The building space air temperature and mean radiant temperature are known to vary spatially. Lumped models, which are the basis for various building energy simulation tools, treat the thermal properties of the air in the entire space to be uniform. Using such tools, modelling spatial non-uniformity in the temperatures is a challenge. In the present work, a novel method is proposed that customises a building energy simulation tool for such applications. The proposed method divides the room into several lumped nodes and models the cross mixing between the nodes. The spatial variation in mean radiant temperature is estimated using a combination of analytical and numerical methods. The proposed approach is validated using real-world controlled experiments. Further, the paper demonstrates the usefulness of modelling the spatial variations in a room with multiple air-conditioning units. It is observed that representing the space as a single lumped node is inadequate for predicting spatial variations in both the air temperature and the glazing surface temperature. The proposed approach effectively models the spatial variations in the air, mean radiant, and operative temperatures. The proposed method outperforms the baselines that model air temperature as a single node and compares well with the measurements with a maximum error of approximately 1.3%. Further, it is shown that the proposed approach helps in achieving a better uniformity in operative temperature in a test-bed that is served by two AC units.

The effect of dimpled surface configurations on heat transfer is investigated for multiple jets issuing from orifices arranged in a 3 x 3 array. The Reynolds numbers during these studies maintained in the range of 5000-40000. To assess the influence of jet and dimple pitch, the studies are performed for different dimple and orifice pitches (p = 3d, 4d, and 5d). Along with these cases, dimple depths of 0.25d and 0.5d and eccentricity between the orifice and the dimple are also studied. The distance between the orifice plate and the test surface is varied from 1d to 6d. To characterize the steady-state heat transfer from the heated target surface to the impinging air jet, the thermal image of the target surface captured with a thermal imaging camera is analysed with thin metal foil heater technique. To evaluate the effectiveness of jet impingement cooling of the dimpled surface, the average Nusselt number and coefficient of variance (COV) are calculated over a defined pitch area of +/- p. It is observed that for the jet orifice and dimple pitches of three nozzle diameter (p = 3d), the flat plate is more efficient than a dimpled surface. However, for greater pitches (p >= 4d), the dimpled surface performed much better in comparison with the flat plate. In case of the shallow dimpled surface (t/d = 0.25), best heat transfer performance is observed for the pitch of 5d. The coefficient of variance (COV) suggests that the Nusselt number is more uniformly distributed for a pitch of 3d.

Experimental study is carried out to explore the influence of nozzle profile on heat transfer for underexpanded impinging jets. Circular and elliptical orifices are used to generate underexpanded jets for underexpantion ratio ranging from 1.25 to 2.67. The supply pressure maintained in the present study ranges from 2.36 to 5.08 times the ambient pressure. IR thermal imaging camera is used to measure surface temperature of thin foil at different nozzle to plate distances. Shadowgraph and pressure distribution are used to understand the flow structure and distribution of circular and elliptical nozzle. It is observed that plate shock and pressure distribution over the plate have significant influence on the local heat transfer. The performance of the circular orifice is far better at lower z/d. The axis switching is observed for an elliptical orifice. Correlation for local heat transfer predicts Nusselt number comparable within 15 % of experimental results.

In the present study, the influence of impinging underexpanded jets on local heat transfer is studied for nozzle pressure ratio (NPR) ranging from 2.4 to 5.1. To measure the local temperature distribution, a thin metal foil technique with Infrared camera is used. The adiabatic wall temperature is taken as the reference temperature for calculating local Nusselt number and recovery factor. The flow structure distributions captured with the shadowgraph technique are compared with the local Nusselt number and recovery factor distributions. Shadowgraph images show that the shock structure in the flow region plays an important role in governing the local heat transfer distribution over the plate. To propose a generalized correlation for local heat transfer for underexpanded jets, three contoured nozzles of exit diameter of 3.6mm, 5.67mm and 8.37mm are studied. Proposed correlations for the local heat transfer show good agreement with the experimental results for larger nozzle to plate distances.

An experimental investigation is carried out to study the local convective heat transfer between smooth wedge shaped plate and a single round underexpanded impinging jet, using thin metal foil technique and IR camera. In the present study experiments are carried out for five different nozzle pressure ratios in the range of 2.36-5.08. The jet-to-wedge apex distance (z/d) is varied from 1 to 12 nozzle diameters. The influence of the included angle of wedge is studied by carrying out experiments for three apex angles of 31.5, 63 and 94.5. Heat transfer coefficient is calculated based on wall temperature. The local Nusselt numbers, stagnation point Nusselt numbers and recovery factor distribution are reported in present study. Shadowgraphs are used to explain distribution of Nusselt number and recovery factor. It is concluded that local Nusselt number and recovery factor are greatly affected by the nozzle pressure ratios but independent of wedge apex angle. (C) 2016 Elsevier Inc. All rights reserved.

