BR112013023706A2 - sistemas e métodos para troca de calor - Google Patents

sistemas e métodos para troca de calor

Info

Publication number
BR112013023706A2
BR112013023706A2 BR112013023706A BR112013023706A BR112013023706A2 BR 112013023706 A2 BR112013023706 A2 BR 112013023706A2 BR 112013023706 A BR112013023706 A BR 112013023706A BR 112013023706 A BR112013023706 A BR 112013023706A BR 112013023706 A2 BR112013023706 A2 BR 112013023706A2
Authority
BR
Brazil
Prior art keywords
section
heat exchange
cooling
heating medium
methods
Prior art date
Application number
BR112013023706A
Other languages
English (en)
Inventor
Barbara Burzinski Hartliep
Ediz Batmaz
Ernst Beutler
Ricardo Reyes-Trevino
Original Assignee
Nestec Sa
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Nestec Sa filed Critical Nestec Sa
Publication of BR112013023706A2 publication Critical patent/BR112013023706A2/pt

Links

Classifications

    • AHUMAN NECESSITIES
    • A23FOODS OR FOODSTUFFS; TREATMENT THEREOF, NOT COVERED BY OTHER CLASSES
    • A23LFOODS, FOODSTUFFS, OR NON-ALCOHOLIC BEVERAGES, NOT COVERED BY SUBCLASSES A21D OR A23B-A23J; THEIR PREPARATION OR TREATMENT, e.g. COOKING, MODIFICATION OF NUTRITIVE QUALITIES, PHYSICAL TREATMENT; PRESERVATION OF FOODS OR FOODSTUFFS, IN GENERAL
    • A23L3/00Preservation of foods or foodstuffs, in general, e.g. pasteurising, sterilising, specially adapted for foods or foodstuffs
    • A23L3/16Preservation of foods or foodstuffs, in general, e.g. pasteurising, sterilising, specially adapted for foods or foodstuffs by heating loose unpacked materials
    • A23L3/18Preservation of foods or foodstuffs, in general, e.g. pasteurising, sterilising, specially adapted for foods or foodstuffs by heating loose unpacked materials while they are progressively transported through the apparatus
    • A23L3/22Preservation of foods or foodstuffs, in general, e.g. pasteurising, sterilising, specially adapted for foods or foodstuffs by heating loose unpacked materials while they are progressively transported through the apparatus with transport through tubes
    • AHUMAN NECESSITIES
    • A23FOODS OR FOODSTUFFS; TREATMENT THEREOF, NOT COVERED BY OTHER CLASSES
    • A23BPRESERVING, e.g. BY CANNING, MEAT, FISH, EGGS, FRUIT, VEGETABLES, EDIBLE SEEDS; CHEMICAL RIPENING OF FRUIT OR VEGETABLES; THE PRESERVED, RIPENED, OR CANNED PRODUCTS
    • A23B7/00Preservation or chemical ripening of fruit or vegetables
    • A23B7/005Preserving by heating
    • A23B7/0053Preserving by heating by direct or indirect contact with heating gases or liquids
    • AHUMAN NECESSITIES
    • A23FOODS OR FOODSTUFFS; TREATMENT THEREOF, NOT COVERED BY OTHER CLASSES
    • A23BPRESERVING, e.g. BY CANNING, MEAT, FISH, EGGS, FRUIT, VEGETABLES, EDIBLE SEEDS; CHEMICAL RIPENING OF FRUIT OR VEGETABLES; THE PRESERVED, RIPENED, OR CANNED PRODUCTS
    • A23B7/00Preservation or chemical ripening of fruit or vegetables
    • A23B7/04Freezing; Subsequent thawing; Cooling
    • A23B7/0408Freezing; Subsequent thawing; Cooling the material being transported through or in the apparatus with or without shaping, e.g. in the form of powder, granules or flakes
    • AHUMAN NECESSITIES
    • A23FOODS OR FOODSTUFFS; TREATMENT THEREOF, NOT COVERED BY OTHER CLASSES
    • A23CDAIRY PRODUCTS, e.g. MILK, BUTTER OR CHEESE; MILK OR CHEESE SUBSTITUTES; MAKING THEREOF
    • A23C3/00Preservation of milk or milk preparations
    • A23C3/02Preservation of milk or milk preparations by heating
    • A23C3/03Preservation of milk or milk preparations by heating the materials being loose unpacked
    • A23C3/033Preservation of milk or milk preparations by heating the materials being loose unpacked and progressively transported through the apparatus
