Refrigeration And Liquefaction

A process for producing refrigeration or liquefaction at cryogenic temperatures usually involves ambient compression of a process fluid with heat rejection to a coolant. During the compression process, the enthalpy and entropy of the fluid are decreased. At the cryogenic temperature where heat is absorbed, the enthalpy and entropy are increased. The reduction in temperature of the process fluid is usually accomplished by heat exchange with a colder fluid and then followed by an expansion. This...

Cryocool Brewing

FIG. 11-116 Propane precooled mixed-refrigerant cycle cooling curve for natural gas. FIG. 11-116 Propane precooled mixed-refrigerant cycle cooling curve for natural gas. coolers are generally classified as regenerative or recuperative. Regenerative coolers use reciprocating components that move the working fluid back and forth through a regenerator. The recuperative coolers, on the other hand, use countercurrent heat exchangers to accomplish the heat transfer operation. The Stirling and...

Tube Velocity In Rising Film Exchangers

FIG. 11-122 Evaporator types. (a) Forced circulation. (b) Submerged-tube forced circulation. (c) Oslo-type crystallizer. (d) Short-tube vertical. (e) Propeller calandria. (f) Long-tube vertical. (g) Recirculating long-tube vertical. (h) Falling film. (i,j) Horizontal-tube evaporators. C condensate F feed G vent P product S steam V vapor ENT'T separated entrainment outlet. zontal heating elements (usually two-pass), but the vertical single-pass heating element is used whenever sufficient...

W W Ww

Enclosure (with venting air heaters )N Divided solids feed (far end ) . In-process rolls or granulator Granular solids discharge (near end) Granular solids discharge (near end) In-process rolls or granulator Conveying and heat-transfer surfaces Operating floor Air distribution and recirculating ducts Vibration isolators Air-supply distribution duct (stationary) Section X-X Divided-solids discharge Section X-X Divided-solids discharge Connections for air or steam ( both ends ) FIG. 11-62...

Kern Unsteady State External Exchanger Isothermal Heating

K7(R + 1 + R2 + 1) - (R + 1 - R2 + 1) ln (Ti - t1) (T1 -12) (Sw M)0 (11-35n) ln (Ti - ti) (T2 - t1) S(wc MC)9 (11-35o) The cases of multipass exchangers with liquid continuously added to the tank are covered by Kern, as cited earlier. An alternative method for all multipass-exchanger gases, including those presented as well as cases with two or more shells in series, is as follows 1. Determine UA for using the applicable equations for counter-flow heat exchangers. 2. Use the initial batch...

Bayonettube Exchangers

This type of exchanger gets its name from its design which is similar to a bayonet sword and its associated scabbard or sheath. The bayonet tube is a smaller-diameter tube inserted into a larger-diameter tube that has been capped at one end. The fluid flow is typically entering the inner tube, exiting, hitting the cap of the larger tube, and returning the opposite direction in the annular area. The design eliminates any thermal expansion problems. It also creates a unique nonfreeze-type...

Equipment For Fusion Of Solids

The thermal duty here is the opposite of solidification operations. The indirect heat-transfer equipment suitable for one operation is not suitable for the other because of the material-handling rather than the thermal aspects. Whether the temperature of transformation is a definite or a ranging one is of little importance in the selection of equipment for fusion. The burden is much agitated, but the beds are deep. Only fair overall coefficient values may be expected, although heat-flux values...

Vaporliquid Separation

Rising Film Evaporator

Product losses in evaporator vapor may result from foaming, splashing, or entrainment. Primary separation of liquid from vapor is accomplished in the vapor head by making the horizontal plan area large enough so that most of the entrained droplets can settle out against the rising flow of vapor. Allowable velocities are governed by the Souders-Brown equation V kV - - p , in which k depends on the size distribution of droplets and the decontamination factor F desired. For most evaporators and...

Process Equipment

The equipment normally associated with cryogenic systems includes heat exchangers, compressors, expanders, throttling valves, and stor age containers. Since the reciprocal or centrifugal compressors used generally operate at ambient temperatures, their operating principles are not covered here but in Sec. 10. Storage containers, are discussed later in Sec. 11. Heat Exchangers Since most cryogens, with the exception of helium II behave as classical fluids, well-established principles of...

Brazedplatefin Heat Exchanger

Brazed-aluminum-plate-fin heat exchangers or core exchangers or cold boxes as they are sometimes called, were first manufactured for the aircraft industry during World War II. In 1950, the first tonnage air-separation plant with these compact, lightweight, reversing heat exchangers began producing oxygen for a steel mill. Aluminum-plate-fin exchangers are used in the process and gas-separation industries, particularly for services below -45 C. Core exchangers are made up of a stack of...

Other Refrigeration Systems Applied In The Industry

Water Water Heat Exchanger Schematics

Absorption Refrigeration Systems Two main absorption systems are used in industrial application lithium bromide-water and ammonia-water. Lithium bromide-water systems are limited to evaporation temperatures above freezing because water is used as the refrigerant, while the refrigerant in an ammonia-water system is ammonia and consequently it can be applied for the lower-temperature requirements. Single-effect indirect-fired lithium bromide cycle is shown in Fig. 11-99. The machine consists of...

Economic Thickness Of Insulation

Optimal economic insulation thickness may be determined by various methods. Two of these are the minimum-total-cost method and the incremental-cost method or marginal-cost method . The minimum-total-cost method involves the actual calculations of lost energy and insulation costs for each insulation thickness. The thickness producing the lowest total cost is the optimal economic solution. The optimum thickness is determined to be the point where the last dollar invested in insulation results in...

Introduction To Thermal Design

Design methods for several important classes of process heat-transfer equipment are presented in the following portions of Sec. 11. Mechanical descriptions and specifications of equipment are given in this section and should be read in conjunction with the use of this material. It is impossible to present here a comprehensive treatment of heat-exchanger selection, design, and application. The best general references in this field are Hewitt, Shires, and Bott, Process Heat Transfer, CRC Press,...

Primary Design Problems

Heat Transfer This is the most important single factor in evaporator design, since the heating surface represents the largest part of evaporator cost. Other things being equal, the type of evaporator selected is the one having the highest heat-transfer cost coefficient under desired operating conditions in terms of J sK British thermal units per hour per degree Fahrenheit per dollar of installed cost. When power is required to induce circulation past the heating surface, the coefficient must be...

Equipment

Cascade Refrigeration System Diagrams

Compressors These could be classified by one criteria the way the increase in pressure is obtained as positive-displacement and FIG. 11-79 Pressure enthalpy diagram for typical two-stage system with two evaporating temperatures, flash-gas removal, and intercooling. FIG. 11-79 Pressure enthalpy diagram for typical two-stage system with two evaporating temperatures, flash-gas removal, and intercooling. dynamic types as shown in Fig. 11-81 see Sec. 10 for drawings and mechanical description of the...

Heating And Cooling Of Tanks

Tank Coils Pipe tank coils are made in a wide variety of configurations, depending upon the application and shape of the vessel. Helical and spiral coils are most commonly shop-fabricated, while the hairpin pattern is generally field-fabricated. The helical coils are used principally in process tanks and pressure vessels when large areas for rapid heating or cooling are required. In general, heating coils are placed low in the tank, and cooling coils are placed high or distributed uniformly...

Cryogenic Instrumentation

Even though the combined production of cryogenic nitrogen and oxygen exceeds the production of any other chemical in the United States, the cryogenic industry does not appear to warrant a separate product line of instruments for diagnostic and control purposes. Low-temperature thermometry is the one exception. The general approach generally is that instruments developed for the usual CPI needs must be modified or accepted as is for cryogenic use. Quite often problems arise when instruments for...

Refrigerant Ph Diagram

Diagram Refrigeration

For a Carnot cycle where A Q TA s , the COP for the refrigeration application becomes note than T is absolute temperature K The COP in real refrigeration cycles is always less than for the ideal Carnot cycle and there is constant effort to achieve this ideal value. Basic Refrigeration Methods Three basic methods of refrigeration mentioned above use similar processes for obtaining refrigeration effect evaporation in the evaporator, condensation in the condenser where heat is rejected to the...

Heattransfer Equipment Load Calculation

First step in the solution of an air-conditioning problem is to determine the proper design temperature conditions. Since both outdoor and indoor temperatures greatly influence the size of the equipment, the designer must exercise good judgment in selecting the proper conditions for his her particular case. Table 11-23 lists winter and summer outdoor temperature conditions in common use for comfort applications for various United States cities. For critical-process air conditioning, it may be...

Lmtd Correction Factor

Mtd Crossflow

FIG. 11-4 LMTD correction factors for heat exchangers. In all charts, R Ti - T2 t2 ti and S t2 _ ti Ti - ti . a One shell pass, two or more tube passes. b Two shell passes, four or more tube passes. c Three shell passes, six or more tube passes. d Four shell passes, eight or more tube passes. e Six shell passes, twelve or more tube passes. f Cross-flow, one shell pass, one or more parallel rows of tubes. g Cross-flow, two passes, two rows of tubes for more than two passes, use Ft i.0. h...

System Selection

Dewar Flask

A combination of insulation and finish produces the thermal-insulation system. Selection of these components depends on the purpose for which the system is to be used. No single system performs satisfactorily from the cryogenic through the elevated-temperature range. Systems operating below freezing have a low vapor pressure, and atmospheric moisture is pushed into the insulation system, while the reverse is true for hot systems. Some general guidelines for system selection follow. Cryogenic...

Thermal Design Of Condensers

Mean Temperature Difference In condensing a single component at its saturation temperature, the entire resistance to heat transfer on the condensing side is generally assumed to be in the layer of condensate. A mean condensing coefficient is calculated from the appropriate correlation and combined with the other resistances in Eq. 11-2 . The overall coefficient is then used with the LMTD no FT correction is necessary for isothermal condensation to give the required area, even though the...

Thermal Design Of Evaporators

Cooling Curve Water And Alcohol

Heat duties of evaporator heating surfaces are usually determined by conventional heat and material balance calculations. Heating surface areas are normally, but not always taken as those in contact with the material being evaporated. It is the heat transfer A T that presents the most difficulty in deriving or applying heat-transfer coefficients. The total A T between heat source and heat sink is never all available for heat transfer. Since energy usually is carried to and from an evaporator...

Compabloc Correction Factor

Oil resistant Fat resistant Food stuffs Mineral oil Water Fats and fatty acids Petroleum oils Chlorinated hydrocarbons Liquids with dissolved chlorine Mineral oil Oxygen rich demin. water Strong oxidants Oxidizing agents Dilute acids Amines Water Hot amp conc. acids Very strong oxidants Fats amp fatty acids Chlorinated hydrocarbons Petroleum oils Many inorganic acids Most all NBR fluids tract two times the bolt diameter and subtract another 50 mm. For depth of corrugation ask supplier, or take...

Teflon Heat Exchangers

Teflon tube shell-and-tube heat exchangers Ametek made with tubes of chemically inert Teflon fluorocarbon resin are available. The tubes are 0.25-in OD by 0.20-in ID, 0.175-in OD by 0.160-in ID, or 0.125-in OD by 0.100-in ID in X 25.4 equal mm . The larger tubes are primarily used when pressure-drop limitations or particles reduce the effectiveness of smaller tubes. These heat exchangers generally operate at higher pressure drops than conventional units and are best suited for relatively clean...

Heattransfer Equipment For Divided Solids

Whiskey Distillation Equipment

Most equipment for this service is some adaptation of a material-handling device whether or not the transport ability is desired. The old vertical tube and the vertical shell fluidizer are exceptions. Material-handling problems, plant transport needs, power, and maintenance are prime considerations in equipment selection and frequently overshadow heat-transfer and capital-cost considerations. Material handling is generally the most important aspect. Material-handling characteristics of the...

Extended Or Finned Surfaces

Efficiency Graph For Annular Fins

Finned-Surface Application Extended or finned surfaces are often used when one film coefficient is substantially lower than the other, the goal being to make hoAoe htAt. A few typical fin configurations are shown in Fig. 11-30a. Longitudinal fins are used in double-pipe exchangers. Transverse fins are used in cross-flow and shell-and-tube configurations. High transverse fins are used mainly with low-pressure gases low fins are used for boiling and condensation of nonaqueous streams as well as...

Aircooled Heat Exchangers

Forced Draft Air Cooled Heat Exchanger

Atmospheric air has been used for many years to cool and condense fluids in areas of water scarcity. During the 1960s the use of air-cooled heat exchangers grew rapidly in the United States and elsewhere. In Europe, where seasonal variations in ambient temperatures are relatively small, air-cooled exchangers are used for the greater part of process cooling. In some new plants all cooling is done with air. Increased use of air-cooled heat exchangers has resulted from lack of available water,...

Equipment For Solidification

Vibratory Transfer Conveyor

A frequent operation in the chemical field is the removal of heat from a material in a molten state to effect its conversion to the solid state. When the operation is carried on batchwise, it is termed casting, but when done continuously, it is termed flaking. Because of rapid heat transfer and temperature variations, jacketed types are limited to an initial melt temperature of 232 C 450 F . Higher temperatures to 316 C 600 F require extreme care in jacket design and cooling-liquid flow...

Tubeside Construction

Tube-Side Header The tube-side header or stationary head contains one or more flow nozzles. The bonnet Fig. 11-35B bolts to the shell. It is necessary to remove the bonnet in order to examine the tube ends. The fixed-tube-sheet exchanger of Fig. 11-36 gt has bonnets at both ends of the shell. The channel Fig. 11-35A has a removable channel cover. The tube ends can be examined by removing this cover without disturbing the piping connections to the channel nozzles. The channel can bolt to the...

Heating And Cooling Of Vessels

A heat-transfer surface C, c specific heats of hot and cold fluids respectively L0 flow rate of liquid added to tank M mass of fluid in tank T, t temperature of hot and cold fluids respectively Ti, ti temperatures at beginning of heating or cooling period or at inlet T2, t2 temperature at end of period or at outlet T0, t0 temperature of liquid added to tank U coefficient of heat transfer and W, w flow rate through external exchanger of hot and cold fluids...

Info

British Thermal Units Conversion

FIG. 11-18 Acceleration losses in boiling flow. C F - 32 1.8. 100 150 200 250 300 Vapor temperature, F. FIG. 11-19 Friction pressure drop in boiling flow. C F - 32 1.8. 100 150 200 250 300 Vapor temperature, F. FIG. 11-19 Friction pressure drop in boiling flow. C F - 32 1.8. where b 2.6 107 SI and 1.0 U.S. customary and using r2 from Fig. 11-18. The frictional pressure drop is derived from Fig. 11-19, which shows the ratio of two-phase pressure drop to that of the entering liquid flowing alone....

Thermal Design Of Tank Coils

The thermal design of tank coils involves the determination of the area of heat-transfer surface required to maintain the contents of the tank at a constant temperature or to raise or lower the temperature of the contents by a specified magnitude over a fixed time. Nomenclature A area Ab area of tank bottom Ac area of coil Ae equivalent area As area of sides At area of top Ai equivalent area receiving heat from external coils A2 equivalent area not covered with external coils Dt diameter of...

Stuhlbarg Pet. Refiner 38 143 April 1959

Coil Support For The Vertical Hairpin

Eng. Chem., 36, 510 1944 give film coefficients for heating and cooling agitated fluids using a coil in a jacketed vessel. Because of the many factors affecting heat transfer, such as viscosity, temperature difference, and coil size, the values in this table should be used primarily for preliminary design estimates and checking calculated coefficients. C F - 32 1.8 to convert British thermal units per hour-square foot-degrees Fahrenheit to joules per square...

Thermal Design Of Reboilers

For a single-component reboiler design, attention is focused upon the mechanism ofheat and momentum transfer at the hot surface. In multicomponent systems, the light components are preferentially vaporized at the surface, and the process becomes limited by their rate of diffusion. The net effect is to decrease the effective temperature difference between the hot surface and the bulk of the boiling liquid. If one attempts to vaporize too high a fraction of the feed liquid to the reboiler, the...

Types And Definitions

TEMA-style shell-and-tube-type exchangers constitute the bulk of the unfired heat-transfer equipment in chemical-process plants, although increasing emphasis has been developing in other designs. These exchangers are illustrated in Fig. 11-35, and their features are summarized in Table 11-11. TEMA Numbering and Type Designation Recommended practice for the designation of TEMA-style shell-and-tube heat exchangers by numbers and letters has been established by the Tubular Exchanger Manufacturers...

Graphite Heat Exchangers

Impervious graphite exchangers now come in a variety of geometries to suit the particular requirements of the service. They include cubic block form, drilled cylinder block, shell and tube, and plate and frame. Description Graphite is one of three crystalline forms of carbon. The other two are diamond and charcoal. Graphite has a hexagonal crystal structure, diamond is cubic, and charcoal is amorphous. Graphite is inert to most chemicals and resists corrosion attack. It is however porous and to...

Plateandframe Exchangers

Plate Frame Heat Exchanger

There are two major types gasketed and welded-plate heat exchangers. Each shall be discussed individually. Description This type is the fastest growing of the compact exchangers and the most recognized see Fig. 11-49 . A series of corrugated alloy material channel plates, bounded by elastomeric gaskets are hung off and guided by longitudinal carrying bars, then compressed by large-diameter tightening bolts between two pressure retaining frame plates cover plates . The frame and channel plates...

Thermal Design For Singlephase Heat Transfer

Shell And Tube Heat Exchanger

Double-Pipe Heat Exchangers The design of double-pipe heat exchangers is straightforward. It is generally conservative to neglect natural-convection and entrance effects in turbulent flow. In laminar flow, natural convection effects can increase the theoretical Graetz prediction by a factor of 3 or 4 for fully developed flows. Pressure drop is calculated by using the correlations given in Sec. 6. If the inner tube is longitudinally finned on the outside surface, the equivalent diameter is used...

Baffles And Tube Bundles

Segment Baffle Heat Exchanger

The tube bundle is the most important part of a tubular heat exchanger. The tubes generally constitute the most expensive component of the exchanger and are the one most likely to corrode. Tube sheets, baffles, or support plates, tie rods, and usually spacers complete the bundle. Minimum baffle spacing is generally one-fifth of the shell diameter and not less than 50.8 mm 2 in . Maximum baffle spacing is limited by the requirement to provide adequate support for the tubes. The maximum...

Principal Types Of Construction

Tema Type Aes

Figure 11-36 shows details of the construction of the TEMA types of shell-and-tube heat exchangers. These and other types are discussed in the following paragraphs. Fixed-Tube-Sheet Heat Exchangers Fixed-tube-sheet exchangers Fig. 11-36b are used more often than any other type, and the frequency of use has been increasing in recent years. The tube sheets are welded to the shell. Usually these extend beyond the shell and serve as flanges to which the tube-side headers are bolted. This...

Thermal Design For Solids Processing

Solids in divided form, such as powders, pellets, and lumps, are heated and or cooled in chemical processing for a variety of objectives such as solidification or fusing Sec. ii , drying and water removal Sec. 20 , solvent recovery Secs. i3 and 20 , sublimation Sec. i7 , chemical reactions Sec. 20 , and oxidation. For process and mechanical-design considerations, see the referenced sections. Thermal design concerns itself with sizing the equipment to effect the heat transfer necessary to carry...

General Design Considerations

Selection of Flow Path In selecting the flow path for two fluids through an exchanger, several general approaches are used. The tubeside fluid is more corrosive or dirtier or at a higher pressure. The shell-side fluid is a liquid of high viscosity or a gas. When alloy construction for one of the two fluids is required, a carbon steel shell combined with alloy tube-side parts is less expensive than alloy in contact with the shell-side fluid combined with carbon steel headers. Cleaning of the...

Fouling And Scaling

Fouling refers to any change in the solid boundary separating two heat transfer fluids, whether by dirt accumulation or other means, which results in a decrease in the rate of heat transfer occurring across that boundary. Fouling may be classified by mechanism into six basic categories 1. Corrosion fouling. The heat transfer surface reacts chemically with elements of the fluid stream producing a less conductive, corrosion layer on all or part of the surface. 2. Biofouling. Organisms present in...

Thermal Design Of Heattransfer Equipment

Introduction to Thermal Approach to Heat-Exchanger Overall Heat-Transfer Mean Temperature Countercurrent or Cocurrent Reversed, Mixed, or Thermal Design for Single-Phase Heat Double-Pipe Heat Baffled Shell-and-Tube Thermal Design of Single-Component Multicomponent Thermal Design of Kettle Vertical Thermosiphon Forced-Recirculation Thermal Design of Forced-Circulation Long-Tube Vertical Short-Tube Vertical Miscellaneous Evaporator Heat Transfer from Various Metal Effect of Fluid Properties on...