Transient Response of Heated Air in an Enclosure With Heat Losses

1959 ◽  
Vol 81 (1) ◽  
pp. 19-23 ◽  
Author(s):  
W. A. Wolfe
Keyword(s):  
Differential Equation ◽  
Heat Capacity ◽  
Air Temperature ◽  
Transient Response ◽  
Heat Losses ◽  
Transient Temperature ◽  
Heated Air

The transient temperature of well-stirred air in an enclosure with heat losses is investigated. The introduction of the heat capacity of the air results in nonorthogonal eigenfunctions for the differential equation of conduction. A method of determining the coefficients of the eigenfunctions is developed and the transient-air temperature calculated for several values of the heat capacity of the air.

scholarly journals Effects of transient temperature on human's heat losses

2016 ◽  
Vol 20 (3) ◽  
pp. 827-830
Author(s):  
Lijuan Wang ◽  
Yuhui Di ◽  
Hui Yin ◽  
Yanfeng Liu ◽  
Jiaping Liu
Keyword(s):  
Energy Balance ◽  
Air Conditioning ◽  
Heat Losses ◽  
Linear Functions ◽  
Quadratic Functions ◽  
Balance Model ◽  
Transient Temperature ◽  
Convection Diffusion ◽  
Comfort Evaluation ◽  
And Diffusion

The objectives of the paper are to analyze human convection, radiation, evaporation, respiration, conduction, and diffusion heat losses when the operative temperature increases from 26-34.4?C and then decreases from 34.4-26?C with a ratio of 1.4?C per 5 minutes. A energy balance model is used for sedentary subject. The results show that during temperature rising, all the heat losses are linear functions of temperature, while during temperature dropping, the convection, diffusion, and respiration heat losses are quadratic functions of temperature. The results are useful for thermal comfort evaluation and heating, ventilation, and air conditioning design.

Analysis of the influence of the internal heat capacity of the university building and weather-dependent regulation of itp on the efficiency of the heating system in standby mode

2021 ◽  
pp. 45-61
Author(s):  
I. Antypov ◽  
◽  
A. Mishchenko ◽  
O. Shelimanova ◽  
S. Tarasenko ◽  
...  
Keyword(s):  
Heat Capacity ◽  
Air Temperature ◽  
Internal Heat ◽  
Thermal Inertia ◽  
Heating System ◽  
Dynamic Mode ◽  
Temperature Deviation ◽  
Limit Value ◽  
Internal Heat Capacity ◽  
Standby Mode

When assessing the thermal condition of the building and the parameters of the microclimate of the premises, the main factors influencing its thermal inertia were identified and taken into account. An assessment of the influence of the resistance of enclosing structures on the efficiency of the heating system, taking into account the influence of external and internal climatic parameters in the dynamic mode. It is shown that the time factor and depth of regulation, as well as the outdoor air temperature are important factors. Researches are carried out and the expediency of introduction of a duty mode of heating of buildings of HIGH SCHOOLS is estimated. The given algorithm of control of process of heat release (especially in the presence of a point of "breaking" - average (them) on the schedule) in addition increases accuracy of the decisions of the specified problems and reduces a temperature deviation by 4 ÷ 6 ° C in comparison with usual ("linear") dependence that allows to correct more precisely release of the heat carrier in system of heating of a structure at introduction of a standby mode. It was found that it took about 6.5 hours to achieve normalized air temperature and space heating in the forced (after a long stay on duty). It is shown that the heat consumption of the system in such conditions of its operation compared to the nominal mode increased by 25 % (taking into account the limit value of the specific allowance from table H1 DBN B.2.5-67: 2013 "Heating, ventilation and air conditioning"), but for the entire period the action of the standby mode savings amounted to about 6-8% of energy consumed. Taking into account the design of the outer walls of the object of study, the temperature graph of the heating system was adjusted taking into account the value of the internal heat capacity of the building when implementing on-duty heating, which, according to preliminary estimates, will: improve comfort in the room; to reduce heating costs of the educational and administrative building of NULES of Ukraine by 10-12 % for the heating period. Key words: microclimate, internal heat capacity of a building, standby mode, heating system, heat loss

scholarly journals The Impact of Infiltration on Heating Systems Dimensioning in Estonian Climate

2020 ◽  
Vol 172 ◽  
pp. 05004
Author(s):  
Raimo Simson ◽  
Taaniel Rebane ◽  
Martin Kiil ◽  
Martin Thalfeldt ◽  
Jarek Kurnitski
Keyword(s):  
Air Temperature ◽  
Indoor Air ◽  
Energy Performance ◽  
Simulation Software ◽  
Heat Losses ◽  
Climatic Data ◽  
Heating Systems ◽  
Air Temperatures ◽  
The Impact ◽  
Calculation Models

In this study we analysed the climatic conditions for infiltration estimation, different calculation methods and infiltration impact on heat load for heating systems dimensioning. To determine the wind conditions at low air temperatures of the coastal- and inland climatic zones in Estonia, 42 years of climatic data for Tallinn and Tartu were investigated. Calculation models with detailed air leakages were constructed of a single and two-storey detached house using dynamic simulation software IDA ICE. Simulations were carried out with the constructed calculation models, simulating various wind and sheltering conditions to determine the heating load of the buildings under measured wind conditions at the design external air temperatures. The simulation results were compared with results calculated with European Standard EN 12831:2017, methodology given in the Estonian regulation for calculating energy performance of buildings and with simulations using the default settings in IDA ICE based on the ASHRAE design day conditions. The percentage of heat losses caused by infiltration was found as 13-16% of all heat losses for the studied buildings. Simulations with historical climate periods showed that even in windy weather conditions the heating system dimensioned by the methods analysed may not be able to provide the required indoor air temperature. Analysis using the coldest and windiest periods showed that when systems are dimensioned by the studied methods, the highest decline in indoor air temperature occurs on the windiest day and not on the coldest day. The impact of high wind speeds and low sheltering conditions resulted up to 50% of all heat losses.

scholarly journals Thermal behaviour of Norway spruce and European beech in and between the principal anatomical directions

Holzforschung ◽  
2011 ◽  
Vol 65 (3) ◽  
Author(s):  
Walter Sonderegger ◽  
Stefan Hering ◽  
Peter Niemz
Keyword(s):  
Differential Equation ◽  
Thermal Conductivity ◽  
Heat Capacity ◽  
Thermal Diffusivity ◽  
Norway Spruce ◽  
European Beech ◽  
Hot Plate ◽  
Principal Directions ◽  
Clear Increase ◽  
Plate Apparatus

Abstract Thermal conductivity (ThCond), thermal diffusivity and heat capacity of Norway spruce (Picea abies [L.] Karst.) and European beech (Fagus sylvatica L.) have been determined for all principal directions – radial (R), tangential (T) and longitudinal (L) – depending on the moisture content (MC) and ThCond was additionally measured in 15° steps between these directions. The ThCond was determined in a guarded hot plate apparatus. For determining thermal diffusivity and heat capacity, the same apparatus was supplemented with thermocouples and the temperature evolution was evaluated numerically by a partial differential equation. The results show expectedly that ThCond increases with increasing MC, whereby the highest increment was observed in T and the lowest in L direction. ThCond is higher for beech than for spruce in all anatomical directions and the conductivity for both species is more than twice as high in L direction than perpendicular to grain. The highest ThCond is found for beech at a grain angle of approximately 15°. The lowest ThCond shows spruce at an angle of approximately 60° between T and R direction. Thermal diffusivity is similar for both species and decreases with increasing MC. Its differences with regard to the anatomical directions correlate with those of the ThCond values. Heat capacity is lower for beech than for spruce and shows a clear increase with increasing MC.

scholarly journals Analytic transient solutions of a cylindrical heat equation

Filomat ◽  
2021 ◽  
Vol 35 (8) ◽  
pp. 2617-2628
Author(s):  
K.Y. Kung ◽  
Man-Feng Gong ◽  
H.M. Srivastava ◽  
Shy-Der Lin
Keyword(s):  
Heat Transfer ◽  
Differential Equation ◽  
Partial Differential Equation ◽  
Heat Conduction ◽  
Heat Equation ◽  
Heat Conduction Equation ◽  
Separation Of Variables ◽  
Transient Heat Conduction ◽  
Transient Temperature ◽  
Transient Solutions

The principles of superposition and separation of variables are used here in order to investigate the analytical solutions of a certain transient heat conduction equation. The structure of the transient temperature appropriations and the heat-transfer distributions are summed up for a straight mix of the results by means of the Fourier-Bessel arrangement of the exponential type for the investigated partial differential equation.

scholarly journals Evaluation of a Premixed, Prevaporized Gas Turbine Combustor for No. 2 Distillate

1977 ◽  
Author(s):  
D. P. Teixeira ◽  
D. J. White ◽  
M. E. Ward
Keyword(s):  
Heat Capacity ◽  
Gas Turbine ◽  
Air Temperature ◽  
Gas Turbines ◽  
Electric Utility ◽  
Nox Emissions ◽  
Pressure Condition ◽  
Control Potential ◽  
Gas Turbine Combustor ◽  
Current Generation

Results of a series of tests on a prevaporized, premixed combustor to evaluate its emissions control potential while operating on No. 2 distillate oil are presented. The concept utilized the heat capacity of the combustor inlet air to absorb the heat of vaporization of the fuel. Tests were conducted at combustor inlet temperatures and pressures characteristic of current generation electric utility gas turbines (345 C and 10 atm). NOx emissions in excess of proposed EPA gas turbine standards (75 ppm at 15 percent O) were observed at the 10 atm pressure condition and are believed to be the result of incomplete evaporation of the fuel Attempts to increase vaporization rates by increasing inlet air temperature were limited by autoignition of the mixture in the fuel preparation ports.

scholarly journals On the Physical Origin of the Semiannual 1 Component of Surface Air Temperature over 2 Mid-latitude and Subpolar Oceans

2021 ◽  
Author(s):  
Fucheng Yang ◽  
Zhaohua Wu
Keyword(s):  
Heat Capacity ◽  
Air Temperature ◽  
Mixed Layer ◽  
Solar Irradiance ◽  
Seasonal Cycle ◽  
Surface Air Temperature ◽  
Physical Origin ◽  
Oceanic Mixed Layer ◽  
Sources And Sinks ◽  
Yearly Period

Abstract With the understanding that seasonal cycle of the temperature are forced principally by the annually evolving solar irradiance, many previous studies have defined seasonal cycle of surface air temperature (SAT) as the sum of yearly-period sinusoidal component and its harmonics, especially semiannual component. In mid-latitude and subpolar regions, the ratio between the semiannual and annual components of solar irradiance is negligibly small but that of the SAT over oceans is not, which remains to be understood. In this study, a simple energy budget model including main energy sources and sinks of oceanic mixed layer is designed to understand this puzzle. It is revealed that, when the oceanic mixed layer is prescribed as a layer of constant depth, the phase and amplitude of the modeled SAT is not consistent with that of the observation. However, when the annually changing heat capacity of the oceanic mixed layer is included, both the amplitude and phase of the modeled SAT share these of the observed SAT, proving that the semiannual component of SAT over mid-latitude and subpolar oceans is a result of the heat capacity-varying oceanic mixed layer in response to annually evolving solar irradiance.

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