energies Article Predicting Conduction Heat Flux through Macrolayer in Nucleate Pool Boiling Mohd Danish 1, * , Mohammed K. Al Mesfer 1 , Khursheed B. Ansari 2 , Mudassir Hasan 1 , Abdelfattah Amari 1 and Babar Azeem 3   Citation: Danish, M.; Al Mesfer, M.K.; Ansari, K.B.; Hasan, M.; Amari, A.; Azeem, B. Predicting Conduction Heat Flux through Macrolayer in Nucleate Pool Boiling. Energies 2021, 14, 3893. https://doi.org/10.3390/ en14133893 Received: 5 May 2021 Accepted: 23 June 2021 Published: 28 June 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Chemical Engineering Department, College of Engineering, King Khalid University, Abha 61411, Saudi Arabia; almesfer@kku.edu.sa (M.K.A.M.); m-hasan@kku.edu.sa (M.H.); aamari@kku.edu.sa (A.A.) 2 Department of Chemical Engineering, Zakir Husain College of Engineering and Technology, Aligarh Muslim University, Aligarh 202001, India; akabadruddin@myamu.ac.in 3 Department of Chemical Engineering, The University of Faisalabad, Engineering Wing, Faisalabad 38000, Pakistan; babar.azeem@tuf.edu.pk * Correspondence: mdansh@kku.edu.sa; Tel.: +966-58-054-0101 Abstract: In the current work, the heat flux in nucleate pool boiling has been predicted using the macrolayer and latent heat evaporation model. The wall superheat (ΔT) and macrolayer thickness (δ) are the parameters considered for predicting the heat flux. The influence of operating parameters on instantaneous conduction heat flux and average heat flux across the macrolayer are investigated. A comparison of the findings of current model with Bhat’s decreasing macrolayer model revealed a close agreement under the nucleate pool boiling condition at high heat flux. It is suggested that conduction heat transfer strongly rely on macrolayer thickness and wall superheat. The wall superheat and macrolayer thickness is found to significantly contribute to conduction heat transfer. The predicted results closely agree with the findings of Bhat’s decreasing macrolayer model for higher values of wall superheat signifying the nucleate boiling. The predicted results of the proposed model and Bhat’s existing model are validated by the experimental data. The findings also endorse the claim that predominant mode of heat transfer from heater surface to boiling liquid is the conduction across the macrolayer at the significantly high heat flux region of nucleate boiling. Keywords: heat flux; pool boiling; wall superheat; conduction 1. Introduction Increased rate of heat transfer attributed to nucleate pool boiling is a vital regime of boiling. The nucleate boiling has been characterized by region of interference and isolated bubbles [1]. The pool boiling was investigated [2] with the help of illustrations of atmospheric pressure. Rough differentiation of various regions of nucleate pool boiling was hypothesized [3]. Previously, researchers [4] reported results comparable to those obtained by the investigators [2], and a marked decline in heat transfer coefficient was noticed in the second transition region. An investigation of saturated pool boiling was conducted pictorially and it was suggested that, as minimum, three and possibly four heat transfer regions be present. Katto and Yokoya [5] recommended a mechanism for nucleate boiling in which the heater surface is characterized by the existence of liquid film on it. In high heat flux region corresponding to nucleate pool boiling, the discrete bubbles leaving from the heated surface cannot escape into free space but amalgamate to form a large vapor mass due to high active site density. The vapor mass so formed still remains connected to the heating surface through a number of vapor column stems while a liquid layer is entrapped between the growing vapor mass and the heated surface. The liquid layer between the vapor mass and the heating surface is termed as “macrolayer.” Whereas the microlayer is a liquid film that is much thinner, between an individual bubble and the heating surface Energies 2021, 14, 3893. https://doi.org/10.3390/en14133893 https://www.mdpi.com/journal/energies