Heat flux correlation models for spray evaporative cooling of vibrating surfaces in the nucleate boiling region

Abstract

New empirical correlation models are constructed to characterise heat transfer associated with spray evaporative cooling of vibrating surfaces -a process involving complex two-phase physics well beyond current numerical simulation capabilities. The proposed correlation models, which account for dynamic, rather than just static surface conditions as in existing models, are constructed using dimensional analysis involving the Generalized Buckingham Π-Theorem. Experimentally-measured spray evaporative cooling data is used to fit the model using the Vibrational Reynolds number and a dimensionless acceleration number which better correlate the influence of surface frequency and amplitude in the nucleate boiling regime. Different coolant flow-rates through a full-cone spray nozzle are used to cool a flat circular test-piece acting as a horizontal surface. The test-piece surface is excited by a shaker through a range of low and high vibration frequencies and amplitudes. The results show that surface dynamic effects certainly influence nucleate boiling, but they also show that surface vibration does not have the same effect for all excess temperatures -dynamic effects can either increase or decrease heat transfer depending on the heat transfer mechanism. These new models are important for thermal management in several areas, particularly involving batteries, power electronics, and electrical machines in automotive and aerospace applications.

An experimentally-verified temperature control simulation model for spray evaporative cooling of vibrating powertrain parts

“…Until the computation cost issue is addressed the practical solution is to exploit Dimensional Similarity. A dynamic correlation model has been constructed in [45] using the Generalised Buckingham Pi method [46]. This has been achieved by identifying the dependent variables assuming heat flux conforms to a function: 𝑞 = 𝜑(𝜌 𝑙 , 𝜌 𝑣 , ℎ 𝑓𝑔 , 𝜇 𝑙 , 𝐶 𝑙 , 𝜎, 𝑇 𝑐 , 𝑇 𝑤 , 𝑃 𝑛 , 𝑃 𝑐ℎ , ∆𝑇 𝑠𝑎𝑡 , ∆𝑇 𝑠𝑢𝑏 , 𝑃 𝑎𝑡 , 𝑢 𝑑 or 𝑢 𝑚 , 𝑚ሶ , 𝑑 32 , 𝑑 𝐻 , 𝐻, 𝑎, 𝜔, 𝑔)…”

“…A dynamic correlation model corresponding to a flat horizontal test-piece, cooled using spray evaporative cooling supplied by a UNIJET nozzle, has been obtained in [45] by fitting to measured experimental data takes the form:…”

Numerical Simulation of Single-Droplet Dynamics, Vaporization, and Heat Transfer from Impingement onto Static and Vibrating Surfaces

“…They used a value of 0.1 in [2] but stated that it could be in the range 0 to 1. Briones and Ervin [3] undertook both experimental measurements and numerical simulations on micrometer-sized droplet impingement and evaporation. They used a mass transfer model based on interfacial surface area density and kinetic theory.…”

“…One of the drawbacks in verifying numerical simulations using experimental data is the enormous computational power needed to simulate complete droplet evaporation. It was reported in [3] that their single-droplet evaporation simulation took 24 days of computer time using parallel processing.…”

“…The effect of surface vibration on spray evaporative cooling is an area that has received very limited previous attention. Sarmadian et al (2020) [3] undertook an experimental investigation specifically on the surface vibration of spray evaporative cooling in the nucleate boiling regime. There have also been a number of experimental studies on evaporative cooling but not involving a spray.…”