    • AHUMAN NECESSITIES
    • A23FOODS OR FOODSTUFFS; TREATMENT THEREOF, NOT COVERED BY OTHER CLASSES
    • A23CDAIRY PRODUCTS, e.g. MILK, BUTTER OR CHEESE; MILK OR CHEESE SUBSTITUTES; MAKING THEREOF
    • A23C3/00Preservation of milk or milk preparations
    • A23C3/04Preservation of milk or milk preparations by freezing or cooling
    • A23C3/045Freezing in loose unpacked form
    • AHUMAN NECESSITIES
    • A23FOODS OR FOODSTUFFS; TREATMENT THEREOF, NOT COVERED BY OTHER CLASSES
    • A23LFOODS, FOODSTUFFS, OR NON-ALCOHOLIC BEVERAGES, NOT COVERED BY SUBCLASSES A21D OR A23B-A23J; THEIR PREPARATION OR TREATMENT, e.g. COOKING, MODIFICATION OF NUTRITIVE QUALITIES, PHYSICAL TREATMENT; PRESERVATION OF FOODS OR FOODSTUFFS, IN GENERAL
    • A23L3/00Preservation of foods or foodstuffs, in general, e.g. pasteurising, sterilising, specially adapted for foods or foodstuffs
    • A23L3/36Freezing; Subsequent thawing; Cooling
    • A23L3/361Freezing; Subsequent thawing; Cooling the materials being transported through or in the apparatus, with or without shaping, e.g. in form of powder, granules, or flakes
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28HEAT EXCHANGE IN GENERAL
    • F28DHEAT-EXCHANGE APPARATUS, NOT PROVIDED FOR IN ANOTHER SUBCLASS, IN WHICH THE HEAT-EXCHANGE MEDIA DO NOT COME INTO DIRECT CONTACT
    • F28D7/00Heat-exchange apparatus having stationary tubular conduit assemblies for both heat-exchange media, the media being in contact with different sides of a conduit wall
    • F28D7/02Heat-exchange apparatus having stationary tubular conduit assemblies for both heat-exchange media, the media being in contact with different sides of a conduit wall the conduits being helically coiled
    • F28D7/024Heat-exchange apparatus having stationary tubular conduit assemblies for both heat-exchange media, the media being in contact with different sides of a conduit wall the conduits being helically coiled the conduits of only one medium being helically coiled tubes, the coils having a cylindrical configuration
    • AHUMAN NECESSITIES
    • A23FOODS OR FOODSTUFFS; TREATMENT THEREOF, NOT COVERED BY OTHER CLASSES
    • A23VINDEXING SCHEME RELATING TO FOODS, FOODSTUFFS OR NON-ALCOHOLIC BEVERAGES AND LACTIC OR PROPIONIC ACID BACTERIA USED IN FOODSTUFFS OR FOOD PREPARATION
    • A23V2002/00Food compositions, function of food ingredients or processes for food or foodstuffs
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28HEAT EXCHANGE IN GENERAL
    • F28DHEAT-EXCHANGE APPARATUS, NOT PROVIDED FOR IN ANOTHER SUBCLASS, IN WHICH THE HEAT-EXCHANGE MEDIA DO NOT COME INTO DIRECT CONTACT
    • F28D21/00Heat-exchange apparatus not covered by any of the groups F28D1/00 - F28D20/00
    • F28D2021/0019Other heat exchangers for particular applications; Heat exchange systems not otherwise provided for
    • F28D2021/0042Other heat exchangers for particular applications; Heat exchange systems not otherwise provided for for foodstuffs
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28HEAT EXCHANGE IN GENERAL
    • F28FDETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
    • F28F2265/00Safety or protection arrangements; Arrangements for preventing malfunction
    • F28F2265/12Safety or protection arrangements; Arrangements for preventing malfunction for preventing overpressure
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28HEAT EXCHANGE IN GENERAL
    • F28FDETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
    • F28F2265/00Safety or protection arrangements; Arrangements for preventing malfunction
    • F28F2265/14Safety or protection arrangements; Arrangements for preventing malfunction for preventing damage by freezing, e.g. for accommodating volume expansion

