Heat Exchanger Technology

Fouling Factor for Different Type of Oil

2009-02-23T14:18:00.000-08:00

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Oil - Fouling Factors in [m²K/W]

	Oil Type	Fouling Factor
	Gasoil	0.00009
	Transformer	0.00018
	Lubrication	0.00018
	Heat Transfer oil	0.00018
	Hydraulic	0.00018

Fouling Factor For Different Type of Gas & Vapor

2009-02-22T13:53:00.000-08:00

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Gas / Vapor - Fouling Factors in [m²K/W]

	Gas / Vapor Type	Fouling Factor
	Hydrogen	0.00176
	Engine exhaust	0.00176
	Steam	0.00009
	Steam with oil traces	0.00018
	Cooling fluid vapours with oil traces	0.00035
	Organic solvent vapours	0.00018
	Compressed air	0.00035
	Natural gas	0.00018
	Stable top products	0.00018

Few Tips on Energy Efficient & Recovery

2009-02-21T15:23:00.000-08:00

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it can, and, as a result, heat-transfer projects are not only justifiable, but downright attractive.

There was a dialog among a few heat exchanger specialist from Alfa Laval, Paul Muller, Exergy LLC, etc. The dialog mainly discussed on strategy to improve heat transfer efficiency, heat recovery and efficient process control during this high energy price arena.

A few tips have been present :

The energy crisis results high prices all of the time shorten paybacks. Energy efficient is one of the way to minimize cost
Energy efficient heat transfer equipment such as Plate Heat exchanger, Gasketed Heat exchanger, Bonded Heat exchanger, etc is one of the option.
For a service using Shell & Tube (S&T), the overall heat transfer coefficient (HTC) is around 300 Btu/h ft2°F. However, the overall heat transfer coefficient (HTC) for a compact heat exchanger can be improved 3-4 times (~1000 to 12000 Btu/h ft2°F).
With higher overall heat transfer coefficient, this may translate into less space, smaller installation and handling cost.
Gasketed Heat exchanger good for maintenance. However shall take additional attention on the compatibility between gasket and fluid.
All welded or Bonded heat exchanger may be considered if there is gasket & fluid compatible problem
For laminar flow, heat transfer rate is only the function of fluid thermal conductivity. Operate heat transfer equipment at laminar flow during turndown could significantly reduce it heat transfer rate
Compact heat exchanger promote turbulence. High turbulence increase heat transfer rate and reduce fouling
Thus plant releasing hot exhaust gas from burner, boiler, gas turbine, etc to atmosphere may take the opportunity to recover heat
Improve temperature control in process system would reduce energy usage

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Why not use Fouling factor by TEMA in PHE ?

2009-02-18T12:14:00.000-08:00

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Tubular Exchanger Manufacturers Association (TEMA) has developed a series of fouling factor for Shell and Tube (S&T). These fouling factor are generally higher than Plate Heat Exchanger (PHE), why not use S&T fouling factors to size PHE ?

Isn't this approach conservative and guarantee the performance ?

Reason being...

Oversized Plate Heat Exchanger (PHE) required extra CAPEX and extra Space for oversized PHE
Tubulence minimise fouling tendencies in correctly sized PHE. Oversized PHE results low actual velocity and increase potential fouling and inefficient heat transfer
HTRI studies showed PHE fouling significant lower than Shell & Tube Heat Exchanger (S&T)... factor of 6.7

GUIDELINE : Do not oversized PHE more than 25% against required area.

