An experimental study of stratified flow in enclosures A.S. Awad a , R.K. Calay a , O.O. Badran b, * , A.E. Holdo a a Department of Aerospace, Automotive and Design Engineering, Faculty of Engineering and Information Science, University of Hertfordshire, Hatfield Campus, UK b Department of Mechanical Engineering, Faculty of Engineering Technology, Al-Balqa’ Applied University, P.O. Box 330116, Amman 11134, Jordan Received 11 November 2006; accepted 26 December 2007 Available online 11 January 2008 Abstract This paper presents an experimental investigation of flow scenarios that lead to stratification within the ventilated enclosures. The effect of supply terminal and extract terminal at various airflow rates on the flow characteristics is experimentally investigated. It has been found that relative influence of inertia and buoyancy forces resolves the stratified flow characteristics. The stratification interface level height and the ventilation flow rates are two main factors in the design of natural ventilation system. The results can be used to obtain a good estimation of the effectiveness of a ventilation system at design stage. Ó 2008 Elsevier Ltd. All rights reserved. Keywords: Stratified flow; Natural ventilation; Temperature distribution 1. Introduction Thermal stratification is often dominant feature of the flow characteristics within ventilated buildings. There may be many heat sources such as occupants and equip- ment within a room that acts like heat sources and thermal plume develop around them resulting into a vertical tem- perature gradient. These sources may develop pure buoy- ancy driven plumes or mixed convection jets as in the supply of hot air in mechanical heating systems. Generally such jets or plumes propagate entraining air from ambient to a height where the temperature within the jets becomes equal to the ambient temperature. At this height flow becomes stratified and there may be a zone above or below the stratified zone where flow is mixed i.e. the temperature profile is uniform. It has been shown that the flow region is usually divided into zones characterised by temperature gradient. The tem- perature gradient within the enclosure is influenced by ven- tilation flow rate and not so much by the position of the heat sources. Thus contaminant removal effectiveness, in displacement ventilation, is influenced by the ventilation flow rate and also sensitive to the level of the source and its position [1,2]. The vertical position of the interface is also related to the ratio of the upper and lower vent areas depending on the nature of the heat source as shown by Fitzgerald and Woods [3]. It has been found in earlier experiment that the height of exhaust is directly propor- tional to the height of the interface i.e. the point where flow becomes stratified. Therefore by modifying the exhaust position the removal of contaminated air from a multipur- pose industrial space can be selectively achieved as pro- posed by Calay et al. [4]. The configurations of building rooms and especially the location of inlet and outlet openings in relation to domi- nant wind direction at the site have major effects on the ventilation rates in buildings. Locating inlet openings near high-pressure surfaces of a building, and exit openings at low-pressure ones produces higher flow rates through win- dows, Ayad [5]. Although in industrial buildings heat sources often are pollutant sources, yet the vertical profile of concentration 1359-4311/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.applthermaleng.2007.12.017 * Corresponding author. Tel.: +962 6 5679773. E-mail address: o_badran@yahoo.com (O.O. Badran). www.elsevier.com/locate/apthermeng Available online at www.sciencedirect.com Applied Thermal Engineering 28 (2008) 2150–2158