Bahram Moshfegh

Modeling of the thermal and hydraulic performance of plate fin, strip fin, and pin fin heat sinks-influence of flow bypass

Tests have been conducted in a wind tunnel with seven types of heat sinks including plate fin, strip fin, and pin fin heat sinks. In the case of strip fin, and pin fin heat sinks, both in-line and staggered arrays have been studied. The pin fin heat sinks had circular and square cross-sections. For each type, tests were run with fin heights (H) of 10, 15, and 20 mm while the heat sink width (B) was kept constant and equal to 52.8 mm. In total, 42 different heat sinks were tested. The width of the wind tunnel duct (CB) was varied in such a way that results were obtained for B/CB=0.84, 0.53, and 0.33. The wind tunnel height (CH) was varied similarly, and data were recorded for H/CH=1, 0.67, and 0.33 while the duct Reynolds number was varied between 2000 through 16500. An empirical bypass correlation has been developed for the different fin designs. The correlation predicts the Nusselt number and the dimensionless pressure drop and takes into account the influence of duct height, duct width, fin height, fin thickness, and fin-to-fin distance. The correlation parameters are individual for each fin design. Further, a physical bypass model for plate fin heat sinks has been developed to describe the bypass effect.

Ventilated-solar roof air flow and heat transfer investigation

The governing parameters for flows generated by heat transfer from solar cell modules to air gaps are discussed. Experimental results are presented from measurements in mock-ups of ventilated facades and roofs. The heat transmitted from the solar cells to the air have been mimicked by the use of heating foils. The inclination angle of the roof, position of solar cell module and the height to width ratio (aspect ratio) have been varied. The bulk properties as the air flow rate in the air gap, local temperatures and velocities have been measured. Results of importance for design of hybrid systems and cooling of solar cells have been obtained.

Experimental investigation of the velocity field and airflow pattern generated by cooling ceiling beams

Abstract In the modern office environment there are numerous heat generating equipment, heat loads from solar radiation and heat produced by people. The loads will often exceed the load the ventilation system can cope with. To meet this demand on extra cooling capacity the commercial market provides cooling ceiling panels and chilled beams. A chilled beam is a source of natural convection, creating a flow, vulnerable to disturbances, of cold air into the occupied zone. Experiments have been conducted in a mock up of an office room; qualitative information has been obtained by visualisation. Instantaneous velocity profiles of the airflow generated by the chilled beam has been registered. In addition, the temperature field below the chilled beam has been measured with a whole field measuring technique. The results show that the airflow from the chilled beam has behaviour similar to a two-dimensional plume but exhibits strong oscillation both sideways and along the chilled beam. These oscillations (intermittence) might cause a sensation of draught but in order to clarify this further investigations are required. Furthermore, airflow generated by heat sources in the room may reverse the flow generated by the chilled beam.

Thermal analysis of super insulated windows (numerical and experimental investigations)

Windows are crucial for peoples experience of the indoor climate, especially in the Nordic countries with cold climate and short days during the winter. This paper reports the first results from an ongoing research project focused on an improved integration of windows with the indoor air climate and peoples perception of the windows. The thermal performance of a well-insulated window has been investigated both numerically and experimentally in a full scale test room. The window under consideration is a low-emissive triple-glazing window with two closed spaces filled with the inert gas krypton. An oxidised metal with low emissivity factor coats one pane in each space. Experimental and numerical investigations on the thermal performance of the window have been conducted for different winter cases. Temperature data obtained by direct temperature measurement using thermocouples and through numerical analysis are presented. The heat transfer through a window construction depends on three mechanisms i.e., conduction, convection and radiation. In this paper the convection-conducting mechanisms have been closely investigated. The numerical predictions agree well with the results from the measurements.

Energy in Swedish industry 2020 – current status, policy instruments, and policy implications

The EU has established so-called 20–20–20 targets, which in relation to energy mean that each Member State shall improve energy intensity levels by 3.3% annually, leading to a reduced primary energy use of 20% by the year 2020, calculated from a projected level based on the primary energy use in 2005. Sweden has established a less ambitious target of 1.7% annual energy intensity improvement through 2020. The aim of this paper is to evaluate, ex-ante, the EU 2020 primary energy target for the Swedish industrial sector. An applied backcasting methodology is used. The assessment made in this paper is that actions that lead to between 31.6 and 33.2 TWh/year reductions in energy end-use are needed if the EU target is to be achieved. Results from this paper shows that the current energy policy instruments are not sufficient to the EU or Swedish targets. Estimations in this paper are that a primary energy target of about 22.3 TWh/year is reasonable. The paper concludes by presenting a roadmap on how the Swedish 2020 target can be achieved through: i) energy management; ii) energy-efficient technology; and iii) energy supply measures, with an approximate cost of 280–300 MEUR or 75–80 kWh per public EUR. Three major additional policy measures are needed compared with the current policy: including all energy carriers, not just electricity, in the Swedish long-term agreements program PFE; setting up networks; and making it possible for third parties, i.e., industry, to deliver excess heat into the monopolized Swedish district heating grids.

Evaluation of RANS Models in Predicting Low Reynolds, Free, Turbulent Round Jet

In order to study the flow behavior of multiple jets, numerical prediction of the three-dimensional domain of round jets from the nozzle edge up to the turbulent region is essential. The previous n ...

A Newly Designed Supply Diffuser for Industrial Premises

Abstract The results of this investigation revealed the airflow distribution from a new design of supply diffuser under non–isothermal conditions. To illustrate the indoor climate parameters in the occupied zone, for both the heating and cooling seasons, an experimental investigation was carried out in industrial premises. The indoor climate was explored at ankle, waist and neck levels for a standing person at different positions, to determine the variation of the thermal comfort indexes and draught rating (DR) with position in the facility. The observed PPD and DR values indicate acceptable levels of thermal comfort in the facility for both summer and winter cases. The conclusion can be drawn that well–distributed airflow saves energy by removing the need for an additional heating and cooling systems during cold and hot weather seasons.

Experimental investigation of downdraught from well-insulated windows

Since the climate in the Nordic countries is cold for several months a year, windows are crucial in building envelopes. The current trend to reduce heat losses by building components has resulted i ...

A Method to Assess the Potential for and Consequences of Energy Retrofits in Swedish Historic Buildings

Abstract The Swedish research project ‘Potential and Policies for Energy Efficiency in Swedish Historic Buildings’ aims to investigate the interdependency between political energy targets and effects on the built heritage. The first part of this paper presents an iterative and interactive method to assess the potential for and consequences of improving the energy performance in a stock of historic buildings. Key elements in the method are: categorisation of the building stock, identifying targets, assessment of measures, and life-cycle cost optimisation. In the second part of the paper, the method is applied to a typical Swedish building. The selected case study shows how the method allows for an interaction between the quantitative assessment of the techno-economic optimisation and the qualitative assessment of vulnerability and other risks. Through a multidisciplinary dialogue and iteration it is possible to arrive at a solution that best balances energy conservation and building conservation in a given decision context.

Impinging Jet Cooling of Wall Mounted Cubes

This paper reports on the flow structure and the surface temperature distribution of a heated wall-mounted cube from an in-line array, subjected to cooling by the combined action of a channel flow and an impinging jet. The impinging jet issues from a round nozzle at the top wall. The turbulent flow field around the cube (measured with Particle Image Velocimetry (PIV)) and the temperature distribution on the surfaces of the cube (evaluated from an infrared imaging system) were determined for two different relative positions of the jet nozzle and the cube. The local flow structure in terms of flow separation and reattachment, and the rolling up of separating shear layers, has a marked influence on the local temperature distribution on the surface of the cube.