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Fouling Factors for Different Type of Water

2009-02-17T14:16:00.000-08:00

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WATER - Fouling Factors in [m²K/W]

Water Type	Tcw < 50 ° C Tf < 120 ° C		Tcw > 50 ° C Tf > 120 ° C
	v < 1 m/s	v > 1 m/s	v < 1 m/s	v > 1 m/s
Sea	0.00009	0.00009	0.00018	0.00018
Brackish	0.00035	0.00018	0.00053	0.00035
Cooling tower with inhibitor	0.00018	0.00018	0.00035	0.00035
Cooling tower without inhibitor	0.00053	0.00053	0.00088	0.00070
City grid	0.00018	0.00018	0.00035	0.00035
River mimimum	0.00018	0.00018	0.00035	0.00035
River average	0.00053	0.00035	0.00070	0.00035
Engine jacket	0.00018	0.00018	0.00018	0.00018
Demineralized or distilled	0.00009	0.00009	0.00009	0.00009
Treated Boiler Feedwater	0.00018	0.00009	0.00018	0.00018
Boiler blowdown	0.00035	0.00035	0.00035	0.00035

Tcw = Water temperature
Tf = Fluid temperature
v = Water velocity

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Wire Matrix Turbulator Improve Heat Transfer in ACHE

2009-02-17T13:53:00.001-08:00

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In one the recent depleted field debottlenecking project, new Booster Compression unit will be installed to boost the depleted well fluid pressure to meet high delivery pressure while maintaining the production forecast market demand. As this unit will be installed on existing platform, space and weight constraint are the major issues. Many efforts have been implemented in order to reduce new installation space and weight. One of them is to reduce the Lube Oil Cooler Size. One of the question raised.

How to reduce lube oil cooler size while meeting duty and flow ?

The following image demonstrates a wire matrix turbulator by hiTRAN

Wire matrix turbulator, known as a HiTRAN® Matrix Element, is inserted into inner tube of Heat Exchanger. The basic principle is to promote fluid mixing, convert laminar flow to turbulence flow pattern, maintaining turbulence flow pattern and improve tube-side heat transfer.

From above image,
- region (A) is laminar flow conditions
- region (B) is turbulence caused by the use of hiTRAN matrix tube Inserts

Case Studies

See below the comparison between Compressor lube oil cooler (Air-Cooled Heat Exchanger) with and without turbulator :

Number of tube rows above each other : 5* (with turbulator) 10* (without turbulator)
Width : 4* m(with turbulator) 7.3* m (without turbulator)
Length : 7.9* m (with tubulator) 12.2* m (without turbulator)
Height : 7.2* m (with turbulator) 9.3* m (without turbulator)

* For reference only

Turbulator has significantly reduce the space consume and weight and it ensure the project to proceed to installation phase. Idea of using turbulator is one of the success story in debottlenecking project especially those have space and weight constraints.

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Control Valve at Inlet or Outlet of HEX ?

2009-02-16T15:07:00.000-08:00

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Product fluid in reactor involve exothermic process is commonly hot. It is then sent to distillation and separation system for catalyst and raw material recovery. Separated product is then cooled by plant wide Cooling Water (CW) before it is sent to storage tank. The product temperature will have to be maintained.

How this temperature is controlled ?

Temperature Control Methods
There are several ways to maintain the product temperature :

Provide a product bypass across the Cooler, control valves on Product bypass line and Outlet line (Split range control) with fixed CW flowrate
Provide a CW bypass across the Cooler, control valves on CW bypass line and CW inlet to Cooler with full product flow across cooler
Provide a CW bypass across the Cooler, control valves on CW bypass line and CW outlet to Cooler with full product flow across cooler
Provide a Control valve at the Cooler inlet with full product flow across cooler
Provide a Control valve at the Cooler outlet with full product flow across cooler

Generally the product flow is fixed by operator based on production plan and the product flow shall not be controlled. Thus, it is always not recommended to provide a control valve at the inlet and outlet of product line for product temperature control.

Disturbance of CW Network Balance
Cooling water is in a network supplying to many heat exchanger through out the plant for cooling purpose. It is normally supplied by a set of centrifugal pump. As centrifugal pump head will be affected flow across, any changes in the CW demand will affect the CW balance in network. This will further affect the pressure in the network and hence the CW flow into other heat exchangers. Thus, it is always recommended not to throttle the CW flow as much as possible to avoid CW balance.

Scaling
Throttling CW flow into heat exchanger would potential lead to low CW flow into heat exchanger, high film temperature at on CW side and promote scaling. The option (ii) and (iii) are always recommended IF throttling on CW side is chosen.