Landscapes

  • Engineering & Computer Science (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Chemical & Material Sciences (AREA)
  • Food Science & Technology (AREA)
  • Polymers & Plastics (AREA)
  • Health & Medical Sciences (AREA)
  • Nutrition Science (AREA)
  • Zoology (AREA)
  • General Chemical & Material Sciences (AREA)
  • Wood Science & Technology (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Heat-Exchange Devices With Radiators And Conduit Assemblies (AREA)
  • Food Preservation Except Freezing, Refrigeration, And Drying (AREA)
  • Cold Air Circulating Systems And Constructional Details In Refrigerators (AREA)
  • Apparatus For Disinfection Or Sterilisation (AREA)
  • Confectionery (AREA)

Abstract

resumo patente de invenção: "sistemas e métodos para troca de calor". a resente invenção refere-se a dispositivos de troca de calor, incluindo dispositivos de resfriador assépticos, e sistemas que incluem os mesmos. métodos para utilizar o dispositivo de troca de calor são também providos. em uma modalidade geral, a presente descrição provê trocadores de calor que têm uma configuração de câmara aberta e incluem uma primeira seção que contém um meio de resfriamento ou aquecimento e uma segunda seção que contém um produto alimentício. a primeira seção inclui um dispositivo de detecção de nível que está configurado para manter um nível de meio de resfriamento ou aquecimento na primeira seção, enquanto impedindo que o meio de resfriamento ou aquecimento pressurize a primeira seção. a configuração de câmara aberta provê uma folga de ar em uma porção de topo da primeira seção que assegura que o meio de resfriamento ou aquecimento que entra na primeira seção esteja na, ou próximo da pressão atmosférica.
BR112013023706A 2011-03-17 2012-03-09 sistemas e métodos para troca de calor BR112013023706A2 (pt)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US201161453921P 2011-03-17 2011-03-17
PCT/US2012/028425 WO2012125440A1 (en) 2011-03-17 2012-03-09 Systems and methods for heat exchange

Publications (1)

Publication Number Publication Date
BR112013023706A2 true BR112013023706A2 (pt) 2016-12-13

Family

ID=45931004

Family Applications (1)

Application Number Title Priority Date Filing Date
BR112013023706A BR112013023706A2 (pt) 2011-03-17 2012-03-09 sistemas e métodos para troca de calor

Country Status (17)

Country Link
US (2) US9572366B2 (pt)
EP (1) EP2685836B1 (pt)
JP (2) JP2014514522A (pt)
CN (1) CN103533838B (pt)
AU (2) AU2012229281B9 (pt)
BR (1) BR112013023706A2 (pt)
CA (1) CA2830378C (pt)
CL (1) CL2013002684A1 (pt)
DK (1) DK2685836T3 (pt)
ES (1) ES2893850T3 (pt)
MX (1) MX352145B (pt)
PL (1) PL2685836T3 (pt)
PT (1) PT2685836T (pt)
RU (1) RU2549759C1 (pt)
SG (1) SG193460A1 (pt)
WO (1) WO2012125440A1 (pt)
ZA (1) ZA201307687B (pt)

Families Citing this family (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102013200473A1 (de) * 2013-01-15 2014-07-17 Krones Ag Verfahren und Vorrichtung zur Kühlung eines Gär- und/oder Lager-Tanks
DE102013200610A1 (de) * 2013-01-16 2014-07-17 Krones Ag Verfahren und Vorrichtung zur thermischen Behandlung eines Produkts
JP5719468B1 (ja) * 2014-06-20 2015-05-20 日本ガス開発株式会社 熱交換器
US9702351B2 (en) * 2014-11-12 2017-07-11 Leif Alexi Steinhour Convection pump and method of operation
US20180357886A1 (en) * 2015-12-01 2018-12-13 Isaac Tavori System, devices and methods for health care worker training, monitoring and providing real time corrective guidance for procedures and practice related to hospital infection control
WO2018204050A1 (en) * 2017-05-05 2018-11-08 Pressed Juicery, Inc. System and process for destroying c. botulinum spores in pressed beverage using thermal pascalization
US11118825B2 (en) * 2018-01-15 2021-09-14 Daikin Industries, Ltd. Ice making system
CN111572524B (zh) * 2020-05-07 2021-03-23 武汉理工大学 一种车辆气压制动压力变化率测量方法及装置
CN114577037A (zh) * 2020-11-28 2022-06-03 中国石油天然气股份有限公司 换热装置和换热设备