An experimental investigation is performed to study the effects of the orifice shape and Mach number (M) on the local heat transfer distribution by normally impinging compressible jets. Four different orifice cross-sections namely circular, elliptical, square and triangular are used and jets Mach number is maintained from 0.4 to 1in present study. The heat transfer is measured by thin foil IR technique for different nozzle to plate distances. To calculated Nusselt number, adiabatic wall temperature is used as a reference temperature. The stagnation point Nusselt number is significantly higher for circular orifice as compared to other three shapes while that for the elliptical orifice is minimum. Recovery factor distribution is independent of the Reynolds number and the Mach number. The square, triangular and elliptical orifice respectively undergoes a 45°, 180° and 90° axis switching.

Influence of chevron nozzle on local heat transfer distribution over a flat plate impinged by incompressible jets is studied for Reynolds numbers of 28,000, 35,000 and 40,000. Ten different chevron nozzle configurations are studied with a pipe diameter of 10.8 mm. Thin metal foil technique is used with IR camera to measure the wall temperature at nozzle to plate distances (z/d) from 1 to 10. An increase in the local Nusselt number by 26-38% compared to that with circular pipe is measured. It is observed that N10 nozzle (with number of chevron tips n = 8 and chevron tip angle theta = 10 degrees) provides best heat transfer performance. A correlation for the average heat transfer is proposed in present study. A multiplication factor is also introduced to predict local Nusselt number for N10 nozzle. (C) 2016 Elsevier Inc. All rights reserved.

Jet impingement experiments are conducted to study influence of nozzle profile on heat transfer for compressible subsonic jets. Three different circular profiles namely contoured nozzle, orifice and pipe are selected for the present experimental study. For each nozzle profile, Mach numbers covered are 0.3, 0.5 and 0.7 and the corresponding Reynolds numbers are around 48,000, 82,000 and 120,000. Appropriate diameters for these nozzles are chosen to maintain nearly same Reynolds number. Thin metal foil technique with infrared red camera is used to measure the heat transfer coefficient and adiabatic wall temperature. Pressure distribution in the stagnation regions is measured for all the cases. Correlations for local heat transfer distribution over the surface are presented in this study. Pipe nozzle provides higher heat transfer coefficient compared to contoured nozzle and orifice. The Mach number affects the heat transfer in the stagnation region. The recovery factor distribution is insensitive to change in Reynolds number. (C) 2016 Elsevier Ltd. All rights reserved.

Experiments are performed to study the effects of nozzle shape, jet temperature and nozzle to distance (z/d(e)) on heat transfer distribution due to impingement of air jet on a smooth flat plate. Thin metal foil technique is employed in this study for measuring local wall temperature. Influence of jet temperature (70-175 degrees C) on local heat transfer and effectiveness is studied for different Reynolds numbers (5000 -23,000) and jet to plate distances (1-10) for circular jets. Influence of nozzle shape (circular, square and triangular) on local heat transfer distribution and effectiveness is studied for Reynolds number of 10,000 and 23,000 at different jet to plate distances. Reynolds number is calculated on the basis of equivalent diameter (10 mm). Nusselt number measured based on equivalent diameter is the highest for a circular nozzle in comparison with square and triangular nozzles. The effect of jet temperature on heat transfer is found marginal and axis switching is observed for non-circular jets. The axis switching for triangular and square nozzles mechanism is governed by omega(x) dynamics. (C) 2015 Elsevier Masson SAS. All rights reserved.

An experimental investigation is performed to study the influence of the shape of the orifice (circular, square, triangular and elliptical), jet to plate distances and Reynolds number on the local heat transfer distribution to normally impinging submerged air jet on smooth and flat surface. The Reynolds numbers were varied from 5000 to 30,000 in the steps of 5000 and the jet to plate distances used were 0.5, 1, 2, 4, 6 and 8. The equivalent diameter (ratio of area to the perimeter) of all the orifices were maintained nearly constant (5.7 mm). The local heat transfer characteristics are estimated using thermal images obtained by infrared thermal imaging technique. For all the shapes, the area averaged Nusselt number increases with increase in Reynolds number. The area averaged Nusselt number at all Reynolds number is observed to be highest at a z/d of 4. Axis switching is observed for all the shapes except circular orifice. The square, triangular and elliptical orifice respectively undergoes a 45 degrees, 180 degrees and 90 degrees axis switch. Pressure loss coefficients of various orifices are reported. (C) 2015 Elsevier Inc. All rights reserved.