Vertical Temperature Profiles and Cooling Load in Large Spaces Ventilated by Stratified Air-Conditioning Systems: Scale-Model Experiment and Nodal Modeling

2020 ◽  
Vol 12 (5) ◽  
Author(s):  
Yukun Xu ◽  
Xin Wang ◽  
Chenlu Shi ◽  
Xiaoqiang Huai ◽  
Fei Wang
Keyword(s):  
Heat Transfer ◽  
Air Temperature ◽  
Air Conditioning ◽  
Heat Transfer Process ◽  
Scale Model ◽  
Temperature Profiles ◽  
Model Experiments ◽  
Thermal Environments ◽  
Load Calculation ◽  
Nodal Model

Abstract An improved heat balance nodal model is proposed to predict the inner wall temperature profiles and calculate the stratified air-conditioning load in large spaces. The model aims to weaken the correlation between load calculation methods and indoor airflow patterns, and to ensure the synchronization of each heat transfer process, so as to be closer to actual situations. The scale-model experiments were conducted in an enthalpy different laboratory in University of Shanghai for Science and Technology (USST) in Shanghai, China. This paper took the air distribution of nozzle air supply system as an example to calculate the inner wall temperatures and the stratified air-conditioning load by the nodal model and verified by the scale-model experiments. The results showed the maximum deviations of the experimental and theoretical values for the inner wall temperatures, the heat transfer load from the nonair-conditioned (NAC) area and the stratified air-conditioning load were all within 5%. The effects of the air temperature in the NAC area on the heat transfer load from the NAC area and the stratified air-conditioning load were analyzed, and the load nomogram was produced. It was found the heat transfer load from the NAC area accounted for 10–30% of the stratified air-conditioning load. The load nomogram compared two methods for determining the air temperature in the NAC area and gave the recommended one. The findings in this paper can be used to further develop load calculation models for non-uniform thermal environments.

Finite difference analysis of respiratory heat transfer

1986 ◽  
Vol 61 (6) ◽  
pp. 2252-2259 ◽  
Author(s):  
E. P. Ingenito ◽  
J. Solway ◽  
E. R. McFadden ◽  
B. M. Pichurko ◽  
E. G. Cravalho ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Loss ◽  
Air Temperature ◽  
Breathing Pattern ◽  
Human Subjects ◽  
Minute Ventilation ◽  
Tracheobronchial Tree ◽  
Temperature Profiles ◽  
Opposite Pattern ◽  
Normal Human

A numerical computer model of heat and water transfer within the tracheobronchial tree of humans was developed based on an integral formulation of the first law of thermodynamics. Simulation results were compared with directly measured intraluminal airway temperature profiles previously obtained in normal human subjects, and a good correlation was demonstrated. The model was used to study aspects of regional pulmonary heat transfer and to predict the outcomes of experiments not yet performed. The results of these simulations show that a decrease in inspired air temperature and water content at fixed minute ventilation produces a proportionately larger increase in heat loss from extrathoracic airways relative to intrathoracic, whereas an increase in minute ventilation at fixed inspired air conditions produces the opposite pattern, with cold dry air penetrating further into the lung, and that changes in breathing pattern (tidal volume and frequency) at fixed minute ventilation and fixed inspiratory-to-expiratory (I/E) ratio do not affect local air temperature profiles and heat loss, whereas changes in I/E ratio at fixed minute ventilation do cause a significant change.

Ground Source Heat Pump Air Conditioning System of Vertical Geothermal Heat Exchangers Heat Transfer Process and Design Calculation Method

2013 ◽  
Vol 291-294 ◽  
pp. 1728-1734
Author(s):  
Shao Qing Liang
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Air Conditioning ◽  
Scientific Basis ◽  
Heat Transfer Process ◽  
Design Calculation ◽  
Geothermal Heat ◽  
Air Conditioning System ◽  
Ground Source ◽  
Geothermal Heat Exchanger

Geothermal heat exchanger is an important part of the GSHP air-conditioning system and different from other traditional air-conditioning systems. This article through to the geothermal heat exchanger heat transfer performance analysis and the design, derived from the geothermal heat exchanger length calculation formula, for actual engineering construction to provide a scientific basis.