Potential affecting Production
Controlling product fluid temperature with product bypass across the Cooler, control valves on Product bypass line and Outlet line (Split range control) and fixed CW flowrate (option i) is one of the common way in temperature control for product cooling. As it minimize the impact to CW network. Nevertheless, there is still concern about manipulating product fluid or mal-operation (controller failure) of control valves would potentially lead to production lost, the option (ii) and (iii) are always the recommended option.

CW Pressurise or Non-Pressurise
Option (ii) and (iv) compare to option (iii) and (v), the difference is the location of main CW line control valve (either at the inlet or the outlet). Providing a control valve at the outlet will have the following advantages :

a) Maintain high pressure in the heat exchanger and higher pressure will results higher heat transfer

b) CW at high pressure will minimise potential of boiling

c) CW at high pressure will minimise potential release of dissolved gases in CW , trap in heat exchanger and reduce heat transfer

d) In event of Control valve failure (failed to full close position), not further Cooling. CW in the heat exchanger will be heated and potentially lead to heat exchanger overpresure due to thermal expansion and/or boiling. The CW will be relieved via Pressure Relief Device provided on the heat exchanger. Providing control valve at the outlet would allow continue CW feeding into the heat exchanger, this minimise the potential of sudden temperature increase and cause heat exchanger due to thermal shock. The downside is release CW into disposal network.

Considering above advantages, it is always recommended to provide control valve on CW line at the outlet IF throttling CW side is chooses.

CONTROLLING SHELL AND TUBE EXCHANGERS
"Controlling Shell & Tube Heat Exchanger", an excellent article by Walter Driedger discussed about all type of control schemes around heat exchanger. Check out.

Tantalum S&T HEX vs Carbon Block HEX...

2009-02-11T15:21:00.000-08:00

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Steel picklers have traditionally used carbon block heat exchanger to heat their shallow tank high turbulence pickle baths. The multi-gasketed designs and fragile nature of graphite heat exchangers still require continuous maintenance and repair which results in expensive downtime and spare parts. This has forced the industry to look for alternatives. The use of metal shell and tube heat exchangers virtually eliminates all of the problems associated with carbon block heat exchangers.

As claimed, some of the benefits of metal shell and tube heat exchangers are :

Cost competitive with Carbon Block Heat Exchangers
Easily retrofittable into existing equipment footprint
Elimination of downtime due to equipment failure
No spare parts to keep in inventory
Superior corrosion resistance
High heat transfer
High steam pressures to reduce required surface area
Fully welded metal design eliminates breakage during handling, installation and operation
Elimination of acid leaks into steam condensate

Typical comparison of a Carbon block HEX to a tantalum S&T HEX

Description	Carbon block HEX	Tantalum S&T HEX
Heat Input(BTU)	1,000,000	1,000,000
Steam Pressure (PSI)	75	75
Typical Overall U (BTU/hrft2.F)	250	650
Surface Area Required (Sq. Ft.)	29*	11.2*
Inventory of Spare Parts Required	YES	NO
Fully Welded Metal Design	NO	YES

Basic heat transfer equation used to calculate required surface area.
*Tantalum heat exchanger surface area required does not take into consideration using a higher pressure steam.

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Source : www.titanmf.com

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Control Around Heat Exchanger

2009-02-05T15:41:00.000-08:00

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CONTROLLING SHELL AND TUBE EXCHANGERS
Shell and tube heat exchangers are among the more confusing pieces of equipment for the process control engineer. The principle of operation is simple enough: Two fluids of different temperatures are brought into close contact but are prevented from mixing by a physical barrier. The temperature of the two fluids will tend to equalize. By arranging counter-current flow it is possible for the temperature at the outlet of each fluid to approach the temperature at the inlet of the other. The heat contents are simply exchanged from one fluid to the other and vice versa. No energy is added or removed.

Since the heat demands of the process are not constant, and the heat content of the two fluids is not constant either, the heat exchanger must be designed for the worst case and must be controlled to make it operate at the particular rate required by the process at every moment in time. The heat exchanger itself is not constant. Its characteristic changes with time. The most common change is a reduction in the heat transfer rate due to fouling of the surfaces. Exchangers are initially oversized to allow for the fouling which gradually builds up during use until the exchanger is no longer capable of performing its duty. Once it has been cleaned it is again oversized...

"Controlling Shell & Tube Heat Exchanger", an excellent article by Walter Driedger discussed about all type of control schemes around heat exchanger. You may download here.

Download

Source : www.driedger.ca

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Webinar for Optimum Heat Transfer by Thermal Fluid

2008-08-24T03:23:00.000-07:00

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Heating system is one of the common utilities in a gas processing, LNG production, refining plant, etc. Heating medium commonly used are Heating oil, thermal fluid, water, etc. In circulating thermal-fluid heating systems, the heat transfer rate is typically controlled to maintain a desired outlet-temperature setpoint of the fluid. However, it is the temperature of the fluid film in contact with the heater walls instead of bulk fluid temperature that often is the key factor affecting fluid life, system fouling, and overall equipment performance.

CE and Solutia are organizing a webinar on Heat Flux & Film Temperature. The webinar presenter is Robert Pelini, P.E., President of RGP Engineering, LLC. who has more than 24 years experience in the design of fired heaters and heat recovery systems and has authored numerous technical articles and
publications on process equipment and energy systems design.

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The webinar will discuss :

The importance of fluid film temperature
Variables that affect film temperature, with specific emphasis on heat flux at the metal surfaces
Various types of fired and electric thermal fluid heater designs and estimation of their heat flux rates
Heat flux rates in convective thermal fluid heaters
How to estimate or check peak fluid film temperature
Common problems and how to avoid them

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Rule-of-thumb to gage suitability of Plate-Heat-Exchanger in Fluid-Contains-solid or Slurry

2008-08-21T23:44:00.000-07:00

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Plate Heat Exchanger having narrow channel most probably "not recommended" for fluid contains solid and/or slurry services. However, there are still many success story of using PHE in abovementioned services.

There are some rule-of-thumbs to gage if a plate heat exchanger suitable for fluid contains solid or slurry :

i) 80% of the particles are less than 70% of the interplate gap on the heat exchanger.

ii) 100% of the particles are less than 90% of the interplate gap

iii) Flowing velocity is below erosional velocity (causes premature plate failure)

iv) The minimum wall temperature is above a point where crystal growth is expected.

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Few Tips on Energy Efficient & Recovery

2008-08-20T21:55:00.000-07:00

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As the price of electricity, natural gas and other fossil fuels continues to climb, chemical processors are more closely examining high-temperature operations and heat-transfer systems to see if more efficiency can be had. In many cases
it can, and, as a result, heat-transfer projects are not only justifiable, but downright attractive.

There was a dialog among a few heat exchanger specialist from Alfa Laval, Paul Muller, Exergy LLC, etc. The dialog mainly discussed on strategy to improve heat transfer efficiency, heat recovery and efficient process control during this high energy price arena.

A few tips have been present :

The energy crisis results high prices all of the time shorten paybacks. Energy efficient is one of the way to minimize cost
Energy efficient heat transfer equipment such as Plate Heat exchanger, Gasketed Heat exchanger, Bonded Heat exchanger, etc is one of the option.
For a service using Shell & Tube (S&T), the overall heat transfer coefficient (HTC) is around 300 Btu/h ft2°F. However, the overall heat transfer coefficient (HTC) for a compact heat exchanger can be improved 3-4 times (~1000 to 12000 Btu/h ft2°F).
With lower overall heat transfer coefficient, this may translate into less space, smaller installation and handling cost. Capital cost may not be low as the fabrication cost for compact heat exchanger is high.
Gasketed Heat exchanger good for maintenance. However shall take additional attention on the compatibility between gasket and fluid.
All welded or Bonded heat exchanger may be considered if there is gasket & fluid compatible problem
For laminar flow, heat transfer rate is only the function of fluid thermal conductivity. Operate heat transfer equipment at lamina flow during turndown could significantly reduce it heat transfer rate
Compact heat exchanger promote turbulence. High turbulence increase heat transfer rate and reduce fouling (read more)
Thus plant releasing hot exhaust gas from burner, boiler, gas turbine, etc to atmosphere may take the opportunity to recover heat
Improve temperature control in process system would reduce energy usage

