This work is an experimental study of the effect of impinging distance on the heat transfer from a cylinder to turbulent isothermal and non-isothermal jets. The isothermal jet is discharged horizontally at the same temperature as the ambient air while the non-isothermal jet is discharged vertically upwards and vertically downwards at a temperature colder than the ambient air. Temperature measurements are made on a heated cylinder using an infrared (IR) camera at five equal impinging distances ranging from Z/d =4 to Z/d=20 and the distributions of the local Frossling numbers are determined. The overall decrease in the average Frossling numbers of the cylinder impinged by the isothermal jet and the cold jets was 25 % and 40% respectively. The peak values of average Frossling number for the isothermal and the cold jets occurred at Z/d=8 and Z/d=4 respectively. The Stagnation Frossling number and the normalized jet centerline velocity for the isothermal and the cold jets were found to be very close to each other at all impinging distances indicating that the effect of buoyancy is negligible in the range of jet temperatures and distances used in the experiment. / Master of Science

This work is an experimental study on heat transfer from a human arm and a model cylinder. Heat transfer from a human forearm to a large jet, representative of a building HVAC vent/outlet was studied using both an IR camera and a heat flux sensor. The isothermal jet was discharged horizontally from a wind tunnel, at the same temperature as the ambient air. The model cylinder was used to validate the heat transfer results with results from previous studies, using both the IR camera and heat flux sensors. Further, a study on heat transfer to impingement jets from a human forearm at various Reynolds numbers (Re = 9500-41000) and impinging distances of four and eight jet diameters was done. Heat transfer from a human arm to such impingement jets were then compared with heat transfer due to natural convection under both open and controlled environments. A significant increase in convection heat transfer with Reynolds number and distance from the jet outlet was observed. A nearly four-fold increase in convection heat transfer coefficient was obtained when a jet with Reynolds number of 9500 was impinged on a human arm when compared to that obtained under natural convection in an open environment. Empirical correlations for predicting the stagnation and average Nusselt number from a human arm were also developed with high values of correlation coefficients for future studies. Impingement jets were found to be an effective means to transfer heat from human bodies and could potentially be used for creating thermally conditioned microenvironments. / M. S. / Impingement jets have been used in a variety of applications such as turbine cooling, electronic cooling and for annealing of metals for enhancing heat transfer due to its large convective heat transfer rates. This study aims at studying the heat transfer to such jets from a human arm and a model cylinder and its potential use in creating thermally conditioned microenvironments in buildings. Thermal microenvironment conditioning refers to controlling the thermal properties of a small zone around the individuals to be conditioned, based on the thermal behavior of the individual. This reduces overall energy consumption by restricting air conditioning to a small area around individuals and can also be potentially be used to cater to the individual occupant’s thermal comfort. Therefore, a large jet representative of an HVAC outlet in buildings was used for this purpose. A horizontal, isothermal jet of air was impinged on a human forearm over a range of jet velocities and the resulting heat transfer rates were compared to that obtained under natural convection (in an open as well as a controlled setting). An IR camera and heat flux sensors were used to measure the heat transfer rates. A nearly four-fold increase in convection heat transfer coefficient was obtained when a jet with Reynolds number of 9500 was impinged on a human arm when compared to that obtained under natural convection in an open environment. Empirical correlations were developed to predict heat transfer from the jet at a given jet velocity with high values of correlation coefficients. Overall, impingement jets were found to be an effective means to transfer heat from human bodies and could potentially be used for creating thermally conditioned microenvironments.