Paper 27: Heat Transfer to Steam-Water Mixtures Flowing in Uniformly Heated Tubes in which the Critical Heat Flux has been Exceeded

1967 ◽  
Vol 182 (8) ◽  
pp. 258-267 ◽  
Author(s):  
A. W. Bennett ◽  
G. F. Hewitt ◽  
H. A. Kearsey ◽  
R. K. F. Keeys
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Wall Temperature ◽  
Heat Transfer Process ◽  
High Mass ◽  
Uniform Heat Flux ◽  
Wall Region ◽  
Temperature Profiles ◽  
Axial Temperature ◽  
Dry Out

Experiments are described on evaporative heat transfer to boiling water in upflow in a vertical electrically heated 0·497-in inside diameter tube at 1000 lbf/in2 (abs.). The main objects were to measure the surface temperature profiles in the region beyond the dry-out point in the channel where liquid ceased to flow on the channel wall, and to investigate the behaviour of the dry-out ‘interface’ between the ‘wetted wall’ and the ‘dry wall’ regions. The test section was made from ‘Nimonic’ as this can withstand the highest temperatures in the ‘dry wall’ region and also has a low temperature coefficient of electrical resistivity, thus allowing a uniform heat flux to be maintained with wide axial temperature variation. The temperature in the ‘dry wall’ region first increased rapidly with distance from the dry-out point, after which it either increased at a slower rate or, at high mass velocities, even decreased. The dry-out ‘interface’ moved reversibly down and up the channel as the heat flux was increased and decreased. Local surface temperatures showed no hysteresis with cycling of heat flux, in contrast with the pool boiling situation. A method of predicting the wall temperature profile in the ‘dry wall’ region has been developed. In this method, the heat-transfer process is considered as being in two steps: wall to superheated steam continuum, and steam continuum to water droplets. The first step was calculated from standard single-phase steam heat-transfer correlations, and the second step was calculated on the basis of simultaneous heat transfer to, and steam diffusion from, the droplets. It was important to take account of the slip between the droplets and the steam. Satisfactory agreement was obtained between measured and predicted wall temperature profiles.

Prediction of the Vertical Temperature Distribution in a Large Enclosure Under Combined Air Conditioning and Natural Ventilation

Solar Energy ◽  
2004 ◽  
Author(s):  
Jun Gao ◽  
Xiao-Dong Li ◽  
Jia-Ning Zhao ◽  
Fu-Sheng Gao
Keyword(s):  
Heat Transfer ◽  
Temperature Distribution ◽  
Air Temperature ◽  
Air Conditioning ◽  
Natural Ventilation ◽  
Vertical Temperature ◽  
Combined System ◽  
Efficient System ◽  
Macro Scale ◽  
Vertical Temperature Distribution

This paper describes a combined system of air conditioning and natural ventilation for large enclosures. A multi-zonal model to simulate the vertical temperature distribution is established. This model describes airflow and heat transfer on a ‘macro’ scale compared to CFD model, but it appears very efficient for engineering application. In this model, air density is considered to change with air temperature. Multiple air jets, buoyancy driven natural ventilation and coupled heat transfer are taken into consideration. It is governed by non-linear equations and is resolved by an iterative solution. A program is compiled to calculate the mass flow and temperature distributions. It shows that the combined system of air conditioning and natural ventilation cut considerably down heat gain in occupied zone. By comparison, the combined system can be expected to give lower temperature both in the enclosure and on interior surfaces. Some cases are calculated, and the results suggest that it depends on many factors such as the height of ventilating opening, the effective opening area, and outdoor air temperature to effectively make use of natural ventilation in the combined system. To sum up, this paper presents an energy efficient system for large spaces and also a theoretical model to design the system and predict the vertical temperature distribution.

