism Design on Air-Conditioning System for Car

In this paper, based on unsteady heat transfer calculation method, the results of the heat transfer through the enclosure of car compartment are given, in order to analyze dynamic energy-saving effect of the regionalism design on air-conditioning system for car. The result demonstrates that the regionalism design on the air-conditioning system has important saving-energy effect.

Thick Film Heater for Sensor Application

A thick film microheater was elaborated. The microheater is intended for fast heating of small volume samples under measurement in optical based system. Thermal analysis of microheater was carried out using finite element method (FEM) for heat transfer calculation as a function of time and space. A nodal heat transfer function was calculated in classical form including all basics mechanisms of heat exchange – heat conduction, convection and radiation were considered. Work focuses on the influence of some construction parameters (ex. length, thermal conductivity of substrate, substrate thickness) on microheater performance. The results show that application of thin substrate of low thermal conductivity and low thickness for miroheater construction and resistor of optimum dimensions leads to significant power consumption decrease and increase of overall optical measurement system performance.

A fire resistance design method for thin-walled steel studs in wall panel constructions exposed to parametric fires

This paper investigates the applicability of a simple fire resistance design method for axially loaded thin-walled steel studs in wall panel assemblies when exposed to parametric fires from one side. The simple method includes calculations of cross-section temperatures and ultimate load carrying capacities at elevated temperatures. The simplified calculation method for heat transfer in the cross-section is based on dividing the cross-section into a number of segments. The thermal properties of these layers are based on weighted averages of the thermal properties of the components contained within. The structural capacity calculation method is based on the Direct Strength Method. Results from the design method are compared with the results from Finite Element simulations for heat transfer and structural analysis (236 models). The calculation results are in good agreement with the simulation results and the proposed method may be used in performance-based fire engineering design of such construction.

The Study on Heat Transfer Model and Algorithm of Multi-Sectional Regenerative Air Heater in Power Plant Boiler Based on Analytical Method

Tri-sectional regenerative air heater is used widely because of its compactness and better performance. Study on the matching analytical calculation method of heat transfer is rarely carried out because of the complicated heat transfer process. This paper developed a model to solve the heat transfer calculation of multi-sectional regenerative air heaters, which usually have several layers. Then we designed the computational procedure to carry out the model. One example of a tri-sectional regenerative air heater with hot layer and cold layer shows the effectiveness of the algorithm, and the results suggest that this approach is valid. The impact of leakage on performance of the regenerative air heater was discussed. There is a negative linear correlation between exhaust gas temperature and air leakage, and boiler efficiency has a nearly linear negative correlation with air leakage.

Regeneratively cooled scramjet heat transfer calculation and comparison with experimental data

Regeneratively cooled scramjet heat transfer calculation method was developed using three-dimensional calculation for engine solid wall heat conduction. The scramjet thermal environment was determined by engine heat flux measurement and the engine three-dimensional combustion flow calculations. Different heat transfer relationships in the laminar, transition and turbulence fuel flow regions were applied. The cooling fuel flow distribution data inside combustion chamber side panel were obtained by three-dimensional fuel cooling flow calculation. The results of a light weight regeneratively cooled combustion chamber heat transfer tests were adopted to verify the calculation method. The comparisons showed good agreement, indicating that the calculation method is applicable.

Simulation of Dynamic Heat Load for Underground Structure Envelope

Analyses the mechanisms of dynamic heat transfer in the underground works envelope and the simplified calculation method for heat transfer. With the cooperative function of MATLAB, Simulink and COMSOL simulate the dynamic variation of the heat load and validate the simulation results by an experiment.