Author: Matthew Thomas HamiltonPublisher:
ISBN:
Category : Electronic apparatus and appliances
Languages : en
Pages : 214
Book Description
Computational Study on Micro-/macro-gravity Effects on Spray Cooling Heat Transfer
Author: Matthew Thomas HamiltonPublisher:
ISBN:
Category : Electronic apparatus and appliances
Languages : en
Pages : 214
Book Description
Experimental Testing and Numerical Modeling of Spray Cooling Under Terrestrial Gravity Conditions
Author: Kerri Michelle BaysingerPublisher:
ISBN:
Category : Cooling
Languages : en
Pages : 116
Book Description
Baseline tests were performed for a spray cooling system using subcooled fluid under terrestrial gravity conditions, and a steady state numerical model of the glass heater pedestal assembly was built using ANSYS finite element software. A parametric study was performed to study the effects of volumetric flow rate, heat transfer rate, and orientation with respect to gravity on the experimental system. The numerical model data was compared with the experimental data in order to determine the spray heat transfer coefficient along the top of the heated surface. For a volumetric flow range gal/hr and a heat load range of W, the estimated spray heat transfer coefficient was on the order of W/(m2-K), regardless of heater orientation. In addition, the heat lost due to conduction in the upward-facing heater pedestal was estimated using both experimental and numerical results, and was found to be 1.0 greater or less than (percent of heat loss due to conduction in glass heater pedestal assembly) greater or less than 2.5%.
Design of A Microgravity Spray Cooling Experiment
Author: Publisher:
ISBN:
Category :
Languages : en
Pages : 14
Book Description
An analytical and experimental study was conducted for the application of spray cooling in a micro gravity and high-g environment. Experiments were carried out aboard the NASA KC-135 reduced gravity aircraft, which provided both the microgravity and high-g environments. In reduced gravity, surface tension flow was observed around the spray nozzle, due to unconstrained liquid in the test chamber and flow reversal at the heat source. A transient analytical model was developed to predict the temperature and the spray heat transfer coefficient within the heated region. Comparison of the experimental transient temperature variation with analytical results showed good agreement for low heat input values. The transient analysis also verified that thermal equilibrium within the heated region could be reached during the 20-25s reduced gravity portion of the flight profile.
Fluid Property Effects on Spray Cooling
Author: Andrea C. AshwoodMaster's Theses Directories
Author: Publisher:
ISBN:
Category : Dissertations, Academic
Languages : en
Pages : 312
Book Description
"Education, arts and social sciences, natural and technical sciences in the United States and Canada".
High Heat Flux Spray Cooling with Ammonia on Enhanced Surfaces
Author: Huseyin BostanciPublisher:
ISBN:
Category : Ammonia
Languages : en
Pages : 110
Book Description
Many critical applications today, in electronics, optics and aerospace fields, among others, demand advanced thermal management solutions for the acquisition of high heat loads they generate in order to operate reliably and efficiently. Current competing technologies for this challenging task include several single and two phase cooling options. When these cooling schemes are compared based on the high heat flux removal (100-1000 W/cm2) and isothermal operation (within several °C across the cooled device) aspects, as well as system mass, volume and power consumption, spray cooling appears to be the best choice. The current study focused on high heat flux spray cooling with ammonia on enhanced surfaces. Compared to some other commonly used coolants, ammonia possesses important advantages such as low saturation temperature, and high heat absorbing capability. Moreover, enhanced surfaces offer potential to greatly improve heat transfer performance. The main objectives of the study were to investigate the effect of surface enhancement on spray cooling performance, and contribute to the current understanding of spray cooling heat transfer mechanisms. These objectives were pursued through a two stage experimental study. While the first stage investigated enhanced surfaces for the highest heat transfer coefficient at heat fluxes of up to 500 W/cm2, the second stage investigated the optimized enhanced surfaces for critical heat flux (CHF). Surface modification techniques were utilized to obtain micro scale indentations and protrusions, and macro (mm) scale pyramidal, triangular, rectangular, and square pin fins. A third group, multi-scale structured surfaces, combined macro and micro scale structures. Experimental results indicated that micro- and macrostructured surfaces can provide heat transfer coefficients of up to 534,000 and 426,000 W/m2°C at 500 W/cm2, respectively. Multi-scale structured surfaces offered even a better performance, with heat transfer coefficients of up to 772,000 W/m2°C at 500 W/cm2, corresponding to a 161% increase over the reference smooth surface. In CHF tests, the optimized multi-scale structured surface helped increase maximum heat flux limit by 18%, to 910 W/cm2 at nominal liquid flow rate. During the additional CHF testing at higher flow rates, most heaters experienced failures before reaching CHF at heat fluxes above 950 W/cm2. However, the effect of flow rate was still characterized, suggesting that enhanced surfaces can achieve CHF values of up to [almost equal to]1,100 W/cm2 with [almost equal to]67% spray cooling efficiency. The results also helped shed some light on the current understanding of the spray cooling heat transfer mechanisms. Data clearly proved that in addition to fairly well established mechanisms of forced convection in the single phase regime, and free surface evaporation and boiling through secondary nucleation in the two phase regime, enhanced surfaces can substantially improve boiling through surface nucleation, which can also be supported by the concept of three phase contact lines, the regions where solid, liquid and vapor phases meet. Furthermore, enhanced surfaces are capable of retaining more liquid compared to a smooth surface, and efficiently spread the liquid film via capillary force within the structures. This unique advantage delays the occurrence of dry patches at high heat fluxes, and leads to higher CHF.
Study of Heat Transfer by Spray Cooling
Author: K ChangApplied Mechanics Reviews
Author: Time and Space Resolved Heat Transfer - Boiling and Droplet Cooling Studies Using Microheaters
Author: Jungho KimPublisher:
ISBN:
Category : Chemistry, Physical and theoretical
Languages : en
Pages : 48
Book Description
Heat transfer by phase change has long been an attractive method of cooling since large amounts of heat can be removed with relatively small temperature differences. The current study focused on making detailed measurements of the heat flux and interfacial motion of isolated droplets (with and without gas) as they impacted an isothermal surface at low and moderate superheats. The heat flux measurements were made using a novel heater array which allowed the local, instantaneous heat flux to be resolved. The results without gas indicate that the vaporization process can be divided into two parts; a first part that is characterized by transient effective heat transfer coefficient, and a second part in which the heat transfer coefficient is constant. The results with gas indicate that a gas bubble can nucleate, grow, and merge within the liquid, resulting in an increase in the droplet diameter. The measurements indicate that significantly smaller droplet evaporation times can be achieved as a result of the increase in liquid-vapor surface area during bubble formation. Recent work on the effects of dissolved gas and subcooling on spray cooling is also discussed.
Author: