An experimental test facility has been designed, constructed, and commissioned for studying the convective heat transfer of an array of 55 impingement jets with a constant heat-flux boundary condition. Spatial variation in timeaveraged Nusselt number as well as spanwise time-averaged Nusselt number are presented for jet Reynolds numbers of 4000, 8000, 12,000, and 15,000 for a jet-to-target standoff distance of z=D 3. For each of these configurations, the exit flow has also been varied to include both single-exit and double-exit configurations. The time and overall areaaveraged Nusselt number is presented as a function of jet Reynolds number. The results show that the time-averaged Nusselt number increases with increasing jet Reynolds number in both the local and spanwise-averaged values. The single-exit configuration provides lower values of local and spanwise-averaged Nusselt number for all jet Reynolds numbers studied compared with the double-exit configuration. This reduction is caused by more crossflow accumulation while it moves toward the exit. Nomenclature film = thermal diffusivity based upon film temperature, natural convection side, m 2 =s D = impingement-jet-nozzle diameter, m g = combined gravitational and centrifugal acceleration on the earth's surface, m=s 2 H = height of the imageable region of the foil heater, H hx; y; t = local impingement jet convective heat transfer coefficient, W=m 2 K I = current, A kx; y; t = local thermal conductivity based on the local film temperature, W=m K l = heated foil length, m N = total number of impingement jet nozzles Nux; y; t = local Nusselt number based on the jet nozzle diameter, hx; y; t D=kx; y; t Nu mean = time and area-averaged Nusselt number Nu natural x; y; t = Nusselt number for natural convection _ m = total mass flow rate through all impingement jet nozzles, kg=s q 00 foil = foil heater heat flux, W=m 2 q 00 losses x; y; t = heat losses on the imaged side of the foil, W=m 2 Ra y x; y; t = Rayleigh number, g T s;spanwise x; t T ambient y 3 = film;natural film;natural Re jet = Reynolds number based on the jet nozzle diameter T ambient = static temperature of the ambient air in the test cell, K T film x; y; t = local film temperature, T upstream T s x; y; t=2, K T s x; y; t = local foil surface temperature, K T s;spanwise x; t = spanwise-averaged surface temperature, 1=H R H 0 T s x; y; t dy, K T upstream = average fluid temperature measured in the pressure chamber, K t = time, s V = voltage drop across the foil heater, V w = heated foil width, m x = horizontal dimension, m y = vertical dimension, m z = normal dimension, m = expansion coefficient, (1=T s;spanwise x; t), 1=K = absolute viscosity, N s=m 2 film;natural= kinematic viscosity based upon film temperature, natural convection side, m 2 =s = ratio of the circumference of a circle to its diameter
