Boiling Project

Pool Boiling Heat Transfer Enhancement

Xiaokang Wu

Apr 22, 2016

BOILING PROJECTPOOL BOILING HEAT TRANSFER ENHANCEMENT

Introduction:With the growing concerns on climate change, the study of energy conversion such as heat transfer has become a critical issue. More than 90% of the power is generated by heat engine. In such heat engines, Boiling heat transfer devices plays an important role. The most important parameters of boiling heat transfer is the critical heat flux (CHF) associated with the heat transfer efficiency. So how to improve the heat transfer efficiency is a big deal.

Enhancing the CHF can have a significant impact on energy conversion

Our goal is to enhance the CHF, which determines the maximum power

density that could be handled by a boiling heat transfer device.

Experimental Set-up

(a) Cartridge heater, (b) ceramic block, (c) testing sample, (d) gasket, (e) polycarbonate tube or glass tank, (f) heater, (g) high speed camera,

(h) Power supply, (i) compression screws, (j) thermocouples.

The bottom heater is used to heat the sample

The top heater is used to heat the water to keep the water temperature at 100 degree

Ceramic block can support the setup,Also can be used as thermal insulationmaterials to prevent heat loss from the heater to ambient environment.

Three thermocouples

• There installed 6-8 mm apart and the first one T1 was 3-5 mm blow the top heater surface.

• The heat flux was calculated from the following equation: The k represents thermal conductivity. There is another way to calculate the heat flux using the Fourier Law. We will talk about this method later, since this method is much complicated.

Calculate the wall superheat

• R’’ represents to the thermal contact resistance of the interface, L and K represent material thickness and thermal conductivity.

where

So we are able to get

Data Analysis• After we get those data. We are able to have• Heat flux VS wall superheat. And change different sample

to record the data, and plot into the graph.

The graph should be looking like above. Each sample can have different heat flux.

Advantages of the setup

• Since the setup is easily taken apart, the testing sample is

easy to change.• The sample can be fixed easily.• Use three thermocouples (T1, T2, T3) to measure the

temperature gradient of the heater resulting in heat flux can be accurately estimated by Fourier Law.

• The setup is not very complicated, but can get more accurate experimental results compare to the simple setups.

Disadvantages of the setup

• It may not be a good idea to use the ceramic block as thermal insulation materials to prevent heat loss from the heater to ambient environment. Since ceramic block’s thermal insulation ability is significantly lower compare to much expensive one.

Plan To Do 1. The water tank can either be polycarbonate tube or be a

glass chamber obtained by designing by glass work.2. Assumed there are two key points which may affect on

CHF. We may do some research later on to determine how they are affecting on CHF.

3. Improve and optimize the setup to obtain the data as accurately as possible

4. Do the uncertainty analysis of the measured heat fluxes, which is mainly from the power supply.

Sample Structure• As long as the different sample structures can make a big

difference to enhance CHF. So determine ‘how it works’ is our main sub-goal.

• Recent studies found boiling augmentation nanostructured surfaces, such as nanowires. Both capillary force and effect of liquid spreading using artificial surfaces with nanostructures depositions can effect the CHF.

Reference

• G. P. Peterson, Yoav Peles, Chen Li (Oct 17, 2007) ‘Nanostructured Copper Interfaces for Enhanced Boiling’. InterScience.

• Ming-Chang Lu, Renkun Chen, Vinod Srinivasan,Van P. Carey (Nov. 27, 2010) ‘International Jounal of Heat and Mass Transfer’. ELSEVIER.

• Z. Yao, Y.W. Lu, S. G. Kandlikar (Mar 4, 2012) ‘Pool Boiling Heat Transfer Enhancement Through Nanostructures on Silicon Microchannels’.