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Not a CE subscriber... click here to subscribe FREE Chemical Engineering (CE)

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Self Cleaning Heat Exchanger - Online Cleaning ?

2008-07-29T23:04:00.000-07:00

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Have you ever seen or heard about SELF CLEANING HEAT EXCHANGER ?

Self Cleaning heat exchanger operating concept is mainly base on fluidization concept. It commonly used for severe fouling service. It has been proposed in 1970s and used for seawater application. Now Self-Cleaning Heat Exchange principle has been extended to evaporation in the tubes.

Operating Principle

The fouling liquid is fed upward through a vertical shell and tube exchanger that has specially designed inlet and outlet channels. Solid particles are also fed at the inlet where an internal flow distribution system provides a uniform distribution of the liquid and suspended particles throughout the internal surface of the bundle. The particles are carried by the upward flow of liquid through the tubes where they impart a mild scraping effect on the wall of the heat exchange tubes, thereby removing any deposit at an early stage of formation. These particles can be cut metal wire, glass or ceramic balls with diameters varying from 1 to 4 mm. At the top of the exchanger the particles disengage from the liquid in a widened outlet channel and are returned to the inlet channel through an external downcomer and are recirculated continuously.

More excellent article and application of Self Cleaning heat exchanger :

Unexpected High Cost of Heat Exchanger Fouling...

2008-07-28T23:14:00.000-07:00

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Heat Exchangers are a significant part of many industrial processes that involve energy exchange. Most of these heat exchangers become fouled with use. The United Engineering Foundation, which hosts a conference every three years on the fouling problem, estimates that the cost of heat exchanger fouling is 0.4 % of global Gross Domestic Product (UEF, 2001). This high cost has lead to frequent study of the fouling problem, including numerous books and conferences on the subject (Somerscales and Knudsen, 1981; Melo et al., 1988; Bott, 1995). Much of this work has focused on particular industries. Crude oil processing, dairy and food processing, and nuclear reactor cooling are all industries that have conducted a large amount of research aimed at understanding and mitigating fouling.

Particulate Fouling of HVAC Heat Exchanger

Particulate fouling of HVAC heat exchangers can lead to negative energy and indoor air quality impacts. This work investigated the mechanisms and consequences of particle deposition on fin-and-tube heat exchangers.

Jeffrey Siegel

Read more...

Please constantly do heat exchanger maintenance to minimize OPEX.

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What type of heat exchanger can be used to handle fluid with solid ?

2008-07-28T15:34:00.000-07:00

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"Plate Type Heat Exchangers V/s STHE - We are planning to replace an existing Shell & Tube HE with a Plate Type HE as the existing one is not offering the desired effect. The duty of the HE is attached. Since one of the fluid handled contains solids, can a PTHE handle it? I would like to know if similar retrofits have been carried out and what are the precautions to be taken while opting for such a change ? "

First of all is to interpret "fluid handled contains solids" :

The process fluid contains solid can be
(a) high concentration, small particle size or;
(b) high concentration, large particle size or;
(c) low concentration, small particle size or;
(d) low concentration, large particle size

Above combination may end-up with different heat exchanger which best suit their own need. Thus, whenever specify solid in fluid, concentration (wt% or ppmw) and particle size (micron or mm) are required to be spelt out so that other (vendor , consultant) can provide the most cost effective solution whilst meeting process demands.

Can PHE take fluid with solid in it ?

PHE is having a very unique feature where narrow channel and proper engineered cross-sectional areas promote turbulence and high heat transfer (convective) capabilities. High turbulence has the potential of removing scale stick on the plate. However, present of solids in fluid promote pluggage in the narrow channel and ultimately results NO flow.

