Abstract

The paper describes a unique method of heat flux measurement, i.e., gradient heatmetry. Gradient heatmetry is performed using gradient heat flux sensors (GHFS) developed on the anisotropic thermoelements basis. The principle of GHFS’ operation leads to the fact that their response time is about 10 ns, and the volt-watt sensitivity does not depend on the thickness. GHFS are compared with other types heat flux sensors, with the GHFS features depending on the materials being described. The theory and examples of gradient heatmetry applications in thermophysical experiment are provided.

Highlights

  • Direct heat flux measurement is one of the most important tasks in thermal physics, power engineering, metalworking, power electronics, etc

  • We have started to apply gradient heat flux sensors (GHFS) in the study of condensation relatively recently but managed to obtain results confirming the applicability of gradient heatmetry

  • The optimal tube tilt in terms of heat transfer during condensation (ψ = 20◦ ) was determined under experimental conditions: on this slope, the heat flux is 12% higher, and heat transfer coefficient (HTC) is 14.9 % higher compared to the vertical tube

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Summary

Introduction

Direct heat flux measurement is one of the most important tasks in thermal physics, power engineering, metalworking, power electronics, etc. The temperature gradient of such an HFS has two components: along the applied heat flux per unit area vector q0 and normal to it [13] This phenomenon is called the transverse Seebeck effect. The electric field intensity vector E⊥ is proportional to the transverse temperature gradient and normal to the vector q0 Since this HFS type generates an output signal proportional to the transverse temperature gradient, they have been called gradient heat flux sensors (GHFS) [14]. A synthetic GHFS is a system of alternating layers of two materials (copper-constantan, chromel-copel, etc.) with different thermal and electrophysical properties [14] Since such sensors consist of separate macrostructures, we call them heterogeneous GHFS (HGHFS). The principle of operation of GHFS and HGHFS is identical, but the operating temperature range of a HGHFS is much wider: working resistance of HGHFS can reach 1300 K and higher

GHFS Principle of Operation
GHFS Design
Application of GHFS
Convective Heat Transfer
Heat Transfer during Steam Condensation
Condensation on the Outer Surfaces of The Tubes
Condensation on the Inner Surfaces of Tubes
Heat Transfer during Boiling
Findings
Conclusions
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