Experimental Investigation of Radiation Effects on Natural Convection in Horizontal Channels Heated From Above

2009 ◽  
Vol 131 (6) ◽  
Author(s):  
Oronzio Manca ◽  
Sergio Nardini
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Air Temperature ◽  
Radiation Effects ◽  
Fluid Layer ◽  
Radiation Heat Transfer ◽  
Temperature Measurements ◽  
Temperature Profiles ◽  
Vertical Coordinate ◽  
Aspect Ratios

Radiation heat transfer affects natural convection of air inside an open-ended cavity with a heated horizontal upper plate and an unheated lower parallel plate. Its effect is the heating of the lower plate, which heats the adjacent fluid layer and could determine secondary motions. In this paper, an experimental study is carried out to describe the effect of high value of surface emissivity on air flow in an open-ended cavity. The investigation is performed by means of wall temperature profiles, smoke visualization, and air temperature measurements. Results are obtained for an emissivity of the horizontal plates equal to 0.8, for aspect ratios between 10.0 and 20.0. By means of flow visualization and local air temperature measurements in the cavity as a function of time, remarkable secondary motions in the cavity are observed for the highest considered surface heat flux (Ra=8.91×103, 6.45×104, and 1.92×105). Measurement of the air temperature in the cavity also shows that radiation causes and damps secondary motions at the same time. Mean air temperature profiles as a function of the vertical coordinate, at different locations along the longitudinal axis, confirm both the main flow path inside the cavity and radiation effect on convective heat transfer. Finally, correlations for average Nusselt numbers and dimensionless maximum wall temperatures, in terms of Rayleigh number and channel aspect ratio, are proposed for natural convection with or without radiative heat transfer contribution for 2.26×103≤Ra≤1.92×105 and 10≤2L/b≤20.

scholarly journals SENSIBLE HEAT TRANSFER ON ATMOSPHERIC-OCEANIC BOUNDARY IN THE OUTER AMBON BAY OF INDONESIA

2015 ◽  
Vol 38 (1) ◽  
pp. 21-29
Author(s):  
Gerry Giliant Salamena
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Air Temperature ◽  
Meteorological Data ◽  
Sensible Heat Flux ◽  
Heat Transfer Process ◽  
Linear Regression Method ◽  
Sensible Heat ◽  
Sst Variability ◽  
Oceanic Boundary Layer

Analysis of air-sea temperatures and sensible heat flux was conducted to investigate heat transfer process on the atmospheric-oceanic boundary for the outer Ambon Bay. The analysis used SST data derived from both satellite product and in situ measurement using linear regression method, as well as meteorological data such as air temperature and wind speed during daytime. The goals of the current work were to evaluate the relationship between SST and air temperature in the outer Ambon Bay, and to investigate the variation of sensible heat flux in association with seasonal variability of the bay. The major findings were: 1) SST was predominantly lower than airtemperature, resulting in the dominance of negative feedback process on the atmospheric-oceanic boundary layer of the bay; 2) the seasonal SST variability was influenced by land heating and upwelling in the Banda Sea; 3) land heating resulted in large gradient of air-sea temperatures, whereas cooler upwelled waters exerted an opposite effect.

A Zonal Model for Large Enclosures With Combined Stratification Cooling and Natural Ventilation: Part 1—Model Generation and its Procedure

2005 ◽  
Vol 128 (3) ◽  
pp. 367-375 ◽  
Author(s):  
Jun Gao ◽  
Jia-ning Zhao ◽  
Xiao-dong Li ◽  
Fu-sheng Gao
Keyword(s):  
Heat Transfer ◽  
Air Conditioning ◽  
Natural Ventilation ◽  
Influential Factors ◽  
Temperature Profiles ◽  
Combined System ◽  
Zonal Model ◽  
Flow And Heat Transfer ◽  
Heat Penetration ◽  
Zonal Models

This paper describes a combined system of stratificated air conditioning and natural ventilation for large enclosures, which uses stratificated air conditioning to cool the occupied part of a space and uses natural ventilation to cool the upper part to reduce heat penetration into the lower air-conditioned part. A zonal model is constructed to predict the vertical temperature profiles of large enclosures under such a combined system. This model incorporates airflow and heat transfer throughout the space into the mass and heat balance equations for each horizontally settled zone. It introduces some particular flow dynamics and thermal effects into the predictions of mean airflows and temperature distributions. Different from those pressure-based zonal models applied generally to the predictions for small building rooms, it is termed a temperature-based zonal model, which uses correlations based on temperature differences in combination with submodels for modeling of mass flow and heat transfer in the large enclosures. The present paper provides a calculation procedure for the model. Model performances are then discussed through analyzing the impacts of some influential factors on the space air temperature profiles.

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