(Click image for better view)

What are the option can be suggested here ?

Probably first and ordinary option is relook into the root-cause of under-performed STHE by analyses the STHE construction, review maintenance frequency and methodology, etc and check if there is oppurtunity to modify existing STHE to increase heat exchange performance.

Somehow if it has to be replaced, there are some type of heat exchanger which properly suitable for "fluid contain solids". There are :

Spiral HE (Alfa Laval , Sentry)
Self-Cleaning HE (KLAREN)

Heat Exchanger Fouling Mechanism, Prevention and Treatment...

2008-07-27T23:47:00.000-07:00

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(Geographic Eligibility: USA)

Heat exchanger fouling has been a headache problem which can not be avoided...however many of us may not aware of it mechanism, prevention and treatment....

Heat Exchanger Fouling Causes Problems In Gas and Liquid System
The article presented six (6) distinctive different mechanism causing Heat Exchangers Fouling e.g. Crystallization, Sedimentation, Chemical reaction & Polymerization, coking, Biological growth and corrosion. This article will only focus on particulate fouling. It discusses particulate fouling mechanisms, prevention and treatment. This article also presented Prediction Model for Particulate Fouling by Kern & Seaton.
by Reza Hashemi and Robert L. Brown, Jr.

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Why Lower Fouling factor in Plate Heat Exchanger ?

2008-06-12T14:36:00.000-07:00

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Fouling in heat exchanger is one of most challenging operation problem. It is the buildup of sediments and debris on the surface area of a heat exchanger and reduce heat transfer.

Fouling will reduce heat transfer, impede fluid flow and increase the pressure drop across the heat exchanger.

Plate heat exchanger as compare to Shell & Tube Heat Exchanger showed lower fouling factor. Have you ever thought of the reasoning behind ?

Fouling in Heat Exchangers (PHE)

(click to download)

This article has briefly discussed types of fouling, fouling factor used in Shell and Tube Heat Exchangers for common fluids, why lower fouling factor in plate heat exchanger (PHE) and, design consideration to reduce effects of fouling....

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Get The Most our of Waste Heat (using Exergy approach)

2007-10-01T08:23:00.001-07:00

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Chemical & Process plant is energy intensive industry. However, so far waste energy in the form of heat, noise, vibration, etc is dissipated to environment without or with some level of recovery. Example of heat recovery is the waste heat recovery unit (WHRU) located at the Gas turbine flue gas outlet, economizer at the boiler flue gas outlet, etc. Generally the flue gas exit temperature still rather high i.e. 250 degC, as compare to ambient temperature of 30 degC, believe there is still heat can be recovered from temperature perspective. But how much energy can be recovered and it this worth for recovery ? How to measure quantity of heat recovered to generate work ?

Exergy is the term to measure the capability of a hot fluid to produce work.

Get the Most out of Waste Heat

Raynald Labrecque & Kiari Goni Boulama

Above article has described a simplified approach to evaluate the exergy content of a hot waste and estimate amount of useful energy can be recovered from waste gases.

Sleeving Extends Heat Exchanger Life

2007-09-25T22:31:00.000-07:00

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Heat exchanger sleeving, a money-saving technology generally associated with the electric power industry, is drawing increasing interest from engineers in the chemical process industries (CPI), as well.

Get More Life Out Of Heat Exchangers
by Stanley Yokell

Sleeving consists of expanding thin tubes (sleeves) into the tubes of a heat exchanger. The expanding process produces a residual, interfacial fit pressure between the outside surface of the sleeve and the inside surface of the tube. The sleeves may be short, for instance about 6 to 16 in., or may extend for the full straight length of the tubes. Typical sleeve thicknesses are 0.01 to 0.03 in., depending upon material of construction and thickness of the original tubes. In addition to the expansion step, sometimes the inner end of the sleeves is welded to the inside wall of the tube.