Family Cites Families (52)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1622024A (en) * 1924-05-02 1927-03-22 Gasoline Recovery Corp Apparatus for cooling and condensation
US1791468A (en) * 1928-02-08 1931-02-03 Albert P Leonard Baffle for heat exchangers
US1912651A (en) * 1931-10-06 1933-06-06 Nusbaum Lee Heat exchange apparatus
US3022985A (en) * 1958-06-06 1962-02-27 Chicago Bridge & Iron Co Silencer and heat recovery system
US3477729A (en) * 1967-05-19 1969-11-11 Durametallic Corp Cooling system for a stuffing box seal
US3426547A (en) * 1967-11-13 1969-02-11 Carrier Corp Control of absorption refrigeration systems
US3482625A (en) * 1968-04-03 1969-12-09 William R Bray Two phase heat exchanger
BE759016A (fr) * 1969-12-18 1971-04-30 Deggendorfer Werft Eisenbau Refroidisseur pour le passage d'une partie reglable d'un vehicule de chaleur maintenu en circulation dans un reacteur
FR2131988B1 (pt) * 1971-04-06 1978-03-31 Krauss Maffei Ag
US4201262A (en) * 1978-08-07 1980-05-06 Goldstein Stanley A Cooler for chilling a working fluid
JPS6129009Y2 (pt) * 1980-03-28 1986-08-27
JPS5771249A (en) * 1980-10-22 1982-05-04 Toshiba Corp Controlling device for cooler
US4471836A (en) * 1982-01-15 1984-09-18 Arthur C. Knox, Jr. Vent condenser
SU1284493A1 (ru) * 1983-08-12 1987-01-23 Всесоюзный Научно-Исследовательский И Проектно-Конструкторский Институт Продуктов Детского Питания И Систем Управления Агропромышленными Комплексами Консервной Промышленности Лини асептического консервировани жидких и пюреобразных пищевых продуктов
DE3411795A1 (de) * 1984-03-30 1985-10-03 Borsig Gmbh, 1000 Berlin Verfahren zum betreiben von rohrbuendelwaermeaustauschern zum kuehlen von gasen
FR2571837B1 (fr) * 1984-10-17 1987-01-30 Air Liquide Appareil de rechauffage de fluide
JPS6188588U (pt) * 1984-11-15 1986-06-10
CA1216280A (en) * 1985-11-05 1987-01-06 Frank Navratil Heat exchanger
JPS62206380A (ja) * 1986-03-05 1987-09-10 Hitachi Ltd 積層熱交換器
US4919541A (en) * 1986-04-07 1990-04-24 Sulzer Brothers Limited Gas-liquid mass transfer apparatus and method
US4768495A (en) * 1986-07-22 1988-09-06 Packless Metal Hose, Inc. Heating apparatus and method
JPH087031B2 (ja) * 1987-01-28 1996-01-29 株式会社日阪製作所 高粘度液の冷却方法
US5106543A (en) * 1990-08-17 1992-04-21 Dodds Diego E F Apparatus and method for controlling the discharge or continuous bleed-off of cooling water and evaporative coolers
US5203121A (en) * 1991-05-09 1993-04-20 Metzger George L Method for filtering and cooling surface finishing compounds
JPH0576328A (ja) * 1991-09-18 1993-03-30 Toppan Printing Co Ltd 温度調節機能付の高圧殺菌処理装置
US5309987A (en) * 1992-07-21 1994-05-10 Astec Method and apparatus for heating and cooling food products during processing
US5400432A (en) * 1993-05-27 1995-03-21 Sterling, Inc. Apparatus for heating or cooling of fluid including heating or cooling elements in a pair of counterflow fluid flow passages
JP2639633B2 (ja) * 1994-11-02 1997-08-13 轟産業株式会社 化学反応装置における熱交換面積調節式の反応熱制御機構
JPH08285430A (ja) * 1995-04-10 1996-11-01 Hoshizaki Electric Co Ltd 冷水供給装置
AU689418B3 (en) * 1996-10-04 1998-03-26 Dale Cameron Ward Apparatus and cooling system
DE59705073D1 (de) * 1997-03-14 2001-11-29 Borsig Babcock Ag Wärmetauscher mit U-Rohren
JPH10262627A (ja) * 1997-03-21 1998-10-06 Hisaka Works Ltd 殺菌装置
RU2133125C1 (ru) * 1997-10-02 1999-07-20 Государственный научно-исследовательский институт экстремальной медицины, полевой фармации и медицинской техники МО РФ Стерилизационно-дистилляционное устройство аптеки
US6076597A (en) * 1997-12-31 2000-06-20 Flowserve Management Company Helical coil heat exchanger with removable end plates
JP2000055441A (ja) * 1998-08-12 2000-02-25 Hitachi Cable Ltd 冷・温水供給装置
DE19848780C1 (de) * 1998-10-22 2000-05-25 Krauss Maffei Kunststofftech Homogenisier- und Temperierbehälter
DE19903833A1 (de) * 1999-02-01 2000-08-03 Behr Gmbh & Co Integrierte Sammler-Wärmeübertrager-Baueinheit
US6394042B1 (en) * 1999-09-08 2002-05-28 Callabresi Combustion Systems, Inc Gas fired tube and shell heat exchanger
US6276264B1 (en) * 1999-10-25 2001-08-21 Dairy Tech Inc Portable batch pasteurizer
CN2404087Y (zh) * 2000-01-26 2000-11-01 淮阴辉煌太阳能有限公司 装配式螺旋套管热交换器
US6189440B1 (en) * 2000-03-21 2001-02-20 Daniel Scott Amundson Continuous flow pasteurizer
AUPR400901A0 (en) * 2001-03-28 2001-04-26 Focus Thermal Technologies (International) Limited Thermal storage device
IL144962A0 (en) * 2001-08-16 2002-06-30 Weizman Michael System and method for detecting flaws in plate-type heat exchanger
JP4727873B2 (ja) * 2001-09-26 2011-07-20 アサヒビール株式会社 冷却システム
JP2003289838A (ja) * 2002-04-05 2003-10-14 Ikeda Shokken Kk 無菌食品の製造方法
JP2005128751A (ja) * 2003-10-23 2005-05-19 Toshiba Electric Appliance Co Ltd 飲料ディスペンサ装置の排水装置
CA2604159A1 (en) * 2005-04-07 2006-10-12 Baker, Alan Paul Improvements in control of heat exchangers
JP2007010202A (ja) * 2005-06-29 2007-01-18 Xenesys Inc 熱交換ユニット
JP2007215447A (ja) * 2006-02-15 2007-08-30 Sanyo Electric Co Ltd 冷菓製造装置
ATE530069T1 (de) * 2007-05-24 2011-11-15 Martin Foerster Pasteurisierungsanlage zum pasteuriseren von tierfutter
JP2009198147A (ja) * 2008-02-25 2009-09-03 Toshiba Electric Appliance Co Ltd 飲料提供装置
US10045089B2 (en) 2011-08-02 2018-08-07 Apple Inc. Selection of encoder and decoder for a video communications session

Also Published As

Publication number Publication date
PT2685836T (pt) 2021-10-15
US20160366918A1 (en) 2016-12-22
MX2013010544A (es) 2013-12-02
CN103533838A (zh) 2014-01-22
PL2685836T3 (pl) 2022-01-17
AU2015207821A1 (en) 2015-08-20
AU2012229281A1 (en) 2013-10-03
ES2893850T3 (es) 2022-02-10
MX352145B (es) 2017-11-10
DK2685836T3 (da) 2021-11-08
EP2685836B1 (en) 2021-08-04
CL2013002684A1 (es) 2014-02-21
AU2012229281B2 (en) 2015-08-20
US10285419B2 (en) 2019-05-14
US9572366B2 (en) 2017-02-21
AU2012229281B9 (en) 2015-08-27
JP2016040514A (ja) 2016-03-24
EP2685836A1 (en) 2014-01-22
ZA201307687B (en) 2015-04-29
CN103533838B (zh) 2015-06-10
AU2015207821B2 (en) 2017-03-30
SG193460A1 (en) 2013-10-30
JP2014514522A (ja) 2014-06-19
RU2549759C1 (ru) 2015-04-27
CA2830378A1 (en) 2012-09-20
CA2830378C (en) 2016-07-19
WO2012125440A1 (en) 2012-09-20
RU2013146347A (ru) 2015-04-27
US20140127365A1 (en) 2014-05-08

Similar Documents

Publication Publication Date Title
BR112013023706A2 (pt) sistemas e métodos para troca de calor
BR112017014161A2 (pt) sistemas e métodos de remoção de calor de centro de dados
BR112015016220A2 (pt) nebulizador térmico para criação de aerossóis estáveis
MX2018000112A (es) Sistema para reducir la temperatura del aire de entrada de un dispositivo.
BR112015003928A2 (pt) disposição de refrigeração para componentes dispostos no espaço interno de um armário de distribuição
BR112015003768A2 (pt) trocador de calor para a refrigeração do armário de distribuição e respectivo arranjo de refrigeração
BR112013027058A2 (pt) sistema individual de fixação intercorporal
BR112012018075A2 (pt) "sistema e método de formação e dimensionamento de goma de mascar e/ou de alteração da temperatura da goma de mascar".
BR102016007236A8 (pt) Montagem de conversão de potência refrigerada
BR112013029406A2 (pt) sistema de ciclo do calor e meio de trabalho
BR112014017614A8 (pt) Artigo para fumar e método para reduzir ou eliminar os aumentos da temperatura de um substrato de formação de aerossol
BR112016018443A2 (pt) Dispositivo e sistema de refrigeração terapêutico
BR112015010878A2 (pt) sistemas e processos de controle de aquecimento de cárter de compressor
BR112014019200A8 (pt) Tanque de entrega de líquido com câmara de expansão
BR112015005737A2 (pt) forno, processo para operar continuamente forno e condensado de fumaça
BR112017028142A2 (pt) aparelho para o preparo de alimentos
BR112015021984A2 (pt) estrutura de restrição de detritos de córrego
BR112013026661A2 (pt) método de entrega de vacina
BR112016015422A2 (pt) formulações de vacina de frasco único
BR112012026945A2 (pt) método e aparelho para controlar a temperatura de um líquido, e, método e aparelho para determinar a temperatura de um líquido
BR112017008114A2 (pt) arranjo de resfriamento para um sistema whr
BR112013016796A2 (pt) aparelho para gerar vapor e sistema de ferro à vapor
BR112015027937A2 (pt) método e sistema para avaliação de uma condição de saúde
BR112014002030A2 (pt) métodos e dispositivos para aquecer ou resfriar materiais viscosos
BR112014029651A2 (pt) circuito de fluido dentro de uma turbomáquina

Legal Events

Date Code Title Description
B06F Objections, documents and/or translations needed after an examination request according [chapter 6.6 patent gazette]
B06A Patent application procedure suspended [chapter 6.1 patent gazette]
B11B Dismissal acc. art. 36, par 1 of ipl - no reply within 90 days to fullfil the necessary requirements