In tubular heat transfer equipment in power plants, sleeving has long been used for one or more of these purposes:

To reduce the prospect of inlet-end tube erosion (short sleeves for this purpose are also called ferrules, and their use is called ferruling)
To restore tubes to service that had been plugged by plant personnel because of known perforations in discrete, identifiable locations
To restore tubes to service that had been plugged because their walls had become excessively thin
To bridge failures in discrete locations of tubes that are otherwise intact; for example, if a tube has a circular crack just beyond the inner face of the tubesheet

Before applying sleeving to similar problems at CPI plants, it is useful to be aware of the sleeving methods and equipment available, be able to determine how sleeves affect the heat transfer performance of heat exchangers, and be able to calculate the changes in pressure drop through the tubes.

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Practical Design Tips for Heat Exchanger Design

2007-09-24T21:55:00.000-07:00

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Heat Exchanger design is one of the common activities in plant design. However, although heat exchanger is designed in proper manner and follow most of the good engineering & design procedure, yet you might fails to achieve the desired performance by a wide margin. With an understanding of some common reasons why this might happen, designers can avoid these problems in the first place, and troubleshooters can recognize the root causes quickly.

Heat Exchanger Duty : Going for Gold
by David Butterworth

Exchangers for single-phase operation, condensing and boiling are considered in that order here; but as we shall see, exchangers often handle a combination of these, and it is not always obvious which process is causing the problem. In fact, some of these problems are quite unexpected and can even take experienced designers by surprise. It must be recognized that the most important cause of problems in exchangers is excessive fouling. Other articles, books, and conferences have been dedicated to this problem, so fouling will not be addressed here. Instead we consider those exchangers that have failed for some reason other than fouling.

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Typical Heat Tranfer Coefficient For Air-Cooled Heat Exchangers

2007-08-20T05:27:00.000-07:00

Basic heat transfer relationships is apply to Air-Cooled Heat Exchanger (ACHE). The fundamental heat ransfer equation :

Q = U. A. LMTD.F

where

U = overall heat transfer coefficient

A = Heat transfer area

LMTD = Log mean temperature difference

F = Correction factor

Typical heat transfer coefficient for Air-Cooled Heat Exchangers

Source : Hudson Product Corporation (HPC)

Source : DELTA T

COLLECTION of Typical Overall Heat Transfer Coefficient (U-factor)

2007-08-17T00:10:00.000-07:00

Generic Heat Transfer equation in heat exhanger,

Q = U.A.LMTD.F

where

Q = Rate of heat transfer

U = Mean overall heat transfer coefficient

A = Heat transfer surface area

LMTD = Log mean temperature difference

F = Correction factor

LMTD = (DT1-DT2) / Ln (DT1-DT2)

Where

DT1 = Th,i - Tc,o

DT2 = Th,o-Tc,i

For a given heat transfer service with known mass flow rates and inlet and outlet temperatures the determination of Q is straightforward and ΔT can be easily calculated if a flow arrangement is selected (e.g. logarithmic mean temperature difference for pure countercurrent or cocurrent flow). This is different for the overall heat transfer coefficient U. The determination of U is often tedious and needs data not yet available in preliminary stages of the design. Therefore, typical values of U are useful for quickly estimating the required surface area. The literature has many tabulations of such typical coefficients for commercial heat transfer services. Below are tabulation of U value for different applications and heat exchanger types.

Source : DELTA T (CheResources, Built-It-Solar)

Source : Engineering Page

Source : The Engineering Tool Box

Related reading

COLLECTION of Fouling Factor (FF) use in Heat Exchanger Design

COLLECTION of Fouling Factor (FF) use in Heat Exchanger Design

2007-08-16T08:54:00.000-07:00

Fouling factor is generally used in the design to cater for heat exchanger deficiency resulted by fouling. TEMA has based on many years of experiences and experiments list out fouling factor for Shell & Tube Heat Exchanger for many services. Only TEMA subscribers are eligible to use this information. However, there are several reputable researchers & manufacturers have shared this information to the public. Following are the collection of fouling factors for different service.